Characterization and Modeling of Mainstream and Alternative Conditioning and Polishing Technologies in Inter-Layer Dielectric and Copper Chemical Mechanical Planarization

Abstract

This dissertation consists of four topics that focused on investigating the fundamental characteristics of chemical mechanical planarization (CMP) processes. These are alternative and conventional pad conditioning technologies, inhibitor characteristics of slurry additives, and pad stains in copper CMP.A high pressure micro jet (HPMJ) technology was used to investigate pad conditioning and evaluated as an alternative to conventional diamond disc pad conditioning in copper and inter-layer dielectric CMP. Results showed that the HPMJ pad conditioning system had the potential of removing slurry residues and polish by-products inside pad grooves and pores on the pad surface, thus leading to improved pad life and reduced wafer-level defects. In addition, a proposed conditioning scheme, namely a combination of diamond and HPMJ pad conditioning, allowed for stable polish results in terms of removal rate and coefficient of friction (COF).The theoretical and experimental investigation of conventional diamond disc pad conditioning was performed to explore the effects of conditioner design factors on removal rate and COF in copper CMP. In this study, conditioning affected pad surface topography and was also capable of modifying the removal rate of copper by changing the COF and the reaction temperature. Both theory and experimental results showed that friction and removal rate should both decrease as the conditioned surface became less abrupt.Ammonium dodecyl sulfate (ADS), an environmentally friendly surfactant, was evaluated as an alternative inhibitor to benzotriazole (BTA) in copper CMP. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA in terms of coefficient of friction (COF), removal rate and temperature. Spectral analysis of shear force showed the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer.The characterization of experimental and numerical formation of pad staining was investigated. Pad staining was a result of material removal and it increased with polishing pressure, wafer rotation rate and polishing time. Experimental results also indicated that pad staining had no significant effect on removal rate. The experimental and simulated pad staining images demonstrated that polish by-products were advected downstream with the slurry flow, and deposited on the pad surface.