Isotropic and Anisotropic Silicon Wet Etching Processes

Isotropic and Anisotropic Silicon Wet Etching ProcessesSilicon wet etching is a crucial process used in the semiconductor industry to form various structures and patterns on silicon substrates. Isotropic and anisotropic wet etching techniques are two types frequently used in the industry, each offering distinct benefits and limitations.

Understanding these etching processes’ differences, equipment, and process parameters is essential to achieving desired results. In this article, we will cover the fundamentals of isotropic and anisotropic silicon wet etching processes along with associated equipment used for wet etching as well as process parameters and tradeoffs between them.

Isotropic Silicon wet Etching

Isotropic silicon wet etching is a method that removes material evenly in all directions from a silicon substrate. It’s often used for creating rounded corners or removing material from large areas of the substrate. To accomplish this task, isotropic etchants, such as potassium hydroxide (KOH etching) or tetramethylammonium hydroxide (TMAH etching), are widely utilized in the semiconductor industry.

The advantages of isotropic etching include its ability to produce uniform etch profiles and rapidly remove large amounts of material. Furthermore, isotropic etching can create smooth surfaces on silicon substrates for applications like wafer thinning and polishing.

However, the use of isotropic etching can have drawbacks as well. Without direct control in the etching process, precise structures with sharp corners or defined edges may prove challenging to create. Furthermore, undercutting of the substrate may occur where material from beneath masking layers is removed by the etchant, which leads to an expansion of features beyond their intended boundaries.

In the semiconductor industry, isotropic etching is often utilized for applications like creating through-holes in silicon wafers, creating microlenses for optical applications, and producing thin silicon membranes for pressure sensors. Isotropic etching can also be used to produce microelectromechanical systems (MEMS) devices, where it may create microfluidic channels or remove sacrificial layers.

Anisotropic Silicon Wet Etching

Anisotropic silicon wet etching is a process that selectively removes material from a silicon substrate in one direction, creating well-defined features with sharp corners and edges. This type of etching uses anisotropic etchants that selectively dissolve material along certain crystallographic planes on the silicon substrate.

One commonly-used anisotropic etchant for silicon is a solution that contains nitric acid and hydrofluoric acid (HNO3/HF). This mixture preferentially removes material from the (111) planes of the silicon substrate, creating features with well-defined sidewalls and sharp corners.

Anisotropic etching offers many advantages, such as creating precise structures with well-defined corners and edges, which makes it ideal for applications such as microelectromechanical systems (MEMS) devices and microfluidic channels. Anisotropic etching may also produce gratings for optical applications where precise control over feature dimensions is essential.

The use of anisotropic etching has some drawbacks. The etching process can be slow for deep etches and the rate can depend on the orientation of the silicon substrate. In addition, anisotropic etchants may result in high aspect ratio features being etched, leading to bowing or bending issues in the substrate.

Anisotropic etching is widely utilized within the semiconductor industry for applications including producing precise features for MEMS devices, creating deep trenches for high-density capacitors, and creating grating structures for optical applications. Anisotropic etching can also be used with isotropic etching techniques to form complex three-dimensional structures.

More details on isotropic and anisotropic silicon wet etching can be found in the following documentation:

Comparing Isotropic and Anisotropic Silicon Wet Etching Processes

Isotropic and anisotropic silicon wet etching differ in their mechanisms and surface morphologies. While isotropic etching removes material uniformly in all directions, anisotropic etching preferentially removes material along certain crystallographic planes. The tradeoffs between using isotropic and anisotropic etching depend on the specific application.

Etching Mechanisms: Isotropic etching involves removing material in all directions at an equal rate, creating a rounded profile. Meanwhile, anisotropic etching removes material along specific crystallographic planes, producing sharp corners and edges. Anisotropic etchants allow precise control over the etched features which makes it useful in creating precise structures.

Etched Surface Morphology: While isotropic etching usually produces a smooth surface, anisotropic etching may produce rough surfaces due to exposed crystallographic planes being exposed. In addition, anisotropic etching can create surface defects like hillocks or pits due to these planes being exposed unevenly.

Tradeoffs of Isotropic and Anisotropic Etching: Selecting isotropic versus anisotropic etching will depend on the application requirements. Isotropic etching is an efficient process for producing uniform etch profiles and quickly removing large volumes of material, making it suitable for applications such as silicon wafer thinning and polishing. However, due to lack of directional control during isotropic etching it may be difficult to create precise structures. Anisotropic etching can create precise structures with distinct corners and edges, making it suitable for MEMS devices and microfluidic channels. However, its selectivity often results in slower etching rates and greater aspect ratios, which requires careful consideration of process parameters and equipment when using this method of production.

Wet Etching Process Parameters

Wet etching is a process that relies on a controlled chemical reaction between an etchant and the substrate to achieve the desired etch profile. Controlling the process parameters is key in creating the desired etch conditions which include etch rate, selectivity, and surface roughness characteristics.

Importance of Controlling Process Parameters: Controlling process parameters is essential to achieve consistent and repeatable wet etching results. Even minor fluctuations in temperature, chemical concentration or agitation can significantly affect the etch rate, selectivity, and surface roughness.  By carefully managing these process parameters it is possible to achieve the desired etch characteristics and ensure both quality and consistency with the final products.

Commonly Controlled Process Parameters in Wet Etching: There are various process parameters commonly controlled in wet etching, including temperature, agitation, chemical concentration, and pH. Temperature impacts the rate of chemical reaction which in turn determines the selectivity and uniformity of an etch. Agitation serves to ensure the even distribution of etchant across substrate surfaces which in turn helps with the uniformity of an etch. In addition, the chemical concentration and pH can alter the rate, selectivity as well as surface roughness of substrate surfaces.

Effects of Process Parameters on Etch Rate, Selectivity, and Surface Roughness: Careful control of process parameters can have an enormous effect on etch rate, selectivity, and surface roughness of substrates. Increasing the temperature may increase etch rates, but can also decrease selectivity which results in undercutting or etching unwanted features. Increasing agitation may improve uniformity while at the same time increase surface roughness. By carefully controlling the process parameters it is possible to achieve the desired etch characteristics while mitigating any undesirable side effects.

Wet Etching Equipment

Silicon wet etching is a common process used in the semiconductor industry for precisely patterning and shaping silicon substrates. There are several types of equipment needed for silicon wet etching, each offering their own distinct set of features and capabilities.

Types of Equipment Used for Silicon Wet Etching: Three primary forms of wet etching equipment used on silicon are manual wet benches, semi-automatic wet benches, and fully automated wet processing systems. Manual benches typically serve low-volume production applications while semi-automatic and fully automated systems are used for high-volume production environments.

Key Features and Capabilities of Wet Etching Systems: Wet etching systems typically include a chemical tank, temperature control system, wafer carrier, and system for stirring the etchant. Semi-automatic and fully automated systems may also include robotic wafer handling, as well as chemical mixing and dispensing systems and inline metrology equipment for monitoring process parameters. These wet etching systems can also be tailored or customized specifically to accommodate various substrates and etchants and be designed for specific applications, such as deep silicon etching for MEMS devices.

Factors to Consider When Selecting Silicon Wet Etching Equipment: When choosing wet etching equipment, several factors should be considered, including required etch rate, etch profile, selectivity, and uniformity. Other aspects may include processing substrate type, chemical compatibility of the etchant with the equipment, and the level of automation required by the application. Cost is also a significant consideration, which could range anywhere between tens of thousands to millions of dollars depending on system complexity and capabilities.

Modutek’s Equipment Support for Isotropic and Anisotropic Wet Etching Processes

Modutek provides an extensive supply of silicon wet etching equipment to support customers using the isotropic and anisotropic wet etching processes. This includes Modutek’s Teflon tanks which come in temperature-controlled and ambient versions. For processes dependent on temperature for controlling etch rate, the tank temperature controllers provide rapid and accurate heating. In addition, concentrations can be maintained through supplementation of de-ionized water with custom tank sizes if needed. Contact Modutek for a free consultation or quote on selecting the right silicon wet etching equipment to support your etching process requirements.

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

How the SPM Clean Process Is Supported in a Web BenchEditor’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 Standard Clean Particle Removal (SC1 Clean) is Supported in a Wet Bench Process

How Standard Clean Particle Removal (SC1 Clean) Is Supported in a Wet Bench ProcessEditor’s Note: This article was originally published in April 2015 and has been updated with additional information and reposted in April 2023.

The SC1 clean process is a widely used method for removing particles and other contaminants from silicon wafers. This process involves using a solution of ammonium hydroxide and hydrogen peroxide, which is heated to a specific temperature and then used to clean the wafers. In this article, we will discuss what the SC1 clean process is, its benefits and advantages, and how it is supported in Modutek’s wet bench equipment.

What is the SC1 Clean Process?

SC1 Clean is the first step in the RCA clean, the procedure required before the high-temperature processing of silicon wafers. Organic impurities attached to silicon, oxide, and quartz surfaces by the solvating and oxidizing actions of NH4OH and H2O2 respectively are eliminated by the particle-removing solution, SC1 Clean. This solution starts a slow regeneration process whereby the silicon wafer’s original surface layer of oxide is broken down and replaced with a new layer. This regeneration process is a highly significant part of particle removal.

SC1 solution is used at 75 or 80°C for approximately 10 minutes. It is composed of:

  • 5 parts deionized water
  • 1-part NH4OH
  • 1-part H2O2

The cleaning procedure begins by heating a mixture of deionized water and NH4OH up to 75°C. Then H2O2 is added and the mixture is allowed to bubble violently before use. The silicon wafer is then soaked in the solution for 15 minutes. After this time the silicon wafer is rinsed in a container of deionized water to clean off the solution. The water is changed several times in order to prevent any removed residue from clinging back on to the surface of the silicon wafer. With the new oxide layer on the surface comes ionic contamination that should be cleaned off in the next steps of RCA Clean.

Benefits and Advantages of the SC1 Clean Process

The SC1 clean process offers several benefits and advantages for semiconductor manufacturers. It provides an efficient method for removing particles and other contaminants from wafers. This can result in improved yields, reduced defect rates, and higher product quality. Additionally, the SC1 clean process is highly repeatable, allowing manufacturers to achieve consistent cleaning results across multiple batches of wafers.

Another advantage of the SC1 clean process is that it is environmentally friendly. The process uses only a small amount of chemicals, which are relatively safe and easy to handle. Additionally, the chemicals used in the SC1 clean process are readily available and relatively low cost, which can result in significant cost savings for manufacturers.

Support for SC1 Clean Process in Modutek’s Wet Bench Equipment

Modutek’s wet bench equipment is designed to support the SC1 clean process and other standard clean processes used in the semiconductor industry. The company’s wet bench equipment is designed to provide precise control over the temperature, concentration, and flow rate of the SC1 clean solution, ensuring optimal cleaning results.

Wet bench equipment from Modutek is also designed to provide maximum process flexibility, allowing users to customize the SC1 clean process to meet their specific cleaning needs. This can include adjusting the cleaning time, temperature, and concentration of the SC1 clean solution to achieve the desired cleaning results.

Overall, the SC1 clean process is an efficient and effective method for removing particles and other contaminants from silicon wafers. With its numerous benefits and advantages, including improved yields, reduced defect rates, and higher product quality, the SC1 clean process is an ideal choice for semiconductor manufacturers looking to improve their manufacturing processes. With Modutek’s wet bench equipment, users can be confident in achieving optimal cleaning results while maintaining maximum process flexibility.

Using Megasonic Cleaning with SC1 Clean

The use of megasonic cleaning is often used with the SC1 cleaning process to improve results. Modutek’s partnership with Kaijo Corporation provides cutting-edge high precision megasonic cleaning technology. Megasonic cleaning can remove particles as small as 0.1 µm with Modutek’s Indirect (MSI Series) bath design. Another option is to use Modutek’s Direct (MSD Series) with the Teflon coated Megasonic transducer. When placed in the cleaning tank, the transducer plate is ideal for using SC1 Clean and is easily accessible for installation and upgrades.

Modutek’s Megasonic cleaning features include:

  • Automatic frequency tracking system
  • High-efficiency generator
  • Upper and lower limit controls
  • Available frequencies: 430kHz and 950kHz

Modutek’s Experience and Expertise

Modutek has been in the business of designing and supplying wet process equipment for over 40 years. This history is sustained by experts who will work with you from design to final equipment installation. Contact Modutek for a free consultation to discuss your process requirements.

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

How the Advanced Ozone Cleaning Process Improves Wafer Yields and Reduces CostsEditor’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

Using Modutek’s Teflon® Tanks with KOH and TMAH Etching ProcessesEditor’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: Static KOH Etching bath with condensing coils

  • 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 robotModutek 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

How Piranha Etch is Used in Silicon Wafer CleaningEditor’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.

Advanced Wafer Drying using Modutek’s IPA Vapor Dryer

Advanced Wafer Drying using Modutek's IPA Vapor DryerThe successful manufacture of tightly packed semiconductor products depends on obtaining low particle counts on silicon wafer surfaces after rinsing. Heat drying and spin dryers may leave water marks and residue as the water evaporates. Modutek’s advanced IPA vapor dryers use the Marangoni drying effect to reduce particle counts to a minimum. The compact dryer unit can be integrated into wet processing equipment as needed. Modutek’s IPA vapor dryers can increase yields and improve output quality based on reduced particle counts compared to other drying methods.

How the IPA Vapor Dryer Works

In Modutek’s IPA Vapor dryer, an even vapor distribution is ensured by introducing the IPA vapor at the top of the dryer. The vapor is generated in a standard one-gallon bottle located in the exhaust compartment and fitted with a level sensor. Changing the bottle is quick and easy. This arrangement reduces IPA consumption but allows enough vapor to develop the surface tension gradient. As water drains from the bath and runs off the silicon wafer, a small amount of IPA vapor interacts with the thin film of water still coating the wafer. Because IPA has a lower surface tension than water, the surface tension gradient causes the water to flow off the wafer surface. As the water retreats, its flow takes along contaminating particles and other impurities, leaving the wafer completely clean. Because no water is left on the wafer surface, water marks from evaporating water are eliminated.

Advanced Wafer Drying Delivers Many Advantages

The main advantage of using Modutek’s IPA vapor dryer is the reduced particle count. Spin dryers can add particles from the centrifugal action of the spinning. Also, some water will be left to dry, leaving water marks. The Marangoni drying effect utilized in the IPA Vapor Dryer significantly improves wafer cleanliness. Other advantages of Modutek’s dryer include compact installation, low IPA use, and a simple design with no moving parts. The dryer design is flexible enough so that it can be integrated into wet processing equipment. The dryer function can use the same tank as rinsing to save space with a single cabinet. Since the wafers don’t spin, there is no risk of breakage, and a typical drying cycle is completed in ten to fifteen minutes.

The Use of Modutek’s IPA Dryer Can Provide Substantial Benefits

A semiconductor manufacturer can reap substantial benefits when Modutek’s IPA vapor dryer is integrated into wet processing equipment. These include the following:

  • Higher throughput due to faster drying times
  • Higher yields due to fewer defects from contaminating particles
  • Lower costs because of low IPA consumption
  • Reduced space due to compact cabinet construction and integration with rinsing
  • No IPA heating required
  • Flexibility due to multiple drying recipes
  • Easy operation with PLC and touchscreen
  • Safe operation with safety interlocks, auto lid, and PVC side shields
  • Interface capable of working with robotics in wet bench
  • No breakage from spinning because there are no moving parts

Additional Features for Specific Applications

In addition to the direct benefits listed above, Modutek’s dryer can be adapted to specific wet process applications. Possible options include an ozone feature that introduces ozone into the cabinet, a quick dump feature, a static eliminator, data logging, and fire suppression. The dryer can handle all wafer sizes and most glass substrates.

Modutek Provides Solutions to Meet Customer Needs  

Modutek understands wet-process semiconductor manufacturing and has the in-house expertise to find the best solutions. When working with customers, Modutek can evaluate customer needs and make specific proposals from their complete line of wet-processing equipment. After delivery and installation, Modutek provides unparalleled support to ensure the equipment continues to meet customer expectations.

Why Chemical Delivery Systems Need Customizing for Your Facility

Why Chemical Delivery Systems Need Customizing for Your FacilityIn any industrial process involving chemicals, careful storage, delivery, and disposal of potentially hazardous substances is essential for both safety and efficiency. The chemicals need to be readily available in the correct amounts wherever required in the process. However, the storage of chemicals in the middle of a production line is unlikely to be practical or safe. This requires chemical delivery systems that can seamlessly fit into a facility without increasing risks or reducing productivity.

There is no single solution for chemical storage and delivery systems for industrial facility designers, and the design and placement of the chemical handling equipment will vary from facility to facility. The way chemicals are used directly impacts the system’s design, and the specific kinds of chemicals involved mean that safety aspects need to be considered case by case.

For example, if solvents are used specific materials with fire suppression features must be incorporated to meet safety requirements.  What’s more, all of this usually will need to fit within the restrictions of the existing building unless a new facility is built from scratch.

Bearing all this in mind, custom chemical delivery systems are the most effective way of solving these common problems, and three key points should be addressed right from the start of the design.

  1. Chemical Storage

Whether your process involves high volumes of a single chemical or mixtures of several different ones, they need to be stored in a way that combines complete safety with easy access. The storage units need to be accessible to receive deliveries from suppliers and be kept in an area where any potential leaks or spills can be contained.  They also need full accessibility for efficient delivery to the production line. Modutek can design chemical delivery systems that access chemical storage units up to 100 yards from their point of use. This keeps dangerous substances in controlled conditions far from their point of use to minimize risks without compromising productivity.

  1. Safe and Efficient Chemical Delivery

In most facilities, there’s much more to chemical delivery than simply pumping fluids from storage to the processing location. The chemicals need to be delivered in the exact quantities the process requires, in the correct sequence, and at the right time intervals.

There will also need to be a mechanism for handling delivery failure without risking damage to the facility or wasting the other materials involved in the process. In addition, the system should keep track of the quantities of each chemical used, streamlining stock management and replenishment. Each of these factors will be different depending on the details of the application, so a chemical delivery system designed by experienced experts is vital.

  1. Safe Chemical Disposal in Line with Regulations

Most chemical processes create waste that is still chemically active and often toxic, corrosive, or dangerous in other ways. Safe collection and disposal procedures are essential to protect the facility’s employees and meet all relevant environmental regulations and legal responsibilities. In most cases, residual chemicals must be neutralized on-site before disposal or collected and securely stored before transportation to a dedicated disposal facility. Depending on the specific chemicals involved, the collection and neutralization process can be hazardous, involving toxic vapors, corrosive liquids, and countless other potential dangers. Again, the choice of chemical-handling equipment used during disposal depends entirely on the range of chemicals involved and the risks they create.

The Bottom Line

If you’re looking for the ideal solution for your facility, Modutek has the in-house expertise, experience, and engineering capability to produce customized chemical delivery systems to meet your specific requirements. Modutek also provides a full range of chemical neutralization, collection, and disposal equipment, to ensure your on-site systems meet regulatory requirements and operate reliably with maximum efficiency and safety. Contact Modutek for a free consultation to discuss your facility’s specific chemical delivery and handling requirements.


Why Megasonic Cleaning is Essential for Silicon Wafer Processing

Why Megasonic Cleaning is Essential for Silicon Wafer ProcessingAdding Megasonic cleaning to standard wafer cleaning methods can reduce costs and improve overall semiconductor fabrication performance. Megasonic cleaning is especially useful for manufacturing silicon wafers with the smallest geometries, where almost complete particle removal is necessary for successful manufacturing. The process uses high-frequency sound waves to clean wafer surfaces and can be integrated into wet bench processing stations. Megasonic cleaning is becoming more essential for silicon wafer processing as product complexity increases.

Megasonic Cleaning Can Lower Costs

When Megasonic cleaning is incorporated into a silicon wafer processing line, lower costs can result from reduced chemical use and increased yields. The cleaning method uses only plain water in the cleaning bath and can be substituted for some chemical-based cleaning steps. For some cleaning applications, inexpensive solvents or mild detergents can be added to the cleaning solution. For example, Megasonic cleaning is often used after RCA clean to produce optimum cleaning results and reduce additional chemical usage.

When used with conventional cleaning methods, Megasonic cleaning results in cleaner wafers to reduce particle counts. Defects on the final semiconductor products are reduced. Yields increase because the reject rate is lower, and output quality increases.

How Megasonic Cleaning Reduces Particle Counts

Megasonic cleaning uses high-frequency sound waves to gently dislodge the smallest contaminating particles when wafers are emersed in a cleaning bath. During the last few years, several semiconductor manufacturers have been producing semiconductor devices that use 7 nm technology. Two leading-edge semiconductor manufacturers have recently done die shrinks to support the production of devices using 5nm and 3 nm processes. With increasingly close packing of semiconductor components, thinner conducting paths, and smaller structures, tiny contaminating particles on the wafer surfaces can block etching and cause component defects. The smaller geometries are especially sensitive to particles down to sub-micron size.

In the Megasonic cleaning process, a high-frequency generator produces an electric signal in the megahertz range. A transducer immersed in the cleaning solution converts the electric signal to sound waves. As the sound waves travel through the cleaning bath, they generate microscopic cavitation bubbles. The bubbles are formed in the sound wave troughs at low pressure and burst at sound wave high-pressure peaks. When a bubble bursts, it releases an energetic cleaning solution jet that strikes the wafer surface and cleans off contaminants. While the jet is powerful enough to remove foreign material from the wafer, it will not damage the underlying silicon.

Chemical cleaning methods effectively remove contaminants, but particles often remain on the wafer surface due to electrostatic and surface tension effects. The chemical action and rinsing are insufficient to remove many of the smallest particles. Megasonic cleaning and the action of the microscopic bubbles and jets dislodge these particles so that they can be rinsed away. The clean wafer is almost completely free of contaminating particles and ready for subsequent processing steps.

How Modutek Integrates Megasonic Cleaning into Semiconductor Manufacturing

While Megasonic cleaning improves cleaning performance throughout the semiconductor manufacturing process, low particle counts are especially critical for pre-diffusion cleans. Modutek has developed a complete line of wet bench stations designed and built using their in-house expertise. As a result, Modutek’s experts can advise customers on how to best integrate Megasonic cleaning in their process line and where it would be the most effective.

Modutek can also evaluate if a final Megasonic pre-diffusion cleaning step would improve process results and recommend additional Megasonic cleaning before critical etching steps. Fabrication with the smallest geometries will benefit the most from using Megasonic cleaning. When customers find that their particle counts at critical process steps are too high, Modutek can help find solutions using Megasonic technology.

Modutek Works with Customers to Provide Solutions

 As a leader in wet process semiconductor manufacturing equipment, Modutek works closely with customers to identify problems and provide innovative solutions. When customers need to upgrade their existing wafer cleaning process, Modutek can incorporate leading-edge technologies to improve wafer cleaning performance.


How Enhanced Automation Equipment Provides Precision Parts Cleaning

How Enhanced Automation Equipment Provides Precision Parts CleaningEnhanced automation equipment provides a more effective and efficient way to clean industrial parts while reducing costs and improving workplace safety. The cleaning methods range from baths with aggressive chemicals to Megasonic cleaning using high-frequency sound waves. For all these cleaning processes, automation can improve consistency and predictability. When the handling of sharp or heavy parts or the mixing of chemicals presents hazards for workers, automation can increase workplace safety. Using enhanced automation equipment can deliver these benefits by taking over the operation of the cleaning process and running it more efficiently.

Automation of the Cleaning Process Can Save You Money

Manual cleaning of parts and monitoring the cleaning process is labor-intensive and time-consuming. Workers must mix the chemicals and place the parts in the bath. If the parts are removed from the bath too soon, the remaining contamination has to be removed by hand. Human error can cause chemical spills or incorrect mixtures. Inconsistencies in the cleaning process can mean poor results that require additional part cleaning.

With enhanced automation, the cleaning process can be optimized. Chemical use is fixed and controlled at optimum values, and spills can be eliminated. Cleaning process times are set, and chemical waste is reduced. Operators can start the automated process and then do other more productive work. When they return, they can remove cleaned parts that are ready for further process steps. Automated precision parts cleaning can reduce costs with lower chemical use and lower workforce requirements.

Automated Cleaning Is Safe for Workers

When workers have to handle parts to be cleaned manually, they must follow safety procedures to minimize the possibility of injuries. Special safety equipment may also be required. Manual cleaning of sharp objects can result in injuries, and handling heavy parts is often difficult, especially when placing them in a chemical bath.

Automated precision parts cleaning systems eliminate many of these safety issues. Heavy parts can be placed in a basket, and the robotics take care of immersing the parts in the chemical bath. The automation system mixes the chemicals and times the cleaning process to ensure all parts are clean. The operators no longer have to handle the chemicals, and the need for manual cleaning is reduced.

Modutek’s Automated Process Stations Can Clean Industrial Parts and Equipment

Modutek has enhanced its automated process stations to clean industrial parts and equipment ranging from the smallest components to parts weighing up to 250 pounds. Typical parts weighing about 50 pounds made of metal or glass can fit into a 2-foot by 2-foot basket. Heavier parts can be placed on a cart and rolled up to the cleaning station. A robot loads the parts into the cleaning station bath, which goes through several automated cleaning and rinsing cycles. The stations can support baskets with parts weighing more than 250 pounds if required. The automated cleaning station design is aimed at cleaning industrial parts that are hard to handle manually.

The automated cleaning process can be observed on a touchscreen showing the major cleaning system components and their status. The touchscreen is also used for programming the cleaning cycles, setting the amounts of chemicals used, the process times, and the rinse cycles. Operators can run the cleaning process and then adapt settings to improve performance. The process is optimized to use the least amount of chemicals to achieve excellent cleaning results.

Modutek’s Expertise in Designing Automated Equipment

Modutek has extensive in-house experience and expertise in designing and building automated process systems. This means Modutek can evaluate customer cleaning processes and requirements and deliver the corresponding industrial parts cleaning equipment to meet their requirements. Modutek’s enhanced automation allows the cleaning stations to reduce chemical use, improve cleaning performance and provide a safer working environment. If you need automated industrial parts cleaning equipment, contact Modutek for a free consultation.