Analyzing and Mitigating Asymmetric Residual Stress in 3D NAND Scaling Based on Process-dependent Modeling
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摘要: 为进一步提升三维结构快闪存储器(3D NAND)架构的性能表现，行业内涌现出一系列水平与垂直微缩设计思路。这些创新设计方案在突破存储密度瓶颈的同时，也带来了新的集成挑战，其中制造过程中的热机械应力影响尤为突出，制约器件生产的良率及性能表现。该文基于局部代表性体积单元(RVE)有限元过程相关建模框架，针对多层堆叠结构及不同区块(Block)架构设计的技术特点，构建了高精度的3D NAND工艺力学模型。通过系统性研究，深入剖析了3D NAND制造过程中不均匀应力产生的根源，并动态监测了不同微缩方案下机械应力水平及分布规律。研究成果对提高良率和器件可靠性具有重要潜在价值，为提升3D NAND存储密度过程中面临的关键难题提供了有效方案。Abstract:
Objective To improve the performance of 3D NAND architecture, a series of horizontal and vertical miniaturization strategies have been proposed. While these designs increase storage density, they also introduce integration challenges. In particular, thermo-mechanical stress during fabrication has become a critical limitation on device yield and performance. This study establishes a high-precision process mechanics model of 3D NAND based on a local Representative Volume Element (RVE) finite element modeling framework, accounting for the multilayer stacked structure and various block architecture designs. By systematically investigating stress evolution during fabrication, the analysis identifies the root causes of stress non-uniformity and characterizes the dynamic distribution of mechanical stress under different miniaturization schemes. These findings have practical relevance for yield improvement and device reliability, addressing key challenges in advancing 3D NAND storage density. Methods This study constructs a high-precision, device-level finite element model of 3D NAND based on the theory of RVE. The simulation of thermal stress evolution throughout the manufacturing process uses the element birth/death technique in Abaqus. The baseline model features a representative 3D NAND structure comprising 8 Nitride/Oxide (N/O) bilayers, each 25 nm thick. Within a 40-nm-wide slit, 15 storage pillars, each with a diameter of 24 nm and spaced at 36 nm intervals, are arranged in a staggered configuration. To explore the effect of stacking layer number on stress evolution, modified models with 6 and 10 N/O layers are also developed. In addition, to examine the effect of different block architecture transitions, models incorporating 5 and 10 pillars per block are analyzed. The material properties used are consistent with those reported in previous studies, where both the calibration of material parameters and the modeling methodology are validated. Results and Discussions Process-dependent simulations were conducted to examine the evolution of stress distribution during key 3D NAND fabrication steps and to assess the effects of vertical stacking layers ( Fig. 7 ) and block architecture designs (Fig. 8 ). The results show that metal volume fraction, the number of pillars in the array region, and the presence of oxide stairs are primary factors influencing stress distribution. A higher metal volume fraction markedly increases internal stress due to thermal expansion mismatch. Asymmetric metal layouts in the Word Line (WL) and Bit Line (BL) directions intensify stress anisotropy between these axes. Pillars in the array region help alleviate stress concentration by generating tensile zones during nitride/metal thermal deformation, thereby reducing the overall compressive stress. In contrast, oxide stairs constrain deformation along the WL direction, inhibiting stress relaxation and resulting in localized compressive regions. These combined mechanisms indicate that increasing the number of WL layers tends to enhance stress asymmetry, whereas block architectures with a larger number of pillars reduce the degree of stress non-uniformity.Conclusions Using a process mechanics model based on the RVE approach, this study explored stress evolution in 3D NAND fabrication. The effects of two major scaling strategies—vertical layer stacking and horizontal block architecture conversion—were systematically analyzed with respect to stress magnitude and directional asymmetry. The results show that asymmetric stress distribution originates during the step etching stage and peaks following WL and slot filling. As the number of vertical stacking layers increases, structural compressive stress intensifies, particularly in the WL and BL directions. Increasing the number of layers from 6 to 10 results in an 8.54 MPa rise in WL compressive stress and a 5.66 MPa rise in BL stress, with the WL–BL stress difference increasing from 20.76 MPa to 24.64 MPa. Larger-area block architectures effectively mitigate stress asymmetry. Compared with the 5-pillar configuration, the 15-pillar architecture reduces WL–BL stress asymmetry by 22.4%. The composite structure of oxide and tungsten, combined with the constraint effects of pillars and stepped oxide on sacrificial layer deformation, plays a central role in modulating stress levels and directional distribution in 3D NAND structures. -
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