Digital Forensic Atomic Force Microscopy of Semiconductor Memory Arrays

Abstract

Atomic force microscopy is an analytical technique that provides very high spatial resolution with independent measurements of surface topography and electrical properties. This chapter assesses the potential for atomic force microscopy to read data stored as local charges in the cells of memory chips, with an emphasis on simple sample preparation ("delidding") and imaging of the topsides of chip structures, thereby avoiding complex and destructive techniques such as backside etching and polishing. Atomic force microscopy measurements of a vintage EPROM chip demonstrate that imaging is possible even when sample cleanliness, stability and topographical roughness are decidedly suboptimal. As feature sizes slip below the resolution limits of optical microscopy, atomic force microscopy offers a promising route for functional characterization of semiconductor memory structures in RAM chips, microprocessors and cryptographic hardware.

High resolution front-side visualization of charge stored in EEPROM with scanning nonlinear dielectric microscopy (SNDM)

“…Various characterization techniques have been proven effective in direct memory data retrieval, including scanning capacitance microscopy (SCM) [5,6], scanning Kelvin probe microscopy (SKPM) [7] and scanning electron microscopy (SEM) [8,9]. However, for techniques like SCM and SKPM that are not significantly disturb the charges in the floating gate so that the data remains unchanged after scanning, no structural details of memory cells have been reported due to their limited resolution, which cast doubts over confidence of accurate data assignment for obtained signals [10]. The more recently explored technique of SEM relies on the interaction between high-energy electron beams and electrons within the floating gates, rendering it a rather destructive technique as data is lost during multiple scans [8,9].…”