The Probe Mark Discoloration on Bond Pad and Wafer Storage

Abstract

In this report, a probe mark discoloration with donut/circle shape was found. The corrosion formed on Aluminum bond pads. The SEM/EDS, TEM/EELS & AES surface techniques were used to identify this corrosion product. All these material analysis results pointed out the role of fluorine to this discoloration. The HAST testing, all the chip samples obtained from wafer center/middle area, were simulated to have been exposed in air for 1 year. HAST test result showed no fluorine source came from the center/middle zones of impact wafers. Another full wafer-level FOSB storage test showed the source of corrosive fluorine came from wafer itself. EDS mapping results, from extreme wafer edge zone, indicated the fluorine element distribution. The mechanism of this novel discoloration was proposed. However, more evidences were necessary for understanding the formation of donut discoloration corrosion.