Study of reactive sputtering phenomena for producing oxide thin films

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.