A scanning photon microscope for non-destructive observations of crystal defect and interface trap distributions in silicon wafers

Abstract

A sophisticated flying spot scanner in which 2 kHz AC surface photovoltages induced in a Si wafer due to the chopped irradiation of a photon beam 0.4 mm in diameter are non-destructively measured through a 25 mu m air gap between the wafer surface and a transparent electrode is developed. Photovoltage distributions on a wafer 50 to 150 mm in diameter are measured in 5 min, and displayed as a 512*480 pixel black and white image. With the use of near infrared (peaking at 896 and 1076 nm) and blue (peaking at 448 nm) photon sources (cathode ray tubes), it is possible to measure crystal defect distribution in the bulk and interface trap distribution at the wafer surface separately. The apparatus is successfully applied to observations of swirl patterns and radiation damage induced by an electron beam in thermally oxidised p-type Si wafers.