In low gas pressure radio frequency (RF) capacitive discharges, high energy electrons, which are responsible for the ionization process, are generated near the RF sheath where the electric field oscillates. The energetic electrons heated from the sheath cannot reach the plasma bulk at high gas pressures or in molecular gases because of their short electron energy relaxation length. In this letter, however, it is shown that from the probe measurements of the electron energy distribution function (EEDF), the high energy electrons at the plasma bulk are observed in the local kinetics regime as the RF bias power increases in an inductively coupled plasma of high mixing ratio of SF6/(Ar + SF6). The generation of the high energy electrons and the EEDF modification could be understood by the enhanced bulk electric field in negative ion rich plasmas, and the EEDF modification presents a direct experimental evidence of the drift-ambipolar electron heating at the plasma bulk.

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