Planar cutoff probe for measuring the electron density of low-pressure plasmas

Abstract

The cutoff probe (CP) is a precise diagnostic technique that measures electron density using two cylindrical probe tips and holders inserted in a low-pressure plasma. However, a recent study has reported that the insertion of the probe tips and holders can perturb the plasma condition and act as a source of error in the measurement of electron density. This study proposes a planar cutoff probe (PCP), which does not have invasive probe tips and holders, to minimize the plasma perturbation during plasma measurement. We embed the PCP on the existing substrate chuck of the plasma chamber instead of inserting an additional probe holder into the chamber. The adjusted conditions for the radii of the probe's antennas and the gap distance between the two probe antennas are obtained via an electromagnetic simulation. The comparative experiment results show that the inferred electron densities of the optimized PCP are in good agreement with those of the previous CP and within reasonable discrepancies stemming from the differences in measurement positions. We believe that the PCP, which can be embedded in the inner surface of the chamber and measure the electron density during the plasma (wafer) process, would be an alternative technical tool to realize advanced process control of plasma based on non-invasive diagnostic methods.

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

“…Recently, to improve throughput and productivity, process monitoring technology has become significant because the price of a patterned wafer has steadily grown and loss by unstable process is no longer negligible [ 6 , 7 , 8 , 9 ]. Particularly, advanced process control (APC), which is a process-tuning technology based on real-time signals from monitoring devices, has attracted strong interest from industry [ 10 , 11 ]. 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 ].…”

“…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 ].…”

“…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 ].…”

Kinetic investigation of the planar Multipole Resonance Probe under arbitrary pressure

“…In the past decade, several planar-type APRS probes have been developed, such as the planar multipole resonance probe (pMRP) [10][11][12][13][14][15][16], curling probe [17][18][19], and flat cutoff probe [20][21][22]. These probes can be flatly embedded into the chamber wall or chuck for minimally invasive process monitoring.…”