SCRATCH-RESISTANT TRANSPARENT BORON-NITRIDE FILMS

Transparent boron nitride (BN) coatings were deposited on glass and Si substrates in a conventional capacitively coupled RF PACVD system sta rting from diborane (diluted in helium) and nitrogen. By varying the p lasma conditions (bias voltage, ion current density), coatings were pr epared with hardness values ranging from 2 to 12 GPa (measured with a nano-indenter). Infrared absorption measurements indicated that the BN was of the hexagonal type. A combination of glancing-angle X-ray diff raction measurements and simulations shows that the coatings consist o f hexagonal-type BN crystallites with different degrees of disorder (n anocrystalline or turbostratic material). High-resolution transmission electron microscopy analysis revealed the presence of an amorphous in terface layer and on top of this interface layer a well-developed frin ge pattern characteristic for the basal planes in h-BN. Depending on t he plasma process conditions, these fringe patterns showed different d egrees of disorder as well as different orientational relationships wi th respect to the substrate surface. These observations were correlate d with the mechanical properties of the films. (C) 1998 Elsevier Scien ce S.A.