Reduction of Aluminum Fluoride Formation during Fluorinated Plasma Etching of Dielectric Passivation Layer over Aluminum Pad

The patterning of the dielectric layer over Aluminium (Al) bond pads is one of the critical processes in fabricating wafer-level packaging. Due to selectivity requirements, dielectric etching over the Al pad requires Fluorine plasma to minimize the loss of Aluminum thickness during the process. Dielectric etching requires a high physical etch component, usually achieved through high RIE power and low pressure. If this high physical etch component is maintained until the entire oxide thickness clears, Al likely to be sputtered away during the over-etching, which results in an excessive amount of Aluminum Fluoride (AlF 3 ) formed. The incomplete removal of the AlF 3 layer during the post-etch treatment contributes to significant device contact resistance. Moreover, the formation of AlF 3 during the process poses potential productivity issues such as process shift and particle contamination, resulting in lower wafer yield and more extended equipment downtime. This work focuses on a process optimization methodology to minimize the AlF 3 formation during fluorine-based dry etching, thereby reducing the burden on the subsequent wet cleaning. Process conditions are selected in such a way that the sputtering yield of Aluminum is the least, while the oxide etch rate is sufficient to clear oxide. Our process strategy is to target the etching of 85% of the oxide film using a higher physical etch component such as higher RIE power and low pressure, and then applying a lower physical component of etching at a much-reduced RIE power to etch the remaining 15% of the oxide layer. Experimental data show that a 70% reduction in RIE power during the soft etch step minimizes the AlF 3 residue formation. A subsequent short wet clean, a commercially available post-etch residue cleaner (NE14) for 30 seconds, is sufficient to remove the remaining AlF 3 from the Aluminium profile sidewalls.