Darren DeNardis

Arrhenius Characterization of ILD and Copper CMP Processes

To date, chemical mechanical planarization (CMP) models have relied heavily on parameters such as pressure, velocity, slurry, and pad properties to describe material removal rates. One key parameter, temperature, which can impact both the mechanical and chemical facets of the CMP process, is often neglected. Using a modified definition of the generalized Prestons equation with the inclusion of an Arrhenius relationship, thermally controlled polishing experiments are shown to quantify the contribution of temperature to the relative magnitude of the thermally dependent and thermally independent aspects of copper and interlayer dielectric (ILD) CMP. The newly defined Prestons equation includes a modified definition of the activation energy parameter contained in the Arrhenius portion, the combined activation energy, which describes all events (chemical or mechanical) that are impacted by temperature during CMP. Studies indicate that for every consumable set combination (i.e., slurry and polishing pad) a characteristic combined Arrhenius activation energy can be calculated for each substrate material being polished.

Tribology and Removal Rate Characteristics of Abrasive-Free Slurries for Copper CMP Applications

This study employs real-time high-frequency frictional force analysis coupled with removal rate studies to quantify the extent of frictional forces encountered during copper polish using abrasive-free slurries and to establish the time-dependent tribological attributes of the process. The study also uses spectral analysis of the frictional force data to validate and explore the subtle characteristics of the formation and extinction of the copper complex layer known to play an integral role in abrasive-free copper chemical mechanical planarization (CMP). It was found that copper removal rates are at least partially driven by coefficient of friction, which is similar to the case of interlayer dielectric (ILD) CMP. Spectral analysis suggests that the periodicity of the copper complex layer formation and abrasion is approximately 10 ms.

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.

Development and Analysis of a High-Pressure Micro Jet Pad Conditioning System for Interlayer Dielectric Chemical Mechanical Planarization

Conventional diamond disc pad conditioning methods employed in chemical mechanical planarization (CMP) have presented several problems for integrated circuit (IC) manufacturers. These include diamond wear, which reduces pad life, and diamond fracture, which causes the semiconductor devices to be scratched by loose diamond fragments. In order to attempt to overcome these problems, a high-pressure micro jet (HPMJ) conditioning system, in which pressurized ultra pure water (UPW) ranging from 3–30 MPa is sprayed on the pad surface, is proposed and developed. This study first analyzes the extent of the kinetic energy of water droplets ejecting from the HPMJ system and its utility in conditioning the pad surface. Subsequently, CMP is used to polish interlayer dielectric (ILD) films using both conventional diamond discs as well as HPMJ conditioning methods. Results, reported in the form of coefficient of friction (COF), removal rate, pad surface roughness and pad surface quality, highlight both the advantages as well as disadvantages of the HPMJ method compared to conventional conditioning schemes.

Modeling Copper CMP Removal Rate Dependency on Wafer Pressure, Velocity, and Dissolved Oxygen Concentration

A controlled atmosphere polishing system (CAP) was used to identify differences in copper chemical mechanical polishing (CMP) removal characteristics by changing oxygen partial pressure. A two-step kinetic mechanism was proposed, including a copper surface passivation layer formation and subsequent removal. A semiempirical, two-parameter model has been developed to simulate removal rates for multiple wafer pressures, pad-wafer velocities, and oxygen concentrations. The model accurately predicts removal trends with calculated root-mean-square errors of 77-125 A/min. A major advantage of the CAP system is that a point-of-use gaseous oxidant was successfully used to polish copper substrates, and slight changes in oxidant partial pressure were found to significantly affect removal rate trends.

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.

Impact of Gaseous Additives on Copper CMP in Neutral and Alkaline Solutions Using a CAP System

A controlled atmosphere polishing (CAP) system was used to determine the effects of various chamber gases on copper chemical mechanical polishing (CMP) in the presence and absence of NH 4 OH and H 2 O 2 . Using 500 kPa oxygen or nitrogen has only slight effects on copper removal rates in the presence of 1 wt % H 2 O 2 . Polishing without H 2 O 2 , performed with controlled oxygen partial pressure, demonstrates removal rates that are 4 times higher than using nitrogen. Polishing using inert gases alone demonstrates an oxidant-starved system that reflects little dependence on wafer pressure or velocity. Addition of NH 4 OH (pH 10) to experiments using oxidizing gases, such as oxygen and air, increases removal rates up to 3×. Removal rates vary linearly with oxygen partial pressure using oxidizing gases for experiments using NH 4 OH at pH 10. A trend indicating a transition from chemical to mechanical control is observed when NH 4 OH concentration is increased at constant oxygen pressure. A copper removal mechanism in the presence of dissolved oxygen has been developed that highlights a buildup of oxidized copper at the wafer surface. The ability to perform CMP in a pressurized gaseous environment has shown that copper removal is a process of mechanical removal, dissolution of abraded material, and copper-oxygen reactions at the wafer surface.

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.

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.