Impact of Mechanical Stress on 3-D NAND Flash Current Conduction

Abstract

This work experimentally investigates current conduction in 3-D NAND under up to 7 GPa of externally applied compressive mechanical stress. The impact of channel crystallinity and geometry is studied by comparing four types of Si channels: polycrystalline full channel, single-crystal full channel, polycrystalline macaroni channel, and single-crystal macaroni channel. In the studied channel types, the mechanical stress was found to cause reversible degradation of I ON (up to one order of magnitude) and I OFF (up to seven orders of magnitude). Using TCAD simulations, I ON and I OFF deterioration are attributed to carrier mobility and Si bandgap decreases under mechanical stress, respectively. The simulations also suggest that both effects depend on the channel morphology, which results in a different extent of stress impact on the four studied types of Si channels.

Impact of Residual Stress on a Polysilicon Channel in Scaled 3D NAND Flash Memory

“…As shown in Figure 2a, the residual stress of the tungsten films after the tungsten replacement gate process was approximately 2.41 GPa, which matches reported experimental data [9]. The residual stress of the polysilicon channel at the final structure in the simulation, as shown in Figure 2b, was −280 MPa, which is also similar to the reported data [10]. The distribution of the residual stress of the polysilicon channel in 3D NAND was then analyzed when scaled.…”

Impact of Residual Stress on a Polysilicon Channel in Scaled 3D NAND Flash Memory

“…As shown in Figure 2a, the residual stress of the tungsten films after the tungsten replacement gate process was approximately 2.41 GPa, which matches reported experimental data [9]. The residual stress of the polysilicon channel at the final structure in the simulation, as shown in Figure 2b, was −280 MPa, which is also similar to the reported data [10]. The distribution of the residual stress of the polysilicon channel in 3D NAND was then analyzed when scaled.…”