Planarization of surface of aluminium nitride substrate with thin silicon oxide film

For use in a microelectronic circuit, as-sintered and polished aluminium nitride substrates have imperfections of surface roughness with pores and open porosity, respectively. The use of a thin coating of silicon oxide was studied for forming 10-mu m-wide patterns on the surface of the aluminium nitride substrate. When polished substrates were used and the thickness of silicon oxide was held at less than 1200 nm, the minimum surface roughness of coated substrates had R(a) of 20 nm and R(max) of 200 nm, and a functional 10-mu m electric circuit pattern could be made. Thermal conductivity of coated substrates decreased from 186 to 179 W/m . K with increasing thickness of silicon oxide up to 1200 nm. The thermal conductivity of coated substrates decreased following the value calculated by an expression for a multilayer board.