Effect of bounce resonance heating on electron energy distribution function

Abstract

The EEDF (Electron Energy Distribution Function) measurement is made in a solenoidal ICP (Inductively Coupled Plasma). A 2-turn copper coil is wound around a pyrex tube with an inner radius of 3.2 cm. The coil is powered by tens W, 10.4 MHz. It is found that with increasing rf power, the EEDF by an rf compensated Langmuir probe evolves into a Druyvesteyn-like EEDF at the low pressure of 1 mTorr in the small solenoidal ICP. The spatial profiles of the rf fields in the ICP against rf power are also measured by a B-dot probe. When the EEDF has a Maxwellain EEDF, the skin depth is comparable to the chamber radius at low rf power and the rf fields deeply penetrates into the center with a considerable amplitude. As rf power increases, the skin depth starts to be localized within the skin layer and then the EEDF transforms into a Druyvesteyn-like EEDF. The transition of EEDF implies that there is an effective electron heating in low energy range. Electron bounce resonance is introduced to explain the EEDF transition against rf power. The energy diffusion coefficients which describe the electron heating in plasma and determine the shape of the EEDF in elastic energy range are calculated with and without the electron bounce resonance. To our knowledge, This work is the first experimental evidence of the electron bounce resonance in ICP.