A focused ion beam uses a precisely controlled stream of charged particles, similar to an electron microscope, to generate an image; unlike the electron microscope, however, the FIB uses a stream of gallium ions, which can also be used to ballistically etch material away from the surface of a device. Since this beam can be targeted so accurately (in some cases, within several nanometers), the site of a defect can be exposed without any disruption of the surrounding circuit. As a result, FIB failure analysis can often be performed more quickly and efficiently than through other methods.
The inherent precision of the FIB also lends itself to performing “micro-surgery” on failing products, rewiring the device to allow minor changes to a device to examine effects on the overall device functionality. In many cases, the first production run of a given product (often referred to as “first silicon”) will have performance issues arising from disconnects between modeling, simulation, and the real-world physics of the device. Editing the design and making a new set of masks is often the only fix; however, the price of a new mask set can be exorbitant, especially considering that the new set of masks will often be nothing more than a test of a designer’s best calculation of the needed change. Before shelling out the tens and hundreds of thousands of dollars for new masks, it is often prudent to take a handful of failing samples to the FIB, where traces can be cut and rewired by patterning conductive traces (usually made of tungsten or platinum) on the device. This allows for a quick, easy, and (most importantly) inexpensive test of any proposed design edits.
Of course, the FIB has many applications beyond FIB failure analysis. A FIB can be used to perform quick cross-sections of a device where the area of interest is relatively small; it can also be used to prepare samples for transmission electron microscopy, which requires extremely thin samples (less than 100 nanometers in many cases) to produce meaningful data.