Heat transfer simulations for pulsed laser annealing of silicon thin film

Abstract

Devices like solar cells and displays require high quality polycrystalline-Si (pc-Si) thin films, which are grown by high temperature crystallization of thin films of amorphous silicon (a-Si) on expensive substrates. Low cost substrates (glass and plastic) help to reduce the cost, but they melt at low temperatures, hence not suitable to grow high quality crystalline films. Recently, pulsed laser annealing appears to be an effective way for crystallization of thin films on low cost substrates with high precision. Optimization of crystallinity of thin films for desired optoelectronic property requires optimization of the laser source, which eventually requires understanding of heat transfer theory at the micro/nano-scale regime. This paper presents heat transfer simulation of very thin silicon (Si) film using COMSOL Multiphysics. The results show that higher power density can melt the film at shorter times compared to lower power density. It is also observed that the top surface of the film can be heated to a much higher temperature than the bottom surface (the interface with the substrate). The annealing depth and temperature at any depth can be precisely controlled by optimizing heat source power density, pulse width and exposure time. Therefore, it is possible to crystallize Si films by controlled melting without melting the substrate.