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 Optimum Particle Reduction is Achieved in a Wet Bench Process

When microscopic particles remain on the surface of silicon wafers during a wet bench process, the resulting semiconductor products may be of reduced quality or even defective. As semiconductor geometries and microscopic structures become smaller and are packed more densely on a silicon wafer, the presence of particles can influence the etch rate around the particle and compromise semiconductor fabrication. The smallest structures and conductor paths can be influenced by particles in the submicron size range and these particles are especially difficult to remove completely.

Modutek has developed innovative solutions that achieve particle reduction through reduced handling of wafers and excellent particle removal. The single chamber IPA Vapor Dryer and the use of megasonic cleaning deliver excellent results. The reduced particle count produces better yields and higher quality output. At the same time, Modutek’s solutions save money through the reduced use of chemicals.

The Single Chamber IPA Vapor Dryer Keeps the Particle Count Low

Modutek’s single chamber IPA Vapor Dryer incorporates rinsing and drying in a single system to save space, reduce costs, and minimize the handling of silicon wafers. The system initially rinses the wafers with de-ionized water and then introduces IPA vapor into the drying cabinet. The vapor comes from a one-gallon bottle that is located in the exhaust compartment for easy changing.

IPA vapor is introduced into the drying chamber from the top to ensure even distribution and reduce the amount of IPA required. When the IPA vapor condenses on the wafers, a surface tension gradient develops between the IPA and the remaining water. When water flows off the wafer surfaces it can remove the contaminating particles. The dry wafer surface doesn’t have any water marks and no particles are added.

One source of particles is the handling of wafers during transfers between stations. Reducing the number of transfers eliminates a source of particle contamination. Modutek’s Single Chamber IPA Vapor Dryer can handle an optional etching feature and drying in the same system. The wafers are rinsed and dried without transferring them to a new station. Since no additional particles are introduced during this process the particle count is kept to a minimum.

Megasonic Cleaning Effectively Removes Particles Without Toxic Chemicals

Megasonic cleaning relies on high-frequency sound waves in the cleaning solution to remove contaminating particles from wafer surfaces. Modutek has partnered with Kaijo Corporation, a world leader in megasonic cleaning systems to incorporate this technology in their wet bench equipment.

A megasonic generator feeds a high-frequency signal to a transducer immersed in the cleaning tank liquid. The transducer converts the signal into sound waves that travel throughout the tank. The sound waves generate microscopic cavitation bubbles that produce a scrubbing action to clean wafers. Particles on the surface of the wafer are dislodged and washed away.

The higher the megasonic frequency, the smaller the cavitation bubbles and the gentler the cleaning action. The microscopic structures etched into silicon wafers are very delicate and could be damaged with rough cleaning. Megasonic cleaning uses frequencies of 950 kHz and higher. The tiny bubbles of megasonic cleaning deliver gentle cleaning action without damaging fragile silicon structures.

Although megasonic cleaning works well with DI water or an SC1 process, adding a mild detergent or solvent can improve cleaning performance. Particles on silicon wafer surfaces often adhere to the surface and can be difficult to remove. Submicron particles may stay within a surface boundary layer, resisting removal. The microscopic bubbles can dislodge such particles, but the addition of solvents or detergents helps dissolve the bonds holding the particles to the surface and can improve particle removal.

Modutek Innovates to Help Meet Customer Challenges

Modutek works closely with customers to identify issues with wet process applications and continually works on developing new innovative solutions. The Single Chamber IPA Vapor Dryer and the megasonic cleaning process are innovations that help reduce particle counts while reducing chemical use and lowering costs. Modutek’s experience with wet processing equipment ensures customers will continually be able to improve their process performance results. Contact Modutek to schedule a free consultation to discuss your specific process requirements.

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.

Achieving Optimum Particle Removal in a Wet Bench Process

Achieving Optimum Particle Removal in a Wet Bench ProcessAs component packing is tighter and circuit geometries trend towards smaller structures, the reduction of submicron particle contamination during the wet bench process steps becomes more important for output quality. When circuit paths are reduced in size, a single submicron particle can block the path and render the final semiconductor component defective. Even when the presence of particles doesn’t cause defects, their influence on semiconductor performance can reduce the quality and lifespan of the final products.

Semiconductor manufacturing facilities and research labs using typical wet bench equipment face challenges when trying to reduce submicron particle contamination to acceptable levels. Innovative solutions such as the use of Megasonic Cleaning and the reduction of wafer handling with a single chamber IPA dryer can help bring down the particle count. When such solutions are integrated directly into the wet bench processing line, throughput and yields can increase. The process may require fewer chemicals and overall facility performance can improve.

How Megasonic Cleaning Reduces Particle Contamination

The use of high-frequency sound waves in cleaning systems is common in many industries but the delicate silicon wafer structures and surfaces require extra-high frequencies to make sure wafers are not damaged. Megasonic cleaners use frequencies of 950 kHz and higher, in the megahertz range, to deliver the soft cleaning action required.

The sound waves from lower frequency systems create microscopic but comparatively large cavitation bubbles in the cleaning bath. The bubbles produce intense scrubbing against the surfaces of the parts to be cleaned, dislodging contaminants and delivering a powerful cleaning action. For the soft surfaces, delicate structures and thin metallic deposits of silicon wafers, such intense cleaning can result in the pitting of surfaces and damage to silicon structures.

In Megasonic cleaning systems, the high-frequency sound waves produce smaller bubbles and more gentle scrubbing. The cleaning action is soft enough to preserve silicon surfaces and structures but strong enough to dislodge contaminating particles. The particles often adhere to the wafer surfaces and are difficult to dislodge with normal rinsing. Megasonic Cleaning breaks the adhesion and creates currents that wash the particles away.

The Megasonic Cleaning action is especially important for submicron particles where the adhesion to the wafer surface inside a boundary layer makes rinsing less effective. The soft scrubbing of tiny bubbles against the wafer dislodges submicron particles effectively and reduces particle contamination.

How the Single Chamber IPA Dryer Reduces Particle Contamination

One of the ways silicon wafers pick up contaminating particles is during the transfer from etching to drying stations. This transfer is especially critical for HF last etching. During the final etching in a wafer fabrication step, the silicon oxide layer is removed through etching with hydrofluoric acid. The wafer is then rinsed and dried before moving on to the next fabrication step. Particles remaining on the wafer surface can interfere with the subsequent fabrication process.

In an innovative development that eliminates this source of particle contamination, a single chamber handles HF last etching and IPA vapor drying. First, hydrofluoric acid is injected into the station chamber to etch the wafer. When etching is complete, the wafer is rinsed with de-ionized water until the acid is neutralized to a safe pH. IPA vapor is then introduced into the station chamber, and after about 15 minutes, the wafers are dry and ready for the next fabrication step. The particle count remains low because the wafers have not been moved throughout the etching and drying process.

Modutek Provides Innovative Semiconductor Manufacturing Equipment for Excellent Results

Modutek works closely with customers to develop innovative wet bench stations that meet their requirements. Attention to customer needs and finding new solutions to common problems allow the company to remain one of the leading wet bench manufacturers.

For Megasonic Cleaning applications, Modutek has partnered with Kaijo Corporation, a world leader in high sound frequency cleaning technology. Modutek’s integration of the Kaijo Megasonic cleaners into the wet bench product line has produced low particle counts that are difficult to obtain with other methods.

Because Modutek designs and builds its own etching and IPA drying stations in house, the company was able to develop its innovative single chamber station and integrate it into its comprehensive wet process product line. In parallel with Megasonic Cleaning, the single chamber station further reduces particle counts, improves yields and reduces costs. On these and other wet process questions, Modutek offers free consultations to ensure customers get the best equipment for their needs.

How Megasonic Cleaners Improve Silicon Wafer Manufacturing

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

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

How Megasonic Cleaning Technology Works

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

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

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

Modutek’s Use of Megasonic Cleaning

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

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

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

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

Why Particle Removal is Essential in Silicon Wafer Cleaning

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

How Particles are Removed from Silicon Wafer Surfaces

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

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

Cleaning Processes

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

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

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

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

Equipment Used for Wafer Cleaning

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

 

How Megasonic Cleaning Improves the Silicon Wafer Cleaning Process

How Megasonic Cleaning Improves the Silicon Wafer Cleaning ProcessAs silicon microscopic circuits and structures shrink in size, the elimination of contaminants from becomes increasingly important. When silicon wafer cleaning is effective, it removes particles as small as 0.1 µm to prevent them from affecting the silicon fabrication process. Traditional wafer cleaning with chemicals may leave some of the smallest particles in place and production line output quality can suffer. The semiconductor components produced may be of inferior quality or fail completely. Megasonic cleaning with sound waves in the MHz range generated in a water cleaning solution can remove particles down to 0.1 µm in size and improve cleaning performance.

How the Megasonic Process Cleans

The Megasonic Cleaning System consists of a high-frequency generator, transducers that convert the electric signal from the generator to sound waves in the water, and a cleaning tank to hold the cleaning solution and the silicon wafers. Sound waves in the MHz frequency range travel through the cleaning liquid and generate microscopic cavitation bubbles in the low-pressure wave troughs. When the bubbles collapse in the high-pressure wave peaks, they produce tiny jets of water.

When the bubbles collapse near a wafer, the resulting jets hit the silicon and dislodge any particles adhering to the surface. The particles are carried away by the water currents and the microscopic bubbles are so numerous that all surfaces are cleaned. The bubbles and the cleaning effect are present throughout the liquid and they penetrate into holes, crevices and microscopic structures, cleaning completely.

Megasonic Cleaning Benefits

In addition to cleaning silicon wafers and removing microscopic particles more effectively than traditional cleaning methods, Megasonic Cleaning provides several other benefits over the use of chemicals. The rise in output quality is accompanied by lower costs, a safer process environment and shorter process times.

When a semiconductor fabrication facility uses fewer chemicals for cleaning wafers, costs decrease. The facility has to purchase smaller amounts of chemicals, storage costs are lower and costs for disposal are less. Depending on the process, Megasonic Cleaning may allow a facility to eliminate certain chemicals completely, resulting in even higher savings.

The Megasonic Cleaning process is safe and environmentally friendly. The megasonic waves and the cleaning solution do not present any danger to equipment or operators who can set a timer and come back when the cleaning process is finished. The water-based solution is not toxic and does not require special disposal. Compared to chemical cleaning, the storage and handling of Megasonic cleaning materials is safe and easy, power consumption is lower and less water is required.

Modutek’s Megasonic Cleaning System

The Modutek Megasonic Cleaning System was developed together with ultrasonic technology leader Kaijo Corporation to reflect the specific demands of silicon wafer cleaning. The high operating frequency in the MHz range ensures gentle but effective cleaning of delicate materials without pitting the silicon surface or damaging the silicon wafer structures.

Modutek’s partnership with Kaijo lets the company offer an integrated system that features the Quava Megasonic generator and transducer within Modutek’s cleaning baths. Megasonic’s baths are available in the indirect heating MSI series that can heat the cleaning solution up to 140 degrees centigrade while the direct heating MSD series can heat the cleaning solution up to 70 degrees centigrade. Both baths are ideal for submicron particle removal with a high power density and high efficiency.

The Megasonic System is available with 600 W, 900 W and 1200 W power ratings at the standard 950 kHz frequency. Frequencies of 200 kHz, 430 kHz, 750 kHz and 2 MHz are also available for applications that require the more robust cleaning action from the lower frequencies or for very delicate components at the higher frequency. In any case, Modutek can advise customers to make sure they select the ideal Megasonic Cleaning configuration for their specific silicon wafer cleaning applications.

How Megasonic Cleaning Technology Improves Silicon Wafer Yields

How Megasonic Cleaning Technology Improves Silicon Wafer YieldsSilicon wafer cleaning is a key process during semiconductor manufacturing that becomes especially critical for smaller microcircuit geometries on 300 mm (approx. 12 inch) silicon wafers. Sub micron particles must be removed from the wafer substrate during processing without damaging the delicate microcircuit structures. Any particles that remain may result in defective semiconductor components or output of low quality.

A process incorporating Megasonic Cleaning technology at higher megahertz frequencies can help remove tiny particles and contaminants without damaging or altering the surface of the wafer. The selection of appropriate frequencies and power levels is important for effective cleaning results. Modutek has partnered with leading ultrasonic cleaning system provider Kaijo Corporation to incorporate Kaijo’s high frequency Megasonic Cleaning technology into the Modutek wet bench process equipment. These wet benches can combine chemical cleaning processes such as SC1 with megasonic cleaning in the megahertz range to remove a high percentage of 0.1 to 0.4 micron particles. Depending on cleaning times and temperatures, cleaning efficiencies of over 99 percent can be achieved.

How Megasonic Cleaning Works

In megasonic cleaning systems, a megasonic frequency generator produces high-frequency sound waves in a liquid via a transducer immersed in a liquid bath. The sound waves are compression waves that generate high pressure at their peaks and low pressure in their troughs. Cavitation bubbles appear in the low-pressure troughs and collapse in the high-pressure peaks. This bubble action in the cleaning liquid removes contaminants from exposed surfaces.

Low ultrasonic frequencies in the range of 20 to 40 kHz produce comparatively large, very energetic bubbles whose collapse can cause cavitation damage to delicate surfaces. For semiconductor cleaning applications, megasonic frequencies in the MHz range generate much smaller, less energetic bubbles. Their gentle cleaning action does not damage the wafer surface while still cleaning effectively.

At the same time, the bubbles agitate the cleaning solution, reducing boundary layers and promoting cleaning solution access to small surface features such as crevices and complex shapes. Using megasonic cleaning in silicon wafer manufacturing improves the effectiveness of the chemical cleaning solution by removing small sub-micron particles through the action of energetic bubbles.

Modutek Megasonic Cleaning Systems

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

Modutek’s Megasonic Cleaning System that utilizes Kaijo’s megasonic generator operates at 950 kHz in the standard version. Frequencies of 200 kHz, 430 kHz, 750 kHz and 2 MHz are also available for cleaning applications that require a more or less robust cleaning action. The Megasonic Cleaning System can operate at power levels of 600, 900 or 1200 W.

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

Decision makers at semiconductor manufacturing facilities can use Modutek’s wet benches that incorporate the use of megasonic cleaning technology to improve yields. Cleaning times are reduced while cleaning effectiveness is higher and lower chemical consumption can contribute to better cost control. Improved removal of small sub-micron contaminants and particles can reduce wafer defects and produce better quality output. If you need to improve wafer processing quality and yields and want a free consultation or quote on using wet bench stations that incorporate megasonic cleaning technology, call Modutek or email Modutek@modutek.com.

Silicon Wafer Cleaning: Effectively Removing Contaminants to Improve Yields

Silicon Wafer Cleaning: Effectively Removing Contaminants to Improve YieldsSuccessful semiconductor manufacturing relies on the effective cleaning of silicon wafers at several stages of the manufacturing process. Impurities, contaminants and residues from process steps have to be completely removed to ensure that the manufactured components have the required functionality and the desired quality. Silicon wafer cleaning equipment such as those offered by Modutek helps increase yields and improves the cleaning process to deliver high quality results.

RCA Cleaning

Standard RCA cleaning, named after the RCA Corporation where it was developed, involves immersion of the silicon wafers in hot acidic and alkaline solutions. The first bath usually contains hydrogen peroxide and ammonium hydroxide while the second bath has hydrogen peroxide with hydrochloric acid. The first solution removes organic contaminants from the surface of the silicon wafers by dissolving the bonds binding the contaminant particles to the silicon and by the oxidizing action of the chemicals. The second solution dissolves and removes alkaline residues and metallic particles.

RCA cleaning is the most common cleaning method used in the semiconductor manufacturing industry. It is especially effective in removing particles responsible for defects in semiconductors. When detected, such defects reduce the semiconductor yields of the manufacturing process and, if not detected, they reduce the quality of the resulting components.

Megasonic Cleaning

Cavitation bubbles created by the use of megasonic cleaning systems complement the chemical cleaning action of RCA cleaning. As semiconductor geometries become smaller and smaller in size, microscopic particles become more important in the creation of defects. Particles that might be too small to impact the function of large components become critical defect-producing factors for the smallest semiconductor structures.

The bubbles of megasonic cleaning systems add a mechanical component to the overall cleaning action. When the cavitation bubbles burst, they release energy that helps dislodge contaminant particles from the silicon substrate. This mechanical cleaning action can speed up the overall cleaning process and make it more effective in removing even the smallest particles.

SPM Clean – Piranha Etch

When silicon wafers are heavily contaminated, for example when contaminants are clearly visible or for the removal of photo resist after wafer processing, piranha etches provide a powerful cleaning method. The cleaning solution is made up of a mixture of hydrogen peroxide and sulphuric acid. The solution is highly corrosive and yields aggressive cleaning to remove large amounts of material. Sometimes wafers can be run through a piranha etch treatment before further cleaning with the RCA method.

FEOL and BEOL Processing

Front End of Line (FEOL) processing is the part of semiconductor manufacturing in which the components, such as transistors, are created in the semiconductor wafer, while Back End of Line (BEOL) processing involves depositing the metallic interconnections. Cleaning may be required after etching, after ion implantation or after metal deposition to remove process residue.

Water-based cleaning removes some of the impurities and RCA cleaning or piranha cleaning may be used to remove masks, photo resist or chemical residue. Ultrasonic cleaning is effective in helping remove particulate contaminants and ozonated deionized water may be used as well. At the end of each cleaning process, the wafers may be dried with isopropyl alcohol (IPA) in preparation for further processing steps.

Silicon Wafer Cleaning Equipment

Modutek has specialized in silicon wafer cleaning equipment for the semiconductor manufacturing industry and can deliver a complete spectrum of semiconductor cleaning solutions. In addition to chemical cleaning stations, Modutek incorporates the use of Megasonic cleaning equipment and IPA dryers.

Modutek silicon wafer cleaning solutions are based on the company’s thirty years of experience in providing semiconductor manufacturing equipment to the semiconductor industry. Modutek’s team of engineers can advise customers on the choice of equipment and design custom cleaning solutions for a wide variety of applications. If you need reliable and effective silicon wafer cleaning equipment in your manufacturing process, contact Modutek at 866-803-1533 or email sales@modutek.com.

Modutek At Semicon Conference in China

Modutek At Semicon Conference in ChinaModutek, a leading provider of leading-edge wet benches and wet process equipment, will have a factory representative at the Semicon Conference in Shanghai China from March 15-17, 2016. Modutek will be with their China Rep Laserwort located in Hall N3 at booth 3401. 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

Stop by the Modutek /Laserwort booth to get information and answer any questions you have about Automated, Semi-Automated and Manual Wet Process Stations used for acid/base, solvent and ozone cleaning or photo resist strip. Modutek also provides IPA vapor drying and Megasonic cleaning equipment to support your manufacturing applications. In addition environmentally friendly acid neutralization systems and air scrubbers are available with all their equipment.

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

  • Fully-automated Wet Bench Equipment
    • Benefits include:
      • Full automation control with touch screen
      • SolidWorks Simulation Professional software
      • SolidWorks Flow Simulation software
      • Servo motor automation
      • All robotics and software designed in house
      • Complete design, assembly and test done according to your specifications
  • Semi-automated Wet Bench Equipment:
    • Benefits include:
      • Automation control with touch screen
      • SolidWorks Simulation Professional software
      • SolidWorks Flow Simulation software
      • Servo motor automation
      • All robotics and software designed in house
      • Complete design, assembly and test done according to your specifications
  • Manual Wet Bench Equipment:
    • Benefits include:
      • High end manual equipment at competitive pricing
      • Meets or exceeds all current safety standards
      • Designed to meet any process requirements
      • Can accommodate custom designs and processes
      • Low cost of ownership
      • Equipment designed for future expansion

Our fully-automated, semi-automated and manual wet bench equipment supports the following applications:

  • KOH Etching
  • Quartz cleaning
  • Ozone Etching
  • Ozone Cleaning
  • SC1 & SC2 featuring Megasonic Cleaning
  • BOE (Buffered Oxide Etching)
  • MEMs processing
  • Plating
  • All solvent applications
  • Hot phosphoric (Nitride Etching)
  • SPM Cleaning
  • Precision Part Cleaning
  • IPA Vapor Dryer
    • Benefits include:
      • Very low IPA consumption
      • No moving parts inside drying chamber which eliminates wafer breakage
      • Most drying cycles completed within 10-15 minutes
      • No watermarks
      • Drying technology can be easily designed into your wet bench eliminating one transfer step
    • The IPA Vapor Dryer supports the following applications:
      • Ozone Cleaning
      • Wafer Drying

Modutek has over 35 years of experience 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. Call 866-803-1533 or email Modutek@Modutek.com for a free quote or consultation to discuss your requirements.