Excimer laser induced doping of phosphorus into silicon

Doping of single-crystal silicon in PF₅ atmosphere by means of an ArF (193 nm) excimer laser has been investigated as a function of laser fluence, number of pulses, and PF₅ gas pressure. We find that phosphorus atoms are only produced by pyrolysis of the PF₅ molecules but not by photolysis. The doping experiments were performed in PF₅ ambients or using an adsorbed PF₅ layer. The results indicate that the incorporation process is external rate limited for doping in PF₅ ambients and mainly diffusion limited when using the adsorbed layer. Moreover, the evolution of the incorporated dose with the PF₅ pressure shows that at low pressures (<0.5 Torr), the phosphorus atoms are supplied by a chemisorbed PF₅ layer formed at the silicon surface, whereas at high pressures the main dopant source appears to be a layer of loosely bound PF ₅ molecules which has been physisorbed at the surface. It is also found that the surface quality is affected neither by the successive irradiation or by the heavy doping.