BIAS Humidity Performance and Failure Mechanisms of Non-Hermetic Aluminum SIC'S in an Environment Contaminated with Cl2

Abstract

The aging of aluminum metallized silicon integrated circuit test vehicles (bare, SiN CAPS only, RTV only, SiN CAPS + RTV) at 85°C, 85% RH and 1 ppm C12 for 2664 hours was carried out with either +10V, ?10V, or 0V d.c. 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 an 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 QC3-6650 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 yase use conditions was calculated to be better than 3 × 107 hours. The results show that the failure rate is less than 1 FIT after 20 years.