Investigation of the plasma uniformity in an internal linear antenna-type inductively coupled plasma source by applying dual frequency

A large area inductively coupled plasma source with an internal linear-type antenna was operated in dual frequency mode (2 MHz/13.56 MHz), and the electrical/plasma characteristics of the ICP source were examined as a function of the relative rf power ratio. When the source was operated in single frequency mode (13.56 MHz only), approximately 8.5% plasma uniformity was observed at 5 kW of 13.56 MHz rf power for the substrate size of 880 mm × 660 mm. The plasma uniformity improved with increasing rf power. However, a further improvement in plasma uniformity to approximately 6.3% could be obtained using the dual frequency mode by applying 0.9 kW of 2 MHz rf power in addition to 5 kW of 13.56 MHz. For 15 mTorr Ar, the plasma density at a dual frequency rf power of 0.9 kW 2 MHz/5 kW 13.56 MHz was 1.6 × 10¹¹/cm³ and the electron temperature was approximately 3 eV. The addition and increase in 2 MHz rf power to the 13.56 MHz power increased the plasma density without increasing the electron temperature.