A completely new and novel electrolytic system, Injection Electrode (IE) assisted electrolysis, has been tried here to improve the quality of the silicon wafer surfaces generated by Electrolytic In-process Dressing (ELID) grinding process. The Experiments were conducted by varying the injection flow rate in order to perform extensive analysis on the effect of injection flow rate on the generated wheel surface condition and the consequent grinding performance. Experimental results showed that lower injection flow rate greatly improved the wheel surface condition resulting in superior ground surface qualities.

A dual-sensor single particle optical sensing method (SPOS) is described for the measurement of the large particle count (LPC) in fumed silica polishing slurries. LPC values were expressed on a silica sphere-equivalent diameter scale rather than a polystyrene latex-equivalent size basis. Linear correlations between LPC and scratch counts on SiO2 surface films for wafers polished under clean room and table-top CMP conditions are demonstrated. However, these correlations were obtained for a limited set of model slurries; and further investigation will be needed to assess the general applicability of dual-sensor SPOS for oxide scratch defect prediction in CMP slurries.

In this study, the effect of BTA on polishing behavior was investigated as functions of H2O2, slurry pH and abrasive particles. The addition of BTA effectively prevented Cu from etching by forming the passivation layer of Cu-BTA regardless of pH and H2O2 concentration in slurry. A thinner passivation layer was grown on Cu in BTA added slurry solutions with a higher contact angle of 60°. The dynamic etch rate, the removal rate with abrasive free slurry, also decreased when BTA was added in slurry at pH 2, 4 and 6. The removal rate of Cu was strongly dependent on types of abrasive particles in slurry. The larger hardness of slurry abrasive particles, the higher removal rates of Cu. The reduction of removal rates in BTA added slurry was determined by the competition between chemical dissolution rate and mechanical abrasion rate.

A stress based engineering model has been developed that predicts the removal rate profile across the wafer as a function of the principal and shear stresses on the wafer. The model reproduces the form of the radial variation in polish rate that is seen without back side air for the current set of consumable conditions and the changes in the polish rate profile that occur when back side air pressure is used on an IPEC-472 tool. The model which is GUI based and can be run in the fab, returns the optimum recipe setting to maximize polish rate uniformity based on the current tool performance. Implementing this model in production resulted in a 50% improvement in within wafer uniformity statistics.

Chemical Mechanical Planarization (CMP) has evolved as one of the most critical and significant process in the manufacturing of semiconductor devices. Copper has become the material of choice for the interconnect wiring. The effect of heat generation at the interface is realized to be significant on copper CMP process. The increase in the oxidation rate of the chemical reaction and viscoelastic properties of polishing pads due to increase in temperature at the surface results in increased removal rates and change in planarization performance. In this research, the effect of temperature on the CMP performance using two most common oxidizing agents, KIO3 and H2O2 has been investigated using the CETRTM bench-top CMP tester. The coefficient of friction at the interface of polishing using both the oxidizers at different temperatures was monitored. The generated surface roughness post CMP was evaluated for samples polished using different oxidizing agents at different slurry temperatures. The AFM study was carried out using Digital InstrumentsTM D3100 instrument. This study is aimed at understanding the effect of temperature on the CMP process performance and the relative sensitivity of two most common oxidizers used in copper CMP towards temperature.

A new application of the electrochemical method, in situ chronoamperometry, has been developed and used as a tool for CMP slurry characterization. The measured current response, i, resulting from a small applied potential is fit to an exponential equation, i = io + A1exp(-t/tD). The fitting parameters serve as a measure of surface reactivity (io), surface film robustness (A1), and the kinetics of film formation (tD). A description of the method and correlations to polishing performance are discussed in this paper.

For highly selective particle-based slurries or fixed abrasive pads, ceria has been identified as the abrasive of choice for the chemical mechanical polishing (CMP) step for shallow trench isolation (STI). The advantageous performance of ceria-based CMP consumables is usually attributed to enhanced chemical reactivity between ceria and oxide materials. In fact, this reaction is a central theme of all ceria polishing models from glass polishing to STI CMP. Previously, experimental evidence in support of the ceria-silica reaction during CMP was virtually non-existent. Recently, we proposed a pH-dependent ceria-silica polishing mechanism based on polishing results, in-situ friction force measurements, and spectroscopic and microscopic investigations. In this report, we have studied the chemical interactions between ceria and silica in the absence of particles using an atomic force microscope (AFM) and a scanning electron microscope (SEM). AFM silicon tapping mode cantilevers were functionalized by depositing a silica coating via chemical vapor deposition (CVD) and thermal oxidation. SEM imaging and compositional analysis was conducted on the cantilevers before and after wear against a ceria thin film, which was grown by pulsed laser deposition. The cantilever wear profile and elemental composition as a function of pH confirms our earlier polishing results and the pH-dependent CMP model for ceria-silica CMP.

EcmpTM is a revolutionary planarization technology uniquely combining removal rate controlled by charge with superior planarization efficiency in the near no shear regime. In addition, the electrochemical removal mechanism has excellent within-wafer profile control. Multiple electrical zones configuration combined with a precise end-point control by electric charge, make it more predictable to control the remaining thickness and profile of copper film. The factors affecting the planarization such as the concentration and the efficiency of the inhibitors will be discussed in this paper. Meanwhile a planarization mechanism for Ecmp will be proposed to match the high planarization efficiency. The effects of applied voltage on removal rate and planarization efficiency will be presented in this paper. The electrical feature allows Ecmp to be a planarization process with removal rate independent of down force, enabling a wide removal rate window based on applied voltage.

There is a need for metrology, characterization and optimization of CMP pad architecture before being put into service. psiloQuest, Inc. has developed a novel polishing pad which is made up of polyolefin material instead of conventional polyurethane. The surface of the pad has been modified to match the surface of the material under going CMP. In this research, we have optimized the PECVD tetraethylorthosilicate (TEOS) surface coating duration and pad thickness for optimum pad output. The pad was then extensively characterized using the several standard metrology techniques such as SEM, XPS and nanoindentation. The CMP performance evaluation of all the candidate pads was done using CETR CP-4TM bench top CMP tester. There was a correlation and interdependence of the pad coating time and surface chemical, micromechanical and tribological properties. However, their impact on the pad CMP performance was found to be indirect, if any. These findings were used to optimize the pad design and architecture before commercialization. The demonstrated methodology can also be implemented for parametric optimization of polishing pads with novel designs in the future.

Friction in the CMP process is a subject of ongoing interest. The sources of friction can be the viscosity of the slurry between the pad and wafer, as well as the physical contact between the pad asperities and the wafer. The contact between the pad and the wafer can be direct or also through slurry particles trapped between the pad asperity and the wafer. We measure the friction between the wafer and the pad by measuring the CMP table current and subtracting out the background level. This is done for different concentrations of silica abrasive between 0 and 13%, as well as for different pressures and table speeds. Two widely different types of silica particles used in CMP are spherical colloid particles and aggregated fumed particles. We also compare the resultant friction behavior by comparing the results for both types of particles. For different abrasive contributions, the friction measurements are compared to the CMP removal rates. This evaluation is also done with a stationary wafer carrier, so that the observed removal rate at a specific point on the wafer is proportional to the local pressure on the wafer. The wafer carrier used for these tests uses a gimbal design. In this case the pressure at the leading edge of the wafer is larger than that at the trailing edge. From these studies we find that, for gimbaled systems with grooved pads, the friction is primarily caused by pad-asperity contact, and the addition of slurry particles does significantly change the friction interaction in the CMP process. Further, the non-uniformity in friction across the wafer is controlled by the pad surface structure and mechanical design of the CMP tool.

The specification for the total thickness variation (TTV) of the device layers on thick-film silicon on insulator (SOI) wafers tighten for future applications. Therefore, the bulk removal polishing process of current technology after grinding cannot meet the demands in terms of flatness. The currently required amount of material removal for polishing out the induced sub surface damage (SSD) of the grinding is very high. Additionally, slurry-based CMP processes show unsatisfactory grindline and topography removal. This in turn reflects negatively to processing times, throughput and overall flatness performance.

Encouraging early results of FA pad use for silicon and SOI polishing have already been further developed [1]. Low SSD grinding has been introduced to silicon manufacturing [[1]]. In this work, an integrated manufacturing process sequence is presented. Starting from low SSD grinding of the bonded SOI wafer couple, an optimized FA CMP step is replacing the conventional bulk polishing with reduced removal. The SSD after FA CMP is investigated by oxide induced stacking fault (OISF) method [[2]] and results are used to adjust the final polishing step of the substrates. The overall process sequence is highly advantageous in terms of performance in TTV and provides a highly competitive and effective method for achieving best possible surface quality with minimized total silicon removal. This method is not only useful for SOI wafers but also in other areas of silicon processing.

The role of the molecular structure - different functional groups, the length of the carbon chain and the relative positions of different functional groups – of several complexing/chelating agents (acetic acid, glycine, ethylene diamine, succinic acid, alanine and amino butyric acid (ABA)) in controlling copper (Cu) removal rates was investigated. The results are consistent with the known activity of –COOH groups at acidic conditions and that of –NH2 groups in an alkaline environment. In comparison with glycine, it was also observed that an increase in the carbon chain length increased the removal rates at acidic pH values and decreased the removal rates at alkaline pH values. Also, Cu removal rates decreased with an increase in the distance between the –NH2 and –COOH groups in an amino acid at all pH values except at 4.

The adhesion force of pad and alumina were experimentally and theoretically investigated in slurry solutions of different pHs. The isoelectric point (IEP) of pad particles was measured to be around pH 3. The wafer surfaces showed negative zeta potentials in the investigated pH ranges with exception of FSG and Ta. Cu and Ta showed higher interaction forces than dielectric materials. The lowest adhesion force was measured between pad particle and wafer surfaces in a slurry solution of pH 11. The magnitude of adhesion force of pad particles was lower than alumina particles.

The synergistic roles of chemical dissolution and mechanical abrasion on the material removal mechanism during CMP process are explored. A set of nano-wear experiments are conducted on electro-plated copper surfaces with systematic exposure to active slurries. Initial results of in situ wear test in chemically active slurry showed an increased material removal rate (MRR) relative to a dry wear test. To understand the synergistic effects of chemical dissolution and mechanical abrasion, we have investigated two plausible mechanisms of material removal. Mechanism-I is based on chemical dissolution enhanced mechanical abrasion. A soft layer of chemical products is assumed to be formed on top of the polished surface due to chemical reaction with a rate much faster than the mechanical abrasion rate. It is then followed by a gentle mechanical abrasion of that soft layer. An increase in the MRR of up to 100% is identified based on the etching time and the down force. Mechanism-II is based on mechanical abrasion accelerated chemical etching. In this case, the nano-wear experiments are first performed to generate local variation of the residual stress levels, and then followed by chemical etching to investigate the variation of the wear depth and the evolution of surface topography due to etching. It is found that the residual stress caused by the mechanical wear enhances the chemical etching rate, as manifested by the increase of wear depth. The developed understanding from these experiments can be used in future studies to control the rates of chemical dissolution and mechanical abrasion as well as investigating the various process-induced defects.

One of the major drawbacks to CMP is the tendency for abrasive particles in slurries to form aggregates, which have the potential to cause defects on wafer surfaces. Therefore, it is crucial to understand the mechanisms by which aggregates are formed so appropriate metrology can be implemented that will identify defect-causing slurries before they are used in the fab. Single particle optical sensing (SPOS) techniques are commonly used to obtain large particle counts (LPC) for slurries. The SPOS technique requires slurry dilution before measuring and the instrument continues to dilute the sample during a measurement. Other techniques that can be used to characterize slurries are particle size distribution by static light scattering (SLS), mean particle size (MPS) by dynamic light scattering (DLS), and zeta potential (ZP) measurements. Like SPOS, all of these techniques require that slurry be diluted prior to measuring and the current method for doing so is with UPW. Diluted slurry demonstrates significantly different ionic strength than the undiluted slurry, and electrolyte concentration has been shown to affect aggregation and electric double layer characteristics of silica particles 2–6. An alternative diluting solution was formulated that simulates the conductivity and pH of the original slurry to mimic the conditions to which particles are actually exposed. It is crucial to identify the metrology that is compatible with high pH solutions and the impact of these solutions on measurements. A second objective of the study is to examine aluminum contamination in slurries. To date, the aluminum content of silica-based CMP slurries and effects on performance have not been well studied. Aluminum is known as a potential contaminant during abrasive and/or slurry manufacturing processes. Known defect free slurries were doped with aluminum and effects on particle aggregation were observed. Specifically, it is of interest to identify the metrology and techniques that may be useful (and those that are not) in monitoring aluminum induced aggregation.

In this study, the interaction between several kinds of surfactants and copper surface was examined to control the dissolution of copper during CMP. Among those surfactants, sodium dodecylsulfate (SDS), one of the conventional anionic surfactants, showed effective interaction with copper and significantly suppressed the dissolution of the copper at acidic and neutral pH ranges in a model copper CMP slurry system consisting of 3 wt% fumed silica, 1 wt% glycine, and 5 wt% hydrogen peroxide in deionized water. The inhibition performance of copper dissolution by SDS is better than that of Benzotriazole (BTA), a conventional inhibiting agent of copper dissolution in a copper CMP slurry.

Delivery systems are often used to supply the slurry used to planarize wafers during semiconductor chip manufacturing. These systems pressurize the slurry to deliver it to the tools and circulate it to help keep the particles in suspension. Pressurization and circulation are accomplished by various means including a variety of pumps and pressure-vacuum technology. Typically, slurry passes through a distribution system approximately 100 times before it is used to polish wafers[1].

The interaction of the wafer, slurry and pad determines the material removal rate during Chemical Mechanical Planarization (CMP). Dual emission laser induced fluorescence (DELIF) provides a means to measure the slurry layer thickness between the wafer and a Fruedenbergy FX9 pad during CMP with high spatial (4.3 μm/pixel) and temporal resolution (2 Hz). In this paper we present some preliminary measurements of pad compression using DELIF to measure the standard deviation of asperity height. Static slurry layer images were captured at high (70 kPa) and low (0 kPa) down-force applied to the wafer. In-situ, dynamic images at 10 kPa downforce applied to etched wafers were imaged. Two wafers were etched such that they contain square wells, one wafer with 27 μm and the other will 14.5 μm deep wells. In the static case, asperity compression is directly related the amount of fluid displaced. In the dynamic case, asperity compression is 35% greater under the 27 μm wells than the 14.5 μm wells.

Among various properties of chemical mechanical polishing (CMP) slurry, selectivity plays a key role in global planarization of high density and small pattern size shallow trench isolation (STI) process. Lack of adequate selectivity can lead to defects such as dishing and erosion. To improve the selectivity of STI CMP process, CMP characteristics of silica and silicon nitride wafer were investigated using colloidal silica slurry as a function of slurry pH. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added to increase the selectivity of the slurry. As a result, selectivity increased from 3 to 25. It was concluded that selective passivation layer formed on silicon nitride wafer surface at acidic slurry pH range was responsible for the observed selectivity increase. Adsorption characteristics of SDS on silica and silicon nitride were measured as a function of slurry pH and concentration of SDS. As indicated by zeta potential behavior under acidic pH conditions, SDS adsorption on silicon nitride was significantly higher han silica due to the electrostatic forces. Significantly higher SDS coating on silicone nitride seems to have resulted in lubrication layer leading to increased polishing selectivity.

Glass substrate has superior shock resistance and higher stiffness for increased rpm and access time than Al/NiP substrate. The main barrier for the use of glass instead of Al/NiP in desktop computers has been the high cost of the glass substrate, which is mostly caused by its need for a long polishing time. Developing a glass CMP slurry that can deliver a higher polishing rate and fewer surface defects is a continuous challenge in the disk industry. We recently discovered that adding montmorillonite particles into a ceria-based glass CMP slurry can significantly increase the polishing rate without sacrificing the surface smoothness. It is the first time, to our knowledge, that this strong synergistic effect between ceria and montmorillonite particles was reported in the glass CMP area. Several physical properties of the ceria- montmorillonite slurries, such as viscosity, zeta potential, and particle size, are characterized in order to understand the mechanism of the synergistic effect.