Three-Dimensional Characterization and Modeling of Stress Distribution in High-Density DRAM Memory Cells

Abstract

The retention time characteristics in DRAM cells are strongly influenced by various leakage mechanisms near the storage node junction. In this work, we present a full three-dimensional analysis of stress distributions in and around the active area of high-density memory cells. We use a combination of high-resolution metrology analysis and 3D numerical modeling to provide quantitative estimates. Since shallow - trench isolation (STI) process used in high-density cells is one of the major contributors to stress, we study the effects of various materials used to fill the trench. Our electron diffraction contrast (EDC) methodology provides a spatial resolution on the order of 10 nm with sensitivity on of the order of tens of MPa and therefore useful for the analysis of scaled high density memory cells.