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The combination of area-selective ALD intermitted with back-etching steps has recently attracted much interest because of its potential in achieving high selectivity. Compared to non-interrupted area-selective ALD this supercycle approach has proven to be very effective in reducing the defectivity on the non-growth areas and thickening the layers on the growth areas.1, 2 In this work we studied the case of selective SiO2 deposition on silicon substrate wafers (growth area) with large ZnO patterns (non-growth area). We will demonstrate the effectiveness of this complementary approach, i.e., deposition and etch-back corrections in a rotary atmospheric-pressure all-spatial processing (= ‘dep/etch’) reactor (Fig. 1) to maximize SiO2 selectivity while obtaining high deposition rates. For the selective spatial ALD part of the supercycle a three-step (‘ABC’-type) recipe was adopted,3 consisting of exposure to: A) inhibitor, B) silicon precursor (BDEAS) and C) O2 plasma. The periodic back-etch intermissions in the supercycle were carried out in the same integrated spatial process reactor by exposing the substrate to a CF4-O2-N2 plasma. The plasma source used for both O2-plasma and the back-etch was of the atmospheric-pressure Dielectric Barrier Discharge (DBD) type4. Figure 2 gives an illustration for a supercycle process with the substrate rotating at 20 rpm and using 3 repetitions of 40 ‘ABC’-cycles and 6 corrective back-etch cycles. During the each set of 40 ‘ABC’-cycles we could selectively grow sufficient (i.e., up to ~3.5 nm) SiO2 layer thickness on the growth area before the first nucleation of SiO2 became apparent on the ZnO non-growth areas. This way some selectivity is gradually lost with the number of ALD cycles increasing. As shown in Fig. 2 the selectivity loss can be repeatedly restored by a CF4-O2-N2 plasma back-etch with no silicon detected on the non-growth area by XPS. We demonstrated that with 3 repeated ‘dep/etch’ supercycles up to 10 nm thick SiO2 could be grown on the growth area. We will discuss how Low Energy Ion Spectroscopy (LEIS), with its extreme sensitivity to the top monolayer(s) of a thin film, can give more and reliable quantitative information on the process selectivity and the defectivity on the non-growth area in terms of surface coverage and derived thickness. In addition, scanning probe FTIR-AFM microscopy can give information about the defects and contaminants at the substrate surface. Furthermore, we extended the selective spatial ALD of SiO2 to other oxidic non-growth areas like Al2O3, IGZO, SnO2, Ta2O5 and ZrO2. 1. R. Vallat, et al., J. Vac. Sci. Technol. A, 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). 4. Y. Creyghton, P. Poodt, M. Simor, F. Roozeboom, US Patent Application 20170137939. Figure 1 |
