How Advanced Ozone Cleaning Reduces Chemical and Solvent Usage

As environmental concerns mount and regulatory compliance becomes more difficult, companies that reduce the use of hazardous chemicals and solvents will have a competitive advantage. In addition to reducing costs, the use of fewer corrosive chemicals improves workplace safety and can lead to better semiconductor manufacturing facility performance. Modutek’s patented advanced ozone cleaning process saves money and reduces the contaminating particle count on wafer surfaces. Depending on process requirements, ozone cleaning can out-perform traditional wafer cleaning with harsh chemicals. Modutek’s ozone cleaning process is compact, fast, and safe.

Advanced Ozone Cleaning Converts Organic Impurities to Carbon Dioxide

Modutek has developed the Cold Strip sub ambient process that operates with deionized water and the Organostrip process that uses a mild acid at room temperature for photo resist strip. This also eliminates the use of NMP solvent base strippers. Both use ozone to clean organic contaminants from wafer surfaces and both leave harmless residues that allow for disposal without special neutralizing procedures.

The Cold Strip Advanced Ozone Cleaning Process operates at four to ten degrees centigrade and uses deionized water to strip silicon wafers of water-soluble inorganic impurities. After the wafers are rinsed with deionized water, ozone is introduced into the chamber. The ozone reacts with the remaining organic impurities and converts them to carbon dioxide. Particle contamination is reduced as well because the ozone reacts with organic particles. Wafers are more effectively cleaned with a reduced particle count.

In the Organostrip process, wafers are rinsed with a solution of a mild acid and ozone at room temperature. The acid has a high ozone solubility that lets the ozonated solution remove organic compounds from the wafer surfaces quickly and completely. The process is compatible with metals such as gold, copper, and aluminum, and the waste products of the Organostrip process are not hazardous.

Modutek uses its DryZone solvent gradient dryer for the Advanced Ozone Cleaning Process that the company developed to address customer concerns. Customers experienced high particle counts and issues with the use of hazardous chemicals, including their effect on the environment. The developed process successfully addresses these issues and delivers effective wafer cleaning.

Modutek’s Advanced Ozone Cleaning Process Provides Substantial Benefits

Modutek developed the Advanced Ozone Cleaning Process to address specific customer concerns, but the Cold Strip and Organostrip processes also improve wafer cleaning and facility operations. The benefits of using ozone cleaning include the following:

  • Reduced cost for process chemicals. The acids used in a traditional wafer cleaning process, such as sulfuric or hydrochloric acids, are expensive, and the cleaning processes such as Piranha clean use substantial volumes of chemicals. Ozone and the mild acids or solvents used in ozone clean are less expensive and the solutions last longer.
  • Reduced cost for chemical handling. The storage, delivery, and disposal of hazardous chemicals used for traditional wafer cleaning is expensive. The handling of ozone and the mild chemicals used for ozone cleaning requires no special measures.
  • Improved workplace safety. The chemical baths used for traditional wafer cleaning often operate at high temperatures and they can be dangerous. The ozone cleaning process chemicals are safe and the operation is done at sub ambient or at room temperature.
  • Higher throughput. Advanced ozone cleaning takes less time than traditional cleaning methods.
  • Improved yields. Ozone cleaning reduces particle counts and results in higher output quality with fewer product defects.

Modutek’s Continued Process Improvement Delivers Innovative Solutions for Customers

Modutek works closely with customers to identify new concerns and solve existing processing problems. Using extensive in-house experience and expertise in wet process technology allows Modutek to provide innovative solutions to meet customer needs. New wet process steps such as Advanced Ozone Cleaning can help customers improve semiconductor manufacturing facility performance and increase profitability.

How Megasonic Cleaning Improves Silicon Wafer Manufacturing

When silicon wafers are cleaned between manufacturing steps, it is critical to remove all contamination from the wafer surfaces. The remaining traces of process chemicals or microscopic particles can disrupt the etching process and result in defective or low-quality semiconductor devices.

Megasonic cleaning uses high-frequency sound waves in the cleaning tank to remove contaminants and particles from the silicon wafers. The technology can save time and money because it works quickly and does not require expensive chemicals. Silicon wafers cleaned with Megasonic cleaning are completely clean with a reduced particle count. As a result, the technology can improve the operation of semiconductor manufacturing lines for semiconductor fabricators and research labs.

Megasonic Cleaning Reduces the Use of Toxic Chemicals

The cleaning of silicon wafers after the completion of each semiconductor manufacturing step is accomplished by soaking the wafers in mixtures of chemicals including hydrochloric acid or sulfuric acid. In addition to the cost of the chemicals themselves, there are ongoing costs related to the storage, delivery, and disposal of these chemicals. The possibility of leaks and the disposal of the waste chemicals represent environmental hazards that are continuously being mitigated with tighter regulations. Reducing the use of aggressive chemicals can save money beyond their direct cost and can improve the environmental footprint of the semiconductor manufacturing facility.

With Megasonic cleaning, a frequency generator produces an electric signal in the MHz range that is transmitted to a transducer. The transducer that is immersed in the cleaning solution converts the signal to sound waves in the cleaning tank. The sound waves create microscopic cavitation bubbles that deliver a gentle scrubbing action against the surface of the silicon wafer. The cleaning intensity is strong enough to dislodge impurities and contaminants but will not damage the wafer surface or the microscopic structures that have been etched into it.

When Megasonic cleaning is used to replace some of the traditional cleaning steps, the use of chemicals is reduced. Megasonic cleaning uses plain water or water with the addition of mild detergents. The cost benefits and reduced environmental impact can be substantial, and the areas where Megasonic cleaning is used will have increased worker safety and reduced chemical exposure.

Megasonic Cleaning Can Deliver Improved Cleaning Performance

While acid baths work well for cleaning general contaminants from silicon wafer surfaces, ensuring low particle counts can be challenging. Contaminating particles can block etching and cause defects in the final semiconductor devices. As functions become more and more closely packed on the wafer and microscopic structures become smaller, a single particle can affect the etched shapes and current paths. A key factor for improving output quality and reducing defects is reducing particle counts to a minimum.

Microscopic particles can be difficult to remove from the surface of silicon wafers because they often develop a static charge that allows them to cling to the wafer. Chemicals can dissolve the substances that make the particle adhere to the wafer surface but the static charge often remains as an additional bond. With Megasonic cleaning, very small cavitation bubbles form and collapse in tune with the sound wave frequency in the MHz range. When a bubble collapses near the wafer surface, it emits a powerful jet that dislodges any particle still clinging to the surface. Wafers that have been cleaned with Megasonic cleaning systems have a lower particle count as well as a high degree of cleanliness.

Modutek Can Help with Megasonic Cleaning Integration

As a leading manufacturer of wet process semiconductor manufacturing equipment, Modutek can help customers integrate Megasonic cleaning into their wafer cleaning process. Modutek offers free consultation and can show customers how to realize the benefits of lower costs, better output quality, and improved yields.

How Specialized Equipment Improves Wafer Cleaning Results

When equipment is specially designed for a specific cleaning process, residue and particle removal from wafers can be improved. A better wafer cleaning process reduces semiconductor defects and can result in improved output quality. Specialized equipment can clean more quickly, allowing higher facility throughput. Specialized and customized equipment can be adapted for batch processing, continuous manufacturing or prototyping, improving production line performance, and reducing costs.

Specialized Equipment Delivers Specific Advantages

Modutek has developed specialized equipment that addresses issues with specific semiconductor manufacturing processes. Resulting advantages include better control of process variables, more efficient cleaning, reduced space requirements, and more flexible automation. While standard solutions are also available and are sometimes sufficient, the specialized equipment will deliver superior results in specific cases.

Piranha Etch Clean is often used for post-etch clean and for the removal of organic matter. Modutek has implemented a specialized control strategy that gives more reliable cleaning results while cutting chemical costs. The “bleed and feed” method provides tight control of temperature and chemical concentration to deliver superior cleaning performance.

A wafer cleaning process used in semiconductor manufacturing such as Piranha Clean has to take place in special tanks that are impervious to the process chemicals. Modutek’s heated quartz tanks minimize particle contamination while delivering precise temperature control. They are available in recirculating and constant temperature models are made from boron-free virgin fused quartz.

For many process steps, wafers must be carefully rinsed after cleaning. Modutek’s specialized quick dump rinsers minimize rinsing time while reducing the consumption of deionized water. Modutek’s specialized design has eliminated particle entrapment by reducing particle contamination at the rinsing stage.

After rinsing, wafers have to be dried while limiting additional particle contamination. Modutek offers IPA vapor drying stations but has developed a specialized single-chamber unit that rinses and dries the wafers without moving them to a new station. Moving the wafers exposes them to additional particle contamination and the single chamber IPA vapor dryer features extremely low particle counts.

As microscopic structures on silicon wafers become smaller and more tightly packed, a reduced particle count becomes critical for some wafer processes. Modutek’s use of Megasonic cleaning uses high-frequency sound waves in a cleaning solution to remove almost all remaining particles on wafer surfaces. The cavitation bubbles created by the sound waves can dislodge even the smallest particles, delivering an almost completely particle-free wafer.

Specialized Software Control for Automation

To control the wafer cleaning process, specialized software and automation can help deliver exactly the cleaning chemicals required while eliminating human error. Modutek uses its own SolidWorks Simulation Professional and Flow Simulation software and can adapt the programs to any process. Modutek’s wet bench stations are available in manual, semi-automatic, and fully automated versions with the automation designed to support the latest wet process technology. The specialized automation can be customized for specific applications to satisfy customer process requirements.

How Modutek’s Specialized Equipment Improves Performance

Specialized equipment can reduce particle counts, improve cleaning, reduce costs and increase production capacity. Modutek works closely with customers in a variety of industries and develops specialized wafer cleaning equipment to meet their unique needs. When additional customization is needed, Modutek can adapt equipment and software as required. Because the company designs and builds its products in-house, it can make the changes needed itself without relying on third parties.

With Modutek’s specialized equipment, customers ranging from large semiconductor manufacturers to small research labs can achieve excellent production results, especially after the additional customization that Modutek can provide. Superior wafer cleaning performance impacts all aspects of semiconductor manufacturing, from initial prototyping to full production line fabrication. Modutek can help with the choice of specialized equipment, suggest customizations, and ensure that the delivered equipment meets expectations.

How Teflon Tanks Improve the KOH Etching Process

How Teflon Tanks Improve the KOH Ethcing ProcessEtching silicon wafers with potassium hydroxide (KOH) is a popular process for semiconductor manufacturing because it is relatively safe compared to other etching methods and because it features good control of the etch rate. When carried out in Teflon tanks, contamination is reduced and the etch rate can be controlled.

A key factor for successful etching is to determine the required etch rate. If the rate is too fast, the KOH may etch too far into the silicon, while if the rate is too slow, the etched holes might be too shallow. Improving the KOH etching process means applying several control methods to the etch rate to ensure the resulting etched shapes are exactly correct.

Process Factors that Affect the KOH Etch Rate

The KOH etch rate in silicon wafers is influenced by the following factors:

  • Process temperature. The higher the temperature of the KOH solution, the faster KOH will etch the silicon.
  • Solution concentration. A higher concentration increases the etch rate. Normally the concentration of the KOH solution is about 30 percent, but it can vary from 10 to 50 percent, with a corresponding effect on the etch rate.
  • Doping. Doping means adding impurities to the silicon crystal. When boron is placed into the silicon crystal lattice at a specific location, etching stops in that direction. Boron doping can influence the shapes to be etched in this way.
  • Crystal lattice orientation. The silicon crystal atoms are arranged in a cubic lattice that has a greater atom density in some directions than in others. Etching is slower in directions with a higher atom density.

All four factors have to be taken into account when designing the mask to obtain the microscopic structures in the silicon. The silicon wafer has to be oriented correctly to give the different etch rates along with the different lattice directions. Doping has to be in a place where etching is required to stop and the correct KOH solution concentration has to be mixed. These are initial conditions that are established before the process starts. A target temperature can be set as well but the temperature can be varied to adjust the etch rate during processing. The ability to vary the etch rate by changing the temperature results in excellent control of the KOH etching process.

Modutek Teflon Tanks Feature Rapid Heating and Precise Temperature Control

Modutek’s Teflon tanks for KOH processing are available in a circulating or a static design. The heat source is either inline or immersed in the overflow weir. An all-Teflon liquid path reduces the possibility of contamination. The heated tanks can improve the KOH etching process with short heat-up times and precise temperature control. As a result, Modutek Teflon tanks can keep the etch rate steady by maintaining an accurate temperature set point or can allow the etch rate to be adjusted with fast and reliable controlled temperature changes.

Both models of Teflon tanks feature uniform heating throughout the baths, level and temperature limit settings, and a drain interlock. Heat up rates are 2 to 3 degrees centigrade per minute and the temperature is controlled with a precision of plus/minus 0.5 degrees centigrade. The operating temperature is from 30 to 100 degrees centigrade and a cooling refluxor with Teflon cooling coils is included.

Modutek’s Teflon tanks are available in standard sizes but can work with customers to design and build systems with custom sizes and special requirements. With their high-quality materials, precise temperature controls, and customization capabilities, Modutek’s Teflon tanks can improve the KOH etching process to deliver better semiconductor manufacturing results. Contact Modutek for a free consultation to discuss your specific process requirements.

Improving Standard Clean Particle Removal in a Wet Bench Process

When silicon wafer yields are not improved with the Standard Clean process, improved particle removal can be achieved with advanced processing equipment. Standard Clean or RCA clean was developed by the RCA company in 1965 and it has changed little since then. It has always been successful in cleaning wafers and removing most particles. However, with silicon circuits and structures decreasing in size and product density on wafers increasing, even the tiniest particles can cause device defects.

RCA clean works by first dissolving and removing organic materials from the surface of the wafers using powerful chemicals. In a second step, metallic impurities are removed and the wafer is rinsed clean. The two-step process and the rinsing remove most particles but the smallest particles often remain attached to the wafer with surface tension and electrostatic charges. Such particles can affect diffusion in wafers or block the etching of electronic structures or circuit paths.

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

How Megasonic Cleaning Works to Improve Standard Clean Particle Removal

The two steps making up the RCA wafer cleaning process are SC1, using a mixture of ammonium hydroxide and hydrogen peroxide, and SC2, using a mixture of hydrochloric acid and hydrogen peroxide. The SC1 process removes most of the contamination from the silicon wafer surface, but introduces metallic ion contaminants that can influence subsequent wafer processing steps. The SC2 process dissolves the remaining contaminants, allowing impurities to be rinsed away as they float to the surface of the cleaning mixture.

Standard Clean takes place in heated inert tanks such as quartz baths that are carefully designed to limit additional contamination. The chemical mixtures are heated to about 80 degrees centigrade and processing takes about 10 minutes for each step. After rinsing, the silicon wafers are clean but may still have an unacceptable number of submicron particles adhering to the wafer surfaces.

Megasonic cleaning can remove the majority of these particles while also dislodging the few larger particles that may still be present. The process involves adding a megasonic transducer to the tank holding the wafers. The transducer converts very high-frequency signals from a megasonic generator into sound waves that travel through the rinsing water to strike the wafer surfaces. Sound wave frequencies are typically at or above 1 MHz but may range as low as 200 kHz depending on the specific cleaning application.

As the sound waves travel through water, they create microscopic cavitation bubbles that form and burst in tune with the sound wave frequency. When the bubbles burst, they produce tiny but intense jets of water. The jets from the bubbles near the wafer surfaces dislodge any remaining particles, leaving them to be rinsed away at the surface of the bath, for example via an overflow weir. The additional Megasonic Cleaning step is very effective in particle removal because the tiny jets break any bonds that make the particles adhere to the wafer. The result is extremely low particle counts on wafers that undergo both the RCA wafer cleaning process and Megasonic Cleaning.

Modutek Designs and Builds Specialized Equipment to Improve Wet Bench Processes

Megasonic Cleaning is one example of Modutek’s implementation of designs and technologies that improve wet process performance for their customers. For over forty years Modutek has been providing specialized semiconductor manufacturing equipment to meet unique industry needs. As a leading semiconductor equipment manufacturer, the company offers free consulting and can provide recommendations on equipment from its complete product lines. When Modutek supplies wet bench equipment to customers, the company follows a well-defined process to ensure their equipment performance meets customer requirements.

The Importance of Pre-Diffusion Cleans in Silicon Wafer Cleaning

The Importance of Pre-Diffusion Cleans in Silicon Wafer CleaningWhen wafer cleaning immediately prior to diffusion is effective, semiconductor manufacturing output is of high quality and the defect rate is reduced. A major pre-occupation of pre-diffusion cleaning is the removal of microscopic particles from the surface of the silicon wafer. Particles can prevent even diffusion and may themselves be diffused into the silicon, causing defects.

Silicon wafer cleaning can be carried out in chemical baths or with megasonic cleaning systems. Several cleaning steps using different processes are sometimes required to get a specific level of cleanliness. The goal is to obtain wafers free from metallic or organic contamination and with as few surface particles as possible. As silicon microstructures are designed with smaller elements and with a higher component density, adequate wafer cleaning becomes more and more critical.

RCA Clean Uses Two Steps to Remove Organic and Metallic Contamination

RCA clean uses ammonium hydroxide, hydrogen peroxide and hydrochloric acid to remove surface contaminants from the silicon wafer. In the Standard Clean 1 (SC1) process, the wafers are placed in a mixture of ammonium hydroxide and hydrogen peroxide. The corrosive mixture removes organic matter but may leave metal ions behind.

In the Standard Clean 2 (SC2) process, the remaining metallic traces are removed by immersing the wafers in a mixture of hydrochloric acid and hydrogen peroxide. At the end of the RCA wafer cleaning process, organic and metallic contamination has been removed while as many remaining particles as possible are rinsed away as well.

Piranha Clean Removes Heavy Organic Contamination

When wafers are heavily contaminated with organic materials such as photo resist, the Piranha process cleans more quickly than RCA clean. The wafers are immersed in a mixture of sulfuric acid and hydrogen peroxide and the mixture may be heated to speed up the reaction. The piranha clean process hydroxilates the wafer surface, making it hydrophilic. This affinity for water is sometimes a useful feature for additional cleaning measures.

Megasonic Cleaning Removes Contaminants and Particles

Megasonic cleaning avoids the use of corrosive chemicals and is especially effective for dislodging microscopic particles from the wafer surface. The Megasonic process works by generating high-frequency sound waves in the cleaning bath. An ultrasonic generator produces the high-frequency electronic signal and a transducer converts the signal into sound waves that travel through the cleaning solution. The sound waves create tiny cavitation bubbles that produce a scrubbing action against the wafer surface. The action of the bubbles cleans the wafer.

Microscopic contaminating particles adhere to the wafer and are difficult to remove. With integrated circuits featuring increasingly smaller geometries, even the tiniest particles can cause defects. Megasonic silicon wafer cleaning operates in the frequency range near or above 1 MHz and the cavitation bubbles agitate the cleaning solution at the operating frequency. Such agitation breaks the bond holding the particle on the wafer surface and the floating particles can be rinsed away.

Modutek Wet Bench Equipment Supports Pre-Diffusion Cleaning Methods

RCA, Piranha and Megasonic cleans are commonly used in pre-diffusion clean, but each fabrication facility optimizes for its own sequence of semiconductor manufacturing processes. A production line may use one or several cleaning methods, and may have special requirements for production parameters such as size, temperature or timing.

Modutek designs and builds its own complete line of wet bench equipment and can advise customers on choosing the best processing stations for their applications. Ideal solutions often require extensive customization to optimize yield and reduce costs to a minimum. Modutek can provide custom solutions including pre-diffusion cleans, and can design new equipment for integration into the customer’s manufacturing line to meet specific wafer processing requirements.

Using the Advanced Ozone Cleaning Process to Improve Wafer Yields

Using the Advanced Ozone Cleaning Process to Improve Wafer YieldsTwo key goals for semiconductor manufacturers are to increase process yields and to reduce chemical usage. Wet process semiconductor manufacturing is sensitive to wafer contamination by microscopic particles that increase final product rejection rates and reduce output quality. The ozone cleaning process can reduce particle counts and improve wafer yields by reducing the number of defective products. At the same time, cleaning organic contaminants from the wafer with ozone reduces the use of expensive and toxic chemicals. Modutek’s Advanced Ozone Cleaning Process allows semiconductor manufacturing facilities to increase throughput and output quality while reducing operating costs.

How Advanced Ozone Cleaning Improves Wet Process Line Performance

Modutek’s Advanced Ozone Cleaning Process uses ozone to remove organic contaminants from the surfaces of silicon wafers during wet bench processing. Ozone is used with either room temperature acidic acid or chilled DI water to clean wafers without aggressive chemicals. In addition to saving money due to reduced use of chemicals, ozone cleaning takes less space and is faster than many chemical-based wet bench processes.

Ozone cleaning takes place in Modutek’s DryZone System. Modutek has developed the Coldstrip sub ambient process and the Organostrip process that operates at room temperature. Both ozone cleaning processes deliver reduced particle counts and increased yields.

The Coldstrip process operates at four to ten degrees centigrade and introduces ozone into the ozone chamber after the wafers have been rinsed with de-ionized water. The rinsing removes non-organic contamination while the ozone combines with the carbon of the organic contaminants to produce carbon dioxide. After completion of the Coldstrip process, the wafers are clean and almost particle-free.

In the Organostrip process, the wafers are rinsed with acidic acid containing ozone. The acidic acid used has extremely high ozone solubility and the high ozone level producing produces rapid decomposition and oxidation. The ambient temperature process eliminates the use of toxic chemicals and the process waste products are harmless.

The Modutek Advanced Ozone Cleaning Process Improves Performance While Saving Money

Modutek developed the Advanced Ozone Cleaning Process to achieve low particle counts and to reduce the use of harmful chemicals. Reduced particle counts are needed for the more compact architecture of modern semiconductors where a single particle can cause defects or lower component quality. Reduced use of chemicals is mandated by increasingly strict environmental regulations while chemical purchase, storage and disposal costs continue to rise. The patented Modutek Advanced Ozone Cleaning Process successfully addresses these issues.

Specific benefits from using the ozone cleaning process include the following:

  • Better wafer yields due to lower particle count
  • Savings from reduced use of chemicals
  • Compatibility with metal films
  • Safer work environment due to absence of toxic substances
  • More environmentally friendly operations
  • Space saving due to more compact equipment
  • No toxic waste disposal issues

Modutek’s Advanced Ozone Cleaning Process increases throughput due to shorter cleaning times and higher yields while cost savings due to reduced use of chemicals are substantial. Semiconductor manufacturers can improve the overall performance of their facility by incorporating Modutek’s DryZone cleaning stations in their wet process lines.

Modutek Can Help Customers with Innovative Solutions

The Advanced Ozone Cleaning Process is one example of Modutek’s initiatives to improve the performance of wet process technology stations and help customers address common problems. The patented process solves issues with current semiconductor manufacturing and helps customers with product quality and with their bottom line.

With Modutek’s emphasis on customer service and on working with customers to improve wet process technology, the company continues to be a leader among semiconductor equipment manufacturers. Customers can rely on Modutek to supply the equipment they need and to provide the support ensuring the equipment meets or exceeds performance expectations.

How Innovative Changes to the SPM Process Improves Results

How Innovative Changes to the SPM Process Improves ResultsWhen the SPM process requires frequent spiking with hydrogen peroxide, precise control is difficult and the useful lifetime of the mixture is reduced. The SPM process, using a mixture of sulfuric acid and hydrogen peroxide, is a popular wafer cleaning process because it quickly removes large amounts of organic material from the surface of silicon wafers. It is ideally suited for stripping photoresist and it hydroxylates surfaces making them hydrophilic (having an affinity for water) in preparation for subsequent wafer processing steps. Spiking with hydrogen peroxide keeps the process going but it means the mixture has to be replaced about once a day. Modutek has developed an innovative way to control the process, resulting in significant cost savings and improved results.

How the SPM Process Cleans Wafers

The mixture of sulfuric acid and hydrogen peroxide removes organic material very quickly because it is highly corrosive, but it is also unstable. The hydrogen peroxide decays to form water that reduces the mixture concentration and slows down cleaning. To keep the process going, the mixture is periodically spiked with hydrogen peroxide, bringing the concentration back up. At the same time, adding hydrogen peroxide to sulfuric acid is exothermic, raising the temperature of the mixture. Cleaning takes place more quickly at higher temperatures, but the hydrogen peroxide decays more quickly as well, influencing control accuracy. Repeated spiking limits the useful life of the mixture to about one day. Daily replacement of the chemicals is expensive and results in delays for the processing line.

“Bleed and Feed” Process Change Saves Money and Improves Output

Modutek has developed an innovative SPM control strategy that prolongs the life of the SPM mixture while precisely controlling mixture temperature and concentration. In the “bleed and feed” method, Modutek uses a two tank system with a clean tank and a dirty tank. Small programmable amounts are regularly drained from the dirty tank and replaced with mixture from the clean tank. To restore the mixture in both tanks, sulfuric acid is added to the clean tank to replace the amount drained and small amounts of hydrogen peroxide are added to both tanks to maintain the required concentration. This semi-continuous process keeps the mixture concentration within narrow limits without spiking and without the temperature changes caused by spiking.

The “bleed and feed” method is PLC-controlled and the amounts to be drained, the replacement amounts and the frequency of operation can all be adjusted for optimal process results. The concentration and temperature of the mixture remain within tight limits and the process control is more accurate. The useful life of the mixture can be extended to as much as a week and the more precise process control gives improved results.

Benefits from “Bleed and Feed” Process Change

Modutek’s “bleed and feed” method means that chemical use and disposal is reduced substantially. When the wafer cleaning process performance is precise and predictable, better repeatability and consistent cleaning times result in better process line performance. When mixture life is stretched from one day to a week, the cost of chemicals is greatly reduced while the process equipment can stay in service longer since it doesn’t have to be shut down as often for changing the mixture. Downtime is lower and throughput increases.

As a leading semiconductor equipment manufacturer, Modutek continues to work closely with customers to develop innovations that can improve process results. The “bleed and feed” control method increases productivity and reduces costs while the decreased use of chemicals is environmentally friendly. The new process control method could be of interest to manufacturing and research facility managers who can use it to lower production costs, improve output quality and decrease the plant’s environmental footprint. Modutek offers free consultation can discuss details on how the new SPM control method can improve the process for your application.

How Specialized Wet Bench Equipment Improves the RCA Clean Process

How Specialized Wet Bench Equipment Improves the RCA Clean ProcessThe RCA clean process removes contaminants from the surface of silicon wafers so that additional wet process semiconductor manufacturing steps can take place. The process consists of two steps, with the SC1 step removing organic compounds and the SC2 step dislodging any remaining metallic residues or particles. Specialized wet benches ensure that contaminant and particle removal is as complete as possible and the silicon wafers remain clean. To accomplish this, the equipment carefully rinses away contaminants and minimizes the handling of the wafers. Automation can be used to replicate process parameters reliably and consistently. Modutek can supply both standard and customized specialized equipment to carry out the RCA clean process.

RCA Clean SC1 Removes Most of the Wafer Surface Contamination

The SC1 cleaning step uses chemicals to dissolve impurities while leaving the underlying silicon surface unaffected. The wafers are placed in a solution containing equal parts of NH4OH (ammonium hydroxide) and H2O2 (hydrogen peroxide) in five parts of de-ionized water. The solution is heated to about 75 degrees centigrade and the wafers are left in the solution for ten to fifteen minutes. Organic residues are dissolved and particles are removed. A thin layer of silicon oxide forms on the wafer and there is some contamination with metallic ions and particles.

RCA Clean SC2 Removes Metallic Impurities

For SC2, the newly cleaned wafers are placed in a bath containing equal parts of hydrochloric acid and hydrogen peroxide in five parts of de-ionized water. The exact ratio may vary depending on the application. The bath is heated to about 75 degrees centigrade with the wafers soaking for about ten minutes. The solution specifically eliminates alkali residues, metal hydroxides and other metallic particles. The wafers are now completely clean and free of all types of particles.

Wafer Cleaning Equipment Has to Fulfill Specialized Functions

Specialized equipment is needed to carry out RCA clean process steps effectively. The required chemicals have to be delivered in the right quantities to the cleaning baths and then, when the chemicals are no longer needed, they have to be neutralized and disposed of safely. The concentration of the chemicals, the bath temperature and the timing are all important for being able to subsequently reproduce the desired cleaning performance. Contaminants and particles have to be rinsed away and filtered out. Key features of effective cleaning are a low particle count on the wafer surface and a resulting low rejection rate for fabricated wafers.

Modutek’s Wet Process Equipment Provides Specialized Features

Modutek’s wet benches and chemical stations support both of the RCA cleaning steps. Chemical delivery systems ensure that the right amounts of chemicals are supplied to the process safely and that waste chemicals are neutralized before disposal. The FM4910 material of construction keeps particle contamination low and is safe to use with the acid and base processes of RCA clean. All baths include a continuous flow de-ionized water chamber with chemical circulation and filtration to rinse away and remove contaminants. The SolidWorks flow simulation software lets operators calibrate dosages precisely and store settings for future use.

As well as fulfilling customer needs from its extensive line of wet process equipment, Modutek can build custom systems for specific applications. Customers who wish to incorporate drying, etching or stripping functions as well as RCA clean in their process lines can rely on Modutek to design and build exactly what they need.

With 40 years of experience in the wet process and technology sector and one of the leading semiconductor equipment manufacturers, Modutek has the expertise in house to provide specialized equipment for the RCA clean process and other semiconductor manufacturing applications. Customers can count on Modutek to help them find effective solutions and supply the corresponding equipment. Contact Modutek for a free quote or consultation to discuss your process equipment requirements.

How Are Isotropic and Anisotropic Processes Used to Improve Silicon Wet Etching?

How Are Isotropic and Anisotropic Processes Used to Improve Silicon Wet EtchingThe microscopic structures produced by silicon wet etching can be created with a high degree of precision by using both isotropic and anisotropic processes. Isotropic etching is faster but may etch under masks to create rounded shapes. Anisotropic etching can be controlled more precisely and can produce straight sides with exact dimensions. In each case, controlling the etch bath temperature and the etchant concentration is critical for successful micro-structure creation and for repeatability for subsequent batches.

How Isotropic and Anisotropic Etching Differ

Silicon wafers have a mono-crystalline lattice structure that repeats in all directions but is not equally dense in all directions. Vertical planes contain a different number of silicon atoms than diagonal planes. This means that etching with certain etchants is slower in the directions with more atoms while it progresses faster in the directions with fewer atoms.

Etchants used for isotropic etching, such as hydrofluoric acid, etch at the same speed in all directions, independently of silicon atom density. For etchants used for anisotropic etching, such as potassium hydroxide (KOH), the etching speed depends on the number of silicon atoms in a crystal lattice plane and therefore depends on the direction of the different planes.

The difference in anisotropic etching speeds allows a better control of shapes etched into the silicon wafers. With a corresponding orientation of the silicon wafer, etching can be timed to produce straight or angled sides and sharp corners. Etching under masks can be reduced.

How Isotropic and Anisotropic Etching Are Used in Semiconductor Manufacturing

Isotropic etching is harder to control than anisotropic etching but it is faster. In the initial stages of silicon wafer fabrication, large features are etched into the silicon. At this stage of manufacturing, etching speed is important for facility throughput. Isotropic etching is used to quickly create these large shapes with rounded sides and corners. Although process engineers and operators have less control over the shape of the feature being etched, accurate temperature and concentration control are still important to ensure that the rounded shapes being created are the same on wafers processed in different batches.

After the large shapes are etched with an isotropic process, the micro-structures and metal paths require better control of the details. Anisotropic etching provides this control as long as the lattice structure of the silicon wafer is oriented correctly. Anisotropic KOH etching is reliable and easily controlled. It can be used to create the precise, straight-sided shapes that are required in the final semiconductor product. Accurate control of the temperature and etchant concentration is even more important for anisotropic etching because these process parameters strongly influence the etching speeds in the various directions and therefore influence the final shapes that are etched.

Modutek Teflon Tanks Support Both Isotropic and Anisotropic Etching

For silicon wet etching processes in which the etch speed is temperature dependent, Modutek’s heated Teflon tanks provide rapid heating and tight temperature control. The tanks are either recirculating or static and they can be built into any new wet bench configuration. The tanks feature 360-degree overflow filtration and uniform heating throughout the bath. The heat-up rate is 2 to 3 degrees centigrade per minute and the temperature control accuracy is plus/minus 0.5 degree centigrade. The temperature controls of these tanks are ideally suited for both isotropic and anisotropic etching.

In terms of control of etchant concentration, Modutek can provide for the injection of de-ionized water into the tanks. Because etchant concentration affects the etch speed, accurate concentration control is important for final product quality and repeatability. Modutek can analyze customer requirements, find and build custom solutions and ensure that process control is precise enough to deliver the required results, both for isotropic and for anisotropic etching.