The growth of thick cBN films employing fluorine chemistry and ECR deposition

Abstract

Energetic ion bombardment in N 2 and Ar plasmas conventionally applied to cubic boron nitride (cBN) deposition restricts the size of cBN crystallites and induces high internal stress levels, limiting the non-delaminating film thickness obtainable (to ∼100 nm). The introduction of fluorine chemistry via a complex He–Ar–N 2–BF 3–H 2 plasma produced in an electron cyclotron resonance (ECR) system overcomes such limitations and enables the preparation of thick cBN films (>1 μm) with low stress. The films were deposited using a low substrate bias (−40 V) and high substrate temperature (900 °C). Fourier-transform infrared (FTIR) spectroscopy shows that the films are composed of >80% cBN. Detailed analysis of BN film structures employing high-resolution transmission electron microscopy (HRTEM) and transmission electron energy loss spectroscopy (EELS) shows that a cBN layer with high phase purity is formed on top of an initial turbostratic BN (tBN) layer, which accounts for the small hexagonal BN (hBN) signal in FTIR spectra. The appearance of characteristic transverse optical (TO) phonon and longitudinal phonon (LO) modes of cBN in visible Raman spectra demonstrates the larger crystalline size (∼100 nm, also confirmed by HRTEM) in contrast to the films reported previously. The ion bombardment, gas composition, substrate temperature and growth time significantly affect the phase purity and crystallinity of the cBN films formed, as further elucidated in this paper.