Poly(methyl methacrylate) as masking material for microelectromechanical system (MEMS) fabrication

In the present study direct current (dc) sputtered poly(methyl methacrylate) (PMMA) films deposited on silicon substrates were evaluated as masking materials for anisotropic etching of silicon in aqueous potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH) solutions. Sputtered PMMA films were characterized by FTIR to ascertain the bonding, by X‐ray photoelectron spectroscopy (XPS) for the elemental composition, and by the contact angle for measuring the adhesion of the film with the substrate. FTIR and XPS data showed the presence of a poly(tetrafluoroethylene)‐like film on the silicon substrate. The interfacial tension was calculated from the contact angle value, which was 0.82 dyne/cm, confirming good adhesion of the film and the substrate. A pattern was lithographically transferred through the masking material on the silicon substrate, and the etch rate of the masking layer was calculated from the masking time data of the films. The etch rate value of 4 Å/min obtained for the masking material is low compared to the etch rate of the conventional masking materials (60 Å/min for SiO₂ and 8 Å/min for Si₃N₄). © 2006 Wiley Periodicals Inc. J Appl Polym Sci 102: 2094–2098, 2006     

Two-step growth of ZnO films on silicon by atomic layer deposition

Two-step growth of ZnO by atomic layer deposition at low temperatures was performed to grow quality ZnO films on silicon substrates: first, the growth of a buffer layer at 130 ?C and second, the growth of the main layer at 210 ?C. Structural and optical properties of the ZnO films deposited on ZnO-buffer/Si(111) were investigated as a function of buffer layer thickness. The films showed a strong UV emission at 380 nm and a weak green emission at 520–570 nm. The ZnO films deposited on a 327 å buffer layer showed overall the best surface morphology and structural and optical properties.     

Effects of Wet Oxidation on the Properties of Sub-10-nm-Thick Silicon Nitride Films

Capacitors were prepared by wet oxidation of 8 nm (80 Å) thick silicon nitride films which had been deposited on polysilicon substrates. The capacitance and breakdown field of these capacitors were measured as a function of the wet oxidation conditions. The properties of the polysilicon films were also investigated by varying the preparation conditions to find a better substrate for the deposition of the ultrathin silicon nitride films. These polysilicon films were prepared using low-pressure chemical vapor deposition at 560° and 625°C on silicon wafers. The films were then annealed at 900°C for 30 min after As doping by implantation with a dose of more than 2 × 10¹⁵/cm². The films deposited at 560°C have a smooth surface and a low electrical resistivity and are thus suitable substrates for the ultrathin silicon nitride films as well as suitable contact electrodes. For the capacitors with an oxide nitride composite layer, the capacitance decreases sharply, but the breakdown field increases with an increase in the wet oxidation time at 900°C. This is due to an increase in the thickness of the oxide—nitride layer. For the capacitors with silicon oxynitride layers created by removing the top oxide of the silicon nitride wet-oxidized at 900°C for more than 35 min, however, the values of both the capacitance and the breakdown field are higher than those of capacitors with an unoxidized silicon nitride layer.     

Titanium Oxide Thin Films on Organic Interfaces through Biomimetic Processing

Titanium oxide (TiO₂) thin films have been deposited on silicon, glass, and plastic substrates by destabilization of an aqueous titanium lactate solution at low temperatures (<100°C). The process uses a commercially available, low-cost precursor and is simple to perform; it involves only control of pH in aqueous, chelated titanium solutions. With this solution technique, high deposition rates (>50 nm/min), film thickness (>100 nm), and excellent film uniformity have been obtained. Uniform coatings can be applied on complex-shaped polymeric substrates and porous membranes. Films can be formed on both sulfonated and untreated polymeric surfaces. As-deposited films on plastic substrates consist of amorphous, hydrated TiO₂. On sulfonated self-assembled monolayers on silicon substrates, nanocrystalline TiO₂ films have been formed. The deposited films exhibit strong ultraviolet (UV) absorption with excellent transmission in the visible wavelength range, which indicates that the coatings may be useful as protective UV blockers for polymeric materials.     

Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon

ABSTRACT: Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750 [DEGREE SIGN]C. Obtained results from structural, optical, and electrical characterizations show that thermal annealing of amorphous silicon deposited on Ni-metalized porous silicon leads to an enhancement in the crystalline quality and physical properties of the silicon thin films. The improvement in the quality of the film is due to the crystallization of the amorphous film during annealing. This simple and easy method can be used to produce silicon thin films with high quality suitable for thin film solar cell applications.     

Composition and chemical structure of ultra-thin a-C:F films deposited by RF magnetron sputtering with high pulsed bias

By applying a negative high pulsed voltage to Si (111) substrates, ultra-thin fluorine carbon films of about 3 nm thick are deposited and completely covered on the samples by RF magnetron sputtering with PTFE target. Angle resolved X-ray photoelectron spectroscopy analysis indicates that the surface of the deposited films is rich in fluorine, and C–F₂, CF–CF and C–F groups in the outmost surface layer are much more than those in the inner layer of the films. The reason for this forming fluorine-rich phenomenon is explained and a two-layer model is proposed.     

Improved adhesion and tribological properties of fast-deposited hard graphite-like hydrogenated amorphous carbon films

Graphite-like hard hydrogenated amorphous carbon (a-C:H) was deposited using an Ar-C₂H₂ expanding thermal plasma chemical vapour deposition (ETP-CVD) process. The relatively high hardness of the fast deposited a-C:H material leads to high compressive stress resulting in poor adhesion between the carbon films and common substrates like silicon, glass and steel. A widespread solution to this problem is the use of an adhesion interlayer. Here we report on the changes in adhesion between the graphite-like a-C:H films and M2 steel substrates when different types of interlayers are used. Insignificant to very small improvements in adhesion were observed when using amorphous silicon oxide (a-SiO_x), amorphous organosilicon (a-SiC_xO_y:H_z) and amorphous hydrogenated silicon carbide (a-SiC_x:H_y) as adhesion layers. However, when sputtered Ti was used as an interlayer, the adhesion increased significantly. The dependence of the adhesive properties on the deposition temperature and interlayer thickness, as well as on the thickness of the a-C:H layer is presented and discussed. The low wear rates measured for the a-C:H/Ti/M2 stack suggest that these films are ideal for tribological applications.     

Ternary Ti–Si–C alloy film formation on GaN and contact properties

Ternary Ti–Si–C alloy films were deposited on GaN substrates (n-type and p-type) by the radio- frequency magnetron sputtering method. The electrical properties of contact films with various chemical compositions were investigated. The microstructures were examined by X-ray diffractometry and transmission electron microscopy. The electrical properties of the contact films were improved after annealing at 873?K for 60?s. Ohmic contact characteristics were obtained for n-type GaN. The TiN phase plays an important role in obtaining the ohmic contact. The effect of deposition and annealing on the electrical properties between Ti–Si–C film and GaN are discussed based on the experimental results.     

Adhesion aspects of poly(p-xylylene) to SiO2 surfaces using γ-methacryloxypropyltrimethoxysilane as an adhesion promoter

The use of organo-silanes as coupling agents offers the potential to create novel structures using materials that would otherwise suffer from poor adhesion. γ-methacryloxypropyltrimethoxysilane (γ-MAPTS) layers were deposited on hydroxylated SiO₂ surfaces using both vapor and solution deposition techniques. The films were characterized using variable angle spectroscopic ellipsometry, infrared spectroscopy, contact-angle measurements and X-ray photoelectron spectroscopy. Film thickness was relatively constant at ～6 Å for solution deposition times from 2 min to 2 h at 60° C. Water contact angle increased from 0° to 45° after silane deposition from solution. Room temperature vapor-deposited γ-MAPTS films showed similar thicknesses to those of solution deposited films but a markedly lower contact angle of 10°. Parylene N was chemical vapor deposited on the γ-MAPTS films and its adhesion was tested using the Scotch^® Tape test. The γ-MAPTS improved adhesion of parylene N to the hydroxylated surface, with the adhesion for the vapor deposited silane films exhibiting a temperature and time dependence.     

Hot filament chemical vapour deposition and wear resistance of diamond films on WC-Co substrates coated using PVD-arc deposition technique

Different Cr- and Ti-base films were deposited using PVD-arc deposition onto WC-Co substrates, and multilayered coatings were obtained from the superimposition of diamond coatings, deposited on the PVD interlayer using hot filament chemical vapour deposition (HFCVD). The behaviour of PVD-arc deposited CrN and CrC interlayers between diamond and WC-Co substrates was studied and compared to TiN, TiC, and Ti(C,N) interlayers. Tribological tests with alternative sliding motion were carried out to check the multilayer (PVD + diamond) film adhesion on WC-Co substrate. Multilayer films obtained using PVD arc, characterised by large surface droplets, demonstrated good wear resistance, while diamond deposited on smooth PVD TiN films was not adherent. Multilayered Ti(C,N) + diamond film samples generally showed poor wear resistance.Diamond adhesion on Cr-based PVD coatings deposited on WC-Co substrate was good. In particular, CrN interlayers improved diamond film properties and 6 μm-thick diamond films deposited on CrN showed excellent wear behaviour characterised by the absence of measurable wear volume after sling tests. Good diamond adhesion on Cr-based PVD films has been attributed to chromium carbide formation on PVD film surfaces during the CVD process.     

Tribological behaviors of carbon series additions reinforced CF/PTFE composites at high speed

The tribological, mechanical, and thermal properties of carbon series additions reinforced CF/PTFE composites at high speed were investigated. In this work, carbon fiber (CF) filled polytetrafluoroethylene (PTFE) composites, which have excellent tribological properties under normal sliding speed (1.4 m/s), were filled with some carbon materials [graphene (GE), carbon nanotubes (CNTs) and graphite (Gr)] respectively to investigate the tribological properties of CF/PTFE composites at high sliding speed (2.1 and 2.5 m/s). The results reveal that the carbon series additions can improve the friction and anti‐wear performances of CF/PTFE, and GE is the most effective filler. The wear rate of 0.8 wt % GE/CF/PTFE was decreased by 50 ? 55%, 55 ? 60%, 40 ? 45% at 1.4, 2.1, and 2.5 m/s compared with CF/PTFE. SEM study shows GE could be helpful to form smooth and continuous transfer film on the surface of counterparts. Meanwhile, GE can improve its tensile strength and elastic modulus obviously. Thin layer structure of GE could enhance the thermal conductivity, which can be helpful to dissipate heat of CF/PTFE composites wear surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43236.     

Influence of substrate material and ion bombardment on plasma-deposited fluorocarbon thin films

The influence of substrate material and ion bombardment on fluorocarbon thin films deposited using a C₂F₆ glow discharge in an rf, parallel plate reactor was investigated. Monitoring of the plasma process by optical emission spectroscopy indicated that the dominant species in the glow discharge was CF₂. Studies of bulk polytetrafluoroethylene (PTFE) and plasma-polymerized fluorocarbon thin-film samples in an XPS system demonstrated that the formation of non-CF₂ species can be induced by ion bombardment of CF₂ molecules. Characterization of the deposited fluorocarbon films by XPS found that the F/C ratio and CF_x distribution (0 < x < 3) in the films were dependent on processing conditions. Fluorocarbon films deposited simultaneously onto Al, glass, steel, and PTFE substrates using a C₂F₆ plasma and a graphite sputter target had measurably different F/C ratios, with the F/C ratio of the films deposited onto the Al substrates consistently lower than the F/C ratios of the films deposited onto the other substrates. When a C₂F₆ plasma was used without a graphite target, the F/C ratio in the film was constant, but the CF_x distribution was different for each of the substrate materials. Analysis of the plasma-polymerized films by TEM revealed that localized growth of fluorocarbon particles occurred during the initial stages of deposition, consistent with an activated growth mechanism. Differences in the F/C ratio for films deposited onto the various substrate materials were attributed to the interaction of the fluorocarbon plasma with the exposed surface of the substrate prior to complete coverage by the polymeric film. © 1994 John Wiley & Sons, Inc.     

Surface Modification of Poly(Tetrafluoroethylene) Films by Graft Copolymerization for Adhesion Improvement with Sputtered In-Sn Oxides

Surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) films was carried out via UV-induced graft Copolymerization with glycidyl methacrylate (GMA), acrylamide (AAm) and hydroxylethylacrylate (HEA) to improve the adhesion strength with sputtered indium-tin-oxide (ITO). The surface compositions of the graftcopolymerized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The graft yield increases with increasing monomer concentration and Ar plasma pre-treatment time of the PTFE films. The T-peel adhesion strength was affected by the type of monomer used for graft Copolymerization, the graft concentration, and the thermal post-treatment after ITO deposition. A double graft-copolymerization process, which involved initially the graft copolymeri/ation with AAm or HEA, followed by graft Copolymerization with GMA. was also employed to enhance the adhesion of sputtered ITO to PTFE. T-peel adhesion strengths in excess of 8 N cm were achieved in the ITO graft-modified PTFE laminates. The adhesion failure of the ITO/PTFE laminates in T-peel tests was found to occur inside the PTFE films. The electrical resistance of ITO on all graft-modified PTFE surfaces before and after thermal post-treatment remained conslant at about 30 Ω square, suggesting that the graft layer did not have any significant effect or. the electrical properties of the deposited ITO.     

Low-temperature deposition of optically transparent diamond using a low-pressure flat flame

The radial uniformity and scaleable nature of flat flames make them an attractive technique for diamond deposition. Due to the high temperatures involved in combustion synthesis, typically molybdenum and silicon have been used as substrates. Here we report low-temperature diamond deposition on glass substrates. Diamond deposition was achieved on ordinary sodium silicate glass at substrate temperatures of 500°C; however, film delamination occurred during cooling after deposition. Vycor™ and Pyrex™ are two glasses that have thermal expansion coefficients that are similar to diamond. Continuous, optically transparent films were successfully deposited on both glasses. The diamond films have been characterized by scanning electron microscopy, Raman spectroscopy and secondary ion mass spectroscopy (SIMS). The dependence of hydrogen and sp²-bonded carbon incorporation in the films on reactant composition was quantified. These films were optically transparent and showed good adhesion as measured by a simple tape test.     

Growth and Adhesion Enhancement of Diamond Films Deposited on Steel Substrates by a Cr–N Interlayer

Diamond film deposition onto iron-based substrates by chemical vapor deposition methods is complicated by the formation of black carbon or graphitic soot on the substrate surface prior to diamond nucleation and growth, by fast diffusion of carbon into the iron substrate, and by poor adhesion of the deposited film. These complications suggested the use of a buffer layer between the deposited diamond film and the iron-based substrate. We review different methods used to improve the adhesion of diamond film to steel substrates. In particular we describe in detail our own studies which involve the use of a Cr-N interlayer. The use of a chromium nitride interlayer has been found to improve significantly the adhesion of diamond films deposited on ferrous substrates. This is achieved by hindering diffusion processes of carbon and iron, very stable mechanical and chemical bonding between the interlayer and the diamond film, and good adhesion of the interlayer to the steel substrate. We also report on our studies related to residual stress present in the films, as well as a correlation between the interlayer properties and adhesion strength of deposited films.     

Interplay between adhesion and interfacial properties of diamond films deposited on WC-10%Co substrates using a CrN interlayer

In this study, the effect of deposition temperature on the adhesion of diamond films deposited on WC-10%Co substrates with a Cr-N interlayer is investigated. Diamond films were deposited at different temperatures (550, 650 and 750 °C), using a hot filament chemical vapor deposition reactor. It was found that the optimal adhesion is obtained for the film deposited at 650 °C. The interplay between carbon interfacial diffusion and the adhesion of diamond films deposited at different deposition temperatures were investigated. The combined use of different characterization techniques (Indentation tests, SIMS, XPS, XRD and SEM) shows that the adhesion strength depends on the thickness of Cr-C layer formed at the interface during diamond deposition, which is strongly influenced by the deposition temperature. It is suggested that at the optimum deposition temperature, thickness of the Cr-C layer is too low to introduce a large thermal stress at the interface and sufficiently thick enough to withstand the propagation of indentation induced cracks.     

Fracture toughness of the interface between CVD diamond film and silicon substrate in the relation with methane concentration in the source gas mixture

Diamond films produced by chemical vapor deposition (CVD) have been reported to show various excellent properties. However, low toughness of diamond films, especially the interface between the films and substrates, has been a severe problem. In order to find the dominant factors to control the adhesive strength of CVD diamond films, we obtained diamond films with various crystalline structures deposited on silicon (100) substrates under various methane concentrations in the source gas mixture. The toughness of the interface between the diamond film and silicon substrate was evaluated for the first time by a recently developed method. The toughness showed an interesting behavior with respect to the variation of methane concentration. The obtained results were quantitatively compared to the data already obtained for the case of CVD diamond particles deposited on silicon substrates.     

Mechanical properties and thermal stability of tungsten boride films deposited by radio frequency magnetron sputtering

Tungsten and boron compounds belong to the group of superhard materials since their hardness could exceed 40?GPa. In this study, the properties of the tungsten boride WB_x coatings deposited by radio frequency magnetron sputtering were investigated. The sputtering was performed from specially prepared targets that were composed of boron and tungsten mixed in a molar ratio of 2.5 and sintered in Spark Plasma Sintering (SPS) process. WB films were deposited on silicon (100) and stainless steel 304 substrates at temperatures of 23 ÷ 770?°C. Microstructure, chemical and phase composition were investigated by using Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD), respectively. The mechanical properties like Vickers hardness and Young's modulus were obtained by using nanoindentation test at a load of 5 ÷ 100 mN. The friction coefficient and wear resistance of αWB coatings were investigated in scratch test and reciprocal sliding wear instrumentation. Moreover, in order to investigate thermal properties, the αWB films were annealed at 1000?°C in argon/air for 1?h and at 250?°C for 2?h in air atmosphere. Results of our research confirm that αWB coatings can be considered as an alternative to superhard materials in the production of wear resistant, long-lasting tools.     

Characteristics of aluminum films prepared by metalorganic chemical vapor deposition using dimethylethylamine alane on the plasma-pretreated TiN surfaces

Aluminum films were prepared on H₂-plasma pretreated TiN substrates at deposition temperatures of 60-250 °C by metallorganic chemical vapor deposition using dimethylethylamine alane as a precursor. The films were highly pure and the growth rates were 3-50 nm/min, where the lowest deposition temperature was 60 °C. The resistivity was as low as 2.8 μΩcm. High substrate temperatures tended to favor a low resistivity and smooth surface morphology of the films, compared to films with a low temperature at a given thickness. Numerous empty pores appeared in the Al films deposited at a temperature below 150 °C when the film thickness exceeded 200 nm. The number of these pores tended to increase with decrease in temperature. However, in films deposited at temperatures above 200 °C, there were no pores and the large grains were interconnected to a high degree. Higher deposition temperatures yielded a greater preference of the (111) orientation of Al films.     

Low‐Temperature Deposition of Hexagonal Boron Nitride via Sequential Injection of Triethylboron and N2/H2 Plasma

Hexagonal boron nitride (hBN) thin films were deposited on silicon and quartz substrates using sequential exposures of triethylboron and N₂/H₂ plasma in a hollow‐cathode plasma‐assisted atomic layer deposition reactor at low temperatures (≤450°C). A non‐saturating film deposition rate was observed for substrate temperatures above 250°C. BN films were characterized for their chemical composition, crystallinity, surface morphology, and optical properties. X‐ray photoelectron spectroscopy (XPS) depicted the peaks of boron, nitrogen, carbon, and oxygen at the film surface. B 1s and N 1s high‐resolution XPS spectra confirmed the presence of BN with peaks located at 190.8 and 398.3 eV, respectively. As deposited films were polycrystalline, single‐phase hBN irrespective of the deposition temperature. Absorption spectra exhibited an optical band edge at ~5.25 eV and an optical transmittance greater than 90% in the visible region of the spectrum. Refractive index of the hBN film deposited at 450°C was 1.60 at 550 nm, which increased to 1.64 after postdeposition annealing at 800°C for 30 min. These results represent the first demonstration of hBN deposition using low‐temperature hollow‐cathode plasma‐assisted sequential deposition technique.