Plasma Etched Vertically Aligned Carbon Nanotube Embedded Polyurethane Surface for Precision Semiconductor Wafer Polishing

Surface polishing and planarization process plays a significant role in achieving desired surface characteristics and ensuring product quality. The process is widely used in precision manufacturing industries including semiconductors, biosensors, displays, and battery packaging, and the requirements for precision polishing is ever increasing toward atomic scale. For productivity and quality, selection and optimization of the polishing pad and abrasive are essential, and realizing a precise surface topology for the polishing pads via advanced materials and plasma treatment can be an effective route for enhancing the efficiency and accuracy of the atomic scale polishing process.<br/>In this study, we propose a novel composite abrasive pad comprising 1D nanoscale fibers embedded in a soft matrix material realized by plasma treatment during fabrication. Here, we synthesize vertically aligned carbon nanotubes (VACNTs) and utilize them as a mechanical abrasive for precision polishing. Different from other conventional precision polishing methods, where the nanoscale abrasives are dispersed in a solution and supplied separately to the polishing pad surfaces, we conceptualized a new composite pad using 1D nano abrasives embedded on the surface. Individual carbon nanotubes exhibit high hardness and have a diameter of less than 10 nanometers which is suitable for abrasion. And their high aspect ratio controlled to be up to 10,000 allows them to be firmly fixed onto the soft matrix material. For the realization of the VACNT-embedded polyurethane pad, the key fabrication step is the selective plasma etching of polyurethane using argon plasma to expose a portion of the VACNTs, thereby creating a fixed-abrasive pad structure. making it suitable for nano-scale composite surface processing. We investigate the selective etching behavior of VACNTs and polyurethane, by adjusting parameters such as power, gas flow rate, and etching time. We then further explore the optimum plasma condition which ensures the VACNTs maintain the vertical alignment without clumping. The plasma step also allows us to form nano-porous structures on the surface of the plasma-etched polyurethane polishing pads. These structures facilitate the circulation of the deionized water used in the polishing process and the storage and discharge of polishing residues, ensuring a defect-free process. By finely tuning the Ar plasma time, we control the size of the nano-porous surface structures and the RMS profile of the pad surface. Based on appropriate plasma treatment, the pad structure exhibits robust VACNT films impregnated with polyurethane, yielding a uniform distribution of the high-aspect-ratio VACNTs. Finally, polishing performance tests are conducted using a pin-on-disk setup on various wafers to correlate the relationship between the plasma-treated pad surface structure and its polishing performance. Our findings reveal that pads with a larger RMS profile removed material at a higher rate, but also decreased the polishing precision, resulting in a rougher surface on the copper wafers. However, by finely tuning the nano-structures on the pad surface via plasma treatment, we were able to strike a balance between the desired polishing precision and speed, and therefore achieve an overall enhancement.