D. Rosales-Yeomans

Effect of Pad Groove Designs on the Frictional and Removal Rate Characteristics of ILD CMP

Real-time coefficient of friction (COF) analysis was used to determine the extent of normal and shear forces during chemical mechanical planarization (CMP) and identify the lubrication mechanism of the process. Experiments were done on a scaled polisher using IC-1000 pads with various surface textures, and Fujimis 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 (ILD) 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.

Design and Evaluation of Pad Grooves for Copper CMP

Variations in the chemical mechanisms of copper chemical-mechanical planarization (CMP) can appear due to the effect of pad grooving on (i) net flow under the wafer, (ii) pad, wafer, and slurry temperature, and (iii) 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 (i) slurry film thickness under the wafer, (ii) friction force at the pad-wafer interface, (iii) pad compressibility, and (iv) 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 (RR), average coefficient of friction, and average pad leading edge temperature. Also a flat (i.e., not grooved) 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 (COF), 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 (FH) temperature model was proposed for copper CMP. In all cases, the model root-mean-square (rms) error fell in the range of 322-674 A/min, while the experimental repeatability error was in the range of 118-1100 A/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 constant) 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.

Implications of Wafer-Size Scale-up on Frictional, Thermal, and Kinetic Attributes of Interlayer Dielectric CMP Process

The interlayer dielectric (ILD) chemical mechanical polishing (CMP) 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 Langmuir-Hinshelwood 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 nossible to detect thermal effects.

Analysis of Pads with Slanted Grooves for Copper CMP

This investigation presents the analysis of concentric grooves with different degrees and directions of slant for the optimization of copper chemical mechanical planarization (CMP) processes. Taking into consideration the common industrial application of the concentric groove pattern, in this study pads were prepared with concentrical grooves having different degrees and direction of slant, such as 0° (zero), ±20°, and ±30°. The slanted groove pads were tested and statistically compared to each other in terms of removal rate, average coefficient of friction, and average pad leading edge temperature. Theoretical examination of the experimental data was performed to establish the mechanical and chemical contributions to the process. A three-step model, in combination with a previously developed flash heating temperature model, was proposed for copper CMP. This model presented an expression to characterize the rate of oxide growth and the addition of a third step to characterize the dissolution rate of copper oxide. The root-mean-square error after predicting the removal rate behavior with the three-step model fell between 351 and 445 A/min, while the experimental repeatability error fell in the range of 150 to 590 A/min for all pads tested in this study.

Experimental and Numerical Analysis of A Novel Ceria Based Abrasive Slurry for Interlayer Dielectric Chemical Mechanical Planarization

In this study, a novel slurry containing ceria as the abrasive particles was analyzed in terms of its frictional, thermal and kinetic attributes for interlayer dielectric (ILD) CMP application. The novel slurry was used to polish 200-mm blanket ILD wafers on an K-groove pad with in-situ conditioning. Polishing pressures ranged from 1 to 5 PSI and the sliding velocity ranged from 0.5 to 1.5 m/s. Shear force and pad temperature were measured in real time during the polishing process. The frictional analysis indicated that boundary lubrication was the dominant tribological mechanism. The measured average pad leading edge temperature increased from 26.4 to with the increase in polishing power. The ILD removal rate also increased with the polishing power, ranging from 400 to 4000 A/min. The ILD removal rate deviated from Prestonian behavior at the highest polishing condition and exhibited a strong correlation with the measured average pad leading edge temperature. A modified two-step Langmuir-Hinshelwood kinetic model was used to simulate the ILD removal rate. In this model, transient flash heating temperature is assumed to dominate the chemical reaction temperature. The model successfully captured the variable removal rate behavior at the highest polishing condition and indicates that the polishing process was mechanical limited in the low polishing region and became chemically and mechanically balanced with increasing polishing power.