How Specialized Equipment Improves Silicon Wet Etching Process

Results from common wet etching processes, such as KOH and Piranha etch, can be improved with the use of specialized equipment.

When specialized equipment is used in a silicon wet etching process, wafer output can increase, defects can be reduced, and output quality can improve. Equipment such as temperature controls, recirculating baths, and special control strategies can optimize specific processes and positively impact facility importance.

1) KOH (potassium hydroxide) etching is a popular process for applications requiring tight control of the etch rate. The KOH speed depends on the concentration of the bath and the temperature. A base etch rate can be attained by using an appropriate concentration and the rate can then be varied by controlling the temperature.

For KOH etching, Modutek Teflon tanks are suitable as they reduce contamination and feature tight temperature control. The TI static tanks and the TFa recirculating tanks are temperature-controlled models while the TT series tanks operate at ambient temperature.

2) Piranha etching, on the other hand, uses a mixture of sulfuric acid and hydrogen peroxide to quickly remove organic residue, such as photoresist from silicon wafer surface. The mixture has to be handled carefully as it is highly exothermic when first prepared.

Modutek quartz baths are specially suitable tanks for Piranha etching, as they can withstand high temperature and can be heated. The QFa series can withstand the initial temperature spike from mixture preparation and the subsequent heating to operating temperature.

3) Buffered oxide etch uses buffered hydrofluoric acid to etch thin films of silicon dioxide or silicon nitride. The Modutek F-series sub-ambient circulating baths are specially designed for buffered oxide etch as they reduce consumption of acid and filter out contaminating particles. It delivers a safe and reliable process with low-cost operation.

4) Silicon nitride etching composes of phosphoric acid and de-ionized water and requires special control measures. The mixture usually operates at its boiling point of about 160 degrees centigrade. As the etching proceeds, de-ionized water evaporates, leaving a more concentrated acid behind. The high the concentration of the acid leads to the increase of the boiling point and the etch rate.

The concentration of the acid has to remain to the lower level to keep the process working consistently, which means adding water to it. However, doing so risks an explosive reaction when the water mixes with acid. Modutek has a control system that frequently adds small quantities of water to the silicon nitride wet etching baths whenever the temperature rises, keeping the concentration stable. The control system ensures a safe and stable operation.

You can learn more by reading our recent article, How Specialized Equipment Improves Silicon Wet Etching Processes. If you have questions or would like to set up a free consultation to discuss your needs, contact Modutek Corporation via email at sales@modutek.com or by calling 866-803-1533.

How Process Controls Improve KOH Etching Results

Potassium hydroxide etching, or KOH etching, is a process for creating silicon microstructures. It is widely used because it etches quickly, and can be set to etch at different speeds in different directions. For instance, technicians may want to etch downward into the silicon wafer more quickly than etching in a horizontal direction. They may want to create a rectangular shape, when the long side has a different etch rate compared to the short side.

The etching direction is influenced by the crystal lattice orientation of the silicon wafer and the possible doping of the wafer with boron. The etching speed, on the other hand, depends on the KOH mixture concentration and the temperature. The concentration can vary from 10% to 50% with 30% KOH by weight representing a common value. The mixture is heated to between 60 to 80 degrees centigrade and held steady at the temperature that gives the desired etch speed. Given the correct crystal orientation, doping in the right places and the correct etch speed, the microstructures will be done at a given time.

Compared to other processes, KOH etching is less hazardous. It is a versatile process for creating silicon microstructures. However, precise and responsive controls are required to get superior results.

To achieve KOH etching results, the etching process has to be set up to include the above mentioned factors to produce the desired result every time the process runs.

Modutek’s Teflon tanks are designed to provide precise temperature controls and accurate support equipment that an effective KOH process requires. Wet bench equipment from Modutek can deliver the KOH mixture to the Teflon tanks at precisely the right concentration.

The precise controls mean that each rate remains exactly at the desired level. The dimensions of the silicon microstructures are etched exactly as intended and the KOH process delivers high-quality output. Modutek provides a full product line of wet bench processing equipment and can adapt the KOH etching tanks and other processing equipment to meet the needs of customers.

The complete article, How Process Controls Improve KOH Etching Results, provides additional information. If you have questions, contact Modutek at 866-803-1533 or email sales@modutek.com to request a free consultation to discuss your wet bench processing equipment needs.

Improving the KOH Etching Using Teflon Tanks

Etching with potassium hydroxide (KOH) is commonly used for general purpose etching of silicon wafers. It's because the process can be tightly controlled, and it is also relatively safe. KOH etching, when done using Modutek’s Teflon tanks, improves the performance through high control accuracy and tight temperature control features on the tank.



The KOH rate is affected by many factors: solution concentration, lattice orientation, doping, and solution temperature. The silicon wafer is masked with a substance such as silicon nitride, which is impervious to KOH. The solution etches the unmasked parts of the silicon wafer. A combination of the measures that affect the etch rate allows operators to etch complex shapes that are used in electronic circuits and microstructures.



A higher concentration leads to an increased etch rate. The KOH concentration can range from about 10% to 50% but is typically around 30% by weight. KOH etching is designed to work with a fixed concentration that is determined at the start of the process and remains in that condition once etching begins.



During the process, the etch rate is controlled through temperature by operators. KOH etching reacts quickly to the temperature changes and the solution temperature can be used to control etching and influence the dimensions of the etched shapes.



 Keeping the temperature constant maintains the different etch rates in different directions constant. Changing the temperature also changes the different etch rates and can influence etched shapes. This is why temperature control is crucial in precise KOH etching. A rapid and precise temperature control system can improve KOH etching performance.



Modutek's Teflon tanks improve KOH etching through tank features such as tight temperature control and high control accuracy. Teflon tanks are designed to eliminate contamination and heated tanks are also available in a circulating design or with an immersion heater in the overflow weir. The tanks are available in standard sizes, but Modutek can manufacture custom sizes as well.



For more details read the complete article, “Improving the KOH Etching Process Using Teflon Tanks.” Contact Modutek to get a quote or consultation on using Teflon tanks as well as other equipment for your manufacturing requirements.

Advantages of Using the KOH Etching Process

The KOH etching process uses a solution of potassium hydroxide to etch silicon wafers and produce microscopic structures in the silicon. In subsequent processing steps, microscopic structures are followed to manufacture integrated circuits, processors, and other electronic devices.

 One of the advantages of using KOH etching is that it is relatively safe compared to other etching processes. It also etches silicon fast and can be precisely controlled. These factors are important especially for batch processing where the process step must be precisely done repeatedly. Unlike other chemical processes that are required for specific cleaning and etching steps, KOH is ideal for general silicon etching.

 In preparing the KOH solution, KOH is added to water in an etching tank made of a material that is impervious to aggressive chemicals. Silicon wafers are masked with silicon nitride or silicon dioxide, substances that KOH does not etch. Once the wafers are immersed in the KOH solution, the silicon is removed from the areas that are not masked by the chemical action of the KOH solution.

 The etch rate can be controlled by changing the concentration of the solution and by changing the temperature. Other factors that influence the etch rate are the crystal lattice planes of the silicon and the presence of boron doping.

 Because the KOH etching process is very sensitive to temperature, it is important to maintain the temperature at the exact set point. That’s why the temperature controller should be accurate during the process and from one batch to the next. Tight control during the etching process ensures that the etch rate remains constant while maintaining precisely the same temperature for a given setpoint from one batch to the next. This ensures accurate reproducibility of process conditions and identical results across different batches.

Modutek’s Teflon tanks allow operators to benefit from all the advantages of the KOH etching process. The tanks are specifically designed for KOH etching and feature a wide temperature range, tight temperature control, and rapid heating. Custom tank sizes are available and custom installations can be done to fit any new or existing wet bench application.

Read the complete article “Advantages of Using the KOH Etching Process” for more details on how Modutek’s Teflon tanks can help operators get all the benefits of KOH etching. For a free consultation or quote contact Modutek at 866–803–1533 or email modutek@modutek.com.

Why Teflon Tanks Are Used with the KOH Etching Process

KOH etching is more preferred compared to many other silicon wafer fabrication methods because it works rapidly and reliably, while handling of the chemicals is relatively safe. The KOH etching process controls the etching speed by relying on a contamination-free environment and using the temperature and KOH concentration.

Only Teflon tanks are used in this process because Teflon is stable and doesn't deteriorate or corrode from using KOH etching.

The KOH etching process controls allow precise and repeatable temperature controls for positive fabrication results and high-quality production. KOH etching in Teflon tanks, along with temperature control, is an exceptional process for silicon wafer nanostructure fabrication in both manufacturing facilities and research environments.

KOH or potassium hydroxide etches silicon quickly and at a stable rate which relies on the concentration of the solution and the temperature of the liquid. Aside from that, this etching process is also influenced by the crystal planes of the silicon and the doping concentration. These factors can be applied for direct etching in certain directions and stop etching at defined points. The result is that KOH etching can produce the accurate nanostructures required if the crystal planes and the doping are used accurately.

Modutek, a company with over 30 years of experience providing semiconductor equipment solutions, offers Teflon tanks that are specifically designed to support the KOH etching process, which ensures high-quality wafer fabrication.

Teflon tanks are used because aside from its stability, they have the ability to eliminate contamination from the tanks or fluid paths by making sure that the KOH solution only comes in contact with Teflon. Teflon is not affected by the corrosive chemical. In addition Modutek’s Teflon tanks are welded using advanced PFA sheet welding techniques, which guarantees reduction of contaminants.

The complete article “Why Teflon Tanks Are Used with the KOH Etching Process” explains more about the necessity of using Teflon tanks when doing KOK etching. If you have questions or would like a free consultation or quote on equipment to support the KOH etching process, please call 866-803-1533 or send an email to modutek@modutek.com. 

How the KOH Etching Process is Improved Using Modutek's Teflon Tanks

Among the various approaches that foundries use to manufacture semiconductors chips, the use of the KOH (potassium hydroxide) etching process is frequently preferred due to the error-free mass production capability it provides. Etching with potassium chloride (KOH) provides more precision and results to better quality control compared to dry semiconductor etching processes that present challenges in process control.

The fluids employed in the KOH etching process are stored in Teflon tanks built within the equipment – these tanks can make KOH etching more cost-effective, more practical and safer than other alternatives available. It’s also possible to structure the KOH etching process in a manner that will create an easily repeatable manufacturing process. When projects come in from different clients, fabrication plants can focus on setting up the equipment and process lines and worry less about safety and reliability issues.

One of the most significant improvements that Modutek brings to the KOH etching process is customized control. Modutek’s tanks have highly customizable temperature settings – temperature control can be achieved either through in-line heating and cooling equipment installed, or through immersion in liquid tanks. Temperature can be adjusted between 30°C to 100°C and changes can be adjusted at a rate of 2°C per minute on average depending on tank size.

Modutek designs Teflon tanks according to the specifications of each client’s installation. Whether a manufacturing facility needs recirculating baths for KOH etching processes or temperature controlled static baths, Modutek's Teflon tanks provide optimum control to reduce water loss and concentration deficiency.

For more details read the complete article titled How the KOH Etching Process is Improved Using Modutek’s Teflon Tanks. Call Modutek at 866-803-1533 if you have questions or would like a quote or email to Modutek@modutek.com.