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

Abstract

In recent years, with the increase of the demand for higher signal transmission speed of ULSI, 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.