The Effect of Wafer Shape on Slurry Film Thickness and Friction Coefficients in Chemical Mechanical Planarization

Lu, Joseph; Coppeta, Jonathan; Rogers, Chris; Manno, Vincent P.; Racz, Livia; Philipossian, Ara; Moinpour, Mansour; Kaufmanc, Frank

doi:10.1557/proc-613-e1.2.1

Cited by 26 publications

(47 citation statements)

References 13 publications

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“…This study considers both force and momentum balance and includes a variety of CMP parameters such as load, relative pad/wafer rotational speed, grain size, and pad roughness under various convex wafer curvature radii. The results are in good agreement with the experiments results of Lu et al 16 This investigation also elucidates CMP particle size and pad roughness effects, a topic inadequately covered in the literature.…”

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confidence: 89%

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Improved Model of Wafer/Pad Powder Slurry for CMP

Jeng

Tsai

2003

J. Electrochem. Soc.

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Chemical mechanical polishing ͑CMP͒ is a key technique for wafer global planarization. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity and particle effects significant. However, particle size and pad asperity have not been considered simultaneously in previous literature. This study presents a grain flow model which applies the average lubrication equation with partial hydrodynamic lubrication theory, thereby analyzing slurry flow between wafer and pad and taking into account both grain flow and roughness effects. This model predicts slurry flow film thickness with various convex wafer curvature radii under a variety of the CMP parameters, including applied load, rotation speed, dome height, particle size, and pad roughness. Furthermore, the influence of particle size and pad asperity on removal rate is investigated. The results compare well with experimental data in the literature.Integrated circuit ͑IC͒ gates of 0.13 m and smaller are making it increasingly important to control thickness and planarity. Chemical mechanical polishing ͑CMP͒ is a popular technique to achieve global planarization of wafers for very large and ultralarge-scale integrated circuits. A typical CMP mechanism is shown in Fig. 1. The wafer is held inside a carrier and pressed onto a rotating pad under a user-defined polishing pressure while a powder slurry flows between wafer and pad. Because the CMP mechanism is inadequately understood and because higher levels of CMP performance are desired, significant research is being directed toward improved physically based models of the CMP process.Nanz and Camilletti 1 conducted a survey and compared the physical effects of CMP models up to 1995. Published CMP models are based mainly on contact mechanics, 2-6 slurry hydrodynamics, 7-10 or lubrication theory. 11 Recently, Tichy et al. 12 ͑1999͒ presented a two-dimensional CMP model including both contact mechanics and lubrication hydrodynamics. To account for pad compressibility, porosity, and slurry delivery effects, Thakurta et al. 13 used lubrication theory to describe lubrication regime ͑40-70 m slurry films͒ and contact regime ͑thinner films͒. Luo and Dornfeld 14 proposed a solidsolid contact model of the CMP process based on plastic contact over the wafer-abrasive interface and pad-abrasive interface. The fluid effect is attributed to the number of active abrasives, but the effects of slurry particles under hydrodynamic contact were not investigated. Liang et al. 15 in real-time CMP experiments investigated the wear behavior of polishing wafers and pads by comparing different polishing slurries with different additives. Under optical microscopy, they found that the polishing removal rate of wafers decreases with decreasing slurry particle size. Lu et al. 16 used dualemission laser-induced fluorescence ͑DELIF͒ to measure slurry thickness and friction force between wafer and polishing pad. They demonstrated that slurry thickness and friction force are dominantly dependent on the s...

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supporting

confidence: 89%

“…Comparison with experiment results.-Lu et al 16 considered wafer shape and measured the average film thickness between wafer and polishing pad. Lu's slurry was Cabot SC-1, with silica particles on the order of 100-200 nm.…”

Section: Simulation and Discussionmentioning

confidence: 95%

Improved Model of Wafer/Pad Powder Slurry for CMP

Jeng

Tsai

2003

J. Electrochem. Soc.

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“…However, the LEP analysis simultaneously considers micro-contact and partial hydrodynamic lubrication. The theoretical results are first compared with the experiment data of Lu et al [18]. The values of film thickness, attack angle, contact area ratio, and varying relative removal rate with applied load and rotation speed for various particle sizes are investigated.…”

Section: Comparison With Experiments Resultsmentioning

confidence: 99%

“…They observed that the polishing removal rate of wafers decreases with decreasing slurry particle size. Lu et al [18] used dual emission laser-induced fluorescence to measure slurry thickness and friction force between the wafer and the polishing pad. They demonstrated that both slurry thickness and friction force are dominantly dependent on the shape of the wafer.…”

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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“…Due to measurement issues, however the absolute distance is only accurate to within 5µm. Friction measurements between the pad and wafer are made during this polishing in addition to DELIF measurements [6]. In post processing these data, friction and gap thickness are correlated in time leading to a better understanding of slurry transport and polishing efficiency.…”

Section: Introductionmentioning

confidence: 99%

In-Situ Friction and Pad Topography Measurements During CMP

et al. 2004

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Duel Emission Laser Induced Fluorescence (DELIF) and friction measurements are taken in-situ during CMP to observe slurry flow beneath a model of an integrated circuit (IC) wafer. Friction measurements average around 7.5 lb and multiple frequencies are observed. Slurry film thicknesses on the order of a 10±3µm were observed during CMP of a flat wafer. The film thickness seems uncorrelated to friction measurements except when the pad and wafer rotation speeds are significantly slowed. DELIF has also accurately measured a 9µm etched step, with noise in the image equal to ±3 µm.

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The Effect of Wafer Shape on Slurry Film Thickness and Friction Coefficients in Chemical Mechanical Planarization

Cited by 26 publications

References 13 publications

Improved Model of Wafer/Pad Powder Slurry for CMP

Improved Model of Wafer/Pad Powder Slurry for CMP

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

In-Situ Friction and Pad Topography Measurements During CMP

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