Selective Staining on Non-Volatile Memory Cells for Data Retrieval

Abstract

A new data retrieval approach utilizing selective staining is explored to differentiate "0" from "1" cells in EEPROM and Flash memory cells with node size of 40 nm and 250 nm. A two-step staining process based on selective oxide etching and copper galvanic displacement deposition is introduced. The underlying mechanism is attributed to the difference in electric field across the tunnel oxide, which originates from the presence or absence of charges stored in the floating gates. With proper sample preparation, the selectively stained and non-stained cells can be characterized with optical microscopy and scanning electron microscopy, to facilitate direct read-out of data in a timeefficient manner. The physical layout of individual memory cells with respect to the stored data is identified. A systematic data retrieval is achieved with an accuracy of 95% at individual bit level. This selective staining technique marks the data permanently on the chip that allows for subsequent analysis and evidence retention.

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“…4b). This binary colour pattern reflects the data pattern stored in the flash memory, where green colour corresponds to data "0" and pink colour corresponds to data "1" [14]. Such colour pattern originates directly from surface morphologies of memory cells and the staining selectivity is further verified with SEM in Fig.…”

“…A clear morphology contrast is observed in the floating gate region, where cell "1" is selectively stained and cell "0" is not. Such selectivity originates from charges stored in the floating gate of cell "0" [14]. During staining, the electric field generated from the stored charges leads to the formation of an insoluble layer.…”

“…SEM) [7], [8]. Recently, a new invasive technique based on selective staining was introduced [14], [15]. It is an electrochemicalbased technique that relies on chemical reactions between a staining solution and memory cells.…”