Multi-step process optimization on high aspect ratio etching for memory devices

We performed a multi-step process optimization for high-aspect ratio etching using a Monte-Carlo based etching process simulation by solving the inverse problem. In this simulation, physical and empirical models are combined to provide a surface reaction model with response process knobs to achieve high accuracy within a short calculation time. We constructed a physical model for surface reactions which includes physical sputtering, chemical sputtering, radical deposition, surface modification by radicals, and thermal isotropic etching. We also updated the physical model to accommodate equipment parameters on the basis of experimental data. In this paper, we optimized 2-step recipe parameters including step time, low frequency RF power, O₂ flow rate and C₄F₈ flow rate. This yielded conditions for achieving straighter profiles. Furthermore, we experimentally verified that one of the proposed recipes has a better profile than that of the baseline condition. We achieved a straighter profile by optimizing multiple parameters with different bottom vs. bow sensitivity and by appropriate multi-step control.