System and method for tin plating metal electrodes

Abstract

Systems and methods for fabricating a photovoltaic structure are provided. During fabrication, a patterned mask is formed on a first surface of a multilayer body of the photovoltaic structure, with openings of the mask corresponding to grid line locations of a first grid. Subsequently, a core layer of the first grid is deposited in the openings of the patterned mask, and a protective layer is deposited on an exposed surface of the core layer. The patterned mask is then removed to expose the sidewalls of the core layer. Heat is applied to the protective layer such that the protective layer reflows to cover both the exposed surface and sidewalls of the core layer.

1 . A system for fabricating electrode grids on a photovoltaic structure, comprising:
 a masking tool configured to form a patterned mask on a first surface of the photovoltaic structure, wherein openings of the patterned mask correspond to grid line locations of a first grid on the photovoltaic structure;   a first plating tool configured to deposit a first core layer of the first grid in openings of the patterned mask;   a second plating tool configured to deposit a first protective layer on an exposed surface of the first core layer while the patterned mask covers sidewalls of the first core layer;   a mask-removing tool configured to remove the patterned mask subsequent to the deposition of the first protective layer; and   a thermal reflow tool configured to apply heat to the first protective layer such that the first protective layer reflows to cover both the exposed surface and sidewalls of the first core layer.   
     
     
         2 . The system of  claim 1 , wherein the first core layer comprises Cu. 
     
     
         3 . The system of  claim 1 , wherein a thickness of the first core layer is between 10 and 100 microns. 
     
     
         4 . The system of  claim 1 , wherein the first protective layer comprises one or more metallic materials selected from a group consisting of:
 tin;   tin-lead alloy;   tin-zinc alloy;   tin-bismuth alloy;   tin-indium alloy;   tin-silver-copper alloy;   tin-lead-zinc alloy; and   tin-lead-copper alloy.   
     
     
         5 . The system of  claim 4 , wherein the first protective layer comprises tin, tin-lead alloy, or both. 
     
     
         6 . The system of  claim 1 , wherein the first protective layer has a melting point that is below 250° C. 
     
     
         7 . The system of  claim 1 , wherein, while depositing the first protective layer, the second plating tool is configured to control a thickness of the first protective layer to be between 0.3 and 10 microns. 
     
     
         8 . The system of  claim 1 , wherein the reflow oven is configured to reflow the first protective layer in a way such that a thickness of the first protective layer is between 0.1 and 5 microns after the reflow. 
     
     
         9 . The system of  claim 1 , further comprising:
 a third plating tool configured to deposit, over a second patterned mask on a second surface of the photovoltaic structure, a second core layer of a second grid;   a fourth plating tool configured to deposit a second protective layer on an exposed surface the second core layer while the second patterned mask is covering sidewalls of the second core layer; and   a second thermal reflow tool configured to apply heat, after the second patterned mask layer is removed, to the second protective layer such that the second protective layer reflows to cover both the exposed surface and sidewalls of the second core layer.   
     
     
         10 . The system of  claim 9 ,
 wherein the first and second thermal reflow tools are configured to reflow both protective layers simultaneously.   
     
     
         11 . The system of  claim 9 ,
 wherein the first and second thermal reflow tools are configured to reflow the first and second protective layers sequentially.   
     
     
         12 . The system of  claim 1 , wherein while applying the heat, the first thermal reflow tool is configured to maintain the first protective layer at a predetermined temperature for a predetermined time period. 
     
     
         13 . The system of  claim 12 , wherein the predetermined time period is between 10 seconds and 2 minutes. 
     
     
         14 . The system of  claim 12 , wherein the predetermined temperature is 10 to 20° C. higher than the first protective layer's melting point. 
     
     
         15 . The system of  claim 1 , wherein the first thermal reflow tool includes one selected from a group consisting of:
 an oven;   a hot plate;   an infrared lamp;   a hot air blower; and   a heated tunnel.   
     
     
         16 . The system of  claim 1 , wherein the patterned mask includes one of:
 a patterned layer of photoresist;   a patterned layer of silicon oxide; and   a patterned layer of silicon nitride.   
     
     
         17 - 20 . (canceled)