Bias Humidity Performance and Failure Mechanisms of Nonhermetic Aluminum SIC's in an Enviornment Contaminated with Cl2

The aging of aluminum metallized silicon integrated circuit (SIC) test vehicles (bare, SiN CAPS only, room temperature vulcanizing (RTV) silicone rubber only, SiN CAPS + RTV) at 85°C, 85 percent relative humidity and 1 ppm CI2 for 2664 h was carried out with either + 10 V, -l0 V, or 0 Vdc bias imposed on the samples. The leakage currents for the encapsulated samples increased slowly over long periods of time in chlorine. Failures were observed in the unencapsulated groups. Subsequent to environmental stressing, specimens were examined using an optical microscope and a scanning electron microscope (SEM) with X-ray capability. No corrosion was observed on the encapsulated samples. The main failure mode of the unencapsulated samples showed corrosive growths containing Al and Cl on the metal tracks. The corrosion was observed to initiate at the Au-Al interconnect on both anodically and cathodically biased bond pads. There were more failures at the anodic electrode. The application of bias is not necessary for corrosion but does increase the failure rate. It is concluded that Dow Corning QC3-6550 RTV silicone rubber is an effective encapsulant in a moist chlorine environment preventing corrosive attack. SiN CAPS are ineffective as sole protection because bond pads remain exposed. A mechanism for corrosion is discussed. It involves the acceleration of the corrosion by the galvanic couple formed at the Au-Al interconnect. An estimate of the median life of the encapsulated samples under worst case use conditions was calculated to be better than 3 x 10
⁷
h. The results show that the failure rate is less than 1 FIT (failure in 10
⁹
device hours) after 20 years. This was obtained by assuming the same acceleration factors as obtained in previous work on encapsulated aluminum.