RF Plasma Power Research Articles

Investigation of amorphous-SiC thin film deposition by RF magnetron sputtering for optical applications

Silicon carbide (SiC) is a rapidly emerging material for photonic applications, thanks to its exceptional optical properties. To be used as a waveguide, SiC thin films must be deposited directly on silica at low temperature. Amorphous SiC films were deposited by RF magnetron sputtering using a single source of high-purity polycrystalline SiC. A systematic study of the chemical, structural and optical properties of the films was carried out, using a combination of XRD, XPS, SIMS, spectroscopic ellipsometry, Raman spectroscopy and UV–Vis absorption spectroscopy. The aim was to link deposition conditions to film properties. By exploring a three-parameter space (RF power, substrate temperature, pressure), we have demonstrated that RF power is the main parameter which controls the entire deposition process and film properties. By simply adjusting the RF plasma power between 150 and 450 W, it is possible to adjust the refractive index at a wavelength of 1.5 μm in the range 2.50–2.75 and vary the bandgap from 2.5 to 1.7 eV. This is attributed to a slight variation in film composition, particularly in terms of Si/C ratio and C–C bond concentration.

Low-Temperature Self-Limiting Growth of Cubic Boron Nitride Via Hollow-Cathode Plasma-Enhanced Atomic Layer Deposition

The two main polymorphs of boron nitride are hexagonal (h-BN) and cubic (c-BN) phases and both show attractive material properties to be employed under extreme environments. h-BN is also known as “white graphene” due to the matching hexagonal crystal symmetry and shows a layered structure which provides advantages as a lubricant material and as gate dielectrics for two-dimensional (2D) transistor channels. On the other hand, c-BN is analogous to another important elemental carbon material, diamond. While the mechanical strength of c-BN is lower than diamond, the thermal and chemical stability is even superior. Both h-BN and c-BN films are therefore strong candidates for applications under harsh ambient, including high-temperature, high-pressure, and corroding factors.BN films and coatings are conventionally grown using high-temperature CVD methods with typical substrate temperatures over 1000 oC. To reduce the deposition temperatures of this material while preserving the attractive crystal properties, alternative lower temperature physical and chemical vapor deposition strategies have been offered in the literature. Plasma-enhanced atomic layer deposition (PEALD) provides significant advantages over other methods such as precision thickness control, ultimate conformality, while reducing the growth temperature substantially. In our previous work, we had demonstrated the crystalline synthesis of h-BN films at substrate temperatures as low as 350 oC, while no growth was observed at lower substrate temperatures.In this work, we aim to demonstrate the feasibility of growing c-BN at substrate temperatures reaching 200 oC via a customized PEALD reactor featuring a large-diameter capacitively-coupled hollow-cathode plasma source with a relatively short source-to-substrate distance. We used Si(100), sapphire, and glass as the substrates to deposit the films. The growth temperature is kept between 150 and 250 °C, 10 sccm of N2 flow is used as a carrier gas and Ar-purging gas flow was kept at 50 sccm. The triethylboron (TEB) precursor and various nitrogen plasma chemistries including different compositions of N2, H2, and Ar gases are utilized. The optimized growth condition is determined from in-situ monitored saturation studies, where the growth-per-cycle (GPC) parameter is noted for different precursor pulse time (15 and 30 ms), rf-plasma power (100 W to 250 W) and plasma-gas chemistries (N2-only, N2/H2, Ar/N2, Ar/N2/H2 at varying ratios). While the 200 °C as-grown BN films exhibited nanocrystalline c-BN with relatively weak crystal peaks as verified by XRD measurements, vacuum annealing at 5 mTorr N2 flow and 700 °C transformed the film structure into single-phase polycrystalline c-BN. The spectroscopic ellipsometer, x-ray reflectivity (XRR), and x-ray photoelectron spectroscopy (XPS) studies will be presented as well as the influence of post-deposition vacuum annealing to further improve the crystalline structure of c-BN films. Basic electrical properties of the grown BN films will be characterized using metal-insulator-semiconductor (MIS) diode temperature-dependent current-voltage (I-V) measurements.A specific effort will be devoted to enhance the as-grown film crystal properties via implementing novel atomic layer plasma annealing processes, which showed its potential for the ultrawide bandgap Ga2O3 alloy. Another research question to be investigated is whether there is a possibility of tuning the material phase from cubic to hexagonal by carefully adjusting growth and in-situ Ar-plasma annealing conditions.

Radiofrequency Plasma‐Assisted Pulsed Laser Deposited Pt/TiOxNy Coatings on Multi‐Walled Carbon Nanotubes as Gas Diffusion Electrodes for the Oxygen Reduction Reaction

AbstractThis study reports on the fabrication and characterization of novel multilayered electrocatalyst nanostructures for the oxygen reduction reaction (ORR). Thin titanium oxynitride (TiOxNy) coatings are deposited on a forest of multi‐walled carbon nanotubes (MWCNTs), directly grown on a stainless‐steel mesh, by capacitively coupled radiofrequency plasma‐assisted pulsed laser deposition (RF‐PAPLD) in a N2 environment. The resulting high‐surface‐area binder‐free electrode is further coated with a low quantity of well‐dispersed Pt nanoparticles (NPs) by PLD in an inert atmosphere. High‐speed imaging of the laser‐induced plasma expansion provided evidence of a higher kinetics of the expanding plume at higher RF plasma powers, changing the morphology of the TiOxNy coatings. X‐ray photoelectron spectroscopy demonstrated that the coatings are homogeneous throughout their thickness, where the TiN, TiON, and TiO bonds exist in all samples. The oxygen content of the coating increases with the RF plasma power. Both TiOxNy/MWCNT and Pt/TiOxNy/MWCNT nanostructures are tested in a gas diffusion electrode setup to evaluate their activity in the ORR. The results showed the superior activity of the Pt/TiOxNy‐0.03 Torr‐30 W/MWCNT, reaching the highest current density of 180 mA cm−2, while the commercial Pt/C electrode with the same Pt loading yielded 105 mA cm−2 at the potential of 0.5 V.

Etching characteristics of low-k SiCOH thin films under fluorocarbon-based plasmas

Low dielectric constant (low-k) SiCOH thin films were prepared on silicon (Si) wafers using plasma enhanced chemical vapor deposition (PECVD) of the precursor tetrakis(trimethylsilyloxy)silane (TTMSS). The deposition RF plasma power was 20 and 100 W. The k-values were 2.14 and 3.2 for the films deposited at 20 and 100 W, respectively. The deposited films then underwent an inductively coupled plasma-reactive ion etching (ICP-RIE) using fluorocarbon-based etching gas of CF4, CF4+O2, and CF4+Ar. After etching, the etch rate and refractive index for the films deposited at 100 W were higher than those at 20 W. The surface roughness decreased for the films at 20 W but increased for those at 100 W after etching. Contact angles decreased indicating a hydrophilic surface after etching. Prominent absorption bands from the Fourier transform infrared (FTIR) spectra were observed as C–Hx stretching, Si–CH3 bending, Si–O–Si stretching, and Si–(CH3)x bending vibration modes. X-ray photoelectron spectroscopy (XPS) showed a significant fluorine concentration on the film surface. From high resolution scans for C1s and F1s in the XPS, dominant peaks were observed as C–H/C–C and C–F3 after etching, respectively. After etching, the k-values and leakage current densities increased from those of as-deposited films.

The effect of RF plasma power on remote plasma sputtered AZO thin films

Aluminium-doped ZnO (AZO) thin films were deposited by remote plasma sputtering of a ZnO:Al2O3 98:2 wt% ceramic target in a pulsed DC configuration. The target power was kept constant at 445 W and the RF plasma power was varied between 0.5 and 2.5 kW. The as-deposited AZO thin films exhibited an optimum resistivity of 6.35 × 10−4 Ω·cm and optical transmittance of 92% at a RF plasma power of 1.5 kW. The thin film microstructure, chemical composition, and residual stress were investigated using SEM, RBS, XPS and XRD. Accurate determination of the chemical composition and correct interpretation of GIXRD data for AZO thin films are a particular focus of this work. The AZO layer thickness was 500–700 nm and Al content in the range of 2.3–3.0 at.%, determined by RBS. The AZO thin films exhibited a strong (002) preferential orientation and grain sizes between 70 and 110 nm. The (103) peak intensity enhancement in GIXRD is proven to be a result of the strong (002) preferential orientation and GIXRD geometrical configuration rather than a change in the crystallite orientation at the surface. XPS depth profiles show preferential sputtering of O and Al using a 500 eV Ar+ beam, which can be reduced, but not eradicated using an 8 keV Ar150+ beam. The preferential sputtering can be successfully modelled using the simulation software TRIDYN. A plasma power of 1.5 kW corresponds to a highly ionised plasma and various microstructural and compositional factors have all contributed to the optimum low resistivity occurring at this plasma power. The grain size exhibits a maximum in the 1.25–1.5 kW range and there is improved (002) orientation, minimising grain boundary scattering. The highest carrier concentration and mobility was observed at the plasma power of 1.5 kW which may be associated with the maximum in the aluminium doping concentration (3.0 at.%). The lowest residual stress is also observed at 1.5 kW.

Simulation of nonlinear standing wave excitation in very-high-frequency asymmetric capacitive discharges: roles of radial plasma density profile and rf power

It is recognized that in large-area, very-high-frequency capacitively coupled plasma (VHF CCP) reactors, the higher harmonics generated by nonlinear sheath motion can lead to enhanced standing wave excitation. In this work, a self-consistent electromagnetic model, which couples a one-dimensional, radial nonlinear transmission line model with a bulk plasma fluid model, is employed to investigate the nonlinear standing wave excitation in a VHF driven, geometrically asymmetric capacitive argon discharge operated at low pressure. By considering a radially non-uniform plasma density profile (case I) calculated self-consistently by the nonlinear electromagnetic model and the corresponding radially-averaged, uniform plasma density profile (case II), we first examine the effect of the plasma density non-uniformity on the propagation of electromagnetic surface waves in a 3 Pa argon discharge driven at 100 MHz and 90 W. Compared to case II, the higher plasma density at the radial center in case I determines a higher plasma series resonance frequency, yielding stronger high-order harmonic excitations and more significant central peak in the harmonic current density J z,n and the harmonic electron power absorption p n profiles. Therefore, under the assumption of the radially uniform plasma density in a CCP discharge, the self-excitation of higher harmonics at the radial center should be underestimated. Second, using the self-consistent electromagnetic model, the effect of the rf power on the excitation of nonlinear standing waves is investigated in a 3 Pa argon discharge driven at 100 MHz. At a low power of 30 W, the discharge is dominated by the first two harmonics. The higher harmonic excitations and the nonlinear standing waves are observed to be enhanced with increasing the rf power, resulting in a more pronounced central peak in the radial profiles of the total electron power absorption density p e, the electron temperature T e, and the electron density n e. For all rf powers, the calculated radial profiles of n e show good agreement with the experimental data obtained by a floating double probe.

Effect of RF Power on the Physical Properties of Sputtered ZnSe Nanostructured Thin Films for Photovoltaic Applications.

Zinc selenide (ZnSe) thin films were deposited by RF magnetron sputtering in specific conditions, onto optical glass substrates, at different RF plasma power. The prepared ZnSe layers were afterwards subjected to a series of structural, morphological, optical and electrical characterizations. The obtained results pointed out the optimal sputtering conditions to obtain ZnSe films of excellent quality, especially in terms of better optical properties, lower superficial roughness, reduced micro-strain and a band gap value closer to the one reported for the ZnSe bulk semiconducting material. Electrical characterization were afterwards carried out by measuring the current–voltage (I-V) characteristics at room temperature, of prepared “sandwich”-like Au/ZnSe/Au structures. The analysis of I-V characteristics have shown that at low injection levels there is an Ohmic conduction, followed at high injection levels, after a well-defined transition voltage, by a Space Charge Limited Current (SCLC) in the presence of an exponential trap distribution in the band gap of the ZnSe thin films. The results obtained from all the characterization techniques presented, demonstrated thus the potential of ZnSe thin films sputtered under optimized RF plasma conditions, to be used as alternative environmentally-friendly Cd-free window layers within photovoltaic cells manufacturing.

Nucleation and growth dynamics of graphene grown by radio frequency plasma-enhanced chemical vapor deposition

We investigated the nucleation and grain growth of graphene grown on Cu through radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at different temperatures. A reasonable shielding method for the placement of copper was employed to achieve graphene by RF-PECVD. The nucleation and growth of graphene grains during PECVD were strongly temperature dependent. A high growth temperature facilitated the growth of polycrystalline graphene grains with a large size (~ 2 μm), whereas low temperature induced the formation of nanocrystalline grains. At a moderate temperature (790 to 850 °C), both nanocrystalline and micron-scale polycrystalline graphene grew simultaneously on Cu within 60 s with 50 W RF plasma power. As the growth time increased, the large graphene grains preferentially nucleated and grew rapidly, followed by the nucleation and growth of nanograins. There was competition between the growth of the two grain sizes. In addition, a model of graphene nucleation and grain growth during PECVD at different temperatures was established.

Low-Temperature As-Grown Crystalline β-Ga2O3 Films via Plasma-Enhanced Atomic Layer Deposition.

We report on the low-temperature growth of crystalline Ga2O3 films on Si, sapphire, and glass substrates using plasma-enhanced atomic layer deposition (PEALD) featuring a hollow-cathode plasma source. Films were deposited by using triethylgallium (TEG) and Ar/O2 plasma as metal precursor and oxygen co-reactant, respectively. Growth experiments have been performed within 150-240 °C substrate temperature and 30-300 W radio-frequency (rf) plasma power ranges. Additionally, each unit AB-type ALD cycle was followed by an in situ Ar plasma annealing treatment, which consisted of an extra (50-300 W) Ar plasma exposure for 20 s ending just before the next TEG pulse. The growth per cycle (GPC) of the films without Ar plasma annealing step ranged between 0.69 and 1.31 Å/cycle, and as-grown refractive indices were between 1.67 and 1.75 within the scanned plasma power range. X-ray diffraction (XRD) measurements showed that Ga2O3 films grown without in situ Ar plasma annealing exhibited amorphous character irrespective of substrate temperature and rf power values. With the incorporation of the in situ Ar plasma annealing process, the GPC of Ga2O3 films ranged between 0.76 and 1.03 Å/cycle along with higher refractive index values of 1.75-1.79. The increased refractive index (1.79) and slightly reduced GPC (1.03 Å/cycle) at 250 W plasma annealing indicated possible densification and crystallization of the films. Indeed, X-ray measurements confirmed that in situ plasma annealed films grow in a monoclinic β-Ga2O3 crystal phase. The film crystallinity and density further enhance (from 5.11 to 5.60 g/cm3) by increasing the rf power value used during in situ Ar plasma annealing process. X-ray photoelectron spectroscopy (XPS) measurement of the β-Ga2O3 sample grown under optimal in situ plasma annealing power (250 W) revealed near-ideal film stoichiometry (O/Ga of ∼1.44) with relatively low carbon content (∼5 at. %), whereas 50 W rf power treated film was highly non-stoichiometric (O/Ga of ∼2.31) with considerably elevated carbon content. Our results demonstrate the effectiveness of in situ Ar plasma annealing process to transform amorphous wide bandgap oxide semiconductors into crystalline films without needing high-temperature post-deposition annealing treatment.

Growth of Si3N4 Thin Films on Si(111) Surface by RF-N2 Plasma Nitriding

Ultra-thin Si3N4 films were grown on Si(111) surface by radio frequency (RF)-N2 plasma exposure at 900 °C with 1–1.2 sccm of a flux of atomic nitrogen. We discuss the effect of various conditions such as N2 flow rate, nitriding time and RF power on the optical, chemical, and structural properties of a nitrided Si3N4 layer. The optical properties, surface morphology and chemical composition are investigated by using ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Cross-sectional TEM images show that an RF power of 350 W induced some damage to the Si(111) surface. The thickness of nitrided Si3N4 was measured to be about 5–7 nm. XPS results shown that the binding energy of Si 2p3/2 located at 101.9 ± 0.1 eV is attributed to the Si–N bonds in the Si3N4 compound. Smooth Si3N4 ultra-thin films were obtained at a nitridation time close to 1 h with an RF power of 300 W, with a measured refractive index (n) nearly to 1.88 at 632 nm. The increase in refractive index with decreased RF-plasma power and nitrogen flow rate is probably attributed to the change in the stoichiometry of the film and less surface damage.

Origin of area selective plasma enhanced chemical vapor deposition of microcrystalline silicon

Plasma-enhanced chemical vapor deposition of silicon from a SiF4/H2/Ar gas mixture is observed on a SiOxNy surface, while under the same plasma conditions, silicon films do not grow on AlOx or on Al surfaces. Transmission electron microscopy confirms that the silicon deposited on SiOxNy has a microcrystalline structure. After the plasma process, fluorine is detected in abundance on the AlOx surface by x-ray photoelectron spectroscopy and energy dispersive x-ray chemical analyses. This suggests that Al–F bonds are formed on this surface, blocking any deposition of silicon on it. In situ ellipsometry studies show that deposition can be initiated on AlOx surfaces by increasing the temperature of the electrodes or increasing the RF plasma power, leading to a loss of selectivity.

Anti-oxidant copper layer by remote mode N2 plasma for low temperature copper\u2013copper bonding

An anti-oxidant Cu layer was achieved by remote mode N2 plasma. Remote mode plasma treatment offers the advantages of having no defect formation, such as pinholes, by energetic ions. In this study, an activated Cu surface by Ar plasma chemically reacted with N free radicals to evenly form Cu nitride passivation over the entire Cu surface. According to chemical state analysis using XPS, Cu oxidation was effectively prevented in air, and the thickness of the Cu nitride passivation was within 3 nm. Based on statistical analysis using the DOE technique with N2 plasma variables, namely, RF power, working pressure, and plasma treatment time, we experimentally demonstrated that a lower RF power is the most effective for forming uniform Cu nitride passivation because of a lower plasma density. When the N2 plasma density reached approximately 109 cm−3 in which the remote mode was generated, high energy electrons in the plasma were significantly reduced and the amount of oxygen detected on the Cu surface was minimized. Finally, low temperature (300 °C) Cu–Cu bonding was performed with a pair of the anti-oxidant Cu layers formed by the remote mode N2 plasma. Cu atomic diffusion with new grains was observed across the bonded interface indicating significantly improved bonding quality over bare Cu–Cu bonding.

OES diagnostic of SF6/Ar gas mixture of ICP discharges for LiNbO3 etching

The results of a study of the influence of technological parameters of the process of plasma chemical etching in inductively coupled plasma on the emission spectra of fluorine and argon atoms are presented. The effects of inductively coupled plasma RF power, operating pressure and bias voltage were studied for 6 different sulfur hexafluoride argon (SF6/Ar) gas mixtures: SF6 (1.5 sccm)/Ar (9.2 sccm), SF6 (7.8 sccm)/Ar (10.8 sccm), SF6 (4.7 sccm)/Ar (6.0 sccm), SF6 (7.0 sccm)/Ar (4.9 sccm), SF6 (11.7 sccm)/Ar (5.4 sccm), SF6 (9.4 sccm)/Ar (3.3 sccm). It is shown that a decrease in the operating pressure and an increase in the RF power of the inductively coupled plasma leads to an increase in the relative intensity of both argon and fluorine lines. Variations in the bias voltage have no significant effect on the emission intensity of the spectral lines of Ar and F.

Ferrite-free closed-loop inductively-coupled low mercury pressure UV lamp

Characteristics of ultraviolet (UV) radiation (254 nm) sources employing ferrite-free inductively-coupled low pressure mercury discharge excited in the closed-loop quartz tube with the inner diameter (ID), dt = 16,6 mm and the length, Λpl = 815 mm were experimentally studied. Discharge was maintained at a frequency of 1,7 MHz and RF powers, Plamp = 95–170 W, in the mixture of mercury vapor (~7–8 mTorr) and buffer gas fill (Ar, 30%Ne + 70%Ar) at pressures of 0,7 and 1,0 Torr. A 3-turn induction coil made from low loss Litz wire (resistivity, ρw = 1,4 × 10–4 Ω cm−1, wire diameter, dw = 1,5 mm) was disposed on the lamp surface along the closed-loop tube perimeter. As lamp RF power increased from 95 to 170 W, induction coil power losses, Pcoil, decreased from 7–9 to 3–4 W while coil power efficiency, ηcoil = 1- (Pcoil/Plamp), grew from 92 to 98%. Lamps with buffer gas at pressure of 1,0 Torr, operated at plasma RF power, Ppl = 105–150 W, had high plasma UV radiation generation efficiency, η254pl, max = Φ254/Ppl = 67%–68%, while lamp UV radiation generation maximal efficiency, η254, max = ηcoilη254pl, max, had slightly lower values of 63%–66%.

The Effect of Plasma Pretreatment on the Morphology and Properties of Hitus Coatings

Abstract WC coatings prepared by High Target Utilization Sputtering (HITUS), a relatively new technology, were deposited on three types of substrates. These were silicon (111), steel (100Cr6), and ceramic (WC-Co). The influence of RF plasma power pretreatment on final properties of WC coatings was investigated with two interlayer materials for bonding. The morphology, roughness, and mechanical properties of coatings were studied. The relation between plasma RF power and roughness was found. No significant change in mechanical properties was detected with change in plasma RF power. The dependence of nanohardness and scratch behavior on HITUS WC coatings was investigated.

Understanding the role of rf-power on AlN film properties in hollow-cathode plasma-assisted atomic layer deposition

In this study, the authors have carried out real-time process monitoring via in situ ellipsometry to understand the impact of rf-plasma power and plasma exposure time on self-limiting aluminum nitride (AlN) growth character and the corresponding film properties. AlN thin films were grown on Si(100) substrates with plasma-enhanced atomic layer deposition using trimethyl-aluminum (TMA) as a metal precursor and Ar/N2/H2 plasma as a coreactant. Saturation experiments have been employed in the range of 25–200 W plasma power and 30–120 s plasma exposure time. In situ multiwavelength ellipsometry identified single chemical adsorption (chemisorption) and plasma-assisted ligand removal events, as well as changes in growth per cycle (GPC) with respect to plasma power. The real-time dynamic in situ monitoring study revealed that GPC and TMA chemisorption thickness gain exhibited plasma power dependent saturation behavior. The amount of chemisorption saturated at ∼2.3 Å for higher rf-power levels, while for 25 and 50 W it went below 1.0 Å, which is mainly attributed to incomplete ligand removal. Besides in situ characterization, ex situ measurements to identify optical, structural, and chemical properties were also carried out on 500-cycle AlN films as a function of plasma power. AlN samples displayed a single-phase hexagonal wurtzite crystal structure with (002) preferred orientation for 150 and 200 W, while the dominant orientation shifted toward (100) at 100 W. 50 W and lower rf-power levels resulted in amorphous material with no apparent crystal signature. Furthermore, it was found that when the plasma exposure time was increased from 30 to 120 s for 25 and 50 W, the amount of chemisorption exceeded the thickness gain values recorded for 150–200 W (∼2.4 Å). However, such a recovery in the chemisorption thickness gain did not restore the crystallinity as the AlN films grown at sub-50 W showed amorphous character independent of plasma exposure time.

Comparative Study on in-situ Ellipsometric Monitoring of III-Nitride Film Growth via Plasma-Enhanced Atomic Layer Deposition

In this paper a comparative in-situ ellipsometric analysis is carried out on plasma-assisted ALD-grown III-nitride (AlN, GaN, and InN) films. The precursors used are TMA, TMG, and TMI for AlN, GaN, and InN respectively, while Ar is used as purge gas. For all of the films N2/H2/Ar plasma was used as the co-reactant. The work includes real-time in-situ monitored saturation curves, unit ALD cycle analysis, and >500 cycle film growth runs. In addition, the films are grown at different substrate temperatures to observe the impact of temperature not only on the growth rate but on how it influenced the precursor chemisorption, ligand removal, and nitrogen incorporation surface reactions. All three nitride films confirm fairly linear growth character. The growth rate per cycle (GPC) for each film is also measured with respect to rf-plasma power to obtain the surface saturation conditions during ALD growth. The real-time in-situ monitoring of the film growth can really be beneficial to understand the atomic layer growth and film formation in each individual ALD cycle.

‘Fire Tube’ Formation in Expanding RF Plasma

Multiple double layers develop during expanding capacitive mode of RF discharge in a linear vacuum vessel in the absence of external magnetic field. Dynamics of multiple double layers have been studied through electric probe diagnostics in nitrogen RF plasma operated at 13.56 MHz frequency. The burst oscillations of the potential, fire tube formations and space charge formations suggest formations of complex structures during the discharge. Our first experimental results provide interesting information about the stability of plasma sheath and space charge effect on it. The visibly bright discharge transforms into multiple intensely coaxial luminous “Fire Tube” structures on increasing the input RF power in plasma.

Dry etching of copper thin films in high density plasma of CH3COOH/Ar

Inductively coupled plasma reactive ion etching of copper thin films patterned with SiO2 masks was carried out using CH3COOH/Ar gas. The etch rate, etch selectivity to SiO2 mask, and the etch profiles of copper films were examined. The evolution study of the etch profile as a function of gas concentration and etch depth revealed the etch sequence and etch mechanism. In the optimized CH3COOH/Ar gas, the systematic approach on the etch characteristics of copper films was performed by changing the etch parameters including inductively coupled plasma (ICP) rf power, dc-bias voltage to substrate, and process pressure. As the ICP rf power and dc-bias voltage increased and the process pressure decreased, the etch rate increased and the etch profile improved. X-ray photoelectron spectroscopy was used to determine the etch mechanism in CH3COOH/Ar gas. Finally, the etching of copper films in the CH3COOH/Ar was achieved with good etch profile with a high degree of anisotropy.

Interface Properties of GaP/Si Heterojunction Fabricated by PE‐ALD

The properties of n‐GaP/p‐Si interface as well as their influence on solar cell performance are studied for GaP layers grown by low‐temperature (380 °C) plasma‐enhanced atomic layer deposition (PE‐ALD). The influence of different plasma treatments and RF power values are explored. The increase of RF power leads to a growth transition from amorphous (a‐GaP) to microcrystalline GaP (μc‐GaP) with either amorphous‐GaP/Si or epitaxial‐GaP/Si interface, respectively. However, when continuous hydrogen plasma is used the amorphous‐GaP/Si interface exhibits better photovoltaic performance compared to the epitaxial one. Values of open circuit voltage, Voc = 0.45–0.55 V and internal quantum efficiencies, IQE > 0.9 are obtained for amorphous‐GaP/Si interfaces compared to Voc = 0.25–0.35 V and IQE < 0.45 for epitaxial‐GaP/Si interfaces. According to admittance spectroscopy and TEM studies the near‐surface (30–50 nm) area of the Si substrate is damaged during growth with high RF power of hydrogen plasma. A hole trap at the level of EV + (0.33 ± 0.02) eV is detected by admittance spectroscopy in this damaged Si area. The damage of Si is not observed by TEM when the deposition of the structures with epitaxial‐GaP/Si interface is realized by a modified process without hydrogen plasma indicating that the damage of the near‐surface area of Si is related to hydrogen plasma interaction.