Wafer Removal Rate Research Articles

Effects of the Solid Concentration of Ceria Slurry on the Removal Rate and Selectivity of Si Wafer during Chemical Mechanical Polishing

Shallow trench isolation via chemical mechanical polishing (CMP-STI) tests of Si wafers using CeO2 slurry were studied. The impact of CeO2 slurry's solid concentration on the SiO2 removal rate and the selectivity ratio The effects of the solid concentration of CeO2 slurry on the removal rate of SiO2 and selectivity (SiO2/Si3N4) were investigated. The CeO2 abrasive was well matched to the XRD standard pattern, confirming that it had a cubic phase and the absence of any impurities. The SEM image showed that CeO2 primary particles had a spherical-like shape with a size within 30-60 nm. Additionally, the prepared CeO2 slurry showed a relatively high dispersion level. The wettability degree of the CeO2 slurry on top of the Si wafer surface was also sufficient. Furthermore, results from polishing tests indicated that both the SiO2 removal rate and the selectivity increased linearly with a rise in CeO2 solid concentration.

Effect of cations on the improvement of material removal rate of silicon wafer in chemical mechanical polishing

For obtaining a sub-nanometer surface, the material removal rate (MRR) is usually very low. It is challenging to achieve sub-nanometer surface with high MRR. To overcome this challenge, in this work, different cations are considered to improve the MRR during CMP for silicon (Si) wafer. When the concentration of NH4+ ions is 125 mmol/L, the MRR of Si wafer reaches 1687 Å/min, increasing 107.8 % compared with the controlled group. It is noted that nanometer silica abrasives remain at a good monodisperse state in CMP. The surface roughness Sa after CMP on a Si wafer is 0.744 nm under a measurement area of 868 × 868 µm2. COF data and X-ray photoelectron spectroscopy indicate that NH4+ ions reduce the electrostatic repulsion between silica nanoparticles and Si, whilst accelerating chemical reactions between Si and developed slurry. This work suggests a novel approach to fabricating sub-nanometer surface of Si wafer with high MRR, which is beneficial for the potential use in semiconductor and microelectronics industries.

Modeling and experimental study on material removal rate of quartz wafer by fixed abrasive lapping

Modeling and experimental study on material removal rate of quartz wafer by fixed abrasive lapping

Effect of radial grooves pads on copper chemical mechanical polishing

In this study, the effect of radial grooves (RG) pads employed in the copper chemical mechanical polishing/planarization (CMP) process was investigated, to improve the copper CMP performance. To this end, four types of pads were selected according to the number of RGs; the numbers of RGs were 0, 8, 16, and 32. The amount of slurry inflow/outflow was calculated for the selected number of RGs over the same duration, and the change in the slurry inflow/outflow according to the rotational speed of the head/platen was determined using a numerical method. The simulation results thus obtained demonstrated the differences in the amount of slurry inflow/outflow according to the number of RGs and the rotational speed of head/platen. At 90 rpm, the new slurry mass fractions of the circular groove (CG) pad and the RG-32 pad were 0.52754 and 0.67606, respectively, and the new slurry mass fraction of the RG-32 pad increased by about 22% compared to the result of the CG pad. Subsequently, the CMP process was performed using four types of pads at different head/platen rotational speed, and Cu removal rates were compared. According to the CMP evaluation results, the Cu removal rates improved with an increase in the number of RGs. At 90 rpm, the Cu wafer removal rates of the CG pad and the RG-32 pad were 4051.3 Å/min and 5047.2 Å/min, respectively, and when the RG-32 pad was used, the Cu wafer removal rate was increased by about 24.6%. Furthermore, the roughness of the Cu wafers was improved by increasing the number of RGs. Therefore, supplying new slurry and releasing the old slurry can affect the performance Cu CMP process.

Charge Utilization Efficiency and Side Reactions in the Electrochemical Mechanical Polishing of 4H-SiC (0001)

Slurryless electrochemical mechanical polishing (ECMP) is very effective in the polishing of silicon carbide (SiC) wafers. To achieve a high material removal rate (MRR) of SiC wafer using ECMP with low electrical energy loss, charge utilization efficiency in the anodic oxidation of the SiC surface was investigated and the underlying mechanism was clarified by modeling the anodic oxidation system of SiC in 1 wt% NaCl aqueous solution. The charge utilization efficiency in the anodic oxidation of SiC was found to be constant when the current density was less than 20 mA cm−2 and significantly decreased when the current density was greater than 30 mA cm−2, resulting in a significant reduction in the MRR. Modeling of the anodic oxidation system indicates that the charge utilization efficiency depended on the potential applied on the SiC surface: the oxidation of SiC occupied the dominant position in the anodizing system when the potential is lower than 25 V vs Ag∣AgCl, charge utilization efficiency greatly decreased when the applied potential was greater than 25 V owing to the occurrence of oxidations of the H2O and Cl−. This research provides both a theoretical and practical foundation for using ECMP to polish SiC wafers.

Single Particle Inductively Coupled Plasma Mass Spectrometry Study of Ceria Nanoparticle Size Distribution from 300mm Wafer Oxide CMP with Microreplicated Pads

This work describes the use of Single Particle Inductively Coupled Plasma Mass Spectrometry (spICP-MS) to measure ceria particle number concentrations and compare changes in size distributions to silicon dioxide wafer removal rates from different chemical mechanical planarization (CMP) processes. Particle number concentrations were measured for the 21 to 559 nm size range at 1nm size resolution. Changes in the ceria particle size distribution after CMP included a decrease in large (>130 nm) particles, an increase in small (<40 nm) particles, an increase in the total number of particles, and a decrease in median particle size. The decrease in median size was as high as 7% and influenced by slurry flow rate, wafer pressure and pad type. A novel microreplicated CMP pad was used which requires no pad conditioning to ensure consistent pad surface features, and the effect of different pad types on removal rate and particle size was isolated. A decrease in the median particle size correlated with higher silicon dioxide removal rates (R2=0.96) for a series of pad types with unique combinations of chemistry and surface features. This new combination of nano particle metrology and control of pad surface features is an improved tool set for modeling advanced CMP processes.

Effect of Radial Groove Pad on Copper Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) is a process that reduces step height by making the flat surface when several types of layers are accumulated in a semiconductor device. The three main factors affecting CMP are pad, slurry and conditioner. Among these factors, the pad helps the flow of the slurry and polish the wafer with direct contact. Through changing characteristic of pad that is number of grooves, design of groove, depth and width of pitch, we can control wafer removal rates, with-in wafer non-uniformity and roughness. In this study we added a radial groove (RG) at the circular groove (CG) pad to investigate what effect of the RG to Cu CMP. A study was conducted on how the number of RG affects the slurry flow, how changes in slurry flow affect the pressure distribution between the pad and the wafer, and how this affects CMP. The number of RG was divided into 0, 8, 16, 32, and the actual CMP process and simulation experiment were conducted together. In simulation part, we use computational fluid dynamics (CFD) to compare for slurry transport rates according to the number of RG. Fig. 1 shows the removal rates according to the number of RG, and when the number of RG increases to 32, it shows that removal rates of RG pad is almost 23% higher than CG pad. We consider that these results are related to changes in slurry flow during polishing. This is due to role of RG in quickly replacing the old slurry with the new slurry. Figure 1

Single Particle Inductively Coupled Plasma Mass Spectrometry Study of Ceria Nanoparticle Size Distribution from Oxide CMP with Microreplicated Pads

This work describes the use of Single Particle Inductively Coupled Plasma Mass Spectrometry (spICP-MS) to measure ceria particle number concentrations and compare changes in size distributions to silicon dioxide wafer removal rates from different chemical mechanical planarization (CMP) processes. Particle number concentrations were measured for the 21 to 559 nm size range at 1 nm size resolution. Changes in the ceria particle size distribution after CMP included a decrease in large (>130 nm) particles, an increase in small (<40 nm) particles, an increase in the total number of particles, and a decrease in median particle size. The decrease in median size was as high as 7% and influenced by flow rate, pressure and pad type. A novel microreplicated CMP pad was used which requires no pad conditioning to ensure consistent pad surface features, and the effect of different pad types on removal rate and particle size was isolated. A decrease in the median particle size correlated with higher silicon dioxide removal rates (R2 = 0.96) for a series of pad types with unique combinations of chemistry and surface features. This new combination of nano particle metrology and control of pad surface features is an innovative tool set for modeling advanced CMP processes.

Effect of Abrasive Particle Size Distribution on Removal Rate of Silicon Wafers

The effects of silica abrasives of five different particle sizes (10 nm, 40 nm, 60 nm, 80 nm and 100 nm) on the removal rate of silicon wafers were studied. The experiments were performed under two conditions, by taking the abrasive particles of uniform size and of two different sizes. The mixture of abrasive particles of two sizes increased the removal rate of the silicon wafer, and this improvement was more apparent when 10 nm particles were mixed with any other particle size. According to the stability of the slurry, the size pair of 10 nm and 60 nm presented the optimal result for the particle size mixing of abrasives. The physical model of the abrasive distribution between the silicon wafer and the polishing pad was established. The mechanism of the effect of mixed abrasive on the increase of silicon wafer removal rate was presented. Further, the contact area between the abrasive and silicon wafer was calculated by MATLAB. Based on this, the removal rate of the silicon wafer by the abrasive with mixed-sized particles was predicted with an error value of less than 10%.

Performance of Trizact™ Microreplicated Pad in W Buff Marathon Process

This work demonstrates the performance of a microreplicated pad used in a W buff polish process. 3M™ Trizact™ microreplicated pads consist of matrix designed asperitity and pore structures that can be tuned independently, into a wide variety of complex 3D structures. More uniform pad asperity diameter and height control allows for better wafer-pad contact interacions. Consequently, microreplicated pads have significantly higher contact area with the wafer surface compared to industry standard hard and soft pads. The unique heringbone groove design allows for efficient slurry transportation and uniform slurry flow distribution – enabling the potential for slurry saving and cost of ownership reduction. The CMP wafer polish results show stable oxide RR (se Figure 1) and consistent W:Ox film selectivity over 3000 wafers. Wafer removal rate recovey was repeatablly fast following periods of wet idle. Stable uniformity/edge profile control were also achieved. Total defect counts were controlled and consistent throughout the duration of the 3000 wafer marathon run. Upon completion of the marathon run, the loss in pad asperity height loss was less than 3 microns (14 %) compared to initial asperity height illustrating the potential to extend the pad life significantly beyond 3000 wafers (see Figure 2). The results illustrate the benefit of micro-replicated asperities in CMP pads, These results are important because of the potential to improve pad performance and reduce the cost of CMP. Figure 1

Effect of Ceria Abrasive Synthesized by Supercritical Hydrothermal Method for Chemical Mechanical Planarization

Scratches on the wafer surface are one of the significant issues during chemical mechanical planarization process. In order to satisfy wiring width shrinking with time, after polishing process, the presence of small scratches on the wafer is considerable issue. To reduce mechanically induced scratches, small-sized ceria particles are synthesized by a supercritical hydrothermal method. Spherical shaped nano ceria primary abrasive size is about 10 nm and secondary particles are uniformly distributed around 40 nm. The SiO2 wafer removal rate is improved through increasing Ce3+ concentration by metal doping during the synthesis. The detailed principle of the material removal is introduced. The polishing test and its removal rates by the supercritical-hydrothermal-synthesized ceria slurries (SHC) are compared to a commercial ceria slurry. Removal rate of SHC catches up about 85% of the commercial one. The Ce3+ concentration of the slurry samples is compared, and the wafer surfaces are scanned for morphology characteristics. Scratch and roughness results of SHC are significantly improved against the results of commercial ceria slurry.

Ultra-Rapid Determination of Material Removal Rates Based Solely on Tribological Data in Chemical Mechanical Planarization

Single-run Stribeck+ curves are constructed using real-time, high-frequency, shear force and normal force data from the wafer-slurry-pad interface during copper and cobalt (on ILD wafers) CMP in conjunction with multiple slurries, pads and conditioning discs at various pressures and relative velocities. To avoid having to perform actual polishing experiments to obtain blanket film removal rates, “big data” sets from the same Stribeck+ curves are used to construct new “Kinetic” curves to help infer relative blanket wafer removal rates. The “Kinetic” curves, which are based on the assumption that material removal is Prestonian, are eventually validated with actual removal rate studies involving different wafer types processed at various pressures-velocity combinations with the same pads, conditioning discs and slurries. A strong correlation is seen between the actual and “inferred” removal rates which renders credibility to our new ultra-rapid and ultra-low-budget approach for determining removal rates that does not require any wafer polishing nor any film thickness metrology.

Highly efficient removal of sapphire by composite nanoabrasive with novel inorganic polyelectrolyte as a binder

Chemical mechanical polishing has shown great prospect in a wide range of microelectronics applications due to the global planarization. For the first time, we proposed a novel branched inorganic polyelectrolyte as an effective binder to modify colloidal silica. The composite abrasives combine the advantages of both colloidal silica and polyelectrolyte, exhibiting good dispersibility, stability in water and outstanding polishing property. The results indicated that the composite abrasive could enhance the material removal rate (MRR) of sapphire wafer up to 23.76%. The optimum removal rate by composite abrasive also yielded a superior surface roughness (Ra) of 1.445 nm. The mechanism between the composite abrasives and sapphire in chemical mechanical polishing process was investigated in detail. X-ray photoelectron spectroscopy test demonstrated that a soft layer was formed on the surface of sapphire. Micro-contact model revealed that the inorganic polyelectrolyte adhered to the surface of colloidal silica could reduce the repulsion between particles and sapphire, thereby accelerating chemical-mechanical reaction rate and achieving rapid surface removal of the sapphire surface.

Insights into the Tribological and Kinetic Attributes of Retaining Rings in Chemical Mechanical Planarization

We have successfully applied the Stribeck+ curve to determine the tribological mechanism involved in the ring-slurry-pad interface during CMP at various pressures and velocities. Using two types of slurries (one for copper and another for inter-layer dielectric polishing) and two differently designed rings made of polyether ether ketone (PEEK), one with sharp slots and the other with rounded slots. We find “boundary lubrication” as the initial dominant lubrication mechanism followed by a transition to “mixed lubrication” as pseudo-Sommerfeld numbers increase. Coefficient of friction (COF) values for the ring with sharp slots are larger than their rounded counterparts. COF values are also higher for inter-layer dielectric (ILD) processes as compared to copper. In all cases, COF values are directly correlated with average pad surface temperature. The trend in Stribeck+ curves are explained by plotting a new parameter, referred to as directivity, which shows the cluster shape evolution to be a real phenomenon (and not an optical illusion due to the log-log nature of the curve, nor the inherent dependence of the two axes on one another) caused by force fluctuations at the extreme ranges of velocity and pressure. Raw data from the Stribeck+ curves are used to construct a new “kinetic” plot to help infer the relative wear rate of the ring thus allowing one to choose process parameters that balance it against wafer removal rate. Validation studies involving extended wear of eight differently formulated retaining rings show a correlation between wear rate and the “inferred” wear rate which renders credibility to our approach regarding the above-mentioned “kinetic” plots.

Influence of slurry components on copper CMP performance in alkaline slurry

In this work, we have designed copper chemical mechanical planarization (CMP) experiments to investigate the effect of slurry components on the planarization performance of copper wafer in the presence of two different surfactants including ammonium dodecyl sulfate (ADS) and fatty alcohol polyoxyethylene ether (AEO). Copper CMP was performed at pH10.5 using hydrogen peroxide (H2O2), silica, benzotriazole (BTA), and FA/O II (a unique alkaline macromolecular organic chelating agent with high activation energy) as an oxidizer, an abrasive, a corrosion inhibitor and a complexing agent, respectively. As hydrogen peroxide is added in the copper slurry, the material removal rate (MRR) increases rapidly and then decreases slowly as a function of the concentration of H2O2. The within-wafer non-uniformity (WIWNU) declines and the surface roughness decreases first and then ascends with the increase of the H2O2 concentration. The addition of BTA has a large effect on the MRR, WIWNU and copper surface roughness. The MRR decreases to approach a minimum as a function of the BTA concentration. While the copper surface WIWNU fluctuates and the surface roughness increases with increasing the amount of BTA. As FA/O II is chosen to be a complexing agent, the MRR increases prominently and the WIWNU decreases with the increase of the FA/O II concentration. The surface roughness also decreases indicating that the addition of FA/O II can effectively improve the surface planarization performance in the present copper CMP experiments. The mechanism of the corresponding experimental results is also elucidated and discussed. All the results show that the copper surface planarization performance could be strictly controlled by proper configuration of the slurry components and an optimal choice of the concentrations of the constituents can obtain a high removal rate, low WIWNU and small surface roughness of the copper wafer in alkaline slurries.

Study on Chemical Mechanical Polishing Performances of Sapphire Wafer (0001) Using Silica-Based Slurry

In this paper, the chemical mechanical polishing (CMP) mechanism of silica-based slurry on sapphire wafer was analyzed. The influences of size and abrasive concentration of silica-based slurry on the material removal rate (MRR) of (0001) sapphire wafer were investigated, respectively. Furthermore, the effect of chemical agents on MRR was mainly studied. It was found that most alkali metal salts and halogen salts except for fluoride salts can be used as polishing promoting agents to increase MRR. The promotion effect of monovalence cations to MRR decreases with the increase of atomic number. The MRR strongly relies on the kind of alkaline agents used in slurries. During the process of sapphire CMP, no chelating reaction occurred when the chelating agent was added to the silica-based slurry. The double-polished sapphire wafer has a transmittance of 86% to visible light and can be used as the optical window for the screen of smart mobile phones and so on.

Study on Sapphire Wafer Grinding by Chromium Oxide (Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;) Wheel

Finishing process of sapphire wafer is meeting huge challenge to fulfill the strict requirement of high surface quality in semiconductor industry. Fixed abrasive process, although can guarantee the profile accuracy, leaves damaged layer on the surface or subsurface of sapphire wafer. Chemical mechanical polishing (CMP) is famous for providing great surface roughness, however, sacrifices surface geometrical accuracy. Therefore, a new chromium oxide (Cr2O3) sapphire grinding wheel based on chemical mechanical grinding (CMG) principle has been developed and its performance has also been put into examination. The experiment result has demonstrated that Cr2O3 possesses an outstanding potential in terms of a high material removal rate of sapphire wafer, meanwhile, largely reduces surface roughness from about 150nm to below 10nm in 1 hour. In addition, the design of experiment (DOE) has also been carried out to study the effect of influencing factors towards ultimate surface roughness of sapphire wafer. It reveals that the revolution speed of sapphire wafer bears twice greater influence towards surface roughness than the revolution speed of grinding wheel.

Combined Diamond Disks in Chemical Mechanical Polishing

This paper presents a combined diamond disk that is designed and manufactured to markedly improve the leveling of diamond tips, thereby reducing the amount of diamond grit. First, a small brazed diamond disk was manufactured. Second, 12-or 24-disk brazed diamond disks were mounted onto a substrate with a diameter of 108 mm for completing the combined diamond disk. Four types of disks were fabricated, and their performances were compared with that of a conventional diamond disk. The experimental results showed that the combined diamond disk has more complete diamond crystal shapes and distribution with better leveling, which increases the effectiveness of the working diamond grits. Compared to a conventional diamond disk, the combined diamond disk achieved a higher wafer removal rate and better uniformity while consuming less pad material. The number of diamond grits required was significantly lower. Roughly, 7,600 and 12,000 diamond grits were used for the 24-and 12-disk brazed diamond disks, respectively, in the new disk, whereas 20,000 diamond grits were used in a conventional diamond disk. In the case of the conventional diamond disk, the diamond tips are leveled to more than 50 μm. However, in the case of the combined diamond disk, the diamond tips can be leveled to less than 30 μm because the diamond tips are already leveled. These results contribute to the understanding of conditioning techniques and further improvement of the chemical mechanical polishing process.

Pad Surface Thermal Management during Copper Chemical Mechanical Planarization

A pad surface thermal management system was developed to improve copper removal rate within wafer non-uniformity by locally adjusting the pad surface temperature. The system consisted of one or more thermal transfer modules, which contacted the pad surface during polishing. Hot or cold water circulated between the thermal transfer module and an external heater or cooler. With the module placed on the pad surface, heat conduction occurred between the module and the pad surface, producing a localized pad surface with higher or lower temperatures. As such, it was expected that local removal rates would change accordingly due to the temperature-sensitive nature of copper chemical mechanical planarization (CMP). In this study, the system was used to adjust the “center-fast” removal rate profile to illustrate its effect during the process. Results showed that, when two thermal transfer modules were employed, local removal rates in the wafer center region decreased significantly while the removal rates near the wafer edge were maintained thereby significantly improving within wafer removal rate non-uniformity.

Effectiveness Evaluation of Novel Pad Dressing Method by Flexible Fiber Dresser - Tool Life Evaluation of Flexible Fiber Dresser

Chemical mechanical polishing/ planarization (CMP) is a key technology for fabricating high-efficient semiconductor devices, and the CMP characteristics (removal rate and accuracy, etc.) is depended on the various consumables represented by slurry, polishing pad and dresser used in the CMP process. Currently, in the pad, there are many studies that have pointed the evaluation methodology and the correlation between the pad surface asperity and the CMP characteristics. On the other hand, the dresser is one of the most important consumables because the dresser can control the pad surface asperity, and the diamond grains electrodeposited dresser (diamond dresser) is frequently used. One drawback point of the diamond dresser is that the dressing performance declines owing to the deterioration of the diamond grains. Previously, we have developed a novel flexible fiber dresser that would ensure high performance and longer life of tools, and we have reported the fundamental characteristics by the flexible fiber dresser compared with that of the diamond dresser. In this paper, we will show the results of tool life evaluation of the flexible fiber dresser using a contact image analysis method. As a result, the flexible fiber dresser can be continuously used over 35 hours. Furthermore, the result of having examined the stability of the removal rate of a silicon wafer is reported. Therefore, we found that the flexible fiber dresser is one of the most effective dressing methods for the polishing pad.