Effect of charge-up of surfaces of sintered Y2O3 and yttrium oxyfluoride on their erosion rates due to ion bombardment

The erosion rate of sintered Y2O3 and yttrium oxyfluoride (Y-O-F) due to Ar ion bombardment was investigated for use in the plasma process chamber. The Ar ion bombardment was performed by irradiations of Ar plasma and Ar ion beam. In addition, charge-up behavior of these ceramics was investigated by two methods. One was the measurement of the surface voltage during the plasma irradiation (the so-called self-bias voltage), and the other was the measurement of the surface voltage generated due to the accumulation of static electricity in the clean room air. It was found that the negative self-bias voltage of the Y2O3 surface was smaller than that of Y-O-F. It was also found that Y2O3 was easily positively charged by the accumulation of the static electricity compared to Y-O-F, which was consistent with the observed relationship of the self-bias voltages between Y2O3 and Y-O-F. For the evaluation of the erosion rate due to Ar ion bombardment, it was found that the material and setting of masks to make the erosion step for evaluating the rate greatly affected the results. When electrically conductive masks with electrically connecting to a substrate were used, the erosion rate of Y-O-F was smaller than that of Y2O3. The results suggested that the intrinsic ion-bombardment-induced erosion rate of Y-O-F was smaller than that of Y2O3, because the ion bombardment energy was expected to be almost the same due to the existence of the conductive masks. On the other hand, when insulating masks were used, the rates of Y2O3 and Y-O-F were almost the same level. Considering the aforementioned charge-up behavior, the results suggested that a relatively larger positive charge-up of the Y2O3 surface during the ion bombardment decelerated injecting ions, resulting in the decrease in ion bombardment energy and, thus, the erosion rate.