Etch Characteristics of SiO2 Using Pulsed Triple-Frequency for Ar/C4F6/O2 Capacitive Coupled Plasmas

Abstract

We investigated the effects of 13.56 MHz radio frequency (rf) power as a medium frequency power on the plasma characteristics and etch properties of an amorphous carbon layer (ACL) and SiO 2 , using Ar/C 4 F 6 /O 2 gas mixtures in a capacitively coupled plasma (CCP) system operated with pulsed superimposed triple-frequency power of 60 MHz (source)/13.56 MHz (bias)/2 MHz (bias). Compared to the dual frequency rf power of 13.56 MHz (400 W)/2 MHz (900 W) or 60 MHz (400 W)/2 MHz (900 W), the use of triple-frequency rf power of 60 MHz/13.56 MHz/2 MHz (900 W) showed a better anisotropic SiO 2 etch profile, with the higher etch selectivity of SiO 2 over the ACL. We observed the best SiO 2 etch characteristics when the rf powers of 60 MHz and 13.56 MHz were set as 60 MHz (200 W)/13.56 MHz (200 W). In addition, when we varied the pulse duty percentage of 13.56 MHz rf power from 25∼100% (continuous wave (CW)), while keeping the rf powers of 60 MHz/13.56 MHz/2 MHz at 200 W/200 W/900 W, respectively, and while maintaining the pulse duty percentage of 60 MHz and 2 MHz at 50%, the use of the synchronized pulse on/off condition (i.e., the use of 50% duty percentage of 13.56 MHz) also showed the best etch characteristics. The best SiO 2 etch characteristics and the highest etch selectivity of SiO 2 over the ACL (observed for both rf power ratios of 60 MHz (200 W)/13.56 MHz (200 W), and for the triple-frequency pulsing with the synchronized pulse on/off) were related to the higher CF x /F ratios, which increased the fluorocarbon polymer passivation on the ACL surface and SiO 2 sidewall during etching.

Comprehensive understanding of the ignition process of a pulsed capacitively coupled radio frequency discharge: the effect of power-off duration

“…fluxes, densities, energies, and spatial uniformity of charged particle densities, as well as the creation of radicals), but can also cause an improvement of actual etching characteristics, e.g. the etching uniformity and rate, the anisotropic etch profile and higher etch selectivity, etc [20][21][22][23][24][25][26].…”

Progress in nanoscale dry processes for fabrication of high-aspect-ratio features: How can we control critical dimension uniformity at the bottom?

“…Pulse bias technology, which simply ramps up the bias power, was introduced almost 10 years ago. 36,[122][123][124] In the off period of the pulse operation, the sheath collapses and the potential at the wafer surface decreases, which allows electrons and negative ions to reach the etching front, thus neutralizing the positive charge build-up. This charge neutralization helps to increase the effective bias power and suppresses the accumulation of positive charges at the hole bottom owing to the transport of negative ions during the pulse-off phase.…”

High energy electrons induced by nonlinear effect in synchronized dual-level radio frequency pulsing capacitively coupled plasmas

“…A third method, the pulsed plasma technique, is to turn the plasma on and off by modulating the RF driving voltages with pulse parameters (such as pulse frequency, duty cycle, etc) during the operation of the plasma processing. It has been reported that both improved etch selectivity and etch uniformity can be achieved, due to decreased gas dissociation and enhanced radical diffusion during pulse off time [13,14]. Meanwhile, the decreased positive ion energy and extraction of negative ions during the pulse off time are believed to play an important role in neutralizing the accumulated electrons and ions in the trenches, respectively, contributing to better control of the etching profile and critical features [9,15].…”