Patent ID: 7951640

Claim:
A method for preparing substrates using metallurgical grade silicon, comprising: melting metallurgical grade silicon in a furnace; solidifying the melted metallurgical grade silicon of 99.9% to 99.999% purity into an ingot; slicing the ingot to obtain a plurality of wafers; cleaning each wafer; depositing aluminum layer on backside of each wafer; depositing a layer of hydrogenated silicon nitride on front surface of each wafer; annealing the wafers at elevated temperature wherein the aluminum layer is maintained on the backside to confine hydrogen during the annealing; removing the hydrogenated silicon nitride from the front surface of each wafer after the annealing; depositing a layer of SiO2 or Si on the front surface of the wafers; etching the deposited layer such that after etching the deposited layer partially remains at grain boundaries of the metallurgical grade silicon on the front surface of the wafers; depositing a layer of intrinsic amorphous silicon directly on the front surface of the wafer and depositing an amorphous n-doped layer over the intrinsic amorphous silicon layer.