Finding Integrated Circuit Defects on GaAs – The III-V Challenge
Generally speaking, most discussion of electronics failure analysis is geared towards finding silicon-based integrated circuit defects. The reason for this is fairly straightforward; silicon is, by far, the most prevalent semiconductor used to create modern electronics, and therefore has the lion’s share of defects associated with it. In some cases, however, silicon circuits are simply insufficient for a given application – especially when extremely high frequency applications are considered. In these cases, it is much more common to use a III-V semiconductor like gallium arsenide (usually referred to as GaAs). Though the high frequency performance of III-V devices may be much greater than their silicon counterparts, their unique construction poses some difficult challenges for a failure analyst hoping to dig into their inner workings.
One of the most important steps in finding any integrated circuit defect after a device has been packaged is decapsulation – the removal of the plastic mold compound from around the die. When the semiconductor die is made of silicon, this process is relatively straightforward – certain acids will dissolve the plastic quickly and efficiently. Using the same acid on a GaAs (or many other III-V) die, however, would end in catastrophe; an inexperienced analyst attempting this type of decapsulation for the first time may end up in a frantic, bewildered state, wondering why the failing die vanished into thin air! Indeed, GaAs and other III-V materials do not stand up well to the acids traditionally used in decapsulation; it is only with specially formulated acid blends, developed through experimentation, that a successful decap can be achieved.
Even once the decapsulation has been successfully accomplished, rooting out an integrated circuit defect on GaAs is still challenging. Electrical test results can be confusing; since most GaAs devices operate in the RF domain, there are often passive filters used to shape the frequency response of the device that, under DC testing, look like short-circuits. As a result, it is often necessary to perform destructive analysis, bypassing the inductive elements by cutting them out of the circuit before performing any in-depth DC comparisons. Fortunately, the construction of most III-V devices is conducive to this sort of microsurgery; circuit density on GaAs is very low, with many parts being comprised of only a handful of circuit elements.
Even though silicon dominates the market, the unique capabilities of GaAs and its derivatives make it indispensible in many applications – especially telecommunications. Though they may fit only into a small niche, it is imperative that these devices are robust and reliable; enlisting the help of an experienced failure analysis team to root out any integrated circuit defects on GaAs devices is one way to help ensure that these devices meet the strict performance demands of the contemporary market.
Derek Snider is a failure analyst at Insight Analytical Labs, where he has worked since 2004. He is currently an undergraduate student at the University of Colorado, Colorado Springs, where he is pursuing a Bachelors of Science degree in Electrical Engineering.