Bill Foote
EECS Department
University of California, Berkeley
Technical Report No. UCB/CSD-90-595
September 1990
http://www2.eecs.berkeley.edu/Pubs/TechRpts/1990/CSD-90-595.pdf
Request PDF Anisotropic wet chemical etching of crystalline silicon: Atomistic Monte-Carlo simulations and experiments An atomic-scale.
A series of programs have been developed to model anisotropic etching of crystalline substances. The focus of this work was on the computation of the geometric offset surfaces for a given object, when the etching of different faces progresses at different rates depending of face orientation. Programs have been developed to calculate the emerging shapes for both two- and three-dimensional geometries.
Since complete information about the anisotropic etch rates in all possible directions have been published for only very few combinations of crystals and etch solutions, we also had to write a rudimentary generator that would produce plausible and self-consistent direction-dependent etch rate functions. This modeling proceeds in stages: From the geometry of the crystal lattice, its atom spacings and angles between bonds, some inferences are made about the probability that certain more or less exposed atoms get attacked and removed by the etchant. With this model the etch rates for several key directions, i.e., for the simple crystallographic planes (100), (110), (210), (111), (211), and (221), have been calculated. The etch rates for the direction in between these key orientations are found by interpolation.
The etching simulator then uses such an artificially generated function or any function that may come from experimental observations and applies it to arbitrary polyhedral shapes. For all edges and vertices it first determines what new bevel faces might form because of strong local maxima and minima in the etch rate function. Then all the faces, the original ones as well as the bevel faces, are advanced at their corresponding etch rates and combined into a new consistent surface description of a solid object. The user can specify the total etching time and the number of intermediate states that should be displayed. The shapes obtained from the etching simulator programs are in good qualitative agreement with the kinds of shapes actually observed in the laboratory.
BibTeX citation:
EndNote citation:
![Anisotropic Anisotropic](/uploads/1/2/6/5/126523636/619953859.png)
Etch rates for silicon, silicon nitride, and silicon dioxide in varying concentrations and temperatures of KOH.
KOH etches silicon depending on the concentration of the KOH solution and temperature. Graphs are provided for the etch rates depending on temperature (in degrees Celcius) for various solution concentrations. Experimentation has found that solutions less than 30% KOH yield rough etching. Addition of isopropyl alcohol has been found to decrease the etch rate by approximately 20%.
Etch rates for 20% KOH solution
Etch rates for 25% KOH solution
Etch rates for 30% KOH solution
Etch rates for 35% KOH solution
Etch rates for 40% KOH solution
Etch rates for 45% KOH solution
Etch rates for 50% KOH solution
Etch rates for 55% KOH solution
Etch rates for 60% KOH solution
KOH Etching of Silicon 110
KOH etches silicon depending on the concentration of the KOH solution and temperature. Graphs are provided for the etch rates depending on temperature (in degrees Celcius) for various solution concentrations. Experimentation has found that solutions less than 30% KOH yield rough etching. Addition of isopropyl alcohol has been found to decrease etch rates by approximately 90%.
Etch rates for 20% KOH solution
Etch rates for 25% KOH solution
Etch rates for 30% KOH solution
Etch rates for 35% KOH solution
Etch rates for 40% KOH solution
Etch rates for 45% KOH solution
Etch rates for 50% KOH solution
Etch rates for 55% KOH solution
Etch rates for 60% KOH solution
KOH Etching of Silicon Dioxide and Silicon Nitride
KOH etching of silicon nitride was not observed in the study. However, the silicon nitride etch rate is under 1 nanometer per hour if it etches at all. If silicon nitride is being used as a mask for silicon etching, potential etching of the silicon nitride need not be taken into consideration. KOH etching of silicon dioxide is observable. The etch rates are considerably slower (1-2 orders of magnitude) than that of silicon but should be considered when deep etching is being done. Temperature dependent graphs for the etch rates of silicon dioxide in various concentrations of KOH are given.
Etch rates for 20% KOH solution
Etch rates for 25% KOH solution
Etch rates for 30% KOH solution
Etch rates for 35% KOH solution
Etch rates for 40% KOH solution
![Simulation Simulation](https://www.silvaco.com/tech_lib_TCAD/simulationstandard/2011/apr_may_jun/a1/Figure_3d.jpg)
Etch rates for 45% KOH solution
Etch rates for 50% KOH solution
Etch rates for 55% KOH solution
Etch rates for 60% KOH solution
Anisotropic Etch Geometry
Silicon 100 etches anisotropically, with a 54.74° angle from the plane. Masked silicon will etch as shown in the diagram.
Anisotropic Crystalline Etch Simulation (ACES)
Anisotropic Crystalline Etch Simulation (ACES) is a PC-based 3-D etch simulator using a continuous CA model and a dynamic method, which offer high computational speed and drastically reduced memory requirements. It's coded by UIUC MASS Group. The program can simulate silicon etching with different surface orientations in selected etchants with variable etch rate ratios. It can receive 2-D mask designs in common mask formats (including CIF, GDSII, BMP), generate 3D profile in standard solid-modeling languages, and display results using an integrated viewer, which is based on OpenGL.
This link is to download ACES Beta 2 for Windows. You will need to extract the contents of the zipped file to a folder. Run the executable program in that file.
This link is to download ACES Beta 2 for Windows. You will need to extract the contents of the zipped file to a folder. Run the executable program in that file.
Reference: J. Electrochem. Soc. Vol 137, 11, Nov 1990, 3612-3632.