MICROSCOPIC INVESTIGATIONS OF SILICON SURFACES PRETREATED FOR USE IN DIAMOND DEPOSITION

The influence of pretreatment of silicon by diamond powder and cubic boron nitride (cBN) powder, as well as by substrate biasing, was investigated. The uncoated silicon surfaces were investigated by scanning electron microscopy, transmission electron microscopy and electron energy loss spectroscopy. The mechanical pretreatment was carried out in an ultrasonic water bath. Polished silicon wafers were dipped in a beaker containing an ethanol-powder mixture. It has been shown that very small diamond or cBN crystals are pressed into the silicon surface. These crystals are not removable even with thorough post-treatment. The size of the crystals, which were pressed into the silicon surface, is between 2 nm and 50 nm, and the density is in the range 10(9)-10(10) crystals cm-2. Increasing pretreatment time causes an increase in crystal number density. All substrates were coated in a microwave chemical vapour deposition system in order to determine the nucleation density, Under the same conditions non-pretreated silicon substrates were coated with the help of substrate biasing. It has been supposed that the nature and the density of residues left on the silicon surface after mechanical pretreatment are important for nucleation. Clusters of diamond microcrystals were formed on the surface of biased pretreated substrates. After deposition a silicon carbide film can be observed in areas not occupied by diamond particles.