Effect of slurry flow rates on tungsten removal optimization in chemical mechanical planarization

Abstract

In this study, to improve the performance of chemical mechanical planarization (CMP), the optimal tungsten removal rate (WRR) was determined using a design of experiments (DOE) method. Critical operating factors, such as the downforce (DF), head and turntable speed (HTS), H2O2 oxidant concentration (OC), and slurry flow rate (SFR), were considered in the CMP process. Process optimization of WRRs corresponding to these factors was then conducted using a DOE method. Results showed that the maximum WRR was observed at high DF, HTS, OC values, but a low SFR according to the DOE analysis. Variations in the polishing temperature were responsible for the effect of SFR on WRR, which was explained by the mechanical removal rate (RRm) and chemical removal rate (RRc). A kinetic model constructed using dynamic etching rate (DER) analysis was used to evaluate the RRc value. The results indicated that the RRc value considerably decreased with increasing SFR because of the decrease in polishing temperature. However, the RRm value rapidly increased in the low-SFR region and reached to saturation in the high-SFR region. This reduction in the WRR was primarily attributable to the presence of a low RRc vale in the high SFR region during the W CMP process.