Substrate pre-treatment by ultrasonication with diamond powder mixtures for nucleation enhancement in diamond film growth

Abstract

Pre-treatment of silicon substrates by ultrasonic abrasion for nucleation enhancement in diamond film formation by hot-filament chemical vapour deposition is discussed. Scanning electron microscopy, atomic force microscopy and visible Raman spectroscopy were employed as analysis techniques. Ultrasonication was applied by suspensions of isopropanol with micro-or nanosized diamond powders, micro-sized metal and alumina particles and mixtures thereof. The root mean square roughness of the ultrasonically pre-treated samples varied from 0.2 to 12.0 nm depending on the applied powder mixture. All samples that were ultrasonically pre-treated had a larger diamond nucleation density than the untreated silicon wafer. As expected, for an effective increment of the diamond nucleation density by several orders of magnitude the application of diamond powder is necessary, since the generation of surface roughness alone is not sufficient to enhance the diamond nucleation kinetics satisfactorily. The simultaneous action of diamond powders and large alumina or titanium particles leads to an increase in diamond nucleation density up to a factor of 10^6. When nano-diamond powder is used, the embedment of diamond fragments is best and in combination with titanium grains (50–75 µm) a diamond nucleation density of 8 × 10^9 cm−2 is obtained. After 8 h of film growth, the diamond surface grains are significantly smaller for the samples that demonstrated higher nucleation densities, whereas the quality of the diamond layers is equal.