Reliable Cu Pillar Undercut Control Using the Endpoint Detection System

This paper addresses the key challenges of copper (Cu) undercut control using the end point detection (EPD) system based on the Applied Materials Raider tool. The Cu etch rate was measured with the timed etch to validate the end point detection on blanket wafers. The end point traces were then collected on C4 pillars under 0, 25, 50, and 100% over etch conditions. C4 pillars undercut amounts were measured using Focused Ion Beam Scanning Electron Microscopy (FIB-SEM). The ability to detect the endpoint (EP) and stop at a defined over etch (OE) from the end point was demonstrated. Based on FIB-SEM and Energy dispersive X-ray (EDX), we have developed an endpoint recipe with minimal undercut.