(Digital Presentation) Investigation of Nanoconfined Wet Etching Mechanism Using MD Simulation

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With the advancement in semiconductor technology, sophisticated multidimensional geometries are being formed resulting in nonconfined spaces. Wet etching these nanoconfined spaces uniformly across different CD sizes is challenging. Typically, etch (ER) decreases with decrease in CD size. One of the reported mechanisms to explain this behavior is the overlapping of electrical double layer (EDL) which prevents the etchants from entering to the nanochannels. In our previous experimental work, we reported a reverse ER trend (ER increase with decrease in CD size) of SiO2 using HF in organic as medium compared to water as medium. These results suggested that EDL model alone cannot explain the full mechanism and other factors need to be considered. Hence, molecular dynamics (MD) simulations are used to explain the mechanism of nanoconfined etching of SiO2 in water and organic solvent. Fig.1 shows the MD simulation result of the number density distribution of diluted HF at the solid-liquid interface in a nanoconfined spaces. When water is the solvent, HF molecules are strongly adsorbed in the solid interface. However, with the organic solvent, the HF molecules are more uniformly distributed in the volume near the surface. As the CD becomes smaller, the HF molecular density in the intermediate region in the space tends to decrease in the aqueous solution and increase in the organic solution. Next, we calculated the diffusion time of HF molecules in the nano-confined trench using the MD simulations, where we found that HF molecules have a faster diffusion time in water than in the organic solvent. This is due to the difference in the interaction between the solid interface, the HF molecules, and the solvent in addition to the viscosity of the solvent. Using EDL model and etching reaction, here we report the wet etching mechanism of nanoconfined spaces from the MD simulation result. Figure 1