The production of a highly polished, damage-free wafer surface is generally acknowledged as a critical first step in the fabrication of semiconductor devices. In the case of gallium arsenide (GaAs), however, little is known concerning the microscopic aspects of the polishing process. A research program is proposed that will determine the effect of wafer polishing (specifically the chemical-mechanical polishing that is commonly used in GaAs substrate fabrication) on the level of surface and subsurface damage in GaAs. The principal tool to be employed in this work is x-ray diffraction performed under conditions to maximize the diffracted intensity from the surface and subsurface regions. Techniques such as diffraction under conditions of grazing incidence reflection, inclined Bragg plane diffraction, and triple crystal diffraction will be utilized for their sensitivity to both the wafer surface and to the subtle defects that are expected to accompany a high quality chemical-mechanical polish. The crystallographic structure of the surface layer, the strain in the surface, and the density of defects with depth below the wafer surface will be characterized as a function of polishing variables such as wafer rotation speed, force on the sample, and the type and feed rate of the chemical polishing solution. This work will result in a quantitative understanding of the factors that govern the formation of defects during the chemical-mechanical polishing of device-quality GaAs substrates.
