Successful development of 20 nm or smaller dynamic random-access memory (DRAM) requires reduction of the leakage current in capacitors with high-k dielectrics. To reduce the leakage current of the capacitor, we fabricated a ZrO₂-based metal-insulator-metal (MIM) capacitor and investigated changes in leakage current characteristics associated with heat budget following capacitor formation. Leakage current characteristics were drastically degraded by applying an additional heat treatment to the MIM capacitor. Through detailed analysis of leakage versus bias voltage (I-V) characteristics, dielectric constants, and high-resolution transmission electron microscopy (HR-TEM) findings, we determined that the leakage current degradation was caused by an increase in Poole-Frenkel (P-F) emission due to an increase in defect density in the dielectrics and an increase in the dielectric constant due to enhancement of the crystallinity of ZrO₂. Based on the experimental results, we propose a new, simple strategy to reduce leakage current without changing the capacitor structure or material used in the DRAM manufacturing process. This simple approach will not only enable mass production of 20 nm DRAM, but also contribute to the development of next-generation DRAMs by reducing the leakage current of the capacitor.