Microstructure and stress investigations of cubic boron nitride thin films

The hypothesis of a stress-induced phase transformation from a basal h-BN (hexagonal boron nitride) layer is one of the most currently accepted to explain the synthesis of c-BN (cubic boron nitride) films deposited under ion bombardment. In the present work, an original method has been used to correlate the phase evolution and the in-depth distribution of stress within the him. This method was based on the complementary use of reactive ion etching, quantitative FTIR and substrate curvature measurements. In addition, the structural organization of these films was also studied by in situ Reflection Electron Energy Loss Spectroscopy (REELS) analyses and REELS depth-profile. The results showed a layered structure exhibiting a pure c-BN volume lying between an upper zone of 3-4 sp(2) bonded monolayers and an h-BN basal layer. The purity of the c-BN volume was confirmed by HRTEM analyses revealing also nanocrystallized grains with (111) planes parallel to the growth direction, indicating a [110] texture perpendicular to the substrate. The stress distribution within the film emphasized a high, nearly homogeneous stress in the major part of the c-BN volume. In the sp(2) basal layer, a sharp peak of very high compressive stress is located. while an interfacial zone corresponding to the transition from h-BN to c-BN is found to retain a very low stress value. This paper reports a new contribution to the study of the mechanism of the stress-induced nucleation of c-BN films deposited under ionic irradiation, and tends to valid this mechanism proposed by McKenzie. (C) 1998 Elsevier Science S.A.