Process for producing glass substrate and glass substrate

Abstract

Provided are a process for producing a glass substrate usable for low-temperature p-SiTFT substrates directly in accordance with a down draw method, and the glass substrate obtained by the process. The process for producing a glass substrate includes a forming step of forming a molten glass into a ribbon shape in accordance with a down draw method, an annealing step of annealing the glass ribbon, and a cutting step of cutting the glass ribbon to give a glass substrate, in which, in the annealing step, an average cooling rate from the annealing point to the (annealing point−50° C.) is lower than an average cooling rate from the (annealing point+100° C.) to the annealing point.

1 - 14 . (canceled) 
     
     
         15 . A glass substrate having a thermal shrinkage of 30 ppm or less when heated from room temperature at a rate of 10° C./min, kept at a holding temperature of 450° C. for 10 hours, and then cooled at a rate of 10° C./min, and having an average surface roughness Ra of 0.3 nm or less and a retardation of 1.0 nm or less. 
     
     
         16 . A glass substrate having a fictive temperature of glass of from the annealing point to the (annealing point+44° C.), and having an average surface roughness Ra of 0.3 nm or less and a retardation of 1.0 nm or less. 
     
     
         17 . The glass substrate according to  claim 15  or  16 , which has a warpage value of 100 μm or less. 
     
     
         18 . The glass substrate according to  claim 15  or  16 , which has a short side of 500 mm or more. 
     
     
         19 . The glass substrate according to  claim 15  or  16 , which has an unpolished surface. 
     
     
         20 . The glass substrate according to  claim 15  or  16 , which comprises a glass having a liquidus viscosity of 10 4.5  dPa·s or more. 
     
     
         21 . The glass substrate according to  claim 15  or  16 , which comprises a glass having a strain point of not lower than 600° C. 
     
     
         22 . The glass substrate according to  claim 15  or  16 , which comprises a glass containing, in terms of percentage by mass, from 50 to 70% of SiO 2 , from 10 to 25% of Al 2 O 3 , from 3 to 15% of B 2 O 3 , from 0 to 10% of MgO, from 0 to 15% of CaO, from 0 to 15% of SrO, from 0 to 15% of BaO and from 0 to 5% of Na 2 O. 
     
     
         23 . The glass substrate according to  claim 15  or  16 , which is for use in a flat panel display. 
     
     
         24 . The glass substrate according to  claim 23 , wherein the flat panel display is a display in which a low-temperature p-SiTFT is formed on the substrate. 
     
     
         25 . A glass substrate produced by the process according to one of the following processes:
 a process comprising:   a forming step of forming a molten glass into a ribbon shape in accordance with a down draw method,   an annealing step of annealing said glass ribbon, and   a cutting step of cutting said glass ribbon to give a glass substrate,   wherein in the annealing step, an average cooling rate from the annealing point to the (annealing point−50° C.) is lower than an average cooling rate from the (annealing point+100° C.) to the annealing point; or   a process for producing a glass substrate, comprising:   a forming step of forming a molten glass into a ribbon shape in accordance with a down draw method,   an annealing step of annealing said glass ribbon, and   a cutting step of cutting said glass ribbon to give a glass substrate, wherein the annealing step includes a first annealing stage of cooling the glass to the annealing point, a second annealing stage of cooling the glass down to Tx (wherein Tx is a temperature falling between the (annealing point−50° C.) and the (annealing point−200° C.)), and a third annealing stage of cooling the glass down to (Tx−250° C.), and an average cooling rate in the second annealing stage is lower than an average cooling rate in the first annealing stage.