Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-04-24
2003-04-01
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C065S030100
Reexamination Certificate
active
06541168
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to lithography, and particularly to optical photolithography glass for use in optical photolithography systems utilizing vacuum ultraviolet light (VUV) wavelengths below 193 nm, preferably below 175 nm, preferably below 164 nm, such as VUV projection lithography systems utilizing wavelengths in the 157 nm region.
The invention relates to VUV transmitting glass that is transmissive at wavelengths below 193 nm, in particular, a photomask silicon oxyfluoride glass suitable for use in the Vacuum Ultraviolet (VUV) 157 nm wavelength region.
BACKGROUND OF THE INVENTION
Refractive optics requires materials having high transmittance. For semi-conductor applications where smaller and smaller features are desired at the 248 and 193 nm wavelengths, high purity fused silica has been show to exhibit the required minimum transmittance of 99%/cm or better.
Projection optical photolithography systems that utilize the vacuum ultraviolet wavelengths of light below 193 nm provide benefits in terms of achieving smaller feature dimensions. Such systems that utilize vacuum ultraviolet wavelengths in the 157 nm wavelength region have the potential of improving integrated circuits with smaller feature sizes. Current optical lithography systems used by the semiconductor industry in the manufacture of integrated circuits have progressed towards shorter wavelengths of light, such as the popular 248 nm and 193 nm wavelengths, but the commercial use and adoption of vacuum ultraviolet wavelengths below 193 nm, such as 157 nm has been hindered by the transmission nature of such vacuum ultraviolet wavelengths in the 157 nm region through optical materials. Such slow progression by the semiconductor industry of the use of VUV light below 175 nm such as 157 nm light has been also due to the lack of economically manufacturable photomask blanks from optically transmissive materials. For the benefit of vacuum ultraviolet photolithography in the 157 nm region such as the emission spectrum VUV window of a F
2
excimer laser to be utilized in the manufacturing of integrated circuits there is a need for mask blanks that have beneficial optical properties including good transmission below 164 nm and at 157 nm and that can be manufactured economically.
The present invention overcomes problems in the prior art and provides a economical high quality improved photomask blanks and VUV transmitting lithography glass that can be used to improve the manufacturing of integrated circuits with vacuum ultraviolet wavelengths.
Use of high purity fused silica as optical elements in photolithography stems from the fact that high purity fused silica is transparent over a wide range of wavelengths, spanning from the infrared to deep ultraviolet regions. Furthermore, high purity fused silica exhibits excellent chemical durability and dimensional stability. It has been suggested in EP 0 636 586 A1 that in order to be suitable for use as a photomask substrate for certain photolithography applications at 248 and 193 nm wavelengths, high purity fused silica made by the direct flame method must contain high molecular hydrogen in the range of 10
17
to 10
19
molecules/cm
3
. Similarly, JP 1-201664 discloses that synthetic quartz glass for use as photomask material whose optical properties have been changed due to sputtering, plasma etching or excimer irradiation, can be restored to its original condition by heat treating the glass in a hydrogen atmosphere. Specifically, this document describes the effect on synthetic quartz of exposure to 248 and 193 nm wavelengths. The effect of exposure to 248 and 193 nm wavelengths on fused silica is also described in “Densification of Fused Silica under 193 nm excitation,” by Borrelli et al, in J. Opt. Soc. Am. B/Vol. 14, No. 7, pp. 1606-1615 (July 1997); and by Allan et al., in “193-mn excimer-laser-induced densification of fused silica,” Optics Letters, Vol. 21, No. 24, pp. 1960-1962 (Dec. 5, 1996).
EP 0 901 989 A1 discloses a manufacturing method for making silica glass substantially free of chlorine. In a direct deposit concurrent vitrifying process silicon tetrafluoride is flame hydrolyzed to provide a silica glass in which fluorine is controlled within the range 100 ppm to 450 ppm and OH group density in the range from 600 ppm to 1300 ppm.
U.S. Pat. No. 5,326,729 discloses quartz glass having excimer laser resistance produced by subjecting the glass to dehydration treatment in a temperature range lower than the transparent vitrification temperature of the glass followed by transparent vitrification and molding to a desired shape, followed by a doping treatment in a hydrogen atmosphere.
U.S. Pat. No. 5,474,589 discloses a UV light permeable fluorine-doped synthetic quartz glass with decreased defects.
Applicants, previously have disclosed several effective methods for improving the optical properties of high purity fused silica when used as an optical lens in photolithography at both the 248 and 193 run wavelength regions. See for example, U.S. Pat. Nos. 5,616,159; 5,668,067 and 5,735,921 all incorporated herein by reference.
Accordingly, it is an object of the present invention to disclose VUV transmitting dry direct deposit vitrified silicon oxyfluoride glasses for use at VUV wavelengths below 193 nm, preferably in the F
2
Excimer Laser 157 nm region, methods of making such glass, and methods of making dry direct deposit vitrified lithography glass articles.
SUMMARY OF THE INVENTION
In the present invention we disclose VUV transmitting dry direct deposit vitrified silicon oxyfluoride lithography glass suitable for use as optical elements, for use as a lens or preferably for use as a photomask substrate at VUV wavelengths below 193 nm. In particular, the inventive direct deposit vitrified silicon oxyfluoride glass production exhibits benifits tailored for optical lithography articles and applications in the photolithography VUV wavelength region around the 157 nm Excimer laser wavelengths and below 193 nm.
The object of the invention is achieved by use of a dry low hydroxy radical fluorine-doped SiO
2
fused direct deposit vitrified synthetic silicon oxyfluoride glass which exhibits high transmittance in the vacuum ultraviolet (VUV) wavelength region while exhibiting excellent thermal and physical properties. By “dry” we mean having an OH content below 50 ppm by weight, preferably dehydrated below 10 ppm OH by weight, and most preferably below 1 ppm by weight.
In another aspect, the object of the invention is further achieved by ensuring that the dry direct deposit vitrified silicon oxyfluoride glass is essentially free of chlorine.
In yet another aspect, the object of the invention is achieved by ensuring a low molecular hydrogen content in the dry direct deposit vitrified glass. By this we mean that the molecular hydrogen (H
2
) content is below 1×10
17
molecules/cm
3
. In a preferred embodiment of the invention, the VUV transmitting dry direct deposit vitrified silicon oxyfluoride glass has a fluorine content in the range of 0.1 to 0.4 weight percent which inhibits laser exposure induced absorption and provides laser exposure durability with minimal transmission loss at 157.6 nm after prolonged exposure. The invention includes a below 193 nm VUV transmitting glass photomask substrate for photolithography at wavelengths of about 157 nm with the glass being a high purity dry direct deposit vitrified silicon oxyfluoride glass with an OH content below 50 ppm by weight, hydrogen content below 1×10
17
molecules/cm
3
and a fluorine content in the 0.1 to 0.4 weight percent range.
The invention includes a process of making VUV transmitting glass silicon oxyfluoride glass that includes providing a hydrogen-free fuel carbon monoxide combustion burner; providing a heat containing direct deposit furnace; providing a supply of carbon monoxide and a supply of oxygen to said carbon monoxide combustion burner to form a carbon monoxide combustion reaction flame, providing a direct glass deposition surface proximate said flame, supplyi
Brown John T.
Currie Stephen C.
Moore Lisa A.
Pavlik, Jr. Robert S.
Schiefelbein Susan L.
Corning Incorporated
Murphy Edward F.
Rosasco S.
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