Etch rates for silicon, silicon nitride, and silicon dioxide in varying concentrations and temperatures of KOH.

KOH Etching

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

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.

 

Reference: J. Electrochem. Soc. Vol 137, 11, Nov 1990, 3612-3632.