Nonlinear Dependence of Cu Dishing Depth on the Microstructure of Polishing Pads during Chemical Mechanical Polishing

Abstract

The relationship between Cu dishing depth ͑DD͒ and Young's modulus of polishing pads during chemical mechanical polishing for various Cu linewidths is investigated. For the Cu width of 150 m, the results show that increasing Young's modulus from 161 to 180 kgf/cm 2 slightly decreased Cu DD; there was a major linear decrease until 195 kgf/cm 2 , and Cu DD was a constant value up to 208 kgf/cm 2 . These three regions are characterized by the threshold, linear, and saturated zones. Scanning electron microscopy results show that the nonlinear behavior is in response to the changes in the ratio of pore areas within the polishing pads. We build a model and define an effective polishing length, L C ‫ء‬ , to predict Cu DD. L C ‫ء‬ is the rotation mode of L C , the static distance between two neighboring pores. The proposed model shows that the three regions are determined by competition between static chemical etching and variable mechanical wearing resulting from the pore area ratio in relation to Young's modulus. The model is useful for understanding the nonlinear behavior between Cu DD and Young's modulus of the pad.Chemical mechanical polishing ͑CMP͒ is widely applied in the planarization of Cu interconnect metallization manufacturing. 1-9 However, various defects, such as Cu dishing and oxide erosion, can occur during the CMP process. Cu dishing depth ͑DD͒ is affected by many process parameters, including the Young's modulus of the polishing pad. 1,2 Metal dishing leads to line resistance deviation, and the resulting surface topography leads to additional problems for the next-level metal-line fabrication. To better understand Cu DD to improve planarization, various models have been established to visualize surface evolution. Many studies assume a direct waferpolishing pad contact, and the concept of the contact mode comes from two objects rubbing against each other during glass polishing. 10-13 Nguyen et al. 10 developed a model for the contact area of the pad and the wafer, the number of contacts, and the size distribution of the contact areas as functions of polishing parameters and pad properties. The magnitude of dishing greatly increased with increasing feature size and the number of contacts. The size distribution of contacts determines the amount of dishing of a metal line. Metal-line dishing also increases with decreasing pad modulus. 12,13 Previous studies on the effect of a pad modulus were limited to Young's modulus regimes larger than 200 kgf/cm 2 and smaller than 160 kgf/cm 2 for low and high magnitude dishing, respectively. Due to the limited range of investigated Young's moduli, the detailed mechanism is still far from being completely understood. In the present study, we investigate the planarization behavior during polishing by extending the range of Young's moduli of polishing pads and Cu linewidths for a complete analysis. A nonlinear dependence was found, which can be divided into three regimes: saturation, linear, and threshold. A model is established to understand the nonlinear behavior and to...

Charge Transfer across a ZnO∕Electrolyte Interface Induced by Sub-Bandgap Illumination: Role of the Surface States

“…From an analysis of the experimental data and theoretical predictions it is determined that the density of the surface states is 3.1 ϫ 10 13 cm −2 and the capture cross section is 1.5 ϫ 10 −16 cm 2 , H533 Journal of The Electrochemical Society, 155 ͑7͒ H529-H535 ͑2008͒ H533 which is in line with literature. 28,29 This can be considered as strong support for the developed model based on a surface-state mediated charge-transfer mechanism. Finally, we have provided a theoretical simulation of the photocurrent transients for strongly varied illumination intensity, thereby illustrating the transformation of the curve shape due to the changes in charge-transfer kinetic parameters.…”