Failure Analysis of NSOP Problem Due to Al Fluoride Oxide on Microchip Al Bondpads

A NSOP due to Al fluoride oxide case was investigated. The NSOP problem on microchip Al bondpads was reported. SEM, EDX, TEM and Auger FA techniques were used to identify the root cause. Optical inspection did not show any abnormality, however, high magnification SEM inspection found the "white dot"-like defects. TEM and Auger analysis results showed that a thicker oxide layer on bondpads, which was about 200-300 A. After studies on failure mechanism, it was concluded that the thicker layer detected by TEM was not Al oxide layer (Al₂O₃), but it was Al fluoride oxide-Al_xO_yF_z which was due to F contamination during polyimide ashing process. In this paper we will further discuss the failure mechanism proposed and explain the formation of the Al fluoride oxide-Al_xO_yF_z. In this paper, the possible root cause and eliminating solution are also studied. After changing a new dedicated ashing process machine, the F contamination was eliminated.