Diamond CVD Techniques

A large variety of carbon-containing gas species have been employed to synthesize diamond by CVD, These include methane, aliphatic and aromatic hydrocarbons, alcohols, ketones, amines, ethers, and carbon monoxide, with methane being the most frequently used reagent. In 

It has been observed that a necessary condition for diamond growth to occur is the presence of a gas-phase non-equilibrium in the region adjacent to the deposition substrate. The gas-phase non-equilibrium is generated through gas-phase activation. The gas-phase activation is achieved typically using one of the three basic methods  

To obtain the gas-phase activation state required for the stable growth of well-crystallized diamond, a variety of energetically assisted CVD techniques have been developed and employed. These may be classified into three major categories  

The advantages and disadvantages of the diamond CVD techniques, along with typical technical data, are summarized in Table  

Method Rate (urn h ) Area (cm l Quality (Raman) Substrate material Advantage Disadvantage 

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The potential for economic scale-up of diamond CVD techniques qualifies it as a viable processing alternative to the HPHT methods for... 

Table 2. Typical Reactor Operating Conditions in Diamond CVD Techniques...

Figure 15 shows the variation of diamond deposition rates by various activated CVD techniques as well as the HP—HT technique (165). It can be seen that the highest growth rate of activated CVD diamond synthesis is stiU an order of magnitude lower than the HP—HT technique. However, CVD has the potential to become an alternative for diamond growth ia view of the significantly lower cost of activated CVD equipmeat and lower miming and maintenance costs. 

Fig. 15. Variation of diamond deposition rates by various activated CVD techniques as well as the HP—HT technique (165).

The activated CVD diamond techniques can be mote attractive in cases where the huge capital investment (several hundred million dollars) requited for the HP—HT technology is not available or where the high level of technical knowledge requited for HP—HT synthesis is not available. In addition, most wear-resistant apphcations requite diamond coatings only of the order of a few micrometers thick. Such coatings can be deposited ditecdy on the finished product without the need for further finishing if CVD techniques are employed. 

All the major CVD techniques for producing diamond films involve pyrolysis of a carbonaceous gas and simultaneously activation of the gas phase to produce a selective etchant such as atomic hydrogen to remove nondiamond carbon phases from the growing film. The various techniques differ mainly in the means used for gas activation. Some basic activation teclmiques that have been used by various researchers involve ... 

Based on the DC plasma CVD technique, Sawabe and co-workers [376] were successful in making a free-standing, transparent, 2 mm x 2 mm, 8 pm thick, (lOO)-oriented diamond platelet. A defect study of the film was done using ESR [406], In the latest result, a free-standing, transparent diamond plate of l-inch in diameter has been made by Sawabe s group. 

By making an updated and systematic review of diamond CVD processes, the objective of this book is to familiarize the reader with the scientific and engineering aspects of diamond CVD, and to provide experienced researchers, scientists, and engineers in academic and industry community with the latest developments in this growing field. The scope of the present book encompasses the development and applications of diamond CVD, starting with a brief description of atomic and crystal structures of diamond and a review of the various processing techniques used in diamond CVD. It is followed by an extensive discussion of fundamental phenomena, principles and processes involved in diamond CVD, with emphasis on the... 

In the following, various CVD techniques for the growth of diamond crystals and films on deposition substrates are discussed in detail. 

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.)...

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