Radical Etching Research Articles

Physiochemical Coupled Dynamic Nanosphere Lithography Enabling Multiple Metastructures from Single Mask.

Metastructures are widely used in photonic devices, energy conversion, and biomedical applications. However, to fabricate multiple patterns continuously in single etching protocol with highly tunable photonic properties is challenging. Here, a simple and robust dynamic nanosphere lithography is proposed by inserting a spacer between the nanosphere assembly and the wafer. The nanosphere diameter decrease and uneven penetration of the spacer during etching lead to a dynamic masking process. Coupled anisotropic physical ion sputtering and ricocheting with isotropic chemical radical etching achieve highly tunable structures with various 3D patterns continuously forming through a single etching process. Specifically, the nanosphere diameters define the periodicity, the etched spacer forms the upper parts, and the wafer forms the lower parts. Each part of the structure is highly tunable through changing nanosphere diameter, spacer thickness, and etch conditions. Using this protocol, numerous structures of varying sizes including nanomushrooms, nanocones, nanopencils, and nanoneedles with diverse shapes are realized as proof of concepts. The broadband antireflection ability of the nanostructures and their use in surface-enhanced Raman spectroscopy are also demonstrated for practical application. This method substantially simplifies the fabrication procedure of various metastructures, paving the way for its application in multiple disciplines especially in photonic devices.

Plasma atomic layer etching of molybdenum with surface fluorination

This work developed a plasma atomic layer etching (ALE) process for molybdenum (Mo) with surface fluorination and ion bombardment. The Mo surface was fluorinated with CHF3 or C4F8 plasmas, and the fluorinated surface was etched by Ar plasma. The fluorocarbon layers were generated with two fluorocarbon sources of CHF3 or C4F8 plasmas on the Mo surfaces. C4F8 plasma generates more fluorine-rich fluorocarbons than CHF3 plasma. The etch per cycle (EPC) of Mo was determined to be 0.8 nm/cycle for CHF3 plasma and 2.8 nm/cycle for C4F8 plasma in the ALE window region. The dependence of the EPC of Mo on the ion energy in the etching step was investigated, and an ALE window was observed in the energy range of 100–225 V. The EPC of Mo increases with increasing Ar plasma time and saturates at 150 s for the CHF3 plasma and 420 s for the C4F8 plasma. Fluorine residue after ALE was as low as 4%, which is lower than radical etching and RIE. The surface roughness was measured at 0.37 nm with the ALE process, which is lower than radical etching and RIE processes.

Study on flexible surface dielectric barrier discharge plasma film for in situ inactivation of bacteria and viruses

COVID-19 is still pandemic in the world although it has lasted for more than two years, in situ real-time disinfection of curved surfaces in public places is extremely urgent. A flexible plasma film based on surface dielectric barrier discharge is proposed in this study. In situ disinfection effect and the influence of curvature on the performance are studied. The results showed that the film could in situ inactivate a variety of pathogens. Specifically, 10 min plasma treatment results in a log reduction of 3.10, 3.42, and 3.03 for Escherichia coli, Staphylococcus aureus, and vesicular stomatitis virus, respectively. The discharge power and disinfection effect of the film are independent of the curvature, which proves that it can be used for in situ disinfection of curved surfaces. It is speculated that the combined effects of a strong electric field and radical etching physical damage as well as the chemical damage of reactive oxygen and nitrogen species to the protein are the main reasons for the inactivation of pathogens. The inhibition of the film to Omicron type SARS-CoV-2 pseudovirus is 99.3%, and the killing rate to natural bacteria is 94.3%. The film can run for at least 10 h without significant reduction in disinfection effect. In addition, large-scale and digitalization increase the practical potential of a disinfection film. In conclusion, this film is expected to realize in situ real-time disinfection of curved surfaces such as the buttons of the elevator or instrument and door handles, which is of great significance in blocking the spread of COVID-19.

Plasma boosted the conversion of waste plastics into liquid fuel by a peroxymonosulfate-hydrothermal process

Plastic wastes are growing fast over the world and impose great burden to eco-system. However, the plastics nurture abundant carbon resource and can be used as ideal raw materials to produce fuels. Hydrothermal process is considered as a promising strategy to convert plastics into fuel under a mild condition, but the conversion efficiency is often limited by the chemical inertness of plastics. Here, we propose a facile plasma treatment method to modify the plastic surface, aimed to boost the conversion of waste plastics into liquid fuel through a peroxymonosulfate (PMS) coupled hydrothermal process. We find that the sample after plasma treatment for 40 s displays 9.2 wt% weight loss with 8 h, which is 6 times that of the pristine sample. The plasma treatment can not only activate the inert surface but also enhanced the PMS activation process by establishing a balance between the radical effect and etching effect.

Hydrogen etch resistance of aluminium oxide passivated graphitic layers

Graphene inherently possesses defect sites and grain boundaries that are vulnerable to chemical etching by hydrogen radicals. In this study, an etch-mitigation method is presented to selectively passivate these sites using atomic layer deposition (ALD) of a H etch-resistant material. First, as a reference experiment, pristine exfoliated graphitic layers are exposed to H radicals to determine the lateral etch rate from defect sites. Next, these samples are compared to graphitic layers in which the defects are selectively passivated by Al2O3, in the same exposure conditions, using atomic force microscopy at every step in the experiment. The results show that etching is slowed down by local deposition of Al2O3 ALD at sites vulnerable to H radical etching.

O·, H·, and ·OH radical etching probability of polystyrene obtained for a radio frequency driven atmospheric pressure plasma jet

Atmospheric pressure plasma jets have great potential for the surface modification of polymers. In this work, the authors report on polystyrene etching by a radio frequency driven atmospheric pressure plasma jet with a focus on the role of H⋅, O⋅, and ⋅OH radicals in this process. The absolute flux of H⋅, O⋅, and ⋅OH radicals reaching the surface of the polymer was determined by a comsol multiphysics reacting fluid dynamics model incorporating detailed transport phenomena in the boundary layer near the substrate. The simulated results of H⋅ and ⋅OH densities in the jet effluent were experimentally verified by two-photon absorption laser induced fluorescence and laser induced fluorescence, respectively. The carbon atom removal flux from the polystyrene surface was taken from previously reported measurements using the same plasma source. The authors show that the boundary layer effects in the interfacial region above the substrate can have a significant impact on the calculated etching probabilities. The reaction probability (β) has a significant uncertainty although a variation of 2 orders of magnitude in β leads to uncertainties of approximately 1 order of magnitude variation in the determined etching probability. The etching probability of polystyrene by ⋅OH radicals was confirmed to be at least an order of magnitude larger than the polystyrene etching probability by O⋅ radicals. The authors also confirmed the weak polystyrene etching probability by H⋅ radicals. The model suggests that the presence of a 30 ppm O2 impurity can lead to the production of ⋅OH radicals in the far effluent of the Ar+1%H2 plasma jet close to the substrate at sufficient densities to enable effective etching.

In Situ Monitoring of Surface Reactions during Atomic Layer Etching of Silicon Nitride Using Hydrogen Plasma and Fluorine Radicals.

The atomic layer etching (ALE) of silicon nitride (SiN) via a hydrogen plasma followed by exposure to fluorine radicals was investigated by using in situ spectroscopic ellipsometry and attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy to examine the surface reactions and etching mechanism. FTIR spectra of the surface following exposure to the hydrogen plasma showed an increase in the concentration of Si-H and N-H bonds, although the N-H bond concentration plateaued more quickly. In contrast, during fluorine radical exposure, the Si-H bond concentration decreased more rapidly. Secondary ion mass spectrometry demonstrated that the nitrogen atom concentration was decreased to a depth of 4 nm from the surface after the hydrogen plasma treatment and indicated a structure consisting of N-H rich, Si-H rich, and mixed layers. This indicated that Si-H bonds were primarily present near the surface, while N-H bonds were mainly located deeper into the film. The formations of the N-H and Si-H rich layers are important phenomena associated with modification by hydrogen plasma and fluorine radical etching, respectively.

(Invited) PEALD and ALE for Area Selective Deposition

Advanced CMOS scaling relies on novel structure and design, as well as material developments, which leads to challenging integration issues. Innovation in gap filling technologies, area selective deposition (ASD) and etch processes should help in reaching this scaling specification. Criteria for an adequate area selective deposition process are: growth only on specific regions, high throughput compatible with industrial demands and no so-called mushroom profiles into adjacent features. Several approaches are currently being investigated for the development of ASD processes, among which ASD by surface deactivation with the use of self-assembled monolayers (SAM) or block copolymers, processing temperatures promoting inherent selectivity, and spatial ALD or selective ALD based on ABC-type cycles [1-3]. The original approach developed in our group consists in taking benefit from an in situ etching step inserted in a standard ALD cycle [4, 5]: this so-called deposition/etch approach is already being used for Si epitaxy by the incorporation of HCl in the gas phase. In this presentation, a short introduction on challenges and opportunities for ASD in high volume manufacturing will be presented. A brief state of the art of ASD strategies with their inherent pros and cons will be provided, to open up a discussion on different deposition/etch approaches for Area Selective Deposition, as illustrated in the figure 1. This figure highlights the benefits of developing isotropic as well as anisotropic etching for ASD. Indeed, isotropic plasma etching relies mainly on radical (ie chemical) etching, whereas anisotropic etching can be induced by an appropriate Ion etching process or plasma Atomic Layer Etching (ALE) development. The PEALD/ALE strategy entails a precise energy control of ions flowing from the plasma onto the substrate (with an energy range between 0 and 50 eV). Therefore, a specific design must be conceived for PEALD tool, consistent with this issue. In our work, a low power RF biasing waveform has been applied to the substrate holder in the Flexal deposition tool from Oxford Instruments. Benefits and drawbacks of this deposition/etch approach will be discussed in terms of throughput, etching impact (contamination, roughness…) and process drift. Finally, two examples will be given illustrating a versatile route for topographically selective deposition, either on sidewalls, as needed for spacer fabrication, [6] or on top and bottom of trenches only. This second example will be discussed in regards of surface selective deposition of dielectrics on metal. [1] A. J. M. Mackus et al, Chem. Mater. 31 (2019) 2-12 [2] G. N. Parsons, J. Vac. Sci. Technol. A 37 (2019) 020911 [3] R. Chen, H. Kim, P. C. McIntyre, and S. F. Bent, Appl. Phys. Lett. 84 (2004) 4017 [4] R. Vallat et al, J. Vac. Sci. Technol. A 35 (2017) 01B104 [5] R. Vallat et al, J. Vac. Sci. Technol. A 37 (2019) 020918 [6] A. Chaker et al, Appl. Phys. Lett. 114 (2019) Figure 1

(Invited) Etching of Advanced Semiconductor Devices

Plasma etching or Reactive Ion Etching (RIE) is the workhorse for patterning of semiconductor devices since the early 1980-ies when it replaced wet etching in manufacturing. Today, RIE is reaching levels of performance which were unimaginable back then. At the same time, etching technologies such as Atomic Layer Etching (ALE), radical, dry vapor and Ion Beam Etching are finding their way into manufacturing for certain applications. We will present an overview of dry etching technologies used in semiconductor manufacturing. The emphasis is on the elementary surface processes and how they impact the performance on the wafer. We will start from less complex etching technologies which use just one kind of etching species, such as neutrals, radicals or ions. Then we combine these techniques into cycling processes which leads to the discussion of ALE. The highest level of complexity is reached in RIE with simultaneous species fluxes. Reactor designs for the various etching technologies and process control will be covered. Finally, and an outlook into the future of semiconductor device etching will be given.

Metal diffusion properties of ultra-thin high-k Sc2O3 films

The diffusion barrier properties of Sc2O3 against metal diffusion were studied. Tin and ruthenium were used as probe materials to study the barrier properties of Sc2O3 in thickness ranges that are of relevance for gate materials. Tin deposition and hydrogen radical etching from Sc2O3 layers of 0.5-1.5 nm thickness, deposited on Ru, show that these Sc2O3 layers effectively block the diffusion of Sn into Ru. We show that Sn adhesion and etching depends strongly on the thickness of the Sc2O3 film. The etch-rate is found to be inversely proportional to the Sc2O3 layer thickness, which we attribute to Sc2O3 becoming a more effective charge transfer barrier at larger thicknesses.

Hydroxyl Radical Etching Improves Adhesion of Plasma‐Deposited a‐SiOxCyHz Films on Poly(Methylmethacrylate)

AbstractPlasma‐deposited thin films comprising a‐SiOxCyHz with some organic content are of considerable interest as protective coatings. Their application has, however, been hampered by marginal adhesion and durability on some substrates. This study found that optimal adhesion was achieved with plasma pre‐treatments utilising vapours from the alcohol family. Our data show that rapid initial etching of the substrate occurs, probably by action of hydroxyl radicals, followed by deposition of a layer some 10 nm thick which appears to provide a surface capable of strong interfacial bonding with a subsequently deposited a‐SiOxCyHz layer. Compared with non‐depositing plasma pre‐treatments, such dual action provides stronger adhesion on PMMA. This opens up new possibilities for applying protective hard coatings on PMMA.magnified image

Mass spectrometric study on inactivation mechanism of spore-forming bacteria by low-pressure surface-wave excited oxygen plasma

In this letter, the etching phenomena of the spore-forming bacteria by oxygen plasma were investigated by using quadrupole mass spectrometry. The etching by-products of H2O and CO2 were obviously detected during the oxygen plasma irradiation by the multiple ion detection measurement. Inactivation of roughly 106 spores population was achieved under almost the same reduced spore shapes for three different incident microwave powers. It is considered from the present results that the oxygen radical etching could cause damage to the germinant receptors located in the inner membrane inevitable for germination of spores, without any damage of the DNA in the cores.

Vapor–solid–solid Si nano-whiskers growth using pure hydrogen as the source gas

This paper describes the growth mechanism and structure of Si whiskers grown on a Si substrate in a tungsten hot filament chemical vapor deposition reactor with pure hydrogen as source gas using a two step process. In the first step, atomic hydrogen etched the silicon surface, forming silicon hydrides that react with tungsten from the filament. The resulting silicide particles deposited on the silicon surface forming a mesh-like pattern. The particles work as an etching mask against hydrogen radical etching of the silicon surface and inverted-pyramids or V-groove-shaped surface texture were obtained. In the second step the filament current was reduced and whiskers grew onto the substrate due to the interaction of the silicon hydrides with the particles and subsequent precipitation of saturated Si. The whiskers were found to have tungsten silicide particles on their tip, suggesting the whisker growth was through the Vapor–Solid–Solid (VSS) mechanism. A balance between the hydrogen radical etching effect and the supply of silicon hydride from the etching reaction on the silicon surface is crucial for the growth of dense silicon whiskers.

X-ray microfabrication and measurement of a terahertz mode converter

Mode converters are critical for frequency-tunable terahertz gyrotrons. This study reports the development of a broadband TE(02) mode converter centered at 0.2 THz. An octafeed sidewall coupling structure was employed and the mode purity was analyzed. The converter was built using the technique of x-ray microfabrication. The x rays irradiated on the SU-8 resist and generated a template of very high thickness of 1.295 mm. Pulse electroplating technique was used to deposit copper on the structure along the template. The parts then went through precise machining and the residual resist was removed via high-flux radical etching. A computer-aided diagnostic system was introduced to measure the performance of the converter. Results suggest that the frequency response of resistivity should be taken into consideration for the devices in terahertz region.

Si substrates texturing and vapor-solid-solid Si nanowhiskers growth using pure hydrogen as source gas

Scanning and transmission electron microscopies have been used to study silicon substrate texturing and whisker growth on Si substrates using pure hydrogen source gas in a tungsten hot filament reactor. Substrate texturing, in the nanometer to micrometer range of mono- and as-cut multicrystalline silicon, was observed after deposition of WSi2 particles that acted as a mask for subsequent hydrogen radical etching. Simultaneous Si whisker growth was observed for long residence time of the source gas and low H2 flow rate with high pressure. The whiskers formed via vapor-solid-solid growth, in which the deposited WSi2 particles acted as catalysts for a subsequent metal-induced layer exchange process well below the eutectic temperature. In this process, SiHx species, formed by substrate etching by the H radicals, diffuse through the metal particles. This leads to growth of crystalline Si whiskers via metal-induced solid-phase crystallization. Transmission electron microscopy, electron diffraction, and x-ray energy dispersive spectroscopy were used to study the WSi2 particles and the structure of the Si substrates in detail. It has been established that the whiskers are partly crystalline and partly amorphous, consisting of pure Si with WSi2 particles on their tips as well as sometimes being incorporated into their structure.

Silicon Whisker Growth Using Hot Filament Reactor with Hydrogen as Source Gas

Si whisker growth on a silicon substrate, using only pure hydrogen gas flow in a hot filament chemical vapor deposition reactor, has been studied by scanning and transmission electron microscopy. At the initial stage of the growth, tungsten–silicide particles are formed due to hydrogen radical etching by the filament. Simultanously the Si substrate exhibits a surface texturing. After long residence times of hydrogen gas in the reactor, silicon whiskers, with diameters between 10 and 50 nm, were observed on the textured silicon surface. Each whisker has a silicide particle at its tip. A mechanism of silicon whiskers growth using this method with hydrogen gas is proposed.

Si Whisker Growth by Hydrogen Radical using Hot Filament CVD Reactor

AbstractThis paper describes the growth mechanism of silicon whisker on a silicon substrate using hot filament CVD reactor. Only hydrogen is used as source gas. The particle layer could be obtained at high filament current condition under hydrogen ambient. XPS analysis result suggests that the particle is composed of tungsten silicide. The deposition condition of the particle layer is much depended on the substrate size, surface condition and the distance between the substrate and the filament. The experimental results suggest that the silicon hydride, which generated at the silicon surface by hydrogen radical etching, react with the tungsten filament material around the filament, depositing on the silicon substrate. The silicon surface is etched by hydrogen radical and its resultant surface morphology is much depended on the particle deposition pattern. Many silicon whiskers, which diameter is varied from 10 to 50 nm, are observed on the textured silicon surface when the residence time of the source gas in the reactor is long. Each whisker has a silicon particle on their tip. The silicon hydride generated by the hydrogen radical etching is much absorbed to the silicide particle when the source gas residence time is long, enabling the silicon whisker growth from the particle. The results suggest that nm size whisker structure is much stable compare to the bulk silicon against etching reaction.

Fabrication of NbN-HEB Mixers With Fluoride Radical Etching Process

Hot electron bolometers (HEBs) are expected to be used as low-noise heterodyne mixers for applications in radio astronomy and remote sensing in the terahertz frequency region. We fabricated and tested HEB mixers for these applications; however, those we made with the conventional process easily broke due to thermal stress and electrical surges. To improve their durability, a new process involving fluoride radical etching was developed. In this process, HEB mixers were fabricated using a relatively thick NbN strip (several tens of nm). Finally, the NbN strip was etched that was less than 4-nm thick enough to operate as HEB mixers by using the fluoride radical etching. We confirmed that fluoride radical etching caused no damage to the etched NbN strip. The dc properties of the HEB mixers fabricated with the new process did not change for fourteen 4.2-300 K thermal cycles for 50 days. The receiver noise temperature of the HEB mixer was evaluated and it was about 615 K at 780 GHz.

Hydrogen Radical Etching Effect on Carbon Nanotube Growth

ABSTRACTThe hydrogen microwave remote plasma CVD was introduced to fabricate carbon nanotubes(CNTs). C2H2 or CH4, used as source gas react with hydrogen radicals introduced from the cavity. In this experiment, hydrogen radical etching effect on the substrate surface could be controlled independently. We confirmed CNTs growth at 400°C under adequate hydrogen radical etching effect on the substrate surface. The result directly suggests that the etching effect of hydrogen radicals on the reaction surface contribute to the low temperature growth of CNTs. The CNT thickness did not depend on the hydrogen radical etching effect but the catalyst layer thickness.

Silicon Surface Texturization Mechanism by Hydrogen Radicals Using Tungsten Hot Filament

ABSTRACTThis paper describes the surface texturing mechanism on crystalline Si using hydrogen radicals generated by a tungsten hot filament. Inverted pyramid or labyrinthV groove structure could be obtained by particle deposition before etching. Mesh like tungsten particle layer, works as an etching mask against hydrogen radical, was obtained when silicon substrate was used. On the other hand, tungstem particles were not deposited as mesh like pattern when SiO2/Si substrate was used. The results suggest that evaporation of silicon hydrides from the silicon surface by hydrogen radical etching causes the mesh like pattern deposition of tungsten particles. Increase of filament current enables short time texturing process of less than 1 minute.