Characterization of Polish-Induced Gouges on Single Crystal Sapphire Substrates

Single-crystal sapphire is known to be among the hardest insulators. Its mechanical properties and chemical inertness make it a challenging material to polish for the atomic-level surface smoothness required for its applications. Mechanical polish with diamond abrasives renders high removal rates but creates unacceptable levels of polish-induced gouges. Chemical mechanical polish on the other hand results in atomic smoothness but is a slow process. Hence, a combination of the two is used in the industry. In this work, we have attempted to characterize gouging and subsurface damage using atomic force microscopy, X-ray diffraction, and cross-section transmission electron microscopy on C-plane and A-plane sapphire induced by diamond abrasive mechanical polish and chemical mechanical polish with colloidal silica. Highlights Chemical mechanical polishing/planarization of two orientations/planes of sapphire (α-Al2O3). Characterization of polish induced gouges - measurement of depth of gouges. Growth of epi-layers, displays, windows for wearable electronics, etc. Characterization of sapphire surface using TEM, XRD and AFM - quantification of results. Use of X-ray rocking curves to determine crystal surface quality.