Accurate detection of interface between SiO2 film and Si substrate

Accurate end point detection of interface for multilayers using focused ion beam (FIB) is important in nanofabrication and IC modification. Real-time end point graph shows sample absorbed current as a function of sputtering time during FIB milling process. It is found that sample absorbed current increases linearly with ion beam current for the same material and changes when ion beam is milling through a different material. Investigation by atomic force microscope (AFM) and FIB cross-sectioning shows that accurate SiO₂/Si interface occurs to where the maximum sample absorbed current occurs. Since sample absorbed current can be real-time monitored in focused ion beam machine, the paper provides a viable and simple method for accurately determining the interface during FIB milling process for widely used SiO₂/Si system.