Abstract:
Reactive sputtering is a technique to deposit compound thin films such as
oxide, nitride, etc. It is well known that in reactive sputtering there are two operation
modes: metal mode and compound mode. The transition between the two modes is
generally avalanche-like and non-linear to reactive gas flow rate, and further shows
hysteresis versus re'active gas flow rate. The nonlinear transition and hysteresis
reduce cotrollability and reproducibility of the reactive sputtering process when I is
operated in the near transition region. Therefore, it is thought to be crucial to reveal
mechanisms involved in mode transition and hysteresis in order to improve stability
and reproducibility of reactive sputtering.
In this thesis, the formation process of oxide films is investigated and discussed
to reveal mechanisms of mode transition and hysteresis. Most importantly, effects of
pumping speed and sputtering current on mode transition and hysteresis have been
discussed. The simulation reveals that the origin of the hysteresis behavior is the
difference of gettering capacity between metal mode and compound mode.
Throughout the discussion, it is emphasized that reactive gas gettering plays an
important role in the total mass balance changes in the reactive sputtering process.
On the basis of the discussion of the reactive sputtering process, a model
simulating mode transition and hysteresis is presented. The model is based on the
physical mechanism involved in target and wall behaviors. The important feature of
the model is that hysteresis can be obtained as a result of the calculating of the timedependent
target condition changes. Hysteresis curves are obtained as a consequence
of time-dependent calculations as a function of reactive gas mass flow rate. It is
further shown by the simulation that the width of hysteresis strongly depends on
pumping speed and sputtering current. These results satisfY the experimental results.
