Hydrodynamic characteristics of the thin fluid film in chemical-mechanical polishing

Chen, J.A.; Fang, Y. C.

doi:10.1109/66.983442

Cited by 26 publications

(22 citation statements)

References 12 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.…”

supporting

confidence: 89%

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: 89%

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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“…The two-dimensional Navier-Stokes equations and mass transport equations for the reactants were solved using finite element techniques. Other wafer scale purely hydrodynamic models of CMP include the work of Park et al [53], Cho et al [54], and Chen et al [55].…”

Section: 31mentioning

confidence: 99%

Material Removal Mechanisms in Lapping and Polishing

et al. 2003

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“…Using this information, the film thicknesses h m , wafer tilts α, and pressure distributions for each wafer were calculated using the hydrodynamic model of Chen and Fang. 13 The film thicknesses obtained range from 28 μm to 56 μm, with wafer tilt angles of 0.0017 • to 0.0082 • . Generally, higher applied pressures and smaller dome heights resulted in thinner films and smaller angles of tilt.…”

Section: Resultsmentioning

confidence: 99%

Copper CMP: The Relationship between Polish Rate Uniformity and Lubrication

Nolan

Cadien

2012

ECS J. Solid State Sci. Technol.

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Chemical Mechanical Polishing of Copper (Cu-CMP) is an important yet poorly-understood nanofabrication technique. In this work, we demonstrate that the degree of non-uniformity in polishing rates, described by the new quantity MRRNU, relates to the lubrication conditions of the polishing couple. MRRNU is the difference between the highest and lowest material removal rates (MRRs) recorded across the wafer surface, normalized by the average MRR. The polish rate non-uniformity that this quantity encapsulates is shown to transition from negative (wafer-scale dishing) to positive (wafer-scale doming) with increasing Sommerfeld number, for the pad and slurry chemistry used here. This is explained by the presence of co-existing lubrication zones in the pad-wafer interface. Each of the zones described, namely the edge zone, hydrodynamic zone and suppression zone, demonstrate a different relationship between pressure and removal rate, resulting in variation in MRR across the wafer. Chemical Mechanical Polishing, or CMP, is a nanofabrication technique used to simultaneously remove material from surfaces and planarize them. It is commonly used within the semiconductor industry to process surfaces of silicon oxide, silicon nitride and both polycrystalline and single-crystal silicon. It has also been used with metals such as aluminum, tungsten and copper, where it is used in conjunction with etching and electroplating techniques to form nanoscale features such as interconnects. A more complete description of the CMP process is available in the literature. 1 Successful application of CMP requires understanding how withinwafer-non-uniformity (WIWNU) develops during polishing. Several factors are known to influence WIWNU for copper CMP, including slurry chemistry, 2,3 pad wear 4 and pad topography. 5 For a given slurry chemistry and pad, WIWNU is also influenced by the polishing pressure and velocity. 6 However, a comprehensive examination of the effects of pressure and velocity on WIWNU has not been conducted. In this study, the combined influence of pressure and velocity on WI-WNU is summarized by the dimensionless Sommerfeld number (So), describing the lubrication regime and hence load transfer mechanism in CMP. The change in WIWNU during polishing, described by the new quantity MRRNU, is shown to correlate strongly with the Sommerfeld number. MRRNU is obtained by measuring the polishing material removal rate (MRR) across the radius of the wafer, then normalizing the difference between the maximum and minimum rates obtained by the mean MRR. Three zones of polishing contact which coexist during polishing are postulated to explain the observed correlation between So and MRRNU.During polishing, the pressure applied to the polishing couple can be transferred between the pad and the wafer through direct contact with the pad and abrasives, through the intervening fluid, or through a combination of both. The mode of load transfer is characterized in tribology by the construction of a Stribeck curve. This is a plot of the Sommerfeld ...

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Hydrodynamic characteristics of the thin fluid film in chemical-mechanical polishing

Cited by 26 publications

References 12 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

Material Removal Mechanisms in Lapping and Polishing

Copper CMP: The Relationship between Polish Rate Uniformity and Lubrication

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