FORCARBON

II. 3 Fabrication of diamond composites via chemical vapour infiltration

Aim of this project is the investigation of new possibilities in producing templates of diamond/metal or diamond/ceramics composites. Therefore, porous structures of different materials (tungsten, copper, silicon carbide, carbon) become infiltrated with diamond (Chemical Vapour Infiltration, CVI). Result is a diamond/metal or diamond/ceramics composite. Important for successful infiltration with diamond is the pretreatment of porous structures for CVI with a diamond suspension as well as parameters like growth rate, infiltration depth and diamond quality over the pore length. Ideal growth conditions for diamond in a pore will be achieved by variation of the process parameters gas pressure, feed gas composition, gas flow and substrate temperature. Complete infiltration is difficult as the pore mouth gets closed at first. This is caused by the overgrowing diamond coating from the surface and the rapidly decreasing concentration of atomic hydrogen and growth species in the pore. The transport rate of atomic hydrogen and growth species must be high (especially in the pore) compared to their duration. A temperature gradient in the porous substrate will allow different growth rates in the pore preventing the pores from closing at the pore mouth first. Also a forced gas flow through the substrate will enhance the transport rate of the essential gas species. For this, a new hot filament plant will be constructed. After three years the diamond infiltration of open pored copper substrates with a thickness of 500 µm should be possible. One application for this penetration structure could be heat sinks in the microelectronic industry, because of their high thermal conductivity and low thermal expansion.