On the Etching Mechanism of Highly Hydrogenated SiN Films by CF4/D2 Plasma: Comparison with CF4/H2

Shih-Nan Hsiao,Masaru Hori,Kenji Ishikawa,Thi-Thuy-Nga Nguyen,Makoto Sekine,Takayoshi Tsutsumi

doi:10.3390/coatings11121535

Abstract

With the increasing interest in dry etching of silicon nitride, utilization of hydrogen-contained fluorocarbon plasma has become one of the most important processes in manufacturing advanced semiconductor devices. The correlation between hydrogen-contained molecules from the plasmas and hydrogen atoms inside the SiN plays a crucial role in etching behavior. In this work, the influences of plasmas (CF4/D2 and CF4/H2) and substrate temperature (Ts, from −20 to 50 °C) on etch rates (ERs) of the PECVD SiN films were investigated. The etch rate performed by CF4/D2 plasma was higher than one obtained by CF4/H2 plasma at substrate temperature of 20 °C and higher. The optical emission spectra showed that the intensities of the fluorocarbon (FC), F, and Balmer emissions were stronger in the CF4/D2 plasma in comparison with CF4/H2. From X-ray photoelectron spectra, a thinner FC layer with a lower F/C ratio was found in the surface of the sample etched by the CF4/H2 plasma. The plasma density, gas phase concentration and FC thickness were not responsible for the higher etch rate in the CF4/D2 plasma. The abstraction of H inside the SiN films by deuterium and, in turn, hydrogen dissociation from Si or N molecules, supported by the results of in situ monitoring of surface structure using attenuated total reflectance-Fourier transform infrared spectroscopy, resulted in the enhanced ER in the CF4/D2 plasma case. The findings imply that the hydrogen dissociation plays an important role in the etching of PECVD-prepared SiN films when the hydrogen concentration of SiN is higher. For the films etched with the CF4/H2 at −20 °C, the increase in ER was attributed to a thinner FC layer and surface reactions. On the contrary, in the CF4/D2 case the dependence of ER on substrate temperature was the consequence of the factors which include the FC layer thickness (diffusion length) and the atomic mobility of the etchants (thermal activation reaction).

Highlights

Introduction published maps and institutional affilSilicon nitride films have been widely used in the semiconductor industry for applications ranging from passivation layer, anti-reflection layer or advanced electrical devices such as FIN-type transistor, 3D NAND memory, etc. [1]
These results indicate that the structure of the FC layer formed on the intensity, it can be deduced that the FC thickness formed by the CF4 /D2 plasma was thicker
The etch rates (ERs) of the SiN films etched by the CF4 /D2 plasma was higher than that by the

Summary

Introduction

Introduction published maps and institutional affilSilicon nitride films have been widely used in the semiconductor industry for applications ranging from passivation layer, anti-reflection layer or advanced electrical devices such as FIN-type transistor, 3D NAND memory, etc. [1]. To prepare the silicon nitride films, many methods are frequently adopted, including low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), plasma-enhanced ALD (PEALD) and chemical reactive rf sputtering, which depend on the property requirements of the applications. Among these methods, PECVD utilizes plasma energy to decompose the precursors, which enable the SiN films to grow at a much lower temperature, by comparing them with the LPCVD. Due to limitations of gas dissociation of the plasma sources, impurities, hydrogen iations.

Results

Discussion

Conclusion