Why Particle Removal is Essential in Silicon Wafer Cleaning

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

How Particles are Removed from Silicon Wafer Surfaces

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

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

Cleaning Processes

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

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

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

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

Equipment Used for Wafer Cleaning

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

 

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

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

Organic Material and Photoresist

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

General Cleaning and Metallic Particles

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

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

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

Native Oxide Layer Removal

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

Other Cleaning Methods

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

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

How Wet Bench Stations Are Tailored for Specific Manufacturing Process Requirements

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The fabrication of semiconductor wafers requires that an elaborate set of chemical etching, stripping and cleaning steps be followed in a precise procedure that can be consistently repeated. The semiconductor manufacturing process requires that the use of hydrofluoric acid and other chemicals which must precisely controlled and monitored. These high-tech processes are critically important to industries that fabricate semiconductors, medical equipment and photovoltaic cells. They require the use of custom-made wet benches designed to assist in the safe and precise control of corrosive chemicals at high temperatures.

Wet bench equipment

Modutek provides a full range of wet bench equipment to address the specialized needs of semiconductor manufacturing facilities and research centers. Wet bench stations can be tailor made according to the specific manufacturing process requirements of a customer.

Citric-nitric passivation wet benches are critical to the passivation of titanium and stainless-steel parts in various industries. Electro-polishing wet bench equipment is deployed in the medical device industry in the manufacture of precision steel, cobalt chrome and titanium components.

Multistage wet process fume hoods with circulation pumps are used in aerospace component manufacture, printed circuit board fabrication, and the semiconductor manufacturing industry. Modutek’s wet bench equipment for the semiconductor industry meets UL2360/FM4910 standards for fire and contamination safety. This enables fabricators to remain compliant with applicable environmental laws.

Titanium anodizing equipment, agitated immersion washers, in-line conveyor washers, spray cabinet washers and other precision equipment are an integral part of the semiconductor industry, as well. Modutek is an industry leader in the design, development and deployment of these and many other kinds of wet bench equipment.

The precision needed in manufacturing equipment

Sulfuric acid-peroxide is a powerful chemical that is critical to the cleaning processes applied to semiconductor wafers. Effective application of this chemical mixture is inherently unstable and requires constant rebalancing. The rebalancing and control is needed to maintain efficiency. The mixture needs to be constantly replenished with hydrogen peroxide at high temperatures, something that can be costly even in simple material costs. Modutek’s high-tech systems not only ensure the correct concentration levels, they also help fabricators contain material costs through the use of an exclusive chemical re-use system to contain material costs. Every part of the process is maintained and monitored by equipment that is software controlled.

The silicon nitride wet etching process is another semiconductor fabrication stage that requires a high level of precision and control. Silicon nitride is used to mask chemical etchings on silicon wafers. Once an etching successfully completes, the masking material requires removal. Typically, a mixture of phosphoric acid and the ionized water is applied. Precise control over the chemical mixture is needed, however, if only to prevent the risk of dangerous heat levels and explosions. Modutek’s wet bench station design addresses this challenge through the use of high-tech safety features and the use of precision software.

Modutek’s in-house design process

From manual to semi-automated and fully automated wet bench stations, Modutek’s products are designed and developed in-house right down to the software. From servo-controlled robots and automated equipment to low-cost manual stations, Modutek’s equipment covers the needs of the industries they serve. With their in house expertise and 35+ years of operation, the company is well equipped to meet and support the requirements of semiconductor manufacturers and research centers. Developing equipment that provides thorough and precise control of the manufacturing process is what sets Modutek apart from other semiconductor equipment manufacturers. Contact Modutek today at 866-803-1533 for a free consultation or quote on wet bench equipment that can be tailor made to support your specific manufacturing requirements.

 

Advancements in Wafer Fabrication Equipment Improve Semiconductor Manufacturing

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While the requirements for high precision control in wafer fabrication have increased, improvements in the fabrication equipment have also kept pace. The higher complexity and smaller size of semiconductor structures require extremely precise process control to ensure adequate output quality and a low component rejection rate. Advancements in automation and in reducing manual handling of the wafers have met these stricter requirements and allowed fabrication shops to increase productivity and reduce costs. Semiconductor equipment suppliers need to provide comprehensive automation solutions to meet in increasing requirements of manufacturers and research centers developing leading edge semiconductor devices.

Automation Advancements

Modutek, a leading semiconductor equipment supplier, provides wafer fabrication equipment that offers fully automated control of the entire processes. Process steps are precisely repeatable resulting in consistent output. Chemical dosage is accurate and the process is executed according to clearly defined steps. While operator intervention is still possible where needed, fully automated stations reduce errors and produce less waste.

Integrated software such as Modutek’s SolidWorks Flow Simulation and SolidWorks Simulation Professional lets operators calculate process variables and track chemical usage. Once the process is programmed, advanced robotics execute the process steps without operator intervention. Operators can rely on a consistent process environment and increased throughput with high output quality.

Both the software and the use of robotics within the automated stations themselves have significantly improved process control and efficiency. Many semiconductor equipment suppliers offer varying degrees of customized solutions for different kinds of wafer manufacturing requirements. At Modutek, both the software as well as the design, assembly and testing of their wet bench stations are carried out at the company’s facilities and are adapted to meet particular process requirements. The ability of suppliers to provide wafer fabrication equipment tailored to meet the unique requirements of semiconductor manufacturers has helped them to improve yields for each specific process they use.

Advanced Equipment Reduces Handling

The last etch process step involves etching the silicon wafer to remove the silicon oxide layer and then drying the clean wafer. Any particle contamination introduced at this point can influence further silicon wafer processing and result in defective or poor quality semiconductor components. Moving the silicon wafers from the last etch process step to a drying chamber risks introducing additional particle contamination. A new product by Modutek combines the last etch (HF) and IPA drying chamber to avoid handling the silicon wafers and substantially reduces the particle count.

The Modutek combined HF last etch and IPA drying chamber is a modified IPA dryer that allows injection of HF acid prior to the start of IPA drying. The ratio-controlled acid etches the wafers down to bare silicon and the wafers are then rinsed with DI water. Once the rinse reaches a pre-defined pH level, the IPA drying process starts with the introduction of IPA vapor from the top. The IPA or Marangoni drying technique avoids watermarks on the wafers. Throughout the process step, the wafers

Benefits from Using Advanced Fabrication Equipment

Modutek offers wet bench stations using the latest technology to improve wafer fabrication equipment and facility performance. With its advanced fully automated stations the company can improve yields by ensuring accurate processing. The software developed in house controls chemical use and precise processing of wafers. The combination of advanced robotics, dedicated software and in house expertise results in consistent, high quality output and reduced costs.

While automation drives a continuous advancement in process reliability and product quality, the elimination of the handling of wafers during transfer into the final drying chamber provides a single substantial improvement through wafer particle reduction. In recent tests only 20 particles (adders) in the 0.3 to 5 micron range were added to the etched substrate in the combined etching/drying system. This single step improvement in the fabrication process can often justify the cost of acquiring the advanced fabrication equipment that will subsequently increase facility performance and profitability.

Modutek has over 35 years of experience providing fully automated wafer fabrication equipment to the semiconductor manufacturing industry. The company has the expertise to advise customers regarding their semiconductor processing needs and can customize their equipment to meet a customer’s application requirements.

Modutek Named Among Top Suppliers in Global Semiconductor Wafer Cleaning System Market

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Modutek is a supplier of wet bench technology, wet processing and chemical handling stations to the semiconductor fabrication industry. The company was recently named as one of the top suppliers in the global semiconductor wafer cleaning system market research report published on eMarkets Europe. Modutek emphasizes in house development of its software and equipment and focuses on a high level of customer support, leveraging the expertise of its own engineers to offer both standard and customized systems. At the forefront of innovative development, the company offers complete solutions to improve semiconductor fabrication facility performance and output quality.

The Characteristics of a Top Supplier

To become a top supplier in any industry a company has to supply high quality equipment that meets the needs of customers over an extended period of time. In the case of semiconductor equipment manufacturers, it means offering silicon wafer processing stations that execute the customer’s processes precisely with high output quality at a reasonable total cost of ownership. Top suppliers will know the details of the different etching, stripping and cleaning processes and will have developed equipment and software that handles them safely and effectively.

Modutek has been supplying the semiconductor equipment industry for over 35 years, building a reputation for high levels of competence and innovation. The company’s wet bench stations support all the common chemical processes for wafer fabrication and Modutek has developed innovative software and process steps that help reduce customer costs while increasing throughput and minimizing defective or low-quality semiconductor products. Modutek’s in house expertise resulting from designing, building and testing its own equipment allows the company to offer customized systems that exactly meet the needs of each customer. A high level of customer service completes the focus on customer satisfaction.

Innovation and Customer Focus

Modutek has become a top supplier to the global semiconductor wafer cleaning system market by introducing innovative solutions to address customer concerns in a changing technical and commercial environment. In general, the company introduces new systems that increase productivity while reducing costs. More specifically, new products allow for maintaining or even increasing yield in the face of challenges from denser component packing and more complex microstructures on the silicon wafer.

In an initiative to reduce wafer particle counts by eliminating particles added during the move from the last etch to the drying chamber, Modutek has introduced a single chamber process. Instead of exposing wafers to contamination during additional handling, the HF acid last etch and IPA drying are performed in the same chamber, eliminating a transfer step. In recent tests, Modutek has been able to demonstrate that the single chamber process is effective in achieving very low particle counts and higher quality outputs.

In addition to such specific innovations, Modutek has developed comprehensive automation solutions that help reduce error and waste. The fully automated Modutek wet process stations deliver accurate chemical dosages and precise process times to ensure exact execution of programmed process steps. Such automation is cost-effective and provides the tight process control required for the latest wafer fabrication tasks.

The Benefits of Choosing Modutek as a Supplier

In addition to the company’s lengthy experience as a semiconductor equipment manufacturer in a field that has a high turnover of suppliers, Modutek distinguishes itself through its in house expertise. All software and equipment design is carried out by Modutek engineers and all equipment is assembled and tested in house. As a result, Modutek can offer unparalleled service and support without having to call on third parties to help out. As a top supplier to its market, Modutek can propose the right solutions to particular customer’s requirements deliver the needed equipment from its extensive range and offer seamless support as needed.

Changes to the SPM Process Improves Efficiency and Results

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The sulfuric acid hydrogen peroxide mixture (SPM) process effectively strips and cleans wafers but suffers from instability due to the decomposition of the hydrogen peroxide. A heated bath improves performance but increases the rate at which hydrogen peroxide changes into water. Periodically spiking the mixture with extra hydrogen peroxide can restore the required concentration but affects the strip rate. As a result, the SPM mixture has to be changed frequently, leading to high costs for chemicals and frequent downtime on wet bench stations. Working closely with a local semiconductor manufacturer, Modutek has developed a “bleed and feed” process upgrade that addresses these problems and results in substantially longer mixture life and improved process results.

The SPM Process

A typical mixture for the SPM strip and clean process is one part hydrogen peroxide to three parts sulfuric acid. The sulfuric acid parts can go as high as 7 parts but once the process has started, if the concentration changes, the strip rate can change as well. The mixture is heated to 130 to 140 degrees centigrade to increase the strip rate. The higher the temperature, the faster the hydrogen peroxide decomposes to water, diluting the mixture.

To keep hydrogen peroxide in the mixture, more of the chemical is periodically added to the process, spiking the concentration back to its original level. Despite this, the mixture is normally usable for only a few hours at a time and typically has to be replaced several times a day. Replacing the mixture is costly and requires repeated downtime when processing has to wait for a new pour. In addition to the costs of the chemicals, there are treatment and disposal costs that are required to comply with environmental regulations.

Modutek’s “Bleed and Feed” Process Change

Modutek has developed a hydrogen peroxide spiking method that keeps the chemical mixture at a predictable concentration and avoids the requirement for frequent replacement. The method reduces consumption of the chemicals and lets the system run for extended periods without down- time.

Using a two-tank dirty and clean tank process, the “bleed and feed” method involves draining a programmable amount of mixture from the dirty tank prior to each process step. Another programmable amount is fed from the clean tank to the dirty tank. Then programmable amount of sulfuric acid is added to the clean tank and both tanks receive programmable amount of hydrogen peroxide.

When the entire mixture has to be replaced, normally about once every week, the system has a quick drain feature that reduces down time and gets the process up and running again quickly. The whole “bleed and feed” spiking method is PLC controlled and the periodic adding and spiking of chemicals allows the mixture to be used continuously for days at a time.

Benefits of the Modutek Process Change

In addition to savings related to the reduced use of chemicals, the new update improves overall efficiency and achieves better results. Instead of having to shut down the wet bench station every shift to pour new acid, the process can run for days and only requires a complete chemical change once per week. In addition, the process is cleaner and can deliver better cleaning and stripping performance.

Modutek is offering the SPM process upgrade on their new wet bench stations and can provide details regarding chemical use and performance. The company has the experience and expertise to help customers more effectively use the SPM and other processes to ensure they obtain the results they need. Call Modutek at 866-803-1533 for any questions you have with using either the updated SPM process or other wet processes needed for your application.

 

Modutek at 2018 Semicon Conference in China

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2018 Semicon Conference ChinaModutek Corporation, a leading provider of wet bench stations and wet process equipment, will be at the Semicon Conference in Shanghai China from March 14-16, 2018 with their factory representative Laserwort Ltd.  They will be located in Hall N2 at booth 2431. Information about the Semicon Conference can be referenced at http://www.semiconchina.org/ and details on Modutek’s attendance at the conference can be referenced at: Modutek at Semicon Conference in China

Come by the Modutek /Laserwort booth to get information and answer any questions you have about using Wet Bench Process Stations for acid/base, solvent and ozone cleaning or photo resist strip.  In addition Modutek will also provide information about the benefits of their new IPA vapor dryer with the HF last process. Modutek serves customers around the world who require any type of wet processing equipment and builds chemical delivery systems for pharmaceutical, biochemical, solar and semiconductor manufacturing.

Additional details on some of Modutek’s products are listed below:

Single Chamber HF Last IPA Vapor Dryer

Benefits include:

  • Most drying cycles completed within 10 to 15 minutes
  • Very low consumption of IPA
  • No moving parts inside drying chamber eliminating wafer breakage
  • Eliminates watermarks
  • Drying technology can be designed into wet bench eliminating one transfer step

Features include:

  • Single drying chamber for DI water rinsing and IPA vapor drying
  • On board HF metering for precision mix ratios
  • Uses an in situ HF etch process with a rinse step before the IPA drying cycle
  • Filter bypass for contamination control with no cassette contact points
  • Easy to change IPA bottles
  • Handles all process sizes (standard wafer carriers to glass substrates)

 

Fully-automated Wet Bench Equipment

Benefits include:

  • In house customization to meet customer process requirements
  • Precise automated process execution and reliable repeatability
  • Full automation control with touch screen
  • Improved yield and reduced errors
  • SolidWorks Simulation software for accurate calculation of process parameters
  • All robotics and software design designed in house
  • Complete design, assembly and test at one location to meet your specifications

 

Semi-automated Wet Bench Equipment:

Benefits Include:

  • Automation control with touch screen
  • Servo motor automation
  • SolidWorks Flow Simulation software
  • SolidWorks Simulation Professional software
  • All robotics and software designed and developed in house
  • Complete design, assembly and test at one location to meet your specifications

 

Manual Wet Bench Equipment:

Benefits Include:

  • High end manual equipment at competitive pricing
  • Meets or exceeds all current safety standards
  • Low cost of ownership
  • Designed to meet any process requirements
  • Can accommodate custom designs and processes
  • Equipment designed for future expansion

 

All wet bench equipment supports the following applications:

  • KOH Etching
  • Quartz cleaning
  • Ozone Strip
  • Ozone Cleaning
  • SC1 & SC2 (RCA Clean)
  • Megasonic Cleaning
  • BOE (Buffered Oxide Etching)
  • MEMs processing
  • All solvent applications
  • Hot phosphoric (Nitride Etching)
  • SPM Cleaning
  • Precision Part Cleaning

Modutek has over 37 years of industry experience and expertise in developing and building wet bench stations and wet process equipment that provides highly reliable results for precision processes. They also provide world-class service, and customer support. Contact Modutek at 866-803-1533 or email [email protected] for a free quote or consultation to discuss your requirements.

 

How the Silicon Nitride Wet Etching Process is Improved by Modutek

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Silicon nitride is used as a mask when etching silicon wafers during the semiconductor manufacturing process. Before the silicon wafer can be processed further, the silicon nitride has to be removed. A solution of phosphoric acid and de-ionized water etches the silicon nitride while leaving the wafer unaffected. As a result, the silicon nitride is stripped from the wafer surface and a clean wafer is left for further fabrication steps.

To optimize the silicon nitride wet etching process, the phosphoric acid solution is kept at a high temperature. This means some of the de-ionized water boils off as steam and has to be replaced. Adding water to phosphoric acid can be extremely dangerous and can result in an explosion. In addition, keeping the temperature of the solution constant is important for accurate control of the stripping process. Modutek has improved both the safety and the control of the nitride wet etching process with its Nb series silicon nitride wet etching baths.

How the Process Works

A solution of 85 percent phosphoric acid and 15 percent de-ionized water is heated to a boil at about 160 degrees centigrade. Some of the water boils off as steam and part of the steam is condensed and placed back in the solution. Some steam escapes and de-ionized water has to be added periodically. The solution is kept at the boiling point by a heater and the process temperature can be tightly controlled. With the Modutek system, nitride etch is uniform and there are no “bumps” in the chemical concentration or temperature.

How Modutek Controls the Etching Process Safely and Accurately

The two challenges faced when operating a boiling phosphoric acid bath is the safe replacement of the de-ionized water lost to steam and an accurate control of the process. If water is added to the solution too quickly, the solution may stop boiling and a film of water can accumulate on top of the viscous acid. If the water of the film then suddenly mixes with the acid, a strong reaction can occur, and an explosion is possible. Adding water in this way also makes accurate control of the process difficult.

In the Modutek system, the heater that boils the solution is always switched on. The solution is always heated up to the boiling point and further heating only increases the boiling rate but not the temperature. This control strategy results in a clearly defined temperature for the boiling solution, which will always be at its boiling point.

The boiling point of a phosphoric acid and water solution varies with the concentration, increasing as the solution loses water to steam. A thermocouple in the bath senses the increasing temperature and gives the signal to add water. De-ionized water is slowly added to the boiling solution. Because the acid is boiling rapidly, the small amounts of water are immediately mixed in and don’t form a surface film. Adding water in this way is safe and controlling the process by monitoring the concentration through the temperature rise is accurate.

Additional Safety Features

Since the silicon nitride wet etching process depends on keeping the solution at the boiling point, additional safety interlocks in Modutek’s etching baths are in place to insure no water is added if the solution is not boiling. A thermocouple above the solution senses the presence of hot steam and shuts off the water valve if steam is not present. To ensure the solution does not overheat, another thermocouple switches off the heaters when the temperature of the solution reaches 170 degrees centigrade. With its advanced control system and the additional safety interlocks, Modutek has improved the silicon nitride wet etching process with better control, accuracy and increased safety.

 

How the KOH Etching Process is Improved Using Modutek’s Teflon Tanks

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Among the different approaches available to foundries that create intricate integrated circuitry on semiconductor chips, etching with potassium hydroxide (KOH) is frequently preferred for the error-free mass-production that it allows.

The improvement in precision that the KOH etching process brings to semiconductor fabrication is attributable in large part to the use of deionized water. When employed with high alkalinity in excess of pH 12, this process can be thermally adjusted for precise degrees of etching.

How does the use of potassium hydroxide improve the semiconductor etching process?

While dry semiconductor etching processes do exist, they tend to present challenges in process control. Semiconductor wafers etched in this way tend to suffer from quality control issues. Dry etching processes can be difficult to build and run, as well — toxic and explosive chemicals often seen as byproducts, after all.

Greater precision

Etching with potassium hydroxide offers greater precision, and lends itself to improved control, as well.

The fluids employed in the KOH etching process are stored in tanks built into the equipment. One of the most cost-effective and meaningful choices to make in KOH etching processes: to place Teflon tanks within the etching equipment in order to hold the fluids employed. Teflon tanks can make the KOH etching process safer than other options available.

It is possible to structure the KOH etching process in a way to easily create repeat manufacturing projects, as well. When such projects come in from different clients, fabrication units can focus their strengths on setting up the equipment, worrying as little as possible about safety or reliability.

Opting for fewer contaminants and greater cleanliness

Customization is one of the greatest most significant improvements that Modutek brings to the KOH etching equipment business — one where generic, mass-produced Teflon tanks are the norm. Modutek’s Teflon tanks are especially capable of bringing impurity quantities to levels that are impressively low. The result is greater reliability and consistency over an extended period of time.

Greater control

Modutek’s Teflon tanks come with highly customizable temperature settings. Temperature control is achieved either through in-line heating and cooling equipment installed, or through immersion in liquid tanks. It is precisely varied anywhere between 30°C to 100°C. Temperature changes dialed up our achieved at a fast rate of 2°C a minute, on average (although tank size does affect response rates).

Modutek brings customization to the table

Modutek designs Teflon tanks for the specific needs of each client installation. Whether a fabrication plant requires temperature controlled recirculating baths for their KOH etching processes or temperature controlled static baths, Modutek’s Teflon tanks deliver both freedom from water loss and freedom from concentration deficiency.

From dual heating Teflon tanks for fast and consistent water-based etching, to the installation of drains and valves that enable rapid cleanup, high-tech remote data interfaces, controllers and timers, Modutek’s clients have their choice of every advance in KOH etching.

 

How to Improve Your Silicon Wet Etching Process

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Semiconductor research labs and fabrication facilities employ high-precision silicon wet etching processes that are capable of delivering quality product in a consistent way. This is no mean feat: the microscopic structures etched on semiconductor wafers require processes that meet microscopic tolerances while reducing the minutest of impurities. Fabs are always on the lookout for improvements to make in these processes; the aim is to minimize the number of errors made during each of several processes. Results depend on constant efforts in the area of identifying the best etching processes, and utilizing the best equipment.

The Wafer Etching Process

The process of etching micro-circuitry on silicon wafers requires a complex multi-layered fabrication approach. It usually requires multiple cleaning, masking, and etching processes that involve the precise deposition of metal traces and components. At different stages along the way, these processes require the use of chemical baths of various kinds, each aimed at achieving different, specific results. At the end of one of these precisely designed processes, silicon wafers with traces, electrical connections and electronic components, all etched on a microscopic scale, emerge ready for market.

There are various requirements for an error-free process — precise control over the speed at which etching is done, and the ability to achieve extreme levels of cleanliness in the work areas in which etching is done, are two primary requirements. There are many others, as well.

Silicon nitride: Silicon nitride is applied to mask parts of wafers during the phosphoric acid etching process. Achieving greater precision in this process delivers superior results. In general, fabs do much better with the fabrication process when they possess over on-the-fly control over acid concentration and temperature.

Piranha etching: At semiconductor fabs, piranha etching is done using a mixture of piranha solution — a blend of hydrogen peroxide and sulfuric acid. Chemical baths need to be carefully controlled to supply the right chemical mix at the right time.

Potassium hydroxide: The etching process requires the use of potassium hydroxide solution in the creation of microscopic structures on semiconductor wafers. Achieving precise and error-free etches requires an ability to closely control the concentration of the solution, the temperature, the orientation of the silicon crystal and silicon purity. These variables can change during the etch process, and error-free results requires the ability to respond by speeding up or slowing down etch rate.

Buffered oxide etch: This is a process that employs hydrofluoric acid in addition to a buffering agent in order to etch fine masking films of silicon dioxide or silicon nitride. When correctly controlled, the process delivers a consistent and repeatable result that works with photoresist.

When it comes to improved silicon etching performance, the key to high-quality results is to utilize processing equipment from a vendor with proven experience and support. Modutek answers this requirement with 35 years in the field. Not only is Modutek able to supply the equipment, they are able to advise clients on the customizations needed to meet their requirements.

Choosing Equipment with the Right Features for Each Stage of the Wafer Etching Process

Modutek’s silicon wet etching equipment comes with some of the most advanced features on the market today:

Flow control and filtration control: Modutek’s precision acid filters are effective down to the 0.2 µm range and are able to work continuously to enable reuse of acid. This provides considerable savings in acid consumption.

Precision control of temperature: An ability to precisely control the temperature of an etching bath can result in lower error rates and reliable output. In any process, Modutek’s equipment comes with the ability to control temperatures to within 1 degree of required settings.

Precision tech design: Potassium hydroxide requires the use of Teflon tanks; piranha solution requires quartz. Modutek designs these tanks in a wide variety of configurations and sizes.

Modutek is dedicated to helping clients find ways to improve the efficiency of their silicon wet etching processes, improve productivity and output quality. To this end, Modutek’s offers extensive consultation and equipment customization needed to meet each customer’s requirements.