Combustion chemical vapor deposition
Encyclopedia
Combustion chemical vapor deposition (CCVD) is a chemical process
by which thin film
coating
s are deposited onto substrates in the open atmosphere.
into highly reactive intermediates, which readily react with the substrate, forming a firmly adhering deposit. The microstructure
and thickness of the deposited layer can be controlled by varying process parameters such as speed of substrate or flame, number of passes, substrate temperature and distance between flame and substrate. CCVD can produce coatings with orientation from preferred to epitaxial
, and can produce conformal layers less than 10 nm thick. Thus, CCVD technique is a true vapor deposition process for making thin film coatings
.
The CCVD coating process has the ability to deposit thin film
s in the open atmosphere using inexpensive precursor chemicals in solution leading to continuous, production-line manufacturing. It does not require post-deposition treatment e.g., annealing
. The throughput potential is high.
Chemical process
In a "scientific" sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by somebody. Such a chemical process commonly involves a chemical reaction of some sort...
by which thin film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
coating
Coating
Coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance...
s are deposited onto substrates in the open atmosphere.
History
In the 1980s, initial attempts were performed to improve the adhesion of metal-plastic composites in dental ceramics using flame-pyrolytically deposited silicon dioxide (SiO2). The silicoater process derived from these studies provided a starting point in the development of CCVD processes. Subsequently, this process was constantly developed and new applications for flame-pyrolytically deposited SiO2 layers where found. At this time, the name "Pyrosil" was coined for these layers. Newer and ongoing studies deal with deposition of other materials (vide infra).Principles and procedure
In the CCVD process, a precursor compound, usually a metal-organic compound or a metal salt, is added to the burning gas. The flame is moved closely above the surface to be coated. The high energy within the flame converts the precursorsPrecursor (chemistry)
In chemistry, a precursor is a compound that participates in the chemical reaction that produces another compound. In biochemistry, the term "precursor" is used more specifically to refer to a chemical compound preceding another in a metabolic pathway....
into highly reactive intermediates, which readily react with the substrate, forming a firmly adhering deposit. The microstructure
Microstructure
Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification...
and thickness of the deposited layer can be controlled by varying process parameters such as speed of substrate or flame, number of passes, substrate temperature and distance between flame and substrate. CCVD can produce coatings with orientation from preferred to epitaxial
Epitaxy
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where the overlayer is in registry with the substrate. In other words, there must be one or more preferred orientations of the overlayer with respect to the substrate for this to be termed epitaxial growth. The...
, and can produce conformal layers less than 10 nm thick. Thus, CCVD technique is a true vapor deposition process for making thin film coatings
.
The CCVD coating process has the ability to deposit thin film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s in the open atmosphere using inexpensive precursor chemicals in solution leading to continuous, production-line manufacturing. It does not require post-deposition treatment e.g., annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
. The throughput potential is high.
Remote combustion chemical vapor deposition (r-CCVD)
The so-called remote combustion chemical vapour deposition is a new vaiant of the classical CCVD process. It likewise uses flames to deposit thin films, however, this method is based on other chemical reaction mechanisms and offers further abilities for deposition of layer systems which are not practicable by means of CCVD, e.g. titanium dioxide.Applications
| Layer material | Application |
|---|---|
| SiO2 | - Silicon dioxide layers are the most commonly deposited layers. Freshly deposited layers are highly reactive and can thus serve as adhesion promoting layers for polymer coatings und bondings. Adhesion can be further improved by application of additional silane-based adhesion promoters such as glymo. - modification of optical properties (e.g. transmission enhancement) - barrier layers against gases such as O2 and ions like Na+ |
| WOx, MoOx | - chromogenic materials in „intelligent windows“ |
| ZnO | - semiconductor - component in transparent conducting oxides (TCO) such as aluminum-doped zinc-oxide (AZO) |
| ZrO2 | - layer protecting against mechanical damages (e.g. abrasion, scratches) |
| SnO2 | - component in various transparent conducting oxides, such as tin-doped indium-oxide Indium tin oxide Indium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey... (ITO) and fluorine doped tin oxide (FTO) |
| TiO2 | - photo catalytic layers |
| Ag | - good electric conductivity - heat protection glass - antibacterial coatings |
| Al2O3 | - protection against corrosion of glas |
Pros and Cons
- Cost-effective, partly because no devices for generation and maintenance of a vacuumVacuumIn everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
are needed - Flexible in use due to various implementations
- Fewer layer materials compared to some low-pressure methods, limited primarily to oxides. The exceptions are some precious metals such as silver, gold and platinum
- Limited to layer materials, for which suitable precursors are available, however, this is the case for most metals
See also
- Chemical vapor depositionChemical vapor depositionChemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
- Atomic layer depositionAtomic layer depositionAtomic layer deposition is a thin film deposition technique that is based on the sequential use of a gas phase chemical process. The majority of ALD reactions use two chemicals, typically called precursors. These precursors react with a surface one-at-a-time in a sequential manner...
, a more precise and conformal coating technology - Physical vapor depositionPhysical vapor depositionPhysical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...
, the deposition of materials from vapor without chemical reactions - Plasma-enhanced chemical vapor depositionPlasma-enhanced chemical vapor depositionPlasma-enhanced chemical vapor deposition is a process used to deposit thin films from a gas state to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of the reacting gases...
Further reading
- Withers, J.C. et al., Aluminum Coatings by a Pyrolytic Spray Chemical Vapor Dispostion Process, 2d Int'l Conf. on CVD (1970)
- A.T. Hunt et al. Combustion Chemical Vapor Deposition: A Novel Thin Film Deposition Technique. Applied Physics Letters. 63: pp. 266–268 1993
- Blandenet, G. et al. Indium Oxide Deposition on Glass by Aerosol Pyrolysis, 5th Int'l Conf on CVD (1975)
- Hirose, Y. et al., The Synthesis of High Quality Diamond in Combustion Flame, 89-12 Proceedings of the Electrochemical Society (1989)