Chemical Mechanical Planarization Pad Research Articles

Development of Novel Conditioning Method Using Thermal Shape Memory Characteristics of Polyurethane CMP Pad

Traditionally, the pad roughness has been maintained by wearing down the polyurethane pad with diamond disk. However, that method generates debris and reduces pad lifetime. This study propose a new approach to pad surface recovery by synthesizing a polyurethane-based raw material that exhibits shape memory behavior and can recover its shape upon heating. The findings suggest that the pad’s surface can be maintained by utilizing its shape memory trait and designing a system to heat the pad. The pad recovery tests were conducted using universal test machine (UTM) samples and found that, in terms of heat recovery, increasing the temperature had a greater effect than increasing the exposure time. CMP test was performed by using three conditioning potions: diamond disk conditioning, heat conditioning, and no conditioning. The results showed that pad asperity was recovered more efficiently with heat conditioning than with no conditioning (demonstrated by a 19% higher removal rate). The experimental results can be expected that combines diamond disk conditioning with heat conditioning could be a superior alternative for pad surface refreshment. Shape memory pads can return to their original form, leading to better chemical mechanical planarization (CMP) performance and an extended pad lifetime.

Development of a Lab-Scale Tribo-Electrochemical Approach for Chemical Mechanical Planarization

During chemical mechanical planarization (CMP), the electrochemical interactions between slurry additives and the polishing substrate metal films favor the formation of easily removable species that are then detached by mechanical abrasion effects of the CMP pad and nanoparticle abrasives in slurry. Yet, neither the mechanical nor chemical aspects alone dictate the CMP process; rather, it is the intertwined dependencies of tribology and electrochemistry that often control the polish performance. This highlights the importance of the functional synergies, otherwise known as tribo-electrochemistry, which has been largely under-explored in the CMP research community.This work discusses the development of a novel small-scale tribo-electrochemical approach for metal CMP. It covers the tool design aspects, tribo-electrochemical measurements such as open circuit potentiometry (OCP) and polarization resistance, and relevance to CMP applications. The system is developed based on a small-scale CMP polisher coupled to a 3-electrode cell design circuit that is connected to a potentiostat. The design utilizes a common type of CMP metal film as the working electrode, with the accompanying pad and slurry consumables serving as baseline for method development. All other process conditions, including rotating speed, downforce, polish-hold duration, and pad conditioning process follow typical CMP standards.The results show tribo-electrochemical responses to the presence of catalyst (C), oxidizer (O), inhibitor (I), and abrasive (A) in the experimental slurries. The data is of significant value in terms of the anodic & cathodic site functions on the CMP metal surface and in the context of material removal. In addition, notable sensitivity to pad texture, downforce, and temperature effects were observed, and removal rate measurements correlated with polarization resistance for varied levels of the O and I additives. In summary, the tribo-electrochemical aspects of CMP have been probed and an innovative analytical approach has been developed and demonstrated.

CMP에서 디바이스 패턴의 실 접촉 면적 측정을 통한 평탄화 규명

Chemical Mechanical Planarization (CMP) is an essential process for device integration and planarization in a semiconductor manufacturing process. The most critical function in the CMP process, is to predict and cover the geometrical characteristics of various sizes and densities, of patterned wafers for local and global planarization. To achieve the wafer-level and die-level planarization, it is necessary to understand the contact mechanism between the CMP pads and the macro-scale patterns. In the macro-scale pattern, pad deformation is divided into two layers: an asperity layer and a bulk pad layer. Through bulk pad deformation, asperity contact distribution within the pattern is predicted. In this paper, the distribution of asperity contact according to the pattern geometrical characteristics was analyzed, through large-area real contact area (RCA) measurement. Bulk pad deformation was predicted by analyzing RCA distribution according to pattern geometry such as pattern size and density, pattern shape and step height according to the polishing time, and applied pressure. Additionally, through the distribution of the contact area and the number of contact points, the rounding phenomenon and planarization characteristics in the pattern CMP were predicted.

SEMI Standards for Consumables for Chemical Mechanical Planarization (CMP)

IC manufacturing is a sophisticated multistep process where parameters need to be monitored and controlled very tightly. Chemical-mechanical polishing (CMP) is an important step in IC manufacturing that is required to achieve global and local planarity for subsequent lithography processes. CMP has been one of the fastest-growing segments of the semiconductor industry for the past 20 years.The CMP process is highly critical for achieving sustainable yields in IC manufacturing. This area is also one of the most difficult to control. Quality issues in the CMP process are extremely expensive and can have a significant impact to device yields and reliability. It is known that CMP consumables, such as CMP pads, CMP slurries, and CMP conditioning disks are critical to achieve the target performance in IC manufacturing processes. As such, reducing the variations in CMP consumables properties through standardized metrology tools and processes has become a high priority for advanced IC manufacturing nodes.In this presentation we will focus on measuring and reporting critical parameters for such critical and widely used consumables in the CMP industry, as CMP pads ([Ref. 1-4]), retainer rings, and conditioning disks.Get InvolvedSEMI Standards development activities take place throughout the year in all major manufacturing regions. To get involved, join the SEMI International Standards Program at: www.semi.org/standardsmembership.For more information please visit our main Web site and current events page. If you have any questions regarding SEMI Standards activities, please contact your local SEMI Standards staff.Standards WatchSEMIwww.semi.org<12/03/2020>

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

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

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

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

패드 돌기의 기하학적 특성을 고려한 디바이스 패턴의 평탄화 모델링

Chemical mechanical planarization (CMP) is a semiconductor process which is necessary for multi-layer interconnection structure. CMP pad is a consumable used in the process and with numerous asperities on the surface that wear out by the load applied from the contact with the wafer. Also, it has a patterned wafer, the step height is gradually removed by contact of the asperities with upper and lower layers. The contact state would be different according to the step height reduction. Likewise, depending on the pattern size at the specific step height, the maximum radius of the asperity curvature differs whether it reaches the down area. In this study, the height distribution of asperities was expressed as a function of time and asperity height taking into account the wear of asperities, and based on the Greenwood-Williamson theory, a mathematical model for material removal rate considering pattern size was derived. The consistency of the novel model is verified with the CMP experiment conducted using oxide patterned wafers, and the experimental data were compared with the residual step height using theoretical removal rate. The root mean square error of the step height reduction was 19.84 nm.

A Quantitative Analysis of Multi-Scale Response of CMP Pad and Implication to Process Assessments

The multiscale characteristics of the pad deformation and its surface morphology control the quality and efficacy of the chemical mechanical planarization (CMP) process. The pad microstructure comprised of cell size, wall thickness and surface roughness exhibit temporal variations in the effective pad stiffness at the pad abrasive interface. An experimental and analytical approach is developed to examine a dry IC-1000 pad response at different length scales, utilizing a nano-indentation with a conical tip of 1μm radius and a flat-punch of 60μm diameter. The quasi-static load-indentation depth plots showed different characteristic trends with varying stiffness at different loading ranges. The measurements showed the role of the porous microstructure to drive a competition between the local cell-membrane indent, bending of cell membrane and the bulk response of the porous pad. These different deformation mechanisms are employed in constructing an equivalent mechanical model for the effective pad elastic stiffness. The model prediction matches well with the force-indentation depth measurements. The developed model is used to investigate the influence of pad property evolution on the propensity of scratch generation during the CMP process. Such physically based models can be utilized to optimize the pad microstructure and morphology to control the spatial and temporal modulation of the material removal rate and the propensity for scratch generation.

Editors' Choice—Efficiency of a CMP Pad at Removing Protective Material from Copper during CMP

The efficiency of a pad asperity and abrasives embedded between the asperity and wafer at removing the protective material on the surface of copper (removal efficiency) during chemical mechanical planarization (CMP) was determined experimentally using current densities from in situ electrochemical measurements while polishing with a slurry containing BTA. The removal efficiency was insentitive to the pressure and sliding velocity, but was dictated by the pad surface topography parameters and abrasive concentration in the slurry. An analytical estimate was derived by comparing the trajectories of a pad asperity and the abrasives embedded in the asperity. Comparison of the experimental and analytical estimate suggests that the asperities are deformed enough by the embedded abrasives to contact the surface of copper at abrasive concentrations up to 1 wt%. At higher concentrations up to 5 wt%, the asperities deflected to a lesser amount, making the force exerted on the copper increase. At these higher concentrations, some of the copper interacting with the squeezed abrasives was plastically deformed, yielding higher removal efficiency than when elastically deformed. The removal efficiency can be used as a standard metric for assessing the material removal ability of various consumables such as slurry, CMP pad and pad conditioner.

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.

Design optimization of diamond disk pad conditioners

Chemical mechanical planarization (CMP) is the major manufacturing step used to planarize semiconductor wafers and obtain mirror surface finish. In CMP, diamond disk pad conditioning is traditionally employed to restore pad planarity and surface roughness. The conditioning tool typically consists of a metal disk with one side embedded with protruding diamond grits (abrasives). The conditioner design has a significant effect on the pad conditioning process and hence the wafer planarization process. This paper proposes the application of engineering optimization methods such genetic algorithm to the conditioner design problem for the first time. A new metric to evaluate conditioning performance based on the conditioning density generated by a specific conditioner design is developed. The metric is applied in a genetic algorithm to optimize conditioner design parameters (including geometric arrangement of diamonds, grit density and disk size). The model searches for the design parameters that produce a desired CMP pad surface texture. Results show that the model can effectively serve as a platform to evaluate and tune conditioner design for different applications in CMP.

New Developments in CMP Pad Conditioner Technology

This paper focuses on the challenges and new developments in chemical mechanical planarization (CMP) pad conditioner technology for the next-generation applications, with a special emphasis on the comparative performance characterization of pad conditioners. Empirical data from a number of case studies are presented. Different design 4" disk pad conditioners were evaluated using a benchtop polisher, a benchtop tribometer, and a 300 mm wafer polisher/tribometer to determine pad cut-rate, pad surface roughness, coefficient of friction (COF), and Cu polishing behavior. Results are presented for the effect of pad conditioner design parameters, including abrasive/feature size and distribution, on the pad cut-rate and pad surface roughness. Such information may be helpful in reducing the fab selection and optimization time for pad conditioners in advanced technology node applications. Present study demonstrates the usefulness of pad conditioner laboratory scale characterization.

Investigation of Correlation between Polishing Characteristic and Pad Roughness during Chemical Mechanical Planarization Process

The Chemical mechanical planarization (CMP) process has become a primary planarization technique required for the manufacture of advanced integrated circuit (IC) devices. As the feature size of IC chips shrinks down to 65 nm and below, the role of CMP as a robust planarization process becomes increasingly important. In this work, we evaluated surface roughness of CMP pad to correlate the roughness with CMP performance such as material removal rate (MRR) and pad lifetime. Pad surface was analyzed by 3-dimensional profiler and scanning electron microscope (SEM). We found that MRR could be varied with the pad life time and roughness. We also found that suitable roughness range is exist to get stable CMP performance. Finally, we introduced ‘pre-conditioning’ method to manage the roughness of CMP pad to get stable CMP performance at the initial pad life time.

Optimization of CMP Pad Surface by Laser Induced Micro Hole

In this paper, the optimization of the chemical mechanical planarization (CMP) pad design is investigated to reduce defect generation during the CMP process. Recently, obtaining the optimum performance from the viewpoint of scratch generation has become the most challenging area in the CMP process. To achieve uniform performance of the process at the defect level, the surface texture and/or groove of the CMP pads should be designed effectively, and their original surface should be maintained throughout their lifetime. Because the transport of slurry and wear debris, which is the source of CMP scratches, is highly dependent on the surface geometry of the CMP pad, maintaining suitable process conditions is considered the most important design factor. In this work, the surface geometries of two CMP pads with different body structures are modified by a laser-induced micro hole; one is a porous-type pad and the other is a nonporous type. Based on the experimental and numerical simulation results, the micro-hole induced pads had a lower defect level than the conventional porous pads without holes because the micro holes acted as a defect source or coarse particle reservoir to prevent micro scratch during the process. In addition, the micro holes of the porous pad showed a lower defect generation than the holes of the nonporous pad as the process time increased.

Effects of diamond size of CMP conditioner on wafer removal rates and defects for solid (non-porous) CMP pad with micro-holes

Wafer removal rates and defects were investigated for 200 mm tetraethyl orthosilicate (TEOS) oxide chemical mechanical planarization (CMP) processes using two types of CMP pads: a porous pad and a solid pad with micro-holes. An initial CMP test conducted with fumed silica based-slurry and a conditioner with 180 μm diamond revealed that the wafer removal rates by the solid pad with micro-holes were approximately 10% lower than those by the porous pad, but scratch type defects were reduced. In order to increase the removal rate of a solid pad with micro-holes to the comparable level of a regular porous pad without changing process parameters, it was decided to modify conditioner design by using different diamond size from 70 to 130 μm. It was found that wafer removal rates increased from 2973 to 2587 Å/min and defect counts reduced from 5.3 to 1.7 by decreasing the diamond size from 180 to 70 μm in the case of the solid pad with micro-holes. Various pad surface analysis results, including contact area estimation and microscopic observations, also revealed that a smaller diamond conditioner generated the pad texture with finer and more regular pad asperities.

Optical and Mechanical Characterization of Chemical Mechanical Planarization Pad Surfaces

Both contact and non-contact methods are used to analyze surface properties of three types of chemical mechanical planarization (CMP) pads: plain, XY grooved, and concentrically grooved. Optical interferometry is used to probe the pad surface without contact and to produce a surface height probability density function (PDF). The right hand contacting tail of the PDF is often found to be exponential for CMP pads and a decay length (λ) as a measure of pad surface abruptness can be extracted. An incremental loading device is developed and used to measure the pad surface mechanical response. A pad–wafer contact model based on Greenwood and Williamson theory is used to interpret the nonlinear features of the pad surface compression data, which, furthermore, enables independent calculation of λ from mechanical data. Surface abruptness (λ) extracted from both methods (optical and mechanical) is found to be consistent for all three types of pads. No significant difference is observed in the pad surface abruptness among the three types of pads.

Study on Stiffness and Conditioning Effects of CMP Pad Based on Physical Die-Level CMP Model

Chemical mechanical planarization (CMP) pad stiffness and conditioning effects were evaluated based on a physical die-level CMP model, with pad effective modulus and asperity height as parameters. In one study, patterned dielectric wafers were polished using polymeric pads of different stiffnesses. In a second study, wafers were polished by standard pads using different conditioning disks. Polishing experimental data (dielectric thickness and step height) were fitted by the physical model, enabling the extraction of the pad effective modulus and asperity height model parameters. A higher pad stiffness gives better within-die uniformity, and the conditioning disk with blocky diamonds achieves up-area only polishing for longer times. Polishing simulations using the physical model reflect a clear pattern density dependence.

Study on the Mechanical Properties of CMP Pads

The mechanical properties of chemical-mechanical planarization (CMP) pads are very important to their performance. In this paper, pads are described in terms of their bulk properties and the properties of their asperity layer for applications in copper CMP. In particular, the elastic properties of these layers are studied. Pads were soaked in a copper polishing slurry or water for specified times and changes in their elastic moduli were measured. In general, pad immersion in water reduced the bulk modulus because the water penetrated the pads and disrupted hydrogen bonds between adjacent polyurethane chains. In addition, it was found that surface grooving affected the pad elastic modulus, especially that of the asperity layer. To evaluate the effect of use in copper CMP on the pad properties, the elastic moduli of the bulk and asperity layers on a pad were measured following pad use in a commercial polisher. The periodic loads during CMP were believed to facilitate the penetration of water into the pads, lowering their bulk elastic moduli. A slight increase in the elastic modulus of the asperity layer was seen as a result of pad use in copper CMP. The inherent variations in modulus measurements for dry pads were also measured.

Spectroscopic and Topographic Investigations of Nanoparticle Abrasive retention in Polyurethane CMP Pads for Cu CMP

ABSTRACTA spectroscopic and topographic investigation of abrasive nanoparticle retention in polyurethane chemical mechanical planarization (CMP) pads has been carried out as a function of ex situ pad conditioning parameters for Cu CMP. X-ray photoelectron spectroscopy (XPS) and scanning electron microscope energy dispersive spectroscopy (SEM-EDS) were utilized to quantitatively characterize the presence of alumina nanoabrasive in the pad following Cu CMP. As expected, conditioning did not modify the overall pad morphology but did increase local asperity roughness with increasing conditioner downforce. As expected, the magnitude of the conditioner downforce reduced the overall average alumina nanoabrasive retention, albeit weakly, as determined via XPS. However, local EDS analysis revealed that increased downforce does significantly reduce nanoabrasive retention at pad asperities. In contrast, increased downforce increased the amount of nanoabrasive present in the polyurethane pad surface pores. Moreover, overall conditioning time was shown to be a more dominant parameter compared to conditioner downforce regarding removal of abrasive particles from both pad asperities and pores.

Investigation of high-pressure micro jet technology as an alternative to diamond disc conditioning in ILD CMP

The efficacy of an alternative to conventional diamond conditioning in chemical mechanical planarization (CMP) was evaluated in this study. The high pressure micro jet (HPMJ) system sprays ultra-pure water (UPW) at pressures ranging from 10 to 20 MPa onto a CMP pad to clean the pad of slurry residue, remove embedded slurry particles, and re-establish pad asperities. The system is employed in an ex situ fashion and is compared to in situ and ex situ diamond conditioning as well as using no conditioning. Real-time frictional force acquisition allows for coefficient of friction ( COF) analysis, which indicates the extent of pad wear. Removal rate analysis, SEM imagery, and pad surface profilometry are also used to evaluate HPMJ as an alternative conditioning technology. Removal rates significantly lower than those associated with diamond conditioning are obtained for the HPMJ system when UPW conditioning is directly followed by polishing. SEM imagery and pad profilimetry indicate these low HPMJ removal rates are due to differences in pad surface chemistry, not pad surface topography. Experiments including a 30 s silicon wafer polish with slurry following HPMJ conditioning to re-establish pad surface chemistry were performed and result in removal rates that are comparable to those obtained using ex situ conditioning. The removal rates obtained using HPMJ conditioning for relative wafer-platen velocities of 0.31 and 0.62 m/s are 8 and 1% higher than those obtained using ex situ diamond conditioning and 18% lower than those obtained using ex situ diamond conditioning for 0.93 m/s. The average COF values for HPMJ conditioning using the intermediate silicon wafer polishes are 15% lower than average COF values associated with ex situ diamond conditioning, suggesting a possible increase in pad life for the HPMJ system.