KOH Etch Rate Calculator

This calculator determines the etch rate of several major silicon crystal planes and thermally grown silicon dioxide (SiO2). KOH as a silicon etchant has been known in the semiconductor industry almost since the industry's inception. [1] The model for KOH etching of silicon has evolved over the years and this calculator coallesces the best parts of different data and models into one simulation. Today, anisotropic alkaline etching of silicon is perhaps one of the most important steps in the manufacture of silicon MEMS devices, used in both bulk and surface micromachining processes. This calculator computes etch rates of silicon <100>, <110> and <111> crystal planes and SiO2 versus solution temperature and solution percent weight, and incorporates the effects of substrate doping and the addition of isopropyl alcohol to the solution.

To use, go to:
http://www.lelandstanfordjunior.com/KOH.html

Is the Calculator Exactly Correct?

No.

How Accurate is it?

This calculator is really a simulation[2], based on experimental data from many sources. There is a large amount of data available for <100> undoped Si, and for SiO2. For other crystal orientations, there is less. For doped silicon, the data is sparse. For different crystal planes and doped Si with the addition of IPA, there is almost none. In fact, at higher %wt for doped Si with IPA, this simulation is a complete extrapolation of the data. So results may vary. The mechanisms of etching are not universally agreed upon in the literature. [3]

Has the calculator been tested?

Yes, but not for all possible cases. The most relaible data is for KOH etch rates of silicon <100> and <110> and for thermally grown SiO2.[4] For Silicon <111>, the measurement of etch rate is ellusive.[5][6] The etch rates are small, and may change with time. It has also been reported that the etch rate may depend on the specific geometry of the sample being etched, including the open area, nearby actively etching <100> planes, and surface orientation. Also, Boron etch stop models are not as thoroughly tested. For one, it is often not known what the exact B concnetration is in a particular sample. The B concentration may not be constant in depth. And, like in the <111> case, the rates tend to be low, and therefore more difficult to measure accurately.

How do you blend data from many sources into one coherent model?

This is the art of science, statistics and modeling. Data is taken from many sources, analyzed statistically to see what data is consistent with the whole set and which data might be errant. Then, using a system of equations with physical relevance (not a random curve fit), a best-fit is made through available and statistically selected data using regression and enhanced visualization tools.

Do you improve the models as more data becomes availbale?

Yes! In fact, you can help that effort by sharing your data, and it will be tested and incorporated where possible. It is important to include all experimental detail, such as how you measured (particularly, doping concentration). The following data would be particularly interesting:

How do I use it?

Go to the calculator main page: http://www.lelandstanfordjunior.com/KOH.html and enter data according to:
  1. Percent Weight of KOH in solution:
  2. Temperature:
  3. Select the Model Options:
  4. Click Calculate Etch Rates, and the following OUTPUTS will appear:

What's not accounted for in this calculator?


Under what conditions might the calculator have significant error?

© 2013-2014 Maria Pace. All Rights Reserved. Send comments or suggestions to Maria Pace mariaepscience@ (run the calculator to get my full email).

Referencing this Calculator in a Publication:

The MLA7 format for citing a website is:
Last name, First name. "Article Title." Website Title. Publisher of Website, Day Month Year article was published. Web. Day Month Year article was accessed. <URL>.

Therefore, a recommended format for referencing this calculator is:
Pace, Maria. "KOH Silicon Etch Calculator." N.p., June 2013. Web. 08 Apr. 2014. <http://lelandstanfordjunior.com/KOH.html>.

You should change the accessed date to the date you accessed it for your paper, and for the date of the page, it is recommended that you look at the "code base" at the bottom of the results page to reference the date (so that any changes in the code can be tracked):
Calculator code build: M1312
For example, would be best to reference the page date as Dec 2013 Or,
Calculator code build: M1312 I1401
would be referenced at Jan 2014 since this is the most recent date of code modification for the particular sections of code that your simulation used. Although non-standard from a library reference point of view, you could just reference the code build.

References:

[1]P.J. Holmes, Academic Press, Ltd. London., "The Electrochemistry of Semiconductors," , p.329 (1962).

[2]H. Camon and Z. Moktadir, Microelectronics J. 28, 4 (1997).

[3]E.D. Palik, H.F. Gray and P.B. Klein, J. Electrochem. Soc. 130, 4 (1983).

[4]H. Seidel, L.Csepregi, A. Heuberger and H. Baumgartel, J. Electrochem. Soc. 137, 11, pp.3612-3626 (1990).

[5]A.J. Nijdam, et. al., J. Micromech. Microeng. 11, (2001).

[6]R.M. Finne and D.L. Klein, J. Electrochem. Soc. 114, 965 (1967).

[7]J.B. Price,Proc. Electrochem. Soc., p.339 Princeton, NJ (1973).

[8]H. Seidel, L.Csepregi, A. Heuberger and H. Baumgartel, J. Electrochem. Soc. 137, 11, pp.3626-3632 (1990).

[9]M. Shikida, K. Tokoro, D. Uchikawa and K. Sato, J. Micromech. Microeng. 10, (2000).

[10]Standard ASTM E291-09 "Standard Test Methods for Chemical Analysis of Sodium Hydroxide and Potassium Hydroxide" (2009).

[11]D.L. Kendall, Annual Review of Material Science 9, 373 (1979).

[12]D.L. Dickensheets, J. MicroElectroMech Sys. 7, 38 (1998).