Ryoji Hoshi

Novel evaluation method of silicon epitaxial layer lifetimes by photoluminescence technique

A novel method, the short wavelength laser excited photoluminescence (PL) technique at room temperature, is applied to evaluate carrier lifetime characteristics of silicon epitaxial (epi) layers, which are grown on heavily doped p+ substrates with approximately 1019 cm-3 of boron. The band-edge PL intensity of the epi-layer is closely related to the carrier recombination lfietime at room temperature. The carrier excitation at 488 nm wavelength and the existence of the p/p+ structure, which acts as a stopper for the excess carrier diffusion, enable one to evaluate the epi-layer lifetime characteristics of the epi-layer thicker than 3 micrometers . Applying the method to epi-quality evaluation of the p/p+ epi-wafers, trace metallic contamination in epi-layers introduced by the epi- growth processes has been evaluated successfully. It has been found that a dilute HF cleaning is enough for the sample preparation instead of surface passivation heat treatment, which is usually required for other lifetime measurements. This is a great advantage of the method which enables one to do an in-line epi-quality monitoring. We also found that molybdenum contamination degraded the epi-lifetime and the time dependent dielectric breakdown of thin oxide films grown on p/p+ epi-wafers in this study.