Plasma Effects on Electrostatic Chuck Characteristics on Capacitive RF Discharge

Abstract

Johnsen-Rahbek electrostatic chuck (ESC) is installed on the cathode side of a capacitive RF discharge, and the ESC voltage-current (V-I) characteristic is measured under various conditions. First, the reference V-I curve is obtained for a grounded aluminum (Al) wafer without discharge. The observed nonlinear characteristic is attributed to the field emission of electrons at irregular contacting surfaces. When the discharge is turned on with an electrically floating wafer, the V-I curve shifts from the reference curve toward the negative direction along the chuck voltage axis. The amount of shifted chuck voltage coincides with the self-bias DC voltage induced on the wafer. This plasma effect on the V-I characteristics can be explained well in terms of the effective chuck voltage, taking into account the self-bias. On the other hand, the replacement of the Al wafer with a silicon (Si) wafer leads to a considerable reduction in the chuck current. When a thin Al foil is inserted between the Si wafer and the aluminum nitride (AlN) spacer layer, the chuck current recovers upto the reference value, suggesting that the Johnsen-Rahbek effect is extremely sensitive to the electrical and mechanical properties of the contacting interface.