Control of the stabilization of cubic boron nitride thin films deposited by unbalanced magnetron sputtering and dc pulsed substrate biasing
Abstract
The formation of cubic boron nitride (cBN) thin films deposited by unbalanced magnetron sputtering and dc pulsed substrate biasing has been studied. Thin films were deposited at different pressures and negative bias voltages to study the effect of the energetic bombardment on the stabilization conditions of the cubic phase of BN thin films. It is shown that it is possible to clearly define a stabilization window for cBN by controlling the sputtering deposition process parameters of pressure and negative substrate bias. It is also shown that at higher deposition pressures charge exchange and momentum transfer collisions in the plasma sheath reduce the bombardment energy of the particles. These collisional processes result in the use of a higher substrate bias voltages for increasing gas pressures in order to maintain the momentum per arriving boron atom, P/a, imparted to the growing film inside the stabilization window for the cubic phase. The end result is a trend where the substrate bias voltage for the formation of cBN increases negatively as a function of pressure times sheath thickness. A series of films were also deposited on different types of substrates in order to study the effects of chemistry and epitaxy on the nucleation of cBN. It was possible to nucleate the BN cubic phase on a wide variety of substrates. Diamond coated silicon substrates were the only ones that showed a marked effect on the nucleation of the cBN, where the FWHM of the FTIR signal was reduced two-fold as compared to the FTIR signal of films deposited on silicon under similar deposition conditions. The experimental results suggest that there is a threshold energy for the bombarding ions below which it is not possible to nucleate cBN. This result, in combination with the fact that P/a controls the cBN stabilization during the nucleation stage and other reported observations pertinent to the cBN thin film formation, leads to a proposed mechanism for the nucleation and growth stages of cBN.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1998
- Bibcode:
- 1998PhDT........59O