The ability to monitor and control damascene processes is essential to rapidly ramping and maintaining consistently high yields. Results from a new method for non-contact characterization of the Cu damascene process are described. High-resolution measurements of Cu structures were performed on product wafers using the Metal Illumination(TM) (MI) measurement technique [1]. This work focused on thickness and dishing measurements of Cu bond pads on product wafers following CMP. The tool also measures high aspect ratio deep submicron Cu line arrays, blanket Cu films, and dielectric properties [2]. MI Measurements on blanket Cu ECD films showed very good correlation to four-point probe (4PP) sheet resistance and SEM thickness. Next, the MI measurement technique was employed to measure the Cu thickness and dishing of bond pads on product wafers following polishing on an orbital CMP toot. With increasing overpolish time, the Cu thickness was shown to decrease and the dishing (defined as the change in Cu thickness across a bond pad) was shown to increase. Further, the degree of Cu thinning and dishing was found to be a strong function of the die location on the wafer, with more severe thinning and dishing for die located near the edge of the wafer. The rapid and fully automated MI measurement technique was also used to perform inline SPC measurements on every wafer in multiple production lots. Variation in the Cu bond pad thickness within a lot and from lot to lot was easily identified, enabling tight control of the CMP process.
