With shrinking interconnect dimensions, as a result of scaling, resistance variations in percentage terms are increasing. Quick and reliable measurements on the interconnect structures are the first step to the detection and implementation of a process-control strategy in order to reduce process related variations. This paper discusses the application of Optical Digital Profilometry (ODP) to the measurement of BEOL parameters, specifically the measurement of post copper-CMP metal dimensions with the intention of understanding CMP related contribution to resistance variations. Traditionally a combination of electrical test, optical metrology and profilometry is needed to understand the contribution of CMP to the interconnect and inter-layer-dielectric (ILD) dimensions. This paper discusses the successful use of ODP to model and measure the dimensions of both the metal and the dielectric in nested patterned structures with different pattern densities for a single level patterned build. Hence this technique could potentially simplify and replace multiple measurement techniques and help in quickly providing relevant information for process monitoring and control.

Novel 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.

Experiments and simulations were performed to investigate the characteristics of staining on pad surface. Experiments were performed on a table-top axisymmetric polishing system, consisting of a 12-inch non-rotating platen and a 4-inch rotating wafer carrier having the same center axis. Results showed that the stain deposited on each land area was found to be darker in the direction of wafer rotation and in the radial direction, suggesting that staining agent was produced by mechanical action during polishing and was advected downstream by the slurry flow. Generally, staining increased with polishing pressure, wafer rotation rate and polishing time. The simulated slurry velocity showed shear flow on the land areas and wafer-driven circulation in the grooves. Thermal model simulation showed 12 degree temperature rise on the reaction at the surface of wafer.

In this study, Ruthenium (Ru) chemical mechanical planarization (CMP) slurry was studied and developed to apply it for the formation of Ru bottom electrode in DRAM capacitor. An acidic chemical was chosen as both oxidant and etchant. The effects of the chemical on polishing and etching behavior were investigated as functions of chemical concentration and pHs. The static etch rate of Ru increased with increase of chosen chemical concentration. Also, thin Ru oxide was generated in chemical solution. The highest etching and removal rate were obtained in slurry of pH 6. Ru over etching was generated due to the high etch rate of Ru, and then good planarity was not obtained. However, because Ru over etching was prevented due to low etch rate of Ru, the plarnarity and isolation of each capacitor in slurry of pH 9 was acquired successfully.

Slurries with ceria abrasives are nowadays widely used for high-end applications like STI. Concerning the pattern dependence of planarization, such slurries exhibit a much more complex behavior than conventional silica-based slurries. The situation is complicated by the fact that depending on often unknown factors like the manufacture of the ceria abrasives and additionally present additives the observed phenomena are also quite diverse. As a consequence, quantitative models are lacking and predictions of post CMP topography that could be used e.g. to derive design rules or optimize dummy fill are not available.

We here present detailed experimental results on one specific slurry system with ceria abrasives that behaves very different from conventional silica-based slurries. Possible causes for this peculiar behavior are discussed to the extent that a statement about their relevance can be made.

A contact model for a single spherical (pad) asperity and a flat (wafer) surface, with an interface filled with spherical (abrasive) particles is introduced. Finite element method is used to determine the deformation characteristics of a single spherical abrasive indenting a hyper-elastic pad material. The asperities in Greenwood and Tripp (GT) model, which is widely used for the contact of rough spheres, are replaced with the spherical particles. Relations are developed to predict pad-to-particle-to-wafer contact in two distinct regimes, where a) pad and the wafer are separated by the particle; and b) all three bodies come in contact simultaneously. The results of the model show that the abrasive particles in the (pad) asperity-wafer interface causes the contact to be distributed over an area larger than that predicted by the Hertz model, while the maximum contact pressure becomes relatively lower. The fraction of the load carried by pad-to-wafer and pad-to-abrasive-to-wafer varies along the contact interface of the pad asperity and wafer.

A laser light scattering technique was used for the identification of defects on silicon dioxide (SiO2) wafers polished with a tungsten CMP slurry. Defects were then classified as scratches and particles using scanning electron microscopy (SEM). The effects of the incident beam illumination and scattering geometry on the defect detection are examined. Appropriate experimental conditions for selective detection of scratches and particles are discussed in conjunction with the estimated defect count and fractional ratio for specific defect types and sizes. The findings are qualitatively consistent with predicted light scattering distributions simulated from silicon bare substrates.

In order to reduce microscratches and obtain minimized dishing and erosion, we have developed new abrasive-free Cu CMP slurries. During the development of these slurries, some electrochemical examination was performed. The most effective knowledge was obtained through the analysis using rotary Cu disk electrode under pressure. On the basis of these studies, new abrasive-free Cu CMP slurries with a high removal rate and excellent planarity were designed and developed. The mechanism of reducing dishing and erosion was also discussed.

Scanning probe microscopy has been widely used to evaluate surface microroughness on Si wafers after chemical mechanical polishing (CMP) processes. In this article, we utilize atomic force microscopy (AFM) combined with laser light scattering to detect nano-scale surface defects called microscratches on CMP-finished Si wafers. We find that most microscratches detected by the combined method are very shallow trenches with widths and depths of 80–200 nm and 0.1–0.2 nm, respectively. The dependence of scattered-light intensity on the size of microscratches agrees with theoretical calculations within one order of magnitude.

Commercially-available WCMP slurries perform differently under diverse modifications: pH variations, dilutions, ageing, etc. In order to understand the physico-chemical basics of the mechanism and selectivity of these slurries, we have performed a number of measurements, including determination of effective CMP removal rates on blank and patterned wafers. The results of the performances of the different modifications have been compared, and a few optimized conditions and recipes derived. Our results surprisingly show that pH has a much greater influence on the removal rate of tungsten and silicon dioxide than the particles content, and that the way a certain pH is reached (or maintained) significantly affects the performances of the prepared slurries.

We propose that nitric acid can be used to dilute selective slurries in order to keep high removal rates. Indeed, diluting slurries with an acidic solution of the same pH maintains particle charges far from zero, and keeps oxidizing conditions stable. However, the effects of the acidic dilution of the slurries include a slight reduction of removal rate and a decrease in defect density

Total contact area between a CMP pad and wafer has emerged as a fundamental property that is directly linked to both removal rate and defectivity. Contact area has been shown to depend on surface morphology as it results from pad microstructure and material properties. Pads exhibiting higher contact area, hence imparting lower point stresses to the wafer, are effective in reducing CMP-related defects. The present study quantifies pad-wafer contact characteristics for both hard and soft porous polyurethane pads as a function of the extent of diamond conditioning. An Instron microtester is used to impart controlled quasi-static pad compression against a sapphire cover slip mounted on a Zeiss confocal microscope. Images collected through the microscope at discrete compressive states are analyzed off-line to quantify the total contact area and the size, shape, and distribution of individual contacts. A relationship is then established between these contact measures and the extent of conditioning. Conditioning decreases the mean asperity contact size as expected, but the evolution of contact regions shows non-intuitive features. In particular, total contact area passes through a minimum within the typical conditioning time of commercial CMP processes, then gradually increases. Clustered contact regions observed at short conditioning times spread out to a more uniform lateral spacing at longer conditioning times. These findings are accounted for by considering the texture subdivision achieved by individual diamonds together with bridging by the conditioning disk of higher regions on an unlevel pad surface. Textures produced by different conditioners on the same pad are quantified in terms of total contact area and number and uniformity of contact points. Formation of an ideal texture of abundant, well-spaced and level asperities is expedited by both conditioner type and treatment time. The results illustrate that evolution of pad contact area under compression is an essential measure for understanding polishing metrics such as wafer removal rate, defect count, and pad wear, and indicate clear direction for next-generation pad microstructures to achieve low-stress planarization.

There are several technology developments, which should have been completed in CN 65 nm (Commercial node) device development, but passed over to CN 45 nm device development. Seven items relating with damascene process, especially connecting with planarization process, are nominated and introduced herein including new advent technologies as enabling solutions for CN 45 nm. First one is low-down-force planarization. Although there are several planarization technologies such as CMP (Chemical Mechanical Polisher), ECMP (Electrical Chemical Mechanical Polisher), ECP (Electrical Chemical Polisher), CE (Chemical Etching) and those combination technologies, it is not decided which is the best one and how low down force is optimized taking into account of CoC (Cost of Consumable) issues. In this report, all planarization technologies are explained using ‘General Principle governing all planarization technologies’, and allowable down force is suggested through stress analysis and fracture toughness analysis. Second one is direct polish on ULK. There may be two approaches. One is to adopt CMP hard mask which dielectric constant would not be changed by direct polish. In this case, non-uniformity of CMP in this hard mask is important. Second is to polish directly on ULK, which dielectric constant would be changed by CMP, then restoration technology should be discussed at a same time. Third one is Ru liner application. When is this technology required? Deposition for Ru seed and polishing of Ru integration are reported. Forth one is watermark free drying of ULK. Vacuum drying and IPA drying (Rotagoni) which is necessary for hydrophobic surfaces are reported. Fifth one is cleaning technologies for less than 45 nm FM. After CN 45 nm, it is difficult to distinguish several defects such as scratches or FM. In this case, soft cleaning methods such as non-contact cleaning would be required. Cavitation jet as one of non-contact type cleanings is reported with its cleaning results. Sixth one is Co-W cap process. Electro-less metal cap technology in order to enhance EM is reported. CMP after Co-W deposition may be useful in order to clean cap surfaces. Seventh one is starting material such as nanotopography and roll off which would affect on CMP performances.

The reduction of wafer scratching is a key goal driving the commercial development of CMP slurries. To better understand the underlying abrasive particle properties critical to the scratch performance of ILD CMP slurries, the scratching behavior of ceria slurries prepared with a range of particle size characteristics are characterized. Scratch results are presented and two effects are proposed to account for the findings. The Removal Rate Effect relies solely on the observed inverse proportionality between scratching and removal rate. This interpretation is consistent with a simple surface balance of scratches but suggests that removal rate differences dominate scratch performance. The Managed Tail Effect considers the effect of particle characteristics on both the creation and the removal of scratches. For a given particle population, the larger particles are assumed to dominate scratch creation. However, larger particles are also seen to drive removal rate which affects the removal of scratches during polishing. This interpretation implies that optimal scratch performance for a ceria ILD CMP slurry will be obtained when the width of the ceria particle's size distribution is optimized relative to its mean.

Post CMP cleaning is necessary for contaminant removal after CMP process. The zeta potential of slurry particle and substrate has been considered to be a critical factor in terms of particle adhesion and removal. The fundamental research such as the calculation and measurement of adhesion forces between slurry particle and wafer surfaces can enhance the understanding of cleaning mechanism and development of cleaning process. The presence of more than two different materials during CMP introduces new defects at the materials interface, corrosion and severe scratches. Device specific chemistry and cleaning process should be introduced and developed for future and current CMP. The highest particle removal efficiency is observed when using cleaning solutions that yields the lowest adhesion force. The effect of frictional and adhesion forces attributed to slurry particles on the quality of Cu surfaces was experimentally investigated during metal CMP process. The magnitude of the adsorption of the organic acid on the slurry particle surfaces can have a significant effect on the frictional behavior as well as the adhesion force. Higher particle adhesion forces resulted in higher friction and might induce defects such as particle contamination and scratches on the polished surface after polishing. The magnitude of particle adhesion force on wafer surfaces in slurries can be directly related to the frictional forces and polished surface quality during CMP process. As low k and poly or bare silicon polishing introduced in fabrication process, the hydrophobicity of these surfaces could affect the defects after polishing. The control of wettability during and after polishing becomes more important in reducing the defects. The organic particles are major defects during metal and poly silicon CMP which may be caused by the surface reaction of organic sources with surfaces.

Colloidal probe technique has been widely employed to measure the adhesion between micro- and nanosize objects using atomic force microscopy (AFM). However, majority of studies concerns model systems, which do not incorporate real abrasive particles. The approach applied allows measuring adhesion between real CMP nanoparticles and different surfaces. Thin polymer film with high affinity to the particles was used to anchor the particles to a surface. Hollow glass bead (20-30 μm) representing flat surface was attached to soft AFM cantilever. Application of large hollow bead and the cantilever with small spring constant allows measuring the interactions with high sensitivity. Titanium, tungsten and tantalum metals were sputtered on the bead surface. The effect of different factors such as pH value, concentration and type of a surfactant on adhesion between surfaces of metals and silica slurry has been studied. Character and intensity of interactions at the moment of contact have been evaluated from experimental force-distance curves.

In this study, different amounts of standard fumed silica and fumed silica contaminated by coarse particles was added as powder to a standard copper CMP slurry to investigate their effects on large particle count, mean particle size, slurry viscosity, frictional force during wafer polishing, and copper removal rate. Standard silica powder consisted of the same particles used in the standard slurry while contaminated silica powder consisted of the same particles used in the standard slurry and additional large size particles. Large particle count analysis indicated that slurry dispersion itself generated large size particles in the slurries. The addition of 0.3% and 1% contaminated silica to the standard slurry caused significant increases in large particle count, and the mean particle size increased with the amount of contaminated silica added to the standard slurry. The slurry viscosity generally increased with the amount of standard and contaminated silica added to the standard slurry under the shear rate of 100 s−1. The standard slurry and slurries added with 0.3% and 1% contaminated silica were used to polish 200-mm blanket copper wafers on the APD-500 polisher that has the unique ability to measure frictional force in real time during polishing. The coefficient of friction increased with the amount of contaminated silica added to the standard slurry. In general, the removal rates for the slurry added with 1% contaminated silica were higher than the standard slurry and slurry added with 0.3% contaminated silica.

This paper describes the fabrication and calibration of micromachined shear stress sensors intended for characterization of the local pad-wafer contact forces present during chemical-mechanical polishing. Sensors consist of arrays of microfabricated poly-dimethyl-siloxane (PDMS) posts and are able to measure forces ranging from 2 to 200 μN. The posts are 100 μm high and have diameters of 40-100 μm. Calibrated post deflection sensitivities are linear and lie between 0.2 μm/μN and 1.3μm/μN. Sensor design, fabrication, and calibration are detailed. Feasibility is established for sensor integration into a CMP scale model test setup, including an optical viewing method for observing post deflection during polishing. Initial micrographs of post deflection during polishing do not yet have sufficient resolution to determine the microscale forces during polishing.

The design of nanostructured materials like CMP slurries on an industrial scale requires the control of disperse systems of nanoparticles as well as of single isolated "bad" particles . It is well known that slurry abnormalities resulting from large abrasive particles and abrasive particles agglomeration can cause defects on wafer surfaces during CMP.

Particle-particle interactions generate secondary nanometer structures, clusters or agglomerates, which can dominate the relevant properties of the bulk material. Size and structure of these particle agglomerates/structures are the result of a dynamic equilibrium between agglomeration and desagglomeration. There is still a lack of understanding of these secondary soft nano- up to micro- particles because no adequate characterization methods are established.

Dilution and other preparation treatment to enable analysis by laboratory methods like TEM or AFM will distort the interparticle forces and will generate artifacts. Hence characterization methods are under investigation which can tolerate a high number of particles in the sensing zone. These high concentration methods often deliver ambiguous results. Consequently different physical principles have to be combined to get unambiguous information on the disperse state.

Performance characteristics of ultrasonic spectroscopy, photon correlation spectroscopy, analytical photo-centrifugation method combined with the high spatial resolution as well as special single particle optical counters are discussed on examples.

Leading edge integrated circuits (ICs) are complicated structures designed to have up to 3 capping layers above a low k dielectric material. The upper capping layer may use TEOS and/or silicon nitride (SiN), while the lower one may use silicon carbon nitride (SiCN), silicon carbide (SiC), or carbon doped oxide (CDO) immediately above the low k dielectric. Therefore, a barrier slurry for copper CMP, in addition to exhibiting a high removal rate of the barrier, must be able to remove the upper capping layer and stop at the underlying dielectric surface.

We have developed a slurry family that can effectively remove TaN, TEOS, SiN, CDO, and/or SiCN, or any combination of these films, or can stop at any one or two film surfaces of TEOS, SiN, CDO, SiCN, and SiC, depending on the specific slurry design. Removal rate control is achieved by one or two additives. One of the additives is an anionic surfactant. When selecting a surfactant, the surfactant hydrophobicity and charge interaction between the surfactant and the wafer surface are two important factors to be considered. This report discusses these two factors in selecting a proper surfactant for a specific slurry application.

Asperity-scale pad deformation and dynamic pad-wafer contact area are crucial to the fundamental understanding of material removal and defect formation mechanisms in CMP. Pad asperity stress and strain are also central to characterizing pad wear rate during polishing and cut rate during conditioning. While it is very difficult to isolate and measure stress and strain in individual asperities, finite element modeling may be used in conjunction with experimental surface characterization to predict asperity-scale deformation and pad-wafer contact. Asperity sub-domains up to 1270 microns across are reproduced from three-dimensional point cloud data on porous polyurethane CMP pads obtained by confocal microscopy, meshed to high resolution, and analyzed using ABAQUS finite element software. Physical properties are derived from dynamic mechanical experiments. Pad stacks are simulated both with and without sub-pads. Results show that while a sub-pad increases pad-wafer contact area overall, it limits the local spreading of individual contact regions as polishing load increases. This finding identifies a direct mechanical origin of the trade-off in pad design between wafer-scale and die-scale planarity. As expected, the real contact area between a pad and wafer is much smaller than the cross-sectional or “bearing” area, but the difference is notably greater when a sub-pad is present. Values of asperity stress and strain under typical CMP polishing pressures reveal that plastic deformation takes place both on and beneath the contacting surface. Hence upon release of the polishing load the asperities do not fully rebound to their pre-compressed shapes. Each pass under the wafer thus reshapes the pad asperities such that a slightly different texture is presented upon the next pass. These deformation mechanics clarify the impact of top pad and sub-pad properties on real contact area, allowing better optimization of CMP pad performance.