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.

We claim: 
     
         1 . A method for forming a thin film material comprising:
 providing a first conduit;   providing a second conduit;   supplying a first deposition stream to said first conduit, said first deposition stream including one or more first deposition species;   supplying a second deposition stream to said second conduit, said second deposition stream including one or more second deposition species, said second deposition stream including at least one species not present in said first deposition stream;   providing a field of microwave radiation;   transferring first energy from said field to said first deposition stream through the boundary of said first conduit, said first energy exciting said first deposition stream, said excited first deposition stream including one or more excited first deposition species; and   transferring second energy from said field to said second deposition stream through the boundary of said second conduit, said second energy exciting said second deposition stream, said excited second deposition stream including one or more excited second deposition species.   
     
     
         2 . The method of  claim 1 , wherein said first energy and said second energy are transferred simultaneously. 
     
     
         3 . The method of  claim 1 , wherein said first conduit and said second conduit are housed within a common microwave cavity, said microwave cavity confining said field of microwave radiation. 
     
     
         4 . The method of  claim 3 , wherein said first deposition stream and said second deposition stream remain unmixed within said cavity. 
     
     
         5 . The method of  claim 1 , wherein said first deposition stream comprises an ion or radical when supplied to said first conduit. 
     
     
         6 . The method of  claim 5 , wherein said second deposition stream comprises an ion or radical when supplied to said second conduit. 
     
     
         7 . The method of  claim 1 , wherein said first deposition stream comprises silicon. 
     
     
         8 . The method of  claim 7 , wherein said first deposition stream further comprises fluorine. 
     
     
         9 . The method of  claim 8 , wherein said one or more deposition species includes a fluorinated form of silane. 
     
     
         10 . The method of  claim 8 , wherein said first deposition stream further comprises boron, phosphorous, or sulfur. 
     
     
         11 . The method of  claim 7 , wherein said first deposition stream lacks hydrogen. 
     
     
         12 . The method of  claim 7 , wherein said second deposition stream comprises hydrogen or fluorine. 
     
     
         13 . The method of  claim 7 , wherein said second deposition stream comprises germanium. 
     
     
         14 . The method of  claim 13 , wherein said second deposition stream further comprises fluorine. 
     
     
         15 . The method of  claim 7 , wherein said second deposition stream comprises boron, phosphorous, or sulfur. 
     
     
         16 . The method of  claim 1 , wherein said first energy forms a plasma from said first deposition stream. 
     
     
         17 . The method of  claim 16 , wherein said second energy forms a plasma from said second deposition stream. 
     
     
         18 . The method of  claim 1 , wherein said excited first deposition stream does not deposit a coating on the boundary of said first conduit. 
     
     
         19 . The method of  claim 18 , wherein said excited second deposition stream does not deposit a coating on the boundary of said second conduit. 
     
     
         20 . The method of  claim 1 , further comprising ejecting said excited first deposition stream from said first conduit and ejecting said excited second deposition stream from said second conduit. 
     
     
         21 . The method of  claim 20 , further comprising mixing said ejected excited first deposition stream and said ejected excited second deposition stream. 
     
     
         22 . The method of  claim 20 , further comprising forming a first thin film material from said ejected excited first deposition stream and said ejected excited second deposition stream. 
     
     
         23 . The method of  claim 22 , wherein said first thin film material is formed on a moving substrate. 
     
     
         24 . The method of  claim 22 , wherein said first thin film material includes amorphous regions. 
     
     
         25 . The method of  claim 24 , wherein said amorphous regions comprise silicon or germanium. 
     
     
         26 . The method of  claim 25 , wherein said amorphous regions further comprise hydrogen or fluorine. 
     
     
         27 . The method of  claim 22 , wherein said first thin film material includes nanocrystalline or microcrystalline regions. 
     
     
         28 . The method of  claim 27 , wherein said nanocrystalline or microcrystalline regions comprise silicon or germanium. 
     
     
         29 . The method of  claim 28 , wherein said nanocrystalline or microcrystalline regions further comprise hydrogen or fluorine. 
     
     
         30 . The method of  claim 22 , wherein said first thin film material is an intrinsic semiconductor. 
     
     
         31 . The method of  claim 22 , wherein said first thin film material is an n-type or p-type semiconductor. 
     
     
         32 . The method of  claim 22 , further comprising forming a second thin film material over said first thin film material. 
     
     
         33 . The method of  claim 20 , further comprising energizing said ejected excited first deposition stream and said ejected excited second deposition stream. 
     
     
         34 . The method of  claim 33 , wherein energizing includes coupling electromagnetic energy to said ejected excited first deposition stream and said ejected excited second deposition stream.