Pressure change after arc ignition in a vacuum arc apparatus for TiN film deposition is measured for various pairs of N2 flow rate (1-50ml/min) and initial pressure (0.01-10Pa). It is found that, after the arc ignition, in some cases the pressure converges to a certain value (operating pressure) and the arc steadily lasts, and in other cases the pressure continues decreasing until the arc self-extinguishes. For instance, at an initial pressure of 10Pa and an arc current of 50A, the arc lasts when the flow rate is more than 8ml/min, but the arc self-extinguishes when the flow rate is less than 8ml/min.
The pressure change is measured while the arc is ignited, sustained for 5min and extinguished. The result is interpreted with a model expressed by N2 flow rate, evacuation rate, Ti evaporation rate, Ti deposition rate and N2 fixation rate (rate of N2 fixing to anode surface). From the relation among evacuation characteristics of the vacuum system, the initial pressure and the operating pressure, N2 fixation rate is obtained as a function of the arc operating pressure. It is found that the N2 fixation rate of 50 A is constantly about 8ml/min for the pressure range from 0.1 to 10Pa.
It is cleared from above two experiments that the arc is able to be sustained only when the N2 flow rate is higher than the N2 fixation rate.