Development of Abrasive-Free Polishing Method for Cu Utilizing Vacuum Ultra-Violet Light

Abstract

In recent years, it is strongly required to improve the Chemical Mechanical Polishing (CMP) technology for Cu. The conventional Cu-CMP slurries, however, have serious problems relating to detrimental impact on environment, because it includes a lot of organic compounds and abrasives. In this study, a new Cu-CMP method, that is, the polishing method utilizing vacuum ultra-violet (VUV) light irradiation and an electrolyzed water was proposed and developed in order to overcome the above-mentioned problem. In the newly-proposed method, the Xe excimer lamp was adopted as the VUV light source. The lamp has a sharp peek of the wave length at 172 nm, and can generate an ozone gas from decomposition of oxygen. The effects of the VUV light irradiation for Cu-CMP are thought to be as follows; 1) an oxidation effect by generated ozone, 2) a photoelectric effect for Cu substrate. Then the polishing experiments for Cu substrate were carried out with in-situ VUV light irradiation. The experimental results revealed that the developed method was effective for obtaining precise smooth surface, namely, the mirror-finished surface under 1 nm Ra was achieved. From the result, it was found that the developed polishing method has an electrochemical effect for polishing, namely, the amount of OH- groups and the density of oxygen or pH of polishing fluid have a strong influence on Cu polishing process.