Understanding Semiconductor Failure Modes
In order to successfully characterize, isolate, and eventually uncover a defect on a semiconductor device, it is necessary to begin with a basic understanding of the problem at hand. A basic description of the failure – for example, “output pin stuck high” or “device draws excessive power” – can go a long way towards helping an analyst formulate a plan for tackling a defective part. Once this basic semiconductor failure mode has been identified, the proper tools and procedures can be chosen to locate even the most miniscule of defects.
Given that the failure mode of a semiconductor device is, at best, a description of a defective part’s errant behavior, it is not always an explicit indicator of the type of defect an analyst is looking for. To build upon the previous example of a part with its “output pin stuck high” (usually meaning that the output pin voltage level is roughly equal to the positive voltage supply), the actual failure mechanism could be an open circuit on an input pin, a leakage path between the output pin and the positive voltage supply, or even a more complex functional failure that will require a deep dive into the circuit to locate. In this case, an analyst must first develop a hypothesis about the most likely cause of failure based on the provided failure mode, any history or other background information they may have about the defective part, and their own past experience. The analyst must then test their hypothesis using whatever bench equipment is necessary, proceeding to more destructive tests only once a reasonable level of proof has been established for a given theory.
Of course, not all failure modes are as complex as the previous example, and years of experience will allow an analyst to translate a vague failure mode description into a fairly good guess as to the type of defect plaguing the device. Devices drawing excessive power, for instance, are almost always due to some sort of short-circuiting or leakage; in these cases, an analyst can rely on tools that detect the excess heat, like thermal imaging or liquid crystal, in order to isolate the defect. Similarly, if the failure mode of a device includes the word “intermittent”, there is a very good chance that the device is afflicted with an open circuit that may still appear functional depending on temperature, device orientation, and other external factors; here, an analyst may choose to study the part with an acoustic microscope to look for package delamination, or to subject the part to thermal stress in order to try and exacerbate the failure.
The first step to any successful analysis is understanding the failure mode of the semiconductor device. With this understanding, an analyst can begin to formulate their ideas about a defect, and choose the proper approach to prove their theory true.
Derek Snider has been an employee at Insight Analytical Labs since 2004, where he currently works as a Failure Analyst. He is an undergraduate student at the University of Colorado, Colorado Springs, where he is pursuing a Bachelors of Science degree in Electrical Engineering.