Ion beam deposition of cubic boron nitride

C. Ronning

II. Institute of Physics, University of Göttingen, Bunsenstr. 7-9, 37073 Göttingen, Germany

cronnin@uni-goettingen.de, Tel: ++49-551-39-7646, Fax: +++ 4493

Abstract

Cubic boron nitride (c-BN) thin films can be deposited with a variety of different methods. These films contain c-BN with an amount of up to 90 % and are usually deposited from the vapor phase by physical vapor deposition (PVD), laser ablation, rf sputtering as well as various CVD techniques under biased conditions. The microstructure of the films usually displays a three phase progression from the substrate to (i) an amorphous layer which contains a mixture of substrate, boron and nitrogen atoms, (ii) a textured hexagonal boron nitride (h‑BN) layer and (iii) a textured nanocrystalline (crystallite size: 5-50 nm) c-BN layer.

c-BN formation is only observed if the growing film is bombarded with energetic ions or neutral atoms, and it is generally accepted that the impact of energetic ions is crucial to achieve c‑BN. A threshold energy of 125 eV was found above which nucleation of c-BN occurs [1]. However, new experiments show that once nucleated the growth of c-BN can be continued even for lower ion energies below the threshold and up to energies of 5 keV. On the other hand, we expect a transition back to h-BN growth for a further increase (towards ion implantation) of the ion energy. A qualitative model [2] has been developed explaining this behavior. A short introduction and the basic ideas of this model will be given. Furthermore, the high and low energy experiments will be presented.

The second important deposition parameter is the substrate temperature; similar to the ion energy, it does influence the nucleation but not the growth of c-BN [3]. The substrate temperature as well as the ion energy is of importance for establishing the initial boundary conditions necessary for c-BN nucleation. The formation of the oriented t-BN intermediate layer provides the boundary conditions for c-BN nucleation. Therefore, c‑BN nucleation with no intermediate layer should be possible on suitable crystalline substrates having a good lattice mismatch and which do no undergo amorphization under ion irradiation. New experiments conducted using mass selected ion beam deposition (MSIBD) show the direct nucleation of c‑BN and w-BN on AlN-substrates. The surface preparation is crucial for the realization of the direct and continued growth of c-BN. This will be demonstrated and various experiments including dry etching techniques under UHV conditions will be presented.

[1] H. Hofsäss et al., Phys. Rev. B 55 (1997) 13230

[2] H. Hofsäss et al., Appl. Phys. A 66 (1998) 153

[3] H. Feldermann et al., Appl. Phys. Lett. 74 (1999) 1552

Keywords: Ion beam deposition, cubic boron nitride, growth model, etching.

Posting online: Yes.