MW PACVD

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.)...

Research on MW PACVD began from the pioneering work of Kamo et The MW PACVD (Tables 1 and 2) is, aside from the HFCVD, the most frequently used method for diamond growth and also the most extensively studied process. The intensive use of the MW PACVD is prompted by the following factors ... 

In spite of some ofthe advantages ofthe MW PACVD over other CVD methods, notably its stability, the deposition rates currently achievable in the... 

It has been reported that diamond films with crystallite size of about 200 nm form at the substrate temperatures aroimd 650°C, while 10-20 nm sized crystaUites occur at the substrate temperatures between 450 and 600°C. Another study " showed that diamond grains ot 160, 13, and 10 nm were grown at the substrate temperature of 800, 600 and 415°C, respectively, in MW PACVD. Clearly, for substrate temperatures lower than 800°C, the crystallite size increases with increasing substrate temperature. These results demonstrated that the crystallite size, surface roughness and hence optical transparency as well as other properties of diamond films can be tailored by varying the substrate temperature. 

The formation of SiC on Si substrates in the initial stages of nucleation was also observed by Waite and Shaht 1 in MW PACVD using XPS. A diamond peak appeared after the incubation period with a simultaneous decrease in SiC peak intensity. However, SiC remained as an impurity even after several hours of deposition. 

In diamond growth experiments on Mo and Si substrates using MW PACVD by Meilunas et al., M02C and SiC layers of approximately 1.5 pm and 10 nm in thickness were observed with SEM within 1 min and after 5 min, respectively. The growth rate of SiC was much less thanthat of M02C. Diamond nanocrystallites were observed after 1 min, and no further carbide layer growth was detected once the surface was covered with diamond. 

SiC 10 nm 1277] MW PACVD 950 0.3-1CH4 0,202 200 30 polished with 0.25 pm diamond paste, ultrasonically cleaned in meihant and DI water Si... 

Figure 4. Dependence of diamond nucleation site density (NSD) on residual diamond partiele density (RDD) under various deposition conditions. The dotted line shows NSD equal to RDD and the solid line shows NSD being 10% of RDD. Solid circles ultrasonic polishing, followed by MW PACVD crosses hand polishing, followed by MW PACVD triangles ultrasonic polishing, followed by HFCVD (filament temperature = 2973 K) squares ultrasonic polishing, followed by HFCVD (filament temperature = 2773 K) open circles ultrasonic polishing, followed by HFCVD (filament temperature = 2573 K) dotted circles fluidized-diamond polishing, followed by MW PACW (Reproduced with permission.)...

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). 

Very high nucleation densities, averaging around 3x10 cm, have been obtained on Si substrates scratched with 0.5 pm diamond paste, cleaned in acetone and deposited with an a-C film in MW PACVD.i l The nucleation densities are several orders. of magnitude higher than diose achieved on Si scratched alone (2x 10 cm ) under the same deposition conditions. 

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