Chemical Mechanical Polishing Pad Research Articles

Chemical mechanical polishing for indium bond pad damascene processing

We investigated chemical mechanical polishing (CMP) of indium, with the goal of obtaining indium bond pads for later cryo-3D integration of quantum computing-related chips, through bonding between these bond pads and indium bumps. Higher removal rates were obtained with soft CMP pads than with hard pads. The latter led to deep scratching, while this effect was much more limited for soft pad CMP. On patterned wafers, indium is cleared well in structured areas using soft pad CMP, leading to relatively high-quality indium surfaces inside bond pads, although corrosion might be of some concern. Pattern density uniformity was an important factor for within-die deviation in indium clearing time. Dishing was much more limited than in earlier work on indium polishing, while surface roughness was also found to be relatively limited. The obtained indium damascene bond pads may be suitable for 3D die-to-die and wafer-to-wafer bonding through indium pad-to-bump bonding.

Study on the Preparation and Performance of Self-Regressive Fixed Abrasive Chemical Mechanical Polishing Pad

Chemical mechanical polishing (CMP) technology is one of the key technologies to realize the global planarization of semiconductor wafer surfaces. With the increasing popularity and universality of its application, more and higher requirements are put forward for ultra-precision machining. As an important part of the CMP system, polishing pads occupy a dominant position. In this paper, a self-regressive fixed abrasive polishing pad (SR-FAPP) was prepared by photo-curing. The physical and mechanical properties of the SR-FAPP and the retreat threshold of the abrasive particles on the SR-FAPP were studied. After the CMP of the SiC wafer with a polyurethane polishing pad and the SR-FAPP, it was found that the material removal rate of the former was 75% higher than that of the latter, and the surface roughness of the latter was 75% higher than that of the former. In the micro-morphology, the scratches on the surface of the latter’s polished SiC wafer were obviously reduced, which effectively improved the unevenness of the scratches on the surface of the SiC wafer after polishing, thus providing a reference for the preparation and performance research of the polishing pad.

Analyzing the effects of pad asperity on chemical mechanical polishing of copper thin film wafer

Copper thin film has been identified as a promising material for multi-level interconnecting materials in IC fabrication due to its unique electrical properties and high electrical conductivity. However, it is very challenging to manufacture a superior planar surface with low dishing and minimal erosion of copper thin film in the chemical mechanical polishing (CMP) process. In this study, the micro-topography model of a soft polishing pad is performed using an X-ray micro-computed tomography scan combined with finite element method simulation to evaluate the contact area between the CMP pad and wafer during the CMP process. Additionally, the material removal rate (MRR) model for the copper wafer is calibrated based on the wear of the material between abrasive particles and the wafer surface. The results of this study not only investigate the effect of CMP pad asperities during the CMP process but also provide a new method for fully calibrating MRR in comparison with CMP experiments for the verification of model parameters.

Investigation of thermal effects in copper chemical mechanical polishing

With the demand for manufacturing large (e.g., 450 mm) wafers, problems arise due to temperature increases associated with the chemical mechanical polishing (CMP) process. Various methods have been employed to stabilize the in-situ polishing temperature. The use of a high-temperature slurry can improve the removal rate, but a degradation in surface morphology occurs during the copper CMP procedure. To explain this mechanism, the effects of temperature on the slurry, CMP pad, and copper wafer were separately investigated. A temperature of approximately 40 °C was demonstrated to be a suitable choice when considering polishing efficiency and quality, thereby facilitating the rapid production of semiconductors. Particle aggregation was also observed with a rise in temperature. The work presented here may allow for a reduction in defects during low-hardness material polishing.

In Situ Metrology for Pad Surface Monitoring in CMP Using a Common-Path Phase-Shifting Interferometry: A Feasibility Study

In the fabrication of semiconductors, chemical mechanical polishing (CMP) is an essential wafer-planarization process. For optimal CMP, it is crucial to monitor the texture of the polishing pad; this leads to homogenous planarization of wafers. Hence, we present a new interferometric approach for in situ evaluation of the CMP pad surface based on a common-path phase-shifting interferometry, with which a series of phase-modulated interference signals immune to external perturbation can be recorded. A nanoscopic surface topology can then be reconstructed to estimate surface roughness using the recorded interference images. The surface mapping performance of the proposed method was tested by retrieving a topology of a vibrating nanostructure in immersion, of which height profiles were consistent with the result from atomic force microscopy (AFM). The method was also validated by examining the surface of a used CMP pad in simulated conditions.

(Invited) Towards Metrology to Enable Standardizing CMP Consumables

In the semiconductor industry, there is a need to establish fundamental, mechanism-based, correlation(s) between process conditions, consumables (e.g., pads and slurries), and observed process performance in Chemical-Mechanical Polishing (CMP) [1-5]. Such understanding can lead to the creation of industry-wide standards that can help reduced cost of ownership. Along these lines, the Chemical Mechanical Planarization Consumables (CMP-C) Task Force under Liquid Chemicals Global Technical Committee within the SEMI Standards Program has been actively developing a guide (SEMI C100) for reporting CMP pad hardness [6], and pad density.In this paper, we revisit our decades old, but still relevant, quest for suitable mechanism-based metrology for CMP-pad. While we focus on polyurethane-based CMP pads, we will touch on alternative pad materials. [10-11]. Using both static and dynamic the dynamic mechanical analysis (DMA) [7-8] and the FTIR [9] we monitored changes in pad polymer properties under various chemical and mechanical stresses. Pad sample were analyzed: prior to use (fresh); after a 24-hr soak in silica-containing oxide slurry (basic); and after oxide polishing (used). Upon comparison it was observed that a characteristic transition feature due to water is present at sub-ambient temperatures in both the slurry soaked and used pads. Exposure of as-received pads to basic oxide slurry results in a broad, high temperature transition thought to be the result of chemical-induced disruption of macrostructural units. Polishing (load-enhanced chemical exposure) introduces further changes to the polymer network represented by an apparent degradation of the pad polymer.References1) P. B. Zantye, et al, 'Chemical mechanical planarization for microelectronics applications, Materials Science and Engineering: R: Reports, 2004, 45, 3–6, doi: 10.1016/j.mser.2004.06.002.2) Zantye, Parshuram B., "Processing, Reliability and Integration Issues In Chemical Mechanical Planarization" (2005). Graduate Theses and Dissertations, https://scholarcommons.usf.edu/etd/9283) S. Deshpande et al, “The Electrochemical Society, find out more Chemical Mechanical Planarization of Copper: Role of Oxidants and Inhibitors”, 2004 J. Electrochem. Soc. 151 G7884) Y. S. Obeng et al., "Impact of CMP consumables on copper metallization reliability," in IEEE Transactions on Semiconductor Manufacturing, vol. 18, no. 4, pp. 688-694, Nov. 2005, doi: 10.1109/TSM.2005.858457.5) Obeng, Yaw S., et al. "Characterization of ‘In-Process’ Degradation of Polyurethane CMP Pads." Chemical Mechanical Planarization V 2002 (2002): 1.6) SEMI C100 - Guide for Reporting Chemical Mechanical Planarization (CMP) Polishing Pads Hardness Used, published by SEMI Standards (https://store-us.semi.org/products/c10000-semi-c100-guide-for-reporting-chemical-mechanical-planarization-cmp-polishing-pads-hardness-used-in-semiconductor-manufacturing, accessed December 15, 2020)7) Li et al, “Dynamic Mechanical Analysis (DMA) of CMP pad materials”, MRS Proceedings, January 2000, Cambridge University Press, DOI: 10.1557/proc-613-e7.3.18) H. Lu et al, "Applicability of dynamic mechanical analysis for CMP polyurethane pad studies” Materials Characterization, 2002, 49, 2, 177-186, DOI: 10.1016/S1044-5803(03)00004-4.9) H Lu, et al., "Quantitative analysis of physical and chemical changes in CMP polyurethane pad surfaces, Materials Characterization", 2002,49, 1, 35-44, DOI: 10.1016/S1044-5803(02)00285-1.10) S. Deshpande, et al. “Surface-modified polymeric pads for enhanced performance during chemical mechanical planarization”, Thin Solid Films, 2005, 483, 1–2, 261-269, DOI: 10.1016/j.tsf.2004.12.063.11) Zantye, P., et al., “Metrology of Psiloquest's Application Specific Pads (ASP) for CMP Applications”. MRS Proceedings, (2004). 816, K5.6. doi:10.1557/PROC-816-K5.6

Kinematic Prediction and Experimental Demonstration of Conditioning Process for Controlling the Profile Shape of a Chemical Mechanical Polishing Pad

The uniformity of the wafer in a chemical mechanical polishing (CMP) process is vital to the ultra-fine and high integration of semiconductor structures. In particular, the uniformity of the polishing pad corresponding to the tool directly affects the polishing uniformity and wafer shape. In this study, the profile shape of a CMP pad was predicted through a kinematic simulation based on the trajectory density of the diamond abrasives of the diamond conditioner disc. The kinematic prediction was found to be in good agreement with the experimentally measured pad profile shape. Based on this, the shape error of the pad could be maintained within 10 μm even after performing the pad conditioning process for more than 2 h, through the overhang of the conditioner.

Contact-Area-Changeable CMP Conditioning for Enhancing Pad Lifetime

Chemical–mechanical polishing (CMP) is a process that planarizes semiconductor surfaces and is essential for the manufacture of highly integrated devices. In CMP, pad conditioning using a disk with diamond grit is adopted to maintain the surface roughness of the polishing pad and remove polishing debris. However, uneven pad wear by conditioning is unavoidable in CMP. In this study, we propose a contact-area-changeable conditioning system and utilize it to conduct a preliminary study for improving pad lifetime. Using the conventional conditioning method (Case I), the material removal rate (MRR) decreased rapidly after 12 h of conditioning and the within-wafer non-uniformity (WIWNU) increased. However, the results of conditioning experiments show that when using a contact-area-changeable conditioning system, uniform pad wear can be obtained in the wafer–pad contact area and the pad lifetime can be extended to more than 20 h. Finally, the newly proposed conditioning system in this study may improve the CMP pad lifetime.

Soft Chemical Mechanical Polishing Pad for Oxide CMP Applications

Chemical mechanical polishing (CMP) is widely accepted as the best planarization technique for fabricating nanoscale devices. A soft CMP pad that can enable higher oxide removal rates (RRs) and good planarity has been proposed for oxide CMP applications. In this study, three pads namely, Pad-1 (hard), Pad-2 (soft), and a commercial pad (hard) were used to polish blanket oxide, and STI patterned wafers. The Pad-2 demonstrated significantly higher RRs and better planarization than the hard pads. Post-polish pad texture analysis on Pad-2 showed a uniform surface asperity distribution. This is due to the novel method of pad manufacturing, which enables precise material placement and consistent pore construction.

A numerical study on slurry flow with CMP pad grooves

In this study, chemical mechanical polishing (CMP) slurry flow is investigated with two pad groove patterns, circular and circular plus radial. First, slurry flow is predicted by a numerical method, and slurry velocity is analyzed by pad groove type. The streamline of the slurry flow and wall shear stress on the wafer show that the radial groove efficiently moves the slurry into the gap between the pad and the wafer, and the effect of improved slurry flow on CMP performance is verified by experimental results. The radial groove also improved process non-uniformity, and a high rotation speed combined with the radial groove improved removal rate and non-uniformity by 11.2% and 63.9%, respectively.

Investigation of the Impact of Pad Surface Texture from Different Pad Conditioners on the CMP Performance

Chemical mechanical polishing (CMP) is a common method for planarization/polishing materials during integrated circuits (IC) fabrication. Pad conditioning is a critical component of a CMP process. Herein, the impact of surface textures created by different types of pad conditioners (PC) such as coarse, mid-coarse, and fine PC on the solid pads are studied. Additional surface texture parameters such as surface height distribution, skewness, Dale Void Volume are used to determine an optimum surface texture that gives desired CMP performance such as material removal rate and within-wafer non-uniformity. It was determined that an optimum surface texture on a solid CMP pad can be obtained with a mid-coarse disk. It is further demonstrated that by the addition of porosity to the pads, it is possible to recreate an optimum surface texture and desired CMP performance, similar to that obtained with a mid-coarse disk and a solid pad. Tribological mechanisms of the different pad and PC combinations are presented using the coefficient of friction. It is concluded that porous pad and fine PC pairing can tackle the issues of slurry transport limitations, lack of asperity contact, and process stability over pad life.

Material removal efficiency improvement by orientation control of CMP pad surface asperities

This paper presents a novel method of improving material removal efficiency in the chemical mechanical polishing (CMP) process by optimizing the surface asperity orientation with respect to polishing motion. Feret's diameter plays a key role in increasing the number of working abrasives. Based on Feret's diameter model, an optimization method is proposed for the conditioning motion of a diamond dresser against a CMP pad. The radial velocity component of the dresser on the CMP pad is maximized by considering its direction of motion based on kinematic motion simulation. In addition, the pad cut rate profile is optimized to be uniform. Analytical and experimental investigations show that the ratio of radial and tangential velocity components is improved, yielding a larger Feret's diameter and 15% increase in the material removal rate.

Effect of Dry Thermal Oxidation on Bulk GaN Substrates Grown by HVPE during CMP

Chemical mechanical polishing (CMP) of bulk GaN substrates via dry thermal oxidation is investigated in this paper. In this work, we study the effects of oxidation with respect to different thermal treatments, change in morphology and thickness on bulk GaN substrates. The results of the study show that a defect-free surface with roughness average (Ra) and material removal rate (MRR) of 0.377 nm and 51 μm/h respectively is achievable by CMP after thermal treatment at 800°C. However, for thermal treatments above 900°C, several pits and defects are observed with significant deformation of the surface likely due to the domination of diffusion-controlled reaction over interfacial reaction-controlled. The molar fractions of the chemical components remained on the polished GaN surfaces are characterized via X-ray photoelectron spectroscopy. It is found that the conversion rate from GaN to Ga2O3 is dependent on the real contact area between CMP pad and GaN substrate surface during the CMP.

Investigation of the pad-conditioning performance deterioration in the chemical mechanical polishing process

The surface roughness of a chemical mechanical polishing (CMP) pad provides microscopic asperities where the actual polishing takes place. Thus, the roughness should be maintained in a proper regimen to obtain stable CMP process quality. A conditioner is a key consumable in the CMP process because it maintains the roughness of the CMP pad surface against surface glazing or flattening during polishing. Because the conditioner mechanically breaks the pad surface to maintain the roughness, previous research has expressed its ability index in terms of the pad wear rate (PWR). In the present study, we investigate the reason for PWR change of CMP pads having vigorously changing moduli with respect to temperature changes during the mass production. The pad property changed steeply in the process temperature range from 60 to 80°C. The tensile strength is a key property change that leads to sudden PWR drop. We found that the shape and configuration of the diamond tip are the major parameters affecting the ability to maintain surface roughness of the pads. Thus, we suggested a proper conditioner design for tungsten (W) CMP based on the experimental data to sustain the process quality and increase the consumable lifetime. As a result, the peak surface roughness has improved from 29.4 μm to 32.6µm and the consumable lifetime was also increased.

Scratching of Patterned Cu/Dielectric Surface Layers by Pad Asperities in CMP

In chemical-mechanical polishing (CMP), as the rough polymer pad slides over patterned structures of metal interconnects and dielectrics the pad asperities themselves, though soft, may scratch the relatively hard layers. The fully plastically deformed pad asperities with high interfacial friction are the primary sources of pad scratching. In this paper, scratching of Cu/dielectric line structures by pad asperities is investigated. First, the scratching criteria and the scratch-regime maps, constructed previously for monolithic layers based on contact mechanics are extended for the patterned layers. Then sliding experiments have been conducted on patterned Cu/dielectric surface layers of various linewidths using solid polymeric pins loaded into the fully plastically deformed state, as well as commercial CMP pads. Specifically, the role of the width of Cu and dielectric lines in comparison with the contact diameter is examined. The theoretical models predict that the scratch criteria for patterns with wide lines are the same as those for monolithic layers, whereas patterns with extremely narrow lines behave as composite layers with effective mechanical properties. Experimental results validate the scratch criteria based on contact mechanics.

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.

Study on the Preparation Technology of Fixed Abrasive Polishing Pad in Chemical Mechanical Polishing

According to the shortcomings of the traditional free abrasive chemical mechanical polishing (CMP), in recent years, the fixed abrasive chemical mechanical polishing (FA-CMP) technology is proposed. It is a new planarization technology developed on the basis of the traditional CMP. Pad is an important and dispensable part in FA-CMP. The cost and quality of FA-CMP pad are determined by the preparation technology. In order to study the FA-CMP pad of the low cost and high quality, in this paper, by reading a lot of literature, 5 kinds of preparation technology of FA-CMP pad are analyzed. Study results will provide some reference for further designing and manufacturing the FA-CMP pad.

Primary study on nonlinear viscoelasticity measurement of chemical mechanical polishing pads by applying on-machine compression test

Polishing pads used for chemical mechanical polishing (CMP) process have strong nonlinear viscoelasticity, which is considered to affect resultant polishing performance. In order to evaluate the material properties of polishing pads, a series of fundamental compression tests were conducted by using a developed on-machine compression tester. From measured stress–strain curves, parameters representing nonlinear elasticity and viscosity of the CMP pads are identified. Analytical results indicated unique nonlinear elasticity due to pad surface asperities and not negligible viscous damping.

Pad Scratching in Chemical-Mechanical Polishing: The Effects of Mechanical and Tribological Properties

In chemical-mechanical polishing (CMP), even the soft pad asperities may, under certain conditions, generate scratches on the relatively hard surfaces being polished. In the present study, contact mechanics models of pad-induced scratching are formulated, and the effects of the hardness of the surface layers and of pad asperities as well as the interfacial friction are elucidated. Additionally, scratch-regime maps are proposed to provide criteria for scratching hard surface layers by the softer pad asperities. Furthermore, scratching indexes are introduced to predict the proportion of asperities in contact that are likely to scratch. The contact mechanics models of scratching have been validated by sliding experiments with two commercial CMP pads (Pad A and IC1000) and various thin-films (Al, Cu, SiO2, Si3N4, TiN and three low-k dielectrics) using deionized water as a “lubricant.” Both the theoretical models and the experimental results show that the number of scratches increases as the scratching index exceeds 0.33. Al and Cu layers are found to be more susceptible to pad scratching due to their low hardness and high interfacial friction. The scratch-regime maps provide practical guidelines for mitigating pad scratching in CMP.

Mechanisms of Local Planarization Improvement Using Solo Pad in Chemical Mechanical Polishing

The mechanism of local planarization improvement using a solo pad in chemical mechanical polishing (CMP) was investigated, and the pad surface temperature was found to be the key factor. The use of a solo pad results in better planarity than that of a stacked pad under the same process conditions. When Cu CMP evaluation was conducted at various platen temperatures, a good correlation of local planarity to pad surface temperature was confirmed regardless of the pad type. Planarity improved when the pad surface temperature was lowered, and the solo pad had a lower temperature than the stacked pad at the same platen temperature. It is considered that the solo pad has a higher heat conductance than the stacked pad, so that heat generated during polishing is transferred to the platen more easily through the solo pad than through the stacked pad. The reason for the better planarity with the lower pad surface temperature was explained by the change in pad elasticity by the temperature.