Shin-etsu Chemical Co., Ltd.

Hisashi Yagi

Masaki Takeuchi

Daijitsu Harada

Kazuo Shirota

Kazuhiko Aoki

Junichiro Nishida

A synthetic quartz glass substrate having a controlled hydrogen molecule concentration is prepared by (a) hot shaping a synthetic quartz glass ingot into a glass block, (b) slicing the glass block into a glass plate, (c) annealing the glass plate at 500-1,250° C. for 15-60 hours, (d) hydrogen doping treatment of the glass plate in a hydrogen gas atmosphere at 300-450° C. for 20-40 hours, and (e) dehydrogenation treatment of the glass plate at 200-400° C. for 5-10 hours.

Synthetic quartz glass substrate and making method

A synthetic quartz glass substrate is prepared by furnishing a synthetic quartz glass block, coating an arbitrary surface and an opposite surface of the block with a liquid having a transmittance of at least 99.0%/mm at the wavelength of birefringence measurement, measuring the birefringence of the block by letting light enter one coated surface and exit the other coated surface, and sorting the block to an acceptable or unacceptable group, based on the measured birefringence value.

Method for preparing synthetic quartz glass substrate

A synthetic quartz glass substrate is prepared by furnishing a synthetic quartz glass block, coating two opposite surfaces of the block with a liquid having a transmittance of at least 99.0%/mm at the wavelength of birefringence measurement, measuring a birefringence distribution on the block by letting light enter one coated surface and exit the other coated surface, and sorting the block to an acceptable group or unacceptable group, based on the measured birefringence distribution.

A method for heat treating a synthetic quartz glass having a hydroxyl concentration with a maximum/minimum difference (&#x394;OH) of less than 350 ppm involves the steps of first heat treatment of holding at 1,150-1,060&#xb0; C. for a time of 0.5-10 hours, cooling down to a second heat treatment temperature at a rate of &#x2212;7&#xb0; C./hr to &#x2212;30&#xb0; C./hr, second heat treatment of holding at 1,030-950&#xb0; C. for a time of 5-20 hours, and annealing at a rate of &#x2212;25&#xb0; C./hr to &#x2212;85&#xb0; C./hr. Two stages of heat treatment ensures that the glass has a low birefringence.

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Joetsu, Japan

Hisashi Yagi