SiN removal process for poly damage control in memory flash

摘要

As the NAND Flash dimension scales down, many scaling problems were caused, such as the poly damage issue during cell STI recess process and SiN remove process. The problems include the cell poly loss uniformity due to the smaller CD and Peri area poly damage issue after cell SiN remove process. Further scaling down beyond 2× generation, it is also facing new scaling limitations, more severe CG (control gate) poly-Si filling problem between FGs (floating gate). We utilized an alternative etching process to the current plasma dry etch. The process is based on the film modification by light ions implantation followed by a selective removal of the modified layer. In this work, we demonstrated the process can remove silicon nitride without poly damage. Meanwhile, it can achieve the FG slimming profile, which benefits for the void-free filling of CG poly-Si.