How Teflon Tanks Improve the KOH Etching Process

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

A key factor for successful etching is to determine the required etch rate. If the rate is too fast, the KOH may etch too far into the silicon, while if the rate is too slow, the etched holes might be too shallow. Improving the KOH etching process means applying several control methods to the etch rate to ensure the resulting etched shapes are exactly correct.

Process Factors that Affect the KOH Etch Rate

The KOH etch rate in silicon wafers is influenced by the following factors:

  • Process temperature. The higher the temperature of the KOH solution, the faster KOH will etch the silicon.
  • Solution concentration. A higher concentration increases the etch rate. Normally the concentration of the KOH solution is about 30 percent, but it can vary from 10 to 50 percent, with a corresponding effect on the etch rate.
  • Doping. Doping 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 in 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 have to be taken into account when designing the mask to obtain the microscopic structures in the silicon. The silicon wafer has to be oriented correctly to give the different etch rates along with the different lattice directions. Doping has to be in a place where etching is required to stop and the correct KOH solution concentration has to be mixed. These are initial conditions that are established before the process starts. A target temperature can be set as well but the temperature can be varied to adjust the etch rate during processing. The ability to vary the etch rate by changing the temperature results in excellent control of the KOH etching process.

Modutek Teflon Tanks Feature Rapid Heating and Precise Temperature Control

Modutek’s Teflon tanks for KOH processing are available in a circulating or a static design. The heat source is either inline or immersed in the overflow weir. An all-Teflon liquid path reduces the possibility of contamination. The heated tanks can improve the KOH etching process with short heat-up times and precise temperature control. As a result, Modutek Teflon tanks can keep the etch rate steady by maintaining an accurate temperature set point or can allow the etch rate to be adjusted with fast and reliable controlled temperature changes.

Both models of Teflon tanks feature uniform heating throughout the baths, level and temperature limit settings, and a drain interlock. Heat up rates are 2 to 3 degrees centigrade per minute and the temperature is controlled with a precision of plus/minus 0.5 degrees centigrade. The operating temperature is from 30 to 100 degrees centigrade and a cooling refluxor with Teflon cooling coils is included.

Modutek’s Teflon tanks are available in standard sizes but can work with customers to design and build systems with custom sizes and special requirements. With their high-quality materials, precise temperature controls, and customization capabilities, Modutek’s Teflon tanks can improve the KOH etching process to deliver better semiconductor manufacturing results. Contact Modutek for a free consultation to discuss your specific process requirements.

How to Select a Supplier from Your List of Semiconductor Equipment Manufacturers

How to Select a Supplier from Your List of Semiconductor Equipment ManufacturersWhen choosing a supplier from a list of semiconductor equipment manufacturers you have to look at a wide variety of factors. Key points to evaluate include the following:

  • Customization capabilities to meet customer requirements
  • Equipment reliability
  • Company experience and expertise
  • Warranties
  • Service and customer support

Only after you have determined which manufacturers can actually supply the equipment you want can you look at cost of ownership and pricing to make your final decision.

Specifying What You Need

Semiconductor fabrication lines and research labs are different and have specific requirements when they want to upgrade lines, replace components or buy new equipment. Sometimes the purchased equipment has to interface with existing systems, sometimes space is a factor and sometimes the physical set-up of the production facilities limit what can be installed. A supplier has to be able to evaluate these constraints and suggest solutions. The equipment proposed often has to be customized to some extent and the supplier has to have the experience and the capability to adapt his standard solutions to particular situations.

Equipment Reliability

Once you have purchased your equipment, it has to keep working with a minimum of downtime. The best way to evaluate the reliability of a supplier’s equipment is to ask for references and reliability statistics. Suppliers should submit normal hours of scheduled downtime, estimates of unexpected downtime and the records of actual installations. Once you have narrowed down the list of suppliers, it’s a good idea to check with some of the references who are not direct competitors of your company and verify what the supplier has submitted.

Warranties, Service and Support

Before you sign a contract with a selected supplier, check on his equipment warranties and his service and support capabilities. Warranties should be simple, comprehensive and of sufficient length. Check on whether the supplier has enough service personnel. Also important is whether he can rely on his own personnel to carry out service or whether he has to call in third parties. If a supplier subcontracts a lot of his equipment manufacturing, he is less likely to have competent service personnel on staff to deal with that equipment. Call support to see how they respond to support requests. Often calling a supplier’s customer support line with an equipment question rather than going through your contacts in sales will give you an idea how well a supplier responds to support requests.


The selection of the right semiconductor manufacturing equipment supplier for additions to a fabrication line or a research lab affects future productivity and output quality. You have to make sure you buy the equipment you need and select a supplier who will keep it working optimally.

Modutek has the experience required and the expertise to advise customers and to support their installations. The company has been in operation for over 35 years and carries out assembly of its equipment and creation of associated software in house. As a result, Modutek can offer expert service and support for all of a customer’s needs. With its commitment to total customer satisfaction and its record of in house development and manufacturing, the company is an excellent choice and a leading supplier among semiconductor equipment manufacturers. If you have any questions about Modutek’s products and support services, take a minute to call and discuss your concerns with one of their customer service representatives.