Process for polishing silicon wafers

Abstract

A process for the chemical-mechanical polishing of silicon wafers is by rotational movement of the silicon surface which is to be polished on a polishing plate which is covered with polishing cloth, with a continuous supply of an alkaline polishing agent which contains abrasives, at least 2 μm of material being removed from the polished silicon surface during the polishing. Immediately after the polishing has finished, and while maintaining the rotational movement, instead of the polishing agent at least two different stopping agents are supplied in succession, each removing less than 0.5 μm of material from the polished silicon surface.

What is claimed is:  
     
         1 . A process for the chemical-mechanical polishing of silicon wafers comprising 
 rotational movement of a silicon surface which is to be polished on a polishing plate which is covered with polishing cloth;    continuously supplying an alkaline polishing agent which contains abrasives, and removing at least 2 μm of material from the polished silicon surface during polishing;    immediately after the polishing has finished, and while maintaining the rotational movement, instead of supplying the polishing agent supplying at least two different stopping agents in succession;    each stopping agent removing less than 0.5 μm of material from the polished silicon surface.    
     
     
         2 . The process as claimed in  claim 1 , comprising polishing 12 silicon wafers simultaneously on one polishing machine.  
     
     
         3 . The process as claimed in  claim 1 , comprising simultaneously polishing of a front surface of the silicon wafers and a back surface of the silicon wafers, with from 2 to 25 μm of material being removed from each surface; and 
 guiding the silicon wafers between two oppositely rotating polishing plates covered with polishing cloth by carriers with cutouts which are suitably dimensioned to receive silicon wafers.  
 
     
     
         4 . The process as claimed in  claim 1 , 
 wherein the first stopping agent smooths the polished silicon surface, and the second stopping agent cleans and preserves the polished silicon surface.    
     
     
         5 . The process as claimed in  claim 1 , 
 wherein the pH of the first stopping agent is lower than that of the polishing agent and the pH of the second stopping agent is lower than that of the first stopping agent.    
     
     
         6 . The process as claimed in  claim 1 , 
 wherein the polishing agent substantially comprises a colloidal mixture of 1 to 10% by weight of SiO 2 , based upon the total weight of the polishing agent, in water with the addition of alkali and has a pH of between 10.5 and 12.0;    the first stopping agent substantially comprises a colloidal mixture of 0.1 to 5% by weight of SiO 2 , based upon the total weight of the first stopping agent, in water with the addition of a polyhydric alcohol and has a pH of between 9.0 and 10.5; and    the second stopping agent substantially comprises a solution of a polyhydric alcohol in water and has a pH of between 7.5 and 9.0.    
     
     
         7 . The process as claimed in  claim 6 , wherein the polyhydric alcohol which is used in the first stopping agent and the polyhydric alcohol which is used in the second stopping agent each comprises a compound selected from the group consisting of glycerol, monomeric glycols, oligomeric glycols, polyglycols and polyalcohols and is used in proportions of from 0.01% to 10% by volume, based upon the total volume of the stopping agent.  
     
     
         8 . The process as claimed in  claim 6 , wherein the first stopping agent and the second stopping agent additionally contain small quantities selected from the group consisting of monohydric alcohols and surfactants.  
     
     
         9 . The process as claimed in  claim 6 , 
 wherein the alkali added to the polishing agent comprises at least one compound selected from the group consisting of Na 2 CO 3 , K 2 CO 3 , NaOH, KOH, NH 4 OH and tetramethylammonium hydroxide, in proportions of from 0.01% to 10% by weight, with the percent by weight based upon the total weight of the polishing agent.    
     
     
         10 . The process as claimed in  claim 6 , 
 wherein the polishing agent contains, as the SiO 2  component, precipitated silica with a grain diameter of between 5 and 50 nm; and    the first stopping agent contains, as the SiO 2  component, pyrogenic silica with a grain diameter of between 5 and 50 nm.    
     
     
         11 . The process as claimed in  claim 6 , 
 wherein ultrapure water is supplied between the supply of first stopping agent and the supply of second stopping agent.