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In order for the Elymat minority carrier diffusion length imaging technique to become a useful and robust manufacturing tool for characterization of silicon wafers, optimum machine settings must be developed and tight control of the measurement process must be maintained to achieve maximum lifetimes and repeatable results. This paper describes a method for determining optimum injection currents to compensate for resistivity characteristics of the sample. Test results, obtained on wafers with resistivity ranging from 0.9 to 20 ohm-cm subjected to 60 measurements each using various combinations of wavelength and photo injection currents, are discussed. This paper also presents test results for the Injection Level Search (ILS) option designed to set the optimum injection level for each individual sample. Finally, the authors make recommendations concerning methods for control of the measurement process (i.e., control charting, troubleshooting, etc.).
Elymat, Minority Carrier Lifetime, Measurement Control
Senior Engineer Specialist, MEMC Electronic Materials Inc., St. Peters, MO
Senior Quality Assurance Physicist, MEMC Electronic Materials Inc., St. Peters, MO