Electron behaviors in afterglow of synchronized dc-imposed pulsed fluorocarbon-based plasmas

Abstract

Electron behaviors in a pulsed dual radio frequency (RF) capacitively coupled plasma of a mixture of C 4 F 8 , O 2 , and Ar gases, where the DC bias of %300 V in the RF-on period was imposed and synchronously increased to %1000 V in the RF-off period, were investigated. The synchronous DC bias prolongs the electron density (n e ) decay and provides emission of Ar at a wavelength of 750.38 nm in early afterglow at 3 µs during the RF-off period of 10 kHz pulse modulation. The rapid n e decay occurred with the electron attachments to the electronegative fluorocarbons, and thus the plasma consisting of positive and negative ions was generated. The DC bias voltage seems to be applied between the electrodes and the positive ions accelerated to the top electrode, and enhanced the secondary electron generation at the top electrode surface in the RF-off period with the ion bombardments, concomitantly with the synchronous emissions.

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

“…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.…”

“…Sirse et al 28 reported the time-resolved measurements of the electron density in pulsed 60 MHz/2 MHz DF CCPs. In earlier studies, 16,17 our group has used synchronized DC-bias on the pulsed dual frequency CCP in a mixture of Ar, C 4 F 8 , and O 2 gases to study the behavior of electron density using a surface wave probe. Despite these studies on diagnostics in discharges using fluorocarbon gases (intended for plasma processing of SiN x , SiO x , etc., for microelectronics), the connection between fundamental plasma properties, such as the electron temperature (T e ), electron density (n e ), and the kinetics of plasma and its species formation in such plasmas is not yet fully understood.…”