Physical approach to enhance the selectivity of SiO2 area-selective deposition using substrate biasing

Area-selective atomic layer deposition (AS-ALD) can provide a solution to current bottlenecks associated with traditional lithography-based patterning in the downscaling of nanoelectronics. However, in practice the deposition selectivity is often limited by the undesired nucleation on the non-growth area. This paper investigates selective ion sputter-etching as a novel physical approach to improve the selectivity. As a test case, the AS-ALD process of SiO2 employing acetylacetone as a small-molecule inhibitor is used, which obtains 60% selectivity at 2.0 nm of SiO2 growth on SiO2 or WO3 as the growth area versus HfO2 as the non-growth area. HfO2 was chosen because this substrate contains heavy atoms that accelerate ion sputter-etching for thin films on top, referred to as sputter yield amplification. A first strategy combining AS-ALD cycles with separate steps of Ar plasma using substrate biasing was investigated, resulting in 95% selectivity for thicknesses in the range of 3–4 nm. For this strategy, perfect repetition of the growth behavior was observed, which shows that the inert Ar ions keep the substrates in their pristine states. In the presence of heavy atoms in the material of the growth area (e.g., WO3), sputter yield amplification was observed, whereby the growth per cycle after etch-back depends strongly on the etch-back frequency. As the second strategy, the ion energy and ion flux of the O2 plasma coreactant were increased to enable ion sputter-etching during the AS-ALD process, resulting in a similar selectivity improvement. Overall, it is concluded that implementing ion sputter-etching can significantly enhance the deposition selectivity of AS-ALD processes.