Preparation and Evaluation of Damage Free Surfaces on Silicon Carbide

A new chemical mechanical polishing process (ACMP) has been developed by the Penn State University Electro-Optics Center for producing damage free surfaces on silicon carbide substrates. This process is applicable to the silicon face of semi-insulating, conductive, 4H, 6H, onaxis and off-axis substrates. The process has been optimized to eliminate polishing induced selectivity and to obtain material removal rates in excess of 150nm/hour. The wafer surfaces and resultant subsurface damage generated by the process were evaluated by white light interferometery, Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), and epitaxial layer growth. Residual surface damage induced by the polishing process that propagates into the epitaxial layer has been significantly reduced. Total dislocation densities measured on the ACMP processed wafers are on the order of the densities reported for the best as grown silicon carbide crystals [1]. Characterization of high electron mobility transistors (HEMTs) grown on these substrates indicates that the electrical performance of the substrates met or exceeded current requirements [2].