Plasma Characteristics of Inductively Coupled Plasma Using Dual-Frequency Antennas

The plasma characteristics of inductively coupled plasma (ICP) sources operated with dual-frequency antennas with frequencies of 2 and 13.56 MHz were investigated and compared with a source operated with a single-frequency antenna at 13.56 MHz. Improved plasma characteristics such as higher plasma density, lower plasma potential, and lower electron temperature were observed with the dual-frequency ICP source owing to the high absorbed power through the lower driving of the frequency antenna. Also, the variation of the dual-frequency power ratios changed the electron energy distribution. Therefore, when silicon was etched using the dual-frequency ICP with CF 4 /Ar, the maximum etching selectivity of silicon over the photoresist could be observed at a 2 MHz rf power ratio of approximately 70% possibly due to the different gas dissociation characteristics for different dual-frequency power ratios, even though the etching rate of silicon increased with the 2 MHz power ratio owing to the increased plasma density. In addition, by using the dual-frequency ICP antennas instead of the single-frequency antenna, the plasma uniformity was also improved.