Cmp apparatus and method of polishing wafer using cmp

Abstract

A CMP apparatus is provided with a replaceable polishing pad, a film thickness sensor, and a polishing control unit for switching polishing conditions in response to a fact that an output value from the film thickness sensor has exceeded a threshold value. The polishing control unit has a memory unit for storing a threshold value corresponding to the thickness of a new polishing pad when the polishing pad is replaced. The memory unit also store conversion information that shows the relationship between the output value of the film thickness sensor and the thickness of the polishing pad when the thickness of the film being polished is constant. The polishing control unit accesses the conversion information, obtain the output value of the film thickness sensor that corresponds to the thickness of the new polishing pad, and record the output value as the threshold value.

1 . A CMP apparatus for polishing a film on a wafer, comprising:
 a replaceable polishing pad;   a film thickness sensor for measuring a thickness of the film via the polishing pad; and   a polishing control unit for switching polishing conditions in response to a fact that an output value from the film thickness sensor has exceeded a threshold value, wherein   the polishing control unit has a memory unit for storing the threshold value corresponding to the thickness of a new polishing pad when the polishing pad is replaced.   
   
   
       2 . The CMP apparatus as claimed in  claim 1 , wherein
 the memory unit further stores conversion information that shows the relationship between the output value of the film thickness sensor and the thickness of the polishing pad when the thickness of the film being polished is constant, and   the polishing control unit accesses the conversion information, obtains the output value of the film thickness sensor that corresponds to the thickness of the new polishing pad, and records the output value as the threshold value.   
   
   
       3 . The CMP apparatus as claimed in  claim 1 , wherein the polishing control unit measures the thickness of the film being polished with aid of the film thickness sensor after a reference wafer provided with the film being polished that has a prescribed thickness is set, and records as the threshold value the output value of the film thickness sensor. 
   
   
       4 . The CMP apparatus as claimed in  claim 1 , wherein the film thickness sensor includes an eddy current sensor. 
   
   
       5 . The CMP apparatus as claimed in  claim 1 , wherein the polishing target is a metal film or a metal compound film. 
   
   
       6 . A wafer polishing method using CMP, comprising:
 a polishing pad setting step for setting a new polishing pad;   a threshold value recording step for recording a threshold value that has been corrected based on a thickness of the new polishing pad;   a high-speed polishing step for performing high-speed polishing of a wafer while a thickness of a film being polished is monitored using a film thickness sensor;   a polishing condition switching step for switching from high-speed polishing to low-speed polishing when an output of the film thickness sensor reaches the threshold value; and   a low-speed polishing step for performing low-speed polishing of the wafer as far as a polishing terminal point.   
   
   
       7 . The wafer polishing method as claimed in  claim 6 , wherein the threshold value recording step includes:
 a step for accessing conversion information that shows a relationship between the output value of the film thickness sensor and the thickness of the polishing pad when the thickness of the film being polished is constant, and obtaining the output value of the film thickness sensor that corresponds to the thickness of the new polishing pad; and   a step for recording the output value as the threshold value.   
   
   
       8 . The wafer polishing method as claimed in  claim 6 , wherein the threshold value recording step includes:
 a step for setting a reference wafer provided with a film being polished that has a prescribed thickness;   a step for measuring a thickness of the film being polished using the film thickness sensor; and   a step for recording the output value of the film thickness sensor as the threshold value.   
   
   
       9 . A method of polishing a wafer, comprising:
 performing a first polishing on the wafer at a first speed;   performing a second polishing on the wafer at a second speed when a film to be polished on the wafer reaches a threshold value; and   calibrating the threshold value when a new polishing pad has been set.   
   
   
       10 . The method of polishing a wafer as claimed in  claim 9 , wherein the calibrating the threshold value comprises measuring a thickness of the new polishing pad and determining threshold value in response to a result of the measuring. 
   
   
       11 . The method of polishing a wafer as claimed in  claim 10 , wherein the determining the threshold value comprises referring to a data table in response to the result of the measuring. 
   
   
       12 . The method of polishing a wafer as claimed in  claim 9 , wherein the calibrating the threshold value comprises stacking a reference wafer on the new polishing pad, measuring a total thickness of the new polishing pad and the reference wafer, and determining the threshold value in response to a result of the measuring. 
   
   
       13 . The method of polishing a wafer as claimed in  claim 12 , wherein the reference wafer has a film of a thickness at which the second polishing is to be initiated. 
   
   
       14 . The method of polishing a wafer as claimed in  claim 9 , wherein the first speed is faster than the second speed.