On the uniformity of electric field controlled plasma sources

Abstract

Electric fields around antenna of ICP sources consist of capacitive as well as inductive ones. By quartz probe using piezoelectric resonance, electric fields were investigated around a single turn antenna. We have observed that the capacitive electric field which is nearly perpendicular to the inductive field is dominant inside a single-turn ring. The surface charge accumulates to cancel the inductive field and, at the same time, generates two orders of magnitude larger perpendicular field. Plasma density profile of normal single one-turn antenna clearly showed that the high capacitive electric field made plasma non-uniform. Two new kinds of antenna so called parallel resonance antenna (PRA) and double stacked antenna (DoSA) were developed and studied. With PRA, inductive electric field of antenna current was controlled to obtain plasma uniformity within 300 mm by changing Cv which was connected to outer antenna piece. Various plasma density profiles could be obtained just by changing capacitance of Cv without changing external parameters such as RF power, pressures, gap distance between dielectric window and substrate. Uniformity of controlled plasma was about 3~5%, however, symmetry of density profile was not so good because of very high voltage of outer antenna of PRA. Two problems of PRA were observed. The first thing was high antenna voltage of outer antenna and this was originated form resonance effect of the outer antenna connected to a variable capacitor serially. High antenna voltage makes plasma non-uniform and process window narrow and moreover, dielectric window would be damaged by bombardment of energetic ions. The second thing is sensitivity of plasma or plasma stbility. Since resonance point of PRA is somewhat sharp, plasma characteristics would be affected by a little change of external environment as well as Cv. DoSA was developed to overcome this kind of asymmetry originated from high antenna voltage. Capacitive electric field of normal single...