GaAs device two-steps junction stain and scanning capacitance microscopy sample preparation

Abstract

The article describes a modified analysis technique to reveal the doping profile of Gallium Arsenide (GaAs) device through two steps wet chemical stain and scanning capacitance microscopy (SCM) verification. Compared with the normal silicon-based device, the GaAs-based device is so acid-sensitive that the die couldn't be isolated from epoxy molding compound (EMC), not to mention junction stain with hydrofluoric acid (HF). We developed a two-steps junction stain which has low cost, large area, two dimensional profile applied on the GaAs-based device to catch doping profile by sulfuric acid (H 2 SO 4 ) solution and citric acid (C 6 H 8 O 7 ) solution in order. The etching rates of AlGaAs and GaAs in sulfuric acid were reported, and we discovered the citric acid also has the selective etching properties as well. Both of the sulfuric acid and citric acid were mixed with hydrogen peroxide (H 2 O 2 ) and water (H 2 O) in specific proportions. All SCM data were collected from cross section samples using Bruker Dimension Icon AFM equipped SCM module which helps identifying the n-type and p-type charge signals from stained area. The SCM probe is a key point for the image resolution, the boron highly doped conductive diamond probe and Pt/Ir probe were compared during the experiment. The diamond probe shows a good resolution image without any DC bias applied on the sample, the Pt/Ir probe can hardly collect the SCM signal instead.