Method of making a semiconductor device that has copper damascene interconnects with enhanced electromigration reliability

#The present invention relates to a method of making semiconductor devices, in particular, devices that include copper damascene interconnects.

#When making advanced semiconductor devices, copper interconnects may offer a number of advantages over those made from aluminum. For that reason, copper has become the material of choice for making such devices' interconnects. As device dimensions shrink so does conductor width—leading to higher resistance and current density. Increasing current density can increase the rate at which copper atoms are displaced when current passes through a copper conductor. Such electromigration can cause vacancies to accumulate, which may lead to voids. If the voids grow to a size that creates metal separation, they may cause an open-circuit failure.

#One way to prevent electromigration from causing interconnect failure is to limit the amount of current that passes through the conductor. That solution to the electromigration problem is impractical, however, because devices will operate at progressively higher currents, even as they continue to shrink. As an alternative, interconnect reliability can be enhanced by doping the interconnect—as adding dopants to the conductor can reduce the rate at which copper diffuses.

#FIG. 1 represents an overhead view of a conductive layer, shown contacting a pair of vias, that is doped with a material that diffuses along the conductive layer in the direction of electron flow.

#FIG. 2 represents an overhead view of a conductive layer, shown contacting a pair of vias, that may be made when practicing the method of the present invention.

#FIGS. 3a and 3b represent cross-sections of structures that may result after certain steps are used to make a semiconductor device using an embodiment of the method of the present invention.

#A method for making a semiconductor device is described. That method comprises forming a conductive layer that contacts a via, wherein the conductive layer includes a sufficient amount of a dopant, which will diffuse in the direction that is opposite to the direction in which electrons will flow through the conductor, to reduce the electromigration of the material that comprises the bulk of the conductor without significantly increasing the conductor's resistance. In the method of the present invention, the via may be formed prior to forming the conductive layer on the via, or the conductive layer may be formed prior to forming the via on the conductive layer.

#In the following description, a number of details are set forth to provide a thorough understanding of the present invention. It will be apparent to those skilled in the art, however, that the invention may be practiced in many ways other than those expressly described here. The invention is thus not limited by the specific details disclosed below.

#The method of the present invention may be used in many contexts. In a preferred embodiment, it is used to improve the electromigration reliability of copper interconnects, which are formed using conventional damascene or dual damascene processes. As illustrated below, the method may be used when forming copper conductors that act as either enclosure structures (i.e., structures that ensure contact between a conductor and a via formed on it) or coverage structures (i.e., structures that ensure contact between a conductor and a via formed under it).