Polishing extremely thin silica sheets and polished sheets

Abstract

A method of manufacturing a sheet of fused silica includes polishing a sheet of fused silica having a thickness of less than 500 μm and a major face surface area of at least 6π square inches. The polishing is performed by removing less than 100 micrometers depth of material of a major surface of the sheet, such as by bonding the sheet to a substrate, polishing a first major side of the sheet, debonding the sheet from the substrate, flipping the sheet, bonding the flipped sheet to the substrate or a new substrate, and polishing a second major side of the sheet. Prior to polishing, the sheet has a peak-to-valley waviness of at least 1 micrometer, but after polishing has peak-to-valley waviness less than 500 nanometers.

What is claimed is: 
     
         1 . A method of manufacturing a sheet of fused silica, comprising steps of:
 polishing a sheet of fused silica having a thickness of less than 500 μm by removing less than 100 micrometers depth of material of a major surface of the sheet;   wherein, following the above steps, the sheet of fused silica has:
 a thickness of less than 300 micrometers, 
 a major face surface area of at least 6π square inches, 
 a total thickness variation of less than 10 micrometers excluding edge rolloff, 
 a peak-to-valley waviness of less than 500 nanometers, and 
 a root mean square roughness over a square millimeter of major surface of less than 100 nanometers. 
   
     
     
         2 . The method of  claim 1 , wherein the polishing step further comprises a step of bonding the sheet to a substrate and then polishing the major surface of the sheet. 
     
     
         3 . The method of  claim 2 , wherein the polishing of the major surface of the sheet is performed without simultaneously polishing a second major surface of the sheet. 
     
     
         4 . The method of  claim 3 , wherein the polishing step further comprises debonding the sheet from the substrate, flipping the sheet, bonding the flipped sheet to the substrate or a new substrate, and polishing the second major surface of the sheet. 
     
     
         5 . The method of  claim 1 , further comprising a step of flattening the sheet of fused silica prior to the polishing step. 
     
     
         6 . The method of  claim 1 , wherein the fused silica is amorphous and is at least 99.99 wt % silicon dioxide. 
     
     
         7 . The method of  claim 1 , wherein the polishing step is performed by removing less than 50 micrometers depth of material of the major surface of the sheet. 
     
     
         8 . The method of  claim 1 , wherein the sheet of fused silica, prior to the polishing step, has peak-to-valley waviness of greater than 3 micrometers. 
     
     
         9 . The method of  claim 1 , further comprising steps of depositing silica soot to form a sheet of silica soot and then sintering the sheet of silica soot to form the sheet of fused silica, prior to the polishing step. 
     
     
         10 . A method of manufacturing a sheet of fused silica, comprising steps of:
 shaping a sheet of fused silica having a thickness of less than 500 micrometers, a major face surface area of at least 6π square inches, and a peak-to-valley waviness of at least 1 micrometer; and   polishing the sheet, after the shaping step, by bonding the sheet to a substrate, polishing a first major side of the sheet, debonding the sheet from the substrate, flipping the sheet, bonding the flipped sheet to the substrate or a new substrate, and polishing a second major side of the sheet,   wherein, following the above steps, the sheet of fused silica has a total thickness variation of less than 10 micrometers excluding edge rolloff and peak-to-valley waviness of less than 500 nanometers.   
     
     
         11 . The method of  claim 10 , wherein the shaping step includes a step of heating the sheet to a temperature below melting temperature of the fused silica. 
     
     
         12 . The method of  claim 11 , wherein the shaping step includes a step of applying a load to the sheet to displace at least a portion of the sheet. 
     
     
         13 . The method of  claim 12 , wherein the shaping step includes, after the heating step, a step of cooling the sheet under the load such that displacement is at least in part set. 
     
     
         14 . The method of  claim 13 , wherein the shaping step is more specifically a flattening step that flattens the sheet such that warp of the sheet is less than 50 micrometers. 
     
     
         15 . The method of  claim 14 , wherein, after the polishing step, the warp is still less than 50 micrometers. 
     
     
         16 . A sheet of fused silica comprising a thickness of less than 300 micrometers, a major face surface area of at least 6π square inches, a total thickness variation of less than 10 micrometers excluding edge rolloff, a peak-to-valley waviness of less than 500 nanometers, and a root mean square roughness over a square millimeter of major surface of less than 100 nanometers. 
     
     
         17 . The sheet of  claim 16 , wherein warp of the sheet is less than 50 micrometers. 
     
     
         18 . The sheet of  claim 16 , wherein the fused silica is amorphous and is at least 99.99 wt % silicon dioxide. 
     
     
         19 . The sheet of  claim 16 , wherein peak-to-valley waviness is less than 100 nanometers. 
     
     
         20 . The sheet of  claim 16 , wherein the total thickness variation is less than 5 micrometers. 
     
     
         21 . The sheet of  claim 16 , wherein the major face surface area is at least 8π square inches.