Nanoscratch characterization of dual-ion-beam deposited C-doped boron nitride films

Boron nitride (BN) films with carbon (C) contents varying from 3-11.8 at. % were fabricated using dual-ion-beam deposition. Films with low C contents (less than or equal to 6.2 at. %) consist mainly of the c-BN structure. The hardness of these films is as high as 43 GPa, and the coefficient of frict ion mu is described by the formula mu = 0.14 W-0.25, where W is the normal load in millinewtons. The critical load of damage is above 50 mN. Because o f the existence of high internal stresses, the films peel off readily from the substrates, and delamination occurs immediately once a scratch track is produced. When more C is added, the formation of the c-BN structure is sup pressed, while a graphite-like structure becomes dominant. The hardness and critical load drop to 8.6 GPa and 6.8 mN, respectively, when the C content is 11.8 at.%. The values of mu remain unchanged. The internal stresses are partially released, thereby leading to improved film adhesion. We have fou nd an optimum C content of 7.2 at.%, at which both the mechanical and adhes ion properties are satisfactory. (C) 1999 American Vacuum Society. [S0734-2 101(99)02806-7].