edfas.org 21 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 4 interchange between up to three different and customizable probe tips. The RPM-3D has a custom-built insulating clip cassette that allows for easy interchange between probe types, ensuring that the optimized probe tip is used for each tier of a slice-and-sense tomographic data set (Fig. 1b-d). Paired with the self-adjusting capability of removal rate (RR) by dynamically varying load force, every single scan improves the quality and speed of data acquisition, automation, high dimensional data handling, and extended volumetric sensitivity (range 102 to 106 nm3) offering volumetric mapping of electrical properties in the area of interest. Three desirable properties of the RPM-3D are compared to the other industry standard tomographic characterization techniques in the table (Fig. 1e). THE SETUP FOR MULTI-PROBE SENSING The RPM-3D has been designed to allow for a fully automated switching and alignment routine, capable of switching, aligning, and compensating for any tip-to-tip variation to en- sure that the landing accuracy and coalignment is ≤ 0.3 µm (Fig. 2a). This is essential for the probe switching capability to ensure localization between a scalpel and sensing component. An initialization step for the alignment of the three probes is performed using a calibration sample as in Fig. 2a. Here, we land each probe on the same location of a densely patterned surface, thus allowing for the compensation of any initial offset between the position of the apex of the three probes. Once aligned, a minimum drift in-between continuous probe switching and re-landing that is estimated to be 200 nm is observed, as measured over hundreds of scans. At the foundation of scalpel scanning probe microscopy (SPM) lies the possibility to control the atomically precise material removal induced by a sliding diamond tip. Previous works have shown the material removal capability for scalpel SPM ranging from 0.5 to 10 nm/scan,[5,6] similar to reports for the RPM-3D material removal in range 3 to 10 nm/ scan. Previous work demonstrated the capability of the multi-probe tool to perform a simple flow “scalpel-switchsense” for the self-extraction of the removal rate using two tips loaded into the custom cassette. As an example, diamond and high-aspect ratio silicon probe have been alternated to remove material and sense the morphology, thus monitoring the material removal process. The Fig. 2 (a) Calibration sample measured with each probe for the alignment of each tip apex, probe switching, and landing executed with a ±0.3 µm accuracy. (b) Schematic view of the block diagram used in the control of RR during multiple read-out scans used in the Scalpel SPM. Note, the RPM-3D can be used to automate the depth sensing process, by alternating machining and sensing with probes switching. The tool can automatically modify the load force to maintain a con- stant RR. (b) (a)
RkJQdWJsaXNoZXIy MTMyMzg5NA==