Biasing time

Gerber et al. [221] investigated the nucleation density of diamond on Si, which was placed on a heated stage, by changing the BEN parameters the CH4 concentration c< 15%CH4/H2, V, the biasing time, and T. The nucleation density became maximum of approximately 10 °/cm for 7],. >740°C at F = -250V, and did not depend on the CH4 concentration. Indeed, c = 5 and 15%CH4/H2 resulted in the same saturated nucleation density. An estimated ion energy for optimum nucleation was 70-80 eV, and hence it was concluded that the BEN process proceeds by a subplantation of hydrocarbon ions. 

A BEN study on refractory metals (Hr, Ti, Ta, Nb, and W) in addition to Cu and Si has been done by Walter et al. [241] using an ASTeX reactor under the conditions given in Table H.l. See also Refs. [242, 243]. Figure 10.25 shows the nucleation density as a function of the biasing time for the refractory metals, Si, and Cu. It is seen that Si has the highest nucleation rate and density, while Cu has the... 

Figure 10.25. Nucleation density as a function of biasing time for various refractory metals compared with Si and Cu [241].

Figure 11.16. Optimum biasing time for different bias voltage. The circles mark hetero-epitaxial films, while the triangles correspond to specimens without significant azimuthal alignment. The biasing times fopt of the HOD films with minimum FWHM for the azimuthal tilt angle are connected by straight lines. The vertical extension of the bright area defines the width of the BEN process time window [293].

The influence of the process parameters on BEN was studied in Ref. [331] using an ASTeX reactor. The substrate used was Si(lOO) of 1-inch in diameter, which was placed on a Mo substrate holder. No carburization was done before the BEN process. The microwave power was 900 W, and the substrate temperature was 725 °C. Laser reflection interferometry (LRI) [330, 331] was used to monitor the diamond nucleation and the subsequent growth rate. The biasing time was determined from the inflection point of the intensity of the LRI. At this point,... 

The nucleation process was monitored by LRI (see Section 11.10), and the application of bias voltage was terminated if diamond nucleation was detected by LRI. No appreciable diamond nucleation was observed in the AC-BEN treatment, if the voltage was less than 125 Vrms ( 175 V peak to peak). The optimum biasing time for the AC-BEN treatment was 45 min, much longer than the DC-BEN treatment that needed only 12 min. In terms of the number of oriented nuclei, it was more than 50% for the AC-BEN treatment, while it was only less than 10% for the DC-BEN treatment. It was hence inferred that concurrent processes of forming an epitaxial SiC layer and the diamond nucleation, induced by the AC-BEN treatment, were responsible for the increase in the number of oriented diamond nuclei. 

Figure 11.53, Current from the electrode to a new (x) and an already diamond-coated ( ) substrate holders during the BEN treatment as a function of the biasing time [364],...

Complete operating instructions for the UUT, including all biases, timing, and serial words... 

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