Hydrogen Plasma Etching Research Articles

Simultaneous Detection of Carbamates and Organophosphate Pesticides at Bare Boron-Doped Diamond Electrodes

Carbamate and organophosphate compounds are widely used pesticides because of their high insecticidal activity, and sometimes as nerve agents because of their crippling inhibition of the enzyme acetylcholinesterase (AChE)1. These compounds accumulate in the food chain and can hijack the nervous system of the target organisms indiscriminately. Traditional electrochemical methods of pesticide detection rely on layered structures atop noble metal or carbon electrodes to assist the loading of AChE, which produces currents proportional to its inhibition level. One of the clear advantages of boron-doped diamond (BDD) as an electrode material is its greater potential window in aqueous solutions, compared to conventional electrode materials2. This allows redox behaviour at extended potentials to be observed without damage to the electrode. Cyclic, differential-pulse, and square-wave voltammetric techniques were used to probe carbaryl (CB), carbofuran (CF), and malathion in Carmody buffers of pH 2–12. Oxidation of CF occurred at the three overpotentials 1.31 V, 1.44 V, and 1.69 V, and a broad reduction peak was observed at 1.10 V, referred against Ag|AgCl. Compared with the oxidation of CB at 1.35 V, these electrochemical differences allowed for simultaneous detection of both compounds. This non-enzymatic sensor demonstrated a linear calibration over a concentration range of 1–100 µM for CB (R=0.9834) and CF (R=0.9938). After exposure to 1 mM malathion, a reduction peak appears that is highly sensitive to pH, attributed to a complex carbon–oxygen adsorbate that is robust to aggressive cleaning methods and only removable by hydrogen plasma etching. This malathion modified surface may be advantageous in future applications such as pH sensing. The oxidised BDD demonstrated failsafe reproducibility, a linear response, and low detection limits at medically relevant concentrations. References Kostelnik, P. Kopel, A. Cegan, M. Pohanka, Sensors, 17 (2017) 676.V. Macpherson, Phys. Chem. Chem. Phys., 17 (2015) 2935-2949.

Hexagonal Nanopits with the Zigzag Edge State on Graphite Surfaces Synthesized by Hydrogen-Plasma Etching

We studied, by scanning tunneling microscopy, the morphology of nanopits of monolayer depth created at graphite surfaces by hydrogen plasma etching under various conditions such as H$_2$ pressure, temperature, etching time, and RF power of the plasma generation. In addition to the known pressure-induced transition of the nanopit morphology, we found a sharp temperature-induced transition from many small rather round nanopits of ~150 nm size to few large hexagonal ones of 300-600 nm within a narrow temperature range. The remote and direct plasma modes switching mechanism, which was proposed to explain the pressure-induced transition, is not directly applicable to this newly found transition. Scanning tunneling spectroscopy (STS) measurements of edges of the hexagonal nanopits fabricated at graphite surfaces by this method show clear signatures of the peculiar electronic state localized at the zigzag edge (edge state), i.e., a prominent peak near the Fermi energy accompanied by suppressions on either side in the local density of states. These observations indicate that the hexagonal nanopits consist of a high density of zigzag edges. The STS data also revealed a domain structure of the edge state in which the electronic state varies over a length scale of ~3 nm along the edge. The present study will pave the way for microscopic understanding of the anisotropic etching mechanism and of spin polarization in zigzag nanoribbons which are promising key elements for future graphene nanoelectronics.

Characterization of hydrogen plasma defined graphene edges

We investigate the quality of hydrogen plasma defined graphene edges by Raman spectroscopy, atomic resolution AFM and low temperature electronic transport measurements. The exposure of graphite samples to a remote hydrogen plasma leads to the formation of hexagonal shaped etch pits, reflecting the anisotropy of the etch. Atomic resolution AFM reveals that the sides of these hexagons are oriented along the zigzag direction of the graphite crystal lattice and the absence of a D-peak within the noise background in the Raman spectra seems to suggest rather high quality zigzag edges. In a second step of the experiment, we investigate hexagon edges created in single layer graphene on hexagonal boron nitride and find a substantial D-peak intensity. Polarization dependent Raman measurements reveal that hydrogen plasma defined edges consist of a mixture of zigzag and armchair segments. Furthermore, electronic transport measurements were performed on hydrogen plasma defined graphene nanoribbons which indicate a high quality of the bulk but a relatively low edge quality, in agreement with the Raman data. These findings are supported by tight-binding transport simulations. Hence, further optimization of the hydrogen plasma etching technique is required to obtain pure crystalline graphene edges.

Effect of hydrogen etching on the electrical prosperities of nanocrystalline diamond film

The nanocrystalline diamond (NCD) were synthesized on silicon substrates by a hot filament chemical vapor deposition (HFCVD) method with varying hydrogen plasma etching time. The hydrogen etching effect on the characteristics of current-voltage, capacitance-frequency and dielectric loss-frequency have been studied. It was founded that the dark current decreased with the etching time. The dielectric properties based on NCDs can be improved with the increasing in etching time, indicating sample with 3 h hydrogen etching exhibited dielectric constant closed to intrinsic diamond and low dielectric loss. The hydrogen etching treatment can provide a feasible approach to enhance the dielectric property of NCD.

Competitive interplay of deposition and etching processes in atomic layer growth of cobalt and nickel metal films

Abstract

Precise control of graphene etching by remote hydrogen plasma

Graphene with atomically smooth and configuration-specific edges plays the key role in the performance of graphene-based electronic devices. Remote hydrogen plasma etching of graphene has been proven to be an effective way to create smooth edges with a specific zigzag configuration. However, the etching process is still poorly understood. In this study, with the aid of a custom-made plasma-enhanced hydrogen etching (PEHE) system, a detailed graphene etching process by remote hydrogen plasma is presented. Specifically, we find that hydrogen plasma etching of graphene shows strong thickness and temperature dependence. The etching process of single-layer graphene is isotropic. This is opposite to the anisotropic etching effect observed for bilayer and thicker graphene with an obvious dependence on temperature. On the basis of these observations, a geometrical model was built to illustrate the configuration evolution of graphene edges during etching, which reveals the origin of the anisotropic etching effect. By further utilizing this model, armchair graphene edges were also prepared in a controlled manner for the first time. These investigations offer a better understanding of the etching process for graphene, which should facilitate the fabrication of graphene-based electronic devices with controlled edges and the exploration of more interesting properties of graphene.

Diamond Deposition on Graphite in Hydrogen Microwave Plasma

Hydrogen plasma etching of graphite generates radicals that can be used for diamond synthesis by chemical vapor deposition (CVD). We studied the etching of polycrystalline graphite by a hydrogen microwave plasma, growth of diamond particles of the non-seeded graphite substrates, and characterized the diamond morphology, grain size distribution, growth rate, and phase purity. The graphite substrates served simultaneously as a carbon source, this being the specific feature of the process. A disorder of the graphite surface structure reduces as the result of the etching as revealed with Raman spectroscopy. The diamond growth rate of 3 – 5 µm/h was achieved, the quality of the produced diamond grains improving with growth time due to inherently nonstationary graphite etching process

Optical emission spectroscopy of gallium phosphide plasma-enhanced atomic layer deposition

The capability of optical emission spectroscopy for in situ study and control of plasma-enhanced atomic-layer deposition (PE-ALD) of gallium phosphide from phosphine and trimethylgallium carried by hydrogen was explored. The gas composition changing during the PE-ALD process was monitored by in situ measurements of optical emission intensity for phosphine and hydrogen lines. For PE-ALD process where phosphorus and gallium deposition steps are separated in time a negative influence of excess phosphorus accumulation on the chamber walls was observed. Indeed, the phosphorus deposited on the walls during PH3 decomposition step is etched by hydrogen plasma during the next trimethylgallium decomposition step leading to uncontrollable and unwanted conventional plasma-enhanced chemical vapor deposition. To reduce this effect, it has been proposed to introduce a step of hydrogen plasma etching, which allows one to etch excess phosphorus before the beginning of gallium deposition step and achieve atomic-layer deposition growth mode.

Hydrogen plasma etching mechanism at the a-C:H/a-SiCx:H interface: A key factor for a-C:H adhesion

Hydrogenated amorphous carbon thin films (a-C:H) do not show good adhesion on ferrous alloys. When a silicon-containing intermediate thin film is chosen, deposition temperatures of at least 300 °C are necessary to provide adequate adhesion. However, a new approach is introduced to achieve similar results at lower temperatures: a selective chemical hydrogen plasma etching before the carbonaceous film deposition. The effect is known but its physicochemical mechanism and kinetics remain open. We have investigated the role of hydrogen etching in the modification of the outermost and innermost interfaces of a-SiCx:H interlayers. The results show that hydrogen radically modifies the interlayer thickness in the outermost region and increases the C/Si ratio in the innermost. Moreover, the hydrogen etching allows the formation of more CC bonds at the outermost interface, which is correlated to better adhesion. Finally, we proposed a mechanism in order to explain physical and chemical changes caused by hydrogen etching.

Correction to: Removal of Tin from Extreme Ultraviolet Collector Optics by In-Situ Hydrogen Plasma Etching

The original version of this article unfortunately contained a mistake in the “Deposition of Stannane (DOS) Chamber” section.

STS Studies of Zigzag Graphene Edges Produced by Hydrogen-Plasma Etching

STS Studies of Zigzag Graphene Edges Produced by Hydrogen-Plasma Etching

Low resistivity of graphene nanoribbons with zigzag-dominated edge fabricated by hydrogen plasma etching combined with Zn/HCl pretreatment

Graphene nanoribbons (GNRs) have attracted intensive research interest owing to their potential applications in high performance graphene-based electronics. However, the deterioration of electrical performance caused by edge disorder is still an important obstacle to the applications. Here, we report the fabrication of low resistivity GNRs with a zigzag-dominated edge through hydrogen plasma etching combined with the Zn/HCl pretreatment method. This method is based on the anisotropic etching properties of hydrogen plasma in the vicinity of defects created by sputtering zinc (Zn) onto planar graphene. The polarized Raman spectra measurement of GNRs exhibits highly polarization dependence, which reveals the appearance of the zigzag-dominated edge. The as-prepared GNRs exhibit high carrier mobility (∼1332.4 cm2 v−1 s−1) and low resistivity (∼0.7 kΩ) at room temperature. Particularly, the GNRs can carry large current density (5.02 × 108 A cm−2) at high voltage (20.0 V) in the air atmosphere. Our study develops a controllable method to fabricate zigzag edge dominated GNRs for promising applications in transistors, sensors, nanoelectronics, and interconnects.

Removal of Tin from Extreme Ultraviolet Collector Optics by In-Situ Hydrogen Plasma Etching

Extreme ultraviolet (EUV) lithography produces 13.5 nm light by irradiating a droplet of molten Sn with a laser, creating a dense, hot laser-produced plasma and ionizing the Sn to the + 8 through + 12 states. An unwanted by-product is deposition of Sn debris on the collector optic, which focuses the EUV light emitting from the plasma. Consequently, collector reflectivity is degraded. Reflectivity restoration can be accomplished by means of Sn etching by hydrogen radicals, which can be produced by an H2 plasma and etch the Sn as SnH4. It has previously been shown that plasma cleaning can successfully create radicals and restore EUV reflectivity but that the Sn removal rate is not necessarily limited by the radical density. Additionally, while Sn etching by hydrogen radicals has been shown by multiple investigators, quantification of the mechanisms behind Sn removal has never been undertaken. This paper explores the processes behind Sn removal. Experiments and modeling show that, within the parameter space explored, the limiting factor in Sn etching is not radical flux or SnH4 decomposition, but ion energy flux. Thus the removal is akin to reactive ion etching.

High-Rate Etching of Copper By High-Pressure Hydrogen-Based Plasma

The copper wiring technique is a vital manufacturing technology for the current ultra-large-scale integrated (ULSI) circuits. In general, these Cu wiring are fabricated by the dual damascene process. The damascene process is mainly composed of chemical mechanical polishing (CMP) and electrical Cu plating techniques. Although these processes are well-established, these processes are fundamentally demonstrated in a wet environment and require expensive consumables and toxic chemicals. Furthermore, since CMP requires the adequate processing load for the efficient machining, the usage of a low-k material as an interlayer insulator, which has low mechanical strength, requires a prolonged processing time. From above background, it is longed-for that the dry etching process for Cu can replace the conventional wet machining process. In the previous study on the conventional dry etching for Cu, chlorine is often used as the typical etchant gas. The chlorine gas is harmful for humans and aggressive toward many of the metals constructing the etching apparatus. Furthermore, because the chlorinated Cu products exhibit a low vapor pressure around room temperature, substrate heating is generally required. On the other hand, it has been revealed that a hydrogen-based plasma can be applied for Cu dry etching at low temperature. This hydrogen dry etching seems attractive in terms of preserving the environment and suppressing the use of toxic chemicals. If a higher etching rate greater than 100 nm/min can be obtained by pure hydrogen plasma etching, it is expected that a hydrogen dry etching method with no toxic chemicals could be substituted for the CMP process. In this study, therefore, we applied the high-pressure hydrogen glow plasma (>100 Torr) to Cu etching in an attempt to achieve a higher Cu etching rate. In the experiment, a localized hydrogen-based plasma is generated at 100 Torr around the tip of a syringe needle electrode (outer diameter of 1mm). The very-high-frequency (VHF; 150 MHz) power source was used for the plasma generation. The samples used in this study were a 1 mm-thick Cu plate for investigating the Cu etching property, a 0.7 mm-thick Si(001) wafer and 0.7 mm-thick SiO2 glass to compare the etching behavior of Cu with other ULSI construction materials. The sample stage temperature was controlled from −20 to 330°C. The H2 gas was supplied to the plasma directly from the needle bore via a mass flow controller during the etching. In this study, to confirm the role of hydrogen in Cu etching, He, Ar and N2 gases were used as the process gas instead of H2. As a result, the Cu etching occurs only when the process atmosphere contains H2 gas, and the etching rates decrease with diluting the hydrogen concentration by He gas. The impact of plasma heating on the Cu etching is negligible, so the etching mechanism of the high pressure H2 plasma differs from that of the electrospark machining. When the sample stage temperature is varied from −20 to 330°C, the Cu etching rate has no obvious dependence on the stage temperature. On the other hand, the Cu etching rate increases linearly with increasing the input power from 30 W to 100 W. The emission intensity of Balmer α line of H atom observed in optical emission spectrum of the plasma also increases linearly with the input power. The Cu etching rate of 500 nm/min can be achieved around the stage temperature of 0°C. Meanwhile, the etching rates for Si and SiO2 around the stage temperature of 0°C are 100 μm/min and 50 nm/min, respectively. The selectivity of the etching rates for Cu and SiO2 suggests that this etching technique could be applied to Cu wiring on a trenched SiO2 layer. The etched Cu surface morphology is rough and exhibits many round pits and bumps. This surface roughening might be due to excessive hydrogen incorporation in the Cu bulk.

Patterning monolayer graphene with zigzag edges on hexagonal boron nitride by anisotropic etching

Graphene nanostructures are potential building blocks for nanoelectronic and spintronic devices. However, the production of monolayer graphene nanostructures with well-defined zigzag edges remains a challenge. In this paper, we report the patterning of monolayer graphene nanostructures with zigzag edges on hexagonal boron nitride (h-BN) substrates by an anisotropic etching technique. We found that hydrogen plasma etching of monolayer graphene on h-BN is highly anisotropic due to the inert and ultra-flat nature of the h-BN surface, resulting in zigzag edge formation. The as-fabricated zigzag-edged monolayer graphene nanoribbons (Z-GNRs) with widths below 30 nm show high carrier mobility and width-dependent energy gaps at liquid helium temperature. These high quality Z-GNRs are thus ideal structures for exploring their valleytronic or spintronic properties.

Plasma-graphene interaction and its effects on nanoscale patterning

Scalable and precise nanopatterning of graphene is an essential step for graphene-based device fabrication. Hydrogen-plasma reactions have been shown to narrow graphene only from the edges, or to selectively produce circular or hexagonal holes in the basal plane of graphene, but the underlying plasma-graphene chemistry is unknown. Here, we study the hydrogen-plasma etching of monolayer graphene supported on $\mathrm{Si}{\mathrm{O}}_{2}$ substrates across the range of plasma ion energies using scale-bridging molecular dynamics (MD) simulations based on reactive force-field potential. Our results uncover distinct etching mechanisms, operative within narrow ion energy windows, which fully explain the differing plasma-graphene reactions observed experimentally. Specific ion energy ranges are demonstrated for stable isotropic ($\ensuremath{\sim}2\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$) versus anisotropic hole growth ($\ensuremath{\sim}20--30\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$) within the basal plane of graphene, as well as for pure edge etching of graphene ($\ensuremath{\sim}1\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$). Understanding the complex plasma-graphene chemistry opens up a means for controlled patterning of graphene nanostructures.

Dislocation in heteroepitaxial diamond visualized by hydrogen plasma etching

The classification of etch pits formed by hydrogen plasma etching on heteroepitaxial diamond has been done by cross-sectional transmission electron microscope (TEM). We demonstrated that the origin of etch pit was mainly [001] threading dislocation. From invisibility criterion of dislocation contrast in TEM observation, this dislocation was identified as edge and 45° mixed dislocation. The correlation between dislocation types and etch pit shape was discussed.

Carbon fibre production during hydrogen plasma etching of diamond films

Different morphology of carbon fibres have been synthesised on diamond films by hydrogen plasma etching in the presence of silicon.

Investigation of Low-Temperature Hydrogen Plasma-Etching Processes for Silicon Wafer Solar Cell Surface Passivation in an Industrial Inductively Coupled Plasma Deposition Tool

A hydrofluoric-acid (HF)-free hydrogen plasma dry etching process prior to the deposition of intrinsic amorphous silicon onto thin n-type planar Czochralski silicon wafers is developed. The influence of substrate temperature, hydrogen flow rate, and power density on the passivation quality is investigated. Advanced characterization using spectroscopic ellipsometry and transmission electron microscopy shows the impact of the etching conditions, especially the temperature and gas flow rates, on the surface quality and interface properties. It is found that the native oxide can only be removed effectively when wafers are subjected to higher temperature or lower hydrogen flow rate. The hydrogen, oxygen, and carbon concentration profiles at the a -Si/ c -Si interface of the plasma-etched samples are studied and compared with the traditionally HF cleaned interface to gain a better understanding of the reasons for the superior passivation quality.

Anisotropic etching of bilayer graphene controlled by gate voltage

Graphene nanostructures are proposed as promising materials for nanoelectronics such as transistors, sensors, spin valves and photoelectric devices. Zigzag edge graphene nanostructures had attracted broad attention due to their unique electronic properties. Anisotropic hydrogen-plasma etching has been demonstrated as an efficient top-down fabrication technique for zigzag-edged graphene nanostructures with a sub-10 nm spacial resolution. This anisotropic etching works for monolayer, bilayer and multilayer graphene and the etching rate depends on substrate temperature with a maximum etching rate at arround 400 C. It has been also founded that the anisotropic etching is also affected by the surface roughness and charge impurities of the substrate. Atomically flat substrates with no charge impurities would be ideal for the anisotropic etching. So far the understanding of hydrogen-plasma anisotropic etching, e.g. whether hydrogen radicals or hydrogen ions dominate the etching process, remains unclear. In this work, we investigated the anisotropic etching of graphene under electrical field modulations. Bilayer graphene peeled off from grahpite on SiO2 substrate was used as the experimental object. 2 nm-Ti (adhesive layer) and 40 nm-Au electrodes was deposited by electronic beam evaporation for electrical contacts. Gate voltates were applied to the bilayer graphene samples to make them either positively or negitively charged. These charged samples were then subjected to the hydrogen anisotropic etching at 400 C under the plasma power of 60 W and gas pressure of 0.3 Torr. The etching rates were characterized by the sizes of the etched hexagonal holes. We found that the etching rate for bilayer graphene on SiO2 substrate depends strongly on the gate voltages applied. With gate voltages sweeping from the negative to the positive, etching rate shows obvious decrease. 45 times of etching rate decrease was seen when sweeping the gate voltages from -30 V (positively charged) to 30 V (negatively charged). This gate-dependent anisotropic etching suggests that hydrogen ions rather than radicals plays a key role during the anisotropic etching process since the negatively charged graphene could neutralize the hydrogen ions quickly thus make them unreactive. The present work provides a strategy for fabrication of graphene nanostructures by anisotropic etching with a controllable manner.