MechE PhD Prospectus Defense : Yiding Zhong

TITLE: UNDERSTANDING AND CONTROLLING WET ETCHING REACTIONS IN NANOCONFINEMENTS

ABSTRACT: As modern semiconductor devices continue to decrease in size, achieving ever more precise fabrication standards becomes paramount. The on-going semiconductor industry’s shift from traditional planar architectures to sophisticated three-dimensional structures like FinFETs and 3-D NAND have substantially increased the complexity of manufacturing processes. Among these processes, wet etching played a crucial role as it offers a cost-effective and less complex alternative for isotropic material removal. However, the ever-decreasing critical dimensions in 3-D semiconductor devices and the resulting nanoscale solid-liquid interactions during the wet etching processes brings new challenges to wet etching, such as distinct reaction kinetics and altered transport dynamics, which can severely impact the reaction rates and rate uniformity. Addressing these issues requires a deep dive into the etching reaction kinetics and transport phenomena specific to nanoconfined spaces—where the behavior of etching agents can differ significantly from bulk processes. Pioneering studies have provided insights into these phenomena, yet a comprehensive understanding remains elusive, especially in how these processes scale down to the increasingly minute dimensions required by current semiconductor technologies. By integrating experimental research with theoretical models, this thesis will explore the fundamental aspects of wet etching in nanochannels, aiming to understand effects of various nanoscale interactions on the change of etching kinetics and to develop methods that improve the rate uniformity. This thesis is divided into three sections, each of which focuses on a fundamental challenge faced by both the scientific community and the semiconductor industry. In the first section, we report on the systematic study on wet etching kinetics of 2-D amorphous-Si-filled nanochannels in KOH etchant solution and discuss on the underlying factors that affect the nanoconfined etching kinetics. In the second section, we aim to quantify the nanoconfinement effects by presenting the wet etching kinetics of 2-D SiO2-filled nanochannels in diluted hydrofluoric acid (dHF) etchant solution. In the third section, we propose to answer the ultimate question of tuning wet etching uniformity in nanochannels. We plan to develop a methodology to fully achieve uniform etching rates by the means of etchant additive. We also aim to fully investigate on the mechanisms behind the uniform etching rate in nanochannels. Overall, this thesis sets the stage for a detailed examination of specific nanoconfinement effects on kinetics of nanoconfined wet etching and proposes solutions to overcome the associated challenges in next-generation semiconductor manufacturing.

COMMITTEE: ADVISOR/CHAIR Professor Chuanhua Duan, ME/MSE; Professor Xin Zhang, ME/ECE/BME/MSE; Professor Scott Bunch, ME/MSE; Professor Jörg Werner, ME/MSE