Defect Reduction in Through Wafer Via Photolithography Processing
As customer requirements reduce the maximum product defects allowed to less than one part-per-million, identifying the source of the occasional defect during wafer processing becomes more challenging. We observed a defect on wafers we call “via rings”. This defect occurs when the street photoresist does not sufficiently protect the plated gold film at the top edge of the through wafer vias during the street etch process. This paper discusses the use of an additional step during the street resist coat process to ensure that the resist properly protects the edges of the vias during the etch process.