Method and lithographic apparatus for measuring and acquiring height data in relation to a substrate

专利摘要:

公开号:NL1036557A1
申请号:NL1036557
申请日:2009-02-11
公开日:2009-09-14
发明作者:Frank Staals；Paulus Antonius Andreas Teunissen；Ronald Albert John Van Doorn
申请人:Asml Netherlands Bv；
IPC主号:

专利说明:

Method and lithographic apparatus for measuring and acquiring height data in relation to a substrate surface
Field of the Invention (0001] The present invention relates to a lithographic apparatus and method for acquiring height data of a substrate surface, to a program and a memory containing the program for acquiring height data and to a method, apparatus, program and memory for correcting height data acquired according to said method.
Description of the Related Art (0002] A lithographic apparatus is a machine that applies a desired pattern to a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC. or several dies) on a substrate (eg, a silicon wafer) Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. reticle and the substrate and is provided to image an irradiated portion of the reticle onto a target portion of a substrate The pattern can be imaged onto an exposure area (die) on the substrate (silicon wafer) In general, a single substra te will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the uscanning "-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. (0003 ] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables.) This is described in more detail below.
In current dual stage apparatus, data is gathered to level every target portion (field) with a level sensor in exactly the same position with respect to the center of the target portion. A possible level sensor is explained in more detail below.
The projection system includes components for direct, shape and / or control of a beam of radiation. The pattern can be imaged onto the target portion (e.g., including part of one, or several, dies) on a substrate, for example a silicon wafer, that has a layer of radiation-sensitive material, such as resist. In general, a single substrate contains a network or adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction, usually referred to as the "scanning" direction, while synchronously scanning the substrate parallel or anti-parallel to this direction.
For the sake of simplicity, the projection system may be referred to as the "lens"; however, this term should be broadly interpreted and compassing various types of projection system, including refractive optics, reflective optics, catadioptric systems, and charged particle optics, for example. The radiation system may also include elements operating according to any of these principles for directing, shaping or controlling the projection beam, and such elements may also be referred to below, collectively or singularly, as a "lens". In addition, the first and second object tables may be referred to as the "mask table" and the "substrate table", respectively.
A lithographic apparatus can contain a single mask table and a single substrate table, but are also available having at least two independently movable substrate tables; see, for example, the multi-stage apparatus described in International Patent Applications WO98 / 28665 and WO98 / 40791. The basic operating principle behind such a multi-stage apparatus is that, while a first substrate table is at the exposure position underneath the projection system for exposure or a first substrate located on that table, a second substrate table can run to a loading position, discharge a previously exposed substrate, pick up a new substrate, perform some initial measurements on the new substrate and then stand ready to transfer the new substrate to the exposure position underneath the projection system as soon as exposure or the first substrate is completed; the cycle then repeats. In this way it is possible to substantially increase the machine throughput, which in turn improves the cost of ownership of the machine. It should be understood that the same principle could be used with just one substrate table which is moved between exposure and measurement positions.
[0008] During exposure processes, it is important to ensure that the mask image is correctly focused on the wafer. Conventionally this has been done by measuring the vertical position of the best focal plane of the aerial image of the mask relative to the projection lens before an exposure or a series of exposures. During each exposure, the vertical position of the upper surface of the wafer relative to the projection lens is measured and the position of the wafer table is adjusted so that the wafer surface lies in the best focal plane.
The scope for adjusting the position of the focal plane of the projection system PL is limited and the depth of focus or that system is small. This means that the exposure area of the wafer (substrate) must be precisely positioned in the focal plane of the projection system PL.
Wafers are polished to a very high degree of flatness but nevertheless deviation of the wafer surface from perfect flatness (referred to as "unflatness") or sufficient magnitude noticeably to affect focus accuracy can occur. Unflatness may be caused, for example, by variations in wafer thickness, distortion of the shape of the wafer or contaminants on the wafer holder. The presence of structures due to previous process steps also significantly affects the wafer height (flatness). In the present invention, the cause of unflatness is largely irrelevant; only the height of the top surface of the wafer is considered. Unless the context otherwise requires, references below to "the wafer surface" refer to the top surface of the wafer onto which will be the masked image.
[00011] During exposures, the position and orientation of the wafer surface relative to the projection optics are measured and the vertical position (Z) and horizontal tilts (Rx, Ry) or the wafer table. WT are adjusted to keep the wafer surface at the optimum focus position.
As described above, imaging a pattern onto a substrate W is usually done with optical elements, such as lenses or mirrors. In order to generate a sharp image, a layer or resist on the substrate W should be in or near the focal plane of the optical elements. Therefore, according to the prior art, the height of the target portion C that is exposed is measured. Based on these measurements, the height of the substrate W with respect to the optical elements is adjusted, e.g., by moving the substrate table WT on which the substrate W is positioned. Since a substrate W is not a perfectly flat object, it may not be possible to position the layer of resist exactly in the focal plane or the optics for the whole target portion C, so the substrate W may only be positioned as well as possible. 00013j In order to position the substrate W in the focal plane as well as possible (e.g., by matching the focal plane to the center of the resist thickness), the orientation of the substrate W can be altered. The substrate table WT may be translated, rotated or tilted, in all six degrees of freedom, in order to position the layer or resist in the focal plane as well as possible.
In order to determine the best positioning of the substrate W with respect to the optical elements, the surface of the substrate W may be measured using a level sensor, as for instance described in U.S. Pat. Patent No. 5,191,200. This procedure may be done during exposure (on-the-fly), by measuring the part of the substrate W that is being exposed or is next to being exposed, but the surface of the substrate W may also be measured in advance. This latter approach may also be done at a remote position. In the latter case, the results of the level sensor measurements may be stored in the form of a so-called height map or height profile and used during exposure to the position W with respect to the focal plane of the optical elements.
In both cases, the top surface of the substrate W may be measured with a level sensor that is determined by the height of a certain area. This area may have a width about equal to or greater than the width of the target portion C and may have a length that is only part of the length or target portion C, which will be explained below (the area being indicated with the dashed line ). The height map of a target portion C may be measured by scanning the target portion C in the direction of the arrow A. The level sensor LS determined the height of the substrate W by applying a multi-spot measurement, such as for instance a 9 -spot measurement. Level sensor spots LSS are spread over the area and, based on the measurements obtained from the different level sensor spots, height data may be collected.
The term "height" as used here refers to a direction substantially perpendicular to the surface of the substrate W, i.e., substantially perpendicular to the surface of the substrate W that is to be exposed. The measurements of a level sensor result in height data, including information about the relative heights or specific positions of the substrate W. This may also be referred to as a height map.
Based on this height data, a height profile may be computed, for instance by averaging corresponding height data from different parts of the substrate (e.g., height data corresponding to similar relative positions within different target portions C). In case such corresponding height data is not available, the height profile is equated to the height data. 100018] Based on height data or a height profile, a leveling profile may be determined to provide an indication of an optimal positioning of the substrate W with respect to a projection system PS. Such a leveling profile may be determined by applying a linear fit through (part of) the height data or the height profile, e.g., by performing a least squares fit (three dimensional) through the points that are inside the measured area.
[00019] As explained above, accurate leveling may require measuring the shape and topography of the substrate, for instance using a level sensor, resulting in height data or (at least part) or the substrate W, based on which a leveling profile can be determined. Such a leveling profile may represent the optimal position of the substrate W with respect to the projection system PS, taking into account the local shape and height of the substrate W.
[00020] By leveling every target portion in exactly the same position with respect to the center of the target portion, variation or exposure focus between target portions on a substrate is reduced.
For example, every target portion could have a leveling sampling pattern with respect to the center of the target portion as shown in FIG. 2. In FIG. 2 M2 - M6 refer to the level sensor spots, covering the target portion widths, which are scanned over the surface over the target portion along the target portion height. During the scanning, a number of measurements are gathered, indicated by the dots in FIG. 2. These dots have a predetermined position with respect to the target portion center.
It is relatively time consuming to take leveling data according to the technique as shown and described with reference to FIG. 2. This is because it is time to take leveling data for each target portion that meets the constraint or positioning the level sensor in the same position with respect to the center or each target portion. In the most common case or columnar target portion layout, this requires a stroke or level sensor readings through each column.
This is further illustrated with reference to FIG. 4, showing a substrate with a variety of target portions and arrows indicating the scanning path or strokes of the level sensor.
SUMMARY OF THE INVENTION
[00024] It is an aspect of the present invention to alleviate, at least partially, the problems discussed above. 0005] According to a first aspect of the present invention, there is provided a lithographic projection apparatus including a support constructed to support a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed and arranged to hold a substrate, a projection system constructed and arranged to project the patterned radiation beam onto a target portion of the substrate, a level sensor constructed and arranged to perform height measurements of at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system, a first actuator constructed and arranged to move the substrate table at least in a first direction perpendicular to a surface of the substrate having a maximum speed, and a second actuator constructed and arranged to move the substrate table at leas t in a second direction perpendicular to a surface of the substrate having a maximum speed, a controller constructed and arranged to generate a stroke of relative movement between the substrate and the level sensor, by controlling the first and second actuator, being the controller is constructed and arranged to combine first and second actuator movement to effect combined movement at a speed higher than the maximum speed of one actuator.
In an embodiment, the controller is constructed and arranged to generate the stroke of combined movement by combining at least 71% of the maximum speed of both actuators.
[000271 Further the controller may be constructed and arranged to generate a stroke of combined movement or both actuators moving the substrate table at generally maximum speed.
The first actuator may be constructed and arranged for cause relative movement in the X direction and the second actuator is constructed and arranged for cause relative movement in the Y direction.
[00029] The substrate table could be movable to effect a scanning exposure or a substrate carried by said substrate holder, and said level sensor is arranged to measure at least one of the vertical position and the tilt about at least one horizontal axis of a target area on said substrate.
The level sensor includes a projection part for directing radiation onto the substrate including a radiation source, a projection grid having slits positioned downstream from the radiation source, and a first reflector positioned to direct radiation from the radiation source towards a substrate surface as level sensor spots, and a detection part for detecting reflected radiation from the substrate surface, including a detector, a detection grid having slits positioned in between the substrate and the detector, and a second reflector positioned to direct light reflected from the wafer surface to a detector, how the grids are positioned to project and detect level sensor spots that are aligned with the stroke of the relative movement.
In a further embodiment, the level sensor spots on the substrate are rotated over generally 45 degrees with respect to the direction of movement or at least one of the actuators.
It may be useful to position at least one of projection grid or detection grid generally in parallel with the substrate surface.
In a preferred embodiment at least one of the projection grid or the detection grid is generally of rectangular shape and has slits generally positioned along the diagonal of the grid.
In an embodiment the substrate table, tilted over an angle corresponds to the angle of the stroke of movement.
At least one of the projection grid or the detection grid is preferably tilted such that the slits are at different distances from the radiation source.
Preferably at least one of the projection grid or the detection grid is tilted around an axis generally perpendicular to a plane formed by traveling direction of the radiation and an axis of the slits.
The projection grid may be tilted such that a tilt angle of the projection grid and an incident angle of the radiation combine to generally 90 degrees (Scheimpflug condition).
[00038] It may be useful to employ a system in which the projection part further comprises a wedge positioned in the path of radiation downstream from the projection grid for adapting the optical path length of the radiation.
[00039] In an embodiment, the detection part further comprises a wedge positioned in the path of radiation upstream from the projection grid for adapting the optical path length of the radiation.
[00040] According to another aspect of the invention, there is provided a method for sensing the level of a substrate carried on a substrate table, in a lithographic projection apparatus, that has a support constructed to support a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed and arranged to hold a substrate; a projection system constructed and arranged to project the patterned radiation beam onto a target portion of the substrate; a level sensor constructed and arranged to perform height measurements or at least part of the substrate to generate height data, first and second actuators for generating a relative moment between substrate and the level sensor, the actuators having a maximum speed, the method including: providing a substrate on the substrate table generating relative movement between the substrate and the level sensor, and sensing a level of the substrate, further including combining the relative movement generated by the two actuators to a velocity higher than the maximum velocity or movement generated by one actuator .
The method could include any of the feature of the apparatus. Further the generated relative movement could be a movement in several strokes. The height measurements could be performed by scanning the least part of the substrate in a scanning direction with a level sensor.
Preferably the first actuator generates a movement in an X-direction and the second actuator generates movement in a Y-direction, and the combined movement is in an XY plane under an angle or at least 20 degrees with respect to the substrate surface .
The movement preferably comprises strokes generally at a 45 degree angle with respect to the X and Y directions.
The method could further include the level sensor projecting radiation on the substrate surface and detecting the reflected radiation from the substrate surface.
[00045] In a further embodiment projecting the radiation further comprises applying a number of beams of radiation on the substrate surface as level sensor spots, the level sensor spots are rotated over a non-zero angle with respect to at least one of the directions or relative movement and combining the relative movement results in a relative movement at generally the same non-zero angle. 00046] Further adapting the optical path length or at least one of the projected radiation or reflected radiation using refraction is useful.
[00047] According to another aspect of the present invention, there is provided a computer program on a data carrier or a computer readable medium, or a computer program product, the computer program or computer program product having code or instructions constructed and arranged to perform the method of: generating relative movement between the substrate and the level sensor sensing the level of the substrate with the level sensor, the generated relative movement is a combined movement or at least two actuators for generating movement or the substrate table relative to the level sensor.
According to another aspect of the present invention, there is provided a device that is made directly or indirectly using the lithography system and / or device manufacturing method and / or computer program or any of the preceding aspects of the invention.
According to still another aspect of the invention, there is provided a method for calibrating a lithographic apparatus including: performing a level sensor scan over the target portion providing level sensor data for the target portion, with the level sensor scan being performed at a relative position with respect to the target portion, and b) determining corrected exposure focus data using the level sensor data and predetermined calibration data to correct for the relative position of the level sensor scan with respect to the target portion. B) comprises: b 1) determining corrected level sensor data using the predetermined calibration data, and b2) determining corrected exposure focus data based on the corrected level sensor data.
B) comprises: bl ') determining exposure focus data using the level sensor data, and b2') determining corrected exposure focus data based on the exposure focus data and the predetermined calibration data.
C) exposing the target portion in accordance with the corrected exposure focus data.
According to an embodiment, the relative position is substantially in the plane of the target portion and substantially perpendicular to a scan direction of the level sensor scan.
[00052] According to an explanation the calibration data can be used to determine corrected exposure focus data to correct for the relative position of a level sensor scan with respect to a target position, including the method: 1-1) performing a first number of calibration level sensor scans or at least one target portion, showing the first number of calibration level sensor scans have a first relative position with respect to the least one target portion, 1-2) performing a second number of calibration level sensor scans of at least one target portion, regarding the second number of calibration level sensor scans have a second relative position with respect to the least one target portion, the second relative position being different from the first relative position, II) determining first calibration data for the second relative position by comparing the second number of calibration level sensor scans to the first number of calibration level sensor scans.
Preferably the second number of level sensor scans are performed by generating a combined relative movement of the substrate and the level sensor with two actuators, moving at a higher speed than the maximum speed of one actuator.
According to yet a further aspect of a computer program is provided on a data carrier, a computer readable medium, or a computer program product, the computer program having code or instructions for sensing the level of a substrate carried on a substrate table, the code or instructions for performing the method of: generating relative movement between the substrate and the level sensor sensing the level of the substrate with the level sensor, the generated relative movement is a combined movement or at least two actuators for generating movement of the substrate table relative to the level sensor.
[00055] According to yet another aspect a system is provided for controlling the position of a substrate, the system including a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform, using height data, a method for positioning a target portion of the substrate with respect to a focal plane of a projection system, performing the method comprises: performing height measurements or at least part of the substrate to generate the height data by generating relative movement between the substrate and the level sensor sensing the level of the substrate with the level sensor, regarding the generated relative movement is a combined movement or at least two actuators for generating movement or the substrate table relative to the level sensor; using predetermined correction heights to compute corrected height data for the height data; and positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data.
[00056] A system for controlling the position of a substrate, the system including a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform a method for calculating correction heights to correct height data obtained by a level sensor, comprising the method comprises: performing height measurements of a target portion of the substrate to generate a height profile by generating relative movement between the substrate and the level sensor and sensing the level of the substrate with the level sensor, the generated relative movement is a combined movement or at least two actuators for generating movement or the substrate table relative to the level sensor; computing a level profile based on the height profile; and determining correction heights by computing the difference between the level profile and the height profile.
Another aspect of the invention provides a computer-readable medium encoded with a computer program containing instructions that are executable by a processor to perform, using height data, a method for positioning a target portion, or a substrate with respect to a focal plane of a projection system, in which the method comprises: performing height measurements or at least part of the substrate to generate the height data by generating relative movement between the substrate and the level sensor and sensing the level of the substrate with the level sensor, being the generated relative movement is a combined movement or at least two actuators for generating movement or the substrate table relative to the level sensor; using predetermined correction heights to compute corrected height data for the height data; and positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data.
Yet another aspect of the invention provides a computer-readable medium encoded with a computer program containing instructions that are executable by a processor to perform, using height data, a method for positioning a target portion, or a substrate with respect to a focal plane of a projection system, comprising the method comprises: performing height measurements of a target portion of the substrate to generate a height profile by generating relative movement between the substrate and the level sensor and sensing the level of the substrate with the level sensor, the generated relative movement is a combined movement or at least two actuators for generating movement or the substrate table relative to the level sensor; computing a level profile based on the height profile; and determining correction heights by computing the difference between the level profile and the height profile.
LETTER DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: [00060] - Figure 1 schematically depicts a lithographic apparatus according to an embodiment of the invention; Figure 2 schematically depicts a target portion, [00062] - Figure 3 is a more detailed view of parts of the apparatus of Figure 1; [00063] - Figure 4 schematically depicts a substrate with a variety of target portions and arrows indicating the scanning path of the level sensor according to the prior art, [00064] - Figure 5 is a detailed view of a wafer stage according to an embodiment ; [00065] - Figure 6 schematically depicts a substrate with a variety of target portions and arrows indicating the scanning path of the level sensor according to a preferred embodiment, [00066] - Figures 7a-7c show three issues of a level sensor grid, [ 000671 - Figures 8-13 schematically show arrangements of a level sensor according to different expenses of the invention.
DETAILED DESCRIPTION
Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL constructed and arranged for a radiation beam B condition (e.g., UV radiation or EUV radiation). a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask) MA and connected to a first positioner PM constructed and arranged to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW constructed and arranged to accurately position the substrate in accordance with certain parameters; and a projection system (e.g., a refractive projection lens system) PS constructed and arranged to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., including one or more dies) or the substrate W.
The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
The support structure supports, i.e., bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is a hero in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" may be considered synonymous with the more general term "patterning device." The term "patterning device" used should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate . It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
The term "projection system" used should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the radiation exposure being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" may also be considered as synonymous with the more general term "projection system".
As shown here, the apparatus is of a transmissive type (e.g., employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g., employing a programmable mirror array or a type referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.
The lithographic apparatus may also be a type of at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, eg, water, so as to fill a space between the projection system and the substrate . Liquid immersion may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.
Referring to Figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to be part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and / or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) or the intensity distribution in a pupil plane or the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
The radiation beam B is incident on the patterning device (e.g., mask MA), which is hero on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which is the beam onto a target portion C or the substrate W. With the aid of the second positioner PW and position sensor IF (eg, an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, eg, so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the mask MA with respect to the path of the radiation beam B, eg, after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate May be aligned using mask alignment marks MAI, MA2 and substrate alignment marks PI, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one that is provided on the mask MA, the mask alignment marks may be located between the dies.
The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (ie, a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion can be exposed. In step mode, the maximum size of the target target exposure limits the size of the target target limits C imaged in a single static exposure. 100082] 2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern beamed to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure target portion limits the width (in the non-scanning direction) or the target portion in a single dynamic exposure, whereas the length of the scanning motion is the height (in the scanning direction) or the target portion.
3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern is imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array or a type as referred to above.
Combinations and / or variations on the modes described above or use or entirely different modes or use may also be employed.
LEVEL SENSOR
The level sensor measures heights of substrates W or of areas on the substrate table WT to generate height data. A surface, or which the height is measured, is brought in a reference position and is illuminated with a measurement beam of radiation. The measurement beam of radiation impinges on the surface to be measured under an angle which is less than 90 °. Because the angle of incidence is equal to the angle of reflection, the measurement beam of radiation is reflected back from the surface with the same angle to form a reflected beam of radiation. The measurement beam or radiation and the reflected beam or radiation define a measurement plane. The level sensor measures the position of the reflected beam or radiation in the measurement plane.
If the surface is moved in the direction of the measurement beam or radiation and another measurement is done, the reflected beam or radiation is reflected in the same direction as before. However, the position of the reflected beam or radiation has shifted the same way the surface has been moved.
The level sensor is arranged to perform a level sensor scan over the target portion providing level sensor data for the target portion.
Figure 3 shows a part of the measurement station region of the lithographic apparatus. The substrate W is a hero on the substrate table WT. Two wafer stage chucks WT are visible in Figure 3. The left hand side is the substrate table in the expose position I and the right hand side is the substrate table WT in the measure position II.
The substrate table WT is connected to actuators. An example of another embodiment of a substrate table WT is shown in figure 5. Actuators 23.24 are connected to a control device 6 with a processor 8 and a memory 10. The actuators may include any type of positioning actuator, such as a piezo -electric actuator, a pneumatic actuator, a linear motor, a Lorer.tz actuator, a cam disk or a spindle. An aspect of a piezo-electric actuator and a cam disk is their high stiffness, thus increasing the eigenfrequencies of the substrate table and increasing the position accuracy. Actuators 23.24 move over respective guides 21.22. The two actuators 23 will be able to bring a tilt around a Z-axis.
Not shown in Figure 5 is an actuator for generating a relative movement in the Z direction. This actuator is also connected to the processor 8. This actuator is controlled to position the substrate surface or substrate W in the focal plane of the projection system in accordance with the height data or corrected height data acquired according to the invention ..
The processor 8 further receives information from position sensors 25 measuring the current position of the substrate table WT or substrate table holder by electric (capacitive, inductive) or optical, e.g., interferometric devices. Figures 1 and 2 show examples of direction definitions Χ, Υ, Ζ. Z is usually used to indicate a height direction, as shown in figure 1 right hand side. The substrate W is positioned in the X-Y plane as indicated in Figure 2. Scanning of the surface according to figure 4 is performed by performing long strokes in the Y direction over the middle part of fields 40 on the substrate W.
Figure 3 shows a system for determining the position of a wafer on the wafer / substrate table WT or "chuck" as it is sometime referred to in the art. This includes two interferometers IF, one on each or opposite side of the substrate table WT. Each interferometer IF is positioned for direct radiation measurement on one of a first pair of mirrors ML that are provided on opposing sidewalls of the table, these mirrors ML being substantially perpendicular to the radiation emitted from the associated IF interferometer.
These will be referred to as the X-mirrors Ml. In addition, each interferometer IF is positioned to direct measurement radiation on a second pair of mirrors or M2 that is angled at 45 degrees to the direction of propagation or radiation from the interferometer IF. These mirrors M2 are provided on opposing sidewalls or the WT table. These will be referred to as the angled mirrors M2. I00093J The X-mirrors M and the angled mirrors M2 are carried on the wafer table WT and so move when the table WT is moved. Radiation reflected from each X-mirror Ml is directed back to its associated interferometer IF and can be used to determine the x-position of the wafer table WT. Radiation reflected from the angled mirrors M2 is directed onto one of a pair of Z-mirrors ZM positioned above the level of the wafer table WT and then subsequently reflected back to the interferometer IF. The dots that are shown on the Z-mirrors ZM or Figure 2 are indicative of the positions where the interferometer IF beams reside during measurements. Z-mirror ZM in combination with a measure of the x-position determined using the X-mirrors Ml, it is possible to obtain an indirect measure of the height of the Z-mirror ZM and so the wafer table WT. 100094] The processor 8 also receives input from a level sensor LS which measures the height and / or tilt information from the target area C on the substrate W where the projection beam PB hits the substrate surface. Preferably, the control device 6 is connected to a reporting system 9, which may include a PC or a printer or any other registration or display device.
The level sensor LS may be, for example, an optical sensor as described here; alternatively, a pneumatic or capacitive sensor (for example) is conceivable. In figure 3 also an air gauge GA is shown in the measure position.
A level sensor is provided to determine a level parameter of the substrate W to enable a controller 6 to position the substrate surface in the focal plane of the projection system PS. The level sensor may comprise a level difference sensor constructed to measure a level difference between the surface of the substrate and the surface of the surrounding structure and the level parameter comprises the level difference. A result of this arrangement may be that measurement of the level difference can be performed as a single action, thus obviating a need to measure the level of the substrate and the surrounding structure separately. Further, the level difference may be measured with existing level sensors used for focus control during exposure of the substrate. (00097] In another embodiment, the level sensor comprises a level measurement sensor constructed to measure a level of the surface of the substrate when held by the substrate table and the level parameter comprises the level of the surface of the substrate. the controller is further provided with a level of the surrounding structure to position the substrate table with respect to the surrounding structure An aspect of this configuration is that this provides for a simple solution, useful in an embodiment being only the substrate table has been moved by the actuators and the surrounding structure is stationary. (000981 The level sensor LS will generally measure the vertical position of one or more small areas (level sensor spots LSS) or harrow, 6-25 mm2 (harrow, 2x4 mm) or the substrate W to generate height data The level sensor LS shown in Figure 3 comprises a radiation source for producing a radiation beam 16, projection optics (not shown) for projecting the light beam 16 onto the substrate W, detection optics (not shown) and a sensor or detector. The level sensor comprises a projection part 2 and a detection part 15.
In particular cases the LSS have a size defined by the length and width of the spot on the surface of the substrate. The length can be defined as the length of the spot in the scanning direction, according to prior art arrangements in the Y-direction. The level sensor spots according to the embodiment of figure 2 are obtained in an embodiment using a level sensor grid 100 as shown in figure 7a. The grid 100 is provided with a grating 101. Each gap 102 has dimensions width 104 x height 105. The width 104 or slit 102 generally agrees with the width of the LSS on the substrate if the grid is positioned in parallel with the substrate surface as would be the case in prior art arrangements. In a particular case the height 105 or the slit 102 in the scanning direction is about 4 times narrower than the width. This will allow a balance between desired resolution or scantling and being able to ignore or take into account measurement results or spots near edges of the substrate (which results are invalid).
The detection part 15 generates a height-dependent signal, which is fed to the processor 8. The processor 8 is arranged to process the height information and to construct a measured height map. Such a height map may be stored by the processor 8 in the memory 10 and may be used during exposure. (0001011 According to an alternative, the level sensor 2.15 may be an optical sensor making use of Moire patterns formed between the image of a projection grating reflected by the substrate surface and a fixed detection grating, as described in US Patent No. 5,191,200 It may be desirable for the level sensor to measure the vertical height of a multiple of positions simultaneously and / or to measure the average height of a small area for each position.
The level sensor spots LSS, M2-M5 according to figure 2 are arranged in a first direction, in Figure 2 in the X-direction. Subsequent measurement of M2 results in the array of measurements according to figure 2. The measurements are repeated. Dependent on the interval time between the measurements and the relative speed of the substrate W with respect to the level sensor, these measurement points are separated by a pitch. The pitch can be adjusted by changing one of the variables. It is relatively straightforward to shorten the time interval and repeat the measurements at a higher rate.
The described described here may of course also be used for other types of level sensors, such as air gauges. An air gauge, as will be known to a person skilled in the art, assessed the height of a substrate W by supplying a gas flow from a gas outlet to the surface of the substrate W. Where the surface of the substrate W is high, ie, the surface of the substrate W is relatively close to the gas outlet, the gas flow will experience a relatively high resistance. By measuring the resistance of the flow as a function of the spatial position of the air gauge above the substrate W, a height map of the substrate W can be obtained. A further discussion of air gauges may be found in EP0380967, incorporated by reference.
According to an alternative, a scanning needle profiler is used to determine a height map of the substrate W. Such a scanning needle profiler scans the height map of the substrate W with a needle, which also provides height information.
[000105] In fact, all types of sensors, may be used that are arranged to perform height measurements of a substrate W, to generate height data.
The level sensing method uses at least one sensing area and measures the average height of a small area, referred to as a level sensor spot LSS, such as the five spots M2-M6 according to Figure 2.
According to an embodiment, the level sensor may simultaneously apply a number of measurement beams of radiation, creating a number of level sensor spots LSS on the surface of the substrate W. As shown in Figs. 1, the level sensor may for instance create five level sensor spots LSS in a row. The level sensor spots LSS scan the area of the substrate W to be measured (for instance target portion C), by moving the substrate W and the level sensor relatively with respect to each other, indicated with arrow A (scanning direction).
Depending on the position of the level sensor spot LSS on the substrate W, a selection mechanism selects the level sensor spot or spots LSS, which are applicable to the higher height data from a measured target area C. Based on the selected level sensors spots LSS, a level profile may be computed.
The depicted apparatus can be used in various modes. For example, in step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the projection beam is projected onto a target portion C at once (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
In order to determine an absolute mirror map, the x-position of the wafer table WT is monitored using the interferometers IF and a plurality of level sensor LS measurements is performed at various different x-positions across the wafer. Each level sensor measurement may optionally be static. In this case, typically each level sensor would take a number of measurements at each measurement point and provide an average value, to reduce the effects of noise. In a typical example, each level sensor may take six hundred readings at a single point, although different sensors may be constructed and arranged to take different numbers or readings and indeed different numbers or readings may be tasks at different positions of the substrate table. As will be appreciated, while increasing the number of measurements, reducing the effects of noise, and also increasing the measurement time. Hence, there is a trade off between calibration time and measurement accuracy. As an alternative to a static measurement, the wafer table WT may be moved along the direction of the level sensor array LS, while the level sensor array LS is taking measurements. Measurement related to specific points of the wafer may be obtained by sampling the sensor outputs at appropriate times. In this case, the number of measurements that are tasks at each point will typically be lower than for the static measurement, and may be only one.
In the example shown in Figure 5, the wafer table WT is movable using a controller 6. In particular, the wafer table WT is moved in parallel to the X-axis using actuators 23 in steps from the extreme left position to the extreme right position. After each step, all level sensors covering a target wafer point take a measurement.
Actuators 23.24 are arranged to generate a relative movement of the substrate table WT with respect to level sensor fixed to the lithographic apparatus. The actuator will have a maximum speed. Scanning according to figure 4 will have a maximum scanning speed in the Y direction limited by this maximum speed.
The controller 6, which is connected to the actuators 23, 24, is constructed and arranged to control the actuators. The controller 6 is also provided with an output signal from a level sensor.
The controller 6 can include any type of controller such as an electronic controller, analogue, digital, or a combination, including, eg, a microprocessor, microcontroller, other type of programming device, application specific integrated circuitry, or any other type or programmable device. The actuator can be connected to the controller via any suitable connection, such as an analogue line, a digital line, a multiplexed digital line, or any other communication channel.
[000115] According to the invention during scanning of the substrate W with the level sensor, the substrate table WT is moved relative to the level sensor in a combined movement generated by a combination of actuating in the X and Y directions. This will allow a scanning speed higher than the maximum speed of one of the actuators, in particular a higher speed than scanning in only the Y - direction according to figure 4.
An embodiment of scanning with the level sensor is shown in Figure 6. According to this embodiment, the level sensor scans the substrate surface using long strokes. The strokes may be elongated in one direction. In another embodiment the strokes could be wavy or periodic. In an embodiment of a Y direction movement, modulation with a movement is in the X direction under the influence of the X actuators 23.
A combined movement of the actuators 23.24 results in strokes at an angle of generally 45 degrees with each axis. Since the movement of the actuators 23.24 is combined, a resulting combined speed is roughly 41% higher. The result is that according to this embodiment scanning of the total surface of the substrate can be performed quicker, resulting in time savings, in particular at the measure position.
Any of the level sensors known to the skilled person can be used in combination with the invention in order to achieve the time saving due to the higher scanning speed.
In an embodiment the substrate table WT is rotated over an angle corresponding to the angle of combined movement of the actuators. This allows the heart line of the target portions 40.41 or figures 3 and 6 to be aligned with the scanning direction according to the invention. In this approach, the substrate table is rotated over 45 degrees for scanning. After scanning, the substrate table can be rotated back the same angle. This allows the projection of radiation according to prior art arrangements.
The level sensor spots according to the embodiment of figure 2 are obtained in an embodiment using a level sensor grid 100 as shown in figure 7a. The grid 100 is provided with a grating 101. Each gap 102 has dimensions width 104 x height 105. Figure 7a shows axis X, Y to indicate a grid coordinate system. The grating 101 is positioned parallel to the X direction over the middle part of the grid 100. Hereherr gX, gY and gZ will refer to this defined grid axis. Further rotation around any of these axes will be referred to hereinafter as gRx, gRy and gRz. gRz refers to rotation of the grid in the plane as shown in figure 7a.
In the embodiment shown in Figure 4, the level sensor directs its radiation beam onto the substrate surface at an angle ALPHA, here defined as the direct angle between substrate surface and incident beam. This angle could be 5-80 degrees, more particularly 5-40, such as 20 degrees. This angle ALPHA will be used hereunder as the incident angle of the level sensor radiation.
[000122J In between the radiation source (not shown) or the ievei sensor and the radiation beam 16 directed at the substrate W, grid 100 is positioned. The grid 100 is part of the detection part 2 or the level sensor. The grating 101 will result in the formation of the level sensor spots according to Figure 2. The grid 100 is positioned perpendicular to the traveling direction of the beam 16.
The size of the level sensor spots LSS depends on the size of the slits 102 and the angle of incidence ALPHA. In an embodiment the grid 100 can be positioned such that the LSS have the same width 104 and an height / length or about height 105 / sin (ALPHA). If ALPHA is about 20 degrees, the size of the spot will be about 3x height 105 of the gap 102 due to the extension of the angle of incidence.
In a first embodiment the arrangement or the grid 100 is maintained and agreed to prior art arrangements. The level sensor spots LSS according to this arrangement will be aligned with the X axis of the substrate surface and will move according to the edition under an angle of 45 degrees with respect to the XY plane of the substrate during the scanning with the level sensor.
In a second embodiment of the level sensor, the level sensor is adapted in order to project the level sensor spots LSS at an angle corresponding to the angle of combined movement generated by the actuators. If the combined movement is oriented as shown in Figure 6, the LSS can be tilted over 45 degrees in the XY plane of the substrate. This can be obtained by tilting the grid 100 over an angle of GAMMA, where GAMMA is generally equal to 45 / sin (ALPHA). The tilt GAMMA is an embodiment around the z-axis (gRz) or the grid, being the rotation axis out of the plane according to figure 7a.
Figure 8 shows schematically this embodiment. The skilled person will be familiar with the representation according to Figure 8-14, the projection optics being part of the projection part of the level sensor is not depicted for clarity sakes. Grid 100 is part of the projection part of the level sensor and is positioned in the path of the radiation beam emitted by a radiation source (not shown) or the projection part. Further optical elements such as mirrors, lenses etc. could be part of the projection part.
By rotating the grid 100 over GAMMA degree around gRz, the level sensor spots are rotated as depicted in Figure 8.
Grid 100 was originally positioned at an angle of 70 degrees with respect to the Z axis. In this way the beam 16 is very close to perpendicular to the lane of gaps 102. However such a position results in the fact that only the central part 110 or the gaps 102 can be in focus on the substrate surface in the embodiment according to figure 8. The optical distance from the top side 111 or the gap 109 to the substrate surface is longer than the distance from the down side 112 or gap 109 to the substrate surface. In an embodiment the grid is positioned such that this effect does not occur. Such positioning to counter the defocus is referred to as the Scheimpflug condition. Instead of a 70 degree tilt with respect to Z, the grid could be tilted 90 degrees. The grid 100 is then generously positioned parallel to the substrate surface W. This will allow the complete set of LSS to be in focus.
Figure 9 shows an embodiment for achieving focussed LSS at an angle of 45 degrees with respect to the XY plane of the substrate W. The grid is positioned such that the LSS obey the Scheimpflug condition, with the complete level sensor spots are now focussed. The grid 100 is tilted over DELTA degrees, about 45 in an embodiment, around grz in order to rotate the spots correspondingly.
According to a third embodiment, figure 10, instead of grid 100, grid 110 according to figure 7b is positioned in the path of radiation 16. Grid 110 differs from grid 100 in that the grating is positioned diagonally over the rectangular body of the grid 110. The result is that the tilt 129 around gRz has changed in respect to the situation according to the first and second embodiment (Fig 8.9). The tilt 129 will be less than angle GAMMA.
According to a fourth embodiment, figure 11, the grid 110 is not tilted around gRz. Such a tilt may, however, require a redesign or current level sensors. According to the third embodiment as shown in figure 10 the grid is rotated with respect to its position according to prior art. Space for such a rotation is not available in some prior art lithographic systems.
Figure 11 shows the grid 110 positioned such that the LSS are rotated over 45 degrees with respect to the XY plane of the substrate surface, while the grid 100 is tilted around gRy over an angle 130. In fact part 120 or grid 110 is more forward (downstream) than part 121 which is more upstream. As the LS spots formed as a result of the gaps near 120 are also positioned more forward in the Y direction of the substrate surface, the tilting around gRy will result in reducing the defocus of the spots in comparison with the embodiment according to figure 10.
Figure 12 shows a further embodiment having basically the same arrangement for the grid 110. The projection part of the level sensor as schematically illustrated in Figure 12 now comprises an optical element 140 in the pathway of the radiation beam 16. The radiation beam will penetrate the optical element 140 and will be influenced in accordance with the refractive index of the material of the optical element.
In an embodiment, the optical element comprises wedges. Since the grid 110 is tilted around gRy with an angle 131, optical element 140 including wedges, preferably wedges adapted for each spot, can compensate phase differences between the spots. This will allow the use of a detection grating according to prior art arrangement. The skilled artisan will understand adapted the wedge thickness to compensate for the focus difference.
Rotation of the grid 100 or grid 110 according to any of the eleven according to figure 8-12 in order to rotate the LSS on the substrate surface will result in a wider LSS array. In figure 2 the width of five LSS is indicated with wLSS. If the grid 100 or 110 is rotated according to any of the mentioned numbers in order to orient the LSS array under an angle of 45 degrees with respect to the XY plane of the substrate surface, this width wLSS will become 1.41 time wider.
The result of the combined movement of both actuators at full speed resulting in 45 degree directed strokes during scanning as illustrated in Figure 4 and the 1.41 wider LS array, will together result in a possible time saving of 50%. Since the speed is increased 1.4 and the width of the LS array is also increased, a prior art level sensor arranged and adapted according to the invention could perform its level sensing method at double speed.
When rotating the LS spots on the grating the originally used width of the LSS may be maintained in order to have an additional gain or LS width. In another embodiment, grid 115 according to figure 7c could be used. Grid 115 has a diagonal grating having more slits 102, eg, 13 instead of 9. Using the modified grid 115 in the according to figures 8-12 would result in having an LSS array generally having the same size of spots on the substrate surface . According to this embodiment, the same density of measurements point for height measurements can be maintained. 1000138] Figure 13 shows a further embodiment having a Scheimpflug positioned grid 110 rotated around gZ over an angle 134, or about 45 degrees, in order to rotate the LSS over 45 degrees. The Scheimpflug condition is obtained by a rotation of the grid around gRx. 1000139] Figures 8-13 only show essential elements of the projection part of a level sensor. The skilled person will understand that corresponding measures can be tasks at the detection part of the level sensor. The detection part also comprises a grid. This can be a grid 100, grid 110 or grid 115. The detection part grids can be rotated around a gRz, gRy, gRx in order to allow detection of the rotated LSS and to be able to measure the Scheimpflug conditioned LSS. The skilled person will understand from the foregoing that it is possible to combine different expands for the projection part and the detection part. However it may improve the simplicity of the design to have the projection and detection part arranged in a similar fashion.
In an embodiment the substrate table, rotated around Rz is in order to align the fields 40 with the improved scanning stroke according to the invention. The substrate table WT is rotated over 45 degrees in order to allow maximum scanning speed. Now LS scanning is performed at higher speed, but with the strokes aligned with the fields 40 on the substrate.
[000141] Since according to at least one aspect of the invention it is proposed to scan the heights of the substrate surface in a direction at an angle with respect to the middle of the fields as illustrated in figure 4, it is proposed according to the invention to correct the measured heights according to any of the methods of the invention. The correction can be a single calibration. The calibration is performed with respect to layout-dependent measurement, with scanning strokes are performed according to figure 4.
The layout independent leveling calibration utilizes a calibration mechanism (such as a fingerprint mechanism) for a robust mechanism to calibrate the effect of layout independent measurement in relatively short time. Using the mechanism described here, it is possible to calibrate using a single substrate or target portion, although calibration may also be done using more then one substrate or target portion. J000143] The calibration identifies a set or at least one special calibration target portion.
Each calibration target portion is scanned multiple times. Each target portion is scanned with the level sensor at least once in every possible pattern or level sensor measurement that has been performed on any target portion on the substrate.
So, during calibration, the least one calibration target portion is measured a number of times where each time the level sensor has a different relative position with respect to the target portion. The relative positions of the scans are chosen such that they correspond to a possible level sensor scan as will be performed during current level sensor measurements as will place for actual exposure.
[000145] By comparing the different calibration scans performed with the different relative positions with respect to the target portion the actual level sensor scans and data as gathered later on for actual exposure can be compensated to minimize differences between the exposure focus between target portions on a substrate is reduced.
[000146] By comparing the different calibration scans, the effect of the relative position of the level sensor scan on the exposure focus data can be predicted and thus compensated.
For the most common columnar layout, the number of calibration scans will be the number of strokes in the independent leveling data acquisition layout. This calibration can be viewed as superimposing all the different patterns or scanning a target portion 41 according to the method of figure 6 on the same target portion 40 scanned according to prior art.
According to an example, two patterns measured according to any method using two actuators according to the invention can be superimposed on a pattern measured according to figure 4 or a corresponding target portion 40.41. Each pattern of the three patterns of measurement on this target portion generates a set of focus exposure set points. The difference between the focus exposure set of points or a layout independent pattern and the layout dependent pattern is the calibration (data) or that layout dependent pattern.
A calibration mechanism is used to generate a robust set of measurements to use as input for the calibration. The standard deviation or all the readings in each calibration target portion is calculated. According to an embodiment, the target portions with the highest standard deviation value are discarded from the calibration. The (remaining) target portions may be averaged point by point to create the calibration data (fingerprint data).
During the current level sensor measurements as performed on a target portion before exposure, the calibration data (fingerprint) can be used to correct the actual exposure focus. By doing so, the difference between exposure focus or different target portions, as far as this result from the fact that the level sensor measurements were performed with a different relative position to the center of the target portion is reduced.
It will be understood that the calibration data (fingerprint) may include corrections for the exposure focus as well as computed based on the level sensor data. However, according to an alternative, the calibration data (fingerprint) may also include corrections for the level sensor data, so exposure focus can be computer based on the corrected level sensor data.
[000152] According to an aspect of the invention, multiple wafers are manufactured with the lithographic apparatus according to the invention. The wafers are manufactured layer after layer. For all layers of a certain series or wafers having the same structure, a calibration measurement according to the invention has been performed. For each layer or a certain series of wafers, a calibration measurement is performed by scanning the heights of the substrate surface after production or said layer, and said data is compared to the data obtained by a method according to the invention, in particular scanning at 45 degrees with respect to the middle of the target areas of the substrate. By comparing the two measurement data, a correction map or calibration data can be obtained for correction the heights measured with the method or apparatus having a higher scanning speed according to the invention.
The data set of heights corresponding to a wafer having said layer produced last is corrected according to the invention with the calibration data obtained according to the correction method of this invention.
The calibration data may have the form of a calibration table, in which for a number of relative x, y positions within a target portion a calibration value is stored that may be used to compute corrected level sensor data. Different calibration tables may be provided for different relative positions or the level sensor scan.
It will be understood that the calibration correction can be applied in many ways. The calibration correction can be used to directly correct the measured level sensor data, and compute exposure focus data based on the corrected level sensor data. Alternatively, the level sensor data can be used to compute exposure focus data, where the calibration data can be used to correct this exposure focus data to obtain corrected exposure focus data.
Although specific reference may have been made above to the use of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows , is not limited to optical lithography. In imprint lithography, a topography in a patterning device, the pattern created on a substrate. The topography of the patterning device may be pressed into a layer or resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
In the present document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation or particle flux, including, but not limited to, ultraviolet radiation (eg, having a wavelength or about 365nm, 355nm, 248nm, 193nm, 157nm or 126nm), extreme ultraviolet radiation (EUV), X-rays, electrons and ions. Also, the invention is described using a reference system of orthogonal X, Y and Z directions and rotation about an axis parallel to the / direction is denoted Ri. Further, unless the context otherwise requires, the term "vertical" (Z) used is intended to refer to the direction normal to the substrate or mask surface, rather than implying any particular orientation of the apparatus. Similarly, the term "horizontal" refers to a direction parallel to the substrate or mask surface, and thus normal to the "vertical" direction.
The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
While specific expired of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (eg, semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope or the clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A lithographic projection apparatus including: a support constructed to support a patterning device, the patterning device being capable or imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed and arranged to hold a substrate; a projection system constructed and arranged to project the patterned radiation beam onto a target portion of the substrate; a level sensor constructed and arranged to perform height measurements or at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system a first actuator constructed and arranged to move the substrate table at least in a first direction perpendicular to a surface of the substrate having a maximum speed; and a second actuator constructed and arranged to move the substrate table at least in a second direction perpendicular to a surface of the substrate having a maximum speed; a controller constructed and arranged to generate a stroke of relative movement between the substrate and the level sensor, by controlling the first and second actuator, the controller is constructed and arranged to combine first and second actuator movement to effect combined movement at a speed higher than the maximum speed or one actuator. 2. A lithographic projection apparatus according to clause 1, the controller is constructed and arranged to generate the stroke of combined movement by combining at least 71% of the maximum speed of both actuators. 3. A lithographic projection apparatus according to clause 2. The controller is constructed and arranged to generate a stroke of combined movement or both actuators moving the substrate table at substantially a maximum speed. 4. A lithographic projection apparatus according to any of the preceding clauses said substrate table is moveable to effect a scanning exposure or substrate carried by said substrate holder, and said level sensor is arranged to measure at least one of the vertical position and the tilt about at least one horizontal axis or a target area on said substrate. 5. A lithographic projection apparatus according to any of the preceding clauses, comprising the level sensor comprising: a projection part for directing radiation onto the substrate containing a radiation source, a projection grid having slits positioned downstream from the radiation source, and a first reflector positioned to direct radiation from the radiation source towards a substrate surface as level sensor spots; and a detection part for detecting reflected radiation from the substrate surface, including a detector, a detection grid having slits positioned in between the substrate and the detector, and a second reflector positioned to direct light reflected from the wafer surface to a detector, grids are positioned to project and detect level sensor spots that are aligned with the stroke of the relative movement. 6. A lithographic projection apparatus according to clause 5, the level sensor spots on the substrate are rotated over substantially 45 degrees with respect to the direction of movement or at least one of the actuators. 7. A lithographic projection apparatus according to clause 5 or 6, at least one of projection grid or detection grid is positioned substantially parallel with the substrate surface. 8. A lithographic projection apparatus according to any of the clauses 5-7, at least one of the projection grid or the detection grid is generally of rectangular shape, having a row of slits positioned at a non-zero angle with respect to its width. 9. A lithograpic projection apparatus according to clause 8, where the slits are positioned substantially along the diagonal or the detection grid. 10. A lithographic projection apparatus according to any of the clauses 6-9, at least one of the projection grid or the detection grid is tilted such that the slits are at different distances from the radiation source. 11. A lithographic projection apparatus according to any of the clauses 6-10, at least one of the projection grid or the detection grid is tilted around an axis substantially perpendicular to a plane formed by traveling direction of the radiation and an axis of the slits. 12. A lithographic projection apparatus according to any of the clauses 6-11, where the projection grid is tilted such that a tilt angle of the projection grid and an incident angle of the radiation combine to substantial 90 degrees. 13. A lithographic projection apparatus according to any of the clauses 6-11, the projection grid is tilted such that a tilt angle of the projection grid and an incident angle of the radiation meet the Scheimpflug condition. 14. A lithographic projection apparatus according to any of the clauses 6-13, the projection part further comprises a wedge positioned in the path of radiation downstream from the projection grid for adapting the optical path length of the radiation. 15. A lithographic projection apparatus according to any of the clauses 6-14, the detection part further comprises a wedge positioned in the path of radiation upstream from the projection grid for adapting the optical path length of the radiation. 16. A method for sensing the level of a substrate carried on a substrate table, in a lithographic projection apparatus, that has a support constructed to support a patterning device, the patterning device being capable or providing a radiation beam with a pattern in its cross -section to form a patterned radiation beam; a substrate table constructed and arranged to hold a substrate; a projection system constructed and arranged to project the patterned radiation beam onto a target portion of the substrate; a level sensor constructed and arranged to perform height measurements or at least part of the substrate to generate height data, first and second actuators for generating a relative moment between substrate and the level sensor, the actuators having a maximum speed, the method including: providing a substrate on the substrate table generating relative movement between the substrate and the level sensor, and sensing a level of the substrate, further including combining the relative movement generated by the two actuators to a velocity higher than the maximum velocity or movement generated by one actuator . 17. A method according to clause 16, the generated relative movement is a movement in several strokes. 18. A method according to clause 16 or 17, where the height measurements are performed by scanning the least part of the substrate in a scanning direction with a level sensor. 19. A method according to any of the clauses 16-18, where the first actuator generates a movement in an X-direction and the second actuator generates movement in a Y-direction, and the combined movement is in an XY plane under an angle or at least 20 degrees with respect to the axis directions 20. A method according to clause 19, the movement is formed by strokes substantially at a 45 degree angle with respect to the X and Y direction. 21. A method according to any of the clauses 16-20, comprising the method further comprises the level sensor projecting radiation on the substrate surface and detecting the reflected radiation from the substrate surface. 22. A method according to clause 21, where the projecting the radiation further comprises applying a number of beams or radiation on the substrate surface as level sensor spots, the level sensor spots are rotated over a non-zero angle with respect to at least one of the directions of relative movement and combining the relative movement results in a relative movement at generally the same non-zero angle. 23. A method according to clause 21 or 22, including the method further comprises adapting the optical path length or at least one of the projected radiation or reflected radiation using refraction. 24. A computer program on a data carrier, a computer readable medium, or a computer program product, the computer program having code or instructions for sensing the level of a substrate carried on a substrate table, the code or instructions for performing the method of : generating relative movement between the substrate and the level sensor sensing the level of the substrate with the level sensor, being the generated relative movement is a combined movement or at least two actuators for generating movement or the substrate table relative to the level sensor. 25. A system for controlling the position of a substrate, the system including a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform, using height data, a method for positioning a target portion of the substrate with respect to a focal plane of a projection system, comprising the method comprises: performing height measurements or at least part of the substrate to generate the height data using a method according to any of the clauses 16-23; using predetermined correction heights to compute corrected height data for the height data; and positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data. 26. A system for controlling the position of a substrate, the system including a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform a method for calculating correction heights to correct height data obtained by a level sensor, according to the method comprises: performing height measurements of a target portion of the substrate to generate a height profile according to any of the clauses 16-24; computing a level profile based on the height profile; and determining correction heights by computing the difference between the level profile and the height profile. 27. A computer-readable medium encoded with a computer program containing instructions that are executable by a processor to perform, using height data, a method for positioning a target portion or a substrate with respect to a focal plane or a projection system, method comprises: performing height measurements or at least part of the substrate to generate the height data according to any of the clauses 16-24; using predetermined correction heights to compute corrected height data for the height data; and positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data. 28. A computer-readable medium encoded with a computer program containing instructions that are executable by a processor to perform, using height data, a method for positioning a target portion or a substrate with respect to a focal plane or a projection system, method comprises: performing height measurements of a target portion of the substrate to generate a height profile according to any of the clauses 16-24; computing a level profile based on the height profile; and determining correction heights by computing the difference between the level profile and the height profile.

权利要求:
Claims (1)
[1]
A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.

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法律状态:
2009-11-02| AD1A| A request for search or an international type search has been filed|

优先权:

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US6454508|2008-03-11|

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