Using RCA Clean in a Wet Bench Process

Posted on August 3, 2023 by admin

Editor’s Note: This article was originally published in May 2015 and has been updated with new information and re-posted in August 2023.

The semiconductor manufacturing industry relies heavily on complex and precise processes to create electronic components we rely on every day. One such process is wafer cleaning – an essential step that removes unwanted particles or residue from silicon wafer surfaces that could otherwise compromise product quality or reliability. RCA Clean has been established as an industry standard wafer cleaning process due to its effectiveness in removing both organic and inorganic contaminants from silicon wafer surfaces.

RCA clean is a wet chemical process developed at Radio Corporation of America that involves a series of sequential steps. The objective is to prepare wafer surfaces for further processing while maintaining their integrity, an aim that aligns directly with the needs of Process Engineers.

Process Engineers focus on cost efficiency, reliability and cleanliness, and equipment design for precise process control. Equipment must be easy to use and deliver repeatable processes while meeting specific demands of a facility’s wet processes requirements.

Understanding RCA Clean in a Wet Bench Process

At its core, RCA Clean is a three-step cleaning process aimed at effectively cleaning silicon wafers. Each step addresses different types of contaminants, such as organic residues, thin layers of native oxide, and finally, ionic contamination.

In the first stage of RCA cleaning, commonly referred to as Standard Clean 1 (SC-1), the mixture consists of:

1 part NH₄OH (ammonium hydroxide)
1 part H₂O₂ (hydrogen peroxide)
5 parts deionized (DI) water.

The SC-1 solution efficiently removes organic residues while simultaneously creating a thin silicon dioxide coating to provide additional protection to the wafer surface. The second step is to rinse with deionized water to remove the SC-1 solution.

Next, a dip into hydrochloric acid and deionized water mixture removes the thin oxide layer formed during Step One. Following this, the Standard Clean 2 (SC-2) begins. This mixture consists of:

1 part HCl (hydrochloric acid)
1 part H₂O₂ (hydrogen peroxide)
5 parts DI water

This step helps remove metallic ions and again forms a thin silicon dioxide layer. The process concludes with another rinse and final dip into deionized water heated to 80°C to remove any remaining residuals.

RCA Clean is essential when it comes to achieving cleanliness, consistency, and process control in semiconductor manufacturing. However, the effectiveness of RCA Clean depends on the reliability of the equipment being used. This means using equipment that effectively supports RCA clean and ensures accurate and repeatable results for process engineers.

How Wet Bench Stations Facilitate RCA Clean

Modutek’s wet bench stations have been carefully designed to enhance the RCA clean process and alleviate some of the challenges Process Engineers encounter. Their design places particular importance on chemical compatibility, cleanliness, control, and safety – essential characteristics for successful wafer cleaning.

The wet bench stations at Modutek builds use materials resistant to the chemicals used in the RCA clean process. This ensures that the equipment remains unaffected by the cleaning solutions, allowing for an uninterrupted process and a longer lifespan.

As for cleanliness, Modutek’s stations are designed to minimize particle contamination. Their design limits air movement and deposition of particulate matter. Additionally, all wet bench station components, including process tanks, are designed for easy cleaning, ensuring optimal cleanliness at all times.

Modutek’s stations feature advanced automation capabilities for process control. These automated systems offer high-precision control over process variables like temperature, cleaning time, and concentration of cleaning solutions. This ensures accurate and repeatable RCA clean results while saving time and minimizing human errors. Process Engineers can use this level of oversight to achieve their desired results consistently while saving time and avoiding human mistakes.

The wet bench stations Modutek provides incorporate numerous safety features that promote maximum protection during semiconductor manufacturing processes. This includes chemical-resistant materials, fire suppression systems, safety interlocks, and emergency power-off capabilities.

One way that Modutek’s wet bench systems use to facilitate the RCA clean process is through their temperature control system. For instance, for optimal cleaning results in the RCA Clean process, the SC-1 and SC-2 solutions must be maintained at specific temperatures to work effectively. Modutek’s wet bench stations have been specifically designed to precisely control the temperature of solutions, ensuring an optimal cleaning process.

Incorporating Megasonic Cleaning with RCA Clean

To further enhance the results of an RCA clean process, the use of Megasonic cleaning can be instrumental. Megasonic cleaning utilizes high-frequency sound waves in a liquid medium to generate microscopic cavitation bubbles. When these microscopic bubbles collapse, they create strong local shockwaves that efficiently dislodge and remove contaminants from silicon wafer surfaces. Megasonic cleaning combined with the RCA process can significantly enhance the silicon wafer cleaning process, offering the precision necessary for creating high-quality semiconductor devices with microscopic geometries.

Modutek’s wet bench systems are designed to incorporate Megasonic cleaning seamlessly. Wet process equipment with Megasonic capabilities can operate at multiple frequencies, allowing Process Engineers to optimize the cleaning process for their specific requirements. This provides optimal particle removal, improved cleanliness, and higher yield without damaging wafers or creating defects. With the integration of Megasonic cleaning, Modutek’s wet bench systems provide a better-optimized solution for wafer cleaning.

Cost Efficiency and Ease of Use with Modutek’s Wet Bench Stations

While cleanliness and process control are essential to Process Engineers, cost efficiency and ease of use should be considered when selecting equipment for wet bench processes. Modutek’s wet bench stations are designed with the end user in mind. They provide high-quality, reliable results at an exceptional value proposition. Modutek recognizes the importance of cost control for semiconductor manufacturing facilities and offers solutions that enhance productivity while reducing the total cost of ownership.

The robust construction and quality of Modutek’s wet bench stations extend their lifespan, meaning fewer replacement costs over time and reduced frequency of replacements. Furthermore, their precise control enables businesses to reduce waste while improving yield for higher profits and increased profitability.

Modutek’s wet bench stations are also designed for maximum operator convenience. The intuitive user interface and clear control parameters enable Process Engineers and equipment technicians to master operations quickly, reducing the learning curve and training time. This easy operation also reduces human errors that could otherwise result in costly process defects.

In addition, Modutek stands behind its products by offering top-tier customer service and maintenance support. This helps facilities maintain productivity with minimal downtime for their equipment. Modutek is dedicated to ensuring minimal equipment downtime to maximize productivity for customers. Modutek also provides on-site service, technical support, and spare parts to address any potential issues promptly and effectively.

Conclusion

The need for meticulous and consistent wafer cleaning in semiconductor manufacturing is paramount, and the RCA clean method, combined with Megasonic cleaning, provides an effective solution for ensuring optimal cleanliness. However, the success of these processes relies heavily upon the equipment utilized.

Modutek’s wet bench systems are carefully designed with precision, ease of use, and cost efficiency in mind, making them an ideal choice for the RCA cleaning process. They address key requirements and challenges faced by Process Engineers, such as chemical compatibility and effective process controls, as well as providing safety and maintenance support.

For Process Engineers seeking reliable, effective, and easy-to-use solutions for their wet process requirements, Modutek provides leading-edge solutions. With a strong track record and expert service, Modutek is a trusted name in the semiconductor manufacturing industry. Contact Modutek to schedule a free consultation to discuss your wafer cleaning process requirements.

Silicon Wafer Etching Processes for Wet Processing Applications

Posted on June 6, 2023 by Douglas Wagner

Editor’s Note: This article was originally published in September 2016 and has been updated with additional information and reposted in June 2023.

The production of semiconductor components relies on the etching of silicon wafers using various processes like KOH etching to create the necessary structures and connections. To meet etching requirements, Modutek offers cutting-edge wet bench technology and equipment suitable for many applications. Whether you are a manager overseeing semiconductor manufacturing facilities, a university researcher, or a process engineer within these organizations, Modutek’s equipment will fulfill your silicon wafer etching requirements.

KOH Etching:

KOH etching utilizes potassium hydroxide (KOH) to etch microscopic structures on silicon wafers. This process is highly dependent upon factors that include temperature of the etching bath, the concentration of KOH, and the crystalline structure and impurities within the silicon. KOH etching is known for being a cost-effective and repeatable technique and is well-known in the industry for its rapid etching capabilities.

Modutek provides PFA Teflon tanks from the TFa or TT series specifically tailored for KOH etching applications. These tanks offer excellent chemical resistance and ensure the safe and efficient implementation of this process. By using Modutek’s state-of-the-art wet bench technology and process components, semiconductor manufacturing facilities, research centers, and universities can rely on Modutek to meet their silicon wafer etching requirements.

Silicon Nitride Etch:

Silicon nitride is a commonly used masking material during the fabrication of integrated circuits. A thin silicon nitride film is applied on silicon wafers before being selectively etched away using hot phosphoric acid. The temperature bath is about 180 degrees Celsius, which is the boiling point of phosphoric acid.

Modutek provides Nb series silicon nitride etch baths that are part of a comprehensive suite of wet bench process components to achieve precise temperature control during silicon nitride etching processes. The silicon nitride etch bath achieves accurate process control and excellent repeatability by carefully controlling the ratio of deionized water to phosphoric acid. In addition, the high level of safety provided by Modutek’s equipment ensures a secure working environment.

Piranha Etch:

In semiconductor manufacturing, the Piranha Etch process is used for cleaning silicon wafers. The process consists of a mixture of sulfuric acid and hydrogen peroxide – typically in proportions of 3:1 for concentrated sulfuric acid to one part 30% hydrogen peroxide. This solution effectively removes organic compounds from wafer surfaces and oxidizes most metals.

Modutek focuses on understanding each customer’s specific silicon wafer cleaning requirements and offers tailored solutions from their extensive wet processing equipment selection. The in-house expertise Modutek provides heated quartz tanks to ensure that the Piranha etch process is carried out with precision and efficiency to ensure silicon wafers are clean and ready for additional processing.

Hydrofluoric Acid (HF) Clean:

Hydrofluoric Acid (HF) is used to specifically remove silicon dioxide (SiO2) layers from wafer surfaces. This is an essential process in semiconductor manufacturing applications, such as creating thin films and depositing new materials. Hydrofluoric Acid has high selectivity for SiO2, which makes it an effective choice for etching oxide layers.

Modutek provides specialized equipment to support the HF clean process. This includes wet benches and chemical delivery systems that offer precise control over HF solution, optimizing the etching process while maintaining a safe and controlled environment. By employing Modutek’s expertise and state-of-the-art equipment, semiconductor manufacturers can efficiently remove SiO2 layers to produce superior silicon wafers.

RCA (SC1&2) Clean:

The RCA Clean process consists of two sequential steps known as SC1 and SC2, and is an established method for eliminating organic and inorganic contaminants from silicon wafers. In the SC1 step, wafers are submerged in a solution consisting of deionized water, hydrogen peroxide (H2O2), and ammonium hydroxide (NH4OH). This solution effectively eliminates organic residues, particles, and metal ions from silicon wafers.

After the SC1 step, wafers undergo the SC2 step, which uses a solution of deionized water, hydrogen peroxide, and hydrochloric acid (HCl). SC2 removes metallic contaminants, native oxides, and any remaining impurities to achieve an ultra-clean surface.

Modutek offers advanced wet bench systems with precise chemical delivery and control systems to support the RCA (SC1&2) clean process. These systems ensure accurate mixing and consistent delivery of chemicals for reliable and consistent cleaning results.

In addition, Modutek’s wet bench technology also provides comprehensive rinsing capabilities for efficient removal of cleaning solutions that reduce contamination risks. Rinsing plays an integral part in eliminating residual cleaning solutions while mitigating the risk of contamination. By including advanced rinsing mechanisms, Modutek’s equipment ensures that wafers are thoroughly cleansed before moving on to further manufacturing steps.

Modutek’s Wet Bench and Process Component Solutions

As a premier provider of semiconductor manufacturing equipment for over 40 years, Modutek provides wet process equipment for a wide variety of semiconductor etching and cleaning applications. Modutek’s wet bench technology delivers reliable, repeatable results safely and accurately. In addition, Modutek helps customers find solutions that meet their semiconductor manufacturing requirements. Contact Modutek for a free consultation on selecting the right equipment to support your specific processing needs.

How the SPM Clean Process is Supported in a Wet Bench Process

Posted on May 4, 2023 by Douglas Wagner

Editor’s Note: This article was originally published in Oct 2016 and has been updated with additional information and reposted in May 2023.

Semiconductor manufacturing involves multiple processing steps which include cleaning silicon wafers. The sulfuric peroxide mix (SPM) cleaning process is widely utilized in semiconductor manufacturing. The process utilizes a mixture of approximately 3 parts sulfuric acid to 1 part hydrogen peroxide which is highly effective at eliminating organic and inorganic contaminants from semiconductor wafers. The SPM process is typically performed in wet benches specifically designed for this cleaning process.

The SPM Clean Process

Sulfuric acid in the SPM solution reacts with organic contaminants like photoresist and residue, while hydrogen peroxide oxidizes and removes inorganic contaminants like metal ions and particles from semiconductor wafers. This reaction generates heat which helps to accelerate cleaning. Process engineers using the SPM process in semiconductor manufacturing need to make sure that the chemical ratio and temperature are maintained within safe limits and that the solution and wafers are contained safely in impervious baths. During the process concentration levels may vary from 3 to 1 to a maximum of 7 to 1 and the temperature used may be as high as 140 degrees centigrade. When the solution operating values are chosen, the baths should be maintained at those concentration and temperature values to keep the strip rate uniform.

Advantages of SPM Clean

SPM Clean offers several advantages over other cleaning methods. Its key advantage lies in its effectiveness at removing organic and inorganic contaminants simultaneously. The process is relatively quick usually taking just a few minutes. In addition, the SPM clean process does not damage or etch the substrate beneath, making it ideal for sensitive materials like silicon dioxide and silicon nitride.

Equipment for the SPM Process

SPM cleaning solutions are typically applied in a wet bench designed specifically to facilitate this cleaning method, typically composed of materials compatible with SPM solutions like polypropylene, Teflon, and quartz. Wet benches come equipped with safety features such as fume hoods, exhaust systems, and emergency shutoff switches to help minimize chemical exposure. For consistent and reliable results, SPM clean process equipment typically features process control and automation features to facilitate consistent operations. SPM solution concentration, temperature, and flow rate can all be carefully managed in order to ensure an efficient cleaning process. In addition, automated wafer handling systems may also help minimize contamination risks while improving process efficiencies.

Safety Considerations

To ensure the safe and effective implementation of the SPM Clean process in wet benches, certain practices should be observed. These include adhering to safety procedures, performing regular equipment and tool maintenance checks, optimizing cleaning process performance, and complying with local regulations for waste management and disposal.

Using the SPM Clean Process in Modutek’s Wet Benches

Modutek provides manual, semi-automatic, and fully automatic wet bench systems that support the SPM clean process. Wet Bench systems are available in a wide variety of configurations as well as in custom designs. The fully automated stations use Modutek’s in-house software for automatic process execution with high accuracy, reliability, and repeatability. The semi-automated stations can achieve similar results with robotic controls at a lower cost. The manual stations have the same safety and process features without the cost of automation.

Quartz Recirculating Baths

To work well, the SPM solution must be heated rapidly in a bath that can withstand high temperatures and that will not react with aggressive chemicals. Heating must be even and controlled within a narrow range. At high temperatures, hydrogen peroxide decomposes and the solution must be spiked with more peroxide to maintain its concentration.

Quartz recirculating baths fulfill all these requirements. The quartz can be manufactured in a pure enough form to withstand the temperatures and corrosion while the recirculation allows tight control of concentration with the addition of chemicals as required.

This spiking allows operators to use the solution for a longer period of time rather than discarding the solution when the concentration falls below acceptable levels. Re-using sulfuric acid for as long as possible reduces costs and is desirable from an environmental point of view as well.

Modutek Series QFa Series Quartz Baths

Modutek’s quartz baths support the SPM Clean process and satisfy key conditions for high safety and reliability as well as low cost of ownership. The tanks are made of semiconductor-grade flame-polished quartz and are insulated with high-density alumina-silica fiber rated to 1260 degrees centigrade. The four-sided heating element promotes fast, even heating and the seamless sloped flange and the dual safety snap switch help ensure safe and convenient operation.

The quartz baths have an operating temperature range of 30 to 180 degrees centigrade and they feature a standard heat-up rate of 2 degrees centigrade per minute. The operating temperature can be controlled to within plus/minus 1-degree centigrade and a liquid level sensor is available as an option.

Standard tanks are available in dimensions ranging from 7.75 to 21.5 inches inner side length and in square and rectangular formats. Depths range from 6.75 to 14.5 inches and available heaters are rated 2 to 6 KW. Modutek can design systems with custom vessel sizes to satisfy specific requirements.

The Bottom Line

Modutek’s wet benches and quartz baths are designed with low cost of ownership in mind while emphasizing features that reduce errors and improve reliability. Semiconductor manufacturers using the SPM process can achieve higher throughput and better output quality using Modutek’s equipment. Contact Modutek for a free consultation or quote on wet bench equipment to support your wafer cleaning processes.

How the Advanced Ozone Cleaning Process Improves Wafer Yields and Reduces Costs

Posted on April 6, 2023 by Douglas Wagner

Editor’s Note: This article was originally published in January 2017 and has been updated with additional information and reposted in April 2023.

Modutek’s advanced ozone cleaning is a highly effective method for removing contaminants from wafers. The process involves using ozone gas, which is a highly reactive oxidant, to break down and remove organic and inorganic contaminants from the surface of the wafer. The process is typically performed in a closed chamber that is designed to contain and recirculate the ozone gas.

How Advanced Ozone Cleaning Works

The advanced ozone-cleaning process works by exposing the wafers to a controlled amount of ozone gas. The gas is generated on-site using an ozone generator and is then injected into the cleaning chamber. The wafer is then exposed to the ozone gas for a specific amount of time, which can range from a few seconds to several minutes, depending on the type and level of contamination.

During the exposure time, the ozone gas breaks down and oxidizes the organic and inorganic contaminants on the wafer surface, converting them into carbon dioxide, water, and other harmless byproducts. The byproducts are then removed from the chamber through a ventilation system, leaving the wafer surface clean and free of contaminants.

The advanced ozone-cleaning process is highly effective at removing a wide range of contaminants, including organic and inorganic compounds, particles, and metals. Additionally, the process is environmentally friendly and does not generate any hazardous waste or byproducts. Overall, advanced ozone cleaning is a safe and effective method for removing contaminants from wafers, resulting in improved yields, reduced costs, and increased productivity.

Advantages and Benefits of Advanced Ozone Cleaning

Advanced ozone cleaning is a highly effective method for removing contaminants from wafers, which can significantly improve wafer yields and reduce manufacturing costs. Unlike traditional cleaning methods, such as wet cleaning and plasma cleaning, advanced ozone cleaning uses ozone gas to break down and remove organic and inorganic contaminants from wafers. In this article, we will discuss the benefits and advantages of using advanced ozone cleaning in the semiconductor manufacturing process.

Improved Cleaning Performance

One of the main advantages of using advanced ozone cleaning is its superior cleaning performance. Ozone gas is a highly reactive oxidant that can effectively remove a wide range of contaminants, including organic and inorganic compounds, particles, and metals. Compared to traditional cleaning methods, advanced ozone cleaning can achieve much higher levels of cleanliness, which can lead to improved wafer yields and reduced defect rates.

Reduced Chemical Usage

Another benefit of using advanced ozone cleaning is its reduced chemical consumption. Traditional cleaning methods often require large quantities of chemicals, which can be expensive and potentially hazardous. In contrast, advanced ozone cleaning uses only a small amount of ozone gas, which is generated on-site and does not require the storage or handling of hazardous chemicals. This can result in significant cost savings and reduced environmental impact.

Better Process Control

Advanced ozone cleaning also offers improved process control compared to traditional cleaning methods. By precisely controlling the amount and duration of ozone exposure, the cleaning process can be optimized for each specific application. This can result in improved process repeatability, reduced variability, and higher product quality.

Reduced Downtime

Using advanced ozone cleaning can also lead to reduced downtime and increased productivity. Traditional cleaning methods often require longer cleaning cycles and can result in extended equipment downtime. In contrast, advanced ozone cleaning can be performed quickly and efficiently, reducing the amount of time equipment needs to be offline. This can result in increased equipment utilization and improved manufacturing throughput.

Lower Cost of Ownership

Finally, advanced ozone cleaning can result in a reduced cost of ownership for semiconductor manufacturers. By improving wafer yields and reducing defect rates, advanced ozone cleaning can lead to increased revenue and reduced waste. Additionally, the reduced chemical consumption, improved process control, and reduced downtime can result in lower operating costs and increased profitability.

The Bottom Line

Advanced ozone cleaning is a highly effective method for removing contaminants from wafers, which can significantly improve wafer yields and reduce manufacturing costs. With its superior cleaning performance, reduced chemical consumption, improved process control, reduced downtime, and reduced cost of ownership, advanced ozone cleaning is an ideal choice for semiconductor manufacturers looking to improve their manufacturing processes.

Modutek Provides Solutions for Manufacturers

Modutek offers equipment for applying the ozone-cleaning process to semiconductor manufacturing and can help determine the ideal configuration for a particular application. The company also delivers equipment for traditional chemical bath cleaning methods and is therefore ideally placed to advise how the new ozone cleaning methods can improve production. Semiconductor manufacturers can take advantage of this capability to cut costs and increase productivity at their facility. Contact Modutek for a free consultation to discuss your specific process requirements.

Using Modutek’s Teflon Tanks with KOH and TMAH Etching Processes

Posted on March 21, 2023 by Douglas Wagner

Editor’s Note: This article was originally published in June 2014 and has been updated with additional information and reposted in March 2023.

KOH (potassium hydroxide) and TMAH (tetramethylammonium hydroxide) are two commonly used chemicals for etching silicon, glass, and other materials. The etching process involves dissolving the surface of the material, leaving behind a desired pattern or shape. When using these chemicals, it is important to choose a tank material that is resistant to their corrosive properties, such as Teflon®.

Modutek provides Teflon® tanks that are well-suited for use with both KOH etching and TMAH etching processes. These tanks are highly resistant to chemical corrosion, making them a safe and reliable option for handling these caustic substances. However, there are several additional considerations that should be kept in mind when using KOH and TMAH for etching.

Etching Rates and Material Compatibility

Another important consideration when using KOH and TMAH for etching is the etching rate. The rate at which these chemicals etch materials can be affected by various factors, including the concentration of the solution, the temperature, and the surface orientation of the material being etched. Proper optimization of these factors is necessary to achieve the desired etching rate and profile.

It is also important to consider the compatibility of the material being etched with the chosen etchant. While KOH and TMAH can etch a wide range of materials, not all materials are compatible with these etchants, and some may require specialized etching solutions. Prior to using these chemicals, it is important to check the compatibility of the material being etched with the chosen etchant.

After etching, residues may be left on the surface of the material being etched. These residues can be removed using a variety of techniques, such as rinsing with deionized water or using a plasma cleaner. The choice of technique will depend on the nature of the residue and the material being etched.

Tank Maintenance and Safety Considerations

Proper tank maintenance is essential for ensuring the longevity of Teflon® tanks used in KOH and TMAH etching processes. The surface of the tank should be kept free from scratches and cleaned regularly with appropriate cleaning agents. Additionally, the tanks should be checked for leaks and other damage periodically to ensure that they remain in good condition.

It is important to take appropriate safety precautions when handling and using these chemicals. Both KOH and TMAH can be dangerous if not handled properly, so it is essential to wear protective gear such as gloves, safety goggles, and lab coats. Proper ventilation should also be used which can be provided with chemical fume hoods. Additionally, proper chemical waste disposal procedures should be followed to ensure the safe disposal of these substances.

Modutek’s Equipment Support for KOH and TMAH Etching

Modutek’s TFa and TI series PFA Teflon® Tanks, and other wet bench equipment, fully support KOH etching and TMAH etching processes. These Teflon® Tanks are designed together with other wet bench equipment to decrease impurities and unwanted byproducts due to advanced welding techniques with PFA sheet material. Continual adjustments to the Si etching process are not necessary after the initial process has been established. Modutek constructs all Teflon® Tanks and related equipment per individual customer specifications, and routinely design products that are compatible with a customer’s existing wet bench equipment.

Modutek’s Teflon® Tanks have an operating temperature range from 30 – 100º C, with a process temperature control of ± 0.5º C and a heat-up rate from 2-3º C per minute (depending on the size of the system). The modular design allows for new installation or upgrades into any wet etching station configuration.

Teflon® Tank Configurations that Support KOH and TMAH Etching:

Temperature Controlled Re-circulating Baths (TFa Series)
Temperature Controlled Static Baths (TI Series)

Teflon® Tank design features:

Manual cover with overlapping seal
Minimizes water lost
No concentration deficiency over a long etch time

Heat source options include:

Teflon® inline heating
Immersion heating in overflow weir for TFa Series and main tank for TI Series

Custom Teflon® Tanks and Additional Options:

Custom size Teflon® tanks can also be built to match any size (no limitations)
Bottom drain features
Magnetic stirrer for agitation (TI and TT series)
Water condensing refluxor system available on all baths
Auto lid feature
DI water or IPA spiking system available

Benefits of Modutek’s Teflon® Tanks:

Modular design
Two available heat sources
All Teflon® fluid path
Process temperature control of ± 0.5º C
Process etch uniformity wafer to wafer <2%
In-house heater maintenance and repair
360-degree overflow filtration
Uniform heating throughout the bath

KOH etching tank with condensing coils and semi auto robot Modutek provides world-class service, installation, and support for all Teflon® Tanks and related wet bench equipment. In addition, Modutek provides quality products that focus on reliability, precision, throughput, usability, and up-time. For more information contact Modutek for a free quote or consultation.

How Piranha Etch is Used in Silicon Wafer Cleaning

Posted on March 7, 2023 by Douglas Wagner

Editor’s Note: This article was originally published in December 2016 and has been updated with additional information and reposted in March 2023.

Silicon wafers are fabricated with repeated etching and cleaning steps to produce the micro-structures required for the final silicon semiconductor products. Piranha or SPM (sulfuric peroxide mix) solutions can clean organic material from wafers and oxidize most metals. The powerful chemical action that makes it a favorite for resist strip and for cleaning wafers with organic residue also makes it difficult to use. High-quality silicon wafer cleaning equipment designed to handle the corrosive chemicals safely is required for carrying out piranha etch safely and effectively.

What is Piranha Etch and How is it Used

Piranha etch is a highly corrosive mixture of concentrated sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) commonly used in the microelectronics industry to clean and etch silicon wafers. It is called “piranha” due to its aggressive nature, similar to the ferocious piranha fish found in the Amazon River.

The most common ratio is approximately three parts acid to one part peroxide, but solutions of up to seven parts acid to one part peroxide are sometimes used. The solution is highly exothermic and is prepared by slowly adding the peroxide to the acid. The mixture heats up rapidly and is often used at temperatures of around 130 degrees C. Once the operating temperature and the desired concentration are reached, the wet bench equipment must heat the solution to maintain the temperature and keep the etch rate constant.

Piranha etch is primarily used to remove organic and inorganic contaminants from silicon wafers, which can negatively affect the performance of electronic devices. The highly oxidizing nature of hydrogen peroxide and the dehydrating property of sulfuric acid make piranha etch highly effective in removing photoresist residues, heavy metals, and other contaminants that may be present on the surface of silicon wafers. The underlying surfaces are hydroxylated, making them hydrophilic or attractive to water, a characteristic that can be used in subsequent silicon semiconductor manufacturing process steps.

Piranha Etch Process Steps

The process of using piranha etch involves several steps. First, the silicon wafer is rinsed with deionized water to remove loose particles or dust. Then, the wafer is immersed in a piranha etch bath for a short period, typically 10-30 minutes, depending on the level of contamination. During this time, the piranha etch reacts with the contaminants on the wafer, breaking them down and removing them from the surface.

After the piranha etch treatment, the wafer is rinsed several times with deionized water to remove any remaining piranha etch solution. It is important to note that piranha etch is a very dangerous substance and should be handled with extreme caution. The mixture is highly reactive, exothermic and produces toxic fumes that can cause severe burns and respiratory problems. Proper safety equipment, such as gloves, goggles, and fume hoods, should always be used when working with piranha etch.

Spiking the Piranha Solution to Maintain Concentration

When a facility wants to reuse a piranha solution for an extended period, the solution must be spiked with extra hydrogen peroxide. Hydrogen peroxide is unstable in the solution and decomposes, reducing the etching power of the bath. Spiking with additional hydrogen peroxide lets operators use a piranha solution for up to eight hours rather than replacing it every two hours. Spiking saves money by conserving sulfuric acid but requires wet bench equipment to handle the process and the spiking.

Modutek’s Silicon Wafer Cleaning Solutions

Modutek’s wet bench and silicon wafer cleaning equipment provide wafer cleaning solutions. The company can supply standard equipment or customize wet bench solutions to meet specific customer requirements. Priorities are high-quality materials, excellent designs, and low cost of ownership to achieve optimized process results. Piranha wafer cleaning is supported with Modutek’s QFa high-temperature recirculating Quartz Tanks and the QA constant temperature baths. Both can be installed in a wet bench station, and the process can be controlled automatically, semi-automatically, or manually.

The QFa series high-temperature re-circulating Quarz Tanks provide fast even heating over a temperature range of 30 to 180 degrees C. The heat-up rate can be up to 2 degrees C per minute, and the temperature control is up to plus/minus 1 degree C. The quartz bath is made of flame-polished semiconductor-grade quartz insulated with silica fiber rated up to 1260 degrees C.

The QA series constant temperature quartz baths are made from the same materials with the same control characteristics as the QFa series, but they feature a magnetic stirrer, an aspirator valve system, a gravity drain, and a quartz bubbler. Both baths are available in standard sizes or can be custom-made to fit customer requirements.

Modutek’s Equipment Provides Safe and Reliable Operation

Modutek can provide a complete range of silicon wafer cleaning equipment that includes baths suitable for piranha cleaning applications. The equipment is designed with safe and reliable operation in mind, and the cleaning equipment eliminates contaminants and impurities to the greatest extent possible. Modutek’s wet bench equipment allows operators to use piranha cleaning methods safely to increase facility throughput while maintaining or improving output quality. Contact Modutek for a free quote or recommendations on using the right equipment for your wafer cleaning application.

Why Pre-Diffusion Cleans Are Essential for Silicon Wafer Processing

Posted on December 20, 2022 by Douglas Wagner

Silicon wafers must be completely clean before they go through the diffusion process. If contaminating particles are present on the wafer surfaces during the diffusion process, they will cause defects in the final semiconductor product. Pre-diffusion cleaning can be carried out with several methods. RCA clean and Piranha etch use chemicals to strip away wafer contamination. Megasonic cleaning uses high-frequency sound waves to dislodge surface contaminants and particles. No matter which cleaning method is chosen, cleaning must be done to reduce contaminating particle counts to a minimum. An experienced manufacturer of wet process stations can integrate the required cleaning methods into wet benches. They can then ensure that the silicon wafers are cleaned thoroughly.

RCA Clean is a Common Silicon Wafer Cleaning Method

RCA clean was originally developed at the RCA corporation and remains a popular all-round silicon wafer cleaning method. It consists of two parts: Standard Clean 1 and 2 (SC1 and SC2). SC1 removes organic material but leaves metallic contamination behind. SC2 cleans the remaining metallic particles and produces a completely clean wafer.

The SC1 cleaning bath contains a solution of ammonium hydroxide and hydrogen peroxide. The cleaning bath is heated to about 75 degrees centigrade, and the wafers are immersed for 10 to 15 minutes. All organic matter and many insoluble contaminants are removed, but some metallic ions stay attached to the wafer surface.

The metallic ions are removed during the SC2 cleaning step. The wafers are placed into a solution of hydrochloric acid and hydrogen peroxide. The solution is heated to about 75 degrees centigrade, and the wafers are immersed for about 10 minutes. Once the wafers are rinsed with deionized water and dried, they are ready for the diffusion processing steps.

Piranha Etch Quickly Cleans Heavy Contamination

When silicon wafers are heavily contaminated or need to be stripped of photoresist from previous process steps, a Piranha mixture is often used to begin the wafer cleaning process. The mix of sulfuric acid and hydrogen peroxide quickly removes large amounts of mainly organic contaminants. While it works more rapidly than RCA clean, it operates at an elevated temperature of 130 to 180 degrees centigrade and is hard to control precisely. Modutek’s proprietary “bleed and feed” process control improves process stability. The advanced controls allow for more precise temperature settings and better cleaning performance while maintaining the rapid removal of contaminants.

Megasonic Cleaning Provides Improved Removal of Contaminating Particles

Megasonic cleaning uses high-frequency sound waves in the cleaning bath to dislodge light contamination from wafer surfaces. The cleaning method features reduced use of toxic and expensive chemicals while reducing particle counts to a minimum. Even the smallest sub-micron particles can distort diffusion and cause defects in the final semiconductor product. These tiny particles are especially difficult to remove because they tightly adhere to wafer surfaces due to static charge and surface tension. Megasonic cleaning generates microscopic bubbles in the cleaning solution. When these bubbles collapse, the resulting scrubbing action removes the particles.

Modutek’s Wet Benches Support Pre-Diffusion Cleans for Specific Wafer Processing Requirements

Modutek wet process stations support all standard silicon wafer cleaning methods. Pre-diffusion cleans can be integrated into a wet bench to satisfy specific customer requirements. Since Modutek designs and builds equipment in-house, wet bench stations can be customized to meet specific customer needs. Based on its in-house expertise, Modutek can recommend solutions for wafer processing and propose equipment from its complete line of wet process stations. Once the equipment is built and delivered, Modutek can provide continuous customer support for the supplied stations. Contact Modutek for a free consultation to discuss your specific process requirements.

How Precise Control of the SPM Process Improves Processing Results

Posted on December 6, 2022 by Douglas Wagner

While the SPM (Sulfuric acid Peroxide Mix) or Piranha process quickly removes organic contaminants such as photoresist, it is difficult to control. The cleaning action depends on both the temperature and the concentration of the mixture. Both vary if the process is left to carry on without intervention. Better controls can improve cleaning performance, reliability, and repeatability while increasing the lifespan of the mixture. Modutek has developed advanced controls that maintain temperature and concentration precisely at their desired levels to improve cleaning results.

The SPM Process Suffers from Decreasing Concentration and Slower Cleaning

The SPM mixture is typically about three parts sulfuric acid to one part hydrogen peroxide. The preparation of the mixture is highly exothermic. Once the mixture stabilizes, the wafer cleaning process occurs in a heated tank at 130 to 180 degrees centigrade. The hydrogen peroxide is unstable and decomposes to form water and oxygen. As the amount of water in the mixture increases and the concentration of hydrogen peroxide goes down, the cleaning effectiveness of the mixture deteriorates.

Small amounts of hydrogen peroxide are periodically added to the mixture to correct the problem of a decreasing hydrogen peroxide concentration. This spiking with hydrogen peroxide causes a sudden temperature increase due to the exothermic nature of the mixing process. While spiking solves the problem of a decreasing hydrogen peroxide concentration, the temperature can’t be kept constant. An SPM mixture that is not spiked is useful for about two hours, but spiking with hydrogen peroxide increases the lifespan of the mixture to about one day.

Modutek Has Developed Advanced Controls to Improve Process Results

Modutek’s “Bleed and Feed” process control strategy keeps the concentration of hydrogen peroxide and the mixture temperature within narrow limits. The temperature variations due to spiking and the need for spiking are eliminated. With concentration and temperature controlled accurately, the strip rate of the mixture remains constant and predictable. Reliable timing and repeatability of the process are excellent.

Modutek achieves these results by using a two-tank control system. The process tank is the “dirty” tank, while the second tank is the “clean” tank. At periodic intervals, a small amount of the mixture is drained from the dirty tank. It is replaced with a fresh mixture from the clean tank. The clean tank mixture is then replenished with new chemicals. A programmable controller controls the process, so the dosage intervals and the amount of mixture to be drained are adjustable and recorded by the programmable controller. As a result, once the process controls are optimized, the SPM wafer cleaning process can be run exactly the same way each time.

Modutek’s “Bleed and Feed” Reduces Costs and Provides Benefits

Customers who have switched to Modutek’s “Bleed and Feed” controls find that their costs are reduced, and the process line performance is better. Modutek’s control strategy reduces chemical use, and the mixture lasts longer when the temperature variations caused by spiking are eliminated. Downtime due to having to replace the bath chemicals is reduced as well. The risk of accidents from operators adding too much hydrogen peroxide or from spills is eliminated. In addition to savings from lower chemical purchases, reduced costs include lower chemical handling, storage, and disposal expenses.

Support for the “Bleed and Feed” Process

Modutek offers the “Bleed and Feed” process controls for the SPM process on new wet process stations. As one of the leading semiconductor equipment manufacturers, Modutek continues to work on improving its silicon wafer cleaning equipment to meet customer needs. Since Modutek designs and builds its equipment in-house, innovative features can be developed to support unique customer requirements. Wet bench processes are often specialized, and Modutek can utilize in-house expertise to customize equipment as needed. Innovation and customization make Modutek a valuable partner for wet bench technology.

How Advanced Ozone Cleaning Reduces Costs and Improves Wafer Yields

Posted on August 4, 2022 by Douglas Wagner

How Advanced Ozone Cleaning Reduces Costs and Improves Wafer Yields When ozone is used to clean silicon wafers, it reduces the use of aggressive chemicals and it can decrease the wafer particle count. Modutek’s advanced ozone cleaning process can clean more quickly than many chemical-based processes and it delivers other benefits. Ozone is used to remove organic contaminants from wafer surfaces in either the Coldstrip sub ambient process or the Organostrip process. Either process can reduce overall wafer fabrication costs and improve manufacturing facility performance.

Advanced Ozone Cleaning Outperforms Chemical Stripping

With increased regulation of the use of dangerous chemicals and pressure on businesses to make their operations more environmentally friendly, Modutek developed the advanced ozone cleaning processes to help semiconductor manufacturers and research labs reduce chemical use. Ozone is introduced in Modutek’s DryZone system in compact units using the Coldstrip or Organo strip processes. Both cleaning methods also feature a reduced particle count compared to chemical cleaning methods.

In the Coldstrip process, wafers are first rinsed with deionized water to remove soluble non-organic contaminants. The process operates at four to ten degrees centigrade. After the rinsing, ozone is introduced into the chamber and combines with the carbon of the organic compounds on the wafer surfaces. The ozone-carbon reaction forms carbon dioxide, leaving wafers clean and almost free of particles.

The Organostrip process also uses ozone but operates at ambient temperature. Ozone is introduced into the process dissolved in acetic acid, a mild solvent in which ozone has a very high solubility. The wafers are rinsed with the ozone-acetic acid solution and the high level of ozone rapidly oxidizes the organic contaminants. The waste products of the process do not require special treatment. Both processes work quickly and feature excellent cleaning performance with low particle counts.

Changing to the Advanced Ozone Cleaning Process Delivers Substantial Benefits

The major benefits of changing from chemical cleaning to an advanced ozone cleaning process is a reduction in the use of toxic chemicals and improved cleaning performance with a lower particle count. These two factors are at the root of additional benefits resulting in cost savings, better yields and improved safety for employees.

Reduced Use of Chemicals

When the use of toxic chemicals is reduced, there are cost reductions in addition to savings resulting from fewer chemical purchases. Other savings include reduced costs for chemical storage, handling and disposal. Employees benefit from lower exposure to harmful chemicals and from increased workplace safety because there is less danger of spills or accidents.

Regulatory compliance costs are also reduced. As environmental regulations become more onerous, costs rise and compliance becomes more difficult. Reduced chemical use results in lower compliance costs, and a more environmentally friendly operation helps improve community relations and the environmental reputation of the business.

Lower Particle Contamination

Lower particle counts are the result of better cleaning performance. Particle counts play ang increasingly important role in wafer structures that are smaller and more tightly packed. Even a single particle can block a conducting path or the etching of a tiny detail. Fewer particles means a lower rate of defective products and higher yields. Product quality and longevity may also be improved.

Improved Cleaning Performance and Wafer Yields with Less Equipment

In addition to a lower particle count, the improved cleaning performance of the advanced ozone cleaning process results in shorter cleaning times within a smaller footprint. Modutek’s DryZone units used for the ozone cleaning process are compact and take up less space than the corresponding chemical cleaning stations. Cleaning is more rapid resulting in higher throughput. As a result of these benefits, the overall performance of the silicon wafer fabrication facility can improve substantially.

Modutek Provides Advanced Equipment for Manufacturers

As one of the leading semiconductor equipment manufacturers, Modutek can advise customers on how to implement a change to ozone cleaning. Modutek offers a free consultation and quote on their equipment, and ensures their equipment will support processes that meet customer requirements.

How the Piranha Etch Process Improves Silicon Wafer Cleaning

Posted on July 7, 2022 by Douglas Wagner

While the Piranha solution quickly removes organic residue from silicon wafers, the process is difficult to control and may produce explosive gas mixtures. The Piranha solution is made up of one part hydrogen peroxide and three parts sulfuric acid, although the ratio may vary for specific applications.

The mixture is exothermic and the heat released when the hydrogen peroxide is added to the sulfuric acid drives up the temperature of the solution towards the normal process operating temperature of 130 to 180 degrees centigrade. Both the temperature and the concentration may vary, reducing the useful lifespan of the solution. When the challenge to control temperature and maintain the concentration is met, the Piranha solution can deliver superior silicon wafer cleaning performance.

Spiking the Piranha Solution Can help Maintain Concentration

The hydrogen peroxide in the Piranha solution is not stable and decomposes to produce water. The rate of decomposition is higher the higher the temperature, and the water dilutes the solution. Operators can compensate for the lower concentration by periodically spiking the solution with additional hydrogen peroxide. As hydrogen peroxide is added, the temperature rises, and more hydrogen peroxide decomposes to form water. This interdependence of the concentration with the temperature complicates keeping a tight control on the process, but spiking the Piranha solution lengthens the solution’s lifespan from a few hours to about one day.

Modutek’s “Bleed and Feed” Method Increases the Piranha Solution Lifespan

Modutek has developed an innovative solution to the control and lifespan issues of the Piranha process. The company uses quartz tanks with a “clean” and a “dirty” tank to provide pre-mixed Piranha solution to the active process. Silicon wafer cleaning takes place in the “dirty” tank while the clean tank has a Piranha solution with a programmable concentration. When the concentration of hydrogen peroxide drops in the “dirty” tank, a small amount of the low-concentration solution is drained from the tank and an equal amount is added from the “clean” tank. Instead of the destabilizing spike of hydrogen peroxide, the small but frequent addition of pre-mixed fresh Piranha solution keeps both the concentration and temperature stable and makes possible a tight control of the process, significantly prolonging lifespan.

The “Bleed and Feed” Method Delivers Important Benefits

Modutek’s “Bleed and Feed” method is fully programmable, allowing operators to adapt it to any application to deliver improved silicon wafer cleaning. The concentrations of the “clean” and “dirty” tanks, the amount of the “bleed” and the amount of the “feed” are all independently adjustable so the desired concentrations can be maintained for an extended period. Specific benefits of the “bleed and feed” method include the following:

Predictable strip rate because both the temperature and the concentration are tightly controlled.
Programmable settings allow a flexible operation.
Risk of an explosion from spiking with too much hydrogen peroxide is reduced.
Longer solution lifespan results in reduced use of chemicals.
Reduced costs for purchase, storage, and disposal of chemicals.
Reliable process parameters result in excellent repeatability between batches and accurate maintenance of process variables over extended operation.
Reduced downtime because the Piranha solution has to be replaced less often.
Safer operation because the process is maintained in a stable equilibrium.

With a more stable Piranha process, silicon wafer cleaning is improved with less contamination and fewer particles. Product defect rates are lower and customers will see higher yields. Overall wet process line performance is improved, with lower costs and better output quality.

Modutek Provides Innovative Solutions for Wet Processing Requirements

Modutek continues to build on its experience in wet process technology and has in house expertise to develop innovative solutions for their customers. The Piranha solution “bleed and feed” method lets customers achieve their production goals more easily. Modutek provides solutions that meet customer needs and ensures that the delivered equipment performs as required. Contact Modutek for a free consultation to discuss the equipment needed to support your specific process requirements.

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