November_EDFA_Digital

edfas.org 23 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 4 turnaround time allocated for analysis must remain as short as possible. Oneway toachieve this is toalign thedif- ferent tools once and performall requiredmeasurements within that alignment. This means bringing the sample under 5 mm WD at a tilt of 54° and using both the nano- probing system and EBAC in this configuration. The nanoprobing systemmust therefore be able tomove and land probes while the microscope stage is at the FIB tilt position. This articledescribes anewworkflowapproach— capable of such performance—that was applied to two typical FA and circuit editing use cases. The first one is a controlled gas injection system(GIS)-assisted FIB induced deposition of a pull-up resistor between two networks. The second use case is an investigation of the localization of a short between two metal layers using EBAC and FIB metal line cutting. EQUIPMENT A FIB-SEM microscope equipped with a GIS from Carl Zeiss AG was used in this experiment. A nanoprobing solution from Imina Technologies SA was installed on the motorized sample stage and electrically connected through a port of the chamber with a custom flange. Two probesweremounted on one side of the platformto allow for easy tilting in the oppositedirectionof their placement. The probers move freely over the platform and stick to it with a small magnet enclosed under their housing. These magnets are strong enough to allow the probers to climb the 54° slope imposed by the FIB tilt position, but are located far enough from the beams to not disturb them in any way. The needles aremounted on the probers such that the roof of the probers is on the same plane as the needles when the prober arm is horizontal (Fig. 2). This configuration allows imaging at short WD (5 mm in this case, but as low as 2 mm for other applications) when tilted by avoiding collisions between the probing system and the pole piece of the microscope. Outside of the microscope chamber, the semiconductor parametric analyzer from Tektronix Inc. and the EBAC system from Point Electronic GmbH were electrically connected to the probes through the flange feedthrough connectors, respectively, for case studies 1 and 2. FA AND CIRCUIT EDITING CASE STUDIES CASE #1: PULL-UP RESISTOR DEPOSITION In some cases of circuit editing, a reference voltage may be required at a specific node of an application- specific integrated circuit (ASIC) sensor. For this, a pull-up resistor of 1 kOhm can be deposited between two dis- tinct networks. The deposition process consists of using the GIS to inject a precursor gas that is decomposed at the surface by an external energy source. Either the electron beam or the FIB can be used for that purpose, although the FIB provides faster deposition rates. The process described in this case study is divided into threemain steps: 1) deposi- tion of the resistor terminal pads connected to the two networks; 2) deposition of a baseline resistor using the electron beam; and 3) deposition of the resistor with the FIB while monitoring its value in real time. To gain access to the networks, the FIB was first used to remove the passivation layer at the locations where the resistor terminalswouldbeplaced. Twomicron-sizedpads were then deposited at these locations to ensure good contactwithbothnetworks andprovide convenient access to the resistor terminals during deposition. A thin layer of platinum was deposited between the two freshly created pads using the electron beam (Fig. 3). Fig. 2 Imina nanoprobing platform (miBot) mounted in the Zeiss Auriga. Left: tilted at 54° with the two probers at the lowest position to avoid collision. Right: with the probes in the same plane as the prober’s roof to allowshort working distances (5 mm).