An analysis of the process of recrystallization of silicon thin films with either a scanning laser or strip heater

Abstract

An analysis of the temperature, stress distribution, and crystal growth was made to model the process of recrystallization of silicon thin films with either a scanning laser or strip heater. The temperature distribution of a wafer with one or more thin film layers was calculated using both Green’s function and Fourier series methods. With increasing velocity, the temperature profile becomes asymmetric and the maximum temperature decreases. Heat flow is influenced by the applied heat profile, the layer thicknesses, thermal properties, heat transfer coefficient between the wafer and substrate, and the velocity of the heat zone. If the heat zone is wider than the wafer thickness the temperature profile may be approximated using a one-dimensional model. Thermal stresses are generated by either a nonuniform temperature or differential thermal expansion between layers. Temperature differences along the film that are greater than 10 °C may plastically deform the silicon film. To crystallize cell-free single-crystal thin films a critical ratio of the thermal gradient to the solidification velocity must be exceeded. The criterion for the crystallization of defect-free material is derived in terms of the solidification rate, heat transfer, and stability of the planar solid-liquid interface during crystal growth. It is predicted that defect-free silicon films are possible at rates below 0.005 cm/sec from a comparison with conventional growth of silicon single crystals.