Remote Plasma Processing of Sapphire Substrates for Deposition of TiN and TiO₂

The paper uses remote plasma assisted deposition, oxidation and nitridation processes for depositing thin films of metallic TiN on crystalline sapphire (0001) substrates. These films on sapphire substrates are being studied as window materials for high power radio frequency (RF) power tubes. A sequence of four process steps has been performed in a reactor chamber that isolates the deposition and surface-processing chamber from the plasma generation region. The chamber is part of an ultra-high-vacuum (UHV) compatible multi-chamber cluster in which the sequence of four process steps can be interrupted after each step, and surface chemistry changes can be identified by in-line Auger electron spectroscopy (AES). The four process steps, performed after an ex-situ chemical clean and blow-dry in nitrogen gas, are (i) a remote plasma-assisted oxidation (RPAO) in which surface contaminants including adventitious carbon are removed; (ii) a remote plasma-assisted nitridation (RPAN) process which forms a superficial layer of generic AlON used to increase surface adhesion of the TiN films; (iii) a remote plasma-enhanced chemical-vapor deposition (RPECVD) process for deposition of 2 to 5 nm thick TiN films, and finally (iv) a second RPAN step that increases the ratio of Ti–N bonding in the TiN films with respect to adventitious O-atom incorporation from the Ti precursor, Ti tetra-butoxide.