Effect of hydrogen on the structure of high-rate deposited SiC on Si by atmospheric pressure plasma chemical vapor deposition using high-power-density condition

Using the atmospheric pressure plasma chemical vapor deposition (AP-PCVD) technique, SiC films were fabricated from the gas mixture of He, H₂, SiH₄ and CH₄ on silicon substrates. High-power-density condition was adopted to sufficiently activate the reactive gas molecules in the plasma. The structure, composition and crystallinity of the films were investigated as functions of the H₂ concentration in the gas mixture and substrate temperature. It was shown that increase in H₂ concentration in the plasma atmosphere reduced the growth temperature of polycrystalline SiC film. As a result, polycrystalline 3C-SiC film of which grain size was of the order of 10 nm could be grown at a substrate temperature of 820 K with a deposition rate of approximately 6.7 nm/s. It was suggested that atomic hydrogen generated with addition of H₂ in the gas mixture considerably affects not only the reaction process at the film-growing surface but also the form of precursors in the atmospheric pressure plasma. The results indicated the possibility of realizing the columnar growth of large 3C-SiC grains on Si substrate when the H₂ concentration and the VHF power were simultaneously increased in the AP-PCVD process.     

Influence of gas pressure on low-temperature preparation and film properties of nanocrystalline 3C-SiC thin films by HW-CVD using SiH4/CH4/H2 system

We investigated an influence of gas pressure on low-temperature preparation of nanocrystalline cubic silicon carbide (nc-3C-SiC) films by hot-wire chemical vapour deposition (HW-CVD) using SiH₄/CH₄/H₂ system. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra revealed that the films prepared below 1.5 Torr were Si-nanocrystallite-embedded hydrogenated amorphous SiC. On the other hand, nc-3C-SiC films were successfully prepared at gas pressure above 2 Torr. The high gas pressure plays two important roles in low-temperature preparation of nc-3C-SiC films: (1) leading to sufficient decomposition of CH₄ molecules through a gas phase reaction and an increase in the incorporation of carbon atoms into film and (2) promoting a creation of H radicals on the heated filament, allowing the sufficient coverage of growing film surface and a selective etching of amorphous network structure and/or crystalline-Si phase. It was found that total gas pressure is a key parameter for low-temperature preparation of nc-3C-SiC films.     

Control of orientation from random to (220) or (400) in polycrystalline silicon films

The control of grain orientation in polycrystalline silicon thin films on glass substrates by low-temperature techniques was investigated. Either (220) or (400) preferential grain orientation could be attained by control of source gas ratio over substrate temperatures between 250°C and 360°C. A remote type plasma chemical vapor deposition system was used with source gas mixtures of SiF₄, H₂ and Ar. The (220) preferential films were obtained with Ar/H₂/SiF₄ gas flow rates of 60/15/30 sccm (respectively), while the (400) preferential oriented films were obtained at higher SiF₄/H₂ ratios (SiF₄/H₂=90/10 sccm). At the higher SiF₄/H₂ ratio during the crystal nucleation stage, either randomly oriented or (400) grains formed followed by the highly preferred deposition of (400) oriented crystallites. Raman scattering and ellipsometry spectra indicated that the (400) oriented films had a very smooth surface.     

Fabrication of diamond-like carbon film on rubber by T-shape filtered-arc-deposition under the influence of various ambient gases

Diamond-like carbon (DLC) films were prepared on rubber substrates using T-shape filtered-arc-deposition (T-FAD), which effectively removes the macrodroplets emitted from the graphite cathode spot from the processing plasma. In the present study, the influence of ambient gas (no gas, Ar, H₂, C₂H₂, C₂H₄, CH₄) was investigated. The DLC films adhered well to the rubber substrate. When the substrate was stretched, the small DLC islands were separated and clefs were opened. The deposition rate on rubber was approximately twice higher than that on a Si substrate. When hydrocarbon gas was introduced as an ambient gas, the deposition rate became higher than that for no gas and H₂ gas. In the cases of C₂H₄ and CH₄ gases, the DLC film was considered to contain a considerable amount of hydrogen. When C₂H₂ gas was used, the highest deposition rate with less surface roughness was achieved.     

Structural changes of hot-wire CVD silicon carbide thin films induced by gas flow rates

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition in a CH₄ gas flow rate of 1 sccm, and the influence of the gas flow rates of SiH₄ and H₂ gases on the film structure and properties were investigated. In the case of a H₂ gas flow rate below 100 sccm, the SiC:H films obtained in SiH₄ gas flow rates of 3 and 4 sccm were amorphous. On the other hand, when the H₂ gas flow rate was above 150 sccm, SiH₄ gas flow rates of 4 and 3 sccm resulted in a Si-crystallite-embedded amorphous SiC:H film and a nanocrystalline cubic SiC film, respectively. It was found that gas flow rates were important parameters for controlling film structure.     

The growth of GaN films by alternate source gas supply hot-mesh CVD method

Gallium nitride (GaN) films and Aluminium nitride (AlN) layers were deposited on SiC/Si (111) substrates by an alternating source gas supply or an intermittent supply of a source gas such as ammonia (NH₃), trimethylgallium (TMG) or trimethylaluminum (TMA) in a hot-mesh chemical vapor deposition (CVD) apparatus. The AlN layer was deposited as a buffer layer using NH₃ and TMA on a SiC layer grown by carbonization on Si substrates using propane (C₃H₈). GaN films were grown on an AlN layer by a reaction between NH_x radicals generated on a ruthenium (Ru) coated tungsten (W)-mesh and TMG molecules. An alternating source gas supply or an intermittent supply of one of the source gases during the film growth are expected to be effective for the suppression of gas phase reactions and for the enhancement of precursor migration on the substrate surface. By the intermittent supply of alkylmetal gas only during the growth of the AlN layer, the defect generation in the GaN films was reduced. GaN film growth by intermittent supply on an AlN buffer layer, however, did not lead to the improvement of the film quality.     

Chemical vapor deposition of NiSi using Ni(PF3)4 and Si3H8

NiSi_x films were deposited using chemical vapor deposition (CVD) with a Ni(PF₃)₄ and Si₃H₈/H₂ gas system. The step coverage quality of deposited NiSi_x was investigated using a horizontal type of hot-wall low pressure CVD reactor, which maintained a constant temperature throughout the deposition area. The step coverage quality improved as a function of the position of the gas flow direction, where PF₃ gas from decomposition of Ni(PF₃)₄ increased. By injecting PF₃ gas into the Ni(PF₃)₄ and Si₃H₈/H₂ gas system, the step coverage quality markedly improved. This improvement in step coverage quality naturally occurred when PF₃ gas was present, indicating a strong relationship. The Si/Ni deposit ratio at 250 °C is larger than at 180 °C. It caused a decreasing relative deposition rate of Ni to Si. PF₃ molecules appear to be adsorbed on the surface of the deposited film and interfere with faster deposition of active Ni deposition species.     

Mechanical and environmental properties of Ge1−xCx thin film

Ge_1−xC_x thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) using GeH₄ and CH₄ as precursors and its mechanical and environmental properties were investigated. The samples were measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum, FT-IR spectrometer, WS-92 testing apparatus of adhesion and FY-03E testing apparatus of salt and fog. The results show that the infrared refractive index of Ge_1−xC_x thin film varies from 2 to 4 with different x values. The adhesion increases with increasing gas flow ratio of GeH₄/CH₄ and decreases with increasing film thickness. The nanoindentation hardness number decreases with increasing germanium content. Three series films exhibit the best anti-corrosion property when the RF power is about 80 W, or substrate temperature is about 150 °C, or DC bias is about −100 V. Furthermore, increasing the gas flow ratio of GeH₄/CH₄ improves the anti-corrosion property of these films.     

Microstructure and surface roughness study of highly crystallized μc-Si:H Films

We have deposited hydrogenated microcrystalline silicon films by standard rf glow discharge plasma CVD technique using a mixture of SiF₄, Ar and H₂ at low substrate temperatures. Although fully crystalline from the beginning of the growth, our films show a significant variation in the ratio of large (LG) and small grain (SG) with further growth, for any H₂ dilution case, though the trend changes for each case. The mean sizes of the LG and SG do not vary much with growth, but a marked variation occurs in the size of the conglomerate grains, as shown by atomic force microscopy (AFM) studies. Notably, a change in the H₂ dilution is found to affect not only the film microstructure, but also the crystalline orientation. We have shown the lateral and longitudinal growth of conglomerate grains to be highly dependent on the crystalline orientation. In studying the effect of film growth on film roughness, we have observed a linear correlation between the rms roughness as measured by AFM and the top surface layer as measured by spectroscopic ellipsometry. We have also succeeded in elucidating the growth mechanisms involved, apropos of surface roughness findings.     

Properties of polycrystalline silicon films prepared from fluorinated precursors

Polycrystalline silicon films have been prepared at low temperature on glass substrate from fluorinated precursors by PECVD technique varying the hydrogen dilution and gas flow rate. Undoped film with dark-conductivity 1.05×10⁻² S cm⁻¹ has been obtained. For n-type poly-Si film the highest conductivity achieved is 2.8 S cm⁻¹. Grain size observed from SEM varies from 4 to 6 μm for undoped and 2 to 3 μm for phosphorous doped films. The main crystalline peak is 〈111〉 whereas the crystallite size calculated from XRD is 350 Å. The optical absorptions and hydrogen contents in the films deposited under different conditions have been studied. Growth kinetics are dominated by the precursors SiF_nH_m (m+n≤3) and concentrations of F and H on the growth surface.     

Microstructure developments of F-doped SiO2 thin films prepared by liquid phase deposition

This study presents a systematic investigation of the microstructure dependence of liquid phase deposition (LPD) of SiO₂ films on solution parameters and deposition temperature. The corresponding deposition rate and film roughness were also evaluated under various deposition conditions. Smooth and sufficiently dense SiO₂ films, which are the prerequisite for reliable low-k dielectric applications, were deposited on both silicon and fluorine-doped tin oxide coated glass substrates from supersaturated hydrofluorosilicic acid (H₂SiF₆) solution with the addition of boric acid (H₃BO₃). It is shown that H₂SiF₆ acid controls the surface morphology and grain structure through surface reaction while H₃BO₃ acid prompts bulk precipitation in solution. For the 208-nm thick SiO₂ film, the breakdown field exceeded 1.9 MV/cm and the leakage current density was on the order of 10^− 9 A/cm² at 4 V, indicating excellent insulating properties of LPD SiO₂ films. The strong presence of Si-O-Si and some Si-F with little Si-OH bond as shown in FT-IR spectra indicate that the LPD SiO₂ films have mostly a silica network with some fluorine (F) content. F-doping was self-incorporated into the silica films from the H₂SiF₆ solution during deposition process.     

Optimization of n nc-Si:H and a-SiNx:H layers for their application in nc-Si:H TFT

The n-type doped silicon thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique at high and low H₂ dilutions. High H₂ dilution resulted in n⁺ nanocrystalline silicon films (n⁺ nc-Si:H) with the lower resistivity (ρ ∼0.7 Ω cm) compared to that of doped amorphous silicon films (∼900 Ω cm) grown at low H₂ dilution. The change of the lateral ρ of n⁺ nc-Si:H films was measured by reducing the film thickness via gradual reactive ion etching. The ρ values rise below a critical film thickness, indicating the presence of the disordered and less conductive incubation layer. The 45 nm thick n⁺ nc-Si:H films were deposited in the nc-Si:H thin film transistor (TFT) at different RF powers, and the optimum RF power for the lowest resistivity (∼92 Ω cm) and incubation layer was determined. On the other hand, several deposition parameters of PECVD grown amorphous silicon nitride (a-SiN_x:H) thin films were changed to optimize low leakage current through the TFT gate dielectric. Increase in NH₃/SiH₄ gas flow ratio was found to improve the insulating property and to change the optical/structural characteristics of a-SiN_x:H film. Having lowest leakage currents, two a-SiN_x:H films with NH₃/SiH₄ ratios of ∼19 and ∼28 were used as a gate dielectric in nc-Si:H TFTs. The TFT deposited with the NH₃/SiH₄∼19 ratio showed higher device performance than the TFT containing a-SiN_x:H with the NH₃/SiH₄∼28 ratio. This was correlated with the N−H/Si−H bond concentration ratio optimized for the TFT application.     

Photoluminescence behaviors in ZnGa2O4 thin film phosphors deposited by a pulsed laser ablation

ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa₂O₄ thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa₂O₄ films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa₂O₄ thin film phosphor.     

Effect of nanostructures formed by oblique co-deposition on transient catalytic reactions

We investigated the effects of nanostructures of obliquely co-sputter-deposited thin films in terms of catalytic properties using pulses of reactant molecules as probes. Pt-Al₂O₃ thin films were fabricated on a Si substrate by simultaneous oblique deposition. The films had columnar structures that grew perpendicular to the substrate. We observed the behavior of NO reduction by H₂ with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto the thin film surface and a time-of-flight mass spectrometer to measure plural products. The obliquely co-deposited films, consisting of columnar nanostructures, showed higher NO reduction activity over a wide range of temperatures than the normally co-deposited films, consisting of uniform structures. The yield of N₂ exceeded that of NH₃ and N₂O for both structures in the high temperature range, whereas the yield of N₂O was more significant for the structures with columns than those without columns at low temperatures. Subtle change of the nanometer-scale structures with the deposition angle was clearly discriminated from the viewpoint of transient catalytic activity.     

Plasma enhanced chemical vapor deposition of nanocrystalline silicon films from SiF4-H2-He at low temperature

A high degree of crystallinity is obtained in nc-Si:H films deposited by r.f. PECVD, produced from SiF₄-H₂-He mixtures. The amorphous-to-nanocrystalline transition is favored because of the presence of F atoms, which preferentially etch the amorphous phase. The addition of He to the SiF₄-H₂ gas mixture gives an increase of F and H atoms in the plasma, thus inducing higher crystallinity. A further improvement in the nc-Si:H film structure and properties is obtained by adjusting the r.f. power and the deposition temperature. Under optimized plasma conditions, substrate temperatures as low as 120°C can be reached for the deposition of nc-Si:H having 100% of crystallinity.     

Ni-silicide precursor for gate electrodes

Ni-silicide film was deposited at a low temperature of 160 °C by CVD using a Ni(PF₃)₄/Si₃H₈ gas system. Injecting Si₃H₈ during the Ni deposition does not affect the deposition rate, but the step-coverage quality deteriorates at high growth temperatures. At high growth temperatures, the Ni/Si ratio of the film deposited on the sidewall varies as the distance from the open area increases. High step-coverage quality and a constant Ni/Si ratio independent of the location of the deposition are strongly required to fabricate a three-dimensional device. These requirements were achieved with this CVD by depositing the Ni-silicide film below 180 °C.     

The reaction mechanism of the spray Ion Layer Gas Reaction process to deposit In2S3 thin films

The spray Ion Layer Gas Reaction (ILGAR) is a well-established, patented and commercial process used primarily to deposit In₂S₃ as buffer layers in thin film solar cells. In this paper we investigate the growth mechanism of the spray In₂S₃ ILGAR process by characterising the intermediate growth stages of films, following the growth mechanism with a quartz crystal microbalance and tracking the gaseous side-and-intermediate products during film growth, using a mass spectrometer. A basic growth mechanism model is then proposed based on an aerosol assisted chemical vapour deposition of an In(O_x,Cl_y,(OH)_z) film, as the first stage process, followed by the conversion of the intermediate film using H₂S gas to In₂S₃.     

High rate reactive deposition of TiO2 films using two sputtering sources

We propose a new high-rate reactive sputter-deposition method with two sputtering sources for fabricating TiO₂ films. One source operates in a metal mode sputtering condition and supplies titanium atoms to the substrate. The other source operates in oxide mode and works as an oxygen radical source for supplying oxygen radicals to the substrate surface for promoting oxidization of titanium atoms. Each sputtering source is separated with a mesh grid from the deposition chamber, and Ar and oxygen gas are introduced separately through the titanium supply and oxygen radical sources, respectively. By using this reactive sputtering system, a deposition rate above 80 nm/min can be obtained for the deposition of TiO₂ films with rutile structure.     

Effect of argon and substrate bias on diamond thin film surface morphology

Nanocrystalline materials are of high interest, because mechanical and physical properties of such materials are different from those or coarse-grained type. Continuous and smooth nanocrystalline diamond (NCD) thin films were successfully grown on mirror polished silicon substrates, using double bias plasma-enhanced hot filament chemical vapour deposition technique. A gas mixture of Ar:CH₄:H₂ and CH₄:H₂ was used as the precursor gas. The effect of the gas composition, flow rate and substrate bias during deposition on diamond crystallite size was investigated. Changing the growth parameters facilitates control of grain size of polycrystalline diamond thin films from microcrystalline to nanocrystalline. The structure of fine-grained NCD films has been studied with scanning electron microscopy and Raman spectroscopy.     

Growth of nanocrystalline diamond films in CCl4/H2 ambient

We investigated the growth characteristics of the nanocrystalline diamond films using CCl₄/H₂ as gas sources in a hot-filament chemical vapor deposition (CVD) reactor. Successful growth of nanocrystalline diamond at typical growth condition of 1.5-2.5% CCl₄ and 550-730 °C substrate temperature has been demonstrated. Glancing angle X-ray diffraction (XRD) clearly indicated the formation of diamond in the films. Typical root-mean-square surface roughness of 10-15 nm and an optimal root-mean-square surface roughness of 6 nm have been achieved. Transmission electron microscopy (TEM) analyses indicated that nanocrystalline diamond film with an average grain size in the range of 10-20 nm was deposited from 2.5% CCl₄/H₂ at 610 °C. Effects of different source gas composition and substrate temperature on the grain nucleation and grain growth processes, whereby the grain size of the nanocrystalline film could be controlled, were discussed.