The effects of plasma pre-treatment and post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of plasma pre-treatment and post-treatment on the DLC films were investigated. Experimental results show that the surface roughness of the substrate, ranging from 0.2 to 1.2 nm, created by the plasma pre-treatment, will affect the surface roughness of the DLC films deposited using methane as the carbon source. However, the film surface roughness (0.1-0.4 nm) is much smaller than that of the substrate. Raman analysis and hardness measurement by nanoindentation indicate that the structure and the hardness of the DLC films are relatively unchanged for the film surface roughness investigated. For the argon or hydrogen plasma post-treatment of the DLC films deposited using acetylene as the carbon source, it is found that surface roughness decreases with the post-treatment time. Although the hardness decreases after post-treatment, it remains relatively constant with increasing post-treatment time.     

Growth control of carbon nanotubes by plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD), which enables growth of vertically aligned carbon nanotubes (CNTs) directly onto a solid substrate, is considered to be a suitable method for preparing CNTs for nanoelectronics applications such as electron sources for field emission displays (FEDs). For these purposes, establishment of an efficient CNT growth process has been required. We have examined growth characteristics of CNTs using a radio frequency PECVD (RF-PECVD) method with the intention to develop a high efficiency process for CNT growth at a low enough temperature suitable for nanoelectronics applications. Here we report an effect of pretreatment of the catalyst thin film that plays an important role in CNT growth using RF-PECVD. Results of this study show that uniform formation of fine catalyst nanoparticles on the substrate is important for the efficient CNT growth.     

Structure control of carbon nanotubes using radio-frequency plasma enhanced chemical vapor deposition

Carbon nanotube structures such as tube diameter, growth site, and formation density are controlled using radio-frequency (RF, 13.56 MHz) plasma enhanced chemical vapor deposition (RF-PECVD) method. We have produced uniformly well-aligned multi-walled carbon nanotubes (MWNTs) grown over the large scale area and linearly arrayed MWNTs grown in a selected area without any highly-sophisticated patterning process. In our RF-PECVD experiment, furthermore, individually grown single-walled carbon nanotubes (SWNTs) or their thin bundles are synthesized for the first time within the scope of the PECVD methods. These results indicate that PECVD method provides the high potential for the further development of nano-technology.     

Mechanical properties of carbon-modified silicon oxide barrier films deposited by plasma enhanced chemical vapor deposition on polymer substrates

Cohesive and adhesive properties of silicon oxide barrier coatings deposited from an oxygen/hexamethyldisiloxane gas mixture by plasma enhanced chemical vapor deposition, with controlled incorporation of carbon on 12 μm thick polyethylene terephtalate films were investigated. The reactor was equipped with a 2.45 GHz slot antenna plasma source and a 13.56 MHz-biased substrate holder. The two plasma sources were operated separately or in a dual mode. It was found that no or negligible internal stresses were introduced in the silicon oxide coatings as long as the increase of energy experienced by the film was compensated by the densification of the oxide. For a range of process parameters and carbon content on the changes of the crack onset strain, adhesion, and cohesion were found to be similar. Generally a high crack onset strain or good adhesion and cohesion were measured for films with an increased carbon content, although this was obtained at the expense of the gas barrier performance. Promising approaches towards high-barrier thin films with good mechanical integrity are proposed, based on coatings with a gradient in the carbon content and in the mechanical properties, on nano-composite laminates, and on organo-silane treatments.     

Role of hydrogen in Sb film deposition and characterization of Sb and GexSby films deposited by cyclic plasma enhanced chemical vapor deposition using metal-organic precursors

To meet increasing demands for chemical vapor deposition methods for high performance phase-change memory, cyclic plasma enhanced chemical vapor deposition of Sb and Ge_xSb_y phase-change films and characterization of their properties were performed. Two cycle sequences were designed to investigate the role of hydrogen gas as a reduction gas during Sb film deposition. Hydrogen gas was not introduced into the reaction chamber during the purge step in cycle sequence A and was introduced during the purge step for cycle sequence B. The role of hydrogen gas was investigated by comparing the results obtained from these two cycle sequences and was concluded to exert an effect by a combination of precursor decomposition, surface maintenance as a hydrogen termination agent, and surface etching. These roles of hydrogen gas are discussed through consideration of changes in deposition rates, the oxygen concentration on the surface of the Sb film, and observations of film surface morphology. Based on these results, Ge_xSb_y phase-change films were deposited with an adequate flow rate of hydrogen gas. The Ge and Sb composition of the film was controlled with the designed cycle sequences. A strong oxygen affinity for Ge was observed during the X-ray photoelectron spectroscopy analysis of Sb 3d, Sb 4d, and Ge 3d orbitals. Based on the XPS results, the ratios of Ge to Sb were calculated to be Ge_0.32Sb_0.68, Ge_0.38Sb_0.62, Ge_0.44Sb_0.56, Ge_0.51Sb_0.49 and Ge_0.67Sb_0.33 for the G1S7, G1S3, G1S2, G1S1, and G2S1 cycles, respectively. Crystal structures of Sb, Ge, and the GeSb metastable phase were observed with various Ge_xSb_y film compositions. Sb crystallinity decreased with respect to Ge crystallinity by increasing the Ge fraction. A current-voltage curve was introduced, and an electro-switching phenomenon was clearly generated at a typical voltage, V_th. V_th values increased in conjunction with an increased proportion of Ge. The Sb crystallinity decrease and V_th increase were explained via the bonding characteristics of each element.     

Structural and optical properties of four-hexagonal polytype nanocrystalline silicon carbide films deposited by plasma enhanced chemical vapor deposition technique

Four-hexagonal polytype films of nanocrystalline silicon carbide (4H-nc-SiC) were deposited by plasma enhanced chemical vapor deposition method with more than 3×10⁴ W m⁻² threshold of power density, high hydrogen dilution ratio, and bias pretreatment. The source gases were silane, methane and hydrogen. Our work showed that under conditions similar to those used for the growth of μc-SiC—except a higher power densities over a threshold, a bigger bias pretreatment on substrates, and a moderate bias deposition—nc-SiC films could indeed be achieved. The Raman spectra and transmission electron microscopy diffraction patterns demonstrated that the as-grown films from the H₂-CH₄-SiH₄ plasma consist of amorphous network and phase-pure crystalline silicon carbide which has the 4H polytype structure. The microcolumnar 4H-SiC nanocrystallites of a mean size of approximately 1.6×10⁻⁸ m in diameter are encapsulated by amorphous SiC networks. The photoluminescence spectra of 4H-SiC at room temperature, peaking at 8.10×10⁻⁷ m using a wavelength of 5.145×10⁻⁷ m of argon ion laser, were obtained at room temperature; the luminescence mechanism is thought to be related to transitions in the energy band gap which could be ascribed to the surface states and defects in the structure of 4H-SiC nanocrystalline in these films due to its small size. The as-grown films showed an optical transmittance of 89% at 6.58×10⁻⁷ m. This higher transmittance is believed to be from the small size and amorphous matrix.     

Adherent amorphous hydrogenated carbon films on metals deposited by plasma enhanced chemical vapor deposition

This paper reports the findings of a study of the structural, mechanical, and tribological properties of amorphous hydrogenated carbon (a-C:H) coatings for industrial applications. These thin films have proven quite advantageous in many tribological applications, but for others, thicker films are required. In this study, in order to overcome the high residual stress and low adherence of a-C:H films on metal substrates, a thin amorphous silicon interlayer was deposited as an interface. Amorphous silicon and a-C:H films were grown by using a radio frequency plasma enhanced chemical vapor deposition system at 13.56 MHz in silane and methane atmospheres, respectively. The X-ray photoelectron spectroscopy technique was employed to analyze the chemical bonding within the interfaces. The chemical composition and atomic density of the a-C:H films were determined by ion beam analysis. The film microstructure was studied by means of Raman scattering spectroscopy. The total stress was determined through the measurement of the substrate curvature, using a profilometer, while micro-indentation experiments helped determine the films' hardness. The friction coefficient and critical load were evaluated by using a tribometer. The results showed that the use of the amorphous silicon interlayer improved the a-C:H film deposition onto metal substrates, producing good adhesion, low compressive stress, and a high degree of hardness. SiC was observed in the interface between the amorphous silicon and a-C:H films. The composition, the microstructure, the mechanical and tribological properties of the films were strongly dependent on the self-bias voltages. The tests confirmed the importance of the intensity of ion bombardment during film growth on the mechanical and tribological properties of the films.     

Polycrystalline AlN films with preferential orientation by plasma enhanced chemical vapor deposition

AlN thin films for acoustic wave devices were prepared by Microwave Plasma Enhanced Chemical Vapor Deposition under different process conditions, employing Si (100) and Pt (111)/SiO₂/Si (100) substrates. The films were characterized by X-ray diffraction, Fourier transform infrared transmission spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The values of the distance between the plasma and the tri-methyl-aluminum precursor injector, the radiofrequency bias potential, and the substrate temperature were central in the development of polycrystalline films. The choice of the chamber total pressure during deposition allowed for the development of two different crystallographic orientations, i.e., <0001> or <1010>. The film microstructures exhibited in general a column-like growth with rounded tops, an average grain size of about 40 nm, and a surface roughness lower than 20 nm under the best conditions.     

Effects of argon and oxygen flow rate on water vapor barrier properties of silicon oxide coatings deposited on polyethylene terephthalate by plasma enhanced chemical vapor deposition

Plasma polymer coatings were deposited from hexamethyldisiloxane on polyethylene terephthalate (PET) substrates while varying the operating conditions, such as the Ar and O₂ flow rates, at a fixed radio frequency power of 300 W. The water vapor transmission rate (WVTR) of the untreated PET was 54.56 g/m²/day and was decreased after depositing the silicon oxide (SiO_x) coatings. The minimum WVTR, 0.47 g/m²/day, was observed at Ar and O₂ flow rates of 4 and 20 sccm, respectively, with a coating thickness of 415.44 nm. The intensity of the peaks for the Si-O-Si bending at 800-820 cm^− 1 and Si-O-Si stretching at 1000-1150 cm^− 1 varied depending on the Ar and O₂ flow rates. The contact angle of the SiO_x coated PET increased as the Ar flow rate was increased from 2 to 8 sccm at a fixed O₂ flow rate of 20 sccm. It decreased gradually as the oxygen flow rate increased from 12 to 28 sccm at a fixed Ar carrier gas flow rate. The examination by atomic force microscopy revealed a correlation of the SiO_x morphology and the water vapor barrier performance with the Ar and O₂ flow rates. The roughness of the deposited coatings increased when either the O₂ or Ar flow rate was increased.     

Study of plasma enhanced chemical vapor deposition of ZnO films by non-thermal plasma jet at atmospheric pressure

Plasma enhanced chemical vapor deposition using a non-thermal plasma jet was applied to deposition of ZnO films. Using vaporized bis(octane-2,4-dionato)zinc flow crossed by the plasma jet, the deposition rate was as high as several tens of nm/s. From the results of infrared spectra, the films deposited at the substrate temperature T_sub = 100 °C contained a significant amount of carbon residue, while the films prepared at T_sub = 250 °C showed less carbon fraction. The experimental results confirmed that the plasma jet decomposed bis(octane-2,4-dionato)zinc in the gaseous phase and on the substrate, and that there should be the critical T_sub to form high-quality ZnO films in the range from 100 to 250 °C.     

Effect of impinging ion energy on the substrates during deposition of SiOx films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO_x films on bell metal substrates using Ar/hexamethyldisiloxane/O₂ glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO_x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si-O-Si chemical structure in the deposited SiO_x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO_x films is further confirmed from XPS analysis. The growth of SiO_x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO_x films for surface protection of bell metal is also explored.     

Annealing and partial pressure ratio effects on ZnO films grown by metal-organic chemical vapor deposition using tert-butanol as oxidant

ZnO films were deposited by metal-organic chemical vapor deposition on (0001) sapphire substrates at various partial pressure ratios of oxygen and zinc precursors (R_VI/II). The annealing and the R_VI/II ratio effects on the vibrational and optical properties of ZnO films have been investigated by Micro-Raman scattering and low temperature photoluminescence (PL) spectroscopy. As confirmed by characterizations used in this study, the quality of the ZnO films was improved by thermal annealing at 900 °C in oxygen ambient. Raman spectra of the as-deposited films show a broad band (BB) centered at about 518 cm⁻¹ whose intensity increases when the R_VI/II ratio decreases. After annealing, the intensity ratio of the BB to the E₂ high (E₂^H) peak decreases rapidly with increasing the annealing time (t_an). The vibrational properties of the annealed films grown at R_VI/II = 1 need only 1 h to be improved in contrast to those of films grown in Zn-rich condition, which need 4 h. From the E₂^H mode frequency, the residual stress in both the as-grown and the annealed films has been estimated. Micro-Raman measurements show that as-grown films are under a compressive stress which vanishes upon annealing and is not strongly dependent on t_an for t_an up to 1 h. PL spectra show that sharp donor bound exciton and A-free exciton emissions are observed for the as-deposited films grown at R_VI/II ≥ 0.5 and are enhanced after annealing for 1 h. However, in ZnO films grown in Zn-rich condition these emissions are absent and a t_an = 4 h is needed to annihilate non-radiative recombination centers and improve their luminescent efficiency.     

Nanoindentation stress-strain curves of plasma-enhanced chemical vapor deposited silicon oxide thin films

Plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiO_x) thin films have been widely used in Micro/Nano Electro Mechanical Systems to form electrical and mechanical components. In this paper, we explore the use of nanoindentation techniques as a method of measuring equivalent stress-strain curves of the PECVD SiO_x thin films. Four indenter tips with different geometries were adopted in our experiments, enabling us to probe the elastic, elasto-plastic, and fully plastic deformation regimes of the PECVD SiO_x thin films. The initial yielding point (σ_I) and stationary yielding point (σ_II) are separately identified for the as-deposited and annealed PECVD SiO_x thin films, as well as a standard fused quartz sample. Based on the experimental results, a shear transformation zone based amorphous plasticity theory is applied to depict the plastic deformation mechanism in the PECVD SiO_x.     

Thin cobalt oxide films for catalysis deposited by plasma-enhanced metal-organic chemical vapor deposition

The plasma-enhanced metal-organic chemical vapor deposition was used to prepare thin films of cobalt oxide starting with cyclopentadienyldicarbonyl-cobalt(I) (CpCo(CO)₂) mixed with argon and oxygen. The films were characterized by Raman and Fourier transform infrared spectroscopies, electron diffraction, and energy dispersive X-ray microanalysis. Their thickness was estimated by ellipsometric measurements. Catalytic properties of the films were tested in oxidation of n-hexane. It has been found that spinel-type Co₃O₄ nanoclusters with a crystallite size of 4-6 nm are formed in the deposits. Amorphous carbon and amorphous CoO_x phases are also observed in the films. The content of these phases depends on the molar fraction of oxygen in the gas mixture. Preliminary catalytic tests have shown that precalcined Cr-Al steel carrier covered by the plasma-deposited films reveals much higher catalytic effect then the non-deposited substrate.     

Effect of the substrate on the properties of ZnO-MgO thin films grown by atmospheric pressure metal-organic chemical vapor deposition

The ZnO-MgO alloys possess attractive properties for possible applications in optoelectronic and display devices; however, the optical properties are strongly dependent on the deposition parameters. In this work, the effect of the glassy and metallic substrates on the structural, morphological and optical properties of ZnO-MgO thin films using atmospheric pressure metal-organic chemical vapor deposition was investigated at relatively low deposition temperature, 500 °C. Magnesium and zinc acetylacetonates were used as the metal-organic source. X-ray diffraction experiments provided evidence that the kind of substrates cause a deviation of c-axis lattice constant due to the constitution of a oxide mixture (ZnO and MgO) in combination with different intermetallic compounds(Mg₂Zn₁₁ and Mg₄Zn₇) in the growth films. The substitutional and interstitial sites of Mg²⁺ instead of Zn²⁺ ions in the lattice are the most probable mechanism to form intermetallic compounds. The optical parameters as well as thickness of the films were calculated by Spectroscopic Ellipsometry using the classical dispersion model based on the sum of the single and double Lorentz and Drude oscillators in combination with Kato-Adachi equations, as well as X-ray reflectivity.     

Transparent conducting indium oxide thin films grown by low-temperature metal organic chemical vapor deposition

We have grown indium oxide thin films on silicon substrates at low temperature by metal organic chemical vapor deposition. Polycrystalline film growth could only be obtained at temperatures below 400 °C. Above 400 °C, metallic indium deposition dominated. We have investigated the effect of substrate temperature and reactor pressure on the film growth and structural properties in the range of 250-350 °C and 5 ^? 10³-4 ^? 10⁴ Pa. The film grown at 300 °C exhibited a resistivity of about 3.6 × 10^− 3 Ω cm and a maximal optical transmittance of more than 95% in the visible range. The film showed an optical band gap of about 3.6 eV.     

Epitaxial growth of RuO2 thin films by metal-organic chemical vapor deposition

Conductive RuO₂ thin films were epitaxially grown on LaAlO₃(100) and MgO(100) substrates by metal-organic chemical vapor deposition (MOCVD). The deposited RuO₂ films were crack-free, and well adhered to the substrates. The RuO₂ film is (200) oriented on LaAlO₃ (100) substrates at deposition temperature of 600°C and (110) oriented on MgO(100) substrates at deposition temperature of 350°C and above. The epitaxial growth of RuO₂ on MgO and LaAlO₃ is demonstrated by strong in-plane orientation of thin films with respect to the major axes of the substrates. The RuO₂ films on MgO(100) contain two variants and form an orientation relationship with MgO given by RuO₂(110)//MgO(100) and RuO₂[001]//MgO[011]. The RuO₂ films on LaAlO₃(100), on the other hand, contain four variants and form an orientation relationship with LaAlO₃ given by RuO₂(200)//LaAlO₃(100) and RuO₂[011]//LaAlO₃[011]. Electrical measurements on the RuO₂ thin films deposited at 600°C show room-temperature resistivities of 40 and 50 μΩ cm for the films deposited on the MgO and LaAlO₃ substrates, respectively.     

Growth of epitaxial sodium-bismuth-titanate films by metal-organic chemical vapor phase deposition

The liquid-delivery spin metal-organic chemical vapor phase deposition method was used to grow epitaxial sodium-bismuth-titanate films of the system Bi₄Ti₃O₁₂ + xNa_0.5Bi_0.5TiO₃ on SrTiO₃(001) substrates. Na(thd), Ti(OⁱPr)₂(thd)₂ and Bi(thd)₃, solved in toluene, were applied as source materials. Depending on the substrate temperature and the Na/Bi ratio in the gas phase several structural phases of sodium-bismuth-titanate were detected. With increasing temperature and/or Na/Bi ratio, phase transitions from an Aurivillius phase with m = 3 to m = 4 via an interleaved state with m = 3.5, and, finally, to Na_0.5Bi_0.5TiO₃ with perovskite structure (m = ∞) were established. These phase transitions proceed at remarkably lower temperatures than in ceramics or bulk crystals for which they had been exclusively observed so far.     

Effects of double passivation for optimize DC properties in gamma-gate AlGaN/GaN high electron mobility transistor by plasma enhanced chemical vapor deposition

Two different materials for double passivation layers have been implemented to an AlGaN/GaN high electron mobility transistor on Si (111) substrate and the improved DC properties are demonstrated. Si₃N₄ and SiO₂ passivation materials are deposited on the gamma gate upper and bottom layers by plasma enhanced chemical vapor deposition. The gamma shape gate can be made by selectively accurate Si₃N₄ or SiO₂ first passivation dry etching with wet etching. The second passivation on gamma gate effectively increases the DC properties. The effects of DC properties of Si₃N₄ or SiO₂ single passivation and Si₃N₄/Si₃N₄ or SiO₂/SiO₂ double passivations are compared. The Si₃N₄/Si₃N₄ double passivation shows the maximum saturation current density and the peak extrinsic transconductance which increases up to 72% and 18%, respectively, more than Si₃N₄ single passivation and also up to 18% and 5% than SiO₂/SiO₂ double passivation.     

Microstructural and frictional control of diamond-like carbon films deposited on acrylic rubber by plasma assisted chemical vapor deposition

In this paper we concentrate on the microstructure of diamond-like carbon films prepared by plasma assisted chemical vapor deposition on acrylic rubber. The temperature variation produced by the ion impingement during plasma cleaning and subsequent film deposition was monitored and controlled as a function of bias voltage and treatment time. Its influence during film growth on the appearance of patterns of cracks and wrinkles, caused by the thermal stresses is evaluated. Different growth modes are proposed in order to explain the smaller patch sizes observed at negative variations of temperature. The coefficient of friction (CoF) of the samples is measured using a pin-on-disk tribometer in non-lubricated conditions. Much lower CoF values than unprotected rubber are seen, which can be correlated with the observed patch size.