Characterization of an oxygen plasma by using a Langmuir probe in an inductively coupled plasma

Oxygen plasmas were investigated by using a Langmuir probe for an inductively coupled plasma with various rf powers, 100 similar to 400 W, and operating pressures; 0.1 similar to 100 mTorr. The probe current ratio ct of the positive and negative currents (I-+(*)[I-e(*) + I--(*)]) increased with the generation of negative ions and had its maximum value in the;pressure region of 40 similar to 70 mTorr. Also, the operating pressure to achieve the maximum ct shifted from the low-pressure region to the high-pressure region with increasing input power because enhanced ion loss through positive-negative ion recombination.