Solar cell emitter region fabrication using substrate-level ion implantation

Abstract

Methods of fabricating solar cell emitter regions using substrate-level ion implantation, and resulting solar cells, are described. In an example, a method of fabricating a solar cell involves forming a lightly doped region in a semiconductor substrate by ion implantation, the lightly doped region of a first conductivity type of a first concentration. The method also involves forming a first plurality of dopant regions of the first conductivity type of a second, higher, concentration by ion implantation, the first plurality of dopant regions overlapping with a first portion of the lightly doped region. The method also involves forming a second plurality of dopant regions by ion implantation, the second plurality of dopant regions having a second conductivity type of a concentration higher than the first concentration, and the second plurality of dopant regions overlapping with a second portion of the lightly doped region and alternating with but not overlapping the first plurality of dopant regions.

1 . A method of fabricating a solar cell, the method comprising:
 forming a lightly doped region in a semiconductor substrate by ion implantation, the lightly doped region of a first conductivity type of a first concentration;   forming a first plurality of dopant regions of the first conductivity type of a second, higher, concentration by ion implantation, the first plurality of dopant regions overlapping with a first portion of the lightly doped region; and   forming a second plurality of dopant regions by ion implantation, the second plurality of dopant regions having a second conductivity type of a concentration higher than the first concentration, and the second plurality of dopant regions overlapping with a second portion of the lightly doped region and alternating with but not overlapping the first plurality of dopant regions.   
     
     
         2 . The method of  claim 1 , wherein forming the lightly doped region and forming the first plurality of dopant regions comprises implanting dopants during a single pass under a stationary mask in an implanter. 
     
     
         3 . The method of  claim 2 , wherein implanting dopants during the single pass under the stationary mask comprises using a mask having a slit pattern for forming the first plurality of dopant regions and a full opening for forming the lightly doped region. 
     
     
         4 . The method of  claim 1 , further comprising:
 thermally annealing the semiconductor substrate subsequent to the ion implantation.   
     
     
         5 . The method of  claim 4 , wherein the lightly doped region, the first plurality of dopant regions, and the second plurality of dopant regions are formed in a back surface of the semiconductor substrate, the back surface opposite a light-receiving surface of the semiconductor substrate, the method further comprising:
 forming a thin tunneling dielectric layer on the light-receiving surface of the semiconductor substrate;   forming a doped amorphous silicon layer on the thin tunneling dielectric layer on the light-receiving surface of the semiconductor substrate prior to the thermally annealing the semiconductor substrate; and   crystallizing the doped amorphous silicon layer during the thermally annealing the semiconductor substrate to form a doped polycrystalline silicon layer on the light-receiving surface of the semiconductor substrate.   
     
     
         6 . The method of  claim 5 , wherein the thermally annealing the semiconductor substrate comprises thermally annealing the semiconductor in an atmosphere substantially comprising nitrogen (N 2 ). 
     
     
         7 . The method of  claim 1 , wherein forming the lightly doped region comprises forming a blanket lightly doped region in the semiconductor substrate. 
     
     
         8 . The method of  claim 1 , wherein forming the lightly doped region comprises forming patterned lightly doped regions in the semiconductor substrate. 
     
     
         9 . The method of  claim 1 , further comprising:
 forming a first plurality of contacts electrically connected to the first plurality of dopant regions; and   forming a second plurality of contacts electrically connected to the second plurality of dopant regions.   
     
     
         10 . A solar cell fabricated according to the method of  claim 1 . 
     
     
         11 . A solar cell, comprising:
 a semiconductor substrate having a light-receiving surface and a back surface opposite the light-receiving surface;   a blanket dopant region disposed in the semiconductor substrate at the back surface of the semiconductor substrate, the blanket dopant region of a first conductivity type of a first concentration;   a first plurality of dopant regions disposed in the semiconductor substrate and overlapping with the blanket dopant region, the first plurality of dopant regions of the first conductivity type of a second, higher, concentration;   a second plurality of dopant regions disposed in the semiconductor substrate and overlapping with the blanket dopant region but alternating with and not overlapping the first plurality of dopant regions, the second plurality of dopant regions of a second conductivity type of a concentration higher than the first concentration;   a first plurality of contacts electrically connected to the first plurality of dopant regions at the back surface of the solar cell; and   a second plurality of contacts electrically connected to the second plurality of dopant regions at the back surface of the solar cell.   
     
     
         12 . The solar cell of  claim 11 , wherein the first conductivity type is P-type and the second conductivity type is N-type. 
     
     
         13 . The solar cell of  claim 12 , wherein the semiconductor substrate is a monocrystalline semiconductor substrate, wherein the first plurality of dopant regions comprises boron dopants, and wherein the second plurality of dopant regions comprises phosphorous dopants. 
     
     
         14 . The solar cell of  claim 11 , wherein the first conductivity type is N-type and the second conductivity type is P-type. 
     
     
         15 . The solar cell of  claim 14 , wherein the semiconductor substrate is a monocrystalline semiconductor substrate, wherein the first plurality of dopant regions comprises phosphorous dopants, and wherein the second plurality of dopant regions comprises boron dopants. 
     
     
         16 . The solar cell of  claim 11 , wherein the second concentration of the first conductivity type is approximately 1E19 atoms/cm 3 , the concentration of the second conductivity type is approximately 1E19 atoms/cm 3 , and the first concentration of the first conductivity type is approximately 1E18 atoms/cm 3 . 
     
     
         17 . A solar cell, comprising:
 a semiconductor substrate having a light-receiving surface and a back surface opposite the light-receiving surface;   a patterned dopant region disposed in the semiconductor substrate at the back surface of the semiconductor substrate, the patterned dopant region of a first conductivity type of a first concentration;   a first plurality of dopant regions disposed in the semiconductor substrate and contacting at least a portion of the patterned dopant region, the first plurality of dopant regions of the first conductivity type of a second, higher, concentration;   a second plurality of dopant regions disposed in the semiconductor substrate and contacting at least a portion of the patterned dopant region, the second plurality of dopant regions alternating with and not overlapping the first plurality of dopant regions, the second plurality of dopant regions of a second conductivity type of a concentration higher than the first concentration;   a first plurality of contacts electrically connected to the first plurality of dopant regions at the back surface of the solar cell; and   a second plurality of contacts electrically connected to the second plurality of dopant regions at the back surface of the solar cell.   
     
     
         18 . The solar cell of  claim 17 , wherein the first conductivity type is P-type and the second conductivity type is N-type. 
     
     
         19 . The solar cell of  claim 18 , wherein the semiconductor substrate is a monocrystalline semiconductor substrate, wherein the first plurality of dopant regions comprises boron dopants, and wherein the second plurality of dopant regions comprises phosphorous dopants. 
     
     
         20 . The solar cell of  claim 17 , wherein the first conductivity type is N-type and the second conductivity type is P-type. 
     
     
         21 .- 22 . (canceled)