High-temperature Chemical Vapor Deposition Research Articles

Characterisation of Extended Defects in Si and Si1−x Gex Alloys: The Influence of Transition Metal Contamination

ABSTRACTPhotoluminescence (PL) spectroscopy, cathodoluminescence (CL) spectroscopy and imaging, transmission electron microscopy (TEM), and preferential defect etching and optical microscopy have been used to characterise dislocations in plastically deformed Si and in Si1−x Gex alloys. The PL spectra from plastically deformed Si produced under clean conditions, contained no dislocation related luminescence features. However, after deliberated Cu contamination and annealing, the PL spectra were dominated by the four main D-bands (D1-D4). CL spectroscopy and imaging revealed that the D3 and D4 bands originate on the slip lines, whereas D1 and D2 are dominant between the slip lines. Pseudomorphic Si1−x Gex layers grown by molecular beam epitaxy (MBE) and forced to relax by Cu contamination and annealing have also been examined. Both the PL and CL spectra were dominated by the D1-D4 bands, and monochromatic CL imaging showed that the D3 and D4 bands originate at the misfit dislocations with the location of the Dl and D2 bands being much less well defined. PL spectra from Si1−x Gex capping layers, grown by MBE on linearly compositionally graded buffer layers, were dominated by bound exciton luminescence features, identical with those observed in bulk grown alloys, and showed relatively weak D-band features. PL spectra obtained after chemical step etching, and CL spectra obtained with different beam energies, showed that the D-bands originated in the buffer layers which contained high densities of misfit dislocations. Well defined monochromatic CL images of the misfit dislocations could only be obtained using a narrow band pass filter centred on the D4 band. No D-band luminescence was observed from Si1−x Gex layers grown by high temperature chemical vapour deposition (CVD). However, after deliberate contamination with Ni, the D-bands became the dominant features and CL imaging clearly showed that the D4 band originates at the misfit dislocations and the D2 band predominantly between the misfit dislocations.

Characterization of tin dioxide interphase coating in alumina/glass composite

The purpose of this investigation was to study the microstructure of tin dioxide (SnO 2) coating formed by chemical vapor deposition (CVD) as an interphase between alumina and glass. Different temperatures and times were used to obtain coatings of this material by CVD. Hydrogen iodide (57% concentration) was used to etch the samples. Low temperature (500°C) CVD resulted in a uniform columnar growth, while the high-temperature (750°C) CVD showed an irregular, lateral growth of the SnO 2 grains. At 500°C, a longer CVD time resulted in much more extended columnar growth. Uniformity in thickness and low surface roughness obtained in the SnO 2 deposit at 500°C and 5 min would appear to offer an ideal interphase for the alumina/glass composite system. The effects of the deposition time and temperature on the growth rate of the SnO 2 grains are discussed.

Surface Chemistry of Fluorine-Containing Molecules Related to CVD Process on Silicon Nitride: SiF4, XeF2, and HF

AbstractThe reactivity of several fluorine-containing molecules on a polycrystalline silicon nitride (Si3N4) surface is studied under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). The chemistry of fluorine on Si3N4 is of interest in understanding the high temperature chemical vapor deposition (CVD) of Si3N4, which uses SiF4 as a starting material. XeF2 is reacted with a Si3N4 surface to prepare and characterize various surface SiFx (1 ≤ × ≤ 3) species. These are identified by the chemical shift induced by the fluorine atoms in the Si (LMM) Auger peak and by changes in the TPD. Of these species, SiF2 is stable to the highest temperature. SiF2 is also formed by the reaction of SiF4 with a Si3N4. Because SiF2 is so stable, its decomposition is proposed as a rate-determining step in the CVD deposition of Si3N4 from SiF4. Gaseous HF, which is a product of the CVD process, does not dissociate on Si3N4 and is therefore unlikely to cause the etch-like marks on the Si3N4 coating that are observed under certain conditions.

TEOS/O<sub>3</sub>系常圧CVD膜の特性(下地依存性)

Organic silicate materials such as TEOS are attracting attention as new silicon sources because of better film quality, excellent step coverage in particular, in atmospheric pressure CVD as well as low pressure (high temperature) CVD and plasma CVD. In AP CVD, addition of ozone (O3) lowers deposition temperatures to around 400°C, and the CVD reaction is thermal (chemical). TEOS/O3 AP-CVD is now well known for very good conformality. Deposition rate of the CVD depends on base materials to be deposited on. On thermal oxide deposition rate is lower and film quality is poorer than on silicon. These facts can be attributed to that the CVD reaction is rate-limited by a surface reaction. Characteristics of TEOS, OMCTS and HMDS/O3 CVD are discussed centering on the base material dependence, which is related to hydrophile of base materials and structure of the organic silicon materials. Two step deposition method is proposed to improve quality of the film deposited on thermal oxide.

High-temperature oxidation-protection CVD coatings for structural ceramics: Oxidation behaviour of CVD-coated reaction-bonded silicon nitride

Chemical vapour deposition of Si 3N 4 by low-pressure (4–10 Torr) pyrolysis (1200–1275 °C) of tetramethssilane-ammonia-hydrogen mixtures ( N: Si = 10) was used to protect reaction-bonded silicon nitride substrates against internal oxidation at 1000–1350 °C. The results reveal the existence of a critical thickness (6 μm) of the coatings and the poorer protectiveness of amorphous deposited coatings compared with crystallized coatings. Under the optimum deposition conditions, better protection was achieved than by the use of more conventional surface modification treatments such as high-temperature flash pre-oxidation.

Tungsten Carbide Erosion Resistant Coating for Aerospace Components

AbstractAn increasing problem faced by the aerospace industry is the erosive wear of engine components. Various PVD protection coatings have been used previously to combat this wear problem, but with limited success. This paper presents results obtained with a low-temperature CVD, erosion resistant, multilayer tungsten carbide coating system. The coating can be deposited at temperatures below 500°C on ferrous alloys used in the aerospace industry. The low temperature of deposition eliminates the problem of degradation of mechanical properties that occurs with normal high-temperature chemical vapor deposition processes. High-cycle fatigue strength and other mechanical property data are presented for coated stainless steel, as well as results on erosion and impact resistance at 90° impingement.

High Temperature microhardness of hard coatings produced by physical and chemical vapor deposition

The microhardness of hard coatings of TiN and HfN prepared by chemical vapor deposition (CVD) and TiN, HfN, ZrN and TiAlN prepared by physical vapor deposition (PVD) were measured between room temperature and 1000°C. The microhardness of the PVD coatings was significantly higher than that of the CVD counterparts at room temperature but all microhardness values tended to converge at 1000°C. Higher N: Ti ratios were found in PVD TiN relative to CVD TiN. X-ray diffraction measurements indicated that the PVD coatings contained high residual compressive growth stresses associated with lattice distortion and very fine grain size, which were confirmed using transmission electron microscopy. Low residual stresses in high temperature CVD coatings are caused by thermal expansion mismatch between coating and substrate. Differences in grain morphology and crystal texture are attributed to varying conditions of energetic bombardment and deposition temperature in the several PVD methods employed. The faster decrease in microhardness with temperature in PVD coatings is caused by the high residual energy and finer grain size.

Synthesis of boron nitride ceramics from poly(borazinylamine) precursors

Several simple monomeric boron and nitrogen reagents have been utilized as starting materials in high-temperature pyrolyses or chemical vapor deposition schemes to prepare hexagonal boron nitride. However, extensive applications and demands for new forms (films, gels, foams, fibers) have recently led to searches for improved syntheses and processing techniques for BN. The authors preliminary studies indicate that an oligomeric borazinylamine gel can be prepared in high yield, and this gel provides a useful precursor for the formation of hexagonal boron nitride. It is also very important to note that this chemistry provides a system which is adaptable to sol-gel processing. Although several features require additional study, it is apparent that the amine cross-linking of borazene fragments offers a beneficial and important advance in the use of borazenes as sources for BN. It is interesting to note that some investigators have suggested that the presence of silica in boron nitride improves its processing characteristics as well as prevents hydrolysis of boron nitride. Therefore, the presence of organosilicon in their synthesis may prove beneficial. Additional studies of chemicall modified borazenes and other cross-linking reagents are in progress.

Stability of SiC-masks for high resolution synchrotron X-ray lithography

Synchrotron X-ray lithography is a promising technique for high volume production of Ultra-LSI devices with latteral resolution down to 0.2 μm. Besides the powerful source, the X-ray stepper, and the high sensitive resist, mask technology is one of the main features in the development of X-ray lithography. For X-ray masks with high contrast a relatively thick absorbing pattern (0.8 μm) on a thin membrane (2.0 μm) is necessary. The achievable overlay accuracy depends mainly on the alignment accuracy of the X-ray stepper and of the stability of the masks. For a given stress in the absorping layer we will discuss the stability of X-ray masks which is mainly determined by the Young's modulus of the membrane material if we compare identical membrane geometries. SiC-membranes deposited by a high temperature CVD process can be fabricated with a Young's modulus as high as the bulk value (4.6×10 11 N/m 2) which is roughly a factor of 3 higher than for other relevant membrane materials. Membranes of 2 μm in thickness have been prepared with excellent transparency for synchrotron and optical radiation. A description of the preparation of the rigid SiC-membrane, as well as results of the transparency and the stability of these membranes against strong X-ray exposure will be given. For a high X-ray absorption a tungsten layer has been selected. Because of the thermal expansion coefficient which is comparable to SiC and the high Young's modulus tungsten is a promising material for sub-half micrometre pattern in a stress compensated absorber system. In view of X-ray masks with minimum distortion a description of the etch performance of the tungsten absorber system on SiC-masks will be given.

Lateral seeding epitaxy by cw Ar laser irradiation and by high temperature chemical vapor deposition technique: S Nagao et al, J Appl Phys, 53 (9), 1982, 6387–6390

Lateral seeding epitaxy by cw Ar laser irradiation and by high temperature chemical vapor deposition technique: S Nagao et al, J Appl Phys, 53 (9), 1982, 6387–6390

Structural and Electrical Properies of Photo-CVD Silicon Nitride Film

Silicon nitride film was deposited by mercury-sensitized photochemical vapor deposition (photo-CVD) utilizing a gaseous mixture of SiH4 and NH3 under 253.7 nm ultraviolet light irradiation. The structural and electrical properties of the film were then evaluated with emphasis on the substrate temperature dependence. The film contains a considerable amount of hydrogen, and less dense than silicon nitride film deposited by high-temperature chemical vapor deposition. The structural properties of photo-CVD silicon nitride film are basically similar to those of silicon nitride film deposited by plasma-enhanced chemical vapor deposition (P-CVD). However, the film has better insulating properties than P-CVD film, with a smaller leakage current, a higher breakdown field and a smaller positive charge density within the film.

Lateral seeding epitaxy by cw Ar laser irradiation and by high temperature chemical vapor deposition technique

A single crystal Si film of [111] orientation has been obtained over patterned amorphous insulating layer stripes for lateral seeding recrystallization. High-temperature, vapor-phase-epitaxial (VPE) growth technique has been utilized to form single and polycrystalline Si films on (111) Si substrate with the insulator stripes. The single crystal film on the exposed Si substrate and polycrystalline film on insulator were recrystallized with a scanning cw Ar laser. Topographical features and crystalline perfection associated with the laser-induced recrystallization were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and TED (transmission electron diffraction). At high power laser irradiation, the resulting recrystallization of polycrystalline Si seeded by single crystal Si deposited on substrate has been observed.

Influence of deposition temperature on the hardness and dimensions of steels with hard coatings produced by chemical vapour deposition

CVD hard coatings are applied to steel parts at high and at medium reaction temperatures. The paper presents an introduction to the effect of CVD temperature on hardness and on the dimensions of the CVD-coated steel parts. In combined high temperature CVD and hardening processes, the coatings are deposited at temperatures which are equal to the austenitizing temperature of the steel base; the coated pieces are then quenched in the CVD reactor. Hence the hardness and dimensions of the steel bases depend on the CVD reaction temperature. The required hardness values of the base may be adjusted by tempering according to the hardness-austenitizing temperature-tempering temperature diagram. If the dimensions of the steel parts exceed about 20 mm, the dimensional changes due to heat treatment are larger than those involved in coatings of the usual thickness of 5–10 μm. Dimensional corrections may be made by means of cold treatment and tempering. In medium temperature CVD processes good dimensional stability of the treated steel parts may be achieved by pretempering the prehardened steel parts at temperatures that are equal to or very near to those which are applied in CVD, and by working the pretempered parts to dimensions which will change to within the allowed tolerances during deposition of the coatings. In these processes, high hardness values in D-type steel bases may be reached by the application of hardening temperatures higher than the usual ones. The anisotropic behavior of D-type tool steels may cause some problems in dimensional stability and in the distribution of internal stresses in the hard coatings; the stresses will be compressive in most kinds of CVD hard coatings.