Metal contact structure for solar cell and method of manufacture

Abstract

In a solar cell having p doped regions and n doped regions alternately formed in a surface of a semiconductor wafer in offset levels through use of masking and etching techniques, metal contacts are made to the p regions and n regions by first forming a base layer contacting the p doped regions and n doped regions which functions as an antireflection layer, and then forming a barrier layer, such as titanium tungsten or chromium, and a conductive layer such as copper over the barrier layer. Preferably the conductive layer is a plating layer and the thickness thereof can be increased by plating.

1 . A solar cell comprising:
 a plurality of P+ and N+ doped regions;   a silicon dioxide layer formed over the plurality of P+ and N+ doped regions;   a plurality of openings in the silicon dioxide layer, the plurality of openings exposing the plurality of P+ and N+ doped regions; and   a plurality of metal contacts on a backside of the solar cell, each of the plurality of metal contacts being formed over an infrared reflecting layer to make an electrical connection to a corresponding region in the plurality of P+ and N+ regions, the infrared reflecting layer comprising aluminum.   
     
     
         2 . The solar cell of  claim 1  wherein the metal contacts comprise copper. 
     
     
         3 . The solar cell of  claim 1  further comprising a barrier layer between the infrared reflecting layer and a corresponding metal contact in the plurality of metal contacts. 
     
     
         4 . The solar cell of  claim 3  wherein the barrier layer comprises titanium tungsten. 
     
     
         5 . The solar cell of  claim 1  further comprising a plating seed layer between the infrared reflecting layer and a corresponding metal contact in the plurality of metal contacts. 
     
     
         6 . The solar cell of  claim 5  wherein the plating seed layer comprises copper. 
     
     
         7 . The solar cell of  claim 1  further comprising a textured surface on a front surface of the solar cell. 
     
     
         8 . A method of fabricating a solar cell, the method comprising:
 forming a plurality of P+ and N+ doped regions;   forming a silicon dioxide layer over the plurality of P+ and N+ doped regions;   forming a plurality of openings in the silicon dioxide layer exposing the plurality of P+ and N+ doped regions; and   forming a plurality of metal contacts, each of the plurality of metal contacts being formed over an infrared reflecting layer to make an electrical connection to a corresponding region in the plurality of P+ and N+ regions, the infrared reflecting layer comprising aluminum.   
     
     
         9 . The method of  claim 8  wherein the metal contacts comprise copper. 
     
     
         10 . The method of  claim 8  further comprising:
 forming a barrier layer between the infrared reflecting layer and a corresponding metal contact in the plurality of metal contacts.   
     
     
         11 . The method of  claim 10  wherein the barrier layer comprises titanium tungsten. 
     
     
         12 . The method of  claim 10  further comprising:
 forming a plating seed layer between the infrared reflecting layer and a corresponding metal contact in the plurality of metal contacts.   
     
     
         13 . The method of  claim 12  wherein the plating seed layer comprises copper. 
     
     
         14 . The solar cell of  claim 8  further comprising:
 texturing a front surface of the solar cell.   
     
     
         15 . A solar cell comprising:
 a plurality of doped regions;   a dielectric layer over the doped regions;   a plurality of metal contacts over the dielectric layer on a backside of the solar cell, each of the metal contacts making an electrical connection to a doped region in the plurality of doped regions by way of an infrared reflecting layer comprising aluminum and through an opening in the dielectric layer.   
     
     
         16 . The solar cell of  claim 15  wherein the dielectric layer comprises silicon dioxide. 
     
     
         17 . The solar cell of  claim 15  further comprising a barrier layer between the infrared reflecting layer and a corresponding metal contact in the plurality of metal contacts. 
     
     
         18 . The solar cell of  claim 17  wherein the barrier layer comprises titanium tungsten. 
     
     
         19 . The solar cell of  claim 15  wherein the metal contacts comprise copper. 
     
     
         20 . The solar cell of  claim 15  further comprising a textured surface on a front side of the solar cell.