Chemical Mechanical Planarization Slurry Research Articles

Fluorescence Correlation Spectroscopic Investigation of Surface Adsorption of CMP Slurry Additives on Abrasive Particles

ABSTRACTAdditive-abrasive interactions in chemical-mechanical planarization (CMP) slurries are investigated using fluorescence correlation spectroscopy (FCS). The FCS technique provides quantitative determinations of the interaction between additives and abrasive particles by characterizing the competitive adsorption of the additive and a fluorescent probe molecule by an abrasive particle. Adsorption of the CMP additives glycine and benzotriazole (BTA) on precipitated and sol-gel colloidal silica abrasives are characterized. Significant differences in the fluorescent probe’s adsorption to the different silica abrasives in the presence of the additives suggest surface chemistry differences between the different types of silica. Extensions of the analysis of FCS data are proposed for improving the quantitative determination of the competitive adsorption of fluorescent probe dyes and CMP additives on abrasive particles.

Introduction of a Dynamic Corrosion Inhibitor for Copper Interconnect Cleaning

Copper has become the material of choice for the interconnects in semiconductor devices due to its low resistance and ease of processing [1]. Device fabrication with copper requires electrochemical deposition and chemical mechanical planarization (CMP). Since the polished copper surface generated during CMP is considered to be one of the most important factors which determine the performance of the interconnect, post-CMP cleaners must efficiently remove residues generated by the polishing process [2]. CMP slurries and post-CMP cleaners frequently include corrosion inhibitors to form a protecting layer on copper surface. If a thick organic film remains on copper after cleaning processes, it can have unfavorable effects on performance of copper interconnects. To minimize this issue, the authors earlier described a corrosion inhibitor which formed a very thin protective layer and that was easily removed by plasma treatment [3, 4].

Impedance Spectroscopy Analysis of Hydration in Ordinary Portland Cements Involving Chemical Mechanical Planarization Slurry

Impedance spectroscopy was used to monitor the hydration in the electrical/dielectric behaviors of chemical mechanical planarization (CMP)-blended cement mixtures. The electrical responses were analyzed using their equivalent circuit models, leading to the separation of the bulk and electrode based responses. The role of the CMP slurry was monitored as a function of the relative compositions of the CMP-blended cements, i.e. water, CMP slurry, and ordinary Portland cement. The presence of Al₂O₃ nanocrystals in the CMP slurries appeared to accelerate the hydration process, along with a more tortuous microstructure in the hydration, with enhanced hydration products. The frequency-dependent impedance spectroscopy was proven to be a highly efficient approach for evaluating the electrical/dielectric monitoring of the change in the pore structure evolution that occurs in CMP-blended cements.

An advanced alkaline slurry for barrier chemical mechanical planarization on patterned wafers

We have developed an alkaline barrier slurry (named FA/O slurry) for barrier removal and evaluated its chemical mechanical planarization (CMP) performance through comparison with a commercially developed barrier slurry. The FA/O slurry consists of colloidal silica, which is a complexing and an oxidizing agent, and does not have any inhibitors. It was found that the surface roughness of copper blanket wafers polished by the FA/O slurry was lower than the commercial barrier slurry, demonstrating that it leads to a better surface quality. In addition, the dishing and electrical tests also showed that the patterned wafers have a lower dishing value and sheet resistance as compared to the commercial barrier slurry. By comparison, the FA/O slurry demonstrates good planarization performance and can be used for barrier CMP.

New possibilities of metal corrosion inhibition by organic heterocyclic compounds

It is shown that many heterocyclic organic compounds, e.g., various azoles, are capable of adsorption on metals with formation of strong bonds with the surface. The approach based on the linear free energy relationship (LFER) principle offers a description of the efficiency of corrosion inhibition by these compounds and provides an understanding of the nature of chemical bonds formed by an organic inhibitor with a metal that needs to be protected. Knowledge of the specifics of interaction between azoles and metal surfaces can be helpful in choosing a promising corrosion inhibitor for drastic conditions, for example, in chemical mechanical planarization slurries where simultaneous mechanical polishing and electrochemical dissolution of the surface usually occur. Corrosion inhibition of steel at high temperatures (≥ 150°C) in mineral acid solutions is yet another example of a new successful use of azoles. It is demonstrated that new possibilities for improving the anticorrosive protection of metals are provided not only by using mixtures of some azoles with carboxylate-type organic corrosion inhibitors but also by constructing bilayer nanocoatings from aqueous solutions. For example, strong adsorption of small amounts of rather an exotic compound, dimegin (disodium salt of deuteroporphyrin), not only promotes the passivation of iron in neutral aqueous solutions but also impedes the local depassivation of the metal. Furthermore, it offers wide possibilities for further improvement of adsorption of other heterocyclic chemical compounds due to preliminary modification of the metal surface even by a small dimegin concentration.

Temperature distribution in polishing pad during CMP process: Effect of retaining ring

Heat generation is inevitable during the chemical mechanical planarization (CMP) process because the mechanical and chemical removal of material is carried out by using abrasives and chemicals in the CMP slurry. In this paper, results obtained from experiments performed on a membrane-type carrier having a retaining ring were used to study the temperature distribution in a polishing pad during the CMP process. To understand and predict the distribution of temperature rise, a kinematical analysis of the temperature distribution was performed by considering the frictional characteristics of the process. The results of this study can be used to predict the temperature distribution in a polishing pad, and such predictions can help in developing a more effective CMP process.

Effect of Complex Agent on Copper Dissolution in Alkaline Slurry for Chemical Mechanical Planarization

With the microelectronic technology node moves down to 45 nm and beyond, and to reduce the RC delay time, low-k dielectric materials have been used to replace regular dielectric materials. Therefore, the down force of chemical mechanical planarization (CMP) needs to decrease based on the characteristics of low-k materials: low mechanical strength. In this study, the effect of new complex agent on copper dissolution in alkaline slurry for CMP was investigated. Based on the reaction mechanism analysis of Cu in alkaline slurry in CMP, the performance of Cu removal rate and surface roughness condition were discussed. It has been confirmed that Cu1 slurry demonstrates a relatively high removal rate with low down force. And also, by utilizing the Cu1 slurry, good result of Cu surface roughness were obtained.

Influence of adhesion of silica and ceria abrasive nanoparticles on Chemical–Mechanical Planarization of silica surfaces

We report on a direct measurement of adhesion between abrasive nanoparticles of irregular shape, which are used in semiconductor industry in the process of Chemical–Mechanical Planarization (CMP), and silica surface. The adhesion of ceria and silica nanoparticles to silica surface is measured in multiple chemistries of different CMP slurries using a specially developed atomic force microscopy (AFM) method. Using this method, we study the influence of adhesion on the main parameters of CMP, removal rate and defectivity, scratches. While being plausible to expect correlation between these parameters and adhesion, it has not been systematically studied as of yet. We observed direct correlation between adhesion and removal rate. Comparing the measured defectivity and adhesion, we observe the presence of some correlation between these parameters. We conclude that both adhesion and shape of abrasive particles influence defectivity, micro-scratches. Direct measurements of the adhesion between abrasive nano-particles and surface can be used in the screening of new slurries as well as various modeling related to wearing of the surfaces.

Selective layer chemical mechanical planarization process mimicked with atomic force microscope

To understand the mechanisms of chemical mechanical planarization (CMP), an atomic force microscope (AFM) was used to characterize polished layer surfaces formed by selective transfer after a series of polishing experiments. The AFM allows one to examine the effects of applying highly localized stress to a surface. In the presence of solutions, tribochemical friction and wear can be investigated. We present the results of fundamental studies of the simultaneous application of chemical agents and mechanical stress using a single asperity model and a solid surface. At the same time, we show the consequences of combining highly localized mechanical stress (due to contact with AFM tip) and exposure to aqueous solutions of known pH. The experiment simulates several features of a single particle–substrate–slurry interaction in CMP. To optimize the CMP process, one needs to obtain information on the interaction between the slurry abrasive particles and the polished surface. To study such interactions, we used AFM. An AFM tip of radius of about 50 nm was used to mimic a single abrasive particle, typical of those found in CMP slurry. Surface analysis of selective layer using the AFM revealed detailed surface characteristics obtained by CMP. Studying the selective layer CMP, of which the predominant one is copper (in proportion of over 85 per cent), we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. It was found that removal mechanisms depend also on the slurry chemistry, potential, percentage of oxidizer, and the applied load. We show that linear scans and raster scans display significantly different material removal rates. Oxide removal happens considerably faster than the copper CMP removal from the selective layer. This is in agreement with generally accepted models of copper CMP. Both long-range and the friction forces acting between the AFM tip and surface during the polishing process were measured. The correlation between those forces and removal rate is discussed. At the same time, this article complements recent observations of tip-induced friction and wear and growth in a number of inorganic surfaces in aqueous solutions.

Effect of slurry aging on stability and performance of chemical mechanical planarization process

Chemical mechanical planarization (CMP) is known to be one of the most challenging processes in microelectronics manufacturing due to the number of variables involved in the design of the process. In particular, the slurries made of nano-sized particles and aggressive chemistries need to be characterized batch to batch and as a function of time to enable robust high volume manufacturing. In this study, the effect of slurry aging on CMP performance was investigated systematically for regular silica based slurry as well as for slurry containing an organic biocide additive to prevent bacteria formation. The parameters examined were particle size distribution, zeta potential, bacteria count, total organic carbon concentration, silicon ion dissolution, material removal rate (MRR), and surface quality. The results indicated that aging influenced slurry performance negatively and even with the addition of biocide, organic contamination was observed at the extended aging periods. The material removal rates decreased significantly by aging and more surface deformations were observed on the wafer surfaces polished with the slurries destabilized with the elapsed time. Slurries containing biocide were detected to be more prone to agglomeration and increase in particle size as the time passes after the slurry is exposed to the environment. Furthermore, the impact of short time slurry aging (conditioning) on particle properties of the slurries containing polymeric additives and the adverse affects of extreme stability in the slurries containing surfactants are also discussed in terms of the two other factors that can cause variability in CMP slurry performance.

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.

Potassium Permanganate as Oxidizer in Alkaline Slurry for Chemical Mechanical Planarization of Nitrogen-doped Polycrystalline Ge2Sb2Te5 Film

For phase-change memory beyond the 30 nm design rule, chemical mechanical planarization (CMP) performing at a high polishing rate, reasonable selectivity, and no corrosion-induced pits is essential for planarizing nitrogen-doped polycrystalline (GST) deposited on the confined memory cell structure. We develop a new alkaline slurry added with used as an oxidizer. The alkaline slurry added with 0.3 wt % has a polycrystalline GST film polishing rate of 5200 Å/min, a polishing rate selectivity between polycrystalline GST and film of 100:1, and no corrosion-induced pit. In addition, polycrystalline GST film CMP using the alkaline slurry added with is observed to follow a cyclic reaction polishing mechanism.

Effects of Slurry Distribution using Diaphram and Centrifugal Pumps on the Defectivity in a Cu CMP Process

Slurry health has been shown to impact defectivity in the chemical mechanical planarization (CMP) process. Improper mechanical handling is known to form large agglomerates in CMP slurries that can lead to increased scratching of the surface. The foremost cause of slurry damage occurs from shear stresses placed on the slurry particles as they pass through the motive force in a distribution system. This paper is a study of two common slurry pumping methods and their contribution to post CMP micro-scratch defects measured on TEOS, Black Diamond l (BD l), Cu blanket wafers, and low-k/Cu integrated patterned wafers. The two specific slurry handling methods studied were the recirculation of slurry in a distribution system by positive displacement (diaphragm) pumps and bearingless centrifugal pump systems.

Tailoring Silica Nanotribology for CMP Slurry Optimization: Ca2+ Cation Competition in C12TAB Mediated Lubrication

Self-assembled surfactant structures at the solid/liquid interface have been shown to act as nanoparticulate dispersants and are capable of providing a highly effective, self-healing boundary lubrication layer in aqueous environments. However, in some cases in particular, chemical mechanical planarization (CMP) applications the lubrication imparted by self-assembled surfactant dispersants can be too strong, resulting in undesirably low levels of wear or friction disabling material removal. In the present investigation, the influence of calcium cation (Ca(2+)) addition on dodecyl trimethylammonium bromide (C(12)TAB) mediated lubrication of silica surfaces is examined via normal and lateral atomic force microscopy (AFM/LFM), benchtop polishing experiments and surface adsorption characterization methods. It is demonstrated that the introduction of competitively adsorbing cations that modulate the surfactant headgroup surface affinity can be used to tune friction and wear without compromising dispersion stability. These self-healing, reversible, and tunable tribological systems are expected to lead to the development of smart surfactant-based aqueous lubrication schemes, which include designer polishing slurries and devices that take advantage of pressure-gated friction response phenomena.

Evaluation of Dielectric Constant through Direct Chemical Mechanical Planarization of Porous Low-k Film

Nanoporous materials are utilized in back end of line (BEOL) processing of current devices. However, their low k-values often alter during device fabrication such as plasma processing and/or wet treatment. In this study, we analyzed the effect of chemical mechanical planarization (CMP) slurries on k-values, and also evaluated three types of nanoporous low-k materials that were exposed to CMP slurries, dry processing, and/or barrier sputtering. We confirm that the k-value increase during direct CMP of porous low-k films is caused by the diffusion of surfactant through the films, depending on the characteristics of the nanoporous film and surfactant. The diffusion is explained by the adsorption of surfactant on sidewalls of continuous pores formed by porogen desorption while it is easily released by post-CMP annealing. In contrast, the increase in k-value during CMP after dry processing is mainly caused by moisture uptake.

Potassium sorbate as an inhibitor in copper chemical mechanical planarization slurry. Part I. Elucidating slurry chemistry

The integration of an advanced inhibitor, potassium sorbate (K[CH 3(CH) 4CO 2]), in a copper CMP slurry based on hydrogen peroxide and glycine is reported. The first part of the study discusses the slurry chemistry by qualitatively describing the processes involved and proposes a mechanism for a hydrogen peroxide–glycine based slurry having sorbate anion as an inhibitor. For this purpose, the specific role of each chemical constituent in the slurry was elucidated at a fundamental level by electrochemical studies, X-ray photon spectroscopy (XPS) and contact angle measurements, all linked to the CMP performance on blanket wafers. Once the polishing mechanism was resolved the influence of the inhibitor was evaluated by CMP processing of patterned wafers.

Potassium sorbate as an inhibitor in copper chemical mechanical planarization slurries. Part II: Effects of sorbate on chemical mechanical planarization performance

This study reports on the effects of potassium sorbate (K[CH 3(CH) 4CO 2]) on copper chemical mechanical planarization (CMP) performance and demonstrates how the performance can be controlled by the inhibitor concentration in the slurry. The study is a continuation of a recent report on the copper polishing mechanism in H 2O 2/glycine-based slurries using sorbate as an inhibitor. CMP performance with respect to the inhibitor concentration in the slurry is evaluated in terms of surface roughness, polishing uniformity and dishing values. CMP results obtained from blanket wafers show that an increased sorbate concentration provides lower roughness values. CMP data obtained from patterned wafers shows that an increased sorbate concentration provides better polishing uniformity and lower dishing values for copper lines. The high solubility of sorbate in water (up to 9 M) is a major advantage for CMP processing.

Poly(ethyleneimine) as a Passivating Agent for Ta Chemical Mechanical Planarization

We report poly(ethyleneimine) (PEI) as a possible passivating agent for Ta during chemical mechanical planarization (CMP). Studies by electrochemical impedance spectroscopy in a model CMP slurry suggest that PEI forms a polymer film atop a Ta electrode, and voltammetry studies of Ta in 2.5 M HF suggest that PEI films suppress the formation of Ta oxide. Because Ta oxide is mechanically hard, suppressing Ta oxide growth may allow reduced downforce or higher removal rates. These observations are consistent with an increase of approximately 3 times in the Ta removal rate in a model CMP slurry upon addition of 3000 ppm PEI.

Ceria CMP Slurry for the Construction of Floating Gates in MLC NAND Flash Memory below 51 nm

A ceria slurry, which is capable of high removal selectivity between silicon oxide and poly-Si, in the chemical mechanical planarization (CMP) process was investigated for the construction of poly-Si gates of a multilevel cell (MLC) NAND flash memory below 51 nm. Anionic phosphate fluorosurfactant was incorporated into the ceria slurry for use as a passivation agent to suppress poly-Si removal. The ceria slurry with fluorosurfactant showed high silicon oxide-to-poly-Si removal selectivity (295: 1), resulting from the passivation layers on the poly-Si due to the selective adsorption of the fluorosurfactant. The selective adsorption behavior of the fluorosurfactant can be explained by the difference in surface characteristics between the oxide and the poly-Si, which was supported by the experimental results.

Measurement of CMP Slurry Abrasive Size Distribution by Scanning Mobility Particle Sizer

This article introduces an abrasive particle size measurement by a scanning mobility particle sizer (SMPS) to measure precise size distribution in the nanoregime. Static light scattering (SLS), which is a conventional method, is compared with the SMPS-based technique. Both measurement techniques differ in the measurement of SiO 2 and CeO 2 abrasive particle sizes. Results showed that SMPS is more sensitive than the SLS equipment due to a single-particle count, which is suitable for representing nanoparticle abrasives. To the best of our knowledge, there has been no article yet about the use of an SMPS for the measurement of abrasive size in chemical mechanical planarization (CMP) technology.