The influence of thermal effects and dielectric films on the electronic quality of p+-doped silicon processed by nanosecond laser

Abstract

Laser doping of silicon is a complex process involving thermal effects and interactions between different materials far from equilibrium and over a short period. In this paper, diffused samples capped with different dielectric films (including bare surfaces) are processed using laser pulses of 20-400 ns duration and characterized by photoluminescence (PL) imaging to study the degradation of the electronic properties of the processed regions. This way, without the interference of a dopant precursor, the thermal and dielectric effects are separately investigated. It is found that the thermal effects (melting and recrystallization of the silicon) do not lead to significant damage and additional recombination, provided no severe silicon evaporation occurs. However, when a dielectric film is present, a considerable increase in recombination is observed, irrespective of laser parameters, indicating the formation of additional defects. The magnitude of the increase in recombination varies substantially, depending on the dielectric used. Repeated pulses appear to repair silicon damage introduced by the first pulse or pulses for long pulse durations but result in a slight degradation for short pulse durations. Combining the PL results and four-point probe measurement of laser-doped samples, it is demonstrated that both high dopant incorporation (sufficient silicon melting) and low recombination can, in principle, be achieved, particularly when samples are processed using long pulse durations and small pulse distances. Show more