Exposure Strategy to Overcome Surface Thermal Localization during Laser Heat-Mode Lithography to Fabricate High-Aspect-Ratio Nanostructures

Owing to its super-resolution laser direct writing capability, laser heat-mode lithography is an excellent alternative lithography technology for nanoscale structure manufacturing. Ho wever, the exposure depth of heat-mode resist materials is limited (to <100 nm) as a result of the high-photothermal conversion principle. This limitation hinders the fabrication of high-aspect-ratio nanoscale structures and the further development of this technology. The optimization of traditional exposure strategies often focuses on Gaussian light-field modulation, which essentially fails to overcome the thermal process limitations inherent in laser heat-mode resist materials. A remarkable linear relationship exists between the line width (critical dimension, CD) and depth. In this study, we conducted a thermal analysis of the exposure process and investigated a means of regulating the thermal field based on the design of the film layer structure. A structure was designed with the following distributions for the thermal conductivity (k) and thermal diffusion coefficient (a): klayer2 > klayer1 > klayer3 and alayer3 > alayer1 > alayer2. This proposed exposure strategy successfully overcame the linear constraint relationship between the CD and depth and made the heat accumulation rate dominate the aspect ratio change. The aspect ratio increased as the heat accumulation rate decreased, and different exposure depths were achieved for the same CD in nano resolution. We experimentally prepared exposed samples on this base using 360 nm-thick Ag8In14Sb55Te23 as a heat-mode resist. The structural exposure depth could exceed 300 nm, which made it possible to achieve a high-aspect-ratio for high-resolution nanoscale structures. We also successfully fabricated a variety of micro- and nanoscale structured arrays with a high exposure depth, a minimum single-line width of 142.6 nm, and an aspect ratio of up to 2.5:1. This demonstrated the effectiveness and universality of the exposure strategy.