Cu Pad Metrology Using Four-Directional BSE Signal of SEM for Hybrid Bonding Applications

Abstract

We propose two SEM‑based indices—(i) a brightness index for fast defect and deep recess measurement using the fourdirectional BSE (backscattered electron) signal average with size‑dependent calibration model, and (ii) a height index calculated by integrating opposing‑detector differences across each pad to quantify Cu‑pad recess in hybrid bonding. Correlating the brightness index with TEM‑measured recess on 200‑nm pads and introducing the size‑dependent calibration model enabled reliable, size‑consistent recess estimation without per‑size recalibration. Comparisons of the height index with AFM confirmed sensitivity down to 110‑nm pads. Top‑view SEM thus provides high‑throughput, sub‑nm‑precision height metrology while preserving inline practicality.