Laser-matter interactions

Abstract Due to the ever-increasing shrinking of semiconductor technology nodes, phenomena such as parasitic and transient enhanced diffusion preclude the use of traditional annealing methods. To face these issues novel annealing techniques with steep temperature gradients are coming into the forefront of semiconductor processing. One of these is laser annealing which presents a series of attractive characteristics such as high power density, localized heating as well as the ability to tune the effective heating depth. This chapter presents basic aspects of laser-matter interaction from the point of view of the main group IV semiconductors, silicon and germanium, and deals with the radiation absorption mechanisms and processes using deep infrared wavelengths as a use case of particular industrial relevance. The effect of heavy extrinsic doping, typical in semiconductor processing, on absorption coefficient is also analyzed. The predominant effect of the interaction between semiconductor and laser radiation is the heating of the former and as such heating mechanisms and heat diffusion are then discussed. The generalized heat equation for a time-modulated beam as well as key parameters for silicon and germanium are also presented. Finally this chapter discusses diffusion and activation kinetics while dealing with the differences between different wavelengths (infrared to ultraviolet) and timescales (ms–ns). Indicative simulation results are also presented and compared to actual experimental data that exhibit minimal diffusion with high degrees of dopant activation close to the maximum theoretical solid solubility limits.