The electrical properties of thin hydrogenated amorphous carbon (a-C:H) insulating films on semiconductor and metal substrates

This thesis examines the electronic and structural properties of hydrogenated amorphous carbon (a-C:H) grown by plasma enhanced chemical vapour deposition (PECVD). The work covers both applied and fundamental aspects of the deposition process. Amorphous carbon has many important applications, in electronic terms its use as a dielectric is receiving greater attention. This is particularly important for application in magnetic head devices as a reader gap insulation layer, where breakdown strengths greater than 5MV/cm are required for 20-50nm films. An extensive study was undertaken to optimise the a-C:H films with respect to their electrical properties. Results presented for dielectric breakdown strength have shown that the required specification can be achieved, with maximum values of 11.5MV/cm. The resistivity varied between 10"1"1-10"1"4 #OMEGA#.cm. Electrical measurements as a function of film thickness suggest improvements as the thickness decreases. Nitrogen doping, using a novel atomic flux source, has been shown to be successful in initially improving electrical resistivity, and shifting the fermi-level away from the valence band towards the mid-gap position. Up to 29 at.% nitrogen was incorporated with minimal structural modifications, as determined by Raman. On substrates other than silicon, namely: aluminium, chromium, nickel, AlTiC and SnO_2:F, films were observed to have increased roughness, poorer adhesion and a more polymer-like quality. These changes were reflected in a reduction in the observed breakdown field to approximately 0.5MV/cm. Films optical and electrical properties were examined using ellipsometry, Kelvin probe and Impedance spectroscopy, while material properties were examined using Raman analysis, elastic recoil detection analysis and atomic force microscopy. A 1D numerical model was developed to estimate the effect of trap densities on the current-voltage characteristics and density values in the range Of 10"1"8cm"-"3 eV"-"1 were evaluated. (author)Available from British Library Document Supply Centre-DSC:DXN042590 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo