Crossing Frequency Method Applicable to Intermediate Pressure Plasma Diagnostics Using the Cutoff Probe

Abstract

Although the recently developed cutoff probe is a promising tool to precisely infer plasma electron density by measuring the cutoff frequency (fcutoff) in the S21 spectrum, it is currently only applicable to low-pressure plasma diagnostics below several torr. To improve the cutoff probe, this paper proposes a novel method to measure the crossing frequency (fcross), which is applicable to high-pressure plasma diagnostics where the conventional fcutoff method does not operate. Here, fcross is the frequency where the S21 spectra in vacuum and plasma conditions cross each other. This paper demonstrates the fcross method through three-dimensional electromagnetic wave simulation as well as experiments in a capacitively coupled plasma source. Results demonstrate that the method operates well at high pressure (several tens of torr) as well as low pressure. In addition, through circuit model analysis, a method to estimate electron density from fcross is discussed. It is believed that the proposed method expands the operating range of the cutoff probe and thus contributes to its further development.

Development of a High-Linearity Voltage and Current Probe with a Floating Toroidal Coil: Principle, Demonstration, Design Optimization, and Evaluation

“…The experimental setup to identify the coefficients and from Equations ( 2 ) and ( 4 ) is shown in Figure 8 . Details of this setup are also described in [ 26 ]. For high power calibration, a cylindrical vacuum chamber with a turbomolecular pump (D-35614 Asslar, Pfeiffer Vacuum, Inc., Asslar, Germany) and a rotary pump (GHP-800K, KODIVAC Ltd., Gyeongsan-si, Korea) are employed as the dummy load in this calibration system.…”

“…To improve process productivity, process monitoring techniques based on plasma diagnostic methods have garnered much attention [ 15 ] since key process parameters such as etching and deposition rates are related to the plasma parameters [ 16 , 17 , 18 , 19 , 20 ]. Plasma diagnostic methods employ an analysis of (i) the current-voltage characteristics of plasma using the Langmuir probe [ 21 , 22 , 23 ], (ii) the response characteristics of plasma to microwaves using resonators (microwave probes) [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ], (iii) the optical emission characteristics of plasma using an optical emission spectrometer (OES) [ 33 , 34 ], and (iv) the voltage and current (VI) waveforms on a powered electrode using VI probes with circuit modeling [ 35 , 36 , 37 ].…”

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

“…The cutoff probe was connected to vector network analyzer 2 (S3601B 100 kHz–8.5 GHz, SALUKI Inc., Taipei, Taiwan) via two SMA cables. The cutoff probe can precisely measure the electron density by measuring the cutoff frequency in S ; details can be found elsewhere [ 9 , 46 , 47 , 48 , 49 ]. In the next section, operation of the MOLE probe at the center of the chamber is first demonstrated compared to the cutoff probe.…”

“…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 ].…”

Determination of Plasma Potential Using an Emissive Probe with Floating Potential Method

“…Basic internal plasma parameters are related with charged particles, called electron density, ion energy, and plasma potential. Various diagnostic tools have been developed to measure internal plasma parameters, such as microwave probes for electron density [ 15 , 16 ], ion energy analyzers [ 17 , 18 ] for ion energy, and electrostatic probes [ 19 , 20 ] for plasma potential. Among these parameters, plasma potential is a crucial parameter, since it confines electrons and dominates the flow dynamics of ions in plasma [ 21 ].…”