Plasma Etching Process Research Articles

Progressively Balanced Supervised Contrastive Representation Learning for Long-Tailed Fault Diagnosis

In this article, a new fault diagnosis problem is formulated, which involves a large number of normal samples and in which almost all the fault classes are few-shot classes. Although this problem is common in many industrial scenarios, it remains a challenge overlooked in previous studies. To develop a novel solution for addressing this challenge, we employ long-tailed distribution in this work and name this new task the long-tailed fault diagnosis accordingly. Specifically, we divide the long-tailed fault diagnosis procedure into representation learning and classification. On this basis, we propose a method using progressively balanced supervised contrastive learning (PBS-SCL) for representation learning and a learnable linear classifier (LLC) for classification. The designed scheme consists of two phases. In the first phase, PBS-SCL is utilized to learn a more discriminative deep representation. In the second phase, an LLC is combined with the learned representation for better classification. Experiments are conducted on both the Tennessee Eastman process (TEP) benchmark dataset and a practical plasma etching process dataset. The results obtained show that the proposed method achieves significantly improved long-tailed fault diagnosis performance compared with existing methods.

Исследование тонких пленок для изготовления туннельных переходов Nb/AlN/NbN и линий передач NbTiN-SiO2-Al.

The surface of thin films of Nb, Al, NbTiN, SiO2, Al2O3 is investigated in this work. These films are necessary for the fabrication of high-sensitive devices of THz range. The fabrication processes of such devices are described briefly. All films were fabricated using a Kurt J. Lesker magnetron sputtering system. The study of the film surface roughness was carried out using a Bruker Ikon atomic force microscope. The surface quality of films is determined not only deposition mode, but plasma etching process also. The best values of the root-mean-square deviation of the surface profile Rq = 2 nm were obtained for the used NbTiN film with a thickness of 325 nm. Thin Al-layers that is used for tunnel barrier formation is studied. It is shown than Al films with a thickness of more than 6 nm are already continuous. The surface roughness of the single-layer and multilayer films has been studied.

Recurrent Neural-Network-Based Model Predictive Control of a Plasma Etch Process

In this article, we propose the development of a recurrent neural network (RNN)-based model predictive controller (MPC) for a plasma etch process on a three-dimensional substrate using inductive coupled plasma (ICP) analysis. Specifically, the plasma etch process is simulated by a multiscale model: (1) A macroscopic fluid model is applied to simulate the gas flows and chemical reactions of plasma. (2) A kinetic Monte Carlo (kMC) model is applied to simulate the etching process on the substrate. Subsequently, proper orthogonal decomposition (POD) is used to derive the empirical eigenfunctions of the plasma model. Then the empirical eigenfunctions are utilized as basis functions within a Galerkin’s model reduction framework to compute a low-order system capturing dominant dynamics of the plasma model. Additionally, RNN is introduced to approximate dynamics of both the reduced-order plasma system and the microscopic etch process. The training data for the RNN models are generated from discrete sampling of open-loop simulations. A probability distribution function is also involved to present the stochastic characteristic of the kMC model. The trained RNN models are then implemented as the prediction model in the development of MPC to achieve desired control objectives. Closed-loop simulation results are presented to compare the performance of the model predictive controller and a proportional-integral (PI) controller, which show that the proposed MPC framework is effective and exhibits better performance than does a PI controller.

Non-revisiting genetic cost-sensitive sparse autoencoder for imbalanced fault diagnosis

It is hard to obtain sufficient fault samples in most real-world industrial scenarios. This has raised the need of addressing the critical issue of imbalanced fault diagnosis that remains a major challenge for popular fault diagnosis methods such as the autoencoder(AE). In this research, we propose a non-revisiting genetic cost-sensitive sparse autoencoder(NrGCS-SAE) solution, which not only incorporates cost-sensitive learning with sparse autoencoder but also solves the problem of class weights assignment. Specifically, sparse autoencoder is adopted as it has better generalization performance than autoencoder, and genetic algorithm(GA) is employed to optimize class weights that are initially unknown. In addition, a non-revisiting strategy is devised to prevent repeated evaluation of the same individual in different generations, which can help increase exploration ability and decrease computing costs. Computational experiments are used to evaluate the proposed NrGCS-SAE solution on the Tennessee Eastman(TE) dataset and the real plasma etching process dataset, which involves both binary imbalanced fault diagnosis and multi-class imbalanced faults diagnosis. As evidenced in the tests, NrGCS-SAE achieves improved performance and more importantly this improvement is consistent in different settings of experiments.

A Real-Time Monitoring Framework for Wafer Fabrication Processes With Run-to-Run Variations

Real-time process monitoring is a vital technique to maintain safety and quality in the wafer fabrication processes. Hence, statistical process monitoring methods such as statistical process control chart, principal component analysis have been widely applied in wafer fabrication. However, these methods often suffer from the performance degradation problem caused by run-to-run (R2R) variations such as uneven duration and R2R drifts. In this paper, we propose a real-time monitoring framework for continuous wafer fabrication processes with uneven duration and R2R drifts. In this framework, processes are divided into several phases and further aligned in a real-time manner to solve the uneven duration problem. Then, R2R drifts are compensated by a down-sampling seasonal autoregressive integrated moving average model and a moving window multi-batch forecast strategy. Finally, multiphase multiway principal component analysis models are built on the compensated data to monitoring the processes. The efficiency of this framework is demonstrated by a case study on a plasma etch process. The results indicate that the proposed framework can diminish the influence of R2R variations and improve the monitoring model performance.

Modeling of Advanced FinFET Dummy Gate Corner Residue Impacted By Clogging

In this work, we model 3-Dimensional (3D) corner residues based on a process flow simulation using the Coventor SEMulator3D virtual platform. The role of clogging existing during plasma etch process in 3D corner formation has been studied based on the simulation results. In particular, the impacts of clogging and plasma aspect ratio distribution functions on corner size in typical etching steps are assessed. Furthermore, tunable model provides insights on the effect of fin height variation. Higher Fin structure could provide more shadowing effects which encourage the aggregation of 3D corner residue. In an advanced model containing multiple dry etch steps, the window of plasma divergence of different steps is also discussed, which is helpful to study and deal with the existing of 3D corner residue. Figure 1

Modeling and analysis of sulfur hexafluoride plasma etching for silicon microcavity resonators

Silicon microcavity resonators are an important component in modern photonics. In order to optimize their performance, it is fundamental to control their final shape, in particular with respect to the involved CMOS compatible, two-step sulfur hexafluoride plasma etching fabrication process. To that end, we use a ray-tracing based pseudo-particle model to enhance a level-set topography simulator enabling us to effectively capture the characteristics of sulfur hexafluoride plasma etching in the low-voltage-bias regime. By introducing a novel and robust calibration procedure and by applying it to experimental data of a reference two-step etching process, we are able to optimize the etch times and photoresist geometry without costly reactor-scale simulations and simultaneously explore beyond conventional statistical process modeling. Through defining objective design criteria by way of Gaussian beam analysis, we analyze the plasma etching process and provide new insights into alternative processing guidelines which impact shape measurements such as cavity opening and parabolic form. By means of scale analysis, we propose that the radius of curvature of the microcavity is optimized with a reduction of the photoresist opening diameter. After simulated fabrication runs, we surmise that the cavity quality parameters are improved by increasing the duration of the first etch step by a factor of 2 and by decreasing the second etch step duration by up to in comparison to the reference two-step etching process. This results in an overall reduction of etch time of at least , allowing to significantly optimize the overall fabrication process.

Modeling of Advanced FinFET Dummy Gate Corner Residue Impacted By Clogging

In this work, we model 3D corner residues based on a process flow simulation using the Coventor SEMulator3D virtual platform. The role of clogging existing during plasma etch process in 3D corner formation has been studied based on the simulation results. In particular, the impacts of clogging and plasma aspect ratio distribution functions on corner size in typical etching steps are assessed. Furthermore, tunable model provides insights on the effect of fin height variation. Higher Fin structure could provide more shadowing effects which encourage the aggregation of 3D corner residue. In an advanced model containing multiple dry etch steps, the window of plasma divergence is also discussed, which is helpful to study and deal with the existing of 3D corner residue.

(Invited) Selective Area Etching and Doping of GaN for High-Power Applications

Selective area doping (SAD) of gallium nitride (GaN), especially p-type doping, is desirable for high-power applications but yet challenging. The lack of this process greatly limits the power device design flexibility, so the reported device figure-of-merits are well below the theoretical calculation/simulation. Selective-area etching followed by regrowth is the approach we choose to overcome this obstacle. For the etching step, instead of adopting conventional Cl-based plasma etching process, we explored in-situ TBCl etching, studied the etching mechanism, and optimized the process to prepare smooth surface and trenches. Room-temperature PL, XPS, and electrical characterizations indicate that TBCl etching creates a low-defect surface. Moreover, selective area growth of p-GaN in a patterned trench was analyzed by atom probe tomography (APT). We found a reverse proportionality between the local growth rate and Mg doping concentration, and the development of fast-growing semi-polar facet from the sidewall. As a consequence, non-uniform Mg doping in non-planar growth is observed.

Erosion of focus rings in capacitively coupled plasma etching reactors

In plasma etching reactors, the structure surrounding the wafer, often called a focus ring (FR), plays an important role in maintaining uniform fluxes of reactants across the wafer. The FR is typically made of dielectric materials. During the plasma etching process, the sheath that forms over the wafer to accelerate ions anisotropically into the surface extends over the FR. Electrical charging of the FR modifies the sheath relative to that over the wafer. On the one hand, one wants the sheath to be uniform across the wafer-FR boundary to enable uniform fluxes to the edge of the wafer. On the other hand, maintaining a high voltage sheath over the FR will erode the FR, which is undesirable as the FR is a consumable component that must be periodically replaced in high volume manufacturing. In this work, we computationally investigated the consequences of dielectric constant ɛr of the FR materials on erosion of the FR. The series capacitance of the FR and its underlying structure is typically smaller than that of the wafer and its underlying structure. As a result, the FR charges quickly relative to the wafer, which then reduces the voltage across the sheath on top of the FR. The ion energy and angular distributions (IEADs) striking the FR are, therefore, generally lower in energy with a broader angular distribution. With ɛr = 2, the ion energies striking the middle to the outer edge of the FR are 30–180 eV, whereas for ɛr = 100, the ion energies are 120–380 eV. At the transition between the wafer and the FR, there is a skew in the IEAD as large as 15° that results from the difference in sheath thickness above the wafer and the FR. This skew and the erosion rate across the FR are functions of the dielectric constant of the FR material. With low ɛr, the FR charges quickly, less plasma is produced above the FR, and there is less voltage across the sheath that results in less FR erosion. Increasing ɛr of the FR produces a higher sheath voltage as well as higher ion fluxes over the FR, which increases erosion, while the skew at the edge of the wafer is less severe. The material of the subsurface portion of the FR, which dominates its capacitance, is an important consideration in the design of the substrate assembly.

Residue-free photolithographic patterning of graphene

Photolithography of graphene using an organic photoresist (PR), whereby the graphene film is patterned into a desired geometry, is required for the fabrication of graphene-based sensors and electronic devices. However, because the PR hardens during the O2 plasma etching process, its complete removal is difficult. Herein, we present a new route to obtain residue-free patterned graphene by introducing a buffer layer between graphene and the PR. The modified photolithography process allows complete removal of the hardened PR and eliminates poly(methyl methacrylate) residues on the graphene surface during the wet transfer process. Density functional theory calculations revealed that the binding strength between the buffer layer and graphene is weaker than that between the PR and graphene. This led to a clean graphene surface without PR and other organic residues. The graphene films patterned using the modified photolithography process are of superior quality; they have the lowest surface roughness, natural hydrophobicity, and the highest transmittance of 94.1% at the wavelength of 550 nm. In addition, graphene-based field-effect transistors fabricated using the new process present the electron mobility of 800 cm2 V−1 s−1, and their charge neutrality point is located near zero bias, indicating that the unintended doping effect was effectively eliminated. This work demonstrates a new process that is compatible with silicon-based nanosystems and can be readily applied in the mass production of residue-free graphene electronics.

Study on the influence of ion incident energy on surface charging in plasma etching

The charging issue on the surface of an isolated mask hole with rough edge has been studied in plasma etching process, as a function of the ion incident energy, E i based on several classical particle dynamics simulation modules of surface charging, surface etching and profile evolution. This study revealed that, on the one hand, various values of E i can lead to different surface distributions of the horizontal and radial component of electric-field (called E-field hereafter for short) and the net charge density above the mask surface. On the other hand, the simulated evolution of the mask profile exhibits a decreased deformation as E i increases. Possible mechanisms of these results during the etching process were discussed. This work sheds important light on the reduction of the mask pattern damage and further improve the quality of the pattern transferring onto the substrate.

Effect of metal mesh addition on polymer surface etching by an atmospheric pressure plasma jet

Atmospheric pressure plasma jet has shown great potential for polymer film treatment, but the etching process of polymer surface by the plasma jet is still not developed. In this paper, the effect of a grounded metal mesh addition on the etching process of polymer surface through the plasma jet was investigated. Comparative study of polymer film treated by the plasma jet with and without a grounded stainless steel mesh (SSM) is systematically investigated by the analysis of etching rate, surface morphologies and chemical compositions. Compared with the plasma etching process with SSM, the etching results without the addition of SSM have much higher etching rate, rougher etched surface, and higher surface oxidation. Finally, the etching process occurring at the plasma/polymer interface was also discussed. Since the addition of SSM could filter out the charged particles in plasma jet, the role of charged particles in the etching process was discussed and the synergetic etching process was proposed based on the structural dependence and chemical analysis of the observed results.

Characterization of AlGaN/GaN degradations during plasma etching for power devices

During the fabrication of a MOS-HEMT, the plasma-etching steps are critical because they can damage the GaN materials and lead to electrical degradation effects. To address these limitations, we studied the influence of plasma parameters on electrical degradation in an AlGaN/GaN heterostructure. In this work, the modifications induced by bias-voltage applied during the SiN capping layer opening are investigated. Physical (XRD, XRR, AFM and TEM) and chemical (XPS) characterizations have been performed to have a better understanding this plasma parameter on GaN damage. These results are correlated with Rsheet measurements to evaluate the electrical degradation in the heterostructure. Finally, degradation mechanisms and recommendation have been proposed to improve the plasma etching process.

Evolution of vacuum ultraviolet emission in dual-frequency capacitively coupled plasmas

In plasma material processing, vacuum ultraviolet (VUV) emission is released from gas discharges, leading to undesirable results. Energetic VUV photons enable the creation of an electron-hole pair current when their energy is larger than the bandgap energy of the plasma-facing top layer during plasma material processing. For example, the high energy of VUV photons from helium (21.2 eV), argon (11.6 eV), and oxygen (13.6 eV) is sufficient to generate induced currents in SiO2 thin films. These feedstock gases are widely used in many procedures utilizing low-temperature industrial plasmas. Thus, the VUV emission evolution with both the power ratio between high (60 MHz) and low (2 MHz) frequencies and pulse duty ratio of the low-frequency radio frequency (rf) power in a dual-frequency capacitively coupled plasma, which is indispensable in modern plasma etching processes, was investigated. Both the power ratio between high and low frequencies and the pulse duty ratio changed the electron temperature, leading to evolution of the VUV emission intensity.

Etching Characteristics and Changes in Surface Properties of IGZO Thin Films by O2 Addition in CF4/Ar Plasma

Plasma etching processes for multi-atomic oxide thin films have become increasingly important owing to the excellent material properties of such thin films, which can potentially be employed in next-generation displays. To fabricate high-performance and reproducible devices, the etching mechanism and surface properties must be understood. In this study, we investigated the etching characteristics and changes in the surface properties of InGaZnO4 (IGZO) thin films with the addition of O2 gases based on a CF4/Ar high-density-plasma system. A maximum etch rate of 32.7 nm/min for an IGZO thin film was achieved at an O2/CF4/Ar (=20:25:75 sccm) ratio. The etching mechanism was interpreted in detail through plasma analysis via optical emission spectroscopy and surface analysis via X-ray photoelectron microscopy. To determine the performance variation according to the alteration in the surface composition of the IGZO thin films, we investigated the changes in the work function, surface energy, and surface roughness through ultraviolet photoelectron spectroscopy, contact angle measurement, and atomic force microscopy, respectively. After the plasma etching process, the change in work function was up to 280 meV, the thin film surface became slightly hydrophilic, and the surface roughness slightly decreased. This work suggests that plasma etching causes various changes in thin-film surfaces, which affects device performance.

Fabrication of Differently Shaped Polymeric Nanoneedle Arrays via Multistep Plasma Etching Using Silica Microparticles as Masks

We established a method to produce differently shaped polymeric nanoneedle arrays using silica microparticles by using multistep plasma etch processes. The etching conditions of each step were determined by exploring etching parameters such as power, bias power, gas composition and amount, pressure and time. The silica microparticles became unstable and irregular nanoneedle arrays were formed due to difference of etching rates between silica and polymer when silica microparticles were etched continuously in one step. Through the introduction of stabilization step in which selective etching is done on silica microparticle to reduce the diameter of silica microparticles and hence to move the center of mass of the silica microparticle inward, the instability of silica mask was removed and irregularity of nanostructures was minimized. As a result, multistep etching process to fabricate polymeric nanoneedle arrays was established. Depending on the conditions of each step, polymeric nanostructure arrays with various morphology were fabricated.

Mechanically Stable Thinned Membrane for a High-Performance Polymer Electrolyte Membrane Fuel Cell via a Plasma-Etching and Annealing Process

Mechanically Stable Thinned Membrane for a High-Performance Polymer Electrolyte Membrane Fuel Cell via a Plasma-Etching and Annealing Process

Thermal stress-induced fabrication of carbon micro/nanostructures and the application in high-performance enzyme-free glucose sensors

Enzyme-free glucose sensors are of great significance for monitoring patients’ blood glucose, but the fabrication of high performance sensors is still challenging. Carbon micro/nanostructures are good candidates for enzyme-free glucose sensors due to good biocompatibility and conductivity, and highly active surface area. In this study, the formation of flower-like carbon micro/nanostructure arrays by the thermal stress from pyrolysis of suspended micro/nanostructures was studied. The modified carbon microelectromechanical system (C-MEMS) technology involved overexposure of photoresist structures, oxygen plasma etching and pyrolysis processes with stainless steel as substrate. The effects of fabrication parameters like exposure time and width of suspended part to the formation of carbon micro/nanostructures were discussed. The novel carbon micro/nanostructures were integrated with copper oxide (CuO) nanofilm for the application of enzyme-free glucose sensors. The electrochemical performances of CuO nanofilm/carbon micro/nanostructures were characterized, and the results showed that the enzymeless glucose sensors demonstrated excellent specificity, good stability, high sensitivity of (1.09 ± 0.05)×103 μA mM−1 cm−2 and low detection limit of 4.51 ± 0.03 μM. The obtained micro/nanostructures have great potential for high performance micro sensors and on-chip energy storage devices, and the presented approach is promising for large-scale manufacturing of carbon micro/nanostructures.

Computational study of plasma dynamics and reactive chemistry in a low-pressure inductively coupled CF4/O2 plasma

Plasma etching continues to play a central role in microelectronics manufacturing. As the semiconductor industry continues to shrink critical feature sizes and improves device performance, etch challenges continue to increase due to the requirement of processing smaller features along with new device structures. With their high density and high-aspect ratio features, these structures are challenging to manufacture and have required innovation in multiple areas of wafer processing. Innovations in this technology are increasingly reliant on comprehensive physical and chemical models of plasma etch processes. In the present paper, we develop a new mechanism of plasma chemical reactions for a low-pressure CF4/O2 plasma. We validate this mechanism against available experimental data using the self-consistent axisymmetric fluid model of inductively coupled plasma discharge. We show that this mechanism is in reasonable agreement with the results of experiments both quantitively and qualitatively. Using this mechanism, we analyze the influence of oxygen fraction in the feed gas mixture on the kinetics of the ion species and the fluorine and oxygen atom yield.