Method for electrochemical plating on semiconductor wafers

Abstract

A method of electroplating conductive material on semiconductor wafers improves deposited film quality by providing greater control over the formation of the film grain structure. Better grain size control is achieved by applying a continuous DC plating current to the wafer which avoids sharp discontinuities in the current as the applied current is increased in successive stages during a plating cycle. Current discontinuities are avoided by gradually increasing the current in a ramp-like fashion between the successive plating stages.

1 . A method of electroplating conductive material on a semiconductor wafer, comprising the steps of: 
 (A) immersing the wafer in a plating bath;    (B) applying a continuous DC current to the wafer in order to effect electroplating of the material onto the wafer; and,    (C) increasing the magnitude of DC current over time as the DC current is being continuously applied to the wafer.    
   
   
       2 . The method of  claim 1 , wherein: 
 step (C) includes increasing the applied DC current to each of a plurality of discrete current levels, and    step (B) includes gradually increasing the applied DC current between the discrete current levels.    
   
   
       3 . The method of  claim 1 , wherein: 
 step (C) includes increasing the applied DC current from at least a first current level to a second current level, and    step (B) includes gradually ramping up the current from the first level to the second level.    
   
   
       4 . The method of  claim 2 , wherein step (C) includes successively increasing the current in 3 stages to respectively deposit an initial film of the material on the wafer, fill gaps in the wafer and fill trenches in the wafer.  
   
   
       5 . The method of  claim 4 , wherein step (B) includes gradually increasing the current between each of the stages.  
   
   
       6 . The method of  claim 1 , wherein step (B) includes gradually ramping up the current between the successive stages.  
   
   
       7 . The method of  claim 5 , wherein the gradual increase in current is essentially linear.  
   
   
       8 . The method of  claim 6 , wherein each of the upward current ramps is linear.  
   
   
       9 . The method of  claim 1 , wherein the continuously applied current in step (B) is a positive current.  
   
   
       10 . The method of  claim 1 , wherein the material is copper.  
   
   
       11 . A method of electroplating a conductive material on a semiconductor wafer, comprising the steps of: 
 (A) immersing the wafer in a plating bath;    (B) applying a continuously positive DC current to the wafer in each of a plurality of separate stages in order to achieve differing plated material structures on the wafer; and,    (C) gradually increasing the applied current between the stages to avoid discontinuities in the current flow to the wafer.    
   
   
       12 . The method of  claim 11 , wherein: 
 step (B) includes increasing the applied DC current to each of a plurality of discrete current levels, and    step (C) includes gradually increasing the applied DC current between the discrete current levels.    
   
   
       13 . The method of  claim 11 , wherein: 
 step (B) includes increasing the applied DC current from at least a first current level to a second current level, and    step (C) includes gradually ramping up the current from the first level to the second level.    
   
   
       14 . The method of  claim 12 , wherein step (B) includes successively increasing the current in 3 stages to respectively deposit an initial film of the material on the wafer, fill gaps in the wafer and fill trenches in the wafer.  
   
   
       15 . The method of  claim 14 , wherein the gradual increase of current in step (C) is linear.  
   
   
       16 . The method of  claim 11 , wherein the gradual increase of current in step (C) is linear.  
   
   
       17 . The method of  claim 13 , wherein the current is ramped linearly.  
   
   
       18 . The method of  claim 11 , wherein the material is copper.  
   
   
       19 . The method of  claim 11 , wherein step (B) the current is applied in 3 stages.  
   
   
       20 . The method of  claim 13 , wherein the material is copper.