Dynamic Contact Characteristics During Chemical Mechanical Polishing (CMP)
- PDF / 126,759 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 35 Downloads / 270 Views
F1.10.1
DYNAMIC CONTACT CHARACTERISTICS DURING CHEMICAL MECHANICAL POLISHING (CMP) Wonseop Choi, Seung-Mahn Lee, and Rajiv K. Singh Department of Material Science and Engineering and Particle Engineering Research Center, University of Florida, Gainesville, Florida 32611-6400, USA
ABSTRACT In chemical mechanical polishing (CMP), it is critical to understand dynamic contact at the pad-particles-wafer interface for desired CMP performance. The dynamic contact is dependent on process variables (platen velocity and down pressure) and particle characteristics (size and concentration), which in turn affect friction force. In this study, we have characterized the dynamic contact at the pad-particles-wafer interface as a function of platen velocity and down pressure. In situ lateral friction force measurements were carried out for silica slurry / sapphire wafer system in order to investigate the dynamic contact during polishing. As solids loading increases, the slope in the friction force vs. platen velocity curve changes from a negative to a positive value. Friction force increases with down pressure for different solids loading conditions. Consequently, friction force is determined as a function of down pressure and platen velocity, validating a dynamic contact mechanism during CMP.
INTRODUCTION Chemical mechanical polishing (CMP) has emerged as the vital process in fabricating a multilevel interconnected ultra large scale integrated (ULSI) circuits [1]. The introduction of CMP in ULSI circuits fabrication makes it possible to eliminate topographic variation created by deposition processes and to achieve global and local planarization. CMP performance is determined by dynamic contact at the pad-particles-wafer interface during CMP. Most knowledge of dynamic contact is originated from the Stribeck curve that defines three contact regimes (asperity contact, mixed contact, and hydrodynamic contact) for ball bearings [2]. Based on the Stribeck curve, Moon reported three contact regimes which detail the influences of fluid film thickness on friction coefficient in the CMP process [3]. Several CMP models related to contact regimes and fluid film thickness have been developed. Runnel et al. exhibited the existence of the fluid layer at the pad-wafer interface and suggested that hydrodynamic force is responsible for material removal rate for the indirect contact regime during CMP [4]. Bhushan et al. analyzed CMP mechanisms under the semidirect contact region by a maintaining a thin fluid film between pad and wafer, thus reducing the role of the asperities in the pad [5]. On the other hand, Cook suggested in glass polishing that wafer be polished by direct contact of particles on wafer surface [6]. Yu also theoretically showed that contact area between pad and wafer is linearly proportional to down force [7]. In spite of the progress in the effort to estimate the dynamic contact at the pad-particles-wafer interface, many studies are limited to the contact of a single particle on the wafer surface or contact between pad and wafer
Data Loading...
