Practical Electron Microscopy and Database

In IC devices, fluorine corrosion can be induced by F contamination as some F-based chemical gases and materials such as CF₄, CHF₃, SF₆, HF, BOE (NH₄F + HF) etc are used in microelectronics wafer fab. On the other hand, wafer shipment package foam materials may also cause the F contamination and corrosion.

For instance, it is well-known that fluorine will often be detected near the surface of bondpads. This is because CF₄ gas is used during bondpad opening fab process. Fluorine slightly reacts with Al and forms [AlF_x]^(x-3)- (e.g. [AlF₆]^3-) or compounds Al_xF_yO_z on the surface of bondpads. Unfortunately, these compounds cannot be cleaned away fully by EKC & DI water cleaning processes. Therefore, it is normal that some percentage of fluorine is detected on bondpads.

Table 2437. Bond-pad contamination in IC devices.

Figure 2437 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] Y. N. Hua, S. Redkar, C. K. Lau, “A Study on Non- Stick Aluminium Bondpads due to Fluorine Contamination using SEM, EDX, TEM, IC, Auger, XPS and TOF-SIMS Techniques,” Proceedings from the 28th International Symposium for Testing and Failure Analysis, Phoenix, Arizona, November, 2002, pp. 495-504.
[2] 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.