Hardness measurements at shallow depths on ultra-thin amorphous carbon films deposited onto silicon and Al2O3-TiC substrates

We carried out shallow depth indentations on ultra-thin hydrogenated amorph ous carbon (a-C:H) films deposited by plasma enhanced chemical vapour depos ition onto silicon and Al2O3-TiC ceramic substrates. These measurements are relevant to data storage and microelectronic applications, which require s ub-50-nm, wear protective overcoats. We used the continuous stiffness measu rement technique to monitor the Young Modulus (E) and the hardness (H) as a function of depth for films with thickness varying from 10 to 50 nm. Raman spectroscopy and atomic force spectroscopy show that the films have simila r roughness and microstructural bonding environment. For all films, the sub -30-nm region shows a continuous increase of E and H with depth, with no di scernible tip calibration artifact. Above 30 nm depth, the effect of the fi lm is predominant, essentially hardening noticeably the silicon and softeni ng slightly the ceramic substrate, with E and H values typical of a-C:H mat erials. Above 50 nm, the E and H curves are dominated by the properties of the substrates. Initial nano-scratch experiments indicate that the films ha ve better wear resistance than the Al2O3-TiC substrate. Therefore, the hard ness and wear of the samples show no correlation at these shallow depths. ( C) 2000 Elsevier Science B.V. All rights reserved.