Influence of preannealing on residual stresses in boron-doped LPCVD polysilicon film

Abstract

An investigation of effects of variables of LPCVD process and subsequent processes on residual stresses in highly doped polysilicon film is carried out. A pre-annealing process for as- deposited polysilicon film was introduced before boron doping in order to be able to change magnitude of residual stress in a larger range. The influence of the pre-annealing on the residual stresses in boron doped polysilicon film was studied. The test results show that boron doping process induces significant residual stress only in LPCVD polysilicon films which are deposited at lower process temperature. There will not be significant doping stress in the polysilicon films if the deposition temperature is higher than 620 degrees C or pre- annealing temperature before the doping is higher than 1000 degrees C. The larger change range of the film stress can be obtained by to change pre-annealing temperature before doping. This method will be useful in the stress control of a multi-layer diaphragm structure.