Atomic layer etching of SiO₂ with Ar and CHF₃ plasmas: A self‐limiting process for aspect ratio independent etching

Abstract

With ever increasing demands on device patterning to achieve smaller critical dimensions, the need for precise, controllable atomic layer etching (ALE) is steadily increasing. In this work, a cyclical fluorocarbon/argon plasma is successfully used for patterning silicon oxide by ALE in a conventional inductively coupled plasma tool. The impact of plasma parameters and substrate electrode temperature on the etch performance is established. We achieve the self‐limiting behavior of the etch process by modulating the substrate temperature. We find that at an electrode temperature of −10°C, etching stops after complete removal of the modified surface layer as the residual fluorine from the reactor chamber is minimized. Lastly, we demonstrate the ability to achieve independent etching, which establishes the potential of the developed cyclic ALE process for small scale device patterning.

Balancing ion parameters and fluorocarbon chemical reactants for SiO2 pattern transfer control using fluorocarbon-based atomic layer etching

“…3. As noticed in our previous work, 13 the substrate temperature has a non-negligible impact on the ALE performances, since it strongly affects the sticking coefficient of the deposited FC polymer and therefore the overall ALE process. 16 In addition, the temperature also has a significant effect on the chemical etching caused by fluorine in the chamber.…”

“…17 chemical reaction between SiO and FC results in a higher etch rate, but at the expense of the film integrity and etch selectivity for SiO 2 over other materials. [18][19][20] However, while we demonstrated that ALE at T = −10°C ensures self-limiting behavior and aspect-ratio independent etching, 13,21,22 to date, no study has been reported on the temperature effect on the ALE patterning of silicon oxide.…”

“…In a previous study, 13 we reported the first demonstration of aspect-ratio independent ALE and the achievement of the theoretically predicted self-limiting behavior and therefore provided a guideline recipe for an optimized SiO 2 patterning at the nanoscale level (down to 30 nm feature size). In addition, we showed the synergy of the ALE process: the combination of the FC deposition step and the Ar etch step causes SiO 2 etching.…”

“…All other parameters are kept constant, with a pressure of p = 10 mTorr and a temperature of T = −10°C, based on the best results of our previous study which we know ensure a self-limiting behavior and aspect-ratio independent etching. 13 The profile evolution of SiO 2 features is shown in Fig. 6(a) for increasing forward DC bias applied during the etch step.…”

“…Here, we present the profile evolution of silicon oxide using a Cr hard mask and we extend our previous investigation by performing a detailed and systematic analysis to gain a better insight into the effect of each parameter on the overall etching process. To this aim, we conduct a series of experiments in which we tune one parameter at a time, while the others are kept at the optimized values of the standard recipe, 13 with the focus on high fidelity transfer and vertical sidewalls fabrication. Our main findings are (i) an intermediate temperature (T = −10°C) allows for slow deposition rates, directional transfer (and therefore vertical sidewalls), and flat bottom surfaces; (ii) the profile is further improved by working at very low pressure ( p = 5 mTorr), since the ion energy is higher and the concentration of radicals is low, which makes the anisotropic etching by Ar ions the dominant process and leads to vertical features with limited undercut; and (iii) higher forward bias power (P Bias = 4W) significantly increases the directionality of the ion bombardment and therefore improves the verticality of the etching profile.…”