Growth process from amorphous GaN to polycrystalline GaN on Si (111) substrates

Amorphous GaN (a-GaN) films on Si (111) substrates have been deposited by RF magnetron sputtering with GaN powder target. The growth process from amorphous GaN to polycrystalline GaN is studied by XRD, SEM, PL and Raman. XRD data mean that annealing under flowing ammonia at 850-950 °C for 10 min converts a-GaN into polycrystalline GaN (p-GaN). The growth mechanism can be mostly reaction process through N³⁻ in amorphous GaN replaced by N³⁻ of NH₃. Annealing at 1000 °C, the appearance of GaN nanowires can be understood based on the vapor-liquid-solid (VLS) mechanism. In addition, XRD, PL and Raman measurement results indicate that the quality of GaN films increases with increasing temperature. The tensile stress in the films obtained at 1000 °C is attributable to the expansion mismatch between GaN and Si, with the gallium in the film playing a negligible role.     

Reflectance and photoluminescence spectra of as grown and hydrogen and nitrogen incorporated tetrahedral amorphous carbon films deposited using an S bend filtered cathodic vacuum arc process

The study of reflectance and photoluminescence (PL) spectra of as grown and also hydrogen and nitrogen incorporated tetrahedral amorphous carbon (ta-C) films, deposited using an S bend filtered cathodic vacuum arc process is reported here. First the effect of negative substrate bias on the properties of as grown ta-C films and next the effect of varying hydrogen and nitrogen partial pressure at a high substrate bias of − 300 V on the properties of hydrogen and nitrogen incorporated ta-C (ta-C:H and ta-C:N) films are reported for the first time. The values of the optical band gap (E_g) evaluated using the reflectance spectra were found to decrease with the increase of the substrate bias in the as grown ta-C films. Hydrogen incorporation up to 1.9 × 10^− 2 Pa partial pressure in as grown ta-C films increased the values of E_g and beyond which the values of E_g decreased while the nitrogen incorporation up to 3.0 × 10^− 1 Pa partial pressure has no effect on the E_g values. The PL spectra indicated a strong peak at ∼2.66 eV in as grown ta-C films deposited at − 20 V substrate bias. This main peak was found to shift to higher energy with the increase of the substrate bias up to − 200 V and thereafter the PL peak shifted towards the lower energy. Other peak at 3.135 eV starts appearing and this is found to start shifting to higher energy for films deposited at higher substrate bias. The intensity of the main PL peak was enhanced at low temperature and several other peaks started appearing in place of the broad peak at ∼3.16 eV. The peak width and area of both the main peak were found to decrease with the increase of substrate bias in as grown ta-C films and with the increase of the hydrogen and nitrogen partial pressure used in depositing ta-C:H and ta-C:N films. The current models on the source of luminescence in amorphous carbon have been discussed.     

Mechanical properties of amorphous and microcrystalline silicon films

Hydrogen-free amorphous silicon (a-Si) films with thickness of 4.5-6.5 μm were prepared by magnetron sputtering of pure silicon. Mechanical properties (hardness, intrinsic stress, elastic modulus), and film structure (Raman spectra, electron diffraction) were investigated in dependence on the substrate bias and temperature. The increasing negative substrate bias or Ar pressure results in simultaneous reducing compressive stress, the film hardness and elastic modulus. Vacuum annealing or deposition of a-Si films at temperatures up to 600 °C saving amorphous character of the films, results in reducing compressive stress and increasing the hardness and elastic modulus. The latter value was always lower than that for monocrystalline Si(111). The crystalline structure (c-Si) starts to be formed at deposition temperature of ∼ 700 °C. The hardness and elastic modulus of c-Si films were very close to monocrystalline Si(111). Phase transformations observed in the samples at indentation depend not only on the load and loading rate but also on the initial phase of silicon. However, the film hardness is not too sensitive to the presence of phase transformations.     

Cracking behavior of evaporated amorphous silicon films

The residual stress in amorphous silicon films deposited by evaporation is investigated with different substrate temperatures. The stress measured from all the films studied in this paper is tensile. The level of stress decreases from 580 MPa to 120 MPa with increasing substrate temperature from 60 °C to 350 °C. When the film becomes thicker, strain increases and cracks are formed for stress relaxation. 10 µm thick amorphous Si films are deposited at 350 °C without cracks. This cracking behavior is theoretically studied and confirmed by experiment.     

Stress and microstructure evolution during growth of magnetron-sputtered low-mobility metal films: Influence of the nucleation conditions

Large tensile stresses (up to 3 GPa) were previously observed in low-mobility metallic Mo_1 − xSi_x films grown on amorphous Si and they were ascribed to the densification strain at the amorphous-crystalline transition occurring at a critical film thickness. Here, we focus on the influence of the nucleation conditions on the subsequent stress build-up in sputter-deposited Mo_0.84Si_0.16 alloy films. For this purpose, growth was initiated on various underlayers, including amorphous layers and crystalline templates with different lattice mismatch, and the stress evolution was measured in situ during growth using the wafer curvature technique. Tensile stress evolutions were observed on amorphous SiO₂ and (111) Ni underlayers, similarly to the stress behaviour found on amorphous Si. For these series, the films were characterized by large in-plane grain size (~ 500 nm). However, on a (110) Mo buffer layer, a different stress behaviour occurred: after an initial tensile rise ascribed to coherence stress, a reversal towards a compressive steady state stress was observed. A change in film microstructure was also noticed, the typical grain size being ~ 30 nm. The origin of the compressive stress source in the metastable Mo_0.84Si_0.16 alloy grown on (110) Mo is discussed based on the stress evolutions measured at varying deposition rates and Ar working pressures, as well as in comparison with stress evolutions in pure Mo films.     

Structure and optical properties of Zr1−xSixN thin films on sapphire

A series of zirconium silicon nitride (Zr_1−xSi_xN) thin films were grown on r-plane sapphire substrates using reactive RF magnetron co-sputtering of Zr and Si targets in a N₂/Ar plasma. X-ray diffraction pole figure analysis, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), optical microscopy, and optical absorption spectroscopy were used to characterize the film stoichiometries and structures after growth at 200 °C and post-deposition annealing up to 1000 °C in ultra-high vacuum. The atomically clean r-plane sapphire substrates induce high quality (100) heteroepitaxy of ZrN films rather than the (111) orientation observed on steel and silicon substrates, but the addition of Si yields amorphous films at the 200 °C growth temperature. After the annealing treatment, films with Si content x < 0.15 have compressive stress and crystallize into a polycrystalline structure with (100) fiber texture. For x > 0.15, the films are amorphous and remain so even after ultra-high vacuum annealing at 1000 °C. XPS spectra indicate that the bonding changes from covalent to more ionic in character as Si―N bonds form instead of Zr―N bonds. X-ray reflectivity, atomic force microscopy (AFM) and optical microscopy data reveal that after post-deposition annealing the 100 nm thick films have an average roughness < 2 nm, except for Si content near x = 0.15 corresponding to where the film becomes amorphous rather than being polycrystalline. At this stoichiometry, evidence was found for regions of film delamination and hillock formation, which is presumably driven by strain at the interface between the film and sapphire substrate. UV-visible absorption spectra also were found to depend on the film stoichiometry. For the amorphous Si-rich films (x > 0.15), the optical band gap increases with Si content, whereas for Zr-rich films (x < 0.15), there is no band gap and the films are highly conductive.     

Laser-induced amorphization and crystallization on Se80Te20−xPbx thin films

Thin films of glassy alloys of a-Se₈₀Te_20−xPb_x (x=2, 6 and 10) was crystallized in a specially designed sample holder under a vacuum of 10⁻² Pa. The amorphous and crystallized films were induced by pulse laser (wavelength: 337.1 nm, frequency: 10 Hz, pulse duration: 4 ns and pulse energy: 0.963 mJ). After laser irradiation on amorphous and crystalline films: optical band gaps were measured. Crystallization and amorphization of chalcogenide films is accompanied by the change in the optical band gap. The change in optical energy gap could be determined by identification of the transformed phase. This change in the optical band gap may be due to the increase in the grain size and the reduction in the disorder of the system.     

Influence of substrate bias voltage on the microstructure and residual stress of CrN films deposited by medium frequency magnetron sputtering

In this study, CrN films were deposited on stainless steel and Si (1 1 1) substrates via medium frequency magnetron sputtering under a systematic variation of the substrate bias voltage. The influence of the substrate bias voltage on the structural and the mechanical properties of the films were investigated. It is observed that there are two clear regions: (1) below −300 V, and (2) above −300 V. For the former region, the (1 1 1) texture is dominated as the substrate bias voltage is increased to −200 V. The lattice parameter is smaller than that of CrN reported in the ICSD standard (4.140 Å) and the as-deposited films exhibit tensile stress. Meanwhile, the surface roughness decreases and the N concentration show a slow increase. For the latter region, the (2 0 0)-oriented structure is formed. However, the lattice parameter is larger as compared with the value reported in the ICSD standard, and the surface roughness increases and the N concentration decreases obviously. In this case, the compressive stress is obtained.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

Mechanical properties of gradient pulse biased amorphous carbon film

A new method to prepare compositional amorphous carbon (a-C) film termed gradient pulse bias is presented. The a-C film prepared this way showed outstanding mechanical and excellent tribological properties. The hardness and reduced modulus of the film are calculated to be 66 GPa and 320 GPa respectively. A wear rate of 1.3 × 10^− 8 mm³/N m and frictional coefficient of 0.1 was also recorded. The novel film is also compared with multilayered and single layer a-C film prepared using the same system.     

Relative fraction of sp bonding in boron incorporated amorphous carbon films determined by X-ray photoelectron spectroscopy

Boron incorporated amorphous carbon (a-C:B) films were deposited by a filtered cathodic vacuum arc system using various percentage of boron mixed graphite cathodes. X-ray photoelectron spectroscopy (XPS) was employed to determine the properties of the films as a function of boron concentration. Deconvolutions of the XPS C 1s core level spectra were carried out using four different components. The relative fraction of sp³ bonding was then evaluated from the area ratio of the peaks at 285.0, 284.1 eV which were individually attributed to sp³ C-C, sp² CC hybridizations. The results showed that the sp³ content of a-C:B film decreases from 73.8 to 58.6% for the films containing boron from 0.59 to 2.13 at.%, and then gradually reduced to 42.5% at a slower rate with boron concentration up to 6.04 at.%. Furthermore, a series of a-C:B films with fixed boron content (2.13 at.%) were prepared to identify the relationship between sp³ bonding and substrate bias. It was found that the fraction of sp³ bonding increased from 50.28% at the bias voltage of 0 V and reached a maximum value of 66.3% at −150 V. As the bias voltage increased up to −2000 V, the sp³ content decreased sharply to 43.9%.     

XPS study of carbon nitride films deposited by hot filament chemical vapor deposition using carbon filament

Amorphous carbon nitride, a-CN_x, thin films were deposited by hot filament CVD using a carbon filament with dc negative bias voltage on the substrate. The effects of the negative bias and the filament components on the binding structure of the films are investigated by XPS. The composition ratio of graphite to amorphous carbon in the filaments affects the bonding structure of carbon and nitrogen in the films, although the nitrogen content in the films is almost same as 0.1. The nitrogen content in the films changes from 0.1 to 0.3 as the negative bias changes from 0 to − 300 V.     

Atomic Vapor Depositions of Ti-Ta-O thin films for Metal-Insulator-Metal applications

Atomic Vapor Deposition technique was applied for the depositions of Ti-Ta-O oxide films for Metal-Insulator-Metal capacitors used in back-end of line for Radio Frequency applications. Composition, crystallinity, thermal stability and electrical properties were studied. Ti-Ta-O films, with the ratio of Ta/Ti ~ 1.5, deposited at 400 °C on TiN electrodes, were amorphous and possessed a dielectric constant of 50 with low voltage linearity coefficients and leakage currents densities as low as 10^− 7 A/cm² at 1 V. The films, deposited on Si wafers, were amorphous up to the annealing temperature of 700 °C and crystallized in orthorhombic Ta₂O₅ phase at higher temperatures.     

X-ray photoelectron spectroscopy for analysis of plasma-polymer interactions in Ar plasmas sustained via RF inductive coupling with low-inductance antenna units

Plasma-polymer interactions have been investigated on the basis of hard X-ray photoelectron spectroscopy (HXPES) together with conventional X-ray photoelectron spectroscopy (XPS) for analysis of chemical bonding states in the surface nano-layers of polymethylmethacrylate (PMMA) films, which were exposed to argon plasmas sustained via RF inductive coupling with multiple low-inductance antenna units. The PMMA films were exposed to argon plasmas on a water-cooled substrate holder. Average ion energies bombarding onto PMMA films were varied in the range of 6-16 eV, which were evaluated as ion kinetic energies at the sheath edge to the ground potential using a mass-separated ion-energy analyzer. The etching of PMMA surface after Ar plasma exposure with an ion dose of 3.4 × 10¹⁸ ions/cm² was measured to be insignificant (less than 20 nm). Surface roughness of PMMA slightly increased from 0.3 nm to 0.4 nm with increasing ion bombardment energy from 6 eV to 16 eV. HXPES was carried out together with conventional XPS to examine chemical bonding states of the PMMA surface in deeper regions (about 54 nm) with HXPES as compared to those observed in shallower regions (8 nm) with the conventional XPS.     

Electroluminescence of as-sputtered silicon-rich SiOx films

Si-rich oxide films (SiO_x, 0 < x < 2) were synthesized by reactive magnetron sputtering of a single Si target in a gas mixture of argon and oxygen. Intense visible electroluminescence was observed from the as-deposited SiO_x film. The microstructure of the as-sputtered SiO_x films was characterized by Raman and X-ray photoelectron spectroscopy techniques. Nanoscale amorphous Si clusters formed in the as-sputtered films. The electroluminescence was attributed to the oxygen-deficient defect luminescent centres and the formation of the amorphous Si nanoclusters.     

Preparation of amorphous FexSi(1 − x) film using unbalanced magnetron sputtering

The preparation of iron-silicon films was performed onto Si (100) substrates by microwave electron cyclotron resonance (ECR) plasma source enhanced unbalance magnetron sputtering. The compositions, microstructures and properties of films under different sputtering powers and annealing conditions were characterized by AES, GAXRD, TEM and absorption spectrum techniques. The results described that the amorphous iron silicon films can be easily prepared by unbalance magnetron sputtering. Even the Fe/Si ratio deviated far from 1:2, such as Fe/Si = 1:14.8 or 1:10, the amorphous iron silicon film with semiconductor properties can also be obtained, which suggests that the Fe/Si ratio is not the only factor to determine whether the samples have semiconducting properties in iron silicon amorphous. After annealing at 850 °C for 4 h, the microstructure of nanometer β-FeSi₂ embedded into amorphous Si still possesses semiconducting characteristics.     

Improvement of bias stability of indium zinc oxide thin film transistors by the incorporation of hafnium fabricated by radio-frequency magnetron sputtering

We report on the fabrication and performance of amorphous oxide thin film transistors with indium zinc oxide (In₂O₃:ZnO = 1:1 mol%) and various ratios of hafnium-doped indium zinc oxide (IZO:HfO₂ = 2:0, 0.3, 0.7, and 1.1 mol%) deposited at the same deposition conditions for semiconductor channel layer. The carrier concentration (N_cp) of the HIZO films was further decreased from 7.08 × 10¹⁷ to 5.0 × 10¹⁶ cm^− 3. This indicates that Hf metal cations effectively suppress carrier generation due to the high electron negativity (1.3) of Hf. In addition, we compared bias instability of both devices after bias temperature stress (BTS) test under on-current state at V_DS of 10 V and I_DS of 3 μA at 60 °C for 420 min. It was found that the Hf metal cations could be effectively incorporated in the IZO thin films as a suppressor against both the oxygen deficiencies and the carrier generation in the ZnO-based system.     

Improvement of thickness uniformity and crystallinity of AlN films prepared by off-axis sputtering

We improved both the thickness uniformity and crystallinity of Aluminum nitride (AlN) films deposited by off-axis sputtering. The results in thickness uniformity and X-ray rocking curve full-width at half-maximum (FWHM) of AlN (0 0 0 2) are achieved to be ±0.2% and 1.4°, respectively on a 100 mm Si (1 0 0) substrate. The residual stress can be controlled from tensile to compressive by varying sputtering parameters such as gas pressure, RF power and DC bias voltage applied to a substrate without degradation in the crystallinity and thickness uniformity.     

Interfacial characteristics and dielectric properties of Ba0.65Sr0.35TiO3 thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering technique. X-ray photoelectron spectroscopy (XPS) depth profiling data show that each element component of the BST film possesses a uniform distribution from the outermost surface to subsurface, but obvious Ti-rich is present to BST/Pt interface because Ti⁴⁺ cations are partially reduced to form amorphous oxides such as TiO_x (x < 2). Based on the measurement of XPS valence band spectrum, an energy band diagram in the vicinity of BST/Pt interface is proposed. Dielectric property measurements at 1 MHz reveal that dielectric constant and loss tangent are 323 and 0.0095 with no bias, while 260 and 0.0284 with direct current bias of 25 V; furthermore, tunability and figure of merit are calculated to be 19.51% and 20.54, respectively. The leakage current density through the BST film is about 8.96 × 10^− 7 A/cm² at 1.23 V and lower than 5.66 × 10^− 6 A/cm² at 2.05 V as well as breakdown strength is above 3.01 × 10⁵ V/cm.     

Bias enhanced nucleation of diamond thin films in a modified HFCVD reactor

In this study we investigated the nucleation of synthetic diamond thin films on Si substrates by double bias enhanced Hot Filament Chemical Vapour Deposition (HFCVD) method. First, we investigated the influence of the bias voltage and secondly the influence of the nucleation time under different bias voltages. The bias voltage was varied from −120 V up to −220 V as well as the nucleation time was changed from 30 up to 120 min in order to obtain the optimized nucleation conditions for following growth of continuous diamond layer. Samples were analyzed by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. SEM was used for determination of cluster sizes and their distribution on the Si surface, while Raman Spectroscopy for determination and analysis of carbon phases.