Single mask stress buffer

Large die such as SRAMs and DRAMs are subject to significant stress resulting from thermal expansion mismatch of the die and packaging materials. The use of polymers as stress buffering media has been widely practiced to increase the reliability of these devices. Many of these devices require that small windows (⩽10 μm) be opened up in the polymer over “fuse links” which are used to reroute or reconfigure inactive circuits. The need for tighter resolution in the stress buffering layer, as well as the desire for shorter process cycle times, has moved the industry from wet etch to photosensitive materials. Photosensitive BCB (Cyclotene) has been widely reported for use as a dielectric in numerous advanced packaging applications. A one mask photo-BCB stress buffer process has also been reported for opening up bond pads and fuse links in underlying SiN die passivation. Traditional passivation/stress buffer processing has required masking and dry etching of the SST followed by coating and patterning of the polymer dielectric (two mask process). The reduction in processing steps and processing time using the one mask BCB process can significantly lower the cost of ownership for passivation/stress buffer layers