Trench Isolation Chemical Mechanical Planarization Research Articles

Restricted hydrolysis reaction of Si3N4 via nonionic polymer adsorption in advanced shallow trench isolation chemical mechanical planarization

The adoption of ultra-fine nanoparticles as an abrasive has garnered notable attention in shallow trench isolation (STI) chemical mechanical planarization (CMP) due to its potential in scratch reduction. However, the poor removal rate, attributed to the physicochemical interaction between abrasive and conventional organic passivation agent, limits the introduction of ultra-fine nanoparticles. Here, a nonionic polymer polyvinyl alcohol (PVA), without particle interaction, is proposed as a novel passivation agent to restrict the hydrolysis reaction of Si3N4 film in the advanced STI CMP process. The selective adsorption of PVA onto the Si3N4 film lowers its removal rate by suppressing the hydrolysis reaction via hydrogen bonding while the removal rate of SiO2 film remains constant. Moreover, the uniformity of SiO2 removal is improved due to the enhanced fluidity of slurry, resulting from increased wettability between pad and slurry. As a result, the removal selectivity between both films has been improved to 113.4:1 and the in-wafer-uniformity (IWU) of SiO2 film is supplemented by 96.8 % simultaneously.

Evaluation of a Photosensitizer Redox Couple for Oxide Removal Rate Tunability in Shallow Trench Isolation Chemical Mechanical Planarization

As technology continues to expand beyond that predicted by Moore’s Law the need to alter chemical mechanical planarization (CMP) processes to meet consumer demands is critical. To achieve higher oxide material removal rates (MRR), slurry formulations have become more complex by implementing rate enhancing additives to increase the slurry’s chemical activity. However, the modulation of MRR in situ requires changes in mechanical parameters, such as downforce, platen speed, and flow rate. These parameters effectively increase the chemical activity of the slurry; however, they can result in greater defectivity due to increased shear force. Therefore, this work employs the use of a photosensitizer redox couple to tune MRR using an external stimulus (i.e., light). Specifically, Rose Bengal (RB) is used to disrupt the adsorbed O2 equilibrium at the CeO2 surface via 1O2 generation. A secondary redox additive is employed to trap the 1O2 thereby preventing readsorption and increasing the number of active surface sites necessary for enhanced MRR. This photosensitized mechanism is supported through the correlation of CMP performance (i.e., MRR) to analytical measurements (i.e., 1O2 generation, contact angle, and quartz crystal microbalance (QCM)) with and without the presence of irradiation.

Role of Molecular Structure on Modulating the Interfacial Dynamics for Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP) Applications

As feature sizes continue to shrink well beyond the 7 nm node, understanding the delicate balance present in the chemical mechanical planarization (CMP) process is of utmost importance. In order to achieve high through-put and defect-free CMP processes it is critical to develop predictive analytical techniques that directly correlate to macroscopic STI CMP performance metrics (i.e. oxide/nitride removal, defectivity, and dishing/erosion). This work employed a suite of techniques to monitor the CeO2 nanoparticle interfacial redox processes in the presence of structurally diverse rate modulating additives. Specifically, utilizing a UV–vis spectroscopic technique, the Ce3+/Ce4+ ratio in the presence of different slurry additives was monitored and proved to directly correlate to removal rate performance (i.e. an increase in Ce3+/Ce4+ ratio shows an increase in rate). This finding coupled with the rate of dissolved O2 evacuation and a modified QCM technique determined the mode of interaction/adsorption which validates that the mechanism of oxide removal does not strictly depend on redox capacity, but also depends on the dynamic O2 equilibrium at the CeO2 nanoparticle surface. It was determined that the modulation of oxide removal was directly related to the distribution of interactions (i.e. steric vs redox) and was highly dependent on the slurry additive functionality.

Engineering Surface Texture of Pads for Improving CMP Performance of Sub-10 nm Nodes

Shallow trench isolation (STI) chemical mechanical planarization (CMP) will continue to be a critical step in the device fabrication of future technology nodes. A CMP process needs the right combination of pad, slurry, and pad conditioner to be able to deliver the best performance. Engineered pad surface along with usage of non-Prestonian ceria slurries can be used to solve key STI CMP challenges. Herein, it is demonstrated that relative to a reference pad, reducing and optimizing pad surface roughness, can help improve material removal rate by 26%–95% at different wafer pressures, lower the dishing by 34%–51% for feature size of 50–200 μm, thereby leading to an improved planarization performance. This work illustrates that the surface texture of a pad can be used to achieve a stable dishing range over different feature scales for various over polish times. Also, optimizing the pad surface roughness minimizes slurry consumption by 33% and enables polishing at a lower downforce. Further, it is demonstrated that relative to a reference pad, defectivity can be improved up to 85% for the pad without impacting the planarization performance by reducing the pad material hardness and polishing at an optimized pad surface roughness.

Correlating Shear Force and Coefficient of Friction to Platen Motor Current in Copper, Cobalt, and Shallow Trench Isolation Chemical Mechanical Planarization at Steady-State Conditions

In a follow up from our earlier work that focused on highlighting the relationship among platen motor current (PMC), shear force (SF), and coefficient of friction (COF) in non-steady-state cases, we examined whether PMC was a reliable indicator that could be used in place of SF and COF data at steady-state conditions. For the 12 cases studied, we examined 60 distinct steady-state steps from their associated Stribeck+ curves. Data averaging, coupled with a trend matching algorithm, showed that for large time spans at steady-state, PMC was a reasonably good indicator of both SF and COF, as 68.5% of the time, PMC and SF trends matched (ranges between 62% to 86%) for all 60 cases. Regarding PMC and COF, we observed trend matching for 68.8% of the time (ranges between 62% and 86%) for all 60 cases. However, correlations between SF and PMC, and also between COF and PMC were found to be very poor (in most cases, non-existent) since at small timescales PMC was not sensitive enough to capture the instantaneous stick-slip occurrences and other important tribological and fluid dynamics phenomena present in CMP.

Development of “Soft” Cleaning Chemistries for Enhanced STI Post-CMP Cleaning

Due to the emergence of sub-10 nm technologies, limiting device defects has become of utmost importance in maintaining high performing integrated circuits. Shallow trench isolation (STI) chemical mechanical planarization (CMP) uses a synergistic balance of ceria (CeO2) nanoparticles and functional chemistry to modulate critical surface adsorption interactions necessary to remove excess topography. Literature has identified that the surface redox state of the CeO2 nanoparticle (Ce3+/4+) is a critical factor in controlling CMP performance. More specifically, controlling the oxygen vacancies has been shown to directly impact removal rate (Ce3+ state), as well as post-CMP cleaning efficiency (Ce4+ state). Current post-CMP cleaning processes utilize oxidation/reduction reactions, etching, encapsulation, and ultrasonic methods as a means of undercutting the particle from the substrate surface. These methods have proven to be highly effective at particle removal but have shown to potentially induce further defectivity due to the aggressive cleaning conditions. This work aims to develop a post-CMP cleaning chemistry that enhances particle removal via soft encapsulation of undesirable nanoparticle/slurry chemistry non-covalent complexes on the wafer surface. By employing a polyelectrolyte/surfactant (PES) matrix, a surface adsorbing/charge-flipping encapsulation process is proposed as a vehicle to remove slurry contamination at low friction. Investigation into the synergy between slurry chemistry and PES cleaning chemistry, with respect to defect aggregate formation, was correlated to the cleaning efficiency as well as friction. Techniques were developed to study real-time properties such as the defect aggregate formation mechanism via in-line dynamic light scattering (DLS), coefficient of friction (COF), particle removal, and scratch defectivity to draw a correlation between cleaning chemistry structure and post-CMP performance.

Development of “Soft” Cleaning Chemistries for Enhanced STI Post-CMP Cleaning

With the rapid miniaturization of advanced technologies, limiting device defects has become of utmost importance in maintaining high performing integrated circuits. Shallow trench isolation (STI) chemical mechanical planarization (CMP) uses a synergistic balance of ceria (CeO2) nanoparticles and functional chemistry to modulate surface adsorption interactions necessary to remove excess topography. This work aims to develop a post-CMP cleaning chemistry that enhances nanoparticle removal via “soft” encapsulation by employing a polyelectrolyte/surfactant (PES) matrix. A surface adsorbing/charge flipping encapsulation process is proposed as a vehicle to remove slurry contamination at low friction. Investigation into the synergy between slurry chemistry and PES cleaning chemistry, with respect to defect aggregate formation, was correlated to the cleaning efficiency as well as friction. Using a suite of techniques to study the real-time defect aggregate formation mechanism it was determined that the supramolecular structure is critical to balance defect forming events with enhanced cleaning efficiency.

Role of Additive Structure on Controlling Ceria/Substrate Interactions Relevant to Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP)

Chemical Mechanical Polishing (CMP) has emerged as a critical process step for achieving global planarization in advanced integrated circuit manufacturing and has lead to the extension of Moore’s Law. Specifically, Shallow Trench Isolation (STI) CMP is used in the electrical isolation of the active components in an integrated circuit by actively removing TEOS and stopping on Si3N4 to achieve angstrom level uniformity and limit defectivity. Planarization of the overburden material is achieved through a balance of an applied mechanical force and the delivery of a colloidal dispersion (slurry) containing ceria (CeO2) nanoparticles, complexing additives, and rheology modifiers to the substrate surface. Currently, STI slurries contain chemical additives that selectively boost material removal rate (MRR) as well as enhance selectivity via non-covalent passivation films formed at the polishing substrate surface. A crucial factor in maintaining a high MRR is the presence of CeO2 surface oxygen vacancies, commonly associated with Ce3+surface oxidation state, which can be achieved either from pre-dispersion particle processing or though additive/nanoparticle surface reactions present in the slurry formulation. This study probed the impact of the slurry additive functionality, such as carboxylic acids, amines, and phenols, on the removal rate and post-CMP defectivity. Results suggest that the Ce3+ oxidation state is critical to performance but the Ce4+ oxidation state is also a viable reaction site as long as it remains uncomplexed and free of any site-blocking additives. The additive adsorption to the CeO2 surface will result in altering the dynamic interplay of the abrasive particle/chemistry at the substrate surface shifting CMP performance. Employing and correlating a suite of modified analytical methods, such as atomic force microscopy (AFM), electrochemical quartz crystal nanobalance (EQCN), dynamic contact angle measurements, fluorescence microscopy, pre/post characterization of particle properties (size and zeta potential), and dynamic contact angle, a strong correlation between surface energy and CMP performance metrics has been uncovered.

Correlating Shear Force and Coefficient of Friction to Platen Motor Current in Copper, Cobalt, and Shallow Trench Isolation Chemical Mechanical Planarization at Highly Non-Steady-State Conditions

In this study we determined the relationships that exist between the coefficient of friction (COF) and platen motor current (PMC), and also between shear force and PMC at highly non-steady-state conditions during chemical mechanical planarization (CMP). For the 12 cases studied (8 for copper, and 4 for dielectric CMP including one as a cobalt buff step), we found that real-time PMC data closely mimicked shear force data as evident from high average values of correlation coefficient and coefficient of determination for all 12 cases (0.913 and 0.835, respectively). As for COF vs. PMC, average correlation coefficient and coefficient of determination for Cases A through D were 0.949 and 0.900, respectively. However, for the remaining 8 cases, correlation coefficients ranged from zero to 0.425, with coefficients of determination ranging from zero to 0.180. The reason behind the strong correlations seen in the first 4 cases, and the lack of any correlation seen in the remaining 8 cases, were explained based on the particulars of the dominant tribological mechanism for each case.

Shallow Trench Isolation Chemical Mechanical Planarization: A Review

Electrical isolation of the billion or so active components in each integrated device is achieved using shallow trench isolation (STI) which requires chemical mechanical planarization (CMP) involving silicon dioxide removal at a high rate and stopping on an underlying silicon nitride film. Several colloidal slurries with various additives can yield the desired high rate selectivity between the oxide and nitride films during CMP while maintaining an acceptably low nitride rate. Here, many of such high selectivity STI CMP slurries described in the literature are reviewed along with the characteristics of the colloidal dispersions like the abrasives, additives, the interactions between them and with the films being planarized and the associated pH range in which the high selectivity is observed. The mechanisms proposed to explain the high reactivity of ceria with oxide, the role of additives in suppressing the nitride removal rate and resulting high selectivity are discussed. Reduction of a multitude of defects in post-CMP processed STI structures still remains an important challenge, especially as the feature sizes continue to shrink.

Ceria-Based Slurries for Non-Prestonian Removal of Silicon Dioxide Films

A slurry with a non-Prestonian dependence on the polishing pressure can help in minimizing dishing and erosion during shallow trench isolation chemical mechanical planarization. Here, we show that ceria-based slurries containing diallyldimethylammonium chloride (DADMAC) yield a non-Prestonian blanket film polish rate with a low threshold pressure (1–2 psi) when polishing plasma-enhanced chemical vapor (PECVD) tetraethylorthosilicate (TEOS) deposited oxide as well as thermal oxide films. The polishing mechanism of this non-Prestonian slurry was investigated by a series of experiments involving zeta potential measurements, thermogravimetric analysis (TGA) and UV-vis spectroscopy and it was shown that more DADMAC molecules are adsorbed on silica particles (as oxide film representatives) than on ceria particles and the binding strength between DADMAC and silica is much higher than that with ceria surface.

Improving Selectivity on Germanium CMP Applications

In the presented paper, the adsorption characteristics of cationic and anionic surfactants on germanium and silica were studied in order to improve selectivity in germanium based shallow trench isolation chemical mechanical planarization applications. It was observed that the very strong or loose self-assembled surfactant structures can help obtain selectivity on the silica/germanium systems. Simultaneously, good defectivity control with a sufficient material removal rate was obtained. The surface charges manipulated by the surfactant adsorption and the hydrophobic nature of the germanium surface were main criteria on the selection of the proper surfactant/oxidizer system. In addition, impact of surfactant addition on particle-particle interactions controlling slurry stability was also investigated in the paper.

Effect of pad surface micro-texture on dishing and erosion during shallow trench isolation chemical mechanical planarization

The effect of pad surface micro-texture on dishing and erosion during shallow trench isolation (STI) chemical mechanical planarization was investigated. To generate different pad surface micro-textures, a 3M A2810 disc (3M) and a Mitsubishi Materials Corporation disc (MMC) were used to condition a Dow® IC1000™ K-groove pad. For each disc, 200-mm blanket TEOS wafers and SKW3-2 STI wafers were polished. Results showed that the two discs generated similar blanket wafer removal rates, while the MMC disc generated significantly higher dishing and erosion compared to the 3M disc during patterned wafer polishing. Pad surface topography was analyzed using laser confocal microscopy after patterned wafer polishing. Results showed that the MMC disc generated a pad surface with significantly higher mean pad summit curvatures than the 3M disc. As the MMC disc generated more and sharper pad asperities, it resulted in higher dishing and erosion as these sharp asperities make greater direct contact with the “down” features.

Control of adhesion force between ceria particles and polishing pad in shallow trench isolation chemical mechanical planarization.

The adhesion force between ceria and polyurethane (PU) pad was controlled to remove the step height from cell region to peripheral region during Shallow Trench Isolation Chemical Mechanical Planarization (STI-CMP) for NAND flash. Picolinic acid was found to be adsorbed on ceria particles at pH 4.5 following a Langmuir isotherm with the maximum adsorbed amount of 0.36 mg/m2. The ceria suspension with full surface coverage of picolinic acid showed a threefold increase in the number of adhered ceria particles on the PU pad over non-coated ceria particles. It was shown that the coverage percent of picolinic acid on ceria corresponds well with the amount percent of adsorbed ceria on PU pad. The change in adsorbed particles was directly reflected in the CMP polishing process where significant improvements were achieved. Particularly, convex areas on the chip experienced higher friction force from the attached abrasives on the PU pad than concave areas. As a result, the convex areas have increased removal rate of step height compared to the ceria suspension without picolinic acid. The changing profiles of convex areas are reported during the step height reduction as a function of polishing time.

Abrasive and additive interactions in high selectivity STI CMP slurries

Ceria based slurries with additives are widely used in shallow trench isolation (STI) chemical mechanical planarization (CMP) process to obtain high selective removal of silicon dioxide over silicon nitride. In this study ceria from different sources were used as abrasives and l-proline and l-glutamic acid were used as additives, with a focus on identifying the interactions between abrasives and additives and their effect of selectivity. Ceria particles were characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) while the additive abrasive interactions were evaluated by UV–Visible spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. While slurries with l-proline yielded high selectivity only with certain type of ceria, slurries with l-glutamic acid were found to be less sensitive to the ceria source than those with l-proline, and yielded high selectivity regardless of the source of ceria used. The purity of the abrasive and its crystal structure appear to play a significant role in determining the selectivity.

Non-Prestonian Behavior of Rectangular Shaped Ceria Slurry in Shallow Trench Isolation Chemical Mechanical Planarization

Rectangular ceria particles were synthesized using the flash creation method. The influence of the morphology of ceria particles and the surfactant concentration on the removal rate was systematically investigated. These ceria slurries with polymeric surfactant molecules as the passivation agents of Si3N4 film, shows an exceptional non-Prestonian behaviors. The non-Prestonian behavior can be attributed to the increase in the contact area of the ceria particles with the SiO2 film, which is dominated by the morphology of the ceria particles. Force measurements using an atomic force microscope (AFM) at different concentrations of polymeric surfactant molecules was used to identify the interactions between the polymeric molecules and the oxide film and analyze the non-Prestonian behavior of ceria slurry having rectangular abrasives.

Synthesis of Silica-Coated Ceria Particles for STI-CMP in a Single Step by Flame Spray Pyrolysis with an Emulsion

Silica-coated ceria particles for STI-CMP (Shallow Trench Isolation Chemical Mechanical Planarization) were prepared in a single step by using a modified flame spray pyrolysis with an emulsion precursor solution. The prepared particles were characterized by using TEM and zeta potential measurement. The isoelectric points (IEPs) of the silica-coated ceria particles are decreased with increasing the amount of silica coating and approach to two, which is IEP of silica. This result macroscopically confirms that silica is reasonably coated on the ceria surface. TEM analysis also supports that the silica layer is indeed formed on ceria particle and the thickness is around 5 nm. The silica-coated ceria suspension was found to have lower viscosity compared with the bare ceria suspension. Therefore, dispersibility of CMP suspension is expected to be enhanced at the expense of decreased polishing rate. However, it is decreased by only 6.5% compared with the polishing rate of bare ceria when 5 wt % of silica is coated on ceria.

Pattern evolution in shallow trench isolation chemical mechanical planarization via real-time shear and down forces spectral analyses

This study explores the transition of force spectral fingerprints of shallow trench isolation chemical mechanical planarization during early evolution of wafer topography and layer transition from silicon dioxide to silicon nitride. Polishing was done on a polisher and tribometer capable of measuring shear force and down force in real-time. Fast Fourier Transformation is performed to convert the force data from time domain to frequency domain and to illustrate the spectral amplitude distribution of the force. Such frequency spectra provide in-depth insights into the interactions among abrasive particles, pad and wafer. Shallow trench isolation patterned wafers are over-polished using cerium oxide slurry. Results show that shear force increases during polishing when the silicon dioxide layer is removed thus exposing the silicon nitride layer. Unique and consistent spectral fingerprints are generated showing significant changes in several fundamental peaks during the early evolution of wafer topography and subsequent layer transition to silicon nitride polishing. Variance of force is also plotted to show the progression of pattern evolution. Results show that a combination of unique spectral fingerprinting, coefficient of friction as well as analyses of force and its variance (based on shear and down force) can be used as to monitor in real-time the polishing progress during shallow trench isolation chemical mechanical planarization.

Slurry-Induced Pad Wear Rate in Chemical Mechanical Planarization

In this study, the extent of the pad wear rate during the shallow trench isolation chemical mechanical planarization process was investigated for several combinations of the type of abrasive particles (i.e., colloidal and fumed silica), abrasive content, and abrasive concentration. Results showed a relation between pad wear rate and abrasive concentration for both fumed and colloidal slurries. Results indicated that the pad wear rate using the colloidal silica slurry was higher by approximately 42 and 6% at 3 and 25 wt % silica, respectively. Under the same abrasive content, pad wear rate for fumed slurry was 23% higher compared to colloidal slurry.

Increase in the Adsorption Density of Anionic Molecules on Ceria for Defect-Free STI CMP

We have investigated the adsorption density of anionic molecules on a ceria surface and its effect on suppressing defects on the films during shallow trench isolation (STI) chemical mechanical planarization (CMP). Intermolecular vacancies in poly(methyl methacrylate) (PMMA) caused by ionic repulsive forces between its carboxyl groups provide adsorption sites on the ceria surface for 3-hydroxypentanedioic acid-3-carboxylic acid (hydrogen citrate), which has a molecular length of 8.39 Å. This allows for an increase in adsorption density. The coadsorption of PMMA and hydrogen citrate on the ceria surface leads to an increase in negative charge at the ceria particle–water interface and provides repulsive forces between the ceria particle and the surface. Ceria slurry prepared with the coadsorption of PMMA and hydrogen citrate shows a suppression of remaining particles (90.9%) and microscratches (100%) on the film, resulting from a decrease in the adhesion force of ceria particles on the film. This effect was analyzed by force measurement using atomic force microscopy.