The use of nitrogen flow as a deposition rate control in reactive sputtering

Abstract

It is well known in reactive sputtering that the deposition rate generally drops drastically at a high enough partial pressure level of the active gas to form a compound on the target surface. At the point where the deposition rate drops, there exists a simple relationship between the consumed nitrogen and the deposition rate of stoichiometric films. This abrupt decrease in deposition rate can be measured indirectly by monitoring the processing gas by mass spectroscopy (MS) and studying the discharge by optical emission spectroscopy (OES). We have shown that it is possible to select a desired deposition rate by simply choosing a correct mass flow value of the active gas (nitrogen) while maintaining correct stoichiometry of the sputtered film. This can be achieved by presetting the mass flow of the nitrogen. Thereafter, the rf power is increased to the transition level, where the surface of the target changes from compound to elemental. The combination of mass flow control and diagnostic tools (MS) and (OES) enables precise control of the process.