Phone: (503) 615-9292 FAX: (503) 615-8903 EMAIL: broesch@qs.com t a d 2 L .e 3 E a -._ 2 Introduction:With few exceptions, the reliability investigations on GaAs circuits over the past two decades have focused on thermally accelerated wearout f a k e mechanisms.Regardless of the measured lifetime, there have been no wearout failures reportd during use of the circuits. Instead, customers do report measurable defect rates and early life failures that often match-up with ykkl fallout failure mechanisms. This study mmtigata a particular defect that not only corresponds with m y of the early life failures, but is also &que to compound semiconductor manufacturing. The defect is generalized as liftoff metal shorting.
Purpose:The intent of this work b to provide information on:I) Classlfyii metal defects,
2)Measuring w h g e effects. and 3) Investigating relationshps between yield and reliability.
History -Bathtub CurveThe reliability of semiconductors has been historically modeled with a traditional "bathtub cunre" [l]. This curve m a p the generic failure rate versus time. Because the faiire rates are highest during the early life and at wearout, the curve suggests three regions of failure rate:Early: This has often been referred to as the "infant" region. The rate b assumed to be caused by defects and constantly decreasing throughout the lifetime of the device. For this discussion we'll name thk the "extrinsic" region. It is the region of specific interest in this study.Random: Thk is the region attributed to a constant f a k e rate. No specif& failure mechanisms have been assochlted with this region, although "defects" have been blamed here as the underlying cause for "random events." Application anomalies, such as overstress or electrostatic damage txe somethnes attributed to this region. In this study, we fmd no evidence that this region exists for normal operation of semiconductors, so we will not include a ''flat bottom" on OUI bathtub. Wearout: This has been the focus of most r e W i studies. Failures are produced under extreme acceleration conditionsprimarily driven by temperature. Failure r a t a increase constantly throughout the useful life of the distribution, and then drop off after the populatim is depleted. In this study, wearont faikne distriiutions are apparent under accelerated condilions, and they are 0-7908-0105-1/00/$0.00 2004 JEDEC Eaw Random weavut Extrinsic shnilar to traditional capacitor Wetest results. Thk coukl be an important region to consider, but wearout is not seen within the expected useful life of an electronic device or even within a human lifehe.Figure 1. An Empirical Bathtub Curve. Each of the batbtub regions contain mdple failure mechanisms and their assockted f a k e distributions.For example, the wearout region would typiCaUy mctude diffusion, electromigratbn, t h d excursion fatigue, corrosion, or dielectric breakdown failure mechanbms. The extrinsic region might contain all the same mechanisms, but under the influence of various defects. Detection of enough defects could produ...