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.