Asymmetric Interference Behavior in 3D NAND Cell and the Reverse Trend Induced by Undercut of Sacrificial Nitride Film

In this letter, the word line (WL) interference behavior in 3D NAND cell and the impact on program sequence of 3D NAND array operation are discussed. The WL interference induced by source-side neighboring cell is always smaller than that induced by drain-side neighboring cell. Due to this asymmetric characteristic, program sequence from top to bottom will have the advantage of suffering less operation window loss resulting from WL interference, over the traditional program sequence from bottom to top. This advantage can be clearly validated by the experimental results. However, at some specific WL’s of the array, the trend is reversed. The root cause of the reverse trend is then clarified to result from the unexpected undercut of sacrificial nitride film occurring during the imperfect vertical channel etching process for 3D NAND array formation.