Mechanism understanding in cryo atomic layer etching of SiO2 based upon C4F8 physisorption

G Antoun,R Dussart,P Lefaucheux,K Maekawa,T Tillocher,J Faguet

doi:10.1038/s41598-020-79560-z

Abstract

Cryogenic Atomic Layer Etching (cryo-ALE) of SiO2 based on alternating a C4F8 molecule physisorption step and an argon plasma step, has been enhanced thanks to a better understanding of the mechanism. First, we used Quadrupole Mass spectrometry (QMS) and spectroscopic ellipsometry analyses to evaluate the residence time of physisorbed C4F8 molecules versus temperature and pressure on SiO2 surface. QMS monitoring of the SiF4 etching by-product also enabled to follow the self-limiting etching behavior. Finally, a SiO2 cryo-ALE process was proposed at a temperature of − 90 °C resulting in a very linear etch over 150 cycles and an Etch amount Per Cycle as low as 0.13 nm/cycle.

Highlights

Cryogenic Atomic Layer Etching of SiO2 based on alternating a C4F8 molecule physisorption step and an argon plasma step, has been enhanced thanks to a better understanding of the mechanism
In order to characterize and understand the mechanisms involved in Atomic Layer Etching at low substrate temperature, a cryo-ALE process was performed
An Ar purge of 30 s is performed in order to remove C4F8 molecules from the chamber

Summary

Introduction

Cryogenic Atomic Layer Etching (cryo-ALE) of SiO2 based on alternating a C4F8 molecule physisorption step and an argon plasma step, has been enhanced thanks to a better understanding of the mechanism. Cryo-Atomic Layer Etching (Cryo-ALE) is proposed as an alternative to etch SiO2 in fluorocarbonbased chemistry but without plasma during the deposition step In this process, the substrate is cooled to a temperature below − 80 °C. At temperatures below − 110 °C, a self-limiting regime was achieved and an etch per cycle as low as 0.4 nm was obtained With this process, fluorocarbon polymer is no longer deposited on the reactor walls significantly reducing chamber contamination and limiting process drift. We report on the residence time of C 4F8 versus temperature and pressure Both ellipsometry and mass spectrometry measurements are used to characterize the adsorption and desorption of C4F8 from the SiO2 surface. The improved understanding of the C 4F8 residence time enabled for a significant extension of the SiO2 cryo-ALE process temperature range towards higher and more practical temperature

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Conclusion