How Teflon Tanks Improve the KOH Etching Process

Etching silicon wafers with potassium hydroxide (KOH) is a popular process for semiconductor manufacturing. It is relatively safe compared to other etching methods and features good control of the etch rate. When carried out in Teflon tanks, contamination is reduced and the etch rate can be controlled.

Determining the required etch rate is the key factor for a successful etching. An etch rate that’s too fast may mean that the KOH may etch too far into the silicon. But an etch rate that’s too slow may result in a shallow etch. Improving the KOH etching process means applying several control methods to the etch rate to ensure the resulting shapes are exactly correct.

The process factors that may affect the KOH etch rate:

  • Process temperature – The higher the temperature of the KOH solution, the faster that the KOH will etch the silicon.
  • Solution concentration – A higher concentration increases the etch rate.
  • Doping – It means adding impurities to the silicon crystal. When boron is placed into the silicon crystal lattice at a specific location, etching stops in that direction. Boron doping can influence the shapes to be etched this way.
  • Crystal lattice orientation – The silicon crystal atoms are arranged in a cubic lattice that has a greater atom density in some directions than in others. Etching is slower in directions with a higher atom density.

All four factors mentioned above need to be taken into account when designing the mask to obtain the microscopic silicon structures. The silicon wafer needs to be oriented correctly to give the different etch rates along with different lattice directions. Doping has to be in place where etching needs to stop, and the correct concentration of KOH solution has to used. These initial conditions need to be established before starting the process.

A target temperature can also be set, but the temperature will be varied to adjust the etch rate during processing. The ability to alter the etch rate by changing the temperature provides excellent control of the KOH etching process.

Modutek’s Teflon tanks provide precise control of the KOH etching process and are available in a circulating or a static design. The heat source can either be inline or immersed in the overflow weir. An all-Teflon liquid path design reduces the possibility of contamination. The use of heated tanks improves the KOH etching process with short heat up times and precise temperature control.

For more details read the complete article, “How Teflon Tanks Improve the KOH Etching Process”. Contact Modutek for free consultation to discuss your needs at 866-803-1533 or email

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