Wafer preparation and iodine-ethanol passivation procedure for reproducible minority-carrier lifetime measurement

Abstract

We have determined that mechanisms of irreproducibility in measurement of lifetime arise from two sources: (i) improper wafer cleaning, and (ii) instability of I-E solution when in contact with a Si wafer. This paper describes a sequential optical oxidation and chemical cleaning procedure that can reproducibly yield the correct values of bulk lifetime. We have observed that surface passivation is optically activated, which often causes an initial increase in the measured lifetime. This initial activation time can be greatly reduced by exposing the wafer in the bag to higher intensity light such as a solar simulator for 5–10 minutes. This procedure yields reproducible, very low recombination surfaces, suitable for measuring tb as high as 2 ms. We will discuss why this cleaning procedure is necessary and propose mechanism of instability in the passivation of I-E/Si.