Elasto-Partial Hydrodynamic Contact Model for Chemical Mechanical Polishing

Tsai, Hung-Jung; Jeng, Yeau-Ren; Huang, Po-Whei

doi:10.1149/1.2359694

Cited by 12 publications

(9 citation statements)

References 38 publications

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“…One-dimensional and two-dimensional pressure profiles were obtained, and the results suggested that a large negative pressure region, which occupied more than 70% of the contact area between the disk and the pad, existed near the leading edge of the disk. Above experimental results were basically accordant with the calculation results of Sundararajan et al, 9 Park et al, 10 Cho et al, 11 Chen and Fang, 12 Kim et al, 13 and Tsai et al,14,15 which were based on the hydrodynamic lubrication theory and the simplified CMP model.All above experimental studies are based on static measurements which ignore the rotation of the wafer. It is quite different from the actual CMP process, in which the wafer carrier rotates synchronously with the platen.…”

supporting

confidence: 85%

In Situ Measurement of Fluid Pressure at the Wafer-Pad Interface during Chemical Mechanical Polishing of 12-inch Wafer

Zhao¹,

He²,

Lu³

2011

J. Electrochem. Soc.

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In this paper, a novel in-situ interfacial fluid pressure measurement system is developed for the practical chemical mechanical polishing (CMP) equipment, in which the pressure sensors are equidistantly embedded in the platen along the radial direction and sweep beneath the wafer surface during CMP. Interfacial fluid pressure mapping is realized for standard 12 blanket wafers at the down pressure of 0.5 ∼ 2.0 psi. The fluid pressure profiles from the leading edge to the trailing edge and the pressure contour maps of the fluid film across the whole wafer surface are constructed and displayed. Results reveal a large positive pressure region located near the wafer trailing edge and a small negative pressure region located near the leading edge, which is quite different from the negative dominated results of previous studies. The fluid pressure can support 15% ∼ 30% of the applied pressure. The down pressure has great effect on the fluid pressure due to the wafer's bend under the applied load. When the down pressure increases, the positive pressure region expands and slightly shifts toward the outer of the pad while the negative pressure region shrinks.Chemical mechanical polishing (CMP) is a necessary process step in the manufacture of multilevel Integrated Circuits (IC). During CMP process, the platen and the wafer carrier rotate in the same direction. Synchronously, the wafer carrier reciprocates along the radial direction of the platen. Polishing pressure is applied on the back surface of the wafer and presses the wafer on the pad, while the slurry is continually injected at the wafer/pad interface. With the combined action of the chemicals and the abrasive particles in the slurry, micro material removal and planarization of the wafer surface are realized. To improve the performance of IC device, copper and low-k materials are used for multilevel connection, which demands CMP to provide global planar polishing surface with low defect. Low downforce CMP is becoming the general trend to prevent damaging the soft copper and the low-k materials in industry. 1 CMP is a complex process as many polishing variables, such as the down pressure, the rotational speed and the slurry flow rate, affect the final polishing results (e.g., the within wafer nonuniformity). However, the process and the mechanism of such affecting of these polishing variables are not quite clear owing to the complex interactions between the wafer surface, the pad asperities, the particles, and the slurry at the wafer/pad interface. Early study found that, when polishing, a thin slurry film was formed at the wafer/pad interface, 2 and the fluid pressure was generated at the interface. Actually, the contact status of the interface is determined by the fluid lubrication effect and the downforce applied on the back surface of the wafer. Therefore, the fluid pressure affects the distribution of the contact stress of the wafer/pad interface directly, which acts as the mechanical action for the polishing. In addition, previous studies have revealed that the...

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supporting

confidence: 85%

In Situ Measurement of Fluid Pressure at the Wafer-Pad Interface during Chemical Mechanical Polishing of 12-inch Wafer

Zhao¹,

He²,

Lu³

2011

J. Electrochem. Soc.

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“…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][11][12][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.…”

mentioning

confidence: 99%

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

Kung¹,

Liu²,

Chang³

et al. 2009

J. Electrochem. Soc.

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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...

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“…The elastic, elastoplastic, and plastic deformations of the polishing pad may be produced during the CMP process. The contact between wafer and pad is assumed as elastic deformation in an earlier paper [35]. In this paper, the wafer-pad contact area was calculated using a micro-contact model that considered the elastic, elastoplastic, and plastic deformations of the polishing pad [32,[36][37][38].…”

Section: The Micro-contact Modelmentioning

confidence: 99%

“…Jeng et al [34] used a micro-contact model to investigate the wafer-pad contact pressure. Then, Tsai et al [35] proposed an elastopartial hydrodynamic contact model for the CMP process. The model combines the effects of partial hydrodynamic grain flow and elastic micro-contact between wafer and polishing pad.…”

Section: Introductionmentioning

confidence: 99%

An improved model considering elastic—plastic contact and partial hydrodynamic lubrication for chemical mechanical polishing

Tsai

Jeng

Huang

2008

Proceedings of the Institution of Mechanical Engineers, Part J:

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Chemical mechanical polishing (CMP) has become a primary technique for planarization of semiconductor wafers in sub-micro device fabrication. A physical CMP model combines the effects of grain flow hydrodynamic lubrication, pad roughness, and asperity contact between wafer and pad. In this study, an improved CMP model, considering both the grain flow with roughness effects and the micro-contact mechanism, is proposed. The model applies the average lubrication equation with partial hydrodynamic lubrication theory and considers the elastic-plastic micro-contact theory. The applied load acting on the wafer is balanced by the slurry pressure in the non-contact area, and the surface asperity contact force in the contact area. The effects of the CMP parameters including applied load, rotation speed, particle size, and pad roughness are studied and discussed. The simulation results compare well with experimental data in the literature and contribute to further understanding in wafer-pad contact mechanism.

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Elasto-Partial Hydrodynamic Contact Model for Chemical Mechanical Polishing

Cited by 12 publications

References 38 publications

In Situ Measurement of Fluid Pressure at the Wafer-Pad Interface during Chemical Mechanical Polishing of 12-inch Wafer

In Situ Measurement of Fluid Pressure at the Wafer-Pad Interface during Chemical Mechanical Polishing of 12-inch Wafer

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

An improved model considering elastic—plastic contact and partial hydrodynamic lubrication for chemical mechanical polishing

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