Study On Pad Performance In Chemical Mechanical Polishing

At present, chemical mechanical polishing (CMP) is widely used in the flatness process of polishing substrate and multilevel interconnections. Polishing pad is a key component of CMP system. It can store the polishing slurry and deliver it to the wafer workpiece evenly. The performances of pad are determined by type and properties of its material, the surface structure and state, and the state of conditioning, etc. However, the function of pad is not widely studied, and theoretical foundation that can guide the production application is insufficient. Based on the theoretical research and experimental analysis, the property of polishing pad is studied systematically in the paper.Based on the G-W contact model and Hertz theory, the contact status between polishing pad and wafer is analyzed at first. A mathematic model of material removal in polishing is obtained by means of the grinding action of single abrasive. The results of study indicate that, polishing pad performance has great influence on polishing efficiency, the harder the pohshing pad, the larger the elasticity modulus, hence, the higher the removal rate (MRR) of polishing;the more micro peak in the surface and the larger size, the higher the removal rate (MRR) of polishing.To study the influence of pad material on polishing effect in polishing, polytetrafluoroethylene pad, non-woven fabric pad and polyurethane pad are selected. Compared with polytetrafluoroethylene pad and non-woven fabric pad, the polyurethane pad is moderate in hardness, and there exist some even micro pores, therefore, the pohshing performance is much better. The polish performance of polyurethane pad is better when polishing pressure is 6.7kPa and rotating speed of pad is 40rpm. The thickness of pad, the structure of groove on pad surface, and state of dipped into water have different influence on the course of CMP. The maximum material removing rate can be got with the radiating type grooves, while the minimum roughness can be got with the ring type grooves. And the performace of polyurethane pad with 1.5mm thick is best. Material removing rate will rise while the pad dipped into water.The paper researched the effect of pad conditioning through a lot of experiments, including the effect of conditioner, conditioning parameters. Obtained the optimum parameters such as conditioning pressure, conditioning time and so on. Conditioning can improves the polishing rateand quality, in-situation conditioning is better than ex-situation conditioning. Pad performance decline during the polishing process, pad conditioning is a good way to renew its performance. The paper designed and manufactured a conditioning device. The device can do in-process conditioning. Studied the effect of conditioner, conditioning pressure, conditioning time, conditioning speed on pad performance and polishing result. Paper got the best conditioning process parameters. When conditioning pressure is 9kPa, conditioning time is 45min, conditioning speed is 120rpm,the polishing result with off-process conditioning is best. In-process conditioning is than off-process conditioning(MRR enhance 16.4%). The conditioning time and interval have important effect on conditioning.