Residual-stress relaxation in polysilicon thin films by high-temperature rapid thermal annealing

Rapid thermal annealing reduces stress in a very short time, compared to regular furnace annealing, and can be an effective method for relaxing residual stress in polysilicon thin films. In this work, the effects of regular furnace and high-temperature rapid thermal annealing (RTA) on the residual stress of LPCVD polysilicon thin films have been investigated. The as-deposited 0.5 μm thick polysilicon films have an initial compressive stress of about 340 MPa, and the residual stress is relaxed quickly after a few cycles of RTA at higher temperatures. The stress dependence on annealing time at temperatures of 900-1150°C has been analysed. Using X-ray diffraction (XRD), micro-Raman spectroscopy and transmission electron microscopy (TEM), we have studied the changes in the microstructure of the thin films induced by the RTA during the stress relaxation. Furthermore, variations in the composition of the surface layer due to annealing have been characterized by X-ray photoelectron spectroscopy (XPS).