Silica glass member and method of manufacturing the same
Provided is a silica glass member which exhibits high optical transparency to vacuum ultraviolet light and has a low thermal expansion coefficient of 4.0×10 −7 /K or less at near room temperature, particularly a silica glass member which is suitable as a photomask substrate to be used in a double patterning exposure process using an ArF excimer laser (193 nm) as a light source. The silica glass member is used in a photolithography process using a vacuum ultraviolet light source, in which the fluorine concentration is 1 wt % or more and 5 wt % or less, and the thermal expansion coefficient at from 20° C. to 50° C. is 4.0×10 −7 /K or less.
1. A silica glass member that is used in a photolithography process using a vacuum ultraviolet light source, wherein
a fluorine concentration is 1 wt % or more and 5 wt % or less,
concentrations of Fe, Cr, Ni, Cu, and Ti are each 1 wt ppm or less,
a linear transmittance of light having a wavelength of 193 nm is 90% or more in a thickness of 6.4 mm, and
a thermal expansion coefficient at from 20° C. to 50° C. is 3.5×10 −7 /K or less.
2. The silica glass member according to claim 1 , wherein a density is 2.16 g/cm 3 or more and 2.19 g/cm 3 or less.
3. The silica glass member according to claim 1 , wherein a concentration of an OH (hydroxyl) group is 10 ppm or less.
4. The silica glass member according to claim 1 , wherein a fictive temperature is 1000° C. or lower.
5. The silica glass member according to claim 1 , wherein a viscosity coefficient at a temperature of 1000° C. is 10 14.5 dPa·s or less.
6. The silica glass member according to claim 2 , wherein a concentration of an OH (hydroxyl) group is 10 ppm or less.
7. The silica glass member according to claim 2 , wherein a fictive temperature is 1000° C. or lower.
8. The silica glass member according to claim 2 , wherein a viscosity coefficient at a temperature of 1000° C. is 10 14.5 dPa·s or less.
9. The silica glass member according to claim 3 , wherein a fictive temperature is 1000° C. or lower.
10. The silica glass member according to claim 3 , wherein a viscosity coefficient at a temperature of 1000° C. is 10 14.5 dPa·s or less.
11. The silica glass member according to claim 4 , wherein a viscosity coefficient at a temperature of 1000° C. is 10 14.5 dPa·s or less.
12. The silica glass member according to claim 1 , wherein a density is 2.16 g/cm 3 or more and 2.19 g/cm 3 or less,
a concentration of an OH (hydroxyl) group is 10 ppm or less, a fictive temperature is 1000° C. or lower, and a viscosity coefficient at a temperature of 1000° C. is 10 14.5 dPa·s or less.
13. A method of manufacturing low thermal expansion silica glass, the method comprising:
preparing silica glass having a fluorine concentration of 1 wt % or more and 5 wt % or less;
heating the silica glass in a heating furnace in a temperature range of from 1000° C. to 1500° C. until the viscosity coefficient reaches 10 14.5 dPa·s or less;
taking out the silica glass from the heating furnace; and
subjecting the silica glass to a quenching (rapidly cooling) treatment and to an annealing treatment again in a temperature range of 400° C. or higher and a temperature which is 1000° C. or lower and has a viscosity coefficient of the silica glass of 10 14.5 dPa·s or less.