Why High Temperature Quartz Baths Are Required for Silicon Wafer Cleaning

Silicon wafers undergo many process steps during the manufacture of semiconductor components and cleaning the wafers properly is an important factor in successful fabrication. Process steps include etching and diffusion, both of which involve coating the wafer with masking material to guide the etching chemicals or diffusion targets. Once a step is completed, the masking chemicals have to be completely removed. If traces remain or if other impurities are introduced, the quality of the final semiconductor product will be affected.

Silicon wafers are cleaned with aggressive chemicals to remove organic masking material and other possible contaminants. As a result, the cleaning solution container has to be able to resist the action of corrosive chemicals while remaining inert without becoming a source of contamination itself. Baths made of quartz are highly stable, resist corrosion and can be designed and built to avoid contamination. Quartz baths are an ideal solution to the challenges of silicon wafer cleaning and the maintaining of high levels of wafer cleanliness.

How Quartz Baths Clean Silicon Wafers

Quartz baths provide a clean and safe container for the chemical reactions that are used in silicon wafer cleaning. Depending on the materials used, the quartz bath may simply hold the wafers and the cleaning chemicals, but some processes require heating, circulating the solution or the addition of chemicals. In each case, the control actions must be accurate, reliable and easily duplicated.

For example, materials such as hydrochloric acid, sulfuric acid and hydrogen peroxide may be used for cleaning the silicon wafers. Quartz is impervious to these strong chemicals and the quartz tanks remain unaffected while the acids clean the silicon wafers. With SPM clean, sulfuric acid and hydrogen peroxide are mixed and maintained at a constant temperature of about 130 degrees centigrade. Periodic spiking with hydrogen peroxide is necessary because it decomposes in the solution. The mixture cleans wafers rapidly but can’t attack the quartz bath container.

Using bath containers that are inert and don’t contaminate is important because the electrical and physical structures making up modern semiconductor components are extremely sensitive to contaminating particles. As these structures become smaller and more tightly packed on a wafer, even a single particle can interfere with the etching or the diffusion process. Such interference from particles reduces the yield of semiconductor components and affects the productivity of the semiconductor manufacturing facility.

The Benefits of Using Modutek’s Quartz Baths

Modutek has over 30 years experience in quartz bath design and manufacture so that the company’s baths fulfill all the basic requirements for semiconductor processing and deliver additional benefits. Modutek can provide standard units where they satisfy customer requirements but can also design and build custom systems for special applications.

Modutek’s QFa series high temperature re-circulating quartz baths are safe and reliable with a low total cost of ownership. The semiconductor grade quartz of the baths is flame polished to reduce contamination and the vessels are designed for an especially long service life. Particle addition from re-circulating flow is kept to a minimum and remote control is available. Tank sizes range from an inner measurement of 7.75 x 7.75 inches and 9 inches high to 21.5 x 11.5 inches and 10.5 inches high. Custom sizes are available as well.

The QFa baths have an integrated heater that provides an operating range of 30 to 180 degrees centigrade. The heaters produce a temperature rise of 2 degrees per minute and control accuracy is plus/minus 1 degree centigrade, these variables depending on the operating conditions. The wide temperature range, fast thermal response and accurate temperature control make the Modutek quartz baths ideal for silicon wafer cleaning. The high precision guarantees excellent repeatability of the process between batches and the fast heating rate reduces process times. Overall, Modutek’s quartz baths can help improve the semiconductor production performance of manufacturing facilities and research labs. For a free quote or consultation on selecting the right equipment for your manufacturing process contact Modutek at 866-803-1533.

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

Why Quartz Baths Are Used in the Wafer Cleaning Process

Why Quartz Baths Are Used in the Wafer Cleaning ProcessThe cleaning of silicon wafers during semiconductor manufacturing uses strong, corrosive chemicals to remove deposits from the surface of the silicon. Critical factors for effective cleaning are an absence of contamination in the chemical bath, the impervious nature of the container and a tight control of the bath temperature. Baths made from high purity quartz don’t react with chemicals used in semiconductor manufacturing and are inert as a source of contamination. Quartz conducts heat well so fast temperature rise and accurate control are possible. A high-quality quartz bath is an ideal container for the semiconductor wafer cleaning process.

How Quartz Baths Are Used

The semiconductor manufacturing process involves multiple steps, each of which may require cleaning of the silicon wafer before or after the production process segment. Highly corrosive chemicals such as sulfuric acid, hydrogen chloride or hydrogen peroxide are used to remove materials such as organic residue from the surface of the wafers in preparation for manufacturing steps such as etching or diffusion. Effective cleaning is a critical factor in the success of semiconductor manufacturing because impurities or contaminating particles left on a wafer can lead to defective products or products of inferior quality.

During the cleaning process, the silicon wafers are immersed in chemicals within the quartz bath. Depending on the cleaning process, the baths may be heated, kept at a given temperature for a defined time period and chemicals may be re-circulated. For example, in RCA clean, wafers are first immersed in a mixture of ammonium hydroxide and hydrogen peroxide. These chemicals remove organic contaminants and particles from the surface of the silicon wafers. After rinsing and drying, the wafers are immersed in a mixture of hydrochloric acid and hydrogen peroxide. In this step metallic contaminants and particles are removed. The wafers are then cleaned for subsequent processing steps.

If particles remain on the wafers or if impurities are introduced during the cleaning process, manufacturing steps such as diffusion will be affected. With microscopic semiconductor structures, even tiny particles can obstruct an electrical connection or affect electrical characteristics. The semiconductor product may then fail prematurely or not work properly. When the quartz container is eliminated as a source of contamination, the focus is on the wafer cleaning process itself and its effectiveness in removing contaminants and particles.

How Quartz Baths Facilitate Reliable Cleaning

Quartz baths can meet all the criteria for effective cleaning of silicon wafers but they have to be designed well and constructed with top quality materials. Modutek series QFa re-circulating baths are made with semiconductor grade flame polished quartz to reduce the possibility of contamination. They feature quick, even heating and are available in a variety of standard as well as custom sizes. Operation is reliable and safe with excellent wafer cleaning performance and high quality output.

Operating characteristics include a temperature range of 30 to 180 degrees centigrade and the tanks can heat the bath at a rate of 2 degrees centigrade per minute. Temperature control is accurate within plus/minus 1 degree centigrade and heating is even through the bath. Standard tank sizes range from 7.75 inches to 21.5 inches a side with a depth of up to 14.5 inches. Custom sizes are available.

Modutek uses its experience of over 30 years designing quartz baths to deliver the highest quality baths with excellent cleaning performance. Modutek baths feature safe operation, reliable output and a low cost of ownership. The company can advise customers how best to meet their semiconductor wafer cleaning needs and can make specific proposals for solutions based on the company’s complete range of wet bench processing equipment.

How Quartz Baths Are Used in a Manufacturing Process

How Quartz Baths Are Used in a Manufacturing ProcessThe manufacture of semiconductor components requires the cleaning, stripping and etching of semiconductor wafers using corrosive chemicals in a tightly controlled environment. Two important factors for achieving improved yields of functional components are keeping the bath free from contaminants and accurately controlling the temperature. High quality quartz baths fulfill these requirements with a tank material that is impervious to the chemicals used in the baths and that facilitates fast even heating by conducting heat efficiently. A well-designed quartz bath is the most effective solution for processing semiconductor wafers in chemicals such as sulfuric or hydrochloric acids, even at elevated temperatures.

Important Characteristics of Quartz Baths

To process semiconductor wafers effectively, quartz baths must be well designed and be made of quality materials. To avoid introducing unwanted impurities into the process the bath must be made of quartz of the highest purity. It must be available in a variety of sizes and heat up rapidly, featuring tight temperature control. Operation must be safe and reliable, ideally based on extensive experience in the design and supply of these products.

Modutek Recirculating Quartz Baths

The Modutek Series QFa quartz baths are high temperature recirculating units manufactured to the highest quality standards. Modutek has over thirty years experience in designing quartz baths and the company uses the expertise acquired with this evolution to offer the best in the industry. Key qualities resulting from this evolutionary process are safety, reliability and low cost of ownership.

For its recirculating quartz baths, Modutek uses semiconductor grade flame polished quartz to keep potential contamination to a minimum. The baths feature fast, even heating and a seamless, sloped flanged design that helps ensure safe operation. Temperatures in the range of 30 to 180 degrees C. can be controlled to plus/minus 1 degree C. and the heat-up rate can be up to 2 degrees C. per minute. Bath sizes range from 7.75 x 7.75 x 9 inches to 21.50 x 11.50 x 10.50 and 17.87 x 10.75 x 14.50 inches while custom sizes are available as well.

Modutek Constant Temperature Quartz Baths

With many of the same quality and operating features as the QFa models, the quartz baths of Modutek Qa series meet the same goals of high safety and reliability combined with a low cost. The process vessel is made of internally flame polished virgin fused quartz, boron-free, and the baths have the same accurate temperature control of 1 degree C. with a heat-up rate of 2 degrees C. per minute. Options include a magnetic stirrer, a quartz bubbler and remote operation timer switches and available sizes are similar to those for the recirculating baths. Modutek quartz baths can be used with confidence to improve semiconductor processing performance.

If you need help selecting quartz baths to use with your manufacturing process, contact Modutek at 866-803-1533 or email [email protected].

Improvements to the Silicon Wet Etching Process

Improvements to the Silicon Wet Etching ProcessAs a result of improvements in design, and materials, the silicon wet etching process can produce better wafer yields with reduced defects. Modutek provides equipment engineered to incorporate such improvements that are designed for reliability, safety and low cost of ownership. The company’s wet etching products include features that offer specific advantages and deliver improved results. Process engineers and fabrication facility managers can order equipment customized to meet their needs and to ensure they receive the process improvements they expect.

Modutek’s QFa Series High Temperature Recirculating Quartz Baths and the Qa Series Constant Temperature Quartz Baths are designed to set the quality standard in quartz baths. Used for etching, stripping and heating, the baths feature fast, even heating to improve process yield and minimize damage from runaway temperatures. The high quality internally flame polished virgin fused quartz process vessels reduce downtime and increase reliability due to longer vessel life.

Although Modutek’s Teflon tanks come in standard carrier sizes, the company will build custom sizes to match any requirement. Tank configurations are Temperature Controlled Recirculating Baths, Temperature Controlled Static Baths and Teflon Ambient Baths. Inline heating or immersion heating are available. Modutek can help design the optimal configuration for both new as well as existing systems you may already have.

Modutek’s silicon nitride etch baths deliver excellent process control while retaining flexibility in installation and operation. The control system monitors the temperature of the bath to determine when adding de-ionized water is required to maintain the acid to water ratio. As water is lost to evaporation, the boiling point of the bath increases and the control system adds small amounts of water to the boiling liquid, ensuring that the water mixes in immediately. This method tightly controls the boiling of the chemicals and avoids “bumping.” The availability of remote metering means that the product is easy to install and Modutek can help find the best solution for any process station.

Modutek’s line of Quick Dump Rinsers can increase process efficiency by reducing rinse times and DI water consumption. The Rinsers feature state-of-the-art engineering to eliminate particle entrapment and minimize rinsing times. Dual overhead spray manifolds, a contoured vessel design and a large machined dump door ensure efficient and rapid operation.

For facilities that could benefit from using KOH etching, Modutek offers customized solutions manufactured according to customer specifications. KOH etching is a repeatable process that delivers fast etching at a low cost. Modutek’s solutions use the company’s Teflon tanks with advanced welding techniques and all-PFA material. The products can be designed to particular specifications or to be compatible with your existing wet bench equipment. Once the wet etching process is established, continual adjustments are not necessary. Modutek can integrate the new products into an existing line to deliver process improvements and increased efficiency.

Making use of improved designs or higher quality materials can generate substantial benefits from reduced costs and better throughput. The increased ability to manufacture customized products that are optimized for a particular application can further improve silicon wet etching results. For any questions about silicon wet etching products or for help selecting the right manufacturing equipment for your requirements call Modutek at 866-803-1533.

Improved Process Control with Modutek’s Silicon Nitride Wet Etching Bath

Improved Process Control with Modutek's Silicon Nitride Wet Etching BathWith over 30 years of experience in the design and manufacturing of silicon wet etching equipment, Modutek has recently introduced their series Nb silicon nitride etch baths, an upgrade to their previously available series Na. The new series features improved process control resulting in greater flexibility and better safety. The Nb series benefits include uniform nitride etching, smooth chemical boiling control, and remote DI water metering.

Silicon nitride etching takes place in a fluid that is 85% phosphoric acid and 15% DI water. The acidic solution boils at 160 degrees C, resulting in some water boiling off as steam. The Modutek Nb series etch bath includes a condenser which returns some of the steam back to the bath, but water has to be added to the bath to replace the steam that escapes.

Adding water to acid can be hazardous, but Modutek has developed a safe procedure to add the required water to the acid bath. When water is added to a viscous liquid such as phosphoric acid, the water stays on top of the acid. As more water is added, a sudden reaction can occur when the water mixes into the acid. Instead, the Modutek bath adds small amounts of water to the acid solution when the liquid is boiling. The boiling action ensures that the water to replace losses through steam is immediately mixed into the solution and avoids sudden large reactions.

To ensure that the acid solution is always boiling, the bath heater is on when the bath is operating. The bath solution remains at the boiling point and the operation of the heater does not have to be controlled. Instead, the temperature controller monitors the temperature to determine when to add water to the bath.

The boiling point of the bath solution varies with the concentration of the acid. As the solution loses water through the escape of steam, the boiling point increases. The temperature controller detects the increase in temperature and adds a small amount of water to restore the concentration of the acid solution. In this way the temperature controller uses the temperature of the boiling solution to maintain the bath concentration at its set point.

Because keeping the solution boiling is critical to the process and for safety, the Modutek silicon wet etching bath includes additional monitoring to detect boiling. A thermocouple located above the surface of the liquid activates an interlock if there is no hot steam over the solution. The interlock cuts power to the water valve and prevents water from being added when the bath solution is not boiling. The same interlock activates when the lid of the bath is off because the loss of steam and heat can cause the solution to stop boiling.

Additional safety interlocks are provided by thermocouples that detect bath overtemperature and tank overtemperature. The former activates an interlock to shut off the heaters when the bath temperature exceeds 170 degrees C, indicating there is a problem with the water supply, the set points or the acid solution itself. The latter shuts off the heaters when the tank overheats, for example if an empty tank is switched on.

Modutek’s silicon nitride wet etching baths feature etched foil resistance heaters, PVDF or teflon condensers with safety covers, a heat-up rate of 2 to 3 degrees C per minute, and process temperature control of plus/minus 0.5 degrees C. Benefits of this design include accurate nitride etching control with good nitride etching uniformity, chemical boiling control without bumping, easy installation with remote metering, and a high level of safety.

To learn more about the Silicon Wet Etching products sold by Modutek Corporation, or to learn how our products can be redesigned to work with your Nitride Etch Baths or Quartz Baths and Sub Ambient Systems (BOE), contact us at 866-803-1533 or email [email protected] to discuss your requirements and get a free quote.

Modutek Introduces Water Ring Seal (WRS) Option in Quartz Baths Products

Quartz_Baths_ProductsModutek’s new Water Ring Seal (WRS) option will extend the heater life of your high temperature quartz bath……guaranteed.  With our new WRS option, any high temperature quartz bath comes standard with a 30 month warranty.

Our WRS design gives you a true 360˚ water ring seal under the top flange of the quartz bath.  This labyrinth seal creates a water seal barrier preventing chemical fumes from entering the heater cavity on any of our quartz bathsSimilar to the AquaSeal®, our WRS design gives you a continuous water flow and a second resource for this option.

Besides the 30 month warranty, the WRS design will help with:

  • Reducing inventory control due to extended bath life
  • Eliminating process down times
  • Overall facilities saving
  • Improving yield
  • Eliminating the possibility of shipping your current quartz bathin for repair once a year

Our two main high temperature quartz bath series for your WRS options are the Qa and QFa Series.  All Modutek’s standard quartz baths come with an Inconel heating element bonded to semiconductor grade quartz.   Our QFa series took the original Qa design and added circulation (overflow) features.  This gives you the ability to continuously filter your chemical in a closed loop design.

Both the Qa and QFa Series Constant Temperature Quartz Baths are a result of over thirty years of evolutionary bath design and a passion for establishing the quality standard in quartz baths.  Since 1980 Modutek has sold over a thousand high temperature quartz baths.  At Modutek, we define quality by the degree of safety, reliability, and cost of ownership engineered into every aspect of all our products.

Our Service and Support:

We provide one year warranties on all of our products, accessories and now 30 months on our WRS option for quartz baths.  Our field support team is available to answer your questions and resolve equipment problems by calling our toll free number: 1-866-803-1533.

Our Equipment:

Our two main high temperature quartz baths for the WRS option consist of our QFa Series and Qa Series.  Both are highly reliable and we have sold thousands of units over the years.  Below are some of the benefits of our Quartz Baths:

  • Nested 4 sided heating element 360º serrated overflow weir
  • Seamless, sloped flange design
  • Dual safety snap switch
  • Facilitates laminar flow while minimizing particulate contamination
  • Fast, more even heating
  • Minimizes damages resulting from runaway temperatures
  • Improves up time and reliability due to longer vessel life

Contact us directly through the web site or by calling 1-866-803-1533.  We will respond within 24 hours during week days.

Silicon Wet Etching Using Modutek’s Nitrite Etch Bath

Silicon Wet Etching Using Modutek’s Nitrite Etch Bath

Silicon Wet Etching Using Modutek’s Nitrite Etch Bath

Modutek has been designing and manufacturing Silicon Wet Etching components and related equipment for over 30 years. Their more recent Nitrite Etch Bath products, including the “Nb” series, is an upgrade to their “Na” series. The Silicon Nitride Etch Bath has been designed and engineered to provide unparalleled process control. You can also expect flexibility and safety as key components of these systems.

Part of what makes the Nb Series silicon nitride etch bath stand out is its two-tiered diagnostic system. This allows the user of the system to monitor the temperature at the same time as it maintains the acid-to-water ratio through supplemented D.I. water. This new metering system makes the Nb easier to install. It also allows for service in existing process stations or in new ones.

Some of the benefits of the Silicon Wet Etching system include, but are not limited to, the following:

  • Controlled Nitride Etching
  • Nitride Etch Uniformity
  • Remote DI water metering system
  • Controls chemicals boiling (no “bumping”)

The silicon nitride etches function in a combination fluid – 85% phosphoric acid (H3PO4) and 15% DI water. These fluids boil at 160°C. Since the water will boil off some of the solution as steam, the NbSeries silicon nitride etch bath includes a refluxor which cools the condenser to cause the steam to condensate back to water which maintains the solution. Please be aware, the condensers are not 100% efficient, which will make it necessary to add water to the solution periodically.

Generally, it is discouraged to add water to acid, but it is required in this case. We have determined some safe ways to do this. For instance, if the acid rapidly agitates or boils, you can add a small amount of water which mixes right away. This poses no safety issues. When the water is added to non-boiling acid, the water sits on top of the acid. More water is added to the top layer of the acid. The water will mix as the heat absorbed by the water makes it boil. The water mixes thoroughly with the acid and the correct reaction occurs.

A basic chemistry rules states, “The temperature of a solution cannot rise above its boiling point, except under special circumstances.” The heater on our system does not have to be controlled the way it is required on other systems. If the heater switch is on, the heater is on. By choosing not to regulate the heater, the heat solution is allowed to boil regardless of the concentration. The system keeps it boiling while water is added to adjust the concentration, which remains at the upper set point.

The Silicon Wet Etching and Nitrite Etch Bath systems also include the following features:

  • Etched-foil resistance heater
  • PVDF or Teflon reflluxor with safety cover
  • Vapor thermocouple
  • Uniformity heat transfer
  • Ease of installation and repair for new or existing wet station configurations

System Specifications include the following:

  • Application: Silicon Nitride Etch
  • Operating temperature range: 30 – 180º C
  • Chemical usage: H20, H3PO4
  • Heat-up rate: 2-3 º C per minute (rate affected by size of system)
  • Process temperature control: ± 0.5º C
  • Vapor thermocouple for chemical boiling control
  • PVDF refluxor with Teflon® cooling coils
  • One year warranty

Companies that need additional features may consider any of the following options. Modutek will work with you to design the Silicon Wet Etching system that best meets your company’s needs. Options include, but are not limited to:

  • Teflon® gravity drain system
  • Auto cover which is pneumatically actuated
  • Remote operation timer switches
  • Aspirator valve system
  • Model C1815a process controller/timer
  • RS232 Interface

To learn more about the Silicon Wet Etching products sold by Modutek Corporation, or to learn how our products can be redesigned to work with your Nitride Etch Baths or Quartz Baths and Sub Ambient Systems (BOE), contact us at 866-803-1533.

Choose Modutek’s Quartz Baths When Safety and Reliability Are a Must

Choose Modutek's Quartz Baths When Safety and Reliability Are a MustThe Quartz Baths designed and manufactured by Modutek Corporation are safe and reliable as well as being cost-effective so it can be integrated into your current production system. With over 30 years of experience developing and evolving the bath designs, they are seen in the industry as the quality standard of quartz baths.

Pure quartz is nearly inert and will not react with most other substances. It is for this reason quartz is the perfect choice for semiconductor processes. Not only is it non-reactive, it is also stable at relatively high temperatures. It has a Mohs hardness of 7 and lacks cleavage which enables it to handle most demanding applications.

Modutek offers different Quartz Bath Products to meet your processing needs:

The QFa Series Quartz Baths provide the following benefits:

  • Fast heating that is more even than other manufacturers
  • A nested, 4-sided heating element that heats to 360 degrees Fahrenheit with a serrated overflow barrier
  • A seamless, sloped flange design
  • Minimizes damages which could result from runaway temperatures
  • Dual safety snap switch
  • Improved up-time and reliability because of the longer vessel life
  • Easier laminar flow while it reduces particulate contamination

It can be used with a variety of chemicals including H2SO4, H202, SC1 and other chemicals. It has an operating range of 30 º – 180 ºC. The operating temperature range can be controlled in ± 1 ºC (depends on controller and process). The operating temperature range has a heat-up rate of 2 º C per minute. (This rate will be affected by the size of the system, the fluid being used and other factors.) It can be used for cleaning, etching and stripping and has a ¾” male Flaretek circulating fluid inlet/outlet.

Options include a liquid level sensor, process temperature controller, custom vessel sizes to meet your specifications, quartz diffuser plate and autolid.

The Qa Series Quartz Bath is a constant temperature quartz bath. It has redundant safety devices, seamless, sloped flange design and a bonded, 5-sided circuit heating element. Benefits include improved process yield by faster, more efficient, and even heating. It minimizes the potential damage caused by runaway temperatures. It also increases uptime and reliability because of longer vessel life.

The options available for the Qa Series Quartz Baths include having a magnetic stirrer, a gravity drain, an aspirator (dilution) valve system, remote operation timer switches, quartz bubbler, and process controller.

Both Series Quartz Baths come in a variety of sizes. If you would like to learn more about the Modutek Corporation Quartz Bath models or want a quote, you may reach us at 866-803-1533.

Options for Silicon Etching Equipment

Options for Silicon Etching Equipment ModutekIf your company needs silicon etching equipment, look no further than Modutek. We have been in business for over 30 years providing silicon wet etching products and semiconductor manufacturing equipment. Turn to a company that has experience and an in-house manufacturing team that works with you to create the product you need.

Silicon wet etching, used to create Micro-Electro-Mechanical System (MEMS) components, often require components as small as 0-100 microns. They are used in countless products today in many industries. Two of these industries – automotive and medical – use MEMS components in products such as sensors for car air bags (MEMS accelerometers) and blood glucose meters for Diabetics.

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