Process Improvement for CF4/02 Microwave Plasma Decapsulation on Cu-Ag Bonding Metallurgy System

CF4/O2 microwave plasma widely used as an alternative method for mold compound decapsulation on copper wire technology devices as it has the capability to preserve wire surface and wire mechanical strength. However, some drawbacks with copper-silver bonding metallurgy system where plasma byproducts (F and O) react with copper (Cu), silver (Ag) and silicon (Si) when exposed to moist air producing undesired compound (AgCuF3, Cu
₂
O, and SiO
₂
) which accumulated at wedge surface that disrupted the inspection process. This reaction occurred right after taking out from microwave plasma chamber. These undesired compound formations led to wire strength degradation and resulting low wedge pull force. Therefore, prevention methods are introduced by using Ultra-High Vacuum (UHV) that able to prevent chemical reaction between plasma by-products with moist air. In addition, laser ablation able to permanently stop all the reactions. SEM inspection on wire surface after the decapped sample treatment in UHV chamber confirmed the absence of undesired compound formation and mechanical wire test shows consistent and repeatable wedge pull force results. This method is proven to provide genuine results in wire inspection analysis as well as mechanical wire test data without any influence by artifact from sample preparation process.