Effect of substrate temperature and bias voltage on the crystallite orientation in RF magnetron sputtered AlN thin films

The crystal orientation and residual stress of AlN thin films were investigated using X-ray diffraction and substrate curvature method. The AlN films were deposited on Si(100) by RF magnetron sputtering in a mixed plasma of argon and nitrogen under various substrate negative bias V_s (up to − 100 V) and deposition temperature T_s up to 800 °C. The results show that lower temperature and moderate bias favor the formation of (002) plane parallel to the substrate surface. On the contrary, strong biasing beyond − 75 V and deposition temperature higher than 400 °C lead to the growth of (100) plane. At the same time nanoindentation hardness and compressive stress measured by substrate curvature method showed significant enhancement with substrate bias and temperature. The biased samples develop compressive stress while unbiased samples exhibit tensile or compressive stress depending on plasma power and temperature. The relationships between deposition conditions and crystallographic orientation of the films are discussed in terms of surface energy minimization and ion bombardment effects.     

Influence of incidence angle and distance on the structure of aluminium nitride films prepared by reactive magnetron sputtering

Aluminum nitride (AlN) films were reactively deposited on (100) oriented silicon substrates by reactive radio frequency (RF) magnetron sputtering for different incidence angles and distances between substrate and target.X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to consider the influence of process parameters such as reactive gas flow rate, grazing incidence angle (α), and distance (d) between substrate and target surface on the property of AlN films. XRD results showed that AlN film prepared at a constant distance (d) of 3 cm and an incidence angle of 45° revealed a mixture of AlN (002), (100), and (101) planes, while the film prepared at α = 0° revealed a strong AlN (002) orientation which has a perpendicular growth direction to the substrate surface. AFM results showed that AlN film prepared at α = 0° exhibited more flat surface morphology than that of film prepared at α = 45°.     

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.     

Magnetron sputter deposition of low-stress, carbon-containing cubic boron nitride films using Ar―N2―CH4 gas mixtures

Cubic boron nitride (c-BN) films produced by PVD and plasma-assisted CVD techniques typically exhibit undesired high compressive stresses. One of the effective and feasible methods to reduce stress and hence improve film adhesion has been a controlled addition of a third element into the film during deposition. In the present study, BN films were grown on to silicon substrates using reactive magnetron sputtering with a hexagonal BN target. An auxiliary flow of methane was mixed into argon and nitrogen as the working gas. The deposition was conducted at various methane flow rates at 400 °C substrate temperature, 0.2 Pa total working pressure, and − 250 V r.f. substrate bias. The microstructure of the deposited films was then examined in dependence of the methane flow rate. With increasing methane flow rate from 0 to approx. 2.0 sccm, the fraction of the cubic BN phase in the deposited films decreased gradually down to approx. 75 vol.%, whereas the film stress was reduced much more rapidly and almost linearly in relation to the methane flow rate. At 2.1 sccm methane, the stress became approx. 3 times reduced. Owing to the significantly decreased film stress, adherent, micrometer thick, cubic-phase dominant films can be allowed to form on silicon substrate. The microstructure of the films will be illustrated through FTIR and XRR.     

Effect of thermal annealing on the microstructure and morphology of erbium films

The effects of thermal annealing on the microstructure and morphology of erbium films were investigated by X-ray diffraction and scanning electron microscopy. All the erbium films were fabricated by electron-beam vapor deposition. The columnar grain sizes of as-received erbium films increased with the substrate temperatures and were enlarged by the coalescence and migration of grains during the high temperature annealing. The intrinsic stresses of erbium films, fabricated at a low substrate temperature (200 °C), were relaxed accompanied with the appearance of cracks on the films surface. The films deposited at 200 °C had (002) preferred orientation, and the film deposited at 450 °C had mixed (100) and (101) texture. The peak positions and the full width at half maximum of (100), (002), and (101) diffraction lines of erbium shift towards higher angles and sharply decrease during the annealing process, indicating that the stress inside the film was relaxed.     

Deposition of amorphous hydrogenated carbon films on Si and PMMA by pulsed direct-current plasma CVD

A pulse-modulated direct-current methane plasma is used to deposit amorphous hydrogenated carbon (a-C:H) films on Si and polymethyl methacrylate (PMMA) substrates. The structure and mechanical properties of the films are examined by applying a negative pulse bias voltage of 0.5 to 3 kV to the substrate at a pulse bias period of 100 to 200 μs. The deposition rate on both Si and PMMA increases with increasing the net input power, independent of the pulse period. The Raman spectra demonstrate that the films on Si are diamond-like carbon (DLC), while those on PMMA are polymer-like or soft amorphous carbon because of higher crystallinity of the sp² phase and lower nanoscale hardness. The residual compressive stress of the films on PMMA is constantly low ranging from 0 to 2 GPa due exclusively to high flexibility of PMMA, which causes the easy relief of the stress and thus the density decrease in the films.     

Effect of bias voltage on microstructure, mechanical and wear properties of Al-Si-N coatings deposited by cathodic arc evaporation

Al-Si-N coatings were deposited on tungsten carbide (WC-Co) and silicon wafer substrates using Cr and AlSi (12 at.% Si) alloy targets using a dual cathode source with short straight-duct filter in the cathode arc evaporation system. Al-Si-N coatings were synthesized under a constant flow of nitrogen, using various substrate bias voltages at a fixed AlSi cathode power. To enhance adhesive strength, the Cr/(Cr_xAl_ySi_z)N graduated layer between the top coating and the substrate was deposited as a buffer interlayer. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Si-N films were investigated. Experimental results reveal that the Al-Si-N coatings exhibited a nanocomposite structure of nano-crystalline h-AlN, amorphous Si₃N₄ and a small amount of free Si and oxides. It was also observed that the deposition rate of as-deposited films gradually decreased from about 25.1 to 18.8 nm/min when the substrate bias was changed from − 30 to − 150 V. The XRD results revealed that h-AlN preferred orientation changed from (002) to (100) as the bias voltage increased. The maximum hardness of approximately 35 GPa was obtained at the bias voltage of −90 V. Moreover, the grain size was inversely proportional to the hardness of the film. Wear test results reveal that the Al-Si-N film had a lower coefficient of friction, between 0.5 and 0.7, than that 0.7 of the AlN film.     

Influence of substrate temperature and bias voltage on the optical transmittance of TiN films

Titanium nitride (TiN) thin films were prepared by means of reactive DC sputtering on quartz and sapphire substrates. Structural, electrical and optical effects of deposition parameters such as thickness, substrate temperature, substrate bias voltage were studied. The effect of substrate temperature variations in the 100-300°C range and substrate bias voltage variations in the 0-200 V DC range for 45-180 nm thick TiN films were investigated. Temperature-dependent electrical resistivity in the 100-350 K range and optical transmission in the 300-1500 nm range were measured for the samples. In addition, structural and morphological properties were studied by means of XRD and STM techniques.The smoothest surface and the lowest electrical resistivity was recorded for the optimal samples that were biased at about V_s=−120 V DC. Unbiased films exhibited a narrow optical transmission window between 300 and 600 nm. However, the transmission became much greater with increasing bias voltage for the same substrate temperature. Furthermore, it was found that lower substrate temperatures produced optically more transparent films.Application of single layers of MgF₂ antireflecting coating on optimally prepared TiN films helped increase the optical transmission in the visible region to more than 40% for 45 nm thick samples.     

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.     

Texture control of ZnO films by inductively coupled plasma assisted chemical vapor deposition

ZnO films were grown on Si (100) and quartz substrates by inductively coupled plasma-assisted chemical vapor deposition using diethylzinc, O₂, and Ar. ZnO films with the (002) preferred orientation (PO) were formed at substrate temperatures > 250 °C regardless of any other changes made to process variables, since the (002) plane has the lowest formation energy with the highest number of unsaturated Zn-ZnO or O-ZnO bonds. At temperatures < 250 °C, the a-axis plane PO such as (100), (110), and (101) as well as the c-axis (002) plane PO were able to form by varying the temperature, plasma power, and deposition rate. The a-axis PO was formed when the radio frequency power was high enough to produce a crystalline ZnO film but was insufficient to form a (002) PO. The a-axis PO was also formed at higher deposition rates ≥ 20 nm/min when the radio frequency power was high enough to produce crystalline ZnO film. Since the (002) plane grew slowly, the grain exposing (002) plane was overgrown by the grains of the a-axis plane at higher deposition rates.     

Effect of deposition angle on the structure and properties of pulsed-DC magnetron sputtered TiAlN thin films

This article reports the comparison of structure and properties of titanium aluminum nitride (TiAlN) films deposited onto Si(100) substrates under normal and oblique angle depositions using pulsed-DC magnetron sputtering. The substrate temperature was set at room temperature, 400 °C and 650 °C, and the bias was kept at 0, − 25, − 50, and − 80 V for both deposition angles. The surface and cross-section of the films were observed by scanning electron microscopy. It was found that as the deposition temperature increases, films deposited under normal incidence exhibit distinct faceted crystallites, whereas oblique angle deposited (OAD) films develop a kind of “tiles of a roof” or “stepwise structure”, with no facetted crystallites. The OAD films showed an inclined columnar structure, with columns tilting in the direction of the incident flux. As the substrate temperature was increased, the tilting of columns nearly approached the substrate normal. Both hardness and Young's modulus decreases when the flux angle was changed from α = 0° to 45° as measured by nanoindentation. This was attributed to the voids formed due to the shadowing effect. The crystallographic properties of these coatings were studied by θ-2θ scan and pole figure X-ray diffraction. Films deposited at α = 0° showed a mixed (111) and (200) out-of-plane orientation with random in-plane alignment. On the other hand, films deposited at α = 45° revealed an inclined texture with (111) orientation moving towards the incident flux direction and the (200) orientation approaching the substrate normal, showing substantial in-plane alignment.     

Studies on the residual stress of fluorine-doped SnO2 film deposited by chemical vapor deposition

Fluorine-doped tin oxide films were deposited on Na-Ca-Si glass substrate at 650 °C by chemical vapor deposition, and then heat treatment was carried out at 200 °C, 400 °C and 600 °C for 4 min in a resistance furnace. The residual stress in SnO₂:F films was systematically measured using the sin²Ψ method based on X-ray diffraction. The incidence angle was adopted as Ψ = 0°, 15°, 20°, 25° and 30°. The results showed that the films were polycrystalline with tetragonal SnO₂ structure, together with a weak peak of SnO phase. All the films exhibited a preferred orientation with the (200) plane. The minimum value of residual stress (− 0.24 ± 0.01 GPa) was obtained when the films were heat-treated at 200 °C.     

Improving hardness of biomedical Co-Cr by deposition of dense and uniform TiN films using negative substrate bias during reactive sputtering

This paper reports the deposition of a fully dense and uniform TiN film to improve the surface hardness of Co-Cr, particularly, by applying a negative substrate bias during reactive direct current (DC) sputtering. As the TiN film was deposited with a negative substrate bias voltage of 150 V, the microstructure of the films was shifted from a columnar to non-columnar one that was observed to have a dense, uniform and smooth surface. In addition, the preferred orientation was the (111) plane when the films were deposited with a negative substrate bias; however, the (200) plane when they were deposited without a substrate bias. The deposition of the dense and uniform TiN film resulted in a significant increase of the hardness of the Co-Cr. The TiN-deposited Co-Cr with a negative substrate bias showed a very high hardness of 44.7 ± 1.7 GPa, which was much higher than those of the bare Co-Cr (4.2 ± 0.3 GPa) and TiN-deposited Co-Cr without a negative substrate bias (23.6 ± 2.8 GPa).     

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.     

Influence of substrate bias voltage on properties of Pt thin films deposited by non-mass separated ion beam deposition method

Pt thin films were deposited on Si substrates by applying a negative substrate bias voltage using a non-mass separated ion beam deposition method. The effect of the substrate bias voltage on the properties of the deposited films was investigated. In the case of Pt thin films deposited without the substrate bias voltage, a columnar structure and small grains were observed. The electrical resistivity of the deposited Pt films was very high (49.3 ± 0.65 µΩ cm). By increasing the substrate bias voltage, no clear columnar structure was observed. At the substrate bias voltage of − 75 V, the resistivity of the Pt film showed a minimum value of 16.9 ± 0.2 µΩ cm closed to the value of bulk (10.6 µΩ cm).     

Ion beam deposition of α-Ta films by nitrogen addition and improvement of diffusion barrier property

Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar + N₂ atmosphere with different pressure ratios of Ar and N₂. The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and diffusion barrier property were investigated. It was found that the fraction of a metastable β-phase in the Ta film deposited at the substrate bias voltage of − 50 V films decreased by adding nitrogen gas, while the α-Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of − 50 V under Ar (9 Pa) + N₂ (3 Pa) atmosphere showed a dominant α-phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier.     

Cathodic arc plasma deposited TiAlSiN thin films using an Al-15 at.% Si cathode

Thin films of TiAlSiN were deposited on SKD 11 tool steel substrates using two cathodes, of Ti and Al-15 at.% Si, in a cathodic arc plasma deposition system. The influence of AlSi cathode arc current and substrate bias voltage on the mechanical and structural properties of the films was investigated. The TiAlSiN films had a multilayered structure in which nanocrystalline cubic TiN layers alternated with nanocrystalline hexagonal AlSiN layers. The hardness of the films decreased with the increase of the AlSi cathode arc current. The hardness of the films also decreased as the bias voltage was raised from − 50 V to − 200 V. The maximum hardness of 43 GPa was observed at the films deposited at the pressure 0.4 Pa, Ti cathode arc current 55 A, Al cathode arc current 35 A, temperature 250 °C and bias voltage of − 50 V.     

The influence of electric field on the microstructure of nc-Si:H films produced by RF magnetron sputtering

Hydrogenated nanocrystalline silicon thin films were prepared by RF magnetron sputtering. Different bias fields (no bias-no ground, grounded and negative bias) were applied to the substrate. The effect of the ion bombardment on the structure, chemical and optical property were studied by Raman spectroscopy, X-ray diffraction, Rutherford backscattering (RBS) and optical transmission spectroscopy. The deposition rate and the optical bandgap decrease as the bias voltage increases from 0 to −50 V. The structural characterization indicates that compressive stress is developed in plane and tensile stress is induced in the growth direction. No significant variation on the chemical composition was observed.     

Effect of Ag doping on the performance of ZnO thin film transistor

Ag-doped zinc oxide (SZO) thin film transistors (TFTs) have been fabricated using a back-gate structure on thermally oxidized and heavily doped p-Si (100) substrate. The SZO thin films were deposited via pulsed laser deposition (PLD) from a 1, 3, and 5 wt.% Ag-doped ZnO (1SZO, 3SZO, and 5SZO, respectively) target using a KrF excimer laser (λ, 248 nm) at oxygen pressure of 350 mTorr. The deposition carried out at both room-temperature (RT) and 200 °C. The SZO thin films had polycrystalline phase with preferred growth direction of (002) as well as a wurtzite hexagonal structure. Compare with ZnO thin films, the SZO thin films were characterized by confirming the shift of (002) peak to investigate the substitution of Ag dopants for Zn sites. The as-grown SZO TFTs deposited at RT and 200 °C showed insulator characteristics. However the SZO TFTs annealed at 500 °C showed good n-type TFT performance because Ag was diffused from Zn lattice site and bound themselves at the high temperature, and it caused generation of electron carriers. The post-annealed 5SZO TFT deposited at 500 °C exhibited a threshold voltage (V_th) of 11.5 V, a subthreshold swing (SS) of 2.59 V/decade, an acceptable mobility (μ_SAT) of 0.874 cm²/V s, and on-to-off current ratios (I_on/off) of 1.44 × 10⁸.     

Study on physical properties of indium-doped zinc oxide deposited by spray pyrolysis technique

Transparent conducting indium doped zinc oxide (IZO) thin films have been deposited on soda-lime glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. In this work the substrate temperature was varied between 350 °C and 500 °C. X-ray diffraction pattern reveals that at 350 °C dominant peak is (100) orientation. By increasing substrate temperature from 350 °C to 450 °C, sheet resistance decreases, from 302 Ω/□ to 26 Ω/□, then at 500 °C increases to 34 Ω/□. In the useful range for deposition (i.e. 450 °C to 500 °C), the orientation of the films was predominantly (002). The lowest sheet resistance (26Ω/□) is obtained at substrate temperature of about 450 °C with the transmittance of about 75%. Study of scanning electron microscopy images shows that films deposited at 400 °C, have grain size as large as 574 nm, while with increasing substrate temperature to 450 °C, grain size becomes smaller and reaches to a value of about 100 nm with spherical shape. At 500 °C grain size value would be around 70 nm with the same spherical shape.