EP2229346A1 - Optical member for euvl and surface treatment method thereof - Google Patents

Optical member for euvl and surface treatment method thereof

Info

Publication number
EP2229346A1
EP2229346A1 EP08866519A EP08866519A EP2229346A1 EP 2229346 A1 EP2229346 A1 EP 2229346A1 EP 08866519 A EP08866519 A EP 08866519A EP 08866519 A EP08866519 A EP 08866519A EP 2229346 A1 EP2229346 A1 EP 2229346A1
Authority
EP
European Patent Office
Prior art keywords
mixed gas
euvl
optical member
concentration
optical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP08866519A
Other languages
German (de)
French (fr)
Inventor
Akio Koike
Yasutomi Iwahashi
Shinya Kikugawa
Kenji Okamura
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AGC Inc
Original Assignee
Asahi Glass Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Asahi Glass Co Ltd filed Critical Asahi Glass Co Ltd
Publication of EP2229346A1 publication Critical patent/EP2229346A1/en
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/22—Masks or mask blanks for imaging by radiation of 100nm or shorter wavelength, e.g. X-ray masks, extreme ultraviolet [EUV] masks; Preparation thereof
    • G03F1/24—Reflection masks; Preparation thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C15/00—Surface treatment of glass, not in the form of fibres or filaments, by etching
    • C03C15/02—Surface treatment of glass, not in the form of fibres or filaments, by etching for making a smooth surface
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7095—Materials, e.g. materials for housing, stage or other support having particular properties, e.g. weight, strength, conductivity, thermal expansion coefficient
    • G03F7/70958—Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/08—Doped silica-based glasses containing boron or halide
    • C03C2201/11—Doped silica-based glasses containing boron or halide containing chlorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/08—Doped silica-based glasses containing boron or halide
    • C03C2201/12—Doped silica-based glasses containing boron or halide containing fluorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
    • C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2201/00—Glass compositions
    • C03C2201/06—Doped silica-based glasses
    • C03C2201/30—Doped silica-based glasses containing metals
    • C03C2201/40—Doped silica-based glasses containing metals containing transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn
    • C03C2201/42—Doped silica-based glasses containing metals containing transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn containing titanium
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2203/00—Production processes
    • C03C2203/50—After-treatment
    • C03C2203/52—Heat-treatment
    • C03C2203/54—Heat-treatment in a dopant containing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C2204/00—Glasses, glazes or enamels with special properties
    • C03C2204/08—Glass having a rough surface
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06—Sources
    • H01J2237/08—Ion sources
    • H01J2237/0812—Ionized cluster beam [ICB] sources

Definitions

  • the present invention relates to an optical member for EUV lithography and to a surface treatment method of an optical surface thereof.
  • an exposure tool for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has hitherto been widely utilized.
  • the exposure tool is hence required to form a circuit pattern image with high resolution on a wafer surface at a long focal depth, and shortening of the wavelength of an exposure light is being advanced.
  • the exposure light source is further advancing from conventional g-rays (wavelength: 436 nm) , i-rays (wavelength: 365 nm) and a KrF excimer laser (wavelength: 248 nm) , and an ArF excimer laser (wavelength: 193 nm) is coming to be employed.
  • g-rays wavelength: 436 nm
  • i-rays wavelength: 365 nm
  • a KrF excimer laser wavelength: 248 nm
  • an ArF excimer laser wavelength: 193 nm
  • an immersion exposure technique and a double exposure technique each using an ArF excimer laser are regarded as being leading.
  • the EUV light as referred to herein refers to light of a wavelength in a soft X-ray region or vacuum ultraviolet region, specifically a light having a wavelength of from about 0.2 to 100 nm.
  • X ⁇ UVL The exposure principle of this EUV lithography
  • Examples of the reflecting optical system to be used for EUVL include a reflective type mask and mirrors such as a light collecting optical system mirror, an illumination optical system mirror and a projection optical system mirror.
  • the reflective type mask is basically composed of (1) an optical member for EUVL (for example, a glass substrate) , (2) a reflective multilayer film formed on the optical surface of the optical member for EUVL and (3) an absorber layer formed on the reflective multilayer film.
  • the mirror is basically composed of (1) an optical member for EUVL (for example, a glass substrate) and (2) a reflective multilayer film formed on the optical surface of the optical member for EUVL.
  • the reflective multilayer film one having a structure in which plural materials having a different refractive index against the wavelength of the exposure light are cyclically laminated one on another in a scale of nm is used.
  • the material Mo and Si are known.
  • Ta and Cr have been investigated for the absorber layer.
  • the optical member for EUVL a material having a low thermal expansion coefficient is required so as not to generate a strain even upon irradiation with EUV light, and the use of glass having a low thermal expansion coefficient or glass-ceramics having a low thermal expansion coefficient have been investigated.
  • the glass having a low thermal expansion coefficient and the glass-ceramics having a low thermal expansion coefficient are hereunder collectively referred to as "low expansion glass” or "extremely low expansion glass” .
  • silica glass in which a dopant is added for the purpose of decreasing a thermal expansion coefficient of glass is most widely used.
  • a representative example of the dopant to be added for the purpose of decreasing a thermal expansion coefficient of glass is ⁇ i.O 2 .
  • Specific examples of the silica glass in which Ti ⁇ 2 is added as a dopant include ULE (registered trademark) Code 7972 (manufactured by Corning Incorporated) .
  • predetermined shape and a predetermined dimension Its optical surface is then processed so as to give a predetermined flatness and a predetermined surface roughness.
  • the optical member for EUVL is required to have an optical surface excellent in smoothness. Specifically, it is necessary to carry out a surface treatment such that the fabricated surface has a flatness of not more than 50 nr ⁇ and a surface roughness (Ra) of not more than 5 nm.
  • Patent Document 1 JP-T-2003-505891
  • an object of the invention is to provide an optical member for EUVL which is used for a reflective type mask, a mirror, etc. for EUVL, has an optical surface excellent in flatness and surface roughness and has excellent strength in the vicinity of a surface layer and in which the generation of a chipped chamfer is inhibited.
  • Another object of the invention is to provide a surface treatment method of an optical surface of an optical member for EUVL.
  • the invention provides a surface treatment method of an optical member for EUVL, comprising applying gas cluster ion beam (GCIB) etching with a source gas containing at least one of fluorine and chlorine to an optical surface of an optical member for EUV lithography (EUVL) , wherein the optical member is made of a silica glass material having an OH concentration of 100 ppm or more, containing Ti ⁇ 2 and containing Si ⁇ 2 as a major component.
  • GCIB gas cluster ion beam
  • the optical member for EUVL has a Ti ⁇ 2 concentration of from 3 to 10 % by mass.
  • the optical member for EUVL has a thermal expansion coefficient of 0+30 ppb/°C at 20 0 C.
  • the temperature of the optical member increases beyond the ordinary assumption.
  • the temperature of the optical member may increase up to a temperature of from 40 to 110 0 C.
  • the optical member of the present invention has a thermal expansion coefficient of
  • ppb/°C at a temperature of from 40 to 110 0 C, for preventing the pitch of a pattern from varying when used as a photomask or the like, and for preventing shape variation when used as a stepper mirror or the like.
  • the optical member for EUVL has a surface roughness (Ra) of not more than 5 nm prior to the application of GCIB etching.
  • the source gas used is any one mixed gas selected from the group consisting of: a mixed gas of SF ⁇ and O 2 ; a mixed gas of SF 6 , Ar and O 2 ; a mixed gas of NF3 and O 2 ; a mixed gas of NF 3 , Ar and O 2 ; a mixed gas of NF3 and N 2 ; a mixed gas of NF3, Ar and N 2 ; a mixed gas of CI 2 and O 2 ; a mixed gas of CI2, Ar and O 2 ; a mixed gas of Cl 2 and N 2 ; a mixed gas of Cl 2 , Ar and N 2 ; a mixed gas of CF 4 and O 2 ; a mixed gas of CF 4 , Ar and O 2 ; a mixed gas of CF 4 and N 2 ; a mixed gas of CF 4 , Ar and O 2 ; a mixed gas of CF 4 and N 2 ; a mixed gas of CF 4 , Ar and N 2 ; a mixed gas of CH 2 F 2 and O
  • the invention provides an optical member for EUVL having been surface treated by the surface treatment method of an optical member for EUVL of the invention.
  • the invention provides an optical member for EUV lithography (EUVL) , which is made of a silica glass material having an OH concentration of 100 ppm or more and a TiO 2 concentration of from 3 to 10 % by mass and containing SiO 2 as a major component, the optical member for EUVL having an optical surface with a surface roughness (Ra) of not more than 5 nm and satisfying the following expression:
  • C 2 oo nm represents a total concentration (ppr ⁇ ) of a fluorine concentration and a chlorine concentration at a depth of 200 nm. from the optical surface; and C 2 onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface.
  • the invention is to provide an optical member for EUV lithography (EUVL) , which is made of a silica glass material having an OH concentration of 100 ppm or more and a TiO 2 concentration of from 3 to 10 % by mass and containing SiO 2 as a major component, the optical member for EUVL having an optical surface with a surface roughness (Ra) of not more than 5 nm and satisfying the following expression:
  • C20nm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface
  • C 2O onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 200 nm from the optical surface.
  • the optical member for EUVL it is preferred that a chamfer is provided along an outer edge of the optical surface.
  • the optical member for EUVL of the invention is excellent in flatness and surface roughness on an optical surface thereof and is favorably used as a reflective type mask, a mirror, etc. for EUVL.
  • the optical member for EUVL of the invention has an enhanced strength in the vicinity of the surface layer on the optical surface side. Accordingly, at the time of manufacturing a reflective type mask or a mirror or at the time of carrying out EUVL, the generation of a chipped corner of the optical member for EUVL or the generation of a chipped chamfer in the case where the corner has been subjected to chamfering processing is inhibited.
  • optical member for EUVL of the invention is favorably obtained by employing the treatment method of an optical member for EUVL of the invention.
  • Fig. 1 is a graph showing fluorine concentrations along the depth direction from the substrate surface.
  • GCIB etching with a source gas containing at least one of fluorine and chlorine is applied to an optical surface of an optical member for EUVL, which is made of a silica glass material having an OH concentration of 100 ppm or more, containing Ti ⁇ 2 and containing SiO 2 as a major component.
  • the optical surface of an optical member for EUVL as referred to herein refers to the surface on which a reflective multilayer film is formed in manufacturing a reflective type mask, a mirror or the like by using the optical member for EUVL.
  • a corner of an outer edge of the optical surface of the optical member for EUVL is usually subjected to chamfering processing.
  • the silica glass material which constitutes the optical member for EUVL contains Ti ⁇ 2 as a dopant for the purpose of decreasing a thermal expansion coefficient.
  • the TiO 2 concentration in the silica glass material is not particularly limited as long as the thermal expansion coefficient of the silica glass material can be made sufficiently low for use as an optical member for EUVL, it is preferably from 3 to 10 % by mass.
  • the thermal expansion coefficient of the silica glass material becomes sufficiently low.
  • the resulting glass is low expansion glass having a thermal expansion coefficient of 0+30 ppb/°C at 20 0 C, and preferably extremely low expansion glass having a thermal expansion coefficient of O ⁇ IO ppb/°C at 20 °C.
  • Low expansion glass and extremely low expansion glass in which TiO 2 is added as the dopant at the foregoing concentration include ULE (registered trademark) Code 7972 (manufactured by Corning Incorporated) .
  • the silica glass material which constitutes the optical member for EUVL contains 100 ppm or more of OH in addition to SiO 2 and TiO 2 .
  • the addition of OH accelerates structural relaxation of the glass, and facilitates realization of a glass structure with a low fictive temperature. Lowering the fictive temperature of the glass can minimize a temperature dependence of the thermal expansion coefficient, and such silica glass material is favorable as the optical member for EUVL.
  • the silica glass material contains OH
  • fluorine or chlorine is incorporated into a deeper portion in the vicinity of the surface layer of the optical member than in case without OH. Accordingly, in the surface treatment method of an optical member for EUVL of the invention, the effects brought about by applying the GCIB etching with a source gas containing at least one of fluorine and chlorine to the optical surface of the optical member for EUVL are favorably exhibited.
  • the effects brought about by applying the GCIB etching with a source gas containing at least one of fluorine and chlorine to the optical surface of the optical member for EUVL are as follows.
  • the GCIB etching as referred to herein is a method of ejecting a reactive substance (source gas), which is gaseous at normal temperature and normal pressure, in a pressurized state into a vacuum apparatus via an expansion type nozzle to form a gas cluster, subjecting the gas cluster to electronic irradiation for ionization, and irradiating the object with the resultant ionized GCIB, thereby etching the object.
  • the gas cluster is constituted of a mass of a atomic group or molecular group which is usually composed of several thousand atoms or molecules.
  • an optical member for EUVL of the invention when the GCIB etching with a source gas containing at least one fluorine and chlorine is applied to the optical surface of the optical member for EUVL, fluorine or chlorine is incorporated into the vicinity of the surface layer on the optical surface side of the optical member for EUVL, specifically into the silica glass material to a depth of about 100 nm from the optical surface of the optical member for EUVL.
  • a compression stress layer can be formed in the vicinity of the surface layer of the optical member for FUVL is enhanced.
  • the generation of a chipped chamfer of the optical member for FUVL at the time of manufacturing a reflective type mask or a mirror or at the time of carrying out EUVL is prevented (second effect) .
  • the GCIB etching is applied to the whole of the optical surface including corners of an outer edge of the optical surface or chamfer parts provided at the corners .
  • the silica glass material which constitutes the optical member for EUVL preferably contains OH in an amount of 200 ppm or more, and more preferably 500 ppm or more.
  • the optical surface to which the GCIB etching is applied is preliminarily polished so as to have a predetermined flatness and a predetermined surface roughness.
  • the preliminary polishing method is not particularly limited and can be widely chosen from known polishing methods which are used for polishing of the surface of a silica glass material.
  • a mechanical polishing method is usually employed.
  • the mechanical polishing method as referred to herein includes, in addition to polishing processing only by a polishing function of abrasive grains, a method of using a polishing slurry to utilize a polishing function of abrasive grains and a chemical polishing function of a chemical in combination.
  • the mechanical polishing may be any of lapping and polishing.
  • Polishing tool(s) and abrasive material (s) to be used can be appropriately chosen among known materials.
  • the lapping is preferably carried out at a surface pressure of from 30 to 70 gf/cm 2 , and more preferably at a surface pressure of from 40 to 60 gf/cm 2 ; whereas the polishing is preferably carried out at a surface pressure of from 60 to 140 gf/cm 2 , and more preferably at a surface pressure of from 80 to 120 gf/cm 2 .
  • the polishing amount the lapping is preferably carried out in a polishing amount of from 100 to 300 ⁇ m; whereas the polishing is preferably carried out in a polishing amount of from 1 to 60 ⁇ m.
  • a surface roughness (Ra) of the optical surface after the preliminary polishing is preferably not more than 5 nm, more preferably not more than 3 nm, and further preferably not more than 1 nm.
  • the surface roughness (Ra) referred to in this specification means a surface roughness as measured by an atomic force microscope with respect to an area of from 1 to 10 ⁇ m square.
  • any one mixed gas selected from: a mixed gas of SF 6 and O 2 ; a mixed gas of SF 6 , Ar and O 2 ; a mixed gas of NF 3 and O 2 ; a mixed gas of NF 3 , Ar and O 2 ; a mixed gas of NF 3 and N 2 ; a mixed gas of NF 3 , Ar and N 2 ; a mixed gas of Cl 2 and O 2 ; a mixed gas of Cl 2 , Ar and O 2 ; a mixed gas of Cl 2 and N 2 ; a mixed gas of Cl 2 , Ar and N 2 ; a mixed gas of CF 4 and O 2 ; a mixed gas of CF 4 , Ar and O 2 ; a mixed gas of CF 4 and N 2 ; a mixed gas of CF 4 and N 2 ; a mixed gas of CF 4 , Ar and O 2 ; a mixed gas of CF 4 and N 2 ; a mixed gas of CF 4 and N 2 ; a mixed gas of CF 4
  • NF 3 :Ar:0 2 (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of NF 3 , Ar and O 2 )
  • CH 2 F 2 : 0 2 (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CH 2 F 2 and O 2 )
  • CH 2 F 2 :Ar:N 2 (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CH 2 F 2 , Ar and N 2 )
  • CHF 3 :0 2 (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CHF 3 and O 2 )
  • CHF 3 :Ar:O 2 (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CHF 3 , Ar and O 2 )
  • Irradiation conditions including a cluster size, an ionization current to be applied to an ionization electrode of a GCIB etching apparatus for ionizing the cluster, an acceleration voltage to be applied to an acceleration electrode of the GCIB etching apparatus and a dose of GCIB can be appropriately chosen depending upon the kind of the source gas and surface properties of the optical surface.
  • the acceleration voltage to be applied to the acceleration electrode is preferably from 15 to 30 kV.
  • optical member for EUVL having been subjected to a surface treatment by the surface treatment method of an optical member for EUVL of the invention (hereinafter referred to as X ⁇ optical member for EUVL of the invention")
  • X ⁇ optical member for EUVL of the invention since fluorine or chlorine is incorporated into the optical surface processed by the GCIB etching, the fluorine concentration or chlorine concentration in the vicinity of the surface layer of the optical member for EUVL becomes higher than tha € ⁇ in a deeper part of the optical member for EUVL.
  • optical member for EUVL of the invention satisfies the following expression.
  • C2oon m represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 200 run from the optical surface
  • C 2 onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface.
  • the value of (log C 2 oonm - log C 2 OmJ /(200 - 20) is a value corresponding to the gradient of the total concentration of the fluorine concentration and the chlorine concentration in the optical member from the vicinity of the surface layer of the optical member toward the deeper part of the optical member. This value is more preferably less than -8.O x 10 ⁇ 3 , and further preferably less than -10.0 x 10 "3 .
  • optical member for EUVL of the invention satisfies the following expression.
  • the value of (C 2 onm ⁇ C 2O onmK is a value corresponding to the gradient of the total concentration of the fluorine concentration and the chlorine concentration in the optical member from the vicinity of the surface layer of the optical member toward the deeper part of the optical member. This value is more preferably 10 ppm or more, and further preferably 15 ppm or more.
  • the optical member for EUVL of the invention is excellent in flatness and surface roughness on the optical surface.
  • the flatness of the optical surface is preferably not more than 100 nm, more preferably not more than 50 nm, and further preferably not more than 30 nm.
  • the surface roughness Ra of the optical surface is preferably not more than 5 nm, more preferably not more than 3 nm, and further preferably not more than 1 nm.
  • the optical surface preferably has a crack initiation load of 50 g or more, more preferably 100 g or more, and further preferably 200 g or more .
  • the crack initiation load is measured in the following manner. That is, after indentation with a Vickers indenter for 15 seconds by a Vickers hardness- measuring equipment, the Vickers indenter is removed, and the vicinity of the indent is observed. The area is divided into four regions taking lines connecting the center and the corners of the indent as boundaries, and the probability of the crack generation is evaluated by examining whether or not a crack is generated in the respective regions.
  • the case where the crack is found in only one of the four regions is designated to be 25 %; the case where the crack is found in only two regions is designated to be 50 %; the case where the crack is found in only three regions is designated to be 75 %; and the case where the crack is found in all of the four regions is designated to be 100 %.
  • the probability of the crack generation is determined. The lowest load at which the probability of the crack generation is 100 % is taken as the crack initiation load.
  • Example 1 is an example of the invention, and Example 2 is a comparative example.
  • Example 1 is an example of the invention, and Example 2 is a comparative example.
  • the same silica glass material-made substrate as in Example 1 was subjected to only the preliminary polishing.

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  • Theoretical Computer Science (AREA)
  • Mathematical Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Glass Compositions (AREA)
  • Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
  • Preparing Plates And Mask In Photomechanical Process (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
  • Surface Treatment Of Glass (AREA)

Abstract

The present invention is to provide an optical member for Extreme Ultra-Violet Lithography which is used for a reflective type mask, a mirror, etc. for EUVL and has excellent flatness and surface roughness on an optical surface thereof and in which chamfer parts are inhibited from being chipped. The present invention relates to a surface treatment method of an optical member for EUVL, including applying Gas Cluster Ion Beam etching using a source gas containing at least one of fluorine and chlorine to an optical surface of an optical member for EUVL, wherein the optical member is made of a silica glass material having an OH concentration of 100 ppm or more, containing TiO2 and containing SiO2 as a major component.

Description

DESCRIPTION
OPTICAL MEMBER FOR EUVL AND SURFACE TREATMENT METHOD THEREOF
Technical Field
The present invention relates to an optical member for EUV lithography and to a surface treatment method of an optical surface thereof.
Background Art
In the lithography technology, an exposure tool for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has hitherto been widely utilized. With the trend toward higher degrees of integration, higher speeds and higher functions of integrated circuits, the refinement of integrated circuits is advancing. The exposure tool is hence required to form a circuit pattern image with high resolution on a wafer surface at a long focal depth, and shortening of the wavelength of an exposure light is being advanced. The exposure light source is further advancing from conventional g-rays (wavelength: 436 nm) , i-rays (wavelength: 365 nm) and a KrF excimer laser (wavelength: 248 nm) , and an ArF excimer laser (wavelength: 193 nm) is coming to be employed. Also, in order to cope with a next-generation integrated circuit whose circuit line width will become not more than 70 nm, an immersion exposure technique and a double exposure technique, each using an ArF excimer laser are regarded as being leading. However, it is considered that even these techniques would able to cover only the generation with a line width of up to 45 nm.
Under the foregoing technical trends, a lithography technique using EUV light as a next-generation exposure light is considered to be applicable over generations of 32 nm and thereafter, and is attracting attention. The EUV light as referred to herein refers to light of a wavelength in a soft X-ray region or vacuum ultraviolet region, specifically a light having a wavelength of from about 0.2 to 100 nm. At present, the use of a lithography light source of 13.5 nm is being investigated. The exposure principle of this EUV lithography (hereinafter abbreviated to XΕUVL") is identical with that of the conventional lithography in that a mask pattern is transferred using a projection optical system. However, since there is no material which is light-transmitting in the EUV light energy region, a refractive optical system cannot be used. Accordingly, a reflecting optical system is inevitably used (see Patent Document 1) .
Examples of the reflecting optical system to be used for EUVL include a reflective type mask and mirrors such as a light collecting optical system mirror, an illumination optical system mirror and a projection optical system mirror.
The reflective type mask is basically composed of (1) an optical member for EUVL (for example, a glass substrate) , (2) a reflective multilayer film formed on the optical surface of the optical member for EUVL and (3) an absorber layer formed on the reflective multilayer film. On the other hand, the mirror is basically composed of (1) an optical member for EUVL (for example, a glass substrate) and (2) a reflective multilayer film formed on the optical surface of the optical member for EUVL.
As the reflective multilayer film, one having a structure in which plural materials having a different refractive index against the wavelength of the exposure light are cyclically laminated one on another in a scale of nm is used. As representative examples of the material, Mo and Si are known. Also, Ta and Cr have been investigated for the absorber layer. As the optical member for EUVL, a material having a low thermal expansion coefficient is required so as not to generate a strain even upon irradiation with EUV light, and the use of glass having a low thermal expansion coefficient or glass-ceramics having a low thermal expansion coefficient have been investigated. In this specification, the glass having a low thermal expansion coefficient and the glass-ceramics having a low thermal expansion coefficient are hereunder collectively referred to as "low expansion glass" or "extremely low expansion glass" .
As such low expansion glass and extremely low expansion glass, silica glass in which a dopant is added for the purpose of decreasing a thermal expansion coefficient of glass is most widely used. A representative example of the dopant to be added for the purpose of decreasing a thermal expansion coefficient of glass is Υi.O2. Specific examples of the silica glass in which Tiθ2 is added as a dopant include ULE (registered trademark) Code 7972 (manufactured by Corning Incorporated) .
In preparing an optical member for EUVL, first of all, a raw material of such low expansion glass or extremely low expansion glass is cut to give a 068128
predetermined shape and a predetermined dimension. Its optical surface is then processed so as to give a predetermined flatness and a predetermined surface roughness.
The optical member for EUVL is required to have an optical surface excellent in smoothness. Specifically, it is necessary to carry out a surface treatment such that the fabricated surface has a flatness of not more than 50 nrα and a surface roughness (Ra) of not more than 5 nm.
At the time of manufacturing a reflective type mask or a mirror or at the time of carrying out EUVL, there arises a problem that a corner of the optical member for EUVL is chipped. For that reason, the corners of the optical member for EUVL are usually subjected to chamfering processing.
However, even in the case where the corners are subjected to chamfering processing, there has been a problem that upon fixing the optical member for EUVL to a fabrication apparatus or an exposure tool, more specifically upon grasping it with a clamp or the like, the chamfer part is chipped.
Patent Document 1: JP-T-2003-505891
Disclosure of the invention In order to solve the foregoing problems accompanied with the background art techniques, an object of the invention is to provide an optical member for EUVL which is used for a reflective type mask, a mirror, etc. for EUVL, has an optical surface excellent in flatness and surface roughness and has excellent strength in the vicinity of a surface layer and in which the generation of a chipped chamfer is inhibited. Another object of the invention is to provide a surface treatment method of an optical surface of an optical member for EUVL.
In order to achieve the foregoing objects, the invention provides a surface treatment method of an optical member for EUVL, comprising applying gas cluster ion beam (GCIB) etching with a source gas containing at least one of fluorine and chlorine to an optical surface of an optical member for EUV lithography (EUVL) , wherein the optical member is made of a silica glass material having an OH concentration of 100 ppm or more, containing Tiθ2 and containing Siθ2 as a major component.
In the surface treatment method of an optical member for EUVL of the invention, it is preferred that the optical member for EUVL has a Tiθ2 concentration of from 3 to 10 % by mass. In the surface treatment method of an optical member for EUVL of the invention, it is preferred that the optical member for EUVL has a thermal expansion coefficient of 0+30 ppb/°C at 20 0C.
In the case where the energy of the EUV light used for exposure is raised in order to raise the throughput of the EUVL exposure tool, the temperature of the optical member increases beyond the ordinary assumption. Specifically, the temperature of the optical member may increase up to a temperature of from 40 to 1100C. In this instance, it is preferred that the optical member of the present invention has a thermal expansion coefficient of
0±30 ppb/°C at a temperature of from 40 to 110 0C, for preventing the pitch of a pattern from varying when used as a photomask or the like, and for preventing shape variation when used as a stepper mirror or the like.
In the surface treatment method of an optical member for EUVL of the invention, it is preferred that the optical member for EUVL has a surface roughness (Ra) of not more than 5 nm prior to the application of GCIB etching.
In the surface treatment method of an optical member for EUVL of the invention, it is preferred that the source gas used is any one mixed gas selected from the group consisting of: a mixed gas of SFδ and O2; a mixed gas of SF6, Ar and O2; a mixed gas of NF3 and O2; a mixed gas of NF3, Ar and O2; a mixed gas of NF3 and N2; a mixed gas of NF3, Ar and N2; a mixed gas of CI2 and O2; a mixed gas of CI2, Ar and O2; a mixed gas of Cl2 and N2; a mixed gas of Cl2, Ar and N2; a mixed gas of CF4 and O2; a mixed gas of CF4, Ar and O2; a mixed gas of CF4 and N2; a mixed gas of CF4, Ar and N2; a mixed gas of CH2F2 and O2; a mixed gas of CH2F2, Ar and O2; a mixed gas of CH2F2 and N2; a mixed gas of CH2F2, Ar and N2; a mixed gas of CHF3 and O2; a mixed gas of CHF3, Ar and O2; a mixed gas of CHF3 and N2; and a mixed gas of CHF3, Ar and N2.
Also, the invention provides an optical member for EUVL having been surface treated by the surface treatment method of an optical member for EUVL of the invention.
Also, the invention provides an optical member for EUV lithography (EUVL) , which is made of a silica glass material having an OH concentration of 100 ppm or more and a TiO2 concentration of from 3 to 10 % by mass and containing SiO2 as a major component, the optical member for EUVL having an optical surface with a surface roughness (Ra) of not more than 5 nm and satisfying the following expression:
( log C2oonm - log C20Hm) / ( 2 00 - 2 0 ) < - 3 . 0 x 1 0 "3 wherein C2oonm represents a total concentration (pprα) of a fluorine concentration and a chlorine concentration at a depth of 200 nm. from the optical surface; and C2onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface.
Also, the invention is to provide an optical member for EUV lithography (EUVL) , which is made of a silica glass material having an OH concentration of 100 ppm or more and a TiO2 concentration of from 3 to 10 % by mass and containing SiO2 as a major component, the optical member for EUVL having an optical surface with a surface roughness (Ra) of not more than 5 nm and satisfying the following expression:
C20nm -C200nm ≥ 5 ppm wherein C20nm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface; and C2Oonm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 200 nm from the optical surface.
In the optical member for EUVL, it is preferred that a chamfer is provided along an outer edge of the optical surface. The optical member for EUVL of the invention is excellent in flatness and surface roughness on an optical surface thereof and is favorably used as a reflective type mask, a mirror, etc. for EUVL. Also, the optical member for EUVL of the invention has an enhanced strength in the vicinity of the surface layer on the optical surface side. Accordingly, at the time of manufacturing a reflective type mask or a mirror or at the time of carrying out EUVL, the generation of a chipped corner of the optical member for EUVL or the generation of a chipped chamfer in the case where the corner has been subjected to chamfering processing is inhibited.
The optical member for EUVL of the invention is favorably obtained by employing the treatment method of an optical member for EUVL of the invention.
Brief description of the Drawings
Fig. 1 is a graph showing fluorine concentrations along the depth direction from the substrate surface.
Best Mode for carrying Out the Invention
In the surface treatment method of an optical member for EUVL of the invention, GCIB etching with a source gas containing at least one of fluorine and chlorine is applied to an optical surface of an optical member for EUVL, which is made of a silica glass material having an OH concentration of 100 ppm or more, containing Tiθ2 and containing SiO2 as a major component.
The optical surface of an optical member for EUVL as referred to herein refers to the surface on which a reflective multilayer film is formed in manufacturing a reflective type mask, a mirror or the like by using the optical member for EUVL. For the purpose of preventing the chipping from occurring at the time of manufacturing a reflective type mask or a mirror or at the time of carrying out EUVL, a corner of an outer edge of the optical surface of the optical member for EUVL is usually subjected to chamfering processing.
The silica glass material which constitutes the optical member for EUVL contains Tiθ2 as a dopant for the purpose of decreasing a thermal expansion coefficient.
Though the TiO2 concentration in the silica glass material is not particularly limited as long as the thermal expansion coefficient of the silica glass material can be made sufficiently low for use as an optical member for EUVL, it is preferably from 3 to 10 % by mass. When the TiO2 concentration falls within the foregoing range, the thermal expansion coefficient of the silica glass material becomes sufficiently low. Specifically, the resulting glass is low expansion glass having a thermal expansion coefficient of 0+30 ppb/°C at 20 0C, and preferably extremely low expansion glass having a thermal expansion coefficient of O±IO ppb/°C at 20 °C.
Specific examples of the low expansion glass and extremely low expansion glass in which TiO2 is added as the dopant at the foregoing concentration include ULE (registered trademark) Code 7972 (manufactured by Corning Incorporated) .
The silica glass material which constitutes the optical member for EUVL contains 100 ppm or more of OH in addition to SiO2 and TiO2. The addition of OH accelerates structural relaxation of the glass, and facilitates realization of a glass structure with a low fictive temperature. Lowering the fictive temperature of the glass can minimize a temperature dependence of the thermal expansion coefficient, and such silica glass material is favorable as the optical member for EUVL.
Further, in the case where the silica glass material contains OH, at the time when the GCIB etching with a source gas containing at least one of fluorine and chlorine is applied to the optical surface of the optical member for EUVL, fluorine or chlorine is incorporated into a deeper portion in the vicinity of the surface layer of the optical member than in case without OH. Accordingly, in the surface treatment method of an optical member for EUVL of the invention, the effects brought about by applying the GCIB etching with a source gas containing at least one of fluorine and chlorine to the optical surface of the optical member for EUVL are favorably exhibited.
In the surface treatment method of an optical member for EUVL of the invention, the effects brought about by applying the GCIB etching with a source gas containing at least one of fluorine and chlorine to the optical surface of the optical member for EUVL are as follows.
The GCIB etching as referred to herein is a method of ejecting a reactive substance (source gas), which is gaseous at normal temperature and normal pressure, in a pressurized state into a vacuum apparatus via an expansion type nozzle to form a gas cluster, subjecting the gas cluster to electronic irradiation for ionization, and irradiating the object with the resultant ionized GCIB, thereby etching the object. The gas cluster is constituted of a mass of a atomic group or molecular group which is usually composed of several thousand atoms or molecules. In the surface treatment method of an optical member for EUVL of the invention, when the GCIB etching is applied to the optical surface of the optical member for EUVL, collisions of the optical surface with the gas clusters produce a multibody impact effect due to interaction with the solid, whereby the optical surface is polished, and the flatness is improved (first effect) .
In the surface treatment method of an optical member for EUVL of the invention, when the GCIB etching with a source gas containing at least one fluorine and chlorine is applied to the optical surface of the optical member for EUVL, fluorine or chlorine is incorporated into the vicinity of the surface layer on the optical surface side of the optical member for EUVL, specifically into the silica glass material to a depth of about 100 nm from the optical surface of the optical member for EUVL. In the vicinity of the surface layer on the optical surface side into which fluorine or chlorine is incorporated, a compression stress layer can be formed. Thereby, the strength in the vicinity of the surface layer of the optical member for FUVL is enhanced. As a result, the generation of a chipped chamfer of the optical member for FUVL at the time of manufacturing a reflective type mask or a mirror or at the time of carrying out EUVL is prevented (second effect) . In order to more effectively exhibit the second effect, it is preferred that the GCIB etching is applied to the whole of the optical surface including corners of an outer edge of the optical surface or chamfer parts provided at the corners .
In order to more effectively exhibit the effect brought about by the GCIB etching, especially the foregoing second effect, the silica glass material which constitutes the optical member for EUVL preferably contains OH in an amount of 200 ppm or more, and more preferably 500 ppm or more.
In the surface treatment method of an optical member for EUVL of the invention, it is preferred that the optical surface to which the GCIB etching is applied is preliminarily polished so as to have a predetermined flatness and a predetermined surface roughness.
The preliminary polishing method is not particularly limited and can be widely chosen from known polishing methods which are used for polishing of the surface of a silica glass material. However, since the use of a polishing pad having a high polishing rate and a large surface area allows polishing processing of a large surface at once, a mechanical polishing method is usually employed. The mechanical polishing method as referred to herein includes, in addition to polishing processing only by a polishing function of abrasive grains, a method of using a polishing slurry to utilize a polishing function of abrasive grains and a chemical polishing function of a chemical in combination. The mechanical polishing may be any of lapping and polishing. Polishing tool(s) and abrasive material (s) to be used can be appropriately chosen among known materials. In the case of employing a mechanical polishing method, in order to make the processing rate high, the lapping is preferably carried out at a surface pressure of from 30 to 70 gf/cm2, and more preferably at a surface pressure of from 40 to 60 gf/cm2; whereas the polishing is preferably carried out at a surface pressure of from 60 to 140 gf/cm2, and more preferably at a surface pressure of from 80 to 120 gf/cm2. As to the polishing amount, the lapping is preferably carried out in a polishing amount of from 100 to 300 μm; whereas the polishing is preferably carried out in a polishing amount of from 1 to 60 μm.
In the case of carrying out the preliminary polishing, a surface roughness (Ra) of the optical surface after the preliminary polishing is preferably not more than 5 nm, more preferably not more than 3 nm, and further preferably not more than 1 nm. The surface roughness (Ra) referred to in this specification means a surface roughness as measured by an atomic force microscope with respect to an area of from 1 to 10 μm square. When the surface roughness on the optical surface after the preliminary polishing exceeds 5 nm, it takes a considerable time to regulate the optical surface so as to give a predetermined flatness and a predetermined surface roughness by applying the GCIB etching in the surface treatment method of an optical member for EUVL of the invention, which causes a cost increase.
As the source gas containing at least fluorine and chlorine to be used for the GCIB etching, it is preferred to use any one mixed gas selected from: a mixed gas of SF6 and O2; a mixed gas of SF6, Ar and O2; a mixed gas of NF3 and O2; a mixed gas of NF3, Ar and O2; a mixed gas of NF3 and N2; a mixed gas of NF3, Ar and N2; a mixed gas of Cl2 and O2; a mixed gas of Cl2, Ar and O2; a mixed gas of Cl2 and N2; a mixed gas of Cl2, Ar and N2; a mixed gas of CF4 and O2; a mixed gas of CF4, Ar and O2; a mixed gas of CF4 and N2; a mixed gas of CF4, Ar and N2; a mixed gas of CH2F2 and O2; a mixed gas of CH2F2, Ar and O2; a mixed gas of CH2F2 and N2; a mixed gas of CH2F2, Ar and N2; a mixed gas of CHF3 and O2; a mixed gas of CHF3, Ar and O2; a mixed gas of CHF3 and N2; and a mixed gas of CHF3, Ar and N2. In these mixed gases, though a suitable mixing ratio of the respective components varies depending upon an irradiation condition and the like, the following are preferred.
SF6:O2 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of SF6 and O2)
SF6:Ar:O2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of SF6, Ar and O2)
NF3: O2 = (0.1 to 5 %):(95 to 99.9 %) (mixed gas of NF3 and O2)
NF3:Ar:02 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of NF3, Ar and O2)
NF3:N2 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of NF3 and N2)
NF3:Ar:N2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of NF3, Ar and N2)
C12:O2 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of Cl2 and O2)
Cl2:Ar:02 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of Cl2, Ar and O2)
C12:N2 = (0.1 to 5 %):(95 to 99.9 %) (mixed gas of Cl2 and N2)
Cl2:Ar:N2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of Cl2, Ar and N2) CF4:O2 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CF4 and O2)
CF4:Ar:O2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CF4, Ar and O2)
CF4:N2 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CF4 and N2)
CF4:Ar:N2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CF4, Ar and N2)
CH2F2: 02 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CH2F2 and O2)
CH2F2=Ar: O2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CH2F2, Ar and O2)
CH2F2: N2 = (0.1 to 5 %} : (95 to 99.9 %) (mixed gas of CH2F2 and N2)
CH2F2:Ar:N2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CH2F2, Ar and N2)
CHF3:02 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CHF3 and O2)
CHF3:Ar:O2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CHF3, Ar and O2)
CHF3 = N2 = (0.1 to 5 %) : (95 to 99.9 %) (mixed gas of CHF3 and N2)
CHF3:Ar:N2 = (0.1 to 5 %) : (9.9 to 49.9 %) : (50 to 90 %) (mixed gas of CHF3, Ar and N2) Irradiation conditions including a cluster size, an ionization current to be applied to an ionization electrode of a GCIB etching apparatus for ionizing the cluster, an acceleration voltage to be applied to an acceleration electrode of the GCIB etching apparatus and a dose of GCIB can be appropriately chosen depending upon the kind of the source gas and surface properties of the optical surface. For example, in order to improve the flatness without excessively deteriorating the surface roughness of the optical surface, the acceleration voltage to be applied to the acceleration electrode is preferably from 15 to 30 kV.
In carrying out the GCIB etching, it is necessary to scan the optical surface with GCIB. As a method for GCIB scanning, raster scanning and spiral scanning are known, and either of these methods may be employed.
In the optical member for EUVL having been subjected to a surface treatment by the surface treatment method of an optical member for EUVL of the invention (hereinafter referred to as Xλoptical member for EUVL of the invention") , since fluorine or chlorine is incorporated into the optical surface processed by the GCIB etching, the fluorine concentration or chlorine concentration in the vicinity of the surface layer of the optical member for EUVL becomes higher than tha€^in a deeper part of the optical member for EUVL.
It is preferred that the optical member for EUVL of the invention satisfies the following expression.
( log C2oonm - log C2onm) / ( 200 - 20 ) < - 3 . 0 x 10"3
Here, C2oonm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 200 run from the optical surface; and C2onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface.
The value of (log C2oonm - log C2OmJ /(200 - 20) is a value corresponding to the gradient of the total concentration of the fluorine concentration and the chlorine concentration in the optical member from the vicinity of the surface layer of the optical member toward the deeper part of the optical member. This value is more preferably less than -8.O x 10~3, and further preferably less than -10.0 x 10"3.
It is preferred that the optical member for EUVL of the invention satisfies the following expression.
C20nm -C200nm ≥ 5 ppm *j|.
The value of (C2onm ~C2OonmK is a value corresponding to the gradient of the total concentration of the fluorine concentration and the chlorine concentration in the optical member from the vicinity of the surface layer of the optical member toward the deeper part of the optical member. This value is more preferably 10 ppm or more, and further preferably 15 ppm or more.
The optical member for EUVL of the invention is excellent in flatness and surface roughness on the optical surface. Specifically, the flatness of the optical surface is preferably not more than 100 nm, more preferably not more than 50 nm, and further preferably not more than 30 nm. Also, the surface roughness Ra of the optical surface is preferably not more than 5 nm, more preferably not more than 3 nm, and further preferably not more than 1 nm.
In the optical member for EUVL of the invention, since a compression stress layer is formed in the vicinity of the surface layer, the strength in the vicinity of the surface layer is enhanced. The optical surface preferably has a crack initiation load of 50 g or more, more preferably 100 g or more, and further preferably 200 g or more .
The crack initiation load is measured in the following manner. That is, after indentation with a Vickers indenter for 15 seconds by a Vickers hardness- measuring equipment, the Vickers indenter is removed, and the vicinity of the indent is observed. The area is divided into four regions taking lines connecting the center and the corners of the indent as boundaries, and the probability of the crack generation is evaluated by examining whether or not a crack is generated in the respective regions. The case where the crack is found in only one of the four regions is designated to be 25 %; the case where the crack is found in only two regions is designated to be 50 %; the case where the crack is found in only three regions is designated to be 75 %; and the case where the crack is found in all of the four regions is designated to be 100 %. By measuring plural specimens, the probability of the crack generation is determined. The lowest load at which the probability of the crack generation is 100 % is taken as the crack initiation load.
Examples
The present invention will be illustrated in greater detail with reference to the following Examples, but the invention should not be construed as being limited thereto. Example 1 is an example of the invention, and Example 2 is a comparative example. Example 1
After preliminary polishing a silica glass material- made substrate (OH concentration: 880 ppm, TiO2 concentration: 7.0 % by mass, dimension: 20 mm x 20 mm x 1.5 mm-thickness) , GCIB etching was applied to the surface of the substrate. The conditions of the preliminary polishing and GCIB etching are as shown below. <Condition of preliminary polishing>
Kind of polishing: Mechanical polishing
Surface pressure: 100 g/cm2. <Condition of GCIB etching>
Source gas: Mixed gas of SF6 and N2 (SF6: N2 = 5 %:95 %)
Acceleration voltage: 24 kV
Cluster size: 3,000
Beam current: 100 urn
Example 2
The same silica glass material-made substrate as in Example 1 was subjected to only the preliminary polishing.
The fluorine concentration along the depth direction from the substrate surface of the quarts glass material- made substrate of each of Examples 1 and 2 was measured using SIMS (secondary ionization mass spectrometer) . The results are shown in Fig. 1.
As is clearly seen from Fig. 1, it was confirmed that in the substrate of Example 1 having been subjected to the GCIB etching, the fluorine concentration in the vicinity of the surface layer in a depth of up to 100 nm from the surface becomes high by incorporation of fluorine. The reason why the fluorine concentration in the surface region even in the substrate of Example 2 which was not subjected to GCIB etching is high is because the substrate surface was washed with hydrofluoric acid prior to the measurement of the fluorine concentration.
Ten sheets of the silica glass material-made substrate of each of Examples 1 and 2 were prepared, and a Vickers indenter of 100 g was indented onto the substrate surface for 15 seconds to evaluate the crack resistance.
It was confirmed that with the glass of Example 1, a crack was not generated in all of the ten sheets, whereas with the glass of Example 2, a crack was generated in all of the ten sheets. From this, the effect of inhibiting the generation of chipping due to GCIB etching could be confirmed. While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
This application is based on Japanese Patent Application No. 2007-336167 filed December 27, 2007, and the contents thereof are herein incorporated by reference.

Claims

1. A surface treatment method of an optical member for EUVL, comprising applying gas cluster ion beam (GCIB) etching with a source gas containing at least one of fluorine and chlorine to an optical surface of an optical member for EUV lithography (EUVL) , wherein the optical member is made of a silica glass material having an OH concentration of 100 ppm or more, containing TiO2 and containing SiO2 as a major component.
2. The surface treatment method of an optical member for EUVL according to claim 1, wherein the optical member for EUVL has a TiO2 concentration of from 3 to 10 % by mass .
3. The surface treatment method of an optical member for EUVL according to claim 1 or 2, wherein the optical member for EUVL has a thermal expansion coefficient of 0+30 ppb/°C at 20 °C .
4. The surface treatment method of an optical member for EUVL according to any one of claims 1 to 3, wherein the optical member for EUVL has a surface roughness (Ra) of not more than 5 nm prior to the application of GCIB etching.
5. The surface treatment method of an optical member for EUVL according to any one of claims 1 to 4, using, as the source gas, any one mixed gas selected from the group consisting of: a mixed gas of SF6 and O2; a mixed gas of SFδ, Ar and O2; a mixed gas of NF3 and O2; a mixed gas of NF3, Ar and O2; a mixed gas of NF3 and N2; a mixed gas of NF3, Ar and N2; a mixed gas of Cl2 and O2; a mixed gas of Cl2, Ar and O2; a mixed gas of Cl2 and N2; a mixed gas of Cl2, Ar and N2; a mixed gas of CF4 and O2; a mixed gas of CF4, Ar and O2; a mixed gas of CF4 and N2; a mixed gas of CF4, Ar and N2; a mixed gas of CH2F2 and O2; a mixed gas of CH2F2, Ar and O2; a mixed gas of CH2F2 and N2; a mixed gas of CH2F2, Ar and N2; a mixed gas of CHF3 and O2; a mixed gas of CHF3, Ar and O2; a mixed gas of CHF3 and N2; and a mixed gas of CHF3, Ar and N2.
6. An optical member for EUVL having been surface treated by the method according to any one of claims 1 to 5.
7. An optical member for EUV lithography (EUVL), which is made of a silica glass material having an OH concentration of 100 pprα or more and a TiO2 concentration of from 3 to 10 % by mass and containing Siθ2 as a major component, the optical member for EUVL having an optical surface with a surface roughness (Ra) of not more than 5 nm and satisfying the following expression:
(log Czoonm - log C20nm)/(200 - 20) < -3.0 x 10~3 wherein C2oonm represents a total concentration (pprα) of a fluorine concentration and a chlorine concentration at a depth of 200 nm from the optical surface; and C2onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 nm from the optical surface.
8. An optical member for EUV lithography (EUVL), which is made of a silica glass material having an OH concentration of 100 ppiα or more and a TiO2 concentration of from 3 to 10 % by mass and containing SiO2 as a major component, the optical member for EUVL having an optical surface with a surface roughness (Ra) of not more than 5 nm and satisfying the following expression: C20nm ~C200nm ≥ 5 ppiTl wherein C∑onm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 20 ran from the optical surface; and C2oonm represents a total concentration (ppm) of a fluorine concentration and a chlorine concentration at a depth of 200 nm from the optical surface.
9. The optical member for EUVL according to claim 7 or 8, having a chamfer provided along an outer edge of the optical surface.
EP08866519A 2007-12-27 2008-09-30 Optical member for euvl and surface treatment method thereof Ceased EP2229346A1 (en)

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JP2007336167A JP5470703B2 (en) 2007-12-27 2007-12-27 EUVL optical member and surface treatment method thereof
PCT/JP2008/068128 WO2009084296A1 (en) 2007-12-27 2008-09-30 Optical member for euvl and surface treatment method thereof

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JP2009155170A (en) 2009-07-16
KR101419576B1 (en) 2014-07-14
TW200928605A (en) 2009-07-01

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