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 accep ted to explain the synthesis of c-BN (cubic boron nitride) films depos ited under ion bombardment. In the present work, an original method ha s been used to correlate the phase evolution and the in-depth distribu tion of stress within the him. This method was based on the complement ary use of reactive ion etching, quantitative FTIR and substrate curva ture measurements. In addition, the structural organization of these f ilms was also studied by in situ Reflection Electron Energy Loss Spect roscopy (REELS) analyses and REELS depth-profile. The results showed a layered structure exhibiting a pure c-BN volume lying between an uppe r zone of 3-4 sp(2) bonded monolayers and an h-BN basal layer. The pur ity of the c-BN volume was confirmed by HRTEM analyses revealing also nanocrystallized grains with (111) planes parallel to the growth direc tion, indicating a [110] texture perpendicular to the substrate. The s tress distribution within the film emphasized a high, nearly homogeneo us stress in the major part of the c-BN volume. In the sp(2) basal lay er, 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 cont ribution to the study of the mechanism of the stress-induced nucleatio n of c-BN films deposited under ionic irradiation, and tends to valid this mechanism proposed by McKenzie. (C) 1998 Elsevier Science S.A.