Accelerated Aging and Failure Mechanism Analysis of Thin Tantalum Film R-C Networks

Accelerated stress testing of tantalum thin-film esistor-capacitor networks was conducted to establish a eans of predicting use level failure rates and to determine he major modes of failure associated with the networks also, a rigorous study was made of the physical mechanisms of failure. Accelerated stress tests were performed simultaneously at a number of conditions involving elevated voltage and temperature as well as at use voltage and temperature levels. The relationships between accelerated stress failure rates and actual failure rates were investigated. The resulting modes of failure include: resistance changes and thermal runaway for the resistors, and leakage current increases and dielectric breakdown for the capacitors. Failure mechanism analysis resulted in significant information on the causes of the observed modes of failure. In conjunction with this study, information on the basic structure of sputtered tantalum and anodically formed Ta2O5 was acquired through the use of electron diffraction and electron microscopy techniques. Plots of the rate of interaction of tantalum resistors with various gases were made at elevated temperatures. In air, the reaction rate was found to be parabolic. The effect of substrate ion migration on resesistors was also studied. Ta2O5 dielectric conduction mechanism studies indicated ionic conduction. Several methods for the location of defects in the Ta2O5 capacitor dielectric films were evaluated; the best results were obtained with a copper plating technique. A detailed study of the defective regions indicated that crystallization of the amorphous Ta2O5 is the principal reason for localized defects.