Planarization Of Wafers Research Articles

Impact of Pad Conditioning on Thickness Profile Control in Chemical Mechanical Planarization

Chemical mechanical planarization (CMP) has been proven to be the best method to achieve within-wafer and within-die uniformity for multilevel metallization. Decreasing device dimensions and increasing wafer sizes continuously demand better planarization, which necessitates better understanding of all the variables of the CMP process. A recently highlighted critical factor, pad conditioning, affects the pad surface profile and consequently the wafer profile; in addition, it reduces defects by refreshing the pad surface during polishing. This work demonstrates the changes in the postpolish wafer profile as a function of pad wear. It also introduces a wafer material removal rate profile model based on the locally relevant Preston equation by estimating the pad thickness profile as a function of polishing time. The result is a dynamic predictor of how the wafer removal rate profile shifts as the pad ages. The model helps fine-tune the pad conditioner operating characteristics without the requirement for costly and lengthy experiments. The accuracy of the model is demonstrated by experiments as well as data from a real production line. Both experimental data and simulations indicate that the smaller conditioning disk size and extended conditioning sweep range help improve the post-CMP wafer planarization. However, the defectivity tends to increase when the conditioning disk sweeps out of the pad radius; hence, the pad conditioning needs to be designed by considering the specific requirements of the CMP process conducted. The presented model predicts the process outcomes without requiring detailed experimentation.

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.

Finite element analysis on von Mises stress distributions of Si DSP

In this paper, we describe a 2D axisymmetric quasi-static finite element model based on 300mm wafer and double-side polishing (DSP) using a COMSOL Multiphysics software. Afterwards, the effects of Young's modulus and Poisson's ratio of polishing pad and the thickness ratio of upper and lower pads on the von Mises stress distribution are observed and chemical mechanical polishing (CMP) experiments are carried out to verify the above numerical calculations. The results show that a harder polishing pad results in a less edge roll-off, where a sharp variation in removal rate is observed near the edge of the wafer, but Poisson's ratio of pad has a less effect on the von Mises stress distribution on the wafer edge. A larger thickness ratio of upper and lower pads leads to a better wafer planarization.

C07 タイル構造研磨パッドによるSiウェハの平坦化加工に関する基礎研究(OS10 班磨技術(2))

C07 タイル構造研磨パッドによるSiウェハの平坦化加工に関する基礎研究(OS10 班磨技術(2))

Characterization of wet pad surface in chemical mechanical polishing (CMP) process with full-field optical coherence tomography (FF-OCT)

Chemical mechanical polishing (CMP) is a key process for global planarization of silicon wafers for semiconductors and AlTiC wafers for magnetic heads. Removal rate of wafer material is directly dependent on the surface roughness of a CMP pad, thus the structure of the pad surface has been evaluated with variable techniques. However, under in situ CMP process, the measurements have been severely limited due to the existence of polishing fluids including the slurry on the pad surface. In here, we newly introduce ultra-high resolution full-field optical coherence tomography (FF-OCT) to investigate the surface of wet pads. With FF-OCT, the wet pad surface could be quantitatively characterized in terms of the polishing pad lifetime, and also be three-dimensionally visualized. We found that reasonable polishing span could be evaluated from the surface roughness measurement and the groove depth measurement made by FF-OCT.

Novel CVD diamond-coated conditioner for improved performance in CMP processes

Conditioning of polishing pads during chemical mechanical planarization (CMP) of wafers is a critical process for maintaining productivity and quality control in the semiconductor industry. This investigation aims at developing a CMP diamond conditioner of a new concept and hence improving the conditioning performance. The novel diamond conditioner was fabricated by coating diamond films on a Si 3N 4 substrate with regularly patterned protrusions. Thanks to the uniform distribution and constant height of protrusions, the novel conditioner exhibited superior performance and durability over the current conditioner, which contains bonded diamond grits of various sizes and shapes with unequal heights. Characterization of the developed novel diamond CVD conditioner has also been made.

Chemical Mechanical Polishing in Elastic Contact and Partial Hydrodynamic Lubrication: Modeling and Experiments

Chemical mechanical polishing (CMP) has become a primary technique for planarization of semiconductor wafers in submicro device fabrication. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity, powder slurry, and wafer-pad contact significant. In this study, a CMP model considering both the elastic microcontact mechanism and the grain flow with roughness effects is presented. The model applies the average lubrication equation with partial hydrodynamic lubrication theory and elastic microcontact theory proposed by Greenwood and Williamson. In experiments, a test rig is used to simulate the CMP process and acquire the signals of polishing. The shear force is measured by a load transducer mounted on the lever and connected with the polishing head during CMP process. Furthermore, the theoretical results are compared with the experimental data. The theoretical and experimental results increase the understanding of CMP process.

Chemical Mechanical Planarization of Cu Pattern Wafer Based Alkaline Slurry in GLSI with R(NH<sub>2</sub>)<sub>n</sub> as Complexing Agent

Chemical mechanical planarization (CMP) of Cu pattern wafer based alkaline Cu slurry in GLSI was investigated. The performance of Cu removal rate and dishing condition were discussed in this paper. Different formation of alkali CMP slurry (Cu1 and Cu2 slurry) were observed by removal rate experiments and showed that alkaline slurry provided a robust polishing performance on initial removal rate, which Cu1 and Cu2 slurry were higher than that of commercial acidity slurry, and in addition, alkaline slurry also have good ending removal rate both in Cu1 and Cu2 slurry and favorable dishing in Cu2 slurry. Furthermore, the result indicated that Cu alkaline slurry with a complexing agent of R(NH2)n, compared with commercial acidity slurry with a inhibitor of Benzotriazol (BTA), have better application foreground for 45nm nod and more advanced nodes.

Effect of Shear and Thermal Characteristics on Chemical Mechanical Polishing

Chemical mechanical polishing has been widely used to achieve global planarization of wafers. In this paper, an improved designed test rig is used to acquire the signals on chemical mechanical polishing. The shear force and temperature-rise are measured during chemical mechanical polishing process. The polishing temperature is measured by T-type thermocouples screwed behind the polishing interface of the carrier. The shear force is measured by a load transducer mounted on the lever and connected with the polishing head. The parameters including down force, rotation speed, particle size and volume flow rate of slurry are investigated. The experimental results provide a good index to end-point-detection. The theoretical simulation by the average lubrication equation coincides with the experimental results. This study contributes to the understanding of chemical mechanical polishing mechanism.

Retaining Ring Design Impact on CMP Process Stability and Optimization

AbstractThe focus of this work is wafer retaining rings and their impact on chemical mechanical planarization (CMP) process stability, yield, and overall cost of ownership (CoO). The study looks at various CMP retaining ring materials and processing methods. Tribological investigations as well as wafer processing are critical to understand the retaining ring and polishing pad environment. Interactions at the ring/pad interface have a major effect on the planarization and defectivity of a polished wafer. Shear and normal forces at this interface, as well as temperature and lubrication regimes, were monitored to establish an empirical model. All process conditions equal, the material properties of retaining rings govern the coefficient of friction (COF) in the ring and pad contact area. Present study demonstrates a lower COF to be an indicator of extended ring lifetime, decreasing WTWNU and removal rate (RR) variation. The study correlates the findings on wafer level data from high volume manufacturing fabs with empirical data generated using applications lab tribological equipment to understand the on-wafer performance as a function of retaining ring material. The study's further aim is to understand for specific applications, the material interactions on-wafer using various retaining ring materials. CMP process optimization can be attained with a better understanding of retaining ring design and material characteristics, as well as polishing head and slurry parameters.

Chemical Mechanical Planarization of TaN Wafers Using Oxalic and Tartaric Acid Based Slurries

This work demonstrates that silica-based slurries (pH 3-8) using oxalic or tartaric acid as a complexing agent can be used for efficient, low pressure chemical mechanical polishing of tantalum nitride (diffusion barrier) in the fabrication of semiconductor devices. Depending on their pH and their oxidizer (H 2 O 2 ) content, these slurries support satisfactory polish rates of TaN up to 100 nm min -1 at a down pressure of 2 psi. Optical profilometry of wafers processed with these slurries shows very good postpolish surfaces. The possible mechanisms for chemically promoted material removal in these slurry systems are discussed.

Statistical and Experimental Analysis of Correlated Time-Varying Process Variables for Conditions Diagnosis in Chemical–Mechanical Planarization

During chemical-mechanical planarization (CMP) of semiconductor wafers, chemical and mechanical process variables are strongly correlated and jointly affect polishing performance. The correlation among these process variables could potentially be utilized to characterize process conditions for the purpose of diagnosis. However, process variables measured during CMP, such as the temperature distribution and coefficient of friction between wafer and pad, vary with time and present in a functional form. This significantly increases the complexity of analyzing correlation patterns and relating them with process conditions. The focus of this paper is therefore twofold: 1) experimental investigation of the correlation between sensing process variables and the implication of correlation pattern changes on process conditions and 2) statistical analysis of correlation patterns between process variables in functional form. In the designed CMP experiment, we investigated two failure modes during CMP process: pad failure and slurry failure. Slurry failure was generated by reducing the percentage of oxidizer to investigate its effects on polishing performance and heat generation on the pad. Pad failure was due to variation of diamond abrasive sizes in the conditioner. The post-CMP study of nonuniformity and defects such as scratches on the wafer was conducted to characterize process conditions. The experimental and statistical results support the investigation of correlation among process variables for condition diagnosis.

Novel Ceria-Polymer Composites for Reduced Defects during Oxide CMP

AbstractTo meet the stringent requirements of device integration and manufacture, surface defects and mechanical stresses that arise during chemical mechanic planarization (CMP) must be reduced. Towards this end, we have synthesized multiple hybrid and composite particles on micron length scales consisting of siloxane co-polymers functionalized with inorganic nanoparticles. These particles can be easily tailored during synthesis, leading to softer or harder abrasion when desired. Upon using these particles for the planarization of silicon oxide wafers, we obtain smooth surfaces with reduced scratches and minimal particle deposition, which is an improvement from conventional abrasive materials like pure silica, ceria and alumina nanoparticle slurries. Tribological characteristics during polishing were examined using a bench top CMP tester to evaluate the in situ co-efficient of friction. Characterization of the hybrid and composite particles has been done using infrared spectroscopy, dynamic light scattering, and electron microscopy. Surface roughness of the wafers was examined using atomic force and optical microscopy while removal rate measurements were conducted using ellipsometry at multiple angles.

Damage-Free Planarization of 2-Inch 4H-SiC Wafer Using Pt Catalyst Plate and HF Solution

We report a damage-free and efficient planarization process for silicon carbide (SiC) using platinum as a catalyst in hydrofluoric acid (HF) solution. In previous studies, 4H-SiC (0001) on-axis wafers were planarized by this process and an extremely flat surface was obtained. However, electronic device substrates require off-axis wafers. In the present study, 4H-SiC (0001) 8° off-axis Si-face wafers were planarized using a Pt catalyst plate and HF solution. In the first trial using these wafers, the surface roughness worsened and a diagonal pattern was observed by phase-shift interference microscopy. The pattern seemed to have been formed when the Pt plate morphology was transcribed onto the wafer. The removal rate of the 8° off-axis Si-face wafer is much greater than that of the on-axis Si-face wafer. Thus, we concluded that the use of a smoother catalyst plate would be necessary to obtain a smooth 8° off-axis Si-face wafer surface. Improving the Pt plate morphology by hand lapping also improved the surface roughness of the processed wafer as compared with the preprocessed surface. The maximum height of the surface irregularity (peak-to-valley, P-V) and root-mean-square roughness were improved to 0.513 nm and 0.044 nm, respectively, as determined by atomic force microscopy (2×2 μm2).

Effect of Nanoparticle Impact on Material Removal

Nanoparticle impacting on a solid surface always occurs in nano-machining processes, such as the chemical mechanical planarization (CMP) of wafers. Although the material removal induced by nanoparticle impact has been observed in some simulations and tests, the contribution of nanoparticle impact to the material removal in a real CMP process is still unclear. In the present work, a cylindrical liquid jet containing SiO2 nanoparticle impacts normally on a glass surface at speeds of 1 ms−1 and 3 ms−1. The desorption of the fluorescent nanoparticles adsorbed on the glass surface has been observed by a fluorescent microscope system and used to evaluate the contribution of the nanoparticle impact to the material removal. The experimental results indicate that the impact has a negligible effect on the material removal of the solid surface if the impacting speed is less than 3 ms−1 and the impacting time is less than 1.5 min. It may be helpful to the understanding of the material removal mechanisms in the CMP processes.

Novel ceria–polymer microcomposites for chemical mechanical polishing

Abrasive particles are key components in slurries for chemical mechanical polishing (CMP). Since the particle characteristics determine surface quality of wafers during polishing, in this research, novel abrasive composite particles have been developed. These composite particles contain nanoparticles of ceria dispersed within cross-linked, polymeric microspheres such that the average mass fraction of ceria is approximately 50% in the particles. The microspheres are formed by co-polymerization of N-isopropylacrylamide (NIPAM) with 3-(trimethoxysilyl)propyl methacrylate (MPS) and contain interpenetrating (IP) chains of poly(acrylic acid) (PAAc). Infrared spectroscopy, dynamic light scattering, and transmission electron microscopy are employed to characterize the composite particles. Planarization of silicon dioxide wafers is studied on a bench-top CMP tester and the polished surfaces are characterized by ellipsometry, atomic force and optical microscopy. Slurries formed from the composite ceria–polymer particles lead to lower topographical variations and surface roughness than slurries of only ceria nanoparticles even though both slurries achieve similar removal rates of ∼100 nm/min for similar ceria content. Polishing with the novel composite particles gives surfaces devoid of scratches and particle deposition, which makes these particles suitable for the next generation slurries in CMP.

Analyzing on Nonuniformity of Material Removal in Silicon Wafer CMP Based on Abrasive Movement Trajectories

Chemical mechanical polishing (CMP) has already become a mainstream technology in global planarization of wafer. The nonuniformity of material removal on wafer surface has a main influence on surface profile of silicon wafer in CMP process. However, the formation mechanism of nonuniformity in wafer CMP has not been fully understood and the influences of CMP process variables on nonuniformity are not fully clear. The nonuniformity of material removal on wafer surface has not been fully understood and the influences of CMP process variables on nonuniformity are not fully clear in CMP process. In this paper, firstly, the equation of particle movement trajectories on wafer surface was built by the movement relationship between the wafer and the polishing pad on a single head CMP machine with line oscillation of carrier. Then the distribution of abrasive trajectories on wafer surface was analyzed at different rotational speed. By the analysis, the relationship between the movement variables of the CMP machine and the With-In-Wafer Nonuniformity (WIWNU) of material removal on wafer surface had been derived. Last, the WIWNU tests were conducted on CP-4 machine. The analysis results are in accord with experimental results. The results will provide some theoretical guide for designing the CMP equipment, selecting the movement variables in CMP and further understanding the material removal mechanism in wafer CMP.

An improved model considering elastic—plastic contact and partial hydrodynamic lubrication for chemical mechanical polishing

Chemical mechanical polishing (CMP) has become a primary technique for planarization of semiconductor wafers in sub-micro device fabrication. A physical CMP model combines the effects of grain flow hydrodynamic lubrication, pad roughness, and asperity contact between wafer and pad. In this study, an improved CMP model, considering both the grain flow with roughness effects and the micro-contact mechanism, is proposed. The model applies the average lubrication equation with partial hydrodynamic lubrication theory and considers the elastic—plastic micro-contact theory. The applied load acting on the wafer is balanced by the slurry pressure in the non-contact area, and the surface asperity contact force in the contact area. The effects of the CMP parameters including applied load, rotation speed, particle size, and pad roughness are studied and discussed. The simulation results compare well with experimental data in the literature and contribute to further understanding in wafer—pad contact mechanism.

미세 표면 구조물을 갖는 패드의 제작 및 STI CMP 특성 연구

Chemical mechanical polishing (CMP) allows the planarization of wafers with two or more materials. There are many elements such as slurry, polishing pad, process parameters and conditioning in CMP process. Especially, polishing pad is considered as one of the most important consumables because this affects its performances such as WIWNU(within wafer non-uniformity) and MRR(material removal rate). In polishing pad, grooves and pores on its surface affect distribution of slurry, flow and profile of MRR on wafer. A subject of this investigation is to apply CMP for planarization of shallow trench isolation structure using microstructure(MS) pad. MS pad is designed to have uniform structure on its surface and manufactured by micro-molding technology. And then STI CMP performances such as pattern selectivity, erosion and comer rounding are evaluated.

Case study and efficient modelling for variational chemical–mechanical planarisation

Chemical–mechanical planarisation (CMP) is an enabling technique to achieve wafer planarity in backend manufacturing processes of integrated circuits. However, CMP also causes variations in metal and dielectric thicknesses because of the non-uniformity of metal feature density. The authors first conducted a case study of CMP-induced variations using an industrial CMP simulator together with a widely used microprocessor hardcore fabricated in a 90 nm technology with eight metal layers and a system-on-chip design fabricated in a 65 nm technology with four metal layers. They revealed a few interesting characteristics on thickness variations and, particularly, vertical and horizontal correlations between variations, although such correlations have been virtually ignored by the existing study on layout optimisation. These characteristics may lead to better modelling and design optimisation for CMP variations. As an example, the authors then proposed a stochastic CMP model to efficiently incorporate CMP variations estimation in the design flow and developed two algorithms to reduce the CMP simulation runs by 7× and 3×, respectively, when compared with generating the stochastic CMP model by detailed CMP simulations.