Rapid Thermal Oxidation of Heavily Doped Silicon for Advanced Solar Cell Processing

Abstract

AbstractCrucial steps in solar cell processing such as emitter diffusion and surface oxide passivation have been carried out by rapid thermal processing (RTP). Rapid thermal diffusion (RTD) of boron into silicon from APCVD borosilicates has been studied. Rapid thermal oxidation (RTO) of the heavily B-doped surfaces of these shallow junctions (0.2 μm) has been studied in view of applicability of this technique in solar cell processing. These shallow diffusions have excellent lateral uniformity over large areas and have high surface concentrations depending on the APCVD deposition conditions and on RTP conditions. The surface passivating oxides resulting from the RTO are exceptionally thick in case of heavy boron diffused surfaces. RTO does not cause considerable drive-in of the diffused junction profiles. In the contrary, the thick RTO oxides considerably reduce the surface concentration, thereby reducing the heavy doping effects in the junctions, making them more suitable emitters for devices such as solar cells. p+nn+ solar cells have been fabricated on n-type CZ silicon wafers by RTD of boron followed by RTO. The cells result in conversion efficiencies as high as 16.2% The passivation effect of RTO oxides have been investigated by analysing RTO MOS capacitors and are compared to conventional furnace oxides.