Method for removing foreign matter from glass substrate surface and method for processing glass substrate surface

Abstract

An object of the invention is to provide a method for removing foreign matter from a glass substrate surface to be finish-processed by a method accompanied with beam irradiation or laser light irradiation on the glass substrate surface. The present invention relates to a method for removing foreign matter from a glass substrate surface, which includes subjecting the glass substrate surface to gas cluster ion beam etching at an accelerating voltage of from 5 to 15 keV.

1 . A method for removing foreign matter from a glass substrate surface, which comprises
 subjecting the glass substrate surface to gas cluster ion beam etching at an accelerating voltage of from 5 to 15 keV.   
     
     
         2 . A method for removing foreign matter from a glass substrate surface, which comprises
 subjecting the glass substrate surface to gas cluster ion beam etching with, as a gas source, at least one gas selected from the group consisting of O 2 , Ar, B, CO 2 , N 2 , N 2 O and a boron hydride.   
     
     
         3 . The method for removing foreign matter from a glass substrate surface according to  claim 1 , wherein the gas cluster ion beam etching is performed under a condition that the etching amount is not more than 20 nm. 
     
     
         4 . The method for removing foreign matter from a glass substrate surface according to  claim 1 , wherein the glass substrate is made of a low expansion glass having a heat expansion coefficient at 20° C. of 0±30 ppb/° C. 
     
     
         5 . The method for removing foreign matter from a glass substrate surface according to  claim 1 , wherein the glass substrate surface before performing the gas cluster ion beam etching has a surface roughness (Rms) of not more than 5 nm. 
     
     
         6 . The method for removing foreign matter from a glass substrate surface according to  claim 1 , wherein the gas cluster ion beam etching is performed under a condition that a cluster size is 2,000 or more. 
     
     
         7 . The method for removing foreign matter from a glass substrate surface according to  claim 1 , wherein the gas cluster ion beam etching is performed while keeping an angle formed by a normal line of the glass substrate and a gas cluster ion beam to be made incident to the glass substrate surface at from 3 to 60 degrees. 
     
     
         8 . The method for removing foreign matter from a glass substrate surface according to  claim 7 , wherein the gas cluster ion beam etching is performed while keeping the glass substrate surface in a state facing downward relative to the horizontal direction by from 3 to 60 degrees. 
     
     
         9 . A method for processing a glass substrate surface, which comprises the steps of:
 removing foreign matter on the glass substrate surface by the method according to  claim 1 ; and   processing the glass substrate surface by a processing method selected from the group consisting of ion beam etching, gas cluster ion beam etching, plasma etching and nano-abrasion.   
     
     
         10 . The method for processing a glass substrate surface according to  claim 9 , wherein the processing method is gas cluster ion beam etching. 
     
     
         11 . The method for processing a glass substrate surface according to  claim 10 , wherein the gas cluster ion beam etching in the processing step is performed at an accelerating voltage exceeding 15 keV, using, as a source gas, a mixed gas selected from the group consisting of: a mixed gas of SF 6  and O 2 ; a mixed gas of SF 6 , Ar and O 2 ; a mixed gas of NF 3  and O 2 ; a mixed gas of NF 3 , Ar and O 2 ; a mixed gas of NF 3  and N 2 ; and a mixed gas of NF 3 , Ar and N 2 . 
     
     
         12 . The method for processing a glass substrate surface according to  claim 11 , wherein the source gas is any one mixed gas selected from the group consisting of: a mixed gas of SF 6  and O 2 ; a mixed gas of SF 6 , Ar and O 2 ; a mixed gas of NF 3  and O 2 ; and a mixed gas of NF 3 , Ar and O 2 . 
     
     
         13 . A method for processing a glass substrate surface, which comprises the steps of:
 measuring a flatness of the glass substrate surface;   removing foreign matter on the glass substrate surface by the method according to  claim 1 ; and   processing the glass substrate surface by a processing method selected from the group consisting of ion beam etching, gas cluster ion beam etching, plasma etching and nano-abrasion,   wherein, in the step of processing the glass substrate surface, a processing condition of the glass substrate surface is set up for each site of the glass substrate on the basis of a result obtained from the step of measuring a flatness.   
     
     
         14 . The method for processing a glass substrate surface according to  claim 13 ,
 wherein the processing method is ion beam etching, gas cluster ion beam etching or plasma etching,   wherein a width of waviness existing on the glass substrate surface is specified on the basis of a result obtained from the step of measuring a flatness of the glass substrate surface, and   wherein the glass substrate surface is processed with a beam having a beam diameter of not more than the width of the waviness in terms of FWHM (full width of half maximum) value.   
     
     
         15 . The method for processing a glass substrate surface according to  claim 14 , wherein the FWHM value of the beam diameter is not more than ½ of the width of the waviness. 
     
     
         16 . The method for processing a glass substrate surface according to  claim 15 ,
 wherein the processing method is gas cluster beam etching, and   wherein the gas cluster ion beam etching in the processing step is performed at an accelerating voltage exceeding 15 keV, using, as a source gas, any one mixed gas selected from the group consisting of: a mixed gas of SF 6  and O 2 ; a mixed gas of SF 6 , Ar and O 2 ; a mixed gas of NF 3  and O 2 ; a mixed gas of NF 3 , Ar and O 2 ; a mixed gas of NF 3  and N 2 ; and a mixed gas of NF 3 , Ar and N 2 .   
     
     
         17 . The method for processing a glass substrate surface according to  claim 16 , wherein the source gas is any one mixed gas selected from the group consisting of:
 a mixed gas of SF 6  and O 2 ; a mixed gas of SF 6 , Ar and O 2 ; a mixed gas of NF 3  and O 2 ; and a mixed gas of NF 3 , Ar and O 2 .   
     
     
         18 . The method for processing a glass substrate surface according to  claim 9 , further comprising subsequent to the step of processing the glass substrate surface, a second processing step for improving a surface roughness of the glass substrate surface. 
     
     
         19 . The method for processing a glass substrate surface according to  claim 18 , wherein the second processing step comprises gas cluster ion beam etching at an accelerating voltage of 3 keV or more and less than 30 keV, using, as a source gas, an O 2  gas singly or a mixed gas of O 2  and at least one gas selected from the group consisting of Ar, CO and CO 2 . 
     
     
         20 . The method for processing a glass substrate surface according to  claim 18 , wherein the second processing step comprises mechanical polishing using a polishing slurry and performed at a surface pressure of from 1 to 60 gf/cm 2 .