Chemo-mechanical Grinding Research Articles

Insights into Interfacial Mechanism of CeO2/Silicon and Atomic-Scale Removal Process during Chemo-Mechanical Grinding of Silicon.

Chemo-mechanical grinding (CMG) is a valid processing method to achieve a low-damage surface of silicon. However, the atomic interfacial mechanism during the CMG is still unclear. Herein, the CMG process of silicon was investigated using first principles and frictional wear tests in which the effects of pressure and speed on the interfacial reaction were comprehensively analyzed. Simulations showed that the formation and breakage of chemical bonds occurred at the CeO2/silicon interface during CMG, and the newly formed chemical bonds were stronger than those on the silicon surface. Also, it was found that the pressure and speed improved the materials removal rate by means of accelerating the interfacial chemical reactions, which is also verified by frictional wear tests. This study provides new insights into the atomic interfacial mechanism during silicon CMG.

Mechanical effect of abrasives on silicon surface in chemo-mechanical grinding

To obtain high-quality surfaces and subsurfaces of ground silicon wafers, chemo-mechanical grinding (CMG) for silicon has been developed by inducing chemical reactions into grinding. Chemical reactions between abrasives and silicon during CMG process have been proved in previous studies. The mechanical effect of abrasives in CMG process is not fully understood. To investigate abrasives’ mechanical effect on material removal and subsurface damage of silicon in CMG process, silicon nanoscratching experiments with CeO2 indenter under a progressive normal load were conducted, and microtopographies of scratch surface and subsurface were observed. For comparison, silicon nanoscratching experiments with diamond indenter were also conducted. Finite element models of silicon nanoscratching with CeO2 and diamond indenters were built to investigate the relationship between stress distribution and damage evolution of silicon. Experimental investigations and simulation results indicate that no obvious material removal of silicon or serious subsurface damage is generated by CeO2 indenter's mechanical action because the wear of CeO2 indenter leads to the release of the stress on silicon. Material removal of silicon during CMG process relies on chemical reactions between soft abrasives and silicon other than stress on silicon generated by soft abrasives.

Chemo-mechanical grinding by applying grain boundary cohesion fixed abrasive for monocrystal sapphire

This paper presents a novel fixed abrasive tool namely grain boundary cohesion fixed abrasive pellet (GBCFAP) which is able to provide higher finishing efficiency as well as better surface/subsurface quality of sapphire substrate during the chemo-mechanical grinding (CMG) process. The manufacturing procedures of GBCFAP are introduced in detail in this paper. It is found that the sintering temperature plays an important role to the strength of GBCFAP, and the strength of GBFCAP could be flexibly adjusted by sintering temperature. The experiment result suggests that the recommended sintering temperature ranges from 600 to 650 °C according to current CMG conditions. Meanwhile, comparing with conventional resin bound CMG wheel, 600 °C sintered GBCFAP CMG wheel performs better in terms of material removal rate and surface/subsurface quality since the chemical effect and mechanical effect during CMG process are well balanced. Meanwhile, the solid phase reaction between sapphire and Cr2O3 abrasive is demonstrated by TEM observation and XPS quantification.

Development of binder-free CMG abrasive pellet and finishing performance on mono-crystal sapphire

Chemo-mechanical-grinding (CMG) is a fixed abrasive process by integrating chemical reaction and mechanical grinding for sapphire wafer finishing, and shows advantages in surface integrity, geometric controllability and waste disposal. However, the material removal rate (MRR) obtained by the traditional CMG wheel is not high enough to meet the requirement from the mass production of sapphire wafers. As a potential solution, a new CMG wheel with extremely high abrasive concentration has been proposed. This paper targets on developing of binder-free abrasive pellets (BAP) with 100 wt% abrasive as well as investigating the performance of BAP in sapphire wafer finishing. The results of CMG experiment reveal that the MRR and surface roughness (Ra) of sapphire wafer finished by BAP constructed CMG wheel are able to reach 1.311 μm/h and 0.993 nm respectively. The characterization by Raman microscope indicates that the finished sapphire wafer also owns excellent subsurface integrity.

Study on the finishing capability and abrasives-sapphire interaction in dry chemo-mechanical-grinding (CMG) process

Chemo-mechanical-grinding (CMG) is a fixed abrasive process by integrating both chemical reaction and mechanical grinding. This paper targets on studying the finishing ability of dry CMG processes for mono-crystal sapphire and understanding the underlying abrasives-sapphire interaction. The experiment results suggest that dry CMG processes by applying either Cr2O3 or SiO2 are able to produce sapphire substrate with an excellent surface quality and subsurface integrity, meanwhile, maintain the geometric accuracy. The underlying abrasives-sapphire interaction termed as solid phase reaction is demonstrated by X-ray photoelectron spectroscope (XPS) analysis. It is suggested that Cr2O3 abrasives is more chemically active against sapphire (Al2O3) when compared with SiO2 abrasives. Combined with a higher mechanical effect provided by Cr2O3 abrasives, the finishing efficiency of Cr2O3 abrasives is almost 2 times higher than traditional SiO2 abrasives. The subsurface integrity characterization by using Raman microscope and transmission electron microscope reveals that Cr2O3 abrasives introduces a shallow damage layer (about 100 nm) on the top surface of sapphire substrate since the chemical effect is not sufficient enough to meet the balance with mechanical effect. With a better mechanical-chemical balance achieved by SiO2 abrasives, a damage free subsurface is obtained. Therefore, besides of traditional SiO2 abrasives, Cr2O3 abrasives is suggested to be another potential candidate for finishing sapphire substrate.

Surface integrity and removal mechanism of silicon wafers in chemo-mechanical grinding using a newly developed soft abrasive grinding wheel

A new soft abrasive grinding wheel (SAGW) used in chemo-mechanical grinding (CMG) was developed for machining silicon wafers. The wheel consisted of magnesia (MgO) soft abrasives, calcium carbonate (CaCO3) additives and magnesium oxychloride bond. Surface topography, roughness and subsurface damage of the silicon wafers ground using the new SAGW were comprehensively investigated. The results showed that the grinding with the new SAGW produced a surface roughness of about 0.5nm in Ra and a subsurface damage layer of about 10nm in thickness, which is comparable to that produced by chemo-mechanical polishing. This study also revealed that the chemical reactions between MgO abrasive, CaCO3 additives and silicon material did occur during grinding, thereby generating a soft reactant layer on the ground surface. The reactant layer was easily removed during the grinding process.

Study on the potential of chemo-mechanical-grinding (CMG) process of sapphire wafer

Chemo-mechanical-grinding (CMG) is a hybrid process which integrates chemical reaction and mechanical grinding between abrasives and workpiece into one process. It has been successfully applied into manufacturing process of silicon wafers where both geometric accuracy and surface quality are required. This paper aims to study the potential of CMG process in manufacturing process of single crystal sapphire wafers. The basic material removal mechanism in terms of chemical effect and mechanical effect in CMG process has been analysed based on experiment results of two different kinds of CMG wheels. The experiment results suggest that chromium oxide (Cr2O3) performs better than silica (SiO2) in both material removal rate (MRR) and surface quality. It also reveals that, no matter under dry condition or wet condition, CMG is with potential to achieve excellent surface quality and impressive geometric accuracy of sapphire wafer. Meanwhile, test result by Raman spectrum shows that, by using Cr2O3 as abrasive, the sub-surface damage of sapphire wafer is hardly to be detected. Transmission electron microscopy (TEM) tells that the sub-surface damage, about less than 50 nm, might remain on the top surface if chemical effect is not sufficient enough to meet the balance with mechanical effect in CMG process.

Chemo-Mechanical Grinding for K9 Optical Glass

K9 optical glass was widely used in national defense and civilian fields. In this paper, chemo-mechanical grinding (CMG) was applied to process the K9 optical glass. Selecting CeO2, MgO and Fe2O3as CMG abrasives, the corresponding CMG tools were purposely developed for the check experiment. High surface and subsurface qualities on the K9 optical glass specimen were obtained as the polished results by the CeO2-CMG tools. Surface roughness and material removal rate were used to evaluate the grinding performance. The low-abrasive ratio of CeO2-CMG tool was proved as the optimal one, by which the surface roughness Ra reached 0.586nm, and the surface morphology appeared smooth and flat. The angle polishing was applied to detect the subsurface quality and the subsurface cracks were not observed.

Experimental Investigation on Hybrid Technology of Ultrasonic Vibration Assisted Chemo-Mechanical Grinding (CMG) Silicon Wafer

For the final finishing of the substrate surface, Chemo-mechanical polishing (CMP) is often utilized. Those processes are able to offer a great sur-face roughness, but sacrifice profile accuracy. On the other hand, Chemo-mechanical grinding (CMG) is potentially emerging defect-free machining process which combines the advantages of CMP. In order to simultaneously achieve high surface quality and high profile accuracy, CMG process has been applied into machining of large size quartz glass substrates for photomask use. In this paper, based on the characteristics of higher machining efficiency and higher surface quality of ultrasonic vibration machining, a new ultrasonic vibration assisted CMG of silicon wafer hybrid technique is achieved by designing elliptical vibrator with longitudinal mode and bending mode. The experimental results show that under the elliptic ultrasonic vibration assistance, the surface roughness is decreased significantly, the surface quality is improved obviously, and moreover caused little or even doesn’t lead to the surface damage.

Grinding Performance Evaluation of the Developed Chemo-Mechanical Grinding (CMG) Tools for Sapphire Substrate

In order to improve the surface quality of sapphire substrates ground by diamond wheel, the chemo-mechanical grinding (CMG) tools for sapphire grinding was investigated in this paper. According to the processing principle of CMG, three CMG tools with different abrasives of SiO2, Fe2O3 and MgO were developed respectively. The compositions of the CMG tools were designed and optimized based on the physicochemical characteristics of sapphire. The grinding experiments were performed with the developed CMG tools and the grinding performance of three kind of tools were evaluated by comparing the surface roughness and the MRR of sapphire. The experiment results show that the grinding performance of SiO2 CMG tool was worst. The surface roughness and MRR corresponding to SiO2 CMG tool were all significantly poorer than Fe2O3 and MgO CMG tools. The highest MRR could be obtained by Fe2O3 CMG tool, but the best surface quality was obtained by MgO CMG tool.

Development of CMG Wheels for Stress Relief in Si Wafer Thinning Process

In recent semiconductor industry, production of ever flatter, thinner and larger Si wafer are required to fulfill the demands in high integration and cost reduction. A severe problem encountered in wafer thinning process is the warp and distortion of wafer induced by the residual stress and subsurface damage. Chemo-mechanical grinding (CMG) process is emerging process which combines the advantages of fixed abrasive machining and chemical mechanical polishing (CMP), offers a potential alternative for stress relief. This paper studies the influence of the wheel manufacturing process on the wheel physical properties. Three-factor two-level full factorial designs of experiment are employed to reveal the main effects and interacted effects of mixing method and filtration of raw materials on the bending strength and elastic modulus of CMG wheel. The difference in wheel properties is discussed by association with CMG performance including wheel wear, grinding force and surface roughness.

Performance improvement of chemo-mechanical grinding in single crystal silicon machining by the assistance of elliptical ultrasonic vibration

As a promising technology for the machining of large-sized Si wafer, chemo-mechanical grinding (CMG) integrates the advantages of fixed abrasive machining and chemical mechanical polishing (CMP), and hence can generate superior surface quality comparable to that by CMP while maintaining the high geometric accuracy. In order to enhance the material removal rate (MRR), attain the work-surface with little damage or defects, and then promote the popularisation of CMG, a new combined grinding method, i.e., elliptical ultrasonic vibration assisted CMG (EUA-CMG), is proposed. Some analysis and experiments were conducted to reveal the processing characteristics of EUA-CMG of single crystal silicon. The result shows that compared with the conventional CMG without ultrasonic vibration, better surface quality and higher MRR can be attained in EUA-CMG.

Effect of Wheel Additive On Chemo-Mechanical Grinding (CMG) of Single Crystal Si Wafer

Chemo-mechanical grinding (CMG) process is a promising process for large-sized Si substrate fabrication at low cost. However, effect of additive in CMG wheel is not completely understood yet. In this paper, three different CMG wheels were developed, in which one excluded additive and the other two contained two kinds of additive i.e. silicon dioxide and sodium carbonate. Grinding experiments were conducted to explore the influence of exclusion of additive and inclusion of different kinds of additive on CMG performance. The grinding characteristics of the three wheels were also analyzed and discussed to reveal the roles of wheel compositions in CMG process. This work provides some fundamental insights for the selection of different types of additive for optimization of CMG wheel.

Two Dimensional Ultrasonic Vibration Assisted Chemo-Mechanical Grinding of Si Wafer

As a new fixed-abrasive machining method, chemo-mechanical grinding (CMG) is developed from chemical mechanical polishing (CMP), with the obvious advantage of geometric accuracy determinacy and no slurry. To improve material removal rate and enhance the popularity of CMG, this paper introduces a combined grinding method, i.e., two dimensional ultrasonic vibration assisted CMG (2D-UACMG). Si wafer is taken as the workpiece and the influence of ultrasonic vibration modes and process parameters on the surface roughness and the material removal is examined. The results show 2D-UACMG can obtain better surface quality with little surface damage at nanometer level compared with the conventional CMG without the ultrasonic vibration.

Molecular Dynamics Simulation of Chemo-Mechanical Grinding (CMG) by Controlling Interatomic Potential Parameters to Imitate Chemical Reaction

This paper reports a molecular dynamics simulation of chemo-mechanical grinding (CMG) of silicon wafer by controlling the interatomic potential parameters to imitate the chemo-mechanical or mechano-chemical reactions between an abrasive grain and a Si wafer. Some comparisons between diamond grinding and CMG were made by using the proposed simulation model. From the simulation results, reductions of surface damages, wears of abrasive grain and scratching forces in CMG were confirmed to be same as observed in actual experiments by a CeO2 abrasive wheel, and the availability of proposed simulation model was verified.

Effects of Sodium Carbonate and Ceria Concentration on Chemo-Mechanical Grinding of Single Crystal Si Wafer

Chemo-mechanical grinding (CMG) process is a promising process for large-sized Si substrate fabrication at low cost. An encountered issue in current CMG process of Silicon (Si) wafers is metallic contaminations on ground Si wafer surface, which is attributed to the existence of sodium carbonate in wheel compounds. In this paper, four different CMG wheels were developed and grinding experiments were conducted to study the effects of exclusion of sodium carbonate and concentration of ceria abrasive on grinding performance. The grinding characteristics of the four wheels were analysized and discussed to reveal the effects of different compositions.

A Novel Single Step Thinning Process for Extremely Thin Si Wafers

The demand for extremely-thin Si wafers is expanding. Current manufacturing technologies are meeting great challenges with the continuous decrease in Si wafer thickness. In this study, a novel single step thinning process for extremely thin Si wafers was put forward by use of an integrated cup grinding wheel (ICGW) in which diamond segments and chemo-mechanical grinding (CMG) segments are alternately allocated along the wheel periphery. The basic machining principle and key technologies were introduced in detail. Grinding experiments were performed on 8-in. Si wafers with a developed ICGW to explore the minimal wafer thickness and grinding performance. The experimental results indicate that the proposed grinding process with the ICGW is an available thinning approach for extremely thin Si wafer down to 15μm

Research on chemo-mechanical grinding of large size quartz glass substrate

Finishing process of quartz glass substrate is meeting great challenges to fulfill the requirements of photomask for photolithography applications. For the final finishing of the substrate surface, chemical mechanical polishing (CMP) is often utilized. Those free abrasive processes are able to offer a great surface roughness, but sacrifice profile accuracy. On the other hand, the fixed abrasive process or grinding is known as a promising solution to improve accuracy of profile geometry, but always introduces damaged layer. Chemo-mechanical grinding (CMG) is potentially emerging defect-free machining process which combines the advantages of fixed abrasive machining and CMP. In order to simultaneously achieve high surface quality and high profile accuracy, CMG process has been applied into machining of large size quartz glass substrates for photomask use. Reported in this paper are CMG performances in finishing of quartz glass substrates including material removal rate (MRR), surface roughness, flatness and optical characteristics.

Observation of Surface Topography during Chemo-Mechanical Grinding (CMG) Process

Observation of Surface Topography during Chemo-Mechanical Grinding (CMG) Process

Elimination of surface scratch/texture on the surface of single crystal Si substrate in chemo-mechanical grinding (CMG) process

Si wafers are widely used as a substrate material for fabricating ICs. The quality of ICs depends on the quality of Si wafers. The chemo-mechanical grinding (CMG) with soft abrasive grinding wheels (SAGW) has been recently found to be a great potential process for machining Si wafers to generate superior surface quality at low cost. However, there have been very few studies on observing variation of topography of scratch/texture and understanding basic eliminating process of scratch/texture on the ground Si wafer. Furthermore, few reports on the variation of surface roughness and material removal rate (MRR) during CMG process and relationship between MRR and surface roughness during CMG process are presented. In this paper, a series of CMG experiments have been conducted to study the elimination process of artificial scratches created on etched Si surfaces and residual textures induced by SD1500 diamond wheel in CMG process, and to understand the topography variations of Si surfaces and some basic grinding characteristics during CMG process.