Surface polishing using vertically aligned carbon nanotubes as fixed-abrasives

Abstract

The mechanical polishing process which uses small and hard abrasives is widely used in various industries, such as product housing, surface finishing of optical equipment, and wafer planarization along with chemical reactions. In particular, with the recent evolution of high-density semiconductors, efforts are being made to develop smaller devices, and at the same time, more fields require carbon-based hard substrates, so polishing technology needs harder and finer abrasives. In the case of fixed-abrasive pads that have abrasives attached on the pad, relatively large abrasives are used because there is a limit to the size of the abrasives that can be attached. Therefore, conventional fixed-abrasive pads are difficult to use in a precise polishing process. As an alternative, the loose-abrasive is currently used in fields that require high polishing precision. In this process, loose-abrasives dispersed in a solution are injected between a polishing pad and surface to perform polishing. However, the loose-abrasive must be removed through the post-cleaning process, so the overall polishing process becomes very complicated, and the process generates significant material wastes. In this study, a novel fixed-abrasive pad was manufactured using carbon nanotubes (CNTs) having a high aspect ratio with a diameter of 10 - 20 nm and a length of 3 μm, to overcome the limitations of conventional polishing pads. The fixed-abrasive polishing pad is manufactured such that vertically aligned carbon nanotubes (VACNTs) synthesized through chemical vapor deposition (CVD) are impregnated in the polyurethane (PU) surface and then only a part of the VACNTs protruded from the surface through oxygen plasma etching. The excellent mechanical strength of CNTs can polish various materials, as well as a nanometer-sized diameter, enabling precise polishing. In addition, the CNT shape with a high aspect ratio can be stably fixed in PU while effectively transmitting force to the substrate. The polishing precision, material removal rate, and planarization performance of the developed fixed CNT polishing pad are quantitatively analyzed, and the abrasion mechanism is confirmed through modeling.