Abstract
High target utilisation sputtering (HiTUS) is a patented remote plasma sputtering technique for the deposition of thin films. A prototype in-line sputter deposition facility, based on the existing standard HiTUS technology, has been developed. Materials deposited by both the standard HiTUS and the prototype in-line system where characterised. This was important in examining the key deliverable of the new system which is uniform deposition of high quality coatings on large (20 cm by 30 cm) substrates. Initially characterisation of the in-line system showed that fully reacted transparent alumina coatings using reactive sputtering could be deposited. The process was found to be reproducible, with a run-to-run variation in peak positions for UV-Vis-IR transmission spectra of less than ±1%. The process conditions and system were investigated to optimise the system performance. Theoretical and experimental investigations showed that the RF plasma and magnetic field shape both affected the uniformity of coating thickness and optical transmission for reactive sputtering processes. Changes to the system configuration to improve the magnetic field shape based on these findings have increased the usable substrate width from 10 cm to approximately 20 cm. Investigating the heating effect of the plasma showed that doubling the RF plasma power (at constant target power) can increase the heat flux to the substrate by a factor of two. For the deposition of tin doped indium oxide (ITO) and aluminium' doped zinc oxide (AZO) increasing the RF plasma power was shown to (i) change the material from amorphous to nanocrystalline, (ii) increase the visible transmission of coatings and (iii) increase the conductivity of the material. These effects are attributed to the increased energy of the plasma species promoting both higher surface mobility and reactivity of adsorbed species. The ITO coatings deposited by the in-line system were similar to those deposited by the standard system with a specific resistivity of less than 4 x 10-4 Ω cm and average visible light transmission of 92%. The in-line HiTUS system was able to deposit ITO material with less than ±10% variation in specific resistivity over 20 cm substrate widths. The investigation has shown that the in-line HiTUS can be used to produce high quality material and that the independent control of RF plasma power and target bias can be used to modify the structure and morphology of deposited thin films. However, the apparent variation in plasma density as a function of distance suggests that the current in-line HiTUS configuration will struggle to match the large area capabilities of magnetron sputtering. The extended plasma source presents a promising future for large area HiTUS systems.