Zihan Zhou,Yunwen Wu,Huiqin Ling,Jie Guo,Su Wang,Ming Li
3D NAND flash memory with vertically stacked cells has been developed to break through the limits of technology nodes. However, during the selective etching process, it is difficult to ensure the byproducts diffuse away from the trenches in the multistacked layers. Once saturated, the byproduct causes abnormal redeposition on the SiO 2 layers. This problem has restricted the development of high-density 3D NAND memory. To solve this problem, the composition and formation mechanism of the redeposited layer must be clarified. In this study, a ternary-wafer system comprising a Si 3 N 4 /SiO 2 /Si 3 N 4 stack was fabricated to study the redeposition mechanism, and the morphology, elastic properties , and chemical composition of the redeposited layer were clarified. The redeposited layer consists of spherical particles with elastic surfaces (average Young’s modulus of 24.17 GPa). The particles were confirmed to comprise colloidal silica gel covered by silanols . By considering the chemistry of silica , the redeposition mechanism was proposed as follows: colloidal silica gel is formed by the aggregation of silicic acids from Si 3 N 4 etching, which adsorb onto the SiO 2 layer through oxide bridges and hydrogen bonding . Our work will contribute to the development of high-density 3D NAND memory.
A TiO 2 nanofilm was prepared on the surface of AZ31 magnesium alloy with controllable thickness through atomic layer deposition (ALD) technique, which can adjust the corrosion behaviors of AZ31 Mg alloy. Compared with the untreated Mg alloys, corrosion current densities ( i corr ) can decline by 58% in the 200-cycles TiO 2 -covered Mg alloy and further decline by up to 74% with the thickness of nanofilm up to 63 nm (400 cycles). The subsequent modification with a cross-linked conversion layer of 3-amino-propyltriethoxysilane (APTES) by a dipping method can produce a compact silane coating on TiO 2 nanofilm, which can seal pinholes of TiO 2 nanofilm and serve as a barrier to further adjust the corrosion behavior of the substrate. The i corr can decline about two orders of magnitude in the TiO 2 /silane composite coating. Making the adjustable corrosion rate come true, which can be attributed to the precise control on the thickness of metal oxide nanofilm and additional protection from the compact silane coating. In vitro study discloses that the TiO 2 /silane hybrid coating shows higher expression of alkaline phosphatase (ALP) and can promote cellular adhesion and proliferation with better cytocompatibility than untreated Mg alloy.
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