A novel room-temperature surface Si3N4 patterned As+ ion implant solution to wafer warpagemodulation in 3D NAND flash fabrication

Abstract

Wafer warpage is one of the most critical challenges for 3D NAND flash fabrication. In this study, room temperature patterned ion implant with various width is applied to release the stress in plasma enhanced chemical vapor deposition (PECVD) fabricated Si₃N₄ film for curl-shape wafer warpage modulation. The implant pattern method can be used to precisely control the local stress in Si₃N₄ films, and thus the 2D (top-view) and 3D wafer profile can be flexibly adjusted from curl-shape to flat. The properties, microstructure, film stress and wafer warpage of Si₃N₄ film before and after implant are analysed by patterned wafer geometry (PWG), Transmission Electron Microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), Electron Paramagnetic Resonance (EPR), X-ray Photoelectron Spectroscopy (XPS), atomic force microscopy (AFM) and nanoindentation. From these analyses, we conclude that the improvement of wafer warpage is related to stress compensation between the implant and non-implant regions. The stress compensation mechanism in PECVD fabricated Si₃N₄ film is attributed to breaking of Si-N, Si-H and N-H bonds in Si₃N₄ film which induces a stress difference between the implant and non-implant regions, ultimately, the film stress on the front and back (Si₃N₄) of 3D NAND can be balanced, causing the wafer warpage change of 3D NAND flash from curl-shape to flat. Since ion implantation is performed at room temperature and can improve the wafer surface roughness, ion implantation is helpful for both the reliability of device and the subsequent process of 3D NAND flash. It is first time reported that a novel room-temperature patterned ion implant method can be used to adjust the local stress and regulate the wafer warpage in 3D NAND flash fabrication.