| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS-WeA |
| Session: | Atomic Layer Etching and Low Damage Processing |
| Presenter: | Ryan Gasvoda, Colorado School of Mines |
| Authors: | N. Leick, Colorado School of Mines R.J. Gasvoda, Colorado School of Mines A. van de Steeg, Eindhoven University of Technology, Netherlands R.A. Ovanesyan, Colorado School of Mines R. Bhowmick, Lam Research Corporation E.A. Hudson, Lam Research Corporation S. Agarwal, Colorado School of Mines |
| Correspondent: | Click to Email |
Due to the continuous shrinking of semiconductor devices combined with the 3D architecture, the demands on dry etching processes have become increasingly stringent. Therefore, the development of more precise etching methods is necessary, and atomic layer etching (ALEt) is a promising technique to enable atomic-level thickness control, directional etching and material selectivity. Recently, ALEt of SiO2 has been extensively studied, using a cyclic process that involves plasma deposition of a fluorocarbon (CFx) layer, followed by an Ar plasma exposure to activate the fluorine for etching.
In this work, SiO2 was etched using an ALEt process based on an octafluorocyclobutane (C4F8) plasma to deposit the CFx layer and an Ar plasma for the removal of the material. In each ALEt half-cycle, in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and in situ four-wavelength ellipsometry were simultaneously used to study the film composition and the change in film thickness, respectively. From these measurements, it was possible to conclude that under the C4F8 plasma conditions used, the CFx layer can be deposited at a growth rate of ~1.65 Å/s, while minimizing the SiO2 removal to negligible amounts. At the end of the CFx deposition step, the predominant IR feature was centered at 1220 cm-1, and can be attributed to CFx (x=1,2,3), while some surface Si-C, Si-F and C-O can also be observed, suggesting the formation of an intermixed SiO2/CFx layer. In line with this result, the IR from the first 10 s of Ar plasma clearly shows the instantaneous removal of SiO2. This removal continues for the 60 s of Ar plasma exposure, and ellipsometry enables us to distinguish between two etch regimes. The first regime has a high etch rate, ~0.5 Å/s, indicating a high F concentration in the intermixed SiO2/CFx layer. As the film etching proceeds, the intermixed layer becomes F-deficient which slows down etching, until finally the SiO2 removal is dominated by inefficient Ar+ sputtering. From these results, SiO2/CFx intermixing seems to be the dominant etching mechanism in this ALEt process.
In addition to the instantaneous removal of SiO2, an increase in the CFx signal was initially detected in the IR during the first 10 s of the Ar plasma exposure. Because at the end of the 60 s Ar plasma step no net incorporation of CFx can be observed, we propose that CFx is initially redeposited from the reactor surfaces and participates in the etching process. This redeposition increases the etch rate during the Ar plasma cycle by providing additional amounts of F from the gas phase, but also undesirably increases the etch rate with increasing ALEt cycles.