High-temperature Chemical Vapor Deposition Research Articles

Electrical Characterization of High-Voltage 4H-SiC Diodes on High-Temperature CVD-Grown Epitaxial Layers

High-temperature chemical vapour deposition (HTCVD) in a vertical chimney reactor was used to grow thick low-doped epitaxial layers of 4H silicon carbide. These layers were used as drift layers in a combined process to manufacture both bipolar and unipolar high-voltage diodes. The resulting diodes were characterized electrically in order to gain knowledge about the electric quality of the HTCVD epitaxial layers to assess the high-voltage properties of this material.

Controlling growth of carbon microtrees

A rapid high temperature chemical vapor deposition method was employed to grow micro-sized tree-like carbon structures on graphite electrodes. Temperature dependence of the nucleation density of carbon micro trees and the influence of methane partial pressure (carbon source) on the growth rate of carbon trees were systematically investigated. Substrate surface effects such as mechanical polishing and introduction of a growth promoter such as ferrocene were also investigated. It was found that all three factors, temperature, methane partial pressure and surface morphology of substrate influence the growth of carbon microtrees.

Growth of crack-free hexagonal GaN films on Si(100)

Hexagonal GaN films have been grown on Si(100) substrates by employing a sputtered AlN buffer layer followed by another high-temperature metalorganic chemical vapor deposition (MOCVD) grown AlN buffer layer. The highly oriented structure of sputtered AlN provides a hexagonal template for subsequent AlN and GaN growth. The GaN films are evaluated by transmission electron microscopy, selected area electron diffraction, x-ray diffraction, and photoluminescence and exhibit a purely hexagonal columnar structure. The orientation of the GaN columns depends on the thickness of both the sputtered AlN buffer layer and the MOCVD grown AlN buffer layer. The surface of GaN films is shiny and crack free up to a thickness of 2 μm studied in this work.

Interface studies of tungsten gate metal–oxide–silicon capacitors

The Si/SiO2 interface in 100-nm-thick chemical vapor deposition (CVD) tungsten gate metal–oxide–semiconductor (MOS) structures exhibits high interface state densities (Dit0>5×1011/cm2 eV) after conventional forming gas anneals over varying temperatures and times. In this letter, we show this is a consequence of the low diffusivity and solubility of molecular hydrogen in tungsten and the high temperature CVD process. We have discovered that atomic hydrogen is more effective in passivating tungsten gate MOS interfaces because of its higher diffusivity in tungsten. Atomic hydrogen can be produced (1) by the reaction of aluminum with water vapor when aluminum is evaporated on the top of tungsten, (2) by hydrogen implantation, and (3) by hydrogen plasma. These techniques can passivate the Si/SiO2 interface effectively in MOS structures (Dit0<5×1010/cm2 eV) with 100-nm thick CVD tungsten gates.

High-quality and low-temperature epitaxial Si films deposited at very high deposition rate

Low-temperature epitaxy at temperatures between 550°C and 650°C using ion-assisted deposition enables the formation of Si films with minority-carrier diffusion lengths deposited at rates previously only conceivable using high-temperature chemical vapor deposition at growth temperatures exceeding 1000°C. Using quantum efficiency and photoluminescence measurements, we investigate charge carrier recombination in Si films formed by ion-assisted deposition at temperatures between 460°C and 650°C. Silicon films deposited at a temperature between 460°C and 510°C display relatively short minority-carrier diffusion lengths peaked at a deposition rate around 0.25μm/min, while we find high diffusion lengths >20μm in Si films deposited at a temperature ⩾550°C with deposition rates between 0.2 and 0.8μm/min. At a deposition temperature of 650°C we achieve a minority carrier diffusion length of 40μm in a 21μm thick epitaxial Si film deposited at a rate of 0.8μm/min.

XPS, Raman spectroscopy, X‐ray diffraction, specular X‐ray reflectivity, transmission electron microscopy and elastic recoil detection analysis of emissive carbon film characterization

AbstractFor a better understanding of the physical and electronic properties of emissive carbon films, one of the best ways is to compare the results obtained with several surface and structural analysis techniques. In this article, different types of carbon film depositions for developing large flat panel displays by field emission displays are analysed and the results are correlated with their emissivity. Pulse laser ablation films, high‐temperature plasma‐enhanced chemical vapour deposition (PECVD) films and low‐temperature PECVD films are characterized by XPS, Raman spectroscopy, X‐ray diffraction (XRD), specular X‐ray reflectivity, transmission electron microscopy (TEM) and elastic recoil detection analysis (ERDA). The analyses lead us to conclude that the sp2/sp3 ratio is not a crucial parameter for carbon film emissivity. Crystalline structure seems more important. The presence of graphite grains is essential for good and uniform emission. Combination of XPS, TEM, XRD, Raman spectroscopy and ERDA is necessary for the study of carbon film emission. Copyright © 2001 John Wiley & Sons, Ltd.

00/02716 Impurity diffusion from uncoated foreign substrates during high temperature CVD for thin-film Si solar cells

00/02716 Impurity diffusion from uncoated foreign substrates during high temperature CVD for thin-film Si solar cells

Highly hydrogen selective ceramic membranes: application to the transformation of greenhouse gases

This paper reports the preparation of modified Vycor glass membranes by several methods: polymerization, dip coating, sol–gel impregnation, and chemical vapor deposition (CVD). It was found that a membrane (here called Nanosil) formed by the high-temperature CVD of tetraethylorthosilicate (TEOS) in inert gas exhibited hydrogen selectivities of 100% with respect to CH 4, CO, CO 2 and H 2O. The transport of hydrogen was not through Knudsen diffusion, but was activated, and probably involved atomic hydrogen species. The membrane was also stable to hydrothermal stresses (10% H 2O at 873 K and 1 bar) for over 150 h of operation. The membrane was employed in a catalytic reactor for the dry reforming of methane, CH 4+CO 2⇌2CO+2H 2, using a 1% Rh/Al 2O 3 catalyst. As a result of simultaneous reaction and separation, conversions were higher than those obtained in a packed-bed reactor operated at the same conditions, and exceeded equilibrium levels.

Current status and advances in the growth of SiC

Recent achievements in crystal growth and homoepitaxy of SiC, mainly of the 4H polytype, have been discussed. Several growth techniques, such as seeded sublimation growth, high temperature chemical vapor deposition, sublimation epitaxy and liquid phase epitaxy have been utilized to develop technological procedures and understand the growth processes better. The advantages of either method have been stressed. The main target has been the reproducible growth of micropipe free substrate material and thick epitaxial layers for device applications. The purity of the layers has been of special interest. The results obtained are indicative for the massive progress that has been achieved in SiC crystal growth during recent years.

Impurity diffusion from uncoated foreign substrates during high temperature CVD for thin-film Si solar cells

In this paper, we study the diffusion of impurities from three types of foreign substrates (graphite, alumina and mullite) during thermal chemical vapour deposition (CVD) of a polycrystalline Si film. For this we use a rapid thermal CVD (RTCVD) system and characterization techniques such as secondary ion mass spectroscopy (SIMS) and deep level transient spectroscopy (DLTS). Results show that, in the case of materials like graphite, metallic contaminants can freely outdiffuse into the deposited layer and the environment. In contrast, the ceramic substrates release only a very limited amount of contaminants during the CVD process, making the need of a diffusion barrier much less severe.

HTCVD growth of semi-insulating 4H-SiC crystals with low defect density

ABSTRACTThe development of a novel SiC crystal growth technique, generically described as High Temperature Chemical Vapor Deposition (HTCVD) is reviewed. The structural, optical and electrical properties of 4H-SiC semi-insulating substrates are investigated with the aim of providing optimal microwave device performances. In particular, alternative compensation mechanisms to vanadium doping in S.I substrates are investigated to eliminate substrate induced trapping effects. Carried out at temperatures above 2100°C, the HTCVD technique uses, as in CVD, gas precursors (silane and a hydrocarbon) as source materials. The growth process can be described as “Gas Fed Sublimation” and proceeds by the gas phase nucleation of Six-Cy clusters, followed by their sublimation into active species that are condensed on a seed. Crystals with diameters up to 45 mm have been obtained with growth rates of 0.6 mm/h. The use of specific process steps, such as in-situ seed surface preparation and micropipe closing are presented and high resistivity wafers with micropipe densities down to 10 cm−2 are demonstrated. 4H-SiC substrates prepared from undoped crystals (with vanadium concentration lower than 5×1014 cm−3) exhibit semi-insulating behavior with a room temperature resistivity of the order of 1010Ω?cm. Infrared absorption measurements show that two types of semi-insulating crystals can be grown, with a spectrum either dominated by the Si-vacancy, or by a previously unreported defect labeled UD-1. These two types of semi-insulating wafers are also differentiated by the temperature dependence of their resistivity, with activation energies of 0.85 and 1.4±0.1 eV, respectively, and by the stability of their resistivity upon an annealing at 1600°C. Initial MESFET devices processed on HTCVD grown substrates show better DC characteristics than devices processed on vanadium doped substrates.

High-temperature chemical vapor deposition. An effective tool for the production of coatings

Abstract Chemical vapor deposition (CVD) processes have a large throwing power and can operate at atmospheric pressure. Therefore, they are economical for many applications. High-temperature CVD processes give a good control of the crystal structure (e.g., epitaxial layers or other special layer structures) and support diffusion processes. The are used, for example, for the following deposition processes: 1) perovskites, 2) yttrium-stabilized ZrO2 layers as ion conductors or heat barrier coatings, 3) aluminide diffusion coatings in long tubes for corrosion protection, and 4) BN on fibers for fiber-reinforced materials. The special properties of the perovskite CVD are discussed in more detail. These processes are described for small- and large-scale applications. The CVD process is simulated by the computer code Fluent.

Chemically Assisted Oxidation of Silicon Nitride

Silicon nitride is barely oxidized in dry or even steam ambients at elevated (1100°C) temperatures. We have observed and studied the chemically enhanced oxidation of silicon nitride films from a variety of sources, that occurs at temperatures below 1050°C. The addition of several hundred parts per million of an additive like to the dry accomplishes this rapid oxidation independent of the films used whether plasma, low pressure, or high temperature chemical vapor deposition is used. The resultant oxidized films etch steadily in dilute HF (100:1) at the rate of tens of nanometers per minute. The oxidation rate observed is faster below 950°C and above this “transition temperature” an incubation period is observed prior to the film conversion. This incubation period becomes longer the higher the temperature, so that at 1050°C, it is of the order of 4 h. Analytic techniques such as X‐ray photoelectron spectroscopy and Fourier transform infrared and electron energy loss spectroscopy were used to determine the composition of the converted film and to gain insight into the possible reactions occurring in this process. This process can be used as an alternative to the plasma or phosphoric acid etching of nitride masking films. © 1999 The Electrochemical Society. All rights reserved.

Microstructure and property changes caused by diffusion during CVD coating of steels

Abstract The interdiffusion of carbon and titanium between a substrate and coating during chemical vapor deposition (CVD) coating of steels influences the microstructures and properties of the coating/substrate compounds. The CVD parameters atmosphere, temperature and pressure as well as the composition of the steel substrates were investigated systematically to optimize the properties of the coating/substrate compounds. The tool and carbon steels AISI H13 (DIN X40CrMoV5-1), AISI A2 (DIN X100CrMoV5-1), AISI 1045 (DIN Ck45) and ∼AISI 1095 (DIN 100V1) were coated by high-temperature CVD TiN, low-pressure CVD TiN and moderate-temperature CVD TiCN. Chemical compositions of coatings and substrates were measured by glow discharge optical spectroscopy (GDOS) and electron probe microanalysis (EPMA). Substrate and coating microstructures were examined in taper sections by light microscopy. Further, the substrate hardness was investigated in the taper sections. In an earlier work, carbon diffusion near the interface was investigated. Low coating pressures combined with high temperatures and high carbon activities of the substrates promoted the diffusion process. In this work, the investigations were extended to deeper substrate regions and to the titanium diffusion. From the carbon profiles in coatings and substrates, a carbon balance was set up for the diffusion from the substrate to the coating during CVD.

FTIR based process control for industrial reactors

Aiming to process control of industrial high yield/high volume CVD reactors, the potential of Fourier transform infrared spectroscopy (FTIR) has been checked as a monitoring tool. Tin oxide deposition on glass by oxidation of dimethyl tin dichlorid in a cold-wall thermal CVD reactor was selected as test case. Four differen FTIR monitoring modes have been evaluated and found feasible: transmission, (gas) emission, reflection and surface emission. The most detailed information of the composition of the gas atmosphere in the deposition zone is derived from the transmission and (gas) emission measurements. The emission mode is best suited for high temperature CVD reactors, needs only low effort for optical adaptation of the monitoring system but higher effort in data treatment for process control. Information on both gas composition and surface layer are derived from the reflection and the surface emission modes. Depending on the polanzation state of the surface emission, spectra contain information either on the sample surface only or on the reacting gas phase, too.

Cumulative deformation and fatigue of diamond — new developments

The soft impressor method has been used here to investigate the response of type-Ib high-pressure:high-temperature diamond and CVD diamond-coated:silicon carbide cutting tools to repeated loading cycles, i.e. simulated fatigue conditions, at room temperature. A mean contact pressure of 16.4 GPa was required to initiate cracking in the single crystal, when subjected to a single load cycle, and this was reduced to a fatigue mean pressure of 3.5 GPa after 200k load cycles. Similarly, the coated specimen failed at a fatigue mean pressure of 5.4 GPa after 16k load cycles. In addition, it was shown that the corners of the tool failed at fewer load cycles for a given mean pressure than the centre regions, presumably due to a greater degree of residual stress at those corners. Since moderately hard steels are capable of developing these fatigue mean pressures and conventional mechanisms of fatigue are unlikely under these conditions, e.g. those involving significant dislocation movement and interaction, it is suggested that future research should be directed towards establishing the possible role of stress corrosion and/or hydrogen embrittlement in this process.

Nitrogen impurity incorporation behavior in a chimney HTCVD process: pressure and temperature dependence

Experimental results are presented for residual nitrogen incorporation in both Si and C face 4H SiC epilayers using the high temperature chemical vapor deposition (HTCVD) process in a chimney reactor. The influence of total pressure, process temperature and input C/Si ratio on the residual nitrogen doping is studied. The results are further confirmed by intentional nitrogen doping experiments. Activation energies of 200 kcal/mol for Si face and 108 kcal/mol for C face samples are obtained for nitrogen incorporation. Possible incorporation mechanisms related to both surface and gas phase kinetics are discussed.

High temperature CVD growth of SiC

Two high temperature CVD techniques, respectively optimised for epitaxial and crystal growth, are presented. A chimney reactor has been developed for fast epitaxy, carried out at 1700–1900°C, with growth rates ranging from 10 to 25 μm h −1, and a material quality close to conventional CVD processes. The growth of 4H-SiC epilayers with low n-type doping (10 14–10 15 cm −3) and carrier lifetimes up to ∼0.4 μs is described, while the feasibility of high voltage Schottky rectifiers (1.8 kV) is demonstrated. On the other side, developments of the stagnant flow HTCVD process, where growth is carried out at 2000–2300°C, are shown to enable growth rates ranging from 0.3 up to 0.8 mm h −1. The main characteristics of HTCVD grown SiC crystals (up to nearly 7 mm thick) are described.

High temperature CVD systems to grow GaN or SiC based structures

Silicon Carbide is presently gaining much attention as a material for high temperature, high speed and high power devices. However, fabricating epitaxial SiC or GaN films is still a challenge since very high growth temperatures (up to 1600°C) must be used. This requires a carefully adapted design of reactors to ensure laminar flow conditions and a controlled depletion of the reactants inside the reactor. A second class of materials that is also playing a more and more important role today are the III nitrides (AlN, GaN, InN and alloys consisting of these). These materials are also grown at high deposition temperatures (up to 1300°C). Furthermore, these materials are grown on special buffer layers grown at much lower temperatures and are typically part of complex heterostructures which require abrupt changes of the growth temperature to realize sophisticated optoelectronic and electronic devices. As an example our high quality InGaN layers were grown at about 700°C and the AlGaN cladding layer of a laser or a LED require temperatures higher than 1100°C. In general, both nitrides and SiC are similar in their challenges to the growth equipment. This study uses a family of high temperature reactors to grow SiC and Nitrides. We describe the use of high temperature reactors to grow SiC and Nitrides. The load capacity ranges from single wafer machines to multiple wafer mass production reactors. All these reactors have a two flow injection system allowing a separated inlet of the various reactants. To achieve maximum uniformity of the growth, the Gas Foil Rotation ® Principle is applied. The multiwafer reactors are Planetary Reactors with double rotation of substrates. Extensive modeling has been used in order to find the optimum reactor geometries. Gas flow dynamics, temperature management and the physical and chemical properties of the precursors were considered in these models. Thus an optimization of uniformity and efficiency and a minimization of undesired parasitic reactions has been obtained. This contribution will work out the differences and the similarities of the high temperature growth of both material systems in AIXTRON reactors already established in production. Results on the growth of SiC and GaN will be presented.

Mechanical behaviour of PVD/CVD-coated hard metals under cyclic loads

The coating of hard metals by conventional CVD technology causes a deterioration of the mechanical properties and restricts their technical application as cutting tools. By the combination of PVD- and CVD-coatings a significant improvement in strength and lifetime was obtained in comparison to conventional CVD-coatings. The investigated coatings were deposited on a WC–(Ti,Ta,Nb,W)C–Co hard metal. The PVD/CVD-coating systems consisted of a TiAlN-PVD coating on which the functional TiN–TiCN–TiN-coating systems were deposited by a high temperature chemical vapour deposition (HTCVD) or a medium temperature chemical vapour depositon (MTCVD) process. Mechanical investigations were carried out under monotonically increasing and cyclic loads at room temperature. These investigations led to the result that especially the mechanical behaviour of coated hard metals under cyclic loads restricts the technical application of these coated materials as cutting tools. Failure mechanisms in the microstructure were investigated by TEM and SAM. It was shown that the TiAlN–PVD-layer exhibits a strong resistance against the propagation of subcritical cracks. Cutting tests with the mentioned PVD/CVD-layer systems showed increased life times compared to CVD coated hard metals. These results were in agreement with the results of the mechanical and microstructural investigations.