Study On Micro-Contact Behavior Of Polishing Pad

For developing integrated circuit (IC) with higher integrated and higher performance, feature size of IC is continually decreasing while the wafer size is increasing, which presents new challenges to the planarization process in IC manufacturing. Chemical mechanical polishing (CMP) is a crucial technique to realize the planarization of wafer surface, in which surface material is removed on atomic scale by the cooperation of chemical reaction and mechanical friction. Surface with high-precision and ultra-smoothness can be achieved by CMP process, and it simultaneously meets the global and local planarization requirements for IC manufacturing.In CMP system, micro-contact behavior of polishing pad dominates the real contact surface and the number of effective abrasives at the polishing interface, which consequently make an important effect on material removal rate and surface quality of CMP. Aiming at the current issues on the theoretical analysis of CMP, contact characteristics and its influence factors are researched through numerical simulation and experimental methods, from the prospective of rough topography, geometric structure, material characteristic, physical and chemical environment and etc., providing the basis for theoretical analysis and parameter optimization of CMP process. Main research contents are as follows:(1) Contact characteristic of thin elastomer is analyzed, and the suitability of asperity-substrate layer series model is discussed based on semi-numerical deterministic analysis method for rough thin elastomer’s contact stiffness calculation. The sources and variation rule of calculation error of this method are analyzed.(2) Contact stiffness of different kinds of polishing pad, such as single-stage groove polishing pad, multilevel groove polishing pad and hole polishing pad, is studied. A new method applying series model to stiffness calculation of groove polishing pad is put forward and modified theoretically about large deformation. Besides, elastic foundation model considering the hole structure of polishing pad is applied to stiffness calculation of hole polishing pad, whose suitability is analyzed. Meanwhile, Young’s modulus of IC1000polishing pad and SUBA Ⅳ polishing pad is measured.(3) Real contact area measure system modeling in-situ situation of CMP process is set up, and real contact area measure device is designed. Through series control of circuit and pneumatic circuit, controllable loading, pulse loading and Shear loading can be undertaken. Under these circumstances, micro-contact behavior of polishing pad can be observed.(4) Under different load, the variation of contact behavior of pad asperity is observed, and the relationship between the real contact area and contact load is studied. The effects of chemical environment, such as dryness, wetness, PH, etc., and pulse load on micro-contact behavior of polishing pad are explored. Study shows that the dependence of real contact area on the applied load appears to be liner; polyurethane susceptible to hydrolytic attack becomes soft in the wet state, wet polishing pad has a bigger real contact area, especially in alkaline environment; due to the viscoelastic behavior of polyurethane, real contact area of polishing pad increases with cyclic loading, especially in the wet state, which can be explained by the cooperation of viscoelastic behavior and hydrolysis reaction.