Low-temperature ALD process development of 200 mm wafer-scale MoS2 for gas sensing application

The unique electronic and mechanical properties of transition metal dichalcogenides (TMDs) make them interesting for industry and research as the demand for two-dimensional (2D) material applications has been increased in the last decade. Most applications make use of the characteristic optical properties of the crystalline material. In this study, a low-temperature atomic layer deposition (ALD) process for layer-by-layer generation on 200 mm wafers is introduced. The deposited layers are characterized by XPS, XRD, Raman spectroscopy and AFM measurements. Four-point probe sheet resistance measurements show the high homogeneity of deposited layers. Compositional analysis reveals amorphous MoOxSy films and thickness measurements via SEM cross section and ellipsometry show a growth rate of about 0.1 nm/cycle. Further improvement of the film quality can be achieved by thermal annealing. MoS2 layers have also been found to be gas-sensitive to various gas molecules. For this application high crystallinity is not necessarily required and hence, this low-temperature wafer-scale process for 2D gas sensors can be integrated into already existing workflows for high-volume production on silicon wafers. Furthermore, it can also be applied on different substrates, for example on flexible thin glasses. The possible implementation to these substrates is also shown.