Diamond-like carbon as an electrical insulator of copper devices for chip cooling

Abstract

A diamond-like carbon (DLC) coating is used to provide the electrical insulation of copper devices used to remove the heat from the chips. A 0.5 μm DLC layer, comprised of hard amorphous carbon layers, is deposited by plasma-enhanced chemical vapor deposition of acetylene in a parallel plate r.f. reactor. The deposition is performed on negatively biased substrates, at a temperature of 140-250 °C. A rigidizing layer of hydrogenated amorphous silicon, 2-5 μm thick, is deposited between the DLC layer and the copper substrates. The described structures have been deposited on copper cooling inserts and their characteristic has been tested on individual inserts as well as on assembled cooling modules. The test results show that the electrical insulation is achieved, without deterioration in thermal conductivity. No scratching was observed in coated devices, while scratches occurred on the surface of the uncoated copper devices tested together with the coated devices. Thus the combination of the copper cooling system with the electrical insulating DLC structure will allow improved cooling of the chips, without danger of interchip shorts or shorts to ground. © 1991.