Editor’s Note: This article was originally published in June 2014 and has been updated with additional information and reposted in March 2023.
KOH (potassium hydroxide) and TMAH (tetramethylammonium hydroxide) are two commonly used chemicals for etching silicon, glass, and other materials. The etching process involves dissolving the surface of the material, leaving behind a desired pattern or shape. When using these chemicals, it is important to choose a tank material that is resistant to their corrosive properties, such as Teflon®.
Modutek provides Teflon® tanks that are well-suited for use with both KOH etching and TMAH etching processes. These tanks are highly resistant to chemical corrosion, making them a safe and reliable option for handling these caustic substances. However, there are several additional considerations that should be kept in mind when using KOH and TMAH for etching.
Etching Rates and Material Compatibility
Another important consideration when using KOH and TMAH for etching is the etching rate. The rate at which these chemicals etch materials can be affected by various factors, including the concentration of the solution, the temperature, and the surface orientation of the material being etched. Proper optimization of these factors is necessary to achieve the desired etching rate and profile.
It is also important to consider the compatibility of the material being etched with the chosen etchant. While KOH and TMAH can etch a wide range of materials, not all materials are compatible with these etchants, and some may require specialized etching solutions. Prior to using these chemicals, it is important to check the compatibility of the material being etched with the chosen etchant.
After etching, residues may be left on the surface of the material being etched. These residues can be removed using a variety of techniques, such as rinsing with deionized water or using a plasma cleaner. The choice of technique will depend on the nature of the residue and the material being etched.
Tank Maintenance and Safety Considerations
Proper tank maintenance is essential for ensuring the longevity of Teflon® tanks used in KOH and TMAH etching processes. The surface of the tank should be kept free from scratches and cleaned regularly with appropriate cleaning agents. Additionally, the tanks should be checked for leaks and other damage periodically to ensure that they remain in good condition.
It is important to take appropriate safety precautions when handling and using these chemicals. Both KOH and TMAH can be dangerous if not handled properly, so it is essential to wear protective gear such as gloves, safety goggles, and lab coats. Proper ventilation should also be used which can be provided with chemical fume hoods. Additionally, proper chemical waste disposal procedures should be followed to ensure the safe disposal of these substances.
Modutek’s Equipment Support for KOH and TMAH Etching
Modutek’s TFa and TI series PFA Teflon® Tanks, and other wet bench equipment, fully support KOH etching and TMAH etching processes. These Teflon® Tanks are designed together with other wet bench equipment to decrease impurities and unwanted byproducts due to advanced welding techniques with PFA sheet material. Continual adjustments to the Si etching process are not necessary after the initial process has been established. Modutek constructs all Teflon® Tanks and related equipment per individual customer specifications, and routinely design products that are compatible with a customer’s existing wet bench equipment.
Modutek’s Teflon® Tanks have an operating temperature range from 30 – 100º C, with a process temperature control of ± 0.5º C and a heat-up rate from 2-3º C per minute (depending on the size of the system). The modular design allows for new installation or upgrades into any wet etching station configuration.
Teflon® Tank Configurations that Support KOH and TMAH Etching:
- Temperature Controlled Re-circulating Baths (TFa Series)
- Temperature Controlled Static Baths (TI Series)
Teflon® Tank design features:
- Manual cover with overlapping seal
- Minimizes water lost
- No concentration deficiency over a long etch time
Heat source options include:
- Teflon® inline heating
- Immersion heating in overflow weir for TFa Series and main tank for TI Series
Custom Teflon® Tanks and Additional Options:
- Custom size Teflon® tanks can also be built to match any size (no limitations)
- Bottom drain features
- Magnetic stirrer for agitation (TI and TT series)
- Water condensing refluxor system available on all baths
- Auto lid feature
- DI water or IPA spiking system available
Benefits of Modutek’s Teflon® Tanks:
- Modular design
- Two available heat sources
- All Teflon® fluid path
- Process temperature control of ± 0.5º C
- Process etch uniformity wafer to wafer <2%
- In-house heater maintenance and repair
- 360-degree overflow filtration
- Uniform heating throughout the bath
Modutek provides world-class service, installation, and support for all Teflon® Tanks and related wet bench equipment. In addition, Modutek provides quality products that focus on reliability, precision, throughput, usability, and up-time. For more information contact Modutek for a free quote or consultation.