@article{xiao_brandon_morsell_nam_bae_lee_shannon_2023, title={Effect of focus ring with external circuit on cathode edge sheath dynamics in a capacitively coupled plasma}, volume={41}, ISSN={["1520-8559"]}, url={https://doi.org/10.1116/6.0002496}, DOI={10.1116/6.0002496}, abstractNote={Capacitively coupled plasmas are widely used in semiconductor processes. The control of plasma to obtain uniform deposition and etching is an open problem, particularly within a few millimeters of the substrate edge. Complex material stacks commonly referred to as focus rings are placed at the wafer edge to provide uniform processes across the entire substrate but have limitations with regard to process window and eventual material erosion. One approach is to combine a focus ring with a tunable external circuit ground path termination to extend the plasma uniformity to the wafer edge over a wider process space. The external circuit coupling focus ring to the ground influences the ion energy profile and the ion angular profile by changing the impedance between the focus ring and the ground and allows wafer edge tuning over a wide range of operating parameters. In this work, it is found that the adjustable external circuit can control the partitioning of bias and RF voltages between the RF powered and passively coupled plasma facing surfaces. The focus ring with an external circuit assembly can also control the spatial distribution of plasma density and, therefore, improve the sheath edge profile. These results point to possible source designs for engineering the distribution of power dissipation and the electric field of the wafer edge in industrial plasma reactors.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Xiao, Yuhua and Brandon, Joel and Morsell, Joshua and Nam, Sang Ki and Bae, KiHo and Lee, Jang-Yeob and Shannon, Steven}, year={2023}, month={May} }
 @article{peterson_ford_brandon_shannon_koh_chua_bera_tian_rauf_kraus_2020, title={Radiofrequency phase resolved electron density measurements with the hairpin resonator probe}, volume={53}, ISSN={["1361-6463"]}, DOI={10.1088/1361-6463/ab6944}, abstractNote={A floating hairpin resonator probe is used to measure electron density within the radiofrequency cycle of a parallel plate capacitively coupled plasma at steady state. A time resolution capable of detecting electron density oscillations within the radiofrequency cycle is demonstrated. Electron density oscillations are observed at the drive frequency over a range of operating conditions including 10–250 mTorr (1.3–33 Pa) in argon driven at 13.56 or 27.12 MHz. Localized electron density oscillation amplitudes show moderate agreement with literature and fluid simulations near the powered electrode and disagreement in the plasma bulk. The technique is useful for studying electron heating mechanisms in radiofrequency discharges due to its high time resolution.}, number={14}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Peterson, D. J. and Ford, K. and Brandon, J. and Shannon, S. C. and Koh, T. and Chua, T. C. and Bera, K. and Tian, W. and Rauf, S. and Kraus, P. A.}, year={2020}, month={Apr} }
 @article{ford_peterson_brandon_nam_walker_shannon_2019, title={Measurement of localized plasma perturbation with hairpin resonator probes}, volume={26}, ISSN={1070-664X 1089-7674}, url={http://dx.doi.org/10.1063/1.5065509}, DOI={10.1063/1.5065509}, abstractNote={In situ plasma diagnostics present the classical problem of the scientific measurement: how does one accurately measure a system without also perturbing it? The uncertainty in the degree of perturbation then reflects an inherent uncertainty in the diagnostic results. Microwave probes are no exception. This work discusses an experimental methodology for quantifying the local perturbation in hairpin resonator probe measurements. By pulsing the delivered power to a plasma, an electron density hairpin spike (HS) is readily detected at generator shutoff. The phenomenon is understood to arise from an apparent density rise as the plasma sheath collapses, thus raising the spatially averaged density measured between the hairpin tines. Other explanations for the density rise are eliminated, and the utility of the HS is presented. Under the conditions investigated, the HS provides an experimental comparison to a previous sheath correction factor developed by Sands et al.}, number={1}, journal={Physics of Plasmas}, publisher={AIP Publishing}, author={Ford, Kristopher and Peterson, David J. and Brandon, Joel and Nam, Sang Ki and Walker, Dustin and Shannon, Steven C.}, year={2019}, month={Jan}, pages={013510} }