Atomic level control of pattern fidelity during SAC etch

Abstract

Self-aligned contact (SAC) etch has been known to be challenging due to its limited process margin on Si3N4 to SiO2 etch selectivity. Understanding of surface modification during Quasi-ALE using fluorocarbon and Ar plasmas are essential to achieve atomic level control of etch pattern fidelity. In this paper, modeling techniques including first principal study, molecular dynamics simulation, chamber scale plasma simulation and Monte Carlo feature scale modeling have been incorporated to achieve physical demonstration of the Q-ALE process. Our study focuses on how the surface is modified by low energy ions followed by polymer accumulation by fluorocarbon neutrals at adsorption step under various plasma conditions to provide wide range of ion, radical densities with varied ion/radical ratios. Detailed surface evolvement including bonds, elements, structures, densities and depth information will be discussed with atomic level precision. In the Ar plasma desorption step, process dependence on ion energy angle distributions (IEADs) and ion fluxes has also been investigated. XPS surface analysis shows good agreement with modeling predictions. Modeling results and theories have reflected to process developments in next generation etchers with advanced pulsing, broad temperature control and other advanced features. Both blanket film etch rate and in-feature etch data will be discussed to validate the theoretical assumptions based on insights from modeling outputs. State of the art solutions with atomic level control and minimized nitride loss during SAC etch will be presented with in-depth fundamental understanding of correlations between innovative etch chamber designs and surface interactions.