Stage Of Film Deposition Research Articles

Synthesis and Characterization of Amorphous Selenium, Cadmium and Silver Selenide Thin Films on Polyamide-6

Increasing photon absorption by capturing light is an important way to increase the efficiency of photovoltaic devices. In this regard, the small optical band gap (Eg) and high absorption coefficient of Se-containing thin nanofilms make them ideal for next generation photovoltaic devices based on selenides. Amorphous selenium was introduced into polyamide-6 (PA 6) via a chemical synthesis in a bath and the influence of the products of its reaction with Cd2+ and Ag+ ions on the film phase composition, topographic and optical properties were evaluated. AFM data have revealed that the surface roughness of the a-Se/PA 6 composite noticeably increases compared to that of unreacted PA 6. However, at later stages of film deposition, the roughness decreases, and the thin film becomes smoother and uniform. The incorporation of solid inorganic nanoparticles into flexible polyamide network causes chain stretching, which has been confirmed by ATR-FTIR spectroscopy data. The data of X-ray diffraction analysis, depending on the stage of synthesis, showed the crystalline composition of the film with peaks of Se8, CdSe, Ag2Se and Ag, which may explain the observed optical properties. The optical properties of the composites indicate a shift in the band gap from 4.46 eV for PA 6 to 2.23–1.64 eV upon the stepwise deposition of amorphous Se, CdSe and Ag2Se. Eg is conveniently located in the visible region of solar energy, making the obtained nanofilms ideal for solar energy harvesting.

MULTIMODE WRINKLING PATTERNS OF IRON FILMS SPUTTER DEPOSITED ON FLEXIBLE SUBSTRATES WITH GRADIENT MODULUS

Wrinkling patterns are beneficial for a wide range of engineering applications including flexible electronics, tuned optics, sensoring, energy harvesting, surface wetting and biomedicine. Here we report on controllable multimode wrinkling patterns of metal (iron) films sputter deposited on flexible substrates with gradient modulus. It is found that disordered wrinkles (G1 wrinkling) form in the weakly crosslinking region at the early stage of film deposition. Disordered labyrinth wrinkles with larger wavelengths and ordered stripe wrinkles localized by cracks (both G2 wrinkling) appear in the strongly crosslinking region for the samples with small film thickness and large thickness, respectively. The coexistence of the labyrinth G1 wrinkling and labyrinth G2 wrinkling (or stripe G2 wrinkling) can be obtained by tuning the substrate modulus and film thickness. The morphologies, evolutions and mechanisms of such wrinkles are discussed in detail based on the stress theory. This study can promote better understanding of the substrate effect on the complex wrinkling patterns.

Oxygen vacancy induced insulator-metal transition in LaNiO3 thin films

The electronic structures of $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ thin films with an oxygen vacancy on a $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrate are investigated using first-principles calculations. We find that the oxygen vacancy induces the insulator-metal transition as the film thickness is increased. For a 1.0-unit-cell-thick $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ film, an insulating state with an energy gap of 1.2 eV is formed as a result of the large exchange and Coulomb interactions between Ni $3d$ orbitals, whereas a negative charge transfer energy causes restoration of the metallic state in films with a 2.0-unit-cell or larger thickness. Thermodynamic study reveals that an oxygen vacancy induced insulating film may be the preferable structure during the initial stage of film deposition. The low calculated formation energy of 0.26 eV for the oxygen vacancy indicates that the nonstoichiometric and insulating film may survive even the annealing process. Finally, work functions for films with various surfaces are discussed.

Residual stress reduction in piezoelectric Sc0.4Al0.6N films by variable-pressure sputtering from 0.4 to 1.0 Pa

Scandium aluminum nitride (ScAlN) films are promising piezoelectric materials for various microelectromechanical systems. However, residual stress in ScAlN films is a serious problem. In this study, Sc0.4Al0.6N films were deposited on silicon (100) substrates by using a reactive magnetron sputtering system. The total gas pressure during the latter stage of film deposition was increased to a high pressure (1.0 Pa) without quenching the plasma and was initiated subsequent to the deposition of an adequate-quality piezoelectric underlayer at a lower pressure (0.4 Pa). The final film is 2.3 μm thick and exhibits a piezoelectric response of 20.1 pC⋅N−1, and its residual compressive stress is about 25% that of a film deposited solely at 0.4 Pa. The result is due to two effects: 1) good crystalline quality of the Sc0.4Al0.6N underlayer due to the atomic peening effect at the low pressure and 2) inherited (002)w growth that is attributed to layer-by-layer selective adsorption of atoms which had lower energies at the higher gas pressure.

The effects of annealing and wake-up cycling on the ferroelectricity of zirconium hafnium oxide ultrathin films prepared by remote plasma atomic layer deposition

The crystalline phases and ferroelectric properties of ZrxHf1-xO2 (ZHO) ultrathin films (5.6–5.8 nm in thickness) prepared by remote plasma atomic layer deposition (RP-ALD) before and after post-annealing and wake-up cycling have been investigated in this study. For the films with high ZrO2 percentages, the plasma bombardment from RP-ALD was able to induce partial ferroelectric orthorhombic (o) crystallization during the film deposition stage. The as-deposited pure ZrO2 ultrathin film exhibited a fully developed ferroelectric polarization hysteresis after wake-up cycling. For the films containing the ferroelectric o-phase in the as-deposited state, post-annealing the films followed by a wake-up cycling procedure could greatly promote ferroelectric switching while maintaining low leakage. The ferroelectric properties of the ZHO ultrathin films were highly dependent on the ZrO2-to-HfO2 ratio and could be tailored by various combinations of post-annealing and wake-up cycling. An increase in the amount of HfO2 has been found to be detrimental to the ferroelectricity, mainly due to the high crystallization temperature of HfO2. For the post-annealed ZHO ultrathin films, the ferroelectricity was governed by the relative amounts of the ferroelectric o-phase and the non-ferroelectric monoclinic (m) phase. The Zr0.5H0.5O2 ultrathin film was the only composition which exhibited a large, stable polarization hysteresis after post-annealing but before wake-up cycling. The annealed Zr0.5H0.5O2 ultrathin film is believed to contain a suitable mix of o and m phases to produce loose grain boundaries, allowing the ferroelectric o-phase crystallites to switch freely under electrical loading.

The Role of Humidity in Tuning the Texture and Electrical Properties of Cu2O Thin Films Deposited via Aerosol‐Assisted CVD

AbstractA study on the effect of carrier gas (CG) humidity on the texture and the resulting electronic properties of Cu2O thin films deposited using aerosol‐assisted chemical vapor deposition (AA‐CVD) at low temperatures (<365 °C) is reported. By increasing the CG humidity, the preferred orientation of the films can be tuned from [110] to [111]. By studying the initial stages of film deposition, a different growth mode is found for dry and humid conditions, which in turn directs the final texture of the films. The analysis of the electric properties of the films by Hall effect shows that carrier concentration remains in the order of 1015 cm−3 when using both dry and humid conditions. Converselly, Cu2O samples deposited with humid CG generally present a higher mobility, up to 17 cm2 V−1 s−1. [111]‐textured Cu2O films with high mobility were used to fabricate a diode by depositing a ZnO layer on top using atmospheric pressure spatial atomic layer deposition (AP‐SALD). The diode shows an excellent rectifying behavior with a high asymmetry close to 104 between −1 and +1 V.

Molecular dynamics simulation of temperature effects on deposition of Cu film on Si by magnetron sputtering

The temperature effects on the growth of Cu thin film on Si (0 0 1) in the context of magnetron sputtering deposition were systematically studied using molecular dynamics (MD) method. To improve the comparability of simulation results at varying temperatures, the initial status data of incident Cu atoms used in all simulations were read from an identical file via LAMMPS-Python interface. In particular, crystalline microstructure, interface mixing and internal stress of Cu thin film deposited at different temperatures were investigated in detail. With raising the substrate temperature, the interspecies mixed volume and the proportion of face-centered cubic (fcc) structure in the deposited film both increased, while the internal compressive stress decreased. It was found that the fcc structure in the deposited Cu thin films was 〈1 1 1〉 oriented, which was reasonably explained by surface energy minimization and the selectivity of bombardment energy to the crystalline planes. The quantified analysis of interface mixing revealed that the diffusion of Cu atoms dominated the interface mixing, and the injection of incident Cu atoms resulted in the densification of phase near the film-substrate interface. More important, the distribution of atomic stress indicated that the compressive stress was mainly originated from the film-substrate interface, which might be attributed to the densification of interfacial phase at the initial stage of film deposition.

BaSi2 formation mechanism in thermally evaporated films and its application to reducing oxygen impurity concentration

Thermal evaporation is a simple and rapid method to fabricate semiconducting BaSi2 films. In this study, to elucidate the BaSi2 formation mechanism, the microstructure of a BaSi2 epitaxial film fabricated by thermal evaporation has been investigated by transmission electron microscopy. The BaSi2 film is found to consist of three layers with different microstructural characteristics, which is well explained by assuming two stages of film deposition. In the first stage, BaSi2 forms through the diffusion of Ba atoms from the deposited Ba-rich film to the Si substrate while in the second stage, the mutual diffusion of Ba and Si atoms in the film leads to BaSi2 formation. On the basis of the BaSi2 formation mechanism, two issues are addressed. One is the as-yet unclarified reason for epitaxial growth. It is found important to quickly form BaSi2 in the first stage for the epitaxial growth of upper layers. The other issue is the high oxygen concentration in BaSi2 films around the BaSi2–Si interface. Two routes of oxygen incorporation, i.e., oxidation of the Si substrate surface and initially deposited Ba-rich layer by the residual gas, are identified. On the basis of this knowledge, oxygen concentration is decreased by reducing the holding time of the substrate at high temperatures and by premelting of the source. In addition, X-ray diffraction results show that the decrease in oxygen concentration can lead to an increased proportion of a-axis-oriented grains.

Investigation on correcting process of spherical rotor imbalance at thin film deposition stage

We propose a method of rotor imbalance correction for electrostatic gyroscope. The method is based on redistribution of the material on the beryllium rotor surface during deposition of the titanium nitride coating by cathodic arc physical vapor deposition (Arc-PVD) technique. The deposition process is carried out using one arc source made of BT-1-00 material, located in the horizontal plane of the vacuum chamber of "Bulat-6" installation at nitrogen pressure of 1.2ˑ10-3 Pa. Size distortion of the rotor caused by thermal expansion during heating to 300 °C, is not more than one hundredth of a micrometer because of the high dimensional stability of beryllium. The titanium nitride coating with a thickness about 1 μm is formed during 30 min deposition on the spherical surface of the rotor with a diameter of 10 mm. The imbalance correction is achieved by deposition of the coating with the center of the coating sphere displaced relative to the geometrical center of the rotor in the direction opposite to the direction of the rotor imbalance vector. The required displacement is determined by the rotor kinematics during the deposition process and is provided by the developed device with three degrees of freedom: two rotational ones – constant and cyclic around two different axes of the rotor, and reciprocating displacement of the rotor relative to the source of the sputtered material along the flow axis of this material. The developed device provides fastening of the rotor in four- needle clamp. The calculation of rotor fixation scheme in this clamp is carried out, ensuring the positioning needles outside the area of the raster pattern formed in the rotor equatorial zone during the next laser marking operation. The experimental data showed that it is possible to produce real rotors with the imbalance correction accuracy within two decimal places of a micrometer.

Phase transformation in thin tungsten films during sputter deposition

For tungsten films sputter-deposited at room temperature, it has been commonly observed that the meta-stable A15 β-phase (β-W) nuclei are initially formed and then coalesced into continuous β-W layer during the early film deposition stage, which transforms into the equilibrium bcc α-phase (α-W) at a so-called critical thickness. Various previous studies, without experimental verifications, attributed the phase transformation to the increased film temperature (~100°C) resulting from the sputtering process. In this study, the substrate temperature was intentionally varied from 20 to 320°C in order to investigate the temperature dependence of the phase transformation, which reveals important characteristics to be contrasted by the prior reports. Based on the energy calculation using the elastic hard-sphere model, sputtered atoms and reflected Ar neutrals in case of W sputtering are shown to possess extraordinarily high energy (60–130eV). These energetic particles, by directly transferring kinetic energy to the lattice atoms on the deposit surface as well as inside the thin (~2.5nm) β-W layer, enhance atomic diffusion and thus drive the phase transformation in W films, which is supported by the conclusion of three dimensional monte Carlo simulation reported in literature. The results of this study indicate that processing efforts for the application of low-resistivity W interconnects should be directed at optimizing sputtering parameters such as power and pressure to control the energetic particles rather than focusing on the optimization of film temperature, which have been considered the dominant parameter for the phase transformation.

Composition and structure variation for magnetron sputtered tantalum oxynitride thin films, as function of deposition parameters

Tantalum oxynitride thin films were produced by magnetron sputtering. The films were deposited using a pure Ta target and a working atmosphere with a constant N2/O2 ratio. The choice of this constant ratio limits the study concerning the influence of each reactive gas, but allows a deeper understanding of the aspects related to the affinity of Ta to the non-metallic elements and it is economically advantageous. This work begins by analysing the data obtained directly from the film deposition stage, followed by the analysis of the morphology, composition and structure. For a better understanding regarding the influence of the deposition parameters, the analyses are presented by using the following criterion: the films were divided into two sets, one of them produced with grounded substrate holder and the other with a polarization of −50V. Each one of these sets was produced with different partial pressure of the reactive gases P(N2+O2). All the films exhibited a O/N ratio higher than the N/O ratio in the deposition chamber atmosphere. In the case of the films produced with grounded substrate holder, a strong increase of the O content is observed, associated to the strong decrease of the N content, when P(N2+O2) is higher than 0.13Pa. The higher Ta affinity for O strongly influences the structural evolution of the films. Grazing incidence X-ray diffraction showed that the lower partial pressure films were crystalline, while X-ray reflectivity studies found out that the density of the films depended on the deposition conditions: the higher the gas pressure, the lower the density. Firstly, a dominant β-Ta structure is observed, for low P(N2+O2); secondly a fcc-Ta(N,O) structure, for intermediate P(N2+O2); thirdly, the films are amorphous for the highest partial pressures. The comparison of the characteristics of both sets of produced TaNxOy films are explained, with detail, in the text.

Control of surface flatness of Ge layers directly grown on Si (001) substrates by DC sputter epitaxy method

The formation of Ge layers on Si (001) substrates with 3.5Ωcm resistivity by the sputter epitaxy method with DC magnetron sputtering has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the sputtering power and the deposited film thickness of Ge. At the initial stage of film deposition, the higher sputtering power yields smaller and more closely packed Ge islands due probably to an increase in the collision rate of the Ge atoms migrating on the Si substrate, which preserves more compressive strains in the films. With the preserved strains, the surface roughening derived from the strain relaxation is reduced. Furthermore, the surface flatness can be improved with the initially smaller islands and additional deposition; this is probably due to the effect of Ge adatom anchoring at concave areas where many bonding sites are available for stable Ge residence. The root-mean-square surface roughness of a 200-nm-thick Ge layer formed at a sputtering power of 100W is about 0.23nm.

Influence of TiO2 buffer layer and post-annealing on the quality of Ti-doped ZnO thin films

Abstract Ti-doped ZnO (TZO) thin films were grown on soda lime glass (SLG) substrate without and with a TiO 2 buffer layer by radio frequency magnetron sputtering and then annealed under vacuum at 450 and 500 °C for 20 min. The structural, electrical, and optical properties of TZO films were investigated. XRD analysis shows that all TZO films are highly textured along the c -axis and perpendicular to the substrate. The structural properties of TZO films are improved by controlling the annealing temperature and inserting a TiO 2 buffer layer. When the films were annealed at 450 °C, the crystallinity increased, but it then decreased slightly with increase in annealing temperature from 450 to 500 °C. Due to superior crystallinity, TZO films annealed at 450 °C exhibited lower resistivity and higher average transmittances in the visible region. The improvements in crystallinity, resistivity and transmittance are more obvious when a TiO 2 buffer layer was inserted. The decrease in resistivity is mainly attributed to an increase in Hall mobility rather than carrier concentration. When the TZO films deposited on bare SLG substrate, the energy band gaps was decreased after annealing at 450 and 500 °C due to the decrease in carrier concentration. However, the absorption edge of TZO films deposited on TiO 2 -buffered substrate was blue shifted, and the energy band gap was increased due to the increase of carrier concentration. In this study, the TZO film with optimal properties was grown on the TiO 2 -buffered substrate and post annealed at 450 °C, achieving a resistivity of 3.76×10 −3 Ω-cm and an average transmittance above 85%. Therefore, it can be concluded that inserting a buffer layer at an early stage of film deposition to improve crystallinity can help achieve low resistivity, high transmittance, and high energy band gap in transparent conducting TZO thin films.

Optical dielectric constant inhomogeneity along the growth axis in ZnO-based transparent electrodes deposited on glass substrates

Simple optical measurements using a conventional spectrometer have revealed that in heavily doped ZnO films deposited on glass, the optical dielectric constant is inhomogeneous along the growth axis. Analyses based on Drude’s model have suggested that the origin of this inhomogeneity is the shorter carrier scattering time τc in the portion in contact with the glass substrate, while τc in the major portion of the films has been estimated to be as long as 1×10−14 s at infrared frequencies. This may imply that if better crystallinity is achieved in the initial stage of film deposition, higher conductivity will be attainable without sacrificing the high transparency of the electrode-on-glass system. In addition, the analyses have disclosed the correlation between the high transparency of the major portion of the films and the frequency dependence of τc that is caused by the dopants (Ga or Al) and makes τc even longer at visible-light frequencies.

Chemisorption of Tetrakis(dimethylamido)titanium on Si(100)-2 × 1: C−H and C−N Bond Reactivity Leading to Low-Temperature Decomposition Pathways

Tetrakis(dimethylamido)titanium, Ti[N(CH3)2]4 or TDMAT, is a metal alkylamide precursor often used in the deposition of titanium nitride films. The mechanisms of decomposition of TDMAT upon its adsorption on the Si(100)-2 × 1 surface are investigated by infrared (IR) spectroscopy, temperature-programmed desorption (TPD), and density functional methods. Two experimental observations, the formation of Si−H bonds at temperatures as low as 220 K and methane desorption at temperatures below 400 K, indicate the scission of C−H and C−N bonds. The unusual low-temperature reactivity of these bonds is explained in terms of bond activation due to the zwitterionic character of the silicon−silicon dimers of the Si(100)-2 × 1 surface. Silicon surface atoms with predominantly nucleophilic character are able to attract hydrogen atoms, forming Si−H bonds. Silicon surface atoms with electrophilic character are able to form N−Si dative bonds that weaken the C−N bond, favoring its scission. Density functional calculations support this model, finding that the C−H scission is favored thermodynamically and kinetically provided that the TDMAT molecule has already undergone dissociative adsorption via N−Ti bond scission. Several decomposition pathways are considered, and in all cases the surface products are stabilized upon the formation of Si−C bonds, which agrees with the formation of an interface with high carbon content when metalorganic precursors are employed. The repercussion of these facile mechanisms of decomposition on the first stages of film deposition is discussed.

Interface broadening due to ion mixing during thin film growth at the radio-frequency-biased electrode in a plasma-enhanced chemical vapor deposition environment

The authors show that ion bombardment in the range of tens to a few hundreds of eV, used in ion- and plasma-assisted deposition processes, can lead to thin film growth dominated by subsurface deposition due to subplantation (shallow implantation). This can cause significant interface broadening during the initial stages of film deposition as a result of ion mixing. First, by studying the modifications of a c-Si(100) target exposed to an O2 plasma at the radio-frequency (rf)-biased electrode using in situ real-time spectroscopic ellipsometry (RTSE), the authors detect implantation, damage, and oxidation to a depth of up to ∼10nm. They validate these results using high resolution transmission electron microscopy and simulate the effects of ion-surface interactions at the rf-biased electrode by using Monte Carlo TRIDYN simulations. The simulation code, which was modified specifically to consider a broadband ion energy source, enabled the authors to reproduce depth and time relevant experimental results with good agreement. In situ RTSE was then used to monitor TiO2 deposition on SiO2 under similar ion bombardment conditions. The authors observed the formation of a 2-to4-nm-thick interfacial layer, depending on the ion-to-neutral flux ratio (ϕi∕ϕn), which was controlled by varying the deposition rate. TRIDYN simulations revealed that oxygen subplantation causes interfacial broadening during the growth through ballistic mixing of Ti and Si atoms at the interface; the interface width scales as ∼(ϕi∕ϕn)1∕2. Intensive ion mixing at ϕi∕ϕn>1 is also shown to be responsible for the ballistic displacement of the majority of surface-deposited Ti atoms into the bulk, so that the growth appears to be dominated by subsurface deposition under conditions of intense ion bombardment.

A Raman spectroelectrochemical investigation of chemical bath deposited Cu xS thin films and their modification

Thin copper sulfide films were deposited from a chemical bath onto glass, silicon, gold and platinum substrates. Films were modified by aging the deposit under ambient conditions, annealing in air, soaking in cupric ion solution, or by fixing the electrode potential. The structure of the deposited film was investigated using neutron reflectometry, Raman scattering, electrochemistry and transmission electron microscopy. Deposited films were shown to be bilayer, with a more dense layer close to the substrate and a less dense layer at the film/solution interface. Modification resulted in the formation of a single layer film of copper sulfide, the composition determined by the extent of copper exchange/transfer with the external environment. SERS results show the presence of a ν(SS) band from the early stages of film deposition.

Comment on “Etch characteristics of CeO2 thin film in Ar∕CF4∕Cl2 plasma” [J. Vac. Sci. Technol. A 21, 426 (2003)

Comments are made on a recent article by Kim, Chang, and Kim [J. Vac. Sci. Technol. A 21, 426 (2003)], which describes the preparation and the x-ray photoemission spectroscopy study of the etching effects produced by Ar-based plasmas of different composition on the surface chemistry of a CeO2 film grown on Si. We discuss some chemical interactions taking place between Ce, Si, and the ambient humidity during the early stages of film deposition, and demonstrate that the many-body effects involved in Ce3d spectra provide a key for better understanding of the etching mechanisms exerted by the plasma treatments.

Loading Fullerene into a Conjugated Polymer Without Chemical Modification

AbstractConjugated polymers doped with fullerenes show excellent photoconversion efficiencies. However, due to the poor solubility of pure C60 in common organic solvents, it was thought that some chemical modifications to C60 were required in order to load conjugated polymers with comparable weights of fullerene. Here, we report a novel way to load large amounts of unmodified C60 fullerene into the conjugated polymer poly(2‐methoxy‐5‐(2′‐ethylhexoxy)‐1,4‐phenylenevinylene), MEH‐PPV. The principle of our approach is to separate the film‐deposition stage from the material‐solidification stage. That is, materials are quickly solidified from dilute solution into colloidal particles, which are large enough to be collected by electrophoretic deposition. Deposition from a mixture of separate suspensions of MEH‐PPV and C60 fullerene resulted in films consisting of isolated particles. In contrast, by using a suspension made of a dilute solution of MEH‐PPV and C60, which was so dilute that traditional techniques such as spin‐coating were not applicable, an MEH‐PPV film doped with 20 mol‐% C60, corresponding to an almost 1:1 ratio by weight of molecularly dispersed C60, was easily obtained. To the best of our knowledge, this is the first report on the successful loading of an equivalent weight ratio of unmodified C60 molecules into MEH‐PPV.

In situ stress measurements during the growth at different temperatures of Ag–Cu(111) multilayers

We studied, at different temperatures, the stress development during the growth of Ag–Cu(111) multilayers. Multilayers, with a nanometric period, were UHV evaporated on Si(111) and stress was monitored in situ by measuring substrate bending. We show that whatever the evaporation temperature may be, the Ag on Cu(111) growth does not develop any representative stress. This quasi-unstressed Ag on Cu(111) growth could be consistent with an intrinsic relaxation resulting from a strong atomic reorganization during early stage (1 monolayer deposited) of interface formation. On the contrary, the Cu on Ag(111) growth develops a temperature-dependent tensile stress. The measured stress at room temperature is 1 GPa and decreases to 0.5 GPa at 110 °C for a 3 nm deposited thickness. This temperature-dependent stress could be related to a weak three-dimensional temperature-dependent growth mode during an early stage of film deposition. Our results also indicate, at 35 °C, a clear stress relaxation for thickness larger than 3 nm, while no relaxation is observed at 110 °C. We show that the Matthews–Blakeslee model is not adequate to describe this relaxation.