Negative Substrate Bias Research Articles

Role of Low-Energy Ion Impact in Plasma Deposition of Cubic Boron Nitride Films

Cubic boron nitride (cBN) is potentially expected as the semiconductor for high temperature condition due to the large band gap, high breakdown field, and high resistance to oxidation. cBN films have been synthesized from vapor phase using a variety of physical vapor deposition such as sputtering and ion beam deposition rather than plasma-enhanced chemical vapor deposition. However, high-energy (>50 eV) ion bombardment for cBN formation results in low-quality cBN films and thus obstructs their electrical applications. In our previous studies, high-quality cBN films were deposited under low-energy ion bombardment (<40 eV) by plasma-enhanced chemical vapor deposition using the chemistry of fluorine. The mean ion energy for cBN formation was reduced greatly, then the resulting films consisted of micron-sized grains with crystallographic morphology. In this study, the deposition mechanism of our cBN films is examined in terms of ion energy, ion flux, and ion to depositing boron flux ratio onto the substrate. The ion energy and the ion to boron flux ratio are determined from the sheath potential and the ratio of incident ion flux to net deposited boron flux, respectively. For negative substrate biases where sp2-bonded BN phase only or no deposit is formed, both the ion energy and the ion to boron flux ratio are high. For positive substrate biases where cBN phase is formed, the ion energy and the ion to boron flux ratio are estimated in the range of a few eV to 35 eV and 100 to 130, respectively. The impact of negative ions is presumed to be negligible due to their low kinetic energy. The impact of positive ions with high ion to boron flux ratios is primarily responsible for reduction of the ion energy for cBN film deposition. [1] K. Teii and S. Matsumoto, Thin Solid Films 576, 50-54 (2015).

Gum Metal thin films obtained by magnetron sputtering of a Ti-Nb-Zr-Ta target

TNTZ quaternary superelastic coatings with a beta structure were successfully deposited by magnetron sputtering of a Ti-Nb-Zr-Ta target. In this work, we discuss the effects of argon pressure and negative substrate bias voltage on the microstructure, morphology, texture, mechanical properties and superelastic behavior of these coatings. The results show that the texture is random at high deposition pressure and it becomes {110} at the lowest deposition pressure (i.e. 0.2Pa). Applying negative bias voltage causes the disappearance of {110} texture and promotes the appearance of {100} and {111} textures. The texture evolution is related to the ion bombardment of the growing film and to the surface mobility of adatoms. The highest hardness and Young’s modulus are obtained for the Gum Metal (GM) film deposited at the lowest deposition pressure (i.e. 0.2Pa) and a bias of −200V. The Evolution of the mechanical properties is discussed as a function of the film density, the compressive stress and grains' size changes. It was found that the film deposited at 0.2Pa and floating potential presents the greatest depth recovery ratio. It is due to the fact that the film is dense and its texture is {110}. The negative bias voltage seems to have an unfavorable effect on the superelasticity.

Influence of negative bias pulse parameters on accumulation of macroparticles on the substrate immersed in titanium vacuum arc plasma

Abstract The paper presents the results of an experimental study of the influence of a substrate negative bias with various pulse lengths and pulse repetition rates ranging from several pulses per second to 10 5 pulses per second on the macroparticle accumulation on the substrate immersed in DC titanium vacuum arc plasma. It was found that the increase of the bias pulse frequency from 10 up to 10 5 pulses per second at pulse length 7 μs, as well as bias pulse lengths from 5 μs to 25 μs at fixed frequency of 30 pulses per second at bias pulse amplitude ˗2 kV and ion-plasma substrate treatment time 30 s led to gradual almost linear up to 3-fold decrease of the surface number density of MPs on the substrate immersed in titanium vacuum arc plasma at plasma ion saturation current density of 10 mA/cm 2 . The decrease of ion current density down to 3.5 mA/cm 2 leads to the reduction of the macroparticle suppression efficiency. The influence of multiple recharging of the macroparticles in plasma and the sheath on the reflection of these macroparticles in the sheath electric field is discussed. It was experimentally found that the shape of MPs and their adhesion to the substrate surface strongly depends on bias pulse, plasma and substrate parameters. It was shown that cooled vacuum arc MPs can be melted in high-voltage plasma sheath.

Substrate-Voltage Modulation of Currents in Symmetric SOI Lateral Bipolar Transistors

The modulation of the currents in a symmetric Semiconductor-on-Insulator (SOI) lateral bipolar transistor with a voltage applied to the SOI substrate is studied. For an n-p-n transistor, a positive substrate bias could greatly increase the collector current, especially at low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE</sub> values, while having relatively little effect on the base current. Similarly, a negative substrate bias could greatly increase the collector current of a p-n-p transistor. The physical mechanisms responsible for the modulation effects are discussed. The potential of using substrate bias to enhance the performance of symmetric SOI lateral bipolar circuits is briefly discussed.

Use of Acoustic Emission During Scratch Testing for Understanding Adhesion Behavior of Aluminum Nitride Coatings

In this work, acoustic emission during scratch testing of the aluminum nitride coatings formed on stainless steel substrate by reactive magnetron sputtering was analyzed to assess the coating failure. The AlN coatings were formed under the variation of substrate temperature, substrate bias potential, and discharge power. The coatings deposited in the temperature range of 100 to 400 °C showed peak acoustic emission less than 1.5%, indicating ductile nature of the coating. However, for coatings formed with substrate negative bias potential of 20 to 50 V, numerous sharp acoustic bursts with maximum emission approaching 80% were observed, indicating brittle nature of the coatings with large number of defects present. The shift in the intensity of the first major acoustic peak toward higher load, with the increasing bias potential, confirmed improved adhesion of the coating. Also, the higher discharge power resulted in increased acoustic emission.

Effect of substrate bias on the structural and electrical properties of sputtered Mo thin films on flexible substrates.

The metal molybdenum (Mo) thin films deposited on flexible substrates can act as the contact electrode of flexible Cu(In,Ga)Se2 or Cu2ZnSn(S,Se)4 solar cells. In this work, in order to enhance the structural and electrical characteristics of flexible Mo thin films, a negative substrate bias was applied during the direct current sputtering of Mo thin films. The flexible substrates used for growing the Mo films were stainless steel foils and polyimides. The characteristics of Mo thin films were studied by x-ray diffraction and sheet resistance measurements. The measured results reveal that an optimal value of negative substrate bias can be found for improving the electrical and structural characteristics of Mo thin films on flexible substrates. The minimum sheet resistances of Mo thin films are 2.50 Ω/sq and 2.73 Ω/sq for the stainless steel foil and polyimide substrates, respectively.

Dependence of Negative Substrate Bias on the Optical and Electrical Properties of W-Doped Vanadium Dioxide Thin Films

W-doped VO2 films were prepared by DC reactive magnetron sputtering with various substrate bias. The microstructure, surface morphology, electrical and optical performances of the films were characterized by x-ray diffraction, scanning electron microscope, four-point probe method and spectrophotometer, respectively. The effect of substrate bias on microstructure, electrical and optical properties of sputtered W-doped VO2 films was studied. The XRD results reveal that all samples exhibit preferential VO2 (011) lattice orientation except the as-grown sample in our experiment. All the samples applied substrate bias show some degree optical switching performance in IR range, while the thermochromic phenomena was observed from resistance-temperature dependence plot only for the samples of substrate bias varied from-100V to-200V. This indicate that the optical and electrical properties of W-doped VO2 films have different sensitivity to substrate bias. Optimal substrate bias of-200V sample shows fine semiconductor-metal-transition performance.

Effects of Substrate Bias on Tribological Properties of Diamondlike Carbon Thin Films Deposited Via Microwave-Excited Plasma-Enhanced Chemical Vapor Deposition

In this study, the structure and tribological performance of the diamondlike carbon (DLC) films were related to deposition parameters. The feasibility of the microwave-excited plasma-enhanced chemical vapor deposition (μW-PECVD) as a process to produce good quality DLC films was the focus. The DLC films were deposited on the steel substrates with a tungsten carbide interlayer via μW-PECVD. The negative substrate bias used during the film deposition was varied. The Raman results revealed that the increased negative substrate bias increased the sp3 bonding in the DLC films as a result of the increased kinetic energy of film-forming ions during the film deposition. The tribological results clearly indicated that the friction and wear of the DLC-coated steel samples against a 100Cr6 steel ball significantly decreased with increased negative substrate bias due to the significantly improved wear resistance of the DLC films.

Performance of ion plating TiAlN coating on YG8

Multi-arc ion plating technology and interactive deposition process are adopted to plate TiAlN hard film on the surface of YG8 cemented carbide cutting tools. Study the influences of the coating film parameters to surface appearance with orthogonal experiment method. Observe substrate samples, TiN transition layer and TiAlN coating film under the scanning electron microscope (SEM). Cutting test, friction and wearing test showed that the coated cutting tools are with more wearing resistance. The main wear mechanisms are adhesion, some accompanied by flake layer of disbanding. Coated cutting tools significantly reduces friction coefficient. By experimental design, the best process parameters are deposition temperature 100°C, substrate negative bias voltage 250 V, nitrogen partial pressure 0.6 Pa.

Controlling nanowire nucleation and growth with a negative substrate bias

Applying a voltage bias to silicon nanowires during growth can influence wire density, diameter and length.

Charge movement in a GaN-based hetero-structure field effect transistor structure with carbon doped buffer under applied substrate bias

Charge trapping and transport in the carbon doped GaN buffer of a GaN-based hetero-structure field effect transistor (HFET) has been investigated under both positive and negative substrate bias. Clear evidence of redistribution of charges in the carbon doped region by thermally generated holes is seen, with electron injection and capture observed during positive bias. Excellent agreement is found with simulations. It is shown that these effects are intrinsic to the carbon doped GaN and need to be controlled to provide reliable and efficient GaN-based power HFETs.

New Findings on the Drain-Induced Barrier Lowering Characteristics for Tri-Gate Germanium-on-Insulator p-MOSFETs

This paper investigates the intrinsic drain-induced barrier lowering (DIBL) characteristics for tri-gate germanium-on-insulator (GeOI) p-MOSFETs through theoretical calculation by analytical solution of 3-D Poisson’s equation corroborated with TCAD numerical simulation. It is found that, relative to the silicon-on-insulator counterpart, there exists a build-in negative substrate bias in the GeOI PFET. This built-in substrate bias, stemming mainly from the large discrepancy in bandgap between Ge and Si, pulls the carriers toward the channel/BOX interface and thus degrades the DIBL of the GeOI PFET beyond what permittivity predicts. This new mechanism has to be considered when designing or benchmarking tri-gate GeOI p-MOSFETs.

Influence of the negative bias in ion plating on the microstructural and tribological performances of Ti–Si–N coatings in seawater

The TiSiN coatings were deposited on Ti6Al4V alloy by multi-arc ion plating with different substrate negative bias to improve the tribological properties of titanium alloy in seawater. The TiSiN coatings have a coupled structure of amorphous Si3N4 and nanocrystalline TiN. The grain size decreases and the coatings become dense with the increase of the negative bias. The hardness of TiSiN coatings increases from 39GPa to 47GPa with the increase of substrate negative bias from 10V to 40V. The tribological tests reveal that the TiSiN coatings have a lower friction coefficient and higher wear rate in seawater compared with in atmosphere. Moreover, the wear rates increase with the increase of bias voltage. The TiSiN coating deposited at bias voltage of 10V shows the best tribological properties in seawater.

The impact of substrate bias on a remote plasma sputter coating process for conformal coverage of trenches and 3D structures

With the progression towards higher aspect ratios and finer topographical dimensions in many micro- and nano-systems, it is of technological importance to be able to conformally deposit thin films onto such structures. Sputtering techniques have been developed to provide such conformal coverage through a combination of coating re-sputtering and ionised physical vapour deposition (IPVD), the latter by use of a secondary plasma source or a pulsed high target power (HiPIMS). This paper reports on the use of an alternate remote plasma sputtering technique in which a high density (>1013 cm−3) magnetised plasma is used for sputter deposition, and additionally is shown to provide IPVD and a re-sputtering capability. From the substrate I–V characteristics and optical emission spectroscopy (OES) data, it is shown that remote plasma sputtering is an inherently continuous IPVD process (without the need of a secondary discharge). Through the reactive deposition of Al2O3 onto complex structures, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) results demonstrate that applying a negative substrate bias during film growth can result in re-sputtering of deposited material and film growth on surfaces obscured from the initial sputter flux. Using 5 : 1 (height : width) aspect ratio trenches, the substrate bias was set to 0,−245 and −334 V. At 0 V substrate bias, the alumina coating is predominantly deposited on the horizontal surfaces; at −344 V, it is predominantly deposited onto the side walls and at −245 V a more uniform layer thickness is obtained over the trench. The process was optimised further by alternating the substrate bias between −222 and −267 V, with a 50% residence time at each voltage, yielding a more uniform conformal coverage of the 5 : 1 aspect ratio structures over large areas.

A study of structural and wear properties of PACVD deposited a‐C:H thin films for application as protective layers on Al alloys

Due to the high strength‐to‐weight ratio, aluminum alloys are commonly used materials in aircraft and automotive industries. However, the low hardness and wear resistance and high friction coefficient limit their applications. In this study, we deposited a‐C:H thin films on 7075 Al alloy substrates without an interlayer by direct current PACVD method. Negative substrate bias was varied to improve the surface mechanical properties. We obtained smooth, homogenous, and well adhered up to 28 μm thick a‐C:H layers on the Al alloy substrates. The structural and mechanical properties were analyzed using Raman spectroscopy, SEM, nanoindentation and Pin‐on‐disc test. Raman spectroscopy showed a higher content of trans(CH)x within the films deposited with low bias and increased sp2 bonding for higher bias depositions. Adhesion test has shown the adhesion grade HF1 to HF4. Coefficient of friction was measured in the range 0.05–0.15 and wear rates of a‐C:H covered samples were significantly reduced in comparison to uncovered substrates. The obtained results show a promising potential of the a‐C:H as wear resistant coatings for the 7075 Al alloy.

Wear and corrosion resistance of CrN/TiN superlattice coatings deposited by a combined deep oscillation magnetron sputtering and pulsed dc magnetron sputtering

Deep oscillation magnetron sputtering (DOMS) is a novel high power impulse magnetron sputtering technique, which offers large voltage oscillation packets to generate a stable high-power discharge plasma with high ionization under virtually arc-free conditions. CrN/TiN superlattice coatings were deposited using a combined DOMS and pulsed dc magnetron sputtering (PDCMS) in a closed field unbalanced magnetron sputtering configuration. The Cr target was powered at 400W by DOMS and Ti target was powered at 2000W by PDCMS. The negative substrate bias (Vs) ranged from 0V to −100V. As the Vs was increased, CrN/TiN superlattice coatings showed a single phase face-centered cubic structure with a strong (111) texture. Correspondingly, the coatings exhibited the dense microstructure with well-defined interfaces between CrN and TiN layers. The increase in Vs led to a decrease in grain size and an increase in the compressive residual stress. The hardness and Young's modulus of the coatings increased with increasing Vs. The H/E* and H3/E*2 ratios and critical loads LC in scratch test showed an initial increase, followed by a decrease. The wear mechanism changed from severe adhesion wear to abrasion wear. The coating deposited at Vs=−60V exhibited mild abrasion wear with the lowest friction coefficient of 0.27 and the lowest specific wear rate of 0.5×10−6mm3N−1m−1 due to high hardness, H/E* and H3/E*2 ratios, LC1 and LC3 of 36GPa, 0.094, 0.316, 15.3N and 24N, respectively. The coatings also exhibited increasing pitting corrosion resistance with lower current density and higher corrosion potential in 3.5wt% NaCl aqueous solution. Combined DOMS+PDCMS techniques can provide the engineering surfaces for the industrial applications with the combined improvement in wear and corrosion resistance.

Water vapor barrier properties of Si–Zn–O/Al multilayer structures

Single-layer Si–Zn–O (SZO) and multilayer SZO/Al films are deposited as water vapor barriers on polyimide (PI) substrates, using magnetron sputtering with SiO2–ZnO composite and Al targets. The effect of negative substrate bias voltage (Vb) on the microstructure and water vapor barrier properties of the single layer SZO and multilayer SZO/Al films is investigated. The as-deposited SZO film is found by X-ray diffraction analysis to be amorphous. For deposition at Vb=0V, the SZO film has a columnar structure and rough surface morphology; the Al film exhibits pinholes on the surface. When moderate bias voltages (Vb=−50V for SZO and −70V for Al films) are applied during deposition, a dense SZO film with smooth surface morphology and a pinhole-free Al film are obtained. An SZO/Al multilayer film shows better water vapor barrier performance than a single-layer SZO, which could be further enhanced by application of Vb to the substrate during film growth.

Deposition of chromium nitride coatings using vacuum arc plasma in increased negative substrate bias voltage

The deposition methods of thin films which allow to obtain good quality coatings are still being developed. The paper presents a particular influence of the substrate bias voltage on the results of the deposition of chromium nitride coatings on HS6-5-2 steel substrates on the front and reverse side of the substrates with respect to the cathode by cathodic arc evaporation. The deposition was carried out at a fixed nitrogen pressure amounted to 3.0 Pa and the negative substrate bias voltages: 70, 150, 300 V. The difference in the deposition rate, phase and chemical composition, amount and dimensional distribution of macroparticles and surface roughness were studied and analyzed. It was found that the coatings obtained on the reverse side of the substrate were characterized by a nearly 3-times smaller amount of surface defects, more than twice the lower surface roughness and similar chemical composition as the coatings deposited on the front side of the substrate. The measurements have also shown that the hardness of the coatings obtained on both sides of the substrate is comparable, and decreases with increasing the negative substrate bias voltage.

Modulating microstructure and optical properties of hydrogenated nanocrystalline silicon photovoltaic materials prepared under hydrogen diluted silane PECVD by various DC bias

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were fabricated by plasma enhanced chemical vapor deposition under the various negative substrate bias voltages with hydrogen as a diluent of silane. The microstructure and optical properties of nc-Si:H thin films were studied by Raman scattering spectroscopy, X-ray diffraction (XRD), transmission electron microscopy, and optical transmission spectroscopy. Raman spectra and XRD pattern reveal that applying negative bias voltages at the moderate level favors the enhancement of crystalline volume fraction, increase of crystallite sizes and decrease of residual stress. We also demonstrated that the negative direct current bias can be used to modulate the volume fraction of voids, refractive index, absorption coefficient, compactness and ordered degree of nc-Si:H films. It is found that the film deposited at −80V shows not only high crystallinity, size of crystallite, and static index n0 but also low residual stress and volume fraction of voids. Furthermore, the microstructural evolution mechanism of nc-Si:H thin films prepared at different bias voltages is tentatively explored.

Enhancement of the mechanical properties of AZ31 magnesium alloy via nanostructured hydroxyapatite thin films fabricated via radio-frequency magnetron sputtering

The structure, composition and morphology of a radio-frequency (RF) magnetron sputter-deposited dense nano-hydroxyapatite (HA) coating that was deposited on the surface of an AZ31 magnesium alloy were characterized using AFM, SEM, EDX and XRD. The results obtained from SEM and XRD experiments revealed that the bias applied during the deposition of the HA coating resulted in a decrease in the grain and crystallite size of the film having a crucial role in enhancing the mechanical properties of the fabricated biocomposites. A maximum hardness of 9.04GPa was found for the HA coating, which was prepared using a bias of −50V. The hardness of the HA film deposited on the grounded substrate (GS) was found to be 4.9GPa. The elastic strain to failure (H/E) and the plastic deformation resistance (H3/E2) for an indentation depth of 50nm for the HA coating fabricated at a bias of −50V was found to increase by ~30% and ~74%, respectively, compared with the coating deposited at the GS holder. The nanoindentation tests demonstrated that all of the HA coatings increased the surface hardness on both the microscale and the nanoscale. Therefore, the results revealed that the films deposited on the surface of the AZ31 magnesium alloy at a negative substrate bias can significantly enhance the wear resistance of this resorbable alloy.