Global and Local Stress Characterization of SiN/Si(100) Wafers Using Optical Surface Profilometer and Multiwavelength Raman Spectroscopy

Abstract

Thin SiN films with various stress levels, from tensile +1.7 GPa to compressive -3.5 GPa, (as estimated by average curvature after SiN film deposition using Stoney's equation) were deposited on blanket Si(100) wafers by plasma enhanced chemical vapor deposition (PECVD). Global and local distortion and stress of SiN/Si(100) wafers were characterized using an optical surface profilometer and multiwavelength Raman spectroscopy. While wafers with tensile stress and compressive SiN films showed significant changes in wafer bowing (direction and curvature), negligible changes in Raman shift in the Si below the SiN film of all wafers were observed, as indicated by applying various excitation wavelengths. Periodic Raman shift fluctuations were observed from all SiN/Si(100) wafers, suggesting a self stress relaxation mechanism at the lattice level. The importance of global (wafer level), local (wafer level) and lattice level stress characterization and its contribution to proper understanding of the mechanisms involved in wafer bowing and stress build up, is discussed.