The Level-Set Method for Multi-Material Wet Etching and Non-Planar Selective Epitaxy

Alexander Toifl,Siegfried Selberherr,Michael Quell,Paul Manstetten,Andreas Hossinger,Josef Weinbub,Xaver Klemenschits

doi:10.1109/access.2020.3004136

Alexander Toifl, Siegfried Selberherr + Show 5 more

Open Access

https://doi.org/10.1109/access.2020.3004136

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Abstract

We present numerical methods to enable accurate and robust level-set based simulation of anisotropic wet etching and non-planar epitaxy for semiconductor fabrication. These fabrication techniques are characterized by highly crystal orientation-dependent etch/growth rates, which lead to non-convex Hamiltonians in their description by the level-set equation. As a consequence, instable surface propagation may emerge, leading to unphysical results. We propose a calibration-free Stencil Lax-Friedrichs scheme and an advanced adaptive time-stepping approach, tailored to the level-set speed functions associated with anisotropic etching and epitaxy. The scheme calculates the numerical dissipation based on information about the local geometry and the nature of the etch rates/growth function, which enables an optimized trade-off between overly rounding of sharp geometric features and stable surface propagation. Furthermore, we introduce the deposition top layer method, which allows for robust handling of multiple material regions in non-planar epitaxy simulations. Both methods are demonstrated in a prototypical implementation, which is used to validate the capability and accuracy of our approaches. In particular, two-dimensional wet etching and three-dimensional epitaxy simulations are performed and characteristic geometry parameters are compared to the ideally expected values, showing robustness and high accuracy.

Highlights

Fabrication techniques which exploit the crystalline nature of semiconductor materials are highly important for cutting-edge semiconductor technologies to enable intricate device geometries
We propose the introduction of a deposition top level-set function, which allows for robust and accurate simulations of anisotropic epitaxy processes on non-planar substrates
DISSIPATION TERMS AND SPATIAL RESOLUTION The etching and epitaxy simulations considered in this study adopt several speed functions which involve the etch/growth rate combinations given in Tab. 1 and referred to as etchants in the following

Summary

INTRODUCTION

Fabrication techniques which exploit the crystalline nature of semiconductor materials are highly important for cutting-edge semiconductor technologies to enable intricate device geometries. In order to enhance the device characteristics of advanced-node semiconductor devices (e.g., FinFETs [5] and stacked nanosheet devices [6], [7]), the exact geometry of epitaxially grown Si or SiGe is crucial Both anisotropic etching and non-planar epitaxy require precise control of the final topography. A. Toifl et al.: Level-Set Method for Multi-Material Wet Etching and Non-Planar Selective Epitaxy. We present a method to calculate the numerical dissipation based on the nature of the speed function V and the local geometry while not resorting to calibration parameters. We propose the introduction of a deposition top level-set function (deposition top layer), which allows for robust and accurate simulations of anisotropic epitaxy processes on non-planar substrates.

NUMERICAL DISSIPATION SCHEME

STENCIL LAX-FRIEDRICHS SCHEME WITH ADVANCED ADAPTIVE TIME STEPPING

SIMULATION SETUP

THREE-DIMENSIONAL NON-PLANAR EPITAXY

RESULTS