Area-selective atomic layer deposition of molybdenum oxide

Area-selective bottom-up synthesis routes of thin films are required to overcome the current limits in lithography, and such growth can be achieved with high quality and nanometer thickness control by area-selective atomic layer deposition (AS-ALD). However, the current range of materials demonstrated deposited by AS-ALD is limited, and no processes for molybdenum oxide have been available so far. In this work, the authors explore the properties of a new ALD precursor, MoCl₄O, for deposition of molybdenum oxides by ALD. MoCl₄O is administered at room temperature during deposition, making it readily available for use. When reacted with a combination of water and ozone, it leads to an AS-ALD process for deposition of MoO_x—the first reported. The process is perfectly selective for growth on glass as compared to Si(100) substrates for deposition temperatures between 200 and 300 °C, with a growth rate of 0.72 Å/cycle at 300 °C. The process is attempted on a range of substrates proving good growth on soda-lime glass and LiF and no growth on Si(100), silica, Na₂CO₃, CaCO₃, Li₃PO₃, or Li₂SiO₃. The findings of this study indicate an activated process by diffusion of sodium or lithium through the film during growth. The obtained films have further been characterized by x-ray photoelectron spectroscopy, scanning electron microscopy, x-ray diffraction, and atomic force microscopy, revealing films with an RSM roughness of 23 nm with the presence of crystalline MoO₂ (C P/m) when deposited at 300 °C and crystalline Mo₉O₂₆ when deposited at 250 °C. The rough MoO_x thin films may be applicable for electrocatalysis, gas sensors, or lithium-ion batteries. The findings of this study enable AS-ALD synthesis of molybdenum oxide with excellent selectivity not dependent on intermittent etching cycles during growth.