Heat treatment method of synthetic quartz glass

Patent metadata

Field	Value
Publication number	US-9487426-B2
Application number	US-201514621732-A
Country	US
Kind code	B2
Filing date	Feb 13, 2015
Priority date	Feb 21, 2014
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

A method for heat treating a synthetic quartz glass having a hydroxyl concentration with a maximum/minimum difference (ΔOH) of less than 350 ppm involves the steps of first heat treatment of holding at 1,150-1,060° C. for a time of 0.5-10 hours, cooling down to a second heat treatment temperature at a rate of −7° C./hr to −30° C./hr, second heat treatment of holding at 1,030-950° C. for a time of 5-20 hours, and annealing at a rate of −25° C./hr to −85° C./hr. Two stages of heat treatment ensures that the glass has a low birefringence.

First claim

The invention claimed is:

1. A method for heat treating a synthetic quartz glass having a hydroxyl concentration with a difference (ΔOH) between maximum and minimum being less than 350 ppm and a hydroxyl concentration of 400 to 600 ppm in a central portion, comprising the steps of:
first heat treatment of holding at a temperature of 1,150 to 1,060° C. for a certain time,
cooling down to a second heat treatment temperature at a certain rate,
second heat treatment of holding at a temperature of 1,030 to 950° C. for at least 5 hours, and
annealing at a rate of −25° C./hr to −85° C./hr.

2. The method of claim 1 wherein the time of the second heat treatment is 5 to 20 hours.

3. The method of claim 1 wherein the time of the first heat treatment is 0.5 to 10 hours.

4. The method of claim 1 , wherein the heat treatment is applied to the synthetic quartz glass in the form of a block which is subsequently sliced and polished to form a substrate.

5. A method for heat treating a synthetic quartz glass having a hydroxyl concentration with a difference (ΔOH) between maximum and minimum being at least 350 ppm and a hydroxyl concentration of 400 to 600 ppm in a central portion, comprising the steps of:
first heat treatment of holding at a temperature of 1,150 to 1,060° C. for a certain time,
cooling down to a second heat treatment temperature at a certain rate,
second heat treatment of holding at a temperature of 1,030 to 950° C. for 10 to 15 hours, and
annealing at a rate of −25° C./hr to −85° C./hr.

6. The method of claim 1 wherein the annealing step includes first annealing step from the second heat treatment temperature to 850° C. at a rate of −25° C./hr to −45° C./hr, and second annealing step from 850° C. to 500° C. at a rate of −25° C./hr to −85° C./hr.

7. The method of claim 1 wherein the step of cooling down to a second heat treatment temperature is at a rate of −7° C./hr to −30° C./hr.

8. The method of claim 1 wherein the synthetic quartz glass to be treated has a hydroxyl concentration of 400 to 600 ppm in a central portion.

9. The method of claim 1 wherein the synthetic quartz glass at the end of heat treatment has a birefringence of up to 2 nm/cm in an effective range subject to irradiation of ArF excimer laser.

10. A method of making a synthetic quartz glass optical member substrate, comprising
forming a synthetic quartz glass ingot by the direct process or indirect process;
hot working the ingot to make a synthetic quartz glass block;
heat treating the synthetic quartz glass block in accordance with the method of claim 1 ;
slicing, lapping and polishing the synthetic quartz glass block to form the substrate.

Assignees

• Shinetsu Chemical Co

Inventors

• Yagi Hisashi
• Takeuchi Masaki
• Harada Daijitsu

Classifications

• C03B19/1453 Primary

  Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering · CPC title

• 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} · CPC title

• C03B25/02 Primary

  in a discontinuous way · CPC title

• C03B2201/23

  doped with hydroxyl groups · CPC title

• C03B25/00 Primary

  Annealing glass products · CPC title