: As semiconductor devices scale toward sub-3 nm nodes, achieving extreme aspect ratio pattern transfer with nanoscale fidelity poses significant challenges, especially in advanced etch-intensive applications such as logic and memory structures. Conventional hardmask systems often suffer from poor etch resistance, insufficient mechanical strength, and limited pattern fidelity during prolonged plasma exposure. In response, this study presents the development of chemically amplified multilayer hardmask (MLHM) stacks with tunable crosslinking mechanisms to enable robust pattern transfer in high-aspect-ratio features exceeding 50:1. The MLHM architecture comprises alternating layers of spin-on carbon (SOC), silicon-rich organic films, and a novel chemically amplified inorganic-organic hybrid layer. The hybrid layer incorporates acid-labile crosslinkers and photogenerated acid catalysts to enable post-apply bake-induced crosslinking, leading to enhanced mechanical rigidity and plasma etch durability. Crosslinking density was tuned by adjusting bake temperature and exposure dose, providing process flexibility to match specific device layer requirements. Characterization using nanoindentation, X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry confirmed the formation of dense, low-hydrogen, and low-ash-content films with improved thermal stability and minimal dimensional distortion. Pattern transfer fidelity was evaluated through integration in extreme ultraviolet (EUV) and 193i lithography processes, showing <2 nm line-edge roughness and >95% pattern transfer efficiency in oxide and nitride etch stacks. Furthermore, oxygen and fluorocarbon plasma etch resistance improved by 2× compared to standard amorphous carbon layers. The results demonstrate that integrating chemically amplified crosslinking control within multilayer hardmask systems enables tailored mechanical and chemical resilience. This approach offers a scalable, EUV-compatible platform for next-generation patterning and etch transfer applications in complex 3D device architectures.