Silane Plasma Research Articles

On the OES line-ratio technique in argon and argon-containing plasmas

Optical emission spectroscopy is used to investigate capacitively coupled argon and argon–hydrogen–silane plasmas. The argon collisional–radiative model (CRM) used to extract the electron density and temperature from the spectra is presented. The electron energy distribution function, which is an input parameter to the model, is discussed in detail. Its strong variation with pressure is found to significantly influence the results for the (effective) temperature. For the analysis of the spectra the common line-ratio technique is applied. Special attention is paid to the choice of lines and a pair of line-ratios for optimum accuracy is suggested. For the argon gas mixture at high partial pressure of the admixed molecular gases the CRM reduces to a corona-like model, extended by a quenching term. The line-ratio method is found to fail under these conditions due to the strong depopulation of the argon 1s states. As a consequence, individual line intensities have to be used and an absolute calibration is required. An easy calibration method, which relies on the results obtained by the line-ratio method in pure argon, is proposed and applied.

Numerical Modeling of an RF Argon–Silane Plasma with Dust Particle Nucleation and Growth

A one-dimensional numerical model and simulation results are presented for a capacitively-coupled radio frequency parallel-plate argon-silane dusty plasma. The model includes self-consistently coupled numerical modules, including a plasma fluid model, a sectional aerosol model, and a simple chemistry model to predict rates of particle nucle- ation and surface growth. Operating conditions considered include 13.56 MHz frequency, 100 mTorr pressure, a 4-cm electrode gap, gas flow through the top electrode with a 30:1 ratio of argon to silane, and applied radio frequency voltage amplitude of either 100 or 250 V. In the higher voltage case two lobes of relatively large particles are formed by ion drag, while fresh nucleation occurs in the void between these lobes. It is shown that the reason that fresh nucleation occurs in the void involves an interplay among several coupled phenomena, including nanoparticle transport, the plasma potential profile, and trapping of silicon hydride anions that drive nucleation in this system.

Thin-film deposition modeling of hydrogenated amorphous silicon in the afterglow of argon plasma

This paper proposes an integrated numerical approach to model the thin-film deposition of amorphous silicon in the afterglow of argon plasma. The investigated plasma enhanced chemical vapor deposition (PECVD) process is governed by gas flow equations, chemical kinetics equations and surface reaction equations. Nineteen species, i.e. Ar, Ar*, Ar+, Si2H6, Si2H4, SiH4, SiH3, SiH2, SiH, H2, H, Si, Si+, SiH3+, SiH2+, SiH+, H2+, H+ and electron (e) are considered, where 52 chemical reaction equations are adopted to describe the reactions in space among silane, hydrogen and argon plasma. Continuity, momentum and energy equations are solved to describe the velocity, pressure and temperature field of gas flow in the process chamber, while the density of neutral species is calculated from the corresponding transport equation considering its convection and diffusion effect, as well as the production and destruction due to chemical reactions. The transport equations of charged species are modeled by a drift–diffusion approximation. The ambipolar diffusion is assumed for charged species in the afterglow of argon plasma due to the vanishing of external electrical field. The equation of energy balance for electron is applied to the estimation of the electron temperature in the process chamber. In this study, ten reaction mechanisms of thin film growth are taken into account. The species considered in the deposition process on substrates are silane, the free radicals of silane, hydrogen, hydrogen atom, silicon atom, the species with dangling bond on the substrate surface covered by active and the passive site. All governing equations are discretized by using a finite volume method and solved by an iterative approach. The variables, such as position, velocity and moment, are expressed by Cartesian coordinates, where the non-staggered variable arrangement is adopted to define field variables. The deferred correction approach is employed to approximate for both diffusion and source terms, where SIMPLE algorithm is used to decouple pressure and velocity. A parallelized numerical scheme is implemented via MPI library. Numerical simulations with different operation parameters are performed to show their influence on the deposition rate. The numerical results indicate the deposition rate exhibits a double-peak characteristic on the substrate and give an average value varying between 5Å/s and 10Å/s for the studied PECVD process in the afterglow of argon plasma.

Infrared Spectrum of the Si3H8+ Cation: Evidence for a Bridged Isomer with an Asymmetric Three‐Center Two‐Electron SiHSi Bond

The IR spectrum of Si3H8(+) ions produced in a supersonic plasma molecular beam expansion of SiH4, He, and Ar is inferred from photodissociation of cold Si3H8(+)-Ar complexes. Vibrational analysis of the spectrum is consistent with a Si3H8(+) structure (2(+)) obtained by a barrierless addition reaction of SiH4 to the disilene ion (H2Si=SiH2(+)) in the silane plasma. In this structure, one of the electronegative H atoms of SiH4 donates electron density into the partially filled electrophilic π orbital of the disilene cation. The resulting asymmetric Si-H-Si bridge of the 2(+) isomer with a bond energy of approximately 60 kJ mol(-1) is characteristic for a weak three-center two-electron bond, which is identified by its strongly IR active asymmetric Si-H-Si stretching fundamental at about 1765 cm(-1). The observed 2(+) isomer is calculated to be only a few kJ mol(-1) less stable than the global minimum structure of Si3H8(+) (1(+)), which is derived from vertical ionization of trisilane. Although more stable, 1(+) is not detected in the measured IR spectrum of Si3H8(+)-Ar, and its lower abundance in the supersonic plasma is rationalized by the production mechanism of Si3H8(+) in the silane plasma, in which a high barrier between 2(+) and 1(+) prevents the efficient formation of 1(+). The potential energy surface of Si3H8(+) is characterized in some detail by quantum chemical calculations. The structural, vibrational, electronic and energetic properties as well as the chemical bonding mechanism are investigated for a variety of low-energy Si3H8(+) isomers and their fragments. The weak intermolecular bonds of the Ar ligands in the Si3H8(+)-Ar isomers arise from dispersion and induction forces and induce only a minor perturbation of the bare Si3H8(+) ions. Comparison with the potential energy surface of C3H8(+) reveals the differences between the silicon and carbon species.

탄소섬유 표면처리에 따른 탄소섬유/폴리프로필렌 복합재료의 기계적 물성 평가

본 연구에서는 탄소섬유의 표면처리에 따른 탄소섬유/폴리프로필렌 복합재료의 기계적 물성을 평가하였다. 탄소섬유와 폴리프로필렌 사이의 계면 결합력을 증가시키기 위해 실란 커플링제 처리와 플라즈마 처리 같은 탄소섬유의 표면처리를 실시하였다. XPS, SEM 그리고 단일섬유 인장강도 시험을 통해 표면 처리된 탄소섬유의 표면 특성을 분석하였으며, Short beam 전단시험을 통해 표면 처리에 따른 복합 재료의 계면 전단 강도를 측정하였다. 실험 결과로부터 플라즈마 처리 시간에 따라 복합재료의 계면 전단 강도는 증가하였으며, 1 분 동안 플라즈마 처리 후 실란 커플링제 처리된 시편의 계면 전단 강도는 처리하지 않은 시편에 비해 48.7% 증가하였다.

Electrical Properties of Ta(Si)N Films Prepared by Atomic Layer Deposition from Tert-Butylimido-Tris-Diethylamido Tantalum, Silane and Hydrogen Plasma

Ta(Si)N films were prepared by atomic layer deposition (ALD) from tert-butylimido-tris-diethylamido tantalum (TBTDET), triethylsilane, and activated hydrogen. Triethylsilane was used as an ancillary reducing agent and as a silicon precursor. The effects of the addition of the triethylsilane at different hydrogen plasma pulse times and power on the electrical properties, particularly stability in air, were investigated. Longer plasma pulse times with high power were effective in decreasing resistivity and increasing stability in air. However, introduction of silane resulted in an increase in resistivity of the films regardless of the hydrogen plasma conditions.

Effect of Hydrogen Content in Intrinsic a-Si:H on Performances of Heterojunction Solar Cells

Influences of hydrogen content in intrinsic hydrogenated amorphous silicon (i-a-Si:H) on performances of heterojunction (HJ) solar cells are investigated. The simulation result shows that in the range of 0–18% of the i-layer hydrogen content, solar cells with higher i-layer hydrogen content can have higher degree of dangling bond passivation on single crystalline silicon (c-Si) surface. In addition, the experimental result shows that HJ solar cells with a low hydrogen content have a poor a-Si:H/c-Si interface. The deteriorate interface is assumed to be attributed to (i) voids created by insufficiently passivated c-Si surface dangling bonds, (ii) voids formed by SiH2clusters, and (iii) Si particles caused by gas phase particle formation in silane plasma. The proposed assumption is well supported and explained from the plasma point of view using optical emission spectroscopy.

Reducing the effects of mismatch between zinc oxide and silicon by silane plasma modification

We investigated the mismatch between zinc oxide (ZnO) and silicon (Si) upon reduction by silane plasma modification in a plasma-enhanced chemical vapor deposition system. This plasma treatment was only carried out for 10 s and the Si–H bonds that were provided by the silane plasma modification as dangling bonds on the Si wafer in addition to functioning as a conjunction layer to reduce the defects. The X-ray diffraction analysis of the ZnO/p-type silicon structure produced by silane plasma modification has a slightly lower full width at the half maximum, which improved the ZnO film’s crystalline properties. After the silane plasma modification ZnO/Si diode is produced, the measured current–voltage characteristics gave favorable rectifying properties and reverse bias had a low leakage current. The ZnO/Si diode under illumination increased the short-circuit current (Isc) from 7.32 to 19.75 mA/cm2, which is an improvement compared with a conventional bare ZnO/Si diode because of the reduced ZnO/Si interface states. Therefore, the silane plasma modification diminishes the effects of the interface and improves the ZnO/Si diode performance.

An optical analysis tool for avoiding dust formation in very-high frequency hydrogen diluted silane plasmas at low substrate temperatures

Control of the formation of dust particles in a silane deposition plasma is very important for avoiding electrical shunts in devices, such as thin film silicon solar cells. In this work we present a noninvasive in situ method for identification of the plasma regime, based on optical emission spectroscopy (OES), which can be applied to silane/hydrogen plasmas at low substrate temperatures. By monitoring the OES spectra as a function of the position perpendicular to the plasma electrodes we developed a method to identify the transition of a plasma from the dust free to a dusty regime, which was confirmed by TEM images of layers deposited in both regimes. Using this technique we mapped this transition as a function of applied forward very-high frequency (VHF) power and hydrogen dilution at different substrate temperatures. The advantage of this technique is that the experiment is insensitive to optical transmission loss at the viewport due to deposition of silicon films. As the transition from the dust free to the dusty regime is substrate temperature dependent and the transition from amorphous to nanocrystalline growth mainly depends on hydrogen dilution, a limited parameter window has been defined in which dust-free amorphous silicon can be deposited at low substrate temperatures. A single simple OES technique can be used for in situ monitoring of amorphous to nanocrystalline transition as well as the onset of the dusty regime in a thin film silicon cell fabrication process.

Low Temperature Growth of Hydrogenated Silicon Prepared by PECVD from Argon Diluted Silane Plasma

In order to contribute to the understanding of the optoelectronics properties of hydrogenated nanocrystalline silicon thin films, a detailed study has been conducted. The samples were deposited by 13.56 MHz PECVD (Plasma-Enhanced Chemical Vapor Deposition) of silane argon mixture. The argon dilution of silane for all samples studied was 96% by volume. The substrate temperature was fixed at 200oC. The influence of depositions parameters on optical proprieties of samples was studied by UV-Vis-NIR spectroscopy. The structural evolution was studied by Raman spectroscopy and X-ray diffraction (XRD). Intrinsic-layer samples depositions were made in this experiment in order to obtain the transition from the amorphous to crystalline phase materials. The deposition pressure varied from 400 mTorr to 1400 mTorr and the rf power from 50 to 250 W. The structural evolution studies show that beyond 200 W, we observed an amorphous-nanocrystalline transition, with an increase in crystalline fraction by increasing rf power and working pressure. Films near the amorphous to nanocrystalline transition region are grown at reasonably high deposition rates (~10 /s), which are highly desirable for the fabrication of cost effective devices. The deposition rate increases with increasing rf power and process pressure. Different crystalline fractions (21% to 95%) and crystallite size (6 - 16 nm) can be achieved by controlling the process pressure and rf power. These structural changes are well correlated to the variation of optical proprieties of the thin films.

Research on Nanocrystalline Silicon Film Solar Cells

Nanocrystalline silicon film has become the research hit of today’ s P-V solar technology. It’s optical band gap was controlled through changing the grain size and crystalline volume fraction for the quanta dimension effect. The crystalline volume fraction in nc-Si:H is modulated by varying the hydrogen concentration in the silane plasma. Also, the crystallinity of the material increases with increasing hydrogen dilution ratio, the band tail energy width of the nc-Si:H concurrently decreases. Two sets of nc-Si:H solar cells were made with different layer thicknesss, their electronic and photonic bandgap, absorption coefficient, optical band gap, nanocrystalline grain size(D), and etc have been stuied. In addition, we discussed the relationship between the stress of nc-Si thin films and H2 ratio. At last nc-Si:H solar cells have been designed and prepared successfully in the optimized processing parameters.

A study of the role of various reactions on the density distribution of hydrogen, silylene, and silyl in SiH4/H2 plasma discharges

Fluid model has been used to study the effect of pressure on the distribution of hydrogen (H), silylene (SiH2), and silyl (SiH3) in hydrogen silane plasma discharges used for deposition of hydrogenated microcrystalline silicon (μc-Si:H) or hydrogenated amorphous silicon (a-Si:H) thin films for solar cells. Time averaged reaction rates have been calculated to study the influence of various reactions on the density distributions of hydrogen, silylene, and silyl. Change in the distributions of hydrogen and silylene from bell shaped distribution at low pressure (1 Torr) to double humped distribution at high pressure (5 Torr) is explained with the help of time averaged reaction rates. Important reactions have been identified that contribute to the production and consumption of hydrogen (H), silylene (SiH2), and silyl (SiH3). The hydrogen consumption reactions SiH4 + H → SiH3 + H2 and SiH3 + H → SiH2 + H2 are found to play a central role in deciding the distribution of hydrogen. On the other hand, silylene consumption reaction SiH2 + H2 → SiH4 is found to play a central role in determining the distribution of silylene. The distribution of these species at high pressure has been explained by using time averaged continuity equation. The code has been optimized by identifying 33 reactions (out of 53 reactions which contribute in the production and consumption of H, SiH2, and SiH3) that have no net effect on the density and distribution of these species. It is observed that dropping of 33 reactions has insignificant effect on the density of all the thin film deposition precursors such as Si, SiH, SiH2, SiH3, and Si2H5. This reduced set of 20 reactions can be used instead of 53 reactions to calculate the density and distribution of H, SiH2, and SiH3 in the fluid simulation of SiH4/H2 plasma discharges.

Analysis of a modified microbond test for the measurement of interfacial shear strength of an aqueous-based adhesive and a polyamide fibre

The microbond test was used to measure the interfacial shear strength (IFSS) between a polyamide fibre and a water-based polyurethane. Due to the low viscosity of the water based polyurethane, the droplet could not be formed using a conventional preparation method. A disc shaped microbond droplet forms when an aqueous-based colloidal polymer adhesive was deposited onto the pin hole in a mounting card with a vertical polyamide fibre in the middle after drying and curing at an elevated temperature. Since the droplets were formed with a disc shape, which differs from the conventional ellipsoid, a finite element analysis of the stress distribution at the interface for these contrastingly shaped droplets were calculated and compared. The stress analysis showed that the interfacial shear stress profiles were well matched for both providing confidence that the disc-shaped droplets could be used for interfacial analysis. The microbond test using a disc-shaped droplet was used to study the influences of silane treatment and plasma treatment on the interfacial shear strength between a polyamide fibre and an aqueous deposited polyurethane. The interfacial shear strength of the fibre after plasma treatment was 10.3 MPa, much higher than that of the control and the silanised fibres, 5.2 MPa and 5.4 MPa respectively. The results showed that the microbond test could be used to investigate the interfacial properties of the polyamide fibre and water-based polymer adhesive.

Computer modelling of the plasma chemistry and plasma-based growth mechanisms for nanostructured materials

In this review paper, an overview is given of different modelling efforts for plasmas used for the formation and growth of nanostructured materials. This includes both the plasma chemistry, providing information on the precursors for nanostructure formation, as well as the growth processes itself. We limit ourselves to carbon (and silicon) nanostructures. Examples of the plasma modelling comprise nanoparticle formation in silane and hydrocarbon plasmas, as well as the plasma chemistry giving rise to carbon nanostructure formation, such as (ultra)nanocrystalline diamond ((U)NCD) and carbon nanotubes (CNTs). The second part of the paper deals with the simulation of the (plasma-based) growth mechanisms of the same carbon nanostructures, i.e. (U)NCD and CNTs, both by mechanistic modelling and detailed atomistic simulations.

Influence of the Electrode Spacing on the Plasma Characteristics and Hydrogenated Amorphous Silicon Film Properties Grown in the DC Saddle Field PECVD System

ABSTRACTA new plasma deposition system was built with the capability of varying the electrode spacing in the DC Saddle Field plasma enhanced chemical vapor deposition system. An ion mass spectrometer was installed just below the substrate holder to sample the ion species travelling towards the substrate. Silane plasma and amorphous silicon film studies were conducted to shed light on the impinging ion species, ion energy distributions, and film properties with varying electrode spacing. The results indicate that decreasing the distance between the substrate and cathode leads to a reduction in the high energy ion bombardment.

Correlation between nanoparticle and plasma parameters with particle growth in dusty plasmas

Since plasma parameters are altered by dust particles, studying how plasma parameters are related to dust particle growth is an important research issue in dusty plasma. In this paper, the correlation between plasma parameters (electron temperature and ion flux) and particle parameters (particle radius and density) is investigated in silane plasma both experimentally using a floating probe and theoretically by solving balance equations including an additional electron and ion loss to the dust. The results reveal that while the ion flux shows two peak values in the early discharge phase and at the end of coagulation phase, the electron temperature shows a sudden increase in the coagulation step and a gradual decrease in the molecular accretion step. Moreover, the calculated results with the secondary electron emission taken into account produce the best fit with the experimental results. Thus the study confirms that the secondary electron emission plays a crucial role in the coagulation of the dust particles.

The silane depletion fraction as an indicator for the amorphous/crystalline silicon interface passivation quality

In silicon heterojunction solar cells, thin amorphous silicon layers passivate the crystalline silicon wafer surfaces. By using in situ diagnostics during plasma-enhanced chemical vapor deposition (PECVD), the authors report how the passivation quality of such layers directly relate to the plasma conditions. Good interface passivation is obtained from highly depleted silane plasmas. Based upon this finding, layers deposited in a large-area very high frequency (40.68 MHz) PECVD reactor were optimized for heterojunction solar cells, yielding aperture efficiencies up to 20.3% on 4 cm2 cells.

Transient Phenomena in Plasma-Enhanced Chemical Vapor Deposition Processes of Thin-Film Silicon

The time-dependent gas phase kinetics in plasma-enhanced chemical vapor deposition (PECVD) processes has been studied. The temporal evolutions of the gas phase species, concentration and plasma parameters are measured in hydrogen-diluted silane plasmas, using plasma diagnostic techniques including mass spectrometry, optical emission spectroscopy, and probe and laser light scattering techniques. It is identified that gas phase kinetics such as electron collisions, chemical reactions, and particle transport play important roles in the transient phenomena of thin-film silicon PECVD processes. The characteristic times of the gas decomposition and depletion, diffusive transport, and nanoparticle growth and drift are discussed.

Hydrogen-dominated plasma, due to silane depletion, for microcrystalline silicon deposition

Plasma conditions for microcrystalline silicon deposition generally require a high flux of atomic hydrogen, relative to SiHα=0→3 radicals, on the growing film. The necessary dominant partial pressure of hydrogen in the plasma is conventionally obtained by hydrogen dilution of silane in the inlet flow. However, a hydrogen-dominated plasma environment can also be obtained due to plasma depletion of the silane in the gas mixture, even up to the limit of pure silane inlet flow, provided that the silane depletion is strong enough. At first sight, it may seem surprising that the composition of a strongly depleted pure silane plasma consists principally of molecular hydrogen, without significant contribution from the partial pressure of silane radicals. The aim here is to bring some physical insight by means of a zero-dimensional, analytical plasma chemistry model. The model is appropriate for uniform large-area showerhead reactors, as shown by comparison with a three-dimensional numerical simulations. The SiHα densities remain very low because of their rapid diffusion and surface reactivity, contributing to film growth which is the desired scenario for efficient silane utilization. Significant SiHα densities due to poor design of reactor and gas flow, on the other hand, would result in powder formation wasting silane. Conversely, hydrogen atoms are not deposited, but recombine on the film surface and reappear as molecular hydrogen in the plasma. Therefore, in the limit of extremely high silane depletion fraction (>99.9%), the silane density falls below the low SiHα densities, but only the H radical can eventually reach significant concentrations in the hydrogen-dominated plasma.

Growth study of indium-catalyzed silicon nanowires by plasma enhanced chemical vapor deposition

Indium was used as a catalyst for the synthesis of silicon nanowires in a plasma enhanced chemical vapor deposition reactor. In order to foster the catalytic activity of indium, the indium droplets had to be exposed to a hydrogen plasma prior to nanowire growth in a silane plasma. The structure of the nanowires was investigated as a function of the growth conditions by electron microscopy and Raman spectroscopy. The nanowires were found to crystallize along the <111>, <112> or <001> growth direction. When growing on the <112> and <111> directions, they revealed a similar crystal quality and the presence of a high density of twins along the {111} planes. The high density and periodicity of these twins lead to the formation of hexagonal domains inside the cubic structure. The corresponding Raman signature was found to be a peak at 495 cm−1, in agreement with previous studies. Finally, electron energy loss spectroscopy indicates an occasional migration of indium during growth.