Journal Article Spatial profiles of interelectrode electron density in direct current superposed dual-frequency capacitively coupled plasmas

Ohya, Yoshinobu  ,  Ishikawa, Kenji  ,  Komuro, Tatsuya  ,  Yamaguchi, Tsuyoshi  ,  Takeda, Keigo  ,  Kondo, Hiroki  ,  Sekine, Makoto  ,  Hori, Masaru

50 ( 15 )  , pp.155201 - 155201 , 2017-04 , IOP publishing
We present experimentally determined spatial profiles of the interelectrode electron density (n e) in dual-frequency capacitively coupled plasmas in which the negative direct current (dc) bias voltage (V dc) is superposed; in the experiment, 13 MHz (P low) was applied to the lower electrode and 60 MHz (P high) to the upper electrode. The bulk n e increased substantially with increases in the external power, P high, P low, and with increases in V dc. When P low was insufficient, the bulk n e decreased as the V dc bias increased. The bulk n e increased due to its dependence on V dc, especially for |V dc|  >  500 V. This may correspond to the sheath voltages (V s) of the lower electrode. The n e values in front of the upper electrode were coupled with the V dc: the V dc dependence first decreased and then increased. The dc currents (I dc) of the upper electrode were collected when a large P low was applied. The value of I dc at the threshold value of V dc  ≈  V s (e.g.  −500 V) increased with an increase in n e. When |V dc| exceeded the threshold, the spatial n e profile and the I dc dependence were changed relative to the electrical characteristics of the dc superposition; this led to a change in the location of the maximum n e, the width of the area of n e depletion in front of the electrodes, and a transition in the electron heating modes.

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