Role In Film Growth Research Articles

The Effect of Charged Ag Nanoparticles on Thin Film Growth during DC Magnetron Sputtering

The possibility that charged nanoparticles (CNPs) are generated in the gas phase during direct current (DC) magnetron sputtering of Ag is studied. Sputtered Ag particles could be captured on an ultrathin amorphous carbon membrane for transmission electron microscopy (TEM) observation. It is confirmed that the average particle size and the total area of deposition under the condition of the positive bias applied to the substrate are bigger than those under the condition of the negative bias applied to the substrate. The results indicate that some of the sputtered Ag particles are negatively charged. To evaluate the contribution of negatively-charged particles to the film growth, Ag thin films were deposited for 30 min on the Si substrate with the substrate biases of −300, 0 and +300 V and analyzed by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and four-point probe. When +300 V was applied to the substrate, the film growth rate was highest with the film thickness of 85.0 nm, the crystallinity was best with the smallest full width at half maximum (FWHM) value of 0.44 and the resistivity was smallest with 3.67 μΩ·cm. In contrast, when −300 V was applied to the substrate, the film growth rate was lowest with the film thickness of 68.9 nm, the crystallinity was worst with the largest FWHM value of 0.53 and the resistivity was largest with 8.87 μΩ·cm. This result indicates that the charge plays an important role in film growth and can be a new process parameter in sputtering.

Measurements and modeling of the impact of radical recombination on silicon nitride growth in microwave plasma assisted atomic layer deposition

High material quality silicon nitride thin film deposition by plasma enhanced atomic layer deposition (PEALD) is necessary for many advanced semiconductor device and memory fabrication applications. Understanding film growth mechanism is quite important not only for the device production control but also device performance due to the strong correlation of film growth speed and film chemical property. Nevertheless, predicting film deposition rates, let alone film quality, is difficult as quantitative surface reaction mechanisms are still not well known and the species fluxes that play the central role in film growth are not easy to measure. In this paper, the authors describe how a plasma reactor model for the nitridation step required in PEALD of silicon nitride can be combined with a phenomenological site balance model to predict film growth rate variation with some key process parameters. The relative insensitivity of growth rates to plasma power are explained by competing destruction and regeneration mechanisms for NH3, an important nitrogen source in Si3N4 growth. The model also helps to reveal why H2 can be important.

Effect of hydrogen partial pressure on growth of Cu2ZnSnS4 films sulfurized using diethyl sulfide

AbstractPolycrystalline Cu2ZnSnS4 films were prepared by thermal treatment of stacked Sn/Zn/Cu metallic precursors in the presence of diethyl sulfide, which is a less hazardous sulfur source than H2S gas. The effect of the hydrogen partial pressure on the crystal phases present in the films was investigated. It was found that sulfur and carbon atoms play an important role in film growth. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation and Characterization of Cu(In,Ga)Se2Thin Films by Selenization of Cu0.8Ga0.2and In2Se3Precursor Films

Se-containing precursor films with two different compositions were prepared by magnetron sputtering from and targets, and then were selenized using Se vapor. The effects of precursor composition and selenization temperature on the film properties were investigated. The results show that Se phase plays a critical role in film growth and electrical properties of CIGS films. The Cu-rich films exhibit different surface morphology and better crystallinity, as compared to the Cu-poor films. All the CIGS films exhibit p-type conductivity. The resistivity of the Cu-rich films is about three orders of magnitude lower than that of the Cu-poor films, which is attributed to the presence of p-type highly conductive Se phase.

Enhanced fatigue characteristics of sol–gel derived PZT thin films

Pb(Zr,Ti)O 3 (PZT) thin films with Zr/Ti ratio of 52:48 were deposited on Pt/Ti/SiO 2/Si substrates using the sol–gel method. Since the conditions of heat-treatment play a great role in film growth, post-annealing processes were conducted under different environments. After standard processing, films were annealed at 600 °C in three different atmosphere—air, O 2 and a two-step process conducted in air for 30 min and then in O 2 ambient, all done for 10 min. Through electron microscopy and X-ray diffraction, we found that all films were crack-free and highly (1 1 1) oriented. Hysteresis measurements showed a generally large polarization value. The fatigue properties differ drastically for all processes, showing an abnormal behaviour near the end of the measurement. The hysteresis loops before and after 1 × 10 10 switching cycles have been slightly changed in both shape and magnitude. Such abnormality and fatigue-free property is an unusual result for PZT films prepared on conventional Pt/Ti/SiO 2/Si substrates.

Effect of Incident Intensity on Films Growth in Pulsed LaserDeposition

Incident intensity, defined by the amount of particles deposited perpulse, is an important parameter in the film growth process of pulsedlaser deposition (PLD). Different from previous models, weinvestigate the irreversible and reversible growth processes by using a kinetic Monte Carlo method and find that island density and filmmorphology strongly depend on pulse intensity. At higher pulseintensities, lots of adatoms instantaneously diffuse on the substratesurface, and then nucleation easily occurs between the moving adatomsresulting in more smaller-size islands. In contrast, at the lowerpulse intensities, nucleation event occurs preferentially between thesingle adatom and existing islands rather than forming new islands, andtherefore the average island size becomes larger in this case.Additionally, our results show that substrate temperature plays animportant role in film growth. In particular, it can determine thefilms shape and weaken the effect of pulse intensity on film growth atthe lower temperatures by controlling the mobility rate of atoms. Ourresults can match the related theoretical and experimental results.

Unusual Switching Behavior Observed in Fatigue-Free Pb1.10Zr0.50Ti0.50O3 Thin Films Prepared on Conventional Pt/Ti/SiO2/Si Substrates

Pb(Zr,Ti)O 3 (PZT) thin films with Zr/Ti ratio of 50:50 were deposited on Pt/Ti/SiO 2 /Si substrates using the sol-gel method. Since controlling the conditions of heat-treatment is a great role in film growth, post-annealing processes were conducted under different environments. After standard processing, the films were annealed at 600°C under 3 different processes—(a) 30 min in air, (b) 30 min in O 2 ambient and (c) 2 step which was conducted first in air and then in O 2 atmosphere during 30 min respectively. Through electron microscopy and X-ray diffraction, we found that every film was crack-free and highly (111) oriented. Hysteresis measurements showed a generally large polarization value. The fatigue properties differ drastically for every process, showing an abnormal increase near the end of the measurement. The hysteresis loops before and after 1 × 10 10 switching cycles declined for the films annealed under a single-step, but as for the film by the two-step process, the hysteresis showed to increase in magnitude. Such abnormality and fatigue-free property is an unusual result for PZT films prepared on conventional Pt/Ti/SiO 2 /Si substrates.

Atomic Force Microscope Observation of Growth and Defects on As-Grown (111) 3C-SiC Mesa Surfaces

AbstractThis paper presents experimental atomic force microscope (AFM) observations of the surface morphology of as-grown (111) silicon-face 3C-SiC mesa heterofilms. Wide variations in 3C surface step structure are observed as a function of film growth conditions and film defect content. The vast majority of as-grown 3C-SiC surfaces consisted of trains of single bilayer height (0.25 nm) steps. Macrostep formation (i.e., step-bunching) was rarely observed, and then only on mesa heterofilms with extended crystal defects. As supersaturation is lowered by decreasing precursor concentration, terrace nucleation on the top (111) surface becomes suppressed, sometimes enabling the formation of thin 3C-SiC film surfaces completely free of steps. For thicker films, propagation of steps inward from mesa edges is sometimes observed, suggesting that enlarging 3C mesa sidewall facets begin to play an increasingly important role in film growth. The AFM observation of stacking faults (SF's) and 0.25 nm Burgers vector screw component growth spirals on the as-grown surface of defective 3C films is reported.

Surface polymerization by ion-assisted deposition for polythiophene film growth.

Cationic polymerization is induced at the gas-solid interface by hyperthermal organic cations coincident on a surface with a thermal beam of organic monomers. This process, termed surface polymerization by ion-assisted deposition (SPIAD), produces films that maintain the chemical structure of the monomer. A polythiophene film is produced here by SPIAD with 100 eV thiophene ions and terthiophene monomers coincident on Si and indium tin oxide (ITO) substrates held under vacuum. X-ray photoelectron spectroscopy observes enhancement in film growth for SPIAD compared with either thiophene ion or terthiophene exposure alone. Polythiophene films grown by both mass-selected and nonmass-selected ions with coincident terthiophene dosing both display similar fluorescence intensities at two wavelengths characteristic of emission from films of the terthiophene monomer. Raman spectra of films from nonmass-selected ions display several vibrations also observed in terthiophene films. Ions therefore play a critical role in film growth from nonmass-selected ions, in addition to any radical or photochemically driven processes that may also occur.

Growth of glassy carbon on natural fibers

Diamond-like carbon films were grown on pyrolised bamboo substrates by hot filament-chemical vapor deposition from ethanol/hydrogen mixtures. Different stages of deposition of films grown on untreated substrates and substrates seeded with diamond dust were compared. Changes in film morphology and structure under changes in these parameters were investigated using scanning electron microscopy and Raman spectroscopy. Diamond-like carbon (DLC) with ball-like morphology on the micrometer scale and glassy DLC with a stacked planar structure were observed for depositions of >2 h on unseeded and seeded substrates, respectively. Gasification of the fibers by hydrogen in the early stages of growth may play a role in film growth, but this requires further study. Nevertheless, DLC films can be grown on pyrolised bamboo substrates, which suggests that other carbonaceous substrates for film fabrication by hot-filament chemical vapor deposition also merit systematic investigation.

Design of gas inlets for the growth of gallium nitride by metalorganic vapor phase epitaxy

The problem of gas inlet design for metalorganic vapor phase epitaxy (MOVPE) of group III nitrides from metal alkyls and ammonia is addressed. The focus is on GaN growth from trimethyl-gallium and ammonia. In traditional reactors with well-mixed inlet streams, parasitic gas-phase reactions between the two precursors may lead to the formation of stable adducts that can condense on cool inlet walls, thus reducing the film growth efficiency. Such reactions may also lead to the formation of particulates through gas-phase condensation reactions (e.g. during AlN growth). A fundamentally-based model was developed to describe the MOVPE of GaN and was used to study the effect of inlet design and reactor operating conditions on film thickness uniformity in vertical stagnation-flow and rotating-disk reactors. The model includes a description of gas-phase kinetics and a simple gas-surface reaction mechanism. The kinetic model was coupled to a two-dimensional transport model describing flow, heat and mass transfer in a vertical MOVPE reactor. Predictions of growth rate compare well to experimental observations from a vertical rotating-disk reactor, without any adjustable parameters. The model was also used to study the distribution of gaseous species in the reactor and their role in film growth. Finite element simulations using a massively parallel computer code (MPSalsa) indicate that the species responsible for film growth are Ga-alkyls and not their adducts with ammonia. Sensitivity analysis was also performed to assess the relative importance of each reaction in determining the growth rate. The model was subsequently employed in the design of axisymmetric, multi-aperture gas inlets feeding precursors into the reactor in an alternating (not well-mixed) fashion. Simulations were performed to study the effect of key design parameters, such as inlet velocities, susceptor rotating speed, inlet to susceptor distance as well as the number and distribution of inlets, on GaN film growth rate and uniformity in industrial scale reactors. Optimal cases are presented that lead to uniform films over large-area substrates. An alternating precursor feed scheme based on concentric rings was found to lead to more uniform films as the number of inlets increased. The other important reactor parameters were inlet velocity, relative size of inlet “rings” and susceptor distance from the inlet.

Parametric study of the in situ growth of BaKBiO thin films by laser ablation

In situ growth of Ba1−xKxBiO3 (BKBO) films by laser ablation has been studied as a function of gas pressure and substrate temperature in O2, N2O, and N2O/O2 (1:1), respectively. The superconducting BKBO films can be grown at 410–500 °C in 15–60 mTorr of O2, at 390–510 °C in 20–2000 mTorr of N2O, and at 390–500 °C in 15–700 mTorr of N2O/O2 (1:1), respectively. Oxygen partial pressure plays an important role in controlling the doping of potassium into the BKBO phase during in situ deposition and hence the growth of the superconducting films. The optimum deposition pressures are 40 mTorr of O2, 30–50 mTorr of N2O, and 20–50 mTorr of N2O/O2 (1:1), under which not only the temperature range available for growing the superconducting films is wider but also the Tc’s of the as-grown films are higher. N2O used as an oxidation gas during growth is efficient in suppressing the crack formation in the BKBO films on cooling. The target composition also plays an important role in film growth. The optimal target composition studied is Ba:K:Bi=0.6:0.8:1.0.

Analysis of the properties of radio frequency ion plated Cu films based on the calculation of the ion energy available per film atom

During plasma assisted film deposition (PAD), the ion energy available per film atom plays an important role in film growth and morphology development. Consequently, it influences the film properties such as stress, adhesion, and dc resistivity. Calculation of the ion energy available per film atom is a little difficult in PAD because of a lack of data on the flux and energy distribution of ions (IED) incident on the film during deposition. In this article, the nature of the IED, in a rf ion plating system used for Cu film deposition, is determined with the help of a theoretical model available in literature and the plasma parameters obtained from Langmuir probe data. Then the ion energy available per Cu film atom (ECu) is calculated to be in the range of 0.5–5 eV/atom. This is further used to explain the variation of film morphology and dc resistivity with the ion plating process variables, viz., pressure, Cu evaporation rate and substrate bias. This range of ECu is insufficient to influence the film thickness significantly via resputtering. The film thickness is influenced to a much greater degree by the evaporation rate due to collisional scattering of the film vapor in the relatively high pressure used during ion plating. The film morphology is shown to improve with increase in the ECu but shows the presence of micro cracks at pressure higher than 2 mTorr, probably due to increased neutral gas adsorption. The data on ECu and morphology is then used to show that the dc resistivity of the films is influenced by grain boundary scattering and partial oxidation during deposition.

Properties of A New Liquid Organo Gold Compound for MOCVD

AbstractDimethyl(1,1,1,5,5,5-hexafluoroaminopenten-2-onato)Au(III), DMAu(hfap) was found to be very promising compound for CVD Au wiring. It is liquid at r.t. and has high vapor pressure (0.5 Torr at r.t.) and high thermal stability (dec.t. 171°C, δE=25.4Kcal/mol) and can be used as a precursor for MOCVD. CVD gold films were grown on Si(100) from DMAu(hfap) in a quartz vacuum chamber, using thermal activation by an electric heater or photo activation through quartz windows by excimer lasers(XeC1 308nm). A growth rate of 10 nm/min was achieved by thermal activation at 250 °C, (evaporation temperature of 30 °C, H2 flow rate at 100 sccm and chamber pressure of 30 Torr). Resistivities ranged between 2.8 and 5.lμΩ-cm, depending on the film morphology. The growth rate of laser CVD gold films had the tendency of increasing with decreasing the substrate temperature. This phenomenon indicates that photolysis of adsorbed species on the substrate plays an important role in film growth by laser CVD.

The mechanism of laser-assisted CVD of germanium

Previous workers have shown that germane does not decompose below 700 K on silica substrates. However, if the germane is irradiated with an ArF or KrF laser, germanium films will grow at temperatures down to 610 K. In the work reported here, the role of the laser in the growth process was explored. First, the species impinging on the substrate during ArF laser-assisted chemical vapor deposition (LCVD) were analyzed with a mass spectrometer. The analysis showed that when germane is irradiated with an ArF laser under growth conditions, digermane is formed in the gas phase. The digermane then impinges on the substrate and pyrolyses. Many other species have been reported previously to be formed transiently during the laser pulse. However, we were not able to detect any other species with a high enough flux onto the substrate to condense at an appreciable rate. Next, temperature programmed decomposition was used to see if photochemical decomposition of chemisorbed germane played an important role in film growth. It was found that a laser dose comparable to that needed for film growth did not produce an appreciable change in the decomposition spectra. Lastly, film growth studies were used to examine the role of the digermane formed by the laser in the film growth process. It was found that a mixture of germane and digermane will decompose on a silica substrate down to 580 K to produce a germanium film. The growth characteristics of the germane/digermane mixtures were virtually the same as those seen in LCVD. Thus, it appears that under the conditions used previously for LCVD, the main role of the ArF laser is to convert some of the germane source gas to digermane. It also has been found that under other conditions, one can grow germanium films down to at least 300 K via digermane photolysis.