Hydrogen Content Of Films Research Articles

Effects of hydrogen content in films on the etching of LPCVD and PECVD SiN films using CF4/H2 plasma at different substrate temperatures

AbstractThe dependences of etching characteristics on substrate temperature (Ts, from –20 to 50°C) of the plasma‐enhanced chemical vapor deposition (PECVD) SiN films (PE‐SiN) and low‐pressure chemical vapor deposition (LPCVD) SiN films (LP‐SiN) with CF4/H2 plasma were investigated. The Fourier‐transform infrared spectroscopy shows that both film types were N–H bond‐rich films, but in different hydrogen contents (PE‐SiN 22.7 at% and LP‐SiN 3.8 at%) from the Rutherford backscattering spectroscopy analyses. A higher hydrogen content led to a thinner fluorocarbon thickness because of the reaction between hydrogen outflux and C and N to form an HCN byproduct. The etch rates (ER) for the PE‐SiN were higher than that of the LP‐SiN at all Ts, due to the different FC thickness and etching mechanisms proposed. The formation of the N−Hx layer on PE‐SiN at low temperature caused the decrease in ER. For the LP‐SiN, the weak dependences of Ts on surface structure and ER were observed.

Analysis of defects in In2O3:H synthesized in presence of water vapor and hydrogen gas mixture

Using hybrid functional-based density functional theory calculations, we analyze the structure and kinetics of defects formed in two competing synthesis routes to prepare hydrogen-doped In2O3 films, using a hydrogen and oxygen gas mixture vs synthesis in the presence of water vapor. For both of these synthesis routes, we find that H+ is the dominant defect species: when the Fermi level is close to the conduction band, H+ has a lower formation energy than other intrinsic or extrinsic defects. Our results also suggest that water molecules spontaneously split into H+ (which occupies octahedral voids) and OH− interstitials (which occupies vacant oxygen lattice sites or oxygen vacancies). From the analysis of the binding energies between these different defects, we conclude that these defects do not cluster and are most likely to stay spatially distributed throughout the films. In addition, the sum of formation energies of an oxygen (i.e., Oi2−) and a H+ interstitial is close to the formation energy of a OH− interstitial, meaning that water molecules are completely split into 2H+ and Oi2− at the synthesis conditions. Further, in the presence of H2 + O2 gas mixture, oxygen interstitials occupy oxygen vacancies while hydrogen interstitials occupy vacant oxygen lattice sites and form bonds with lattice oxygens. Our analysis of the defect equilibria suggests that the hydrogen content in films synthesized in the presence of water vapor is higher than films synthesized in the presence of a hydrogen gas mixture. At high dopant concentrations, a hydrogen bond network is formed in the system and this leads to large distortions in the lattice.

Study on the effect of process conditions on the thermo-optic coefficient of amorphous silicon films

A thermo-optical coefficient (TOC) test platform based on FILMeasure-20 was designed and the thermal coefficient of hydrogenated amorphous silicon (a-Si:H) thin films material at 1330 nm was tested. a-Si:H were deposited on the quartz glass using a plasma-enhanced chemical vapor deposition (PECVD) system. Fourier transform infrared spectrometer (FTIR) was used to characterize the infrared spectral feature of films. The hydrogen content of films was influenced by different radio frequency (RF) power and deposition pressure conditions according to the FTIR spectra and theoretical analysis, and the thermo-optic effect of a-Si:H varied with temperature characteristics. Experimental results indicated that selecting the appropriate process conditions to prepare a-Si:H films can effectively increase or avoid the impact of thermo-optical effect on the optical devices.

Influence of Hydrogen Content on Optical and Mechanical Performances of Diamond-Like Carbon Films on Glass Substrate

The protective layer for cover glass of touch panel screen for electronic mobile devices is required to have good mechanical properties and decent optical transparency simultaneously. The hydrogenated diamond-like carbon (a-C:H) films were deposited on glass substrate by RF-PECVD in the negative stage potential mode (NP mode), as well as the ground stage potential mode (GP mode). The impact of hydrogen content, affected by stage potential and RF power, on optical and mechanical properties was investigated. The results show that hydrogen content decreases with increasing RF power, due to the dehydrogenation effect. Higher hydrogen content in films results in lower refractive index, lower extinction coefficient, lower optical absorptions, larger optical band gap and higher transmittance, but lower hardness and wearing resistance. Therefore, although the GP mode DLC is optically favorable because of higher hydrogen content, the NP mode one is far more superior from mechanical standpoint. A compromise can be reached to deposit an ultrathin layer of DLC in NP mode, which offers a good combination of properties to meet the requirement for the protective layer of cover glass.

MgH2 thin films deposited by one-step reactive plasma sputtering

The morphology, crystal structure, hydrogen content, and sorption properties of magnesium hydride thin films prepared by reactive plasma-assisted sputter deposition were investigated. Few micrometers-thick films were deposited on Si and SiO2/Si substrates, at low pressure (0.4 Pa) and close to room temperature using (Ar + H2) plasma with H2 fraction in the range 15–70%. The microstructure and hydrogen content of the films are closely related to the surface temperature and hydrogen partial pressure during the deposition process. Operating in pulsed-plasma mode allows the hydrogenation rate of the MgH2 thin film to top up to 98%, thereby producing a nearly fully hydrogenated film in a single-step process. The positive effect of the pulsed process is explained by the significant decrease in the whole energy flux incident on the surface and the favourable impact of the transient process for the rearrangement/relaxation of the materials. As for the hydrogen storage properties, desorption experiments and cycling of the films show the destabilizing effect of Mg2Si formation at the interface between the film and the Si substrate resulting in a drastically increased desorption kinetics compared to less reactive SiO2 substrate. However, the reaction is regrettably not reversible upon hydrogenation and the hydrogen storage capacity is consequently reduced upon cycling. Nevertheless, the deposition process carried out on inert substrates would offer true potential for reversible storage. Finally, our experimental results, which show the possibility to preferentially grow the metastable medium pressure γ-MgH2 phase, open possibilities for the synthesis of more complex metastable phases such as magnesium-based ternary compounds.

Growth mechanism of hydrogenated amorphous carbon films: Molecular dynamics simulations

The microstructure and growth mechanism of hydrogenated amorphous carbon films, deposited from different hydrocarbon sources and at various incident energies, are investigated by molecular dynamics (MD) simulations. At low energies, molecular adsorption dominates the process of the film growth, so the incident molecules tend to preserve their original molecular structures. As the incident energy rises, film density increases firstly and then becomes stabilized, while hydrogen content decreases because of molecular fragmentation and the increase in sputtering yield of hydrogen atoms. Hydrogen atoms play an important role in the growth of hydrogenated amorphous carbon films. The formation of sp3 structures at low energies, for example, mainly attributes to the hydrogen adsorption and the formation of C–H bonds; while at high energies the subplantation of carbon atoms and formation of C–C bonds are most responsible to the formation of sp3 structures. An increase of hydrogen content in source gas could lead to lower film density, higher hydrogen content in film and a general increase of sp3 fraction. The existence of dangling bonds in incident radicals facilitates easier adsorption than neutral molecules at low energies, resulting in higher deposition yield and sp3 fraction. This trend, however, diminishes at high energies when extensive molecular fragmentation occurs.

Investigation of the amorphous to microcrystalline phase transition of thin film prepared by electron cyclotron resonance chemical vapor deposition method

Hydrogenated silicon (Si:H) thin film growth by hydrogen dilution method and its phase transition were investigated in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. These amorphous and microcrystalline structured silicon thin films were deposited on glass and silicon substrates. The structure, optical and electrical properties of these films were identified by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscope (SEM), UV–visible spectroscopy, and dark/photo conductivity measurements. The dilution ratio (H2/SiH4) was varied to obtain different qualities of silicon thin films and we found that a phase transition from amorphous to microcrystalline could be obtained when dilution ratio (H2/SiH4) is above 0.71. These films with lower microstructure parameter (R*=0.07) and hydrogen content (CH=18%) have low optical gap (1.85), and exhibit the highest photo conductivity (σph) of 2.2E−5Ω−1cm−1 and lowest dark conductivity (σd) of 1E−9Ω−1cm−1 at the phase transition boundary. Due to proper atomic hydrogen could break the weaker SiSi and SiH bonds to form the rigid structure, and then the lower microstructure parameter and hydrogen content could be achieved. The lower hydrogen content in films makes the optical gap to be lower for absorbing more photons which is the reason why there is a better photo response at the phase transition boundary. Furthermore, high-quality hydrogenated silicon thin films are realized through the diluted control of both silane and hydrogen flow rates. Finally, we demonstrate that high quality intrinsic hydrogenated silicon thin films deposited with high growth rate (~1nm/s) using ECR-CVD, are suitable as absorber in a-Si solar cells.

Analysis of Hydrogen Content in Hydride Film by Elastic Recoil Method

The essential principle of elastic recoil detection analysis (ERDA) of hydrogen content in the film and the experimental method were described briefly. The energy spectrum of the recoiled hydrogen atom can be obtained by the elastic collision of incident ion beam with hydrogen atoms in film, and the spectrum can be transferred easily into hydrogen concentration and depth profile. For illustrating the application of ERDA in hydrogen storage research, a beam of helium ion was used to recoil hydrogen in titanium hydride and deuteride film to obtain hydrogen contents and depth profiles. This technique was believed to be powerful in determining hydrogen content in hydride films.

Analysis of Hydrogen Content in Hydride Film by Elastic Recoil Method

The essential principle of elastic recoil detection analysis (ERDA) of hydrogen content in the film and the experimental method were described briefly. The energy spectrum of the recoiled hydrogen atom can be obtained by the elastic collision of incident ion beam with hydrogen atoms in film, and the spectrum can be transferred easily into hydrogen concentration and depth profile. For illustrating the application of ERDA in hydrogen storage research, a beam of helium ion was used to recoil hydrogen in titanium hydride and deuteride film to obtain hydrogen contents and depth profiles. This technique was believed to be powerful in determining hydrogen content in hydride films.

A comparison of grain nucleation and grain growth during crystallization of HWCVD and PECVD a-Si:H films

From TEM, XRD and Raman measurements, we compare the crystallization kinetics when HWCVD and PECVD a-Si:H films, containing different initial film hydrogen contents ( C H), are crystallized by annealing at 600 °C. For the HWCVD films, the nucleation rate increases, and the incubation time and the full width at half maximum (FWHM) of the XRD (111) peak decrease with decreasing film C H. However, the crystallization kinetics of HWCVD and PECVD films of similar initial film C H are quite different, suggesting that other factors beside the initial film hydrogen content affect the crystallization process. Even though the bonded hydrogen evolves very early from the film during annealing, we suggest that the initial spatial distribution of hydrogen plays a critical role in the crystallization kinetics, and we propose a preliminary model to describe this process.

Effect of Substrate Temperature on the Optical Properties of a-Si:H Films by RF-PECVD

Hydrogenated amorphous silicon films were grown by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) and the substrate temperature of samples changed in the range of 175-275 ℃. Fourier-transform infrared spectrometer (FTIR) was used to characterize the infrared spectral feature of films deposited on KBr substrate. The hydrogen content of films was influenced by substrate temperature according to the FTIR spectra and theoretic analysis. The refractive index (n), extinction coefficient (k), thickness of films and optical band gap (Eg(FB)) were obtained through Forouhi Bloomer (FB) model in spectrum ellipsomet (SE). Appearance of fracture was analyzed by scanning electron microscopy (SEM) to make sure the result of film thickness. The optical band gap (Eg(Tauc)) and cutoff wavelength were also deduced by Tauc formula, and the difference between Eg(FB) and Eg(Tauc) was within 0.015 eV.

Development of AFM Tensile Test Technique for Evaluating Mechanical Properties of Sub-Micron Thick DLC Films

This paper describes mechanical properties of submicron thick diamond-like carbon (DLC) films used for surface modification in MEMS devices. A new compact tensile tester operating under an atomic force microscope (AFM) is developed to measure Young's modulus, Poisson's ratio and fracture strength of single crystal silicon (SCS) and DLC coated SCS (DLC/SCS) specimens. DLC films with a thickness ranging from 0.11 /spl mu/m to 0.58 /spl mu/m are deposited on 19-/spl mu/m-thick SCS substrate by plasma-enhanced chemical vapor deposition using a hot cathode penning ionization gauge discharge. Young's moduli of the DLC films deposited at bias voltages of -100 V and -300 V are found to be constant at 102 GPa and 121 GPa, respectively, regardless of film thickness. Poisson's ratio of DLC film is also independent of film thickness, whereas fracture strength of DLC/SCS specimens is inversely proportional to thickness. Raman spectroscopy analyses are performed to examine the effect of hydrogen content in DLC films on elastic properties. Raman spectra reveal that a reduction in hydrogen content in the films leads to better elastic properties. Finally, the proposed evaluation techniques are shown to be applicable to sub-micron thick DLC films by finite element analyses.

The synthesis of silicon nitride layers in a planar induction reactor

A method is developed for the synthesis of silicon nitride layers using planar inductive activation of reagent gases: monosilane and nitrogen (or ammonia). Mechanical characteristics of the resulting silicon nitride films were investigated with the help of ellipsometry. The composition of the synthesized layers was studied by means of IR spectroscopy. It is shown that the amount of hydrogen and the nature of its bonding in the growing silicon nitride layers are determined by synthesis temperature and nitrogen or ammonia to monosilane ratio [N 2/SiH 4] in reagent flow. A decrease in the total hydrogen content of films to 4% was observed with [N 2/SiH 4]=3. Under this technological mode of synthesis, an increase in the concentration of Si–N bonds occurs along with a decrease in the concentrations of Si–H and N–H bonds. The developed synthesis method allowed us to synthesize silicon nitride layers with low hydrogen content (4%) from nitrogen and monosilane at a temperature below 300 °C. Technological regimes were determined for the route of manufacture of the microbolometric matrix.

On the influence of short and medium range order on the material band gap in hydrogenated amorphous silicon

We examine different types of order measured in hydrogenated amorphous silicon (a-Si:H) and their effect on the optical absorption (band gap). We first review previous experimental work determining order on a short-range scale as probed by Raman spectroscopy, and provide, using molecular dynamics simulations, a theoretical explanation for why the band gap increases when this type of ordering is improved. We then present results on a-Si:H films deposited by hot wire chemical vapor deposition (CVD) and plasma enhanced CVD where the short-range order, from Raman spectroscopy, does not change, but order on a larger or medium-range scale does. This order is determined by measuring the width of the first x-ray diffraction peak, and was varied by depositing films at different substrate temperatures and∕or different hydrogen dilutions. We find that the film band gap also increases when this type of ordering improves, and we provide a possible mechanism to explain these trends. We also suggest that much of the previous literature showing an increase in band gap with increasing film hydrogen content should be treated with caution, as these works may not have accurately deconvoluted the effects of optical adsorption due to film hydrogenation from those due to both types of lattice ordering. Finally, we argue that this same trend may apply, to a limited extent, to microcrystalline silicon.

Compositional analysis of silicon nitride films on Si and GaAs by backscattering spectrometry and nuclear resonance reaction analysis

This paper describes the application of proton and α-backscattering spectrometry for the determination of atomic ratio of Si to N in 1100–5000 Å silicon nitride films on Si and GaAs. The conventional α-Rutherford backscattering spectrometry is suitable for the analysis of films on Si; it is rather inadequate for films on GaAs due to higher background from the substrate. It is shown that these films can be analysed by 14N(α,α)14N scattering with 3.5 MeV α-particles. Proton elastic scattering with enhanced cross sections for 28Si(p,p)28Si and 14N(p,p)14N scatterings, is also suitable for analysing films on GaAs. However, the analysis of films on Si by this technique is difficult due to interferences between the signals of Si from the film and the substrate. In addition, the hydrogen content in films is determined by 1H(19F,αγ)16O nuclear reaction analysis using the resonance at 6.4 MeV. The combination of backscattering spectrometry with nuclear reaction analysis provides compositional analysis of ternary Si1−(x+y)NxHy films.

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C 7H 8, CH 4, and a CH 4+H 2) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy. Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10 −8–10 −9 mm 3/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.

Hot-wire chemical vapor deposition of high hydrogen content silicon nitride for solar cell passivation and anti-reflection coating applications

The stoichiometry and hydrogen content of hot-wire (HW)-grown silicon nitride was examined as a function of SiH 4/NH 3 flow ratio. The effect of post-deposition hydrogenation treatment on overall film hydrogen content was determined. The hydrogen release properties in Si-rich and N-rich nitride layers were characterized by annealing treatments. Defect hydrogenation was studied using Fourier transform infrared spectroscopy on platinum-diffused silicon substrates. HW nitride layers were deposited onto diffused emitter String Ribbon silicon substrates, producing cells with comparable short circuit current density, open circuit voltage, fill-factor, and efficiency to those fabricated using plasma chemical vapor deposition nitride layers.

The irradiation studies on diamond-like carbon films

Diamond-like carbon (DLC) films have been deposited on glass substrates using radio-frequency (r.f.) plasma deposition method. γ-ray, ultraviolet (UV) ray and neutron beam were used to irradiate the DLC films. Raman spectroscopy and infrared (IR) spectroscopy were used to characterize the changing characteristics of SP 3C–H bond and hydrogen content in the films due to the irradiations. It showed that, the damage degrees of the γ-ray, UV ray and neutron beam on the SP 3C–H bonds are different. Among them, the damage of γ-ray on the SP 3C–H bond is the weakest. When the irradiation dose of γ-ray reaches 10×10 4 Gy, the SP 3C–H bond reduces about 50% in number. The square resistance of the films is reduced due to the irradiation of UV ray and this is caused by severe oxidation of the films. Compared with that of the as-deposited one, the IR transmittance of the films irradiated by both γ-ray and neutron beam is increased to some extent. By using the results on optical gap of the films and the fully constrained network theory, the hydrogen content in the as-deposited films is estimated to be 10–25 at.%.

Kinetics and mechanisms of laser-induced decompositions of hydrogenated amorphous carbon films on magnetic hard disks

Laser-induced structural decompositions of hydrogenated amorphous carbon films deposited by dc-magnetron sputtering on magnetic hard disks were studied using a microbeam Ar+ laser (514.5 nm). The laser had varying powers between 3.0 and 0.3 mW at a focused circular spot of 2.5 μm diameter, corresponding to approximate fluence rates between 6×104 to 6×103 J cm−2 s−1. The effect of laser power on decomposition rate could be expressed by an exponential equation. Based on the relationship between laser power and temperature, relative apparent activation energies for film decompositions were obtained and found to decrease with the increase of film hydrogen content and the elapse time of laser irradiation. All the films irradiated with laser powers between 0.75 and 0.3 mW followed the apparent first-order reaction. The reaction order tended to increase at higher laser powers and hydrogen content in the films.

The Use of STIM and PESA to Measure Profiles of Aerosol Mass and Hydrogen Content, Respectively, across Mylar Rotating Drums Impactor Samples

A method has been developed for measuring profiles of aerosol mass on thin (480 w g/cm 2 ) Apiezon-L coated Mylar films employed in rotating drum aerosol impactor samplers using the ion beam analysis technique scanning transmission ion microscopy (STIM). The greased Mylar films are excellent impaction substrates and possess excellent uniformity in projected density, making them an ideal substrate for STIM analysis. The uniformity in projected density of a film enables STIM with a 3 MeV proton beam to produce profiles of aerosol mass with an accuracy of better than 90% and a mass sensitivity approaching 10 w g/cm 2 . Further, we have extended proton elastic scattering analysis (PESA) to the same films, achieving measurement of an organic surrogate. Although the films contain ∼ 20 w g/cm 2 hydrogen, the spatial uniformity in film hydrogen content enables PESA with a 3 MeV proton beam to produce profiles of hydrogen arising solely from the aerosols with an accuracy to within - 1 w g/cm 2 and a mass sensitivi...