Planarization Process Research Articles

Fabrication of microstructures on curved hydrogel substrates

Emerging wearable devices are very attractive and promising in biomedical and healthcare fields because of their biocompatibility for monitoring in situ biomarker-associated signals and external stimulus. Many such devices or systems demand microscale sensors fabricated on curved and flexible hydrogel substrates. However, fabrication of microstructures on such substrates is still challenging because the traditional planar lithography process is not compatible with curved, flexible, and hydrated substrates. Here, we present a shadow-mask-assisted deposition process capable of directly generating metallic microstructures on the curved hydrogel substrate, specifically the contact lens, one of the most popular hydrogel substrates for wearable biomedical applications. In this process, the curved hydrogel substrate is temporarily flattened on a planar surface and metal features are deposited on this substrate through a shadow mask. To achieve a high patterning fidelity, we have experimentally and theoretically investigated various types of distortion due to wrinkles on 3D-printed sample holders, geometric distortion of the substrate due to the flattening process, and volume change of the hydrogel material during the dehydration and hydration processes of the contact lens. Using this method, we have demonstrated fabrication of various titanium pattern arrays on contact lenses with high fidelity and yield.

Metasurface enabled on-chip double-beam scheme for SERF atomic magnetometer

Double-beam atomic magnetometer (AM) working in spin-exchange relaxation-free (SERF) regime is drawing growing attention due to high sensitivity (femtotesla-level) and non-intrusion characteristics. Nowadays, chip integration of AMs in pursuit of dramatical reduction in volume has become a major trend as it is especially favorable for future high-spatial-resolution biomagnetism imaging. While micro-fabricated vapor cell with only two transparent windows (due to planar nano fabrication processes) has become the major obstacle to achieve double-beam scheme on chip. In this study, an ultra-compact on-chip double-beam scheme based on emerging metasurface is proposed for SERF atomic magnetometer application. With in-surface incident both pump light and probe light, this planar device enables optical-path manipulation of linearly-polarized probe beam to precise intersect with pump beam. Our method supports angle manipulation of probe light up to 45 degrees with efficiencies reaching 70%. The device is designed with silicon nitride with thickness of 0.6 um, which can be directly fabricated on the transparent window of vapor cell through basic CMOS compatible processes. In addition, there are more advantages of this method including dramatic volume reduction and potential low-cost mass fabrication, which is promising for future applications including high-resolution biomagnetism imaging and portable atomic devices.

Surface Planarization of CdZnTe Wafers: Effect of Slurry Formulation and CMP Processing Parameters on Surface Planarity

This study investigates the effect of chemical mechanical planarization (CMP) processing parameters such as platen velocity, the concentration of the oxidizer and abrasive nanoparticle, slurry pH and surfactant types on the surface roughness of cadmium zinc telluride (CdZnTe) substrate. It was found that these parameters have a significant effect on the quality of the polished surfaces. It was found that lower platen velocity, lesser concentration of abrasive particles, basic slurry pH, and addition of anionic surfactant (SDS) into the CMP slurry solution showed improved surface planarity. Optical Surface Profiler and atomic force microscopy (AFM) techniques were used to monitor the surface topography before and after polishing. A notable root-mean-square surface roughness, (Rq), ∼0.9 nm, has been obtained on the polished CdZnTe (CZT) surface over a scan area of 481 × 361 μm2 under the optimized conditions of 60 rpm relative velocity, slurry pH of 9, 3.75 vol% of oxidizer (H2O2) and 1.25 wt% of abrasive (SiO2 nanoparticle). A probable mechanism of the present CMP surface planarization of CZT substrate has been proposed. Unlike the conventional surface planarization processes, which involve two-step lapping followed by CMP for the CZT surfaces, we have developed a single step CMP process to obtain good surface planarity.

CMP에서 디바이스 패턴의 실 접촉 면적 측정을 통한 평탄화 규명

Chemical Mechanical Planarization (CMP) is an essential process for device integration and planarization in a semiconductor manufacturing process. The most critical function in the CMP process, is to predict and cover the geometrical characteristics of various sizes and densities, of patterned wafers for local and global planarization. To achieve the wafer-level and die-level planarization, it is necessary to understand the contact mechanism between the CMP pads and the macro-scale patterns. In the macro-scale pattern, pad deformation is divided into two layers: an asperity layer and a bulk pad layer. Through bulk pad deformation, asperity contact distribution within the pattern is predicted. In this paper, the distribution of asperity contact according to the pattern geometrical characteristics was analyzed, through large-area real contact area (RCA) measurement. Bulk pad deformation was predicted by analyzing RCA distribution according to pattern geometry such as pattern size and density, pattern shape and step height according to the polishing time, and applied pressure. Additionally, through the distribution of the contact area and the number of contact points, the rounding phenomenon and planarization characteristics in the pattern CMP were predicted.

Study of synergy of monoethanolamine and urea on copper corrosion inhibition in alkaline solution

• Cu corrosion in TMAH-containing solution is investigated. • MEA and urea are used as corrosion inhibitors to retard the Cu corrosion. • The synergy of MEA and urea on Cu corrosion inhibition is concentration ratio dependent. • Cu corrosion becomes more serious at low concentration ratio of MEA to urea. • Cu corrosion is effectively retarded at high concentration ratio of MEA to urea. Tetramethylammonium hydroxide (TMAH) is an important constituent used in the post cleaning process of chemical mechanical planarization and lithography; however, its corrosive property causes damage to the Cu metallization. Addition of corrosion inhibitor in the cleaning solution is a promising method to protect Cu. In this study, two corrosion inhibitors, monoethanolamine (MEA) and urea, are used to investigate their synergy on the Cu corrosion protection. Electrochemical and four-point probe methods are adopted to analyze the corrosion behaviors of Cu. Microstructural characterizations of Cu are performed using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. X-ray photoelectron spectroscopy is used to realize the adsorption behaviors of inhibitors on the Cu surface. The results of corrosion current ( I corr ) and charge transfer resistance ( R ct ) indicate that addition of MEA and urea at an identical concentration does not produce a typical synergistic effect on the Cu corrosion protection due to mutual interference of two inhibitors. An increase of the MEA concentration overcomes the mutual interference, giving rise to a reduction of I corr and an increase of R ct . The effective retardation of the Cu corrosion is attributed to the sufficiency of inhibitors which can construct a dense protection layer on the Cu surface.

Degenerate competing three-particle systems

We study systems of three interacting particles, in which drifts and variances are assigned by rank. These systems are degenerate: the variances corresponding to one or two ranks can vanish, so the corresponding ranked motions become ballistic rather than diffusive. Depending on which ranks are allowed to “go ballistic” the systems exhibit markedly different behavior, which we study here in some detail. Also studied are stability properties for the resulting planar process of gaps between successive ranks.

Effect of water film on the nano-scratching process of 4H-SiC under the constant load

The effects of water film and scratching load on tribological properties are investigated by molecular dynamics simulation. Water film is found to reduce the average friction coefficient and enhance heat dissipation of scratching process. The long dislocations in 4H‐SiC are related to the formation of continuous and stable Si-Si bonds, and the water film can inhibit the formation of dislocations by affecting Si-Si bonds. Scratching in water-wetted environments has a positive effect on improving surface quality and reducing sub-surface damage, but has a negative impact on the material removal rate. The effect of increasing load is opposite to that of adding water. These results confirm the lubrication effect of water film in global planarization process from a theoretical perspective.

Coupling Supramolecular Assemblies and Reactive Oxygen Species (ROS) with Megasonic Action for Applications in Shallow Trench Isolation (STI) Post-Chemical Mechanical Planarization (p-CMP) Cleaning.

Due to the continued miniaturization of semiconductor devices, slurry formulations utilized in the chemical mechanical planarization (CMP) process have become increasingly complex to meet stringent manufacturing specifications. Traditionally, in shallow trench isolation (STI), CMP, a contact cleaning method involving a poly(vinyl alcohol) (PVA) brush, is used to effectively transfer cleaning chemistry to the oxide substrate. This PVA brush can cause nonuniform cleaning chemistry transport, increased interfacial shear force, and cleaning-induced defectivity from brush loading. Previous work with traditional cleaning processes has shown that using “soft” supramolecular cleaning chemistries has dramatically improved cleaning efficacy while also minimizing the number of induced p-CMP defects. To minimize these effects, noncontact cleaning via the implementation of megasonic action has gained attention. This work employs “soft” cleaning chemistries with Cu2+–amino acid complexes, which can catalyze the formation of critical reactive oxygen species (ROS), and evaluates the p-CMP performance under megasonic action. Results from a second-order kinetic model indicate that megasonic conditions (i.e., time and power), “soft” cleaning chemistry structure (i.e., shape and charge), and the generation of ROS all play a critical role in cleaning efficacy under low shear stress conditions.

Design of “Low Stress” Post-CMP Cleaning Processes for Advanced Technology Nodes

As integrated circuit and logic device feature sizes approach the 3-nm node, limiting induced defectivity during Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) is of utmost importance. The CMP process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Traditionally, a contact cleaning method involving a poly-vinyl alcohol (PVA) brush is used to transfer cleaning chemistry to the substrate of interest as well as provide the necessary mechanical energy for defect removal. While this process is effective in contaminant removal its reliance on shear forces can induce secondary defect modes, such as scratching. To minimize the aforementioned induced defectivity during contact p-CMP processes, the implementation of non-contact modalities has become of the utmost importance. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials such as SiC, GaN, carbon-doped oxides, and metals. More specifically, “OVER”-cutting and “soft” cleaning processes that balance the modulation of surface reaction kinetics (chemical and adsorption) with advanced low shear force environment will be evaluated. For example, employing supramolecular cleaning chemistries coupled with reactive oxygen species (ROS) generating complexes under megasonic action were evaluated for effective SiC cleaning. Results from a second order kinetic model indicate that processing conditions (i.e., time and power), “soft” cleaning chemistry structure (i.e., shape and charge), and the generation of ROS all play a critical role in cleaning efficacy under low stress conditions in the megasonic field. Utilizing a suite of dynamic analytical techniques (i.e., atomic force microscopy, quartz crystal microbalance, contact angle, zeta potential, and electrochemical analysis, shear force analysis) a correlation between interfacial reaction mechanisms and effective p-CMP cleaning will be presented.

Exploring the controlling mechanisms for gradient evolution in unsteady detonation flows

Proper characterization of the transient interaction between shock front motion and chemical energy release is the key for further understanding of unsteady detonation dynamics. We have shown that the gradients could be the adequate intermediate quantities to reflect the transient interaction between shock front motion and chemical energy release through the Lagrangian particle analysis of the simulated direct detonation initiation (DDI) process in H2–O2–Ar mixtures. Specifically, the “shock change equations” are verified to describe the direct relation between the shock front motion and the gradients immediately behind the shock. Moreover, given the time derivatives of shock speed, the gradient evolution in the induction zone can be reproduced by the gradient evolution equations that are deduced from the Euler equations, no matter if the shock front undergoes rapid deceleration or acceleration. While in the reaction zone where the heat release is significant, it is demonstrated that the evolutions of velocity, pressure, and their gradients can be described by the Zel'dovich–von Neumann–Döring model with a constant wave speed that is below the Chapman–Jouguet speed, no matter if the shock front undergoes rapid deceleration or acceleration. These two distinct controlling mechanisms are verified in both planar and spherical DDI processes, showing their general applicability. This work suggests a new perspective, in terms of gradient evolution, for further understanding the unsteady detonation dynamics.

UAV Communication Network Modeling and Energy Consumption Optimization Based on Routing Algorithm.

Topological information is provided, and research on the design of routing protocols for UAV self-assembling networks is conducted, in order to enable fleet communication transfer between UAVs and UAVs and enhance their communication transmission rate in the self-assembling network. A new routing protocol is proposed through greedy forwarding and peripheral forwarding of UAV self-assembling network communication data, UAV self-assembling network planarization processing, dynamic adjustment of routing mode based on topological information, and routing protocol decision content generation. The proposed network is described using stochastic geometry theory, with the UAV and building locations modeled as two independently distributed Poisson point processes and the building shape modeled as a rectangular body with height obeying the Rayleigh distribution. An estimated equation for typical user coverage is produced using this model. The simulation results show that the approximate expression matches with the simulation results with reduced computational complexity, which verifies the validity of the approximate analysis. By comparing it with the clustering-based routing protocol, it is concluded that the new routing protocol conditions for UAV self-assembly network can realize the communication transmission between UAVs and drones and further promote their communication transmission rate.

Scaling limits for planar aggregation with subcritical fluctuations

We study scaling limits of a family of planar random growth processes in which clusters grow by the successive aggregation of small particles. In these models, clusters are encoded as a composition of conformal maps and the location of each successive particle is distributed according to the density of harmonic measure on the cluster boundary, raised to some power. We show that, when this power lies within a particular range, the macroscopic shape of the cluster converges to a disk, but that as the power approaches the edge of this range the fluctuations approach a critical point, which is a limit of stability. The methodology developed in this paper provides a blueprint for analysing more general random growth models, such as the Hastings-Levitov family.

Effect of ionic strength on amorphous carbon during chemical mechanical planarization

A hard mask is an essential to prevent pattern collapse resulting from leaning, wiggling, or other defects. It is critical to achieve high removal rates of hard masks. The process of amorphous carbon chemical mechanical planarization (CMP) forms OH radicals on the surface by an oxidation and breaks bonds in the weakest area. Electrolytes with different ionic strengths were added, to facilitate the formation of OH radicals. When electrolytes were added, the removal rates increased by approximately 2.3 times over those without any additives. The increase in surface roughness is another significant factor. The roughness increased in all cases. In particular, a mixed slurry achieved the best results, with a mean surface roughness value of 0.147 nm for a scanning area of 5 × 5 μm2. Thus, the ionic strength of the electrolyte is critical in the CMP of amorphous carbon.

Design of “Low Stress” Post-CMP Cleaning Processes for Advanced Technology Nodes

The Chemical Mechanical Planarization (CMP) process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Traditionally, a contact cleaning method involving a poly-vinyl alcohol (PVA) brush is used to transfer cleaning chemistry to the substrate of interest as well as provide the necessary mechanical energy for defect removal. While this process is effective in contaminant removal its reliance on shear forces can induce secondary defect modes, such as scratching. To minimize the aforementioned induced defectivity during contact p-CMP processes, the implementation of non-contact modalities has become of the utmost importance. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials such as SiC, carbon-doped oxides, and metals. “Soft” cleaning chemistry structure (i.e., shape and charge), and processes play a critical role in cleaning efficacy under low stress conditions.

Palladium Chemical Mechanical Planarization in Packaging and Barrier Level Integration

Palladium (Pd) is a chemically inert material known for its ability to improve processing cost and reliability for the packaging level microelectronics integration. In addition, it is used as a sacrificial layer for copper (Cu) integration as a barrier material to protect the copper from oxidation. Successful implementation of Pd requires chemical mechanical planarization (CMP) process in both applications, where selectivity is desired between the Cu, tantalum nitride (TaN), and nitride (Ni) films against Pd. This paper focuses on removal rate selectivity tuning for Pd thin films in a commercial silica-based Cu-CMP slurry compared to a baseline silica slurry as a function of the slurry temperature. Detailed analyses of the integrated materials are presented, investigating the effect of temperature on surface wettability and CMP selectivity. Pd passivation is also presented by electrochemical analysis in the presence of an oxidizer for the selected polishing slurries. It is observed that lowering the slurry temperature promotes palladium CMP removal rate selectivity against Ni, Cu, and TaN by modifying slurry viscosity and wafer surface wettability with no detrimental effect observed on the surface defectivity.

Lasing action in a strongly coupled silicon nanowire pair.

High-index dielectric nanostructures are of particular interest for nanoscale lasing due to their low absorption losses. However, the relatively weak near-field restricts the isolated dielectric cavities as low-threshold integrated on-chip laser sources. Here, we demonstrate lasing action in a silicon nanowire pair with 32 nm gap coated with dye-doped shell on the silicon-on-insulator platform. It is found that the quality factor Q is dominated by the coupling of the silicon nanowire pair, which depends on the gap size, the nanowire width, and the dye thickness. A lasing peak at the wavelength of 529 nm with FWHM of 0.6 nm is experimentally realized by the Si nanowire pair width, and the corresponding pumping power threshold is ∼34 µW/cm2. The proposed strategy, based on the well-established Si planar process, lays the groundwork for practical integrated nanolasers that have potential applications in photonic circuits.

Basic exploration and research on magnetoelectric synergistic rheological finishing

Both the magnetorheological effect and the electrorheological effect can effectively constrain and clamp abrasives for polishing processing. This paper proposes a magneto-electric synergy rheological finishing (MERF) method. Based on a magnetoelectric composite field simulation, magnetoelectric synergistic rheological finishing equipment is built. A polishing slurry with both electrorheological and magnetorheological effects is prepared for processing a 2-inch single-crystal silicon wafer. Comb-type electrodes and cylindrical flat-bottomed magnetic poles are used to construct magnetoelectric composite fields. Under the action of a magnetoelectric composite field, a hemispherical polishing pad with abrasives distributed in strips can be obtained. By conducting a test, a smooth and gentle arc cross section of the removed contour can be obtained. The removal rate of MERF was 4.04 mg/h, which was between those of electrorheological finishing (ERF) and magnetorheological finishing (MRF). The surface roughness Ra reached 1.80 nm, and the depth and width of the machining traces were the largest. Magnetoelectric synergistic rheological finishing equipment can realize processing under electric fields, magnetic fields, and magnetoelectric composite fields. The MERF method can effectively enhance the semifixed binding force and distributional uniformity of the abrasive and achieve a more efficient and uniform planarization process.

Planar polishing process method based on real-time dressing of a polishing pad surface.

Planar polishing is an important manufacturing process for high-precision planar components. In this study, a real-time dresser and a planar polishing process based on real-time dressing for large-aperture optical plane components were developed. Efficient dressing of a polishing pad surface can be achieved with the real-time dresser. Compared with the conventional method, real-time correction for the surface shape of the polishing pad was realized via the temperature parameter t in the real-time dresser, and this parameter can be optimized through optimization experiments. Finally, a series of experiments was carried out to verify the effectiveness of the real-time dresser on surface dressing. Through the real-time dressing of the polishing pad surface, the flatness peak-valley deviation and the root-mean-square deviation of the flat optical element surface (430×430mm) can reach 3λ and 0.9λ, which is improved by 25% and 33%, respectively.

Conformal 3D printing of a polymeric tactile sensor

• Conformal additive manufacturing of soft tactile sensors on a curved surface is new. • Sensors printed by conformal and conventional additive manufacturing were compared. • Conformal printing of sensors on non-flat surfaces can avoid manufacturing errors. • Conformal printing of sensors can be employed in future robotics and prosthetics. Conventional additive manufacturing processes are generally inadequate for printing electronics on a curved surface. When printing a curved functional structure, the typical way of generating the extrusion path only in a horizontal plane could cause various issues such as impreciseness and disconnect in the printed part. In this work, conformal 3D printing of a soft tactile sensor is presented in which curvilinear extrusion paths were generated for the printing of a curved sensor. An extrusion-based multi-material direct printing system was employed to print the sensor, and ultraviolet light was used to polymerize the printed layers. An ionic liquid–based pressure-sensitive polymer membrane, carbon nanotube-based conductive electrodes, and a soft polymeric insulation layer were conformally 3D printed to fabricate the curved sensor on a fingertip model. The conformally printed sensor was evaluated under different conditions. Sensors 3D-printed using conformal and planar slicing processes were compared to investigate the effect of curvilinear slicing on the printed parts. The results show that conformal 3D printing is able to overcome the fabrication limitations of conventional planar processing while also retaining the functionality of the printed structures.

Programmable patterning fabrication of laser-induced graphene-MXene composite electrodes for flexible planar supercapacitors.

The development of laser-induced graphene (LIG) has been regarded as an effective method for satisfying the substantial requirements for the scalable fabrication of graphene-based electrode materials. Despite the rapid progress in fabricating LIG-based supercapacitors, the incompatibility between material modification and the device planarization process remains a challenging problem to be resolved. In this study, we demonstrate the attributes of novel LIG-MXene (LIG-M) composite electrodes for flexible planar supercapacitors fabricated by direct laser writing (DLW) of MXene-coated polyimide (PI) films. During the DLW process, PI was transformed into LIG, while MXene was simultaneously introduced to produce LIG-M. Combining the porous structure of LIG and the high conductivity of MXene, the as-prepared LIG-M-based supercapacitor exhibited superior specific capacitance, five times higher than that of the pristine LIG-based supercapacitor. The enhanced capacitance of LIG-M also benefited from the pseudocapacitive performance of the abundant active sites offered by MXene. Moreover, the planar LIG-M-based device delivered excellent cycling stability and flexibility. No significant performance degradation was observed after bending tests. Arbitrary electrode patterns could be obtained using the DLW technique. The patterned in-series LIG-M supercapacitor was able to power a light-emitting diode, demonstrating significant potential for practical applications.