Low Temperature Site-Specific Pulsed Laser Annealing of MoS₂

A precise, non-thermal, ultrashort pulsed laser process for selective and localized structural modification relevant to two-dimensional (2D) transition-metal-dichalcogenides (TMDs) ultra-thin films is reported. The approach enables site-specific pulsed laser annealing (SSPLA) and is shown to be effective in improving the electrical and structural properties of CVD-grown MoS₂ thin film devices with precision and control. High spatial overlapping of laser pulses is employed to anneal regions of MoS₂ thin films on SiO₂-Si substrates using laser fluences less than 12 mJ cm⁻² which is less than the threshold fluence for causing damage on surfaces. The process is implemented in ambient air at specific sites using laser beam scanning technology. Raman spectra confirm the conversion of amorphous to crystalline MoS₂. The application of the site-specific annealing process confirms a reduction in actual MoS₂ path resistance by up to a factor of four in devices. Cross sectional STEM confirms thinning and improvements to the degree of crystallization of partially crystallized films. AFM data indicates enlargement of isotropic grain structures with increasing fluence. The evidence suggests that crystallization occurs by local solid-state diffusion at low temperatures. The site-selective process is highly suitable for scalable precision back end of line processing in semiconductor wafer fabrication.