Synthetic quartz glass substrate for excimer lasers and making method

Abstract

When a synthetic quartz glass substrate is prepared from a synthetic quartz glass block, (I) the block has a hydrogen molecule concentration of 5×10 17 -1×10 19 molecules/cm 3 , (II) the substrate has a hydrogen molecule concentration of 5×10 15 -5×10 17 molecules/cm 3 , (III) the substrate has an in-plane variation of its internal transmittance at 193.4 nm which is up to 0.2%, and (IV) the substrate has an internal transmittance of at least 99.6% at 193.4 nm. The synthetic quartz glass substrate has a high transmittance and a uniform transmittance distribution, and is adapted for use with excimer lasers, particularly ArF excimer lasers.

1 . A synthetic quartz glass substrate for use with excimer lasers which is prepared from a synthetic quartz glass block wherein 
 (I) the synthetic quartz glass block has a hydrogen molecule concentration of 5×10 17  to 1×10 19  molecules/cm 3 ,    (II) the synthetic quartz glass substrate has a hydrogen molecule concentration of 5×10 15  to 5×10 17  molecules/cm 3 ,    (III) the synthetic quartz glass substrate has an in-plane variation of its internal transmittance at wavelength 193.4 nm which is up to 0.2%, and    (IV) the synthetic quartz glass substrate has an internal transmittance of at least 99.6% at wavelength 193.4 nm.    
     
     
         2 . The synthetic quartz glass substrate of  claim 1  wherein when ArF excimer laser radiation is irradiated at an energy density per pulse of 10 mJ/cm 2  and a shot number of 2×10 6  pulses into the surface thereof, the synthetic quartz glass substrate experiences a change of transmittance with a variation of up to 0.5%.  
     
     
         3 . The synthetic quartz glass substrate of  claim 1  wherein the in-plane birefringence of the synthetic quartz glass substrate has a maximum of up to 2 nm/cm.  
     
     
         4 . A method for preparing a synthetic quartz glass substrate for use with excimer lasers, comprising the steps of (i) hot shaping a synthetic quartz glass ingot at a temperature in the range of 1700 to 1900° C. into a block of desired shape, (ii) annealing the synthetic quartz glass block at a temperature in the range of 1,000 to 1,300° C., (iii) slicing the synthetic quartz glass block as annealed into a substrate of desired thickness, and (iv) polishing the synthetic quartz glass substrate as sliced, 
 said method further comprising the steps of heat treating the synthetic quartz glass substrate as sliced at a temperature in the range of 700 to 1,300° C. for a time, and then irradiating ultraviolet radiation thereto for a time.    
     
     
         5 . The method of  claim 4  wherein the synthetic quartz glass substrate as sliced has a thickness of up to 40 mm.  
     
     
         6 . The method of  claim 4  wherein the synthetic quartz glass substrate as sliced is heat treated for a time of 5 to 24 hours.  
     
     
         7 . The method of  claim 4  wherein the synthetic quartz glass substrate as sliced is irradiated with ultraviolet radiation for a time of 12 to 60 hours.