Copper Copper Chemical Mechanical Polishing Research Articles

Competitive effect between corrosion inhibitors in copper chemical mechanical polishing

Corrosion inhibitors are critical to realizing local and global planarization in copper chemical mechanical polishing (CMP). It is necessary to explore the interaction between components of composite corrosion inhibitors. This study reported a type of composite corrosion inhibitors of 1,2,4-triazole (TAZ) and 5-methyl-benzotriazole (5-MBTA) having a competitive effect between TAZ and 5-MBTA, different from the conventional synergistic effect. It is revealed that after adding either TAZ or 5-MBTA or their combination, the copper surface quality can be improved, while the copper material removal rate (MRR) ranks: TAZ > TAZ + 5-MBTA > 5-MBTA. For the competitive effect, TAZ and 5-MBTA can be co-adsorbed on the copper surface. Meanwhile, the electrochemical results indicate that the corrosion inhibition effect can rank: 5-MBTA > TAZ + 5-MBTA > TAZ, implying that TAZ and 5-MBTA may compete for the adsorption sites. The competitive effect may root in the different molecular structures, presumably the benzene ring. According to the corrosion wear mechanism of copper CMP, the stronger the corrosion inhibition effect, the lower the MRR. Therefore, the MRR of the composite corrosion inhibitors is between TAZ and 5-MBTA. The finding provides an enhanced understanding of composite corrosion inhibitors in the copper CMP.

Copper Chemical Mechanical Polishing Performances of Polystyrene/Ceria Hybrid Abrasives with a Core/Shell Structure

The core/shell structured hybrid abrasives, featuring polystyrene (PS, 280–300 nm in size) cores and ceria (CeO2, 10–20 nm in thickness) shells, were introduced into copper chemical mechanical polishing (CMP) processes. The slurry chemistry based on the synergy among glycine–hydrogen peroxide-benzotriazole was used in combination with the obtained polystyrene/ceria (PS/CeO2) abrasives. Moreover, the use of a medium/high-hardness pad (IC-1000) was compared to the use of a soft pad (MD-Chem). The copper CMP characteristics were evaluated in terms of material removal rate, surface roughness as well as cross-sectional profile analyses. After CMP with PS/CeO2 hybrids in combination with a soft pad, the average roughness of copper layer decreased from 1.89 to 0.56 nm, and a mean removal rate of 254 nm/min was achieved. With respect to conventional ceria particles, the PS/CeO2 hybrid abrasives contributed to the reduction of the mechanical damage and the number/depth of scratch/pit. The improved copper CMP performances might result from the reduced overall hardness and elastic modulus of PS/CeO2 hybrid particles. These experimental results revealed that the PS/CeO2 composite abrasives further presented potential CMP applications for mechanically challenging materials such as copper and low-k dielectrics.

Passivation Kinetics of 1,2,4-Triazole in Copper Chemical Mechanical Polishing

Optimizing the copper slurry, especially the corrosion inhibitor, is critical to its successful application in copper chemical mechanical polishing (CMP) for the next-generation ultra-large scale integrated circuits manufacturing. In this paper, 1,2,4-triazole was considered to be a promising alternative to the conventional benzotriazole (BTA). The passivation kinetics of 1,2,4-triazole on the copper surface was investigated with several different electrochemical techniques, including open-circuit potential, potentiodynamic polarization, cyclic polarization and chronoamperometry. The results of the chronoamperometry experiments show that the peak response If and the time constant τf of the current density from the faradaic reactions are critical to the passivation kinetics of 1,2,4-triazole. Based on the electrochemical results and the existing material removal model, the material removal mechanism of copper when being polished with the slurry containing colloidal silica, H2O2, glycine, 1,2,4-triazole and with pH 6.0 is inferred to be corrosion-enhanced wear dominant. Additionally, the passivation kinetics parameters of 1,2,4-triazole were compared with those of BTA. Icorr, If and τf of 1,2,4-triazole are all larger than those of BTA, which can be used to partly explain why 1,2,4-triazole's passivation is relatively weaker than that of BTA and its resultant suitability as an alternative corrosion inhibitor for copper CMP.

Effect of slurry components on chemical mechanical polishing of copper at low down pressure and a chemical kinetics model

The practical use of low dielectric constant materials as inter-layer dielectrics is driving the demand for copper chemical mechanical polishing (CMP) at low down pressure, which is a challenge for the traditional CMP technology. To solve this issue, it is necessary to develop a chemically dominant CMP process at low down pressure. The chemical oxidation and dissolution of the oxidized copper are more important than mechanical. In this paper, the ingredient and prescription of slurry is found, which is used to achieve high surface removal rates and certain Within-Wafer Non-Uniformity at a down pressure of 4.3 kPa. The CMP slurry contains silica sols, H 2O 2 and chelating agent. A model of copper CMP at low down pressure based on the methods of chemical kinetics and oxidation reaction is presented. The model prediction trends are consistent with the experimental data.

Study on the Effect of Nonionic Surfactant in Copper CMP Slurry

The effect of surfactant in alkaline slurry for copper chemical mechanical polishing (CMP) was studied through polishing experiments with slurries containing different weight percentage of four nonionic surfactants respectively. The results indicate that properly chosen nonionic surfactants with proper weight percentage could result in little negative influence on the material removal rate, but can help to improve copper wafer surface quality significantly. Alkylphenol ethoxylates was found to be an excellent surfactant for alkaline slurry and a surface roughness of Ra 0.89nm and a material removal rate of 526 nm/min were obtained when polishing with the slurry containing 0.25 wt% alkylphenol ethoxylates, while the surface roughness and the material removal rate were Ra 1.34nm and 525 nm/min respectively when polishing with the origin slurry. The density of polishing defects such as scratches and etch pits decreased significantly. The action mechanism of surfactant was further analyzed based on the experiment results.

Electrochemical characterization of copper chemical mechanical polishing in l-glutamic acid–hydrogen peroxide-based slurries

The effect of l-glutamic acid as complexing agent in the presence of hydrogen peroxide as oxidizer in copper chemical mechanical polishing (CMP) slurry is investigated. In the CMP process, the work surface is moved against a pad, with slurry flowing between the surface and the pad. The polish rate was found to be stable over a wide range of hydrogen peroxide concentration. High concentration of either l-glutamic acid or hydrogen peroxide leads to a reduction in polish rate, but a high concentration of both chemicals does not reduce the polish rate. In the absence of hydrogen peroxide, the Cu polish rate was 0 for all the l-glutamic acid concentrations investigated. However, potentiodynamic polarization curves do not show any sign of passivation when l-glutamic acid was present in the solution. In situ open circuit potential measurements show that copper redox reactions as well as hydrogen peroxide redox reactions contribute in determining the electrochemical behavior. We propose that l-glutamic acid inhibits the copper dissolution by adsorption onto the metallic copper, but enhances copper dissolution by complexing copper ions. The results show that it is possible to conduct controllable copper CMP in mildly acidic slurries with hydrogen peroxide as oxidizer and l-glutamic acid as complexing agent.

Effects of pattern characteristics on copper CMP

Copper chemical mechanical polishing (CMP) is influenced by geometric characteristics such as line width and pattern density, as well as by the more obvious parameters such as slurry chemistry, pad type, polishing pressure and rotational speed. Variations in the copper thickness across each die and across the wafer can impact the circuit performance and reduce the yield. In this paper, we propose a modeling method to simulate the polishing behavior as a function of layout pattern factors. Under the same process conditions, the pattern density, the line width and the line spacing have a strong influence on copper dishing, dielectric erosion and topography. The test results showed: the wider the copper line or the spacing, the higher the copper dishing; the higher the density, the higher the dielectric erosion; the dishing and erosion increase slowly as a function of increasing density and go into saturation when the density is more than 0.7.

Cation Effect on Copper Chemical Mechanical Polishing

We examine the effect of cations in solutions containing benzotriazole (BTA) and H2O2 on copper chemical mechanical polishing (CMP). On the base of atomic force microscopy (AFM) and material removal rate (MRR) results, it is found that ammonia shows the highest MRR as well as good surface after CMP, while KOH demonstrates the worst performance. These results reveal a mechanism that small molecules with lone-pairs rather than molecules with steric effect and common inorganic cations are better for copper CMP process, which is indirectly confirmed by open circuit potential (OCP).

Evaluation of Pad Groove Designs under Reduced Slurry Flow Rate Conditions during Copper CMP

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 grooves) 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 (CMP).

Effect of temperature on copper damascene chemical mechanical polishing process

The effects of different process parameters on tribology and surface defects were studied till date, but there has been minimal study to understand the effect of temperature on the copper chemical mechanical polishing (CMP) process. The effect of temperature on tribology and surface defects during copper CMP employing different pad materials and slurries has been explored. From the results, it was seen that the coefficient of friction and removal rate increased with an increase in slurry temperature during polishing. The experimental data indicated that the increase in temperature results in an increase in amounts of metal dishing and metal loss. The dishing and metal loss in the interconnect features initially increased with an increase in temperature and then decreased at elevated temperatures. With an increase in temperature the copper films peeled off from the wafer due to low adhesion with low-k dielectric material at higher temperatures. The electrical properties of the planarized devices showed dra...

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 . 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.

Design of experiment (DOE) method considering interaction effect of process parameters for optimization of copper chemical mechanical polishing (CMP) process

Chemical mechanical polishing (CMP) has been widely accepted for the metallization of copper interconnection in ultra-large scale integrated circuits (ULSIs) manufacturing. It is important to understand the effect of the process variables such as turntable speed, head speed, down force and back pressure on copper CMP. They are very important parameters that must be carefully formulated to achieve desired the removal rates and non-uniformity. Using a design of experiment (DOE) approach, this study was performed investigating the interaction effect between the various parameters as well as the main effect of the each parameter during copper CMP. A better understanding of the interaction behavior between the various parameters and the effect on removal rate, non-uniformity and ETC (edge to center) is achieved by using the statistical analysis techniques. In the experimental tests, the optimized parameters combination for copper CMP which were derived from the statistical analysis could be found for higher removal rate and lower non-uniformity through the above DOE results.

Effect of Slurry Injection Position on Slurry Mixing, Friction, Removal Rate, and Temperature in Copper CMP

In this study, the extent of mixing of old and new slurry on the polishing pad is varied by the use of three different points of injection. Influences of the conditioner and bow wave on slurry mixing can be inferred from the experimental results, which include coefficient of friction data and pad and substrate thermal data. Results measured under identical lubrication mechanisms show that the slurry injection position can play a significant role in slurry mixing and slurry utilization efficiency. Slurry injection positions that induce lower slurry mixing are found to increase copper removal rate. Simulations of the bow wave and slurry puddle support the interpretation of the mixing phenomenon. This work underscores the importance of optimum slurry injection geometry and flow for obtaining a more cost effective and environmentally benign copper chemical mechanical polishing (CMP) process.

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 and . Using oxygen or nitrogen has only slight effects on copper removal rates in the presence of . Polishing without , performed with controlled oxygen partial pressure, demonstrates removal rates that are 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 (pH 10) to experiments using oxidizing gases, such as oxygen and air, increases removal rates up to . Removal rates vary linearly with oxygen partial pressure using oxidizing gases for experiments using at pH 10. A trend indicating a transition from chemical to mechanical control is observed when 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.

A Model of Copper CMP

A model of copper chemical mechanical polishing (CMP) based on methods of chemical kinetics is presented which includes both chemical and mechanical processes. This CMP model explains observed patterns in removal rates for peroxide and nonperoxide-based slurries as a function of oxidizer concentration, polishing pressure and speed, etchant concentration, and pH.

Novel Use of Surfactants in Copper Chemical Mechanical Polishing (CMP)

AbstractIn this study, the interaction between several kinds of surfactants and copper surface was examined to control the dissolution of copper during CMP. Among those surfactants, sodium dodecylsulfate (SDS), one of the conventional anionic surfactants, showed effective interaction with copper and significantly suppressed the dissolution of the copper at acidic and neutral pH ranges in a model copper CMP slurry system consisting of 3 wt% fumed silica, 1 wt% glycine, and 5 wt% hydrogen peroxide in deionized water. The inhibition performance of copper dissolution by SDS is better than that of Benzotriazole (BTA), a conventional inhibiting agent of copper dissolution in a copper CMP slurry.

The impact of scaling on metal thickness for advanced back end of line interconnects

In this paper, a universal model to predict the amount of allowable metal thinning for the control of copper chemical–mechanical polishing (CMP) is presented. In the model, all the non-planarity, like dishing and erosion, resulted from the copper CMP process, is assumed accumulative. This amount after a certain levels of wiring should never be greater than the thickness of a single wiring level. Otherwise the circuit connections will be failure, since the metal is not at the right position. Based on this criterion, an equation is derived and the percentage of allowable metal thinning to the metal thickness is defined as F MT. The calculated F MT for the 180, 130, 90, 65 and 45 nm generations are 15%, 10%, 9%, 8%, and 7%, respectively. For the 130 and 90 nm generations, these numbers are close to the guidance of 10% recommended in the 2003 International Technology Roadmap for Semiconductors (ITRS). However, for the 65 nm and the 45 nm generations, the calculated F MT factors are smaller than that in the roadmap, suggesting that tighter copper CMP process control is required in the future generations.

Robust operation of copper chemical mechanical polishing

The unusual concentration effect in copper chemical mechanical polishing (CMP) is verified experimentally and operation-relevant models are derived. First, the well-known Preston equation is modified by taking the concentration effects into account. Next, a linear model is proposed to describe dishing as functions of and typical operation variables. Combining both models, we are able to locate feasible operation region without constraint violation. Finally, the robust operation procedure is incorporated into a realistic CMP operation strategy: soft landing. A systematic procedure is proposed to ensure robust operation for copper CMP.

Characterization and Control of Copper CMP with Optoacoustic Metrology

ABSTRACTWe discuss applications of optoacoustic film thickness metrology for characterization of copper chemical-mechanical polishing (CMP). We highlight areas where the use of optoacoustics for CMP characterization provides data complementary to that obtained by other techniques because of its ability to directly measure film thickness with high spatial resolution in a rapid, non-destructive manner. Examples considered include determination of planarization length, measurement of film thickness at intermediate stages of polish, and measurement of arrays of metal lines.