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14 September 1994 Mapping of silicon wafers on shallow, middle, and deep level centers
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The new nondestructive contactless method of analyzing plane distribution of some electrophysical parameters of silicon wafers is proposed for discussion. This method makes possible the easy control of the volume lifetime, oxygen precipitates density and resistivity variation on plates square with a laser spot diameter resolving. In the experiment the microwave photoconductivity kinetics curves were obtained at 1000 points on the area 7.5 X 1.875 mm. Each of these curves was one of two types -- the exponential decay (with two parameters: time and amplitude) and decay with the long tail (in rough description with four parameters). As it was shown in preliminary studies from exponential decay it's possible to obtain information about volume lifetime variation (or after additional experiment -- about the surface quality) while from nonexponential decay the additional information about oxygen precipitates concentration can be obtained. The fundamentally new opportunity which becomes possible due to mapping is the obtaining of the resistivity variation picture. Roughly speaking, this picture can be obtained from the analyzing of the amplitude of exponential decay. As the lifetime is measured independently and microwave device tuning is not changed drastically from point to point -- so one can obtain the picture of wafer resistivity from computer processing of pictures of amplitude and time constant of exponent.
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Vadim A. Nikitin "Mapping of silicon wafers on shallow, middle, and deep level centers", Proc. SPIE 2334, Microelectronics Manufacturability, Yield, and Reliability, (14 September 1994);

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