Abstract: A method for enhancing adhesion ability between copper and silicon nitride is disclosed. The present method comprises following steps: first, provide a substrate and then form a copper layer on the substrate; second, form a copper phosphide layer on the copper layer; and finally, form a silicon nitride layer on the copper phosphide layer. Herein, the copper phosphide layer is formed by a plasma enhanced chemical vapor deposition process. Therefore, any copper oxide layer that covers copper layer is replaced by the silicon phosphide layer and then adhesion between copper and silicon nitride is improved. Moreover, the silicon phosphide comprises two advantages: low resistance than copper oxide and efficiently prevent copper diffuses into surrounding dielectric layer.