Method of fabricating an emitter region of a solar cell

Abstract

Methods of fabricating emitter regions of solar cells are described. Methods of forming layers on substrates of solar cells, and the resulting solar cells, are also described.

1 . A method of fabricating an emitter region of a solar cell, the method comprising:
 forming, in a furnace, a tunnel oxide layer on a surface of a substrate; and, without removing the substrate from the furnace,   forming an amorphous layer on the tunnel oxide layer;   doping the amorphous layer to provide a first region comprising N-type dopants and a second region comprising P-type dopants; and, subsequently,   heating the amorphous layer to provide a polycrystalline layer comprising an N-type-doped region and a P-type-doped region.   
     
     
         2 . The method of  claim 1 , wherein the substrate comprises silicon, the tunnel oxide layer comprises silicon dioxide, the amorphous layer comprises silicon, the N-type dopants comprise phosphorous, and the P-type dopants comprise boron. 
     
     
         3 . The method of  claim 1 , wherein forming the tunnel oxide layer comprises heating the substrate in the furnace at a temperature of approximately 900 degrees Celsius. 
     
     
         4 . The method of  claim 3 , wherein heating the substrate in the furnace at the temperature of approximately 900 degrees Celsius further comprises heating at a pressure of approximately 500 mTorr for approximately 3 minutes in an atmosphere of oxygen to provide the tunnel oxide layer having a thickness of approximately 1.5 nanometers. 
     
     
         5 . The method of  claim 1 , wherein forming the tunnel oxide layer comprises heating the substrate in the furnace at a temperature less than 600 degrees Celsius. 
     
     
         6 . The method of  claim 5 , wherein heating the substrate in the furnace at the temperature of less than 600 degrees Celsius further comprises heating at a temperature of approximately 565 degrees Celsius, at a pressure of approximately 300 Torr, for approximately 60 minutes in an atmosphere of oxygen to provide the tunnel oxide layer having a thickness of approximately 1.5 nanometers. 
     
     
         7 . The method of  claim 1 , wherein forming the amorphous layer comprises depositing the amorphous layer in the furnace at a temperature less than 575 degrees Celsius. 
     
     
         8 . The method of  claim 7 , wherein depositing the amorphous layer in the furnace at the temperature less than 575 degrees Celsius further comprises heating at a temperature of approximately 565 degrees Celsius at a pressure of approximately 350 mTorr in an atmosphere of silane (SiH 4 ) to provide the amorphous layer having a thickness approximately in the range of 200-300 nanometers. 
     
     
         9 . The method of  claim 1 , wherein both the tunnel oxide layer and the amorphous layer are formed at a temperature of approximately 565 degrees Celsius, and wherein heating the amorphous layer to provide the polycrystalline layer comprises heating at a temperature of approximately 980 degrees Celsius. 
     
     
         10 . A method of forming layers on a substrate of a solar cell, the method comprising:
 loading, into a furnace, a wafer carrier with a plurality of wafers, the wafer carrier having one or more wafer receiving slots loaded with two wafers positioned back-to-back;   forming, in the furnace, a tunnel oxide layer on all surfaces of each of the plurality of wafers; and, without removing the plurality of wafers from the furnace,   forming an amorphous layer on the tunnel oxide layer, the amorphous layer formed on all portions of the tunnel oxide layer except on the portions in contact between wafers positioned back-to-back.   
     
     
         11 . The method of  claim 10 , wherein for the wafers positioned back-to-back, a ring pattern of the amorphous layer is formed on the back of each wafer. 
     
     
         12 . The method of  claim 11 , further comprising:
 subsequent to forming the amorphous layer, applying a cleaning solution to the back of each wafer, the cleaning solution comprising an oxidizing agent; and, subsequently,   applying a texturizing solution to the back of each wafer, the texturizing solution comprising a hydroxide.   
     
     
         13 . The method of  claim 12 , where in the oxidizing agent is selected from the group consisting of ozone and hydrogen peroxide (H 2 O 2 ), and wherein the hydroxide is selected from the group consisting of potassium hydroxide (KOH) and sodium hydroxide (NaOH). 
     
     
         14 . The method of  claim 10 , wherein each of the plurality of wafers comprises silicon, the tunnel oxide layer comprises silicon dioxide, and the amorphous layer comprises silicon. 
     
     
         15 . The method of  claim 10 , wherein forming the tunnel oxide layer comprises heating each of the plurality of wafers in the furnace at a temperature of approximately 900 degrees Celsius. 
     
     
         16 . The method of  claim 15 , wherein heating each of the plurality of wafers in the furnace at the temperature of approximately 900 degrees Celsius further comprises heating at a pressure of approximately 500 mTorr for approximately 3 minutes in an atmosphere of oxygen to provide the tunnel oxide layer having a thickness of approximately 1.5 nanometers. 
     
     
         17 . The method of  claim 10 , wherein forming the tunnel oxide layer comprises heating each of the plurality of wafers in the furnace at a temperature less than 600 degrees Celsius. 
     
     
         18 . The method of  claim 17 , wherein heating each of the plurality of wafers in the furnace at the temperature of less than 600 degrees Celsius further comprises heating at a temperature of approximately 565 degrees Celsius, at a pressure of approximately 300 Torr, for approximately 60 minutes in an atmosphere of oxygen to provide the tunnel oxide layer having a thickness of approximately 1.5 nanometers. 
     
     
         19 . The method of  claim 10 , wherein forming the amorphous layer comprises depositing the amorphous layer in the furnace at a temperature less than 575 degrees Celsius. 
     
     
         20 . The method of  claim 19 , wherein depositing the amorphous layer in the furnace at the temperature less than 575 degrees Celsius further comprises heating at a temperature of approximately 565 degrees Celsius at a pressure of approximately 350 mTorr in an atmosphere of silane (SiH 4 ) to provide the amorphous layer having a thickness approximately in the range of 200-300 nanometers. 
     
     
         21 . A substrate of a solar cell, comprising:
 a tunnel oxide layer comprising silicon dioxide disposed on all surfaces of a silicon wafer; and   a polycrystalline layer disposed on the tunnel oxide layer, the polycrystalline layer disposed on all portions of the tunnel oxide layer except on a back side of the silicon wafer which comprises a ring pattern of the polycrystalline layer.   
     
     
         22 . A substrate of a solar cell, comprising:
 a tunnel oxide layer comprising silicon dioxide disposed on all surfaces of a silicon wafer; and   an amorphous layer disposed on the tunnel oxide layer, the amorphous layer disposed on all portions of the tunnel oxide layer except on a back side of the silicon wafer which comprises a ring pattern of the amorphous layer.