Nucleation enhancement biasing

In an effort to enhance diamond nucleation and to control film morphology, extensive work on the nucleation and early growth stages has been performed. As a result, technology problems associated with the nucleation of polycrystalline diamond films have been adequately addressed. A number of nucleation enhancement methods have been developed that enable the control of nucleation density over several orders of magnitude. Nucleation density has been increased from < 10 cm on untreated substrates up to 10 cm on scratched or biased substrates. The effects of surface conditions on nucleation processes have been investigated to provide the guideline for the selection of optimum surface pretreatment methods. In this chapter, substrate materials, surface pretreatment methods and their influences on diamond nucleation are discussed. 

The mechanisms of the nucleation enhancement by biasing have been addressed in several studies, as depicted in Fig. 8. 

Figure 8. Schematic diagram showing the mechanisms of diamond nucleation enhancement on biased substrates, (a) Negative biasing carbon-containing cations are accelerated toward the substrate surface, (b) Positive biasing electrons are accelerated toward the substrate surface and bombard carbon-containing molecules adsorbed on the surface. (Reproduced with permission.)...

As discussed in Ch. 6, diamond nucleation enhancement may be achieved by, for example, predeposition of a thin DLC layer in combustion flame or DC glow-discharge plasmas, or, by carburization/biasing to develop a complete SiC layer on the substrate surface in MW PACVD. 

In an in-depth study of diamond nucleation on Si in MW PACVD,0 1 substrates were pretreated by negative biasing in a 2 vol.%CH4-H2 plasma. The biasing enhanced diamond nucleation density on unscratched Si wafers, up to 10 cm" , as compared to 10 cm" on scratched Si wafers and 10 -10 cm-2[279] Qjj untreated Si wafers (Fig. 6). 

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