Evaluation of chip passivation and coatings using special purpose assembly test chips and porous silicon moisture detectors

Two devices which can be used to evaluate the ability of chip passivation or postbond coatings to protect a Si device from moisture penetration and resultant Al corrosion are described. The first device is a test chip with a number of Al triple track and other corrosion measurement structures. The authors present HAST (highly accelerated stress test) data to illustrate the use of this chip in measuring failure rates and determining failure modes. The second device is a rugged, moisture-sensitive porous Si capacitor, which is compatible with high-temperature passivation and postbond IC processing. Data are presented showing the stability of the device relative to that of an anodized Al moisture sensor and showing the variation of capacitance with moisture level. Data are also presented showing that the capacitor can respond to a point source of water located over the porous region but remotely from the top electrode