Residual stress in porous silicon film with micro-Raman spectroscopy

Abstract

Porous silicon (PS) film was widely used in micro-systems sensors duo to its special properties. Nevertheless, intrinsic and processing residual stresses always introduced into porous silicon, always inducing the collapses and cracks inside the film and on the interface when the PS structure in service and/or during manufacture and storage. This paper presents a systematic study on the Raman stress measurement of porous silicon. Firstly, a theoretical model on the analytic relationship between stress and Raman-shift is presented by analyzing the micro-structures and transversely isotropy property of forest-like porous silicon film prepared on Si wafer by electrochemical etching. Meanwhile, the nano-indentation and digital Speckle correlations is utilized to determined the Young's moduli and Poisson's ratios of the PS samples, respectively. Based on the theoretical model and material parameters above, the coefficients in the Raman to stress relationship of porous silicon are achieved. By applying Micro-Raman spectroscopy, the distribution of intrinsic residual stress along the depth of PS-film/Si-substrate structure is measured. Then, a dynamical capillarity experiment is preformed to analyze the real-time stress transformation during PS drying, and the failure mechanisms by capillarity are discussed.