Chloride-based Chemical Vapor Deposition Research Articles

Characterization of highly textured piezoelectric AlN films obtained from aluminum and ammonium chloride by a simple vapor deposition process

We report a simple and efficient deposition technique for the growth of highly-textured AlN thin films. The proposed chloride-based chemical vapor deposition approach is based on widely available precursors and an unsophisticated experimental set-up. The films were characterized by electron microscopy, X-ray diffraction, Raman spectroscopy and cathodoluminescence. We studied the correlations between the deposition conditions and the properties of the resulting films, such as morphology, microstructure, features of the Raman spectra, and piezoelectric characteristics. In particular, we show that the minimum of the Raman bands A1(TO)/ E2(h) intensity ratio, under excitation along c-axis, corresponds to the maximum of the piezoelectric coefficient. The films deposited under the optimized conditions are composed of well-aligned column-like crystallites. These films have a piezoelectric coefficient of 5.5–6.5 pC/N, which approaches the highest values reported for this material. The simplicity, efficiency and high quality of the resulting films make the proposed deposition approach highly interesting for a wide range of practical applications.

Effect of Process Parameters on Dislocation Density in Thick 4H-SiC Epitaxial Layers Grown by Chloride-Based CVD on 4° Off-Axis Substrates

The effect of process parameters such as growth temperature, C/Si ratio, etching time, and Si/H2 ratio on dislocation density was investigated by performing KOH etching on 100 μm thick epitaxial layers grown on 4° off axis 4H-SiC substrates at various growth conditions by a chemical vapor deposition (CVD) process using a chloride-based chemistry to achieve growth rates exceeding 100 μm/h. We observe that the growth temperature and the growth rate have no significant influence on the dislocation density in the grown epitaxial layers. A low C/Si ratio increases the density of threading screw dislocations (TSD) markedly. The basal plane dislocation (BPD) density was reduced by using a proper in-situ etch prior to growth.

Process stability and morphology optimization of very thick 4H–SiC epitaxial layers grown by chloride-based CVD

The development of a chemical vapor deposition (CVD) process for very thick silicon carbide (SiC) epitaxial layers suitable for high power devices is demonstrated by epitaxial growth of 200µm thick, low doped 4H–SiC layers with excellent morphology at growth rates exceeding 100µm/h. The process development was done in a hot wall CVD reactor without rotation using both SiCl4 and SiH4+HCl precursor approaches to chloride based growth chemistry. A C/Si ratio <1 and an optimized in-situ etch are shown to be the key parameters to achieve 200µm thick, low doped epitaxial layers with excellent morphology.

Epitaxial growth of SiC with chlorinated precursors on different off-angle substrates

This study focuses on the epitaxial growth of silicon carbide (SiC) epitaxial layers, adopting the chloride-based chemical-vapor-deposition (CVD) process, which allows to achieve ten times higher growth rate compared to the standard process based on the mixture of a silicon-containing gas and a hydrocarbon.In order to improve the material quality, substrates with different off-angles were used, since low off-angle substrates result in a reduction of killer defects for specific devices. Different growth mechanisms dominate for different substrate off-cut and an accurate set up of dedicated surface preparation procedures and tuning of growth parameters are needed. This study demonstrates that silicon-rich gas inputs are favorable for lower off-angle (nominally on-axis) substrates, while carbon-rich are beneficial for higher off-angles (usually 8° off-axis for 4H–SiC).Methyltrichlorosilane (MTS) is shown to be the best precursor to achieve the presented results.

Ab initio study of isolated chlorine defects in cubic SiC

The electronic properties and formation energy of isolated Cl defects in SiC were investigated by first-principles calculations. Chlorine was studied in a substitutional position, in either a carbon (ClC) or a silicon site (ClSi), and in two interstitial positions (Cli), either tetrahedral or octahedral configurations. Our calculations revealed that ClC is energetically favored and it is a likely candidate to explain the nature of the experimentally observed Cl incorporation reported in SiC epilayers grown by chloride-based chemical vapor deposition.

SiC epitaxy growth using chloride-based CVD

The growth of thick epitaxial SiC layers needed for high-voltage, high-power devices is investigated with the chloride-based chemical vapor deposition. High growth rates exceeding 100μm/h can be obtained, however to obtain device quality epilayers adjustments of the process parameters should be carried out appropriately for the chemistry used. Two different chemistry approaches are compared: addition of hydrogen chloride to the standard precursors or using methyltrichlorosilane, a molecule that contains silicon, carbon and chlorine. Optical and electrical techniques are used to characterize the layers.

Chloride Based CVD of 3C-SiC on (0001) α-SiC Substrates

A chloride-based chemical-vapor-deposition (CVD) process has been successfully used to grow very high quality 3C-SiC epitaxial layers on on-axis α-SiC substrates. An accurate process parameters study was performed testing the effect of temperature, in situ surface preparation, precursor ratios, nitrogen addition, and substrate polytype and polarity. The 3C layers deposited showed to be largely single-domain material of very high purity and of excellent electrical characteristics. A growth rate of up to 10 µm/h and a low background doping enable deposition of epitaxial layers suitable for MOSFET devices.

Chlorinated precursor study in low temperature chemical vapor deposition of 4H-SiC

Low temperature (1300 °C) chemical vapor deposition (CVD) of SiC has gained interest in the last years for being less demanding in terms of reaction chamber lifetime, but also for allowing higher p-type dopant incorporation. Chloride-based CVD at low temperatures has been studied using chloromethane with tetrachlorosilane or silane, respectively and with or without controlled HCl addition. In this study we explore the use of methyltrichlorosilane (MTS) at growth temperatures (1300 °C) significantly lower than what is commonly used for homoepitaxial growth of SiC (1600 °C). MTS is a molecule containing all the needed precursor atoms; its effects are compared to the standard CVD chemistry, consisting of silane, ethylene, and HCl. Very different chemistries between the two precursor systems are proposed; in the case of MTS, C/Si ratios higher than 1 were required, however using the standard chemistry ratios lower than 1 were needed to obtain a defect-free epitaxial layer. We also demonstrate the need of using Cl/Si ratios as high as 15 to achieve a growth rate of 13 μm/h for 8° off-axis 4H-SiC epitaxial layers at 1300 °C. Limitations due to the low growth temperature are discussed in light of the experimental evidence on the growth mechanism as determined by the morphology degradation and the limited growth rate. Finally a comparison between the epilayers morphology obtained on 4H-SiC substrates with different off-cuts are presented, confirming the importance of lower C/Si ratios for 4° off-axis material and the inevitable growth of the cubic SiC polytype on on-axis substrates.

Optimization of a Concentrated Chloride-Based CVD Process for 4H–SiC Epilayers

Concentrated homoepitaxial growths of 4H–SiC was performed using a chloride-based chemical vapor deposition (CVD) process on different off-angle substrates (on-axis, 4 and 8° off-axis toward the direction). A suitable combination of gas flow and process pressure is needed to produce the gas speed that yields an optimum cracking of the precursors and a uniform gas distribution for deposition over large areas. The use of low pressure and the addition of chlorinated precursors bring the added benefit of achieving higher growth rates. A systematic study of the gas speed’s effect on the growth rate, uniformity, and morphology on the 4H–SiC epitaxial layers was performed. Growth rates in excess of were achieved on 50 mm diameter wafers with excellent thickness uniformity (below 2% σ/mean without rotation of the substrate) and smooth morphology using only 1/10 of the typical gas carrier flow and process pressure demonstrating the feasibility of a concentrated chloride-based CVD process for 4H–SiC. Thermodynamic calculations showed that the improved thickness uniformity could be due to a more uniform gas phase composition of the silicon intermediates. The concentration of the intermediate increases by a factor of 8 at a reduced carrier flow, while all the other hydrogenated silicon intermediates decrease.

Chloride-Based SiC Epitaxial Growth toward Low Temperature Bulk Growth

In this study, chloride-based chemical vapor deposition (CVD) of SiC is used either to grow epitaxial layers at high growth rate and to facilitate homopolytypic growth on on-axis substrates or to g...

Acceptor incorporation in SiC epilayers grown at high growth rate with chloride-based CVD

A systematic p-type doping study has been performed on 4H- and 6H-silicon carbide (SiC) epilayers grown at high growth rate using chloride-based chemical vapor deposition. The effect of temperature, pressure, growth rate, C/Si-, Cl/Si-ratios and dopant flow on the incorporation of the acceptor atoms aluminum and boron has been studied. The C/Si-ratio on the aluminum incorporation has similar behavior to what has been reported for the standard non-chlorinated low growth rate process, while no clear effect of C/Si-ratio was observed for the boron incorporation. A higher Cl/Si-ratio seems to lead to lower the aluminum and boron incorporation either due to more effective silicon supply at high Cl/Si-ratio or due to removal of dopant atoms from the surface by chlorine. The doping concentration is stable to the variations in silicon molar fraction, growth pressure and growth temperature for the aluminum-doped layers. Also p-type doping with gallium was tested.

Single‐Crystalline AlGaN:Mn Nanotubes and Their Magnetism

Single-crystalline AlGaN:Mn nanotubes (see figure) with a an outer diameter less than 200 nm and a length of a few micrometers are prepared by a chloride-based chemical vapor deposition process. The nanotubes exhibit room-temperature ferromagnetism without evidence of a ferromagnetic transition, showing that the structural and compositional modulation of 1D nanostructures could open up a way of exploring new classes of diluted magnetic semiconductors.

Effects of an Electroplated Platinum Interlayer on the Morphology and Phases of Chemically‐Vapor‐Deposited Alumina on Single‐Crystal, Nickel‐Based Superalloy

The feasibility of preparing a thin layer of α‐Al2O3 on the surface of a single‐crystal, Ni‐based superalloy was examined using a chloride‐based chemical vapor deposition (CVD) process previously developed for cutting tool applications. A coating directly deposited by this method on the alloy surface consisted of ∼1 μm α‐Al2O3 crystals in a matrix of amorphous Al2O3. When the alloy surface was predeposited with an electroplated Pt layer, the coating was mostly α‐Al2O3, but with the presence of fine microcracks on the coating surface. In comparison to the results observed for pure Pt substrate, the role of the Pt interlayer was apparently to promote the rapid formation of κ‐Al2O3 nuclei, which subsequently transformed to α‐Al2O3 during the CVD growth process.