Function Of Substrate Bias Voltage Research Articles

Influence of substrate bias voltage on crystallographic structure, optical and electronic properties of Al/(Ta2O5)0.85(TiO2)0.15/p-Si MIS Schottky barrier diodes fabricated by dc magnetron sputtering

Thin films of (Ta2O5)0.85(TiO2)0.15 were prepared on p-Si and quartz substrates by reactive magnetron sputtering and the influence of substrate bias voltage (Vb) on their structural and electrical properties was studied. The crystal structure of the prepared films was elucidated by X-ray diffraction (XRD) studies. The structure of the as deposited films was found to be amorphous and the surface roughness of the films was found to be low. The crystallinity of the films was observed to be improved by increasing the substrate bias voltage. The XPS results revealed that the composition of the films were nearly stoichiometric with Vb at 0V and −150V. The optical properties of the films at various substrate bias voltages were also studied. The optical band gap of the films formed at various Vb values from 0 to −150V decreased from 4.49 to 4.39eV as revealed from the optical transmission spectra. The fabricated Al/(Ta2O5)0.85(TiO2)0.15/p-Si metal-insulator-semiconductor (MIS) Schottky diodes leakage currents at −1.5V decreased from 4.65 × 10−6A (unbiased) to 3.73 × 10−8A (Vb = −100V). On the other hand, the sample biased at Vb= −150 V exhibited an increase in leakage current (2.99 × 10−4A) when compared to all other prepared samples. Furthermore, the electrical parameters such as Schottky barrier height and ideality factor were calculated for the Al/(Ta2O5)0.85(TiO2)0.15/p-Si MIS Schottky structure and systematically investigated as a function of substrate bias voltage using current-voltage (I-V) and capacitance-voltage (C-V) characteristics.

Structural characterization of ion-vapor deposited hydrogenated amorphous carbon coatings by solid state 13C nuclear magnetic resonance

In the present study, unique structural heterogeneity was observed in ion-vapor deposited a-C:H coatings by performing 13C MAS and 1H-13C CPMAS experiments on solid state nuclear magnetic resonance devices. Two distinct types of sp2 C clusters were discovered: one of them denoted as sp2 C′ in content of 3–12 at. % was non-protonated specifically localized in hydrogen-absent regions, while the other dominant one denoted as sp2 C″ was hydrogenated or at least proximate to proton spins. On basis of the notably analogous variation of sp2 C′ content and Raman parameters as function of substrate bias voltage in the whole range of 0.5 kV–3.5 kV, a model of nano-clustering configuration was proposed that the sp2 C′ clusters were embedded between sp2 C″ clusters and amorphous sp3 C matrix as trapped interfaces or boundaries where the sp2 carbon bonds were highly distorted. Continuous increase of bias voltage would promote the nano-clustering and re-ordering of dominant sp2 C″ clusters, thus results in a marked decrease of interspace and a change of the content of sp2 C′ clusters. Further investigation on the 13C magnetization recovery showed typical stretched-exponential approximation due to the prominent presence of paramagnetic centers, and the stretched power α varied within 0.6–0.9 from distinct types of sp2 C clusters. Differently, the magnetization recovery of 1H showed better bi-exponential approximation with long and short T1(H) fluctuated within 40–60 ms and 0.1–0.3 ms approximately in content of 80% ± 5% and 20% ± 5%, respectively, varying with various bias voltages. Meanwhile, the interrupted 13C saturation recovery with an interval of short T1(H) showed that most of quick-relaxing protons were localized in sp2 C″ clusters. Such a short T1(H) was only possibly resulted from a relaxation mechanism associated with electron-nuclear dipolar interaction or spinning diffusion, and its partial distribution in sp2 C″ clusters may imply more complex configurations of unpaired electrons in studied a-C:H coatings.

The parameter space of hydrogen content added to Ar–nitrogen sputtering gas and substrate bias voltage for the formation of cubic boron nitride thin film deposited by unbalanced magnetron sputtering method

The parameter space for the formation of cubic phase of boron nitride thin films as a function of substrate bias voltage and hydrogen content added to Ar–N2 reactive sputtering gas was proposed. Cubic boron nitride (c-BN) films were deposited by unbalanced magnetron sputtering (UBM) method. Thin (100μm) Si strips (3×40mm2) were used as substrates. A boron nitride target was used, which was connected to a radio frequency (RF) power supply set at 400W. High frequency power connected to a substrate holder was used for self-biasing of up to −110V. The deposition pressure was 0.27Pa with a flow of Ar (18sccm) — N2 (2sccm) mixed gas irrespective of hydrogen addition. Hydrogen gas up to 16sccm was added to the Ar–N2 mixed gas. The addition of hydrogen tended to decrease the threshold substrate bias voltage for c-BN formation. Even under low bias voltage, where only hexagonal boron nitride (h-BN) formed under the Ar–N2 gas atmosphere, c-BN began to form with the addition of hydrogen to the gas. The surface of the film was very flat irrespective of the amount of added hydrogen. The deposition rate reduced with increasing hydrogen content. The residual stress decreased to 2GPa with a hydrogen flow of 10sccm, while maintaining the c-BN fraction in the film above 60%. The role of the hydrogen during the c-BN formation was briefly discussed.

Substrate bias effect on structure of tetrahedral amorphous carbon films by Raman spectroscopy

Diamond-like carbon (DLC) films form a critical protective layer on magnetic hard disks and their reading heads. Now tetrahedral amorphous carbon films (ta–C) thickness of 2 nm are becoming the preferred means due to the highly sp 3 content. In this paper, Raman spectra at visible and ultraviolet excitation of ta–C films have been studied as a function of substrate bias voltage. The spectra show that the sp 3 content of 70 nm thick DLC films increases with higher substrate bias, while sp 3 content of 2 nm ultra-thin films falls almost linearly with bias increment. And this is also consistent with the hardness measurement of 70 nm thick films. We proposed that substrate bias enhances mixing between the carbon films and either the Si films or Al 2O 3TiC substrate such that thin films contain less sp 3 fraction. These mixing bonds are longer than C–C bonds, which inducing the hardness decreasing of ultra-thin DLC films with bias. But for 70 nm DLC, the effect of mixing layer can be negligible by compared to bias effect with higher carbon ion energy. So sp 3 content will increase for thick films with substrate bias.

Effects of substrate bias voltage on projection growth in chromium nitride films deposited by arc ion plating

Projection growth in chromium nitride films deposited by arc ion plating was studied as a function of substrate bias voltage by scanning electron microscope and stylus instrument. Most of projections were observed as the tops of tapered crystallite developed on droplets. Most of the droplets were implanted under the projections, although there existed some droplets on film surface. And growth morphology of projections on droplets was strongly affected by substrate bias voltage. Under the condition of low substrate bias voltage, projections grew larger than droplets to roughen the film surface. On the other hand, under the condition of high bias voltage, diameters of projections were smaller than the droplets to be embedded to flatten the surface as film deposition progresses further. Then, the number and size of projections on film surfaces and surface roughness of the film decreased with an increase in substrate bias voltage. Besides, droplets adhering on film surface shadowed the underlying film from further deposition of chromium nitride, resulting in the appearance of toroidal shaped voids along the droplets. Though these toroidal shaped voids developed upward from the shaded bottom surface along the droplets at low bias voltage, these voids became smaller to be detected just beneath the droplet at the higher bias voltage. These results imply that the resputtering effect on geometrical projections, strengthened by the increase in substrate bias voltage, as generally accepted, would cause the decrease of the deposition rate on projections much more than on the flat surface of the film, and resputtered materials would also fill the space between the droplets and the film surface, resulting in the embedment of projections as film deposition progresses.

Effect of substrate bias voltage and substrate on the structural properties of amorphous carbon films deposited by unbalanced magnetron sputtering

Amorphous carbon (a-C) films have been produced by unbalanced magnetron sputtering (UBMS) on silicon (Si), aluminium (Al), and chromium (Cr) substrates as a function of substrate bias voltage. The chemical bonding configurations were investigated by Raman and near-edge X-ray absorption fine structure (NEXAFS) spectroscopies. It was found that the structural changes induced by bias voltage are substrate-dependent, revealing the key role of the substrate type on film microstructures. The Raman G peak position and I D/ I G ratio were strongly dependent on substrate material and negative bias voltage. Negative bias voltage had a small effect on the structure of carbon films on metal substrates (Al and Cr). However, the films on silicon showed significant change in the structure with bias voltage. The intensity and area of π* peak at the C K (carbon) edge increased with the increase of substrate bias voltage. The NEXAFS analysis was in agreement with Raman observations, which clearly indicated an increase of sp 2 content with increasing bias voltage. The films deposited in the low-bias voltage regime (50–100 V) showed reduced sp 2 configurations. The possible changes of structure with substrate bias are thoroughly discussed.

Two mechanisms of diamond phase formation during magnetron sputter deposition of amorphous carbon films

The diamond phase formation mechanisms are analysed by a new phenomenological model of deposition of diamond-like carbon (DLC) films on Si(001) substrate. Experimental observations that make base for this model are reviewed briefly. Only the main processes, such as adsorption of carbon atoms on the surface, formation of SiC, diamond, and graphite sites, are assumed to take place. Compressive stress, induced by ion subplantation, is regarded as a main factor causing the transformation of graphite to diamond. Relationship between stress and ion energy is given by Davis’ formula. According to this model, dependences of film deposition rate versus time and dependences of film composition versus film thickness are calculated that are in agreement with experimental ones. Also, the ratio of sp/sp volume fractions as a function of substrate bias voltage was calculated. Modelling of experimental curves show that under conditions of sputter deposition of DLC films there are at least two diamond phase formation mechanisms: (i) on the surface during carbon adsorption, and (ii) in the bulk of film by subplantation induced graphite transition to lonsdaleite (hexagonal diamond).

FABRICATION OF AMORPHOUS CARBON MICRO-MEMBRANES BY DEEP REACTIVE ION ETCHING TECHNIQUE

International Journal of Computational Engineering ScienceVol. 04, No. 03, pp. 581-584 (2003) Poster PapersNo AccessFABRICATION OF AMORPHOUS CARBON MICRO-MEMBRANES BY DEEP REACTIVE ION ETCHING TECHNIQUELIUJIANG YU, B. K. TAY, D. SHEEJA, Y. Q. FU, and J. M. MIAOLIUJIANG YUIon Beam Processing Laboratory, Block S1, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore Search for more papers by this author , B. K. TAYIon Beam Processing Laboratory, Block S1, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore Search for more papers by this author , D. SHEEJAIon Beam Processing Laboratory, Block S1, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore Search for more papers by this author , Y. Q. FUSchool of Mechanical and Production Engineering, NTU, Singapore - 639798, Singapore Search for more papers by this author , and J. M. MIAOSchool of Mechanical and Production Engineering, NTU, Singapore - 639798, Singapore Search for more papers by this author https://doi.org/10.1142/S1465876303001800Cited by:1 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractThe primary problem of large intrinsic compressive stress induced during the deposition of amorphous carbon (a-C) films prepared by Filtered Cathodic Vacuum Arc (FCVA) technique has been overcome by preparing the films in conjuction with high substrate pulse biasing. However, it has been observed that the stress reduction is achieved by sacrificing the mechanical properties such as hardness and Young's modulus of the films. Hence the mechanical properties of the films were studied as a function of substrate bias voltage. In addition, to demostrate these low stress films, one-micron thick, a-C membranes were fabricated by photolithography technique together with deep reactive ion etching (deep RIE) and wet KOH etching.Keywords:a-C filmssubstrate biasMEMSmicro-membranes References X. Shiet al., J. of Appl. Phys. 79, 7234 (1996). Google ScholarX. Shi, L. K. Cheah and B. K. Tay, Thin Solid Film 312, 160 (1998). Google ScholarB. K. Tayet al., Surf. Coat. Technol. 105, 155 (1998). Crossref, Google ScholarG. M. Pharret al., Appl. Phys. Lett. 68, 779 (1996). Crossref, Google Scholar B.K. Tay, D. Sheeja and L.J. Yu, Diamond and Related Materials, in press . Google Scholar Andr'e Anders , Handbook of Plasma Immersion Ion Implantation and Deposition ( John Wiley & Sons , 2000 ) . Google Scholar FiguresReferencesRelatedDetailsCited By 1Diamond-like carbon for MEMSErwin Peiner, Arti Tibrewala, Ralf Bandorf, Holger Lüthje and Lutz Doering et al.26 June 2007 | Journal of Micromechanics and Microengineering, Vol. 17, No. 7 Recommended Vol. 04, No. 03 Metrics History Keywordsa-C filmssubstrate biasMEMSmicro-membranesPDF download

High rate etching of AlN using BCl 3/Cl 2/Ar inductively coupled plasma

Inductively-coupled-plasma reactive ion etching of AlN was investigated using BCl 3/Cl 2/Ar gas chemistry. AlN etch rates were studied as a function of substrate bias voltage (−150 to −400 V), ICP coil power (200–900 W) and chamber pressure (2–10 mT). Using an electroplated Ni mask, up to 50 μm deep AlN structures were etched. This is the first demonstration of deep etching of AlN at high etch rates using inductively-coupled-plasma. The results reported in this study can be used for bulk micro-machining AlN substrates.

Effects of substrate bias voltage on plasma parameters in temperature control using a grid system

In this paper we investigate the effects of substrate bias voltage on plasma parameters in temperature control using a grid system in inductively coupled plasma. Electron temperature can be controlled from 2.5 eV to 0.5 eV at 1 mTorr Ar plasma using grid bias voltage, and the electron temperature is a strong function of substrate bias voltage. The main control parameter determining the electron temperature is the potential difference between grid-biased voltage and the plasma potential in the temperature controlled region (ΔφII,g). When substrate bias voltage is negative, plasma parameters do not vary with substrate bias voltage due to constant ΔφII,g

High rate etching of SiC using inductively coupled plasma reactive ion etching in SF6-based gas mixtures

Inductively coupled plasma (ICP) reactive ion etching of SiC was investigated using SF6 plasmas. Etch rates were studied as a function of substrate bias voltage (−3 to −500 V), ICP coil power (500–900 W), and chamber pressure (1–6 mT). The highest etch rate (970 nm/min) for SiC yet reported was achieved. Anisotropic etch profiles with highly smooth surfaces free of micromasking effects were obtained. The addition of O2 to the SF6 plasma was found to slightly increase the etch rate.

Silicide formation in cobalt/amorphous silicon, amorphous Co [sbnd]Si and bias-induced Co [sbnd]Si films

The silicide formation in cobalt/amorphous silicon multilayer films, amorphous cobalt-silicon films, and bias-induced cobalt-silicon films has been examined by differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. For amorphous cobalt-silicon and bias-induced cobalt-silicon films, Co 2Si forms as a firstsilicide phase, followed by the formation of CoSi and CoSi 2. For a Co/a-Si multilayer film with the atomic concentration ratio of the cobalt to silicon layer being 1:2, CoSi is found to be formed as the first silicide phase. It is confirmed that CoSi, Co 2Si, CoSi, and CoSi 2 form sequentially as the scanning temperature increases. The observed phase sequence is analyzed by the effective heat of formation. A structure factor in addition to the effective heat of formation is used to explain the difference in the formation of the firstphase between cobalt/amorphous silicon multilayer films, amorphous cobalt-silicon alloy films, and bias-induced cobalt-silicon films. For the case of bias-induced cobalt-silicon films prepared at various substrate temperatures and bias conditions, the phase sequence and crystallinity of cobalt silicide have a stronger dependence on the substrate bias voltage than on the substrate temperature due to the effects of collisional cascade mixing, in-situ cleaning, and an increase in the number of nucleation sites by ion bombardment on the growing surface. Also, bias-induced epitaxial CoSi 2 layer is grown at 200 °C,a much lower temperature than molecular beam epitaxy. In order to quantitatively explain low-temperature epitaxial growth of the CoSi 2 layer, the Ar ion energy transferred to Co and Si atomsand the resputtering yield as a function of substrate bias voltage are calculated.

XPS study of carbon/inconel bilayers as a function of substrate bias

X-ray photoelectron spectroscopy (XPS) was used to study the chemical content of sputter deposited carbon/inconel bilayers as a function of substrate bias voltage. The thickness of the layers was 10 Å for inconel and 12.5 Å for carbon; they have been used as the low and high index materials in X-ray multilayers that operate at 45 Å wavelength, at normal incidence. The objective was to investigate the most favourable growth conditions. The carbon layer formed a continuous film only for samples grown with a bias voltage of −40 V. Single layers of carbon and inconel were also studied as a function of substrate bias using grazing X-ray reflection (GXR) to investigate the effect of ion bombardment on the surface quality of the layers. The smoothest inconel single layers were obtained with a moderate substrate bias (−40 to −60 V) while the roughness of single carbon layers was not affected by the substrate bias. We conclude that the open structure observed in bilayers grown with substrate bias voltages other than −40 V is due to the rougher underlying inconel layer, which in turn ‘roughens’ the thin carbon layer.

Atomic constraint in hydrogenated ‘‘diamond-like’’ carbon

Carbon bonding environments (measured by nuclear magnetic resonance spectroscopy) and compressive stress in plasma-deposited hydrogenated diamond-like carbon (DLC) films have been examined systematically as a function of substrate bias voltage. These results are related in terms of random network theory to show that hard DLC formed in an intermediate voltage range (100–400 V) consists of small graphitic clusters linked in a random network which is stiffened by a high density of quaternary carbon.

Langmuir diagnostics of an rf-magnetron discharge used for ion-assisted growth of PbTe epilayers

The plasma potential and the electron density and electron temperature of an rf magnetron discharge used for the ion-assisted growth of PbTe epilayers on BaF2 are measured using Langmuir probe diagnostics. The effect of rf potentials at the probe on the measured plasma parameters is reduced by driving the probe to follow the plasma potential. The discharge parameters are determined as a function of substrate bias voltage and substrate rf power. The ion energy and flux necessary for the epitaxial growth of (111) PbTe on (111) BaF2 are determined.

The abrasive wear resistance of sputter ion plated titanium nitride coatings

Previous work has shown that under abrasive wear conditions it is not sufficient to consider coating hardness in isolation when seeking a guide to coating selection; it is more meaningful to talk in terms of the load-bearing capacity of the coating-substrate system. For titanium nitride coatings deposited onto austenitic stainless steel the variation in resistance to abrasive wear has been evaluated as a function of substrate bias voltage and the results have been compared with these earlier studies. Substrate bias has been identified as a particularly important system's parameter, since it allows some stress relaxation to occur within the coating because of its effect on porosity levels; this has important consequences with regard to adhesion, wear resistance and film hardness. With low substrate bias voltages, coatings degrade by a microchipping mechanism since fracture occurs relatively more easily in such open columnar microstructures, which are further characterized by low levels of internal stress accompanied by a poor load-bearing capacity. With increasing substrate bias much denser coatings are produced which result, initially, in better resistance to abrasive wear through increased load support. However, these improvements in coating microstructure result in higher levels of internal stress and these, when taken along with a reduction in the scratch adhesion critical load for failure Lc, eventually lead to a decrease in abrasive wear resistance with increasing bias voltage. The mechanism(s) by which the coatings degrade are described as a function of substrate bias, and the results are correlated with measurements of hardness, internal stress and critical load for coating detachment.

Steady-state mass balance approach to substrate biased rf sputtering

An analysis is given of the net mass flux from target to film during steady-state substrate biased rf sputtering. Expressions are derived for film composition and growth rate in terms of relative sputtering rates of atomic species in the surface region of the target and film, and the geometrical transfer efficiencies between target and film. Calculations have been carried out of predicted film composition as a function of substrate bias voltage for several cases, and a comparison is made with experimental data.