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NAND Flash Memory

2018/12/03

NANO flash memory is non-volatility memory, and the stored data will not disappear when the power is OFF. Due to its advantages, such as low energy consumption, less volume, and high tolerance for vibration, fall, and mechanical crash, NANO flash memory has been wildly used as memory card for data storage in remoted electronic products.

 

The data in the NANO flash memory is stored at the floating gate (FG). The key issue for the fabrication of NANO flash memory is how to provide high-quality insulating layer in order to prevent stored electron charge in the floating gate leaking. Also, how to gain the maximum coupling ration of capacitance in order to lower the operation voltage and energy loss is important.

 

For such products, the key fabrication technology falls on growth thickness and uniformity of three-layer dielectric material between floating gate and control gate (CG).The thickness of silicon oxide – nitride – oxide (ONO) in this three-layer dielectric material is only a few angstroms. It becomes crucial to monitor the light elements (O, N, and Si) in such thin films during fabrication development.

 

 

TEM image of Samsung NAND flash.

(a) Planar-view image of memory area

(b) Cross-section image along word line

(c) Cross-section image along bit line

(d) Cross-section image of ONO between FG and CG.

 

 

This figure below exhibits TEM/EELS and TEM/EDX analysis on ONO material. From the TEM image, the thickness of ONO is 5.8, 2.9, and 4.6 nm, respectively. The variation of chemical composition for elements of interest can be clearly identified from EDX line scan, which is consistent with TEM image.

 

(a) EELS mapping on ONO material

(b) EDX line scan