A COMPARISON OF MINORITY-CARRIER LIFETIME IN AS-GROWN AND OXIDIZED FLOAT-ZONE, MAGNETIC CZOCHRALSKI, AND CZOCHRALSKI SILICON

Dislocation-free p-type float-zone (FZ), magnetic Czochralski (MCZ), and Czochralski (CZ) silicon wafers with resistivity of ~50 Ω-cm were investigated before and after oxidation. Prior to any heat-treatment, FZ material showed highest minority-carrier lifetime (τr) with lifetimes approaching 5 ms. Lifetime in as-grown FZ material appears to be limited primarily by point defects generated due to thermal gradient and temperature fluctuation. As-grown CZ material showed lowest lifetimes of the order of 550 µs because of high concentration of point defects and residual impurities. This paper demonstrates for the first time that, unlike CZ, crucible-grown MCZ material of resistivity as low as 30–60 Ω-cm can have a lifetime as high as 2.5 ms. MCZ lifetime is limited by the residual impurities from the crucible and poly, even though the melt convection is reduced considerably. With the starting materials of comparable quality, the MCZ lifetime could be better than FZ because it has fewer defects due to stable liquid/solid interface. After oxidation, both FZ and MCZ samples gave a lifetime of ~550 µs which could not be explained on the basis of oxidation-induced point defects, because lifetime was limited by impurities diffused-in during high-temperature processing. Unlike FZ and MCZ, CZ material gave a postoxidation lifetime of only 100 µs due to high density of decorated defects, even though the impurity diffused-in concentration was the same. © 1990, The Electrochemical Society, Inc. All rights reserved.