On the photon-enhanced diffusion of phosphorus in silicon wafers during rapid isothermal processing
For the diffusion of phosphorus in silicon it has been reported that rapid thermal processing (RTP) leads to an enhanced diffusion compared to conventional processing in quartz tubes (CFP). This enhancement has been attributed by several authors to photoelectrical or photochemical effects induced by visible and/or UV photons from tungsten halogen lamps (THL) used in RTP. In this work, we attempt to verify the proposed photon-enhanced diffusion of P in Si. An extensive study has been carried out using a special RTP reactor equipped with tungsten halogen lamps and additional excimer UV lamps. Various P sources such as spin-on dopants (SOD), APCVD Pdoped SiO2 and POCl3 pre-diffused wafers have been tested. The experimental results show no evidence of photonenhanced diffusion. For all dopant sources, additional irradiation of the dopant covered surface with high-energy photons causes neither a significant difference in the sheet resistance nor in the P profile compared to diffusion without photon irradiation. An important output of these experiments is that the implementation of excimer UV lamps in future RTP furnaces designed for PV applications is not necessary.