On the e to H mode transition in a dual frequency (2 and 13.56 MHz) inductively coupled plasma

Abstract

The E to H transition is investigated in 2 MHz, 13.56 MHz, and dual frequency (2 MHz + 13.56 MHz) inductively coupled plasmas (ICPs). At argon gas pressures of 1 mTorr and 10 mTorr, the E to H transition power of 2 MHz ICP is the lowest and the transition power of 13.56 MHz ICP is the highest. However, at pressures of 25 mTorr and 50 mTorr, the transition power of 13.56 MHz ICP decreases and the transition power of 2 MHz ICP significantly increases. Interestingly, despite these changes, the E to H transition in the dual frequency operation occurs at the power between the 2 MHz and the 13.56 MHz transition power. The measurement shows that the plasma density in dual frequency operation is from about 1.1 to 11.7 times higher than that in single frequency operation, but this is changed with the pressure. For quantitative analysis, a global model including the capacitive coupling and the inductive coupling in the solenoidal ICP was developed and the E to H transition powers were calculated. It turns out that the results at various pressures and frequencies agree well with the experimental measurements and the relevant physical mechanism is also presented.