Beyond binary patterning: polypropylene carbonate as a versatile thermal resist for high-fidelity grayscale Nanofabrication.

Thermal scanning probe lithography (t-SPL) is a high-resolution nanopatterning technique that employs a heated probe for precise, maskless patterning. Polypropylene carbonate (PPC) has emerged as a promising resist material for t-SPL due to its favorable thermal decomposition behavior. In this study, we investigate the use of PPC as a thermal resist in t-SPL, leveraging its chain unzipping and random scission mechanisms to achieve controlled material removal. The effects of various parameters on the patterning of PPC films, such as temperature, tip height, and force pulse, are systematically examined. Upon exposure to the heated tip, PPC undergoes localized sublimation at the contact area, enabling nanopatterning with the lateral resolution down to 50 nm and the vertical resolution down to sub-nanometer. This approach achieves stepped cyclic and sinusoidal grayscale patterns with controllable depth and size. Furthermore, we demonstrate grayscale pattern transfer by etching the PPC patterns into dielectric layers using optimized dry etching processes. This approach offers precise depth control and shows strong potential for applications in photonic and nano-electronic device fabrication.