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.     

Residual compressive stress in sputter-deposited TiC films on steel substrates

Polycrystalline TiC films with thickness between 0.1 and 2.8 microm were deposited by r.f. sputtering onto 1010 steel and borosilicate glass substrates at 200°C. All films were found to be in a state of compression. For a film grown under a given set of deposition conditions, the incremental compressive stress, i.e. the average stress in the uppermost deposited layer, was generally found to be largest near the film-substrate interface and to become constant with film thickness t_f for t_f ? 0.3 microm. However, for a given t_f the incremental stress increased with a decrease in the argon sputtering pressure P_Ar. Experimental results showed that the incremental compressive stress in bulk films could be directly related to the trapped argon concentration. Argon incorporation is due to the burial of energetic species incident on the growing film surface from two primary sources: energetic neutrals produced by Ar⁺ ions scattered off the target in binary collisions and Ar⁺ ions accelerated to the substrate owing to its induced negative potential with respect to the positive space charge region in the r.f. discharge. The trapped argon concentration from both contributions increased with decreasing P_Ar. All films grown on steel substrates exhibited good adhesion as indicated by indentation and diamond stylus scratch tests. The residual compressive stress in the films was found to be beneficial for wear-related applications in which the film was subjected to a large tensile stress.     

The effect of the backscattered energetic atoms on the stress generation and the surface morphology of reactively sputtered vanadium nitride films

During the reactive magnetron sputtering of transition metal nitrides in an Ar-N₂ ambient, Ar⁺ and N₂⁺ plasma ions are neutralized upon impingement on the target and are backscattered towards the growing film as neutral Ar and N species, respectively. Based on simulations, as well as on plasma and on film characterization techniques we manifest the relationship between the bombardment by the backscattered energetic atoms and the properties of reactively sputtered vanadium nitride (VN) films. Depending on the N₂ flow (q_N2) two bombardment regimes are established. In the first regime, (q_N2 < 20 sccm) the contribution of the N species to the energetic bombardment is insignificant. The major bombarding species in this regime are the backscattered Ar species, as well as positive plasma ions and sputtered atoms. These species have relatively low energies and subplantation ratios and thus, their energy is transferred to the surface of the growing film. In the second regime (q_N2 > 20 sccm) the backscattered N atoms are the major bombarding species and their flux to the growing film increases with increasing the N₂ flow. We argue that the backscattered N atoms have higher energy and subplantation ratio in comparison to the other bombarding species. As a result, a higher part of their energy is dissipated in the bulk of the film. The two bombarding regimes correlate well with the residual compressive stresses and the surface roughness of the films. Films grown at q_N2 < 20 sccm exhibit low compressive stresses and their roughness drops when q_N2 is increased. This consistent with the low subplantation ratio and the transfer of the energy of the bombarding species to surface the growing film. The compressive stresses of films grown at q_N2 > 20 sccm are higher, than those of the films grown in the first regime, and increase with increasing N₂ flow. This is attributed to the subplantation of the bombarding N species in the growing film.     

Effects of oxygen-argon mixing on the properties of sputtered zirconium dioxide film

Partially stabilized ZrO₂-Y₂O₃ films (PSZ) were deposited using an r.f.-diode cathode sputter deposition system. The variation of film structure according to changes in the deposition parameters is described. The results show that the oxygen concentration of the oxygen-argon sputtering gas used for deposition of PSZ films can be used to control the microstructure of the films and their roughness. We found the optimal oxygen concentration to be 10%, resulting in a dense and homogeneous structure within the film, and a smoother surface. At the optimal oxygen concentration of 10% the refractive index and the absorption coefficient of the films showed a clear maximum and minimum, respectively. We consider that addition of oxygen to neutral argon sputtering gas both decreases the sputtering yield and increases the substrate bombardment by neutral oxygens.     

Atomic defects and stresses in r.f.-sputtered SiO2 thin films

The influence of a number of technological factors on the optical and dielectric properties of thin amorphous SiO₂ films obtained by r.f. sputtering of fused quartz in an argon atmosphere was investigated.Using IR spectroscopy and the measurement of the a.c. conductivity the films obtained are shown to have the radiation defects of the C₁^- type induced by the high energy particle bombardment during sputtering.The observed shift in the main IR absorption band of the films as a function of their thicknesses is related to the stresses due to the difference in thermal expansion coefficients of the film and the substrate as well as their structural disparity.     

Deposition of AlN films by reactive sputtering: Effect of radiofrequency substrate bias

Piezoelectric AlN thin films were deposited on Silicon substrates by triode reactive sputtering. The variation of residual stress versus bias voltage on the substrate was investigated. A compressive stress was always observed with a maximum value for a negative substrate bias of 50 V. For higher negative bias voltage values, the compressive stress decreases. X-ray diffraction measurements showed two kinds of growth orientation. First, without bias voltage, films are well crystallized and (002) oriented. Second, with bias voltage, the (002) orientation disappears and a small peak appears (situated in the 2θ = 32°-33° range) which can be attributed to (100) orientation. Finally, the influence of compressive stress and ion bombardment on the change of orientation is discussed.     

Stress and texture in HIPIMS TiN thin films

Titanium nitride (TiN) films in the thickness range of 0.013 µm to 0.3 µm were grown by high power impulse magnetron sputtering (HIPIMS) on silicon substrates in two deposition modes: a) the substrate was grounded and b) − 125 V bias was applied to the substrate. On the films we performed microstructure-, film texture- and film stress-analysis. The films deposited under − 125 V bias experienced a more energetic ion bombardment than the films deposited on grounded substrates. This difference in ion bombardment energy is reflected in the different microstructure. In contrast to previous results for TiN films grown by conventional reactive magnetron sputtering, we observe no major film stress gradient for increasing film thicknesses. We explain this observation from the absence of a 200-to-111 texture crossover during film growth.A moderate ion bombardment leads to TiN films with (111) texture, while an intense ion bombardment leads to films with (001) texture (Greene et al.; Appl. Phys. Lett. 67 (20) 2928-2930 (1995)). At the same time (001) oriented grains are much more susceptible to compressive stress generation by ion bombardment than (111) oriented grains.     

X-ray diffraction study of thermal stress relaxation in ZnO films deposited by magnetron sputtering

X-ray diffraction stress analyses have been performed on two different thin films deposited onto silicon substrate: ZnO and ZnO encapsulated into Si₃N₄ layers. We showed that both as-deposited ZnO films are in a high compressive stress state. In situ X-ray diffraction measurements inside a furnace revealed a relaxation of the as-grown stresses at temperatures which vary with the atmosphere in the furnace and change with Si₃N₄ encapsulation. The observations show that Si₃N₄ films lying on both sides of the ZnO film play an important role in the mechanisms responsible for the stress relaxation during heat treatment. The different temperatures observed for relaxation in ambient and argon atmospheres suggest that the thermally activated stress relaxation may be attributed to a variation of the stoichiometry of the ZnO films. The present observations pave the way to fine tuning of the residual stresses through thermal treatment parameters.     

Intrinsic stress in diamond-like carbon films and its dependence on deposition parameters

The compressive stresses and the hydrogen content inside diamond-like carbon films were measured for various deposition conditions. Four methods of film deposition were tested: primary beam containing CH₄; primary beam containing CH₄ with simultaneous bombardment of second beam of energetic argon ions; primary beam containing C₄H₁₀, and sputter deposition of graphite with the addition of hydrogen gas. The compressive stresses in the films were attributed mainly to the bombarding energy of the ion beam. An additional contribution to the compressive stresses probably came from the complex species in the discharge. The contribution of the hydrogen to the stresses in the films did not seem to be obvious.     

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.     

Modifications in the unit cell geometry of sputtered niobium films caused by high energy ion bombardment

The effect of high energy ion bombardment on the structure of sputtered niobium films has been studied. The 1000 Å films were sputtered onto silicon substrates. The films were oriented with a [110] fiber texture and were found to have a monoclinically distorted cell characteristic of compressive stress, where the stress direction is parallel to the film surface. Bombardment with 300 keV Xe⁺ ions, which for the most part did not reach the silicon interface, merely expanded the volume of the distorted as-sputtered niobium unit cell. However, bombardment with 600 keV Xe⁺ ions, which have a mean range extending to the interface, relaxed the unit cell toward the configuration of a cubic geometry.     

R.F. reactive sputter deposition of hydrogenated amorphous silicon carbide films

The preparation of hydrogenated amorphous silicon carbide films by r.f. reactive sputtering of a silicon target in Ar-CH₄ gas mixtures with and without an r.f. bias on the substrates was studied. Starting with a pure silicon target and increasing monotonically the CH₄ percentage from 0% to about 10%, films with 1 ⩾ x ⩾ 0 were obtained at decreasing deposition rates. After sputtering for some hours in methane-rich gas mixtures, carbon atoms were incorporated into the silicon target surface, probably as a result of atomic peening, and nearly stoichiometric SiC films were prepared by sputtering of such a target in pure argon. The different mechanisms of film formation, deposition rate, composition, hardness, friction coefficient and stresses in the films as functions of the partial pressure of methane and the value of the r.f. bias were investigated. The IR spectra offilms with different carbon contents were analysed. The greatest hardness was found for nearly stoichiometric SiC films deposited with a bias.     

Effect of bias voltage on growth property of Cr-DLC film prepared by linear ion beam deposition technique

Cr-containing diamond-like carbon films were deposited on silicon wafers by a combined linear ion beam and DC magnetron sputtering. The influence of the bias voltage on the growth rate, atomic bond structure, surface topography and mechanical properties of the films were investigated by SEM, XPS, Raman spectroscopy, AFM, and nano-indentation. It was shown that the chromium concentration of the films increased with negative bias voltage and that a carbide phase was detected in the as-deposited films. The surface topography of the films evolved from a rough surface with larger hillocks reducing to form a smoother flat surface as the bias voltage increased from 0 to −200 V. The highest hardness and elastic modulus were obtained at a bias voltage of about −50 V, while the maximum sp³ bonding fraction was acquired at −100 V. It was suggested that the mechanical properties of the films not only depended on the sp³ bonding fraction in the films but also correlated with the influence of Cr doping and ion bombardment.     

Study of FePt films prepared by reactive sputtering

In the present study, ⁵⁷FePt films are prepared with reactive ion beam sputtering using mixture of argon and nitrogen gases. Energy-dispersive X-ray reflectivity is used to estimate the thickness of the as-deposited films. Structural and magnetic properties of the as-deposited and annealed films are studied using grazing incidence X-ray diffraction (GIXRD), magneto-optical Kerr effect (MOKE) and conversion electron Mossbauer spectroscopy (CEMS). Significant difference in structural and magnetic properties i.e., formation of ordered L1₀ phase and perpendicular magnetic anisotropy are observed for the films prepared with mixture of nitrogen and argon as compared to the film prepared with argon only. From the GIXRD, peaks corresponding to the ordered face-centred tetragonal FePt phase are observed for the films prepared with mixture gas. The results of CEMS clearly show the perpendicular magnetic anisotropy (PMA) for the films prepared with mixture of nitrogen and argon. The observed enhanced chemical ordering and the development of PMA in the films prepared with mixture gas is due to the role played by the defects created as a consequence of nitrogen escape in the films with high temperature annealing.     

Measurement of the noibium/sapphire interface toughness via delamination

Niobium films were deposited on sapphire substrates using both physical vapor deposition (PVD) and ion beam assisted deposition (IBAD) at an ion energy of 1000 eV and an ion-to-atom arrival rate ratio of 0.4. The interface between the niobium film and the sapphire substrate was doped with up to 7.6 monolayers of silver. The films were patterned into fine lines using photolithography. During the photolithography process, curling and buckling were observed. The curling indicated a stress gradient in which the top of the film is tensile with respect to the bottom of the film, while buckling demonstrated that a portion of the film thickness must have been in compression. An analysis of the delamination showed that the critical energy release rate for the interface was on the order of 1 J m^–2, and that the compressive stress is of the order 1 GPa. The higher energy release rate of the IBAD samples confirmed that the stronger interface is due either to the orientation relationship between the ion beam textured niobium film and the (0001) sapphire surface or the interface mixing caused by ion bombardment.     

Ion bombardment-induced enhancement of the properties of indium tin oxide films prepared by plasma-assisted reactive magnetron sputtering

Research on tin doped indium oxide (ITO) has for many years been stimulated by the need to simultaneously optimize the electrical, optical and mechanical properties, and by new challenges related to the deposition of transparent conducting oxides on flexible plastic substrates. In the present work, we investigate the growth and optical, electrical, and mechanical (hardness, elastic modulus and stress) properties of ITO films deposited by plasma assisted reactive magnetron sputtering (PARMS) from an indium-tin alloy target. PARMS achieves an effective control of bombardment by reactive species (e.g., O₂⁺, O⁺) on the surface of the growing film by varying the bias voltage, V_B, induced by a radiofrequency power applied to the substrate. Stress-free films possessing high transparency (> 80% — film on glass) and low resistivity (4 × 10^− 4 Ω cm) can be deposited by PARMS under conditions of intense ion bombardment (≤ 600 eV).     

The compressive stress transition in Al,V, Zr,Nb and W metal films sputtered at low working pressures

Investigation of internal stresses in thin sputtered films of Al, V, Zr, Nb and W extends the observation of compression at low working pressures that was originally detected with Cr (D. W. Hoffman and J. A. Thornton, Thin Solid Films, 40 (1977) 355–363) and probes the atomic mass dependence of the transition pressure that was subsequently detected with Ti, Ni, Mo and Ta (J. A. Thornton and D. W. Hoffman, J. Vac. Sci. Technol., 14 (1977) 164–168). The observation of compressive stresses at sufficiently low sputtering pressures in all ten of the elements so far examined strongly supports the generality of this phenomenon. The five new metals under study also confirm the overall increase of the transition pressure with atomic mass indicated by the metals examined earlier. However, periodic deviations from the general trend are now evident among the group IVB, VB and VIB elements examined. The electrical conductivity and optical reflectance of the sputtered metal films exhibit abrupt changes in behavior near the transition pressure for compressive stresses. Above the transition pressure the conductivity and reflectance drop off rapidly; below the transition pressure these properties tend to level off at maximum values for the sputtered metal films. The interpretation of these observations in terms of a peening mechanism of energetic particle bombardment is discussed. Data are presented for films up to 0.3 μm thick sputtered onto glass substrates at a nominal deposition rate of 1 nm s^?1 over the pressure range 0.067–4.0 Pa of argon.     

Residual stresses and Raman shift relation in anatase TiO2 thin film

Anatase TiO₂ film (100-1000 nm thick) grown on glass, sapphire (0001), and Si (100) substrates by pulsed dc-magnetron reactive sputtering were evaluated for stress and strain analysis using Raman spectroscopy and curvature measurement techniques. The X-ray analysis revealed that films prepared for this study were purely anatase, and the measurements indicate that the film exhibit that (101) is the preferred growth orientation of the crystallites, especially for the film thicker than 100 nm. Curvature measurements and Raman spectroscopy, with 514.5 nm excitation wavelength, phonon line shift were used for stress analysis. A comparison between Raman lineshapes and peak shifts yields information on the strain distribution as a function of film thickness. The measurements of residual stresses for crystalline anatase TiO₂ thin film showed that all thin film were under compressive stress. A correlation between Raman shifts and the measured stress from the curvature measurements was established. The behavior of the anatase film on three different substrates shows that the strain in film on glass has a higher value compared to the strain on sapphire and on silicon substrates. The dominant 144 cm^− 1E_g mode in anatase TiO₂ clearly shifts to a higher value by 0.45-5.7 cm^− 1 depending on the type of substrate and film thickness. The measurement of the full width at half maximum values of 0.59-0.80 (2θ°) for the anatase (101) peaks revealed that these values are greater than anatase powder 0.119 (2θ°) and this exhibits strong crystal anisotropy with thermal expansion.     

Structure and magnetic properties of Fe films with pyramid-like nanostructures deposited by oblique target direct current magnetron sputtering

Fe thin films were deposited by oblique target direct current magnetron sputtering on Si (100) and (111) substrates. The structure, surface morphology and magnetic properties of the thin films were characterized using X-ray diffraction, field emission scanning electron microscopy, and superconducting quantum interference device magnetometer, respectively. The results reveal that the structure of the as-deposited Fe thin films is body-centered cubic with the preferential [110] crystalline orientation. A pyramid-like nanostructure with sharp tip was formed on the surfaces of Fe thin films under appropriate sputtering power. Formation of the pyramid-like nanostructure is mainly owed to the enhancement of atomic mobility and the bombardment effect with increasing of sputtering power. Meanwhile, the crystalline orientation of Si substrate and the intrinsic stress in the films are expected to have little contribution to the formation of the pyramid-like nanostructure. The magnetic anisotropy was found in the as-deposited Fe thin films, and varies with the thickness of the Fe thin films. As the film thickness increases from 604 to 1,786 nm, the magnetic anisotropy field and the uniaxial anisotropy constant increase from 3.8 to 5.6 kOe, and from 0.4 × 10⁶ to 1.1 × 10⁶ erg/cm³, respectively, which indicates that besides magnetocrystalline anisotropy, stress induced anisotropy and shape anisotropy also exist in the as-deposited Fe thin films.     

Carbon nitride films deposited by reactive sputtering and pulsed laser ablation

Carbon nitride films were deposited by reactive sputtering process and by pulsed laser ablation process with substrate bias. By applying the RF bias, it enables the ion irradiation on to the depositing film surface continuously. ECR plasma source was used for reactive sputtering. Nd:YAG laser (λ=532 nm, 210 mJ) was used to ablate a graphite target in the nitrogen atmosphere. The film properties were examined by XPS, Raman, nanoindentation measurement, and FE-SEM. It was shown that the films deposited by reactive sputtering had smooth surface and its hardness of approximately 30 GPa. However, the films deposited by pulsed laser ablation had uneven surface and low hardness. Both processes, the atomic composition ratio of N/C and sp³ bonding ratio increased with ion bombardment energy up to 100-150 eV, and level off above it. The maximum atomic composition ratio of N/C was 0.35 for reactive sputtering and 0.24 for laser ablation.