Plating method

Abstract

Methods of depositing layers of copper that selectively incorporate certain impurities are provided. Such copper layers reduce stress-induced void formation in wide copper lines under vias.

1 . A method of depositing copper comprising the steps of: a) contacting an electronic device substrate having an aperture with a copper electroplating bath comprising a source of copper ions, an electrolyte, and a disulfide-containing accelerator; b) depositing a layer of copper in the aperture using a duty cycle comprising 1) applying a first current density for a first period to electrochemically reduce the disulfide-containing accelerator to a thiol compound at a copper surface; and 2) applying a second current density for a second period; and c) repeating step b) until a desired copper deposit is obtained; wherein the second current density is less than the first current density.  
   
   
       2 . The method of  claim 1  wherein the copper deposit comprises from 1 to 500 ppm of average total impurities after annealing of the copper.  
   
   
       3 . The method of  claim 2  wherein the impurities comprise one or more of carbon, oxygen, nitrogen, sulfur and chloride.  
   
   
       4 . The method of  claim 1  wherein the first period is up to 5 seconds.  
   
   
       5 . The method of  claim 4  wherein the duty cycle has a frequency of 0.1 to 10 Hz.  
   
   
       6 . The method of  claim 1  wherein the first current density is in the range of 10 to 100 mA/cm 2 .  
   
   
       7 . The method of  claim 1  wherein the second current density is in the range of 1 to 20 mA/cm 2 .  
   
   
       8 . The method of  claim 1  wherein the duty cycle has a ratio of step 1) to step 2) of 1:1 to 10:1.  
   
   
       9 . An electronic device comprising a first layer of metal and a second layer of metal, wherein the first layer of metal comprises average total impurities in the range of up to 10 ppm and the second layer of metal comprises average total impurities in the range of 10 to 100 ppm.  
   
   
       10 . The electronic device of  claim 10  wherein the first and second metal layers are copper.