Diamond films

Diamond is an allotropic form of carbon. Synthetic diamond is generally synthesized in high pressure and high temperature conditions similar to the conditions under which natural diamond is formed. However, it is also possible to obtain high quality diamond film by chemical vapor deposition from a carbon precursor and hydrogen gas mixture.

The key parameter of diamond growth is to obtain a high concentration of hydrogen radical near substrate surface. It contributes to the stabilization of the sp3 dangling bonds. Without this stabilizing effect, these bonds would not be maintained and the diamond plane would collapse to the graphite structure. The other function of atomic hydrogen is to remove graphite selectively. The etch rate of graphite is twenty times higher than the diamond one.

Several techniques are used in order to activate the gas phase.

Due to the high surface energy of diamond, its nucleation occurs through the formation of islands or clusters (Volmer-Weber mode), which then grow to impinge upon each other and coalesce. Nucleation is a critical phase in the diamond deposition process due to its strong influence on film roughness and pinhole formation.

The substrate surface must be treated before deposition to achieve high nuclei density. Several techniques have been studied including ion bombardment, diamond powder scratching, and ultrasonic treatment with a diamond solution. NeoCoat has developed a very efficient, specific nanoseeding method, which guarantees nuclei density higher than 10¹¹ cm^-2 and no damage to the substrate surface.

Except on single-crystal diamond substrate, diamond film exhibits a polycrystalline structure. As the temperature of the process is around 800-900°C and high nuclei density is easier to achieve on carbide-forming material, diamond films are generally deposited on silicon-based material (Si, SiC, Si₃N₄) or refractory metals and alloys.

To change the conductivity value of diamond film, a boron-based component is added to the gas mixture during diamond deposition. A fine adjustment of boron precursor flow allows us to deposit diamond film with variable conductivity.