The Stress and Microstructure analysis of Polycrystalline Silicon Films Deposited by LPCVD

Abstract

ABSTRACTAmorphous (a-Si) and polycrystalline silicon(c-Si) films have been obtained by low pressure chemical vapor deposition (LPCVD) in fixed silane flow at low pressure (200 mtorr) with variable growth temperature. Measurement of residual stress of polysilicon films growth between 570°C to 620°C was reported. Residual stress of polycrystalline silicon depends on film microstructure. The poly-silicon microstructure is a strong function of LPCVD growth temperature and pressure. In this work, Raman Scattering and X-ray diffraction (XRD) were used to study the film structure and composition. The multilayer optical model of Spectroscopic ellipsometry (SE) was used to crosscheck the crystallinity fraction. The surface roughness was identified by Atomic force microscopy (AFM) and SE. The residual stress changed from compressive to tensile and back to compressive for deposition temperature between 570°C and 620°C. Film’s c-Si fraction increased as a function of deposition temperature. The roughness surface was found at deposition temperature of 580°C. For deposition temperature larger then 580°C, all films shown (200) texture. The (220) grain size increased from 18.6 nm to 25 nm when deposition temperature increased from 580°C to 620°C. The film residual stress change can be explained by grain structure, surface stress and volume stress. At deposition temperature from 580°C to 587°C, grain is equi-axes type and volume stress dominate which cause the tensile stress. For temperature higher then 587°C inverse conical grain formed from oxide interface to surface and surface stress dominate cause the stress back to compressive. The columnar structure formed when deposition temperature > 600°C, grain growth push the compressive stress decrease again.