Low Temperature Area Selective Atomic Layer Deposition of Ruthenium Dioxide Thin Films Using Polymers as Inhibition Layers

Area selective atomic layer deposition (AS-ALD) is an interesting bottom-up approach due to its self-aligned fabrication potential. Ruthenium dioxide (RuO2) is an important material for several applications, including microelectronics, demanding area selective processing. Herein, it is shown that ALD of RuO2 using methanol and RuO4 as reactants results in uninhibited continuous growth on SiO2, whereas there is no deposition on polymethyl methacrylate (PMMA) blanket films even up to 200 ALD cycles, resulting in around 25 nm of selective RuO2 deposition on SiO2. The excellent selectivity of the process is verified with X-ray photoelectron spectroscopy, X-ray fluorescence, and scanning transmission electron microscopy. AS-ALD is possible at deposition temperatures as low as 60 degrees C, with an area selective window from 60 to 120 degrees C. The deposition of RuO2 using other coreactants namely ethanol and isopropanol in combination with RuO4 increases the process's growth rate while maintaining selectivity. Testing different polymer thin films such as poly(ethylene terephthalate glycol), (poly(lauryl methacrylate)-co-ethylene glycol dimethacrylate), polystyrene, and Kraton reveals an important relationship between polymer structure and the applicability of such polymers as mask layers. Finally, the developed method is demonstrated by selectively depositing RuO2 on patterned SiO2/PMMA samples, followed by PMMA removal, resulting in RuO2 nanopatterns.

Automated summary

This article explores the method of area selective atomic layer deposition (AS-ALD) using methanol and RuO4 as reactants to achieve continuous deposition of RuO2 on SiO2 while no deposition occurs on PMMA. The process demonstrates excellent selectivity at deposition temperatures as low as 60 degrees C. The study also reveals the relationship between polymer structure and the applicability of different polymer thin films as mask layers. Finally, the method is demonstrated by selectively depositing RuO2 on patterned SiO2/PMMA samples, resulting in RuO2 nanopatterns after PMMA removal.