5 Important Things to Know When Buying Wet Bench Stations

Because semiconductor manufacturing relies on a large number of process steps and complicated sequencing, wet benches need to be tailored to meet requirements for a specific application. Before focusing on the process-specific requirements, there are general questions that should be answered. This helps narrow down the selection criteria before making the purchasing decision.

General questions include the level of automation, whether stainless steel solvent stations are required, whether a chemical delivery system is needed and whether any special options for rinsing and drying would be beneficial. Any process steps that require special etching or cleaning equipment can then be considered. Such a structured approach helps with selecting the best wet process station configuration and with integrating special equipment within the wet bench station.

1. Automated Wet Bench Stations

Modutek’s product line of wet benches can be fully automated, semi-automatic or manual. Fully automated stations can run batches without operator intervention and offer excellent repeatability if the same product is manufactured several times. Reliable processing with the use of the Modutek SolidWorks Simulation Professional and SolidWorks Flow Simulation software helps increase throughput and yield.

Semi-automatic stations provide the same increased safety and reduction of human error as fully automated stations without the higher price of full automation. Servo-controlled robots provide high precision and reduce handling. Manual stations are a low-cost option that offers all the process features of the automated stations without the robotics and the cost of automation.

2. Stainless Steel Solvent Stations

Modutek stainless steel stations are an excellent solution for solvent applications. They are available in the manual to fully automated versions and in dry-to-dry configurations. Like the acid stations, they can be used with the Modutek SolidWorks Simulation Professional and SolidWorks Flow Simulation software to calculate chemical doses and the process parameters. Solvent station design can include fume hoods and all stations satisfy fire safety standards.

3. Chemical Delivery Systems

Whether a chemical delivery system is needed depends on the volumes and types of chemicals used in the fabricating process. Chemical delivery systems help avoid spills and make tracking of chemical neutralization and disposal easier. Modutek can custom design the system to exactly meet the needs of an application and a key factor for using a chemical delivery system is when high precision is needed for the chemical dosages.

4. Rinsing and Drying

Once an etching or cleaning process step is complete, the wafers have to be rinsed and dried without introducing any contaminants or particles. Rinsing and drying equipment can fulfill special requirements and improve the process. For example, the Modutek IPA dryer combines rinsing and drying in one station while the quick dump rinser improves process efficiency. Both reduce particle contamination and improve process yields.

5. Special Etching or Cleaning Equipment

Some semiconductor fabrication may require special equipment for specific etching or cleaning process steps. For example, etching of aluminum layers on wafers or the removal of submicron particles can be carried out with wet bench equipment that Modutek has specifically designed for the purpose. Modutek’s Vacuum Metal Etcher automatically etches aluminum layers with great precision and immediately removes hydrogen bubbles as they are generated. In addition Modutek can incorporate the use of Megasonic cleaning equipment to dislodge and remove the tiniest particles from wafers to be processed. This and other kinds of specialized equipment can be integrated into the process line of a wet bench.

Modutek Can Help With the Final Selection

Once customers know the things mentioned above and the requirements of their wet process application, Modutek can suggest appropriate solutions from their complete line of wet process equipment. The company designs and builds all its own equipment and meets standard industry certifications of compliance. Because the work is all done in house, Modutek can customize equipment easily and can offer outstanding customer support and service. All equipment is tested before delivery and includes a comprehensive warranty.

How Fully Automated Wafer Fabrication Equipment Improves Process Control

As the microscopic structures etched on silicon wafers become more complicated and densely packed, precise process control and the elimination of particle contamination become increasingly important. The accuracy of chemical dosages and the timing of steps have to be consistent and the handling of wafers must be reduced to a minimum. Fully automated wafer fabrication equipment can help ensure that these conditions for the production of high-quality semiconductor components are met.

Software is the Key to Full Automation

Manual and semi-automatic wet processing equipment rely on operators to mix chemicals and transfer wafers. The correct execution of the process steps depends on operator training, the operator following instructions and the instructions being accurate. Errors or inconsistencies in execution can result in defective products, production line down time and low quality output. Throughput is reduced and productivity suffers. The semiconductor manufacturing facility’s overall operations are less efficient and less profitable.

When software runs the wafer fabrication equipment, it eliminates the variability introduced by manual operation and inconsistent documentation. Once a process runs correctly, the software can be saved, and it will always run the same process exactly the same way in the future. Batches are consistent and components work as designed.

The use of software to run fully automated stations can have the following benefits:

  • Exact chemical ratios are ensured and are maintained from batch to batch.
  • The timing of process steps is precise and repeatable.
  • Process variables can easily be optimized by programming small changes in the software.
  • Accurate chemical dosages result in reduced waste and lower chemical use.
  • Chemical neutralization and disposal are reliable and easily documented.
  • Worker safety is enhanced because operators are less exposed to toxic chemicals.

These benefits come from programming automatic controls to manage the cleaning and etching of the silicon wafers. The software calculates how much of each chemical is needed for a particular process step. It controls the adding of the chemicals to the process tank, times the process step, drains the chemicals and neutralizes the waste chemicals. Once the variables in the software are optimized, the software will run the optimized process the same way every time. The results are predictable and consistent.

The Use of Robotics Reduces Contamination

Particle contamination becomes a bigger problem when the structures and conductors on the silicon wafers are small or tightly packed. For the smallest microscopic structures, a single particle may block a conductor, distort a structure or affect diffusion. The result can be an increase in defective products, products with a reduced life span or products that don’t have the desired characteristics.

Manually moving or handling wafers can be a source of particle contamination. Robotic parts are designed with low particle counts in mind and the movement of wafers can be reduced to a minimum. The exact motions are programmed and performed the same way each time.

In fully automated systems, only the robotic arms transport the wafers and no manual handling by operators is required. Once the automated sequence is started, the robotics controlled by the software move the wafers through the process without operator intervention. Fully automated robotic systems reduce particle contamination and improve semiconductor manufacturing facility performance.

Modutek Offers Fully Automated Wafer Fabrication Equipment and Wet Bench Stations

Modutek’s product line includes fully automated wafer fabrication equipment and wet bench stations. The company programs its own SolidWorks Simulation Professional and SolidWorks Flow Simulation software and makes extensive use of robotics to deliver excellent process control and high-quality output. Modutek’s software is developed in house and all wet process stations are assembled in the company’s San Jose facility. This means that Modutek specialists can optimize the automation to deliver the best possible performance and that they can customize the equipment for special applications.

The full range of benefits that Modutek’s fully automated stations include the following:

  • Reduced chemical usage
  • Improved etch rates
  • Higher yields
  • Better throughput
  • Excellent repeatability
  • Can handle both acid and solvent applications
  • Can work with standard wafer carrier sizes and custom sizes up to 30″ x 60″
  • Extensive tracking of process variables
  • Highest output quality

To make sure that the desired performance is maintained and to track all relevant data, the Modutek fully automated stations provide data logging and data access through Ethernet. Customers can record process variables and track key characteristics through an optimization period or during normal processing. These records can be valuable for quality assurance purposes and for demonstrating compliance with environmental regulations.

Modutek Supports the SECS/GEM Semiconductor Industry Protocol

The SECS (SEMI Equipment Communications Standard) and the GEM (Generic Equipment Model) protocol standards specify how automated semiconductor fabrication equipment can communicate with a host computer. Developed by the Semiconductor Equipment and Materials International organization, the standards define interfaces, messaging and communication capabilities. Communication can be via TCP/IP networks or an RS-232 connection. This means the control system of the fully automated wet process station can communicate with hosts that could range from a local computer to a server in the cloud.

Modutek’s fully automated stations support this protocol and can supply a variety of data to the hosts while receiving remote commands to start or stop a process and to choose stored recipes or programs. In an automated fabrication facility, an operator can remotely control their automated stations and can remotely log data and operating parameters. A library of recipes and software programs for specific process steps can be accessed by the automated stations that can carry out fabrication steps with a minimum level of local operator involvement.

Based on their expertise in the field of wet process semiconductor manufacturing and the hands-on experience of its specialists, Modutek can recommend automated semiconductor fabrication equipment and can build systems to meet the specific needs of customer applications. All software and robotics are designed, built and tested at Modutek’s San Jose facility.

The company leverages this capability to offer its customers custom automation solutions. Modutek’s fully automated stations can operate in a simple locally automated cycle where local operators log and verify operations. They can also function as part of an automated fabrication facility controlled remotely with data and operating parameters stored in the cloud.

With more than 35 years of experience, Modutek continues to provide innovative and reliable equipment for semiconductor manufacturing. For a free consultation or quote contact call 866-803-1533 or email [email protected]

 

Wet Processing Application Capabilities Provided by Modutek

Modutek provides a complete line of wet processing equipment to semiconductor manufacturing plants and research facilities. The company’s wet process stations support all common cleaning and etching applications. Modutek works with customers to continuously improve wet processing performance and reduce contamination and particle counts to a minimum. Wet process applications supported by Modutek equipment include the following:

Standard Clean 1 (SC1 Clean)

The SC1 Clean process uses a mixture of ammonium hydroxide and hydrogen peroxide in water to remove organic material and other non-metallic contaminants from the surface of the silicon wafer. Additional cleaning steps are required if metallic particles have to be removed.

RCA Clean

RCA Clean is a two-step process in which the first step, immersing the silicon wafer in a mixture of ammonium hydroxide and hydrogen peroxide, is similar to SC1 Clean. The second step bathes the silicon wafer in a mixture of hydrochloric acid and hydrogen peroxide. This step removes metallic contamination and particles from the wafer surface, leaving it ready for further process steps.

SPM Process Clean

SPM Clean stands for cleaning with a sulfuric peroxide mixture and the method bathes silicon wafers in a solution of sulfuric acid and hydrogen peroxide. SPM Clean is also known as Piranha Clean and it removes heavy organic material contamination such as photoresist from the surface of the silicon wafer.

KOH Etch

KOH etching uses a potassium hydroxide solution for anisotropic etching of the silicon wafer. The process is safe and reliable and produces precise etching that can be controlled by varying the KOH concentration and the temperature. KOH etch is one of the most common etching applications.

Nitride Etch

Silicon nitride masks are etched with phosphoric acid to create highly selective etch masks where silicon dioxide masks can’t be used. While silicon dioxide masks resist etching with KOH, for example, sometimes long etching times mean that the etching selectivity versus silicon may not be enough and silicon nitride masks are used instead.

Aluminum Etch

Aluminum layers are deposited on silicon wafers to create conducting paths between the semiconductor components on the wafer. The aluminum layers have to be etched so that only the desired conducting paths are left. Etching is performed under vacuum using a variety of etchants, including phosphoric and nitric acids. The vacuum eliminates the hydrogen bubbles created in a chemical reaction with the etchants.

Modutek Equipment That Supports These Wet Processing Applications

A complete line of wet process equipment has to include chemical handling systems, stations that can support the different cleaning and processing methods and automation where needed. Modutek has chemical delivery, pumping and neutralization systems; different types of baths, tanks and rinsers; as well as fume hoods, scrubbers and dryers. The company can advise customers on the different options for a wet process line and deliver suitable equipment.

For chemical handling, Modutek can offer chemical delivery systems, pumps carts, lift stations and chemical collection systems. The systems include bulk storage or local storage container options and, once collected, the chemicals can be neutralized.

Processing and cleaning station options include quartz baths and Teflon tanks. Rotary wafer etching systems are available as are vacuum metal etchers and stainless steel solvent stations. Baths can be sub-ambient, ambient or temperature controlled. Stations can be manual, semi-automatic or fully automated. In each case, controls and automation deliver a precise and reliable setting of variables and excellent repeatability of process steps.

Modutek’s extensive experience in developing wet processing equipment and on-going efforts to develop advanced process systems provide customers with superior performance with lower cost of ownership. For a free quote or consultation on selecting the right equipment for your manufacturing process contact Modutek at 866-803-1533.

 

Isotropic and Anisotropic Silicon Wet Etching Processes

The silicon wet etching of monocrystalline wafers produces microscopic structures that are used in micromechanical devices and semiconductor components. Areas of the silicon wafer not to be etched are protected by masks made of materials such as silicon dioxide or silicon nitride. The exposed areas of the silicon are etched when the wafer is immersed in a chemical bath.

In isotropic etching, an isotropic etchant such as hydrofluoric acid etches the silicon equally in all directions. This means that the wafer is etched directly downwards and also sideways under the mask. The resulting cavity has rounded corners and edges and is larger than the opening in the mask.

For anisotropic etching, the anisotropic etchant such as potassium hydroxide (KOH) etches with different speeds in different directions. This means that the etch rate in the downward direction can be faster than in the sideways directions under the mask. When properly designed, the anisotropic etch can produce cavities with straight sides and less undercutting of the mask.

More details on isotropic and anisotropic silicon wet etching can be found in the following documentation:

How Anisotropic Etching Works

In monocrystalline silicon wafers, the silicon atoms are arranged in a crystal lattice. The crystal has planes which have different atom densities. For example, the 111 plane in silicon is a diagonal plane that has a different atom density than the vertical 100 or 110 planes. As a result, the etching speed for certain etchants differs according to the plane of the silicon crystal through which etching takes place.

To design a successful anisotropic etching process, the etching speed of the etchant and the orientation of the crystal planes have to be coordinated. For example, if the aim is to etch a deep cavity with straight walls, the crystal planes with a slow etching speed have to be oriented along the cavity walls while the plane with a high etching speed should form the bottom. Rather than producing etched cavities with rounded walls and edges, anisotropic etching can create clearly defined straight-walled cavities along the silicon crystal planes.

Controlling the Etching Speed to Obtain Specific Structures

The silicon wafer masks define where etching can take place but the depth of the etched cavity and its shape can be determined by choosing the right etchant and controlling the etching rate. Isotropic etching is often used to create larger features in the initial stages of silicon wafer processing while anisotropic etching can produce straight-edged microstructures in the finishing stages.

Beyond the choice of the type of etching used, the etch rate depends on the concentration of the etchant and the etching solution temperature. Once the etch rate is determined for an etchant concentration at a specific temperature, the masked wafer is immersed in the etchant just long enough to produce the size of cavity required. In each case the precise concentration has to be mixed and the temperature has to be maintained at the target level. Subsequent wafers can be processed exactly the same way for reproducible results.

Differences between Isotropic and Anisotropic Silicon Wet Etching

While isotropic etching is harder to control precisely and hydrofluoric acid is difficult to handle, isotropic etching is faster than anisotropic etching. As a result it is often used for large geometries for which etching speed is an important factor. Anisotropic KOH etching is more precise but it depends on the orientation of the silicon crystal planes. If the wafer crystal orientation doesn’t match the requirements of the process, the resulting cavity will not have the desired characteristics.

Silicon wet etching equipment such as Modutek’s Teflon tanks support both types of processes and they come in temperature controlled and ambient versions. For processes dependent on temperature for controlling etch rate, the tank temperature controllers provide rapid and accurate heating. Concentration can be maintained through supplementation of de-ionized water and custom tank sizes are available if needed. For a free consultation or quote on selecting the right silicon wet etching equipment for your etching process contact Modutek at 866-803-1533.

 

Safely Controlling the Silicon Nitride Etching Process

Safely controlling the Silicon Nitride Etching ProcessSilicon nitride etch removes silicon nitride from silicon wafers during the fabrication process of semiconductor components. A solution of phosphoric acid in water etches silicon nitride rapidly and consistently as long as the temperature of the solution and the concentration of phosphoric acid are kept constant. Maintaining consistent process conditions during the silicon nitride wet etching process is difficult because adding water to phosphoric acid can result in an energetic explosive reaction. The accurate monitoring of the solution is extremely important for safe control of the process.

The Silicon Nitride Wet Etching Process

Silicon nitride is used as a mask to produce micro-structures and connections in semiconductor manufacturing. In most etching applications, the etch rate can be varied by changing the temperature or chemical concentration, but silicon nitride etch is best controlled at its boiling point and at a concentration of 85 percent phosphoric acid in a de-ionized water solution.

The phosphoric acid etching solution is a viscous liquid that is heated until it boils at about 160 degrees centigrade. The high temperature means some of the water will boil off and be lost as steam, increasing the acid concentration of the remaining liquid. As the concentration increases, the boiling point of the solution rises and water has to be added to keep the process variables constant.

The addition of water to the solution is dangerous because, if too much water is added at once, the solution stops boiling and the added water collects as a film above the viscous acid. As the temperature rises again and the acid starts boiling, the large quantity of water from the film mixes with the acid and may cause an explosive reaction.

Instead, the control system has to ensure that only small amounts of water are added at a time and these small amounts are immediately mixed with the remaining acid solution. Such a control strategy results in constant process characteristics, a safe operation and a high quality output.

How Modutek’s Nb Series Wet Etching Baths Ensure Safe Operation

Modutek has developed a bath control system that combines consistency with safe operation. For the Nb series etching baths, the phosphoric acid solution is kept boiling with a constantly-on heater that maintains the solution at its boiling point. As water evaporates and the acid concentration rises, the boiling point increases and the solution temperature goes up. The temperature rise is detected by a thermocouple and a small amount of water is added to the solution to bring the concentration back down.

Because the solution is constantly boiling, the small amount of water is immediately mixed in with the rest of the acid. The amount of water is too little to stop the solution from boiling and the heater is powerful enough to always maintain a vigorous boiling condition. To ensure that water is added only when the solution is boiling, a second thermocouple senses the presence of steam above the bath liquid and blocks the addition of water when no steam is present. A third thermocouple monitors the bath temperature to switch off the heater if the liquid overheats.

The Benefits of the Modutek Silicon Nitride Etch Bath

The advanced control system of Modutek’s Nb series baths allows semiconductor manufacturers and research labs to safely implement the silicon nitride wet etching process to achieve optimum consistency characteristics. The temperature and concentration of the etching bath remain within tight limits due to the two-level control, monitoring the temperature to correct the acid concentration.

Modutek offers the Nb series baths in their fully automatic, semi-automatic and manual wet bench stations as part of its complete line of wet process equipment. The company constantly works with customers to continuously develop improvements in wet process technology. Contact Modutek for a free consultation to discuss your specific process requirements.

How Quick Dump Rinsers Improve Silicon Wet Etching Results

Manufacturing lines in semiconductor fabrication facilities and research labs use corrosive chemicals to clean and etch silicon wafers. Depending on the semiconductor product, a silicon wafer may undergo multiple steps in baths containing chemicals such as hydrochloric acid or hydrogen peroxide. When the cleaning or etching process in a particular fabrication step is complete, the chemicals must be rinsed from the wafer before the silicon wafer can be processed further. Quick Dump Rinsers provide a quick and effective way of thoroughly rinsing the wafers without introducing new contaminants.

How Quick Dump Rinsers Work

Once wafers are placed into the rinser, powerful jets spray de-ionized water over the wafers to remove all traces of chemicals. As the rinse tank fills up, chemical residue and contaminating particles are flushed out and rise to the surface. A nitrogen gas bubbler system serves to agitate the de-ionized water further, removing additional contaminants from the surface of the wafers. An overflow weir allows the surface water to flush the chemicals and particles out of the tank. When the rinsing process is complete, the quick dump door at the bottom of the tank opens and the water drains out in a matter of seconds.

The key characteristics of a Quick Dump Rinser are rapid operation, complete removal of contaminants and avoiding the addition of new contamination. Rapid operation helps reduce the use of de-ionized water and saves process time. If traces of chemicals are not completely removed, etching of the wafer might continue and result in defective or low quality products. The same is true if particles are not eliminated or are added during the rinse. Since rinsing has to be carried out at the end of many process steps, Rinser performance is critical for product output quality.

Modutek’s DR Series Quick Dump Rinser Features

Modutek’s Quick Dumps Rinsers are designed to meet the needs of advanced semiconductor fabrication. Wet process semiconductor manufacturing facilities and research labs can use the Modutek rinsers as stand-alone units or integrated into a wet process manufacturing line. The rinsers work quickly and deliver completely clean wafers. They incorporate the following features:

  • Contoured vessel design
  • Nitrogen bubbler on all models
  • Natural polypropylene or PVDF (option) tanks, nozzles and fittings
  • Large machined dump door without gaskets or seals
  • 360 degree overflow weir

Modutek’s design minimizes de-ionized water consumption and reduces rinse times while ensuring effective rinsing. The tanks require a de-ionized water supply, a source of pressurized nitrogen and a 120 or 24 V AC power supply. Options include a reclaim system, Teflon nozzles, fittings and valves, and special process cover configurations. The rinsers are available in a variety of sizes.

How Modutek’s DR Series Rinsers Improve Silicon Etching Results

Semiconductor manufacturing makes use of ever smaller microstructures and circuit connections. During wet etching of the silicon wafers, even a tiny particle can block a circuit path or deform microstructure design. Modutek’s rinsers are designed and constructed to avoid particle contamination.

The contoured vessel and machined trap door avoid entrapment of particles in corners or in cracks around seals and gaskets. The nitrogen bubbler helps dislodge any particles remaining on the surfaces of the silicon wafers. The 360 degree overflow weir gets rid of contaminants in the surface water quickly and the polypropylene material avoids the addition of metallic particles from fittings.

Modutek’s DR Series Quick Dump Rinsers are state-of-the-art process rinsing modules that work quickly and rinse completely. Used together with wet bench stations from Modutek’s extensive line of silicon wet etching equipment they can deliver exceptional performance for semiconductor manufacturing facilities and research labs. Contact Modutek for a free consultation on selecting the best equipment that will meet your manufacturing requirements.

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

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