Etching of solar cell materials

Abstract

A solar cell is fabricated by etching one or more of its layers without substantially etching another layer of the solar cell. In one embodiment, a copper layer in the solar cell is etched without substantially etching a topmost metallic layer comprising tin. For example, an etchant comprising sulfuric acid and hydrogen peroxide may be employed to etch the copper layer selective to the tin layer. A particular example of the aforementioned etchant is a Co-Bra Etch® etchant modified to comprise about 1% by volume of sulfuric acid, about 4% by volume of phosphoric acid, and about 2% by volume of stabilized hydrogen peroxide. In one embodiment, an aluminum layer in the solar cell is etched without substantially etching the tin layer. For example, an etchant comprising potassium hydroxide may be employed to etch the aluminum layer without substantially etching the tin layer.

1 - 20 . (canceled) 
     
     
         21 . A solar cell, comprising:
 a silicon dioxide layer disposed on a silicon substrate, wherein the silicon dioxide layer includes a vias;   an aluminum layer disposed over the a silicon dioxide layer, wherein the vias allows for the aluminum layer to contact a doped region of the silicon substrate;   a titanium-tungsten (TiW) layer disposed over the aluminum layer;   a first copper layer disposed over the titanium-tungsten (TiW) layer;   a second copper layer disposed on the first copper layer; and   a solderable metallic layer comprising tin disposed on the first copper layer.   
     
     
         22 . The solar cell of  claim 21 , wherein the solderable metallic layer comprises an electroplated tin layer. 
     
     
         23 . The solar cell of  claim 21 , wherein the silicon dioxide layer has a thickness of 950 Angstroms. 
     
     
         24 . The solar cell of  claim 21 , further comprising an interconnect lead soldered on the solderable metallic layer. 
     
     
         25 . The solar cell of  claim 21 , wherein the solderable metallic layer has a thickens of 5 microns. 
     
     
         26 . The solar cell of  claim 21 , wherein the first copper layer has a thickness of 1600 Angstroms. 
     
     
         27 . The solar cell of  claim 21 , wherein the second copper layer has a thickness of 20 microns. 
     
     
         28 . The solar cell of  claim 21 , wherein the titanium-tungsten (TiW) layer has a thickness of 1000 Angstroms 
     
     
         29 . The solar cell of  claim 21 , wherein the aluminum layer comprises aluminum having 1% silicon alloy. 
     
     
         30 . A solar cell, comprising:
 a silicon dioxide layer disposed on a silicon substrate, wherein the silicon dioxide layer includes a vias;   a sputtered aluminum layer disposed over the a silicon dioxide layer, wherein the vias allows for the sputtered aluminum layer to contact a doped region of the silicon substrate;   a sputtered titanium-tungsten (TiW) layer disposed over the sputtered aluminum layer;   a copper seed layer disposed over the sputtered titanium-tungsten (TiW) layer;   an electroplated copper layer disposed on the copper seed layer; and   a solderable metallic layer disposed on the electroplated copper layer, wherein the solderable metallic layer comprises an electroplated tin layer.   
     
     
         31 . The solar cell of  claim 30 , wherein the solderable metallic layer has a thickens of 5 microns. 
     
     
         32 . The solar cell of  claim 30 , wherein the electroplated copper layer has a thickness of 20 microns. 
     
     
         33 . The solar cell of  claim 30 , wherein the copper seed layer has a thickness of 1600 Angstroms. 
     
     
         34 . The solar cell of  claim 30 , wherein the sputtered titanium-tungsten (TiW) layer has a thickness of 1000 Angstroms 
     
     
         35 . The solar cell of  claim 30 , wherein the sputtered aluminum layer comprises aluminum with having 1% silicon alloy. 
     
     
         36 . A solar cell, comprising:
 a silicon dioxide layer disposed on a silicon substrate, wherein the silicon dioxide layer includes a vias;   a metal stack disposed over a portion of the a silicon dioxide layer, wherein the vias allows for the metal stack to contact a doped region of the silicon substrate;   an electroplated copper layer disposed on the metal stack, wherein the metal stack allows for electrical connection between electroplated copper layer and the doped region of the silicon substrate; and   a solderable metallic layer disposed over the electroplated copper layer, wherein the solderable metallic layer comprises an electroplated tin layer.   
     
     
         37 . The solar cell of  claim 36 , wherein the metal stack comprises:
 a sputtered aluminum layer disposed over a portion of the a silicon dioxide layer, wherein the vias allows for the sputtered aluminum layer to contact a doped region of the silicon substrate;   a sputtered titanium-tungsten (TiW) layer disposed over the sputtered aluminum layer; and   a copper seed layer disposed over the sputtered titanium-tungsten (TiW) layer.   
     
     
         38 . The solar cell of  claim 36 , wherein the solderable metallic layer has a thickens of 5 microns. 
     
     
         39 . The solar cell of  claim 36 , wherein the copper seed layer has a thickness of 1600 Angstroms. 
     
     
         40 . The solar cell of claim  46 , wherein the electroplated copper layer has a thickness of 20 microns.