NOVEL EVALUATION METHODS OF SILICON EPITAXIAL LAYER LIFETIMES BY PHOTOLUMINESCENCE TECHNIQUE AND SURFACE-CHARGE ANALYSIS

A novel method, the short wavelength laser excited photoluminescence ( PL) technique at room temperature, was applied to evaluate carrier lif etime characteristics of silicon epitaxial (epi) layers which are grow n on heavily doped p(+) substrates with similar to 10(19) cm(-3) of bo ron. The carrier excitation at 488 nm enables one to evaluate the life time characteristics of epi-layers thicker than 3 mu m. Method of surf ace charge analysis (SCA) was also applied to the epi-layer lifetime e valuation. Applying these methods to silicon epitaxial wafers with the p/p(+) structure, a trace metallic contamination in the epi-layers in troduced during the epi-growth processes has been evaluated successful ly by the PL method and the SCA method. In case of the PL method, it h as been found that no heat treatment for surface passivation is requir ed for the epi-layer evaluation. This implies a great advantage of the method which enables evaluation of the ''as-grown'' epi-qualities. We have observed that degraded epi-layer lifetimes by iron contamination in the as-grown p/p(+) wafers recover remarkably even by a slight sur face passivation heat treatment. This indicates a strong iron getterin g capability of the heavily boron doped substrates.