Chemical Vapor Deposition最新文献

Thin films of lanthanum phosphate (LaPO₄) are produced by atomic layer deposition (ALD) for the first time, using a precursor combination of (CH₃)₃PO₄, La(thd)₃ (Hthd = 2,2,6,6-tetramethylhepta-3,5-dione), H₂O, and O₃. The deposition process is studied via an in-situ quartz crystal microbalance (QCM) and found to be a two-step process in which both water and ozone contribute to the growth. The best results are obtained when both water and ozone are pulsed simultaneously. The growth is self-limiting by nature, and a stoichiometric LaPO₄ phase can be obtained for a 1:1 pulsed ratio of the two precursors. The resulting LaPO₄ films are amorphous as deposited, and crystallize to the monoclinic structure after annealing in air for 10 h at 1350 °C. The LaPO₄ thin films can also be doped by calcium during growth by replacing some of the La(thd)₃ pulses by Ca(thd)₂. Films where 4.4% of the lanthanum in LaPO₄ is replaced by calcium are obtained.

The industrial need for high-throughput and low-cost ZnO deposition processes has triggered the development of atmospheric vapor-phase deposition techniques which can be easily applied to continuous, in-line manufacturing. While atmospheric CVD is a mature technology, new processes for the growth of transparent conductive oxides on thermally sensitive materials or flexible substrates are being developed, such as atmospheric plasma-enhanced (PE)-CVD and atmospheric spatial atomic layer deposition (ALD). In this article, the challenges and recent results on the growth of ZnO under atmospheric pressure by CVD, PE-CVD, and spatial ALD are reviewed and the use of these films as transparent electrodes in thin film solar cells are presented.

Silicon films with a sharp biaxial texture on low-cost, flexible metal tapes are prominent materials for cost-effective photovoltaics. The cost of such materials can be further reduced by the application of easily scalable chemical deposition methods. In the present article, we report on the application of CVD to obtain epitaxial silicon films on Ni alloy tapes with metal-organic (MO)CVD-produced buffer layers. Two types of buffer layer architecture are presented, which enable textured silicon growth on textured Ni(Cr,W) alloy and on non-textured Hastelloy tape. The Si film appears highly textured and demonstrates chemical purity, indicating the possibility of application of proposed Si/buffer/metal heterostructures formed by CVD for the photovoltaic industry.

Atomic layer deposition (ALD) is used to control the interatomic interactions of Eu and Ti in multilayered structures, as measured by characterizing the luminescent properties of the deposited material. Luminescent multilayer structures of Eu₂O₃ and TiO₂ are deposited as thin films by ALD at 300 °C using Eu(thd)₃/O₃ and TiCl₄/H₂O (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) as precursor systems. The individual layer thickness of the multilayered structure is produced from first N ALD cycles Eu₂O₃ and then N ALD cycles TiO₂ (N = 1 to 50), while the total film thickness is kept constant. The thinnest distinct layers are detected for N = 10, where each layer is measured to be less than 0.4 nm thick. The as-deposited films are smooth (root mean square (rms) roughness < 0.4 nm) and amorphous, independent of the layer thickness, N. The refractive index and extinction coefficient are also independent of N, while the luminescence efficiency is constant for N up to 10 cycles, and decreases for thicker superlayers. Annealing deteriorates the layered structures, causing a decrease in luminescence efficiency for thin superlayers, while thick superlayers increase in efficiency upon annealing. The films are characterized by spectroscopic ellipsometry (SE), photoluminescence (PL), X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray reflectivity (XRR), and atomic force microscopy (AFM).

A new heteroleptic titanium precursor with a mixed oxygen/nitrogen coordination sphere [Ti(dmap)₂(NMe₂)₂] (Hdmap = 1–dimethylamino–2–propanol) is synthesized by a simple elimination reaction on tetrakis–dimethylaminotitanium(IV) [Ti(NMe₂)₄]. The compound shows encouraging results in terms of chemical and thermal stability compared to the parent alkyl amide [Ti(NMe₂)₄], and is therefore more suitable for MOCVD applications. TiO₂ thin films are grown on Si(100) and ITO-coated borosilicate glass substrates via MOCVD in the temperature range 500–800°C. The deposition temperature has a significant effect on the phase and microstructure of the TiO₂ films obtained, which influences the functional properties. The optical bandgaps of the films are in the range 2.92–3.36 eV. The best photocurrent response (1.5 mA cm⁻² under AM 1.5G conditions) in aqueous electrolytes is observed for films grown at 700°C having improved crystallinity and porous columnar structure.

In this study the atomic layer deposition (ALD) of TiO₂ and ZrO₂ using two heteroleptic amido-guanidinate precursors, [Ti(NEtMe)₃(guan-NEtMe)] and [Zr(NEtMe)₃(guan-NEtMe)], together with water or ozone as oxygen sources, are investigated. All processes exhibit self-limiting growth at a deposition temperature of 275°C. The zirconium precursor especially gives high growth rates (0.8/1.0 Å per cycle with H₂O/O₃). The films are also relatively smooth, as determined by atomic force microscopy (AFM). The composition of the films is examined using X-ray photoelectron spectroscopy (XPS) and time of flight elastic recoil detection analysis (TOF-ERDA). When using ozone as the oxygen source the films present very high purity. The results are compared and discussed with respect to earlier studies on guanidinate, as well as homoleptic amido precursors.

The structure-driven properties of vanadium oxide have inspired enormous developments in the last decades, especially as a smart material for energy, sensors, and optoelectronics. The large variety of stable and metastable structures of vanadium oxide is discussed, based on the calculated formation energies and a broad overview of their structure-related properties. The established chemical deposition processes from the gas phase are reviewed with a particular emphasis on the implemented precursors and the obtained vanadium oxide phases. Although a significant fraction of relevant vanadium oxide compounds is achieved by these methods, there are still rewarding challenges related to their controlled elaboration and the investigation of their responsive properties.

In this paper we report on the first example of Fe₂O₃/CuO composites fabricated by a two-step vapor-phase synthetic strategy. The target route is based on the CVD of Fe₂O₃ nanorod arrays on Si(100) at 400 °C starting from Fe(hfa)₂TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine), followed by radio frequency (RF) copper sputtering for various process durations, and final ex-situ annealing in air. The combined use of complementary structural, morphological, and chemical analyses give evidence of the formation of pure nanocomposite systems, characterized by the presence of the sole ϵ-Fe₂O₃ and CuO phases. The unique features of the adopted approach enable an efficient surface decoration of ϵ-Fe₂O₃ rods by CuO nanoparticles a few nm in diameter, resulting in an intimate contact between the two oxides, and a CuO content tunable through variations of the sole sputtering time.

Pure tin oxide (TO) films are deposited onto glass substrates at various substrate angles relative to the source position by a simple and inexpensive method of atmospheric pressure (AP)CVD. The deposition temperature is constant at about 500°C, and oxygen with a flow rate of 100 sccm is used as both the carrier gas and the oxidizing agent. Investigation of the sheet resistance shows that resistivity varies between 106 and. 241 Ω/□. X-ray diffraction (XRD) also reveals that the structure is polycrystalline with the preferred orientation of (110) for all films deposited at the various substrate angles. Scanning electron microscopy (SEM) images also reveal a uniform and impacted structure on the surface of all the films. Optical properties show clear changes as a result of the substrate position versus the source.

The atomic layer deposition (ALD) process, an alternative to CVD, is universally appreciated for its unique advantages such as excellent repeatability, conformity, and thickness control at the atomic level. ALD precursor chemistry has mainly been based on homoleptic compounds such as, but not limited to, metal halides, alkylamides, and alkoxides, however these precursors have drawbacks such as possible halide contamination and low thermal stabilities in the case of the alkylamides and alkoxides. Consequently, heteroleptic precursors have been investigated as alternatives to the existing homoleptic counterparts, leading to the development of several advantageous processes. Nevertheless, there is no thematic review dedicated to the heteroleptic precursors and their properties, and it seems that no coherent strategy has been adopted for the development of heteroleptic precursors. This review gives a brief description of ALD and presents studies on the deposition of thin films of groups 4 and 5 metal oxides using ALD. A description of the general ALD properties of homoleptic precursors, in addition to a review on the thermal ALD of groups 4 and 5 metal oxides from heteroleptic precursors, is provided. Trends in the properties of heteroleptic ALD precursors, based on the literature review and recent experimental data, are discussed.