Copper Chemical Mechanical Planarization Research Articles

A Liposome-Containing Slurry for Tungsten Chemical Mechanical Polishing

Chemical mechanical planarization (CMP) has become an essential process in the manufacturing of advanced semiconductor devices found in cell phones, computers, and other everyday electronics. The three major applications of CMP involve the planarization of structures and films made of copper, tungsten, and silicon dioxide at wafer level. While CMP of silicon dioxide or interlayer dielectric materials represents the earliest application of CMP and copper CMP has become an enabling and fast-growing segment of CMP, tungsten CMP remains steady in production volume and growth. The yield of a CMP process is heavily dependant upon the performance of its corresponding slurry, a stable colloidal aqueous dispersion of abrasive particles and various chemical additives. It is generally true that, other than the dispersed abrasive particles, all other chemical additives are homogenously dissolved in a single aqueous phase. In this paper, we report the design and performance of a liposome-containing slurry for tungsten CMP. More specifically, in addition to the abrasive particles and other chemical additives commonly found in a metal CMP slurry, this new slurry contains a model catalyst that is encapsulated inside of liposome. The caged catalyst does not interact with the oxidizer outside until the polish. The purpose of encapsulating a catalyst is to increase the pot lifetime of the slurry and reduce the static etch caused by the reaction between the catalyst and the oxidizer if they are exposed to each other directly. In this study, we demonstrated that, by caging the catalyst, the static etch rate is significantly reduced and the pot lifetime is significantly increased. The material removal rate remains high. In this paper, the basic design of such slurry is first introduced. The evidence for the encapsulation of a representative catalyst is presented. The performance of such slurry on the polish of blanket and patterned wafers is discussed.

Cu CMP에서의 연마 균일성에 관한 기계적 해석

Most studies on copper Chemical Mechanical Planarization (CMP) have focused on material removal and its mechanisms. Although many studies have been conducted on the mechanism of Cu CMP, a study on uniformity in Cu CMP is still unknown. Since the aim of CMP is global and local planarization, the approach to various factors related to uniformity in Cu CMP is essential to elucidate the Cu CMP mechanism as well. The main purpose of the experiment reported here was to investigate and mechanically analyze the roles of slurry components in the formation of the uniformity in Cu CMP. In this paper, Cu CMP was performed using citric acid(<TEX>$C_{6}H_{8}O_{7}$</TEX>), hydrogen peroxide(<TEX>$H_{2}O_{2}$</TEX>), colloidal silica, and benzotriazole(<TEX>$BTA,\;C_{6}H_{4}N_{3}H$</TEX>) as a complexing agent, an oxidizer, an abrasive, and a corrosion inhibitor, respectively. All the results of this study showed that within-wafer non-uniformity(WIWNU) of Cu CMP could be controlled by the contents of slurry components.

Influence of Microstructure on Aggressive Chemical Mechanical Planarization Processes for Thick Copper Films

ABSTRACTNovel die-stacking schema using through-wafer vias may require thick electrodeposited copper and aggressive first-step chemical mechanical planarization (CMP). However, the effect of microstructural parameters, including surface orientation and grain size, on the CMP behavior of thick electrodeposited copper is not well understood. Here we explore the relationship be-tween the surface orientation of copper grains and local CMP removal parameters using electron backscatter diffraction and topography correlation techniques. In the present work, solid copper disks are studied which are annealed to produce samples with differing grain sizes. In addition, aggressive CMP is performed on copper films (30 μm) electrodeposited on silicon. At the bulk level, the slurry composition is found to have the greatest effect on the removal rate and surface roughness. At the microstructural level, the nature of the grain boundaries (e.g. coincidence site lattice (CSL) vs. non-CSL boundaries) is shown to impact the depth of grooving at the grain boundaries. A relationship between surface orientation and local removal rate is found.

Measurement of Ultrathin Film Mechanical Properties by Integrated Nano-scratch/indentation Approach

AbstractThe thickness and property measurements of thin films on a substrate are crucial for a wide range of applications. Classical techniques have relied on various physical properties to identify film thickness, independent of its mechanical properties. Here, a new experimental technique is devised to evaluate the film thickness, its stiffness and its flow stress. The technique utilizes the variation of the measured apparent modulus of a ductile film on a substrate from a nano-indentation experiment, in conjunction with the measured normal and tangential forces and the scratch depth in a nano-scratch experiment. These combined measurements are calibrated through a simple statically admissible model to yield the unknown quantities. The measurements reasonably agree with the finite element predictions and are ascertained by XPS film thickness measurements. The technique is applied to study the formed oxide nano-layer during copper chemical mechanical planarization process.

Chemical mechanical planarization of copper using abrasive-free solutions of oxalic acid and hydrogen peroxide

In this work we study aqueous solutions of oxalic acid and hydrogen peroxide as possible abrasive-free slurries for chemical mechanical planarization (CMP) of Cu. We show that the addition of (3 wt%) colloidal silica abrasive particles has no measurable effects on the already relatively high polish rates of Cu. These results suggest that chemical rather than mechanical effects dominate removal of Cu surface layers in this system. The Cu removal efficiency of this slurry can be controlled by adjusting its acidity and H 2O 2 content. By combining measurements of Cu polish and dissolution rates with electrochemical experiments, we propose a reaction scheme that describes the mechanism of Cu removal in abrasive-free solutions of H 2O 2 and oxalic acid as a function of pH and H 2O 2 concentrations.

Study of Non-Preston Phenomena Induced from the Passivated Additives in Copper CMP

The requirement for the superplanarization of interconnect nanotechnology beyond poses an urgent need to study the complicated behavior of copper CMP. It is common practice in advanced copper chemical mechanical planarization (CMP) polishing to add the inhibitor into the slurry to keep the copper surface perfect and smooth and to protect the copper surface from corrosion. It is beneficial to have the polishing pressure cushion between abrasives and wafer under the different pattern features and is most important to overcome the planarization limitation. This study describes the behavior of non-Preston’s phenomena under the passivated additives (inhibitors) and develops a model to explain the mechanism of the passivated-and-oxidated kinetics with non-Preston’s polishing, which explains the mechanism of copper surface reactions during polishing. Furthermore, our model shows that the three regions are due to different relationships between removal rate and polishing pressure. Three regions are characterized as the threshold, linear, and saturated zones, which are governed by the chemical etching, the depth of abrasive particles indent into the copper oxide, and the oxidation rate, respectively. Most of all, the removal rate change can be simulated and predicted by the ratio between the inhibitor and oxidizer concentrations. Therefore, this study does not only contribute the understanding of the non-Preston’s behavior but also provides the model under the assumption of the sequential stacked films of passivation and oxide films on the copper surface. The potentiodynamic methods are employed to test the assumption used in the mechanism and model.

The Effect of Frictional and Adhesion Forces Attributed to Slurry Particles on the Surface Quality of Polished Copper

The effect of frictional and adhesion forces attributed to slurry particles on the quality of copper surfaces was experimentally investigated during copper chemical mechanical planarization process. The highest frictional force of and adhesion force of were observed in a deionized water-based alumina slurry. On the other hand, the smallest frictional force of and adhesion force of were measured in an alumina slurry containing citric acid. However, frictional and adhesion forces of silica particles in the slurry were not significantly changed regardless of the addition of citric acid. These differences were explained by the strong adsorption of citric ions on alumina but not on silica, which was verified by the charge reversal of alumina in zeta potential measurements. Higher particle adhesion forces resulted in higher friction. A higher magnitude of particle contamination and scratches was observed on polished copper surface in slurry condition with higher adhesion and friction forces.

Comparison of dicarboxylic acids as complexing agents for abrasive-free chemical mechanical planarization of copper

Abrasive particles used in chemical mechanical planarization (CMP) of copper often agglomerate and cause scratches on the finished surface. Abrasive-free CMP offers a feasible solution to this problem, and our present work examines four dicarboxylic acids (oxalic, malonic, succinic and glutaric, with increasing carbon chain lengths) as possible complexing agents for such a chemically dominated CMP process. At pH 3.0–4.0, oxalic and malonic acids are most effective for abrasive-free Cu removal. The rates of Cu dissolution and polish (with or without abrasives) are correlated with pH dependent distributions of mono-anionic (for oxalic and malonic) and neutral (for succinic and glutaric) acid species. The surface morphologies of a Cu wafers obtained by abrasive-free CMP in these acids also are more defect free and flat compared to those obtained using abrasives.

The Effects of Copper CMP Slurry Chemistry on the Colloidal Behavior of Alumina Abrasives

The effects of common slurry additives on the colloidal behavior of alumina suspensions used for copper chemical mechanical planarization (CMP) were investigated. The alumina suspensions were characterized by zeta potential and agglomerate size distribution measurements with various chemical additives. To simulate the slurry during copper CMP, the effect of the addition of diameter copper particles was studied. The presence of copper caused a decrease in agglomeration for pH values less than 6.5 and an increase in agglomeration ranging from for pH values greater than 7 in aqueous solutions. Addition of glycine caused the formation of a soluble Cu-glycine complex that decreased agglomeration at pH values less than 4. The addition of did not affect the effective alumina agglomerate size without copper, but with copper in the solution the majority of the alumina agglomerated to for all pH values. However, increasing concentration to decreased the agglomerate size by . The pH of the slurry had the largest effect on the zeta potential and agglomerate size distributions.

Effects of CMP Slurry Chemistry on the Zeta Potential of Alumina Abrasives

The colloidal behavior of alumina in typical copper chemical mechanical planarization (CMP) solutions was investigated through the measurement of zeta potential and particle cluster size distribution. The effects of various common additives on zeta potential for alumina slurries used in copper CMP were studied. Addition of to glycine stabilized the zeta potential for alumina for a large pH range. Although slurry pH has the largest effect on zeta potential and particle cluster size distribution, sodium dodecyl sulfate caused alumina to maintain a small aggregate size while ethylenediaminetetraacetic acid caused alumina to agglomerate over the entire pH range investigated.

Characterization of copper-hydrogen peroxide film growth kinetics

As copper chemical mechanical planarization modeling efforts become increasingly more sophisticated, it is important to understand the individual steps that have been found to play integral roles in the removal process such as oxidation, film dissolution, abrasion, and dissolution of by-products. This study focuses on copper oxidation using H 2O 2, which is the most common oxidant added to slurries in the industry today. Ellipsometry, atomic adsorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques were used to study copper film growth characteristics. Ellipsometric results complemented microbalance results concluding that copper film growth occurs in hydrogen peroxide solutions of varying concentrations at pH 5. The film growth profile for 1 wt.% hydrogen peroxide reaches a saturation point at approximately 500 Å after about 12 h. Growth profiles for 0.25 and 1 wt.% H 2O 2 are similar, while significantly faster growth occurs at 4 wt.% H 2O 2. SEM images reveal that 50–100 nm copper oxide/hydroxide crystals are observed for t < 60 min and 200–300 nm crystals are formed at 24 h, indicating that reaction by-products diffusing away from the film-metal interface contribute to film growth. XPS spectra indicate Cu(I) and Cu(II) oxides and Cu(OH) 2 for t < 5 min and only cupric oxide and hydroxide for t > 10 min.

Galvanic Corrosion Between Copper and Tantalum under CMP Conditions

Chemical mechanical planarization (CMP) has emerged as the most viable method to planarize copper thin films during fabrication of integrated circuits. The final stage of copper CMP requires the simultaneous polishing of copper and the barrier metal, where the metals are prone to galvanic corrosion due to exposure to slurry. In this study, the extent of galvanic corrosion between copper and tantalum was estimated using electrochemical polarization measurements. A novel setup was designed to make direct measurement of the galvanic current between copper and tantalum and was successfully used to measure galvanic current in two different chemical systems. Galvanic corrosion current values obtained from polarization and direct measurements are compared and their implications during barrier polishing are discussed.

Surface Evolution during the Chemical Mechanical Planarization of Copper

Stressed surfaces are configurationally unstable under chemical etching wherein they may evolve to reduce their total energy. This paper investigates how such an effect may influence the planarization rate in a Chemical Mechanical Planarization (CMP) process. Nano-wear experiments on electro-plated copper surfaces have been conducted with systematic exposures to chemically active slurry. The nano-wear experiments have been first performed to generate local variation of the residual stress levels, followed by chemical etching to investigate the variation of the wear depth and the evolution of surface topography. It is found that the residual stress caused by the mechanical wear enhances the chemical etching rate.

Utility of dodecyl sulfate surfactants as dissolution inhibitors in chemical mechanical planarization of copper

An important component of the slurries used in chemical mechanical planarization (CMP) is an appropriately chosen corrosion/dissolution inhibitor, which facilitates selective material removal from protrusions while protecting recessed regions of the surface. The present work demonstrates the utility of two environmentally benign anionic surfactants, sodium dodecyl sulfate (SDS) and ammonium dodecyl sulfate (ADS) as dissolution inhibitors. Using a standard slurry (1 wt% glycine with 5 wt% H2O2 at pH = 4.0) typically used for Cu CMP and combining measurements of open circuit potentials and contact angles with those of Cu removal rates, we show that both SDS and ADS suppress chemical dissolution and polish rates of Cu. The dissolution inhibition efficiencies of ADS and SDS measured in these experiments are found to be superior to those of benzotriazole (BTA), a traditional inhibiting agent used for copper CMP.

Impact of CMP Consumables on Copper Metallization Reliability

Over the past few years, the chemical mechanical planarization (CMP) community has systematically characterized the device reliability issues associated with the introduction of copper metallization into integrated circuit fabrication. To gain further understanding of the impact of CMP processing on device performance, this paper reports in detail the interactions of simulated copper slurries and pristine segmented polyurethanes. These studies clearly show that polyurethane is fundamentally incompatible with some of the chemicals used in copper CMP, such as hydrogen peroxide. Experimental copper polishing data on both polyurethane and polyolefin-based pads are compared. The pad performance differences between the polyurethane and polyolefin-based pads are explained based on the chemistry of the base polymers used in the pad fabrication. These results are incorporated into the design and fabrication of a new class of polyolefins-based application specific pads.

Wear Phenomena in Abrasive-Free Copper CMP Process

The role of process parameters in wear mechanisms of abrasive-free copper chemical mechanical planarization (CMP) process has been investigated in this study. Qualitative analyses were performed to figure out the wear mechanisms by using scanning electron microscopy, atomic force microscopy, and energy-dispersive X-ray. Also, quantitative analysis was performed using the material removal rate model of abrasive-free CMP process. Chemical etching (corrosive wear), fatigue wear, particle adhesion, and abrasion wear have been found as the wear mechanisms in abrasive-free copper CMP, and sliding-induced chemical etching has been established as the dominant wear mechanism by both qualitative and quantitative analysis. However, increase of pressure and decrease of relative velocity and slurry flow rate give the dominance of chemical wear, and vice versa. In addition, some sort of incomplete growth and faceting of cupric layer have been observed on the wafer at some polishing conditions.

Semi-abrasive free slurry with acid colloidal silica for copper chemical mechanical planarization

New semi-abrasive free slurry for copper chemical mechanical planarization (CMP) was investigated through the addition of below 0.5 wt% acid colloidal silica, hydrogen peroxide and other additives. The additives as stabilizers for hydrogen peroxide as well as accelerators in tantalum nitride CMP were also evaluated. This semi-abrasive free slurry provides good hydrogen peroxide stability, excellent colloidal silica dispersion ability and easiness of post-CMP cleaning. The extent of enhancement in tantalum nitride CMP was verified through an electrochemical test. This approach may be useful for the application of single and first step copper CMP slurry with one package system.

Corrosion Inhibiting Effect on Copper Chemical Mechanical Planarization (CMP) in Fe(NO3)3 Based Slurries

The slurry of Copper chemical mechanical planarization for ultra large-scale integrate circuit (ULSI) usually contains oxidizer, etchant, complexing reagent and corrosive inhibitor. In planarization process, the corrosive inhibitor has an important effect on the planarization. Only if the concave surface of the wafer is properly protected from corrosion by the inhibitor, the process can obtain perfect surface planarity. In this paper, with Fe(NO3)3 as an oxidant and several corrosive inhibitors selected, the corrosive efficiency of slurries are investigated. The static etching rate and the polishing material removal rate of wafer are obtained. The electrochemical behavior of the slurry is investigated by the potentiodynamic polarization studies. And the inhibitive efficiency of the related corrosive inhibitors is calculated from the polarization data. X-ray diffraction is applied to analyze the composition modification of the copper surface. Atom force microscopy is applied to measure the surface topography of corrosive copper wafer and the value of surface roughness is measured by ZYGO surface analysis system. The result shows that the benzotriazole (BTA) is a perfect corrosive inhibitor. With addition of 0.1wt% BTA into 1.5wt% Fe(NO3)3 solution, the inhibitive efficiency can reach 99.1%. The polishing test shows that if only 1.5wt% Fe(NO3)3 is added as an oxidizer without any other additive, the surface roughness of the polished wafer is 26.9Å, while with 0.1wt%BTA added in the meantime, 5.2 Å of surface roughness can be obtained.

A Method for Direct Measurement of Substrate Temperature during Copper CMP

A novel method was developed to directly measure the substrate temperature during copper chemical mechanical planarization (CMP). Using specially designed wafer carriers, substrate temperatures were obtained in real-time with an infrared camera. Results indicate that substrate temperatures are higher than pad temperatures. In addition, the substrate temperature distribution appears to be closely related to slurry flow beneath the substrate during polishing. A three-dimensional thermal model was also developed to simulate the pad and wafer temperatures. Simulations support the interpretation of the experimental data.

Citric Acid as a Complexing Agent in CMP of Copper: Investigation of Surface Reactions Using Impedance Spectroscopy

Polishing slurries used in chemical-mechanical planarization (CMP) of copper typically include a complexing agent and an oxidizer. Our present work investigates the effectiveness of citric acid as a complexing agent for with employed as an oxidizer. We show that the rate of copper removal from increases when both citric acid and are used in acidic solutions () and decreases drastically in alkaline solutions (), as well as in citric acid without any in the slurry. We investigate the underlying surface reactions of these effects by using Fourier transform electrochemical impedance spectroscopy (FTEIS) in combination with potentiodynamic measurements. We analyze the relative roles of citric acid, , and solution pH in removal, and develop a reaction scheme describing the surface chemistry of in this system. The results presented here also demonstrate how FTEIS can be used for quantitative investigation of surface reactions in complex CMP systems.