Enhanced nucleation density of chemical vapor deposition diamonds by using interlayer

Effects of interlayers on diamond nucleation were investigated for the Si substrates. Interlayers were deposited on the diamond-abraded Si substrates by rf sputtering prior to diamond growth using microwave plasma chemical vapor deposition (CVD). Compared with 1 × 108/cm2 for the just abraded substrate, the nucleation density was greatly enhanced to 1 ∼ 2 × 109/cm2 by 50 nm thick interlayer, irrespective of the kind of interlayer material used in this study (Si, Mo, Ti, Pt, Ag, TiN, or SiO2). As the thickness of the Si interlayer increased from 20 to 500 nm, the nucleation density reached a maximum value, 3 × 109/cm2 at 100 nm. However, the growth rate was monotonically reduced from ∼300 nm/h to ∼100 nm/h. For the 700 nm thick Si interlayer, no diamond growth was observed. These results indicate that there is an optimum interlayer thickness around 100 nm for the higher nucleation density. The role of the interlayer in enhancing the nucleation density is believed to protect the nucleation sites generated by the diamond abrasion, otherwise they could be considerably etched away by atomic hydrogen during the initial diamond deposition.