We present results of experimental measurements, simulations, and models to better understand etching of SiN with H3PO4 in 3D NAND structures. SiN and SiO2 etch rates were measured on blanket wafers, and those etch rates were used to simulate etching of 3D NAND structures. Results show that the etching is reaction limited, and that diffusion and acid flow rate has no effect on the local etch rate, but temperature and concentration do affect the etch rate.

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The etching of silicon nitride using phosphoric acid with silicon dioxide as a mask is an important process step used in the production of 3D NAND devices. This paper examines the theory of formation of a silica film onto the silicon dioxide surface during this etching step by performing a shell balance analysis of silica species in the etched out liquid volume of the 3D NAND structures. The method of moments is used to solve for the moments of the distribution of particle sizes, and this is used to solve for the potential energy barrier for silica particles to adhere to the silicon dioxide surface.

Analytical prediction of capillary pattern collapse is done by balancing the capillary forcesdue to the curved liquid interface with the elastic forces due to the bending of the structure. This paperintroduces a more realistic model where there is an array of repeating lines and spaces, and compares itto the traditional model of two single lines with liquid-filled space in between. This paper also includesthe influence of a non-vertical sidewall angle, and its effect on the overall elastic force. Results showthat the repeating structures and non-vertical sidewall angles both predict a higher critical height beforecollapse occurs compared to the traditional model.