Study on Improving the CMP Performance by Various Pad Conditioner Designs and Fixed Nanodiamond Pad

Abstract

Chemical mechanical polishing (CMP) has become a critical planarization technique in the manufacture of advanced integrated circuit devices. It can effectively remove the topography of thin film on wafer, and achieves the good planarization either in local or global region, and also the polished object will have the excellent surface quality. Recently, new materials and architectures have been introduced in the manufacturing process of IC production, so some consumables still require further study and development, mainly due to the stricter requirements. In this dissertation, the improvement in CMP performance by various pad conditioner designs and fixed nanodiamond pad was investigated experimentally. The main consumables under research, which included the polishing pad and the pad conditioner, in CMP performance were evaluated, and the polishing planarization was also analyzed and improved. The fixed nanodiamond pad was the developed consumable, and through a series of experiments in silicon CMP to obtain the proper pad design and verify the pad’s validity. In the comparison of the performance of the experimental fixed nanodiamond pad, several commercial slurries were adopted. In citing the findings from the experimental results, the value and practicality of this study was discussed. The surface roughness and thickness of the polishing pad influenced the material removal rate directly, and the uniformity of both the surface roughness and thickness of the polishing pad were significant factors of the with-in wafer non-uniformity in CMP process. The compressibility and the friction force could be used to evaluate the polishing pad. Using a corrective conditioning profile, the non-uniformity of material removal rate was significantly improved, and also the service time of the polishing pad was lengthened. The design of pad conditioner was critical as it determined the efficiency of the grooving action. The pad conditioner chose the polycrystalline diamond as its substrate, which could increase the wear resistance. The diamond cutting tips on pad conditioner had the same size, shape, and protrusion height, which was beneficial for the dressing behavior and stability. The effect of various fixed abrasive pad designs on polishing characteristics during silicon wafer polishing was investigated. Due to the different manufacturing method for these fixed nanodiamond pads, the abilities of controlling the nanodiamond particles were different. Consequently, the surface roughness of the polished silicon wafer was remarkably improved by the fixed nanodiamond pad, and result also revealed that the pad hardness was a key factor in keeping the abrasives effective in the pad-wafer interface. In comparison with the performance of slurry process in silicon CMP, although the fixed nanodiamond pad process had a relatively low polishing efficiency that depended simply on the mechanical abrasion. For the same reason, a relatively thick damaged layer was formed in the polished silicon subsurface, as the fixed nanodiamond pad was used. However, it was comparable with the slurry process in terms of surface topography of polished silicon wafer, due to its extremely small and nearly spherical particles.