SiClx radicals, the silicon etching by-products, are playing a major
role in silicon gate etching processes because their redeposition on the
wafer leads to the formation of a SiOClx passivation layer on the
feature sidewalls, which controls the final shape of the etching profile.
These radicals are also the precursors to the formation of a similar layer
on the reactor walls, leading to process drifts. As a result, the
understanding and modelling of these processes rely on the knowledge of
their densities in the plasma. Actinometry technique, based on optical
emission, is often used to measure relative variations of the density of the
above mentioned radicals, even if it is well known that the results obtained
with this technique might not always be reliable. To determine the validity
domain of actinometry in industrial silicon-etching high density plasmas, we
measure the RF source power and pressure dependences of the absolute
densities of SiClx (x = 0−2), SiF and SiBr radicals, deduced from UV
broad band absorption spectroscopy. These results are compared to the
evolution of the corresponding actinometry signals from these radicals. It
is shown that actinometry predicts the global trends of the species density
variations when the RF power is changed at constant pressure (that is to say
when only the electron density changes) but it completely fails if the gas
pressure, hence the electron temperature, changes.