Abstract
We have tracked down one of the major causes for nonuniformities in film
thickness in large-area deposition of hydrogenated amorphous silicon,
a-Si:H. To simulate improper substrate-to-electrode attachment we
deliberately introduced a gap behind the substrate. The
rf-excitation-frequency dependence of the influence of this gap on the
deposition rate is presented. We show that a local small gap behind the
glass has a detrimental effect on the local deposition rate, and
therefore on the uniformity of the films. For example, at a frequency of
60 MHz typically the reduction of the deposition rate amounts to 25%
when a gap of 1 mm is present. To explain the observed effects the
plasma-sheath dynamics are considered. The relations between the dc
self-bias voltage, the amplitude of the applied rf voltage, and the
deposition rate are determined experimentally. A theoretical model that
explains the reduction of the deposition rate is presented. We conclude
from the model that the ion density in the sheath is independent of the
excitation frequency.
Original language | English |
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Pages (from-to) | 3546-3551 |
Journal | Journal of Applied Physics |
Volume | 80 |
Issue number | 6 |
DOIs | |
Publication status | Published - 1 Sept 1996 |