d Toho Engineering Company, Yokkaichi, Mie, JapanReal-time coefficient of friction ͑COF͒ analysis was used to determine the extent of normal and shear forces during chemical mechanical planarization ͑CMP͒ and identify the lubrication mechanism of the process. Experiments were done on a scaled polisher using IC-1000 pads with various surface textures, and Fujimi's PL-4217 fumed silica slurry over a wide range of applied pressures and relative pad-wafer velocities. Stribeck curves showed that pad texture dictated the overall lubrication mechanism of the system. Average COF results yielded valuable information regarding the overall range of frictional forces associated with each type of surface texture. The linear correlation between COF data and interlayer dielectric ͑ILD͒ removal rate was consistent with previously published correlation graphs involving a variety of conventional pad textures and fumed silica concentrations. Spectral analysis of real-time friction data was used to elucidate the lubrication mechanism of the process in terms of the stick-slip phenomena and to quantify the total amount of hydrodynamic chattering as a function of various pad surface textures. For a given lubrication mechanism, analysis of the spectra for various textures indicated significant differences that were attributed to the amount of slurry present in the pad-wafer interface.Chemical mechanical planarization ͑CMP͒ has played an enabling role in attaining planar interconnection and metal layers essential for the realization and miniaturization of high-performance devices. To ensure stable and high-performance CMP characteristics, optimization of the slurry and the pad in terms of their chemical and mechanical properties is essential. Furthermore, understanding and optimizing the interactions between the pad and the slurry are important as they relate to the fluid dynamics of the process ͑espe-cially for 300 mm wafers͒ where the need to ͑i͒ minimize slurry dispense volumes, (ii) attain uniform slurry flow, (iii) discharge debris generated during polishing ͑such as pad fragments and polish by-products͒ and (iv) prevent subsequent particle redeposition are paramount. 1 Another key attribute resulting from the interactions between the slurry and the pad is the magnitude of shear forces in the pad-slurry-wafer region associated with a given set of process and consumable parameters. While increasing shear force ͑or frictional force͒ is shown to increase material removal rates, 2,3 high amounts of force can adversely affect the quality of the processed wafers by increasing the number of defects generated during the process 4 and by causing delamination of the underlying insulating films ͑especially low-strength porous or organic low k dielectrics͒. 5 Given the fact that shear force is the product of downforce and the coefficient of friction, the magnitude of shear force can be reduced by either reducing the wafer pressure, or by reducing the coefficient of friction in the pad-slurry-wafer region. The former method can be quite a costly...
Variations in the chemical mechanisms of copper chemical-mechanical planarization ͑CMP͒ can appear due to the effect of pad grooving on ͑i͒ net flow under the wafer, ͑ii͒ pad, wafer, and slurry temperature, and ͑iii͒ reactants and polish debris concentration. Furthermore, changes in the mechanical abrasion of the passive film might appear due to the effect of pad grooving on ͑i͒ slurry film thickness under the wafer, ͑ii͒ friction force at the pad-wafer interface, ͑iii͒ pad compressibility, and ͑iv͒ pad-wafer contact area. The effective transport of slurry in and out of the pad-wafer interface becomes critical particularly for processes in which by-products are detrimental to polishing rates. By combining logarithmic and spiral grooves, paths are created to introduce fresh slurry into, and spent slurry and debris out of, the pad-wafer interface. The experimentally grooved pads were tested and statistically compared to a commercial pad in terms of removal rate ͑RR͒, average coefficient of friction, and average pad leading edge temperature. Also a flat ͑i.e., not grooved͒ pad was included in this study to evaluate in general the effect of pad grooves in copper CMP. The results indicate that the pad achieving the highest relative values for RR, coefficient of friction ͑COF͒, and T p is the one that combines a negatively directed logarithmic groove with a positively directed spiral groove. This pad results in a 24% increase in RR and a 28% increase in COF compared to the concentrically grooved pad. To establish the mechanical and chemical contributions to the process, experimental data were then theoretically evaluated. A three-step model in combination with a previously developed flash heating ͑FH͒ temperature model was proposed for copper CMP. In all cases, the model root-meansquare ͑rms͒ error fell in the range of 322-674 Å/min, while the experimental repeatability error was in the range of 118-1100 Å/min. This model presented an expression to characterize the rate of oxide growth ͑k 1 ͒ and the addition of a third step to characterize the dissolution rate of copper oxide ͑k 3 ͒. The relative values of k 1 and k 2 ͑mechanical rate constant͒ as a function of pV showed that the process was more limited by film removal through mechanical abrasion, especially at low values of pV. However, as pV increased this limitation was reduced and there was a transition to a more balanced process.Interlevel dielectric and metal chemical-mechanical planarization.-In general, chemical-mechanical planarization ͑CMP͒ technology can be divided into two areas, interlevel dielectric ͑ILD͒ and metal CMP; both polishing processes are in some ways similar. 1 The same type of equipment used for dielectric polishing can also be used for metal polishing. The type of pads used in ILD and metal CMP are also similar. However, there are important differences that need to be considered. One of these differences, in fact a very important one, is the chemical effect of the slurry on the substrate to be polished. During ILD CMP, the surface of the wa...
The main objective of this investigation is to verify if "smart" groove designs can increase slurry utilization, by controlling the amount of slurry transferred from the pad grooves to the land area-wafer interface, resulting in process optimization. Based on previous studies concerning Logarithmic-Spiral as well as Concentric Slanted grooves, two groove designs were selected to be evaluated and compared to the popular industrial groove design ͑concentric grooves͒ under reduced slurry flow rate conditions during copper polishing. The effect of several process parameters were investigated, including pad groove design, applied wafer pressure, and slurry flow rate. Theoretical examination of the experimental data was performed by applying a three-step copper RR model, in order to establish the effect of groove designs on the chemical and mechanical mechanisms present during copper chemical mechanical polishing ͑CMP͒.
The interlayer dielectric ͑ILD͒ chemical mechanical polishing ͑CMP͒ process was characterized using frictional forces, material removal rates, thermal measurements, and theory. Experiments were performed on a novel 200 mm tribometer in which friction force was acquired in two directions, giving a complete resolution of the force vector in the CMP process. A thermal study of the pad surface was conducted using an infrared video camera to simultaneously measure temperature changes. A LangmuirHinshelwood model with a reaction temperature based on a flash heating hypothesis was applied to the experimental data to evaluate the chemical and mechanical contributions during ILD CMP. The results obtained from the 200 mm tribometer were compared to those from a 100 mm tribometer. Results showed that the scale-up of the ILD process from 100 to 200 mm caused a transition from a mechanically limited regime, in which it was still possible to detect thermal effects, to a higher degree of mechanical limitation where it was no longer possible to detect thermal effects.
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