Control of the Reactive Sputtering Process Using Two Reactive Gases

Reactive sputtering when two reactive gases are used presents special problems. Both reactive gases affect the plasma conditions, which means that both affect common feedback control signals such as the cathode voltage and optical emission signals. Two reactive gases require that unique signals for each reactive gas be acquired and that control of each of the reactive gases is done separately. Modeling has confirmed that the way to control the process when two reactive gases are present is to produce two individual single-valued parameters. For this process, the single-valued parameters for the partial pressures of the reactive gases can be supplied from a mass spectrometer or from an optical emission spectrometer (looking at individual gas lines). The reactive sputtering of titanium in a combined oxygen/nitrogen atmosphere using partial pressure control of each reactive gas is shown. A combination where one of the gases is controlled in partial pressure mode and the other in a flow mode can lead to unstable operating conditions. To gain stability of the process when two reactive gases are used requires that the partial pressure of each gas be controlled individually.