November_EDFA_Digital

edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 4 22 FASTER AND MORE ACCURATE FAILURE ANALYSIS: CIRCUIT EDITING AND SHORT LOCALIZATION PERFORMED AT SAME FIB TILT ANGLE USING MULTIPLE TECHNIQUES William Courbat, Imina Technologies SA, Switzerland Jörg Jatzkowski, Fraunhofer IMWS, Germany courbat@imina.ch EDFAAO (2019) 4:22-28 1537-0755/$19.00 ©ASM International ® INTRODUCTION In the field of semiconductor failure analysis (FA), choosing the best investigation technique for the particu- lar application depends on the allocated time per analysis and the level of accuracy thatmust be achieved. [1] A recent trend aimed at optimizing these two variables involves combining the use of different tools and techniques to acquiremore accurate data at a faster rate. As an example, passive voltage contrast (PVC) was often used by itself to determine opens and shorts in a circuit, but is now being replaced by a combination of nanoprobing and electron beam absorbed current (EBAC) measurements. [2] In this technique, twoprobes areplaced, oneona local signal line and the other at the ground of the sample. These probes collect the charges generated by the electron beam and absorbed by the sample. If the probe on the local metal line is the least resistive path for the charges absorbed at a defined area of the sample, then the corresponding area will appear bright on the image. However, if there is no direct path to the metal line probe, the charges will sink to the ground probe, causing the corresponding area to appear dark on the image. This allows the user to determine with high accuracy which lines of a circuit are connected to eachother,making this combined technique an indispensable tool todetect shorts andopens onother- wise difficult to analyze circuits. [3] Another important tool in FA investigations is the focused ion beam (FIB), as it has become the standard tool to artificially create opens and shorts in a circuit as well as to prepare transmission elec- tronmicroscope (TEM) lamellas. [4] However, most FIBuses are performed under a stage tilt angle of 50-54°, which corresponds to the positionwhere the ions are hitting the sample surface perpendicularly. Therefore, the probing system must comply with the tilting requirements of the stage and bring the sample to a working distance (WD) of 5 mm, which is the usual coincidence point between the electron beam and the ion beam (Fig. 1). This needs to be accomplished without causing colli- sions between the probing system and the FIB, the pole piece, or any other detectors/parts in the chamber. A workflow combining nanoprobing, EBAC, and FIB will undeniably benefit the semiconductor FA community as it allows greater accuracy and flexibility compared to apply- ing each of these techniques independently. However, the Fig. 1 Schematic of the nanoprobing platform tilted to FIB position. It must be raised such that the sample is at the coincidence point of the electron and the focused ion beams.