Round-robin test of EPD measurement on undoped GaAs wafers

Abstract

Undoped LEC GaAs wafers were etched with molten KOH and the influence of measuring conditions upon the value of measured EPD (etch pit density) was investigated by a round-robin test. The result on the size of pits showed that the counting error was minimal when the size was in the range of 20 to 40 μm, meaning that in this size range, individual pits were easily discernible. Another result showed that there was an increase of about 20% in the EPD as the microscope magnification was changed from × 100 to × 200. The extent of the measurement field is also an important factor in determining the EPD: EPD fluctuation decreased as the measurement field was extended. The location of measurement points in the <100 > and <110 > directions was studied using an automatic EPD counter, and the average of the EPD agreed within +-25% with the average value based on overall mapping data if 13 or more measurement points on a 2 inch diameter wafer and 17 or more on a 3 inch diameter wafer were employed.