Hardness and stiffness of amorphous SiCxNy chemical vapor deposited coatings

Thick amorphous SiCxNy coatings have been deposited by chemical vapor deposition at 1000-1200 degrees C from the TMS-NH3-H-2 system. Hardness (H) and stiffness (E) were measured by nanoindentation with a Berkovich indenter. The relative influence on H and E have been investigated using an experimental design by varying: deposition temperature; pressure; and ammonia flow rate. The deposits exhibit a high chemical complexity in a large domain of composition (0.04 less than or equal to x/x + y)less than or equal to 0.67) with Si(C4-nNn) units connected by sp(3)-sp(2) carbon configurations. Correlations between the mechanical features and the chemical bonding and local order around the different atoms have been established. Two groups of samples have been distinguished depending on the x/(x+y) ratio. Below x/(x+y)=0.1, the N-rich coatings were obtained in which the main bond was Si-N and H and E tended to decrease from 27 to 31 GPa and 224 to 289 GPa, respectively, with increasing numbers of Si-C, C-N and C-C bonds. For 0.38 less than or equal to x/(x+y)less than or equal to 0.67, the C-rich coatings were obtained for which the increases of H and E from 29 to 38 GPa and 240 to 360 GPa, respectively, have been correlated to the increasing proportion of SiC4 units. (C) 1999 Elsevier Science S.A. All rights reserved.