Hyosang Lee

Effects of Disk Design and Kinematics of Conditioners on Process Hydrodynamics during Copper CMP

This study focuses on determining the effect of conditioner disk design, kinematics, and pressure on the slurry distribution under the wafer as measured by the slurry film thickness between the wafer and the pad during actual polishing. Film thicknesses are measured using dual emission UV-enhanced fluorescence, which for thickness measurement requires the slurry to be tagged with two different fluorescent dyes. Results indicate that the wafer is tilted toward the center of the pad and that the extent of wafer tilt is a strong function of conditioning disk pressure. Increasing the oscillation frequency of the conditioner disk or the rotation rate decreases the slurry film thickness and the film thickness increases with slurry flow rate.

Theoretical and experimental investigation of conditioner design factors on tribology and removal rate in copper chemical mechanical planarization

Three theories connecting conditioning with material removal rates by the coefficient of friction are proposed and experimentally verified. The conditioning theory is employed to provide a specific prediction on how the number of active diamonds, cut rate, and cut furrow geometry affect pad surface abruptness. The same surface abruptness parameter was a factor in both the coefficient of friction and removal rate theories. The theory predicts a priori that friction and removal rate should decrease as the conditioned surface became less abrupt. Simple models of cut rate and active diamond count further indicate that abruptness should decrease with increasing conditioner load. Mitsubishi Materials Corporation conditioners with 60, 100, and 200 grit sizes are used to test the theory in an experiment in which conditioner load is varied from light to heavy. Polishing experiments and pad profilometry verified the main predictions of the theory.

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.

Study of Inhibition Characteristics of Slurry Additives in Copper CMP using Force Spectroscopy

Using a reference slurry, ammonium dodecyl sulfate (ADS), an anionic and environmentally friendly surfactant, was investigated as an alternative to BTA for its inhibition and lubrication characteristics. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA. Coefficient of friction (COF) was the lowest when the slurry contained ADS. This suggested that adsorbed ADS on the surface provided lubricating action thereby reducing the wear between the contacting surfaces. Temperature results were consistent with the COF and removal rate data. ADS showed the lowest temperature rise again confirming the softening effect of the adsorbed surfactant layer and less energy dissipation due to friction. Spectral analysis of shear force showed that increasing the pad-wafer sliding velocity at constant wafer pressure shifted the high frequency spectral peaks to lower frequencies while increasing the variance of the frictional force. Addition of ADS reduced the fluctuating component of the shear force and the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer. By contrast, in the case of BTA, there were no such observed benefits but instead undesirable effects were seen at some polishing conditions. This work underscored the importance of real-time force spectroscopy in elucidating the adsorption, lubrication and inhibition of additives in slurries in CMP.

Diamond Conditioner Wear Characterization for a Copper CMP Process

Conditioner wear, copper polish rates, pad temperature and coefficient of friction (COF) are measured for two novel Mitsubishi Materials Corporation designs during an extended wear and polishing test. Both designs are coated with a film to reduce substrate wear and chemical attack. Using optical interferometry, changes in the coating that result in gradual changes in diamond exposure are measured. Theories of the COF, conditioning, and polishing are applied to explain the observed performance differences between the designs.

Thermal, Tribological, and Removal Rate Characteristics of Pad Conditioning in Copper CMP

High Pressure Micro Jet (HPMJ) pad conditioning system was investigated as an alternative to diamond disc conditioning in copper CMP. A series of comparative 50-wafer marathon runs were conducted at constant wafer pressure and sliding velocity using Rohm & Haas IC1000 and Asahi-Kasei EMD Corporation (UNIPAD) concentrically grooved pads under ex-situ diamond conditioning or HPMJ conditioning. SEM images indicated that fibrous surface was restored using UNIPAD pads under both diamond and HPMJ conditioning. With IC1000 pads, asperities on the surface were significantly collapsed. This was believed to be due to differences in pad wear rates for the two conditioning methods. COF and removal rate were stable from wafer to wafer using both diamond and HPMJ conditioning when UNIPAD pads were used. Also, HPMJ conditioning showed higher COF and removal rate when compared to diamond conditioning for UNIPAD. On the other hand, COF and removal rates for IC1000 pads decreased significantly under HPMJ conditioning. Regardless of pad conditioning method adopted and the type of pad used, linear correlation was observed between temperature and COF, and removal rate and COF.

Characterization of Slurry Residues in Pad Grooves for Diamond Disc and High Pressure Micro Jet Pad Conditioning Processes

Slurry residues inside pad grooves are quantified by UV-enhanced fluorescence (UVEF) technique for conventional diamond disc and high pressure micro jet (HPMJ) pad conditioning methods. Results show that with HPMJ pad conditioning, slurry residues inside pad grooves decrease with time at twice the rate compared to diamond disc conditioning. Therefore, this suggests that HPMJ pad conditioning is a viable method to extend pad life and possibly improve wafer-level defectivity.

Analysis of Formation of Pad Stains in Copper Chemical Mechanical Planarization

A stain model was developed to simulate stain formation on the pad surface in copper chemical and mechanical planarization (CMP). The model consisted of the incompressible Navier–Stokes equations, the heat equation with advection, material removal rate model, a model for generation, transport and deposition of the polishing by-product that produces the stain. Slurry velocity simulations showed shear flow on the land areas and wafer-driven circulation in the grooves. The simulated temperature on the pad and the wafer surface increased gradually in the radial direction; furthermore, temperature simulations showed a 12 °C rise in the reaction temperature on the copper wafer surface. The simulated pad stains deposited on the copper land areas were darker in the direction of wafer rotation, suggesting that the generated staining agents were advected downstream by the slurry flow and deposited on the pad surface in the direction of the wafer rotation. Simulated stain images were in qualitative agreement with experimental results.

Development of a Pad Conditioning Method for ILD CMP using a High Pressure Micro Jet System

The goal of this study is to determine if High Pressure Micro Jet (HPMJ) conditioning can be used as a substitute for, or in conjunction with, conventional diamond pad conditioning. Five conditioning methods were studied during which 50 ILD wafers were polished successively in a 100-mm scaled polisher and removal rate (RR), coefficient of friction (COF), pad flattening ratio (PFR) and scanning electron microscopy (SEM) measurements were obtained. Results indicated that PFR increased rapidly, and COF and removal rate decreased significantly, when conditioning was not employed. With diamond conditioning, both removal rate and COF were stable from wafer to wafer, and low PFR values were observed. SEM images indicated that clean grooves could be achieved by HPMJ pad conditioning, suggesting that HPMJ may have the potential to reduce micro scratches and defects caused by slurry abrasive particle residues inside grooves. Regardless of different pad conditioning methods, a linear correlation was observed between temperature, COF and removal rate, while an inverse relationship was seen between COF and PFR.