How Quartz Tanks Provide High Reliability and Safety for Wafer Processing

How Quartz Tanks Provide High Reliability and Safety for Wafer ProcessingBecause quartz is an inert substance that does not take part in acid chemical reactions, quartz tanks are ideal containers for silicon wafer processing. The flame-polished quartz used in Modutek’s quartz tanks is impervious to the powerful acids used for processes such as SC1, SPM, and the Piranha process. Quartz tanks are designed to minimize particle contamination and to accurately control the temperature when required. As a result, quartz tanks deliver superior results for wet bench semiconductor fabrication.

Quartz Tanks Reliably Reduce Particle Counts

As semiconductor products require tighter packing of components, a reduced particle count becomes more important. The size of the microscopic structures etched into silicon wafers is reduced to such an extent that a single particle can distort the required shape. The resulting semiconductor chips can be defective or have reduced quality. Sometimes the performance could be better, or the lifespan is reduced. A low particle count is critical for achieving excellent quality output and a high yield from the semiconductor fabrication line.

Modutek’s quartz tanks reduce particle contamination to improve process results. The high-purity flame-polished quartz used in Modutek’s quartz tanks makes it chemically inert to most chemical compounds, including acids, water, and salt. Since the quartz crystal does not react with the chemicals used in semiconductor fabrication, contamination from the quartz tanks is eliminated.

The quartz tank design reduces particle contamination as well. Modutek’s quartz tanks are based on over 30 years of tank design experience to minimize particle contamination. The seamless design and sloped housing construction eliminate places where particles could become lodged. Actual results from real-world fabrication confirm that Modutek’s quartz tanks deliver low particle counts.

Accurate Quartz Tank Temperature Controls Produce Precise Results

For many wet bench processes, the etch rate depends on how the process is set up. The temperature, concentration, silicon wafer crystal lattice orientation, and possible doping of the silicon wafers all influence the etch rate. Except for the process temperature, they are all determined at the start of the process. The temperature, on the other hand, varies. It rises quickly at the beginning and can change as the etching progresses. Precise temperature control is required for reliable etching results.

The etch rate is critical for determining the shapes and details of the microscopic structures etched into the silicon wafer. If etching does not proceed at the right speed, the etched shapes may be too large or too small. The resulting semiconductor products won’t have the expected characteristics and may have to be discarded.

Modutek’s quartz tanks feature a rapid temperature rise to the temperature set point and precise control. The temperature can be set at up to 180 degrees Centigrade. The temperature rises at up to 2 degrees C per minute and is controlled with a precision of plus/minus 1 degree C. The rapid temperature rise helps achieve high throughput, and the tight temperature control provides excellent repeatability.

Quartz Tank Design Influences Output Quality

The quality of silicon wet etching results depends on low particle counts and accurate control of the process temperature. Modutek’s quartz tanks are designed with these two factors in mind. The tanks support wet bench processes such as SC1 and SPM and deliver consistent etching results. Reduced particle counts and excellent etch rate control are consistent during continuous manufacturing and across different batches.

Modutek Provides Safe and Reliable Equipment

Modutek works closely with customers to improve their wet processing manufacturing results, resolve problems and find solutions. Quartz tanks and other equipment that Modutek provides deliver high reliability and safe operation to support various wet processes. Contact us for a free quote and consultation to discuss your specific requirements.

Equipment Innovations Improve Silicon Nitride Etch Processing

Equipment Innovations Improve Silicon Nitride Etch ProcessingWhen silicon nitride wet etching is used to etch masks on silicon wafers, precise control of the etch rate is important. If the etch rate varies, the mask may not be correct and the microscopic structures to be created in the silicon may not have the right shape or depth. In the silicon nitride wet etching process, the etch rate depends on both the temperature and the concentration of the etching solution. Both may vary as the process progresses and precise control becomes difficult. An ideal control strategy maintains both the concentration and the temperature at known levels. The etch rate then remains constant and the mask is etched accurately according to the applicable specification.

Silicon Nitride Mask Etching Is Effective but Hard to Handle Safely

Semiconductor manufacturers and research labs use silicon nitride wet etching because the process etches the mask material quickly and reliably. A mixture of 85 percent phosphoric acid and 15 percent deionized water is heated to the boiling point. As the mixture boils, it releases steam that reduces the amount of water in the etching solution. As the concentration of phosphoric acid rises, so does the boiling point, the temperature of the mixture and the etch rate. To keep the process under control, deionized water has to be added to bring the concentration back down.

Adding water to phosphoric acid is exothermic. To prevent a sudden increase in temperature, water has to be added in small amounts, but if too many small amounts are added to the mixture, it will stop boiling. The water then forms a thin film on top of the mixture and eventually mixes with the phosphoric acid all at once, leading to a sudden temperature spike and a possible explosion. A complex control system with variable set points can ensure safe operation but control of the etch rate is poor.

Modutek’s Silicon Nitride Etch Controls Are Simple and Precise

Modutek addresses the control issues of silicon nitride wet etching by heating the etch bath continuously. An always-on heater heats the original 85/15 percent phosphoric acid/deionized water mixture to its boiling point of 165 degrees centigrade. As the mixture loses steam and the concentration and temperature both start to rise, a thermocouple detects the slightly increased temperature and triggers the addition of a small amount of deionized water. The added water is immediately mixed into the etching solution by the boiling action. The amount added restores the concentration and keeps the temperature at the boiling point.

Modutek has refined this control concept to accurately maintain the etching solution exactly at its original concentration and at its boiling point. As a result, with both the concentration and the temperature remaining constant, the etch rate remains predictable and constant as well. Mask etching is reliable and the final mask has precisely the desired characteristics.

Because the Modutek control strategy relies on maintaining the etching solution at the boiling point, the control system has additional safety features to identify dangerous conditions that could result if the mixture stops boiling. Two thermocouples detect the presence of steam over the hot acid and acid overtemperature. If there is no steam, the mixture is no longer boiling. If the acid temperature is too high, the solution is no longer being maintained at the original boiling point. In either case, the process is shut down because equipment failure is likely and a dangerous condition may be present.

Modutek Provides a Complete line Equipment Solutions

Modutek offers a complete line of silicon wet etching equipment and works with customers to develop innovative solutions to their problems. The silicon nitride etching control system improves etching performance and results remain consistent over different batches. The number of defective products is reduced and product quality increases. When customers purchase etching systems and other equipment, Modutek will ensure they meet their requirements. Contact Modutek for a free consultation to discuss your specific process requirements.

How Quick Dump Rinsers Improve Wet Processing Results

While effective and rapid rinsing with a low particle count remains a key benefit of quick dump rinsers, reduced water usage is also becoming more important. Special design measures can lower the amount of water required to rinse the silicon wafers while retaining fast and efficient operation with a low level of particle contamination.

Low water consumption is especially important in some regions such as the Western U.S., where a long-term drought makes water conservation mandatory. Even in other areas, a reduced use of the deionized water used in silicon wafer fabrication saves money and is environmentally responsible. Modutek has pioneered the design of quick dump rinsers that feature efficient use of deionized water, fast operation, and low particle entrapment.

Quick Dump Rinser Benefits that Incorporate Reduced Water Usage

Modutek’s quick dump rinsers feature a state-of-the-art design for efficient operation while minimizing rinse time, reducing the particle count, and keeping deionized water usage to a minimum. Modutek’s quick dump rinsers offer the following characteristics:

  • Efficient Rinsing. The units have dual spray manifolds and low misting nozzles for quick and complete rinsing away of chemical residues.
  • Nitrogen Bubbler. The bubbler generates nitrogen bubbles as the tank fills, removing additional contaminants and particles.
  • 360 Degree Overflow Weir. As the dislodged impurities rise to the surface, they are flushed away across the overflow weir and out of the tank.
  • Programmable Water Use. Modutek’s quick dump rinsers can be programmed to use less water.
  • Contoured Bottom. The rinser bottom is contoured around a wafer cassette, reducing the amount of water required.
  • Large Machined Trap Door. The machined trap door doesn’t need gaskets or seals that could trap particles, and the large size lets water drain rapidly.
  • Polypropylene Construction. High-quality smooth polypropylene construction ensures that the tank is not a source of contamination with new particles.
  • Automatic Dump and Refill. The rinsing controller can be set to automatically dump and refill every two hours, reducing bacterial growth and minimizing the possibility of contamination.
  • Optional Reclaim System. An optional reclaim system further reduces water consumption and lowers costs.
  • Variety of Standard Sizes. Modutek offers seven standard tank sizes for their quick dump rinsers, and can accommodate many special customer needs.

Modutek has designed the quick dump rinser to operate as a stand-alone unit or for integration into a silicon wet etching process line. The rinser can improve the overall performance of the line and lower costs while reducing the number of defective products.

Benefits of Using Modutek’s Quick Dump Rinser

Modutek’s design is based on extensive experience working with wet process equipment to address key customer concerns. Benefits include the following:

  • The reduced water consumption due to rapid rinsing and a water-conserving design lowers costs and reduces the environmental impact.
  • The machined trap door and laminar flow of rinsing water reduce the particle count and improve output quality.
  • The smooth polypropylene construction avoids additional contamination and reduces the percentage of rejects.
  • Quick rinsing allows increased throughput for the production line and reduces costs.

From its close working relationship with customers, Modutek can address the challenges manufacturers often have with meeting higher product densities, smaller silicon structures, and increasing regulation with using chemicals and water. Modutek continuously works to improve silicon wafer processing capabilities, while keeping in mind the overall costs of ownership and efficient wafer processing.

Modutek Provides Innovative Solutions to Meet Customer Needs

Modutek’s quick dump rinsers represent years of innovative design and development. These systems let semiconductor manufacturers and research facilities reduce water consumption while increasing output and reducing the number of product defects. Overall facility performance is improved through cost reduction and improved output quality. Contact Modutek for a free quote or consultation to discuss your specific processing requirements at 866-803-1533 or email

How Better KOH Etching Results Are Achieved Using Teflon Tanks

While KOH etching is widely used, the process controls and the process tanks can play a major role in obtaining the desired results. Improved KOH etching means precise control of the etch rate and a low particle count. When the etch rate is exact and consistent, the etched shapes in the silicon wafer will be as specified and the final semiconductor product will function as expected. When particle counts are low, the number of defective products will go down and yield will increase. Combining Teflon tanks with high-precision control systems can deliver superior etching results while reducing waste and increasing output quality.

How KOH Etching Can Be Controlled and Improved

KOH etching uses a solution of potassium hydroxide to etch silicon wafers. The etch rate is influenced by the bath temperature, the concentration of potassium hydroxide, the orientation of the silicon crystal lattice, and possible doping of the silicon. Each of these factors helps determine how quickly etching proceeds in the horizontal and vertical directions.

The cubic crystal lattice of the silicon has different atom densities in different directions. The wafer can be oriented in such a way that etching proceeds more quickly in a given direction. Doping, or adding impurities to the silicon, can be used to stop the etching at a particular location in the wafer. While both these factors can influence the etch rate and the microscopic silicon structures, they are fixed before the etching process begins.

Because the etch rate partly depends on the KOH concentration, it is critical to add the right amount of KOH to water. An accurate chemical delivery system can help ensure that the etching tank contains the right solution concentration before the etching process starts.

The etch rate speeds up with an increasing temperature. This means that the tank and solution temperature must be raised quickly to the specified level and must be maintained precisely at the set point for the duration of the etching process. Accurate temperature control is important for improved etching performance.

Modutek’s Teflon Tanks and Controls Help Achieve Better Etching Results

Modutek provides temperature-controlled Teflon tanks and precise chemical delivery systems needed for excellent etching rate control for improved KOH etching results. These two process variables determine the KOH etch rate once the doped silicon wafer is placed in the process tank with the correct lattice orientation. After the etching process begins, the temperature becomes the critical factor in obtaining the desired etching results.

Modutek’s Teflon tanks are designed to minimize particle contamination and deliver fast heating with accurate temperature control. The tanks have an all-Teflon liquid path and are available in circulating or static models. The heater can be located in the overflow weir or inline. Even heating throughout the tanks ensures that the etching rate is the same everywhere.

To facilitate etch rate control, Modutek’s Teflon tanks heat up quickly at a rate of 2 to 3 degrees centigrade per minute. Once the set point is reached, the temperature controller maintains the temperature at plus or minus 0.5 degrees centigrade. The tanks can operate at 30 to 100 degrees centigrade and temperature and level limit settings can be applied. KOH etching proceeds quickly and reliably to produce the desired microscopic silicon structures.

Modutek Designs Teflon Tanks to Match Customer Requirements

Modutek’s in-house team works closely with customers to ensure that their wet process equipment meets their needs. While standard Teflon tanks are available, Modutek will design and build custom sizes with special features as required. Whether standard or custom designs, the high-quality materials, and precision controls ensure that KOH etch results satisfy even the most demanding requirements and that the Teflon tanks deliver the expected performance. For a free quote or consultation to discuss your specific process requirements contact us or call 866-803-1533.

Innovative Table Top Units that Support Chemical Wet Processing

Research, proof of concept, or prototyping often require the production of single silicon semiconductors or a small number of functional units. Using a semiconductor manufacturing line for this purpose is expensive and lacks flexibility. Wet process manufacturing can be scaled back to reduce equipment size without losing functionality. Modutek has developed table top units that can carry out the most important silicon wet etching functions to produce small volumes of semiconductor products quickly and efficiently.

Modutek’s Table Top Units Support the Most Common Kinds of Chemical Wet Processing

The table top chemical wet processing units that are compact, self-supporting systems made up of a Teflon tank or stainless-steel solvent tank and a control box. The tanks are available as ambient or temperature-controlled models and can be static baths or recirculating baths with a filter. They support KOH etch, buffered oxide etch (BOE), solvent resist strip and they can be fitted out for other types of wet processing.

The temperature-controlled tanks feature fast temperature rise, uniform heating, and accurate temperature maintenance. Tanks have an all-Teflon fluid path, level, and temperature alarms, and a drain interlock. Their size makes them ideal for small batches, test units, or multiple versions of a basic design.

KOH Etch Using Modutek Table Top Units

KOH etching is widely used because it is relatively safe and easy to control. The concentration of the potassium hydroxide and the temperature of the bath are the key variables for determining the etch rate. Once the concentration is set, the table top units can control the temperature to get the desired etch rate. The rapid temperature rise speeds up the overall process and improves efficiency. The precision of the temperature control ensures that the etched cavities in the silicon wafer are exactly as required and provide for excellent repeatability.

The table top units are designed to minimize impurities and deliver high-quality output. Design changes in semiconductor structure are reliably carried out while the basic structures of the original design remain identical from one process run to the next.

The Table Top Units Can Handle Solvent Resist Strip

Solvents used in semiconductor manufacturing can remove resist, oils, and organic contaminants from silicon wafers in preparation for further processing steps. Acetone, isopropyl alcohol (IPA) and ethylene diproxitol (EDP) are solvents commonly used to clean wafers, remove photoresists, and in pattern transfers for the creation of microscopic structures on the wafer. The solvents are inflammable and require special safety measures to reduce the risk of fire and explosion, and they have to be disposed of safely. Modutek’s table top system supplies all of this in an easy-to-install design package.

Sub Ambient Buffered Oxide Etch (BOE) with Table Top Units

The BOE process is used to etch thin layers of silicon dioxide or silicon nitride with hydrofluoric acid and a buffer. For sub ambient BOE, the table top units are fitted with a chiller/heater that permits an operation in the 10-to-60-degree centigrade range. The sub ambient filtered etch bath reduces acid consumption and delivers highly efficient filtration. The table top units feature a safe and reliable operation at a comparatively low cost.

Modutek Can Design Custom Units for Special Applications

As a leading manufacturer of silicon wet etching equipment, Modutek designs builds and tests their own products in-house. Modutek works closely with customers to develop innovative approaches that solve industry problems. Contact Modutek for a free quote or consultation for specialized equipment that meets your wet processing requirements.

Improving Silicon Wafer Processing with High Temperature Quartz Tanks

Because silicon wafer processing uses acids and bases, the process requires tanks that are impervious to aggressive chemicals. Quartz tanks are stable and do not take part in wet process chemical reactions, even at the high temperatures reached during some of the process steps. Modutek’s quartz tanks use pure flame-polished quartz to reduce impurities that might contaminate the chemical reactions. To keep the temperature at the setpoint, Modutek has added precise temperature controls. As a result, Modutek’s quartz tanks represent an ideal way to implement wet process wafer fabrication steps.

Quartz Tanks Improve Output by Reducing Contamination

The output quality of wet process semiconductor manufacturing is directly affected by contamination during silicon wafer processing. When microscopic particles adhere to wafer surfaces, wafer etching can be disrupted and the semiconductors produced by the manufacturer can be defective or of poor quality. A major concern during silicon wafer processing is the reduction of the particle count on the surface of each wafer.

The high-purity semiconductor grade quartz used in Modutek’s tanks is made up of a crystal lattice containing tightly-held atoms of silicon and oxygen. These elements remain locked in the lattice while the wet process chemical reactions of wafer cleaning, stripping, and etching take place. This ensures that the quartz tanks act as neutral containers and don’t add contaminants or particles to the wafers.

After processing a wafer through one of the many steps of semiconductor manufacturing, a wafer has to be clean and almost completely free of particles. When Modutek’s quartz tanks are used for processing, potential particle contamination from the tanks is significantly reduced. The tanks are based on over 30+ years of bath design and feature a seamless, sloped flange construction. This is especially important for semiconductor manufacturing as industry trends have been moving toward tighter packing and reduced structure sizes. This means even a single small particle can block an etched path or result in a defective structure. By reducing particle counts, Modutek’s quartz tanks improve manufacturing results.

Quartz Tanks with Tight Temperature Control for Improved Etching Precision

The exact shape and location of etched structures in the silicon are critical for the correct functioning of the final semiconductor device. Etching speed determines the shapes of the etched structures in the silicon and the speed is controlled by the chemical concentration and the reaction temperature. The chemical concentration is set at the beginning of the process steps for most of the processes, but the temperature can be used to control the etching speed.

Modutek’s quartz tanks are designed to keep the temperature at exactly the setpoints required for the process and to deliver the anticipated etch speed. The bath temperature can be controlled precisely up to 180 degrees centigrade and the tanks feature a quick temperature rise of up to 2 degrees centigrade per minute with an accuracy of plus/minus 1-degree centigrade.

Heating is even and the fast rate of temperature increase improves throughput. The high accuracy allows precise prediction of etching distances and reliable repeatability of the process when different batches are manufactured. Tank design provides high reliability and safety with a view to a low total cost of ownership.

Using the Right Quartz Tanks Improves Processing and Overall Output Quality

As a leading semiconductor equipment manufacturer, Modutek works with customers to design processing equipment that will help them meet manufacturing requirements. Modutek’s recirculating and constant temperature quartz tanks improve silicon wafer processing by reducing contaminating particle counts and ensuring precise control of etching. The reduced particle counts and the reliable production of required etched shapes reduce defects and rejects in manufactured devices. Contact Modutek for a free consultation and quote on selecting the right equipment to support your manufacturing requirements.

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 Specialized Equipment Improves Silicon Wet Etching Processes

Results from common wet etching processes such as KOH and Piranha etch can be improved with the use of specialized equipment. Depending on the process, key parameters can be controlled especially well and innovative procedures can reduce particle counts. When specialized equipment is used in silicon wet etching processes, 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 overall facility performance.

KOH Etching is Reliable and Easy to Control

Etching with potassium hydroxide (KOH) is a favorite process for applications requiring tight control of the etch rate. The KOH etch 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.

Modutek Teflon tanks are specially suited for KOH etching because they minimize contamination and feature tight temperature control. The TI static tanks and the TFa recirculating tanks are temperature-controlled models while the TT series of tanks operate at ambient temperature. The TI and TFa models operate over a temperature range of 30 to 180 degrees centigrade and temperature control is within plus/minus 0.5 degrees centigrade. Modutek Teflon tanks with KOH etching feature excellent output quality with low defects and high reproducibility.

Piranha Etch Works Quickly

Piranha etch uses a mixture of sulfuric acid and hydrogen peroxide to quickly remove organic residue such as photoresist from silicon wafer surfaces. The mixture has to be handled carefully because it is highly exothermic when first prepared. Normal operation is often at around 130 degrees centigrade so the process requires tanks that can withstand high temperatures and can be heated.

Modutek quartz baths are ideal tanks for Piranha etching. The QFa series high temperature circulating baths can withstand the initial temperature spike from mixture preparation and the subsequent heating to operating temperature. The quartz tanks heat at a rate of two degrees centigrade per minute and temperature accuracy is plus/minus one-degree centigrade. Modutek quartz baths with Piranha etch represent an inexpensive, safe and reliable etching process.

Buffered Oxide Etch (BOE) Etches Silicon Dioxide

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 reduce consumption of acid and filter out contaminating particles. Temperatures of 10 to 60 degrees centigrade are maintained within plus/minus 1-degree centigrade and the sub-micron particle filter reduces the particle count and improves yields. Modutek has designed the F-series baths especially for BOE applications and delivers a safe and reliable process with low-cost operation.

Silicon Nitride Etching Requires Special Control Measures

A phosphoric acid and de-ionized water mixture etches silicon nitride in a process that requires special stabilizing controls. The mixture usually operates at its boiling point of about 160 degrees centigrade. As the etching proceeds, de-ionized water evaporates, leaving an increasing concentration of acid behind. The higher concentration increases the boiling point and the etch rate. To keep the process working consistently, the concentration has to be restored to the lower level.

Adding enough water to restore the concentration risks an explosive reaction when the water mixes with the acid. Modutek has designed a control system that frequently adds small quantities of water to the silicon nitride wet etching baths whenever the temperature rises. The small amount of water is mixed in immediately and the concentration remains steady. Modutek’s specialized control system ensures improved stability and safe operation.

Modutek’s extensive experience in wet process fabrication allows the company to design and build specialized equipment to meet the needs of its silicon wet etching process customers. Such special equipment can improve output quality, reduce costs, and increase yields.

How Process Controls Improve KOH Etching Results

How Process Controls Improve KOH Etching ResultsWhile potassium hydroxide (KOH) etching is a versatile process for creating silicon microstructures, precise and responsive controls are required to get superior results. The KOH wet bench process is popular because KOH etches quickly and it is less hazardous than some other processes. Combined with accurate chemical delivery and reliable process controls, KOH etching can deliver exact etching dimensions and reproducible results for batch processing.

KOH Etching Can Create Complex Shapes

The KOH process is used widely because, in addition to etching quickly, it can be set up to etch at different speeds in different directions. For example, 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, where the long side has a different etch rate than the short side.

The etching direction is influenced by the crystal lattice orientation of the silicon wafer and possible doping of the wafer with boron. The etching speed depends on the KOH mixture concentration and temperature. To obtain improved KOH etching results, the etching process has to be set up to include all these factors and produce the desired result every time the process runs.

When the microstructures to be etched into the wafer require different etching speeds, the process uses the fact that the crystal lattice can be denser in one direction than another. Because there are more atoms to etch away in the denser direction, etching progresses more slowly. Boron doping is a way to stop etching in a particular direction. KOH will not etch areas with boron impurities, so etching stops at the doped silicon.

Once the wafer with the correct crystal orientation and doping is ready for etching, a basic etch speed can be determined with the KOH concentration. The etch speed is controlled by the KOH mixture temperature but the concentration has to be high enough for the desired etch speed.

Typical KOH concentrations can vary from 10 percent to 50 percent with 30 percent KOH by weight representing a common value. The mixture is heated to between 60 and 80 degrees centigrade and held steady at the temperature that gives the desired etch speed. With right wafer crystal orientation, doping in the right places and the correct etch speed, the microstructures will be completed in a given time.

Teflon Tanks with Precise Controls Produce Improved Output

The Teflon tanks designed and manufactured by Modutek feature the precise temperature controls and accurate support equipment that an effective KOH process requires. To etch the silicon wafer with a high degree of accuracy, operators have to make sure the concentration of KOH is at exactly the right value and have to be able to control the temperature within narrow limits.

Modutek’s wet bench equipment can deliver the KOH mixture to the Teflon tanks at the right concentration. The tank temperature controls can produce a heating rate of 2 to 3 degrees centigrade per minute, leading to rapid correction of temperature deviations. The controller accuracy is plus/minus 0.5 degrees centigrade, precise enough for excellent etching speed control.

The precise controls mean that the etch rate remains exactly at the desired level. The dimensions of the silicon microstructures are etched exactly as planned and the KOH process delivers high-quality output. Equally important is that the next time a batch is run with identical requirements and settings, the output is reproducible and the silicon microstructures are the same.

Modutek offers a complete line of wet bench processing equipment and can adapt the KOH etching tanks as well as other processing stations to meet the needs of its customers. All equipment is designed and built-in house, allowing for extensive customization and unparalleled customer support and service.

How Quick Dump Rinsers Improve Silicon Wet Etching Processes

How Quick Dump Rinsers Improve Silicon Wet Etching ProcessesWhen silicon wafers in a wet etching process need rinsing, quick dump rinsers provide fast and effective rinsing of chemicals and particles. In semiconductor fabrication lines such as those of semiconductor manufacturers and research labs, silicon wafers are etched with chemicals. Once the required structures and current paths have been etched into the silicon, the chemicals have to be rinsed off to prevent continued etching. Modutek’s quick dump rinser uses de-ionized water to wash away all traces of chemicals while introducing no new sources of particle contamination. When rinsing is complete, the quick dump rinser drains rapidly. It combines excellent rinsing performance with fast processing and reduced particle counts.

What Makes a Quick Dump Rinser is Efficient and Effective?

Modutek has applied state-of-the-art engineering techniques to design a quick dump rinser that reduces de-ionized water consumption while featuring a short rinsing time and particle reduction. The large trap door and the contoured rinsing vessel shorten dump times and promote laminar flow to rinse away contaminants. The machined dump door has no seals or gaskets that could entrap particles and the smooth polypropylene construction of the tank ensures that it is not a source of new particle contamination.

When the silicon wafers are placed in the rinser, de-ionized water jets rinse the chemicals from the wafer surfaces. The tank fills, bringing the rinsed contaminants to the surface where they leave the tank through the overflow weir. A nitrogen bubbler generates gas bubbles that rise through the water, removing additional contaminants and particles. At the end of the rinse cycle, the trap door at the bottom of the tank opens to quickly drain the water. The whole process is fast and rinsing is complete without added contamination.

Quick Dump Rinsers Provide Substantial Benefits

The use of quick dump rinsers can improve production line performance and output quality. Modutek has designed its quick dump rinser to address wet process manufacturing concerns, including water use, rinsing effectiveness, particle counts and timing. When quick dump rinsers work rapidly, effectively removing chemicals and particles, throughput can increase and the product rejection rate can go down.

Fast rinsing reduces de-ionized water use. Modutek’s 360-degree overflow weir lets contaminated water exit the tank easily and reduces particle entrapment. Dual overhead spray manifolds and low misting nozzles improve rinsing performance with an even distribution of the spray. The nitrogen gas bubbler and tank design promote an even flow around the wafers and the large dump door drains the tank completely in seconds.

Key benefits include reduced costs, fewer product defects and faster production line operation. Reduced de-ionized water use lowers costs and an optional reclaim system can result in additional savings.

The tight packing of semiconductor structures and their decreasing size makes the process more and more sensitive to particle contamination. Even the tiniest particle can cause defects in the final product. Modutek’s quick dump rinser is designed to reduce particle counts and the product failure rate can decrease as a result.

Rinsing is required after many of the wet process production steps and any time saved with a quick dump rinser is multiplied by the number of times rinsing takes place in the semiconductor fabrication production line. The Modutek quick dump rinser delivers these benefits by addressing overall semiconductor manufacturing requirements.

Modutek Works to Improve the Silicon Wet Etching Process for Customers

In addition to quick dump rinsers, Modutek is committed to helping its customers with standard and custom silicon wet etching equipment. The company’s complete wet process product line includes quartz tanks, Teflon tanks and silicon nitride etch baths. Modutek offers free consultation and can ensure that the delivered systems fulfill the needs of its customers.