Capacitively coupled wafer-bearing cathodes are widely used in etching and deposition processes. Uniform electric field and plasma density across the wafer surface are necessary for process control all the way to the edge of the wafer. Terminating structures at the wafer edge such as focus rings are used to improve uniformity and minimize costly edge exclusion. The focus ring can be viewed as an arbitrary impedance element at the wafer edge that balances the sheath voltage above it and the region above the wafer, minimizing field variation at the wafer edge. To validate this assumption, a one-dimension circuit model with focus rings was developed. The simulations were compared to experimental results measured using hairpin probe, VI probe, and a retarding field energy analyzer (Impedans RFEA). It was found that the focus ring coupling acts as a voltage divider only in high voltage cases, and the sheath voltage drop over the focus ring will increase in low voltage cases and does not rigorously follow the voltage divider model typically used.
Inductively coupled plasmas driven by pulsed RF power have been used by the semiconductor industry for decades as they offer numerous advantages compared to continuous mode discharges. Current state-of-the-art global models characterize the plasma under conditions where power delivery is user defined and typically constant. This work details the development of an integrated global plasma-circuit model, which couples a transient plasma model with a broader circuit model that captures the behavior of the power delivery system. The transient response of electron density ne and the magnitude of the delivered and reflected power is captured for the duration of a pulse event. The plasma model incorporates negative feedback mechanisms that enhance the magnitude of reflected power in the early ON-cycle. These feedback mechanisms include a skin depth-dependent derivation of plasma impedance and a generalized electron energy distribution function. These mechanisms decrease the rate of power delivery and dnedt in the early power on cycle. Data taken in the global plasma-circuit model was benchmarked to hairpin probe measurements that were taken on the NC state’s inductively coupled argon oxygen system. Experimental data were taken using a working gas of high purity argon at pressures ranging from 2.67 to 6.67 Pa, and center point electron densities were measured in the range of 109–1010cm−3.
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