Role of neutral transport in aspect ratio dependent plasma etching of three-dimensional features

Fabrication of semiconductor devices having three-dimensional (3D) structures places unprecedented demands on plasma etching processes. Among these demands is the frequent need to simultaneously etch features with a wide variety of aspect ratios (AR) on the same wafer. Many plasma etching processes exhibit aspect ratio dependent etching (ARDE)—different etch rates for features that have different aspect ratios, usually slower for larger AR. Processes subject to ARDE require over-etch to clear the larger AR features, which increases the need for high selectivity and low damage. Despite these issues, the physical processes which contribute to ARDE are not well understood. In this paper, results are discussed from a computational investigation on the root causes of ARDE during Ar/Cl2 plasma etching of Si, and, in particular, the role which neutral transport plays in this process. Parametric studies were performed varying neutral-to-ion flux ratios, surface recombination rates of atomic Cl, and neutral and io...