Hardmask engineering by mask encapsulation for enabling next generation reactive ion etch scaling

Abstract

Miniaturization and scaling of semiconductor devices require development of innovative techniques to sustain advancements. A promising trend is the migration from 2D to 3D device architectures that necessitate fabrication of high-aspect-ratio narrow features through layers of different materials. Reactive ion etching can achieve this but poses unique challenges due to the requirement of etch chemistries capable of etching dissimilar materials with varying etch rates while maintaining high productivity. The choice of hardmask is also crucial, as it plays a critical role in determining efficacy of the etch process and the final shape of the feature being etched. To address these challenges, we introduce a new concept of hardmask engineering that involves a bilayer hardmask scheme consisting of a patterned conventional hardmask encapsulated with a thin layer of etch-resistant ruthenium (Ru) layer. Experimental results for etching multilayer stacks consisting of alternating pairs of SiO2 and Mo show that this engineered hardmask results in improved hardmask remaining and etch profile with smaller critical dimensions (CDs). Technology computer-aided design simulations with the Ru encapsulation layer on conventional carbon hardmask demonstrate increased poly-Si etch depth with reduced bow CD. This concept can be extended to any semiconductor nanofabrication step involving high-aspect-ratio etching where precise control of CDs is essential in the vertical direction.