A 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 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 small-molecule inhibitor is used, which obtains 60% selectivity at 2.0 nm of SiO2 growth on SiO2 or WO3 as growth area versus HfO2 as 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 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.