Rapid electron density decay observed by surface-wave probe in afterglow of pulsed fluorocarbon-based plasma

Abstract

To elucidate the pulsed fluorocarbon plasma behavior, a surface-wave probe with high time resolution was used to measure the electron density n e in the afterglow of plasma. In a dual-frequency capacitively coupled plasma of fluorocarbon chemistry, e.g., an O2-based C4F6 and Ar mixture, n e vanished rapidly in a short time (∼5 µs), whilst the dc current flowing onto the top electrode biased at −300 V decreased very slowly (decay time ∼70 µs). This observation is clear evidence of ion–ion plasma formation by electron attachment in the afterglow. We point out that the electron attachment rates for fluorocarbon radicals significantly affect the electrons and ion–ion plasma behaviors observed at the afterglow phase.

Effects of Ion Bombardment Energy Flux on Chemical Compositions and Structures of Hydrogenated Amorphous Carbon Films Grown by a Radical-Injection Plasma-Enhanced Chemical Vapor Deposition

“…The DF-CCP was characterized by the plasma surface waves (SW Probe), previously called the plasma absorption probe (PAP) method, optical emission spectroscopy (OES) [26][27][28][29][30].…”

Study of optical emission spectroscopy using modified Boltzmann plot in dual-frequency synchronized pulsed capacitively coupled discharges with DC bias at low-pressure in Ar/O2/C4F8 plasma etching process

“…In addition, the use of a negative DC-bias on the top electrode in the dual-frequency pulsed CCP etcher was recently reported to be an advanced and effective way to suppress negative ion charge accumulation in the HARE processes. 16,17 Also, an earlier study 27 with the superposition of negative DC-bias with the CCP etcher has shown to enhance the etch uniformity over 30 cm diameter wafers. In this sense, it is essential to understand this advanced etching process for a better understanding of the plasma characteristics, the generation of plasma species, and process control for HARE.…”

“…However, there is a need for independent control of ion energy and flux, particularly in the plasma processes demanding high aspect ratio etching (HARE) for nanometer-size contacts. 8 Consequently, an additional power source as the second frequency excitation was proposed 8 and used in different theoretical [9][10][11][12] and experimental 4,[13][14][15][16][17][18][19][20] studies as the dual-frequency (DF) operation.…”

“…23 The application of pulse discharge was found as an effective way to reduce the concern of charge build-up. 16,17,24,25 In pulsed CCP discharge, during the off-period of the applied RF power, the electron temperature would significantly drop to maintain adequate electron density. Notably, the etching process operated by the pulsed CCP discharge efficiently produced chemically active plasma species along with negative ions in comparison to a continuous wave (CW) discharge operated with the same power.…”

“…In particular, dual-frequency (DF) pulsed Ar-rich/fluorocarbon plasmas are being used for plasma etching processes in various radio-frequency (RF) plasma etchers. [16][17][18][19][20]28 A steady advancement in the diagnostic techniques for plasma analysis has enabled us to understand plasma etching. To this end, there are some studies on plasma diagnostics of the DF etching plasmas to understand and control the fluorocarbon etching processes.…”