Forming and filling a recess in interconnect with alloy to minimize electromigration

Abstract

In a method for filling an interconnect opening to form an interconnect of an integrated circuit, the interconnect opening is formed within an insulating layer. The interconnect opening is partially filled with a conductive material to form a recess within the conductive material toward a top of the interconnect opening, and the recess is disposed within the interconnect opening. An alloy is conformally deposited to fill the recess. Any conductive material and the alloy on the insulating layer are polished away such that the conductive material and the alloy are contained within the interconnect opening. A thermal anneal is then performed such that the conductive material and the alloy form into a conductive fill of a single grain structure within the interconnect opening. An additional encapsulating material is formed to cover a top surface of the conductive fill during the thermal anneal from the dopant of the alloy diffusing out of the alloy and along the top surface of the conductive fill. A bulk encapsulating layer is formed on top of the additional encapsulating material and on top of the insulating layer. The present invention may be used to particular advantage when the conductive material that partially fills the interconnect opening is copper, and when the alloy that fills the recess is a copper alloy with a dopant metal having a solid solubility in copper that is less than 0.1 atomic percent at room temperature and having a concentration in the copper alloy that is greater than the solid solubility in the copper alloy. In this manner, the additional encapsulating material on the top surface of the conductive fill prevents lateral drift of the conductive material comprising the conductive fill along a bottom surface of the bulk encapsulating layer.