Power accuracy and source-pull effect for a high-power RF generator

RF high-power generators are extensively used for plasma etching technologies. In order to achieve high quality for the Silicon wafer process, power accuracy and stability become critical requirements for RF generators. Since a plasma chamber is regarded as a nonlinear active load, load-pull effect has been investigated thoroughly in recent years. However, power measurement is not just related to load situations. Source mismatch also plays an important role for power stability and accuracy. In this paper, power accuracy for a high-power RF generators is investigated through theoretical estimation and direct experiments. For low-reflection loads, the source-mismatch effect is dominant in power measurement error when a calibrated V-I probe is used for reflection and power measurement. In order to investigate this effect, a series of load-pull experiments have been made on a commercial RF generator with power feedback. It is shown that a given source mismatch can be greatly reduced through power feedback [14][15]. The remaining source mismatch effect becomes a comprehensive result related to three factors: the dynamics of nonlinear capacitance of the power transistors, static mismatch from the output filters and the load situation. Between the source mismatch and load reflection, there are some interesting relationships that can be used to correct the power error and thus improve system performance for the generator.