Metal contact structure for solar cell and method of manufacture
View Patent ↗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 method of fabricating a solar cell, the method comprising:
providing a wafer having a front side enabling entry of light into the wafer and a back side opposite the front side;
forming a silicon oxide layer on a surface on the back side of the wafer such that a plurality of openings in the silicon oxide layer expose doped regions of the solar cell;
forming a metallized seed layer on the silicon oxide layer wherein the metallized seed layer also extends through the openings to contact the doped regions,
the metallized seed layer including an infrared reflecting layer comprising aluminum and operating as an infrared reflector, wherein said metallized seed layer includes a plating seed layer, and wherein the metallized seed layer includes a diffusion barrier layer over the infrared relecting layer, the plating seed layer being over the diffusion barrier layer;
forming a plating mask over the plating seed layer;
plating an electrically conductive layer over the plating seed layer;
removing the plating mask: and
selectively etching the metallized seed layer that was under the plating mask.
2. The method as defined by claim 1 , wherein the diffusion barrier layer comprises titanium tungsten.
3. The method as defined by claim 2 , wherein the plating seed layer comprises copper.
4. The method as defined by claim 1 wherein forming the silicon oxide layer includes etching holes through the silicon oxide layer to permit the metallized seed layer to contact the doped regions.
5. The method as defined by claim 1 wherein forming the plating mask over the plating seed layer includes defining contacts and a grid pattern.
6. The method as defined by claim 1 , and further including, after plating the electrically conductive layer over the plating seed layer applying a cap layer over the electrically conductive layer, thereby protecting the electrically conductive layer from an etchant during the etching of the seed metal layer under the plating mask.
7. The method as defined by claim 6 wherein the cap layer comprises plated tin.
8. The method as defined by claim 6 wherein the cap layer comprises an electroless plated metal.
9. The method as defined by claim 4 wherein forming the silicon oxide layer includes applying a chemical paste on the silicon oxide layer where holes through the silicon oxide are to be etched.
10. The method as defined by claim 9 wherein the chemical paste is applied by printing.