Method for loading a blank composed of fused silica with hydrogen, lens element and projection lens

Patent metadata

Field	Value
Publication number	US-10427965-B2
Application number	US-201615013499-A
Country	US
Kind code	B2
Filing date	Feb 2, 2016
Priority date	Aug 2, 2013
Publication date	Oct 1, 2019
Grant date	Oct 1, 2019

Abstract

A method for loading a blank composed of fused silica with hydrogen, including loading the blank at a first temperature (T 1 ) and a first hydrogen partial pressure (p 1 ), and further loading the blank at a second temperature (T 2 ) which is different from the first temperature and at a second hydrogen partial pressure (p 2 ) which is different from the first hydrogen partial pressure. The first and second temperatures (T 1 , T 2 ) are lower than a limit temperature (T L ) at which a thermal formation of silane in the fused silica of the blank commences. Also disclosed are a lens element produced from such a blank and a projection lens that includes at least one such lens element.

First claim

What is claimed is:

1. A method for loading a blank composed of fused silica with hydrogen,
comprising:
loading the blank at a first temperature (T 1 ) of less than 475° C. and a first hydrogen partial pressure (p 1 ), and
further loading the blank at a second temperature (T 2 ) of less than 300° C. and at a second hydrogen partial pressure (p 2 ) which is different from the first hydrogen partial pressure,
wherein the first temperature and the second temperatures (T 1 , T 2 ) are lower than a limit temperature (T L ) at which a thermal formation of silane in the fused silica of the blank commences, and
wherein the loading and the further loading results in a silane content in all locations of the blank of less than 5×10 14 molecules/cm 3 .

2. The method according to claim 1 , wherein the further loading of the blank is at a higher hydrogen partial pressure (p 2 >p 1 ) than is the loading.

3. The method according to claim 1 , wherein the limit temperature (T L ) at which the thermal formation of the silane in the fused silica of the blank commences is determined prior to the loading.

4. The method according to claim 3 , wherein the limit temperature (T L ) is determined based on a change (dK/dF) in absorption coefficient (K) of the fused silica of the blank with respect to an energy density (F) during irradiation of the blank with pulsed laser radiation at a wavelength of 193 nm.

5. The method according to claim 1 , wherein the blank is further loaded at a temperature (T 2 ) of less than 400° C.

6. The method according to claim 1 , wherein the blank is loaded at a hydrogen partial pressure (p 1 ) of less than 20%.

7. The method according to claim 1 , wherein the blank is further loaded at a hydrogen partial pressure (p 2 ) of 50% or more.

8. A lens element composed of fused silica and providing a surface and a further surface configured to transmit radiation therethrough,
wherein, at a distance (d 1 ) of 1 mm from the surface, the lens element has a hydrogen content ([H 2 ]) of at least 5×10 16 molecules/cm 3 ,
wherein, in an inner volume of the lens element, the hydrogen content ([H 2 ]) falls to a minimum value of 10% or less of the hydrogen content ([H 2 ]) at the surface, and
wherein, at a distance (d 2 ) of 8 mm from the surface, the hydrogen content ([H 2 ]) falls to 50% or less of the hydrogen content ([H 2 ]) at the surface; and
wherein at all locations in the volume of the lens element a silane content is less than 5×10 14 molecules/cm 3 .

9. The lens element according to claim 8 , wherein a silane content varies over a thickness (D) of the lens element by not more than 50%.

10. The lens element according to claim 8 , wherein, at a distance (d 2 ) of 8 mm from the surface, the hydrogen content ([H 2 ]) falls to 40% or less of the hydrogen content ([H 2 ]) at the surface.

11. The lens element according to claim 8 , wherein the hydrogen content ([H 2 ]) as far as a distance (d 3 ) of 25 mm from the surface falls to 10% or less of the hydrogen content ([H 2 ]) at the surface.

12. The lens element according to claim 8 , wherein the hydrogen content ([H 2 ]) rises in a thickness direction (z) of the lens element from the minimum value to the further surface for passage of radiation to not more than 30% of the hydrogen content ([H 2 ]) at the surface.

13. The lens element according to claim 8 , which has, during irradiation with pulsed laser radiation at a wavelength of 193 nm, a change dK/dF in absorption coefficient (K) with respect to an energy density (F) of less than 5×10 −4 cm×pulse/mJ.

14. The lens element according to claim 8 , which has an OH content of less than 200 ppm by weight.

15. The lens element according to claim 8 , which has a refractive index (n) of less than 1.560830 for radiation at a wavelength (λ B ) of 193.368 nm.

16. The lens element according to claim 8 , wherein a wavefront distortion resulting from compaction during an irradiation of the lens element with pulsed laser radiation at a wavelength of 193 nm rises no more than linearly with pulse number of the laser radiation.

17. The lens element according to claim 8 , which exhibits no formation of microchannels after receiving a dose of 200 billion pulses having a pulse duration of in each case 150 ns at an energy density of 0.5 mJ/cm 2 /pulse or at a dose of 3.5 billion pulses having a pulse duration of in each case 130 ns at an energy density of 6.5 mJ/cm 2 /pulse.

18. A projection lens, comprising at least one lens element according to claim 8 .

19. The projection lens according to claim 18 , wherein the lens element is a last lens element of the projection lens.

20. A lens element composed of fused silica and providing a surface and a further surface configured to transmit radiation therethrough,
wherein at least at one location in an inner volume of the lens element a hydrogen content ([H 2 ]) is less than 2×10 15 molecules/cm 3 ,
wherein the hydrogen content ([H 2 ]) at the surface and at the further surface is between 1.5 times and 5 times the hydrogen content ([H 2 ]) at the at least one location,
wherein a silane content at the surface and at the further surface of the lens element is between 1.1 times and 2.20 times the silane content at the at least one location; and
wherein at all locations in the volume of the lens element a silane content is less than 5×10 14 molecules/cm 3 .

21. A lens element composed of fused silica, wherein a ratio between a maximum silane content and a minimum silane content in a volume of the lens element is lower than a square root of the ratio between a maximum hydrogen content ([H 2 ]) and a minimum hydrogen content ([H 2 ]) in the volume of the lens element and wherein at all locations in the volume of the lens element a silane content is less than 5×10 14 molecules/cm 3 .

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Eva Eric

Classifications

• C03B19/066 Primary

  for the production of quartz or fused silica articles (other processes specially adapted for the production of quartz or fused silica articles C03B20/00) · CPC title

• G02B13/143

  for use with ultraviolet radiation · CPC title

• C03C2201/21

  containing molecular hydrogen · CPC title

• G02B1/02

  made of crystals, e.g. rock-salt, semi-conductors (G02B1/08 takes precedence) · CPC title

• G03F7/70958

  Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties · CPC title