Tungsten Chemical Mechanical Polishing Research Articles

Tribological Behavior of Metal CMP and Detection of Process Abnormality

We examined a real-time coefficient of friction (COF) monitoring to evaluate the correlation between the pad surface response during polishing and material removal rate for metal chemical-mechanical polishing (CMP) applications. The results showed that a correlation of the removal rate and COF in tungsten (W) CMP was contrary to that in copper (Cu) CMP. Polishing by-products generated during CMP affects the friction force between the probing tip and the pad surface. The balance between the chemical and mechanical factors indicates the different frictional behavior between W CMP and Cu CMP. Furthermore, we detected the failures in the CMP process, which extracts an out-of-range deviation of the continuously monitored COF in product wafers, and reveal them in tantalum CMP. These results demonstrated the usefulness of an in situ CMP process monitor.

Electrochemical corrosion effects and chemical mechanical polishing characteristics of tungsten film using mixed oxidizers

In this paper, the effects of mixed oxidizers on tungsten-chemical mechanical polishing (W-CMP) process were studied using three different kinds of oxidizers such as Fe(NO 3) 3, KIO 3 and H 2O 2. Moreover, the interaction between the tungsten film and the oxidizer was discussed by potentiodynamic polarization test, in order to compare the CMP performances and electrochemical behavior of the tungsten film as a function of mixed oxidizers. The potentiodynamic polarization results indicated that the corrosion current densities of the 5 wt% H 2O 2 and 5 wt% H 2O 2 + 5 wt% Fe(NO 3) 3 were higher than the other mixed oxidizers. Such an electrochemical corrosion effect implies that slurries with the highest removal rate have a high dissolution rate at lower pH. Therefore, we conclude that W-CMP performances are strongly dependent on the kind of oxidizers and the amounts of oxidizer additive.

텅스텐 CMP에서 산화제 영향에 관한 연구

Chemical mechanical polishing(CMP) has become the process of choice for modem semiconductor devices to achieve both local and global planarization. CMP is a complex process which depends on numerous variables such as macro, micro and nano-geometry of pad, relative velocity between pad and wafer stiffness and dampening characteristics of pad, slurry, pH, chemical components of slurry, abrasive concentration, abrasive size, abrasive shape, etc. Especially, an oxidizer of chemical components is very important remove a target material in metal CMP process. This paper introduces the effect of oxidizer such as <TEX>$H_2O_2,\;Fe(NO_3)_3\;and\;KIO_3$</TEX> in slurry for tungsten which is used in via or/and plug. Finally the duplex reacting mechanism of <TEX>$oxidizer(H_2O_2)$</TEX> through adding the <TEX>$catalyst(Fe(NO_3)_3)$</TEX> could acquire the sufficient removal rate in tungsten CMP.

혼합 산화제를 사용한 텅스텐 막의 전기화학적 부식 및 CMP 특성

In this paper, the effects of oxidants on tungsten chemical mechanical polishing (CMP) process were investigated using three different oxidizers such as Fe(NO₃)₃, KIO₃ and H₂O₂. Moreover, the interaction between the tungsten film and the oxidizer was discussed by potentiodynamic polarization measurement with three different oxidizers, in order to compare the effects of W-CMP and electrochemical characteristics on the tungsten film as a function of oxidizer. As an experimental result, the tungsten removal rate reached a maximum at 5 wt％ Fe(NO₃)₃concentration, and when 5 wt％ H₂O₂was added in the slurry, the removal rate of W increased. Also, the microstructures of surface layer by atomic force microscopy(AFM) image were greatly influenced by the slurry chemical composition of oxidizers. It was shown that the surface roughness and removal rate of the polished surface were improved in Fe(NO₃)₃than KIO₃. The electrochemical results indicate that the corrosion current density of the 5 wt％ H₂O₂ and 5 wt％ H₂O/sub 2+/＋ 5 wt％ Fe(NO₃)₃was higher than the other oxidizers. Therefore, we conclude that the W-CMP characteristics are strongly dependent on the kinds of oxidizers and the amounts of oxidizer additive.

Effects of different oxidizers on the W-CMP performance

In this paper, we investigated the effect of oxidizers on tungsten-chemical mechanical polishing (W-CMP) process with three different kinds of oxidizers, such as H 2O 2, Fe(NO 3) 3, and KIO 3. In order to compare the removal rate (RR) and within-wafer non-uniformity (WIWNU%) of three oxidizers, we used alumina (Al 2O 3)-based slurry of pH 4. According to the CMP tests, three oxidizers had a different removal mechanism on tungsten surface. Also, the microstructures of surface layer by atomic force microscopy (AFM) image were greatly influenced by the slurry chemical composition of oxidizers. The difference in removal rate and roughness of tungsten surface are believed to cause by modification of chemical reaction and mechanical behavior of Al 2O 3 abrasive particles in CMP slurry due to the adding of oxidizer.

Effects of oxidant additives for exact selectivity control of W- and Ti-CMP process

Tungsten is widely used as a plug for the multi-level interconnection structures. However, due to the poor adhesive properties of tungsten (W) on SiO 2 layer, the Ti/TiN barrier layer is usually deposited onto a SiO 2 layer in order to increase the adhesion ability with the tungsten film. Generally, for the tungsten chemical mechanical polishing (W-CMP) process, the passivation layer on the tungsten surface during CMP plays an important role. In this paper, the effects of oxidants controlling the polishing selectivity of the W/Ti/TiN layer were investigated. The alumina (Al 2O 3)-based slurry with H 2O 2 oxidizer was used for CMP applications. As an experimental result, for the case of 5% oxidizer added, the removal rates were improved and a polishing selectivity of 1.4:1 was obtained. Therefore we conclude that the W and Ti metal CMP characteristics are strongly dependent on the amounts of H 2O 2 oxidizer additive.

A Model of CMP: III. Inhibitors

A model of chemical mechanical polishing (CMP), based on a steady-state balance between chemical growth kinetics for a surface film and its mechanical removal rates, is extended to include the effects of inhibitors on the polishing rate. The general case provides qualitative insights into the process and presents a quantitative measure of inhibitor effectiveness. The model is applied to the case of tungsten CMP, with modifications in some details based on the complexity of the tungsten oxide surface film. The model is used to interpret data for three inhibitors in four slurry formulations and to explain their qualitatively different behaviors. © 2003 The Electrochemical Society. All rights reserved.

Formation of Tungsten Oxide Defects during Tungsten CMP

Most tungsten chemical mechanical polishing (CMP) processes utilize a subsequent cleaning process referred to as post-CMP cleaning for removal of contaminated layers. Even after a proper post-CMP cleaning has treated polished wafers, several defects such as slurry particles, microscratches, and metallic impurities are still easily observable. In this study, a new kind of defect has been observed at the stage between overpolishing and post-CMP clean in the course of the tungsten CMP. The circular-shape defect was composed of very thin tungsten oxide, which could be removed by several treatments such as HF solution dipping, additional oxide CMP, and the treatment of concentrated ammonium hydroxide solution during poly(vinyl alcohol) brushing. Among them, the most available method without any further process issues was the use of concentrated ammonium hydroxide solution. © 2003 The Electrochemical Society. All rights reserved.

Integrated Tungsten Chemical Mechanical Polishing Process Characterization for Via Plug Interconnection in Ultralarge Scale Integrated Circuits

One integrated tungsten (W) chemical mechanical polishing (CMP) process characterization with wide production margin is developed for W plug application in sub-quarter micron technology. In this study, it is identified that donut-type function failure and reliability degradation on a designed application specific integrated circuit (ASIC) product vehicle result from an extra oxide layer atop the W plugs. W recess in via holes makes the plugs more vulnerable to oxide layer formation. CMP polish rate uniformity, layout dependence of via holes and queue-time (Q-time) control between WCMP and post-cleaning treatment are key parameters for preventing failure from interfacial oxide layer. Integrated optimization of WCMP process combined with W extrusion by a slight oxide polish immediately after WCMP is proposed to achieve a robust W plug process. Significant yield improvement from 45% to 82% in wafer edge region and 0% failure in three qualification lots in a product reliability test are demonstrated.

Application of a CMP Model to Tungsten CMP

A general model of chemical mechanical polishing (CMP) has been derived which shows the dependence of the polishing rate on the concentration of chemicals and abrasives in the slurry. This paper applies the model to tungsten CMP and describes the chemistry of tungsten CMP in some detail. © 2001 The Electrochemical Society. All rights reserved.

Galvanic Corrosion of TiN-W Electro-couple During Tungsten Chemical Mechanical Polishing

Galvanic Corrosion of TiN-W Electro-couple During Tungsten Chemical Mechanical Polishing

Modeling and Characterization of Tungsten Chemical and Mechanical Polishing Processes

Due to the complexity of chemical mechanical polishing (CMP) in general and metal CMP in particular, modeling of CMP processes has been pursued only minimally in the literature. A fundamental understanding of these metal CMP processes is needed to minimize manufacturing and development costs that will continue to escalate as more devices migrate to subhalf-micrometer technologies where metallization schemes are more complicated. In this work, we have used two different models to characterize the tungsten CMP process. While the chemical Preston model is used to explain the effect of process parameters on the mean polish rate, the slurry transport model is useful in explaining the within wafer uniformity for the polishing process. We successfully validated the chemical Preston model using design of experiment (DOE) data and demonstrated the importance of slurry transport and the pad to wafer gap, to the within wafer uniformity for the embossed and regular politex polishing pads. We showed that better uniformity is obtained throughout the wafer with the embossed politex than the regular politex pad due to the presence of grooves in the embossed pad, which allow for better slurry transport across the pad. We effectively characterized the process and studied the effects of changing the various tool and process parameters on process performance. © 2001 The Electrochemical Society. All rights reserved.

Polyurethane Pad Degradation and Wear Due to Tungsten and Oxide CMP

ABSTRACTPolyurethane polishing pads are commonly used for chemical-mechanical polishing (CMP) of semiconductor wafers. Structural, chemical, and mechanical property changes of the polishing pads due to CMP are examined. Tungsten and oxide film layers are polished from the wafer surface using the polishing pad and abrasive slurry system. The polishing pad surface is flattened with polishing, and hence, reducing the effective area for slurry transport. The abrasive is used for abrading off the film from the surface. W, Al, I, and K accumulate in the polishing pad after tungsten CMP and Si accumulates after oxide CMP. Material accumulates in the pad pores and grooves. Electron Microprobe X-ray Analysis and Wavelength Dispersive Spectrometry (WDS) were used to examine the changes across the thickness of the pad. Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the changes to the polyurethane isocyanate group. The reduction in the isocyanate group and increase in the hydroxyl group after tungsten CMP indicates that a hydrolysis reaction of the isocyanate to form carboxylic acid occurs.

Stabilization of High Ionic Strength Slurries Using the Synergistic Effects of a Mixed Surfactant System

The stability of colloidal slurries is an important parameter in many industries due to problems that can arise as a result of particle settling. Particle settling is often caused by the shielding of surface charges on the particles which otherwise would prevent coagulation and subsequent settling. This is particularly a problem in high ionic strength slurries, where large amounts of ions serve to enhance the charge shielding and compression of the electrical double layer around the particles. This phenomenon has been investigated for industrially significant slurries used for tungsten and copper chemical mechanical polishing (CMP). It has been found that the effects of addition of conventional stabilizing agents (e.g., ionic surfactants, polymers) to these high ionic strength slurries are neutralized by the electrolytes in solution. However, the synergistic combination of a properly chosen ionic and nonionic surfactant has been found to be a suitable stabilizing agent for this type of system. For the CMP slurries investigated, the synergistic effect has been shown to be maximum for combinations of sodium dodecyl sulfate anionic surfactant and a variety of polymeric nonionic surfactants. The stabilization observed for these mixed surfactant systems has been explained in terms of adsorption of ionic surfactant on particle surfaces and nonionic surfactant molecules penetrating the film of the ionic surfactant due to hydrocarbon chain interactions. This brings about the steric stabilization of the slurry.

Studies on passivation behavior of tungsten in application to chemical mechanical polishing

Chemical mechanical polishing (CMP) is considered to be the enabling technology for meeting the planarization requirements in &amp;lt;0.35 μm feature sized multilevel semiconductor device fabrication. CMP of tungsten is done in order to planarize and remove excess tungsten in the process to form inter-level contacts. Considerable importance is given to the role played by the passive oxide film formation on the surface during tungsten CMP. In this study, x-ray photoelectron spectroscopy (XPS) is used to understand the oxide growth mechanism in tungsten. Tungsten wafers are polarized to different anodic potentials in static pH 4 solutions of KIO3 and H2O2, two commonly used oxidizers in CMP. XPS measurements are employed to probe the chemical and stoichiometric changes in the surface oxide films treated under these conditions. These results are then compared with the electrochemical polarization results.

Investigation of the Kinetics of Tungsten Chemical Mechanical Polishing in Potassium Iodate‐Based Slurries: II. Roles of Colloid Species and Slurry Chemistry

We investigated the role of colloid species and slurry chemistry in tungsten chemical mechanical polishing. Specifically, we measured polish rate and process temperature in potassium iodate‐based slurries as a function of colloid species and concentration, slurry pH, and potassium iodate concentration, as well as polish pressure and polish rotation rate. We investigated slurries containing yttrium-, zirconium-, cerium-, and aluminum‐based oxide and hydroxide colloids. We found that the colloid species had a large effect on polish rate and process temperature. The colloids showed two orders of magnitude in the polish rate range from ∼15 to under otherwise identical experimental conditions (same polisher, pad, slurry chemistry, pressure, and rotation rates). Colloids of the same metal species from different sources also showed a large range in polish rates. Process temperature was a function of colloid species, however, the trend in polish rate did not always follow that of process temperature. Both polish rate and process temperature were dependent on potassium iodate concentration and slurry pH (controlled with a buffer). We also introduce a heuristic polish mechanism to investigate the role of the colloid surface chemistry and its interaction with the tungsten surface. The data indicate that the surface characteristics of the colloid and how this surface interacts with the tungsten surface play a significant role in the mechanism of tungsten removal during polish. © 1999 The Electrochemical Society. All rights reserved.

Chemical Mechanical Polishing of Tungsten: Effect of Tungstate Ion on the Electrochemical Behavior of Tungsten

Chemical Mechanical Polishing of Tungsten: Effect of Tungstate Ion on the Electrochemical Behavior of Tungsten

Development of a Robust KIO3 Tungsten CMP Process

A production worthy, Tungsten Chemical Mechanical Polish (CMP) process using a commercially available K103 slurry was developed, characterized, and tested for sub-0.35μm multilevel interconnect fabrication. The effects of pre-tungsten CMP process on tungsten polish are reported in detail. A head-to-head comparison of the optimized KIO3 process with the standard Fe(NO3)3 process is described. Critical CMP tool parameters (process and hardware) were flexed using statistically valid experimental designs. The advantages and disadvantages of a post tungsten polish, oxide buff, are discussed. Across-wafer non-uniformity, specifically the enhanced polish rate of tungsten at the wafer edge, was significantly reduced with the optimized process parameters and hardware setup. Also, an automated endpoint system was utilized and a set of robust endpoint algorithms were developed to minimize the amount of oxide loss during tungsten CMP processing. Finally, the positive effects of the optimized KIO3 tungsten CMP process on interconnect integration and die yield are reported.

Effect of Particle Size during Tungsten Chemical Mechanical Polishing

The size of the abrasive particles plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing in silica show contradictory conclusions. To the best of our knowledge, a systematic study of the effect of particle size on tungsten polishing has not been published. This paper describes the controlled measurements that were conducted to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 to diam were used in these experiments. The polishing experiments showed that the local roughness of the polished surfaces was insensitive to alumina particle size. The removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. ©1999 The Electrochemical Society

Effect of Particle Size During Tungsten Chemical Mechanical Polishing

Abrasive particle size plays a critical role in controlling the polishing rate and the surface roughness during chemical mechanical polishing (CMP) of interconnect materials during semiconductor processing. Earlier reports on the effect of particle size on polishing of silica show contradictory conclusions. We have conducted controlled measurements to determine the effect of alumina particle size during polishing of tungsten. Alumina particles of similar phase and shape with size varying from 0.1 μm to 10 μm diameter have been used in these experiments. The polishing experiments showed that the local roughness of the polished tungsten surfaces was insensitive to alumina particle size. The tungsten removal rate was found to increase with decreasing particle size and increased solids loading. These results suggest that the removal rate mechanism is not a scratching type process, but may be related to the contact surface area between particles and polished surface controlling the reaction rate. The concept developed in our work showing that the removal rate is controlled by the contact surface area between particles and polished surface is in agreement with the different explanations for tungsten removal.