Modelling of ZMR process for fabrication of SOI

Abstract

SOI is a single crystal thin silicon film isolated by an insulating layer or a fully insulating substrate. SOI has many structural advantages and SOI material can be used in many applications. ZMR is a process for obtaining SOI structure by the recrystallization of a polycrystalline layer on an insulator using focused heat source. The focused heat source raises the local temperature of the polysilicon film above the melting point. Then the molten zone formed solidifies laterally as the heat source is scanning over the wafer. The major issues in ZMR process have been the origin of defects such as subboundaries. Heat transfer plays a critical role during ZMR. The temperature profiles of the silicon film during ZMR process have been shown to play a major role in the crystal growth. The formed crystal quality is dependent on the morphology of the solidifying liquid/solid interface and the width of molten zone. In this thesis, the two-dimensional pseudo-steady-state ZMR model has been developed in which the conduction of solid, liquid silicon and $SiO_2$, the convection in molten zone and the radiation are included. Numerical solutions from the model include flow field in the molten zone, temperature field in the full SOI structure and the location of solid/liquid interface in the silicon thin film and silicon substrate. The finite element method is used for discretization of partial differential equations of the mathematical model. The formed nonlinear algebraic equations set is linearized by the Newton-Raphson iteration scheme. The set of linear algebraic equations is solved using the frontal solver. The solutions of field variables and interface location and shapes are obtained simultaneously. We can conclude that the one-dimensional assumption which has been used by many other researchers is almost valid but nonplanar melt/solid interface shape necessiates the use of higher dimensional model. The effects of the various system parameter are investi...