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

Patent metadata

Field	Value
Publication number	US-2016145137-A1
Application number	US-201615013499-A
Country	US
Kind code	A1
Filing date	Feb 2, 2016
Priority date	Aug 2, 2013
Publication date	May 26, 2016
Grant date	—

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 ) 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, 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.

2 . The method according to claim 1 , wherein the further loading of the blank is at a lower temperature (T 2 <T 1 ) than is the loading.

3 . 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.

4 . 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.

5 . The method according to claim 4 , 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.

6 . The method according to claim 1 , wherein the blank is loaded at a temperature (T 1 ) of less than 475° C.

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

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

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

10 . 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.

11 . The lens element according to claim 10 , wherein a silane content varies over a thickness (D) of the lens element by not more than 50%.

12 . The lens element according to claim 10 , 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.

13 . The lens element according to claim 10 , 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.

14 . The lens element according to claim 10 , 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.

15 . 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, and 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.

16 . 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.

17 . The lens element according to claim 10 , 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.

18 . The lens element according to claim 10 , which has an OH content of less than 200 ppm by weight.

19 . The lens element according to claim 10 , which has a refractive index (n) of less than 1.560830 for radiation at a wavelength (λ B ) of 193.368 nm.

20 . The lens element according to claim 10 , wherein at all locations in the volume of the lens element a silane content is less than 5×10 14 molecules/cm 3 .

21 . The lens element according to claim 10 , 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.

22 . The lens element according to claim 10 , 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.

23 . A projection lens, comprising at least one lens element according to claim 10 .

24 . The projection lens according to claim 23 , wherein the lens element is a last lens element of the projection lens.

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Eva Eric

Classifications

• C03C2201/21

  containing molecular hydrogen · CPC title

• G02B1/02

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

• C03C2201/23

  containing hydroxyl groups · CPC title

• 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

• C03C2203/54

  in a dopant containing atmosphere · CPC title