Effective Closed-Loop Control for Reactive Sputtering Using Two Reactive Gases

Reactive sputtering is becoming a more widely accepted practice for the deposition of many useful compound thin films. The use of closed-loop control for the deposition of such films is also increasing in popularity. The closed-loop process for forming binary compounds, typically oxides or nitrides, is conveniently accomplished using one of several feedback mechanisms coupled to a high-speed reactive gas control valve. Optical emission, target voltage and mass spectroscopy have all been successfully used to provide feedback for such processes when using a single reactive gas. The presence of two reactive gases in a reactive sputtering process adds significant complexity and presents the issue of competing reactions. Since both reactive gases can affect the state of the target surface and the plasma conditions, both also affect common feedback control signals such as the cathode voltage and optical emission. Modeling has shown that the way to control a two-gas reactive sputtering process is to produce individual control signals for each gas. In this study, partial pressure signals for each reactive gas were used to control the deposition of SiOxNy and TiOxNy compounds. The results of this study are presented here and shown to support the modeled behavior. The two-gas, closed-loop approach is then demonstrated to provide a stable, high rate solution for the deposition of these highly complex thin film materials.