4. Chemical Mechanical Polishing

Chemical mechanical planarization (CMP) has emerged as an indispensable processing technique for planarization in submicron multilevel VLSI. An analytic model of the material removal rate is proposed for CMP. The effects of applied pressure and polishing velocity are derived by considering the chemical reaction as well as the mechanical bear-and-shear processes. The material removal rate is less linearly correlated to the pressure and relative velocity than that predicted by the frequently cited empirical Preston equation [1]. The effects of CMP kinematic variables on wafer nonuniformity are also investigated. The significance of velocity uniformity is demonstrated by both analysis and experiment. For the endpoint detection, an accurate in situ monitoring method can significantly improve both yield and throughput. A model for CMP polishing pad temperature that is capable of predicting the CMP endpoint in situ is established, based on the total consumed kinematic energy. The process endpoint is detectable by application of the proposed regression method to the measured temperature rise. In addition, the chapter develops an endpoint monitoring method that uses acoustic emissions that occur during CMP. The method considers differences in friction characteristics between the polishing pad and the copper metal overlay. For the flow of slurry between wafer and pad, this study provides a visualized characterization of the amount and distribution of the fluid film between wafer and pad. Digital photographs taken through the transparent carrier and dyed fluid are used to analyze the fluid film.