Development of vacuum technologies for the preparation of high-purity thin films in simple systems
It has been demonstrated that reactive magnetron sputtering can be controlled in low pumping speed vacuum system through observation of the spectral line emission by the plasma emission monitor (PEM). Confining the deposition process in an enclosed volume has provided the gettering-pumping action needed to deposit films with good quality reducing the active contamination that low pumping vacuum system suffers. TiN films of specular quality has been optimised by observing the emission line of the sputtered titanium. It was shown that optimum TiN film is formed when the consumption of nitrogen flow at the metal line set point is a maximum. This optimisation is characterised by a clear minima of ultimate resistivity and better selective optical properties. Films of TiN deposited using the balanced magnetron source had higher resistivity than the metal titanium in contrast to its bulk properties. That was explained by their lower densities. The lack of activation energy of the growing film during deposition resulted in a columnar structure separated by voids which is a normal microstructure of low film density. By adding activation energy, from an unbalanced magnetron source, a plasma beam was leaked to the substrate subjecting the growing film to energetic ions of sufficient energy to modify the structure of the film. Films were shown to have resistivities lower than the metal titanium. This characterisation was verified by examining their structure by SEM which showed dense films. The reactive gas consumption gave also a good indication of the process control and the optimisation of dielectric films of Ti02 and Zr02. Optimum films characterised by lowest absorption and high refractive index were shown to form when the consumption of oxygen is low at the lowest metalline set point within the limit of the plasma emission monitor. This shift occurred because the much tighter control of reactive gas pressure which is consequently higher for oxides than for nitrides. Films of TiN were also deposited at a low magnetTon potential. Increasing electron injection reduced the operating potential of the sputtered titanium resulting eventually in a reduction of sputtering rate and consequently a reduction in nitrogen consumption. Films made at lower target potentials had lower resistivities due to the enhanced reactivity and increasing ion current density bombarding the film.