Removal Rate In Chemical Mechanical Polishing Research Articles

Rapid Estimation of Removal Rate of Chemical Mechanical Polishing of Gallium Nitride Substrate by Quantitative Diagnosis of Cathodoluminescence Images

Rapid estimation of the removal rate of the chemical mechanical polishing (CMP) process of a gallium nitride (GaN) substrate contributes to the quick diagnosis of CMP progressing, leading to accelerated process development. The present study discusses the feasibility of using cathodoluminescence (CL) imaging for a rapid diagnosis of the removal rate of the CMP process. Mechanically induced subsurface damage was detected as black lines in the CL images due to nonradiative recombination. To quantitatively understand the CL images from the GaN substrate, the CL images was analyzed for the mean image brightness. We developed an advanced theory interpreting CL image brightness as a logistical function with the CMP processing time by assuming that the mechanically induced damages at and near the surface exponentially decrease with depth from the surface. Therefore, the CMP progress was successfully characterized by analyzing CL images in CMP process with the logistic functions, which provided a rapid estimation of the CMP removal rate.

Selection of Abrasive for Chemical Mechanical Polishing of the 304 Stainless Steel

Chemical mechanical polishing (CMP) technology is widely used in ultra-precision machining of various materials, and the abrasive are an important component of CMP slurry. In this paper, the effects of the abrasive type, the abrasive size and its concentration on material removal rate (MRR) and surface quality in CMP 304 stainless steel were studied through a series of experiments. The results show that the MRR in CMP 304 stainless steel using slurry with the white corundum abrasive is the highest, and the MRR in CMP 304 stainless steel using slurry with the silica abrasive is the lowest, but the surface quality in CMP 304 stainless steel using slurry with the silica abrasive is the best. The MRR and surface roughness increase with the increase of abrasive size, but the surface roughness increases slowly with the increase of abrasive size. With the increase of abrasive concentration, the MRR first increases and then decreases, while the surface roughness value changes slightly, indicating that the abrasive concentration in polishing slurry has little effect on the surface quality. These research results can provide a reference for the design of CMP slurry.

Effects of Temperature on Removal Rate in Cu CMP

Chemical mechanical polishing(CMP) realizes a surface planarity through combined mechanical and chemical means. In CMP process, Preston equation is known as one of the most general approximation of the removal rate. Effects of pressure and relative speed on the mechanical property of Cu CMP has been investigated. On the other hand, The amount of abrasion also increased with changes in pressure and speed, resulting in a proportional increase of temperature during CMP. Especially this temperature is an important factor to change chemical reaction in a Cu CMP. However, when the slurry temperature became higher than 70°C, the removal rate went lower due to abrasives aggregation and scratching occurred on the Cu film. Therefore, it was found that the slurry temperature should not exceed 70°C during Cu CMP. Finally, authors could increase the pressure, speed and slurry temperature up to a ceratin level to improve the removal rate without surface defects.

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 mixed elastohydrodynamic lubrication model for simulation of chemical mechanical polishing with double-layer structure of polishing pad

Mixed elastohydrodynamic lubrication (EHL) model has been used to study slurry flow and contact pressure distribution in the chemical mechanical polishing (CMP) process. However, in various mixed EHL simulation frameworks, only a single-layer polishing pad is considered. Consequently, the double-layer polishing pad, which is widely used in semiconductor industry, cannot be designed and optimized from the tribology perspective with the assistance of theoretical simulation. In this paper, multi-layered elastic theory (MLET), which is frequently used to calculate flexible pavement response to truck loading, is introduced into the mixed EHL model. Pad deformation calculated by the MLET has a similar accuracy to that by the 3D finite element method, but its computational cost is much lower. It is very important for accurate and efficient simulation of the tribological behavior and material removal rate (MRR) in CMP. Based on the new simulation method, advantages of a different double-layer structure of polishing pad are discussed. It is found that the upper-hard lower-soft pad has better performance for improving the uniformity of MRR when the wafer surface is uneven, but the boundary exclusion region is bigger than single-layer pad and upper-soft lower-hard pad. The upper-soft lower-hard pad has advantage to reducing the edge exclusion, but the effect is not remarkable when the thickness of the upper layer is not extremely thinner than the lower layer.

The Effect of Pad-asperity Curvature on Material Removal Rate in Chemical-mechanical Polishing

In chemical-mechanical polishing (CMP), surface asperities of the polishing pad play a key role, for they transmit normal force and impart tangential motion to the hard, nano-scale abrasive particles in the slurry. It has been shown recently, however, that the soft pad asperities themselves often generate micro-scale scratches on the surfaces being polished. To mitigate scratching by pad asperities, therefore, topography control by flattening pad asperities has been proposed and experimentally validated. In this study, the effects of asperity-flattening on pad topography and the material removal rate are investigated. It is found both theoretically and experimentally that even at a relatively high pressures only the tallest of the asperities are flattened and the ratio of asperity radius-to-standard deviation of heights is increased, but the average roughness itself is little affected. Specifically, surface profiles of new and asperity-flattened pads indeed show that the average roughness of about 5μm is changed less than ten percent. Concurrently, the material removal rate is increased by about 30 percent due in part to the increased real area of contact––the result of increased asperity radius of curvature and decreased standard deviation of asperity heights.

A mixed elastohydrodynamic lubrication model with layered elastic theory for simulation of chemical mechanical polishing

Mixed elastohydrodynamic lubrication (mixed EHL) model has been successfully used to study phenomena in chemical mechanical polishing (CMP) process. However, in various mixed EHL simulation frameworks, a polishing pad's deformation cannot correctly be described by adopted models for pad deformation such as elastic half-space model and Winkler elastic foundation model. Thus, a more accurate model for pad deformation is needed, since this is the prerequisite for an accurate prediction of contact pressure and material removal rate, which is critical for improvement of polishing quality. In this paper, a layered elastic theory, which is frequently used to calculate flexible pavement response to truck loading, is introduced into the mixed EHL model. It is found that this theory has a similar accuracy to the traditional 3D finite element method for calculating the pad deformation. However, its computational cost is much lower, which is especially important for accurate and efficient simulation of mechanical behavior and material removal rate (MRR) in CMP. In order to highlight benefits of the proposed theory, simulations are carried out based on three different pad deformation models with the mixed EHL model. The pad deformation behavior is found to have a significant influence on the final simulation results, especially the MRR prediction. By comparing the different simulation models, the proposed layer elastic theory is found to be an optimal model for describing the polishing pad deformation behavior in CMP and can provide accurate simulation results on contact pressure distribution and the material removal rate.

Exploration on chemical mechanical planarization of ZnO functional thin films for novel devices

Zinc oxide (ZnO) is an attractive material for its application in the electronics, optics, acoustics, and sensor field. With the shrinking of minimum feature size of the devices and the increasing of devices function layers, surface planarization of each layer is demanded in the devices manufacturing. However, ZnO thin films deposited directly have high surface roughness which could cause device performance degradation. Therefore, ZnO thin films must be planarized in order to obtain high density and high integration devices. In this paper, chemical mechanical polishing (CMP) was used for ZnO thin films planarization, these films were deposited on 4inch Si blanket wafer by RF magnetron sputtering. The influence of the process parameters on CMP removal rate including pressure, platen speed was discussed, and the results demonstrated that removal rate still exist when there is no pressure and velocity, hence Preston equation was slightly modified. The effect of slurry pH on CMP removal rate was also investigated in detail after considering different corrosion rate of ZnO films in different solution. After optimizing CMP process parameter, the removal rate of ZnO films was up to 165.1nm/min, and the surface root mean square roughness was reduced from 16 to 1.9A.

Influence of Wafer Edge Geometry on Removal Rate Profile in Chemical Mechanical Polishing: Wafer Edge Roll-Off and Notch

In the chemical mechanical polishing (CMP) process, uniform polishing up to near the wafer edge is essential to reduce edge exclusion and improve yield. In this study, we examine the influences of inherent wafer edge geometries, i.e., wafer edge roll-off and notch, on the CMP removal rate profile. We clarify the areas in which the removal rate profile is affected by the wafer edge roll-off and the notch, as well as the intensity of their effects on the removal rate profile. In addition, we propose the use of a small notch to reduce the influence of the wafer notch and present the results of an examination by finite element method (FEM) analysis.

A study on the correlation between pad property and material removal rate in CMP

Chemical mechanical polishing (CMP) is a process with relative motion between pad and wafer while supplying slurry which abrasive particles are dispersed. This process consists of mechanical action by contact between pad and wafer and chemical action by the slurry chemicals. There are various factors affecting on material removal rate (MRR) in CMP. Especially, the pad plays a role of mechanical action by direct contact with wafer. Real contact area (RCA) between pad and wafer is an important factor when considering real contact pressure, friction and wear of pad asperities, which affects on the MRR and within wafer non-uniformity (WIWNU). This paper proposes a correlation between pad property and MRR in CMP process. The pad after conditioning had sharp asperities and changed to blunt ones as the polishing time became longer. This phenomenon was clarified by the roughness parameter of Rku. The high Rku pad just after conditioning made a high real pressure to the wafer, resulting in high MRR during CMP.

Diamond Conditioner Microwear Effect on Pad Surface Height Distribution in Tungsten Chemical Mechanical Polishing

In this study, the surface topographies of chemical mechanical polishing (CMP) pad samples for varying levels of diamond microwear of a conditioner have been measured using a confocal microscope and an X-ray computer tomography (CT) scanner. The experimental results showed that the increase in the pad debris on the pad surface reduced the pad height ratio of the asperity called the “top surface area (TSA) ratio”. In addition, the overall removal rate in tungsten CMP was more dependent on the TSA ratio after polishing than on that after conditioning because the pad surface condition became worse with deformed asperities and micropores due to the insufficient conditioning.

Relationships between Contact Image Analysis Results for Pad Surface Texture and Removal Rate in CMP

In chemical mechanical polishing (CMP) process, the removal rate is affected by the actual contact conditions between the wafer and the polishing pad. Further, the free abrasives in the slurry attack the wafer at the regions of actual contact. The polishing pad is one of the most important consumable materials in CMP since the pad surface texture changes during wafer polishing and substantially influences the actual contact conditions. Therefore, methods for quantitative evaluation of the pad surface texture have been proposed by various research institutes. We have developed a novel method for the quantitative evaluation of the polishing pad surface texture; this method is based on contact image analysis using an image rotation prism. We have proposed the use of four effective evaluation parameters: the number of contact points, the contact ratio, the maximum value of the minimum spacing of the contact points, and the half-width of the peak of the spatial fast Fourier transform (FFT) of a contact image. We determine the changes in the polishing pad surface texture on the basis of the proposed evaluation parameters in serial batch polishing tests. In particular, we focus on the relationships between the proposed evaluation parameters and the removal rate, which changes with an increase in the number of batch polishing tests. The evaluation parameters are linearly correlated with the removal rate. Hence, the removal rate is improved not only with an increase of the number of contact points and the contact ratio but also with a decrease in the size of the cohesion regions and the spacing between the contact points.

Material removal rate in chemical-mechanical polishing of wafers based on particle trajectories

Distribution forms of abrasives in the chemical mechanical polishing (CMP) process are analyzed based on experimental results. Then the relationships between the wafer, the abrasive and the polishing pad are analyzed based on kinematics and contact mechanics. According to the track length of abrasives on the wafer surface, the relationships between the material removal rate and the polishing velocity are obtained. The analysis results are in accord with the experimental results. The conclusion provides a theoretical guide for further understanding the material removal mechanism of wafers in CMP.

Effect of Process Parameters on Friction Force and Material Removal in Oxide Chemical Mechanical Polishing

The relationship between sliding friction and material removal was investigated using a sensor to measure dynamic friction force according to process parameters such as pressure, velocity, conditioning, abrasive concentration, and slurry pH during oxide chemical mechanical polishing (CMP). Friction force and material removal linearly depend on applied load and relative velocity. A high relative velocity also has an effect on the boundary condition between the wafer and the pad, and friction force reduces with increase in relative velocity. Friction force reduces with polishing time during oxide CMP with ex situ conditioning because of the changes in pad roughness parameters such as Ra, Rp, Rpk, and Rsk. Thus, the in situ conditioning method increases removal rate and improves nonuniformity. Friction force can be uniformly distributed on the oxide wafer as abrasive concentration increases owing to the reduction in friction force loaded on one abrasive particle, improving the nonuniformity of removal rate. In oxide CMP using alkali-based slurry, the effective formation and mechanical removal of the Si–OH bond layer on the SiO2 surface also affect the temporal decrease in friction force and result in a higher removal rate, in comparison with the results of a high friction force and a low removal rate in oxide CMP using neutral-based slurry.

The Effects of Interfacial Particles on the Contact of an Elastic Sphere With a Rigid Flat Surface

In chemical mechanical polishing (CMP), a rigid wafer is forced on a rough elastomeric polishing pad, while a slurry containing abrasive particles flows through the interface. One of the important factors that influence the material removal rate in CMP is the magnitude of contact force transmitted to the abrasive particles trapped at the contact interface. The total push-down force is distributed to the direct contact between the wafer and the pad, and to the three-body contact between the wafer, the pad, and the abrasive particles. The presence of the abrasive particles alters the asperity contact, which otherwise can be described by Hertz contact relationships. In this study, the effect of the interfacial particles on the single asperity contact is investigated. An approach used by Greenwood and Tripp (1967, “The Elastic Contact of Rough Spheres,” ASME J. Appl. Mech., 34, pp. 153–160) to study the contact of rough spheres is utilized since the presence of the particles provides a rough character to the contact. The results show that the contact behavior becomes non-Hertzian with decreasing contact force and increasing elastic modulus, particle size, and particle concentration. The role of the interfacial particles is to spread the contact over a larger area while lowering the maximum contact pressure at the center of contact predicted by Hertz contact. The conditions required to transfer the contact force on the particles effectively are also described.

Modeling of Back Pressure Distribution on the Wafer Loaded in a Multi-Zone Carrier in Chemical Mechanical Polishing

The within-wafer non-uniformity (WIWNU) of material removal rate in chemical mechanical polishing (CMP) is important for IC manufacture. The non-uniform distributions of polishing pressure and the relative speed between the wafer and the polishing pad are main factors affecting the WIWNU. In this paper，based on the contact mechanics and the elastic plate theory, a compensate pressure computing model is presented, in which the effects of kinematic parameters are taken into acount. By modelling and calculating, the desired compensate back pressure distribution is obtained. In the last section the design of a schematic carrier with multi-zone, in which the compensate back pressure can be applied, is presented. The model and the design can be used for providing theoretical guide to the development of CMP equipments and selection of the kinematic variables in CMP process.

Heat and its effects to chemical mechanical polishing

Heat is an indispensable factor in understanding the removal rate and WIWNU (within wafer non-uniformity) in CMP (chemical mechanical polishing). The principal heat generation mechanism results from the two-body abrasion mode. Experiments are implemented using the on-machine temperature measuring system with an IR digital camera. This paper investigates the primary process parameters affecting heat generation and temperature distribution on pad surfaces. Meanwhile, the change of temperature affects the characteristics of both slurry and pads. The change in the pH value of the slurry due to the alteration of temperature affects the surface state of the abrasive particles and therefore the agglomeration of abrasives happens above a certain temperature. Moreover, the temperature changes the first and second elastic moduli of the pads and their real contact area, which is closely related to the removal rate and WIWNU.

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.

Impact of Abrasive Particles on the Material Removal Rate in CMP

The effects of particle size within the chemical mechanical polishing (CMP) process are investigated using a microcontact wear model which considers the particle effects between the polishing interface during load balancing. The present theoretical results are in good agreement with the experimental data published previously. The current study provides a detailed understanding of the effects of the abrasive particles from an interfacial perspective.

Effect of CVD Temperature on Orientation, Roughness, and Chemical Mechanical Polish Removal Rate of W Thin Films

The deposition temperature for tungsten films used as interconnects on Si integrated circuits is found to strongly influence the subsequent chemical mechanical polishing (CMP) removal rate. Careful analysis of the films by orientation imaging microscopy showed a direct correlation between the chemical vapor deposition temperature and the area fraction of (114) vs. (110) oriented tungsten grains. The CMP removal rate decreased as the fraction of (114) oriented grains in the film increased. © 2002 The Electrochemical Society. All rights reserved.