Plasma Deposition of Amorphous Semiconductors at Microwave Frequencies

Abstract

Apparatus and method for plasma deposition of thin film photovoltaic materials at microwave frequencies. The apparatus inhibits deposition on windows or other microwave transmission elements that couple microwave energy to deposition species. The apparatus includes a microwave applicator with conduits passing therethrough that carry deposition species. The applicator transfers microwave energy to the deposition species to transform them to a reactive state conducive to formation of a thin film material. The conduits physically isolate deposition species that would react to form a thin film material at the point of microwave power transfer. The deposition species are separately energized and swept away from the point of power transfer to prevent thin film deposition. The invention allows for the ultrafast formation of silicon-containing amorphous semiconductors that exhibit high mobility, low porosity, little or no Staebler-Wronski degradation, and low defect concentration.

1 . A deposition process comprising:
 providing a field of microwave radiation, said field having boundaries that define a first region;   delivering a first precursor to said first region, said first precursor comprising silicon;   transferring energy from said microwave radiation to said first precursor in said first region, said microwave radiation exciting said first precursor to form an energized deposition medium;   directing said energized deposition medium away from said first region, said energized deposition medium exiting said first region and progressing toward a substrate;   directing a second precursor to said substrate, said second precursor not passing through said first region, said second precursor combining with said energized deposition medium to form a thin film material on said substrate.   
     
     
         2 . The process of  claim 1 , wherein said first precursor further comprises fluorine. 
     
     
         3 . The process of  claim 1 , wherein said first precursor comprises SiF 4 . 
     
     
         4 . The process of  claim 1 , wherein said first precursor lacks hydrogen. 
     
     
         5 . The process of  claim 1 , wherein said energized deposition medium is ionized. 
     
     
         6 . The process of  claim 1 , wherein said energized deposition medium is in a first state remote from said substrate and a second state adjacent said substrate. 
     
     
         7 . The process of  claim 6 , wherein said first state comprises a plasma. 
     
     
         8 . The process of  claim 7 , wherein said second state lacks a plasma. 
     
     
         9 . The process of  claim 1 , wherein said substrate is electrically biased. 
     
     
         10 . The process of  claim 9 , wherein said bias is an AC bias. 
     
     
         11 . The process of  claim 1 , wherein the temperature of said substrate is between 300° C. and 500° C. 
     
     
         12 . The process of  claim 1 , wherein the temperature of said substrate is between 325° C. and 475° C. 
     
     
         13 . The process of  claim 1 , wherein the temperature of said substrate is between 350° C. and 450° C. 
     
     
         14 . The process of  claim 1 , wherein said second precursor comprises silicon. 
     
     
         15 . The process of  claim 14 , wherein said second precursor further comprises hydrogen. 
     
     
         16 . The process of  claim 15 , wherein said second precursor comprises silane. 
     
     
         17 . The process of  claim 15 , wherein said second precursor comprises disilane. 
     
     
         18 . The process of  claim 15 , wherein the molar flow ratio of said second precursor to said first precursor is between 0.3 and 2.0. 
     
     
         19 . The process of  claim 15 , wherein the molar flow ratio of said second precursor to said first precursor is between 0.5 and 1.75. 
     
     
         20 . The process of  claim 15 , wherein the molar flow ratio of said second precursor to said first precursor is between 0.75 and 1.5. 
     
     
         21 . The process of  claim 15 , wherein the molar flow ratio of said second precursor to said first precursor is between 0.6 and 4.0. 
     
     
         22 . The process of  claim 15 , wherein the molar flow ratio of said second precursor to said first precursor is between 1.0 and 3.5. 
     
     
         23 . The process of  claim 15 , wherein the molar flow ratio of said second precursor to said first precursor is between 1.5 and 3. 
     
     
         24 . The process of  claim 1 , wherein said thin film material comprises amorphous silicon. 
     
     
         25 . The process of  claim 24 , wherein said thin film material further comprises nanocrystalline, microcrystalline, or polycrystalline silicon. 
     
     
         26 . The process of  claim 24 , wherein said thin film material is formed at a deposition rate of at least 20 Å/s. 
     
     
         27 . The process of  claim 24 , wherein said thin film material is formed at a deposition rate of at least 50 Å/s. 
     
     
         28 . The process of  claim 24 , wherein said thin film material is formed at a deposition rate of at least 100 Å/s. 
     
     
         29 . The process of  claim 24 , wherein said thin film material is formed at a deposition rate of at least 150 Å/s. 
     
     
         30 . The process of  claim 1 , wherein said thin film material exhibits essentially no Staebler-Wronski degradation upon exposure to an AM-1 solar spectrum for at least 14 hours. 
     
     
         31 . The process of  claim 1 , wherein said thin film material exhibits essentially no Staebler-Wronski degradation upon exposure to an AM-1 solar spectrum for at least 26 hours. 
     
     
         32 . The process of  claim 1 , wherein said thin film material exhibits essentially no Staebler-Wronski degradation upon exposure to an AM-1 solar spectrum for at least 85 hours. 
     
     
         33 . The process of  claim 30 , wherein said thin film material is formed at a deposition rate of at least 20 Å/s. 
     
     
         34 . The process of  claim 30 , wherein said thin film material is formed at a deposition rate of at least 50 Å/s. 
     
     
         35 . The process of  claim 30 , wherein said thin film material is formed at a deposition rate of at least 100 Å/s.