Fabrication and Characterization of 2-inch diameter AlN Single-Crystal Wafers cut From Bulk Crystals

Abstract

ABSTRACTAluminum nitride (AlN) boules larger than 2 inches in diameter were grown by the sublimation-recondensation technique. X-ray Laue diffraction was used to characterize the crystallinity and orientation of the boules, and 2” dia. substrates were sliced with typical thickness of ∼500 μm. The wafers were then polished in order to meet the common standards for wafer thickness and flatness. The Al-terminated surface was finished with a proprietary chemical-mechanical process and showed RMS roughness of 0.5 nm or less as measured by atomic force microscopy (5×5 μm area). Currently, the substrates have some polycrystalline regions that are highly textured but about 85% of the total area is monocrystalline. The dislocation density in the crystalline regions of the substrate was measured by preferential chemical etching and then determining the resulting etch pit density (EPD). The etching technique involves potassium hydroxide and has been qualified through correlation with x-ray topography measurements of the dislocations. Measured EPD varied from 250 cm−2to 3×104cm−2. Other structural defects such as low angle grain boundaries, prismatic slip bands, inversion domains, have also been observed. The rare appearance of these defects will be discussed even though their role in the epitaxial growth of GaN and AlGaN is yet to be clarified.