We investigated the mechanical effect of an abrasive in an abrasive-free-like (AFL) slurry using CMP evaluation and ζ potential evaluation. The amount of abrasive strongly influenced CMP performance. We found out the optimum amount of abrasive for optimal CMP performance. The ζ potential of the abrasive was positive, and those of the Cu and barrier metal were negative. We discussed a planarization model of the AFL slurry in detail based on the ζ potential results obtained.

The effect of CMP process parameters (pressure and pad hardness) on the ceria and silica abrasive particle-size distribution (PSD), morphology, and surface composition when polishing oxide and nitride surfaces was investigated in detail. The PSD was observed to shift post-CMP, with ceria and silica exhibiting a decrease and increase, respectively, in the number of particles towards the tail end of the distribution. The shift in ceria PSD was observed to increase as pad hardness increased. An increase in polish pressure and work surface hardness resulted in an equivalent shift in the PSD when polished on a soft pad. The inclusion of an additive reduced the oxide removal rate, and the abrasive particles exhibited the presence of a thin organic coating on the surface. The difference in material removal mechanisms and selectivity when polishing oxide and nitride with ceria and silica-based slurries was also investigated in detail.

In the work presented the coefficient of friction (COF) was firstly determined metrologically by a systematic assessment of motor currents for different products of pressure and velocity (p v). With all seven test slurries it could be shown that the inserted energy ECMP is proportional to the product of pressure and velocity. The COF of the parameter domain considered here does not depend on the inserted energy or the product of p v in a first approximation. For all tested slurries it was demonstrated that, both the COF and the removal rate (RR) behave analogously (low COF→ low RR).

Measurements of the viscosity η have shown that η is not a constant in the shear rate range relevant for CMP. Using the obtained viscosity values a mean slurry film thickness in the range of 2,5 -C 6 μm could be calculated.

There is a widespread interest in development and characterization of CMP consumables due to an existing and potential market, as the CMP process becomes widely accepted in the field of microelectronics fabrication. A non-destructive Ultra Sound Testing (UST) technique developed at the University of South Florida has been successfully used in the past to map the variation of specific gravity over the entire volume of the pad. To gage the impact of the variation in specific gravity with in the body of the polishing pad, the results of UST of pads need to be correlated with actual polishing performance of the pad. In this research, UST was performed on IC 1000 Suba IV/ A4 polishing pad, and novel polyurethane pads, Pad A (with sub pad) and Pad B (without sub pad). The novel pads have been specifically developed for Interlayer Dielectric (ILD) polishing. 6 inch coupons from polishing pad regions of interest (high and low ultra sound transmission) determined after the ultrasound map were punched out and further evaluated. The mechanical properties of the pad material from the coupons were evaluated using Dynamic Mechanical Analysis (DMA) and tribological properties were evaluated by performing CMP on 6 inch coupons in the CETR CMP tester.

This paper reviews the contact mechanics between the surface of a wafer and the asperity of the polishing pad for CMP from basic asperity such as spherical, rectangular, and conical shapes to more general asperity with a height distribution. This paper also proposes a practical method to bridge a measured profile of pad asperity in microscopic scale to a set of simple parameters which describe the elastic behavior for CMP process simulation in larger scale. We show a scalable CMP simulation using the proposed pad asperity parameters.

Low-abrasive content slurries for copper (Cu) chemical-mechanical planarization (CMP) have been developed to achieve removal rate and removal uniformity comparable to conventional slurries. They can improve post-CMP defectivity, improve topography and allow operation at lower polish pressures that are more compatible with the low-dielectric constant (low-k) materials required for current and future high-performance interconnects. Integration of these slurries into a yielding product with 9-level Cu/low-k metallization requires fundamental learning and process characterization. This paper discusses the some of the challenges encountered during development, integration, and qualification of a low-abrasive Cu CMP process for Texas Instruments (TI) Incorporated's 90 nm technology node with copper/organosilicate interconnect. As abrasive content is reduced, the slurry chemistry must play a larger role in CMP removal. A more aggressive reactive chemical formulation requires an effective inhibitive component to keep Cu static etch rate low. As a result, wafer-scale process and consumable interactions, die-scale planarization efficiency, and feature-scale removal rates each become more sensitive to process changes. Pressure and temperature have larger effects on removal rate/profile than conventional slurries, and complete clearing of Cu puddled over underlying topography becomes more difficult. Successful integration of these slurries, however, can achieve excellent results in dishing and erosion topography, Cu thickness uniformity, and Cu loss in small features such as vias and landing pads. Low-abrasive content solutions are also more stable and easy to handle in slurry distribution vessels and lines, have lower scratch and residue defectivity, and have greatly extended margin for overpolish. As lowabrasive content Cu slurry options continue to evolve to become manufacturable solutions, their benefits far outweigh the costs and challenges encountered in their successful integration.

We present the influence of the electrochemical plating recipe and the bath chemistry on Cu grain size evolution and its link to corrosion of Cu interconnects. Our results demonstrate the fact that Cu corrosion depends on the combination of (i) solution type and (ii) Cu quality. The latter is influenced by geometrical factors such as line width and pattern density as well as the electroplating parameters such as plating recipe and bath chemistry. Organic and inorganic acid based model-CMP solutions are used to make a comparison in terms of the interactions with the Cu surface. It is shown that an organic acid based solution etches Cu independent of the Cu quality. However, etching by an inorganic acid based solution reveals line width (0.2 μm <w<1.0 μm) and pattern density dependence (16%< pd< 72 %) with the narrow lines being etched more rapidly both for isolated and semi-dense structures. This kind of geometry dependent etch behavior by the inorganic acid based solution is also shown to be a function of the electroplating process parameters in contrast to an organic acid based one.

The effect of nano-size silica abrasives in chemical mechanical polishing (CMP) of copper is studied in order to reduce mechanical stresses during polishing, which may minimize defects such as surface scratches, copper peeling, dishing and erosion. In order to achieve low stress polishing of copper while maintaining removal rate efficiency, the formation of chemically modified surface layer, which can be mechanically removed by small size and low hardness abrasives, is critical. Complexing agents play an important role in the formation of a removable surface layer in the presence of the oxidizer, which is responsible for oxide formation, and the inhibitor, which passivates the surface. A new removal mechanism is proposed by correlating results of surface roughness after polishing with removal and etch rates. The effects of large silica and alumina abrasives, ranging from 200-1000 nm in diameter, are also studied to compare the different removal mechanisms.

We used a non-contact metrology system based on laser-induced surface acoustic waves to evaluate the thickness uniformity of electroplated copper. Several wafers were prepared using different plating conditions that affect the copper overburden thickness and uniformity. Measurements of overburden were made on a variety of pattern features including trench arrays of several pattern densities, solid bond pads, and the surrounding field area. In general, the overburden was found to be thicker above the arrays of narrow linewidth, as compared to the surrounding field. However, the magnitude of this “mounding” effect is dependent on the plating process, pattern density, and position on the wafer. For example, as the accelerator in the plating solution increases, the mounding on a 50% density line array varies from zero to 5000 Angstroms. Under all plating conditions used, the mounding was found to be progressively higher as the pattern density of the array increases (in the range of 20% to 50% copper). The solid pads were found to have conformal filling, in all cases. It was also found that the overburden in the field area is reduced as the adjacent mounding increases, presumably because the reactant in the plating bath becomes depleted in the vicinity of the high overburden regions above the arrays.

Chemical mechanical planarization (CMP) has found extensive application in the fabrication of micro-electro-mechanical systems (MEMS). Nickel and Nickel based alloys are known to possess favorable properties that make them promising candidates to realize movable structures for MEMS applications. The development of CMP slurry chemistry for Ni that provides good CMP performance is the key in enabling CMP technology for Nickel based MEMS device fabrication. Unfortunately, very little work has been reported in terms of the electrochemical interaction of Ni with various CMP slurry constituents such as oxidizers, complexants and inhibitors. In this study, CMP of nickel was performed using H2O2 as oxidizer and alumina particles as abrasives. Electrochemical techniques were used to investigate the dissolution/passivation behavior of high-purity Ni under static and dynamic conditions in slurries at pH 4 with the addition of oxidizer, complexing agent and nickel salt. The affected surface layers of the statically etched Ni-disc were investigated using X-ray photoelectron spectroscopy (XPS). The Ni removal rate increased with the addition of oxidizer and further increased with the addition of complexing agent and nickel salt. The electrochemical results indicate that the surface chemistry and electrochemical characteristic of Ni play an important role in controlling the polishing behavior.

It is generally accepted that there is a minimum hardness requirement for abrasive particles to be used in CMP (Chemical Mechanical Polishing) slurries. For copper CMP, the common abrasives are various types of alumina and silica. It has also long been suspected that a softer organic based abrasive could significant reduce the defects during polishing. In this study, for the first time, we demonstrated the usefulness of an organic particle as abrasive in formulating copper CMP slurry. The unexpected consequence of using such soft hydrophilic particles is its low sensitivity of material removal rate for copper towards polishing down force and platen speed. In addition, due to its unique particle surface properties, the slurry gives high selectivity in removal rate for copper over barrier, cap, and dielectric materials. In this paper, some basic physical and chemical characteristics of the particles and slurry will be first presented. The performance of this new slurry in relation to conventional slurries on blanket and patterned wafers will be discussed.

This study compares the oxidative dissolution, passivation, and polishing behavior of copper chemical mechanical polishing in the presence of hydrogen peroxide, glycine and copper sulfate. High purity discs were used to study the dissolution and oxidation kinetics under static and dynamic conditions at pH 4 with varying H2O2 concentrations. Changes in surface chemistry of the statically etched copper-disc were investigated using X-ray photoelectron spectroscopy (XPS). With the addition of glycine and copper sulfate to the slurry, the copper removal rates increased significantly and the maximum removal rate shifted to a H2O2 concentration of 3%. Electrochemical investigation indicates an enhanced dissolution of copper, which might be due to the strong catalytic activity of Cu(II)-glycine complexes in decomposing H2O2 to yield hydroxyl radicals. XPS results suggest that the passivation at higher H2O2 concentrations in the presence of glycine and copper sulfate is provided by the OH radicals adsorbed on Cu surface.

In the scribe lane, which is located at the frame neighboring two chips, most of the test patterns for monitoring electrical characteristics of memory device as well as various key patterns for photo process are formed. The pattern density of these regions is lower than that of the main chip area, and cause nitride erosion by dishing phenomena during HSS STI CMP process. Nitride erosion occurred in the scribe lane region, could the affect erosion properties of cell region in main chip area, results in within die remain nitride variation and marginal fail in device operation. In this work, in order to prevent these problems, pattern design in the scribe lane was modified so as not to occurs within die remain nitride variation. The effects of improvement in within die remain nitride variation were investigated by FIB-TEM analysis and its correlation with electrical properties were explained.

Since the early days of copper CMP much research and development effort was put into formulation of new copper and barrier CMP slurries. Two major motivations for this effort are the improvement of process performance for currently used integration schemes and the preparation for new integration schemes using low-k and ultra low-k dielectric materials. In this paper a systematic procedure for topography investigation after copper and barrier CMP is presented. The procedure is applied to four different copper slurries in order to compare after copper and after barrier CMP topography performance. As a result of the post copper CMP topography investigations, a discussion of advantages and disadvantages of non-selective and selective barrier polish processes will be presented. To complete the discussion of potential topography correction during barrier CMP, an investigation of an observed pronounced dielectric erosion close to large metal features or within high metal density arrays with medium or high selective barrier CMP processes will be presented.

There are many elements affecting CMP performance such as the slurry, pad, process parameters and pad conditioning. Among these, the pad is considered to be one of the most important parts because of its deterioration during polishing. However, specific pad design techniques have not yet been fully investigated. In this paper, conventional polyurethane pad characteristics are investigated. A pad design based on this analysis is suggested. Prototype pads are fabricated using micro molding and are used in an experiment for examining the pad deterioration mechanism.

The IGAM engineering company for applied mechanics Ltd. developed an active piezocontrolled carrier for CMP. It uses several, by means of piezo-stacks individually controllable rings. The carrier is optimized regarding its stiffness and reliability by means of threedimensional finite element calculations. The high stiffness and positioning accuracy of the system allows the exact control of different surface profiles and thus the purposeful attitude of the pressure and removal profile independently of the polishing pressure. Tests show a very homogeneous pressure and removal distribution in the circumference of the wafer. The concept is transferable on further wafer diameters, whereby the width of the individual zones can be widely adapted to the requirements of the desired removal profile. Results of finite element analysis for a 12” prototype are available. The variable concept allows to upgrade existing CMP machines. The aims of current developments are the integration of in-situ-pressure determination to control the process, wireless transfer of energy and data to the carrier and the control of the local removal profile.

Magnetic bearing technology is widely used in various technical fields, and is particularly appreciated in the semiconductor industry, where it is applied to the turbo molecular pump and wafer transfer system due to the excellent controllability it provides, even at speeds as high as 50,000 rpm. This report discusses the adoption of magnetic bearing technology to control the wafer carrier tilt angle during polishing. When the wafer is polished on a viscoelastic pad, the wafer carrier is inclined and pressed into the pad. Therefore, the reaction force on the wafer from the pad is concentrated at the wafer edge, increasing the polish rate at the edge relative to the rest of the wafer. Modification of the tilt angle is thought to offer a possible means of normalizing the distribution of the reaction force from the pad and correcting the nonuniformity of the polish rate. The wafer carrier was confirmed to press slightly into the pad and to be tilted 18 × 10-5 rad by the viscoelasticity of the pad (without tilt angle control). Constant current control led to better control of the polish rate profile relative to feedback control. The polish rate in the outer area of the wafer was increased by tilting the carrier to the positive side, and the polish rate of the wafer center area could be reduced by tilting it to the negative side. The best profile was obtained with control current of Im = -0.4 A. When the wafer carrier was tilted in the reverse direction, the polish rate became almost zero. It was concluded that hydro-planing occurred between the wafer and the pad. Accordingly, this report demonstrates the possibility of improving the polish rate profile by maintaining the wafer carrier in a horizontal position using magnetic control.

CMP has been described qualitatively in terms of alternating cycles of chemical formation and mechanical removal of a thin layer on the wafer surface. A quantitative model of CMP has been developed2-7 which is based on mechanisms for surface kinetics, treating mechanical removal as one step in the mechanism. This model has been used successfully to explain removal rates for tungsten and thermal oxide CMP. In particular, for tungsten CMP the removal rate increases steeply with increasing oxidizer concentration at low concentrations, and then approaches an asymptotic maximum removal rate at high concentrations. The model explains this by starting with the assumption that mechanical abrasion removes only tungsten oxide but not tungsten metal. It then focuses on the fraction of wafer surface covered by a tungsten oxide layer. At low oxidizer concentrations, the oxide formation rate is small compared the removal rate, so only a small fraction of the surface is oxidized and the removal rate is small. At high oxidizer concentrations, the oxide formation rate is large compared to the removal rate, so most of the surface is oxidized and the removal rate is large. Increasing the oxidizer concentration in the high oxidizer concentration region does not significantly increase the surface fraction of tungsten oxide, and the removal rate approaches a constant value.

This paper describes a new model, which analyzes the effects of the polishing conditions on nanotopography after polishing silicon (Si) substrates. The thickness uniformity of dielectric oxide-films after Chemical Mechanical Polishing (CMP) is affected by nanotopography of the Si substrate. Therefore, reducing nanotopography in Si substrates is essential in order to obtain highly uniform dielectric film thickness after CMP. We have developed a model based on Preston's equation for estimating the change in nanotopography of Si substrates due to polishing. In this model, various conditions relating to the structure of the polishing apparatus, the polishing pad material and the motion of the substrate can be taken into consideration. To investigate the influence of the polishing conditions on nanotopography, we compared experimental polishing results with calculations using this model. Thus, it was clarified that the generation of nanotopography in the polishing process that determines the final shape of the substrate, depends on the history of the pressure and contact distance produced during the process.

In spite of the fact, that the main purpose of CMP is the planarization of surfaces, most processes are optimized with respect to the removal rate. This might be due to a lack in techniques for the determination of the planarization behavior. The commonly used expression “Planarization Length” implies a maximum lateral extension over which the planarization is obtained and which can not be improved. Several attempts have been made to determine the planarization length by studying the CMP on different test patterns. The general problem in the interpretation of the data is the interaction of neighboring pattern with different pattern densities. This problem does not apply to the most simple pattern possible, which is a single step with an extension of the up and down areas much larger than the planarization length. In this case the spatial derivative of the resulting contour after CMP is directly the demanding transfer function to be used for the convolution. This concept, initially proposed by Boning et. al., was applied to evaluate the polish of copper and silicon oxide. Wafers with concentrically steps in Cu or SiO2 films with an extension of 1 to 5 cm have been prepared. During polish, the initially infinite steep step widens up, yielding the planarization length as a function of the removal respective the polishing time. Significant differences in the evaluation of the planarization length could be quantified depending on the pad, slurry and tool parameters. Our first experiments revealed a decrease in planarization length by the addition of BTA in a copper slurry. We believe that the SPR method enables a unambiguous, pattern independent determination of the planarization capability in CMP.