Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/06—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/06—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
  • C03B19/066—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction for the production of quartz or fused silica articles
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/12—Other methods of shaping glass by liquid-phase reaction processes
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
  • C03B19/1453—Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B20/00—Processes specially adapted for the production of quartz or fused silica articles, not otherwise provided for
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B32/00—Thermal after-treatment of glass products not provided for in groups C03B19/00, C03B25/00 - C03B31/00 or C03B37/00, e.g. crystallisation, eliminating gas inclusions or other impurities; Hot-pressing vitrified, non-porous, shaped glass products
• • 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
  • C03C4/00—Compositions for glass with special 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
  • C03C4/00—Compositions for glass with special properties
  • C03C4/0085—Compositions for glass with special properties for UV-transmitting glass
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/07—Impurity concentration specified
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/07—Impurity concentration specified
  • C03B2201/075—Hydroxyl ion (OH)
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
  • C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
  • C03B2201/22—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with deuterium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
  • C03B2201/23—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with hydroxyl groups
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/32—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with aluminium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/40—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn
  • C03B2201/42—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn doped with 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
  • 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
  • C03C2201/22—Doped silica-based glasses containing non-metals other than boron or halide containing deuterium
• • 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

Definitions

• the present invention relates to synthetic silica glass materials, optical elements and devices comprising the same and method of making the same.
• the present invention relates to synthetic silica glass material capable of being used in the optical elements in lithographic devices operating at a wavelength below about 300 nm, optical elements comprising the same, lithographic systems comprising such optical elements, process for making such glass material, and soot preform produced in such process.
• the present invention is useful, for example, in making synthetic fused silica glass materials for optical elements used in deep UV and vacuum UV lithographic devices, especially those involving immersion lithography in which linearly polarized UV light is employed.
• fused silica optical members such as lenses, prisms, filters, photomasks, reflectors, etalon plates and windows, have been manufactured from bulk pieces of fused silica made in large production furnaces.
• Bulk pieces of fused silica manufactured in large production furnaces are known in the art as preforms, boules or ingots. Blanks are cut from boules or ingots, and finished optical members are manufactured from glass blanks, utilizing manufacturing steps that may include, but are not limited to, cutting, polishing, and/or coating pieces of glass from a blank.
• optical members are used in various apparatus employed in environments where they are exposed to ultraviolet light having a wavelength of about 360 nm or less, for example, an excimer laser beam or some other ultraviolet laser beam.
• the optical members are incorporated into a variety of instruments, including lithographic laser exposure equipment for producing highly integrated circuits, laser generation equipment, medical equipment, nuclear fusion equipment, or some other apparatus which uses a high-power ultraviolet laser beam.
• Laser technology has advanced into the short wavelength, high energy ultraviolet spectral region, the effect of which is an increase in the frequency (decrease in wavelength) of light produced by lasers.
• short wavelength lasers operating in the UV and deep UV (DUV) and vacuum UV wavelength ranges, which include, but are not limited to, lasers operating at about 248 nm, 193 nm, 157 nm and even shorter wavelengths.
• Excimer laser systems are popular in microlithography applications, and the shortened wavelengths allow for increased feature resolution and thus line densities in the manufacturing of integrated circuits and microchips, which enables the manufacture of circuits having decreased feature sizes.
• a direct physical consequence of shorter wavelengths (higher frequencies) is higher photon energies.
• fused silica optics are exposed to high irradiation levels for prolonged periods of time, and this may result in the degradation of the optical properties of the optical members.
• light-induced degradation adversely affects the optical properties and performance of the fused silica optics by decreasing light transmission levels, discoloring the glass, altering the index of refraction, altering the density, and increasing absorption levels of the glass.
• many methods have been suggested for improving the optical damage resistance of fused silica glass.
• polarization-induced birefringence polarization-induced birefringence
• PIB polarization-induced birefringence
• the induced birefringence, especially polarization-induced birefringence, is of particular concern to immersion lithography systems where a liquid fills the gap between the last lens element and the wafer in order to enlarge the numerical aperture of the lens system.
• the polarization state of the UV radiation needs to be controlled, desirably linearly polarized.
• the induced birefringence in the glass alters the polarization state of the UV radiation, causing reduction of phase contrast and system resolution. Therefore, for deep UV and vacuum UV immersion lithographic systems, it is highly desirable that the glass material used in making the lens elements has low induced birefringence damage, especially a low polarization-induced birefringence, when exposed to linearly or elliptically polarized UV radiation, in addition to low light-induced wave- front distortion ("LIWFD”) and high transmission.
• LIWFD light-induced wave- front distortion
• an OD-doped synthetic silica glass material capable of being used in the light path of the lithographic irradiation of a lithographic device operating at a wavelength below about 300 nm, comprising OD and optionally OH, wherein the ratio of n(OD)/(n(OD)+n(OH)) is higher than 2XlO- 4 .
• the glass comprises less than about 500 ppm by weight of OH and 0.15-1400 ppm OD.
• the glass comprises less than about 150 ppm by weight of OH and about 0.1-1400 ppm OD. [0012] In yet another embodiment of the first aspect of the present invention, the glass comprises less than about 20 ppm by weight of OH and about 0.01-1400 ppm OD. [0013] In still another embodiment of the first aspect of the present invention, the glass comprises less than about 20 ppm by weight OH and between about 0.01-300 ppm OD. [0014] In still another embodiment of the first aspect of the present invention, the glass comprises less than about 20 ppm by weight OH and between about 0.01-150 ppm OD.
• the glass comprises less than about 1 ppm by weight OH and between about 0.01-150 ppm OD.
• a second aspect of the present invention is an optical member capable of being used in the light path of the lithographic irradiation of a lithographic device operating at a wavelength below about 300 nm comprising the OD-doped synthetic silica glass of the present invention described summarily above and in detail below.
• the optical member is a refractive optical member where the irradiation travels through at least part of the body of the optical member.
• a third aspect of the present invention is a lithographic system comprising the optical member of the present invention described summarily above and in detail below.
• the lithographic system is an immersion lithographic system.
• the lithographic system may operate at about 248 nm, 193 nm or even shorter.
• a fourth aspect of the present invention is a process for making OD-doped synthetic silica glass material capable of being used in the light path of the lithographic irradiation of a lithographic device operating at a wavelength below about 300 nm, comprising the following steps:
• step (II) depositing the a plurality of particles on a supportive deposition surface at an elevated temperature such that the particles are consolidated into transparent glass material in situ, wherein: either in step (I), the a plurality of particles provided are D-containing and/or in step (II), the deposition and consolidation are carried out in a D-containing atmosphere, such that the obtained silica glass comprises OD and optionally OH, and the ratio of n(OD)/(n(OD)+n(OH)) is higher than about 2XlO "4 , in certain embodiments preferably higher than about 0.1, in certain other embodiments higher than about 0.3, in certain other embodiments higher than about 0.5, in certain other embodiments higher than 0.8, in yet still other embodiments higher than about 0.9.
• a fifth aspect of the present application is a process for making OD-doped synthetic silica glass material capable of being used in the light path of the lithographic irradiation of a lithographic device operating at a wavelength below about 300 nm, comprising the following steps:
• A providing a particle preform comprising a plurality of particles comprising silica;
• B optionally purifying and/or drying the particle preform;
• step (E) optionally treating the consolidated glass obtained in step (D) in the presence OfH 2 , HD and/or D 2 , wherein in at least one of steps (A), (B) 5 (C) 5 (D) and (E), OD is introduced into or formed in the glass.
• a sixth aspect of the present invention is a process for making OD-doped synthetic silica glass, comprising the following steps: (a) providing a plurality of OD-doped particles comprising silica; and
• a seventh aspect of the present invention is a particle preform formed during a process of the present invention generally described above and in detail below,
• An eighth aspect of the present invention is a process for making OD-doped synthetic silica glass capable of being used in the light path of the lithographic irradiation of a lithographic device operating at a wavelength below about 300 nm, comprising the following steps:
• the OD-doped synthetic lithographic silica glass of the present invention has the advantage of higher optical performance at certain wavelength shorter than about 300 nm, such as at 193 nm, compared to conventional silica glass which is essentially non-OD- doped.
• FIG. 1 is schematic illustration of a proposed mechanism accounting at least partly for polarization-induced birefringence in silica glass comprising OH and/or OD moieties.
• FIG. 2 is a schematic illustration of a proposed mechanism accounting at least partly for polarization-induced birefringence in silica glass comprising OH and/or OD moieties, and the difference in terms of level of polarization-induced birefringence between glasses having different n(0D)/(n(0D)+n(0H)) ratios.
• FIG. 3 is a schematic illustration of a proposed mechanism accounting at least partly for the polarization-induced birefringence and light-induced wavefront distortion (LIWFD) in silica glass comprising OH and/or OD moieties, and the difference in terms of level of polarization-induced birefringence and LIWFD between glasses having different n(OD)/(n(OD)+n(OH)) ratios.
• LIWFD light-induced wavefront distortion
• FIG. 4 is a schematic illustration of a proposed mechanism accounting at least partly for the induced absorption (IA) in silica glass comprising OH and/or OD moieties, and the difference in terms of level of induced absorption between glasses having different n(OD)/(n(OD)+n(OH)) ratios.
• IA induced absorption
• FIG. 5 is a schematic illustration of a proposed mechanism accounting at least partly for the induced absorption in silica glass comprising OH and/or OD moieties, and the effect of doped hydrogen molecules (H 2 , D 2 and/or HD) in reducing induced absorption.
• FIG. 6 is a diagram showing the OH concentration ([OH]) and OD concentration ([OD]) profiles of a consolidated silica glass sample produced according to one embodiment of the processes of the present invention for making OD-doped silica glass of the present invention.
• FIG. 7 is a diagram showing the [OH] and [OD] profiles of a consolidated OD- doped silica glass prepared according to one embodiment of the process of the present invention for making OD-doped silica glass of the present invention.
• FIG. 8 is a diagram showing polarization-induced birefringence, measured at 633 nm, of a series of OD-doped silica glass samples of the present invention, and a series of OH-doped silica glass samples, having various levels of molecular H 2 or D 2 , as a function OfN(P)-F, where F is fluence, and N(P) is number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of about 200 /J-cm ⁇ -pulse "1 and a pulse length of approximately 25 ns and a repetition rate of about 4 kHz to which the glass samples were exposed.
• FIG. 8 is a diagram showing polarization-induced birefringence, measured at 633 nm, of a series of OD-doped silica glass samples of the present invention, and a series of OH-doped silica glass samples, having various levels of molecular H 2 or D
• FIG. 9 is a diagram showing normalized polarization-induced birefringence of the same samples of FIG. 8, as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of about 200 /J-cm ⁇ -pulse "1 and a pulse length of approximately 25 ns and a repetition rate of about 4 kHz to . which the glass samples were exposed.
• FIG. 10 is a diagram showing normalized LIWFD measured at 633 nm of the same series of OD-doped silica glass samples of the present invention, and the same series of OH-doped silica glass samples as presented in FIG.
• FIG. 11 is a diagram showing normalized LIWFD measured at 193 nm of the same series of OD-doped silica glass samples of the present invention, and the same series of OH-doped silica glass samples as presented in FIG. 8 above, as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of about 200 /J-cm ⁇ -pulse "1 and a pulse length of approximately 25 ns and a repetition rate of about 4 kHz to which the glass samples were exposed.
• FIG. 12 is the OH concentration ([OH]) and OD concentration ([OD]) profiles of a consolidated silica glass sample produced according to one embodiment of the processes of the present invention for making OD-doped silica glass of the present invention.
• FIG. 13 is a diagram showing polarization-induced birefringence, measured at 633 nm, of a series of OD-doped silica glass samples of the present invention, and a series of OH-doped silica glass samples, having various levels of molecular H 2 , as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of 600 /J-cm ' ⁇ pulse "1 and a pulse length of approximately 21 ns and a repetition rate of about 4 kHz to which the glass samples G, H, J and K were exposed, and a fluence of 200 ⁇ j-cm " 2 -pulse " ' and a pulse length of approximately 25 ns and a repetition rate of about 4 kHz to which the glass samples F and L were exposed.
• FIG. 14 is a diagram showing normalized polarization-induced birefringence of a series of OD-doped silica glass samples of the present invention, and a series of OH- doped silica glass samples, having various levels of molecular H 2 , as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of 600 ⁇ J-cm "2 -pulse " ' and a pulse length of approximately 21 ns and a repetition rate of about 4 kHz to which the glass samples G, H, J and K were exposed, and a fluence of 200 ⁇ j-cm " 2 -pulse " ' and a pulse length of approximately 25 ns and a repetition rate of about 4 kHz to which the glass samples F and L were exposed.
• FIG. 15 is a diagram showing normalized LIWFD measured at 633 nm of the same series of OD-doped silica glass samples of the present invention, and the same series of OH-doped silica glass samples G, H, J and K as presented in FIG. 14 above, as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of 600 /J-cm ⁇ -pulse "1 and a pulse length of approximately 21 ns and a repetition rate of about 4 kHz to which the glass samples were exposed.
• FIG. 15 is a diagram showing normalized LIWFD measured at 633 nm of the same series of OD-doped silica glass samples of the present invention, and the same series of OH-doped silica glass samples G, H, J and K as presented in FIG. 14 above, as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a flu
• 16 is a diagram showing normalized induced absorbance, normalized IA, measured at 193 nm of the same series of OD-doped silica glass samples of the present invention, and the same series of OH-doped silica glass samples G, H, J and K as presented in FIG. 14 above, as a function of number of pulses of a pulsed laser beam having a wavelength of about 193 nm, a fluence of 600 /J-cm ⁇ -pulse "1 and a pulse length of approximately 21 ns and a repetition rate of about 4 kHz to which the glass samples were exposed.
• FIG. 17 is a diagram showing the OH concentration ([OH]) and OD concentration ([OD]) profiles of a consolidated silica glass sample produced according to one embodiment of the processes of the present invention for making OD-doped silica glass of the present invention.
• D-containing compound means a chemical compound or an elemental substance comprising deuterium atom(s) ( ⁇ H or ⁇ D , "D") and optionally pronium atom(s) ( JH , "H"), in which the ratio of n(D)/(n(D)+n(H)) is higher than the natural isotopic abundance of D, where n(D) is the total number of D atoms in the molecule of the D-containing compound, and n(H) is the total number of H atoms in the molecule of the D-containing compound.
• D-containing compound thus include, but are not limited to: D 2 , DH, CD 4 , CDH 3 , D 2 O, DHO, and the like.
• D-containing means that an elemental substance, a compound, a material, or an atmosphere in which the ratio of n(D)/(n(D)+n(H)) is higher than the natural isotopic abundance of D.
• hydroxyl(s) or OH means a moiety or a group of moieties each consisting of an oxygen atom and a pronium atom (H).
• the oxygen atom may be 16 0, 17 O or 18 O, or mixtures thereof at any proportion.
• n(0H) means the total number of OH moieties in a material.
• n(OD) means the total number of OD moieties in a material.
• a hydroxyl-doped or OH-doped material means the material comprises OH moieties and optionally OD moieties, and the ratio of n(OH)/(n(OD)+n(OH)) in the material is equal to or higher than the natural isotopic abundance of H.
• a material in which all the OH moieties originate from normal water comprising H 2 O and D 2 O at essentially the natural isotopic abundances of H and D is regarded as OH- doped.
• a deuteroxyl-doped or OD-doped material means the material comprises OD moieties and optionally OH moieties, and the ratio of n(0D)/(n(0D)+n(0H)) in the material is higher than the natural isotopic abundance of D.
• OY means OH or OD or if not specified, both.
• Y-Y' means D 2 or H 2 or, if not specified, HD or any mixture or combination of two or three of them at any proportion.
• F-doped in the present application, it is meant that the glass comprises at least 1 ppm by weight of fluorine.
• the material can be used in the light path of the lithographic irradiation while the lithographic device is being operated during the normal use for the intended function, i.e., performing lithography function in, e.g., the process of making semiconductor devices; and [0054] (ii) The material can be used in the light path for the purpose of re-directing or manipulating the lithographic irradiation.
• One of ordinary skill in the art of lithography understands that for a material to be capable of being used in the light path of the lithographic irradiation of a lithographic device operating at a certain wavelength, the material should have the required composition and properties, such as internal transmission, laser induced wavefront distortion, induced absorption, and the like.
• One of ordinary skill in the art of lithography also understands that it is generally desired that the materials can be made at a reasonably low cost to the manufacturer and to the society at large (thus lower negative environmental impact if possible).
• the silica glass is desired to have an internal transmission at about 248 nm of at least 99.00%/cm. It is highly desired, in certain applications, especially lithographic applications for making semiconductor chips operating at about 193 nm, the silica glass has an internal transmission of at least 99.00%/cm at about 193 nm.
• the silica glass is desired to have a sodium concentration of lower than about 100 ppm by weight, in certain embodiments lower than about 50 ppm, in certain other embodiments lower than about 10 ppm.
• the silica glass has a sodium concentration of lower than about 500 ppb by weight, in certain embodiments lower than about 100 ppb, in certain embodiments lower than about 50 ppb, in certain other embodiments lower than about 10 ppb.
• Fictive temperature is a temperature at which a frozen-in glass structure would be at equilibrium.
• the Si-O-Si bond angle is a function of fictive temperature.
• the infrared absorption wavelength, or frequency, of Si-O-Si species varies with bond angle. Thus infrared absorption can be used to determine an approximate fictive temperature.
• An empirical relation between fictive temperature and absorption frequency is given in the prior art such as Agarwal et al., A simple IR spectroscopic method for determining fictive temperature of silica glasses, Journal of Non-crystalline Solids 185 (1995) 191.
• Raman scattering can also be used to determine flctive temperature using the scattering frequency of silica defects related to strained ring structure.
• the term "polarization-induced birefringence” means the peak measured birefringence level in the center portion of the uniformly exposed area of the glass after a certain time interval or laser pulses, if a pulsed laser beam is used, less the initial birefringence of the glass before the exposure.
• the polarization-induced birefringence levels as claimed in the present application are magnitude (absolute value) thereof.
• a linearly polarized pulsed laser beam at approximately 193 nm having about 3 mm diameter with a given fluence and pulse length is directed to a fixed area of the glass sample.
• the birefringence at the center portion of the exposed area is measured after a certain number of pulses.
• the polarization-induced birefringence value is calculated by subtracting the initial birefringence of the glass from the measured center birefringence.
• induced edge birefringence means the measured peak birefringence level in the peripheral portion outside of but abutting the exposed area (i.e., the area right at the aperture where the light intensity changes from nominal value to zero) of the glass after a certain time interval or laser pulses, if a pulsed laser beam is used, less the initial birefringence of the glass before the exposure.
• the induced edge birefringence of the silica glass is measured after a linearly polarized pulsed laser beam at approximately 193 nm having about 3 mm diameter with a given fluence and pulse length has been directed to a fixed area of the glass sample for a certain period of time or a given number of pulses.
• the induced edge birefringence value is calculated by subtracting the initial birefringence of the glass from the peak measured birefringence at the peripheral portion.
• low polarization-induced birefringence means a polarization- induced birefringence of less than or equal to 0.1 nm/cm measured at about 633 nm after being subjected to 5x10 9 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 /J-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
• normalized polarization-induced birefringence is calculated from the measured polarization-induced birefringence as follows:
• PIB(N) is normalized polarization-induced birefringence
• PIB(M) is magnitude (i.e., absolute value thereof irrespective of sign thereof) of measured polarization-induced birefringence in nm/cm measured at about 633 nm
• Ni is number of pulses in billion pulses
• F is fluence of the linearly polarized ArF laser to which the glass is exposed to in mJ-cm ' ⁇ pulse "1 .
• a single sample may have differing PIB(N) when measured at differing Ni and F. Where Ni and F are not specified, the PIB(N) value is average value.
• LB633 is the bulk LIWFD measured at 633 nm in nm/cm (could bear a "+” or “-” sign, depending on whether the glass compacts or expands)
• LB 193 is bulk LIWFD measured at 193 nm in nm/cm (could bear a + or- sign, depending on whether the glass compacts or expands)
• N 5 is number of pulse in million of the linearly polarized ArF excimer laser to which the sample was exposed to when the LB633 or LB 193 is measured
• F is the fluence of the ArF excimer laser in mJ-cm ⁇ -pulse "1
• ⁇ is pulse length of the ArF excimer laser in ns.
• IA Induced absorption
• IA(N) Normalized induced absorption
• T ⁇ is the internal transmission of the glass in terms of %/cm prior to laser exposure
• T 2 is the internal transmission of the glass in terms of %/cm after laser exposure
• N'F 2 where N' is number of pulses in the million, F is fluence of the ArF laser to which the glass is exposed to in mJ-cm "2 -pulse " ', and ⁇ is pulse length of the ArF excimer laser in ns.
• variation of refractive index or “refractive index variation,” or “An” means the maximal variation of refractive indices measured in a plane perpendicular to the optical axis of the glass material or glass optical member along a predetermined direction by using interferometry at about 633 nm (He-Ne laser) (with tilt and piston taken out, as indicated infra).
• the refractive index variation along a certain direction does not include tilt or piston.
• the optical axis of a glass optical member, a glass blank, or a piece of glass material is selected to be perpendicular to a plane (a cross-section) in which the measured refractive index inhomogeneity is the smallest, in order to obtain a glass member having large clear aperture area.
• the preferred method, also the method used herein, for determination of interstitial molecular H 2 in fused silica is Raman scattering.
• Raman spectrometry is obtained using a T64000 spectrometer from HORIBA Jobin Yvon Inc. with an EEV charge-coupled device (CCD) detector.
• CCD charge-coupled device
• the hydrogen molecule concentration in molecules/cm 3 was obtained from the ratio of the intensity detected from the hydrogen molecule scattering peak at 4135 cm '1 (I 4B5 ) to the intensity of the silica scattering peak at 800 cm “1 (Isoo), i.e., Unsfkoo, in the laser Raman spectrum (See, V. S.
• the OH group has characteristic absorption bands near 2.72 ⁇ m (3676 cm “1 ), 2.21 ⁇ m (4525 cm “1 ) and 1.38 ⁇ m (7246 cm “1 ) in fused silica. Concentration of OH was measured by FTIR using the peak height of either the 3676 cm “1 or the 4525 cm “1 absorption band. [0069] The OH concentration, c, in moHiter “1 , is derived from the Beers-Lambert Law
• OD Concentration of OD in ppm by weight was calculated from c ' in moHiter "1 using the density of the silica glass (approximately 2.2 g/cm 3 ) and molecular weight of OD (approximately 18 g/mol).
• the constant e ' for high purity silica glass at a particular wavelength is available in the prior art.
• a "particle preform" means an object having a shape and comprising a plurality of solid particles.
• a particle preform in the present application may be, for example, a soot preform consisting essentially of silica soot particles obtained from flame hydrolysis processes, a green body comprising a number of silica particles obtained from the sol-gel process, and the like.
• the term "soot dispenser” means a device which dispenses preformed soot particles by, e.g., spraying.
• the present inventors In search of silica glass materials with desired optical properties, especially in terms of initial internal transmission, LIWFD, light-induced absorption, polarization- induced birefringence, and the like, the present inventors have unexpectedly found that OD-doped high purity fused silica glass exhibits comparable, and in certain important respects, superior, performance than non-OD-doped glass with comparable OH concentration. The present invention is based on this discovery.
• Silica glasses comprising D 2 has been disclosed and studied in the prior art before.
• D 2 molecular deuterium
• United States Patent No. 5,325,230(A) to Yamagata et aL mentions that D 2 , as well as H 2 , may be doped into fused silica glass.
• this reference does not provide an example of D 2 doped silica glass.
• doping silica glass with OD Still, it does not mention the potential impact of doping silica glass with D 2 on the optical properties of the glass.
• J.E. Shelby Molecular diffusion and solubility of hydrogen isotopes in vitreous silica, Journal of Applied Physics, Volume 48, No.
• the material of the present invention may be used in and for other applications, including but not limited to: lithography at about 248 nm, lithography at about 157 nm, i-line, g-line lithography, laser generators, lithographic inspection devices, and the like.
• the present inventors have prepared synthetic silica glass materials doped with OD capable of being used in below 300 nm UV lithographic applications. As mentioned above, the present inventors have found that, unexpectedly, OD-doped lithographic synthetic silica glass materials, especially those with a high n(OD)/(n(OD)+n(OH)) ratio, tend to have better optical properties than non-OD-doped silica glass with essentially the same level of total concentration of OH and OD ([OH]+[OD]).
• OD-doped high purity fused silica glass exhibits improved light induced absorption (IA) over the corresponding OH-doped high purity fused silica glass.
• IA light induced absorption
• the data in FIG. 16 shows this improvement.
• the data is plotted as normalized induced absorbance (Normalized IA, IA(N)) at 193 nm which is calculated as described above.
• the present inventors have found that, to achieve a low level of polarization- induced birefringence in the silica glass, it is desired that the OH concentration in the glass is less than 500 ppm by weight, preferably less than 300 ppm, more preferably less than 100 ppm, still more preferably less than 50 ppm, most preferably less than 20 ppm.”
• the present inventors present the following explanation of the mechanism of polarization-induced birefringence in fused silica glass comprising OH and/or OD, as well as the mechanism accounting for the lower polarization-induced birefringence in fused silica glass having a higher n(OD)/(n(OD)+n(OH)) ratio.
• the explanation is schematically illustrated in FIGS. 1-3 of the present application. In these three figures, Y represents H or D, and hydrogen bonds are shown as dotted lines.
• FIG. 1 schematically illustrates a proposed mechanism aiming to interpret at least part of the polarization-induced birefringence generated in OH- and/or OD-containing silica glass.
• Formulae (Fl) and (F2) represent the partial structures of a silica glass prior to and after exposure to UV irradiation, respectively. It is believed that initially, prior to the exposure to UV light, Si-OY bonds are randomly arranged in the SiO 2 network and certain hydrogen bonds are formed. Exposure to UV light can provide enough allowing activation energy for -OY (or -Y) bond movement
• FIG. 2 schematically illustrates a photochemical reaction possibly involved in the polarization-induced birefringence phenomenon in a manner slightly different from that of FIG. 1.
• the mechanism involves the breakage of certain hydrogen bonds pre-existing in the partial glass structure (F3) prior to exposure and the formation of new hydrogen bonds in the partial glass structure (F4) after exposure.
• the reaction rate Jc(Y) of the photoreaction is Jc(R) and k(O), respectively, when the atom Y in the figure is H and D, respectively. It is hypothesized by the present inventors that, due to the significant mass difference between D and H (approximately 2 times difference), the reaction rate Jc(O) is significantly lower than kQ ⁇ ).
• the present inventors propose another mechanism in an effort to account for both LIWFD and polarization-induced birefringence as a result of exposure to linearly or elliptically polarized UV irradiation. This proposed mechanism is essentially a two-step reaction involving the breakage and formation of both hydrogen bonds and covalent bonds.
• the first step a photolysis reaction having a reaction rate of &i(Y), involves the breakage of a covalent bond b (a Si-O bond) and possible breakage of a hydrogen bond a in the partial structure (F5) prior to exposure.
• the reverse reaction of this first step has a reaction rate of Jc ⁇ (Y).
• the second step having a reaction rate of Jc 2 (Y), involves the breakage of bond c (an O-Y bond) in an intermediate structure (F6), the formation of new bond d(a Si-O bond) and e (a Y-O bond), and possibly the formation of a new hydrogen bond/in the post-exposure partial structure (F7).
• FIG. 4 explains at least partly the induced absorption of OH/OD-containing silica and the differing degrees thereof at various n(0D)/(n(0D)+n(0H)) ratios at approximately the same level of total [0D]+[0H] in the glass.
• E' center Si-
• Si-O- both believed to be absorbing in the deep UV and/or vacuum UV.
• E' center has a center absorption peak at about 215 nm, and extends to about 193 nm.
• the E' centers and Si-O- centers created in the photolysis reaction from structure (F8) to structure (F9) is reversible to a certain degree.
• some of the absorption centers would automatically heal by the reverse reaction from structure (F9) to structure (F8).
• the OD-doped silica glass of the present invention is capable of being used in lithography below about 300 nm. It can be used in lithographic devices operating at longer wavelength, such as in the I-line lithography at about 365 nm.
• the OD-doped silica glass of the present invention is capable of being used as refractive lens elements in the light path of the UV irradiation utilized in the dry lithographic devices operating at about 248 nm.
• the OD- doped silica glass of the present invention has the composition and property requirements for use as refractive lens elements in the light path of the UV irradiation utilized in the immersion lithographic devices operating at about 248 nm.
• the OD-doped silica glass of the present invention is capable of being used as refractive lens elements in the light path of the UV irradiation utilized in the dry lithographic devices operating at about 193 nm.
• the OD- doped silica glass of the present invention has the composition and property requirements for use as refractive lens elements in the light path of the UV irradiation utilized in the immersion lithographic devices operating at about 193 nm.
• One of ordinary skill in the art of lithography knows that for silica glasses to be used as lens elements in these applications, stringent requirements regarding optical performance such UV transmission, UV degradation in terms of induced absorption, light induced wavefront distortion (LIWFD), refractive index homogeneity, fictive temperature, birefringence, light induced birefringence, must satisfied.
• LIWFD light induced wavefront distortion
• the present inventors have discovered that high purity fused silica glass doped with OD has, inter alia, superior performance in polarization-induced birefringence when subjected to linear polarized irradiation. Therefore, the glass of the present invention, especially those doped with high ratio of OD, can be advantageously used in immersion lithographic technology.
• the OD- doped silica glass may be used as the material for lens elements in reflective lithography operating in the vacuum UV and X-ray spectrum.
• the natural isotopic abundance of deuterium (D) is about 1.15XlO "4 by mole.
• the OD-doped silica glass of the present invention has an n(D)/(n(D)+n(H)) higher than about 2xlO "4 , thus higher than the natural isotopic abundance of D.
• the synthetic silica glass material of the present invention may be essentially devoid of OH. However, it is not ruled out that it may contain a certain level of OH in the glass.
• the OD-doped synthetic silica glass of the present invention has an n(OD)/(n(OD)+n(OH)) ratio of higher than about 0.05, in certain embodiments preferably higher than about 0.1, in certain embodiments preferably higher than about 0.2, in certain embodiments preferably higher than about 0.3, in certain embodiments preferably higher than about 0.4, in certain embodiments preferably higher than about 0.5, in certain other embodiments preferably higher than about 0.8, in certain other embodiments preferably higher than about 0.90, in certain other preferred embodiments higher than about 0.95, in certain other embodiments preferably higher than about 0.99.
• High purity synthetic silica glass with various levels of [OD] can be obtained by using the soot-to-glass method.
• High isotopic purity D 2 O having a higher than 99.9% of n(D)/(n(D)+n(H)) may be employed in the soot- to-glass method of the present invention, to be described infra as one of the processes of the present invention, can be used to produce synthetic silica glass with n(OD)/(n(OD)+n(OH)) higher than 99%.
• synthetic silica glass with various levels of n(OD)/(n(OD)+n(OH)) can be produced.
• the oxygen atoms in the OD and optionally OH moieties, may be 16 0, 17 O and 18 O at their natural isotopic abundances.
• the silica glass of the present invention may comprise higher percentage of 17 O and 18 O, especially 18 O (a stable isotope), than their respective natural isotopic abundances.
• the glass has an OH concentration of lower than about 600 ppm by weight, in certain preferred embodiments preferably lower than about 160 ppm, in certain other preferred embodiments lower than about 50 ppm, in certain other embodiments preferably lower than about 20 ppm, in certain other embodiments preferably lower than about 1 ppm, in certain other embodiments still preferably lower than 0.1 ppm.
• the glass has an OD concentration of lower than about 1400 ppm by weight, in certain preferred embodiments lower than about 1000 ppm, in certain preferred embodiments lower than about 800 ppm, in certain other preferred embodiments lower than about 500 ppm, in certain other preferred embodiments lower than about 300 ppm, in certain other preferred embodiments lower than about 150 ppm, in certain other preferred embodiments lower than about 50 ppm, in certain other preferred embodiments lower than about 20 ppm, in certain other embodiments lower than about 1 ppm, in certain embodiments between about 0.1-1400 ppm, in certain other embodiments between about 0.1-1000 ppm, in certain embodiments between about 0.1-800 ppm, in certain other embodiments between about 0.1-500 ppm, in certain other embodiments between about 0.01-150 ppm, in certain other embodiments between about 0.01-50 ppm, in certain other embodiments between about 0.01-20 pp
• the glass has less than about 500 ppm by weight of OH and 0.15-1400 ppm OD. In certain embodiments of the OD-doped synthetic silica glass of the present invention, the glass comprises less than about 150 ppm by weight of OH and about 0.1-1400 ppm OD. In certain other embodiments of the OD-doped synthetic silica glass of the present invention, the glass comprises less than about 20 ppm by weight of OH and 0.01-1400 ppm OD.
• the glass comprises less than about 20 ppm by weight of OH and about 0.01-300 ppm OD.
• the glass has an essentially constant ratio of concentration of OD ([OD]) to the concentration of OH ([OH]) in different locations in the glass, i.e., [OD]/[OH].
• essentially constant ratio it is meant that the difference between the maximal ratio (R ma ⁇ ) and the minimal ratio (R m i n ) as measured has the following relationship: 2(R max - Rmin)/(Rmax+Rmin) ⁇ 0.1.
• the glass has a [OD] variation, measured in a plane essentially perpendicular to the optical axis of the glass, of less than about 10 ppm by weight, in certain embodiments less than about 5 ppm, in certain other embodiments less than about 2 ppm, in certain other embodiments less than about 1 ppm, in certain other embodiments less than about 0.1 ppm.
• the glass has, in addition to the or in absence of the [OD] variation described in this paragraph, an [OH] variation, measured in a plane essentially perpendicular to the optical axis of the glass, of less than about 10 ppm by weight, in certain embodiments less than about 5 ppm, in certain other embodiments less than about 2 ppm, in certain other embodiments less than about 1 ppm.
• the OD-doped synthetic silica glass of the present invention may be essentially free of dopants other than OD and OH. However, it is not ruled that the OD-doped synthetic silica glass of the present invention comprises dopants such as Al, F, Cl and Ti.
• the Ti-containing OD-doped silica glass of the present invention may be advantageously used in the substrates for reflective optical elements, especially those requiring high thermal dimensional stability, such as those used in reflective lithography technology operating in vacuum UV and X-ray spectra.
• F-doped silica glass of the present invention may comprise, for example, fluorine in the amount of less than 1000 ppm by weight, in certain embodiments less than about 500 ppm, in certain other embodiments less than about 300 ppm, in certain other embodiments less than about 100 ppm, in certain embodiments less than about 50 ppm, in certain other embodiments less than about 10 ppm.
• the OD-dopes silica glass of the present invention it comprises less than about 150 ppm by weight of OH, about 0.1-1400 ppm by weight OD and about 1-500 ppm by weight F.
• the glass comprises less than about 20 ppm by weight of OH, about 0.01- 1400 ppm OD and about 1-500 ppm F. In certain other embodiments of the OD-doped synthetic silica glass of the present invention, the glass comprises less than about 20 ppm by weight of OH, about 0.01-300 ppm OD and about 1-500 ppm F.
• the OD-doped synthetic silica glass may be doped with molecular H 2 , HD and/or D 2 .
• the OD-doped synthetic silica glass of the present invention has a concentration of [H 2 ], [HD] and [D 2 ], in total, of between IxIO 15 to IxIO 19 molecules/cm 3 , in certain embodiments higher than about 5xlO 15 molecules/cm 3 , in certain embodiments higher than about 1x10 16 molecules/cm 3 , in certain preferred embodiments below about 5x10 18 molecules/cm 3 , in certain other preferred embodiments below about 5x10 17 molecules/cm 3 , in certain other preferred embodiments below about IxIO 17 molecules/cm 3 , in certain other preferred embodiments between about IxIO 16 to 1x10 17 molecules/cm 3 .
• the ratio of (2n(H 2 )+n(HD))/2(n(H 2 )+n(HD)+n(D 2 )) is higher than 0.1, in certain preferred embodiments higher than about 0.3, in certain other preferred embodiments higher than about 0.5, in certain other embodiment higher than about 0.7, in certain other preferred embodiments higher than about 0.9.
• the ratio of (2n(H 2 )+n(HD))/2(n(H 2 )+n(HD)+n(D 2 )) in the glass is essentially the natural isotopic abundance of H by mole.
• the ratio of (2n(D 2 )+n(HD))/2(n(H 2 )+n(HD)+n(D 2 )) is higher than 0.1, in certain preferred embodiments higher than about 0.3, in certain other preferred embodiments higher than about 0.5, in certain other embodiment higher than about 0.7, in certain other preferred embodiments higher than about 0.9. In certain preferred embodiment, the ratio of (2n(D 2 )+n(HD))/2(n(H 2 )+n(HD)+n(D 2 )) in the glass is essentially the natural isotopic abundance of D by mole.
• the glass has an essentially constant ratio R' of [D 2 ]Z[H 2 ] at different locations of the glass.
• essentially constant ratio it is meant that the difference between the maximal ratio (R' max ) and the minimal ratio (R' m j n ) as measured has the following relationship: 2(R' max -R' min )/(R'ma ⁇ +R'min) ⁇ 0.1. In certain embodiments, 2(R' max -
• the glass has a concentration variation of OH and OD ([OH]+[OD]) measured in a plane perpendicular to at least one direction of less than about 50 ppm, in certain embodiments preferably less than about 30 ppm, in certain other embodiments preferably less than about 20 ppm, in certain other embodiments less than about 10 ppm, in certain other embodiments preferably less than about 1 ppm, in certain other embodiments preferably less than about 0.1 ppm.
• the glass has a Cl concentration less than about 100 ppm, in certain embodiments less than about 50 ppm, in certain other embodiments less than about 10 ppm.
• Cl concentration less than about 100 ppm, in certain embodiments less than about 50 ppm, in certain other embodiments less than about 10 ppm.
• alkali, alkaline earth and transition metals can be detrimental to the transmission characteristics silica glasses. See, for example, Schultz, P. C, Optical Absorption of the Transition Elements in Vitreous Silica, Journal of The American Ceramic Society, 57 (7), pp 309-313, (July 1974); United States Patent No. 6,174,509 Bl to Corning Incorporated, Pure Fused Silica, Furnace and Method; United States Patent No.
• United States Patent No. 6,174,509 Bl discloses an article produced by collecting molten silica particles in a refractory furnace in which at least a portion of the refractory has been exposed to a halogen-containing gas to react with contaminating metal ions in the refractory. Improvement in the zircon refractory, as disclosed in United States Patent No. 6,174,609, alleviated the affect of sodium ion contamination in a fused silica article.
• the standard manufacturing processes described above is capable of consistently producing fused silica lens blanks with 99.5%/cm. Reduction of metal contaminants, which have a major impact on UV transmission, has played a major role in the production of higher transmission fused silica. The effects of metals, such as sodium, potassium and iron, are evident at the lO's of parts per billion level.
• the standard process has demonstrated the ability to produce fused silica having transmission of 99.65%/cm, without sacrificing glass homogeneity, but not in the quantity needed to make large production quantities of lens blanks and not with the consistency to serve as a basis for a production process.
• high purity synthetic silica glass material are required to have a very low level of alkali metals, alkaline earth and transition metals in order to have a sufficient transmission properties (e.g., absorption, induced absorption, fluence-dependent- transmission, birefringence, light-induced birefringence, LIWFD, and the like) in the wavelength of interest in the UV, such as for use as refractive members in KrF and ArF lithography devices.
• Certain metals having multiple oxidation states can cause more absorption at one oxidation state than at others.
• the glass comprises less than 100 ppm by weight, in certain embodiments less than about 50 ppm, in certain embodiments less than about 10 ppm, in certain embodiments preferably less than 1 ppm, in certain embodiments preferably less than 500 ppb, in certain embodiments less than about 300 ppb, in certain embodiments less than about 100 ppb, in certain embodiments less than 50 ppb, in certain embodiments preferably less than about 20 ppb, in certain other embodiments preferably less than about 10 ppb, of any alkali metal, any alkali earth metal, and any transition metal.
• sodium is one of the most difficult to reduce from the glass composition because it is virtually ubiquitous and can be introduced into the glass in the handling process. Sodium also diffused into consolidated glass and soot preforms extraordinarily fast at elevated temperatures, especially at above 800 0 C.
• the glass in order for the glass to have the capability to be used as refractive optical element in a lithographic device operating at a wavelength below about 300 nm, such as at about 248 nm or 193 nm, it is typically desired that the glass comprises sodium lower than about 100 ppb by weight, in certain embodiments lower than about 50 ppb, in certain embodiments lower than 30 ppb, in certain embodiments lower than about 10 ppb (such as for use in lithography devices operating at about 193 nm), and in certain embodiments lower than 5 ppb.
• the present inventors have made OD-doped high purity silica glass with such low level of sodium.
• the glass comprises any transition metal at less than 2 ppb.
• the glass comprises any transition metal at less than 1 ppb. In certain other embodiments, the glass comprises any transition metal at less than 0.5 ppb. In certain embodiments, especially for glasses to be used as refractive optical member in ArF laser lithography devices, it is preferred that the glass comprises any individual element in all oxidation states of the following in concentrations less than 2 ppb by weight, in certain embodiments preferably less than 1 ppb, in certain other embodiments less than 0.5 ppb, in certain other embodiments less than 0.1 ppb: Ti (+2, +4, for example), V (+5, +4, for example), Cr (+6, +3, for example), Mn (+6, +4, +2, for example), Fe (+3, +2, for example), Co (+3, +2, for example), Ni (+2, for example), Cu (+2, +1, for example), Zn (+2, for example), Ge (+4, +2, for example), Zr (+4, for example), Ag (+1, for example), Cd (+1, for example), Sn (+4, +2, for example), Pb (+4, +2,
• the OD- doped synthetic silica glass of the present invention comprises less than 100 ppm by weight, in certain embodiments less than about 50 ppm, in certain embodiments less than about 10 ppm, in certain embodiments preferably less than 1 ppm, in certain embodiments preferably less than 500 ppb, in certain embodiments less than about 300 ppb, in certain embodiments less than about 100 ppb, in certain embodiments less than about 50 ppb, in certain embodiments preferably less than 30 ppb, in certain other embodiments preferably less than 10 ppb, of any and all metals in all oxidation states in total.
• the glass exhibits a light-induced wavefront distortion (LIWFD), measured at 633 nm, of between -0.1 and 0.1 nm/cm, in certain preferred embodiments between -0.5 to 0.5 nm/cm, in certain other preferred embodiments between about 0 and 1 nm/cm, in certain other preferred embodiments between about 0 and 0.5 nm/cm, when subjected to 10 billion pulses of a laser beam operating at approximately 193 ran and having a fluence of approximately 70 ⁇ J/(cm 2 -pulse) and a pulse length of approximately 25 ns.
• LIWFD light-induced wavefront distortion
• the glass exhibits, in addition to or in absence of the LIWFD properties described above, a normalized wavefront distortion L633 when subjected to excimer laser pulses at about 193 nm of less than or equal to about 20 billion pulses, measured at about 633 nm, wherein -1.0 ⁇ L633 ⁇ 1.0, in certain embodiments -0.5 ⁇ L633 ⁇ 1.0, in certain embodiments -0.1 ⁇ L633 ⁇ 1.0, in certain embodiments 0 ⁇ L633 ⁇ 1.0, in certain preferably embodiments 0 ⁇ L633 ⁇ 0.5, in certain other preferred embodiments 0 ⁇ L633
• ⁇ 0.4 in certain other embodiments preferably 0 ⁇ L633 ⁇ 0.3.
• the glass exhibits, in addition to or in absence of the LIWFD and L633 properties described above, a normalized wavefront distortion Ll 93 when subjected to excimer laser pulses at about 193 nm of less than or equal to about 20 billion pulses, measured at about 193 nm, wherein -1.0 ⁇ L193 ⁇ 1.0, in certain embodiments -0.5 ⁇ L193
• ⁇ 1.0 in certain embodiments -0.1 ⁇ Ll 93 ⁇ 1.0, in certain embodiments 0 ⁇ L 193 ⁇ 1.0, in certain embodiments preferably 0 ⁇ Ll 93 ⁇ 0.5, in certain embodiments preferably 0 ⁇ L193 ⁇ 0.4, in certain other embodiments preferably 0 ⁇ L193 ⁇ 0.3.
• the glass exhibits less than about 1 nm/cm, in certain embodiments preferably less than 0.1 nm/cm, of polarization-induced birefringence (magnitude) measured at about 633 nm after being subjected to 5x10 9 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ J-cm ' ⁇ pulse "1 and a pulse length of about 25 ns.
• polarization-induced birefringence magnitude
• the glass exhibits less than about 1 nm/cm, in certain embodiments preferably less than 0.1 nm/cm, of polarization-induced birefringence (magnitude) measured at about 633 nm after being subjected to 1x10 10 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ J-cm ' ⁇ pulse "1 and a pulse length of about 25 ns.
• polarization-induced birefringence magnitude
• the glass exhibits less than about 0.1 nm/cm of polarization-induced birefringence (magnitude) measured at about 633 nm after being subjected to 2xl0 ⁇ 0 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 /J-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
• polarization-induced birefringence magnitude
• the glass exhibits less than about 0.04 nm/cm of polarization-induced birefringence (magnitude) measured at about 633 nm after being subjected to 2xlO 10 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ J-cm ' ⁇ pulse "1 and a pulse length of about 25 ns.
• the glass exhibits higher than about 0.001 nm/cm of polarization-induced birefringence (magnitude) measured at about 633 nm after being subjected to 2xlO 10 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ J-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
• polarization-induced birefringence magnitude
• the glass exhibits higher than about 0.01 nm/cm of polarization-induced birefringence (magnitude) measured at about 633 nm after being subjected to 2x10 10 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 ⁇ j-cm ⁇ -pulse "1 and a pulse length of about 25 ns.
• polarization-induced birefringence magnitude
• the glass exhibits a normalized polarization-induced birefringence less than 10, in certain embodiments less than 5, when subjected to linearly-polarized excimer laser pulses at about 193 nm of less than or equal to about 20 billion pulses.
• the glass exhibits a polarization-induced birefringence less than about 0.04 nm/cm, in certain embodiments less than about 0.02 nm/cm of polarization-induced birefringence measured at about 633 nm after being subjected to 2x10 9 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 200 ⁇ j-cm ⁇ -pulse "1 and a pulse length of about 25 ns, in certain embodiments less than about 0.02 nm/cm of polarization- induced birefringence measured at about 633 nm after being subjected to 5x10 9 pulses of linearly polarized pulsed laser beam at about 193 nm having a fluence of about 200 /J # cm " ⁇ pulse "1 and a pulse length of about 25 ns.
• the glass exhibits a normalized polarization-induced birefringence less than 2, in certain embodiments less than 1, in certain embodiments less than 0.5, when subjected to linearly- polarized excimer laser pulses at about 193 nm of less than or equal to about 2 billion pulses.
• the glass exhibits a normalized polarization-induced birefringence less than 2, in certain embodiments less than 1, in certain embodiments less than 0.5, when subjected to excimer laser pulses at about 193 nm of less than or equal to about 5 billion pulses.
• the glass exhibits a no ⁇ nalized polarization-induced birefringence less than 2, in certain embodiments less than 1, in certain embodiments less than 0.5, when subjected to excimer laser pulses at about 193 nm of less than or equal to about 8 billion pulses.
• the glass exhibits an initial internal transmission at about 193 nm of at least 99.00%/cm, in certain embodiments desirably at least 99.50%/cm, in certain embodiments desirably at least 99.65%/cm, in certain embodiments preferably at least 99.75%/cm, in certain other embodiments preferably at least 99.80%/cm.
• the glass exhibits a fictive temperature of lower than about 1150 0 C. In certain other embodiments of the OD-doped synthetic silica glass of the present invention, the glass exhibits a fictive temperature of lower than about 1000°C. In certain embodiments of the glass of the present invention, it exhibits a fictive temperature of higher than about 800 0 C.
• the glass exhibits a refractive index variation measured in a plane perpendicular to at least one direction of less than about 10 ppm, in certain embodiments preferably less than about 5 ppm, in certain other embodiments preferably less than about 2 ppm, in certain other embodiments preferably less than about 1 ppm, in certain other embodiments preferably less than about 0.5 ppm.
• optical glass member comprising the OD-doped synthetic silica glass material of the present invention described in general and in detail above and illustrated below.
• the optical glass member advantageously is used in the light path of an irradiation having a wavelength of shorter than about 300 nm, though the glass member of the present invention may be used in the light path of irradiation having a longer wavelength, such as in the visible spectrum, or in the infrared spectrum.
• the OD-doped glass of the present invention is particularly advantageous for use in certain infrared applications where OH is undesirable and OD is acceptable.
• Non- limiting examples of such glass member of the present invention may include, but are not limited to, optical members for use as refractive lens elements, sputter targets, and the like.
• the refractive lens elements may be used in, e.g., lithographic scanners and steppers machines, laser generators, laser etalons, lithographic inspection devices, and the like.
• the OD-doped glass optical member of the present invention is particularly suited for devices involving high-fluence irradiations due to its improved laser damage resistance.
• Still another aspect of the present invention is a lithographic system comprising at least one optical member of the present invention.
• the lithographic system is advantageously an immersion system in which at least one lens element is allowed to contact a liquid.
• Emersion lithographic systems usually utilize linearly polarized irradiation. Due to the high resistance to polarization-induced birefringence damage, the OD-doped synthetic silica glass member of the present invention is particularly suitable for such lithographic systems. Due to the excellent performance of the OD-doped glass material of the present invention, as mentioned supra, it may be used in traditional dry lithographic tools operating below about 300 nm, such as at about 248 nm, 193 nm and 157 nm. [00116] The OD-doped synthetic silica glass material of the present invention may be produced by using various methods, such as the direct-to-glass method, the soot-to-glass methods and the sol-gel processes, to name a few.
• the OD-doped silica glass of the present invention may be produced by: (i) utilizing D-exchanged or D-enriched starting materials to produce silica; (ii) making silica glass in a D-rich environment; or (iii) doping silica glass with OD.
• the first method contemplated by the present inventors is a direct-to-glass method. Broadly speaking, this process includes the following steps:
• step (II) depositing the a plurality of particles on a supportive deposition surface at an elevated temperature such that the particles are consolidated into transparent glass material in situ, wherein: in step (II), the deposition and consolidation are carried out in a D-containing atmosphere, such that the obtained silica glass comprises OD and optionally OH, and the ratio of n(OD)/(n(OD)+n(OH)) is higher than about 2x10 ⁇ 4 , in certain embodiments preferably higher than about 0.05, in certain embodiments preferably higher than about 0.1, in certain other embodiments higher than about 0.3, in certain other embodiments higher than about 0.5, in certain other embodiments higher than 0.8, in yet still other embodiments higher than about 0.9, in certain other embodiments higher than about 0.95.
• the a plurality of particles comprising silica may be provided by flame hydrolysis of at least one precursor compound comprising silicon, such as silicon halides (such as SiCl 4 ) or organosilicon compounds.
• silicon halides such as SiCl 4
• organosilicon compounds such as octamethylcyclotetrasiloxane (OMCTS).
• OMCTS octamethylcyclotetrasiloxane
• the precursor compound may comprise D at a level higher than its natural isotopic abundance (such as D-containing OMCTS), in which case the particles p_er se are usually OD-doped when originally produced.
• the precursor compound may comprise D at a level no more than its natural isotopic abundance, yet the precursor compound is allowed to undergo flame hydrolysis in an atmosphere comprising D at a level higher than its natural isotopic abundance, such as an atmosphere comprising added D 2 O or D 2 O produced from burning D-containing compound as fuel, such as CD 4 , CDH 3 , CD 2 H 2 , D 2 , HD, and the like.
• the particle comprising silicon may be pre-fabricated or produced in situ in the same furnace where they are deposited and consolidated in step (II). Where they are pre-fabricated, they may be provided in step (I) via a soot dispenser, sprayed to the supportive deposition surface and allowed to consolidate.
• step (II) may be carried out in an environment that is D-containing or not, depending on the level of OD in the pre-fabricated particles and the desired level of OD in the final consolidated glass. If the pre-fabricated particles are not D-containing, step (II) should be carried out in a D-containing environment (such as in the presence of D 2 O or D 2 gas or combinations thereof) in order to introduce OD into the consolidated glass.
• This direct-to-glass method for making the OD-doped silica glass of the present invention may be plasma-assisted.
• step (II) By adjusting the ratio of n(D)/(n(D)+n(H)) in the atmosphere in which the particles are produced, and in the atmosphere in which step (II) is carried out, one can produce OD-doped final glass with desired level of OD-doping.
• the supportive deposition surface in step (II) is an essentially planar deposition surface of a horizontal rotating table.
• the glass in order to obtain OD-doped fused silica glass for use in deep UV and vacuum UV lithographic devices, the glass should be produced by using high purity raw materials and processing agents in a very clean environment, and care should be taken to avoid contamination by metals detrimental to the desired properties.
• Low metal impurities are obtained via high purity starting materials and apparatus for making the soot (and corresponding consolidated glass) and/or purifying the soot (and apparatus used to consolidate the soot) with, e.g., Cl 2 or Cl 2 + CO, to remove trace metals.
• step (I) it is also possible to dope the OD-doped synthetic silica glass material with various dopants, such as F, Al, Ti, and the like, in a direct-to-glass furnace.
• the particles in step (I) may have essentially the same composition or differing compositions (e.g., certain particles comprising dopants and particles essentially free of dopants can be mixed and provided in step (I)).
• the consolidated glass produced in step (II) may be further subjected to the following step:
• step (III) treating the consolidated glass obtained in step (II) in an atmosphere comprising H 2 and/or HD and/or D 2 .
• step (III) The purpose of step (III) is to adjust the level of molecular hydrogen (H 2 , HD and/or D 2 ) in the consolidated glass to a desired level. Hydrogen molecules doped at desired level in the glass can improve the optical performance of the material.
• Such hydrogen- treatment is desired to be conducted below about 600 0 C. In certain cases it may be desired to be conducted at above about 600 0 C. Generally, it is desired that it is carried out at below about 1000 0 C.
• the treatment time and temperature of step (III) is chosen such that the sum total of the concentration of H 2 , HD and D 2 in the treated glass is between about 0.5xl0 15 to about 5xlO 19 molecules/cm 3 , in certain embodiments preferably from about 0.5xl0 15 to about 5xlO 18 molecules/cm 3 , in certain other embodiments preferably from about IxIO 15 to about IxIO 18 molecules/cm 3 in certain embodiments preferably from about 0.5xl0 16 to about 5x10 18 molecules/cm 3 , in certain other embodiments preferably from about IxIO 16 to about IxIO 18 molecules/cm 3 .
• the atmosphere in which step (III) is D-containing i.e., the atmosphere has a ratio of
• step (III) (2n(D 2 )+n(HD))/2(n(H 2 )+n(D 2 )+n(HD)) higher than the natural isotopic abundance of D. It is also desired that after step (III), the ratio of [D 2 ]/[H 2 ] at different locations in the glass is essentially constant, i.e., the distribution profiles of D 2 and H 2 are essentially the same (though maybe at differing concentrations).
• step (III) the atmosphere is essentially non-D-containing, i.e., the atmosphere has a ratio of (2n(H 2 )+n(HD))/2(n(H 2 )+n(D 2 )+n(HD)) higher than or about equal to the natural isotopic abundance of H.
• step (III) Another method of the present invention for making OD-doped synthetic silica glass of the present invention, termed "particle-to-glass" herein, involves the formation of a porous particle preform. This method comprises the following steps:
• A providing a particle preform comprising a plurality of particles comprising silica;
• B optionally purifying and/or drying the particle preform;
• step (E) optionally treating the consolidated glass obtained in step (D) in the presence of H 2 , HD and/or D 2 , wherein in at least one of steps (A), (B), (C), (D) and (E), OD is introduced into or formed in the glass. Generally, it is preferred that in at least one of steps (A), (B), (C) and (D), OD is introduced into the glass.
• step (A) comprises the following steps: (Al) providing a plurality of particles; and (A2) depositing the particles on a supporting surface to form the particle preform.
• the supporting surface is preferred to be rotating in certain embodiments.
• the particles may be provided by (Al .1) flame hydrolysis of at least one silicon-containing precursor compound (such as silicon halides (e.g., SiCl 4 ) or organosilicon compounds.
• organosilicon compound As non-limiting example of organosilicon compound, mention may be made of octamethylcyclotetrasiloxane (OMCTS)), which may be plasma-assisted; or (Al.2) a soot dispenser, which may be plasma-assisted; or (Al.3) other plasma-assisted process.
• OCTS octamethylcyclotetrasiloxane
• Al.2 a soot dispenser
• Al.3 other plasma-assisted process.
• the particle-to-glass process involving step (Al .1) is termed "soot-to-glass" process. Soot-to-glass process for making regular non-OD-doped high-purity fused silica glass is described in, for example, co-pending, co-assigned patent application No.
• Particles provided by step (Al .1) may be OD-doped or non-OD-doped. Where D-containing compounds are used in the flame hydrolysis process, the particles provided are usually OD-doped. If the atmosphere of the flame hydrolysis process of step (Al.1) comprises D 2 O, the particles thus provided are usually OD-doped.
• Step (A2) can be carried out by various methods such as (A2.1) outside vapor deposition; (A2.2) inside vapor deposition; (A2.3) vapor axial deposition; (A2.4) planar deposition, and the like.
• A2.1 outside vapor deposition
• A2.2 inside vapor deposition
• A2.3 vapor axial deposition
• A2.4 planar deposition
• step (A) The sol-gel process may be employed in step (A) to produce the particle preform, which comprises the following steps:
• Step (A(i)) may be carried out in the presence of or from at least one D- containing compound.
• step (A(i)) may be carried out in the presence OfD 2 O.
• the sol-gel can be produced by the hydrolysis of a silicon-containing precursor compound (such as siloxane) in liquid D 2 O.
• the particle preform produced in step (A) comprises OD-doped silica particles.
• the sol-gel process includes a step of hydrolysis of a silicon-containing precursor compound (such as a silane, siloxane, or polysiloxane) in an aqueous media to produce a sol-gel of silica.
• a silicon-containing precursor compound such as a silane, siloxane, or polysiloxane
• the sol-gel can then be cast into a green body, which is a form of the particle preform in the meaning of the present application.
• the green body may be partially dried before further processing in subsequent steps (B)-(E).
• Particle preforms produced by flame hydrolysis and sol-gel processes may comprise undesirably high amount of OH and OD.
• Particle preforms produced from sol- gel process may even comprise substantial amounts of H 2 O and/or D 2 O.
• Particle preforms (typically called soot preforms) produced by flame hydrolysis methods mentioned above (IYD, OVD, VAD, PD) involving the burning of fuels comprising H and/or D (H 2 , D 2 , CH 4 , CDH 3 , and the like, for example) and/or precursor compounds comprising H and/or D (OMCTS, for example) typically comprise in the soot particles OH and OD groups.
• low OH/OD glass such as those comprising a total concentration of OH and OD of less than 500 ppm, in certain embodiments preferably lower than 300 ppm, in certain embodiments preferably lower than about 150 ppm, in certain embodiments preferably lower than about 50 ppm, may be desired for high purity silica glass for use in optical members used in UV and deep UV lithography devices.
• a particle preform comprises below about 1 ppm by weight of total OH and/or OD
• the particle preform is considered essentially dry for the purpose of the present application.
• Drying agents such as dry inert gas, including but not limited to He, Ar, N 2 , and the like, may be used to reduce the H 2 O, D 2 O, OH and/or OD in the particle preform, at an elevated temperature, such as higher than 500 0 C, in certain embodiments higher than about 800 0 C.
• CO, CO 2 , and the like may be used as drying agent as well. CO may react with silica particles to produce defects in the glass. Such defects may be healed as described infra.
• Preferred drying agents are F 2 , Cl 2 , Br 2 , halogen compound, CO, CO 2 , and compatible mixtures thereof.
• the halogen compound is preferably selected from HX, COX 2 , SOX 2 , CX 4 and SX 6 , where X is selected from F, Cl, Br and combination thereof .
• the most preferred drying agent is Cl 2 and Br 2 , without or including CO and mixtures thereof.
• Particle preforms produced by sol-gel processes typically contain high levels of Fe, Na, and the like, which are detrimental to the optical performance of the glass in deep UV and vacuum UV spectra. Once the glass is consolidated and the contaminants are incorporated into the consolidated into the glass, their removal becomes difficult. Therefore, it is highly desirable that prior to consolidation, where necessary, the particle preform is subjected to purification such that contaminant concentrations are reduced to a desired level prior to consolidation of the preform. [00133] Many of the drying agents for removing H 2 O, D 2 O 5 OD and/or OH from the particle preform have contaminant stripping function as well. Those drying agents, when used in the drying process, may function to purify the particle preform simultaneously.
• drying and purifying may advantageously be carried out at the same time, or if desired, different agents may be used to achieve these two different functions.
• Preferred purifying agents include, but are not limited to, Cl 2 , F 2 , Br, a halogen-containing compound, CO, CO 2 , and the like, and mixtures and combinations thereof.
• the halogen-containing compound may be HX, COX 2 , SOX 2 , CX 4 and SX 6 , and the like, where X is selected from F, Cl, Br and combination thereof.
• the most preferred drying agent are Cl 2 and Br 2 , with or without CO, and compatible mixtures thereof.
• the particle preform may be further doped in step (C) prior to consolidation in step (D). It is also generally understood that doping dopants into consolidated glass is difficult, while doping particle preforms can be carried out in a controlled manner.
• the particle preform, with or without the drying/purifying step (B) may be further doped with dopants such as OD, OH, F, Cl, and the like. Doping at elevated temperature such as higher than 500 0 C, in certain embodiments higher than about 800 0 C, is desirable in order to expedite the doping process.
• F- containing compounds such as HF, DF, COF 2 , SOF 2 , SiF 4 , CF 4 and SF 6 may be used. Therefore, during the drying and/or purifying step (B), the doping of F may be carried out.
• Cl 2 and Cl-containing compounds such as HCl, COCl 2 , SOCl 2 and CCl 4 may be used. Therefore, during the s drying and/or purifying step (B), the doping of Cl may be carried out. Thus steps (B) and (C) may be carried out at least partially simultaneously.
• step (B) the particle preform can be dried and purified to a level essentially free of OH and/or OD.
• step (C) the dried particle preform is controllably doped with OH and/or OD to a desirable level so that the final consolidated OD-doped glass has the desired OD and/or OH concentrations. Doping is desirably effected at an elevated temperature such as higher than 500 0 C, in certain embodiments higher than about 800 0 C.
• the doping atmosphere may comprise D 2 , HD, D 2 O, CH 3 OD, C 2 H 5 OD, CH 3 COOD, and other OD-containing compounds.
• the doping atmosphere may comprise H 2 , HD, H 2 O, CH 3 OH, C 2 HsOH, CH 3 COOH, and other OH-containing compounds.
• H 2 and/or HD may react with the SiO 2 glass to produce Si-OH and/or Si-OD in the glass. It is known that reaction between hydrogen gas (D 2 , DH and/or H 2 ) and SiO 2 can lead to the formation of oxygen-deficient sites in the silica glass.
• the particle preform is treated in an oxidizing atmosphere to heal the defects before or during consolidation of the particle preform into dense glass if hydrogen gas is used as a doping agent in the doping atmosphere.
• hydrogen gas is used as a doping agent in the doping atmosphere.
• D 2 O and/or H 2 O are used as the doping agent in the doping atmosphere, they may be fed as they are into the doping environment, or formed in situ by, e.g., reactions between D 2 /H 2 and O 2 fed into the environment separately.
• the doping atmosphere may be adjusted to contain the OD- containing and OH-containing compounds having the desired partial pressures thereof.
• the most preferred OD-doping agent for the particle preform is D 2 O.
• D 2 O at higher than 99.9% by mole of isotopic purity is commercially available.
• the most preferred OH- doping agent for the particle preform is H 2 O.
• the doping atmosphere may be adjusted to have the desired D 2 O and H 2 O partial pressures to obtain the desired [OD] and [OH] concentration in the final glass.
• the particle preform may be treated in a doping atmosphere comprising a D-containing compound, such as an OD-containing compound, such as D 2 O, for a sufficient time, such that a desirable amount of OH in the particle preform is exchanged by OD.
• the particle preform may comprise certain amount of OD before step (C), and in step (C), it is doped or exchanged with OH only to achieve the desired [OD] and [OH] concentrations in the final glass.
• the doping atmosphere may comprise, in addition to doping compounds, O 2 , and inert gases.
• Steps (B) and/or (C) may be carried out in the presence of other reductive gases than H 2 and D 2 , such as hydrocarbons, D-containing hydrocarbons, and the like.
• step (C(A) the particle preform is treated in an oxidative atmosphere in a step (C(A)).
• the oxidation agent in the oxidative atmosphere may be, for example, O 2 , O 3 , D 2 O, H 2 O, and the like.
• step (D) of the process of the present invention the particle preform is consolidated into dense silica glass. Steps (C) and (D) may be carried out at least partially simultaneously, meaning that, at least part of the doping is carried out while the particle preform is consolidated into dense glass.
• Step (C(A)) described above and step (D) may be carried out at least partly simultaneously, meaning that, at least in part of step (D), at least part of the oxygen-deficient defects in the glass is oxidized and healed.
• the particle preform is heated to an elevated temperature, desirably higher than 1000 0 C, in certain embodiments higher than 1200 0 C, in certain embodiments higher than about 1400 0 C, where the particles are sintered into dense glass.
• Temperature elevation rate during consolidation step (D) may be controlled in a manner such that a homogeneous distribution of dopants such as OH, OD, F and the like is achieved.
• Step (D) may be conducted in a consolidation atmosphere comprising inert gas such as He 5 Ar, N 2 , and the like.
• the consolidation atmosphere may further comprise O 2 and/or D 2 O and/or H 2 O at a desired level.
• the O 2 , D 2 O and/or H 2 O can function to oxidize and heal the oxygen- deficient sites in the glass.
• the consolidation atmosphere may be essentially devoid OfH 2 O and HDO.
• the consolidation atmosphere may further comprise H 2 , D 2 , HD, and the like.
• reaction between such reductive gases with silica glass at elevated temperature can lead to the formation of defects in the glass.
• glasses with high [OH] and/or [OD] tend to have less defects than glasses with lower [OH] and [OD] when treated in a reductive atmosphere at high temperature, such as an atmosphere comprising H 2 , HD and/or D 2 .
• Step (E) of this process of the present invention involves hydrogen doping the consolidated glass with a hydrogen doping atmosphere comprising molecular H 2 , HD and/or D 2 .
• the hydrogen doping atmosphere may comprise essentially no D 2 and HD even for glasses doped with high percentages of OD, especially if the hydrogen loading temperature is relatively low, such as below about 500 0 C.
• the hydrogen doping atmosphere is essentially devoid of HD and H 2 where the hydrogen doping temperature is higher than 50O 0 C.
• the loading ofH 2 or D 2 does not appreciably alter the [OH] and [OD] in the glass.
• the hydrogen doping may be advantageously carried out at a temperature below about 600 0 C (cold loading), or to expedite the process, at a temperature above about 600 0 C (hot loading). However, it is usually conducted at a temperature below 100O 0 C. Due to the laws of diffusion, to reach the same loaded hydrogen level in the glass, cold loading tends to take longer time.
• non-OD-doped silica glass tends to have worse polarization-induced birefringence performance at higher [OH]. It was also stated in this patent application that the amount of polarization-induced birefringence was approximately proportional to the [OH] in an OH-doped silica glass. Therefore, for the sake of acceptable polarization-induced birefringence performance, for non-OD-doped synthetic silica glass, it is generally preferred that it has an [OH] of less than 500 ppm, in certain embodiments preferably less than 160 ppm, in certain other embodiments less than 50 ppm.
• the present inventors expect that the OD-doped high purity synthetic silica glass of the present invention, especially those essentially devoid of OH will exhibit very low polarization-induced birefringence even with a high [OD] up to or exceeding 1000 ppm.
• high [OD] silica glass at least those essentially free of OH, may be useable in applications where non-OD-doped silica glasses with comparable [OH] cannot be used.
• These high [OD] glasses can be produced with much higher efficiency and speed because it can be hot loaded, compared to the non-OD-doped, low [OH] glasses, which are typically required to be cold loaded.
• Another method of making the OD-doped synthetic silica glass of the present invention includes the following steps:
• Step (b) melting the particles at an elevated temperature to obtain a transparent glass.
• Step (a) in this process may comprise the following steps:
• step (a4) optionally treating the particles in an oxidative atmosphere to at least partly heal oxygen-deficient sites in the particles. wherein at least in one of steps (al), (a2), (a3) and (a4), OD moieties are introduced into the particles.
• the particles comprising silica may be generated by flame hydrolysis or sol-gel processes as described above in connection with the particle-to-glass process wherein the particle preforms are finally consolidated instead of melted to form the glass.
• step (a2) the purifying and/or drying may be carried out mutatis mutandis as described above in connection with the particle-to-glass process wherein the particle preforms are finally consolidated instead of melted to form the glass.
• Low level of metal impurities can be obtained via high purity starting materials and apparatus for making the soot (and corresponding consolidated glass) and/or purifying the soot (and apparatus used to consolidate the soot) with, e.g., Cl 2 or Cl 2 + CO, to remove trace metals.
• step (a3) the doping may be carried out mutatis mutandis as described above in connection with the particle-to-glass process wherein the particle preforms are finally consolidated instead of melted to form the glass.
• step (a4 ⁇ ) the treatment may be carried out mutatis mutandis as described above in connection with the particle-to-glass process wherein the particle preforms are finally consolidated instead of melted to form the glass.
• step (b) the glass is heated to a temperature where the glass is melted, such as at a temperature higher than 1500 0 C, in certain embodiments above 1800 0 C, in certain embodiments about 2000 0 C.
• the melted glass may be further homogenized when melted in order to obtain a high homogeneity of composition and property in the final glass. Where homogenization is carried out, the glass particles melted may have essentially the same composition or differing compositions.
• the particles may be an admixture of particles having differing [OH] and [OD].
• the final glass obtained has a uniform [OH] and/or [OD].
• Homogenization of consolidated glass can be carried out as well.
• the consolidated OD-doped synthetic silica glass of the present invention or mixtures thereof, irrespective of the method of making may be heated to an elevated temperature, such as above 1500 0 C, in certain embodiments above 1800 0 C, where they are melted and homogenized to form a glass with uniform composition and properties.
• the final, cooled, consolidated glass may be further doped with molecular hydrogen as described above in connection with the_particle-to-glass process wherein the particle preforms are finally consolidated instead of melted to form the glass, mutatis mutandis.
• OD-doped silica glass material of the present invention by H/D exchanging a consolidated, dense silica glass comprising OH and/or OD in an atmosphere comprising H 2 , D 2 and/or HD at an elevated temperature, e.g., higher than
• the dense glass may be made of direct-to-glass processes, or may be made of soot-to-glass or sol gel processes mentioned supra.
• a dense glass comprising essentially no OD such as an OH-doped glass made of traditional direct-to-glass process in non-D-containing
• OD-doped glass at various n(OD)/(n(OD)+n(OH) can be made by D 2 -loading the glass at an elevated temperature, such as about 900 0 C, for a sufficient period of time. Glasses with very low [OH], such as n(OD)/(n(OD)+n(OH)) higher than 0.5, in certain embodiments higher than about 0.8, in certain embodiments higher than about 0.9, can be successfully made.
• the synthetic silica glass material of the present invention can be further processed into optical members for use in the light path of lithographic irradiation of a lithographic device operating at a wavelength of below about 300 nm, such as about 248 nm, 193 nm and even shorter.
• the optical member may take various geometry and size.
• the optical member may be used in low-fluence or high-fluence irradiation paths.
• a process for making optical member based on the silica glass of the present invention can be a combination of the processes of the present invention for making the glass material and additional steps of processing the glass material of the present invention.
• Example Ia An OD-doped fused silica glass was made by using the soot- to-glass process as described in co-pending, co-assigned patent application No. 11/148,764, entitled "HIGH REFRACTIVE INDEX HOMOGENEITY FUSED SILICA GLASS AND METHOD OF MAKING SAME" and filed on June 8, 2005 now published as United States Patent Application Publication No. 2006-0137398 Al, the relevant part of which is incorporated herein by reference.
• silica soot preform was formed by depositing a plurality of soot particles obtained by flame hydrolysis of a Si-containing precursor compound, octamethylcyclotetrasiloxane (OMCTS), on the rotating surface of a mandrel.
• OCTS octamethylcyclotetrasiloxane
• the soot preform thus prepared was OH-doped.
• the soot preform was subsequently D/H exchanged and OD-doped with 99.9+% isotopic purity D 2 O by placing the preform into a consolidation furnace set at approximately 1100 0 C and bubbling helium containing 2.5% oxygen through liquid D 2 O into the consolidation furnace for 6 hours to obtain the OD-doped soot.
• the OD-doped soot preform was then sintered to a consolidated OD-doped silica glass in a helium atmosphere containing D 2 O by raising the furnace temperature approximately 1400 0 C. Following consolidation the silica glass was placed in a nitrogen purged holding oven at about 1100 0 C for about 24 hours and cooled at less than a 25 °C/hr to 850 0 C then cooled to room temperature (this silica glass was used for Samples C, D and F in TABLE I). Deuteroxyl-doping was successful, wherein the consolidated glass comprised about 130 ppm by weight of OD and less than 1 ppm of OH.
• an OD-doped fused silica glass was made by using the soot- to-glass process as described in Example Ia.
• the soot preform thus prepared was OH- doped.
• the soot preform was subsequently D/H exchanged and OD-doped with 99.9+% isotopic purity D 2 O by placing the preform into a consolidation furnace set at approximately 1100 0 C and bubbling helium containing 2.5% oxygen through liquid D 2 O into the consolidation furnace for 6 hours to obtain OD-doped soot.
• the OD-doped soot preform was then sintered to a consolidated OD-doped silica glass in a helium atmosphere containing D 2 O by raising the furnace temperature approximately 1400 0 C.
• the silica was placed in a nitrogen purged holding oven at 1100 0 C for 24 hours and cooled at less than 25°C/hour to 85O 0 C then cooled to room temperature (this silica was used for sample H shown in TABLE I).
• Another sample was then placed in a nitrogen purged holding oven ramped to HOO 0 C then cooled at less than l°C/hour to 800 0 C then cooled at less than 25°C/hour to room temperature (this silica was used for sample G shown in TABLE I).
• an OD-doped fused silica glass was made by using the soot- to-glass process as described in Example Ia.
• the soot preform thus prepared was OH- doped.
• the soot preform was placed in a consolidation furnace set at 1100 0 C and treated for 4 hours flowing helium containing 1.6 % by volume Cl 2 and 0.3 % by volume CO; this process was used to remove all the OH and trace metals from the soot preform.
• the soot preform was then exposed at 1100 0 C for 8 hours to D 2 O and O 2 by flowing helium containing 2.5 % by volume O 2 through a D 2 O containing bubbler; this process removed all of the chlorine and re-oxidized any reduced silica from the previous step.
• the soot preform was then sintered to a consolidated OD-doped silica glass in a helium atmosphere containing D 2 O by raising the furnace temperature approximately 1400 0 C. Following consolidation the OD-doped silica was placed in a nitrogen purged holding oven at 1100 0 C for 24 hours and cooled at less than 25°C/hour to 85O 0 C then cooled to room temperature.
• Deuteroxyl-doping was successful, wherein the consolidated glass comprised about 220 ppm by weight of OD and about 8 ppm of OH. [OD] and [OH] along the radial direction of the glass was measured and presented in FIG. 17. Samples of this OD-doped silica glass were post-loaded with H 2 to about 3xlO 16 molecules/cm 3 at 425 0 C. The fictive temperature of this material was measured to be 1085 0 C. This sample had an internal transmission at 193 nm of 99.66%/cm.
• Example 2 This sample had less than 10 ppm by weight of Cl, less than 10 ppb by weight of sodium, less than 10 ppb by weight of total alkali metals, less than 10 ppb by weight of total alkaline earth elements, and less than 1 ppb by weight of iron, chromium or nickel. [00161] Example 2
• silica soot preform was formed by depositing a plurality of soot particles obtained by flame hydrolysis of a Si-containing precursor compound on the rotating surface of a mandrel. The soot preform thus prepared was OH-doped.
• the soot preform was subsequently partially D/H exchanged and OD-doped with 99.9+% isotopic purity D 2 O by bubbling helium through liquid D 2 O into the consolidation furnace during the consolidation process in a manner similar to the described in Example Ia.
• Deuteroxyl-doping was successful, wherein the consolidated glass comprised about 40-50 ppm by weight of OD and about 10 ppm of OH.
• [OD] and [OH] along the radial direction of the glass were measured and presented in FIG. 7. It is interesting to note that at different locations in the radial direction, both [OD] and [OH] vary, yet the ratio of [OD]/[OH] remains essentially constant. This indicates that the OH groups in the soot preform were exchanged to OD groups at essentially the same proportion.
• Samples A, B, C, D, E, F, G, H, J, K and L were found to comprise less than 10 ppb by weight of sodium, less than 10 ppb by weight in total of alkali metals, less than 10 ppb by weight in total of alkaline earth metals, and less than 1 ppb by weight of Fe, Cr or Ni.
• Samples A, B, C, D, F and H had internal transmission at 193 nm of about 99.78%/cm; Samples E, G, H, K and L were found to have internal transmission of about 99.74%/cm; and Sample J was found to have an internal transmission at 193 nm of about 99.70%/cm.
• Samples A, B, C, D, E, F, G, H, J, K and L have the compositions as listed in TABLE I below:
• the horizontal axis represents N(P)-F, where N(P) is the number of pulses in the millions, and F is the fluence of the linearly polarized 193 nm excimer laser pulses in mJ/(cm 2 -pulse).
• N(P) is the number of pulses in the millions
• F is the fluence of the linearly polarized 193 nm excimer laser pulses in mJ/(cm 2 -pulse).
• the OH-doped fused silica glass used was Corning Incorporated glass code 7980 which was made by using the direct-to-glass process as described United States Patent No. 6,698,248 B2.
• the glass tested contained approximately 1000 ppm OH and had less than 10 ppb sodium, less than 10 ppb total alkali, less than 10 ppb total alkaline earth elements, and less than 1 ppb iron, chromium or nickel.
• D/H was accomplished by placing 10mmx25mmx200 mm samples in a clean quartz muffle and heating the samples to 900 0 C for 30 days in 5.4% D 2 in N 2 bubbled through 99.9+ % D 2 O in order to produce an OD-doped fused silica glass containing approximately 1000 ppm by weight of OD, less than 20 ppm by weight of OH and no additional metal contamination.
• OD-doped silica glass of the present invention can be made by D/H exchange of OH-doped silica glass.

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