Polishing Pad Research Articles

Removal function of annular polishing pad based on translation-rotation motion

Removal function of annular polishing pad based on translation-rotation motion

Energy dissipation and constitutive modeling for a mechanistic description of pad scratching in chemical–mechanical planarization

A thermomechanical model to describe the mechanisms of polishing pad scratching in chemical–mechanical planarization (CMP) has been formulated and investigated. CMP is a necessary process in integrated circuit (IC) fabrication to planarize wafers with nanoscale features after patterned layer deposition. Polishing pad asperities can produce microscale scratches on the wafer surface during CMP, reducing IC manufacturing yields. The constructed thermomechanical model accounts for stresses of the pad and wafer contact and also provides the means to track input energy dissipation during CMP. Tracking energy dissipation offers information about processes that may influence scratch production. This knowledge ultimately produces a greater physical understanding of CMP for the prevention of pad scratching. Polishing pad stress relaxation experiments demonstrate the importance of viscoelastic and plastic strain energy dissipation with its effects on the wafer stress field. Scratch producing ability of the polishing pad is found to decrease with use in CMP, with slurry soaking and increasing polishing time. Mechanical behavior of the polishing pad is demonstrated to differ when in compression and in tension. Compressibility of the pad material is shown to be significant in stress modeling through experimental measurement of polishing pad volume change. Differential scanning calorimetry of used polishing pad samples revealed energy dissipation into the polishing pad surface with increasing polishing time of CMP. Energy dissipation processes influence pad scratching in CMP. Analytical wafer stress field modeling unveils that the scratching ability of a polishing pad decreases when it is less stiff or has a smoother surface.

Modelling of the Polished Profile in Computer-Controlled Polishing by a Sub-Aperture Pad

High-quality part surfaces with high surface finish and form accuracy are increasingly in demand in the mold/die and optics industries. The computer-controlled polishing (CCP) is commonly used as the final procedure to improve the surface quality. This paper presents a theoretical and experimental study on the polished profile of CCP with sub-aperture pad. A material removal model is proposed based on the evaluation of the amount of material removed from the surface along a direction orthogonal to the tool path. The model assumes that the material removal rate follows the Peterson equation. The distribution of the sliding velocity at the contact region is presented. On the basis above, the approaches to calculate the polished profiles are developed for the sub-aperture pad polishing along a straight path and a curved path. The model is validated by a series of designed polishing experiments, which reveals that polishing normal force, angular spindle velocity, feed rate and polishing path all have effects on the polished profile. The result of experiments demonstrates the capability of the model-based simulation in predicting the polished profile.

Investigation into Chemical Mechanical Polishing Mechanism of Hard-to-Process Materials Using a Commercially Available Single-Sided Polisher

Chemical mechanical polishing (CMP) is one of the most important processes for fabricating highly planarized substrates such as sapphire for light emitting diodes (LEDs). However, sapphire is categorized as a hard-to-process material; therefore, a long processing time is required because of the low polishing efficiency (i.e., removal rate). This study investigates the CMP mechanism for hard-to-process materials using the following polishing evaluation parameters: (1) the velocity ratio, which is defined as the ratio of slurry flow velocity between the wafer and polishing pad during CMP to the pad tangential velocity, (2) the standard deviation of the velocity ratio distribution, and (3) the polisher vibration acceleration during CMP. Each parameter was measured at five rotational speeds and two polishing pressures for a total of ten conditions using a commercially available single-sided polisher. Moreover, the influence of each parameter on the removal rate was demonstrated via a multiple correlation analysis. As a result, we revealed that the velocity ratio and polisher vibration acceleration are strongly related with the removal rate.

Investigation into material removal influenced by edge effect in polishing

Edge effect is unavoidable in polishing process when the polishing pad passes by the workpiece edge, which influences the entire form accuracy of free-form surfaces of optical components in computer-controlled polishing, or even reduces their effective aperture. This article focuses on a theoretical and experimental investigation into the material removal influenced by edge effect for polishing along a certain path. The contact pressure distribution models for polishing the workpiece edge are summarized and modified into four representative models: linear model, skin model, linear skin model and divided skin model, which are adopted to calculate the theoretical material removal profiles orthogonal to the straight or curved polishing path, in this article. So, the material removal models are built in the process of polishing along tool path instead of polishing on a single point. And experiments are carried out to choose the most suitable contact pressure distribution model according to the comparison of experimental profiles and the different theoretical profiles. Experimental results reveal the influences of edge effect on material removal and a modified parameter is introduced into the theoretical material removal profile for the curved path to coincide with the experimental profile better. In addition, some qualitative analyses about how to reduce the edge effect are also given in this article.

선형 롤 CMP에서 플로팅 노즐을 이용한 연마 특성에 관한 연구

Conventional etching technology is in the face of problems such as dishing, erosion resulting from non-uniform removal of film. Advanced printed circuit board (PCB) requires accurate wire formation with the aid of planarization by chemical mechanical polishing (CMP). Linear roll CMP is a line contact continuous process which removes the film by pressurization and rotation while slurry is supplied to polishing pad attached to the roll. This paper focuses on the design of floating nozzle on the linear roll CMP equipment which makes the slurry supply uniformly on the roll pad. Experimental results show that removal rate using the floating nozzle increases 3 times higher than that without it and non-uniformity is less than 15%.

Material removal mechanism of cluster magnetorheological effect in plane polishing

A cluster magnetorheological (MR) plane polishing based on a combination of magnetorheological finishing (MRF) and cluster mechanism (arrange in a regular array) has been developed for large planar optical workpiece. In this paper, the polishing pressure of an individual MR micro-grinding head on workpieces was investigated, and the mathematical model for cluster MR plane polishing was established based on the Preston equation and the properties of the workpiece material. An arc-shaped polishing belt was processed on monocrystalline 6H-SiC and Si wafer by the cluster MR polishing apparatus which polishing disk inlaid with cylindrical flat bottom magnetic pole arrange in the same direction regularly and monocyclically. The profile of arc polishing belt’s cross section and the surface morphology were observed and analysed to verify the obtained model. The abrasives with different size were found to have an equal effect on the processed surface because of the accommodated-sinking effect of the polishing pad constituted by the cluster MR micro-grinding head. It was found that the monocrystalline 6H-SiC and Si wafer were polished in a plastic mode with a smooth, damage-free surface.

Chemistry and Formation of the Beilby Layer During Polishing of Fused Silica Glass

The chemical characteristics and the proposed formation mechanisms of the modified surface layer (called the Beilby layer) on polished fused silica glasses are described. Fused silica glass samples were polished using different slurries, polyurethane pads, and at different rotation rates. The concentration profiles of several key contaminants, such as Ce, K, and H, were measured in the near surface layer of the polished samples using Secondary Ion Mass Spectroscopy (SIMS). The penetration of K, originating from KOH used for pH control during polishing, decreased with increase in polishing material removal rate. In contrast, penetration of the Ce and H increased with increase in polishing removal rate. In addition, Ce penetration was largely independent of the other polishing parameters (e.g., particle size distribution and the properties of the polishing pad). The resulting K concentration depth profiles are described using a two‐step diffusion process: (1) steady‐state moving boundary diffusion (due to material removal during polishing) followed by (2) simple diffusion during ambient postpolishing storage. Using known alkali metal diffusion coefficients in fused silica glass, this diffusion model predicts concentration profiles that are consistent with the measured data at various polishing material removal rates. On the other hand, the observed Ce profiles are inconsistent with diffusion based transport. Rather we propose that Ce penetration is governed by the ratio of Ce–O–Si and Si–O–Si hydrolysis rates; where this ratio increases with interface temperature (which increases with polishing material removal rate) resulting in greater Ce penetration into the Beilby layer. Calculated Ce surface concentrations using this mechanism are in good agreement to the observed change in measured Ce surface concentrations with polishing material removal rate. These new insights into the chemistry of the Beilby layer, combined together with details of the single particle removal function during polishing, are used to develop a more detailed and quantitative picture of the polishing process and the formation of the Beilby layer.

Phase Transformation of Monocrystalline Silicon Induced by Polishing With Diamond Abrasives

A newly developed semi-fixed flexible polishing tool called sol-gel (SG) polishing pads can satisfy the polishing demand of silicon wafers with scratch-free and nano-roughness surface. However, an obvious damage layer emerges on the surface of monocrystalline silicon wafer after polished by SG polishing pads with diamond abrasives. In this paper, combined characterizations consist of grazing incidence X-ray diffraction, Raman spectroscopy (RS), focused ion beam-scanning electron microscopy (FIB-SEM), transmission electron microscopy (TEM), and SEM were used to observe the damage layer together with the polishing residue. The results indicated that the surface monocrystalline silicon transformed to α-Si and nano-Si. Analysis on the polishing processes under the same experimental parameters with different tools and abrasives revealed that the material removing scale about 100-300 nm may account for the generation of damage layer.

Investigation of increased removal rate during polishing of single-crystal silicon carbide

The application field of silicon carbide (SiC) as a next-generation compound semiconductor is expanding because of its significant advantages: high power, high frequency, low coefficient of thermal expansion, and high thermal conductivity. Many researchers have investigated SiC polishing for the manufacturing of semiconductor substrates using SiC. However, because SiC is a chemically and mechanically stable material, these researchers have faced difficulties due to its very low polishing rate (95–540 nm/h). Therefore, methods are required for increasing the material removal rate of SiC. The aim of this study was to investigate the increase in removal rate during the polishing of single-crystal SiC subjected to simultaneous polishing and dressing by using a diamond-impregnated polishing pad. Two types of pads—containing 1 and 5 wt% nanodiamond—were fabricated, and their performances were compared with that of a polyurethane polishing pad. A novel arrangement of conditioners was created in brazed diamond patterns, which were radially arranged in a cluster with 3–4 grits per cluster. Furthermore, a combined diamond disk was developed. The surface characteristics of the nanodiamond-impregnated pads, as well as the surface roughness, surface damage, and removal rate of the SiC polished with these pads and diamond disks, were investigated and compared with the corresponding attributes displayed by a polyurethane polishing pad and a conventional diamond disk. Experimental results showed that the removal rate of SiC with dressing was approximately 73 % higher than that of without dressing. The novel conditioner resulted in a dressing rate approximately two times higher and a removal rate approximately 38 % higher than those obtained by using the conventional diamond disk. In addition, SiC polishing tests revealed that the nanodiamond-impregnated polishing pads provided better surface roughness with no damage, as well as a removal rate approximately 2.5 times higher than that provided by the polyurethane polishing pad.

Thermal Effects of Mechanical Polishing and Conditioning on Polishing Pads

Polishing process is a primary technique for planarization of material surface in manufacture fabrication. The pad structure and its material properties are important to determine the polish rate and planarity that can be achieved by the polishing process. Besides, the pad conditioning is used to regenerate the surface of the polishing pad surface by breaking up the glazed areas. Because the polishing and pad conditioning mechanism is inadequately understood and because higher levels of pad polishing performance are desired, the investigation of experiment becomes more important.In this paper, a high precision polishing machine has established. With an improved design, a test rig can be easily used to simulate the polishing, pad conditioning process and acquire the signals of temperature. The temperature of test pads (i.e. Rodel IC1000A, Rodel IC 1000B and Opetech SB 660) is measured during polishing and pad conditioning process. For the self-design test rig, its surface temperature is measured by T-type thermocouples screwed behind the polishing (or conditioning) interface of the carrier. The experimental results provide a temperature index to end-point-detection and contribute to understanding of the mechanism on polishing pads.

A study of chemical products formed on sapphire (0001) during chemical–mechanical polishing

A study of chemical products formed on sapphire (0001) during chemical–mechanical polishing is presented. The results demonstrated that the formation and removal of chemical products both proceeded from the hexagonal close-packed sapphire Al-O layers described as atomic terraces, and the material removal rule of sapphire (0001) during chemical–mechanical polishing is the regular removal of chemical products formed from the atomic terraces, which were successfully characterized by AFM with super-sharp scanning probes. Besides, we also found that the surface with screw dislocations could not be polished completely by CMP due to the crystal distortion energy, and a hard polishing pad could remove scratches more effectively than a soft one

The effects of abrasive yielding on the polishing of SiC wafers using a semi-fixed flexible pad

A newly developed sol-gel (SG) polishing pad can satisfy the processing demands of SiC wafers by providing scratch-free polished surfaces with nano-roughness. The main characteristic of this polishing tool is the semi-fixed abrasive together with the flexible matrix. In this article, contrastive experiments involving polishing of SiC wafers with three different types of tools were conducted to confirm the machining mechanism of the SG polishing pad. The results indicate that the abrasives in the pad exhibit yielding effects during the polishing process, contributing to the achievement of a mirror-like wafer surface. In addition, larger abrasives can be chosen for the SG polishing pad to obtain relatively high wafer surface quality instead of smaller ones, thereby avoiding the agglomeration problem of ultrafine abrasives.

Development of a real-time force-controlled compliant polishing tool system with online tuning neural proportional–integral–derivative controller

This article presents a real-time force-controlled pneumatic compliant polishing tool with self-supplied abrasives making the abrasives added to the contact area between the polishing pad and workpiece, which can lead to good polishing performance. And a force–position decoupling pneumatic servo system for polishing force control is presented to solve the problem of force–position coupling in the traditional polishing process. However, it is difficult to realize satisfactory control performance due to the problems of time variance, compliance, hysteresis and nonlinearity in pneumatic servo system. This article proposes an online tuning neural proportional–integral–derivative controller to improve force control performance. The real-time polishing force control results of pneumatic servo control system are investigated by adopting proposed neural proportional–integral–derivative control strategies with data acquisition card and RTW toolbox in MATLAB/Simulink. The real-time experimental results of polishing force control indicate that the excellent control performance can be achieved by the proposed neural proportional–integral–derivative controller no matter the reference force is constant or varied. Compared with those by traditional proportional–integral–derivative controller, the duration for stabilizing the polishing force is shorter and the error between the output force and the reference is smaller by the proposed neural proportional–integral–derivative controller.

Study on 6H-SiC Crystal Substrate (0001) C Surface in FA-CMP Based on Diamond Particle

Through experimental study on the role of the free abrasive in chemical mechanical polishing, in this paper, four different types of abrasive which were chosen were used for the research of material removal rate(MRR) and surface quality of SiC single crystal . Finally ,Diamond abrasive which is considered was the most suitable for chemical mechanical polishing(CMP) abrasive of SiC Crystal Substrate. With diamond Particle polish pad polishing, it is draw a comparison result on the influence of the free abrasive and consolidation abrasive for the material removal rate and surface quality of 6H-SiC. The results showed that: the MRR is 140nm / min, the material removal rate if fixed abrasive chemical mechanical polishing(FA-CMP) more than three times that of traditional CMP, fixed abrasive chemical mechanical polishing pad, are involved in a large proportion of micro abrasive cutting, can greatly improve the material removal efficiency. And results from the test procedure, the FA-CMP surface has scratches after more technical problems for the polishing pad, the surface damage is relatively free of abrasive chemical mechanical polishing is more serious.

Modelling of Grain Motion for Three-body Abrasion

Surface formation for three-body abrasion is essentially more difficult to model than for two-body abrasion. In contrast to grains embedded in the polishing pad and therefore time-invariant tool geometry for two-body abrasion, here a variable tool geometry is prevailing as a result of the rolling abrasive grains. Nevertheless, three-body abrasion is an important abrasive process in the surface finishing of glass and ceramics and the modelling of the surface formation for mechanical abrasive machining with loose grains is required for a better process understanding and enhanced process design.The modelling of the surface formation for three-body abrasion is dealt with by splitting the integral removal volume under the polishing pad into the removal of single grains and distributing the total polishing force according to the interaction of individual grains with the workpiece material. This new methodical approach intends to determine the material removal in discrete time steps for every grain and further on the generated new surface topography. Data from polishing experiments like concentration and form of abrasives, polishing load, surface topography and integral removal are applied to set up this analytic-empiric model. Crucial elements of this model are the geometry of single grains, their rolling motion under load and the principle of material removal. In this paper the simulation of the rolling motion of single abrasive grains using a numerical time step model is introduced.

Characteristics of Sapphire Wafers Polishing Depending on Ion Conductivity of Silica Sol

CMP(Chemical Mechanical Polishing) Processes have been used to improve the planarization of the wafers in the semiconductor manufacturing industry. Polishing performance of CMP Process is determined by the chemical reaction of the liquid sol containing abrasive, pressure of the head portion and rotational speed of the polishing pad. However, frictional heat generated during the CMP process causes agglomeration of the particles and the liquidity degradation, resulting in a non-uniform of surface roughness and surface scratch. To overcome this chronic problem, herein, we introduced NaCl salt as an additive into silica sol for elimination the generation of frictional heat. The added NaCl reduced the zata potential of silica sol and increased the contact surface of silica particles onto the sapphire wafer, resulting in increase of the removal rate up to 17 %. Additionally, it seems that the silica particles adsorbed on the polishing pad decreased the contact area between the sapphire water and polishing pad, which suppressed the generation of frictional heat.

Further Investigation of Slurry Additives for Selective Polishing of SiO2 Films over Si3N4 Using Ceria Dispersions

Following our earlier analysis of amino acids, we investigated the effectiveness of acetic acid, pyridine, and sorbitol that were chosen to represent carboxylic acid, amine and alcohol functional group families, respectively, as additives in ceria dispersions for polishing SiO2 and Si3N4 films. By comparing the speciation of the additives available and the material removal rates with respect to pH, we identified that the removal rates of nitride, but not oxide, are suppressed to <1 nm/min in the pH range where the additive species containing a protonated amino group or a neutral carboxylic group or a neutral hydroxyl group are dominant. All of these species are strong hydrogen bond donors and can form strong hydrogen bonds with Si3N4 surface while their corresponding bonding on SiO2 surface sites is weaker. The stronger hydrogen bonding hinders Si3N4 hydrolysis and suppresses Si3N4 removal. In contrast, the weakly bound additive species are easily removed from the SiO2 surface by the polishing pad and the ceria abrasives, leading to high SiO2 to Si3N4 removal rate selectivity. Similar results were also obtained with valeric acid, imidazole, glucose, sucrose, and mannitol, confirming the importance of a strong hydrogen bond formation in a broader class of additives.

G1300106 鋳鉄ラップと多孔質ウレタンパッドの相似性

In this paper, we examined the processing characteristics of the cast iron plate and the urethane resin porous polishing pads. The similarities between the cast iron lapping plate and the porous urethane resin polishing pad are described. It was known that the conditioning state of tool surface affects the processing characteristics greatly. To improve the performance of conventional tools, we developed the metallic fiber lapping tools and the epoxy resin pads. The metallic fiber tool can grip the abrasives on the lapping area with microasperity. The epoxy resin polishing pad showed higher removal rate and lower surface roughness than a conventional urethane resin polishing pad, because of high hydrophilic property.

Measurement and Analysis of Single-Pass Conditioning Furrows in CMP Pad Surfaces

Diamond conditioning of polishing pads is an essential step in chemical mechanical planarization (CMP) that generates favorable surface texture for wafer polishing. Texture formation is governed by polymer fracture mechanics and depends on the characteristics of individual diamonds and their arrangement on the disk, the conditioning recipe (downforce and sliding speed), and the pad polymer mechanical properties and porosity. This work focuses on measurement of furrows formed in CMP pad surfaces using a diamond element, extracted from an industry-standard conditioning disk, comprising a single row of eight to ten diamonds having representative variations in protrusion and shape. Differences among the diamonds lead to various degrees of engagement with the pad surface and a corresponding mix of fracture modes typical of a commercial process. The observed spacing between adjacent furrows allows each to be linked to the diamond from which it originated—and its fracture characteristics to be related to features of the particular diamond. The experiment and analysis are illustrated by comparing three pad materials having dissimilar pore loadings.