Plasma Etching Process Research Articles

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.

Anisotropic and low damage III-V/Ge heterostructure etching for multijunction solar cell fabrication with passivated sidewalls

This article presents a complete plasma etching process to etch high aspect ratio patterns on III-V/Ge solar cell heterostructure with low damage for the fabrication of multijunction solar cells with a through cell via contact architecture. A SiCl 4 /H 2 chemistry was studied with different hydrogen dilutions within the plasma (0%, up to 67%) and with different cathode temperatures (20 ∘ C, up to 200 ∘ C). This chemistry choice creates a SiCl x -based inhibiting layer on the sidewalls that promotes anisotropic etching through the epitaxial heterostructure. The study suggests that a high hydrogen flow and a low temperature reduce the chemical reactions that create sidewall erosion. A high hydrogen flow appears to provide a hydrogen passivation of the non-radiative defects on the III-V heterostructure sidewall during the etching process. III-V/Ge triple junction solar cells with standard grid line and busbar front and back contacts have been fabricated and via-holes were plasma-etched through the active layers in order to investigate the impact of hydrogen passivation on the photovoltaic performance. The results demonstrate that the hydrogen passivation enables an open-circuit voltage increase that persists even after 5 months. This plasma process can also be used for the mesa etching step on multijunction solar cells with standard contacts. Thus, it could provide an appealing pathway to increase the conversion efficiency of state-of-the-art multijunction solar cells with standard contacts. To complete the etching process, a liner is used to protect the sidewall properties and a time-multiplexed Ge etching process is proposed to finalize the patterning and even open a pathway towards III-V/Ge plasma dicing. • A complete etching process is proposed to etch deep and anisotropic vias through a III-V/Ge heterostructure. • A low temperature SiCl 4 /H 2 plasma process is well suited to etch III-V/Ge heterostructures with limited sidewall erosion. • High H 2 flow enables a defect passivation on the etched sidewalls and it persists over several months.

Fabrication of Graphoepitaxial Gate-All-Around Si Circuitry Patterned Nanowire Arrays Using Block Copolymer Assisted Hard Mask Approach.

We demonstrate the fabrication of sub-20 nm gate-all-around silicon (Si) nanowire field effect transistor structures using self-assembly. To create nanopatterned Si feature arrays, a block-copolymer-assisted hard mask approach was utilized using a topographically patterned substrate with well-defined Si3N4 features for graphoepitaxially alignment of the self-assembled patterns. Microphase-separated long-range ordered polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block-copolymer-derived dot and line nanopatterns were achieved by a thermo-solvent approach within the substrate topographically defined channels of various widths and lengths. Solvent annealing parameters (temperature, annealing time, etc.) were varied to achieve the desired patterns. The BCP structures were modified by anhydrous ethanol to facilitate insertion of iron oxide features within the graphoepitaxial trenches that maintained the parent BCP arrangements. Vertical and horizontal ordered Si nanowire structures within trenches were fabricated using the iron oxide features as hard masks in an inductively coupled plasma (ICP) etch process. Cross-sectional micrographs depict wires of persistent width and flat sidewalls indicating the effectiveness of the mask. The aspect ratios could be varied by varying etch times. The sharp boundaries between the transistor components was also examined through the elemental mapping.

Demonstration of various optical directed logic operations by using an integrated photonic circuit.

Optical directed logic is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic operations. In this Letter, we propose and demonstrate an integrated photonic circuit which can implement five different optical logic operations by utilizing two optical modes. The proposed device is fabricated on a silicon-on-insulator substrate by using electron beam lithography and inductively coupled plasma etching processes. The static experimental results show that the fabricated device can implement five different operations correctly-XOR, XNOR, NOR, NOT, and AND-from which we can see that the signal-to-noise ratios are larger than 17.6 dB over the entire C band for all five logic functions. At last, all five logic operations with the speed of 10 Kbps are demonstrated. The proposed device with simple structure, large bandwidth, and versatility would be a promising candidate for information processing in optical mode division multiplexing networks.

BCl3/Ar plasma etching for the performance enhancement of Al-doped ZnO thin films

Al-doped ZnO (AZO) has attracted significant attention as a transparent electrode with low cost, high transmittance, high electrical conductivity, and excellent mechanical flexibility. A high-resolution patterning process is required for its application to next-generation displays, which can be achieved through the plasma etching process. In this study, we investigated the etching mechanism for Al-doped ZnO thin films in a BCl3/Ar-based plasma system and observed the performance of the thin-film surface after the etching process. The etch rate of the AZO thin films was highest at BCl3/Ar = 25:75, and increased as the power of the radio frequency source and bias increased. The etching mechanism was elucidated through optical emission and X-ray photoelectron spectroscopic analyses and confirmed to be the interaction between the bombardment of Ar ions and the chemical reaction of Cl and Cl2 radicals. BCl3-based plasma etching induces various changes in the properties of the AZO thin-film surface. The surface of the AZO thin film becomes very smooth, the work function increases by approximately 200 meV, and the bandgap increases by approximately 0.03 eV after the etching process in BCl3-based plasma. In addition, the electrical properties, such as sheet resistance and carrier mobility, are significantly improved. The results of this study may be applied for the development of high-performance optical and electronic devices.

A study on the etching characteristics of atmospheric pressure plasma for single-crystal silicon wafer

Atmospheric-pressure (AP) plasma sources have attracted researchers in many engineering fields, due to its low cost and easy handling. The AP plasma technique has been successfully applied on the surface figuring and texturing of Si, fused silica, RS-SiC, and SiC, etc. However, these studies focus more on better control for surface figuring of the substrate. The understanding of how the Si surface roughening or smoothing is occurred during the AP plasma etching using He-based CF4 mixture gas has seldom been reported. The present study starts from a parametric study of O2 addition concentration to He-based CF4 plasma. A groove is initially etched on a single-crystal silicon wafer by the CCP-type parallel-plate plasma etcher, to study the etching rate, surface morphology, material removal characteristics, and surface roughness evolution after the plasma etched removal. It is revealed that the material removal with a typical profile is achieved without introducing further damage. At the same time, the surface finish and surface integrity were enhanced by the AP plasma. The underlying mechanism of the process was investigated. Additionally, the optimized gas composition is then applied to the larger area etching by the computer-controlled scanning with different feed rates. Based on the experimental results, the surface evolution during the plasma etching process is revealed in detail. The surface removal profile also demonstrates that this method can provide an alternative way to achieve damage-free material removal for a larger area substrate by the duplicating of the typical removal profile with different etching path.

Assessment Of Cl 2 /CHF 3 Mixture For Plasma Etching Process On Barc And Tin Layer For 0.21 µm Metal Line: Silterra Case Study

In wafer fabrication manufacturing, aluminum etching process is a dry plasma etching process used as main process for construction of aluminum (Al) interconnects structures. As customer requirement changed for faster, more reliable and lower cost chips, chip manufacturers have learned to reduce the size of component on a chip in order to achieve those requirements(Ibrahim, Chik, & Hashim, 2016). As the geometry of the chip getting smaller, the width of Al line wiring specification also shrinking. To print the smaller geometry pattern requirement, the thickness in masking process also has to be reduced for better resolution. Such a thinner resist will create a challenge during plasma etching to ensure a minimal resist loss process which required new type of equipment but this research insist to sustain similar equipment. The use of oxide film as a hard mask has been evaluated by other researchers but alternative approach still needed to suit specific requirement of semiconductor factory installation base. This approach does require a process integration change and require a full technology qualification and easily take a lengthy qualification procedures especially when to qualify the existing products. It is worth trying at the situation of no other solution available. The challenge of insufficient margin for the metal line etching process for 0.2 µm width has caused the deformed metal pattern formation. This chemistry study of Cl2/CHF3 as a replacement gas to existing Cl2/O2 to address Organic backside anti refractive coating (OBARC) was evaluated and proven novelty where detail discussed in the following content.

Decrease in Particles by Substituting Conductive Magnesium-Oxide Based Ceramics for Conventional Electrode Materials Used in Process Chamber of Plasma Etching

The corrosion of ceramic chamber parts causes particles in plasma etching process, so that the production yield and the overall equipment effectiveness (OEE) at LSI mass production line are decreased. We have developed magnesium oxide (MgO)-based ceramics whose corrosion resistance in reactive plasma is higher than conventional ceramic materials. In this study, we have prepared a shower-head-type electrode by using MgO-based ceramics, and demonstrated that the number of particles generated from the electrode is much lower than that generated from a conventional electrode made from aluminium oxide. The MgO-based ceramics contributes to improvement of the production yield and the OEE.

Durable superhydrophobic cotton fabrics prepared by surface-initiated electrochemically mediated ATRP of polyhedral vinylsilsesquioxane and subsequent fluorination via thiol-Michael addition reaction

Fluorinated polyhedral oligomeric silsesquioxane (F-POSS) is one of the most popular candidates at present for superhydrophobic coating. Because of its ultralow surface energy, F-POSS has usually been dissolved with expensive fluoro-solvents, and the melting temperature of F-POSS is not high (122–140 °C), which will cause its loss during use. So trying to polymerize/crosslink F-POSS molecules and/or directly graft F-POSS to substrate is important. In this work, we report the SI-eATRP grafting of methacryl POSS (MA-POSS) on cotton and the subsequent amine catalyzed thiol-methacrylate Michael addition reaction of poly(MA-POSS) with 1H, 1H, 2H, 2H-perfluorododecyl-1-thiol (PFDT) for the fabrication of a durable poly(MA-POSS)-PFDT coating. The cotton fabric coated with poly(MA-POSS) was nearly superhydrophobic after 4 h of SI-eATRP process under potentiostatic condition of −0.40 V. Although the water contact angle (WCA) was ~148°, water droplets tended to adhere to the cotton fabric surface even when the fabric was turned upside down. After fluorination, WCA was increased to ~160°, and water drops could slide off when the fabric was slightly tilted. The sliding angle (SA) was ~10°. The as-prepared poly(MA-POSS)-PFDT coating was durable against repeated washing and physical abrasion. After 30 accelerated washing cycles (equals to 150 home laundering cycles), the coated fabric still showed superhydrophobicity. After 800 abrasion cycles over sandpaper, the WCA was still as high as 149°. In addition, the coated fabric had self-healing ability and could restore its superhydrophobicity after plasma etching through heat treatment. After 10 cycles of plasma etching and heat-induced healing process, the WCA of the coated fabric kept at ~154°. Such a durable superhydrophobic fabric coating may find applications in the development of functional clothing for a variety of purposes.

Fabrication of micro/nano multifunctional patterns on optical glass through chalcogenide heat-mode resist AgInSbTe

Heat-mode resists can spatially confine the laser hot spot to achieve subwavelength exposure by laser direct writing. However, due to the lack of systematic research on the dry etching mechanism of them, micro/nano patterning on optical glass materials through heat-mode resists has not been realized with standardized plasma processes. In this paper, the fabrication of sub-wavelength micro/nanostructures on silica substrates through the heat-mode resist is reported. A chalcogenide alloy AgInSbTe (AIST) works as the heat-mode resist. The anti-etching mechanism of the AIST resist in fluorine-based plasma gas was explored with the X-ray photoelectron spectroscopy. High etching selectivity, surface quality, and fidelity are achieved by optimizing the plasma-etching processes. Experimental and theoretical results confirm the effectiveness and feasibility of this technology. A series of micro/nano-pattern structures on silica are prepared, where the minimum feature size is 130 nm, which is about 1/3 the laser wavelength. This work paves an effective and convenient way for the fabrication of subwavelength optical elements on transparent glass substrates.

Multiscale Modeling and Recurrent Neural Network Based Optimization of a Plasma Etch Process

In this article, we focus on the development of a multiscale modeling and recurrent neural network (RNN) based optimization framework of a plasma etch process on a three-dimensional substrate with uniform thickness using the inductive coupled plasma (ICP). Specifically, the gas flow and chemical reactions of plasma are simulated by a macroscopic fluid model. In addition, the etch process on the substrate is simulated by a kinetic Monte Carlo (kMC) model. While long time horizon optimization cannot be completed due to the computational complexity of the simulation models, RNN models are applied to approximate the fluid model and kMC model. The training data of RNN models are generated by open-loop simulations of the fluid model and the kMC model. Additionally, the stochastic characteristic of the kMC model is presented by a probability function. The well-trained RNN models and the probability function are then implemented in computing an open-loop optimization problem, in which a moving optimization method is applied to overcome the error accumulation problem when using RNN models. The optimization goal is to achieve the desired average etching depth and average bottom roughness within the least amount of time. The simulation results show that our prediction model is accurate enough and the optimization objectives can be completed well.

Optimization on Dry-Etching Process for High-Density STT-MRAM

STT-MRAM (Spin-Transfer-Torque Magnetic Random-Access-Memory) with high-density is considered as one of the most promising storage candidates with potential applications. Considering the fabrication process of STT-MRAM, the patterning process has an obvious influence on the density and the quality of the storage cells. In the paper, optimization on the plasma etching process is conducted for the improvement of the pattern density. By the adjustment of the process and the introduction of the amorphous carbon as the sacrificial hard mask, the density of the patterned cells is improved, in which the bottom electrode spacing is optimized. In this way, the etching process is suitable for higher density STT-MRAM integration, while providing an practical approach for the high-density MTJ arrays. The simulation results demonstrate that the density of STT-MRAM can be improved by the proposed etching process. The optimization would be useful for future high-density STT-MRAM fabrication.

Interplay between charging and roughness on two adjacent mask holes during plasma etching

The surface roughness of a mask surface strongly limits the perfect pattern transfer from the mask to the substrate during the plasma etching process, which results in the deformation of etched features and greatly damages the mask pattern. For the understanding and, ultimately, the control of roughness, the interplay between two adjacent mask holes with nanoscale roughness profile under charging effects was investigated based on a reliable modeling framework. This study first verified that two adjacent mask holes with same/different roughness (i.e., same/different amplitude and wavelength) as well as with various sizes can lead to obviously different distributions of electric field (E-field), etching rate, and the profile evolution. These distributions are quite unlike those of an isolated hole. This work next shows that the interaction between two holes cannot be ignored. Specifically, the E-field strength and the etching rate in the area between two holes are weaker than those in the outermost area. As a result, the profiles moved away from each other. Then, charging phenomenon on a channel hole with a common source line slit trench structure was also studied. The mechanism was systematically analyzed. This work will aid in the understanding of the physical property of the mask and might optimize the etching technology.

Performance Evaluation of CNN-Based End-Point Detection Using In-Situ Plasma Etching Data

As the technology node shrinks and shifts towards complex architectures, accurate control of automated semiconductor manufacturing processes, particularly plasma etching, is crucial in yield, cost, and semiconductor performance. However, current endpoint detection (EPD) methods relying on the experience of skilled engineers result in process variations and even errors. This paper proposes an enhanced optimal EPD in the plasma etching process based on a convolutional neural network (CNN). The proposed approach performs feature extraction on the spectral data obtained by optical emission spectroscopy (OES) and successfully predicts optimal EPD time. For the purpose of comparison, the support vector machine (SVM) classifier and the Adaboost Ensemble classifier are also investigated; the CNN-based model demonstrates better performance than the two models.

The Role of Oxygen on Anisotropy in Chromium Oxide Hard Mask Etching for Sub-Micron Fabrication

Chromium and its oxides have been playing a vital role in the fabrication of micro- and nano-scale structures in numerous applications for several decades. Controllable, robust and anisotropically dry-etched hard masks and their optimal etch recipes are required in state-of-the-art device fabrication techniques. In terms of manufacturability and repeatability, a mechanistic understanding of the plasma-etching process of chromium oxide (Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) is necessary for its adoption as a hard mask. We present a systematic investigation of plasma etching of chromium oxide films via an inductively coupled plasma-reactive ion etching (ICP-RIE) system in nanoscale. The effects of plasma composition, ICP source power and HF platen power on the etch rate, sidewall profile, surface morphology, and dc-bias have been methodically investigated. We paid particular attention to studying how oxygen content can be used to control the etch profile of nano trenches using chlorine/oxygen gas mixtures, including extremes of very low and very high oxygen content. It was found that chromium oxide etch mechanisms are dependent strongly on the oxygen level. We achieved desirable vertical sidewalls with reasonable etch rates when the oxygen content is in the range 10-40% in the plasma. Oxygen content below 10% resulted in positively tapered etch profiles with low etch rates. On the other hand, bowl-like etch profiles with undercut formation was observed at high oxygen content above 40%, caused by re-emission of the reactive species at this regime. As a hard mask material, patterning Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films compared to Cr metal is advantageous in terms of etch uniformity and reproducibility. Contrary to Cr, Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is not as sensitive to chamber wall conditions.

Fast scatterometric measurement of periodic surface structures in plasma-etching processes

To satisfy the continuous demand of ever smaller feature sizes, plasma etching technologies in microelectronics enable the fabrication of device structures in the nanometer range. To control these processes, real-time access to the structure’s dimensions is needed. We develop a special method of optical critical dimension metrology and evaluate the feasibility of reconstructing the etched dimensions from experimental reflectivity spectra of the surface, taken about every second. For a periodic 2D model structure etched into a silicon, we develop and test a fast algorithm.To reduce the computing time, we generate a library of spectra before the etching. We demonstrate that, by replacing the numerically simulated spectra in the reconstruction algorithm by spectra interpolated from the library, it is possible to compute the geometry parameters in times less than a second. Finally, to also reduce memory size and computing time for the library, we reduce the scanning of the parameter values to a sparse grid.

Plasma Etching Behavior of YOF Coating Deposited by Suspension Plasma Spraying in Inductively Coupled CHF3/Ar Plasma

Dense yttrium oxyfluoride (YOF) coating was successfully deposited by suspension plasma spraying (SPS) with coaxial feeding. After deposition for 6 min at a plasma power of 105 kW, the thickness of the YOF coating was 55 ± 3.2 µm with a porosity of 0.15% ± 0.01% and the coating rate was ~9.2 µm/min. The crystalline structure of trigonal YOF was confirmed by X-ray diffractometry (XRD). The etching behavior of the YOF coating was studied using inductively coupled CHF3/Ar plasma in comparison with those of the Al2O3 bulk and Y2O3 coating. Crater-like erosion sites and cavities were formed on the whole surface of the Al2O3 bulk and Y2O3 coating. In contrast, the surface of the YOF coating showed no noticeable difference before and after exposure to the CHF3/Ar plasma. Such high resistance of the YOF coating to fluorocarbon plasma comes from the strongly fluorinated layer on the surface. The fluorination on the surface of materials was confirmed by X-ray photoelectron spectrum analysis (XPS). Depth profiles of the compositions of Al2O3, Y2O3, and YOF samples by XPS revealed that the fluorination layer of the YOF coating was much thicker than those of Al2O3 and Y2O3. These results indicate that if the inner wall of the semiconductor process chamber is coated by YOF using SPS, the generation of contamination particles would be minimized during the fluorocarbon plasma etching process.

Multiscale modeling and neural network model based control of a plasma etch process

In this paper, we present a multiscale model with application to the plasma etch process on a three dimensions substrate lattice with uniform thickness using the inductive coupled plasma (ICP). Specifically, we focus on a etch process on silicon with patterned resistive mask. And a multiscale model is developed to simulate both the gas-phase reactions and transportation phenomena in Cl2/Ar plasma chamber as well as the complex interactions that occurs on the silicon substrate. A macroscopic continuous fluid model, which based on partial differential equations (PDEs), is applied to simulate the plasma reactions as well as the transportation phenomena. The fluid model is constructed in COMSOL MultiphysicsTM. Subsequently, the microscopic interactions that taken place on the substrate are simulated by a kinetic Monte Carlo (kMC) model. A spatial-temporal discrete method is applied to address the issue in computing the fluid model and the kMC model concurrently, in which kMC models are parrallelly computed in discrete locations and data exchange between the fluid model as well as the kMC models are implemented in discrete time. Additionally, neural network (NN) is implemented to approximate the kMC model in order to reduce the computational complexity for model-based feedback control. The NN model is then used in a predictive real-time optimizer that optimize the setpoints of a set of critical proportion integral (PI) loops to achieve desired control objectives. Simulation results shows that the model is accurate and the controllers are effective.

Photolithography-free fabrication of a-IGZO thin film transistor with interconnecting metal lines

Amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistor (TFT) was successfully fabricated by the imprint lithography and plasma etching processes without using a photolithography process. The TFT is provided with two horizontally and vertically crossed electrode lines. In order to isolate the horizontal electrode line on the bottom surface, fine holes were drilled in the top vertical electrode line to separate the bottom electrode line. A 50 × 50 μm2 channel-sized TFT with connecting metal lines was completed easily using one imprint process and continuous etching process in one chamber. The TFT exhibited a linear mobility of 14.5 cm2/Vs, and a current on/off ratio of 2.07 × 105 at the drain voltage of 0.5 V. Since this TFT fabrication method utilizes self-aligned imprint lithography, there is no difficulty in alignment when using photolithography, and it can be utilized as a more complex and fine TFT array fabrication process through process improvement.

Exploring the Effects of Placement and Electron Angular Distribution on Two Adjacent Mask Holes During Plasma Etching Process

The charging effect generated by the accumulation of negative charges on a mask surface strongly limits the perfect pattern transfer from the mask to the substrate during the plasma etching process, which leads to the deformation of etched features and severely damages the mask pattern. This study first verified that various placements of the holes will result in different distributions of the electric filed (E-field) and the etching rate. This work next shows that the electron angular distribution (EAD) is closely related to the damage to the mask pattern. Based on a reliable modeling framework, the effects of changing the EAD on the distributions of spatial E-field and the etching rate were examined focusing on two adjacent and asymmetrically-shaped mask holes. Specifically, both the E-field strength and the etching rate around the edge of the two mask holes can be greatly reduced by narrowing the EAD, meanwhile, the number of electrons penetrating into the bottom of two holes will be significantly increased. These results will reduce the mask pattern damage and improve the etching of high-aspect-ratio features into a substrate. In the cases of different EADs, the simulated evolution rates of these two mask holes and the E-field strength inside the holes verify these conclusions. The mechanism is discussed in detail. This work will greatly help to optimize the etching technique.