How Quartz Tube Stations Work and the Benefits They Provide

Among the many processing steps involved in the manufacture of semiconductor components are high-temperature operations such as diffusion of materials into the silicon wafers. Quartz tubes are an ideal vessel for these process steps because the tubes can withstand the temperatures required and are inert enough to minimize contamination.

Typically, the silicon wafers are placed into a horizontal quartz tube large enough to hold the wafers and their supports. The quartz tube cleaning station can heat the contents up to over 1000 degrees centigrade. In a diffusion process, impurities such as phosphorus are introduced into the quartz tube.

Once the process is complete, the quartz tube is contaminated and has to be cleaned for the next batch of wafers. Complete and reliable cleaning is essential for the semiconductor manufacturing process because contaminating particles can cause defects in the semiconductor components or result in inferior product quality.

How Quartz Tube Cleaning Works

Quartz tube cleaning is a custom-designed process because the dimensions and cleaning requirements of quartz tube furnaces can vary widely. Quartz tubes are mechanically delicate, so they have to be handled with care. At the same time the cleanliness requirements are rigorous so that all traces of the contaminating material have to be removed. Finally, the rinsing and drying process must not introduce any new particles into the quartz tube. The cleanliness of the tube directly impacts the performance of the semiconductor manufacturing facility.

In horizontal quartz tube cleaning stations, the tube is inserted into the cleaning enclosure and cleaned with an acid spray. The acid dissolves and removes the contaminant from the high-temperature furnace. A subsequent rinse cycle removes all traces of the acid from the tube surfaces. A drying cycle can speed up drying without introducing particles into the cleaning enclosure. Mechanical handling of the tubes reduces the possibility of breakage due to human error and minimizes opportunities for the entry of contaminating particles. Safety interlocks, exhaust fans and safety shields protect operators from the hazardous chemicals.

Modutek’s Quartz Tube Stations Offer Numerous Benefits

A key factor in effective customization of quartz tube cleaning stations is that the supplier has to design and build the stations so that they can make the required adjustments. Modutek designs and builds all process, etching and cleaning components in house at the company’s San Jose, California facility. Equipment is customized exactly according to the requirements of the specific application.

In addition to providing customized equipment, Modutek can supply the degree of automation required by the customer. Cleaning process steps can be initiated manually or the whole cycle can be completely automated. Different steps can initially be run and timed manually and then, when optimum performance is reached, automated operation can be locked in.

Full automation reduces human error and keeps operators safe by allowing them to monitor the cleaning process remotely. Automated quartz tube cleaning stations will run the same cleaning job exactly the same way, with identical timing and dosages. Results from an automated system are predictable and uniform and the system can be programmed for the best possible results.

Modutek’s horizontal quartz tube cleaning stations are an excellent solution for semiconductor manufacturers. Rugged and reliable with one-piece construction up to ten feet long, the basic units offer many options for additional features. Once the requirements of the cleaning application are satisfied, Modutek can offer design add-ons such as holding tanks, automation features, a T/C sheath cleaner or a bottle washer. Modutek is a leading semiconductor equipment manufacturer that provides continuous product innovations and improvements along with the highest degree of customer service and support.

Reviewed and Approved by Douglas Wagner
President & CEO, Modutek Corporation

How the IPA Vapor Dryer Improves Wafer Processing Results

how-the-ipa-vapor-dryer-improves-wafer-processing-results

Not every advancement in semiconductor fabrication produces results that are usable in industry. To be of value, advancements need to be consistently repeatable when used on an industrial scale. Modutek’s IPA vapor dryer falls into this category, helping semiconductor fabricators improve both yields and processing times.

Modutek’s IPA vapor dryers are custom-engineered with in-house experts working in partnership with a client’s technical staff. From a thorough understanding of a client’s manufacturing process, Modutek works to make sure their equipment is designed and tested to meet the requirements.

The Marangoni IPA Vapor Dryer Design

Silicon wafers require cleaning, rinsing and drying at certain stages of the fabrication process. The results need to be as close to perfection as possible, with no watermarks, and minimal particle contamination. In the past, these results were obtained through rapid spinning and heat drying. These simple methods no longer work with the latest high-density wafers, however. Not only is water hard to remove from complex shapes, drying without leaving watermarks is impossible.

Contamination from incorrect cleaning and drying can cause serious product malfunction and high failure rates. This is where drying by isopropyl alcohol comes into play. IPA drying by the vapor method, delivers wafers that are completely free of watermarks and with minimal contamination. Modutek’s IPA vapor drying system is both cost-effective, and ready for seamless integration into the standard wet bench process or free-standing design.

How the IPA Vapor Dryer Design Works

Modutek’s IPA vapor dryer design is unique in a number of ways. This design delivers high-quality results through serving IPA vapor at the upper reaches of the drying tank. This makes sure that vapor distribution is even. Since the surface tension of isopropyl alcohol is lower than that of water, such vapor serving introduces a gradient of surface tension where isopropyl alcohol meets with a layer of water on the wafer surface. With this type of drying effect, water quickly leaves the wafer surface, and leaves it completely dry and clean. Since the water does not actually evaporate, it leaves the watermarks behind. The drying process takes no longer than 15 minutes.

The Advantages of Modutek’s IPA Vapor Dryer

Modutek’s in house experts in IPA vapor dryer design work together with a clients’ technical team to design and create IPA dryers that specifically meet their application requirements. Clients are able to come to Modutek’s facility for testing to make sure that their equipment works as expected.

With extensive experience in the wafer processing industry, Modutek is fully able to provide top-notch equipment and customer support at every stage of the design process, during delivery and after the sale. With expertise in semiconductor processing equipment, Modutek is able to address every specific client need for this industry. Contact Modutek for free consultation on the equipment needed for your specific wafer manufacturing process.

 

 

 

Improving Wafer Processing with Automated Equipment

Fully and semi-automated wafer processing equipment can help improve wafer output quality by providing consistent chemical processing dosages and timing, however these settings must be first be determined. One way to find optimal process settings is to operate in manual and then in semi-automated mode where settings can easily be adjusted. This is especially true of new process development where the exact parameters are not known. Wafer fabrication facilities can first try out initial settings in manual mode and tweak or “fine tune” them to obtain the desired output. Using semi-automated stations to run the parts of the process that are finalized while making additional adjustments gives optimal results. These can then be made permanent in a fully automatic station.

Steps for Improving the Fabrication Process

Although the overall process is known and the chemicals to be used are set, a new fabrication process may initially not work as desired. Perhaps the etching is not at the expected speed, or the results are not consistently reliable. While the effects of changing chemical concentrations and timing for bath exposure are known, the optimum variables for the specific process have to be found.

After an initial run, the problem areas can be identified and variables such as chemical dosages and timing can be adjusted. Skilled and experienced operators can carry out the fabrication steps and make changes easily on a manual station. In manual mode, the operator is completely in control and nothing happens unless the operator initiates the action. Such control can be important when determining initial settings for a new process.

Once the major parts of the new process work as expected, there may still be minor adjustments necessary to achieve targets such as faster processing, better quality output or reduced chemical use. For such adjustments, use of a semi-automated station saves time. Instead of carrying out all the steps manually, the semi-automated station can run the parts of the process that don’t need adjusting. These parts will run reliably without operator intervention, as programmed and without deviation from the correct set points. The operator can then focus on the final adjustments to optimize and then utilize fully automated wafer process equipment

Subsequent Tailor Made Full Automation

Once the parameters and variables for the desired yield and performance have been determined, a tailor-made software and automation package can be assembled. This package, in a fully automated station, reproduces the custom settings of the manual and semi-automated process steps and uses them to consistently produce the desired results. Carrying out the fine tuning of the process on manual and semi-automated stations first allows the fully automated station with the optimized settings to scale up to full production right away. The tailor-made solution for a specific new process can immediately produce the desired yields and process characteristics.

For semiconductor fabrication facilities that often bring online new processes, using manual and semi-automated stations to fine tune the process and develop a tailor-made solution can be an attractive alternative to optimization on a fully automated station. Full automation is still desirable for production runs because of the greater reliability, accuracy and reproducibility that such stations deliver. Once the optimized software and automation package is running production on a fully automated station, the station will produce consistently high-quality output, high yields, low defect rates and use chemicals efficiently.

Modutek can work closely with each customer to determine the best way of optimizing new processes. The company’s full line of wafer processing equipment including manual, semi-automated and fully automated wet bench stations lends itself to this kind of optimization to produce ideal outcomes. Wafer fabrication facilities that consistently optimize new processes can lower overall costs and improve facility performance. Contact Modutek for a free quote or consultation on selecting the right equipment to support your manufacturing process requirements.

 

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 [email protected].

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 [email protected].

 

Modutek at 2018 Semicon Conference in China

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.

 

The Benefits of Using Modutek’s Quartz Tube Cleaning Stations

The semiconductor wafer is the substructure on which the circuitry of every computer chip is laid down. Semiconductor wafers are fabricated in high-tech foundries, and require a precise, ultra-clean operation. One of the most basic requirements of a semiconductor wafer operation: reliably clean quartz tubes. Quartz tube cleaning stations are required equipment at every semiconductor foundry.

Most have several units stationed at different parts of the manufacturing process, each one specifically tuned and adjusted to the requirements of specific applications. Since the quartz tube cleaning process requires the use of corrosive chemicals, it takes an involved manufacturer and installer of quartz tube cleaning stations to design and install custom units for specific client needs.

How do quartz tube cleaning stations help?

Quartz tubes being delicate articles, cleaning them can be risk-prone. The ideal quartz tube cleaning process, therefore, minimizes human handling at every stage. This is the reason automated quartz tube cleaning stations are essential at any semiconductor wafer foundry.

With Modutek’s quartz tube cleaning stations, the handling of tubes during the cleaning process is mostly avoided — cleaning stations are designed to keep quartz tubes in motion while they are etched, and powerful nozzles direct water spray at the quartz tubes to maximize coverage Custom-designed cleaning stations come with many other options that can be applied to specific needs. Automated processes and nitrogen-drying can help in specific parts of the manufacturing process, for instance.

What do quartz tube cleaning stations look like?

The quartz tube cleaning stations designed and fabricated by Modutek are built out of white polypropylene. The cleaning processes are controlled by systems that can be turned to manual or automated mode, and units can be customized to specific height levels to perfectly fit the processes to which they are to be applied. Workers at these stations are protected from the acid cycle with PVC safety shields, and other standard features include hand-sprayers for deionized water, and Teflon guns for nitrogen use.

Clients are presented with a wide array of choices comes to customization. The station can be constructed out of FM 4910, or can include a hot nitrogen drying process as needed, for example. The right kind of holding tanks, automated bottle washers and other features can be designed and applied where necessary, and quality certifications required by third parties are arranged for, as well.

Automation Where it’s Needed

Modutek’s quartz tube cleaning stations can be designed and customized with optional automation for process lines that need it. From automated program recipes to tube roller systems, every part of the process can be made more efficient with automation. The operator merely monitors and controls the process through information presented on a screen, and can control various functions remotely. From bottle washing to drying, every part of the process is remotely monitored.

Automated processes do not actually require operator intervention. Processes, once they are set off, can go through to completion without operator input. Manual functions, when they are necessary in certain processes, can be remotely controlled at any point.

A process design that is set up to help the operator test different cycle times, is one of the most important parts of a properly designed automated system. Modutek offers a well-designed process to aid in testing. Once the right times are discovered, they can be locked in place to prevent accidental change

Modutek’s quartz tube cleaning stations, whether manual and automatic, are fully designed in-house. In-house design expertise helps ensure superior performance in any installation. With ultra-cleanliness being a basic requirement of the semiconductor fabrication process, customization to individual process needs is an absolute necessity for effective design. Modutek’s close control of the design of these appliances helps make it happen. Clients find Modutek’s complete, end-to-end support immensely helpful in the design of their lines. Whatever the application, Modutek has the expertise to evaluate, assess, design and deliver turnkey solutions.

 

Advantages of HF-Last Etching and IPA Drying in One Chamber

In the final stage of silicon wafer cleaning the silicon oxide layer has to be removed and the clean wafer dried without contamination. When wafers are removed from the HF etching process and transferred to a drying chamber, the extra handling increases the chances for wafers to pick up contaminating particles. Such particles cause errors in the further processing of the wafers and can result in final semiconductor products that are defective or of poor quality. Carrying out the final etching and the wafer drying in one chamber reduces the possibility of contamination and can result in better output quality. The latest field results from a customer using Modutek’s single chamber HF-last and IPA vapor dryer show a substantial reduction in particle counts on wafer substrates.

The Single Chamber Process

Modutek uses IPA vapor (Marangoni) drying in a free-standing unit with one drying chamber for DI water rinsing and drying. The IPA vapor is generated in a standard one gallon bottle and is introduced into the drying chamber through the top cover to ensure even distribution. IPA consumption is low but is still adequate to give surface tension drying across all wafers and substrates. The Marangoni drying technique results in wafers without any watermarks.

To allow single step etching and drying in one chamber, Modutek modified the IPA vapor dryer to include HF (hydrofluoric) acid injection before the start of the standard IPA vapor drying process. The HF acid injection is ratio controlled and provides an oxide etch down to bare silicon. Once etched, the wafers are rinsed to a controlled pH level. When the required pH level is reached, the IPA drying process begins without moving the wafers. The particle count on the wafers remains low.

Field Results

Modutek has supplied the new single chamber HF-last IPA dryer to customers and the first large scale results are now in. In the 0.3 to 5 micron range, fewer than 20 particles (adders) were added to the etched substrate after using the Modutek etching/drying combined system. These particle counts are substantially below those achieved using the previous process in this particular field trial. Semiconductor manufacturing facility managers and research center engineers can compare these results to particle counts resulting from their current process and may be able to achieve significant improvements using the Modutek equipment.

The number of microscopic particles on wafers is becoming more and more critical as micro-structures and electronic features become smaller. Where comparatively large conducting areas and physical structures can work well even when they contain a disruptive particle, particles in the way of smaller structures either result in defective semiconductor components or in components whose characteristics are not as specified.

Modutek’s single chamber technology lets semiconductor manufacturing facilities improve output performance and increase yield. The entire etching, rinsing and drying process took only about 15 to 20 minutes in this application. One customer is reviewing particle counts, yields and output quality throughout the entire operation because it is likely that the improved facility performance with the Modutek system can justify the cost of acquiring the new equipment.

How Modutek Can Help

Modutek has over 35 years of experience providing wet processing 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 fit particular applications. Their state-of-the-art equipment has helped wet process facilities meet their production goals in the past and the new single chamber HF-last etch and IPA vapor dryer can now help customers improve overall production line performance and increase facility profitability.

 

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.

Wet Processing Systems for Solar Cell Manufacturing

Wet Processing Systems for Solar Cell ManufacturingSolar cell manufacturing facilities and research labs use wet processing equipment to etch and clean solar cell silicon wafers. Efficient removal of wafer saw damage, adding of texture, chemical polishing and cleaning of the wafers with reliable, safe wet processing systems is a key factor for increased facility productivity and high quality output. Modutek offers the latest wet bench and ozone cleaning technology to meet customer requirements either with standard systems or customized solutions.

Silicon Wafer Saw Damage Removal

Solar cell silicon wafers are cut from silicon bricks with wire saws, leaving a damaged surface with irregular crystal structure and a damaged crystal lattice. The wafers are placed in an etching bath that removes a thin layer of damaged crystal and leaves a smooth and uniform surface. Modutek wet processing equipment delivers high throughput with accurate controls and consistent results for this process.

Silicon Wafer Texturing

Silicon wafers used for solar cells absorb more light and convert light to electricity more efficiently when their front surface is etched with a microscopic texture. The texture reduces reflection of light from the solar cell surface and promotes internal reflection. For monocrystaline silicon, an etching bath removes small pyramid shapes from the surface of the silicon, leaving an even, consistent texture. For multi crystal silicon, the surface can be etched the same way, but the result is uneven and less effective due to the different orientations of the crystals. Alternative solutions with ion-etching and masks are available.

Chemical Polishing

After the front of the wafer is textured, the rear side remains comparatively rough. Such roughness can reduce the life span of the solar cell and impacts performance. By polishing the rear side of the cell and the edges in an etching bath, internal light reflection is improved and a higher efficiency cell can be manufactured.

Ozone Pre-Cleaning

The cutting of silicon wafers with a wire saw uses a slurry applied to the wires. The cut wafers are contaminated with the slurry and have to be cleaned before they can be etched, textured and polished. The Modutek Ozone Cleaning Process uses ozone dissolved in a mild acid bath to deliver high-performance cleaning at low cost.

The Modutek Ozone Cleaning Process reduces the use of expensive and environmentally harmful chemicals while improving throughput and producing wafer output with fewer defects. The equipment itself is less expensive than other cleaning solutions and there are lower costs due to reduced use of water and for disposal of waste.

Modutek Wet Processing Systems for the Solar Industry

Modutek has been providing wet processing equipment for semiconductor manufacturing for over 35 years and has the experience to examine customer applications and recommend the best solutions. For solar cell manufacturers, Modutek can offer the right equipment for cleaning, etching, polishing and texturing the silicon wafers and can make recommendations on the processes to be used.

In some cases it may make sense to combine saw damage removal with texturing or with polishing and different chemical baths may be appropriate for different customer needs. Modutek can advise customers which wet processing systems they need and can customize equipment if required. Modutek supplies wet processing systems and related equipment to solar cell manufacturers in the United States as well as around the world. Contact Modutek for a free quote or consultation to discuss which equipment to use for your application requirements.