Ion beam synthesis of the diamond like carbon films for nanoimprint lithography applications

Ion beam deposited hydrogenated undoped as well as SiO_x (SiO_x + N₂, SiO_x + Ar) doped DLC thin films were deposited and evaluated as possible anti-adhesive layers for nanoimprint lithography. Film surface contact angle with water was investigated as a measure of the surface free energy and anti-sticking properties. Contact angle of the DLC films was independent of SiO_x doping and ion beam energy. Air-annealing resistance in terms of the contact angle with water of the synthesized diamond like carbon films was investigated. Optical transmittance spectra of the DLC films in UV-VIS range were measured to investigate it as possible anti-sticking layers for UV imprint lithography applications. DLC films with the most promising combination of the UV absorption and anti-sticking properties were revealed. Preliminary imprint tests with uncoated and thin DLC film coated hot imprint stamps were performed.     

Hydrophobic properties of the ion beam deposited DLC films containing SiOx

Diamond like carbon (DLC) films received considerable interest due to outstanding mechanical and tribological properties as well as chemical inertness and hydrophobicity. That combination is particularly interesting for possible application of the DLC as anti-sticking layers in novel lithographic techniques such as nanoimprint lithography, because Si, quartz and Ni - the most often used materials for imprint stamp formation - have high surface energy and, as a result, bad anti-adhesive properties. In present study, SiO_x containing DLC thin films were synthesized from hexamethyldisiloxane vapor and hydrogen gas mixture by direct ion beam deposition. Anti-sticking properties of the grown DLC thin films were evaluated measuring surface contact angle with water. Chemical composition and structure of the deposited films were investigated by X-ray photoelectron spectroscopy and FTIR spectrometry. Morphology of the films was measured by atomic force microscopy. Effects of hexamethyldisiloxane flux on structure, anti-sticking properties and surface morphology of the SiO_x containing DLC thin films were defined.     

SiOx-doped DLC films: Charge transport, dielectric properties and structure

In the present study, SiO_x-doped diamond-like carbon (DLC) films were synthesized by ion beam deposition on different substrates. Electrical properties, morphology and structure of the DLC films were investigated. Poole-Frenkel emission was the main carrier transport mechanism in all investigated metal-SiO_x-doped DLC-metal samples. Dielectric properties of the samples were dependent on both the bottom and top electrode metal. The trans-polyacetylene chain vibrations detected from the Raman spectra have been observed for all the SiO_x-doped DLC films. Different dielectric properties of the film deposited onto the different metal interlayers were explained both by different roughness of the metal films and by different structure of the ion beam-synthesized SiO_x-doped DLC films.     

Effects of oxygen partial pressure and ion doping on the ferroelectricity and microstructures of sputter-deposited Bi3.25La0.75Ti3O12 films

The effects of oxygen partial pressure during deposition and V and P doping on the microstructures and ferroelectricity of sputter-deposited Bi_3.25La_0.75Ti₃O₁₂ (BLT) films on Pt/SiO₂/Si(100) were studied. At the deposition pressure of 4 mTorr the O₂/(Ar+O₂) ratio in the range of 0.4–0.5 allowed the films to achieve a larger remnant polarization (2P_r). For the (Bi_3.25La_0.75)(Ti_3−xV_x)O₁₂ films, the 2P_r first increases with increasing the V concentration (x) up to 0.03, then gradually decreases in the range of x=0.05–0.1 and drastically decreases at x=0.15. The doping of V into the BLT films can simultaneously induce two contrary effects on the 2P_r, i.e., reducing the amount of oxygen vacancies and decreasing the grain size, which result in the improvement and degradation of 2P_r, respectively. The two effects are similar to those induced by the factor of oxygen partial pressure during deposition. The degradation of 2P_r for the P-doped BLT films can be ascribed to the dissociation of BiO bonds and reduction of grain size due to P doping.     

Effects of ambient oxygen pressures and substrate temperatures in pulsed laser deposited Zn0.85Li0.15O thin films

Li doped zinc oxide Zn_1−xLi_xO (x = 0.15) thin films were grown by using the pulsed laser deposition method. The depositions were done onto Pt(111)/Ti/SiO₂/Si(100) substrate set at temperatures ranging from 300 °C to 700 °C, with varying the ambient O₂ pressure range of 3-20 mTorr. The effects of substrate temperatures and ambient O₂ pressures on the surface morphology and structural properties of the Zn_0.85Li_0.15O thin films were investigated by using the scanning probe microscopy and X-ray diffraction spectra, respectively. Also the chemical structures of the films were investigated by observing the X-ray photoelectron spectra of the core and shallower levels. We observed the deep blue PL emissions centered at about 390 nm (3.20 eV) from the Zn_0.85Li_0.15O thin films. It was investigated with respect to the ambient O₂ pressures during the deposition. It is considered that the deep blue PL emission in the Zn_0.85Li_0.15O thin film may be related to the incorporation of oxygen vacancies.     

Metal-doped diamond-like carbon films synthesized by filter-arc deposition

Diamond-like carbon (DLC) thin films are extensively utilized in the semiconductor, electric and cutting machine industries owing to their high hardness, high elastic modulus, low friction coefficients and high chemical stability. DLC films are prepared by ion beam-assisted deposition (BAD), sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), cathodic arc evaporation (CAE), and filter arc deposition (FAD). The major drawbacks of these methods are the degraded hardness associated with the low sp³/sp² bonding ratio, the rough surface and poor adhesion caused by the presence of particles. In this study, a self-developed filter arc deposition (FAD) system was employed to prepare metal-containing DLC films with a low particle density. The relationships between the DLC film properties, such as film structure, surface morphology and mechanical behavior, with variation of substrate bias and target current, are examined. Experimental results demonstrate that FAD-DLC films have a lower ratio, suggesting that FAD-DLC films have a greater sp³ bonding than the CAE-DLC films. FAD-DLC films also exhibit a low friction coefficient of 0.14 and half of the number of surface particles as in the CAE-DLC films. Introducing a CrN interfacial layer between the substrate and the DLC films enables the magnetic field strength of the filter to be controlled to improve the adhesion and effectively eliminate the contaminating particles. Accordingly, the FAD system improves the tribological properties of the DLC films.     

Adsorptive properties of albumin, fibrinogen, and γ-globulin on fluorinated diamond-like carbon films coated on PTFE

Fluorinated diamond-like carbon (F-DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapor deposition (CVD) by changing the ratio of tetrafluoromethane (CF₄) and methane (CH₄). To enhance the adhesion strength of the F-DLC film to the PTFE substrate, the PTFE surface was modified with a N₂ plasma pre-treatment. XPS analysis of the films showed that the C–C bond decreased with increases in the CF₄ ratio, whereas the C–F bond increased with the CF₄ ratio. The F/C ratio of the film also increased with the CF₄ ratio. The pull-out test showed that the adhesion strengths of the films (CF₄-0–60%) were improved with the plasma pre-treatment. In the film without the plasma pre-treatment, adhesion strength increased with the CF₄ ratio. In contrast, in the case with the plasma pre-treatment, the adhesion strength of the F-DLC film decreased with the increased CF₄ ratio. Regarding the adsorption of albumin, fibrinogen, and γ-globulin, the amount of adsorbed albumin on the film decreased with an increasing CF₄ ratio, and the amount of adsorbed fibrinogen and γ-globulin increased with the CF₄ ratio. The CF₄-0% DLC film showed the most adsorbed albumin and the least adsorbed fibrinogen and γ-globulin. This indicates that the CF₄-0% DLC film has higher anti-thrombogenicity than the F-DLC film.     

Deposition of boron doped DLC films on TiNb and characterization of their mechanical properties and blood compatibility

Abstract

Diamond-like carbon (DLC) material is used in blood contacting devices as the surface coating material because of the antithrombogenicity behavior which helps to inhibit platelet adhesion and activation. In this study, DLC films were doped with boron during pulsed plasma chemical vapor deposition (CVD) to improve the blood compatibility. The ratio of boron to carbon (B/C) was varied from 0 to 0.4 in the film by adjusting the flow rate of trimethylboron and acetylene. Tribological tests indicated that boron doping with a low B/C ratio of 0.03 is beneficial for reducing friction (μ = 0.1), lowering hardness and slightly increasing wear rate compared to undoped DLC films. The B/C ratio in the film of 0.03 and 0.4 exhibited highly hydrophilic surface owing to their high wettability and high surface energy. An in vitro platelet adhesion experiment was conducted to compare the blood compatibility of TiNb substrates before and after coating with undoped and boron doped DLC. Films with highly hydrophilic surface enhanced the blood compatibility of TiNb, and the best results were obtained for DLC with the B/C ratio of 0.03. Boron doped DLC films are promising surface coatings for blood contacting devices.     

Vibrational and AFM studies of adsorption of glycine on DLC and silicon-doped DLC

A better understanding of protein adsorption onto surfaces of materials is required to control biocompatibility and bioactivity. Diamond-like carbon (DLC) is known to have excellent biocompatibility. Various samples of a-C:H and silicon-doped a-C:H thin films (Si-DLC) were deposited onto silicon substrates using plasma-enhanced chemical vapour deposition (PECVD). Subsequently, the adsorption of the simplest amino acid glycine onto the surfaces of the thin films was investigated to elucidate the mechanisms involved in protein adhesion. The physicochemical characteristics of the surfaces, before and after adsorption of glycine, were investigated using Raman spectroscopy and atomic force microscopy (AFM). The Raman study highlighted a slight decrease in the I _D/I _G ratio with increasing the silicon dopant levels. Following exposure to glycine solutions, the presence of bands at ~1735 and ~1200 cm⁻¹ indicates that the adsorption of glycine onto the surfaces has taken place. Glycine was bound to the surfaces via both deprotonated carboxyl and protonated amino groups whilst, as the silicon content in the DLC film increased the adsorption of glycine decreased. AFM analysis showed that the surface roughness increased following exposure to glycine. These results show that at low silicon doping the adsorption of the amino acid was enhanced whilst increased doping levels led to a reduced adsorption compared to undoped DLC. Therefore, doping of DLC may provide an approach to control the protein adsorption.     

Preparation and characterization of DLC/SiO2/Al2O3 nanofiltration membrane

High quality ceramic thin films were fabricated by thin film deposition process in semiconductor field in order to fabricate high performance carbon/SiO ₂ /Al ₂ O₃ membrane. α-Al ₂ O ₃ substrate was used as a supporting material. A severe thermal stress and rough surface for active ceramic top layer such as zeolite were observed. To overcome thermal stress, intermediate layer of SiO₂ and diamond-like carbon (DLC) thin film were used. SiO ₂ and DLC thin films on porous alumina support were deposited using plasma-enhanced chemical vapour deposition (PECVD). Homogeneous and smooth surfaces and interfaces of DLC/SiO ₂ /Al ₂ O ₃ membrane were observed by FESEM. The phases of DLC and SiO ₂ thin films were identified by X-ray diffraction pattern. Gas permeabilities of the nanofiltration membrane with DLC/SiO ₂ /Al ₂ O ₃ were observed at various annealing temperatures. Mixed gas permeability of the membrane with 1 μm-thick SiO₂ and 2 μm-thick DLC thin film annealed at 200 °C was ～18 ccm at 1018 mb back pressure.     

Surface energy modification of SiOxCyHz film using PECVD by controlling the plasma processes for OMCTS (Si4O4C8H24) precursor

SiO_x films produced from octamethylycyclodisiloxane (Si₄O₄C₈H₂₄, OMCTS) with oxygen carrier gas have a low contact angle. The surface energy of the SiO_x films can be changed by controlling the plasma process. SiO_xC_yH_z films were deposited on polycarbonate substrates by plasma enhanced chemical vapor deposition using OMCTS without oxygen carrier gas. The input power in the radio frequency plasma was changed to optimize the surface energy of the resulting SiO_xC_yH_z film. The plasma diagnostics, surface energy and surface morphology were characterized by optical emission spectrometry, contact angle measurements and atomic force microscopy, respectively. The chemical properties of the coatings were examined by Fourier transform infrared spectroscopy. The surface energy of the SiO_xC_yH_z films produced using a room temperature plasma process could be controlled by employing the appropriate intensity of excited neutrals, ionized atoms, molecules and energy (input rf power and bias), as well as the suitable dissociation of OMCTS.     

Plasma properties of CrOx films synthesized by a cathodic arc evaporation process

The plasma in a cathodic arc evaporation process used for the deposition of Cr_1−xO_x films was studied by an optical emission spectroscopy (OES). With the introduction of Ar and oxygen into the chamber at deposition pressures from 0.7 Pa to 2.7 Pa, high density of evaporated chromium catalyzes the decomposition of oxygen reactive gas, and induces the formation of Cr_1−xO_x films. Optical emission spectra including atomic and ionized Cr, excited and ionized oxygen revealed that excitation, ionization and charge transfer reactions of the Cr-O plasma occurred during the Cr_1−xO_x deposition process. A simplified empirical model which incorporates the relevant atomic processes in the gas phase with the chemical composition and deposition rate of the deposited Cr_1−xO_x coating was developed. Rhombohedral Cr₂O₃ and tetragonal CrO₂ were observed in the Cr_1−xO_x coatings deposited at higher pressure than 1.3 Pa. The Cr_1−xO_x coating depicted a dense and compact microstructure with well-attached interface.     

Characteristics of SiOx thin films deposited by atmospheric pressure chemical vapor deposition as a function of HMDS/O2 flow rate

SiO₂-like thin films were deposited using a modified dielectric barrier discharge with a gas mixture of hexamethyldisilazane (HMDS)/O₂/He/Ar and their film characteristics were investigated as functions of the HMDS and O₂ flow rates. As the HMDS flow rate was increased, higher amounts of Si-(CH₃)_x bonds and lower amounts of Si-OH bonds were observed in the deposited SiO_x, due to the increase in the amount of the less dissociated HMDS, which also caused an increase of the surface roughness. The addition and increase of the oxygen flow to HMDS/He/Ar brought the stoichiometry of SiO_x close to SiO₂ and decreased the surface roughness by decreasing the amount of Si-(CH₃)_x bonds through the increased decomposition and oxidation of HMDS, even though the deposition rate was decreased. However, when the O₂ flow rate was higher than a certain threshold, the surface roughness increased again, possibly due to the decrease in the extent of HMDS dissociation caused by the decreased plasma density at the higher oxygen flow rate. By using an optimized gas mixture of HMDS (150 sccm)/O₂ (14 slm)/He (5 slm)/Ar (3 slm), SiO₂-like thin films with a very low impurity level and having a smooth surface could be obtained with a deposition rate of approximately 42.7 nm/min.     

Sputter deposition of dielectric films using a magnetic field for protection from high energy electrons

Thin films of SiO₂ and Al₂O₃ were prepared by r.f. sputtering. For protection from energetic electrons in the plasma, deposition was carried out in an area protected by a magnetic field of appropriate strength.The deposited films are free of pinholes, show sound insulation characteristics and have good adhesion to the substrate.     

Preparation of B2O3-P2O5-SiO2 coating films by the sol-gel method

ThexB₂O₃ · (20-x) P₂O₅ · 80SiO₂ (in mol%) glass films withx=0, 10 and 20 have been prepared from metal alkoxides by carrying out the coating in a dry atmosphere. These coating films have shown a larger value of load at scratch and a smaller shrinkage during heat-treatment by replacing P₂O₅ in the films with B₂O₃. It has been found that B₂O₃ more effectively reduces the glass transition temperature of SiO₂ glass than P₂O₅. The concentrations of sodium ions, which migrated from soda-lime-silica glass substrates during the film formation, were higher in phosphosilicate and borophosphosilicate films than in borosilicate and pure silica films. This finding should be ascribed to the gettering effects of phosphorus for sodium ions.     

Atmospheric pressure PECVD of SiO2 thin film at a low temperature using HMDS/O2/He/Ar

SiO₂-like thin films were deposited at a low temperature (< 50 °C) by a remote-type, atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) using a pin-to-plate-type, dielectric barrier discharge with gas mixtures containing hexamethyldisilazane (HMDS)/O₂/He/Ar. The film characteristics were investigated according to the HMDS and O₂ flow rates. To obtain a more SiO₂-like thin film, an adequate combination of HMDS and oxygen flow rates was required to remove the -(CH₃)_x bonding in the HMDS and to oxidize the Si in HMDS effectively. At the optimized flow rates, the surface roughness of the SiO₂-like thin film was also the lowest. By using HMDS (50 sccm) and O₂ (500 sccm) flow rates in the gas mixture of HMDS/O₂/He (2 slm)/Ar (600 sccm), SiO₂-like thin films with a low impurity (< 6.35% C) were obtained at a deposition rate of approximately 10.7 nm/min.     

Amorphous carbon buffer layers for separating free gallium nitride films

The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al₂O₃) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the “GaN film–Al₂O₃” substrate interface decreases, which facilitates separation of the GaN layers.     

Characterization of the silicon oxide thin films deposited on polyethylene terephthalate substrates by radio frequency reactive magnetron sputtering

Transparent silicon oxide films were deposited on polyethylene terephthalate substrates by means of reactive magnetron sputtering with a mixture of argon and oxygen gases. The influences of process parameters, including the oxygen flow ratio, work pressure, radio frequency (RF) power density and deposition time, on the film properties, such as: deposition rate, morphology, surface roughness, water vapor/oxygen transmission rate and flexibility, were investigated. The experimental results show that the SiO_x films deposited at RF power density of 4.9 W/cm², work pressure of 0.27 Pa and oxygen flow ratio of 40% have better performance in preventing the permeation of water vapor and oxygen. Cracks are produced in the SiO_x films after the flexion of more than 100 cycles. The minimum transmission rates of water vapor and oxygen were found to be 2.6 g/m² day atm and 15.4 cc/m² day atm, respectively.     

ZnO/Al2O3 coatings for the photoprotection of polycarbonate

ZnO and ZnO/Al₂O₃ thin films were deposited by r.f. magnetron sputtering on polycarbonate (PC) films in order to protect this polymer against photodegradation. The composition, structure and optical properties of the ceramic coatings were characterised. CO₂-plasma treatments were applied to PC in order to improve the coating adhesion. The PC surface energy was characterised by wettability measurements and the chemical bonds were analysed by XPS.It was found that ZnO coatings improve the stability of PC to UV radiations and that an intermediate alumina coating inhibits the photocatalytic oxidation of PC at the PC/ZnO interface. Additionally an external alumina coating brings a high hardness to the coating.     

The effect of defects on the optical nonlinearity of thermally poled SiOx thin films

Defects were deliberately induced in SiO_x thin films during their deposition using a helicon plasma activated reactive evaporation technique. The films were thermally poled and the poling induced second-order optical nonlinearity was investigated by measuring the second harmonic generation of the samples. It was found that oxygen-rich SiO_x thin films containing mainly peroxy radicals enabled a much larger optical nonlinearity than stoichiometric SiO₂ films after poling, and their optical nonlinearity was long-time stable; while silicon-rich SiO_x thin films containing mainly oxygen vacancy defects presented a smaller and unstable optical nonlinearity after poling.