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.     

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.     

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.     

Aluminum-induced crystallization of amorphous silicon films deposited by hot wire chemical vapor deposition on glass substrates

Aluminum-induced crystallization of amorphous silicon films is discussed. Amorphous Si films were deposited by hot wire chemical vapor deposition onto Al coated glass substrates at 430 °C. Complete crystallization of a-Si films was achieved during a-Si deposition by controlling Al and Si layer thicknesses. The grain structure of the poly-Si films formed on glass substrate was evaluated by optical and electron microscopy. Continuous poly-Si films were obtained using Al layers with a thickness of 500 nm or less. The average grain size was found to be 10-15 μm, corresponding to a grain size/thickness ratio greater than 20.     

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.     

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.     

Chemical and electrical characteristics of low temperature plasma enhanced CVD silicon oxide films using Si2H6 and N2O

Silicon oxide films have been deposited at low temperatures in the range of 30–250 °C using Si₂H₆ and N₂O by conventional plasma enhanced chemical vapor deposition technique. The dependencies of deposition temperatures on the film properties are studied. The leakage current and the etch rate of these low temperature films compare favorably to films deposited by silane and TEOS at higher temperatures, respectively.     

Evolution of structural and optical properties of nanostructured silicon carbon films deposited by plasma enhanced chemical vapour deposition

Nanostructured silicon carbon films composed of silicon nanocrystallites embedded in hydrogenated amorphous silicon carbon matrix have been deposited by plasma enhanced chemical vapour deposition technique using silane and methane gas mixture highly diluted in hydrogen. The structural and optical properties of the films have been investigated by X-ray diffraction, Raman, Fourier transform infrared, ultra violet-visible-near infrared and photoluminescence spectroscopies while the composition of the films has been obtained from nuclear techniques. The study has demonstrated that the structure of the films evolves from microcrystalline to nanocrystalline phase with the increase in radio frequency (rf) power. Further, it is shown that with increasing the rf power the size of silicon nanocrystallites decreases while the optical gap increases and a blueshift of visible room temperature photoluminescence peak can be observed.     

Investigation of alumina-silica films deposited by pulsed injection metal-organic chemical vapour deposition

This work is devoted to deposition of alumina-silica films using an innovative pulsed injection metal organic chemical vapour deposition technique and aluminium tri(iso-propoxide) (Al(i-OPr)₃) and tetraethoxysilane (TEOS) as precursors. The deposited aluminium silicate films have been characterised by scanning electron microscopy, infrared spectroscopy, X-ray diffractometry and capacitance-voltage (C-V) measurements. The investigation of the deposition at different Si/Al ratios and substrate temperatures has shown that the growth rate increases with the increase of Al(i-OPr)₃ proportion in solution and decreases as the proportion of TEOS increases. We have also shown that aluminium content in the film increases at lower deposition temperatures while silicon content increases at higher temperatures. The permittivity of the films determined from C-V measurements decreases with increasing substrate temperature. It was found that films deposited at substrate temperatures of 600 or 700 °C and with the highest Si/Al ratio have the lowest dielectric permittivity. This research should be useful for further development of MOCVD technology for the deposition of aluminosilicate-based dielectric materials with controlled dielectric permittivity.     

Suppression of hydrogen-ion drift into underlying layers using plasma deposited silicon oxynitride film during high-density plasma chemical vapor deposition

Hydrogen ions drifting into underlying layers during HDP-CVD were successfully suppressed by the insertion of plasma deposited silicon oxynitride (p-SiO_xN_yH_z) film, and the hydrogen-trapping mechanism was clarified. The hydrogen ions are trapped in bonding states, not in interstitial ones. After HDP-CVD undoped silicate glass (HDP-USG) film deposition on the p-SiO_xN_yH_z film, the decrease of the dangling bonds in the p-SiO_xN_yH_z film measured by ESR was much lower than the increase of the desorbed hydrogen concentration measured by TDS. These results suggest that new hydrogen-trapping sites are mainly generated from ESR-inactive bonds by drifted hydrogen ions and atomic hydrogen during HDP-CVD.     

Micro-scratch analysis and mechanical properties of plasma-deposited silicon-based coatings on polymer substrates

Advanced optical applications require multifunctional coatings with specific mechanical properties, such as resistance to damage and good adhesion to different types of substrates, including polymers. In the present study we deposited amorphous hydrogenated silicon nitride (SiN_1.3) and oxide (SiO₂) films on polycarbonate and on silicon substrates by plasma enhanced chemical vapor deposition (PECVD), using a dual-mode microwave/radio frequency plasma system. The film adhesion was determined by the micro-scratch test. Depth-sensing indentation and substrate curvature measurements were used to evaluate the microhardness. Young's modulus and residual stresses of the films. The adhesion strength, represented by the critical load, L_c, when the film starts to delaminate, was determined as a function of the substrate material and the energy of bombarding ions. A direct correlation between the L_c values and the mechanical properties of the films was found. The formation of different crack patterns in the coatings during the scratch procedure is explained in terms of stress release mechanism depending on the mechanical properties of the film, the substrate and the interface region. In addition, different models applicable to the evaluation of the work of adhesion in the case of hard coatings on soft substrates are critically reviewed.     

Aging of silicon-based dielectric coatings deposited by plasma polymerization

Silicon-based dielectric coatings were deposited from tetravinylsilane or a mixture of tetravinylsilane with oxygen gas by pulsed plasma. The coatings in the form of a-SiC:H or a-SiOC:H alloy were stored at ambient conditions for 800 h to investigate aging effects. The SiH, SiC, and CH_x species in the plasma polymer film were identified as responsible for strong oxidation of the deposited material. The increased oxygen concentration up to 19 at.% in the dielectric coatings resulted in a decrease of the refractive index. Oxygen concentrations > 10 at.% resulted in reduction of mechanical properties of dielectric coatings deposited at powers ≥ 2.5 W. Suitable deposition conditions were deduced to reduce aging effects.     

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.     

Silica nanofilms deposited by atmospheric pressure plasma liquid deposition

Silica coatings were deposited onto pure silicon surfaces by a deposition technique known as atmospheric pressure plasma liquid deposition using liquid tetraethylorthosilicate (TEOS) as a precursor. Deposition parameters were varied, including power, TEOS flow rate, helium flow rate, and substrate distance, in order to assess their influence on the growth rates and refractive index as well as the formation of surface particulates and organic content of the coatings. Growth rates were accurately controlled in the range of 0.5 nm s^− 1 to 7.2 nm s^− 1, with thin-films having refractive indices ranging from 1.1 to 1.4, indicative of layers with different levels of porosity. The results suggest that, with careful selection of deposition parameters, this (atmospheric pressure) plasma-based deposition technique could be used to achieve coherent, particulate free, smooth dense inorganic silica coatings.     

Investigation of structural properties of ITO thin films deposited on different substrates

The influence of the substrate nature on the structure and morphology of ITO thin films grown by thermal evaporation in vacuum is investigated. The as-prepared metal films with Sn/In molar ratio of 0.1 were subsequently annealed for 2 h at 723 K in air (to obtain tin doped indium oxide), then annealed in vacuum at 523 K, followed by UV irradiation (to reduce the electrical resistivity). Irrespective of substrate nature, XRD data evidence a (222) preferential orientation in films. Substrate nature, annealing in vacuum and UV irradiation influence the structure, morphology, optical, electrical and surface wetting properties of the films' surface.     

Preparation of SiO2 thin films using the Cat-CVD method

Using the catalytic chemical vapor deposition (Cat-CVD) method, a-Si and SiN_x films have been the main focus of studies. SiO₂ films have not been studied because of the limited life of catalysts such as tungsten or molybdenum in an oxidative atmosphere. In this report, we describe oxide film preparation using an iridium catalyst. We determined the most appropriate catalyst material for the oxide film process by exposing heated materials in tetraethoxysilane (TEOS) or O₂ gas. As the result, it was confirmed that the Ir catalyst works in a slow oxidative atmosphere. Using the Ir catalyst, SiO₂ films were deposited in two gas combinations: TEOS and N₂O, and SiH₄ and N₂O. Although the SiO₂ film processed with the combination of TEOS and N₂O was stoichiometric, its breakdown voltage is not sufficient. The SiO₂ film processed with the combination of SiH₄ and N₂O showed good electrical property.     

Thermoelectric properties of SiC thick films deposited by thermal plasma physical vapor deposition

SiC thick films of about 300 µm could be prepared with a deposition rate above 300 nm/s by thermal plasma physical vapor deposition (TPPVD) using ultrafine SiC powder as a starting material. The thermoelectric properties were investigated as a function of composition and doping content. The nondoped films showed n-type conduction. Although the Seebeck coefficient reached as high as -480 µV/K, the power factor was only around 1.6 × 10^-4 Wm^-1 K^-2 at 973 K due to the relatively high electrical resistivity. In order to reduce the electrical resistivity and to deposit layers with n-type and p-type conduction, N₂, B and B₄C were selected as the dopants. Nitrogen-doped samples exhibit n-type characterization, B and B₄C-doped samples exhibit p-type characterization, and the electrical resistivity decreased from 10^-2–10^-3 to 10^-4–10^-5 Ωm after doping. The maximum power factor of the nitrogen-doped SiC and the thick films deposited with B₄C powder reached 1.0 × 10^-3 and 6.4 × 10^-4 Wm^-1 K^-2 at 973 K, respectively.

© 2003 Elsevier Science Ltd. All rights reserved.     

Deposition of BaTiO3 thin films by plasma MOCVD

Barium titanium trioxide (BaTiO₃) thin films were deposited on fused silica or silicon wafer substrate from barium dipivaloylmethanate (II) (Ba(dpm)₂) and titanium tetraisopropoxide (IV) (TTIP) used as precursors in an oxygen microwave plasma. The substrates were dielectrically heated and the substrate temperatures were around 900 K during the film deposition. The deposition was performed for 15 min and the deposits were identified as BaTiO₃ by means of X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy, and ellipsometry. Oxygen and barium atoms and TiO and CO molecules were identified in the plasma. These species would produce higher deposition rates at lower substrate temperatures than those did in the usual thermal metalorganic chemical vapor deposition (MOCVD). The dielectric constant of the BaTiO₃ thin film that was directly deposited on the silicon wafer substrate was as low as 10¹ order of magnitude. Because the deposit reacted with the substrate and an interdiffusional layer was formed, the platinum layer was coated on the silicon wafer substrate in order to prevent the formation of an interdiffusional layer. The dielectric constant then increased to 10³ order of magnitude.     

Investigation of the properties of diamond-like carbon thin films deposited by single and dual-mode plasma enhanced chemical vapor deposition

In this study diamond-like carbon (DLC) films were deposited by a dual-mode (radio frequency/microwave) reactor. A mixture of hydrogen and methane was used for deposition of DLC films. The film structure, thickness, roughness, refractive index of the films and plasma elements were investigated as a function of the radio frequency (RF) and microwave (MW) power, gas ratio and substrate substance. It was shown that by increasing the H₂ content, the refractive index grows to 2.63, the growth rate decreases to 10 (nm/min) and the surface roughness drops to 0.824 nm. Taking into consideration the RF power it was found that, as the power increases, the growth rate increases to 11.6 (nm/min), the variations of the refractive index and the roughness were continuously increasing, up to a certain limit of RF power. The Raman G-band peak position was less dependent on RF power for the glass substrate than that of the Si substrate and a converse tendency exists with increasing the hydrogen content. Adding MW plasma to the RF discharge (dual-mode) leads to an increase of the thickness and roughness of the films, which is attributed to the density enhancement of ions and radicals. Also, optical emission spectroscopy is used to study the plasma elements.