How Quartz Tanks Improve Wafer Manufacturing

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsThe aggressive chemicals used in wet process wafer manufacturing have to be contained in process tanks that can resist etching and corrosion while remaining inert. Depending on the application, a process may require heating, filtration or the regular addition of chemicals. Quartz tanks from Modutek are made from semiconductor grade flame-polished quartz and are impervious to the acids and bases used in wafer processing. They minimize contamination of the wafers with particles and can be supplied in heated and re-circulating models. The high quality of the bath material along with advanced control strategies developed by Modutek help improve wafer manufacturing performance.

Cleaning Silicon Wafers Using Quartz Tanks

Wet bench processing of silicon wafers consists of fabrication steps such as etching and diffusion with cleaning required in between the steps. Wafers may be masked to etch specific parts of the wafer or to confine diffusion to certain target areas. After each process step is complete, the masking material has to be cleaned off.

Cleaning the wafers completely without contamination is critical because subsequent processing steps are affected if the wafer is not completely clean. With the microscopic architecture of semiconductor components becoming more tightly packed, even a single particle can result in a badly formed structure or conductor. When such malformations are incorporated into the final product, they can be the cause of defective or lower quality semiconductor components.

Specialized Process Controls Help Improve Wafer Manufacturing Results

Specialized quartz tanks from Modutek are based on over 30 years of experience and incorporate features to guarantee safe, reliable operation while delivering excellent wafer manufacturing results. Custom sizes, fast and even heating, reduced downtime and long vessel life help improve manufacturing facility performance and reduce costs. Quartz tank controls allow operators to program reproducible process environments and make sure temperatures and chemical concentrations are consistent. The three areas for which specialized control systems are useful are heating, chemical spiking and filtration.

Modutek high temperature re-circulating baths and constant temperature tanks heat up rapidly with a temperature rise of up to two degrees centigrade per minute. The operating temperature can range from 30 to 180 degrees centigrade and the temperature controller holds the temperature within plus or minus one degree centigrade. Quick heating helps improve throughput and accurate temperature control helps ensure high quality results.

For some chemical processes the concentration of chemicals can change during the process. Periodic spiking restores the chemical concentration to the desired level. Modutek has developed an innovative “bleed and feed” spiking method for the sulfuric acid and hydrogen peroxide (SPM) process.

The hydrogen peroxide of the SPM process decomposes and has to be replenished frequently. For traditional spiking, the mixture has an overall lifespan of only several hours. In Modutek’s clean tank/dirty tank using the “bleed and feed” spiking method, programmable amounts of mixture are drained from the dirty tank and transferred from the clean tank to the dirty tank. Programmable amounts of acid and peroxide are then added to the tanks. This method keeps the mixture fresh and increases the mixture’s lifespan to about one week.

In addition to controls for temperature and concentration, Modutek’s quartz tanks can reduce particle counts and wafer contamination. The quartz re-circulating tank can filter out particles down to 0.2 microns, improving output quality and reducing component failure rates.

Modutek’s quartz tanks are based on more than 30 years of experience and incorporate features to guarantee safe, reliable operation while delivering excellent wafer manufacturing results. Custom sizes, fast and even heating, reduced downtime and long vessel life help improve manufacturing facility performance and reduce costs.

Modutek continues to develop innovative techniques in the construction and use of quartz tanks for semiconductor manufacturing processing. The design of the quartz tanks and the associated advanced controls are a key factor in the production of semiconductor components of the highest quality. With extensive experience working with manufacturers in the development of advanced temperature, concentration and filtration controls, Modutek helps improve wafer manufacturing. Contact Modutek for a free consultation or quote on equipment designed to meet specialized manufacturing requirements.

How Megasonic Cleaning Improves Silicon Wafer Manufacturing Results

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsTraditional silicon wafer cleaning uses aggressive chemicals to strip wafers and remove particles during semiconductor manufacturing. As semiconductor components such as processors, switches and memory chips become more tightly packed, removing all traces of contamination on the wafer surface becomes important for the production of high quality components and the reduction of component failure rates. Even sub micron particles can block the formation of a conducting path or a key structural component. Ensuring the removal of sub micron particles with traditional cleaning and rinsing has become challenging. Megasonic cleaning can remove even the tiniest particles from silicon wafers and improve process reliability.

How Megasonic Cleaning Works

Cleaning parts with megasonic sound waves in a cleaning solution is a quick and effective way of removing contamination from part surfaces. This cleaning method uses a range of high frequencies with the lower end used for less fragile pieces. The highest frequencies are used for the most delicate parts or parts with soft surfaces.

The sound waves in the cleaning solution create microscopic cavitation bubbles in the wave pressure troughs and the bubbles collapse in the wave peaks. When a bubble collapses, it emits a tiny but energetic jet of cleaning solution that dislodges contaminants and particles from part surfaces. Lower frequencies create comparatively large bubbles with stronger jets while the higher frequencies produce cleaning action with smaller bubbles and lower jet energy.

Because semiconductor components often include very delicate structures and soft layers of deposits on the silicon, only the highest frequencies deliver cleaning gentle enough to avoid structural damage and pitting. Megasonic cleaning takes place with frequencies around the 1 MHz level and higher and delivers effective cleaning without damage. The cleaning method is especially good at dislodging and removing particles as small as 0.1 microns with tiny bubbles breaking the particle’s adhesion to the underlying silicon wafer.

Modutek’s Megasonic Cleaning Solution

Modutek has partnered with Kaijo Shibuya Corporation, a world leader in Megasonic and ultrasonic cleaning technology, to create a line of Megasonic cleaning equipment suitable for use in semiconductor manufacturing. Megasonic cleaning systems can either be turn-key and integrated in fully automated wet bench station, or supplied as individual Megasonic generators and transducers.

Turnkey systems include the cleaning tank with the transducers already mounted while individual components can be integrated in existing semiconductor manufacturing lines. Equipment such as the Spot Shower, Mega Puck and Mega Tube allow operators to direct the Megasonic cleaning action to specific areas in the cleaning tank or on the surfaces of the silicon wafers. Megasonic cleaning reduces sub micron particle counts and can help produce better manufacturing results.

Modutek Megasonic Cleaning Features and Benefits

Systems using high frequency sound waves to clean silicon wafers have to be able to function at several frequencies, depending on the fragility of the parts to be cleaned. At the selected frequency, the megasonic transducers have to deliver enough power to fill the cleaning tank with sound waves, ensuring equal and consistent cleaning without dead spots. Ideally the bath and the transducers should be able to operate at elevated temperatures because some semiconductor manufacturing processes may use heated baths.

Modutek’s Megasonic cleaning systems operate at 950 kHz but frequencies between 200 kHz and 2 MHz are also available. High efficiency generators and full-power transducers deliver up to 1200 W of cleaning power and the systems can operate with bath temperatures of up to 140 degrees centigrade. These features deliver unparalleled cleaning performance without pitting or damage to silicon micro structures. The superior removal rate for particles down to 0.1 microns increases semiconductor component yields, reduces the number of defective components and improves product quality. For a free consultation or quote contact Modutek at 866-803-1533 or email [email protected].

Customized Table Top Chemical Process Tanks

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsFor small operations and specialized applications requiring semiconductor fabrication capabilities it often doesn’t make sense to construct wet processing lines that produce products at volume. Table top process tanks can allow research labs, universities and start-up companies to produce single parts or low-volume output. These organizations may need proof of concept components or prototypes for testing. Small chemical process tanks deliver the capability to fabricate such products in a customized unit designed for the specialized applications.

Customization is the Key to Effective Table Top Systems

Table top chemical process tanks for specialized output are heavily customized to reflect their unique purposes. Tank size, chemicals used, controls, heating and circulation are all adapted to the particular use. Because Modutek designs and builds all of its wet bench equipment in house, the company is ideally situated to undertake the customization required for this special application. Modutek has been working with customers to provide table top chemical process tanks that are easy to install and use safely, for example under an existing fume hood. Customers can purchase a complete unit with the special features and characteristics they need.

Features and Benefits of the Modutek Table Top Systems

Modutek’s table top chemical process tanks are a further development of their wet bench Teflon tanks but other configurations are available. Specific features include the following:

  • Installation.The tanks are mobile and can be placed wherever convenient for safe operation. Sizes and shapes are fully customized to match the use and the space available.
  • Circulation.Tanks can be static or fitted with overflow circulation and filtration. Circulating tanks have a 360 degree serrated overflow weir and an all-Teflon fluid path. Both static and circulating tanks are made of all PFA Teflon.
  • Heating.Tanks are ambient temperature or temperature controlled. For heated tanks, the operating temperature is 30 to 100 degrees centigrade. The heat-up rate is 2 to 3 degrees per minute and the temperature control is accurate within plus/minus 0.5 degrees centigrade.
  • Process.The tanks are usually Teflon tanks for KOH and related wet processes. Acid and solvent process capabilities are also available.
  • Wafer Holders.The systems usually come with standard carrier sizes for single or double capacity. Custom wafer holders are available.
  • Controls.Process controllers to handle temperature and timing are available. Inputs can include level switches, temperature alarms and a drain interlock. Remote operation is also possible.

Modutek can assemble the table top unit with the required features exactly as specified by customers. Benefits include reliable and safe operation, consistent process variables and repeatable outputs and results.

Table Top Systems Designed and Built to Meet Requirements

As a leader in wet bench technology, Modutek has the in house expertise to design and build innovative semiconductor fabrication equipment such as table top chemical process tanks. The company can draw on its comprehensive line of wet bench stations to adapt standard equipment for such special applications. Because Modutek engineers and technical personnel create these customized units, the company can provide complete after sales support and repair services. Contact Modutek for a free quote or consultation to discuss your specific chemical process application requirements.

 

Selecting the Right Acid Neutralization System for Your Application

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsAcid neutralization systems treat the effluent from semiconductor wet process fabrication facilities and other industrial processes to make it safe for release into the environment. The right system for an application will add alkaline chemicals to the acidic solution and raise the pH close to the neutral level of 7 while recording process data to ensure regulatory compliance.

Depending on the type of operation, an acid neutralization system can be selected that either works continuously or in batches. Continuous flow systems treat large volumes of effluent that have a consistent composition and work best with waste water that doesn’t require complex treatment. Batch neutralization systems are often applied to smaller volumes that are difficult to treat. Each kind of system can benefit from full automation to carry out the neutralization process precisely and keep accurate records.

How Acid Neutralization Systems Work

Because releasing untreated acidic waste water is environmentally hazardous and pollutes water ways, governments have imposed regulations on the producers of industrial waste. An acid neutralization system treats and measures the acidity of waste water as it exits the production line. Depending on the process, a suitable neutralizing chemical is added to reduce the acidity. Sensors verify that the neutralization process has reduced the pH of the waste water to a level in keeping with the applicable regulations and the liquid can then be released.

For compliance purposes, keeping a record of treatment and release is extremely important. To enforce the regulations, authorities will often require proof that the prescribed pH levels were maintained at all times. A print-out from a fully automated system showing the process steps that were carried out and the corresponding pH values can be valuable in proving that a company is not the source of any pollution that has been found.

Continuous Flow Neutralization Systems

High volume production lines produce the same components continuously using the same process and produce a constant flow of effluent that varies comparatively little in its composition. These applications are ideally suited to continuous flow acid neutralization systems because the continuous addition of neutralizing chemicals with only a slight variation can easily be controlled and monitored.

The flow can be from a few to several hundred gallons per minute, and once the neutralization requirements are known, the amounts of neutralizing chemicals required can be calculated. The acid neutralization system monitors the input, makes small adjustments to the quantities of neutralizing chemicals to respond to process changes, and monitors the output for compliance with regulations. A record of discharges and their characteristics is available in the form of a digital chart recorder.

Batch Neutralization Systems

In the production of prototypes, the manufacture of small quantities of specialized components and the use of processes that consist of discrete, independent steps produce waste water in small batches that can best be processed by batch neutralization systems. These batches of waste chemicals often need extensive treatment and may require different neutralizing chemicals to meet the allowed discharge pH levels.

Depending on the process and the required neutralizing chemicals, batch neutralization systems can take pH readings, add the calculated chemical doses and then verify that the pH has increased to an acceptable level. In terms of automation and record keeping, the same considerations apply as for continuous flow neutralization systems.

Modutek’s Acid Neutralization Systems

Modutek offers fully automated acid neutralization systems in batch neutralization or continuous flow designs. The compact systems can be customized for specific applications and to fit into an available space. Modutek’s acid neutralization system can be placed indoors or outdoors and can handle flows from 5 to 500 gallons per minute. The microprocessor pH control delivers precise doses of neutralizing chemicals and provides accurate records on a digital chart recorder to prove seamless compliance with discharge regulations. Contact Modutek for a free quote or consultation to discuss your application and acid neutralization requirements.

5 Important Things to Know When Buying Wet Bench Stations

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsBecause 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

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsAs 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

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsModutek 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

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsThe 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

How Quick Dump Rinsers Improve Silicon Wet Etching ResultsManufacturing 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.