The probe marker discoloration on Al pad and wafer storage

Abstract

In this report, a novel probe marker discoloration corrosion on Al pad, with donut/circle shape, was found. This probe marker discoloration corrosion was found at the stage of blue tape. Back to check the wafer process, no clear corrosion was found before CP probing test. In order to identify the microstructure & components of this probe marker discoloration corrosion, SEM/EDS, TEM/EELS & AES analysis were applied. These structure & surface analysis results indicated this discoloration is a combination of Aluminum, Fluorine and Oxygen. No Fluoride was detected on the normal region of Al pad. All these results implied the role of fluorine element to induce this probe marker discoloration corrosion. The source of F element is critical in this case, so the testing and storage conditions would be supposed to be important for the formation of probe marker discoloration corrosion. The HAST testing with condition of temperature 130°C and RH 85% for 21 hours, all the chip samples were simulated to have been exposed in air without N2 cabinet storage or MBB bag storage for 1 year. This HAST test result showed none of exhibition of discoloration or existed discoloration chips being deteriorated. Another storage test based on regular full wafer FOSB storage showed existed discoloration chips being deteriorated. This FOSB storage test indicated the source of corrosive F element maybe come from wafer itself. The EDS element mapping data indicated the F element enriched Al pad on wafer extreme edge area was clearly identified. The source of F element was found. And the storage of processed wafer would play a key role in the formation of discoloration corrosion.