Photon Emission Microscopy (PEM) Fault Isolation
With the subtle nature of some of today’s complex failures, advanced isolation techniques are critical in determining the best place to inspect for root cause of failure. Depending on the electrical fail signature, different isolation methods should be employed to guarantee that the correct region is being exercised.
Sage Analytical Laboratories Photon Emission Microscopy (PEM) solution is the answer to many variations of early turn-ons, late turn-ons, and electrical shifts.
Photon emission is the leading non-invasive technique used in identifying and pinpointing device level issues, as well as higher level gross fails. Photon emission microscopy works on the principle of mapping active devices. In this case, active is defined as a region where carriers (electrons, holes) are actively recombining in silicon. When carriers recombine, they emit light (a quantized photon) that can be overlain on an optical capture of the die. Not only does this PEM measure location, but a relative magnitude of emission may be interpolated from the results. This allows for in-depth interpretation of operation.
Examples of failures that may be detected or isolated include:
- Devices with shifted characteristics
- Devices with improper junctions
- Circuits that are operational when they should not be
- Circuits that are not operational when they are expected to be
- Over-current damage sites
- Leakage currents
Photon emission signals can be tricky to interpret, which is where experience comes into play. In many cases, the photon emission sites are displaying devices along a net that are being driven differently than expected. In these cases, the emitting devices are not always the devices with defect, but may be tied to a failing device which is causing them to be driven harder, or in an unpredicted manner. By using layout and schematic correlation to trace the likely paths, and FIB isolation in conjunction with the data, very subtle failures can come to light through the use of PEM techniques.