Plasma process modulation from polymerization to etching in C4F8/Ar plasma by nitrogen gas addition

additionLow-pressure C₄F₈ based plasmas are widely used in semiconductor fabrication such as deposition or etching with various gas mixtures [1,2]. Although, oxygen gas has been widely used in C₄F₈ plasmas to control the depositing layer thickness, it is reported the oxygen atoms could deteriorate polymer-based surfaces during processes [3]. Therefore, in this work, the effects of nitrogen addition to C₄F₈/Ar plasmas was studied to modulate deposition process without severe surface damages. From the results, by nitrogen gas addition, it was found that the thickness of the deposited layer on the Si substrate was dramatically reduced from 194.3 nm to 3.4 nm and the cross-sectional views of the Si substrate clearly indicated that the plasma process was switched from polymerization to etching. By means of plasma spectroscopy and surface analyses, we can conclude the nitrogen atoms in plasma could scavenge fluorocarbon molecules involved in polymer deposition through the formation of CN molecule and release of F atoms [4].

[1] D. M. Chen, L. S. Engelmann, R. L. Bruce, E. A. J. Gottlieb, S. Oehrlein, Fluorocarbon assisted atomic layer etching of SiO2 and Si using cyclic Ar/C4F8 and Ar/CHF3 plasma, J. Vac. Sci. Technol. A, 34 (2016) 01B101, doi: 10.1116/1.4935462.

[2] I. Chun, A. Efremov, G. Y. Yeom, K. Kwon, A comparative study of CF4/O2/Ar and C4F8/O2/Ar plasmas for dry etching applications, Thin solid films, 579 (2015) 136-143. https://doi.org/10.1016/j.tsf.2015.02.060.

[3] Y. S. Mor, T. C. Chang, P. T. Liu, T. M. Tsai, C. W. Chen, S. T. Yan, C. J. Chu, W. F. Wu, F. M. Pan, W. Lur, S. M. Sze. Effective repair to ultra-low-k dielectric material (k2.0) by hexamethyldisilazane treatment, J. Vac. Sci. Technol. B, 20 (2002) 1334-1338, doi: 10.1116/1.1488645.

[4] C. Tsai, D. L. McFadden, Gas-phase atom—radical kinetics of N and O atom reactions with CF and CF2 radicals, Chem. Phys. Lett, 173 (1990) 241-245, https://doi.org/10.1016/0009-2614(90)80086-S.