Precursor Cat-CVD a-Si films for the formation of high-quality poly-Si films on glass substrates by flash lamp annealing

Amorphous Si (a-Si) films with lower hydrogen contents show better adhesion to glass during flash lamp annealing (FLA). The 2.0 µm-thick a-Si films deposited by plasma-enhanced chemical vapor deposition (PECVD), containing 10% hydrogen, start to peel off even at a lamp irradiance lower than that required for crystallization, whereas a-Si films deposited by catalytic CVD (Cat-CVD) partially adhere even after crystallization. Dehydrogenated Cat-CVD a-Si films show much better adhesion to glass, and are converted to polycrystalline Si (poly-Si) without serious peeling, but are accompanied by the generation of crack-like structures. These facts demonstrate the superiority of as-deposited Cat-CVD a-Si films as a precursor material for micrometer-thick poly-Si formed by FLA.     

Effect of hydrogen on SiNx films deposited by Cat-CVD method

This study is aimed at improving the characteristics of silicon nitride (SiNx) film deposited by catalytic chemical vapor deposition (Cat-CVD) method. Cat-CVD method can deposit SiNx films that have low hydrogen content and high density at low temperature without any plasma damage to substrates. Usually silane (SiH₄) and ammonia (NH₃) are used for source gases. Then adding hydrogen (H₂) gas to source gases makes characteristics of Cat-CVD SiNx improved. When using H₂ gas, hydrogen content in SiNx film becomes lower and electronic reliability becomes higher.     

Fabrication of PTFE thin films by dual catalytic chemical vapor deposition method

Dependence of catalyzing materials on deposition of polytetrafluoroethylene (PTFE = ”Teflon” in commercial) films by catalytic chemical vapor deposition (Cat-CVD) method is investigated. It has been clarified that Ni-containing catalyzers has a catalyzing effect that can decompose hexafluoropropylene-oxide (HFPO) to form PTFE films. A novel method named Dual Cat-CVD is also proposed. In the method, carbonized and fluorinated surface of Ni-containing catalyzer is removed and refreshed using atomic hydrogen generated by additionally introduced tungsten (W) catalyzer in the same chamber. This Dual Cat-CVD method enables to recover the deposition rate of PTFE films drastically.     

Finite element simulation of the effects of process parameters on deposition uniformity of chemical-vapor-deposited silicon carbide

A two-dimensional model was developed to simulate chemical vapor deposition process for preparing SiC coating by MTS + H₂ system in a vertical hot-wall reactor. The effects of process parameters, including deposition temperature, the flux of mixed gases, the ratio of H₂ and Ar, and the volume ratio of MTS and mixed gases, on deposition uniformity of SiC coating were calculated by finite-element method. The CVD process was optimized by an orthogonal L₉(3)⁴ test to deposit uniform SiC coating. The results show that the deposition uniformity of SiC is influenced greatly by the deposition temperature and the ratio of H₂ and Ar, and little by the flux of mixed gases and the volume ratio of MTS and mixed gases. The optimal deposition uniformity of SiC can be obtained under the operating condition as follows: deposition temperature 900 °C, the flux of mixed gases 0.6 l/min, H₂: Ar = 1:0, and the volume ratio of MTS and mixed gases 1:10. Part of calculated results is validated by corresponding experimental data, which implies that this model is valid and reasonable to characterize CVD process of SiC coating.     

Chemical vapour deposition of superconductors

Chemical vapour deposition processes (CVD) can produce metastable fine-grained materials as well as epitaxial coatings and can have a very large throwing power depending on the process parameters. Therefore, CVD is an prospective method to deposit high-temperature superconducting materials withT _c⩾10 K. One of the first superconductors which were produced was Nb₃Sn on tapes and single wires. This superconducting material is, however, today produced by metallurgical methods. Since the detection of Nb₃Ge, CVD has become for these coatings the main method of production for the following reasons: high deposition rates, possibility to dope the material by addition of further doping gases to the CVD-process, continuous process. These coatings were deposited on tapes. For the first time the large throwing power of the CVD process was utilized for the deposition of B1 -NbC _x N _y , on carbon fibre bundles. This opens the possibility to produce multifilamentary structures used for magnetic applications. The structure of the coating can be varied by changing the gas properties, by addition of further gases, by an ultrasonic field, by ignition of a gas discharge and by multi-layering. CVD could also be a prospective method for producing the new class of superconductors withT _c⩾30 K.     

Comparison of a-Si TFTs fabricated by Cat-CVD and PECVD methods

We investigate the characteristics of amorphous silicon thin film transistors (a-Si TFTs) fabricated by plasma-enhanced chemical vapor deposition (PECVD) and catalytic CVD (Cat-CVD), and their stability under bias and temperature (BT) accelerated stress. The Cat-CVD a-Si TFTs have off-leak current as small as 10^− 14 A, and a smaller threshold voltage shift under the BT stress. The superiority in off-leak current and stability is observed in the Cat-CVD a-Si TFTs fabricated at both 320 °C and 180 °C. The high performance and stability of the Cat-CVD a-Si TFTs will enable to use low-cost glass substrates and result in a cost reduction of TFT fabrication.     

Electrical properties of silicon nitride films deposited by catalytic chemical vapor deposition on catalytically nitrided Si(100)

Thin film transistor incorporating silicon nitride (SiN_x) films deposited by catalytic chemical vapor deposition (Cat-CVD) on silicon exhibit some problems such as a large-threshold voltage shift and a large hysteresis loop width of the capacitance vs. voltage (C–V) characteristics. In this work, in order to solve these problems, the surface of the silicon substrate is catalytically nitrided before SiN_x deposition. Inserting the nitridation layer, injection-type hysteresis loop of C–V curve is reduced from 1.3 to 0.05 V and large threshold voltage shift to the negative direction is reduced from 4 to 1.8 V.     

Resistance characteristics to oxidation of the metal-catalyzer for Cat-CVD

In order to obtain oxide films using catalytic chemical vapor deposition (Cat-CVD), oxidation experiments for catalyzers of Alumel, Al Chrom-O, Chromel, Hastelloy C-276, Kanthal, Kovar, Inconel-600, Inconel-601, Inconel X-750, Iron Chrome 30, Moleculoy, Monel, Ni, Nickel Chrome, Pt, SUS-304, SUS-316, Super Invar, and Ti have been carried out. The electric resistance measured for each metal heated at 900 °C, exposed for 30 min in O₂ atmosphere, have revealed that Alumel, Al Chrom-O, Chromel, Hastelloy C-276, Kanthal, Inconel-600, Inconel-601, Inconel X-750, Iron Chrome 30, Moleculoy, Ni, Nickel Chrome, Pt, SUS-304, and SUS-316 are in resistance to oxidation.     

New application of Cat-CVD technology and recent status of industrial implementation

Recent progress in application of Cat-CVD (Hot Wire CVD) technology is overviewed, along with recent status of industrial implementation of this technology. Although the use of Cat-CVD technology in factories has not been open to the public, the technology appears to fit for the fabrication of ultra-high frequency devices of compound semiconductors, compound semiconductor lasers, solar cells, and formation of coating films for other devices. The issues for practical use of this technology are also discussed, together with promising future of this Cat-CVD technology.     

AlGaN/GaN HEMTs passivated by Cat-CVD SiN Film

We demonstrate the excellent performance of a 140 W AlGaN/GaN HEMT in the C-band, which is passivated by a Cat-CVD SiN film. The interface trap density of the AlGaN surface passivated by Cat-CVD film after NH₃ treatment is 3 × 10¹² cm^− 2, which is the smallest of investigated deposition techniques. The lowest interface trap density achieved by the Cat-CVD technique makes it possible to operate the AlGaN/GaN HEMT in the C-band. We clarify that the Cat-CVD technique is necessary for developing future amplifiers.     

New rapid diamond synthesis technique; using multiplexed pulsed lasers in laboratory ambients

 QQC, Inc. has developed a revolutionary diamond deposition technique which does not require a vacuum, or H₂, or ”chemical” or physical pre-treatment of surfaces. The process utilizes a combination of various pulsed lasers and is performed at the laboratory p−t conditions: with CO₂ and N₂ as shrouding gases. Crystalline diamond films and DLC or, more accurately, tetrahedral non-crystalline carbon (TNC) have been formed on various substrates. On WC cutting tools the rate of deposition of crystalline diamond is approximately 1 μm/sec. In the context of fabricating a diamond coating on a substrate, the entire pre-surface treatment and material synthesis process including a coating regime, is performed in one step. Received: 10 September 1997/Accepted: 25 September 1997     

Super H2O-barrier film using Cat-CVD (HWCVD)-grown SiCN for film-based electronics

“Super H₂O-barrier film” with a water vapor transmission rate (WVTR) less than 1 mg/m²/day has been developed. The barrier layer is a single layer of amorphous SiCN grown by organic Cat-CVD (O-Cat-CVD) with a thickness of 100 nm. SiCN has been grown by using a gas mixture of monomethylsilane (MMS; Si (CH₃)H₃), NH₃ and H₂ on polyethylene-naphthalate (PEN) film substrates. It has been found that the WVTR drastically depends on the W-filament temperature of O-Cat-CVD. The WVTR changed from 5 × 10⁻¹ to 1 × 10⁻³, corresponding to the W-filament temperature increase from 1100 to 1200 C. We have recently succeeded in developing the “super H₂O-barrier film” by the coating of single layers of SiCN for both sides of the PEN film without using the widely used polymer/inorganic multilayer coating. The both-side coating has been found to be crucial to avoid the H₂O penetration into PEN films and also to avoid the breakdown of the SiCN/PEN interface caused by the H₂O accumulation at the interface.     

温度对化学气相沉积碳化硅涂层的影响

以三氯甲基硅烷和氢气为气源,研究了化学气相沉积碳化硅过程中,温度(850-1350℃)对沉积速率、反应物消耗效应、涂层形貌和相结构的影响.用磁悬浮天平在线实时称量基体质量变化进行动力学研究;采用扫描电镜和X射线衍射对样品做了表征.结果表明,沉积过程存在四个控制机理:a区(<1000℃)为表面反应动力学控制;b区(1000-1050℃)主要是HCl对沉积的抑制作用;c区(1050-1300℃)是表面化学反应和传质共同控制;d(>1300℃)为传质为限速步骤.由于不同的控制机制,导致所得涂层的形貌存在差异.含碳含硅中间物质浓度的减小、HCl增多和MTS的分解共同导致反应物消耗效应.涂层由热解碳和碳化硅两相组成,温度的升高使热解碳相减少,碳硅比接近1.     

Advantage of plasma-less deposition in Cat-CVD to the performance of electronic devices

Advantage of plasma-less deposition in catalytic chemical vapor deposition (Cat-CVD) is demonstrated in performance of amorphous-silicon (a-Si) thin-film transistors (TFTs), by comparing with a-Si TFTs fabricated by plasma-enhanced CVD (PECVD). Cat-CVD a-Si TFTs show 2 or 3 orders of magnitude lower off-current than PECVD ones. Exposure of Cat-CVD TFTs to an argon or a hydrogen plasma severely increases their off-current, while the off-current recovers by chemically etching the plasma-damaged surface layer. It is concluded that PECVD damages the a-Si surface to a depth of several tens of nm, whereas Cat-CVD induces no serious damage to the film surface and therefore induces no deterioration of electrical properties.     

Deposition of device quality silicon nitride with ultra high deposition rate (> 7 nm/s) using hot-wire CVD

The application of hot-wire (HW) CVD deposited silicon nitride (SiN_x) as passivating anti-reflection coating on multicrystalline silicon (mc-Si) solar cells is investigated. The highest efficiency reached is 15.7% for SiN_x layers with an N/Si ratio of 1.20 and a high mass density of 2.9 g/cm³. These cell efficiencies are comparable to the reference cells with optimized plasma enhanced (PE) CVD SiN_x even though a very high deposition rate of 3 nm/s is used. Layer characterization showed that the N/Si ratio in the layers determines the structure of the deposited films. And since the volume concentration of Si-atoms in the deposited films is found to be independent of the N/Si ratio the structure of the films is determined by the quantity of incorporated nitrogen. It is found that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high 7 nm/s for device quality SiN_x films, much faster than commercial deposition techniques offer [S. von Aichberger, Photon Int. 3 (2004) 40].     

空心叶片内腔化学气相沉积设备及抗氧化涂层研究

由于高效气冷空心叶片内腔的结构越来越复杂,采用物理气相沉积(PVD)和等离子喷涂(PS)技术不能进行空心叶片内腔冷却通道的涂层防护,化学气相沉积可以进行冷却通道内表面抗氧化涂层的防护.通过CVD涂层设备的研制、涂层沉积工艺、高温涂层性能等研究,对内腔涂层的涂覆机理、工艺方法和内腔涂层的应用进行了讨论.结果表明:研制的CVD设备可靠、工艺参数稳定、内腔表面涂层涂覆达到100%,所研究的化学气相渗铝涂层具有优良的高温抗氧化性能,其在先进航空发动机高效气冷空心叶片内腔表面有很好的工程应用前景.     

Synthesis and characterization of nano-crystalline CVD diamond film on pure titanium using Ar/CH4/H2 gas mixture

Titanium and Ti alloys have poor tribological properties and deposition of a well adherent diamond coating is a promising way to solve this problem. But diamond film deposition on pure titanium and Ti alloys is always difficult due to the high diffusion coefficient of carbon in Ti, the large mismatch in their thermal expansion coefficients, the complex nature of the interlayer formed during diamond deposition, and the difficulty of achieving very high nucleation density. A nano-crystalline diamond (NCD) film can resolve Ti and Ti alloys weak tribological performance due to its smooth surface. A well-adhered NCD film was successfully deposited on pure Ti substrate by using a microwave plasma assisted chemical vapor deposition (MWPCVD) system in the environment of Ar, CH₄ and H₂ gases at a moderate temperature. Detailed experimental results on the preparation, characterization and successful deposition of the NCD film on pure Ti are discussed.     

Recent situation of industrial implementation of Cat-CVD technology in Japan

Efforts of industrial application of Cat-CVD technology are surveyed. Recent movement of industrial implementation is also reviewed by showing examples in Japanese industry. Cat-CVD technology is originally developed as a new tool for fabricating semiconductor devices, however, recently, use of the technology is attempted in various fields such as chemical, mechanical and bio-technical engineering. It is shown that Cat-CVD has high feasibility as a fundamental technology of modern industries.     

Structure, hardness and thermal stability of TiAlBN coatings grown by alternating deposition of TiAlN and BN

Hardness and thermal stability of TiAlBN coatings prepared by alternating deposition of TiAlN and BN with high rotation speed of substrate holder (∼7 rpm) have been investigated. The TiAlN and BN were deposited by reactive sputtering of Ti_0.5Al_0.5 and BN targets with N₂ and Ar reactive gases, respectively. Despite alternating deposition, the TiAlBN coating did not show layered structure due to high rotation speed of substrate holder. By TEM analysis, the TiAlBN coating was observed to be nanocomposite with grain less than 10 nm in size. Compared to TiAlN coating, the TiAlBN nanocomposite coating showed superior hardness. Furthermore, the hardness of the coating increased after the heat-treatment in N₂ atmosphere up to 800 °C. By comparison with TiAlN/BN nanoscale multilayered coating prepared by the same deposition method except the lower rotation speed of substrate holder (∼1 rpm), the hardness enhancement after annealing, ‘self-hardening’, of the TiAlBN nanocomposite coating is believed to be due to the sharpness in chemical composition at the interface between TiAlN and BN phase.     

Flash-lamp-crystallized polycrystalline silicon films with high hydrogen concentration formed from Cat-CVD a-Si films

We investigate residual forms of hydrogen (H) atoms such as bonding configuration in poly-crystalline silicon (poly-Si) films formed by the flash-lamp-induced crystallization of catalytic chemical vapor deposited (Cat-CVD) a-Si films. Raman spectroscopy reveals that at least part of H atoms in flash-lamp-crystallized (FLC) poly-Si films form Si-H₂ bonds as well as Si-H bonds with Si atoms even using Si-H-rich Cat-CVD a-Si films, which indicates the rearrangement of H atoms during crystallization. The peak desorption temperature during thermal desorption spectroscopy (TDS) is as high as 900 °C, similar to the reported value for bulk poly-Si.