Effects of Humidity and Organic Coating on Surface Potential Propagation in Passivated Devices

Abstract

Potential propagation over the surface of hermetically sealed or plastic coated semiconductor products may produce failure. A special test structure has been used to characterize the rate of propagation as a function of a number of parameters: humidity, temperature and selected organic coatings. A surface memory effect associated with exposures to humid ambients is discussed. This effect may explain in part the surprisingly wide range of surface instability observed in units hermetically sealed using state-of-the-art packaging techniques. Organic coatings, e.g. silicone varnish, reduce the influence of humidity at temperatures below 90°C. Arrhenius plots obtained in detailed studies at high temperatures allow estimation of stability performance in the 150'C to 200°C range as a function of material composition and curing time.

An Effect of Organic Electron Donors and Acceptors on a Real Silicon Surface

“…The conductivity value for benzene (,-~10-~ mho cm -1) is large enough to support the propagation of drain potential over the silicon surface, but is too low to be observed directly in terms of source-drain leakage. Such propagation, supported by low conductivity of a solid organic dielectric material at elevated temperatures, is well established (10). This model is also consistent with the observed increase of conduction with drain bias (with a time lag of 1-2 sec).…”

Water Absorption and Densification of Phosphosilicate Glass Films

“…The PSG film, which is generally deposited using chemical vapor deposition, is porous and active for water absorption. It has long been known that water absorption adversely affects electrical characteristics of devices (1)(2)(3)(4), and accelerates corrosion of aluminum metallization (5)(6)(7). Water adsorption in PSG films also reduces adherence of photoresist on the oxide (8,9).…”

“…Presumably HF would also etch Si at high temperatures. Indeed, a glass flat has been patterned by blowing HF onto its surface while locally heating to 600~ with a COs laser (5).…”

Passivation Coatings on Silicon Devices

“…Various test devices and accelerated testing te,chniques have been developed for evaluating the stability of passivated devices under severe environmental conditions (314,256,238,257). For plastic-encapsulated devices, a moisture-containing ambient constitutes an effective means for accelerating ion migration effects or chemical or galvanic corrosion of the metallization pattern on the chip (182,28,237,33,7,90,256,121,29,238,229,291,236,257,189,23,166,176,177).…”