(Invited) Materials Selectivity in Atomic Layer Etching of SiO2, Si, and Si3N4 Using Plasma Process Sequences

Abstract

Using steady-state Ar plasma in conjunction with periodic injection of a defined number of C4F8 molecules and synchronized plasma-based Ar+ ion bombardment enables controlled removal of SiO2 layers with a thickness in the Angstrom-range.1 The physical sputter rate of SiO2 vanishes for Ar+ ion bombardment with a maximum ion energy of 20 eV and lower, whereas for a fluoroccarbon-coated SiO2 surface, chemical modifications of the SiO2 surface are induced by low energy ion bombardment and SiO2 etching is initiated. In this work we examined SiO2:Si and SiO2:Si3N4 etching selectivity and the roles of maximum ion energy, etching step length (ESL), FC surface coverage, and fluorocarbon precursor selection in controlling these. By optimization of ALE process parameters, e.g. low ion energies, ESL, and FC film deposition per cycle, highly selective SiO2 to Si3N4 etching can be achieved for conditions where FC selectively accumulates on Si3N4 surfaces.2 Surface oxidation of Si takes place during the Ar+ ion bombardment step, and makes it more difficult to achieve abrupt and highly selective removal of thin SiO2 layers from Si. Mechanism of the observed ALE behaviors will be discussed using real-time and post-plasma surface analysis data. 1 D. Metzler, R. Bruce, S. Engelmann, E. A. Joseph, and G. S. Oehrlein, J. Vac. Sci. Technol. A 32, 020603 (2014). 2 C. Li, D. Metzler, C. S. Lai, E. A. Hudson, and G. S. Oehrlein, J. Vac. Sci. Technol. A 34, 041307 (2016). * I gratefully acknowledge the essential contributions and collaboration of Kang-Yi Lin, C. Li, D. Metzler, S. Engelmann, R. Bruce, E. Joseph , C. S. Lai, and E. A. Hudson on which this talk is based. Additionally, funding from Semiconductor Research Corporation (No. 2017-NM-2726), National Science Foundation (CBET-1134273), and US Department of Energy (DE-SC0001939) is thankfully acknowledged.