Silicon Nitride Coatings on Copper

Abstract

Silicon nitride was deposited on copper substrates at room temperature by a reactive sputtering technique. The coatings, in the thickness range 500–1500Aå, were amorphous, transparent, and had glass‐like smoothness. They were tightly adherent to the substrate. Infrared analysis indicated the coatings were pure silicon nitride when precautions were taken to eliminate oxygen and water from the system. The coatings exhibited dielectric constants of 8–11 with a dissipation factor less than 10−2 at 1000 cycles/sec. The ductility approached 1% as measured on a copper substrate. The coatings reduced the charge passing across the metal/electrolyte interface when the coated samples were anodically treated in sodium hydroxide, sulfuric acid, and phosphoric acid. The coatings provided good resistance to attack of the copper surface in ammonium hydroxide and sodium hypochlorite; provided moderate protection in concentrated acids, mediocre protection in sodium thiosulfate and sodium sulfide solutions, and very little protection in concentrated nitric acid.