Understanding 3D anisotropic reactive ion etching of oxide-metal stacks

Abstract

Scaling semiconductor devices necessitates the fabrication of high-aspect-ratio narrow features through the precise etching of multiple layers comprising alternating materials, each with sub-20 nm thickness. However, etching dissimilar materials, such as alternating metal and oxide layers, pose significant challenges due to inherent discrepancies in vertical and lateral etch rates. This study demonstrates the feasibility of etching a stack comprising 10 layers of silicon dioxide (SiO2) and molybdenum (Mo) using an Oxford Instruments ICP RIE tool operating at a low power regime (bias < 250 V). We evaluated different etch chemistries, including Cl2/CHF3 and CF4/CHF3, and the role of CH4 as a passivation gas to control the lateral etch rates. Mask encapsulation with Ru was employed to protect the hardmask during the etching process, enabling successful etching of 10 layers without lateral recess. Experimental results were validated using Sentaurus™ TCAD software to investigate the impact of gas chemistry on the stack etch rate. Our findings provide valuable insights into the performance of various etch chemistries, demonstrating the effectiveness of the evaluated chemistries and the role of CH4 in improving profile characteristics. The integration of experimental and computational approaches facilitates the optimization of process parameters for advanced integrated circuit fabrication.