Growth behavior of cubic boron nitride (cBN) phase in B-C-N film deposited on Si substrate with non-uniform ion flux

B-C-N film with a ∼450 nm thickness was prepared on a (100) oriented silicon wafer (4 cm × 4 cm) by unbalanced magnetron sputtering of a B ₄C target with a unipolar pulsed DC substrate bias. At a substrate bias of -250 V, a cubic boron nitride (cBN) phase appeared in the B-C-N film when the nitrogen content was over 6.7 vol% in Ar-N₂ reactive gases. For the B-C-N film deposited on unipolar pulsed DC biased Si substrate with Ar-16.7%N₂ reactive gas, the content and formation behavior of the cBN phase along with the film thickness were critically dependent on the substrate position due to the difference in ion flux. In contrast to the circular central region of a substrate 2.5 cm in diameter, where cBN was nucleated and grown on hexagonal boron nitride (hBN) in a layered manner, the cBN phase was co-grown with the hBN phase and was surrounded by hBN at the circumference region of the circle. Only hBN was observed at the outer region of the circle. The microstructure of B-C-N film in which cBN is surrounded by hBN is believed to be effective in reducing residual stress developed by the nucleation of a cBN phase.