Direct Laser Writing Dry Lithography of High-Resolution Micro-/Nanostructures in AgSb₄Te Thin Film for Tunable Perfect Absorber

Direct laser writing is promising for fabrication of functional structures due to its high speed, low cost, and facile operation. However, high resolution is difficult to be implemented due to wet development-induced structural collapse. Ag-doped Sb4Te thin film is proposed for high-resolution direct laser writing dry lithography. The crystalline structures and binding environment of AgSb4Te thin films are investigated. The dry lithographic characteristics suggest that the developing selectivity of exposed to as-deposited film is as high as 17 under CHF3/O-2 gas and the minimum linewidth of patterns can reach 80 nm via adjusting grating period. Developing selectivity mechanism is ascribed to exposure induced phase separation along with generation of Sb component and Ag7Te4 phases. The Sb component can be readily etched due to the lack of Ag atom protection and then etching of residual Ag7Te4 phase is further promoted while the uniformly distributed Ag atoms in as-deposited film restrain its etching. In addition, nanohole array is fabricated onto AgSb4Te thin films and tunable absorbance can be realized by adjusting pattern period and phase-change process. This work may provide a useful guide for the investigation of direct laser writing lithography mechanism and functional device fabrication.