Growth and properties of hydrogen-free DLC films deposited by surface-wave-sustained plasma

Hydrogen-free diamond-like carbon (DLC) films were deposited by a new surface-wave-sustained plasma physical vapor deposition (SWP-PVD) system in various conditions. Electron density was measured by a Langmuir probe; the film thickness and hardness were characterized using a surface profilometer and a nanoindenter, respectively. Surface morphology was investigated using an atomic force microscope (AFM). It is found that the electron density and deposition rate increase following the increase in microwave power, target voltage, or gas pressure. The typical electron density and deposition rate are about 1.87 × 10¹¹–2.04 × 10¹² cm^− 3 and 1.61–14.32 nm/min respectively. AFM images indicate that the grain sizes of the films change as the experimental parameters vary. The optical constants, refractive index n and extinction coefficient k, were obtained using an optical ellipsometry. With the increase in microwave power from 150 to 270 W, the extinction coefficient of DLC films increases from 0.05 to 0.27 while the refractive index decreases from 2.31 to 2.11.     

The growth and chemical structure of thin photonic films formed from plasma copolymerization. Part II. Effect of monomer feed location

Plasma copolymerization of benzene and octafluorocyclobutane (OFCB) has been successfully applied in the fabrication of photonic films with controllable refractive index profiles by accurately adjusting the comonomer feed ratio and feed locations during plasma enhanced chemical vapor deposition (PECVD). XPS, IR, and spectroscopic ellipsometry were used to determine the deposition rate, chemical composition/structure, and optical properties of the PECVD films. Three different feed locations were chosen for the OFCB monomer including downstream from the plasma zone (DS), the plasma zone edge (PE), and the center of the plasma zone (PZ). The benzene was always fed in at the DS position. For both plasma homo- and copolymerization, film deposition rates were highest utilizing the PZ feed. The addition of small amounts of benzene increased these deposition rates substantially, but also led to a dramatic decrease in the F/C ratio and significant variations in different structural units (CF_x(x=1−3)) indicating the complex subtleties of plasma copolymerization. The refractive indices of the polymer thin films scaled linearly with the F/C values determined from the film composition studies.     

Tailoring terpenoid plasma polymer properties by controlling the substrate temperature during PECVD

Polymers derived from natural, minimally‐processed materials have recently emerged as a more sustainable alternative to synthetic polymers, with promising applications in biocompatible and biodegradable devices. Plasma‐enhanced deposition is well‐suited to one‐step, fast, and efficient synthesis of highly crosslinked inert polymers directly from natural resources, however, fabrication of biologically active polymers remains a challenge. Plasma processing parameters influence the properties such as surface energy, roughness, morphology, and chemical composition of deposited polymers and thus their final applications. This article reports on the important role of substrate temperature (T_S) in the chemical composition, wettability, refractive index, and crosslinking density of plasma polymers derived from terpenoids. Experiments are conducted as a function of deposition power P_d, and substrate temperature, T_S. T_S varied from 40 to 280 °C and is externally controlled. Atomic force microscopy analysis reveals the change in deposition mechanism attributed to shadowing effect at higher T_S and P_d. Increase in band gap (E_g) with high T_s deposition for terpenoid based plasma polymers is observed. Swelling behavior analyzed by in situ ellipsometry affirms the enhanced crosslink density with increasing deposition rate. Fourier transform infrared analysis exhibits the formation of additional chemical moieties with increasing T_S. Increase in deposition rate with increasing T_S at higher P_d supports the theory of direct incorporation of depositing particles as dominant mechanism of plasma polymerization in this study. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45771.     

Film growth and relationship between microstructure and mechanical properties of a-C:H:F films deposited by PECVD

Results of a systematic investigation on the effects of some deposition parameters (partial pressure of CF₄ and self-bias voltage) on the microstructure, mechanical and tribological properties of a-C:H:F films are presented. The films were deposited by r.f.-PECVD using CH₄–CF₄ mixtures. The film composition was measured by ion beam analysis and, combining these results with the film thickness, the film density was determined. The structural arrangement was probed by Raman spectroscopy and the chemical bonding was investigated by infrared absorption and X-ray photoelectron spectroscopies. The hardness was measured by microindentation and the internal stress was determined by measuring the changing of the substrate curvature after the film deposition. The friction coefficient was measured by lateral force microscopy. The results indicate that the properties of a-C:H:F films are controlled by the ionic bombarding during the film growth. For a fixed self-bias, the increase of the CF₄ partial pressure leads to a transition from diamond-like to a polymer-like structure, to a higher fluorine incorporation and to a decrease of both hardness and internal stress. The friction coefficient decreases too. The fluorine incorporation also increases with the increase of the self-bias and was associated to higher plasma decomposition. Fluorine-poor polymer-like films were deposited at low self-bias (−50 V). In both situations, fluorine incorporation occurs at the expenses of the hydrogen content and the reduction of the energy of the bombarding species results in less dense and soft films with a polymer-like structure.     

Aluminum Silicate Films Obtained by Low-Pressure Metal-Organic Chemical Vapor Deposition

Amorphous alumina-silica films with film thickness of 0.41–2.69 μm were prepared on glass and silicon substrates by metal-organic chemical vapor deposition using a mixture of aluminum tri-sec-butoxide (ATSB), hexamethyldisilazane (HMDSN), and argon. By controlling the inputs of ATSB and HMDSN, alumina-silica thin films could contain varied compositions and adjustable properties. Basically, the codeposition of alumina and silica to form alumina-silica using ATSB and HMDSN had a faster growth rate than their individual components. The internal stress could be adjusted by deposition temperature and reactant inputs. Adhesion could be improved by having a silicon-rich thin film, whereas an aluminum-rich film could have slightly higher hardness. Optical properties, e.g., refractive index and optical transmittance, were also measured.     

Direct current cathodic glow discharge polymerization of methane and butane

The deposition of a polymeric material on the surface of the cathode of a direct current (dc) glow discharge was investigated for methane and butane. The cathode region of a dc glow discharge is not a plasma in a strict sense. Consequently, the deposition of a polymeric material to the cathode surface differs significantly from so-called plasma polymerization of the same monomer (starting gas or vapor) that deposits on a substrate placed in a glow discharge plasma. Using methane and n-butane, the influence of the molecular weight of the monomer (M), volume flow rate, and discharge power on the deposition rate in a dc glow discharge were investigated and compared with those in an audio frequency and a radio frequency glow discharge. It was found that the deposition rate expressed in (thickness growth rate)/(M) is linearly proportional to the current density, which implies that cathodic polymerization is controlled by the cathode region parameter (not plasma parameters). The refractive indices (632.8 nm) for the cathodic polymers are in the range of 2.2–2.4 while those for plasma polymers are in the range of 1.5–1.7. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 237–245, 1998     

Growth and characterization of fluorocarbon thin films grown from trifluoromethane (CHF3) using pulsed‐plasma enhanced CVD

Trifluoromethane (CHF₃) was used as a precursor gas in pulsed‐plasma enhanced CVD to deposit fluorocarbon films onto Si substrates. The film composition, as measured by X‐ray photoelectron spectroscopy (XPS) of the C1s peak, was observed to change as the plasma duty cycle was changed by varying the plasma off‐time; this offers a route to control the molecular architecture of deposited films. FTIR results indicate that the film is primarily composed of CF_x components, with little or no C H incorporation into the film. The rms roughness of the films is extremely low, approaching that of the Si substrate; the low growth rate and consequent high‐power input/thickness is believed to be partly responsible. CHF₃ produces films with higher % CF₂ compared to other hydrofluorocompound (HFC) monomers (CH₂F₂ and C₂H₂F₄). However, the deposition kinetics for all three HFC gases display similar trends. In particular, at a fixed on‐time of 10 ms, the deposition rate per pulse cycle reaches a maximum at an off‐time of approximately 100 ms. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 842–849, 2000     

氮化硅薄膜生长随时间演化过程及其特性研究

氮化硅SiN_x薄膜凭借介电常数高和稳定性好的特点而被广泛应用于光电器件中,但薄膜的厚度对器件的性能有重要影响。针对此问题采用等离子体化学气相沉积技术,以高纯NH₃、N₂和SiH₄为反应气体,优化其他沉积参数,通过改变沉积时间来生长SiN_x薄膜。用X射线衍射谱(XRD),紫外-可见光光谱(UV-VIS)、傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)对薄膜结构进行表征,详细研究了沉积时间与薄膜厚度的关系以及沉积时间对薄膜性能的影响。试验结果表明:所制备的样品为非晶SiN_x薄膜结构,薄膜厚度随沉积时间均匀增加;薄膜折射率随沉积时间的增加而增大,光学带隙基本不随时间变化。SEM测试结果表明,随着沉积时间增加,薄膜致密性与均匀性越来越好,氧含量也越来越少,说明薄膜致密性提高可以有效阻挡O原子进入薄膜,阻止后氧化现象的发生。     

Electro-optical performances of nanostructured SrTiOx films: The effect of plasma power,Ar/O2 ratio and annealing

The present work evaluates the effects of plasma power and oxygen mixing ratios (OMRs) on structural, morphological, optical, and electrical properties of strontium titanate SrTiO_x (STO) thin films. STO thin films were grown by magnetron sputtering, and later thermal annealing at 700°C for 1 h was applied to improve film properties. X-ray diffraction analysis indicated that as-deposited films have amorphous microstructure independent of deposition conditions. The films deposited at higher OMR values and later annealed also showed amorphous structure while the films deposited at lower OMR value and annealed have nanocrystallinity. In addition, all as-deposited films were highly transparent (~80%–85%) in the visible spectrum and exhibited well-defined main absorption edge, while the annealing improved transparency (90%) within the same spectrum. The calculated direct and indirect optical band gaps for films were in the range of 3.60-4.30 eV as a function of deposition conditions. The refractive index of the films increased with OMRs and the postdeposition annealing. The frequency dependent capacitance measurements at 100 kHz were performed to obtain film dielectric constant values. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 μC/cm² charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). The leakage current density was relatively low (3 × 10⁻⁸Acm⁻² at +0.8 V) indicating that STO films are promising for future dynamic random access memory applications.     

Responsive plasma polymerized ultrathin nanocomposite films

The plasma polymerization of NIPAAM and titanium isopropoxide monomers into responsive ultrathin films with responsive optical properties using plasma enhanced chemical vapor deposition is reported. The composite ultrathin films possess a large window for potential changes in their refractive index from 1.60 to 1.95. We demonstrated that these polymer films exhibit fast (transition time below 2 s), large, reversible, and repeatable changes to their thickness and refractive index as a function of periodic environmental humidity changes.     

Anisotropy and densification of polymer ultrathin films as seen by multi-angle ellipsometry and X-ray reflectometry

The chain conformations of cyclo-olefin polymer (COP) and polystyrene (PS) in less than 200-nm thick films on silicon wafers were investigated on the basis of the refractive index measured by multi-angle spectroscopic ellipsometry (MASE), and density measured by X-ray reflectometry (XRR). For both COP and PS, the density measured by XRR increases by decreasing the film thickness to below 50 nm. Densification may be caused by close packing of unentangled polymer chains in ultrathin films spincast from dilute solutions with polymer concentrations less than the overlap concentration (C*). For COP films, the refractive indices at incident angles of 45° and 70° measured by MASE agree well with those calculated by the Lorentz–Lorenz equation, indicating that densification of COP ultrathin films enhances their refractive indices. For PS films thinner than 50 nm, although the refractive index at an incident angle of 45° agrees with a calculation based on the Lorentz–Lorenz equation, one at 70° significantly deviates downward. A comparison of them with the results of quantum chemical calculation (QCC) suggested a plane-arrangement of benzene rings in PS ultrathin films, which was likely brought about by stacking of benzene rings and attractive interaction between π-electrons in the benzene rings and the substrate surface.     

Measuring the thickness of ultra-thin diamond-like carbon films

This paper examines the challenge posed by the measurement of thickness of sub-50 nm diamond-like carbon (DLC) films deposited onto silicon substrates. We compared contact profilometry (CP), optical profilometry (OP), contact atomic force microscopy (CAFM), tapping atomic force microscopy (TAFM) and X-ray reflectometry (XRR). Generally, CP, CAFM, TAFM and XRR give similar thickness values except for the case of the more compliant samples measured by CP and CAFM. Moreover, the theoretically precise XRR technique gives significant standard deviation due to the layering of the DLC film. For those transparent samples, OP always gives an erroneous measurement. These metrological artefacts are compared to calculations of mechanical deformation (CP and CAFM), energy dissipation (TAFM) and thin film interferences (OP). The OP artefact is used to extract the film’s refractive index, in good agreement with literature values. Finally, the comparative data obtained in this study also shows that the density and refractive index of the 10 nm thick films are constituently lower than those of the 50 nm thick films. This scaling effect, which is consistent with known growth mechanisms for DLC, further complicates the measurement of thickness by optical techniques.     

Remote plasma enhanced metal organic chemical vapor deposition of TiN for diffusion barrier

TiN films were deposited with remote plasma metal organic chemical vapor deposition (MOCVD) from tetrakis-diethyl-amido-titanium (TDEAT) at substrate temperature of 250–500°C and plasma power of 20–80 W. The growth rate using N₂ plasma is slower than that with H₂ plasma and showed 9.33 kcal/mol of activation energy. In the range of 350–400°C., higher crystallinity and surface roughness were observed and resistivity was relatively low. As the temperature increased to 500°C., randomely oriented structure and smooth surface with higher resistivity were obtained. At low deposition temperature, carbon was incorporated as TiC phase, as the deposition temperature increases, carbon was found as hydrocarbon. At 40 W of plasma power, higher crystallinity and rough surface with lower resistivity were obtained and increasing the plasma power to 80 W leads to low crystallinity, smooth surface and higher resistivity. It may be due to the incorporation of hydrocarbon decomposed in the gas phase. Surface roughness was found to be related to the crystallinity of the film.     

Demonstration of SiO2/SiC-based protective coating for dental ceramic prostheses

SiO₂/SiC coatings were deposited onto ceramics disks using plasma-enhanced chemical vapor deposition. The effects of deposition pressure and gas-flow ratio on the refractive index, extinction coefficient, and SiC composition were studied. For the highest studied SiH₄ to CH₄ gas-flow ratio of 1.5, the refractive index increased by 17% from 2.53 (at the wavelength of 845 nm) to 2.96 (at the wavelength of 400 nm). For the lowest studied SiH₄ to CH₄ gas-flow ratio of 0.5, the refractive index only increased by 4% from 2.11 (at the wavelength of 845 nm) to 2.20 (at the wavelength of 400 nm). At higher deposition pressures, the variation in refractive index of the SiC coatings was significantly lower showing a slight increase from 1.93 (at a wavelength of 845 nm) to 1.96 at a wavelength of 400 nm. Except for the case of a low SiH₄ to CH₄ gas-flow ratio of 0.5, for light with wavelengths ≤650 nm, the extinction coefficient of the SiC coatings increased significantly. Light with a wavelength >650 nm had an extinction coefficient near 0 in all cases. After annealing the sample at 400°C for 4 hours, hydrogen-related bonds broke and the stress of the film was reduced from −245 to −71 MPa. By utilizing different thicknesses of SiC, the full standard dental shade guide was matched with the ΔE of each coated disk being less than 3.3 compared to the shade guide.     

Characterization of Optical Thin Films by Spectroscopic Ellipsometry

Spectroscopic ellipsometry was used to rapidly and nonde- structively characterize ion-plated SiO₂ and Ta₂O₅ films on glass substrates as a function of temperature. The analysis provided the density (as a function of depth) and optical properties of the films. The SiO₂ film had a higher refractive index than is typical for thermally grown SiO₂. This was attributed to compaction of the film during the deposition process. Similarly, the ion-plated Ta₂O₅ film had the high refractive index characteristic of a high-density film. The films were not affected strongly by temperature during heating >100°C.     

Ferroelectric properties of pure ZrO2 thin films by chemical solution deposition

Ferroelectricity in pure zirconia (ZrO₂) thin films, manufactured on Si (100) substrates via the chemical solution deposition method using all-inorganic aqueous salt precursor, has been demonstrated for the first time. The influence of thickness on the crystalline structure and ferroelectric properties of the thin films were measured and showed that they were strongly affected by the film thickness. The structural data indicated that as the film thickness increased from 30 nm to 50 nm, the m-phase fraction increased, and a phase transition from orthorhombic to cubic and then tetragonal occurred near the main diffraction peak of 30.7°. The lowest m-phase fraction of 15.4% was obtained in the pure ZrO₂ film with a thickness of 30 nm, and after 10³ field cycling, it exhibited the highest relative permittivity of 39.6 as well as the highest residual polarization of 8.5 μC/cm².     

Characteristic Study of Silicon Nitride Films Deposited by LPCVD and PECVD

This paper analyzes and compares the characteristics of silicon nitride films deposited by low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD), with special attention to the hydrogenation and chemical composition of silicon nitride films. Three different LPCVD processes at various DCS and NH₃ gas flow rates and deposition temperatures, together with PECVD using SiH₄ and NH₃ and ICP CVD using SiH₄ and N₂, were compared. The silicon nitride film deposition rate decreases with an increasing NH₃/DCS ratio in LPCVD, which also leads to an increase in the refractive index and a decrease in the residual stress in the film. There is nearly no hydrogen incorporated in the LPCVD films, which differs from PECVD and ICP CVD that show significant Si-H and N-H bonds. The chemical composition of silicon nitride films is mostly Si-rich, except for the LPCVD process at high NH₃/DCS ratio with near stoichiometric chemistry.     

Preparation of nanocrystalline titanium carbonitride coatings using Ti(N(Et)<Subscript>2</Subscript>)<Subscript>4</Subscript>

Titanium carbonitride films with a thickness of 80–150 nm have been synthesized by low pressure chemical vapor deposition from a gas mixture of tetrakis(diethylamino)titanium and ammonia at temperatures of 773–973 K. The film properties have been studied by spectroscopy (IR, XPS, and EDS), scanning electron and atomic force microscopy, and ellipsometry. The studies have shown that the films consist of polycrystals with a size of 15–80 nm; their structure contains chemical bonds of titanium with atoms of carbon, nitrogen, and oxygen. The film composition is consistent with the data of the previously performed thermodynamic modeling of the deposition of different condensed phases in the Ti-C-N-H-O system. As the deposition temperature increases in the range under study, the refractive index of the films increases from 2.1 to 2.7.     

High-density DLC films prepared using a magnetron sputter type negative ion source

Diamond-like carbon (DLC) films have been deposited at room temperature using a magnetron sputter type negative ion source (MSNIS). The film characteristics such as density, surface roughness, film structure and thicknesses are obtained and analyzed using X-ray reflectivity (XRR), XPS and AFM methods. XRR results showed that the density of the film varies from 1.9 to 3.0 g/cm³ with respect to the different deposition parameters. At average negative carbon ion energy 700 eV and Cs injector temperature 150 °C, the densest film (3.0 g/cm³) was observed at 1 nm/s deposition rate. The surface roughness of the film was less than 1.0 nm in most cases for the 10-nm thickness film. XPS peak showed no Cs content on the film. The films prepared at different negative ion production yields and negative ion energies were compared. The result suggests that the density is the strong function of negative ion energy and the negative ion production yield.Higher cathode voltage induced denser film, while Cs flow rate had optimum temperature condition around 150 °C.     

Preparation and characterization of TiO2 thin films by PECVD on Si substrate

Titanium oxide thin films were prepared on p-Si(l00) substrate by plasma enhanced chemical vapor deposition using high purity titanium isopropoxide and oxygen. The deposition rate was little affected by oxygen flow rate, but significantly affected by RF power, substrate temperature, carrier gas flow rate, and chamber pressure. Morphology of the film became coarser with increasing deposition time and chamber pressure, and the film showed less uniformity at high deposition rates. It was also found that the overall deposition process is controlled by heterogeneous surface reaction below 200°C., but controlled by mass transfer of reactants at higher temperatures. TiO₂ films deposited at temperatures lower than 400°C was amorphous, but showed the anatase crystalline structure upon 400°C deposition. The dielectric constant was about 47 for the films post-treated by rapid-thermal annealing (RTA) at 800°C. The leakage current was about 2×10⁻⁵ A/cm² for the films deposited at 400°C and RTA-treated at 600°C. However, it was decreased to less than 3×10⁻⁷ A/cm² for the film RTA-treated at 800°C.