A combination of layout improvements and inner layer dielectric (ILD)
material improvements provides a bond pad stack that is robust for both
gold (Au) and copper (Cu) wires in circuits with only one or two pad
metal layers. The layout improvements involve removing all vias between
the top metal layer and the metal layers below top metal in the area
under the passivation opening (where probe tips and the bond wire are
placed). This allows for a more homogenous material without via
discontinuities, thereby reducing stress concentration points in the ILD.
The ILD material improvement involves adding a layer of silicon nitride
in addition to the silicon oxide layer. Traditionally, the ILD consists
of either spun-on or high density plasma (HDP) oxides. The growth of the
thin layer of silicon nitride over the oxide on the topmost ILD layer
provides a composite of significantly increased toughness and prevents
cracks or other damage from propagating into the underlying active
circuits and routing.