Chemical Mechanical Polishing Conditions Research Articles

Solid-silica core/mesoporous-silica shell composite abrasives: synthesis, characterization, and the effect of mesoporous shell structures on CMP

The silica-based composite abrasive particles containing solid silica (sSiO2) cores and mesoporous silica (mSiO2) shells exhibit potential applications in efficient and damage-free chemical mechanical polishing (CMP) due to their special mechanical and/or chemical characteristics. In this work, the composite particles composed of sSiO2 cores and worm-like mesoporous silica shells (sSiO2/W-mSiO2) or dendritic mesoporous shells (sSiO2/D-mSiO2) were obtained by a modified Stober method combined with a biphase stratification approach. And the effects of mSiO2 shell structures of the silica-based composites on oxide CMP performance and structural stability were further investigated. TEM and XRD analyses revealed that the sSiO2/W-mSiO2 composites exhibited an improved mesochannel organization in silica shells with respect to the sSiO2/D-mSiO2 particles. The polishing results showed that the substrates after finishing with the as-obtained silica-based composite abrasives presented a superior surface quality with respect to conventional solid silica particles with a comparable particle size. Moreover, an improved organization in silica shells contributed to the improvement of surface quality and mechanical stability during CMP processes. In addition, the sSiO2/D-mSiO2 abrasives exhibited an enhanced material removal rate by comparison with the sSiO2/W-mSiO2 under the same CMP conditions. This work provides an experimental basis for exploring the relationship between the polishing performance and the mesoporous shell structure of silica-based composite abrasives.

Prediction of Removal Rates in Chemical–Mechanical Polishing (CMP) Using Tribocorrosion Modeling

The influence of electrochemical parameters, open circuit potential, and passivation kinetics, on the removal rates of tungsten in chemical–mechanical polishing (CMP) was investigated in the presented study. Removal rates were measured on a CMP machine, while electrochemical test were performed separately, both using technical CMP slurries. Electrochemical parameters are shown to have a strong influence on tungsten removal rate in CMP. Tungsten removal rate increases with the open circuit potential (electrode potential) and with passivation charge density. A model of Kaufman mechanism previously developed for sliding tribocorrosion of tungsten was adapted to the CMP conditions. This model describes removal rate in terms of both mechanical and electrochemical parameters and was found to effectively rationalize experimental results obtained in different CMP solutions according to their electrochemical properties.

A Full Wafer-Scale PAML Modeling Approach for Predicting CMP

Chemical mechanical polishing (CMP) is a complex, multi-scale problem with several order of physics. As it is a subtractive manufacturing process, it involves cutting tool–workpiece interaction. The cutting tool in CMP are nanoscale abrasives trapped in the contact between the workpiece (wafer) and a soft, rotating pad. These abrasives are suspended in a liquid medium and transported across the interface to provide even material removal. The current model presents an expansive wafer-scale framework that not only accounts for the solid–solid contact mechanics and wear, but also utilizes the mechanics of the slurry through fluid and particle dynamics. Results from this work include the temporal evolution of hydrodynamic fluid pressure, contact stress and material removal at the die and wafer scales. Comparisons with published CMP experiments have been made, and the results are favorable. Parametric studies have been conducted to predict the influence of different polishing parameters on the material removal rate. With this new framework, the entire wafer–pad interface can be studied under the influence of the four major physical interactions (contact mechanics, fluid mechanics, particle mechanics, wear). The result is a significantly faster multi-physical model that can simulate realistic CMP conditions without sacrificing accuracy.

Planarization mechanism of alkaline copper CMP slurry based on chemical mechanical kinetics

The planarization mechanism of alkaline copper slurry is studied in the chemical mechanical polishing (CMP) process from the perspective of chemical mechanical kinetics. Different from the international dominant acidic copper slurry, the copper slurry used in this research adopted the way of alkaline technology based on complexation. According to the passivation property of copper in alkaline conditions, the protection of copper film at the concave position on a copper pattern wafer surface can be achieved without the corrosion inhibitors such as benzotriazole (BTA), by which the problems caused by BTA can be avoided. Through the experiments and theories research, the chemical mechanical kinetics theory of copper removal in alkaline CMP conditions was proposed. Based on the chemical mechanical kinetics theory, the planarization mechanism of alkaline copper slurry was established. In alkaline CMP conditions, the complexation reaction between chelating agent and copper ions needs to break through the reaction barrier. The kinetic energy at the concave position should be lower than the complexation reaction barrier, which is the key to achieve planarization.

Chemical Mechanical Polishing of Glass Disk Substrates: Preliminary Experimental Investigation

Glass disk substrates are used in a wide range of portable devices because of their relatively high resistance to heat and shocks compared with aluminum substrates. Chemical mechanical polishing (CMP) is an available method to eliminate residual surface defects induced by grinding/lapping to meet final product requirements. In this work, CMP experiments with a low-cost fabric cloth pad were performed to study the effects of four key process factors on the material removal rate (MRR), flatness, and surface finish of polished glass disk substrates, and to explore the feasibility to achieve high machining efficiency, sub-nanometric surface roughness, and micrometric flatness of polished glass disk substrates simultaneously under optimized CMP conditions. The experimental results and analyses reveal that the interaction of pad rotational speed and polish head rotational speed had significant effect on the roughness (Ra), down force, and the interaction of down force and pad rotational speed had significant effects on the flatness, and down force and pad rotational speed had significant effects on the MRR. After compromise and prioritization analyses are performed, a combination of the four variables, which is the combination of 50 g/cm2 for down force, 40 rpm for pad rotational speed, 20 rpm for polish head rotational speed, and 100 ml/min for slurry supply velocity, is obtained to achieve high machining efficiency, sub-nanometric surface roughness and micrometric flatness of polished glass disk substrates simultaneously.

Chemical mechanical polishing characteristics of ITO thin film prepared by RF magnetron sputtering

Indium-tin-oxide (ITO) thin films have attracted intensive interest because of their unique properties of good conductivity, high optical transmittance over the visible region and easy patterning ability. ITO thin films have found many applications in anti-static coatings, thermal heaters, solar cells, flat panel displays (FPDs), liquid crystal displays (LCDs), electroluminescent devices, sensors and organic light-emitting diodes (OLEDs). ITO thin films are generally fabricated by using various methods, such as spraying, chemical vapor deposition (CVD), evaporation, electron gun deposition, direct current electroplating, high frequency sputtering, and reactive sputtering. In this research, ITO films were grown on glass substrates by using a radio-frequency (RF) magnetron sputtering method. In order to achieve a high transmittance and a low resistivity, we examined the various film deposition conditions, such as substrate temperature, working pressure, annealing temperature, and deposition time. Next, in order to improve the surface quality of the ITO thin films, we performed a chemical mechanical polishing (CMP) with different process parameters and compared the electrical and the optical properties of the polished ITO thin films. The best CMP conditions with a high removal rate, low nonuniformity, low resistivity and high transmittance were as follows: platen speed, head speed, polishing time, and slurry flow rate of 30 rpm, 30 rpm, 60 sec, and 60 ml/min, respectively.

1722 Si0_2-CMPにおける材料除去メカニズムに関する研究 : SiO_2-CMPにおける研磨微粒子の吸着特性(OS1-1 機械工学が支援する微細加工技術I,OS1 機械工学が支援する微細加工技術)

Material removal mechanism of CMP (Chemical Mechanical Polishing) remain largely unknown because CMP material removal phenomena are influenced by a lot of polishing parameters CMP simulation method based on new model of the CMP material removal phenomena can be calculated to CMP performance without optimization of the CMP condition by human experience In order to clarify influence on adsorption between SiO_2 fine particles and SiO_2 wafer surface by KOH slurry (pH 10 5, 11 5, 12 5), we attempted dipping experiment, dropping slurry experiment and observing experiment As results of these experiments, it is indicated that adsorption of SiO_2 fine particles depend on temperature and pH of solution.

Analysis on Contact Forms of Interface in Wafer CMP Based on Lubricating Behavior

Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the semiconductor manufacturing process. In this paper, the distinguish method of lubricating behavior in wafer CMP had been analyzed in theory firstly. Then, the tests of wafer CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal wafer CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on wafer surface constantly. The contact form between the Wafer and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP. Keywords: Chemical mechanical polishing, material removal mechanism, lubrication form, boundary lubrication.

Study on Lubricating Behavior in Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the metal and hard-brittle crystal substrate manufacturing process. In this paper, the distinguish method of lubricating behavior in CMP had been analyzed in theory firstly. Then, the tests of CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on hard-brittle crystal substrate surface constantly. The contact form between the workpiece and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in hard-brittle crystal substrate CMP.

Breaking-In a Pad for Scratch-Free, Cu Chemical-Mechanical Polishing

This paper presents a quantitative analysis of the topography and material properties of new and broken-in chemical-mechanical polishing (CMP) pads. Approximately 50 Cu wafers were polished under typical CMP conditions to break-in the pad. The changes in material properties were measured using a Hysitron TriboIndenter, and the changes in the topography of the pad were measured using a Tencor P-10 Profilometer. Additionally, scanning electron microscopy micrographs are presented to show the qualitative difference between broken-in and new pad surfaces. Polishing 56 Cu wafers decreased the average pad modulus from 0.66 to 0.34 GPa and the average pad hardness from 0.05 to 0.03 GPa. Furthermore, as a result of breaking-in the pad, the average asperity radius of curvature increased from 16 to 93 μm. The increase in the pad asperity radius of curvature decreased the severity of scratching.

Study on Factors in Time-Dependent Dielectric Breakdown Degradation of Cu/Low-k Integration Related to Cu Chemical–Mechanical Polishing

We studied Cu/low-k integration to test the time-dependent dielectric breakdown (TDDB) reliability of Cu interconnects. We described the TDDB lifetime dependence on SiOC damage caused by sputtering and chemical–mechanical polishing (CMP) processes. The TDDB lifetime of the structure without a cap-SiO layer was three orders of magnitude shorter than that of the structure with the cap layer. However, the film properties of cap-SiO films thinner than 30 nm have a leakage path that allows TDDB degradation to occur easily. We also confirmed that narrowing of intermediate wiring levels with metal-to-metal spacing approaching 100 nm degrades TDDB performance. Moreover, we showed the possibility that chemical attack and mechanical destruction during the polishing cause degradation of TDDB. Optimizing CMP conditions and eliminating the CMP-surface leakage path likely improve line-to-line insulating reliability, such as leakage current and TDDB, because these reliabilities are dominated by the extrinsic failure mode.

A chemical mechanical polishing model based on the viscous flow of the amorphous layer

Based on the theoretical analysis of the molecular dynamics simulation of sliding contact between a single micro-particle and a smooth flat surface, a new dominant mechanism of viscous flow of the amorphous layer on wafer surface for the material removal in chemical mechanical polishing (CMP) process is proposed. Furthermore, a new mathematical model characterizing the material removal rate in CMP process is developed by using micro-contact mechanics and particle size distribution theory on the basis of this mechanism. Particularly, a new important parameter k, representing the ability to remove the amorphous layer from wafer surface by a single particle, is firstly put forward and integrated in the model. The model not only incorporates the mechanical effects of the slurry particles and chemical role of the slurry, but also includes the influences of other important factors on CMP process such as wafer material properties, pad surface profiles and operating variables. The model has also been verified by the experiments shows good agreement with those experimental data in the same CMP conditions. This research will provide a new platform for further investigation in CMP mechanism of material removal.

Dynamical Mechanism of Chemical Mechanical Polishing Analyzed to Correct Preston’s Empirical Model

The dynamical mechanism of chemical mechanical polishing (CMP) is described. The relationships between removal rate and CMP parameters were evaluated by directly measuring the frictional force acting on a wafer under actual CMP conditions. According to the evaluation using various types of slurries, we devised a new relationship to replace Preston’s empirical equation by taking into account the dynamic frictional coefficient and the polishing efficiency. The quantitative analysis revealed that the removal rate was proportional to frictional force rather than down force, and the dynamic frictional coefficient and the polishing efficiency remain constant by the change of the down force. The change of removal rate by the sliding speed is varied depending on the kind of slurries. The polishing efficiency tends to be degraded by the increase of the sliding speed, while the dynamic frictional coefficient can either increase or decrease depending on the slurries. This suggests that the CMP mechanism changes by the sliding speed.

Chemical–mechanical polishing behavior of tantalum in slurries containing citric acid and alumina

The effects of H 2O 2, citric acid and Al 2O 3 content on the electrochemical behavior, surface characteristics and metal removal rates in simulated Ta chemical–mechanical polishing (CMP) have been investigated. Electrochemical measurements indicated that Ta could be easily passivated in all citric acid base slurries prepared in this investigation. The passive film could be removed under CMP condition. The addition of H 2O 2 into the slurries could assist repassivation of Ta under polishing condition. X-ray photoelectron spectroscopy (XPS) revealed that the passive film formed on Ta surface in the citric acid slurries consisted of Ta 2O 5 and TaOH. The presence of H 2O 2 enhanced the formation of Ta 2O 5 on Ta surface. The removal rate obtained in the simulated CMP investigation increased with the amount of Al 2O 3, either in DI water or in the 0.01 M citric acid +9 vol.% H 2O 2 slurries. The surface roughness of Ta after CMP in 0.01 M citric acid +9 vol.% H 2O 2 slurries was higher than that in DI water base slurries when the Al 2O 3 content was low. A significant reduction in surface roughness combined with a high removal rate could be obtained if the Al 2O 3 content in the 0.01 M citric acid +9 vol.% H 2O 2 slurries was increased to above 10 wt.%.

상대속도를 고려한 CMP 공정에서의 연마제거율 모델

Chemical Mechanical Polishing(CMP) process becomes one of the most important semiconductor processes. But the basic mechanism of CMP still does not established. Slurry fluid dynamics that there is a slurry film between a wafer and a pad and contact mechanics that a wafer and a pad contact directly are the two main studies for CMP. This paper based on the latter one, especially on the abrasion wear model. Material Removal Rate(MRR) is calculated using the trajectory length of every point on a wafer during the process time. Both the rotational velocity of a wafer and a pad and the wafer oscillation velocity which has omitted in other studies are considered. For the purpose of the verification of our simulation, we used the experimental results of S.H.Li et al. The simulation results show that the tendency of the calculated MRR using the relative velocity is very similar to the experimental results and that the oscillation effect on MRR at a real CMP condition is lower than 1.5%, which is higher than the relative velocity effect of wafer, and that the velocity factor. not the velocity itself, should be taken into consideration in the CMP wear model.

Mechanisms of Chemical-Mechanical Polishing of SiO2 Dielectric on Integrated Circuits

One of the fundamental mechanisms of chemical-Mechanical polishing (CMP) is the mechanical interaction between the wafer and polishing pad. This interaction was simulated in experiments. The vertical displacement of the wafer with respect to the polishing pad, the fictional drag of the wafer against the pad, and the pressure of the slurry trapped between the wafer and pad were measured. These experiments were performed over a range of commercially common CMP conditions. In addition, polishing rates were measured for CMP performed under induced hydrodynamic conditions where the wafer was separated from the pad by a film of slurry. It was found that no appreciable polishing occurred under hydrodynamic CMP conditions. Under commercial CMP conditions, it was found that the wafer contacts the polishing pad asperities as evidenced by near-zero wafer displacement and high friction coefficients (˜0.4). It was also found that pad conditioning (intentional roughening) causes a suction force to develop between the wafer and pad. This suction force draws the wafer into further contact with the pad, by as much as 20 μm, and corresponds to peak slurry vacuum pressures of 12 kPa (1.7 psi). Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997