PECVD silicon and nitride postbond films for protecting bondpads, bonds and bondwires from corrosion failure

It was demonstrated experimentally that the ultimate strain of PECVD thin-film silicon nitride coatings increased as the films were made thinner, giving them better mechanical properties for protecting underlying bulk Al structures such as bondwires, bond, and bondpads. In sections of under a micron, the films did not crack over Al bonds or bondwires during standard industrial temperature cycling. Temperature ramping tests indicated that 1000-A films had at least three times the ultimate strain expected from bulk values. Film thickness was consistent around bondwires and in the vicinity of the bonds from the plasma deposition. The most susceptible part of the films was the area in the occluded cavity under the foot of the bond. The spread of Al metallization corrosion under these films proceeded at a slower rate than the thinner films due to their more favorable mechanical properties. The results of this project indicate that PECVD silicon nitride films are good candidates as protective films for mounted and bonded microelectronic or hybrid devices and have the potential of outperforming polymeric films by a wide margin.<
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