Visualization of the curving of crystal planes in β-Ga2O3 by X-ray topography

Abstract

The curving of crystal planes (CCP) in semiconductor wafers poses significant challenges for subsequent epitaxial growth and device processing, and must, therefore, be mitigated. This paper demonstrates a method of using the shift of the apparent Bragg angles measured by X-ray topography (XRT) to reconstruct and visualize the three-dimensional shape of curved β-Ga2O3 crystal planes. General geometrical considerations regarding the CCP are presented first, followed by simulations of the CCP using some simple models, including the cylindrical, spherical, ellipsoidal, and saddle-shaped models. Based on the results obtained from the simulations, the method of experimentally deducing the vector field of the surface normal by means of ω-rocking XRT measurements is described, based on which, the shape of the (002) plane in the β-Ga2O3 substrate grown by edge-defined film-fed growth is visualized. If a synchrotron source is unavailable, the method demonstrated here can also be performed using conventional laboratory X-ray diffraction equipment. The visualization of CCP provides crucial feedback for the optimization of crystal growth and wafer fabrication processes.