Plasma activated CVD

Glaze coatings (58) are appHed to dry or bisque-fired clay ceramics to form a strong, impermeable surface that is aesthetically pleasing. Protective ceramic coatings can also be deposited by CVD (68,90). Plasma activated CVD has been used extensively to produce diamond and diamondlike films. Diamond films can also be used to make optical coatings with a tailored refractive index. 

Up to now three chemical vapor deposition (CVD) techniques have proved suitable for the preparation of high quality optical fibers the outside vapour phase oxidation (OVPO) process8, the modified CVD (MCVD) process9 and the plasma-activated CVD (PCVD) process10. The last mentioned process will be the main subject of this article. To give a better appreciation of the principles the alternative processes will be described briefly. 

Coatings are made by CVD, MT (medium temperature)-CVD, PVD, and plasma-activated CVD. The latter technique was recently successful in producing adherent diamond layers. The keenest edges are now produced by PVD coating. 

Ways have been investigated to reduce or avoid leaching of plasticizers. Barreto et al. (2012) deposited a barrier coating onto PVC, resulting in a reduction of more than 80% of leaching of the plasticizer. The barrier was established by means of plasma-activated CVD used to polymerize octamethylcyclotetrasiloxane (OMCTS) and hexamethyldisiloxane (HMDSO). Covalent bonding of the plasticizer to PVC... 

In most cases, CVD reactions are activated thermally, but in some cases, notably in exothermic chemical transport reactions, the substrate temperature is held below that of the feed material to obtain deposition. Other means of activation are available (7), eg, deposition at lower substrate temperatures is obtained by electric-discharge plasma activation. In some cases, unique materials are produced by plasma-assisted CVD (PACVD), such as amorphous siHcon from silane where 10—35 mol % hydrogen remains bonded in the soHd deposit. Except for the problem of large amounts of energy consumption in its formation, this material is of interest for thin-film solar cells. Passivating films of Si02 or Si02 Si N deposited by PACVD are of interest in the semiconductor industry (see Semiconductors). 

Plasmas can be used in CVD reactors to activate and partially decompose the precursor species and perhaps form new chemical species. This allows deposition at a temperature lower than thermal CVD. The process is called plasma-enhanced CVD (PECVD) (12). The plasmas are generated by direct-current, radio-frequency (r-f), or electron-cyclotron-resonance (ECR) techniques. Eigure 15 shows a parallel-plate CVD reactor that uses r-f power to generate the plasma. This type of PECVD reactor is in common use in the semiconductor industry to deposit siUcon nitride, Si N and glass (PSG) encapsulating layers a few micrometers-thick at deposition rates of 5—100 nm /min. 

In PECVD, the plasma generation region may be in the deposition chamber or precede the deposition chamber in the gas flow system. The latter configuration is called remote plasma-enhanced CVD (RPECVD). In either case, the purpose of the plasma is to give activation and partial reaction/reduction of the chemical precursor vapors so that the substrate temperature can be lowered and still obtain deposit of the same quaUty. 

Gartner, G., Jamiel, P., and Lydtin, H., Plasma-Activated Metalorganic CVD of Illb Oxides/Tungsten Layer Structures, Proc. of 11th Int. Conf on CVD, (K. Spear and G. Cullen, eds.), pp. 589-595, Electrochem. Soc., Pennington, NJ 08534 (1990)... 

Thermal CVD, reviewed above, relies on thermal energy to activate the reaction, and deposition temperatures are usually high. In plasma CVD, also known as plasma-enhanced CVD (PECV) or plasma-assisted CVD (PACVD), the reaction is activated by a plasma and the deposition temperature is substantially lower. Plasma CVD combines a chemical and a physical process and may be said to bridge the gap between CVD andPVD. In this respect, itis similar to PVD processes operating in a chemical environment, such as reactive sputtering (see Appendix). 

In a plasma-activated reaction, the substrate temperature can be considerably lower than in thermal CVD (see Ch. 5, Sec. 9). This allows the coating of thermally sensitive materials. The... 

A thick (> 1 jum) field oxide layer is formed after the implant activation. The field oxide is generally deposited nsing low-pressnre CVD (LPCVD) or plasma-enhanced CVD (PECVD) process becanse the Si-face of SiC has very low oxidation rate and becanse consumption of the implanted layer must be minimized. The field oxide layer is then patterned by selectively etching to remove all oxide from the... 

In general, several possible chemical reactions can occur in a CVD process, some of which are thermal decomposition (or pyrolysis), reduction, hydrolysis, oxidation, carburization, nitridization and polymerization. All of these can be activated by numerous methods such as thermal, plasma assisted, laser, photoassisted, rapid thermal processing assisted, and focussed ion or electron beams. Correspondingly, the CVD processes are termed, thermal CVD, plasma assisted CVD, laser CVD and so on. Among these, thermal and plasma assisted CVD techniques are widely used, although polymer CVD by other techniques has been reported. ... 

In addition to microelectronic and optical applications, polymers deposited using thermal and plasma assisted CVD are increasingly being used in several biomedical applications as well. For instance, drug particles microencapsulated with parylenes provide effective control release activity. Plasma polymerized tetrafiuoroethylene, parylenes and ethylene/nitrogen mixtures can be used as blood compatible materials. An excellent review of plasma polymers used in biomedical applications can be found in reference 131. 

A variety of CVD methods and CVD reactors have been developed, depending on the types of precursors used, the deposition conditions applied, and the forms of energy introduced to the system to activate the chemical reactions desired for the deposition of solid fihns on snbstrates. For example, when metalorganic compounds are used as precursors, the process is generally referred to as MOCVD (metalorganic CVD), and when plasma is nsed to promote chemical reactions, this is called plasma-enhanced CVD (PECVD). There are many other modified CVD methods, such as LPCVD (low-pressure CVD), laser-enhanced or assisted CVD, and aerosol-assisted CVD (AACVD). 

Recognition of TiN as a supreb barrier to diffusional and electrical activity has resulted in extensive research on the CVD of TiN for microelectronic layers. Significant advances have been made in the area of plasma-assisted CVD where dc glow , ECR , and helicon plasmas have all been used. Implementation of such plasmas can reduce the processing temperature of reaction (b) to 400°C. For plasma deposition of TiN using titanium isopropoxide, the deposition temperature can be as low as 100°C, where the chemistry is outlined as follows ... 

In the previous chapters we dealt with tungsten depositions using thermally activated reactions only. Two other techniques will now be discussed namely plasma enhanced CVD of tungsten and the deposition of tungsten by photo activation. 

CVD can also be classified using its activation methods. Thermal activated CVD processes are initiated only with the thermal energy of resistance heating, RF heating or by infrared radiation. They are widely used to manufacture the materials for high-temperature and hard-to-wear applications. In some cases enhanced CVD methods are employed, which includes plasma-enhanced CVD (PECVD), laser-induced CVD (LCVD), photo CVD (PCVD), catalysis-assisted CVD and so on. In a plasma-enhanced CVD process the plasma is used to activate the precursor gas, which significantly decreases the deposition temperature. 

The conventional CVD method uses thermal energy to activate chemical reactimis, which is commonly known as thermally activated CVD (TACVD). CVD reactions can be initiated by using different energy sources. Plasma and light energy are currently being used to activate the chemical reactions. Other types of CVD include atomic layer epitaxy, metal-organic CVD, flame-assisted CVD, and electrochemical vapor deposition. They are briefly discussed herewith [1,5]. 

Plasma-enhanced CVD (PE-CVD), a CVD technique that activates gases by... 

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