High-pressure Sputtering Research Articles

Sputtering-Pressure Dependent Optical and Microstructural Properties Variations in DC Reactive Magnetron Sputtered Titanium Nitride Thin Films

Titanium nitride thin films were prepared using DC reactive magnetron sputtering process in a 99.998% reactive nitrogen atmosphere. The sputtering pressure was varied to study its influence on the as-deposited films, using low (0.80 Pa), intermediate (3.40-5.33 Pa) and high (11.33 Pa) sputtering pressures. The deposited films possessed colour that ranged from dark blue, characteristic of oxygen-rich titanium nitride films, to reflective golden yellow, reminiscent of stoichiometric TiNx films. Studies on the optical and microstructural properties were carried out using UV-visible spectrophotometry, scanning electron microscopy (SEM) and X-ray diffractometry. Characterization results showed variation in the optical and structural properties of the film depending on the deposition sputtering pressure with relatively higher enhancement in the optical transmittance of up to 97.52% in the visible region for films deposited under high and intermediate sputtering pressure conditions. The deposition rate of the films was found to decrease with sputtering pressure. In the same vein, the optical transmittance of the films reduced from 97.52 to 10.05% and the transmission band shifted towards higher wavelength with the decrease of the sputtering pressure.

Direct Evaluation of Electron Traps in Amorphous In-Ga-Zn-O Thin Film Transistors Using Transient Capacitance Technique

Electron traps in the channel region of amorphous In–Ga–Zn–O (a-IGZO) thin film transistors (TFTs) were evaluated using capacitance transient responses from thin (50 nm) metal-oxide-semiconductor diodes. It was found that the carrier transport was mainly dominated by the conduction band tail states. The trap density of a-IGZO deposited at 5 mTorr was higher than that at 1 mTorr, providing direct evidence that the trap density in the channel layer decreased by decreasing the sputtering pressure during the IGZO deposition. The defect states with activation energies of ∼0.2 eV were observed only a-IGZO deposited at 5 mTorr. The reduction of the corresponding TFT mobility should be originated from the increase in the conduction band tail states. The high pressure sputtering is suggested to enhance the structural fluctuation in a-IGZO films, at least in the structure surrounding defect, resulting in an increase of the concentration of the electron traps.

Structure and dielectric properties of sputtered bismuth magnesium niobate thin films

The Bi1.5MgNb1.5O7 (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O2/(O2+Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O2/(O2+Ar) mixing ratio of sputter atmosphere was required. The deposited Bi1.5MgNb1.5O7 cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~50% at a maximum applied bias field of 1.5MV/cm, with low dielectric loss of ~0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films.

Accurate control of friction with nanosculptured thin coatings: Application to gripping in microscale assembly

Chromium thin films were sputter deposited implementing the GLancing Angle Deposition (GLAD) method, which is a thin film deposition technique where the incident vapor flux – composed of atoms and molecules from gas phase – strikes onto the substrate at tilted angles α. Oriented chromium columns were produced with various column angles β (from 0 to 60°) closely linked to the sputtering pressure and incidence angle α. Three sputtering pressures of 0.11, 0.40 and 0.53Pa were used. Incidence angle α of the sputtered particles was systematically changed from 0 to 80°. Tribological properties were investigated as a function of these operating parameters. Results reveal that the tribological behaviour is strongly correlated with the structure and especially the growth mechanism of the films, which are both linked with the operating sputtering parameters. Thus, at the lowest sputtering pressure (0.11Pa), gradual variations of the tribological properties and wettability are observed as a function of the incidence angle α, which are interesting for tailoring surfaces displaying a gradient of wettability. In contrast, at higher sputtering pressures (>0.2Pa), local variations of static friction coefficient, wettability and lateral contact stiffness are systematically observed as a function of the column angle β—and then the incidence angle α. Basically, these results enable to tailor tribological properties by tuning the incidence angle α in order to control the transition from sticking to sliding in micro-gripping.

Pt3Y electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

We report here that significant electrocatalysis occurs during oxygen reduction reaction (ORR) at the Pt3Y alloy thin film electrodes. In addition, we synthesized Pt3Y alloy nanocatalysts for use in proton exchange membrane fuel cells, fabricated by using a high pressure sputtering technique in a gaseous mixture of Ar and He. Rather than the dense film deposited by conventional sputtering techniques, the resulting structure was comprised of a Pt3 Y alloy nanocatalyst layer with an average particle size of 10–12 nm. The Pt3Y alloy nanocatalysts were characterized by scanning electron microscopy, transmission electron microscopy, high-resolution X-ray photoelectron spectroscopy, and X-ray absorption near edge spectroscopy. The cell performance of the membrane electrode assembly with multiple layers of sputter-deposited Pt3Y alloy nanoparticles and spray-deposited Nafion–carbon-ink improved dramatically compared to that obtained with the Pt only nanoparticles. The high performance of Pt3Y alloy nanocatalysts fabricated at a sputtering pressure of 200 mTorr (Ar/He = 1) was due to miniaturization of the Pt3Y alloy particles, formation of the porous catalyst layer, and enhancement of the kinetic activity for ORR.

Influence of Sputter Pressure on the Texture and Magnetic Properties of Barium Ferrite Thin Films

Abstract M-type barium ferrite thin films were deposited onto sapphire (00l) substrates by radio frequency magnetron sputtering. Columnar grains were formed on the surface of the films under lower sputter pressure with bubble magnetic domains, which is originated from high magnetocrystalline anisotropy of the film. Magnetic hysteresis loops agree with the change of the morphology, where in-plane and out-of-plane loops are quite different of the samples prepared under high sputtering pressures, while they are almost identical under low pressures. The influence of the sputtering pressure was understood by that with the increase of the pressure, resputtering of the film is hindered. Nucleation with c-axis normal to the film plane was enhanced. Thus samples prepared under low pressure have more acicular crystallites which have c-axis parallel to the film plane.

Effects of Sputter Parameters on Electrochromic Properties of Tungsten Oxide Thin Films Grown by RF Sputtering

Abstract The electrochromic properties of tungsten oxide films grown by RF sputtering were investigated. Among the sputterparameters, first the Ar:O 2 ratios were controlled with division into only an O 2 environment, 1:1 and 4:1. The structure of eachfilm prepared by these conditions was studied by X-ray diffraction, X-ray photoelectron spectroscopy and Rutherfordbackscattering spectroscopy. The sputter-deposited tungsten oxide films had an amorphous structure regardless of the Ar:O 2 ratios. The chemical compositions, however, were different from each other. The stoichiometric structure and low-density filmwas obtained at higher O 2 contents. Electrochemical tests were performed by cyclic voltammetry and chronoamperometry at0.05 M H 2 SO 4 solutions. The current density and charge ratio was estimated during the continuous potential and pulse potentialcycling at − 0.5 V and 1.8 V, respectively. The film grown in a higher oxygen environment had a higher current density anda reversible charge reaction during intercalation and deintercalation. The in-situ transmittance tests were performed by He-Nelaser (633 nm). At higher oxygen contents, a big transmittance difference was observed but the response speed was too slow.This was likely caused by higher film resistivity. Furthermore, the effect of sputtering pressure was also investigated. Thestructure and surface morphology of each film was observed by X-ray diffraction and scanning electron microscopy. A roughsurface was observed at higher sputtering pressure, and this affected the higher transmittance difference and coloration efficiency.Key wordstungsten oxide, RF sputtering, electrochromism.

Anomalous thermal oxidation of gadolinium thin films deposited on silicon by high pressure sputtering

Thin gadolinium metallic layers were deposited by high-pressure sputtering in pure Ar atmosphere. Subsequently, in situ thermal oxidation was performed at temperatures ranging from 150 to 750 °C. At an oxidation temperature of 500 °C the films show a transition from monoclinic structure to a mixture of monoclinic and cubic. Regrowth of interfacial SiO x is observed as temperature is increased, up to 1.6 nm for 750 °C. This temperature yields the lowest interface trap density, 4 × 10 10 eV −1 cm −2, but the effective permittivity of the resulting dielectric is only 7.4. The reason of this low value is found on the oxidation mechanism, which yields a surface with located bumps. These bumps increase the average thickness, thus reducing the capacitance and therefore the calculated permittivity.

Towards metal electrode interface scavenging of rare-earth scandates: A Sc 2O 3 and Gd 2O 3 study

Amorphous Gd 2O 3 and Sc 2O 3 thin films were deposited on Si by high-pressure sputtering (HPS). In order to reduce the uncontrolled interfacial SiO x growth, firstly a metallic film of Gd or Sc was sputtered in pure Ar plasma. Subsequently, they were in situ plasma oxidized in an Ar/O 2 atmosphere. For post-processing interfacial SiO x thickness reduction, three different top metal electrodes were studied: platinum, aluminum and titanium. For both dielectrics, it was found that Pt did not react with the films, while Al reacted with them forming an aluminate-like interface and, finally, Ti was effective in scavenging the SiO 2 interface thickness without severely compromising gate dielectric leakage.

Structural and optical properties of nanocrystalline WO3 thin films

The nanocrystalline WO3 thin films were deposited by r.f. magnetron sputtering on quartz and p- type Si (100) substrates at a constant power of 25 W and at three different sputtering pressures (0.05, 0.01 and 0.5 mbar) and post annealed at different temperatures. The deposited films were characterized by XRD, UV–VIS spectrophotometry, ellipsometry and atomic force microscopy (AFM). The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and post annealed at 573 and 673 K have the predominant orthorhombic phase, whereas at 0.1 mbar and 573, 673 K triclinic phase is predominant. When sputtering pressure is at 0.5 mbar the predominant phase is monoclinic when annealed at 473 K and triclinic at 673 K. The optical energy gap is influenced significantly by sputtering pressure and post annealing temperatures. The optical energy gap of the films deposited at higher sputtering pressures and post annealed at lower temperatures is high due to smaller crystallite sizes. The thickness of all deposited films at different conditions is around 200 nm.

Electrical characterization of high-pressure reactive sputtered ScO x films on silicon

Al/ScO x/SiN x/ n-Si and Al/ScO x/SiO x/ n-Si metal–insulator–semiconductor capacitors have been electrically characterized. Scandium oxide was grown by high-pressure sputtering on different substrates to study the dielectric/insulator interface quality. The substrates were silicon nitride and native silicon oxide. The use of a silicon nitride interfacial layer between the silicon substrate and the scandium oxide layer improves interface quality, as interfacial state density and defect density inside the insulator are decreased.

Effect of Sputtering Pressure on the Formation of Semiconducting Mg<sub>2</sub>Si Films

Semiconducting Mg2Si films were fabricated on Si (111) substrates by magnetron sputtering and subsequent annealing, and the effects of sputtering pressure on the Mg2Si film growth were studied. The structural and morphological properties of Mg2Si films were investigated by the means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the Mg2Si (220) main diffraction peak intensity increased and then decreased with the increasing of sputtering pressure. The (220) diffraction peak got its maximum at 3.0 Pa sputtering pressure. The intensity of Mg2Si (200) and (400) diffraction peaks increased rapidly as the sputtering pressure decreased when the pressure was lower than 1.5 Pa. The films prepared at higher sputtering pressure had very irregular microstructures, and the surface of semiconducting Mg2Si films became smoother with the decreasing of the sputtering pressure.

Properties of barium hexa-ferrite thin films dependent on sputtering pressure

M-type barium ferrite thin films were deposited onto sapphire (00l) substrates by radio frequency magnetron sputtering. An ultra-thin layer about 20nm was deposited and annealed before continuous deposition of the films up to 500nm under different sputtering pressures: 0.2, 0.5, 0.8 and 1.0Pa, respectively. It was found that the atomic ratios of Fe to Ba increased from 9.3 to 15.0 with the increase of the pressure. The films sputtered at all pressures have c-axis normal to the film plane by a four circle X-ray diffractometer, which is an improvement of the films directly sputtered on the substrate. Needle-like grains were formed on the surface of the films under higher sputter pressure with bubble domains, which is originated from high magnetocrystalline anisotropy of the film. Magnetic hysteresis loops recorded by vibrating sample magnetometer agree with them, where in-plane and out-of-plane loops of the samples prepared under high sputtering pressures are quite different, while they are almost identical of the samples under low pressures. The influence of the sputtering pressure was understood by that with the increase of the pressure, resputtering of the films was increased. Nucleation with c-axis normal to the film plane was deteriorated. Thus samples prepared under high pressure have more needle-like crystallites which have c-axis parallel to the film plane.

Effect of interlayer trapping and detrapping on the determination of interface state densities on high-k dielectric stacks

The influence of the silicon nitride blocking layer thickness on the interface state densities (Dit) of HfO2/SiNx:H gate-stacks on n-type silicon have been analyzed. The blocking layer consisted of 3 to 7 nm thick silicon nitride films directly grown on the silicon substrates by electron-cyclotron-resonance assisted chemical-vapor-deposition. Afterwards, 12 nm thick hafnium oxide films were deposited by high-pressure reactive sputtering. Interface state densities were determined by deep-level transient spectroscopy (DLTS) and by the high and low frequency capacitance-voltage (HLCV) method. The HLCV measurements provide interface trap densities in the range of 1011 cm−2 eV−1 for all the samples. However, a significant increase in about two orders of magnitude was obtained by DLTS for the thinnest silicon nitride barrier layers. In this work we probe that this increase is an artifact due to the effect of traps located at the internal interface existing between the HfO2 and SiNx:H films. Because charge trapping and discharging are tunneling assisted, these traps are more easily charged or discharged as lower the distance from this interface to the substrate, that is, as thinner the SiNx:H blocking layer. The trapping/detrapping mechanisms increase the amplitude of the capacitance transient and, in consequence, the DLTS signal that have contributions not only from the insulator/substrate interface states but also from the HfO2/SiNx:H interlayer traps.

Magnetic properties of iron nanoparticle

Magnetic properties of Fe nanoparticles with different sizes synthesized by a physical deposition technique have been investigated experimentally. We have used a high pressure sputtering technique to deposit iron nanoparticles on a silicon substrate. The nanoparticles are then analyzed using atomic force microscopy (AFM), transmission electron microscopy (TEM), and superconducting quantum interference device techniques. TEM and AFM data show that the particle size could be tuned by adjusting the deposition conditions. The magnetic properties have been investigated from temperature dependent magnetization M(T) and field dependent magnetization M(H) measurements. The results show that two phases including both ferromagnetic and superparamagnetic particles are present in our system. From these data we extracted the superparamagnetic critical size to be 9 nm for our samples. Ferromagnetic particles are single magnetic domain particles and the magnetic properties can be explained by the Stoner and Wohlfarth model. For the superparamagnetic phase, the effective anisotropy constant, Keff, decreases as the particle size increases.

Effect of sputtering pressure and post-annealing on hydrophilicity of TiO 2 thin films deposited by reactive magnetron sputtering

A series of TiO 2 thin films was deposited onto glass substrates without intentional heating or biasing by magnetron sputtering of a titanium target using Ar/O 2 reactive mixtures over a broad range of total sputtering pressures from 0.12 Pa to 2.24 Pa. Each of the film types was deposited by the threshold poisoned mode at a specific given oxygen flow rate monitored in-situ by optical emission spectroscopy. Both the sputtering pressure and thermal annealing are the key factors for the TiO 2 films to yield fast-response superhydrophilicity with a water contact angle of 5°. The mechanism of superhydrophilicity for the TiO 2 films deposited by high-pressure sputtering will be discussed based on empirical studies of X-ray diffractometry, high-resolution scanning microscopy and atomic force spectroscopy.

Electrical Characterization of High-Pressure Reactive Sputtered Sc2O3 Films on Silicon

Al/ScOx/NiOx/n-Si and Al/ScOx/SiOx/n-Si metal-insulator-semiconductor capacitors have been electrically characterized. Scandium oxide was grown by high pressure sputtering on different substrates to study the dielectric/insulator interface quality. The substrates were silicon nitride and native silicon oxide. The use of nitrided silicon interfacial layer between the silicon substrate and the scandium oxide layer improves interface quality, as interfacial state density and defect density inside the insulator are decreased.

Scandium oxide deposited by high-pressure sputtering for memory devices: Physical and interfacial properties

Scandium oxide (ScOx) thin layers are deposited by high-pressure sputtering (HPS) for physical and electrical characterization. Different substrates are used for comparison of several ScOx/Si interfaces. These substrates are chemical silicon oxide (SiOx), H-terminated silicon surface and silicon nitride (SiNx), obtained by either electron-cyclotron-resonance chemical vapor deposition or plasma enhanced nitridation of the Si surface. Transmission electron microscopy images show that a 1.7 nm thick SiOx layer grows when ScOx is deposited on H-terminated silicon surface. We demonstrate that interfacial SiNx has some advantages over SiOx used in this work: its permittivity is higher and it presents better interface quality. It also avoids Si oxidation. An improvement of one order of magnitude in the minimum of interface trap density is found for SiNx with respect to the SiOx, reaching values below 2×1011 cm−2 eV−1. HPS deposited ScOx films are polycrystalline with no preferential growth direction for the used deposition conditions and their properties do not depend on the substrate. This material could be a candidate for high-k material in flash memory applications.

Enhancement of Ti+ density in high-pressure magnetron sputtering plasmas

This paper discusses the ionization ratio and the ionization mechanism of atomic titanium in high-pressure (10–150 mTorr) magnetron sputtering plasmas employing a titanium target. The spatial distributions of Ti and Ti+ densities in a magnetron sputtering plasma source were visualized by laser-induced fluorescence imaging spectroscopy. It was observed that the ionization ratio of Ti was enhanced significantly in the downstream region by increasing the discharge pressure. The correlation between the ionization ratio and the deposition profile of Ti film inside a trench was examined, and it was confirmed that a deposition condition with a high ionization ratio resulted in a deposition profile with a high bottom coverage. Several experiments were carried out to investigate production processes of Ti+ in high-pressure magnetron sputtering plasmas. We examined the contributions of electron impact ionization, Penning ionization, charge exchange collision with Ar+, and three-body recombination. However, the experimental results revealed that none of the four processes was the dominant production process of Ti+.

Ion beam analysis of high pressure deposition of epitaxial PZT thin films

Abstract Epitaxial thin films of Pb(Zr 0.53 Ti 0.47 ) (PZT) ferroelectric ceramic were successfully grown on Sr(Nb)TiO 3 (SNTO) single crystal substrates by an high-pressure RF sputtering technique. Pure O 2 was used as working gas at a pressure above 1 Torr. The crystalline films properties were evaluated by θ –2 θ DRX scans. From these measurements we concluded that the PZT layers were single crystalline and c -axis oriented with a (001)PZT||(001)SNTO crystallographic relationship. Film composition and film–substrate interface characteristics were studied by bombardment of the samples with a 2560 keV 3 He + beam. Rutherford Backscattering (RBS) technique was applied to fit the experimental spectra in order to deduce the elemental depth concentration profile of the films. The high-pressured technique represents a useful and capable method to obtaining in situ epitaxial ferroelectric thin film with high quality structural, compositional and dielectric properties, without post deposit treatment.