Method for measuring transmittance of optical members for ultraviolent use, synthetic silica glass, and photolithography apparatus using the same

A method for manufacturing a silica glass, comprising the steps of:

• synthesizing a silica glass ingot;
• heat-treating the silica glass ingot;
• cutting out a plurality of silica glass pieces from the heat-treated silica glass ingot;
• evaluating transmittances of the plurality of silica glass pieces, comprising the steps of:
• cleaning the plurality of silica glass pieces,
• for each of the plurality of silica glass pieces, measuring a transmittance of the silica glass piece within a predetermined time period from completion of the cleaning during which a rate of decrease in the transmittance of the silica glass piece remains substantially constant, and
• for each of the plurality of silica glass pieces, correcting the measured transmittance to a transmittance at an evaluation time arbitrarily selected within the predetermined time period in accordance with the constant rate of decrease in the transmittance and a time at which the transmittance is measured;
• and
• selecting silica glass pieces, from among the plurality of silica glass pieces, that have a loss coefficient of about 0.0050 cm−1 or less as determined from the transmittance evaluated in the step of evaluating.

A method for evaluating a transmittance of an optical member for ultraviolet use, the method comprising the steps of:

• cleaning a surface of the optical member;
• measuring a transmittance of the optical member with respect to ultraviolet light within a predetermined time from completion of the cleaning during which a rate of decrease in transmittance remains substantially constant;
• and
• deriving a transmittance of the optical member at an evaluation time arbitrarily selected within the predetermined time period from the transmittance measured in the step of measuring in accordance with the constant rate of decrease in transmittance and a time at which the transmittance is measured in the step of measuring.

A method for a quality control in manufacture of a plurality of synthetic silica glass members, the plurality of synthetic silica glass members being manufactured under substantially similar manufacturing conditions, the method comprising the steps of:

• cleaning surfaces of the plurality of synthetic silica glass members;
• measuring the transmittances of the plurality of synthetic silica glass members within a predetermined time period from completion of the cleaning during which a rate of decrease in the transmittance remains substantially constant, at least some of the plurality of synthetic silica glass members being measured at different times;
• and
• for each of the plurality of synthetic silica glass members, converting the transmittance measured in the step of measuring to a transmittance at an evaluation time arbitrarily selected within the predetermined time period in accordance with a time at which the transmittance is measured in the step of measuring and the constant rate of decrease, the evaluation time being set to be the same for all of the plurality of synthetic silica glass members, thereby enabling evaluation of the transmittance without effects of different transmittance decreases due to the different times at which the transmittances are measured in the step of measuring.

A method for selecting synthetic silica glass members that meet a predetermined standard from a plurality of synthetic silica glass members, the method comprising the steps of:

• cleaning surfaces of the plurality of synthetic silica glass members;
• measuring transmittances of the plurality of synthetic silica glass members within a predetermined time period from completion of the cleaning during which a rate of decrease in the transmittance remains substantially constant, at least some of the plurality of synthetic silica glass members being measured at different measurement times;
• for each of the plurality of synthetic silica glass members, converting the transmittance measured in the step of measuring to a transmittance at a fixed evaluation time substantially close to the time of the completion of the cleaning in accordance with a time at which the transmittance is measured in the step of measuring and the constant rate of the transmittance decrease, thereby extrapolating an initial transmittance;
• and
• selecting among the plurality of silica glass members silica glass members that meet the predetermined standard in accordance with the initial transmittance extrapolated in the step of converting.