The effects of capacitor termination at an internal ICP antenna on the power coupling, plasma parameters and impurity incorporation

During the ICP (inductively coupled plasma) process, a very high self-bias voltage is induced along the coil, which can cause sputtering of dielectric materials covering the coil. This problem can be solved by installing a capacitor between the coil end and ground. The effect of the capacitance termination was investigated by measuring the voltages at both of coil ends, plasma parameters and the impurity contents on the Si substrate after Ar plasma treatment at different ICP powers. The voltages at the coil ends decreased by half and the induced self-bias voltage approached zero under resonance conditions. The capacitance was approximately 200 pF, with both coil inlet and outlet voltages the same. In the range of this critical capacitance of 200 pF, the harmonics between coil and plasma decreased and the plasma density increased to 120–250% by controlling pressure and power compared to that with the grounded coil end. When the pressure was 1 and 5 mTorr, the plasma density doubly increased. Impurity concentrations were also suppressed drastically by the capacitance termination.