Process control in plasma decapsulation: Preventing damage to the copper wire bonds & controlled removal of Si3N4 passivation layer

Semiconductor packages with 23 um copper bond wires are decapsulated by an atmospheric pressure Microwave Induced Plasma (MIP). Potential damage to the copper bond wires due to fluorine or oxygen radicals in the plasma is investigated. Parameters like CF4 amount, input power level, and O2 addition that may influence the Si3N4 passivation etching rate are evaluated. Theory behind the changes in Si containing material etching rate due to processing parameter variation is proposed based on the dissociation of CF4 gas in the plasma. SOT 23 packages are decapsulated in 6 minutes by the high radical flux plasma without damage. Real-time imaging of the plasma etching process made controlled removal of the molding compound and the subsequent Si3N4 passivation layer possible. Comparison with acid decapsulation is made and methods to prevent damage on internal components in a semiconductor package during plasma decapsulation are proposed.