(Invited) Atomic Layer Etching of SiO2 and Other Materials Using Plasma Process Sequences

Tuesday, 30 May 2017: 14:00
Churchill B2 (Hilton New Orleans Riverside)
G. S. Oehrlein (University of Maryland)
Angstrom-level precision in etching of SiO2 is possible using steady-state Ar plasma in conjunction with periodic injection of a defined number of C4F8 molecules and synchronized plasma-based Ar+ ion bombardment.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. The question of SiO2:Si3N4 etching selectivity was studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Since Si3N4 has a lower physical sputtering energy threshold than SiO2, Si3N4 physical sputtering can take place after exhausting the chemical etchant at the end of each cycle for certain ion energies and leads to Si3N4/SiO2 etching selectivity. By optimization of the 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.2Mechanism of the observed ALE behaviors will be discussed using real-time and post-plasma surface analysis data. We will also discuss current challenges with the application of these approaches to other materials.

Acknowledgements: I am pleased to acknowledge the essential contributions and collaboration of D. Metzler, C. Li, S. Engelmann, R. Bruce, E. Joseph, C. S. Lai, and E. A. Hudson to this work, and thank National Science Foundation (CBET-1134273), US Department of Energy (DE-SC0001939) and Semiconductor Research Corporation for funding.

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).