(Invited) Area-Selective Spatial ALD of SiO2 Interleaved with Etch-Back Supercycles: Quantification of Area Selectivity By Low Energy Ion Scattering

Abstract

Area-selective ALD interleaved with etch-back steps in a supercycle fashion has recently been reported as very effective in achieving high selectivity. Such supercycles can result in lower defectivity on the non-growth area and thicker layers on the growth area, as compared to solely area-selective ALD.1, 2 Here, we use low energy ion scattering (LEIS) to probe the selectivity of the first supercycle, consisting of plasma-enhanced selective spatial-ALD of SiO2 and conventional CF4-based reactive ion etching (RIE). Given its extreme sensitivity to the top monolayer(s) of a thin film, LEIS can reliably quantify the selectivity/defectivity on the non-growth areas in terms of surface coverage and derived thickness.A three-step approach was used for the area-selective spatial ALD of SiO2,3 which consisted of inhibitor, silicon precursor (BDEAS), and O2 plasma exposures. The process selectivity as a function of the number of cycles was probed using LEIS to monitor the SiO2 surface coverage on the non-growth area. After 20 spatial ALD cycles, no silicon was detected on the non-growth area (detection limit 2 % SiO2 surface coverage), implying excellent process selectivity. Increasing the number of ALD cycles resulted in a gradual loss of selectivity. Interestingly after 110 ALD cycles, the SiO2 coverage was 86%, indicating a not yet closed layer. At the same time, a SiO2 thickness of 11 nm was measured on the growth area, using spectroscopic ellipsometry. As the last step of the super-cycle, a 3 seconds RIE was sufficient to bring the SiO2 coverage back to zero on the non-growth area, while an 8 nm thick SiO2 layer was left on the growth area.The data presented in this work demonstrate the effectiveness of combining area-selective spatial ALD + etch-back corrections to achieve extreme SiO2 selectivity while retaining high deposition rates. Finally, we have extended the plasma-enhanced area-selective spatial ALD of SiO2 to other oxides and metals non-growth areas. REFERENCES 1. R. Vallat et al., JVSTA, 35, 01B104 (2017).2. S. K. Song et al., Chem. Mater. 31 4793-4804 (2019).3. A. Mameli et al., ACS Nano, 11, 9303-9311 (2017). Figure 1