Pulsed DC reactive magnetron sputtering of dielectrics.

摘要

In a single magnetron reactive sputtering system, the deposition of dielectrics on a substrate is accompanied by their deposition on all surfaces inside the vacuum chamber. Coating of the target and the anode produces, in the extreme, arcing. To eliminate arcing, pulsed plasmas are used for reactive sputtering of dielectrics. The time behavior of the current and voltage characteristics, the effect of pulse timing, and the frequency of arcing under various conditions of pressure, plasma current, and target conditions were studied. It was found that arcing was continuous after the frequency decreased to a critical frequency or lower. The critical frequency depended on the reverse time, the current and the pressure. The condition for arc-free operation was established: the amount of charge deposited on the dielectric surface during the on-time must be fully discharged during the off-time. Therefore, to keep the arc-free discharge running, increasing the on-time requires a corresponding increase in the off time.; Biasing was proven to be the method of preference to control the ion bombardment and the energy flux to the growing film. The substrate biasing in the pulsed DC sputtering improves substantially the quality of thin films. Two important results, regarding applications of pulsed DC biasing in plasma processing, were arrived at.; Langmuir probe studies of pulsed plasmas properties were done. Spatial distribution of time-averaged plasma parameters in the magnetron, their dependence on the frequency, gas mixtures and pressure, were investigated. The data show that the plasma properties are non-uniformly distributed under the magnetron. The time-resolved data show that during the off time the plasma density decays initially rapidly and later more slowly, but it is not extinguished during the off time. Although the plasma density increases initially rapidly at the beginning of the on-time, it takes time for it to reach a plateau; this time is necessary for sheath reestablishment. At the beginning of the on-time, there is a spike in the electron temperature. Possible explanation of it is presented.