Thermal plasma CVD

In further sections extensions or adaptations of the PECVD method will be presented, such as VHF PECVD [16], the chemical annealing or layer-by-layer technique [17], and modulation of the RF excitation frequency [18]. The HWCVD method [19] (the plasmaless method) will be described and compared with the PECVD methods. The last deposition method that is treated is expanding thermal plasma CVD (ETP CVD) [20, 21]. Other methods of deposition, such as remote-plasma CVD, and in particular electron cyclotron resonance CVD (ECR CVD), are not treated here, as to date these methods are difficult to scale up for industrial purposes. Details of these methods can be found in, e.g., Luft and Tsuo [6]. 

Loffler et al. successfully deposited a-Si H solar cells on their in-house ZnO grown by expanding thermal plasma CVD [52]. They reached initial efficiencies of around 10%, and supported also the need to improve the ZnO/p-layer interface. 

A promising alternative is surface textured doped zinc oxide films. ZnO films can offer excellent transparency and are highly resistant to hydrogen plasmas [78]. Textured ZnO films have been prepared by several deposition techniques. Examples are boron doped zinc oxide (ZnO B) prepared by low-pressure chemical vapor deposition (LPCVD) ([79,80], see also Chap. 6) or ZnO films deposited by expanding thermal plasma CVD [81], Quite recently, ZnO films for back contacts of solar modules have been developed using chemical bath deposition [82]. 

Figure 2. Schematic diagram of various CVD techniques for diamond synthesis, (a) HFCVD (b) MW PACVD (c) ECR MW PACVD (d) DC PACVD (e) RF PACVD (0 DC thermal plasma CVD (g) RF thermal plasma CVD (h) flame (combustion) CVD.l (Reproduced with permission.)...

Reaction conditions similar to those in the DC thermal plasma CVD can be obtained in an inductively coupled, radio-frequency induced thermal plasma at atmospheric pressure, as shown schematically in Fig, 2g. This technique was first reported by Matsumoto et al. in 1987.Very high... 

In spite of the poor energy efficiency and difficult process control in both the DC thermal plasma CVD and the RF thermal plasma CVD, the high growth rates achieved with these methods represent a milestone in diamond CVD technology. Within less than a decade, deposition rates have been... 

A recent study on DC thermal plasma CVD of diamondf demonstrated the existence of an optimum pressure at 270 torr, at which the... 

The low temperature synthesis of diamond films has been investigated in the substrate temperature range of 350-800°C in RF thermal plasma CVD, and diamond films of reasonable quality have been obtained at 550-600°C which are considerably lower than those generally considered as... 

Substrates are usually immersed in the plasmas in MW, DC and RF PACVD processes or separated from the plasmas in DC and RF thermal plasma CVD processes. A. substrate is generally placed 0.5-2 cm. fi-om the hot filament in the HFCVD, or fi om the flame burner nozzle in the combustion CVD, and up to 5 cm from the thermal plasma nozzle in the DC thermal plasma CVD.f " Report on distances greater than several centimeters has not been found in published literature, which may be attributable to... 

Shimada S, Fuji Y, Tsujino J, Yamazaki I (2010) Thermal plasma CVD and wear resistance of double layered Ti-Si-B-CATi-B-C coatings on WC-Co cutting tools with various roughness. Surf Coat Technol 204(11) 1715-1721... 

Describe the various processes and equipment used in R D and production such as thermal CVD, plasma CVD, photo CVD, MOCVD, and others. 

The various CVD processes comprise what is generally known as thermal CVD, which is the original process, laser and photo CVD, and more importantly plasma CVD, which has many advantages and has seen a rapid development in the last few years. The difference between these processes is the method of applying the energy required for the CVD reaction to take place. 

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). 

Plasma CVD was first developed in the 1960s for semiconductor applications, notably for the deposition of silicon nitride. The number and variety of applications have expanded greatly ever since and it is now a major process on par with thermal CVD. 

Advantages of Plasma CVD. As shown in Table 5.4, with plasma CVD, a deposit is obtained at temperatures where no reaction whatsoever would take place in thermal CVD. This is its major advantage since it permits the coating of low-temperature sub-... 

In addition to the thermal CVD systems mentioned above, molybdenum is deposited by plasma CVD using Reaction (3) in hydrogen.Annealing is required to remove incorporated carbon and oxygen. 

In addition to the thermal CVD reactions listed above, tungsten can be deposited by plasma CVD using Reaction(l)at350°C.[ ll P At this temperature, a metastable alpha structure (aW) is formed instead of the stable be.c. Tungsten is also deposited by an excimer laser by Reaction (1) at < 1 Torr to produce stripes on silicon substrate.P l... 

In addition to the thermal CVD reactions mentioned above, plasma CVD is used for the low temperature deposition of boron.i l... 

Saitoh, H., et al., Synthesis of C-BN Film by Thermally Activated RF Plasma CVD Method, Japan New Diamond Forum, pp. 57-59, New Diamond (1988)... 

Common deposition reactions are based on the combination of silane with various oxidizers, either as thermal CVD or plasma CVD as follows 1... 

Plasma CVD and thermal laser CVD are also used particularly in the deposition of GaAs. The formation of epitaxial GaAs at 500°C and polycrystalline GaAs at 185°C has been reported,... 

Some of the most significant developments in the CVD of Si02 include experiments in plasma CVD at 350°C via electron cyclotron resonance (ECR) to gain improved control of the deposition rate and obtain a quality equivalent to that of the thermally grown oxide (see Ch. 5). Deposition from diacetoxyditertiarybutoxy silane at 450°C has also been shown to significantly improve the Si02 film properties. " ]... 

The expanding thermal plasma chemical vapor deposition (ETP CVD) technique has been developed in the group of Schram [20, 556] and has been used for the... 

Other CVD Processes. CVD also finds extensive use in the production of protective coatings (44,45) and in the manufacture of optical fibers (46-48). Whereas the important question in the deposition of protective coatings is analogous to that in microelectronics (i.e., the deposition of a coherent, uniform film), the fabrication of optical fibers by CVD is fundamentally different. This process involves gas-phase nucleation and transport of the aerosol particles to the fiber surface by thermophoresis (49, 50). Heating the deposited particle layer consolidates it into the fiber structure. Often, a thermal plasma is used to enhance the thermophoretic transport of the particles to the fiber walls (48, 51). The gas-phase nucleation is detrimental to other CVD processes in which thin, uniform solid films are desired. 

In contrast to plasma spraying, low pressure plasma CVD does not require any remote handling technique. However, there is yet no experience with large scale applications of this method, particularly in metallic vessels. This is the first goal towards which future studies have to be directed. Very little is also known about the adherence of the coatings deposited by low pressure plasma CVD and their resistance against thermal shock. The choice of the best material for such coatings is presently open to discussion. 

In addition to thermally-created CVD films, much work has been done using glow discharges to modify the deposition. Therefore, Chapter 2 reviews the fundamentals of plasma-enhanced CVD (PECVD). Initially, the basic character of a plasma is covered. Then we discuss the influence of the reactor configuration on the plasma behavior and PECVD deposition. The two major PECVD reactor systems are reviewed, and then several new concepts are considered. 

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