Characterization of PECVD Si3N4 thin film in multiple oxide–nitride stack for 3D-NAND flash memory

Abstract

3D-NAND flash memory is currently essential in the semiconductor industry due to the interference issue between memory cells of the conventional planar type. In order to vertically stack the memory, an oxide–nitride stack structure is formed using plasma enhanced chemical vapor deposition (PECVD) equipment. Thereafter, part of the silicon nitride (Si3N4) layer is removed by wet etching using phosphoric acid (H3PO4) to make space for the memory cell. At this time, it is important to selectively wet etch only the Si3N4 film while protecting the silicon oxide (SiO2). Therefore, in this study, the process parameters that affect the etch rate in PECVD were derived, and the correlation with the hydrogen content, surface roughness, and thin film density, which are the thin film characteristics that the parameters affect, were investigated. Through the experimental results, we confirmed that hydrogen content increases according to the deposition pressure, affects the surface roughness, and can be an important factor in improving the wet etching rate.