Failure Analysis of Discolored Bondpads in Wafer Fabrication

Abstract

Discolored bondpads & non-stick failure in 0.6 μm wafer fab process with the hot Al alloy metallization was investigated. SEM, EDX & AES techniques were used to identify the root causes. Failure analysis results showed that discolored bondpads & non-stick failure were caused by TiN residue introduced during L95 bondpad opening wafer fab process. TiN residue on bondpad might have led to non-stick bondpad issue. The results also showed that it was difficult to determine the trace amount of TiN residue on bondpad using EDX technique due to its limitations. In this work, Auger surface analysis technique was used to determine TiN residue on bondpads with Al/TiW/Ti metallization. Auger results showed that Ti & N peaks were detected on discolored bondpads. It has resulted in non-stick bondpad failure. The solution to eliminate TiN residue on bondpads was to increase etch time at L95 bondpad opening wafer fab process. After using the new recipe with longer etch time, Auger results on the bondpads showed that no Ti & N peaks were detected and the bond-pull testing also passed.

Impact of the Volatile Acid Contaminants on Copper Interconnects Electrical Performances

“…The control of volatile acids in the environment of metallic interconnects or bond pads is a major concern of IC manufacturing. Indeed, defectivity due to corrosion issues or crystal growth phenomena (1,2,3) are often related to these species and to their great ability to be deposited on Cu or Al surfaces (4). The contamination can happen directly from ambient air or indirectly by cross-contamination from FOUP outgassing (5).…”