This type 2 project is an in-depth research study focussing on the in-situ control of plasma assisted deposition of cubic boron nitride film with the final goal to understand and model the chemistry and physical mechanism of their generation.
Great progress has been achieved compared to the state of the art of c-BN deposition at the beginning of the project. An extensive data collection reduced the uncertainties concerning c-BN deposition existing so far. Due to the knowledge of the required deposition parameters, the ICP deposition method could be adapted successfully to c-BN deposition.
A model was developed which showed selective sputtering of h-BN to be the dominating mechanism for c-BN deposition. This model is in good quantitative agreement with ion assisted CVD as well PVD experiments and shows both to rely on the same parameter ranges. C-BN nucleation was investigated experimentally revealing also in this point the same principle mechanisms in CVD and PVD. With PVD, lattice matching between the nucleation layer and the c-BN on top of it was found which is expected to strongly influence the nucleation step. Further experimental work showed hydrogen to be detrimental for c-BN growth which can explain some slight differences between CVD and PVD deposition. Furthermore, the effect of stoichiometry was investigated which led to the discovery of a preferential nitrogen sputtering mechanism.
The comparison of two boron precursor showed that the contamination level is highly reduced by the use of B2H6. Films containing a fraction of c-BN were also prepared by ECR-microwave method for high ion density and ion energy in agreement with the proposed model. In addition this method is very promising in terms of up-scaling as homogeneous deposits can be obtained for substrates larger than 50 mm in diameter.
Due to adhesion failure, c-BN films are not suited for industrial applications so far. Concerning this, the situation is comparable to the knowledge about the basic deposition process at the beginning of this project: isolated studies exist but a general concept and systematic investigations are missing so far. First approaches, which include a simple model of stress build-up were undertaken to solve this problem. However, a large quality of experimental as well as theoretical work is necessary to get more insight into this complex phenomenon. It is expected that the quality of c-BN films strongly benefits from a more detailed understanding of the deposition process.
By comparison of quality and chemical nature of cubic BN films generated by different plasma deposition techniques (radio-frequency, micro-wave, remote plasma and hot filament technique) the partners will collect data which allow clear judgement on which technique is the most promising one in terms of desired quality and costs effectiveness, and the most suitable one for up-scaling to large area films, and high deposition rates processes.
By development and deployment of in-situ and non intrusive diagnostics (ellipsometry, emission and mass-spectroscopy, electrical and thermal conductivity probes) both the film growth and the plasma gas phase will be analyzed.
On a quantitative basis, the target is to obtain deposition rates of the order of micrometres per hour on substrates areas up to 1 dm2.
The project is divided into two parts :
Part 1 (24 months) : set-up of PACVD chambers, plasma diagnostics techniques and in-situ measurements.
Part 2 (24 months) : investigation of the influence of hardware and process parameters settlings on plasma composition and cubic BN properties on Si and steel substrates.