Area-Selective Atomic Layer Deposition of SnS₂ Nanosheets for Applications of Back-End-of-Line-Compatible Transistors

As semiconductor devices are miniaturized (to dimensions of nanometers), the accurate alignment of each layer on the desired location poses a challenge in the fabrication of multilayer-stacked devices. Area-selective deposition has attracted interest in resolving alignment issues in nanoelectronics. Herein, we demonstrate the area-selective atomic layer deposition (ALD) of SnS₂, a promising two-dimensional channel material for the application of back-end-of-line (BEOL)-compatible transistors, on SiO₂ (growth area) and Al₂O₃ (nongrowth area). We employed a super cycle comprising acetylacetone injection as an inhibitor, SnS ALD cycles, and H₂S plasma for the area-selective deposition of SnS₂. Although SnS ALD possesses good selectivity, the H₂S plasma used for the transformation of SnS to SnS₂ deteriorated the Al₂O₃ surface and resulted in nucleation in the nongrowth area. The acetylacetone injection in the super cycle was selectively adsorbed by Al₂O₃ and protected it from the H₂S plasma. The synergistic effects of the selectivity of the SnS ALD process and protection of the Al₂O₃ surface exhibited excellent selectivity for SnS₂. In the super cycle, the increase in the number of SnS cycles enhanced growth incubation on Al₂O₃ and induced the appearance of the SnS phase on SiO₂ as the growth area. By optimizing the super-cycle conditions, ∼7 nm of selective SnS₂ deposition was achieved on Al₂O₃ and SiO₂. The proposed strategy will help enhance the area-selective deposition technology for two-dimensional semiconductors in BEOL-compatible transistors.