Deposition Of High-quality Thin Films Research Articles

Thin Films: Area‐Selective Growth of HfS2 Thin Films via Atomic Layer Deposition at Low Temperature (Adv. Mater. Interfaces 23/2020)

The 2D semiconductor hafnium sulfide, HfS2, is deposited for the first time using atomic layer deposition in mild conditions and at low temperature (100 °C). The surface reactions are specific and allow for area-selective deposition of high-quality thin films on self-assembled molecular monolayers. When properly protected from air, the material is pure, stoichiometric, and ordered on a short range as deposited. More details can be found in article number 2001493 by Julien Bachmann and co-workers.

Vacuum deposition of high-quality thin films displaying spin transition near room temperature

We report on thermally evaporated, crystalline films of [Fe(HB(tz)3)2] (tz = triazolyl), which display spin transition around 338 K.

Amorphous Zr-based thin films fabricated by magnetron sputtering for potential application in hydrogen purification

Amorphous hydrogen separation membranes are under development because of their resistance to hydrogen embrittlement, improved mechanical properties, resistance to corrosion and most importantly lower intrinsic cost. The Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUBMSIP) is a versatile technique for deposition of high quality thin-films of almost any composition, while enabling the control of film size, thickness and shape. In this work, it was demonstrated that thin-films (∼3–6μm) of amorphous Zr40.5Ni59.5, Zr54Cu46 and Zr30Cu57.5Y12.5 could be deposited onto glass substrates by the CFUBMSIP technique. XRD measurements only showed one broad peak for each alloy, with a peak centred between 36° and 42° 2θ, indicating that the films were amorphous. Surface analysis by SEM and confocal microscopy suggest deposition of continuous films. The thermal stability of the films appears to be mainly governed by the alloying elements and their compositions. However, the measured activation energies indicated that the nucleation and growth mechanism in the magnetron sputtered films may be different from that reported for melt-spun amorphous alloys with similar compositions.

Hot wire chemical vapor deposition chemistry in the gas phase and on the catalyst surface with organosilicon compounds.

CONSPECTUS: Hot wire chemical vapor deposition (HWCVD), also referred to as catalytic CVD (Cat-CVD), has been used to produce Si-containing thin films, nanomaterials, and functional polymer coatings that have found wide applications in microelectronic and photovoltaic devices, in automobiles, and in biotechnology. The success of HWCVD is largely due to its various advantages, including high deposition rate, low substrate temperatures, lack of plasma-induced damage, and large-area uniformity. Film growth in HWCVD is induced by reactive species generated from primary decomposition on the metal wire or from secondary reactions in the gas phase. In order to achieve a rational and efficient optimization of the process, it is essential to identify the reactive species and to understand the chemical kinetics that govern the production of these precursor species for film growth. In this Account, we report recent progress in unraveling the complex gas-phase reaction chemistry in the HWCVD growth of silicon carbide thin films using organosilicon compounds as single-source precursors. We have demonstrated that laser ionization mass spectrometry is a powerful diagnostic tool for studying the gas-phase reaction chemistry when combined with the methods of isotope labeling and chemical trapping. The four methyl-substituted silane molecules, belonging to open-chain alkylsilanes, dissociatively adsorb on W and Ta filaments to produce methyl radical and H2 molecule. Under the typical deposition pressures, with increasing number of methyl substitution, the dominant chemistry occurring in the gas phase switches from silylene/silene reactions to free-radical short chain reactions. This change in dominant reaction intermediates from silylene/silene to methyl radicals explains the observation from thin film deposition that silicon carbide films become more C-rich with a decreasing number of Si-H bonds in the four precursor molecules. In the case of cyclic monosilacyclobutanes, we have shown that ring-opening reactions play a vital role in characterizing the reaction chemistry. On the other hand, exocyclic Si-H(CH3) bond cleavages are more important in the less-puckered disilacyclobutane molecules. Metal filaments are essential in HWCVD since they serve as catalysts to decompose precursor gases to reactive species, which initiate gas-phase reaction chemistry and thin film growth. We discuss the structural changes in metal filaments when exposed to various precursor gases. Depending on the nature of the radical intermediates formed from the hot-wire decomposition and subsequent gas-phase reactions, metal silicides and carbides can be formed. Overall, study of the gas-phase reaction chemistry in HWCVD provides important knowledge of the chemical species produced prior to their deposition on a substrate surface. This helps in identifying the major contributor to alloy formation on the filament itself and the film growth, and consequently, in determining the properties of the deposited films. An integrated knowledge of the gas-phase reaction chemistry, filament alloy formation, and thin film deposition is required for an efficient deposition of high-quality thin films and nanomaterials.

Atomic layer deposition of transparent semiconducting oxide CuCrO2 thin films

Atomic layer deposition (ALD) is a vital gas-phase technique for atomic-level thickness-controlled deposition of high-quality thin films of CuCrO2 on various substrate morphologies owing to its self-limiting gas-surface reaction mechanism.

Pulsed laser deposition of high-quality thin films of the insulating ferromagnet EuS

High-quality thin films of the ferromagnetic-insulator europium(II) sulfide (EuS) were fabricated by pulsed laser deposition on Al2O3 (0001) and Si (100) substrates. A single orientation was obtained with the [100] planes parallel to the substrates, with atomic-scale smoothness indicates a near-ideal surface topography. The films exhibit uniform ferromagnetism below 15.9 K, with a substantial component of the magnetization perpendicular to the plane of the films. Optimization of the growth condition also yielded truly insulating films with immeasurably large resistance. This combination of magnetic and electric properties open the gate for novel devices that require a true ferromagnetic insulator.

Influence of high power impulse magnetron sputtering plasma ionization on the microstructure of TiN thin films

HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N2 atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge current (Id) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti1+, Ti2+ and atomic nitrogen N1+. Ti1+ ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off times. Langmuir probe measurements showed that the peak plasma density during the pulse was 3 × 1016 m−3. Plasma density, and ion flux ratios of N1+: N21+ and Ti1+: Ti0 increased linearly with peak current. The ratios exceeded 1 at 30 A. TiN films deposited by HIPIMS were analyzed by X-ray diffraction, and transmission electron microscopy. At high Id, N1+: N21+ > 1 and Ti1+: Ti0 > 1 were produced; a strong 002 texture was present and column boundaries in the films were atomically tight. As Id reduced and N1+: N21+ and Ti1+: Ti0 dropped below 1, the film texture switched to strong 111 with a dense structure. At very low Id, porosity between columns developed. The effects of the significant activation of the deposition flux observed in the HIPIMS discharge on the film texture, microstructure, morphology and properties are discussed.

The role of lattice mismatch in the deposition of CdTe thin films

Cadmium telluride (CdTe) is the most well-established II–VI compound largely due to its use as a photonic material. Existing applications, as well as those under consideration, are demanding increasingly stringent control of the material properties. The deposition of high-quality thin films is of utmost importance to such applications. In this regard, we present a report detailing the role of lattice mismatch in determining the film quality. Thin films were deposited on a wide variety of substrate materials using the pulsed laser deposition (PLD) technique. Common to all substrates was the strong tendency toward the preferential alignment of CdTe’s (111) planes parallel to the substrate’s surface. X-ray diffraction analysis, however, revealed that the crystalline quality varied dramatically depending upon the substrate used with the best results yielding a single-crystal film. This tendency also manifested itself in the surface morphology with higher structural perfection yielding smoother surfaces. The film quality showed a strong correlation with lattice mismatch. Texture analysis using the [111] pole figure confirmed that improvements in the lattice mismatch led to a higher degree of in-plane alignment of the (111) grains.

Functionalized polysiloxane thin films deposited by matrix-assisted pulsed laser evaporation for advanced chemical sensor applications

Abstract High-quality thin films of fragile chemoselective polymers with precise and accurate thickness, density and chemical integrity are required for advanced chemical sensor applications. While these attributes are difficult to achieve by conventional methods, we have successfully demonstrated the matrix-assisted pulsed laser evaporation (MAPLE) deposition of thin films of especially synthesized fluoro-alcohol substituted carbo-polysiloxane polymer coatings. The quadrupled output of a Nd:YAG laser (265 nm) served as the laser source and depositions were done in a background pressure of N2. Using various solvents appropriate to solvate this polymer (e.g. tetrahydrofuran, acetone and chloroform) and varying the laser fluence, we optimized the deposition of high-quality thin films on 1 cm2 double-polished silicon substrates. The best solvent used as matrix was proved to be acetone. Under these conditions, the important functional groups were reproduced and observed by Fourier Transform Infrared Spectroscopy (FTIR) as compared to the drop cast films and the surface roughness was analysed using Atomic Force Microscopy (AFM) and found to be much smoother than conventional wet deposition techniques.

Optical spectroscopy diagnostics and thin film deposition of laser ablated rare earth–Ni 2B 2C plasma plumes

We describe optical spectroscopy diagnostics of UV laser ablated rare earth–Ni 2–B 2–C superconducting targets. In the light of this characterization, we have optimized the parameters for high-quality thin film deposition of borocarbide compounds. Our measurements have evidenced relevant differences in the flow velocity as well as in the spatial divergence of different plasma components. This is related to the influence of the different masses of the atoms of the multicomponent target during plume expansion. These results have led us to identify the target-to-substrate distance and substrate temperature as the critical parameters for the deposition of high-quality thin films, as clearly evidenced by residual resistivity ratio measurements.

Engineered tantalum aluminate and hafnium aluminate ALD films for ultrathin dielectric films with improved electrical and thermal properties

ABSTRACTContinued scaling of device dimensions requires deposition of high-quality thin films with a thickness of 50 angstroms or less. Nucleation effects in typical CVD processes make it difficult to achieve continuous films in this thickness regime. Atomic layer deposition (ALD), a technique developed over 25 years ago but applied to IC processing only recently, enables deposition of ultra-thin films with atomic-scale precision. This technique offers 100 percent step coverage of high aspect ratio features, as-deposited films which are amorphous and free of pinholes, excellent within-wafer uniformity and wafer-to-wafer uniformity, and favorable electrical properties. Moreover, ALD offers the opportunity to engineer material properties by creating layered structures (nanolaminates) and mixtures (alloys) which combine advantageous properties of different materials. These last features may be critical in efforts to replace silicon dioxide as the industry's dielectric workhorse if no single material emerges as a suitable direct replacement. The nanolaminate capability of ALD will be discussed with physical and electrical data on nanolaminates of aluminum oxide with tantalum pentoxide and aluminum oxide with hafnium oxide. Individual nanolaminate layers can be varied from tens of angstroms to as little as 1-2 atomic layers. Data for Al2O3/Ta2O5and Al2O3/HfO2alloys will also be presented demonstrating the ability to create materials with controlled, variable composition. The alloy and nanolaminate capabilities enable the creation of graded interfaces and atomically smooth transitions between different materials. Prospects for application of these materials to gate stacks and capacitors will be assessed.

Generation of charged liquid cluster beam of liquid-mix precursors and application to nanostructured materials

A novel technique for generating a charged liquid cluster beam (CLCB) of liquid-mix precursors has been developed by using flow-limited electrostatic spraying facilitated by field-injection charging. The technique is inherently capable of generating charged nanodrops of controlled size, chemical composition, and stoichiometry, which are very susceptible to heat treatment and pyrolysis. It is, therefore, possible to convert a CLCB spray into solid nanoparticles by exposing it to a heated carrier gas. Deposition of high-quality thin films or nanocrystallites on a substrate is also possible by directing the CLCB spray onto a heated substrate. Since all of the nanodrops in the CLCB spray are charged, an electromagnetic lens can be employed to conveniently control their trajectories for direct writing of micropatterns. This paper briefly describes the physical processes underlying the CLCB technique, the apparatus, and the preliminary results illustrating the application potential of the CLCB technique.

New approach to low temperature deposition of high-quality thin films by electron cyclotron resonance microwave plasmas

An electron cyclotron resonance microwave plasma processing system consisting of a plasma chamber and a processing chamber as well as a new apparatus called the ‘‘species selector and energy controller (SSEC)’’ are described in detail. Silicon dioxide (SiO2) films fabricated using this system without and with the SSEC are used for various experiments to demonstrate that the SSEC can effectively suppress the damaging effects resulting from the bombardment on the substrates and the on-growing films by energetic particles and photons produced in the plasma during film deposition, as well as effectively reduce the upstream diffusion of the reactant gas from the processing chamber to the plasma chamber, thus suppressing the formation of microdust particles due to the heterogeneous gas phase reaction. The film growth for the films fabricated without the SSEC is due mainly to mass-limited reaction and that with the SSEC is due to surface rate-limited reaction. The electronic properties of the SiO2 films fabricated with the SSEC at temperatures higher than 250 °C approach those of high-quality thermally grown silicon oxides. The effects of the SSEC on the film properties and the film growth mechanism are also discussed.

High superconducting transition temperatures in sputter-deposited YBaCuO thin films

The recent discovery of a remarkable new family of high critical temperature superconducting oxides has excited extraordinary interest and research activity worldwide1–6. The prospect of superconducting devices and machines operating in liquid nitrogen and at higher temperatures is seen as an unprecedented technological development. There are potential applications in microelectronics and computers, energy storage and transmission, transport, high technology engineering, sensors and instrumentation. For many applications it is essential to prepare these materials in the form of thin films on suitable substrates. Currently, most of the research effort and all of the available published information relates to the fabrication of bulk samples from powders. At Cambridge our primary objective has been to achieve the deposition of high-quality thin films. We have taken this course because, (1) deposition from a multi-target sputter system gives great flexibility and enables us to cast a wide parameter net in composition and temperature to ensure early identification of key superconducting phases, (2) the deposition and processing of 0.5 µm films can be carried out very rapidly with one or possibly more system cycles per day and (3) measurements on thin films provide quantitative information on basic superconducting parameters and are likely to lead to the first practical applications of these remarkable materials. Here we report preliminary results on the deposition of relatively homogeneous films with transition temperature onsets up to 99 K. First results are reported on film deposition conditions, film composition and structure, and on the effect of post-deposition anneals on superconducting properties.