The adhesion between a silicon nitride layer and polycarbonate substrate was improved by employing a silicon interfacial layer which was deposited by a microwave plasma enhanced chemical vapor deposition technique. The silicon interfacial layer had an interpenetrating layer composed of the two materials, which provided an anchoring effect. In the interpenetrating layer, it was assumed that chemical bonding between carbon of the polycarbonate substrate and the silicon interfacial layer occurred through the oxygen when the radio frequency power was used in the fabrication process. The oxygen originated in the polycarbonate substrate. During the silicon interfacial layer deposition, carbon was sputtered and oxygen reacted with silicon.