Wafer Chemical Mechanical Polishing Research Articles

Novel ceria/graphene oxide composite abrasives for chemical mechanical polishing

The structure and particle distribution of the abrasive used in chemical mechanical polishing (CMP) directly affect the performance of polishing and quality of the resulting surface. The ceria (CeO2) nanomaterial has been extensively employed in polishing abrasives. Increasing the Ce3+ content is known to improve removal efficiency and enable optimal surface quality. In this study, we increased the Ce3+ content on the CeO2 surface by growing CeO2 nanoparticles in situ on graphene oxide (GO; CeO2@GO) to develop novel composite abrasives for the high-performance CMP of silicon wafers. The designed composite abrasive fully utilized the special structure of GO and the effect on the charge-transfer between CeO2 and GO, which increase the Ce3+ content and number of chemical reaction sites available during the polishing process. This accelerates the generation rate of the oxide layer on the surface of the silicon wafer and increases the removal rate while improving surface quality. The removal rate of the composite abrasives reached 190.58 ± 13 nm/min, which is 50% higher than that of pure CeO2 abrasives. Moreover, the average surface roughness (Ra) of 0.278 ± 0.07 nm within the confines of a 5.0 × 5.0 μm2 region was achieved using the novel composite abrasives. This study offers a straightforward method to enhance the content of Ce3+ in materials and provides a novel route for obtaining efficient composite abrasives.

Virtual metrology of material removal rate using a one-dimensional convolutional neural network-based bidirectional long short-term memory network with attention

Material removal rate (MRR) is a key parameter for chemical mechanical polishing (CMP). It can affect the polished product quality, and has often been used as an indicator of CMP performance. Virtual Metrology (VM) is an technique for estimating the target value without physical measurement. It can reduce measurement time and save the cost of measurement tools. In this paper, we propose a VM framework, One-Dimensional Convolutional Neural Network-based Bidirectional Long Short-term Memory Network with Attention (1DCNN_BiLSTMwA), for monitoring the condition of components in a wafer chemical mechanical polishing system, to solve the complex data pre-process and feature extraction issue of traditional VM, and to achieve high accuracy of prediction. To evaluate the effectiveness of the proposed method, an empirical dataset from a semiconductor CMP process was used. According to the results of comparison, the proposed 1DCNN_BiLSTMwA has the lowest prediction error and outperforms 1DCNN, LSTM, BiLSTM models and the other machine learning techniques with statistical features and hand-designed features. A weighted, deep learning model was also used to improve performance. The experimental results demonstrate the practical viability of the proposed approach.

High efficiency chemical mechanical polishing for silicon wafers using a developed slurry

Improving the material removal rate (MRR) of silicon wafers is a challenge in chemical mechanical polishing (CMP), to meet the demands of the development of integrated circuits. In this study, four environmentally friendly additives, including sorbitol, gluconic acid, citric acid, and ammonium citrate, were incorporated into polishing slurries to promote the MRR of silicon wafers. The polishing results reveal that the highest MRR was obtained by ammonium citrate as an additive. When the concentration of ammonium citrate was 0.05 mol/L, the MRR increased by 71.6% to 1979.88 Å/min, and the surface roughness Sa was decreased from 1.131 nm to 0.563 nm. Meanwhile, the polishing slurry containing colloidal silica as abrasives maintained good dispersibility. Polishing mechanism was interpreted using electrochemical analysis, X-ray photoelectron spectroscopy, and coefficient of friction tests. It is indicated that NH4+ions, generated by hydrolysis of ammonium citrate, could modify the electrical characteristics of the silicate layer and catalyze the chemical reactions between Si atoms and H2O on the surface of silicon wafers. This work emphasizes the interfacial action between the polishing slurry and silicon wafers and provides a new idea for high efficiency CMP of silicon wafers in the manufacture of integrated circuits and photovoltaic industry.

Highest Quality and Repeatability for Single Wafer 150mm SiC CMP Designed for High Volume Manufacturing

Silicon Carbide (SiC) provides excellent characteristics such as superior thermal conductivity, high carrier mobility and extreme chemical stability in comparison with those of Silicon (Si). SiC is already showing significant device performance benefits in power devices, high performance communication, and LED lighting. However, SiC presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Today, mechanical polishing techniques on industrial batch CMP tools are the predominant methods for SiC wafer surface treatment, but material removal rate (MRR), surface defects and wafer flatness control are reaching fundamental limits with increasing wafer diameter. Batch processing typically results in a higher amount of surface scratches and defects, higher wafer to wafer variability, and higher wafer breakage rates. A unique single wafer chemical mechanical polishing (CMP) technique on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers was developed to create a virtually defect-free surface. A polishing head has been designed to manipulate polishing pressures at various zones of the wafer. This capability can modulate the removal thickness at each region on the wafer surface, resulting in a highly uniform wafer profile. Additionally, a CMP slurry has been formulated to maximize MRR from 2μm/hr to over 8.5μm/hr. Potassium permanganate has been selected as an oxidant and aluminum oxide particles as the abrasive. The oxidant concentration and abrasive content along with slurry pH level have also been optimized for ideal chemical and mechanical activity. Scratch-free wafer surfaces are observed with atomic force microscopy (AFM) and bright field (BF) and dark field (DF) inspection techniques. Roughness on the Si face is reduced to below 0.08nm. Total length of surface scratches was reduced to 10mm or less. Industrial metrics of wafer flatness, including total thickness variation (TTV) and local thickness variation (LTV) are modulated and improved. A test run completed on 25-wafers shows an overall 31% improvement of TTV post CMP process.

Recent developments and applications of chemical mechanical polishing

This article discusses advanced developments and applications of chemical mechanical polishing (CMP) published recently in the selected papers indexed by Web of Science. The topics covered are advances in slurry and abrasives, pads and conditioning, CMP for semiconductor device manufacturing, CMP for other applications, modeling and simulations, and CMP with ultrasonic vibrations, lasers, photocatalysts, or UV lamps. Nonspherical abrasive particles have been developed for CMP, resulting in increased material removal rates (MRRs). Advanced conditioning methods have been proposed to uniformly generate pad surface shapes. Fixed abrasive CMP has advantages with higher MRRs. New models for designing the pad and conditioner have been proposed, and more uniform pad shapes can be obtained. Integrated advanced process control improves the wafer-to-wafer variation. Dental implants treated by CMP perform equally or better than the baseline-machined implants and the biphasic calcium phosphate-treated implants. The slurry distribution and the abrasive behavior can be simulated by means of multiphase modeling. Molecular dynamics simulations can explore the mechanism of CMP. CMP of wafers can be simulated using an atomic force microscope with its tapping mode. Theoretical models have been developed to calculate removal depths, study the chemical action in CMP, and explore the crystal orientation effects. CMP assisted by ultrasonic vibrations increases CMP MRRs and lowers the roughness of polished surfaces. CMP assisted by using UV lamp power, femtosecond lasers, or photocatalysts enhances CMP MRRs.

Data-driven Approach to Material Removal Rate Prediction in Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) has been widely used in the semiconductor sector for creating planar surfaces with the combination of chemical and mechanical forces. CMP is very complex because several chemical and mechanical phenomena (e.g., surface kinetics, contact mechanics, stress mechanics, and tribochemistry) are involved. Due to the complexity of the CMP process, it is very challenging to predict material removal rate (MRR) with sufficient accuracy. While physics-based methods have been introduced to predict MRR, little research has been reported on data-driven predictive modeling of MRR in the CMP process. This paper presents a novel decision tree-based ensemble learning algorithm that trains a predictive model of MRR on condition monitoring data. A stacking technique is used to combine three decision tree-based learning algorithms, including the random forests (RF), gradient boosting trees (GBT), and extremely randomized trees (ERT). The proposed method is demonstrated on the data collected from a wafer CMP tool that removes material from the surface of the wafer. Experimental results have shown that the decision tree-based ensemble learning algorithm can predict MRR in the CMP process with very high accuracy.

Study on high efficient sapphire wafer processing by coupling SG-mechanical polishing and GLA-CMP

Abstract A novel surface finish process sequence has been developed with a sequential process employing sol-gel (SG) semi-fixed abrasive polishing tool and gas-liquid assisted chemical mechanical polishing (GLA-CMP) instead of general copper-resin lap or plate (CP) and chemical mechanical polishing (CMP) to enhance the surface finishing efficiency for sapphire wafer. The surface and subsurface quality of sapphire wafer after the SG and GLA-CMP process have been compared with those by CP and CMP, respectively. Results show that the SG polishing can offer a better surface quality in terms of both surface roughness and sub-surface damage for the next fine polishing step. Based on the contact mechanics models, yielding effects of the SG polishing pad are found to be effective to scratch mitigation. This trend is consistent with experimental results. Furthermore, oxygen is applied as catalyst to improve the removal material rate (MRR) of sapphire by GLA-CMP. It is found that oxygen concentration can improve MRR of sapphire polishing. Among four combinations of CP, SG, CMP, and GLA-CMP, the machining by coupling SG and GLA-CMP shows the maximum MRR approximately as high as 77.6 nm/min, more than 10.23% larger than that of CP-machined wafer and traditional CMP. Ultra-smooth wafer surface with damage-free can be achieved by this new process sequence and the sapphire wafer with qualified surface can be obtained within 50 min by GLA-CMP, which is 90 min shorter than the original 140 min polished by the conventional CMP method. Compared to the conventional surface finish process sequence, the proposed sequence shows superior processing efficiency and quality for sapphire wafers.

Correction to: Establishing a theoretical model for abrasive removal depth of silicon wafer chemical mechanical polishing by integrating a polishing times analytical model and specific down force energy theory

Correction to: Establishing a theoretical model for abrasive removal depth of silicon wafer chemical mechanical polishing by integrating a polishing times analytical model and specific down force energy theory

Establishing a theoretical model for abrasive removal depth of silicon wafer chemical mechanical polishing by integrating a polishing times analytical model and specific down force energy theory

This study uses the polishing pad with cross pattern, and it is supposed that the contact area between polishing pad surface of cross pattern and wafer is Gaussian distribution to establish and analyze an innovative abrasive removal depth theoretical model of chemical mechanical polishing (CMP) silicon wafer. In this model, it uses the binary image pixel division to calculate polishing times and it derives the contact force of each abrasive particle and uses the specific down force energy (SDFE) theoretical equation to calculate the abrasive removal depth on each abrasive particle after down force being applied. This study carries out CMP silicon wafer experiment as well as atomic force microscopy (AFM) measurement experiment of SDFE of silicon wafer. The abrasive removal depth of silicon wafer acquired from simulation analysis is compared with the abrasive removal depth of silicon wafer obtained from CMP experiment of silicon wafer, and the difference in between will also be analyzed. It shows that the difference between the results of simulation and experiment is in the acceptable range.

A novel approach of chemical mechanical polishing for cadmium zinc telluride wafers.

A novel approach of chemical mechanical polishing (CMP) is developed for cadmium zinc telluride (CdZnTe or CZT) wafers. The approach uses environment-friendly slurry that consists of mainly silica, hydrogen peroxide, and citric acid. This is different from the previously reported slurries that are usually composed of strong acid, alkali, and bromine methanol, and are detrimental to the environment and operators. Surface roughness 0.5 nm and 4.7 nm are achieved for Ra and peak-to-valley (PV) values respectively in a measurement area of 70 × 50 μm2, using the developed novel approach. Fundamental polishing mechanisms are also investigated in terms of X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. Hydrogen peroxide dominates the passivating process during the CMP of CZT wafers, indicating by the lowest passivation current density among silica, citric acid and hydrogen peroxide solution. Chemical reaction equations are proposed during CMP according to the XPS and electrochemical measurements.

CMP 공정에서 압력과 정반속도가 사파이어 웨이퍼 재료제거율에 미치는 영향

Kumoh National Institute of Technology(Received January 15, 2016; Revised March 18, 2016; Accepted Mach 20, 2016)Abstract − This study investigates the characteristics of the sapphire wafer chemical mechanical polishing(CMP) process. The material removal rate is one of the most important factors since it has a significant impacton the production efficiency of a sapphire wafer. Some of the factors affecting the material removal rate includethe pressure, platen speed and slurry. Among the factors affecting the CMP process, we analyzed the trends inthe material removal rate and surface roughness, which are mechanical factors corresponding to both the pressureand platen speed, were analyzed. We also analyzed the increase in the material removal rate, which is pro-portional to the pressure and platen speed, using the Preston equation. In the experiment, after polishing a 4-inchsapphire wafer with increasing pressure and platen speed, we confirmed the material removal rate via thicknessmeasurements. Further, surface roughness measurements of the sapphire wafer were performed using atomicforce microscopy (AFM) equipment. Using the measurement results, we analyzed the trends in the surface rough-ness with the increase in material removal rate. In addition, the experimental results, confirmed that the materialremoval rate increases in proportion to the pressure and platen speed. However, the results showed no associationbetween the material removal rate and surface roughness. The surface roughness after the CMP process showeda largely consistent trend. This study demonstrates the possibility to improve the production efficiency of sap-phire wafer while maintaining stable quality via mechanical factors associated with the CMP process.Keywords − polishing(연마), roughness(표면거칠기), material removal rate( 재료제거율), sapphire wafer(사파이어 웨이퍼)

XPS, UV–vis spectroscopy and AFM studies on removal mechanisms of Si-face SiC wafer chemical mechanical polishing (CMP)

Chemical mechanical polishing (CMP) removal mechanisms of on-axis Si-face SiC wafer have been investigated through X-ray photoelectron spectroscopy (XPS), UV–visible (UV–vis) spectroscopy and atomic force microscopy (AFM). XPS results indicate that silicon oxide is formed on Si-face surface polished by the slurry including oxidant H2O2, but not that after immersing in H2O2 solution. UV–vis spectroscopy curves prove that •OH hydroxyl radical could be generated only under CMP polishing by the slurry including H2O2 and abrasive, so as to promote oxidation of Si-face to realize the effective removal; meanwhile, alkali KOH during CMP could induce the production of more radicals to improve the removal. On the other side, ultra-smooth polished surface with atomic step structure morphology and extremely low Ra of about 0.06nm (through AFM) is obtained using the developed slurry with silica nanoparticle abrasive. Through investigating the variations of the atomic step morphology on the surface polished by different slurries, it's reveals that CMP removal mechanism involves a simultaneous process of surface chemical reaction and nanoparticle atomic scale abrasion.

Research and Implementation on Critical Technology of Chemical Mechanical Polishing Tool for 300 mm Wafer

As the feature size scales down and the implementation of multilevel metallization, chemical mechanical polishing(CMP) has become one of the most important technologies in the ultra-large-scale integrated circuits manufacturing. However, the 300 mm wafer CMP tool is being increasingly monopolized by only a few foreign companies, and therefore the research level of 300 mm wafer CMP in our country is far behind other countries such as U.S., Japan, and South Korea. The critical technology of the 300 mm wafer CMP tool is studied. Firstly a 300 mm wafer multi-zone polishing head with pressure control system is developed, vacuum chuck and floating retainer ring are also available in the polishing head. And then the static and dynamic performance of the closed-loop pressure control system is tested. Finally a 300 mm wafer CMP tool is developed, and the 300 mm wafer CMP process flow is developed, improved, and optimized, which establishes the foundation for experimental research. The experimental results show that a material removal rate of 671.3 nm/min, and a within wafer non-uniformity of 3.93 % can be realized by the developed 300 mm wafer CMP tool.

Study on CMP Test Technology of 65 nm and below Node Wafers with Copper Interconnects

It is of significance to research high-removal efficiency and low-cost CMP process for the 65 nm and below node. Chemical mechanical polishing (CMP) can realize the planarization of the wafer with free defects, free contamination and below nanometer level roughness. Test project of CMP slurry is main contain of these detections such as pH value, chelating agent content, SiO2 gel particle size, ζ-potential detection and the observation by Transmission electron microscopy (TEM). End point detection method of pattern wafer CMP usually includes the non destructive optical measurement, motor current feedback measurement and polishing pad temperature test. The main problems of the measurement for pattern wafer CMP are critical dimension (CD), section, film thickness, defects and particles measurement. Some of the new type of testing technology, such as atomic force profiler (AFP), can be used to compare CMP effect, such as dishing, erosion, tungsten plugs, the height of steps and flatness of the wafer, which is significant for wafer CMP research.

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.

Mechanism and Experimental Investigation on Silicon Wafer Hybrid Polishing by Ultrasonic-Elliptic-Vibration Chemical-Mechanical

Considering the technical status and existing problems of traditional silicon wafer chemical mechanical polishing (CMP), especially for the diameter of silicon wafer increasing, constantly, the surface quality and efficiency of silicon wafer polishing are becoming an urgent problem to be solved, so the research subject of ultrasonic vibration hybrid polishing new technique was proposed. By means of mechanism theoretical analysis research, firstly, the processing mechanism of hybrid polishing was studied systematically. An investigation of polishing mechanisms based on the micro-contact model between the polishing pad and the polishing surface of silicon wafer was developed. Polishing mechanism theoretical analysis shows that when ultrasonic vibrations combined with mechanical and chemical, the performance of polishing slurry is improved in the process of CMP, therefore to create favorable conditions. To verify the established theory, then, a series of experiments to investigate the traditional CMP are conducted, as well as the polishing tool with the forms of ultrasonic vibration, the polishing pad, the polishing surface quality, velocity at polishing point v, and slurry supplying Q on silicon wafer polishing. Experiment findings showed that, in the same polishing conditions, especially, hybrid polishing by ultrasonic-elliptic-vibration has gained more advantage over the effect of silicon wafer polishing. When ultrasonic-elliptic-vibration is put in polishing tool, the silicon wafer polished surface roughness Ra from the traditional method of polishing 0.077μm going down to the 0.042μm, the no-smooth rate KR which describes the polished surface morphology is significantly improved, and the material removal rate increases by 18%. Experimental research findings of the surface quality and the material removal mechanism are shown to be consistent with the theoretical analysis.

Preparation of silane modified SiO2 abrasive particles and their Chemical Mechanical Polishing (CMP) performances

Abstract Surface modified SiO 2 particles in an aqueous environment with γ-aminopropyl triethoxysilane (APTS)/methyl trimethoxysilane (MTMOS) are introduced as abrasive in the slurry. The modified silica particles are characterized by Particle Size/Zeta Potential Analysis, Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). In addition, the enhancement of polishing rate owning to the modified silicon particles in silicon wafer Chemical Mechanical Polishing (CMP) is observed.

Experiment on Non-Uniformity of Material Removal on Wafer Surface in Wafer CMP

In the manufacturing process of ultra large scale integrated circuits (ULSI), chemical mechanical polishing (CMP) has already become a practical and main planarization technology because of its global and local planarization ability. The non-uniformity of material removal on wafer surface is one of important indicators of surface precision in wafer CMP process. In this paper, According to the σ calculation method, the calculation equation of the non-uniformity of material removal was put forward. Then, the CMP experiments on the non-uniformity of material removal were conducted under different rotational speed on a CMP machine CP-4. The WaferCheck-7200 equipment, with the theory of non-contact capacitive thickness measurement, was used to detect the thickness of each point on silicon wafer surface. After calculation, the non-uniformity of material removal on the silicon surface was obtained under different polishing speed. The test results can provide some theoretical guide for further understanding the form mechanism of the non-uniformity of material removal and the material removal mechanism in wafer CMP.

Study on Characteristic of Abrasives in Chemical Mechanical Polishing of Silicon Wafer

In order to understand the material removal mechanism in the process of chemical mechanical polishing (CMP), the states of abrasives in the slurry and on the polishing pad in CMP process have been studied by testing. It was concluded that although the abrasive in the slurry is in the form of agglomeration, but the abrasive on the polishing pad are in approximately uniform layer distribution. The different CMP slurries had been designed for CMP test of MRR. According to analyzing the test results, it was concluded that the mechanical action produced by the abrasive is the main mechanical action in wafer CMP process and the MRR mainly results from the interaction between the mechanical action of the abrasives and the chemical action of slurry. These results will provide a reliable basis for the building of abrasive trajectory model and a theoretical guide to further understanding the material removal mechanism in wafer CMP.

Study on Contact Forms in Wafer Chemical Mechanical Polishing in Nanomachining

Chemical Mechanical Polishing (CMP) has become the most widely used planarization technology in the semiconductor manufacturing process. Problem statement: Studying the Contact Forms in Wafer Chemical Mechanical Polishing. Approach: A series test on the abrasion behavior and the lubricating behavior was conducted and then the test results were investigated by the abrasion and lubrication theory. Results: By the test results and analysis, it showed that the Material Removal Rate (MRR) was mainly due to the interaction between abrasives and polishing slurry and the main material removal of wafer surfaces was two bodies abrasive wear under chemical interaction. By the Stribeck curves obtained, 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. Conclusion: By the analysis results, it was concluded that 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.