Electrode metallization for high permittivity oxide RF thin film capacitors

High permittivity oxide thin film capacitors for RF components should be integrated on the chip to form a complete miniaturized module, with other semiconductor or thin film components such as inductors, isolation capacitors, and bias resistors. The quality factor (Q) values of the RF capacitors are strongly dependent on electrode conductivity. Alas the best conducting metals (e.g. Ag, Cu, Al) are not thermodynamically stable during deposition of high permittivity oxide films with high temperature and oxygen atmosphere. On the other hand, refractory metals (e.g. Mo, W) endure high temperatures, but are prone to oxidation. Therefore, a diffusion barrier is a prerequisite for integrating refractory metals to achieve a stable electrode structure.

In this study both non-reactive and sacrificial diffusion barriers with Mo metallization were investigated on Si/SiO2 substrates. Also, noble metals (Au and Pt) as oxidation resistant materials were examined. Annealing at 650 °C was performed to the electrode stacks in an open-end air furnace and in vacuum with protective gas.

The chemically inert materials Au and Pt failed to endure the high annealing temperature. Au became extremely rough and cracks appeared. Massive grain growth and adhesion loss occurred with Pt film. Mo electrode withstood the oxidizing ambient conditions with a sacrificial Si or Al–Ti diffusion barrier. Moderate increase in surface roughness was observed after the annealing due to oxidation. Also, thermally stable AlN, Si3N4, and SiO2 diffusion barriers were able to block oxygen from the Mo electrode.