Ultrathin Bi2O3 interlayers for defect and grain-boundary engineering toward improved dielectric performance in ALD ZrO2 DRAM capacitors

초록

ZrO2 is a key high-k dielectric for dynamic random-access memory (DRAM) capacitors; however, continued scaling requires the simultaneous improvement of dielectric constant and leakage current density, which remains challenging due to inherent trade-offs. Conventional approaches based on bulk phase engineering or interfacial layer insertion often introduce additional limitations in electrical performance and process integration. Here, we propose an alternative strategy employing ultrathin Bi2O3 interlayers to engineer defect and interfacial properties in TiN/ZrO2/TiN capacitor stacks. Atomic layer deposition of Bi2O3 using Bi(Et)3 and O3 reveals strongly substrate-dependent nucleation behavior, with suppressed growth on Si and self-limiting growth on polycrystalline ZrO2 and TiN, indicating preferential interaction with defect- and grain-boundary-rich regions. When incorporated at ZrO2 interfaces, the ultrathin Bi2O3 layers simultaneously enhance the dielectric constant, reduce leakage current density by approximately one order of magnitude, and enable further equivalent-oxide-thickness (EOT) scaling, while maintaining robust breakdown characteristics. Structural analyses confirm that these improvements occur without measurable changes in the crystalline phase or grain size of ZrO2. These results demonstrate that ultrathin Bi2O3 interlayers provide an effective route to overcome the trade-off between dielectric constant and leakage current density through localized defect and grain-boundary engineering, rather than bulk phase modification, offering a practical pathway for advanced DRAM capacitor scaling.

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