Method of observing pattern evolution using variance and fourier transform spectra of friction forces in cmp

Abstract

A method of determining pattern evolution of a semiconductor wafer during chemical mechanical polishing prior to polishing end point by determining the periodic change in the variance and FT or FFT frequency spectra of shear force and change in variance and FT or FFT frequency spectra of COF, shear force and/or down force between the semiconductor wafer and the polishing pad. By comparing features of the data and spectra thus obtained, analysis leading to a deeper understanding of the changes that occur as CMP processes occur as well as diagnostic analysis of specific CMP processes and specific wafers can be accomplished

1 . A method of determining pattern evolution of a semiconductor wafer during chemical mechanical polishing prior to polishing end point by measuring the change in the shear force and the down force between the semiconductor wafer and the polishing pad over time. 
   
   
       2 . The method according to  claim 1 , wherein the said pattern evolution is determined according to the change in the coefficient of friction (COF) calculated between the semiconductor wafer and the polishing pad calculated from the SF and the DF over time. 
   
   
       3 . The method according to  claims 1  and  2  wherein measurements are made periodically. 
   
   
       4 . The method according to  claims 1  and  2 , wherein shear force (SF) is determined by measurement of two components of the SF perpendicular to each other and calculation of the resultant shear force. 
   
   
       5 . The method according to  claims 1  and  2 , wherein down force (DF) is determined by measuring the load applied to the polishing pad and the semiconductor wafer. 
   
   
       6 . The method according to  claim 1 , wherein pattern evolution of the wafer is determined by extracting frequency components using fourier transform (FT) of DF, SF and COF during different time periods prior to polishing end point and determining the change in intensity change of extracted frequency components. 
   
   
       7 . The method according to  claim 6  wherein the fourier transform used is fast fourier transform (FFT). 
   
   
       8 . The method according to  claim 1 , wherein the surface of the film to be polished is irregular when polishing is initiated. 
   
   
       9 . The method according to  claim 1 , wherein a CMP slurry containing at least one member selected from the group consisting of silicon dioxide, cerium oxide particles and ammonium polyacrylate or an ammonium acrylate copolymer is used. 
   
   
       10 . The method according to  claim 1  wherein the variance of the shear force is determined. 
   
   
       11 . The method according to  claim 1  wherein the variance of the down force is determined. 
   
   
       12 . The method according to  claim 2  wherein the variance of COF is determined. 
   
   
       13 . The method according to  claim 1 , wherein the film to be polished contains tantalum, tantalum nitride, silicon oxide, silicon nitride, silicon oxynitride or other types of low k dielectrics. 
   
   
       14 . The method according to  claim 1  wherein the determination of the pattern evolution from changes in the SF and DF and numbers or quantities derived from them is accomplished by data processing means.