Use in-line AFM to monitor STI profile in 65-nm technology development

Abstract

In the 65nm process development, use traditional top-view SEM and off-line XSEM and TEM to monitor STI profile became insufficient and inefficient. How to find one non-destructive, in-line monitor method to monitor trench depth, step height, and micro-planarity of STI (Shallow Trench Isolation) module profile become more important and challenge than before. In-line AFM just cover this challenge during 65nm process development stage. In this paper, we report how to use in-line Atomic Force Microscope (AFM) technology to monitor STI module profile. Use of this technology on profile step-height and critical dimension in production facilities offers superior precision, accuracy, non-destructive. high throughput and cost effective measurement result. Meanwhile, this paper outlines the implementation of AFM based metrology in an automatic production facility. We focus on the process step just after nitride removed, two key applications on this step, one is to monitor the step height difference and the other is to monitor divot depth at the interfaces height difference between the active area and the isolation area within the STI module. Because the STI step height and divot after oxide fill might dominate the device threshold voltage value(Vt), we check the step height and divot of STI from SiN removed step to the step of thin gate oxide AEI. Then we check and trace where these defect occurred. We also measured 11 points on 300mn wafer to come out one wafer-level topographic chart to monitor its cross-wafer uniformity. Besides, we compared and correlated the AFM measurement result with FA TEM data. It shows good correlation result between X3D AFM and FA TEM. It means this in-line measurement method could efficient act as one important role on advanced STI module process development.