| Research Abstract |
From the theoretical analysis of the photoconductivity decay method (WLT) with small alpha delta-function carrier injection pulse and photoconductivity modulation method (SRMI and R-SRMI) with large alpha carrier injection pulse, it is found that SRMI and R-SRMI are more sensitive than the WLT method. Furthermore, R-SRMI method is insensitive to tau_b, because the R-SRMT signal is defined as the value subtracted SRMI (large alpha injection) from the BRMI (small alpha injection). The R-SRMI has inverse relation to SRMT and is related to S_<eff> closely. The R-SRMI is insensitive to tau_b and is very suitable for i) different condition Si wafers, especially surface active region, ii) a wafer which has distribution of tau_b and/or resistivity in LST processes. SRMI and R-SRMI measurements can reduce the calculation time compared to the photoconductivity decay curves analysis (WLT ; tau_b and S_<eff>).
The laser-microwave characterization systems (WLT, SRMI and R-SRMI measurement) are successively applied to several wafer processes, detection of surface contamination of the starting wafer, oxidation and its dry etching, ion implantation and annealing processes, junction formation by impurity diffusion, alloying processes etc. The change of the SRMI and/or R-SRMI at contaminated wafer surface are two to three times larger than those of WLT values. The SRMI and R-SRMI mapping measurement systems with laser-microwave are convenient, practical and useful ways for characterizing the Si wafer in various device fabrication processes.
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