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

Ordering a Wet Bench Station for Your Specific Process Requirements

Semiconductor manufacturing requires many process steps that must be followed and controlled in a very precise manner. Process requirements can include cleaning, etching, developing and stripping. Handling the aggressive chemicals means special attention has to be given to safety and disposal. The physical characteristics required in the production line have to be considered as well. Special features such as recirculation, heating, additional process control and degree of automation can be ordered.

Not all semiconductor equipment manufacturers can offer a complete line of wet bench stations incorporating the latest technology and using their own software. The many options and differing process requirements mean that almost every installation is customized to some extent. An experienced supplier who can provide advice and deliver the best systems is needed for achieving optimal results.

Physical Requirements Affect the Ordering Process

The three types of physical factors influencing the wet bench equipment specifications are the available space, wafer size and wafer throughput. Limited space for new installations or a requirement to integrate with an existing system may mean that compact stations are required. The baths must be able to accommodate the wafer size proposed for the application. Throughput is governed by the number of cassettes that can be processed per bath, the number of stations, the estimated process duration and the estimated downtime for replacing chemicals, maintenance and other process-related factors.

Space limitations are often critical. Factors that can reduce space requirements are what functions a station can execute and whether some functions, such as rinsing and drying, can be combined or need separate spaces. Chemical delivery systems can take space or might be placed remotely or behind the productions line. Such questions can be explored with a qualified supplier.

Throughput is often a critical variable affecting profitability. Automatic transfer of wafers between stations and automatic process control may save time. How the process is controlled, for example in a piranha “feed and bleed” type of operation, may affect how long a chemical bath can be used without changing the chemicals and may also affect downtime for maintenance. Often advanced technology from a leading supplier can increase throughput.

Wet Bench Equipment, Controls and Accessories Have to Support the Process Chemistry

Wet bench processes such as RCA clean, KOH and Piranha use highly aggressive chemicals. The equipment has to resist the corrosive substances and feature safeguards to keep operators secure. Some processes, such as silicon nitride etching, have to have special controls. Processes using especially dangerous chemicals such as hydrofluoric acid require additional safety measures.

Equipment for specific wet bench processes can include the following:

  • Quartz baths for cleaning etching and stripping applications. High temperature recirculating or constant temperature baths.
  • Teflon tanks for etching applications. Heated, recirculating and ambient temperature.
  • Silicon nitride wet etching bath. Special control features for silicon nitride removal with phosphoric acid.

Semiconductor fabrication facilities, research labs and universities that require wet process equipment first have to make sure that prospective suppliers can provide equipment with the special features needed. Heating control accuracy and precise calculation of dosages is essential for high quality output and a low product failure rate. Suppliers who manufacture, assemble and program their own equipment can be relied upon for complete after sales support and service.

Modutek Can Help

Modutek has worked closely with semiconductor fabricators and has extensive experience in providing semiconductor manufacturing equipment. The company assembles its own systems in their San Jose California facility and company specialists program their own software and controls. Modutek has state of the art wet bench stations and has pioneered improvements for processes such as silicon nitride removal and Piranha etching. With its in house expertise, the company can analyze customer requirements and propose the best solutions.

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

Selecting Silicon Wet Etching Equipment for Your Application

Silicon wet etching equipment is required in the manufacture of semiconductor components and selecting the right equipment is essential for maintaining facility performance and excellent product quality. The products produced from these facilities range from relatively simple electronic parts to complex components with intricate microstructures and an electronic/physical structure interaction. These varying requirements mean that most systems have to be customized for the specific application.

Selecting wet etching equipment along with related accessories and controls may require expert help because the system parts have to be closely integrated and seamlessly take the silicon wafers through many fabrication steps. Precision dosages, accurate temperature control and exact timing are important for consistency. Manufacturers who assemble their own equipment and program their own software will be able to give the most useful advice on system selection.

Getting the Right Tanks and Baths

Tanks made of different materials and with different options support different chemical processes. Quartz baths are used for cleaning with processes such as RCA and SPM while Teflon tanks are used for etching applications such as KOH and TMAH. Stainless steel tanks are for solvent baths and all the tanks have to be made from high-quality materials that reduce contamination.

Tank features that are specific to various processes can include heating, cooling and re-circulating. Chemicals are heated to speed up etching and cleaning but the temperature has to be tightly controlled to ensure etching is precise and repeatable. Sub-ambient filtered etch baths are used with buffered oxide etch (BOE) and can operate in a 10 to 60 degree Celsius temperature range. Recirculation keeps the temperature constant and can include filtering.

Silicon nitride wet etching is a special case because the baths need a two-tier control system that avoids temperature bumps from the addition of water to the phosphoric acid used in the process. Control measures are needed to maintain the water acid ratio by adding small amounts of water while ensuring that the water immediately mixes with the acid. If an application requires nitride etch, this type of control feature is essential.

Automation Can Improve Throughput and Yield

Automation of different process steps can make the process run exactly as desired and allows operators to program variables with excellent results for subsequent batches. Wet benches can be operated manually, semi-automatically or with full automation. Manual control lets operators set process parameters and calculate chemical doses before starting and monitoring the process. In semi-automatic operation, many of the process steps are carried out robotically but still under the control of the operator. Full automation runs the entire process.

Automation impacts the performance of silicon wet etching equipment in several ways, including the following:

  • Reduced human error.
  • Reduced chemical use
  • Increased etching accuracy
  • Improved etch rates

These factors become especially important with semiconductor products in which components are densely packed or which have intricate microstructures. Better control of temperatures, dosages and timing means product defects are fewer, yields are higher and product quality is improved. Running the same automated program again results in excellent repeatability. Reducing operator interaction with harmful chemicals increases safety and employee job satisfaction.

Modutek Provides Industry-Leading Silicon Wet Etching Equipment

Modutek can provide silicon wet etching equipment for all common wet bench processes and has the expertise to customize systems for specific customer applications. All equipment is assembled in house at the San Jose, California facility and the software is designed and programmed by the company’s specialists. Modutek has extensive experience in semiconductor manufacturing equipment and can help customers select the best silicon wet etching systems to satisfy their requirements.

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

How Chemical Delivery Systems Are Customized for Specific Applications

Many types of industrial plants and research centers use chemicals in their operations and need systems that can handle these often dangerous substances effectively. The chemical delivery system has to be able to store the chemicals, deliver them to the point of use and handle disposal. Depending on the application, chemical mixing and a degree of automation may also be required. Key characteristics of chemical delivery systems include the following:

  • Reliability. Dependable systems must deliver the right amounts of chemicals as required.
  • Accuracy. Most processes need specific amounts of chemicals at various times. The dosage and timing has to be precise.
  • Efficiency. The system must be easy to operate manually and to program for automatic operation.
  • Reduced Waste. Only the amounts of chemicals and water needed are delivered and material is recycled as much as possible.
  • Repeatability. A process step can be carried out repeatedly and always get the same result.
  • Safety. The system must deliver reduced operator error and reduce potential operator exposure to harmful chemicals.

Designing chemical delivery systems with these characteristics means the systems will have a high degree of customization with regard to many of the system components and functions. A provider will have to custom design and manufacture the equipment to fit the location, the application and any specific customer requirements.

The Volume of Chemicals Needed Impacts the System

Some processes only need small amounts of chemicals for spiking solutions or for processing small mixtures while other applications require bulk chemical supply. For spiking, delivering precise dosages is critical while for bulk chemical use receiving and storage are important. Small chemical volumes can be stored wherever there is a small space available but large volumes may need space for large chemical totes along with a load cell interface to keep track of chemical use. Each application depends on site layout and available room for the chemical delivery equipment. Systems have to be customized to fit into the available space.

How Chemicals Are Used Influences Customized Controls

Bulk supply of a single substance needs relatively simple controls but mixing and blending several chemicals needs software and relatively complicated systems. The toxicity and aggressiveness of the chemicals impacts the peripheral physical systems to ensure against leaks, spills and the possible exposure of employees. Each chemical delivery system has unique requirements for functions such as mixing, acidity, etching capability and chemical disposal. Customized controls can accomplish these tasks as long as the basic system has the necessary flexibility and the supplier has the expertise and experience to customize the controls.

Facility Layout Affects System Design

Often an ideal layout situates a small storage container near the process where the chemical is being used. In other systems, it may make sense to bring the chemical from remote storage to the process and pipe the used products away for disposal. While the chemical delivery part of the system is clear, the placement of the system components depends on available space and detailed operational practices. In each case, the physical details of the system have to be adjusted for the site and site-specific operations.

Modutek Can Meet Customization Requirements

With extensive expertise in the field of chemical delivery systems, Modutek has the capability to adapt these systems as needed by their customers. Because the company designs and manufactures its own equipment, it can make changes and adjustments to satisfy specific requirements. Customers can take advantage of Modutek’s in house design and production capabilities to get exactly the systems they need. The resulting customized chemical delivery systems are safe and of the highest quality.

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

Improving Silicon Wafer Cleaning with the Piranha Etch Process

The Piranha etch process removes organic material from silicon wafers rapidly and completely. Semiconductor manufacturing involves the repeated etching and cleaning of the silicon wafers and the Piranha mixture is a favorite method for the resist strip of wafers to prepare them for further processing. Modutek can provide high temperature re-circulating and constant temperature quartz baths and the company has developed a new “bleed and feed” control method to improve the silicon wafer cleaning process.

Modutek Quartz Baths for Piranha Etch

Modutek quartz baths are based on extensive experience and the use of the highest quality materials. The baths themselves are made of virgin boron-free fused quartz in a flame-retardant polypropylene housing. The QFa series is a high temperature re-circulating bath with a temperature range of 30 to 180 degrees centigrade while the Qa series is a constant temperature bath with the same temperature range.

Both bath series are temperature controlled to plus/minus 1 degree centigrade with a heat-up rate of 2 degrees centigrade per minute. Process control can be fully automated, semi-automatic or manual. The baths are available in a variety of sizes and Modutek will construct custom units as required. The units are ideal for Piranha etch applications because of their quick and even heating, accurate temperature control and extended vessel life.

Improving Piranha Process Control

The Piranha process uses an aggressive mixture of sulfuric acid and hydrogen peroxide to dissolve organic residue on the silicon wafers. The mixture is heated to about 130 degrees centigrade to improve the strip speed. Control of the cleaning is difficult because mixing sulfuric acid and hydrogen peroxide is exothermic and heats up the solution when the mixture is first prepared. As the mixture cools, it has to be heated to maintain its temperature and the strip rate.

The hydrogen peroxide in the mixture is unstable and decomposes to form water, diluting the mixture and slowing the strip rate. Heating the mixture increases the rate of decomposition of the hydrogen peroxide. To keep the concentration and the strip rate constant, the sulfuric acid and hydrogen peroxide mixture is periodically spiked with extra hydrogen peroxide. This addition keeps the strip rate elevated but the overall process is hard to control and the mixture has to be replaced completely about once per day. To improve the Piranha process and silicon wafer cleaning, the concentration and temperature variation issues have to be addressed.

The Modutek “Bleed and Feed” Process Control Method

Modutek has developed a method of improving control of the Piranha process by using a two tank system with a clean and a dirty tank. When the concentration of hydrogen peroxide goes down, a small amount of mixture from the dirty tank is drained and discarded. The drained amount is replaced from the clean tank. The stripping process can continue and the concentration is maintained at the desired level. The clean tank has its sulfuric acid and hydrogen peroxide replenished. All “feed and bleed” amounts are programmable to match specific process variables.

Benefits of the Process Change

The “bleed and feed” control method can be fully automated and the frequent addition of small amounts of sulfuric acid and hydrogen peroxide mixture keeps the strip rate constant and allows for continuous use of the mixture over an extended period of time. The benefits include:

  • Savings of chemicals can reach 75 percent while chemical purchase and disposal costs are correspondingly lower.
  • Process efficiency is increased due to less downtime for replacement of the chemicals.
  • Process results are improved due to a more constant strip rate.

As a leading semiconductor equipment manufacturer, Modutek provides customers with high quality equipment that offers the highest degree of process control. Modutek supports the new “bleed and feed” process change for Piranha strip in the company’s new wet bench stations. Call for a free consultation to discuss your specific process requirements.

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

Selecting a Wet Bench Manufacturer That Meets Your Process Requirements

Semiconductor device fabrication can be a complex process. Often, it can take as many as eight weeks to complete a manufacturing cycle. During this process it’s critical to use wet bench stations that are built with high quality components that work reliably. This is needed to ensure that every manufacturing process involved complies with important industry standards.

How do you choose the right wet bench manufacturer and station to ensure that all your process requirements are met? There are a few areas that you need to consider:

Confirm the Wet Bench Station That Directly Meets Your Needs

A wet bench needs to address all your requirements.

  • Do you need full automation, semi automation or manual control? Fully automated stations use robotics for all the process steps and are typically used to optimize through put on well developed process. Semi automated stations use robotics for some process steps with some operator interaction. Manual wet bench stations are least expensive option and are often used when developing a new process that requires a manual interaction and does not use any robotics for automation.
  • The use of compatible materials is important. You need to consider what kind of processes engineers will use the wet bench for, and confirm the kind of fire-resistant plastics that must be used.
  • Consider the types of chemicals that will be used in the wet bench. Will corrosive chemical solvents be used? If solvents such as Acetone, NMP or Photo Resist Striping will be used a stainless steel solvent station will be need that uses corrosion-resistant material and provides fire suppression features.
  • The wet bench manufacturer should supply equipment that is in compliance with all fire safety and electrical safety codes.

If it’s difficult to find a ready-designed wet bench unit that needs all these needs, you should consider contacting the manufacturer for a custom solution.

Choose a Turnkey Solution

A wet bench manufacturer should be a one-stop outlet that has an extensive product line. They should offer complete, fully integrated systems. A complete turnkey solution is what you should choose. You should order your semiconductor wet process equipment from a vendor who not only provides you with the wet bench that you need, but also includes full installation, after sales service, technical support, and warranty support. If the unit is capable of accepting improvements and updates down the line, such improvements should be offered by the vendor, as well.

Look at Reputation and Longevity

Look for a vendor who comes with a good reputation for product quality and customer service and has been in business for awhile. Wet bench equipment is a long-term purchase. It can be beneficial to maintain a relationship with the supplier, for help with installation, repairs and updates along the way. It is also important to choose a well-established supplier. A wet bench manufacturer who has been business for decades is likely to stay in business and honor the warranty support offered.

Choose Modutek for Your Wet Bench Needs

Modutek has been the leading supplier of wet bench and wet processing equipment for over 38 years. During this time, the company has become one of the leaders and innovators in the business. Modutek does more than supply standardized wet bench equipment. The company offers clients the ability to customize and configure their equipment as they need it. Modutek’s design engineers work closely with clients to meet specific requirements.

Modutek designs all its equipment and software in-house, and, for this reason, is far more capable of offering perfectly customized solutions, when compared to other manufacturers who outsource much of their design and software.

Modutek Offers a Wide Range of Options

Semiconductor fabrication is complex process. Clients are usually not able to accept one-size-fits-all solutions. It is for this reason that Modutek offers a number of options.

Fully automated wet benches: These appliances offer wafer fabrication, using the company’s own SolidWorks Simulation Professional software. The system is known to improve production times, with high throughput for better yields.

Semi-automated wet benches: Semi-automation offers greater precision than manual control, but is more affordable than full-automation. A servo-activated robot offers three levels of automation. Just as with fully automated wet benches, the semi-automated ones come with deep software control.

Manual wet benches: These appliances offer all the features of the automated and semi-automated ranges, except that they do not use robotics. Equipment of this kind can be affordable, and it is expandable, as well.

Modutek’s wet benches offer dry-to-dry processing. They allow drying without the need to use separate appliances. It speeds up wafer processing, and allows for higher yields.

Modutek is one of the best-known names in the wet processing industry. All of Modutek’s products are designed and assembled at the company’s facilities in San Jose. With its year-long guarantee on all its products, and a name that has set high standards for quality and reliability. Modutek is a premier semiconductor wet bench manufacturer and wet process equipment supplier that you can trust. Call 866-803-1533 for a free consultation to discuss your specific process requirements.

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

 

Modutek at 2019 Semicon Conference in China-Hall N3 Booth 3243

Modutek Corporation, a leading supplier of wet bench stations and wet process equipment, will be at the Semicon Conference located at the Shanghai International Expo Center in China from March 20-22, 2019. At the Conference Modutek and their factory representative Laserwort Ltd., will be located in Hall N3 at booth 3243. Additional details about the Semicon Conference in China can be referenced at: http://www.semiconchina.org/

Representatives at the Modutek /Laserwort booth will be available to answer questions and provide information on using Wet Bench Stations for acid/base, solvent and 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 and builds customized wet bench stations and wet processing equipment for customers in many industries including 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:

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

Features include:

  • Single drying chamber for DI water rinsing and IPA vapor drying
  • Easy to change IPA bottles
  • Filter bypass for contamination control with no cassette contact points
  • On board HF metering for precision mix ratios
  • Uses an in situ HF etch process with a rinse step before the IPA drying cycle
  • 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 38 years of industry experience and expertise in designing and building wet bench stations and wet process equipment that provides highly reliable and consistent results for precision processes. They also provide world-class service, and customer support. Contact Modutek for a free consultation or quote at 866-803-1533 or email [email protected].

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

 

Why Pre-Diffusion Cleans Are Important for Silicon Wafer Cleaning

Why Pre-Diffusion Cleans Are Important for Silicon Wafer CleaningPre-diffusion cleans are carried out several times during the semiconductor manufacturing process, and each time the chemical residues and particles on the wafers have to be removed as completely as possible. If silicon wafers still have surface contamination when they are placed in the diffusion oven, diffusion may be uneven and the resulting semiconductor products may be defective.

The several methods available for wafer cleaning either use chemical baths or Megasonic cleaners to remove surface contaminants from the silicon wafers. Modutek offers a complete line of wet bench stations that support pre-diffusion wafer cleaning as well as other semiconductor fabrication processes.

The Importance of the Pre-Diffusion Wafer Cleaning Process

The contamination with particles on silicon wafer surfaces prior to diffusion is a key factor in reducing the yield of electronic components in semiconductor fabrication plants and research facilities. Particles may be diffused into the silicon and create electric defects or they may block diffusion behind the particle. After diffusion, particles may affect etching and interfere with microscopic conductors. The resulting electronic components may have to be scrapped.

As microscopic structures in silicon become smaller and more detailed, large particles become more disruptive on both an electrical and the physical scale. Even tiny particles that were previously considered unimportant can affect the smallest silicon structures. When electronic products are defective, it affects facility productivity and reduces throughput. Performance is lower and profitability is reduced. In some cases, the products are not defective but their life expectancy may be reduced and the manufacturer’s reputation is affected. An effective pre-diffusion wafer cleaning process results in fewer defects and a higher quality output.

How Pre-Diffusion Cleaning is Carried Out

Before being placed in the diffusion oven, silicon wafers are immersed in chemical or Megasonic baths. Surface impurities are dislodged, dissolved or chemically neutralized. Complete cleaning may take more than one process and the following methods are commonly used.

RCA cleaning is a popular method consisting of two components, SC1 and SC2, where the SC stands for standard clean. For SC1, the wafers are immersed in a solution of ammonium hydroxide and hydrogen peroxide. The aggressive chemicals remove all organic compounds from the wafer surfaces but may leave traces of metallic contamination. As a result, during SC2, the wafers are placed in a mixture of hydrochloric acid and hydrogen peroxide that removes any remaining metal ions.

An alternative to the RCA standard clean methods is the Piranha clean, especially useful for applications with heavy wafer contamination. It consists of a sulfuric and hydrogen peroxide mixture that rapidly removes material such as photo resist. A further feature of Piranha clean is the hydroxylation of the silicon wafer surface, making it hydrophilic or attractive to water, a characteristic useful for some subsequent process steps.

Megasonic cleaning uses high-frequency sound waves in a cleaning solution to dislodge contaminants from the surface of the silicon wafer. This cleaning method does not use harsh chemicals, and a generator is used to produce a signal in the MHz range at a specified power level. A transducer in the cleaning tank converts the signal to sound waves in water. The sound waves create microscopic cavitation bubbles with a strong scrubbing action that removes particles. Depending on the manufacturing process, semiconductor manufacturing facilities use one of these methods for pre-diffusion cleaning.

Modutek Pre-Diffusion Cleaning Equipment

Modutek’s wet bench chemical stations provide a complete range of pre-diffusion cleaning solutions. The company can offer equipment that supports each of the above cleaning methods as well as other semiconductor fabrication processes. All of Modutek’s pre-diffusion cleaning baths produce silicon wafers with extremely low particle counts while all of the company’s equipment is designed for high quality output, fast processing and efficient operation resulting in superior manufacturing facility performance. Contact Modutek for a free consultation or quote on equipment designed to meet specific manufacturing requirements.

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

 

Advantages of Using the KOH Etching Process

Advantages of Using the KOH Etching Process for Silicon EtchingThe KOH etching process uses a potassium hydroxide solution to etch silicon wafers and produce microscopic structures in the silicon. In subsequent semiconductor fabrication steps, the micro structures are used in the manufacture of integrated circuits, processors and other electronic devices.

Compared to other etching processes KOH etching is comparatively safe, etches silicon rapidly and can be tightly controlled. These characteristics are especially important for batch processing when a process step has to be reproduced precisely many times. While other chemical processes are required for specific semiconductor cleaning and etching steps, industrial plants and research facilities prefer the KOH process for general silicon etching.

How the KOH Etching Process Works

The KOH solution is prepared by adding KOH to water in an etching tank made of material impervious to aggressive chemicals. Silicon wafers are masked with silicon nitride or silicon dioxide, substances that the KOH solution does not etch. When the wafers are immersed in the KOH solution, silicon is removed from the areas that are not masked by the chemical action of the KOH etching solution.

The etch rate can be controlled by changing the concentration of the solution and by changing the temperature. The concentration is fixed once the process is established and is usually around a 30% solution by weight, but may be as low as 10% and as high as 50%. Typically the solution temperature is about 60 to 80 degrees centigrade and the etch rate increase is very sensitive to an increase in temperature.

Other factors influencing the etch rate are the crystal lattice planes of the silicon and the presence of boron doping. Different crystal lattice orientations are etched at different rates so that the crystal lattice planes influence the design of the masks and their placement. Boron doping can be used to stop the etching in a specific direction. Taken together, all the ways the etch rate can be controlled allow the creation of complex shapes in the silicon.

Controlling KOH Etching

Obtaining the desired etching results from the KOH process can be divided into two groups of control measures. The concentration, doping and lattice orientation are determined initially before the process starts and establishes itself. At that point, temperature control can still change the etching rate. The initial control measures can be put in place with the required precision, concentration and other characteristics but the temperature of the etching solution must be controlled accurately on a continuing basis.

Because the KOH etching process is very temperature sensitive, maintaining the temperature at the exact set point is important. The temperature controller must be accurate during the process and also from one batch to the next. Tight control during the etching process ensures that the etch rate remains constant while precisely keeping the same temperature for a given set point from one batch to the next ensures accurate reproducibility of process conditions and identical output across different batches.

Modutek’s Teflon Silicon Etch Tanks

Using Modutek’s Teflon tanks allows operators to fully benefit from the advantages of KOH etching. The tanks are designed with KOH etching in mind and feature a wide temperature range, tight temperature control and rapid heating. Custom sizes are available and custom installations can be designed to fit any new or existing wet bench application.

Heating in Modutek’s Teflon tanks is either in line or through an immersion heater in the overflow weir. Temperatures can be controlled to plus/minus 0.5 degrees centigrade and the temperature range is 30 to 100 degrees centigrade. The heating rate is 2 to 3 degrees per minute, depending on the size of the system, and heating is even throughout the bath. Since temperature control is a key requirement for successful KOH etching, these system characteristics allow for excellent reproducibility between batches and for the precise control needed for high quality output.

Apart from excellent temperature controls, Modutek’s Teflon tanks feature all TFA Teflon with advanced manufacturing techniques designed to minimize contamination. Options such as an auto lid feature or a condensing refluxor are available if needed. Modutek Teflon tanks are an ideal solution for KOH etching applications and the company can help select the model and options that best satisfy specific customer needs. Contact Modutek for a free consultation on selecting the right equipment for specific process requirements.

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

 

Why Chemical Lift Station Pumps Are Needed for Wet Bench Stations

why-chemical-lift-station-pumps-are-needed-for-wet-bench-stations2Once a wet bench process step is completed, the remaining chemicals and waste water have to be drained and transferred to an area for neutralization and disposal. Depending on the physical layout of the semiconductor manufacturing facility, gravity draining may either not be possible at all or may be insufficient in terms of flow and speed. Chemical lift station pumps take over the transfer of chemical solvent in a controlled and optimized way. The removal of chemical solvents and waste liquids is accomplished rapidly and completely, leaving the wet bench station ready for a new process step.

Lift Station Pumps for New Installations

While it may be possible to design new installations without lift station pumps and relying only on gravity drains, changes in the facility, expansions or upgrades may require the retrofitting of pumps. In that case, lift station pumps have to be included in separate stations that are often located behind the wet bench stations. These separate stations take up valuable floor space that could otherwise be dedicated to productive process elements. As a result, incorporating lift station pumps in new wet benches is more desirable.

Modutek can add lift station pumps to their wet bench stations and use them to pump acids, solvents and related chemicals and solutions in their semiconductor manufacturing equipment. The lift stations automatically monitor the lift station tanks. When fluids are detected in the tank via the installed level sensors, the corresponding pump is activated to transfer the liquid from the processing station to the facility’s neutralization area. Incorporating the lift pumps in the processing stations is an efficient and compact solution for new installations.

Adding Lift Stations to Existing Processing Lines

When wet bench processing lines are used with a new process or are upgraded, the gravity drains that were previously adequate may no longer deliver the required flow. Lift stations have to be added to deliver the anticipated performance. Often extensive customization of the lift stations is required to accommodate them in the existing facility.

Modutek can help find solutions to adding chemical lift stations to wet processing lines. The company has a complete line of chemical lift stations for installation outside existing wet processing stations. Modutek engineers evaluate process requirements and plant layout to propose equipment that works best for a particular application.

Modutek’s chemical lift stations have all-plastic fluid paths for resistance to corrosion and feature an automatic constant ON with level sensing governing operation. Standard pumps are vertical centrifugal polypro with other pump options and a double containment option available. The polypro holding tank can be built to the size required and the designs are customized to meet flow requirements. Level sensing is via four float-type level sensors signaling low/low, low, high and high/high. Remote control is available.

Modutek Delivers Customization and Support

Modutek can analyze the requirements of a wet bench installation and propose ideal solutions because the company designs and builds their wet bench equipment in house at their facility in San Jose. With almost 40 years experience in wet bench technology, Modutek has the expertise to find optimum solutions and implement them using their own equipment. Chemical lift stations for existing installations and lift station pumps incorporated into new wet bench stations often require extensive customization. Such customization can include different geometry, size, materials, and control logic to meet unique customer requirements. Modutek can rely on in house experience to adapt its equipment for a specific application. Once delivered and installed, Modutek can provide unparalleled customer support because the company doesn’t use third party suppliers. The Modutek specialists carrying out wet bench and lift station service are backed up by the Modutek personnel who designed and built the equipment.

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