How Stainless-Steel Stations Provide Safe Solvent Processing

Solvents used in semiconductor manufacturing can remove 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 photoresist and in pattern transfers for the creation of microscopic structures on the wafer.

But since these solvents are also inflammable, they require special safety measures to reduce the risk of fire and explosion, and they have to be disposed of safely. Stainless steel wet benches incorporating stainless steel processing tanks are designed with features that provide safe processing of solvents.

Safe operation of stainless-steel solvent stations has to include the following safety measures:

  • Fire suppression – Measures can include electrical design limiting the potential energy of sparks so they can’t ignite solvents and designing equipment to Class 1, Division 2 specifications
  • Fire fighting – It has to be able to extinguish fires. For inflammable liquids such as solvents, gas-type fire systems such as those using carbon dioxide are needed.
  • Protection against exposure – Many solvents are harmful when workers are exposed to them over extended periods, either through direct contact or through breathing the fumes. A complete enclosure of the solvent processing tanks along with effective exhausts limits the amount of solvent to which workers can be exposed.
  • Protection against leaks – A complete enclosure of the solvent processing tanks should also have a leak detection feature.
  • Safe disposal – Disposal of used solvents has to be carried out safely and according to environmental regulations. Disposal can be on site, if the facility has the corresponding capability, or the waste can be stored in a carboy for pick-up by a specialized disposal company.

Modutek’s stainless steel stations are made of 304 stainless steel and are available in fully automatic, semi-automatic, or manual versions. Dry to dry and fume hood designs are possible, and the stations feature casters and leg levelers.

Modutek’s semi-automated and fully automated wet benches have a built-in SolidWorks simulation software that calculates the process flow characteristics, and all design, assembly, and testing is carried out in-house. As a leading wet bench manufacturer, Modutek works closely with customers to design and customize equipment to meet each client’s requirements.

For more details read the complete article, “How Stainless-Steel Stations Provide Safe Solvent Processing”. If you have questions after reading the article or would like to set up a free consultation to discuss your particular needs, contact Modutek via email Sales@Modutek.com or by calling 866-803-1533,

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 Sales@Modutek.com.

How On-Site Acid Neutralization Provide Safe Chemical Disposal

Choosing the right acid neutralization system is crucial. With overall standards getting tighter, it is important to have a system that can automatically add the required neutralizing chemicals to acid waste left over once the semiconductor process step is done.

Such a system should use the least amount of chemicals while ensuring adequate neutralization of waste to comply with the environmental standards. It has to have enough capacity to handle the waste chemical flow. It must also operate reliably, protecting against spills and documenting chemical use and discharge.

Automated acid neutralization systems can operate in either two ways:

  • Continuous flow – this is ideal for large-scale operations. Because the nature of the waste chemicals is known and remains consistent over time, the neutralization process can add fixed amounts of low-pH chemicals to continuously neutralize the waste flow.  Neutralization can be fine-tuned because the overall process doesn’t change.
  • Batch – this is better suited for the production of small quantities of semiconductor products. Typical applications are prototype production, production of small quantities for testing or the manufacture of special components. In this system, the waste chemicals have to be neutralized in small batches. Each process is different. This type of system has to measure the pH of the waste chemicals and determine what low-pH additions are appropriate. The neutralization is different for each batch as is each outflow.

Complete automation of a continuous flow comparatively easy because the process parameters are known and don’t change. The automation only has to add the required amount of neutralizing chemical on a continuous basis and record the resulting pH.

However, doing a complete automation of batch neutralization systems, however, can be challenging. The key variables, the process, and the chemicals involved can vary depending on the batch. First, it has to measure the batch pH and add an amount of low-pH neutralizer. Depending on the chemicals involved, the automated system may have to add different neutralizing chemicals in several stages to achieve the required output. Compared to a fully automated continuous flow system, a fully automated batch neutralization system is complicated to program and difficult to set up. Operator involvement to select the type of neutralization required can simplify the process of the automated system, making it more effective.

Automated acid neutralization systems can help reduce chemical use, reduce spills, and ensure regulatory compliance. The system automatically adds the required chemicals to the waste solution, tracks chemical use, measures outflow pH, and records the results. As a result, workplace safety is increased, and human error is reduced. The records of chemical use and outflow pH can show that the environmental standards are met.

Modutek offers a full line of chemical handling equipment, along with acid neutralization systems. Read their complete article, “How On-Site Acid Neutralization Systems Provide Safe Chemical Disposal”. If you have questions, or would like to set up a free consultation, send an email to Sales@modutek.com or call 866-803-1533.

Using Acid Fume Scrubbers to Maintain a Clean Work Environment

When semiconductor manufacturing process steps involve etching or cleaning with acids, the process station produces fumes, which can be harmful. Acid droplets in the exhaust can cause health risks for workers and corrode equipment.

To address these issues, semiconductor manufacturers need acid fume scrubbers to remove and neutralize acid droplets in the process exhaust. Once the acidic mist passes through the scrubbers, the resulting air is clean enough to be discharged into the workplace or outside. It results in a cleaner and safer work environment for workers.

Acid fume scrubbers work by passing the mist over a wet bed made up of special, large surface packing material. The scrubber has to be able to handle the flow volume from the process exhaust.

Acid fume scrubbers from Modutek use a high surface area packing material made by industry leader Lantec. The packing material is kept wet with a solution that contains acid neutralizing chemicals. As the acid mist passes over the surface of the wet packing material, the acid droplets dissolve in the neutralizing chemicals, removing them almost completely. The discharge air will now be mostly free of acid mist, resulting in a clean and non-corrosive air output.

Modutek’s acid fume scrubbers can remove up to 99% of acid mist. They are available in sizes ranging from 500 to 25,000 CFM. This capacity range will satisfy the flow requirements from the smallest to the largest process volumes.

Benefits and advantages of using Moduteks’s acid fume scrubbers:

  • The high acid mist removal improves workplace air quality.
  • The user-friendliness of the scrubbers means operators do not need extensive training and can reliably achieve operational targets.
  • Low cost of operation and maintenance allows for a quick return on investment.
  • The design flexibility and wide range of capacities ensure that there is a system suitable for most applications.

In addition to wet process station applications, acid fume scrubbers can be used with other chemical handling equipment Modutek offers to provide a clean and safe working environment.

Modutek has additional information in their recent article, “Using Acid Fume Scrubbers to Maintain a Clean Work Environment.” If you have questions after reading the complete article, or would like to set up a free consultation, contact Modutek via email at Sales@modutek.com or by calling 866-803-1533.

How Process Controls Are Improved with Automated Wet Bench Equipment

When semiconductor manufacturing is automated, tight process control can improve overall facility performance.

Among the advantages of an optimized manufacturing process is the reduction of consumption of consumables and more uniform production results. Once a batch has run successfully, an automated process ensures that it will run the same way for the next batches. Well-designed automation will also help reduce silicon wafer handling and particle contamination.

Wet process equipment should also be able to customize the automated functions to meet the needs of the application. Once the process is set up, it can run with a minimum amount of operator interference and monitor.

Here are some of the advantages of an optimized automated wet bench equipment:

  • It can reduce chemical use – A fully automated wet bench equipment uses the least amount of chemicals required to carry out the etching or cleaning function and continues do so reliably.
  • Output quality is improved – With fully automated wafer fabrication equipment, semiconductor component output is consistent with fewer defects and rejections.
  • It reduces environmental impact – Automation can ensure that acid and solvent chemical waste is neutralized, and an automated system can block discharge if the output pH is not within predefined limits. Since all chemical use and discharge is tracked, compliance with environmental regulations can easily be demonstrated.

 Depending on what kind of semiconductor components are being produced, a manufacturing or research facility may require highly customized equipment to carry out the process steps required. The automation has to be flexible enough to accommodate custom process steps and the equipment provider should be experienced enough to customize both equipment and automation.

Ideally, the equipment provider should work with customers to exactly define what is required and then design and develop the wafer fabrication equipment with the required automation.

An experienced equipment provider, such as Modutek, designs and builds its own equipment in house based on extensive experience in wet process technology, leaving it in the ideal position to customize wafer processing equipment as needed to meet specific customer requirements.

Our latest article, How Process Controls Are Improved with Automated Wet Bench Equipment, goes into further detail. After you’ve read it, if you have questions or would like to set up a free consultation to discuss your specific needs, contact us at Sales@Modutek.com or by calling 866-803-1533.

How Chemical Carts Provide Safe Handling and Disposal of Chemicals

The chemicals used in the etching and cleaning semiconductor wafers are usually aggressive. That’s why it’s crucial that they should be stored, delivered to the process, and disposed of properly and safely.

Chemical handling equipment, such as chemical carts (also referred to as chemical pump carts or chemical collection carts), are a convenient way to remove waste chemicals from the process and ready them for disposal.

Modutek’s chemical carts are specifically designed for safe pumping and containment of the chemicals and for moving them to a safe location for further treatment. They allow operators to quickly remove used chemicals from a process line and let the process continue to the next step with a minimum of delay. They are easily rolled up to the process tank that contains the used chemicals and operators can safely transfer even toxic or corrosive chemicals. 

Chemical cart design features:

  • Compact profile at 36 inches long, 18 inches wide, and 42 inches high.
  • Made of white polypropylene resistant against acids (also available in stainless steel for solvent applications).
  • Mounted on lockable swivel casters.
  • Suction wand for emptying process tanks.
  • Independent discharge tube for transfer of waste chemicals to a neutralization system.
  • Pneumatic pump, three-eighths inch.
  • On-cart five-gallon chemical tank with double containment (Department of Transport-approved).
  • High-level sensor interlocked with pump for added safety.
  • All-Teflon piping.

Modutek’s chemical carts allow operators to receive, store, deliver, and discharge these toxic and dangerous chemicals safely. These well-designed carts can help reduce waste, deliver accurate dosages to the process, and track chemical use.

Containment of spills is a crucial safety and environmental issue that can be addressed by good design practices. Modutek’s extensive experience with wet process technology and acids used ensure that the company’s chemical handling equipment operate in a completely safe and reliable manner.

Units similar to chemical carts can take on other functions. For instance, chemical delivery system can handle chemical reception, storage, and delivery to the process. They can include bulk storage such as in large tote chemical containers that can supply high volumes of chemicals, or 55-gallon drums located at the process. These systems can include software for dosage control and software can also control the mixing of chemicals.

Read our newest article, How Chemical Carts Provide Safe Handling and Disposal of Chemicals, to learn more. If you would like to discuss your specific needs or get answers to your questions, contact us via email at Sales@Modutek.com or by calling 866-803-1533.

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.

Improving Standard Clean Particle Removal in a Wet Bench Process

When the Standard Clean process doesn’t result in improved silicon wafer yields, improved particle removal can be done with advanced processing equipment.

Standard Clean, or RCA Clean, was developed by RCA company in 1965 and it has remained pretty much the same since then. While it has been successful in cleaning wafers and removing most particles, with silicon wafers and structures decreasing in size and increasing product density on wafers, even the tiniest particles can cause device defects.

The submicron particles are hard to remove completely with chemicals or by rinsing. The use of megasonic cleaning technology to generate very high-frequency sound waves in the wafer bath provides the capability to dislodge all remaining particles, allowing them to be rinsed away. Megasonic cleaning improves Standard Clean particle removal process, ensuring defect-free production of microscopic structures on the silicon wafer.

How does megasonic cleaning work to improve standard clean particle removal? Here are the two steps that make up the RCA wafer cleaning process:

  • SC1 – It uses a mixture of ammonium hydroxide and hydrogen peroxide. It removes most of the contamination from the silicon wafer surface but introduces metallic ion contaminants that can influence subsequent wafer processing steps.
  • SC2 – It uses a mixture of hydrochloric acid and hydrogen peroxide. It dissolves the remaining contaminants, allowing impurities to rinsed away as they float to the surface of the cleaning mixture.

Megasonic cleaning can remove the majority of these particles while also dislodging the few larger particles that may still be present. The process involves adding a megasonic transducer to the tank holding the wafers. The transducer converts very high-frequency signals from a megasonic generator into sound waves that travel through the rinsing water to strike the wafer surfaces.

As the sound waves travel through water, they create microscopic cavitation bubbles that form and burst in tune with sound wave frequency. As the bubbles burst, they produce tiny jets of water. The jets from the bubbles near the wafer surfaces dislodge any remaining particles, leaving them to be rinsed away at the surface of the bath. This results in an extremely low particle count on wafers that undergo both the RCA and megasonic cleaning.

Learn more about the wafer cleaning process by reading our recent article, Improving Standard Clean Particle Removal in a Wet Bench Process. Modutek, a leading semiconductor equipment manufacturer, is available if you have questions or would like to set up a free consultation. You may call 866-803-1533 or send an email to sales@modutek.com.

The Importance of Pre-Diffusion Cleans in Silicon Wafer Cleaning

In semiconductor manufacturing, pre-diffusion cleaning removes microscopic particles from the surface of the silicon wafer, leading to high-quality output and reduction of defect rates.

Why is pre-diffusion cleaning of the wafers important? As silicon microstructures are designed with smaller elements and with a higher component density, adequate wafer cleaning becomes more critical. Particles that remain in the wafer can prevent even diffusion and may themselves be diffused into the silicon, causing defects.

Several cleaning steps using different processes are sometimes required to achieve a specific level of cleanliness. The goal of pre-diffusion cleaning is to obtain wafers free from organic or metallic contamination and with few surface particles as possible.

Silicon wafer cleaning can be carried out in many ways:

  • RCA Clean, which uses two steps:
    • Standard Clean 1 (SC1) – The wafers are placed in a mixture of ammonium hydroxide and hydrogen peroxide. The corrosive mixture removes organic matter but may leave metal ions behind.
    • Standard Clean 2 (SC2) – The remaining metal ions are removed by immersing the wafers in a mixture of hydrochloric acid and hydrogen peroxide. At the end of the wafer cleaning process, organic and metallic contamination has been removed while as many remaining particles as possible are rinsed away as well.
  • Piranha Clean – It cleans heavily contaminated organic materials (such as photo resist) faster than RCA Clean. The wafers are immersed in a mixture of sulfuric acid and hydrogen peroxide and the mixture may be heated up to speed up the reaction.
  • Megasonic Cleaning – Megasonic cleaning is an ideal alternative to RCA Clean and Piranha Clean, since it doesn’t use corrosive chemical baths in cleaning the wafers. Instead, the megasonic process works by generating high-frequency electronic signal and a transducer converts the signal into sound waves that travel through the cleaning solution. The sound waves carry cavitation bubbles that produce a scrubbing action against the surface of the silicon wafer. The action of the bubbles cleans the wafer. Megasonic silicon wafer cleaning operates in the frequency range near or above 1 MHz and the cavitation bubbles agitate the cleaning solution at the operating frequency. Such agitation breaks the bond holding the particle on the wafer surface and the floating particles can be rinsed away.

Read our complete article, The Importance of Pre-Diffusion Cleans in Silicon Wafer Cleaning, to learn more about the process. You can also contact Modutek to discuss your questions or get a free consultation by sending an email to 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.