Laser irradiation aluminum doping for monocrystalline silicon substrates

Abstract

Various laser processing schemes are disclosed for producing various types of hetero-junction and homo-junction solar cells. The methods include base and emitter contact opening, selective doping, metal ablation, annealing to improve passivation, and selective emitter doping via laser heating of aluminum. Also, laser processing schemes are disclosed that are suitable for selective amorphous silicon ablation and selective doping for hetero-junction solar cells. Laser ablation techniques are disclosed that leave the underlying silicon substantially undamaged. These laser processing techniques may be applied to semiconductor substrates, including crystalline silicon substrates, and further including crystalline silicon substrates which are manufactured either through wire saw wafering methods or via epitaxial deposition processes, or other cleavage techniques such as ion implantation and heating, that are either planar or textured/three-dimensional. These techniques are highly suited to thin crystalline semiconductor, including thin crystalline silicon films.

What is claimed is: 
     
         1 . A method for providing a highly aluminum doped p-type region in a silicon substrate, said method comprising:
 providing a monocrystalline silicon substrate;   applying an aluminum metal contact to a surface of said monocrystalline silicon substrate;   selectively heating said aluminum metal contact via laser irradiation, thereby causing said aluminum and a portion of said monocrystalline silicon substrate in proximity to said aluminum to reach a temperature sufficient to allow at least a portion of said silicon to dissolve in said aluminum; and   allowing said aluminum and said portion of said monocrystalline silicon substrate in proximity to said aluminum to cool, thereby forming an aluminum-rich doped silicon layer on said monocrystalline silicon substrate.   
     
     
         2 . The method of  claim 1 , wherein said monocrystalline silicon substrate comprises an epitaxial silicon substrate. 
     
     
         3 . The method of  claim 1 , wherein said temperature comprises at least approximately 577° C. for a eutectic aluminum-silicon melt formation. 
     
     
         4 . A method for providing a highly doped p-type selective emitter in a back-contact/back-junction solar cell, said method comprising:
 providing a monocrystalline silicon substrate having n-type base doping;   forming an emitter region on a surface of said monocrystalline silicon substrate, said emitter region having p-type doping;   forming an aluminum metal contact on said emitter region;   selectively heating said aluminum metal contact via laser irradiation, thereby causing said aluminum and a portion of said emitter region in proximity to said aluminum to reach a temperature sufficient to allow at least a portion of said silicon to dissolve in said aluminum; and   allowing said aluminum and said portion of said emitter region in proximity to said aluminum to cool, thereby creating a highly doped selective emitter region.   
     
     
         5 . The method of  claim 4 , wherein said monocrystalline silicon substrate is an epitaxial silicon substrate. 
     
     
         6 . The method of  claim 4 , wherein said temperature comprises at least approximately 577° C. for a eutectic aluminum-silicon melt formation. 
     
     
         7 . A method for providing a highly aluminum doped region in a front-contact solar cell, said method comprising:
 providing a monocrystalline silicon substrate having a first doping type;   forming an aluminum metal contact on a back side of said monocrystalline silicon substrate;   selectively heating said aluminum metal contact via laser irradiation, thereby causing said aluminum and a portion of said silicon in proximity to said aluminum to reach a temperature sufficient to allow at least a portion of said silicon to dissolve in said aluminum; and   allowing said aluminum and said portion of said silicon in proximity to said aluminum to cool, thereby creating a highly aluminum doped region on said back side of said monocrystalline silicon substrate.   
     
     
         8 . The method of  claim 7 , wherein said monocrystalline silicon substrate is an epitaxial silicon substrate. 
     
     
         9 . The method of  claim 7 , wherein said temperature comprises at least approximately 577° C. for a eutectic aluminum-silicon melt formation. 
     
     
         10 . The method of  claim 7 , wherein:
 said first doping type comprises n-type doping; and further wherein   said portion of said silicon in proximity to said aluminum comprises a doped emitter region; and further wherein   said highly aluminum doped region comprises a selective emitter region.   
     
     
         11 . The method of  claim 7 , wherein:
 said first doping type comprises p-type doping; and further wherein   said highly aluminum doped region comprises a back-surface field region.   
     
     
         12 . The method of  claim 1 , wherein said laser comprises either a continuous wave laser or a pulsed laser having pulse length greater than approximately 10 nanoseconds. 
     
     
         13 . The method of  claim 4 , wherein said laser comprises either a continuous wave laser or a pulsed laser having pulse length greater than approximately 10 nanoseconds. 
     
     
         14 . The method of  claim 7 , wherein said laser comprises either a continuous wave laser or a pulsed laser having pulse length greater than approximately 10 nanoseconds. 
     
     
         15 . The method of  claim 1 , wherein said laser has a wavelength of approximately 10.6 micrometers or less. 
     
     
         16 . The method of  claim 4 , wherein said laser has a wavelength of approximately 10.6 micrometers or less. 
     
     
         17 . The method of  claim 7 , wherein said laser has a wavelength of approximately 10.6 micrometers or less. 
     
     
         18 . The method of  claim 4 , wherein said epitaxial thin film solar cell has a thickness in the range of approximately 10 to 100 microns. 
     
     
         19 . The method of  claim 18 , wherein a front surface of said epitaxial thin film comprises three-dimensional pyramids or prisms formed via a textured template liftoff process. 
     
     
         20 . The method of  claim 18 , wherein said epitaxial thin film comprises a substantially planar epitaxial film formed via an epitaxial silicon liftoff process. 
     
     
         21 . The method of  claim 7 , wherein said epitaxial thin film solar cell has a thickness in the range of approximately 10 to 100 microns. 
     
     
         22 . The method of  claim 21 , wherein a front surface of said epitaxial thin film comprises three-dimensional pyramids or prisms formed via a textured template liftoff process. 
     
     
         23 . The method of  claim 21 , wherein said epitaxial thin film comprises a substantially planar epitaxial film formed via an epitaxial silicon liftoff process.