Plasma Bombardment Research Articles

Atomic Layer Densification of AlN Passivation Layer on Epitaxial Ge for Enhancement of Reliability and Electrical Performance of High-K Gate Stacks

The impact of atomic layer bombardment (ALB) on the aluminum nitride (AlN) passivation layer between the HfO2 gate dielectric and the n-type epitaxial germanium (Ge) was investigated. The ALB technique was performed with the layer-by-layer, in situ helium/argon plasma bombardment in each cycle of atomic layer deposition (ALD) of AlN. An increase in the film density and a decrease in nitrogen vacancies, as manifested by the X-ray reflection and X-ray spectroscopy, were observed in the AlN layer treated by the ALB process. The improvements in the AlN quality contribute to a reduction of the equivalent oxide thickness from 1.36 to 1.19 nm of the AlN/HfO2 gate stack, together with the suppression of the gate leakage current, the interfacial state density, and the slow trap density. The reliability tests reveal promising reliability of the AlN/HfO2 gate stack with a small flat-band voltage shift under the constant voltage stress and a high operation voltage of ∼2.4 V projected for a 10 years time-dependent-dielectric-breakdown lifetime. All of the results point that the ALB technique can effectively enhance the material/interface properties, electrical characteristics, and reliability of nanoscale devices, which is critical and beneficial to the next-generation high-speed and low-power nanoelectronics.

Plasmonic titanium nitride via atomic layer deposition: A low-temperature route

To integrate plasmonic devices into industry, it is essential to develop scalable and CMOS compatible plasmonic materials. In this work, we report high plasmonic quality titanium nitride (TiN) on c-plane sapphire grown by plasma-enhanced atomic layer deposition. TiN with low losses, high metallicity, and a plasma frequency below 500 nm was achieved at temperatures less than 500 °C by exploring the effects of chemisorption time, substrate temperature, and plasma exposure time on the material properties. A reduction in chemisorption time mitigates premature precursor decomposition at TS > 375 °C, and a trade-off between reduced impurity concentration and structural degradation caused by plasma bombardment is achieved for 25 s plasma exposure. 85 nm thick TiN films grown at a substrate temperature of 450 °C, compatible with CMOS processes, with 0.5 s chemisorption time and 25 s plasma exposure exhibited a high plasmonic figure of merit (|ε′/ε′′|) of 2.8 and resistivity of 31μΩcm. As a result of the improved quality, subwavelength apertures were fabricated in the TiN thin films and are shown to exhibit extraordinary transmission.

Low Temperature RF-Plasma Initiated Rapid and Highly Ordered Fracture on Ag Nanowires

Highly ordered Ag particle-chains (AgPCs) have been obtained from Ag nanowires (AgNWs) by radio frequency (RF) plasma treatment. Such conversion is attributed to the fast nonequilibrium diffusion of Ag atoms (liquid-like behavior) on AgNWs surfaces through the plasma bombarding. Further, the formed AgPCs highly coincide with the predictions by Rayleigh instability. In contrast to heat treatment, AgPCs are formed rapidly, highly ordered and at temperature below 100 °C. Furthermore, aperiodicity and wire–wire welding instead of highly ordered particle-chains has been observed as the AgNWs are overlapped by plasma treatment. This work should provide a new perspective for metallic particle-chains fabrication.

Leakage current lowering and film densification of ZrO2 high-k gate dielectrics by layer-by-layer, in-situ atomic layer hydrogen bombardment

A layer-by-layer, in-situ H2 plasma treatment in each cycle of atomic layer deposition, referred to as “atomic layer hydrogen bombardment” (ALHB), is applied to improve electrical properties of ZrO2 high-k gate dielectrics. The H2 plasma bombardment facilitates the adatom migration due to energy delivery to each as-deposited monolayer from the H2 plasma. In addition, the H2 plasma treatment contributes to the removal of precursor ligands for the release of steric hindrance. Hence the ALHB treatment leads to film densification and suppression of oxygen vacancies of ZrO2, as evidenced by X-ray reflectivity and X-ray photoelectron spectroscopy characterizations. As a result, ~90% decrease of gate leakage current is achieved in the ZrO2 high-k gate dielectrics with capacitance equivalent thicknesses of ~1.3 nm and ~0.6 nm in metal-insulator-semiconductor and metal-insulator-metal capacitors, respectively. The results manifest that the ALHB treatment is a promising technique to enhance dielectric and electrical characteristics of nanoscale thin films, for further progress of advanced devices such as sensors, solar cells, memories, and nanoelectronics.

Interaction of oxygen with polystyrene and polyethylene polymer films: A mechanistic study

In this work, first principles calculations combined with advanced surface diagnostics are used to unravel the mechanisms of plasma oxygen interaction with organic films of interest for advanced patterning in semiconductor device manufacturing. Results from a combination of x-ray photoelectron spectroscopy (XPS) diagnosed oxygen plasma exposed polystyrene films and first principles modeling of organic films (polystyrene, polyethylene, and derivatives) provide insights into how organic films are oxidized by oxygen atoms. XPS measurements show the rapid formation of C-O structures and their saturation after oxygen exposure on both pristine and argon bombarded polystyrene samples. Quantum mechanics calculations confirm that C-OH formation can be immediate without recourse to previously formed dangling bonds. Multiple oxygen impacts are required for scission of pristine ethylene carbon strands. Therefore, ethylene films can be converted to polyols that are stable, whereas more likely strands are broken before polyol formation through the formation of water and C=O. On the contrary, intermediate compounds with adjacent C=O bonds are not likely to form stable structures. The combination of XPS measurements and modeling implies that the oxidation of polystyrene and polyethylene is self-limiting on both hydrogen saturated and dehydrogenated (after argon ion plasma bombardment) surfaces.

Effect of Argon Plasma Treatment on Surface-Treated Titanium

This work compares the consequence of argon bombardment plasma treatment on sandblasted large-grit, acid-etched (SLA) and hydroxyapatite (HA) treated titanium surface. Titanium disc specimens were distributed into two groups depends on the surface treatment (SLA, HA). The SLA and HA-coated surfaces were further subdivided according to non-plasma and plasma treatments. An argon plasma treatment was done at ambient temperature under vacuum. The specimens (surface treated) were subjected to surface analysis using field-emission scanning electron microscopy, a three-dimensional optical profiler, and X-ray photoelectron spectroscopy (XPS). Furthermore, contact angle examination was performed via the sessile drop technique.

Impact of NH3 plasma treatment for solution-processed indium oxide thin-film transistors with low thermal budget

The challenges associated with low-temperature solution-processed metal oxide thin-film transistors (TFTs) have hindered the realization of flexible oxide electronics at temperatures lower than 200 °C. NH3 plasma treatment is embarked upon as a route to effectively transform the chemical precursors to semiconducting metal oxides with high electrical quality. NH3 plasma-activated indium oxide (InOx) TFTs with saturated mobility 2.48 cm2V−1s−1 have been obtained at temperature as low as 150 °C. The low-temperature activation mechanism of NH3 plasma treatment for InOx films and the role of post-annealing in the fabrication process of InOx TFTs have been explored. Research shows that NH3 plasma treatment activates InOx films based on plasma bombardment, radicals doping and radical reactions; then, unreacted radicals and interstitial radicals were effectively removed by extra thermal energy from post-annealing. In comparison to thermal annealing, NH3 plasma treatment with moderate post-annealing is capable of achieving high degrees of condensation and densification reactions for InOx film and modulating the carrier concentration in a manner suitable for high-performance semiconducting behavior with low thermal budget. However, The InOx film after NH3 plasma treatment exhibited a non-uniform geometry due to the effect of plasma-induced damage in the local regions of InOx film, which restricts its commercial application. Some strategies were reported to eliminate the effect of plasma-induced damage by changing plasma conditions or pre-annealing temperature. The results demonstrated that changing plasma conditions by decreasing the plasma chamber temperature or the plasma power can eliminate plasma-induced damage, but attenuate the electrical performance of InOx TFT; nevertheless, changing pre-annealing temperature to 30 °C not only effectively eliminate plasma-induced damage, but also further improve the electrical performances of InOx TFT. These results provide a way for fabricating low-temperature oxide circuitry and supply an effective idea for avoiding plasma-induced damage.

Effective Antibacterial Glass Fiber Membrane Prepared by Plasma-Enhanced Chemical Grafting.

This paper reports a novel glass fiber membrane with an effective antibacterial performance by chemical grafting of quaternary ammonium salt (QAS) which is enhanced by a plasma bombardment technique. Plasma bombardment as a pretreatment of the membrane can increase the QAS anchored on the membrane from 0.8 to 1.3 wt %. The chemical grafting technique can increase the membrane zeta potential from negative values to positive values in aqueous solutions at various pHs. Furthermore, the plasma-enhanced chemical-grafting membrane has more positive zeta potentials (49.0 mV at pH = 7) than the chemical-grafting membrane without the plasma bombardment technique (38.9 mV at pH = 7). In the antibacterial performance evaluation, the Escherichia coli survival rate decreased from 127.0% of the pristine membrane to 4.1 and 11.3% of the plasma-enhanced chemical-grafting membrane and the chemical-grafting membrane, respectively. In addition, the plasma-enhanced chemical-grafting membrane shows durable antibacterial activity against E. coli with copious water rinsing as much as 3 L·cm–2.

The evolution of MoS2 properties under oxygen plasma treatment and its application in MoS2 based devices

CVD molybdenum disulfide (MoS2) is shown to chemically oxidize rapidly after pure oxygen plasma bombardment. Atomic force microscopy (AFM), photoluminescence spectrum (PL), Raman spectrum and X-ray photoelectron spectroscopy (XPS) are employed to characterize the physical and chemical properties and indicate that MoO3 is easily formed from MoS2. The result of AFM shows that thickness of the film increases from 0.9 to 1.79 nm after oxygen plasma treatment, which is mainly due to the difference in lattice structure between pristine MoS2 and generated MoO3. XPS analysis shows that the intensity of the S2s peak is reduced to 0 after oxygen plasma treatment. Also, the intensities of Mo4+ peaks disappear at 233.2 eV and 230 eV, leaving only the Mo6+ peaks at 232.5 eV and 235.65 eV, which strongly proves the transformation of MoS2 to MoO3. Further, we use oxygen plasma to treat few-layer MoS2, and find that the top oxidized layer can protect the lower MoS2 from further oxidation. Finally, we obtain p-type doped transistors with this method.

Remarkable improved solar transmission of VO2 smart windows by partial controlled oxygen plasma bombarding

The vanadium dioxide (VO2) based smart windows are developed to reduce energy consumption and improve thermal and visual comfort by controlling the solar flux entering into a building. In this paper, the solo oxygen plasma bombarding is adopted at low temperature (30 °C) for the solar transmission improvement in VO2 smart windows, which helps to overcome the constraints of destruction in toughened VO2 windows by annealing. Various oxygen flow rates were used to assist the plasma to identify the influence and mechanism in thermochromic VO2 films for the first time. The oxygen plasma treatment leads to an effective composition modulation and microstructure reconstruction in the VO2 films to create new functionalities. The conversion between VO2 and V2O5 can be controlled and maintained stable during the O2 flow range of 120–160 sccm (called stable zone). Favorable results are achieved in the stable zone compared with the untreated VO2 films, the relative improvement of luminous transmission Tlum (380–780 nm) is 44%, meanwhile, the increase of Tsol (380–2500 nm) is 30% with a negligible decrease of 1.5% in ΔTsol. Additionally, the solar transmission of VO2 films can be emphatically improved with preserved phase transition behaviors. It reveals that the proposed technique is simple, efficient and performed with ease in working tolerance, and can be applied widely in the VO2 smart window field.

The effects of annealing and wake-up cycling on the ferroelectricity of zirconium hafnium oxide ultrathin films prepared by remote plasma atomic layer deposition

The crystalline phases and ferroelectric properties of ZrxHf1-xO2 (ZHO) ultrathin films (5.6–5.8 nm in thickness) prepared by remote plasma atomic layer deposition (RP-ALD) before and after post-annealing and wake-up cycling have been investigated in this study. For the films with high ZrO2 percentages, the plasma bombardment from RP-ALD was able to induce partial ferroelectric orthorhombic (o) crystallization during the film deposition stage. The as-deposited pure ZrO2 ultrathin film exhibited a fully developed ferroelectric polarization hysteresis after wake-up cycling. For the films containing the ferroelectric o-phase in the as-deposited state, post-annealing the films followed by a wake-up cycling procedure could greatly promote ferroelectric switching while maintaining low leakage. The ferroelectric properties of the ZHO ultrathin films were highly dependent on the ZrO2-to-HfO2 ratio and could be tailored by various combinations of post-annealing and wake-up cycling. An increase in the amount of HfO2 has been found to be detrimental to the ferroelectricity, mainly due to the high crystallization temperature of HfO2. For the post-annealed ZHO ultrathin films, the ferroelectricity was governed by the relative amounts of the ferroelectric o-phase and the non-ferroelectric monoclinic (m) phase. The Zr0.5H0.5O2 ultrathin film was the only composition which exhibited a large, stable polarization hysteresis after post-annealing but before wake-up cycling. The annealed Zr0.5H0.5O2 ultrathin film is believed to contain a suitable mix of o and m phases to produce loose grain boundaries, allowing the ferroelectric o-phase crystallites to switch freely under electrical loading.

Deuterium Transport and Retention in Liquid Ga and Li Under Steady-State Plasma Bombardment

The experiments on deuterium plasma-driven permeation through liquid Ga and Li were conducted in a linear plasma device VEHICLE-1. Deuterium transport parameters such as diffusivity and surface recombination coefficient for Ga and Li were measured from the experiments. By using the measured transport parameters, deuterium dynamic retentions in Ga and Li under steady-state plasma bombardment were evaluated with the DIFFUSE code. It has been found that the deuterium dynamic retention in Ga is ~five orders of magnitude lower than that in Li under present experimental conditions. After exposed to the steady-state deuterium plasma at temperatures from 78 °C to 360 °C, deuterium static retentions in liquid Ga are measured by the thermal desorption spectroscopy. It has been found that the deuterium static retentions in Ga are close to the dynamic retentions when the exposure temperatures are below 250 °C.

Generating Defect‐Rich Bismuth for Enhancing the Rate of Nitrogen Electroreduction to Ammonia

AbstractThe electrochemical N2 fixation, which is far from practical application in aqueous solution under ambient conditions, is extremely challenging and requires a rational design of electrocatalytic centers. We observed that bismuth (Bi) might be a promising candidate for this task because of its weak binding with H adatoms, which increases the selectivity and production rate. Furthermore, we successfully synthesized defect‐rich Bi nanoplates as an efficient noble‐metal‐free N2 reduction electrocatalyst via a low‐temperature plasma bombardment approach. When exclusively using 1H NMR measurements with N2 gas as a quantitative testing method, the defect‐rich Bi(110) nanoplates achieved a 15NH3 production rate of 5.453 μg mgBi−1 h−1 and a Faradaic efficiency of 11.68 % at −0.6 V vs. RHE in aqueous solution at ambient conditions.

Generating Defect-Rich Bismuth for Enhancing the Rate of Nitrogen Electroreduction to Ammonia.

The electrochemical N2 fixation, which is far from practical application in aqueous solution under ambient conditions, is extremely challenging and requires a rational design of electrocatalytic centers. We observed that bismuth (Bi) might be a promising candidate for this task because of its weak binding with H adatoms, which increases the selectivity and production rate. Furthermore, we successfully synthesized defect-rich Bi nanoplates as an efficient noble-metal-free N2 reduction electrocatalyst via a low-temperature plasma bombardment approach. When exclusively using 1 H NMR measurements with N2 gas as a quantitative testing method, the defect-rich Bi(110) nanoplates achieved a 15 NH3 production rate of 5.453 μg mgBi -1 h-1 and a Faradaic efficiency of 11.68 % at -0.6 V vs. RHE in aqueous solution at ambient conditions.

Outer Divertor Damage Characterization from Deuterium Plasma Bombardment in Graphene-Coated Tungsten in the C-2W Device

This research explores the performance of graphene as a coating for plasma-facing components (PFCs) in a nuclear fusion environment. Our recent studies have shown that graphene can act as a resistant layer against plasma exposure and ion bombardment. PFCs tend to develop surface morphologies that lead to mass loss of the wall material, potentially diminishing their lifetime and degrading plasma performance. We present a characterization of graphene-coated samples of W irradiated in the C-2W divertor. Energy analyzers were used to determine average ion fluxes to the samples on the order of 1018 D+/cm2. Two samples were exposed over 1210 plasma discharges. Raman spectroscopy showed that slow ions (30 < E < 100 eV) interact strongly with the graphene, introducing vacancies into the membrane (ID/IG ~ 0.7), making it possible to assess the limiting factors on such a coating’s lifetime. We also found that graphene slows down impurity deposition on the material surfaces due to graphene’s stable configuration and low surface energy. This first attempt at testing the coating in a large-scale fusion experiment aims to expand the possible wall candidates for PFCs.

Metal-Catalyst-Free Growth of Patterned Graphene on SiO2 Substrates by Annealing Plasma-Induced Cross-Linked Parylene for Optoelectronic Device Applications.

A metal-catalyst-free method for the direct growth of patterned graphene on an insulating substrate is reported in this paper. Parylene N is used as the carbon source. The surface molecule layer of parylene N is cross-linked by argon plasma bombardment. Under high-temperature annealing, the cross-linking layer of parylene N is graphitized into nanocrystalline graphene, which is a process that transforms organic to inorganic and insulation to conduction, while the parylene N molecules below the cross-linking layer decompose and vaporize at high temperature. Using this technique, the direct growth of a graphene film in a large area and with good uniformity is achieved. The thickness of the graphene is determined by the thickness of the cross-linking layer. Patterned graphene films can be obtained directly by controlling the patterns of the cross-linking region (lithography-free patterning). Graphene-silicon Schottky junction photodetectors are fabricated using the as-grown graphene. The Schottky junction shows good performance. The application of direct-grown graphene in optoelectronics is achieved with a great improvement of the device fabrication efficiency compared with transferred graphene. When illuminated with a 792 nm laser, the responsivity and specific detectivity of the detector measured at room temperature are 275.9 mA/W and 4.93 × 109 cm Hz1/2/W, respectively.

A Review of Recent Studies on Particle Recycling From Liquid Metals With/Without Convection Under Plasma Bombardment

From the recent experiments on liquid metal plasma-facing components, convection appears to play an important role in maintaining reduced recycling conditions. Either it is natural or forced convection, the transport of the implanted particle is accelerated in the depth direction whereby the surface saturation would be delayed or avoided. Reviewed in this paper are some of the recent studies on particle recycling from liquid metals under plasma bombardment with the emphasis on liquid convection effects. Natural convection has been observed to enhance deuterium plasma-driven permeation. In addition, the effects of J × B forced convection on particle recycling have been extensively studied under steady-state hydrogen, deuterium, helium, and argon plasma bombardment. Also, preliminary fluid dynamics analysis has been conducted to interpret these experimental observations.

Chemically assisted physical sputtering of Tungsten: Identification via the [formula omitted] transition of WD in TEXTOR and ASDEX Upgrade plasmas

Tungsten (W) is a preferred plasma-facing material for areas of high particle and power impact in present day and future fusion devices. The lifetime of W plasma-facing components (PFCs) under steady-state conditions is limited by erosion processes induced by energetic impinging particles such as impurities (carbon C, oxygen O, nitrogen N, etc.) and hydrogen isotopes above the threshold energy for Physical Sputtering (PS). We discovered for the first time, in addition to the bare physical sputtering process of W, a second W erosion mechanism at PFCs in TEXTOR (limiter surfaces) and ASDEX Upgrade (divertor target plates) during deuterium plasma bombardment. The tungsten deuteride molecule WD has been identified spectroscopically via the 6Π→6Σ+ transition in parallel to ordinary neutral W line emission of the WI transition (5d5(6S)6s 7S3 → 5d5(6S)6p 7P4) at λ=400.9nm used as measure to quantify the bare PS process or, more precisely, the gross erosion of W. We identified the underlying process for the molecular release as Chemically Assisted Physical Sputtering (CAPS) as observed also in the case of beryllium or lanthanum. Measurements in TEXTOR and ASDEX Upgrade showed a dependence of the WD band emission on the surface temperature - connected to the deuterium content in the near W surface - as well as on the flux and energy of impinging energetic particles. A quantification of the released WD is not yet possible due to lack of appropriate molecular data for the conversion of photons into particles, but the spatially resolved ratio of atomic (WI) and molecular photon flux (WD) indicates that the release takes place at the same time, but differently distributed along the target plates and limiters reflecting the variation in the described critical parameters (impinging ion flux, ion impact energy, and material temperature) along the surface. The plasma conditions in front of the interaction zone are in both cases fully ionising with an electron temperature Te > 10eV, thus, recombination into WD can be excluded.

Ultrasmall Grained Pd Nanopattern H2 Sensor.

Precise control of the size and interfaces of Pd grains is very important for designing a high-performance H2 sensing channel because the transition of the Pd phase from α to β occurs through units of single grains. However, unfortunately, the grain controllability of previous approaches has been limited to grains exceeding 10 nm in size and simple macroscopic channel structures have only shown monotonic response behavior for a wide concentration range of H2. In this work, for the first time, we found that Pd channels that are precisely grain-controlled show very different H2 sensing behavior. They display dual-switching response behavior with simultaneous variation of the positive and negative response direction within single sensor. The Pd nanopattern channel having smallest grain size/interface among previous works could be fabricated via unique lithographic approaches involving low-energy plasma (Ar+) bombardment. The ultrasmall grain size (5 nm) and narrow interface gap (<2 nm) controlled by Ar+ plasma bombardment enabled both the hydrogen-induced lattice expansion (HILE) (Δ RH2 < 0) and surface electron scattering (Δ RH2 > 0) mechanisms to be simultaneously applied to the single Pd channel, thereby inducing dual-switching response according to the H2 concentration range. In addition, the unique high-aspect-ratio high-resolution morphological characteristics made it possible to achieve highly sensitive H2 detecting performance (limit of detection: 2.5 ppm) without any hysteresis and irreversible performance degradation. These noteworthy new insights are attributed to high-resolution control of the grain size and the interfaces with the Pd nanostructure channel.

Low temperature growth of carbon nanotubes by microwave plasma stimulated by CO2 as weak oxidant and guided by shadow masking

Operating at a moderate MW power of 600 W and employing optimized Fe nanoparticles as catalyst, growth optimization of multi-wall CNTs at a relatively low substrate temperature has been performed using tubular microwave plasma enhanced-CVD system. Moderately high energy density plasma facilitates formation of essential precursors for CNT growth. Two intriguing techniques have been integrated in the growth process. Specific shadow masking arrangement by specially designed stainless steel multiple mask assembly protects the growth surface from etching by direct plasma bombardment. CO2 has been used as an auxiliary gaseous component added to the (CH4 + H2) plasma. Instrumental presence of CO2 as a weak oxidant in the plasma accomplishes the removal of a-C coverage from the Fe catalyst nanoparticles via etching by atomic O and thereby, re-triggers their catalytic reactivity and ensures the persistent growth of CNTs. Altogether, a perpetual growth of multiwall CNTs has been realized through tip-growth process at the lowest substrate temperature (300 °C) reported so far in PECVD.