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In Si device fabrication lifetime measurements are frequently used for the routine control of heavy metal contamination induced by wafer processing. Today commercial, cleanroom-compatible tools are available for a number of lifetime measurement techniques, namely the Photoconductive Decay (PCD) method, the Surface Photovoltage (SPV) method, and the Elymat technique. All three methods are well suited for routine measurements in a manufacturing line. We present a number of correlation results between the different methods and show up some possible pitfalls connected with lifetime measurements. These pitfalls are often connected with the injection level, i.e. the ratio of the minority and majority carrier concentration during the measurement. The role of the injection level is discussed in the context with charge carrier trapping, Fe impurities and oxygen precipitates. Because of its practical relevance the properties of Fe in silicon are discussed in detail including comparisons between the bulk-sensitive lifetime methods and surface-sensitive techniques like Total Reflection X-Ray Fluorescence (TXRF). Furthermore, some results are given about the segregation of Fe in bulk Si and Si oxide after oxidation processes. Finally typical examples are presented for the application of the Elymat and SPV technique including the routine monitoring of furnace processes and the characterization of handling-induced backside contamination.
minority carrier diffusion length, injection level, charge carrier trapping, photoconductive decay, surface photovoltage, Elymat, Fe impurities, oxygen precipitates
Siemens AG, Semiconductors, Plant Regensburg, Regensburg,