Comparision of transient plasma parameters in multi-source pulsed RF CCP configurations

摘要

Summary form only given. Low pressure plasmas driven by RF power sources driven in the MHz range of frequencies where applied power is pulsed on the millisecond time scale can provide very unique conditions for materials processing not easily achievable with comparable power densities using continuous wavelength power application. The electrical transients generated by these rapid pulses present unique challenges for efficient power delivery and control; these challenges are compounded further in systems with multiple power sources, particularly in operating conditions were either the pulse cycles are not synchronized or only a subset of the operating generators are pulsed. The transient response of these pulsed plasmas, specifically the differences between “traditional” pulsed systems where no power is applied for a given timeframe versus conditions where a subset of RF power delivery is continuously delivered throughout the pulse cycle is of particular interest to plasma equipment manufacturers.Transients in pulses have been analyzed for three different cases: 1.) traditional single source pulsing, 2.) two power single source pulsing, and 3.) multiple source drive with single source pulsing. Pulse locked nanosecond scale CCD imaging, OES, Langmuir probe and time resolved voltage/current/phase measurements have been used to measure fundamental plasma parameters and compare these three operating conditions. Sheath thickness and electron density are obtained directly from diagnostics and compared to predicted value obtained from an empirical model that estimates these conditions using in-line RF metrology. Two power level pulsing conditions are used to refine the model for a wide range of pulse conditions and correlation to imaging and probe measurements. This model is then used to compare plasma conditions during offcycle times where electrical impedance measurement is not possible.