How Acid Fume Scrubbers Work to Maintain a Clean Work Environment

Creating silicon wafer microstructures, integrated circuits, and processors requires an extensive multi-step process of etching, stripping, and cleaning silicon wafers. Chemicals such as sulfuric acid, hydrochloric acid or hydrogen peroxide carry out these operations effectively but give off vapor that is harmful for workers inside the workspace and for the environment outside. In addition to affecting worker health, there are regulatory compliance issues for a safe working environment. Acid fume scrubbers remove the harmful vapors from the air, leaving a clean workspace and clean air to be discharged outside the manufacturing facility. Modutek’s acid fumes scrubbers are especially effective and have a low cost of operation as well.

Acid Fume Scrubber Operation

The exhaust air from wet process stations will often contain droplets of the acid used in the process. Even as a mist of fine droplets, these acids remain extremely corrosive and may impact worker health, especially if inhaled. With increasingly strict regulations regarding worker safety and environmental impacts, such exhaust air has to be treated before being released into the workspace or outside.

Acid fume scrubbers neutralize the acid vapors and clean the exhaust air so that it is no longer dangerous for workers or harmful to the environment. The exhaust air containing the acid fumes is passed over a bed of wet packing material. The liquid in the packing material bed includes a chemical that neutralizes the acid safely. The acid droplets dissolve in the neutralizing liquid as the vapor passes over the wet packing bed and the acid is neutralized as it is absorbed from the exhaust air. The air exiting the acid fume scrubber contains only traces of acid and is safe.

The effectiveness of the scrubbers depends on the volume of air the scrubbers can handle and the surface area of the wet packing that is exposed to the acid fumes. Modutek’s acid fume scrubbers use packing material from packing technology leader Lantec to achieve an especially high surface area in the packing bed. To match the air exhaust requirements, Modutek acid fume scrubbers are available with air handling capacities from 500 to 25,000 CFM. Matching the air handling capacity to the high packing material surface area can result in acid fume removal from the exhaust air of up to 99 percent. At the same time, a water re-circulating system with pH control keeps the water consumption to a minimum and operating costs are low. Installing Modutek acid fume scrubbers lets wafer fabrication facility managers keep their workspaces clean and operating environment safe.

The Benefits of Using Acid Fume Scrubbers

When acid fumes get into the workplace, it impacts the workers and can corrode machinery. Even small concentrations can have negative effects over time. A clean work environment is especially important in semiconductor wafer fabrication because contaminants on the wafers affect the quality of the final product. As a result, placing acid fume scrubbers in the air exhausts of wet stations can improve worker health and improve product quality.

Modutek’s high efficiency acid fume scrubbers are complemented by a safe operating environment and an operator-friendly user interface. Double containment construction adds extra safety and there is a bottom drain for easy maintenance. The flow and pressure gauges give the operator a complete picture of the process while level control and metered discharge help ensure proper operation. With the neutralization of the acid taking place within the scrubber, operation of the scrubber is completely safe.

When the work environment is clean, workers will perform better, especially if they know they don’t have to be concerned about their health. Modutek’s acid fume scrubbers ensure that a clean and healthy work environment is possible, even in the face of using chemicals common in wet process wafer fabrication facilities. Contact Modutek for a free quote or consultation on selecting the right fume scrubber for your facility.

 

How Customized Equipment Has Improved the Silicon Wafer Cleaning Process

Different customized systems or custom components may improve silicon wafer cleaning processes because customers have special requirements or because the process characteristics are unusual. Suppliers taking on such projects must have extensive in-house experience and expertise together with a board line of silicon wafer cleaning equipment to provide custom solutions. When customization is required, effective solutions can improve throughput, lower costs, and result in higher output quality and yield. Modutek has both the experience and in-house expertise required to offer such customized equipment.

Customized Software

Modutek’s SolidWorks Simulation Professional and SolidWorks Flow Simulation software allows customers to calculate chemical doses accurately as well as track chemical usage. Such calculations are especially important for custom installations because the inputs and the values obtained may be non-standard. Modutek develops and writes all its own software so the company can make adjustments and implement software customization whenever it’s required by a customer. This means that customers can rely on software that corresponds to their customized systems rather than trying to operate a custom system with standard software. Modutek’s software can tailored to precisely control and monitor even the most customized installations.

Custom-Fit Equipment

A lot of the equipment that goes into a silicon wafer cleaning installation has to fit into an existing space or fit other limiting installation parameters. Such custom-fit equipment may include:

  • Megasonic systems
  • Teflon tanks
  • Quartz baths
  • or other custom equipment

Modutek can build custom versions of these components to fit any existing or new wet process system to optimize the silicon wafer cleaning process. Megasonic cleaning systems can be customized for frequency and power while tanks can be sized according to custom requirements and can be fitted with heaters or re-circulating pumps as required. In each case, Modutek can analyze the silicon wafer cleaning application and recommend the most appropriate solution.

Custom Wet Bench Station Design

When preparing a custom wet bench station design, Modutek first looks at the process specifications. The software, chemical delivery systems, baths and wafer handling must all fit together to satisfy the process requirements. Sometimes customized components can be used in a standard configuration but at other times specially designed components may be arranged in a custom system.

This approach provides end-user flexibility while respecting customer specifications and ensuring that the equipment performs as expected. All systems are designed and built at Modutek’s company facilities based on their own in-house expertise and experience.

Customized Wet Process Systems

Wet process systems can be customized at the component or system level, but they can also feature customized levels of automation. Standard systems are manual, semi-automatic or fully automatic but special solutions are always possible. Customers may want a manual system but also want certain process sub-steps to run automatically. A customer may want the handling of hazardous chemicals to be fully automated for safety reasons but want the rest of the process to be manual. On the other hand, a fully automatic system may have a requirement for operator intervention at a specific point. Because Modutek designs these systems in-house, such customization is seamless and problem-free.

Customized wet process systems can find application in many research and industrial fields. A customized system is often needed for prototype development and testing since the prototype can have unusual or unique features. Cutting-edge research and development in industry or at universities may also require the special characteristics available from customized systems. Even full production manufacturing facilities may need customization if they want to try special cost-cutting or quality-enhancing production methods. In each case Modutek can analyze the requirements and propose solutions.

With over 35 years of experience in wet process technology, Modutek has pioneered customization as a tool for improving silicon wafer cleaning processes and continues to develop unique customized solutions for its customers. If you need a customized solution for your application contact Modutek for a free consultation or quote.

How Silicon Wet Etching Processes Are Improved with Specialized Equipment

how-silicon-wet-etching-processes-are-improved-with-specialized-equipmentWhile Modutek’s wet bench equipment supports all common wet etching processes, the continuous development of new wet bench technologies allows the company to offer specialized equipment that can improve performance for specific applications. Key factors for high output quality, fast processing, high yields and reliable outcomes are cleanliness, repeatability, tight control and precise dosages. Modutek’s standard line of silicon wet etching equipment already scores highly on these factors but the company’s specialized equipment can further improve performance for certain processes.

Buffered Oxide Etch (BOE)

The BOE process requires tight and precise temperature control while filtering lowers the particulate count and reduced acid consumption results in lower costs. Modutek’s F-series sub-ambient circulation bath is specially designed for BOE applications and addresses these factors. The temperature controller is accurate to less than plus/minus one degree centigrade in a range from 10 to 60 degrees centigrade with sub-ambient capability. The circulating bath includes 10.0 to 0.2 micron filtration and is designed for low acid consumption. Using a wet bench system specialized for the BOE process can reduce costs and defects in products while providing safe and reliable operation.

Piranha Etching

The sulfuric acid/hydrogen peroxide mixture of the Piranha solution is extremely corrosive, and the mixture is exothermic when first prepared. The Modutek QFa Series of Quartz High Temperature Recirculating Baths are ideal for withstanding the high temperatures, first of the initial heating after mixing and then during the process that is heated to preserve mixture reactivity. The baths have heaters that can raise the temperature of the mixture by two degrees Centigrade per minute and the temperature controller can maintain the temperature at plus/minus one degree centigrade over a range of 30 to 180 degrees centigrade. These Modutek quartz baths are characterized by the high degree of safety, reliable operation and low cost of ownership.

Potassium Hydroxide (KOH) Etching

Modutek Teflon tanks are ideal for use in KOH etching because they can be custom fitted to any wet bench configuration and come in three models to satisfy common heating and recirculating requirements. The TFa and TI series of Teflon tanks are temperature controlled to an accuracy of plus/minus 0.5 degrees centigrade over a range of 30 to 100 degrees centigrade. The TFa series are overflow re-circulating models while the TI series are static. The TT series are static ambient temperature models. All Teflon tanks are made from PFA Teflon with special welding techniques to minimize the presence of undesirable by-products in the process and to reduce contamination. Modutek’s Teflon tanks improve KOH process control, increasing reliability and reproducibility of process conditions.

Silicon Nitride Etching

Etching silicon nitride with a phosphoric acid deionized water mixture is challenging because the concentration changes as the deionized water evaporates and because adding water to the process can cause an explosion. Modutek’s silicon nitride wet etching bath is specially designed to address these issues and provide reliable and safe process control. The mixture is kept at the boiling point, which changes as the concentration increases. Depending on the temperature of the mixture, small amounts of deionized water are added to the boiling mixture to maintain the concentration at the required level. Using the boiling point temperature as an indication of the concentration and allowing the boiling mixture to immediately distribute small amounts of water lets Modutek control the process while maintaining safe operation.

With its extensive experience in silicon wet etching process technology, Modutek can deliver specialized equipment suited to a particular process and help customers select the right equipment for their applications. With equipment specially designed for the process used, customers obtain superior results while often saving money as well. Contact Modutek for a free consultation or quote on using the right silicon wet etching equipment for your application.

 

New SPM Process Provides 75% Improvement in Chemical Savings

new-spm-process-provides-75-improvement-in-chemical-savings2

Earlier this year Modutek started implementing its new SPM process with automatic adjustment of the sulfuric peroxide mix concentration and the company now has benchmark results from real process applications. Normally the SPM mixture deteriorates continuously as the hydrogen peroxide turns to water and dilutes the concentration. The SPM mixture has to be completely replaced every eight hours or so at the outside. Costs are substantial for downtime during new mixture pour and for the replacement of the chemicals as well as for neutralizing and disposing of the corrosive mixture in an environmentally safe way. Trying to lengthen the period during which an SPM mixture can be used has been an ongoing process for many companies but without results that provide a safe and reliable alternative.

In the Modutek “Bleed and Feed” system, a “dirty” tank and a “clean” tank are used to continuously compensate for changes in the mixture concentration caused by the degradation of hydrogen peroxide. Periodically when needed, a programmable amount of mixture is drained from the dirty tank and another programmable amount of mixture is automatically transferred from the clean tank to the dirty tank. To compensate, an appropriate amount of sulfuric acid is added to the clean tank and both tanks receive enough hydrogen peroxide to restore the concentration. The “Bleed and Feed” process is designed to maintain the SPM mixture concentration automatically over extended periods.

Benchmark Results from a Real “Bleed and Feed” Application

One of Modutek’s customers that use their semiconductor manufacturing equipment now has real-life results from the use of the company’s “Bleed and Feed” SPM process improvements. The results show significant reductions in chemical use, downtime for re-pour and disposal volumes. Detailed results are based on a 2 6-inch carrier bath size with an 8-hour shift and are as follows:

  • Volume of sulfuric acid used reduced by 77%
  • Chemical disposal volume reduced by 75%
  • Acid neutralizer use reduced
  • Acid re-agent use and cost reduced
  • No downtime to drain and re-pour
  • System drains reduced from three times a day to once a week
  • Increased throughput
  • No original process result changes
  • Increased safety due to less operator interaction with dangerous chemicals

While other companies have tried to develop other SPM clean process improvements involving less chemical use, Modutek’s system is now proven to provide excellent results in real life applications and operate reliably.

Improved SPM Process in Custom Designed Systems

While Modutek has developed a greatly improved method for maintaining SPM process mixture concentrations and reducing chemical use, the new method can be applied in any custom-designed SPM process wet bench. Modutek designs and assembles wet bench products and semiconductor manufacturing equipment at their facility in San Jose, California and can supply systems that exactly meet its customers’ requirements.

Process engineers and facility managers concerned about the environmental impact of high toxic chemical use and the increasing costs of chemicals such as sulfuric acid can contact Modutek for a free quote or consultation to discuss solutions to these issues. Modutek can suggest wet bench systems and follow up with proposals from their complete line of wet bench products. If the SPM process is needed by a customer, Modutek now has the benchmark results on reduced chemical use and improved facility operation.

 

How Chemical Delivery Systems Are Designed to Meet Customer Requirements

how-chemical-delivery-systems-are-designed-to-meet-customer-requirements2Many industrial activities require the supply of a variety of chemicals for their manufacturing or production processes. Because the industrial process may include special procedures and the use of specific chemicals, chemical delivery systems often have to be custom-designed to exactly meet the needs of a facility. Typical custom requirements deal with the quantities of chemicals required, how often chemicals have to be changed, how accurate the delivery or the mix has to be and the repeatability of a specific process. Safe handling is an important issue when the chemicals delivered are hazardous, as is safe neutralization and safe disposal. Customized systems can address each of these issues and ensure that the critical requirements are satisfied while leaving out unimportant features for a cost-effective solution.

Delivery Volumes

The quantities of chemicals used greatly impacts the design of the chemical delivery system. Large totes remote from the process can continuously deliver large volumes over extended periods while local drums and tanks can deliver smaller volumes but can be changed when the process requires a different chemical or when a new production process is started. In each case, load or level sensing has to be available so production personnel can plan the required chemical delivery. Software allows operating personnel to predict flows and requirements so adequate supplies are available.

Precision and Repeatability

Different industrial processes have different requirements for precision. For example, research projects often have to record exactly what chemicals were used and their precise quantity. Some semiconductor manufacturing processes also require high precision but others don’t. Precision is linked to repeatability. If a process has to run exactly the same way each time, the level of precision for chemical delivery has to be the same for each run.

Custom design can guarantee that the levels of precision and repeatability required for a process can be achieved, but such features are expensive. Customization means critical requirements are met but if high precision is not required, costs are reduced to cover what is essential for the process.

Safe Handling and Disposal

Customization is especially important for safety because each chemical has its own hazards and each process presents different dangers. Customized chemical delivery systems provide an additional level of safety to employees in the handling the chemicals and operating the delivery systems for specialized applications. Custom designs look at measures such as double-walled containment, corrosion-resistant fluid paths and leak detection for safe handling. Neutralization and disposal requires a customized approach due to the different ways chemicals are used but also because of the different regulations for safe chemical disposal.

Custom Chemical Delivery Solutions from Modutek

Modutek has the experience, the product line and the customization capabilities to satisfy specific customer needs and deliver high-quality, reliable and safe chemical delivery systems. The company designs and assembles all systems in house at their factory in San Jose, California. Because of the presence of in-house expertise for all important subsystems including the chemical delivery software, Modutek can respond exactly to the customization requirements of each manufacturing or production facility and deliver custom solutions that respond to customer needs.

From tote, drum and tank storage possibilities through systems with high precision capabilities, Modutek can deliver the storage and repeatability features needed. The SolidWorks Simulation Professional and SolidWorks Flow Simulation software lets customers calculate precise mix and flow volumes. All chemical delivery systems are characterized by high levels of operator safety and special regulatory requirements for the disposal of toxic chemicals can be incorporated into the custom design as needed. With Modutek’s chemical delivery system designs, customers can be sure they are getting the systems they need. For a free quote or consultation contact Modutek at 866-803-1533 or email [email protected].

How Robotics Have Revolutionized Semiconductor Manufacturing

The automation over the last 25 years of wet bench stations used for semiconductor manufacturing has resulted in more efficient production and an increase in output quality. When the handling and mixing of the chemicals, the handling of the silicon wafers and the timing of the process steps were carried out manually, mistakes could result in defective products. Semiconductor equipment manufacturers have developed automation that has resulted in improved yields and less waste.

Modutek has been on the forefront of developing robotics and process control software that allows fully automatic or semiautomatic processing of silicon wafers. In this way, the entire semiconductor manufacturing process is controlled accurately and reliably. Chemical quantities and process timing are precise, process parameters are reproducible, and material handling is safe. Contamination is reduced with robotic wafer handling. For all these reasons, adding robotics to a wet bench processing line is a cost-effective solution for better facility performance.

Modutek’s Leadership in Wet Bench Robotics

During the company’s history of making wet process equipment, Modutek has focused on the integration of the latest technology in-house and with its own team of specialists. Founded in 1980, Modutek manufactured components such as quartz heated baths, nitride etch baths and rinsing systems. In 2002, Modutek acquired Sysmax Inc. with its advanced automation technology and from there developed its own robotics.

Advances in robotics have allowed Modutek and other semiconductor equipment manufacturers to offer semi-automated and fully automated stations. These wet benches and chemical stations can control the whole semiconductor manufacturing process with no or limited operator intervention. Both fully automated and semi-automated stations produce excellent process uniformity with semi-automated stations and robotics available at a lower cost if full automation is not required.

A key Modutek advantage for this type of equipment is that all process control software and robotics are designed and assembled in-house. The team working in the company’s San Jose, California manufacturing facility carry out all development work for both the SolidWorks Simulation Professional and SolidWorks Flow Simulation software and for the associated robotics. All silicon wafer fabrication equipment is also tested in-house using de-ionized water. As a result, Modutek can offer unparalleled support and customization services.

Advantages and Benefits

The primary motivators for installing fully automated wafer fabrication equipment are to reduce costs and improve output quality. Elimination of human error and increased precision of chemical use means less waste and high-quality products.

Modutek’s SolidWorks Simulation Professional and SolidWorks Flow Simulation software can calculate correct dosages and track chemical usage. With tighter environmental regulations, efficient chemical use not only reduces costs directly but also makes environmental compliance easier and less costly. When the composition of chemical baths is tightly controlled, the etch rate or wafer cleaning is predictable and consistent.

Automatic chemical delivery is not only more reliable than a manual procedure – it is also safer. Spills of hazardous or corrosive chemicals are less likely, and employee safety is increased.

Robotic handling of wafers can reduce contamination and deliver cleaner wafers for subsequent processing steps. The reduced size of features in semiconductor microstructures means that a single particle can block etching of a key feature or impact doping in a critical part of the semiconductor component. It is vital to keep contamination of wafers to a minimum, and robotic handling of wafers reduces the sources of particle contamination.

While some semiconductor manufacturing applications can be automated with standard solutions, in many cases the particular needs of a specific customer can require a degree of customization of the robotics and the process control software. Because Modutek does its own robotics and software design, developing custom applications is never a problem. Modutek’s team knows exactly how each part of the automated systems work and how to make the necessary adjustments.

With Modutek’s more than 35 years of experience, the company continues to promote innovation in robotics for semiconductor manufacturing. Robotics has made the wafer fabrication process more efficient, more predictable and safer. With its complete line of automated equipment, Modutek continues to bring these benefits to customers. For a free consultation or quote contact call 866-803-1533 or email [email protected]

How Megasonic Cleaners Improve Silicon Wafer Manufacturing

The cleaning of silicon wafers is one of the key process steps needed in semiconductor manufacturing. This as become even more critical as micro circuit geometrics continue to shrink on 300 mm silicon wafers. Sub micron particles must be removed from the wafer substrate without damaging the delicate microcircuit structures from previous process steps. Particles that remain may result in defective semiconductor components that don’t work or low quality devices that have sub-par performance.

Incorporating Megasonic cleaning technology in the wafer cleaning process effectively removes sub-micron particles and contaminants without damaging or altering the wafer surface. In order to clean effectively selecting the appropriate frequency and power level is important. Modutek has partnered with Kaijo Shibuya Corporation to incorporate their high frequency Megasonic cleaning systems directly into Modutek’s wet bench process equipment. The wet bench stations combine chemical cleaning processes such as RCA or SC1 with Megasonic cleaning in the megahertz range to remove particles and contaminants down to 0.1 microns. Depending on the cleaning temperature and duration, cleaning efficiencies of over 99 percent can be achieved.

How Megasonic Cleaning Technology Works

Megasonic cleaning systems use a high frequency generator to create high frequency sound waves through the use of a transducer that is immersed in a liquid filled cleaning tank. The compression waves that are generated from the sound create high pressure at their peaks and low pressure at their troughs. Small cavitation bubbles appear in the low-pressure troughs and collapse in the high-pressure peaks. The action of the bubbles in the liquid effectively removes contaminants and particles from the exposed surfaces.

Lower ultrasonic frequencies in the 20-100 kHz range produce relatively large energetic cavitation bubbles which can cause damage to delicate part surfaces. For applications associated with semiconductor cleaning, megasonic cleaning in the megahertz range is required since it generates much smaller energetic cavitation bubbles. The gentle cleaning action from bubbles at the megasonic frequency range will effectively clean without damaging the wafer surface.

The action of cavitation bubbles in the cleaning tank will also agitate the cleaning solution which reduces boundary layers and allows the cleaning solution access very small surface areas such as crevices and complex shapes. The use of megasonic cleaning in silicon wafer manufacturing improves the overall effectiveness of the chemical cleaning solution by removing small sub-micron particles through the action of energetic bubbles.

Modutek’s Use of Megasonic Cleaning

Modutek has used their partnership with Kaijo Corporation to continually improve the cleaning performance of their wet benches by using Kaijo’s Megasonic Cleaning technology. Kaijo is a world leader in megasonic and ultrasonic cleaning systems and Modutek incorporates the Quava megasonic cleaning system generator into their wet bench stations for this application.

The Megasonic cleaning system incorporated within Modutek’s wet bench station utilizes Kaijo’s standard megasonic generator which operates at 950 kHz. Frequency ranges of 200 kHz, 430 kHz, 750 kHz as well as 2 MHz are also available for cleaning applications that require a more or less robust cleaning action. There are three versions of Megasonic cleaning systems available which provide power levels of 600, 900 or 1200 Watts.

Modutek incorporates the use of Megasonic cleaning into their wet benches using either indirect or direct bath designs. Indirect Megasonic cleaning can operate at temperatures of up to 140 degrees centigrade while the direct design places a Teflon-coated transducer directly into the tank and can operate at temperatures up to 70 degrees centigrade. Both design options provide optimal sub micron particle removal without causing cavitation damage to the silicon wafers at the standard 950 kHz frequency.

Process engineers at semiconductor manufacturing fabs have effectively used Modutek’s wet benches stations that incorporate the use of megasonic cleaning to improve semiconductor device yields. The time needed for cleaning wafers is reduced while cleaning effectiveness is higher with less chemical consumption. The use of Megasonic technology has improved the removal of small sub-micron contaminants and has reduced wafer defects to produce better quality semiconductor devices. If you need to improve wafer manufacturing processes and device yields call Modutek for a free consultation or quote at 866-803-1533 or email [email protected].

Why Teflon Tanks Are Used with the KOH Etching Process

KOH etching is a preferred silicon wafer fabrication method because it works rapidly and reliably while handling of the chemicals is relatively safe. The process relies on a contamination-free environment and uses the temperature and KOH concentration to control the etching speed. Teflon tanks are used in this process because the Teflon is stable and doesn’t degrade. The KOH etching process controls allow accurate and repeatable temperature control for reliable fabrication results and high-quality production. KOH etching in Teflon tanks with temperature control is an excellent process for silicon wafer nanostructure fabrication in both manufacturing facilities and research environments.

How KOH Etching Works

KOH or potassium hydroxide etches silicon quickly and at a constant rate that depends on the concentration of the solution and the temperature of the liquid. In addition to these controllable variables, silicon etching is influenced by the crystal planes of the silicon and the doping concentration. These factors can be used to direct etching in certain directions and to stop etching at given points. The result is that KOH etching can produce the precise nanostructures needed as long as the crystal planes and doping are used correctly.

The controllable variables have to be kept tightly to set values and variations have to be minimized. Important factors are the maintenance of the KOH solution at the desired concentration and temperature. The Teflon tanks have to be designed to support the consistent and accurate etching necessary for defect-free wafer fabrication.

Modutek Teflon Tank Features

Modutek Teflon tanks are designed to support KOH etching leading to wafer fabrication of the highest quality. The temperature-controlled tanks are available in re-circulating and static versions and come in standard sizes for single or double carrier capacities as well as in custom sizes when required. The re-circulating tanks have an all-Teflon fluid path, and in the available custom configurations, are easy to integrate into existing fabrication lines.

Modutek Teflon tanks eliminate contamination from the tanks or fluid paths by ensuring the KOH solution only comes into contact with Teflon, which in unaffected by the corrosive chemical. In addition, Teflon welding for the tanks is carried out with advanced PFA sheet welding techniques that reduce impurities and by-products. The result is that the KOH solution stays pure.

A key element of the KOH etching process control is the initial concentration of the KOH solution and keeping it constant throughout the process step. Modutek Teflon tanks have sealed lids that minimize water loss, even during lengthy etching. Water condensing systems and de-ionized water spiking systems are available if the application requires it.

The other variable affecting the etch rate is the temperature of the KOH solution. Modutek tanks have either inline heating or immersion heating in the overflow weir. Temperature can be controlled between 30 and 100 degrees Centigrade with an accuracy of plus/minus 0.5 degrees Centigrade. Heating is rapid with an average heat-up rate of 2 to 3 degrees Centigrade per minute depending on the details of the installation. Rapid heating and tight control result in superior etching performance and consistent output.

To make operation of the KOH etching flexible and convenient, the Modutek Teflon tanks systems have standard drain interlocks and low level, high limit, and high-temperature alarms. Temperature process controllers and remote operation timers are also available.

Modutek Teflon KOH tanks are designed specifically for applications such as KOH etching and Modutek can supply custom systems specially adapted to customer requirements. Tank sizes and controls can be designed to match customer applications. Modutek can rely on its experience and expertise to supply KOH etching systems that meet the highest quality standards and deliver the best output possible.

 

Why Particle Removal is Essential in Silicon Wafer Cleaning

During silicon wafer processing, impurities and particles are deposited on wafer surfaces or are left over from previous process steps. Such particles can cause defects in the final semiconductor product. With the reduced size of today’s silicon wafer microstructures, even the tiniest particles can block etching and affect the diffusion processes. The result appears in the final semiconductor circuit as either as a defect or reduce quality and life expectancy of the product. As a result, the focus of many wafer cleaning operations is to leave the silicon wafer surface intact but free of contaminating particles.

How Particles are Removed from Silicon Wafer Surfaces

The removal of particles can be difficult because they often have a chemical or electrostatic affinity for the silicon surface. They are attracted to the silicon wafer because of electrostatic charges and specific mechanisms have to be used to dislodge and remove them. The smaller the particle, the more such attraction may play a role and the harder it is to remove every particle from the wafer.

Mechanisms to remove particles include silicon wafer cleaning with a chemical that reacts with the particles, cleaning with a solution that dissolves the particles or washing the particles from the wafer surface. In each case, a specific type of equipment is required and traditional standard processes can be used together with new technologies aimed at removing even the smallest particles.

Cleaning Processes

Many chemical processes used to clean silicon wafers have remained unchanged since they were first used 30 years ago. These methods use aggressive chemicals to remove contamination from the wafers, which are then rinsed with de-ionized water and dried. These methods remove most of the contaminants but are less effective in removing the smallest particles. Refined older methods and new technologies such as megasonic cleaning are now often used to complete the cleaning process.

Cleaning methods used at different stages of the silicon wafer fabrication process include the following:

  • The RCA clean process, often carried out in two steps called SC1 and SC2, prepares a wafer for further processing. SC1 cleans wafers with a mixture of ammonium hydroxide and hydrogen peroxide to remove organic residue. SC2 uses hydrochloric acid and hydrogen peroxide to remove metallic residues and particles.
  • The Piranha cleaning process removes large amounts of organic residue such as photoresist. It uses sulfuric acid and hydrogen peroxide in a particularly corrosive mixture that acts quickly but must be handled with care.
  • Megasonic cleaning dislodges particles and other contaminants using microscopic cavitation bubbles generated by a megasonic cleaning system. The bubbles form and collapse in time with the MHz sound waves, delivering a scrubbing action that overcomes particle attraction to the silicon wafer surface.
  • The Ozone cleaning process uses ozone to convert organic particles and contaminants to carbon dioxide. All organic traces on a wafer surface are completely removed, leaving the silicon wafer free from particles.

One of the most critical processes for silicon wafer cleaning is the pre-diffusion clean process that takes place just before the wafers are placed in the diffusion oven. Any of the above methods or a combination of cleaning methods can be used to ensure that wafers are free of particles and the diffusion will be even and consistent.

Equipment Used for Wafer Cleaning

Modutek’s wet bench technology supports all the above cleaning methods and can be provided within their manual, semi-automated or fully automatic systems. The company can offer equipment for traditional cleaning and for the new megasonic and ozone methods as well. All cleaning equipment is available in standard configurations but Modutek can also design custom products to meet the needs of any of their customers’ silicon wafer cleaning requirements. If you need highly reliable equipment to support your semiconductor manufacturing processes call Modutek for a free consultation or quote at 866-803-1533 or email [email protected].

 

How Pre-Diffusion Cleans Are Used in the Wafer Cleaning Process

The silicon wafers processed in semiconductor manufacturing facilities and research centers are repeatedly cleaned in aggressive chemical cleaning baths used to remove surface contaminants from the wafers. The cleaning is important because surface impurities affect the diffusion of dopants in the diffusion ovens. Depending on the next diffusion step, wafers have to be completely clean and several types of material may have to be removed. The wafer cleaning process can include multiple cleaning methods to prepare the wafers for the subsequent diffusion step.

Organic Material and Photoresist

When the previous manufacturing step included masking, wafers may still have photoresist adhering to their surfaces. Any such materials have to be removed because they will interfere with the doping process. If contamination is heavy, Piranha etch, a mixture of sulfuric acid and hydrogen peroxide is often used. The sulfuric acid dissolves the carbon-based compounds and the peroxide oxidizes the carbon to carbon dioxide, which is given off as a reaction product.

General Cleaning and Metallic Particles

For lighter organic contamination the two-step RCA clean process (originally developed by RCA Corporation) is often used. The first or SC1 step cleans organic contamination from the wafers but not metallic particles. The second or SC2 step removes the metallic particles and creates a protective layer on the silicon surface.

SC1 clean involves immersing the wafers in an aqueous mixture of ammonium hydroxide and hydrogen peroxide. This removes traces of organic matter and non-metallic contaminants but it leaves metallic particles on the wafer surfaces. These particles have to be removed before diffusion takes place because they may otherwise be embedded into the wafer in addition to the desired doping and cause defects in the semiconductor material.

In SC2, a hydrochloric acid and hydrogen peroxide solution in deionized water dissolves the metallic particles and leaves a clean wafer surface. In addition, a passivation layer is created that protects the silicon from further contamination. The wafers are now ready for further processing.

Native Oxide Layer Removal

The SC1 clean results in an oxide layer forming on the silicon wafers, and even if SC1 is not used, silicon oxide forms naturally on the clean, bare wafers. For some semiconductor fabrication steps, the native silicon oxide layer has to be removed. The silicon oxide layer is stable and very few chemicals can attack and remove it. Hydrofluoric acid is often used but it is extremely dangerous to handle and a safe set-up is important. Usually the wafers are dipped briefly into the acid, which acts very quickly. After a rinse with deionized water and drying, the wafers are ready for the diffusion oven.

Other Cleaning Methods

For some semiconductor fabrication processes, Modutek has pioneered wafer cleaning methods that avoid the use of harsh chemicals. Megasonic cleaning uses megasonic sound waves in a cleaning solution to dislodge particles and clean wafers. Vibrations and the cavitation bubbles of the high-frequency waves dislodge submicron particles and remove contaminating films. Modutek’s ozone treatment is a fast and cost-effective alternative to chemical cleaning for some applications. The ozone converts organic residue to carbon dioxide and does not leave metallic particles behind.

With its extensive experience in wet processing applications and its expertise in providing high-quality wafer cleaning process equipment, Modutek can advise customers on solutions for their semiconductor fabrication needs. The company can evaluate specific fabrication processes and suggest equipment from its complete line, ensuring that the proposed stations fulfill requirements safely and effectively. Modutek’s wet benches support the pre-diffusion cleaning processes as well as general cleaning, stripping and etching and they are available in manual, semi-automated and fully automated stations. Contact Modutek at 866-803-1533 for a free quote or consultation to discuss which process equipment will work best to support your application.