Abstract
A new plasma diagnostic tool called the planar cutoff probe (PCP), recently developed by Kim et al. [Plasma Sources Sci. Technol. 28, 015004(2019)], can be embedded into a chamber wall or wafer chuck electrode for non-invasive electron density measurements. The application feasibility of the probe has so far been demonstrated in terms of signal-to-noise ratio; however, for the successful application of the PCP to real plasma processing, its design should first be optimized based on a comprehensive investigation of its characteristics. Therefore, in this paper, the effects of various parameters on the measurement characteristics of the PCP are investigated and analyzed via 3D full electromagnetic wave simulation. Results show that PCP measurement discrepancies vary by numerous controllable parameters, namely, wafer thickness and relative dielectric constant, antenna distance, input electron density, and chamber pressure. Based on these findings, the condition with the smallest measurement discrepancy and where PCP measurement performance is least affected by the parameters is found and discussed.
Highlights
Plasma process monitoring has become crucial in advanced plasma processing since the processing window has shrunk and the related steps have increased in complexity.1–3 To date, simple plasma monitoring devices such as voltage–current probes4–6 and optical emission spectrometers1–3 have been utilized, because they are inexpensive and easy to be installed on processing chambers
√ that f cutoff is equal to f pe (=8980 ne) is crucial, because this condition allows electron density to be inferred by measuring f cutoff without any correction.35,38,39. From this point of view, the planar cutoff probe (PCP) may seem to have a disadvantage for measurement performance because the PCP requires correction factors depending on wafer thickness to correctly infer electron density
As in the wafer thickness case, the PCP shows a very similar trend of measurement discrepancy for varying wafer dielectric constants: increasing dielectric constants are accompanied by decreasing measurement performance
Summary
Plasma process monitoring has become crucial in advanced plasma processing since the processing window has shrunk and the related steps have increased in complexity. To date, simple plasma monitoring devices such as voltage–current probes and optical emission spectrometers have been utilized, because they are inexpensive and easy to be installed on processing chambers. There is another method called the calorimetric probe to infer the electron density based on the measurement of electron energy flux.20,21 Microwave probes, such as the multipole resonance probe, hairpin probe, and cutoff probe, show high measurement accuracy and are free from RF noise issues, but they are not suitable to process monitoring since they operate invasively; the invasive method can cause plasma perturbation due to probe insertion, particle contamination from its antenna, probe body, and holder, and projection of the probe shape on the wafer, especially in a deposition process. To improve the curling probe diagnostic accuracy, Arshadi et al proposed an analytic form with a simple hairpin model deriving electron density from the standing wave resonance frequency.23 Another example of a microwave probe is the one developed by Schulz et al called the planar multipole resonance probe (pMRP), which measures the multipole resonance frequencies in an absorption frequency spectrum based on the same operation principle as the multipole resonance probe.
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