Area-selective atomic layer deposition (AS-ALD) has the potential to eliminate lithography and etching steps during nanomanufacturing, and can thereby solve some of the current challenges the semiconductor industry is facing with moving to smaller dimensions. Thin films of MoO3, and other molybdenum oxides, have applications in catalysis, gas sensors, photovoltaics, electrochromic devices, batteries, and more. AS-ALD, however, has not been used to grow molybdenum oxides until now.

Kvalvik et al. found a simple process for growing thin films of molybdenum oxides with ALD by using MoCl4O as the precursor. When dosed at room temperature during deposition, the MoCl4O reacted with water and ozone to yield deposition of molybdenum oxides.

“The range of currently available molybdenum-based processes suitable for ALD is limited,” said author Ola Nilsen. “We were therefore excited to find a new process based on a simple type of chemistry.”

The authors also realized that the growth of molybdenum oxides depends on the chemistry of the substrates they were grown on. The films grew on glass and LiF, but not on a variety of other substrates including silicon wafers, which surprised the authors. This allows the deposition to be performed in an area-selective manner.

The MoCl4O precursor is thermally stable for depositions up to at least 350 C, which is significantly higher than for other molybdenum sources. This led the authors to believe that the precursor is suitable for deposition of ternary or more complex molybdenum oxides by ALD. They hope to see more use of MoCl4O and other oxychlorides as ALD-precursors in future work.

Source: “Area-selective atomic layer deposition of molybdenum oxide,” by Julie Nitsche Kvalvik, Jon Borgersen, Per-Anders Hansen, and Ola Nilsen, JVST: A (2020). The article can be accessed at https://doi.org/10.1116/6.0000219.