As nanoelectronic devices continue to shrink in response to demands for smaller and faster low-power, high-density devices, wasteful fabrication techniques are being replaced with methods that predetermine processing windows based on plasma parameter measurements. A cutoff probe comprising coaxial cables wrapped in Teflon is typically used for this measurement. However, because Teflon can be destroyed under high-density plasma conditions, a change in the dielectric material of the coaxial cable may be considered for process plasma or high-density plasma measurements. However, the nature of these changes has not been examined. Hence, this study analyzes the plasma measurement characteristics of a cutoff probe using electromagnetic wave simulations and a plasma equivalent circuit model focusing on the dielectric permittivity and thickness of the coaxial cable-based cutoff probe. According to the results, as the dielectric constant of the insulator of the coaxial cable increased from 1 to 20, the transmission intensity at the cutoff frequency decreased from –68 to –81 dB. Furthermore, with the increased thickness of the insulator, the transmission intensity at the cutoff frequency increased from –80 to –64 dB. The characteristic changes are explained using a circuit model that verifies that changes to the insulator’s dielectric constant and thickness affect the characteristic impedance of the cable, but not the plasma density measured by the cutoff probe. Nevertheless, the intensity of the observed transmission spectrum is affected. Hence, these findings are expected to contribute to the optimization of cutoff probes used for high-density plasma parameter measurements.

Keywords: Plasma diagnostic, Cutoff probe, Cutoff frequency, Transmission spectrum