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    • 专利摘要:
    A method of treating or operating a radiation source apparatus (SO), for instance for generating EUV radiation for device lithography, is disclosed. The method is for use with radiation source apparatus having a chamber (220) arranged to hold a plasma (210) for radiation generation, with the plasma excited from a metal fuel in use by a first plasma generator (LA). The method comprises flowing a gas (via 41) comprising hydrogen and boron hydride through the chamber with the gas in an excited state comprising free radicals of hydrogen. The presence of the boron hydride with the hydrogen radicals in the gas is effective cleaning or reducing build-up of metal fuel deposits on surfaces of the chamber or associated optics, particularly on reflective surfaces of the radiation collector mirror (CO). The method is particularly suitable for use with tin fuel. The hydrogen free radicals may be generated by the plasma (210) for radiation generation itself, or may involve exciting the gas using a second, separate free radical generator (41). The method may be used to reduce deposition whilst the radiation source apparatus is in use for generation of radiation or may be applied as a treatment for cleaning whilst radiation generation is interrupted.
    公开号:NL2009846A
    申请号:NL2009846
    申请日:2012-11-20
    公开日:2013-06-26
    发明作者:Harmeet Singh
    申请人:Asml Netherlands Bv；
    IPC主号:
    专利说明:

    RADIATION SOURCE AND METHOD FOR LITHOGRAPHIC APPARATUS AND
    DEVICE MANUFACTURE
    Field
    [0001] The present invention relates to methods for treating and/or operating a radiation source, such as an EUV radiation source for use in lithography, and to lithographic apparatus and methods for manufacturing devices using the radiation source.
    Background Art
    [0002] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
    [0003] Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.
    [0004] A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1):
    (1) where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of
    [0005] In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Such radiation is termed extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.
    [0006] EUV radiation may be produced using a plasma. A radiation source apparatus for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector apparatus for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as particles of a suitable material or a stream of a suitable gas or vapour. Typically, the fuel may be a metal fuel such as lithium or tin. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector which may form part of the radiation source apparatus. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The radiation source apparatus may include an enclosing structure or chamber arranged to provide a vacuum or low pressure environment to support the plasma. Such a radiation source apparatus is typically termed a laser produced plasma (LPP) source.
    [0007] Discharge Produced Plasma (DPP) radiation sources generate radiation, such as extreme ultraviolet radiation (EUV) from a plasma formed by means of a discharge, and in particular may involve high temperature vaporisation of a metal fuel for the generation of radiation by directing an excitation beam such as a laser beam towards the metal fuel. Metal, typically in molten form, may be supplied to discharge surfaces of plasma-excitation electrodes and vaporized by means of irradiation with an excitation beam such as a laser beam whereby a high temperature plasma may be subsequently excited from the vaporized metal fuel by means of a high voltage discharge across the electrodes.
    [0008] The DPP radiation source apparatus may include an enclosing structure or chamber arranged to provide a vacuum or low pressure environment to support the plasma. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, such as a mirrored normal incidence radiation collector, which may form part of the radiation source apparatus. In such a case, the radiation source apparatus may be referred to as a source collector apparatus.
    [0009] As used herein, the term vaporization is considered to also include gasification, and the fuel after vaporization may be in the form of a gas (for instance as individual atoms) and/or a vapour (comprising small droplets). The term "particles" is used herein includes both solid and liquid (a i.e., droplet) particles.
    [0010] For EUV radiation source apparatus, such as set out above, where radiation is generated from a plasma excited from a metal fuel, a problem that arises is that the metal fuel may deposit and build up on the internal surfaces of the apparatus, such as on the inside of the chamber holding the plasma and on mirrored surfaces of and radiation collector.
    [0011] Debris particles of metal fuel may be generated as an undesirable byproduct of the generation of radiation, and these debris particles, as well as metal fuel in vaporised/gaseous state from the plasma, may deposit on internal surfaces of the radiation source apparatus and particularly on the radiation collector.
    [0012] Eventually, it may become necessary to clean the internal surfaces of the radiation source apparatus, particularly mirrored radiation collector surfaces. It is desirable to maximize the period over which the radiation source apparatus can be used for generation of radiation between such cleaning procedures. It is also desirable to minimize the amount of metal fuel depositing upon internal surfaces of the radiation source apparatus, particularly on mirrored surfaces of the radiation collector. It is also desirable to clean deposited metal fuel without the need to dismantle the radiation source apparatus.
    SUMMARY
    [0013] Therefor, what is needed is to provide methods for treatment or for operation of a radiation source apparatus generating radiation such as EUV radiation from a plasma excited from a metal fuel, in order to address these problems and other problems discussed above.
    [0014] An aspect of the present invention provides a method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, with the plasma excited from a metal fuel in use by a first plasma generator, the method comprising flowing a gas comprising hydrogen and boron hydride through the chamber with the gas in an excited state comprising free radicals of hydrogen (also referred to herein in the abbreviated form “a gas in an excited state”).
    [0015] The chamber will be substantially closed, although there may typically be apertures therein in order to allow radiation generated by the radiation source apparatus to exit from the radiation source apparatus into the optical system of a lithographic apparatus.
    [0016] The first plasma generator may be any suitable plasma generator such as a laser produced plasma source or a discharge produced plasma source as described herein. The metal fuel may be any suitable metal fuel for generation of a plasma to generate radiation such as EUV radiation. Typical fuels include lithium and tin.
    [0017] The gas may be flowed through the chamber through an entrance orifice and exit the chamber through an exit orifice, with the gas comprising boron hydride and hydrogen supplied in a pre-mixed state. In another suitable arrangement, the hydrogen and boron hydride may be supplied separately into the chamber, for instance as separate gas streams, and may for instance be mixed therein, by diffusion, or by other means.
    [0018] The gas may be excited to form free radicals of hydrogen by the first plasma generator in use. Hence, the first plasma generator may also act as a first free radical generator whilst the apparatus is used to generate radiation.
    [0019] The radiation source apparatus may, for instance, be a laser produced plasma apparatus, wherein the first plasma generator comprises a laser beam directed at the metal fuel. Such a first plasma generator may also generate hydrogen free radicals in the gas.
    [0020] Alternatively or additionally, the gas may be excited to form free radicals of hydrogen by a second free radical generator, separate from the first plasma generator. For instance, the gas comprising hydrogen and boron hydride may be flowed through the chamber whilst the apparatus is not in use for generation of radiation (for instance with the first plasma source not on) and then the gas comprising hydrogen and boron hydride replaced by an operation gas prior to using the apparatus for generation of radiation. The operation gas may, for instance, be an inert gas such as argon or, for instance, may be hydrogen free from boron hydride, such as pure hydrogen.
    [0021] The second free radical generator may be any suitable means for generation of hydrogen free radicals from the gas and may be located within the chamber or outside the chamber. For instance the second free radical generator may comprise second plasma generator for generation of a second plasma for excitation of free radicals. The second free radical generator may be selected from the group consisting of a thermal cracker, inductively coupled plasma generator, and a microwave plasma generator. It will be evident that for second free radical generators which are plasma generators, the hydrogen free radicals will be generated by the second plasma generated by the plasma generator, or by radiation therefrom.
    [0022] The gas may be excited to form free radicals of hydrogen by the second free radical generator prior to entry of the gas into the chamber, for instance at a location in or near a gas entrance orifice so that excitation of hydrogen free radicals may take place in the gas outside the chamber and then the free radicals flow into the chamber with the gas.
    [0023] The gas in an excited state may be flowed through the chamber whilst the radiation source apparatus is not in use for generating radiation.
    [0024] The radiation source apparatus may a discharge produced plasma (DPP) apparatus, wherein the first plasma generator comprises a laser beam directed at the metal fuel to generate metal fuel vapour and a pair of discharge electrodes arranged for generation of the plasma for radiation generation by electrical discharge through the metal fuel vapour.
    [0025] The gas in an excited state may be directed to flow over reflective surfaces of a radiation collector within the chamber. This may be achieved by the use of nozzles or vanes, for instance, to direct the flow within the chamber.
    [0026] The gas flowing through the chamber may comprise from 10 to 500 Pa partial pressure of hydrogen, for instance from 50 to 200 Pa and from 0.1 to 5 Pa partial pressure of boron hydride, such as from 0.5 to 2 Pa.
    [0027] The gas may suitably consist essentially of hydrogen and boron hydride, meaning that other gases or vapours are not deliberately added to the gas but are merely present as naturally occurring impurities, for instance at partial pressures of less than say 0.05 Pa.
    [0028] In this specification, partial pressures are measured at 25QC.
    [0029] The flow rate for the gas through the chamber of the radiation source apparatus is suitably in the range of 50 to 1000 standard litres per minute, for instance 60 to 500 standard litres per minute such as 80 to 200 standard litres per minute for a chamber having a volume of 1000 litres. For chambers of differing volumes, suitable flow rates may be determined in proportion.
    [0030] Suitably, the metal fuel is a tin fuel, meaning that the fuel consists essentially of tin, with other elements present as naturally occurring impurities, for instance with non-tin elements present at total levels of 1% by weight or less.
    [0031] An aspect of the present invention also provides a method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by a first plasma generator, the method comprising flowing a gas comprising hydrogen through the chamber, wherein the gas is excited to form free radicals of hydrogen by a second free radical generator. The second free radical generator may be as set out hereinbefore in relation to the previous aspect of the present invention.
    [0032] An aspect of the present invention provides a device manufacturing method comprising projecting a patterned beam of radiation onto a substrate, wherein the beam of radiation is generated using a radiation source apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma for radiation generation excited from a metal fuel in use by a first plasma generator which is an excitation radiation beam, the method comprising flowing a gas comprising hydrogen and boron hydride through the chamber, wherein the gas is excited to generate free radicals of hydrogen by the plasma for radiation generation, when in use for generation of radiation.
    [0033] The excitation radiation beam may suitably be a laser beam, and may, for instance, be focused onto the metal fuel source to form the plasma. The excitation radiation beam is thus acting as first plasma generator for this aspect of the present invention and the resulting plasma is also acting to form hydrogen free radicals from the gas whilst the radiation source is in operation to generate radiation such as EUV radiation.
    [0034] An aspect of the present invention provides a lithographic apparatus comprising an illumination system configured to condition a radiation beam, a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam,=a substrate table constructed to hold a substrate, and a projection system configured to project the patterned radiation beam onto a target portion of the substrate. The illumination system comprises a radiation source apparatus comprising a first plasma generator and a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by the first plasma generator. The lithographic apparatus further comprising an arrangement for flowing a gas comprising hydrogen through the chamber, and a second free radical generator arranged to excite the gas to generate hydrogen free radicals in the gas flowing through the chamber.
    [0035] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.
    BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
    [0036] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.
    [0037] FIG. 1 depicts a lithographic apparatus according to an embodiment of the present invention.
    [0038] FIG. 2 is a more detailed view of the apparatus.
    [0039] FIG. 3 is a more detailed view of the source collector apparatus of the apparatus of Figures 1 and 2.
    [0040] FIG. 4 depicts a schematic plan view of a radiation source apparatus adapted for use with a method according to an embodiment of the present invention.
    [0041] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.
    DETAILED DESCRIPTION
    [0042] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.
    [0043] The embodiment(s) described, and references in the specification to "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
    [0044] Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A
    machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.
    [0045] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented.
    [0046] Figure 1 schematically shows a lithographic apparatus LAP including a source collector module SO according to an embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation); a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask or a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; 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 configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.
    [0047] 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.
    [0048] The support structure MT holds the patterning device MA 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 held 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.
    [0049] The term “patterning device” 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. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
    [0050] 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.
    [0051] The projection system, like 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, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since other gases may absorb too much radiation. A vacuum environment or a low pressure environment may therefore be provided to portions beam path with the aid of a vacuum wall and vacuum pumps.
    [0052] As here depicted, the apparatus is of a reflective type (e.g., employing a reflective mask).
    [0053] 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.
    [0054] Referring to Figure 1, the illuminator IL receives an extreme ultra violet radiation beam from the source collector apparatus SO. Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., lithium or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma ("LPP") the required plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. The source collector apparatus SO may be part of an EUV radiation system including a laser, not shown in Figure 1, for providing the laser beam exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, disposed in the source collector apparatus. The laser and the source collector apparatus may be separate entities, for example when a C02 laser is used to provide the laser beam for fuel excitation. The laser beam may be passed from the laser to the source collector apparatus with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the source collector apparatus, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.
    [0055] The illuminator IL may comprise an adjuster 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) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as facetted field and pupil mirror devices. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
    [0056] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After being reflected from the patterning device (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PS2 (e.g., an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g., 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 PS1 can be used to accurately position the patterning device (e.g., mask) MA with respect to the path of the radiation beam B. Patterning device (e.g., mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.
    [0057] The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the support structure (e.g., 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 (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 C can be exposed.
    2. In scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted 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 support structure (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.
    3. In another mode, the support structure (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern 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 of a type as referred to above.
    [0058] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
    [0059] Figure 2 shows the apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector apparatus SO. An EUV radiation emitting plasma 210 may be formed by a discharge produced plasma source. EUV radiation may be produced by a gas or vapour, for example Li vapour or Sn vapour, in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 210 is created by, for example, an electrical discharge causing an at least partially ionized plasma. Partial pressures of, for example, 10 Pa of Li, Sn vapour or any other suitable gas or vapour fuel may be required for efficient generation of the radiation. In an embodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.
    [0060] The radiation emitted by the hot plasma 210 is passed from a source chamber 211 into a collector chamber 212 via an optional gas barrier or contaminant trap 230 (in some cases also referred to as contaminant barrier or foil trap) which is positioned in or behind an opening in source chamber 211. The contaminant trap 230 may include a channel structure. Contamination trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 230 further indicated herein at least includes a channel structure, as known in the art.
    [0061] The collector chamber 212 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses collector CO can be reflected off a grating spectral filter 240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus IF is located at or near an opening 221 in the enclosing structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.
    [0062] Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device 22 and a facetted pupil mirror device 24 arranged to provide a desired angular distribution of the radiation beam 21, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 21 at the patterning device MA, held by the support structure MT, a patterned beam 26 is formed and the patterned beam 26 is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by the wafer stage or substrate table WT.
    [0063] More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 240 may optionally be present, depending upon the type of lithographic apparatus. Further, there may be more mirrors present than those shown in the Figures, for example there may be 1- 6 additional reflective elements present in the projection system PS than shown in Figure 2.
    [0064] Collector optic CO, as illustrated in Figure 2, is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is desirably used in combination with a discharge produced plasma source, often called a DPP source.
    [0065] Alternatively, the source collector apparatus SO may be part of an LPP radiation system as shown in Figure 3. A laser LA is arranged to deposit laser energy into a metal fuel, such as tin (Sn) or lithium (Li), creating the highly ionized plasma 210 with electron temperatures of several 10s of eV. The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma, collected by a near normal incidence collector optic CO and focused onto the opening 221 in the enclosing structure 220.
    [0066] Turning to Figure 4, this figure shows a schematic representation of a radiation source apparatus for use with the method of an aspect of the present invention. In common with the embodiment shown in Figure 3, a laser LA is arranged to deposit laser energy into a metal fuel such as tin or lithium, in this case tin, to create the highly ionised plasma 210. The energetic radiation generated from the plasma is collected by the collector optic CO and focused onto the opening 221 in the chamber or enclosing structure 220.
    [0067] The chamber 220 is provided with a gas inlet pipe 40 and a gas outlet pipe 42. The gas inlet pipe 40 has a free radical generator 41 located within it.
    [0068] In use, a gas of hydrogen and boron hydride, in this example consisting of hydrogen and boron hydride, with a hydrogen partial pressure of 100 Pa and boron hydride partial pressure of 1 Pa, is flowed into the chamber 220, passes through the free radical generator 41, and a enters the chamber 220 through inlet pipe 40. The gas passes over the collector mirror CO and exits the chamber 220 through the outlet pipe 42. In this embodiment, the free radical generator 41 is a microwave plasma generator, but other suitable plasma generators may be used instead. In addition to any free radicals generated by the free radical generator 41, hydrogen free radicals may also be generated in the gas by the metal fuel plasma 210.
    [0069] The presence of the boron hydride at a partial pressure of 1 Pa typically may reduce EUV intensity at 13.5 nm by approximately 3%, and so the radiation source apparatus may still be operated efficiently whilst the gas of hydrogen and boron hydride, at the partial pressures indicated, is flowed through chamber 220. In order to maintain clean internal surfaces without excessive build-up of metal fuel deposits, it may not be necessary to operate the free radical generator 41 whilst the radiation source apparatus is in use to generate EUV radiation. This is because the hydrogen free radicals generated by the metal fuel plasma 210 may be sufficient to give cleaning. In the event that deposits of metal fuel build up during operation of the radiation source apparatus, generation of radiation may be interrupted for a period of and higher pressures of hydrogen and boron hydride used to provide greater scavenging rates, using the free radical generator 41 to generate hydrogen free radicals from the gas in the absence of plasma 210. It will be evident to the person skilled in the field that various combinations of use of the fuel plasma 210 and the free radical generator 41 may be used to generate cleaning of the apparatus either using the gas at low pressure during radiation generation and/or using the gas at higher pressures specifically for cleaning. So, for instance, in addition to generation of hydrogen free radicals by the plasma 210, whilst the apparatus is used for generation of radiation, further free radicals may also be generated simultaneously by the second free radical generator 41.
    [0070] The apparatus as shown in Figure 4 is also suitable for use with a gas comprising hydrogen in the absence of boron hydride.
    [0071] The present invention as set out hereinbefore may provide a number of advantageous features.
    [0072] When the gas is excited to form free radicals of hydrogen by the first plasma generator in use, whilst the apparatus is used to generate radiation, but this provides the benefit that the maintenance of clean surfaces arising from the scavenging of deposited metal from the surfaces by the excited gas comprising hydrogen and boron hydride takes place at the same time as the operation of the source apparatus to generate radiation, such as EUV radiation. In other words, the surfaces may be maintained in a clean state over long periods of time without the need to strip down the radiation source apparatus for cleaning. With this mode of operation, no special cleaning cycle may be required because the maintenance of clean surfaces occurs whilst radiation is being generated. The partial pressures of hydrogen and boron hydride are selected to provide good cleaning whilst not causing excessive attenuation of the intensity of the generated radiation by absorption. This mode of operation of the method of the present invention is particularly useful for LPP radiation source apparatus, where it is conventional to use hydrogen as a gas within the chamber of the radiation source and so no particular change to the apparatus operating method is required other than the addition of boron hydride into the gas flow.
    [0073] Alternatively or additionally, the gas may be excited to form free radicals of hydrogen by a second free radical generator, separate from the first plasma generator. For instance, the gas comprising hydrogen and boron hydride may be flowed through the chamber whilst the apparatus is not in use for generation of radiation (for instance with the first plasma source not on) and then the gas comprising hydrogen and boron hydride replaced by an operation gas prior to using the apparatus for generation of radiation. The operation gas may, for instance, be an inert gas such as argon, for instance for a DPP radiation source, or may be hydrogen free from boron hydride, such as pure hydrogen, for an LPP radiation source. This may by suitable in circumstances where it is undesirable to operate the first plasma generator in the presence of a gas comprising hydrogen and boron hydride. For instance, with LPP radiation sources, the attenuation of EUV radiation arising from the presence of boron hydride during operation may be unacceptable. For instance, with DPP radiation sources it may be undesirable and to use hydrogen as a gas surrounding the plasma whilst radiation is being generated as this may lead to degradation of electrode surfaces. In order to use the present invention for treatment of DPP radiation source apparatus, it may be appropriate to use the method of the present invention as a cleaning cycle, wherein the operation gas such as argon is first replaced by the gas comprising hydrogen/boron hydride whilst generation of radiation is interrupted. This provides the benefit that the DPP radiation source may still be treated in order to remove metal deposits from surfaces without the need to strip down the apparatus and expose the internal surfaces to atmospheric pressure.
    [0074] The gas flowing through the chamber may comprise from 10 to 500 Pa partial pressure of hydrogen, such as 50 to 200 Pa, and from 0.1 to 5 Pa partial pressure of boron hydride, such as 0.2 to 2 Pa. By the use of such levels, adequate removal of deposited metal fuel may be possible without excessive attenuation of radiation, particularly EUV radiation, by the gas. Lower partial pressures may give inadequate cleaning and higher partial pressures may lead to excessive loss in radiation intensity in the EUV region of the spectrum. This is particularly undesirable when the gas is flowed through the chamber whilst the radiation source apparatus is in use for the generation of EUV radiation.
    [0075] In this specification, a method of treating or operating a radiation source apparatus, for instance for generating EUV radiation for device lithography, is disclosed. The method is for use with radiation source apparatus having a chamber arranged to hold a plasma for radiation generation, with the plasma excited from a metal fuel in use by a first plasma generator. The method comprises flowing a gas comprising hydrogen and boron hydride through the chamber with the gas in an excited state comprising free radicals of hydrogen. The presence of the boron hydride with the hydrogen radicals in the gas is effective cleaning or reducing build-up of metal fuel deposits on surfaces of the chamber or associated optics, particularly on reflective surfaces of the radiation collector mirror. The method is particularly suitable for use with tin fuel.
    [0076] The hydrogen free radicals may be generated by the first plasma generator itself, or may involve exciting the gas using a second, separate free radical generator. The method may be used to reduce deposition whilst the radiation source apparatus is in use for generation of radiation or may be applied as a treatment for cleaning whilst radiation generation is interrupted.
    [0077] It has been found that the addition of a small amount of boron hydride to hydrogen, in the presence of hydrogen free radicals, generated either by the plasma for radiation generation itself or by a separate free radical generator, can lead to a surprising improvement in the cleaning of metal fuel deposited upon surfaces within a radiation source apparatus. Without wishing to be bound by theory, it is believed that the presence of boron hydride within the gas allow for improved removal of metal fuel deposits when in the presence of hydrogen free radicals. Boron has only 3 electrons in its outer shell and so forms strong Lewis acid compounds. Boron hydride exists only as a dimer B2H6 known to form hydride compounds with metals such as tin, e.g., H3B-SnH3. Due to the strong Lewis acid behaviour of boron, it is to be expected that dimers comprising both boron and metal may be formed upon addition of boron hydride to hydrogen gas, in the chamber, with hydrogen free radicals present. Boron hydride is extremely volatile so the co-dimers of boron hydride and metal should be more volatile than metal hydrides formed in the presence of hydrogen alone. Hence, the addition of boron hydride to hydrogen may lead to a substantial and surprising improvement in cleaning performance.
    [0078] An aspect of the present invention, already mentioned hereinbefore, also provides a method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by a first plasma generator, the method comprising flowing a gas comprising hydrogen through the chamber, wherein the gas wherein the gas is excited to form free radicals of hydrogen by a second free radical generator. For this aspect of the present invention, the presence of boron hydride within the gas is desirable but not essential. The use of a separate second free radical generator allows for high levels of hydrogen free radicals to be generated in order to provide cleaning of surfaces so that effective cleaning may be achievable without the need for incorporation of additional boron hydride.
    [0079] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer 1C, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
    [0080] Although specific reference may have been made above to the use of embodiments of the present invention in the context of optical lithography, it will be appreciated that the present 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 defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of 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.
    [0081] 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.
    [0082] While specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced otherwise than as described. For example, the radiation source apparatus may be a DPP source with the method of the present invention applied in a separate cleaning cycle whilst the source is not actively generating EUV radiation. 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 present invention as described without departing from the scope of the claims set out below.
    [0083] The term “EUV radiation” may be considered to encompass electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm, or example within the range of 5-10 nm such as 6.7 nm or 6.8 nm.
    [0084] It should be understood that while the use of words such as “preferable”, “preferably”, “preferred” or “more preferred” in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the present invention as defined in the appended claims. In relation to the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.
    [0085] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.
    [0086] The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description.
    Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.
    [0087] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.
    The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. Other aspects of the invention are set out as in the following numbered clauses:
    CLAUSES
    1. A method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, with the plasma excited from a metal fuel in use by a first plasma generator, the method comprising flowing a gas comprising hydrogen and boron hydride through the chamber with the gas in an excited state comprising free radicals of hydrogen.
    2. The method of clause 1 wherein the gas is flowed through the chamber in an excited state comprising free radicals of hydrogen during operation of the radiation source.
    3. The method of clause 1 or clause 2 wherein the gas is excited to form free radicals of hydrogen by the first plasma in use.
    4. The method of clause 3 wherein the radiation source apparatus is a laser produced plasma apparatus, wherein the first plasma generator comprises a laser beam directed at the metal fuel.
    5. The method of any preceding clause wherein the gas is excited to form free radicals of hydrogen by a second free radical generator separate from the first plasma.
    6. The method of clause 5 wherein the second free radical generator is a second plasma generator.
    7. The method of clause 5 wherein the second free radical generator is selected from the group consisting of a thermal cracker, a microwave plasma generator and an inductively coupled plasma generator.
    8. The method of any one of clauses 5 to 7 wherein the gas is excited to form free radicals of hydrogen by the second free radical generator prior to entry of the gas into the chamber.
    9. The method of any preceding clause wherein the gas in an excited state is flowed through the chamber whilst the radiation source apparatus is not in use for generating radiation.
    10. The method of any preceding clause wherein the radiation source apparatus is a discharge produced plasma apparatus, wherein the first plasma generator comprises a laser beam directed at the metal fuel to generate metal fuel vapour and a pair of discharge electrodes arranged for generation of the plasma for radiation generation by electrical discharge through the metal fuel vapour.
    11. The method of any preceding clause wherein the gas is directed to flow over reflective surfaces of a radiation collector within the chamber.
    12. The method of any preceding clause wherein the gas flowing through the chamber comprises from 10 to 500 Pa partial pressure of hydrogen and from 0.1 to 5 Pa partial pressure of boron hydride.
    13. The method of any preceding clause wherein the gas consists essentially of hydrogen and boron hydride.
    14. The method of any preceding clause wherein the metal fuel is a tin fuel.
    15. A method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by a first plasma generator, the method comprising flowing a gas comprising hydrogen through the chamber, wherein the gas is excited to form free radicals of hydrogen by a second free radical generator.
    16. A device manufacturing method comprising projecting a patterned beam of radiation onto a substrate, wherein the beam of radiation is generated using a radiation source apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma for radiation generation excited from a metal fuel in use by an excitation radiation beam, the method comprising flowing a gas comprising hydrogen and boron hydride through the chamber, wherein the gas is excited to generate free radicals of hydrogen by the plasma for radiation generation when in use for generation of radiation.
    17. The device manufacturing method of clause 16 wherein the excitation radiation beam is a laser beam.
    18. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate; wherein the illumination system comprises a radiation source apparatus comprising a first plasma generator and a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by the first plasma generator, the lithographic apparatus further comprising an arrangement for flowing a gas comprising hydrogen through the chamber, and a second free radical generator arranged to excite the gas to generate hydrogen free radicals in the gas flowing through the chamber.
    19. A method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, with the plasma excited from a metal fuel in use by a first plasma generator, the method comprising; flowing a gas comprising hydrogen and boron hydride through the chamber with the gas in an excited state comprising free radicals of hydrogen.
    20. The method of clause 19, wherein the gas is flowed through the chamber in an excited state comprising free radicals of hydrogen during operation of the radiation source.
    21. The method of clause 19, wherein the gas is excited to form free radicals of hydrogen by the first plasma in use.
    22. The method of clause 21, wherein: the radiation source apparatus is a laser produced plasma apparatus, and the first plasma generator comprises a laser beam directed at the metal fuel.
    23. The method of clause 19, wherein the gas is excited to form free radicals of hydrogen by a second free radical generator separate from the first plasma.
    24. The method of clause 23, wherein the second free radical generator is a second plasma generator.
    25. The method of clause 24, wherein the second free radical generator a thermal cracker, a microwave plasma generator or an inductively coupled plasma generator.
    26. The method of clause 23,wherein the gas is excited to form free radicals of hydrogen by the second free radical generator prior to entry of the gas into the chamber.
    27. The method of clause 19, wherein the gas in an excited state is flowed through the chamber whilst the radiation source apparatus is not in use for generating radiation.
    28. The method of clause 19, wherein: the radiation source apparatus is a discharge produced plasma apparatus, and the first plasma generator comprises a laser beam directed at the metal fuel to generate metal fuel vapor and a pair of discharge electrodes arranged for generation of the plasma for radiation generation by electrical discharge through the metal fuel vapor.
    29. The method of clause 19, wherein the gas is directed to flow over reflective surfaces of a radiation collector within the chamber.
    30. The method of clause 19, wherein the gas flowing through the chamber comprises from about 10 to 500 Pa partial pressure of hydrogen and from about 0.1 to 5 Pa partial pressure of boron hydride.
    31. The method of clause 19, wherein the gas comprises hydrogen and boron hydride.
    32. The method of clause 19, wherein the metal fuel is a tin fuel.
    33. A method of treating or operating a radiation source apparatus, the apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by a first plasma generator, the method comprising: flowing a gas comprising hydrogen through the chamber, wherein the gas is excited to form free radicals of hydrogen by a second free radical generator.
    34. A device manufacturing method comprising: projecting a patterned beam of radiation onto a substrate, the beam of radiation being generated using a radiation source apparatus comprising a chamber arranged to hold a plasma for radiation generation, the plasma for radiation generation excited from a metal fuel in use by an excitation radiation beam, flowing a gas comprising hydrogen and boron hydride through the chamber, and exciting the gas to generate free radicals of hydrogen by the plasma for radiation generation when in use for generation of radiation.
    35. The device manufacturing method of clause 34, wherein the excitation radiation beam is a laser beam.
    36. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam, the illumination system comprises a radiation source apparatus comprising a first plasma generator and a chamber arranged to hold a plasma for radiation generation, the plasma excited from a metal fuel in use by the first plasma generator; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; an arrangement configured to flow a gas comprising hydrogen through the chamber; and a second free radical generator arranged to excite the gas to generatehydrogen free radicals in the gas flowing through the chamber.
    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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    引用文献:
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    法律状态:
    2013-11-20| WDAP| Patent application withdrawn|Effective date: 20131014 |
    优先权:
    申请号 | 申请日 | 专利标题
    US201161579974P| true| 2011-12-23|2011-12-23|
    US201161579974|2011-12-23|
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