Si3N4 thin films were prepared by RF magnetron sputtering using N2 or Ar as the sputtering gas. The films were amorphous, with the deposition rate for Ar-sputtered films increasing with RF power and Ar pressure. Sandwich samples having both Al and Au electrodes were prepared. Capacitancevoltage measurements indicated that the contacts for Nj-sputtcred samples were ohmic, while Ar-sputtered samples with Al electrodes exhibited depletion regions. Values of the relative permittivity of 6.3 (AI electrodes) and 6.8 (Au electrodes) were determined from geometric capacitance variations in Ny-sputrered films. Current density-voltage characteristics normally showed ohmic and space charge limited conductivity with trap levels distributed exponentially within the insulator band gap, but exceptionally in N2-sputtered films with Au electrodes electroforming behaviour was observed, with Poole-Frenkel conductivity in the preformed region. Hopping was dominant at low temperatures. AC conductivity was higher for Ar-sputtering, and with Au electrodes. These effects were related to the possible structure of the films, and the diffusion of Au. AC conductivity increased with increasing frequency and temperature, appearing to be via a free band process at high temperatures and hopping at low temperatures. Plausible values of the density of localised states were deri ved using Elliott's model, but this could not be considered uni versally applicable. Loss tangent was also frequency and temperature dependent in Ny-sputtered films, showing a minimum value which shifted towards higher frequencies with increasing temperature. In Ar-sputtered samples minima were not observed in the frequency range covered. The model of Goswami and Goswami appears consistent with these results, particularly in the former case. Variations in the loss tangent values with the sputtering gas and electrode species were consistent with the observed conducti vity variations. Optical properties were also investigated. In Ar-sputtered films, the optical band-gap appeared narrower and the optical absorption higher than for Ny-sputtered films, and a direct transition was also identified. Values of the electrical properties determined for such sputtered films are comparable to those prepared using more sophisticated methods, particularly in the case of Nj-sputtered films. Sputtering may therefore prove useful in semiconductor processing, where a relatively inexpensive method of deposition is required.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:311646 |
| Date | January 2000 |
| Creators | Awan, Shamshad Akhtar |
| Publisher | Keele University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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