Effects of nitrogen doping on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like-carbon films

Nitrogen-doped diamond-like carbon (DLC) or amorphous hydrogenated carbon (a-C:H) films were grown by plasma enhanced chemical vapor deposition using methane and nitrogen gases as precursors. The effects of nitrogen trifluoride (NF₃) on these nitrogen-doped DLC films were also investigated. The deposition rate decreases sharply with the addition of nitrogen in the absence of NFF₃ due to dilution, while it increases in the presence of NFF₃ due, presumably, to the reduction of activated hydrogen species by the fluorine radical (F϶. X-ray photoelectron spectra reveal a nitrogen concentration in the range of 9.3 to 13.8% in these DLC films with a C Is electron binding energy of 287-288 eV, indicating the diamond-like structure. Infrared spectra of DLC films indicate the presence of amino groups (N-H) and nitrile and/or isonitrile (C= N) groups giving strong evidence of sp carbon. Diamond like carbon films deposited in CHF₄ +NF₄ (with and without NFF₃) have a lower refractive index, a lower bulk resistivity, and a lower optical bandgap than films deposited using CHF₄ due to a lower hydrogen content in the films. Moreover, the bulk resistivity of these films decreases by over four orders of magnitude and the optical bandgap decreases from 2.65 eV to about 0.75 eV following annealing at a temperature of 500°C.     

Rectifying Characteristics of Heterostructures with Diamond and Diamond- Like Carbon Films

Semiconducting diamond-like carbon (DLC) films were deposited on n-type Si substrates by the electrodeposition method, and diamond films were formed on the carbon film and/or a Si substrate directly by the hot-filament chemical vapor deposition method. Rectifying heterostructures of Al/DLC/Si/Al, Al/diamond/Si/ Al, and Al/diamond/DLC/Si/Al were fabricated. The Al/DLC/Si/Al structure has a bulk resistivity of 6 × 10⁵ Ω-cm and a rectification ratio close to two orders of magnitude. Experimental results demonstrate that the Al/diamond/DLC/Si/Al bilayer structure can significantly reduce the leakage current to about 10^-10 A and increase the rectification ratio by 3-5 orders of magnitude at 5 V, compared with that of the other two structures. Possible reasons are given for the changes of the rectifying characteristic.     

High density plasma chemical vapor deposition of diamond-like carbon films

This work was based on the studies of the influence of the plasma process on the characteristics of diamond-like carbon (DLC) films deposited by high density plasma chemical vapor deposition (HDP-CVD). DLC is a material that shows several good characteristics like high electrical resistivity, lower dielectric constant, high breakdown field, lower stress, high density, and hardness and chemical inertness. This material is important actually in mechanic, optic, and chemistry and mainly in microelectronic areas. For microelectronic process the best results were obtained by plasma of pure methane: low dielectric constant (1.7) and high resistivity 5×10¹³ Ω cm.     

Electrical properties of carbon nitride thin films: Role of morphology and hydrogen content

The influence of hydrogen content and ambient humidity on the electrical properties of carbon nitride (CN_x) films deposited by reactive magnetron sputtering from a graphite target in Ar discharges mixed with N₂ and H₂ at a substrate temperature of 350°C have been investigated. Carbon films deposited in pure Ar exhibit a dark resistivity at room temperature of ∼4 × 10⁻² Ωcm, while the resistivity is one order of magnitude lower for CN_0.25 films deposited in pure N₂, due to their denser morphology. The increasing H₂ fraction in the discharge gas leads to an increased resistivity for all gas mixtures. This is most pronounced for the nitrogen-free films deposited in an Ar/H₂ mixture, where the resistivity increases by over four orders of magnitude. This can be related to a decreased electron mobility as H inhibits the formation of double bonds. After exposure to air, the resistivity increases with time through two different diffusion regimes. The measured electrical properties of the films are related to the apparent film microstructure, bonding nature, and ambient humidity.     

The influence of rf induced bias on the properties of diamond-like carbon films prepared using ECR-CVD

The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron resonance chemical vapor deposition (ECR-CVD) method with radio-frequency (rf) bias is reported. The structural characteristics of the DLC films were characterized using Raman spectroscopy. The effects of the self-generated dc bias resulting from the rf power on the optical gap, Raman spectra, infrared (IR) absorption, and film hardness in depositions carried out at 7 and 15 mTorr process pressures were investigated. Under conditions of 100 W microwave power and for dc bias variation ranging from −10 to −200 V, there is evidence from Raman scattering analysis to show an increase in the DLC-like characteristic in films deposited at low dc bias at both process pressures. The variation of the D and G line peak position and intergrated intensity ratio (I_D/I_G) in the Raman spectra correlates well with the film hardness profile. There does not seem to be a relationship between the variation of the C-H absorption peak intensity in the IR spectra (bonded hydrogen content) and the optical gap, although films with the highest optical gap tend to show a relatively higher C-H absorption peak intensity in the IR spectra. Films deposited at high dc bias showed a reduction in the C-H infrared absorption, suggesting a reduction in the bonded hydrogen content.     

Atomic layer deposition of titanium nitride from TDMAT precursor

TiN was grown by atomic layer deposition (ALD) from tetrakis(dimethylamino)titanium (TDMAT). Both thermal and plasma enhanced processes were studied, with N₂ and NH₃ as reactive gases. Using an optimized thermal ammonia based process, a growth rate of 0.06 nm/cycle and a resistivity of 53 × 10³ μΩ cm were achieved. With an optimized plasma enhanced NH₃ process, a growth rate of 0.08 nm/cycle and a resistivity of 180 μΩ cm could be obtained. X-ray photo electron spectroscopy (XPS) showed that the difference in resistivity correlates with the purity of the deposited films. The high resistivity of thermal ALD films is caused by oxygen (37%) and carbon (9%) contamination. For the film deposited with optimized plasma conditions, impurity levels below 6% could be achieved. The copper diffusion barrier properties of the TiN films were determined by in-situ X-ray diffraction (XRD) and were found to be as good as or better than those of films deposited with physical vapor deposition (PVD).     

Efficient Outdiffusion of Hydrogen from Mg-Doped Nitrides by NF<Subscript>3</Subscript> Annealing

High concentration (more than 1 × 10¹⁸ cm⁻³) of hydrogen atoms remaining in Mg-doped GaN epitaxial layers grown by metalorganic chemical vapor deposition even after conventional annealing in N₂ ambient could induce degradation in GaN-based devices containing Mg-doped layers. In this study, by annealing Mg-doped nitrides in NF₃ ambient, we successfully reduced residual hydrogen below mid-10¹⁷ cm⁻³, which is much smaller than by N₂ annealing. NF₃ annealing enhances outdiffusion of hydrogen from the bulk, which is possibly because the nitrogen and fluorine radicals decomposed from NF₃ accelerate desorption of hydrogen adatoms from the surface. The proposed method for Mg activation would improve the reliability of GaN-based light-emitting diodes and laser diodes.     

Pulsed laser deposition of titanium nitride and diamond-like carbon films on polymers

We have investigated the deposition of titanium nitride (TiN) and diamond-like carbon (DLC ) films on polymethylmethacrylate (PMMA) substrates using pulsed laser deposition (PLD) technique. The TiN and diamond-like films were deposited by laser ablation (KrF excimer laser λ = 248 nm, pulse duration τ～25 × 10^?9 s, energy density ～2?15J/cm²) of TiN and graphite targets, respectively, at room temperature. These films were characterized by transmission electron microscopy, scanning electron microscopy, x-ray diffraction, Auger electron spectroscopy, UV-visible absorption spectroscopy, and Raman spectroscopy. The TiN films were smooth and found to be polycrystalline with average grain size of 120Å. The diamond-like carbon films were amorphous with a characteristic Raman peak at 1550 cm^?1. The TiN films are highly adherent to the polymer substrates as compare to DLC films. The adhesion strength of DLC films on polymers was increased by interposing thin TiN layer (200Å) on polymers byin-situ pulsed laser deposition. The DLC films were found to be amorphous with good adhesion to TiN/PMMA substrates.     

Effects of DC power on the properties of DLC coatings on the OPC drum

Diamond-like carbon (DLC) films were deposited on the organic photoconductor (OPC) drum of the laser printer using the dc-remote plasma enhancement chemical vapor deposition (RPECVD) method. Only methane (CH₄) was used as a source gas for DLC coating. The transmittance of the DLC coatings is over 90% and the hardness of the DLC film (130 nm thick) coated OPC drum is higher than 1,000 H_v. Effects of dc-power on the physical properties of the DLC film and the electrophotographic properties of the DLC coated OPC drum were investigated. The hardness and the deposition rate of the DLC film deposited on the OPC drum increased but the transmittance and the surface roughness nearly did not change with increasing the dc power of the dc-RPECVD. The residual potential, the acceptance voltage, and the dark decay rate significantly increase but the photodischarge rate decreases with increasing the dc power of the RPECVD. The optimum dc power is 8.6 kW (950 V, 6A). The friction coefficient of the OPC drum is also lowered by DLC coating. In addition, it was found that the DLC deposition rate could be doubled by imposing magnetic fields around the cathode.     

Moisture absorption studies of fluorocarbon films deposited from pentafluoroethane and octafluorocyclobutane plasmas

The moisture absorption and diffusion characteristics of fluorocarbon films deposited from pentafluoroethane (PFE) and octafluorocyclobutane C₄F₈ plasmas are presented. The moisture absorption studies were carried out using a quartz crystal microbalance in a controlled environment. X-ray photoelectron spectroscopy and Fourier transform infrared (IR) spectroscopy were used to monitor the changes in bulk and surface chemical structure and composition of the deposited films. The equilibrium moisture uptake at relative humidity >90% was lower than 0.13 wt.% for films deposited from PFE or C₄F₈ monomers. Humidity cycling measurements showed no moisture chemisorption in the deposited films. Attenuated total reflectance infrared spectroscopy (ATR-IR) spectra of the deposited films indicated negligible change in the bulk composition of the deposited films. The estimated diffusivities of water in the deposited fluorocarbon films were of the order of 10⁻¹⁰ cm²/sec, and films deposited from C₄F₈ monomer showed higher diffusivity as compared to films deposited from PFE monomer. The equilibrium moisture uptake is affected by the presence of polar groups, the F/C ratio, and the O/C ratio. The relatively high diffusivity of water in the fluorocarbon films is attributed to the lack of polar groups in the deposited films. Adsorption onto the surface followed by diffusion into the bulk is proposed as the mechanism for moisture absorption in the fluorocarbon films. Finally, the moisture uptake of the fluorocarbon and hydrofluorocarbon films is compared to that of a conventionally used microelectronic polymer, polyimide (PI 2611), in order to evaluate the effect of polar groups and fluorine content on diffusion and equilibrium moisture uptake.     

Structural and electrical properties of plasma-deposited silicon nitride from SiH4-N2 gas mixture

Plasma-deposited silicon nitride films were produced from SiH₄-N₂ gas mixture. Their composition, chemical bonds, and electrical properties were investigated by varying the deposition conditions. The silicon nitride films from SiH₄-N₂ gas mixture exhibit (i) less hydrogen, (ii) higher thermal endurance, (iii) higher density, and (iv) smaller etching rate than those of the films deposited from SiH₄, and NH₃ gas mixture. These results can be partly attributed to lower hydrogen concentration. As the Si/N ratio approaches the stoichiometric value, 0.75, the resistivity and the breakdown strength are increased. They are 10¹⁵Ωcm and 9MV/cm, respectively, at Si/N≃0.85. Interface state density between silicon and silicon nitride layers is as low as 1& #x223C; 5xl0¹¹cm⁻² eV⁻¹. On leave from The Northwest Telecommunication Engineering Institute, Xi’an, The People’s Republic of China.     

Optical properties of ZnO thin films grown on diamond-like carbon by pulsed laser deposition

ZnO/diamond-like carbon(DLC)thin films are deposited by pulsed laser deposition(PLD),and the room-temperature photoluminescence(PL)is investigated.Using a fluorescence spectrophotometer,we obtain the PL spectra of DLC/Si and ZnO/Si thin films deposited at different substrate temperatures.The ZnO/DLC thin films show a broadband emission almost containing the entire visible spectrum.The Gaussian fitting curves of PL spectra reveal that the visible emission of ZnO/DLC thin films consists of three peaks centered at 381 nm,526 nm and 682 nm,which are attributed to the radiative recombination of ZnO and DLC,respectively.The Commission International de l,Eclairage(CIE)1931(x,y)chromaticity space of ZnO/DLC thin films indicates that the visible PL spectrum is very close to the standard white-light region.     

The effects of carrier gas and substrate temperature on ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on glass substrates in the temperature range of 350–470 °C under an atmosphere of compressed air or nitrogen (N₂) by using ultrasonic spray pyrolysis technique. Structural, electrical and optical properties of the ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical two-probe and optical transmittance measurements. The ZnO films deposited in the range of 350–430 °C were polycrystalline with the wurtzite hexagonal structure having preferred orientation depending on the substrate temperature. The ZnO films deposited below 400 °C had a preferred (100) orientation while those deposited above 400 °C mostly had a preferred (002) orientation. The resistivity values of ZnO films depended on the types of carrier gas. The ZnO thin films deposited under N₂ atmosphere in the range of 370–410 °C showed dense surface morphologies and resistivity values of 0.6–1.1 Ω-cm, a few orders of magnitude lower than those deposited under compressed air. Hydrogen substition in ZnO possibly contributed to decreasing resistivity in ZnO thin films deposited under N₂ gas. The Hall measurements showed that the behavior of ZnO films deposited at 410 °C under the N₂ atmosphere was n-type with a carrier density of 8.9–9.2×10¹⁶ cm^-3 and mobility of ～70 cm²/Vs. ZnO thin films showed transmission values at 550 nm wavelength in a range of 70–80%. The values of band gaps extrapolated from the transmission results showed bandgap shrinkage in an order of milli electron volts in ZnO films deposited under N₂ compared to those deposited under compressed air. The calculation showed that the bandgap reduction was possibly a result of carrier–carrier interactions.     

Effect of Sputtered ZnO Layers on Behavior of Thin-Film Transistors Deposited at Room Temperature in a Nonreactive Atmosphere

In this work we present the electrical characterization of ZnO-based thin-film transistors fabricated at room temperature. The ZnO films were deposited by radiofrequency magnetron sputtering at variable argon pressure (3 mTorr to 10 mTorr) at room temperature. The sputtered ZnO films were polycrystalline with hexagonal structure and electrical resistivity ranging from 10¹ Ω cm to 10⁸ Ω cm for films deposited from 3 mTorr to 10 mTorr. The trend in the electrical behavior of the devices was found to be due to the variation of the electron concentration of the ZnO films. The devices with better performance showed a field-effect mobility of 2.9 cm²/Vs, threshold voltage of 20 V, I _on/I _off ≈ 10⁶, and electrical resistivity of ~10⁸ Ω cm. In addition, linear behavior of I _on/I _off with deposition pressure was observed. The lowest I _on/I _off ratio (~2) was calculated for devices with ZnO layers deposited at 3 mTorr, and the highest ratio (~10⁶) for devices processed at 10 mTorr. Hall-effect measurements were performed on ZnO films showing the lowest resistivity. The layer grown at 3 mTorr showed a Hall mobility of μ _H = 8.9 cm²/Vs and carrier concentration of n = 4.2 × 10¹⁶ cm⁻³ with resistivity of ρ = 31.8 Ω cm. For films deposited at 5 mTorr, the Hall mobility, carrier concentration, and resistivity were μ _H = 7.9 cm²/Vs, n = 3.4 × 10¹⁶ cm⁻³, and ρ = 38.4 Ω cm, respectively. Films deposited at 8 mTorr and 10 mTorr could not be measured due to their high resistance.     

Preparation and electrical properties of inas thin films

Thin films of InAs have been deposited on mica substrates through a vacuum evaporation technique by means of controlling the substrate and source temperatures. The films with large crystal grain were found to have the best electrical properties. The maximum electron mobility of 12, 400 cm²/V·sec at room temperature was obtained in an undoped film of 3 Μm thickness at a donor concentration of 3.5 × 10¹⁶ cm⁻³. The temperature dependence of both electron mobility and resistivity of these films was slightly lower than those reported for bulk crystal type InAs.     

Atomic Layer Deposition of Aluminum Nitride Using Tris(diethylamido)aluminum and Hydrazine or Ammonia

Aluminum nitride (AlN _x ) films were obtained by atomic layer deposition (ALD) using tris(diethylamido) aluminum(III) (TDEAA) and hydrazine (N₂H₄) or ammonia (NH₃). The quartz crystal microbalance (QCM) data showed that the surface reactions of TDEAA and N2H4 (or NH₃) at temperatures from 150 to 225°C were self-limiting. The rates of deposition of the nitride film at 200°C for systems with N₂H₄ and NH₃ coincided: ~1.1 Å/cycle. The ALD AlN films obtained at 200°C using hydrazine had higher density (2.36 g/cm³, 72.4% of bulk density) than those obtained with ammonia (2.22 g/cm³, 68%). The elemental analysis of the film deposited using TDEAA/N2H4 at 200°C showed the presence of carbon (~1.4 at %), oxygen (~3.2 at %), and hydrogen (22.6 at %) impurities. The N/Al atomic concentration ratio was ~1.3. The residual impurity content in the case of N₂H₄ was lower than for NH₃. In general, it was confirmed that hydrazine has a more preferable surface thermochemistry than ammonia.     

Diamond-like carbon protective films for organic photoconductors

The deposition of a protective film to increase the hardness of an organic photoconductor (OPC) surface is an effective method of lengthening the lifetime of the OPC. In this work, diamond-like carbon (DLC) protective films were deposited onto OPC samples by the electron cyclotron resonance (ECR)-microwave plasma chemical vapor deposition (MPCVD) method with low substrate temperature. The DLC films were deposited with optimized deposition conditions and exhibited high transmissivity and high electrical resistivity. The films caused a remarkable increase in the hardness of the OPC surface, by a factor of 2.5∼5.4. The acceptance voltage, dark decay rate, photodischarge rate, and contrast potential of the OPC protected by DLC film were improved. These results show DLC is a suitable protective film for OPC.     

Deposition of thin Bi2Te3 and Sb2Te3 films by pulsed laser ablation

Bi₂Te₃ and Sb₂Te₃ films were obtained by pulsed laser ablation. The films were deposited in vacuum (1 × 10⁻⁵ Torr) on single crystal substrates of Al₂O₃ (0001), BaF₂ (111), and fresh cleavages of KCl or NaCl (001) heated to 453–523 K. The films were 10–1500 nm thick. The structures of the bulk material of targets and films were studied by X-ray diffractometry and transmission high-energy electron diffraction, respectively. Electrical properties of the films were measured in the temperature range of 77–300 K. It is shown that the films possess semiconductor properties. Several activation portions are observed in the temperature dependences of resistivity; the energies of activation portions depend on the film thickness and crystallite size.     

Low temperature aluminum oxide deposition using trimethylaluminum

Aluminum oxide films (amorphous and γ-Al₂O₃) have been deposited by the oxidation of trimethy1aluminum. Process parameters have been evaluated and optimized to obtain reasonable growth rates and film properties for deposition temperatures between 300 and 400° C. Values of the dielectric constant (7.5 – 7.8), the dielectric strength (7.5 – 7.9 × 10⁶ V/cm), the index of refraction (1.54 – 1.67), and the resistivity (> 10 ohm-cm) compare favorably with Al₂O₃, films grown with other processes at higher deposition temperatures. Film analysis by secondary ion mass spectrometry identified a distribution of carbon and sodium impurities.     

Effects of annealing on the characteristics of ZnO films deposited in various O2/(O2+Ar) ratios

C-axis oriented ZnO films are deposited on polished diamond substrates in various O₂/(O₂+Ar) ratios using the radio frequency (RF) magnetron sputtering technique and are subsequently annealed in oxygen ambience under the same conditions. Structural, morphologic and electrical properties of ZnO films are characterized by X-ray diffraction (XRD), high-resistance instrument, energy dispersive X-ray spectroscopy (EDS) and scanning electronic microscopy (SEM). As the O₂/(O₂+Ar) ratio increasing from 1/12 to 5/12, the crystallinity of the as grown ZnO films becomes better and the electrical resistivity increases slowly. After annealing, the ZnO films deposited in O₂/(O₂+Ar) =1/12 and 3/12 are improved greatly in crystallinity, and their electrical resistivity is enhanced by two orders of magnitude, while those deposited in O₂/(O₂+Ar) =5/12 are scarcely changed in crystallinity, and their resistivity is only increased by one order. In addition, the ZnO films deposited in O₂/(O₂+Ar) =3/12 and annealed in oxygen are with the best crystal quality and the highest resistivity.