Etch and deposition co-optimization: a pathway to enabling high aspect ratio 3D NAND Flash ONON channel hole patterning

3D NAND flash scaling relies mainly on increasing vertical stack height, thus putting challenges mostly on film deposition and etch. Among various fabrication steps, high aspect ratio (HAR) ONON channel hole etch remains the most critical step. One unique aspect of the 3D NAND process flow is that nitride film in the ONON pair is a sacrificial layer that is been replaced with W at a later stage. The SiN removal process flow provides opportunities to look at possibilities of optimizing oxide and nitride films at different layers to enable better channel hole etch, such as enlarging bottom hole CD, reducing bowing and twisting in the middle area, and etc. In this paper, we will highlight the approaches and benefits on deposition and etch co-optimization as one potential pathway to overcome barrier in HAR ONON channel hole patterning. Besides ONON HAR, hard mask is another key focus. We will also discuss the possible mask material selection consideration based the overall film properties, etch selectivity and final clean/removability perspectives.