Finding the optimum design of the planar cutoff probe through a computational study

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.

Development of the Measurement of Lateral Electron Density (MOLE) Probe Applicable to Low-Pressure Plasma Diagnostics

“…The APC gathers monitoring data in real-time and diagnoses whether plasma processing steps are normal or not based on post-process algorithms [ 12 , 13 , 14 ]. Non-invasive measurement devices create tremendous monitoring data such as optical emission spectra, voltages applied and current flowing through the discharge electrode or antenna, capacitor positions in an impedance matcher, throttle valve positions, gas flow rates, and plasma parameters such as electron density and temperature [ 13 , 15 , 16 , 17 , 18 ].…”

“…Electron density is a significant factor among these monitoring parameters since it is believed to be directly related to processing time and quality [ 2 , 5 , 10 , 11 , 17 , 18 ]. To measure electron density non-invasively, various diagnostic methods have been developed, including actinometry and the line ratio method by analyzing optical emission spectra [ 6 , 19 , 20 ], laser Thomson scattering by measuring scattered laser light [ 20 , 21 ], and planar microwave probes by analyzing reflected or transmitted microwave signals [ 18 , 22 , 23 ]. They all have been frequently employed in the research field but some optical and laser methods have limitations for industrial application, as follows.…”

“…Based on the plasma cutoff phenomenon, which was firstly employed in a microwave interferometry measuring phase shift due to the plasma cutoff for measuring the line-integrated electron density [ 27 , 28 ], You et al developed the planar cutoff probe (PCP), which measures the cutoff frequency in the transmission microwave frequency spectrum (S ), which is defined as transmitted power of port 2 over radiated power from port 1 in a frequency spectrum [ 10 , 11 , 18 , 25 ]. They proposed the planar cutoff probe [ 11 ], developed it as a real-time monitoring instrument [ 17 ], and further optimized and analyzed the PCP [ 10 , 18 ].…”

“…Based on the plasma cutoff phenomenon, which was firstly employed in a microwave interferometry measuring phase shift due to the plasma cutoff for measuring the line-integrated electron density [ 27 , 28 ], You et al developed the planar cutoff probe (PCP), which measures the cutoff frequency in the transmission microwave frequency spectrum (S ), which is defined as transmitted power of port 2 over radiated power from port 1 in a frequency spectrum [ 10 , 11 , 18 , 25 ]. They proposed the planar cutoff probe [ 11 ], developed it as a real-time monitoring instrument [ 17 ], and further optimized and analyzed the PCP [ 10 , 18 ]. Sugai et al developed the planar curling probe (CP), based on the quarter-wave resonance (QWR) on a curling antenna, that measures the shift of QWR frequency induced by plasma in the reflection microwave frequency spectrum (S ), which is defined as reflected power of port 1 over radiated power from port 1 in a frequency spectrum [ 22 , 29 , 30 , 31 ].…”

“…Second, a simple probe design expands its applicability, such as enabling installation into an electrostatic chuck (ESC) as well as on vacuum chamber walls, with improved assembly tolerance. It should be noted that the capability to be installed onto chamber walls in place of an ESC or powered radio-frequency (rf) electrode has various advantages: addressing rf noise issues induced by high power application, minimizing process perturbation (with no requirement for any modification of an ESC or rf electrode before probe insertion) [ 17 , 18 ], and lowering the thermal damage from high-energy ions and neutrals created near the rf electrode.…”