Epitaxial growth of heavily boron-doped Si by Al(B)-induced crystallisation at low temperature for back surface field manufacturing

Abstract

P-type polycrystalline Si film on a foreign substrate can be fabricated at temperatures lower than 773 K by an aluminium-induced crystallisation process. However, the ultimate carrier concentration of the Si film is limited to approximately 3 × 10¹⁸ cm⁻³ because of the low solid solubility of Al in Si at temperatures below 773 K. In this study, a process called B-AIC is developed in which boron is co-doped with Al to increase the carrier concentration in Si films to ∼10¹⁹ cm⁻³ at temperatures as low as 673 K. The carrier concentration can be tuned by the initial thickness of a-Si layer in the B-AIC process. Beside the fabrication of polycrystalline Si film on glass, the epitaxial growth of this heavily doped p⁺⁺-Si film can also be realized on a single crystalline Si wafer via a solid phase epitaxy mechanism.