Title: Influence of Fluorination and Oxygenation Sources on the Thermal Atomic Layer Etching of Amorphous MoS2

Program: Materials Science and Engineering MS

Committee Chair: Elton Graugnard

Committee: Elton Graugnard, Jeffrey Elam, Dave Estrada

Abstract: Atomic layer etching (ALE) has emerged as a pivotal technique in the precise fabrication of two-dimensional (2D) materials, particularly molybdenum disulfide (MoS2), which holds promise for energy-efficient semiconductor devices due to its large band gap and high mobility in monolayer form. The ability to precisely etch amorphous and crystalline MoS2 films provides a pathway for controlling thickness, which is critical to achieving desired electrical and optical properties. Previous studies used MoF6 and H2O in thermal ALE of MoS2. Here, we report studies of alternate fluorination and oxygenation sources and evaluate their impact on thermal ALE of amorphous MoS2 films. Oxygen sources included water, oxygen, and ozone, while fluorine sources included HF/Pyridine and MoF6. Etch rates, morphology, and surface chemistry post ALE were characterized using spectroscopic ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. Results indicate HF with the combination of H2O showed no signs of etching at temperatures between 200 to 300 °C, while HF and O3 showed an etch rate of 0.35 Å/cycle and an average mass loss of 25 ng/cm2 at 200 °C per ALE cycle. Further, MoF6 and O3 at 200 °C exhibited a substantially higher etch rate with 7.2 Å/cycle and an average mass loss of 126 ng/cm2 per ALE cycle. The results indicate a strong influence by the fluorine and oxygen sources on the etch behavior for MoS2. The high etch rate for MoF6 and O3 may indicate continuous etching rather than ALE, which involves self-limiting chemistry. Additional research will be needed to fully understand the chemical reactions involved in each process and the extent to which they are self-limiting. These results provide insights into precursor options for tailoring the etching processes needed to integrate MoS2 into high volume semiconductor manufacturing.