Synthetic silica with low polarization-induced birefringence, process for producing the same and lithographic apparatus comprising the same

摘要

Synthetic silica glass material suitable to be used in the beam path of lithographic radiation below about 300 nm in lithography apparatus, and which is less than about 1 nm / cm, preferably less than 0.1 nm / cm, of polarization-induced birefringence measured at about 633 nm after having been exposed to 5 × 10 pulses of a linearly polarized pulsed laser beam at about 193 nm having a fluence of about 40 μJ · cm per pulse and a pulse length of about 25 ns, the synthetic silica glass material consisting essentially of synthetic silica, Dog OH and Hvon contains 1 x 10 molecules per cmis less than 5.0 x 10 molecules per cubic ym, the OH concentration in the glass being lower than 50 ppm by weight and the glass containing less than 10 ppb of alkali metals, alkaline earth metals or transition metals ,