POLISHED ALUMINUM NITRIDE SUBSTRATE COATED WITH SILICON-OXIDE FILM

Polished aluminium nitride substrates have imperfections of surface ro ughness in the form of cavities due to the loss of grains. Measurement s using the Image Processing System and the Dimensional Measurement me thod, revealed that cavities with diameters larger than 10 mu m existe d in quantities of about 22.5 x 10(5) pieces on a substrate of 152 mm( 2) and that their depths were about 1.3 mu m. The cavities also had sh arp edges and steep cliffs. The application of a thin coating of silic on oxide was studied for obtaining a smoother surface of the polished aluminium nitride substrate. The depth of the coated cavity decreased with increasing thickness of the film, and the shape of the cavities, especially their sharp edge and steep cliff could not be seen clearly as the thickness of the him increased. However, even if the him thickn ess was as great as 1.2 mu m, cavities of about 0.21 mu m depth remain ed on the coated substrate. A 10 mu m comb electric pattern could be m ade on the surface of the substrate coated with 0.5 mu m of him. All p atterns exhibited 1856 blocks (a block has 29 lines) and were uniform without any broken portions.