Chemical Mechanical Polishing Slurry Research Articles

Local Corrosion of the Oxide Passivation Layer during Cu Chemical Mechanical Polishing

In this article, we analyze the effect of complexing agents in Cu chemical mechanical polishing slurry on the formation of oxide and the evolution of stress. The passivation property and surface morphology of the oxide on the surface showed significant differences depending on the kind of complexing agent. Oxalic acid showed fast oxide formation with poor passivation performance, and this caused large tensile stress evolution over 250 MPa in the Cu film. The synergetic effect of stress evolution and temperature increase due to the friction during the polishing caused severe pitting of the Cu surface after polishing in oxalic-acid-based slurry.

Investigation of Slurry Chemical Corrosion on TaN Barriers with Plasma Treatment

In this study, the corrosion between the copper (Cu) seed and the films with various Ar-sputtering amounts is investigated in acidic chemical mechanical polishing (CMP) slurries. The results show that the intrinsic corrosion of the films increases with increasing the Ar-sputtering amount because Ar sputtering causes the grain boundary of the film increase. The galvanic corrosion of the film increases with increasing the Ar-sputtering amount because the N-rich surface of the film is removed by Ar bombardment. The equivalent circuit, simulated using data from electrochemical analysis, reveals changes in resistance and capacitance elements of the electrochemical system. In the acidic CMP slurry, the charge-transfer resistance of the corrosion decreases with increasing the Ar-sputtering amount, whereas the resistance of a tantalum–oxide layer shows the opposite trend because decreasing the N content of the films enhances the oxidation rate of the Ta metals.

Enhancement of Selectivity of Oxide-to-Nitride Films on Organic Additive in Nano-ceria Slurry for Shallow Trench Isolation Chemical Mechanical Polishing

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Large‐Scale Synthesis of Water Dispersible Ceria Nanocrystals by a Simple Sol–Gel Process and Their Use as a Chemical Mechanical Planarization Slurry

AbstractCeria nanocrystals with a cube shape were synthesized from the hydrolytic sol–gel reaction of cerium salt in the presence of oleylamine. The overall synthetic process is very simple and readily applicable to the large‐scale synthesis of tens of grams of product in a single reaction in air. These ceria nanocrystals are readily dispersible in aqueous media without the addition of any extra dispersing agent. The aqueous dispersion of the ceria nanocrystals was successfully used as a chemical mechanical polishing slurry, and it exhibited high removal selectivity between silicon oxide and silicon nitride at pH 7.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Pad roughness variation and its effect on material removal profile in ceria-based CMP slurry

The pad roughness plays a key role in material removal in oxide chemical mechanical polishing (CMP) process. Its variation also has an effect on within wafer non-uniformity. The R pk among roughness parameters, which is related to pad wear characteristics, was investigated to find the correlation between spatial roughness distribution of a polishing pad, and material removal profile in CMP, using two different types of slurries. The removal rate of ceria-based slurry for STI CMP was higher in the wafer center than that of the silica-based slurry. This is because the pad roughness distribution in a convex shape is formed across the pad radius in the contact area between pad and wafer instead of the degradation of pad roughness during CMP. Also, there is an increase of R pk results in the increase of average friction force by comparison with the decrease of friction force in CMP using silica-based slurry. This result may be expected as the effect of the chemical tooth of ceria abrasive and slurry accumulation in the wafer center causes a roughening of the pad surface just as sandpaper.

Etching Rate Enhancement of Copper by Adding Sulfur Compounds in Chemical-Mechanical Polishing Slurries

In the chemical mechanical polishing (CMP) process, we have discovered that the Cu etching rate can be enhanced without affecting the Cu slurry's pH by adding a small amount of the sulfur compounds MPS and Na2S2O3. Adding the sulfur compounds to the H2O2 slurry results in an increment in the oxidation reduction potential (ORP). The electrochemical model (mixed potential) showed that the ORP increment leads to enhancement of the Cu oxidizing reaction. Because XPS and Raman analysis of the Cu surface revealed that the Cu etching rate in CMP is limited by the Cu oxidizing reaction, we concluded that the Cu etching rate is enhanced by the addition of sulfur compounds to the Cu oxidizing reaction to increase the ORP increment.

Controlled chemical mechanical polishing of polysilicon and silicon dioxide for single-electron device

In this article, the authors report experimental results of the chemical mechanical polishing (CMP) of silicon dioxide (SiO2) and polysilicon to produce nanoscale features with very smooth surfaces. The sizes of the features polished ranged from 30to500nm. For polysilicon polishing, the nanostructures were defined in positive tone e-beam resist and the pattern was transferred to the oxide substrate using reactive ion etching. These etched nanostructures (70nm deep trenches) were conformally filled with low pressure chemical vapor deposited polysilicon and polished using a CMP system. Polishing planarized the sample and removed the polysilicon overburden to expose the filled trenches in the SiO2. The polished structures were studied using scanning electron microscopy (cross sections) and atomic force microscopy (surface). The authors report controllable CMP to realize ∼20nm thick layers after polishing, with rms roughness of ∼0.3nm. Better control of the CMP process (few nm/min removal rate) was demonstrated by using diluted slurry or pure de-ionized water as the CMP slurry.

Etching Rate Enhancement of Copper by Adding Sulfur Compounds in Chemical-Mechanical Polishing Slurries

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Galvanic Corrosion Between TaN[sub x] Barriers and Copper Seed

In semiconductor metallization processes, the galvanic corrosion of metals should be controlled to improve the process integrity. Refractory metals such as tantalum and tantalum nitride (TaN x ) are widely used as a barrier metal to prevent the copper (Cu) metal from diffusing into the dielectric layers. In this study, the galvanic effect between the Cu seed and the TaN x film, which is deposited with different nitrogen (N 2 ) gas flow rates was investigated using chemical mechanical polishing slurries. It was found that the galvanic corrosion of the TaN x films decreased whereas the galvanic corrosion of the Cu seed increased as the N 2 gas flow rate increased. The whole Cu corrosion rate was higher than that of the TaN x films because the intrinsic corrosion of the Cu seed dominated the overall Cu corrosion rate in the acidic slurry, but for the TaN x films the galvanic corrosion dominated. This study also proposed a model to reveal the galvanic effect between the Cu seed and various TaN x films.

Consumable Approaches of Polysilicon MEMS CMP

Chemical-mechanical polishing (CMP), one of the dominant technology for ULSI planarization, is used to flatten the micro electro-mechanical systems (MEMS) structures. The objective of this paper is to achieve good planarization of the deposited film and to improve deposition efficiency of subsequent layer structures by using surface-micromachining process in MEMS technology. Planarization characteristic of poly-Si film deposited on thin oxide layer with MEMS structures is evaluated with different slurries. Patterns used for this research have shapes of square, density, line, hole, pillar, and micro engine part. Advantages of CMP process for MEMS structures are observed respectively by using the test patterns with structures larger than 1 urn line width. Preliminary tests for material selectivity of poly-Si and oxide are conducted with two types of silica slurries: <TEX>$ILD1300^{TM}\;and\;Nalco2371^{TM}$</TEX>. And then, the experiments were conducted based on the pretest. A selectivity and pH adjustment of slurry affected largely step heights of MEMS structures. These results would be anticipated as an important bridge stone to manufacture MEMS CMP slurry.

Electrochemical Testing of Tantalum and Copper in Chemical Mechanical Polishing Slurries

Potentio-dynamic polarization, electrochemical impedance spectroscopy (EIS), and galvanic current techniques were used to study the electrochemical behaviors of copper and tantalum in chemical mechanical polishing (CMP) slurries. It was found that a chemical agent, guanidine chloride, had a significantly specific effect in etching tantalum. When tantalum was galvanically coupled to copper in a commercial CMP slurry, tantalum was preferentially corroded and copper was protected from corrosion.

Effect of concentration gradient on the anodic behavior of tungsten

Potentiodynamic and potentiostatic polarization experiments, the electrochemical impedance spectroscopy, the rotating disk electrode technique, and surface pH measurements were used to study the effect of tungstate ions on the anodic behavior of tungsten (W). Deliberately added tungstate ions, which are also tungsten dissolution products, were found to decrease the anodic currents at around the point of zero charge, increase the anodic currents in the neutral to weakly basic range and have no effect on the anodic currents in the strongly basic conditions. This variable effect was attributed to the competition between the stabilization of the tungsten oxide due to higher concentration of the dissolution products next to the metal surface and the stabilization of the local pH as a result of the enhanced polymerization reactions of the tungstate species. The surface pH measurements showed that the polymerization reactions kept the W surface pH higher (i.e. closer to the bulk pH) in the absence of a pH buffer in the neutral and weakly basic solutions. The tungstate ion was considered as a potentially useful additive in W chemical mechanical polishing (CMP) slurries, since this ion could increase the stability of the oxide phase to be removed by polishing and serve as a pH buffering agent.

Electrochemical Testing of Tantalum and Copper in Chemical Mechanical Polishing Slurries

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Effects of Suspending Abrasives on the Lubrication Properties of Slurry in Chemical Mechanical Polishing of Silicon Wafer

The lubrication properties of the slurry between the silicon wafer and the pad in chemical mechanical polishing (CMP) are critical to the planarity of the silicon wafer. Moreover, the suspending abrasives, which are contained in the slurry, have an extremely important influence on the lubrication properties of the slurry. In the CMP process of the large-sized silicon wafers, the influence of suspending abrasives on the slurry becomes more prominent. In order to explore the effects of suspending abrasives on the lubrication properties of the slurry under the light load conditions, a three-dimensional lubrication model based on the micro-polar fluid theory is developed. The effects of suspending abrasives on the fluid pressure acting on the wafer and the distribution of the slurry film between the silicon wafer and the pad are discussed.

Interaction between abrasive particles and films during chemical-mechanical polishing of copper and tantalum

Chemical-Mechanical Polishing (CMP) of copper is a critical step for the formation of interconnect on wafer during the manufacturing of advanced microelectronic devices. One of the key performance metrics of a copper CMP slurry is the removal rate selectivity between copper and its corresponding adhesion/barrier layer such as Ta or TaN. In order to create a slurry that has the desirable and/or tunable removal rate selectivity, it is critical to understand the influential factors that control the removal rates. In this study, such influential factors are elucidated based on the relative importance of interaction between abrasive particle and the film to be polished. More specifically, particles with varying bulk and surface properties are used to obtain the removal rate selectivity for copper and Ta. It is found that the Ta material removal rate has a direct correlation with the effective hydroxyl content on the surface of abrasive particles. The material removal rate and surface quality of copper, on other hand, is heavily influenced by the hardness of the abrasive particles and the presence of oxidizer/complexing agent. The reliance on the interaction with abrasive surface hydroxyl groups for Ta removal is further confirmed with a set of experiments in which the silica surface hydroxyl content are significantly reduced via alkylation of the hydroxyl groups. As expected, the surface treatment that remove some of the surface hydroxyl groups also reduce the Ta material removal rate. The difference in removal mechanism for copper and tantalum is also explained with the distribution of the abraded materials between spent slurry and pad.

Lithium Tantalate (LiTaO3) 웨이퍼의 CMP에 관한 연구

Compound semiconductors are the semiconductors composed of more than two chemical elements. Lithium Tantalate(LiTaO₃) wafer is used for several optical devices, especially surface acoustic wave(SAW) device. Because of the lithography in SAW device process, LiTaO₃ polishing is needed. In this paper, the commercial slurries(NALCO2371^(TM), ILD1300^(TM), ceria slurry) used for chemical mechanical polishing(CMP) were tested, and the most suitable slurry was selected by measuring material removal rate and average centerline roughness(Ra). From these result, it was proven that ILD1300^(TM) was the most suitable slurry for LiTaO₃ wafer CMP due to the chemical reaction between solution in slurry and material.

Removal characteristics of hillock on SnO2 thin film by chemical mechanical polishing process

SnO 2 is one of the most suitable materials for gas sensors. The microstructure and surface morphology of SnO2 films must be controlled because the electrical and optical properties of SnO2 films depend on these characteristics. We investigated the effects of chemical mechanical polishing (CMP) on the variation of morphology of SnO2 films prepared by rf sputtering system. The commercially developed ceria-based oxide slurry, silica-based oxide slurry, and alumina-based tungsten slurry were used as CMP slurry. Nonuniformities of all slurries coincided with stability standards of less than 5%. Silica slurry had the highest removal rate among three different slurries. In addition, the particle size analysis showed that silica slurry had an abrasive with the largest average particle size of the three. Based on the atomic force microscopy analysis of thin film topographies and root mean square values, silica slurry has excellent properties that allow the application of SnO2 thin films as gas sensor materials.

Simulation on chemical mechanical polishing using atomic force microscope

A micro-contact model for chemical–mechanical polishing (CMP) of silicon wafer is presented. The model is developed on the basis of the Greenwood-Williamson micro-contact mechanics. The atomic force microscope (AFM) is used as a polishing test apparatus to evaluate the removal rate by a single particle in a CMP slurry. Using this model and AFM, the simulation on polishing of SiO2 is performed. The model is evaluated by comparing the simulated polishing rate and that experimentally determined by real CMP processes. The simulation result and experiment result are in good agreement. It suggests that the combination of the model and AFM polishing test can be used to estimate the removal rate of SiO2 CMP and may be used to study the effects of different materials, slurry and operating condition on CMP process.

Agglomeration characteristic of particles in alumina slurry by addition of chemicals and milling process for Cu CMP

Chemical mechanical polishing (CMP) has been widely accepted for the global planarization of multi-layer structures in semiconductor manufacturing. It is generally known that the implementation of optimum slurry composition is one of the important issues. In this experiment, we observed and analyzed the variation by the addition of chemicals and milling time of Cu CMP slurry. The particle size in slurry has influence on polishing rate and defect. The particles with milling process were assayed with the elapse of time and addition of chemical additives. The results showed that the particle size in slurry became smaller by increasing of bead amount and milling time. Additional milling time was appended to examine agglomeration of particle by milling time. The particle size after milling process became bigger with the increase of time due to absence of dispersion stability. It was confirmed that viscosity and particle size increased sharply with addition of tartaric acid in slurry with alumina-C as abrasive.

Colloidal Silica based High Selectivity Shallow Trench Isolation (STI) Chemical Mechanical Polishing (CMP) Slurry

AbstractAmong various properties of chemical mechanical polishing (CMP) slurry, selectivity plays a key role in global planarization of high density and small pattern size shallow trench isolation (STI) process. Lack of adequate selectivity can lead to defects such as dishing and erosion. To improve the selectivity of STI CMP process, CMP characteristics of silica and silicon nitride wafer were investigated using colloidal silica slurry as a function of slurry pH. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added to increase the selectivity of the slurry. As a result, selectivity increased from 3 to 25. It was concluded that selective passivation layer formed on silicon nitride wafer surface at acidic slurry pH range was responsible for the observed selectivity increase. Adsorption characteristics of SDS on silica and silicon nitride were measured as a function of slurry pH and concentration of SDS. As indicated by zeta potential behavior under acidic pH conditions, SDS adsorption on silicon nitride was significantly higher han silica due to the electrostatic forces. Significantly higher SDS coating on silicone nitride seems to have resulted in lubrication layer leading to increased polishing selectivity.