Local damage free Si substrate ultra thinning for backside emission spectral analysis using OBPF for LSI failure mode detection

Abstract

In this study, we focused on an emission spectral analysis using OBPF, since emission spectral analysis is possible even with weak emissions. We also developed Si substrate local damage free thinning by ablation laser processing, and alkali solution wet etching for Si backside emission spectral analysis. The emission spectral analysis using an OBPF was effective for estimating the LSI semiconductor device failure mode and was able to classify the three failure modes of: gate oxide thin film leakage, P-N junction leakage and nMOSFET saturation current (Idsat) where gate floating occurs. Furthermore, we were able to estimate the failure mode, including metal/metal line short mode, from power approximation formula: Y=aXb of a photon count increase rate by rising applied voltage at a PEMs observation. Each failure mode has it’s own coefficient “b” value. These two techniques allow a much more precise estimation of the representative failure mode of LSI semiconductor devices. Next, we developed damage free and large area local Si substrate thinning for backside emission spectral analysis at an isolated point. This technique uses a 266nm DUV pulse laser ablation process and Si substrate crystal anisotrophic wet etching by KOH alkali solution. We achieved a damage free thinning area of approximately 2.6×2.6mm2. In addition, we developed a very precise, nondestructive calculation method for Si substrate with thickness of less than 2.3μm by combining the interference fringe of equal thickness with an optical microscope, and an SEM image from depth of primary electron penetrations. The emission spectral analysis using OBPF from Si substrate backside became possible as an addition to surface analysis by combining thinning techniques with thickness calculations. We succeeded in estimating the failure mode by backside emission spectral analysis using these techniques.