A novel method of preparation of silicon-on-diamond materials

A new method of preparation of silicon-on-diamond materials is discussed in detail. Pre-characterization of the samples surfaces has been carried out, in order to calculate the optimal pressure for surface contact before the bonding process. The method is based on pulsed laser irradiation, in the 20 ps–7 ns range, at a wavelength of 355 nm, for which diamond is transparent and silicon highly absorbing. Under these conditions the material melts locally, within 100 nm at the interface, giving rise to amorphous silicon and silicon carbide. The mechanical strength of the bonding has been assessed by adhesion tests. Preliminary result on resistance to thermal annealing at 400 C in air is also reported. Uniformity of the silicon–diamond interface has been verified by scanning electron microscopy. Raman and infrared spectroscopy allowed to detect and estimate quantitatively the amorphous Si and SiC phases at the interface. A finite element simulation has been carried out, taking into account the processes occurring during the laser pulse and the subsequent cooling of the materials. As a result, energy densities per pulse required to melt locally diamond and silicon have been obtained as functions of the pulse width, giving a rationale to the formation of the SiC bond in terms of diamond–silicon inter diffusion. The experimental results of bondings performed at various energy density and pulse widths are in agreement with the model. The experimental results and the theoretical predictions are compared and discussed.