Relationship between sputter cleaning parameters and surface contaminants

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Abstract
In an abnormal dc glow discharge sputtering system the current at a constant voltage and pressure is often found to decrease from an initially high value to a steady-state level as the cathode surface is sputtered. We have investigated the relationship between this decrease in current and the level of cathode surface contamination by periodically analyzing the surface during sputter cleaning using the soft x-ray appearance potential technique. We find that the excess initial current results from contaminating gas liberated from the chamber wall and cathode surface by the action of the discharge. The rate at which cathode surface contaminants are removed and the residual level that is indicated by the steady-state discharge current are both strongly dependent on the over-all cleanliness of the discharge system. With proper attention to cleanliness, however, it is found that the steady-state discharge current can be used as a process control variable, indicating the attainment of a relatively clean cathode surface.