This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Figure2428 shows an example of C, O, and Si contaminated bond pads. Area S6 had an abnormal film on the native Al oxide, while area S5 presented nonhomogeneous, loose and empty Si_xAl_yC_zO_m materials in the hemispherical defect.  These pad defects existed only at wafer edge because backside grinding was the root cause of the contamination.

[1] Paul Yu, Jamie Su, Qiang Gao, Ming Li, Chorng Niou, Study of Aluminum Pad Contamination Sources during Wafer Fabrication, Shipping, Storage and Assembly, International Symposium on High Density packaging and Microsystem Integration, 2007. HDP '07.