Deep Plasma Etching Research Articles

Fabrication of Bulk Tungsten Microstructure Arrays for Hydrophobic Metallic Surfaces Using Inductively Coupled Plasma Deep Etching.

Hydrophobic surfaces have attracted great attention due to their ability to repel water, and metallic surfaces are particularly significant as they have several benefits, for example they self-clean and do not corrode in marine environments, but also have several applications in the aircraft, building and automobile industries. Tungsten is an ideal material for metallic surfaces due to its remarkable mechanical properties. However, conventional micromachining methods of micro- or nanostructures, including mechanical fabrication and laser and wet etching are incapable of balancing functionality, consistency and cost. Inspired by the etching process of silicon, deep etching of bulk tungsten has been developed to achieve versatile microstructures with the advantages of high efficiency, large scale and low cost. In this article, fabrication methods of tungsten-based hydrophobic surfaces using an ICP deep etching process were proposed. Micro- or hierarchical structure arrays with controllable sidewall profiles were fabricated by optimizing etching parameters, which then exhibited hydrophobicity with contact angles of up to 131.8°.

Customized Patterning of Deep Nanowell Structures in Polymer Electrolyte Membranes for Highly Enhanced Fuel Cell Performances

Surface microstructuring of polymer electrolyte membranes (PEMs) has been considered as an effective strategy to extend the three-phase boundary in PEM fuel cells (PEMFCs). However, it is still unclear which parameters are the most critical for maximizing cell performance. In this study, in order to elucidate the correlation between the membrane surface topography and PEMFC performances, we employed solvent-assisted nanotransfer printing and plasma deep etching techniques, which allow independent control of structural parameters. This approach enables the formation of various catalyst–membrane interface structures with controlled pattern periods and aspect ratios. Our systematic customization reveals that nanowell patterned membranes partially filled with carbon-supported platinum (Pt/C) can significantly improve fuel cell performance, which is driven by both reducing kinetic resistance and mass transport resistance. In particular, the sample with a pattern period of 1200 nm and a well depth of 1100 nm exhibited the best performance, a current density of 1000 mA/cm2 at a cell voltage of 0.6 V, and a maximum power density of 583 mW/cm2. These values are 53 and 41% higher than those with unpatterned membranes, respectively, at the same Pt loading.

β -Ga2O3 Schottky barrier diodes with 4.1 MV/cm field strength by deep plasma etching field-termination

In this work, we demonstrate a deep mesa etch design for efficient edge field termination in β-Ga2O3 Schottky barrier diodes (SBDs). The proposed design enabled parallel plate fields higher than 4.1 MV/cm with negligible change to the device ON characteristics. The effect of BCl3/Cl2-based dry etch on (100) and (010) etched vertical sidewalls is also analyzed. A remarkable anisotropy in depletion was observed for etch along (100) and (010) sidewalls. This work provides insight into the impact of etching on n-type Ga2O3 and shows a promising method to realize efficient field termination for high breakdown field strength SBDs.

Laminar drag reduction in a closed channel using bioinspired textured surfaces

Low flow drag is of great importance to a variety of engineering applications, and an effective way to achieve low drag is to use bioinspired microstructured surfaces. This work aims to reduce the skin-friction drag in closed channel flow using textured surfaces inspired by leaves of indocalamus and rice. A channel formed from a polydimethylsiloxane chunk and a silicon wafer was fabricated to study the drag reduction behavior for water or liquid paraffin oil in laminar flow. Bioinspired textures were processed on the silicon wafer surface using the deep silicon plasma etching method. The pressure drop of water or paraffin oil passing through textured channels with different velocities was measured. The maximum pressure drop reductions for the paraffin oil flow with a low velocity (Re ≈ 1) and for the water flow with a high velocity (Re < 1000) were about 5.1 and 27.3%, respectively. The contact angles of the bioinspired textured surface are also presented, and mechanisms to explain the drag reduction are proposed. Hydrophobicity leading to a change from a liquid–solid interface to a liquid–air interface is believed to provide the drag reduction for water flow, while the thin oil film formed on the textured surface due to oleophilicity helps reduce the oil flow drag.

Fabrication of DNA-Templated Pt Nanostructures by Area-Selective Atomic Layer Deposition

We report the fabrication of DNA-templated Pt nanostructures by area-selective atomic layer deposition. A DNA-templated self-assembled monolayer was used to mediate the area-selective deposition of Pt. Using this approach, we demonstrated the fabrication of both single- and two-component nanostructure patterns, including Pt, TiO2/Pt, and Al2O3/Pt. These nanoscale patterns were used as hard masks for plasma deep etching of Si to fabricate anti-reflection surfaces. This work demonstrated a gas-phase, DNA-templated fabrication of metal nanostructures, which complements earlier work of solution-based DNA metallization. The nanostructures obtained here are useful for applications in nanoelectronics, nanophotonics, and surface engineering.

Combined analysis methods for investigating titanium and nickel surface contamination after plasma deep etching

Plasma etching techniques can result in damage and contamination of materials, which, if not removed, can interfere with further processing. Therefore, characterisation of the etched surface is necessary to understand the basic mechanisms involved in the etching process and enable process control and cleaning procedures to be developed. A detailed investigation by means of the combined use of scanning electron microscopy coupled with energy‐dispersive X‐ray spectrometry (SEM/EDS), X‐ray photoelectron spectroscopy (XPS) and optical microscopy (OM) has been carried out on deep titanium trenches etched by plasma. This innovative approach has provided a further insight into the microchemical structure of the surface contamination layer on both the titanium and the nickel hard mask surfaces. The described experiments were conducted on 25 to 100‐μm wide trenches, first etched in bulk titanium by an optimised Cl2/SF6/O2‐based inductively coupled plasma process, through an electroplated nickel hard mask. The results allow to identify chlorine, fluorine and carbon as the main contaminating agents of the nickel mask and to associate three oxidation states around the etched trenches highlighting certain specific aspects related to the passivation mechanism. These observations reinforce the scientific relevance of the combined use of complementary optical and imaging analytical techniques.

A study of the microstructure modification of a space crawling robot adhesive feet based on discrete element method

According to the on-orbit maintenance mission requirements of a proposed space cooperative spacecraft, a new type of space crawling robot, which can be mounted on a grasping manipulator, is proposed. After the active spacecraft and the faulty target form a connection, the crawling robot can move to the spot on the faulty target that requires maintenance to be performed using fine operations. In this paper, the adhesion technology of space crawling robots was studied, and an adhesive microarray structure, which imitates gecko setae, was proposed. The simulation model was established using the discrete element software EDEM. The effects of the structural parameters, such as the contact area, length–diameter ratio, length, diameter, and density, on the adhesion characteristics of the microarrays in zero-gravity space environment were analysed using simulation. Based on the simulation results, a plasma deep etching process was used to process the microarray specimens. The desorption process was tested in the ground environment using the water droplet method, and the tangential desorption force was tested. The experimental data show that the tangential adhesion decreases with an increase in the spacing and the length–diameter ratio. The experimental results are very consistent with the simulation results, which further demonstrated the correctness of the discrete element simulation with respect to the desorption process and the rationality of the optimal design of the microarray structure.

A micromachined water-immersible scanning mirror using BoPET hinges

This paper reports a new micromachined two-axis water-immersible scanning mirror using BoPET (biaxially-oriented polyethylene terephthalate) hinges. A new fabrication process based on deep plasma etching on a hybrid silicon-BoPET substrate was developed to enable high-resolution patterning and batch fabrication capability. For demonstration, a prototype scanning mirror was designed, fabricated and tested. It has an overall size of 5 × 5 × 5 mm3, which is comparable to that of a typical silicon-based micro scanning mirror. With a short-hinge design, the size of the mirror plate reaches 4 × 4 mm2 to provide an even larger aperture for optical or acoustic beam steering. In the air, the resonance frequencies of the fast and slow axes are 420 Hz and 190 Hz respectively. When immersed in water, the resonance frequencies are reduced to 330 Hz and 160 Hz, respectively. The tilting angles of the mirror around the fast and slow axes follow a linear relationship with the driving current up to ±3.5°. With both axes driven simultaneously, stable and repeatable raster scanning patterns were obtained in both air and water. The micromachined water-immersible scanning mirrors could be useful for various scanning optical and acoustic microscopic imaging applications in both air and liquid environments.

High aspect ratio etched sub-micron structures in silicon obtained by cryogenic plasma deep-etching through perforated polymer thin films

Abstract Cryogenic plasma deep-etching for silicon sub-micron structures was studied with the use of modified poly(styrene) (PS) perforated masks obtained from laterally phase separated PS and poly (lactic acid) PLA blend thin films. PS mask was stained by heavy metal (ruthenium) or transferred to an intermediate hard mask (silicon oxide). For the stained mask, optimization of standard STiGer cryogenic plasma etching process led to etched Si cavities with minimal defects at rate of 0.8 μm/min but within a limited depth (~1.4 μm). For intermediate hard mask, optimized STiGer etching process was used in order to improve the reproducibility and to obtain the deeply etched features up to 10 μm depth with minimal defects. A higher etch rate of around 1.2 μm/min was achieved.

Deep etched and released microstructures in Zerodur in a fluorine-based plasma

In this paper, we demonstrate the dry-etch release of free-standing mechanical elements with a high aspect ratio from a Zerodur wafer. Our previous research was focussed on deep plasma etching of Zerodur and the determination of characteristic process parameters such as selectivity, sidewall angle and etch rate. Nevertheless, the releasing of structures is more challenging. The achievable sidewall angle in fluorine-based plasma of 71°, and a low selectivity limits the etch depth. Here, we show a double-sided process, which allows a high aspect ratio and structure heights of 150 μm and above. We implement a process that allows a damage-free finishing of the micromechanical elements. The chemical sidewall composition of the released structures was carefully investigated. A strong build up of non-volatile products at specified positions of the structures results from the two-directional process and the structure geometry. This is discussed in the article and can be applied to other glasses and glass ceramics with complex composition, too.

Deep plasma etching of Parylene C patterns for biomedical applications

We report on the plasma etching of thick (∼23μm) Parylene C structures. Parylene C is a transparent polymer that benefits from high biocompatibility, flexibility and chemical inertness, and has gained increased attention over the years in the biomedical field. In the manufacturing process, highly defined structuration steps of Parylene C are essential, but techniques based on laser, scalpel and wet etching have shown to be unsuitable for properly cut structures. Plasma etching remains nowadays the most widespread option, though fast etching rate, lack of residues and high aspect ratios are still hard to achieve. To overcome these issues, the selection of both mask material and plasma conditions is crucial. Here, three masks - metal, positive and negative photoresists - are tested as stencils, and several plasma parameters are briefly studied in order to obtain the highest etching rate while maintaining good coverage. We showed that increasing the RF power up to a considerable 2800W while maintaining a moderate physical contribution (bias power, pressure, temperature), is optimal in the achievement of fast PaC etching without inducing thermal stress. Besides, the addition of a short fluorinated plasma in the midst of the process is shown to alleviate residues. For the first time, negative photoresist Intervia Bump Plating (BPN) coating followed by ICP11Inductively coupled plasma. -RIE22Reactive ion etching. are used in order to pattern Parylene C-based structures, with a clean cut, vertical profile and fast etching rate (∼0.87±0.06μm/min) and a selectivity of 0.5. This solution was carried out to release unitary Parylene-based neural probes from a silicon wafer. Finally, cytotoxicity assays on these neural implants were performed to make sure that no trace of mask or stripper residues jeopardizes device biocompatibility.

Photoswitched Cell Adhesion on Azobenzene-Containing Self-Assembled Films.

Stimuli-responsive surfaces that can regulate and control cell adhesion have attracted much attention for their great potential in diverse biomedical applications. Unlike for pH- and temperature-responsive surfaces, the process of photoswitching requires no additional input of chemicals or thermal energy. In this work, two different photoresponsive azobenzene films are synthesized by chemisorption and electrostatic layer-by-layer (LbL) assembly techniques. The LbL film exhibits a relatively loose packing of azobenzene chromophores compared with the chemisorbed film. The changes in trans/cis isomer ratio of the azobenzene moiety and the corresponding wettability of the LbL films are larger than those of the chemisorbed films under UV light irradiation. The tendency for cell adhesion on the LbL films decreases markedly after UV light irradiation, whereas adhesion on the chemisorbed films decreases only slightly, because the azobenzene chromophores stay densely packed. Interestingly, the tendency for cell adhesion can be considerably increased on rough substrates, the roughness being introduced by use of photolithography and inductively coupled plasma deep etching techniques. For the chemisorbed films on rough substrates, the amount of cells that adhere also changes slightly after UV light irradiation, whereas, the amount of cells that adhere to LbL films on rough substrates decreases significantly.

Study of High Aspect Ratio NLD Plasma Etching and Postprocessing of Fused Silica and Borosilicate Glass

In this paper, we report magnetic neutral loop discharge (NLD) plasma etching of fused silica (FS) and borosilicate glass (BSG), demonstrating high aspect ratio deep etch (100 μm) with vertical walls (<;3° deviation from vertical). This paper for the first time presents the systematic study of FS and BSG deep etching in NLD plasma. Four different masking materials have been explored including metal, amorphous silicon, bonded silicon, and photoresist. Etch parameters were optimized to eliminate unwanted artifacts, such as micro-masking, trenching, and faceting, while retaining a high aspect ratio (up to 7:1 for FS and 8:1 for BSG). In addition, a method for sidewall roughness mitigation based on postfabrication annealing was developed, showing the sidewall roughness reduction from the average roughness (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) 900 to 85 nm. Further advances in deep plasma etching processes may enable the use of FS and BSG in the fabrication of precision inertial MEMS, micro-fluidic, and micro-optical devices.

Deep SiO2 etching with Al and AlN masks for MEMS devices

Silicon oxide-based materials such as quartz and silica are widely used in microelectromechanical systems (MEMS). One way to enhance the capability of their deep plasma etching is to increase selectivity by the use of hard masks. Although this approach was studied previously, information on the use of hard masks for the etching of silicon-oxide based materials on 200 mm substrates is scarce. We present the results of etching process development for amorphous silicon oxide using Al and AlN masks with a view of the application of the results for the etching of silica and quartz. Three gas chemistries (C4F8/O2, CF4 and SF6) and their mixtures were compared in an industrial reactive ion etch (RIE) chamber with two plasma sources. It was established that pure SF6 is the best etchant and AlN is a better mask than Al for providing higher selectivity and a sidewall angle close to vertical. A range of etching parameters for micromasking-free etching was established and etched structures of up to a 4 : 1 aspect ratio were created in 21 μm-thick oxide using the process with an etch rate of 0.32–0.36 μm min−1 and a selectivity to AlN mask of (38–49) : 1.

A Spatial ALD Oxide Passivation Module in an All-Spatial Etch-Passivation Cluster Concept

Conventional Atomic Layer Deposition (ALD) is also a cycled process, with the extra benefit of the half-reactions being self-limiting, thus enabling layer-by-layer growth. A major obstacle holding ALD from large-scale, high-throughput manufacturing has been the very low deposition rate. This was overcome only recently by introducing the spatial atmospheric-pressure version 1]. Today, spatial ALD is used commercially by the solar industry, and soon other application domains will follow. Shallow and deep plasma etching with nanoscale accuracy is also increasingly based on alternating half-cycles of a directional etch and an isotropic deposition of a passivating polymer layer (usually fluorocarbon or oxyfluoride). Also here the process rates are slow, and to speed up atomic precision etching we conceived a spatially-divided concept as well [2,3]. The process is converted from time- into spatially separated by inserting inert gas-bearing ‘curtains’ of heights down to ~100 μm that confine the reactive gases to individual injection slots in a gas injector head. By moving substrates back and forth under the head one accomplishes the alternate etch/ passivation cycles without idle times needed for switching pressure or purging. The pressure settings range from low-pressure for etching to (sub)atmospheric for passivation, and can be optimized for each separate process zone thus maximizing the total etch rate. A further improvement towards an all-spatial etch approach is in the passivation cycle where the conventional polymer passivation layer is replaced by a spatial atmospheric-pressure ALD-grown oxide passivation layer; see Fig. 1). We have conducted both thermal ALD of Al2O3 at 200 oC and plasma-enhanced SiO2 ALD at 50 oC in pre-etched high aspect ratio trenches (65 nm width and 9 μm depth) in a rotary spatial atmospheric-pressure reactor, and showed - with non-optimized processing and equipment - step conformality values of ³ 80 % for the Al2O3 and 70 % for the SiO2 which is sufficient for most passivations. We conducted a preliminary etch/ALD oxide passivation/etch cycle on a Si-sample with a trench-patterned hard SiO2 mask on top. The sample was processed in two separate (non-connected) reactor chambers, each chamber being supplied with a surface Dielectric Barrier Discharge (DBD) micro-plasma source. The following process cycle was carried out: 1) a 1 min. plasma etch step using SF6/O2 on a biased, non-moving Si-substrate in the low-pressure chamber at room temperature, 2) the thermal deposition of an Al2O3 passivation of only 5 monolayers (5 rotations) in the rotary spatial atmospheric pressure ALD reactor described as above, 3) an identical 1 min. plasma etch step in the low-pressure chamber. The cross-sectional etch profile thus obtained (Fig. 2) showed two typical scallops on the trench sidewall, revealing that both directional and lateral etch had been accomplished in a mixed anisotropic/ isotropic regime where as little as 5 monolayers of Al2O3 passivation were sufficient to preserve the shape of the scallop carved out in the first cycle. Another remarkable observation was the flat etch front of the trench bottom. This may be indicative for the robustness of ALD-grown Al2O3 passivation, and desired in atomically smooth precision etching. In continuous etching trench bottoms are often micro-trenched due to ion scattering from the trench sidewalls which results in faster etching of the side corners. We note that these results have been obtained with non-optimized processing and equipment, so we are confident that further optimization will give more improvements and insights. The process variables are manifold: gas concentration, pressure in the etch and passivation chambers, plasma power, substrate voltage biasing, room temperature processing, plasma source-to-substrate distance, passivation with other spatial ALD oxides like SiO2. We conclude by stating that this all-spatial concept, called ALD-enabled RIE, may find industrial use in cost-effective back-end- and front-end-of-line processing, especially in patterning of structures that require minimum interface, line edge and fin sidewall roughness (i.e., atomic-scale fidelity with selective removal of atoms and retention of sharp corners). Besides in CMOS scaling this concept may also become an important option for fast etching of silicon (or III/V) in die dicing, TSV and MEMS processing.

Submicronic etched features of silicon with high aspect ratio obtained by cryogenic plasma deep-etching through perforated polymer thin films

ABSTRACTWe report the preparation of nanomasks for silicon plasma etching, which is not based on full top-down approaches such as conventional lithographic process. We used laterally phase separated polymers thin films (30 to 100 nm thick) obtained from immiscible polymer blends of poly(styrene) PS and poly(lactide) PLA, PS being the major component, spin-coated onto silicon substrates. Despite the high incompatibility of the two polymers, submicronic domains were obtained in the film. The selective extraction of the minor component (PLA) led to the formation of a perforated layer of PS at the top of the silicon substrate, and was used as a mask for the selective etching of the silicon. For that purpose, we used a cryogenic etching process where the silicon substrate was cooled at a cryogenic temperature (∼ -120°C) and exposed to a monocyclic SF6/O2 plasma. It was possible to etch anisotropic profiles with vertical sidewalls and minimal defects. Etched feature with an aspect ratio of 7 were obtained in these conditions. We determined that the selectivity of etching (Si/PS) was 11:1, with a silicon etching rate of 0.8 µm/min. The selectivity of these masks was further increased when using the inorganic replicas of the polymer template (50:1) or with chemical modifications of the PS by RuO4 (80:1), allowing for increased aspect ratio etched features (up to 20 in the latter case). Optimized etching processes (such as STiGer process) were also used in order to improve the reproducibility and robustness of the method.

Разработка процесса глубокого плазменного травления кремния для технологии трехмерной интеграции кристаллов

Plasma etch process for thought-silicon via (TSV) formation is one of the most important technological operations in the field of metal connections creation between stacked circuits in 3D assemble technology. TSV formation strongly depends on parameters such as Si-wafer thickness, aspect ratio, type of metallization material, etc. The authors investigate deep silicon plasma etch process for formation of TSV with controllable profile. The influence of process parameters on plasma etch rate, silicon etch selectivity to photoresist and the structure profile are researched in this paper. Technology with etch and passivation steps alternation was used as a method of deep silicon plasma etching. Experimental tool «Platrane-100» with high-density plasma reactor based on high-frequency ion source with transformer coupled plasma was used for deep silicon plasma etching. As actuation gases for deep silicon etching were chosen the following gases: SF6 was used for the etch stage and CHF3 was applied on the polymerization stage. As a result of research, the deep plasma etch process has been developed with the following parameters: silicon etch rate 6 µm/min, selectivity to photoresist 60 and structure profile 90±2°. This process provides formation of TSV 370 µm deep and about 120 µm in diameter.

Nanoimprinting of TiO 2 –SiO 2 photocurable materials with high titanium concentration for CF 4 /O 2 etch selectivity

The nanofabrication of nanometre-scale multiple-level structures by nanoimprint lithography and CF4/O2 etching rates was investigated for nanoelectro mechanical systems and three-dimensional (3D) wafer-level packaging. A TiO2–SiO2 sol–gel photocurable material with high titanium concentration of 20.9 wt% was developed for CF4/O2 etch selectivity with a pattern transferring carbon layer in a bi-layer process. The nanostructures of 3D micropatterns, holes with 200 nm diameter and 130 nm-wide dense lines with line edge roughness of ∼10 nm were provided. The CF4/O2 etching rate of the TiO2–SiO2 photocurable material was ∼3.7 times lower than that of the referenced SiO2 sol–gel photocurable material. The CF4/O2 etch rates of titanium-based photocurable materials were confirmed for deep plasma etching processes.

Research and development of deep anisotropic plasma silicon etching process to form MEMS structures

Process characteristics of deep silicon etching as a function of its operational parameters are investigated. A process of deep anisotropic plasma etching process is developed and optimized to form MEMS silicon structures. The results of the work are used in forming MEMS working structures.

Inductively coupled plasma deep etching of InP/InGaAsP in Cl2/CH4/H2 based chemistries with the electrode at 20 °C

A Cl2/CH4/H2 inductively coupled plasma process without additional heating or wafer bonding is developed for the InP/InGaAsP material system. Vertical and smooth sidewalls can be observed in the scanning electron microscope images. The main factors of etch rate, selectivity, and sidewall roughness are analyzed relative to the gas concentration in a full factorial design of the experimental procedure. Under optimized conditions, an etch depth of more than 3 μm with smooth and vertical sidewalls can be obtained. A strong indication of a passivation effect of CH4 is obtained.