Angstrom-level precision in etching of SiO2
is possible using steady-state Ar plasma in conjunction with periodic injection of a defined number of C4
molecules and synchronized plasma-based Ar+
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
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 Si3
has a lower physical sputtering energy threshold than SiO2
physical sputtering can take place after exhausting the chemical etchant at the end of each cycle for certain ion energies and leads to Si3
etching selectivity. By optimization of the ALE process parameters, e.g. low ion energies, ESL, and FC film deposition per cycle, highly selective SiO2
etching can be achieved for conditions where FC selectively accumulates on Si3
Mechanism 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).