Tag Archives: Semiconductor Manufacturing

How Stainless-Steel Stations Provide Safe Solvent Processing

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How Stainless Steel Stations Provide Safe Solvent ProcessingSolvents used in semiconductor manufacturing can remove oils and organic contaminants from silicon wafers in preparation for further processing steps. Acetone, isopropyl alcohol (IPA) and ethylene diproxitol (EDP) are solvents commonly used to clean wafers, remove photoresists, and in pattern transfers for the creation of microscopic structures on the wafer. The solvents are inflammable and require special safety measures to reduce the risk of fire and explosion, and they have to be disposed of safely. Stainless steel wet benches incorporating stainless steel processing tanks are an ideal solution for safe processing with solvents.

Safety Requirements for Stainless Steel Wet Bench Stations

The safe operation of stainless-steel solvent stations has to include the following safety features:

  • fire suppression
  • fire fighting
  • protection against exposure
  • protection against leaks
  • safe disposal

Fire is one of the principal safety hazards because solvents or their vapors can catch fire and explode. Fire suppression measures can include electrical design limiting the potential energy of sparks so they can’t ignite solvents and designing equipment to Class 1, Division 2 specifications.

Firefighting equipment has to be able to extinguish fires, should they occur. For inflammable liquids such as solvents, gas-type fire systems such as those using carbon dioxide are needed. It’s critical to have corresponding safety protocols and procedures to ensure workers are evacuated before triggering the extinguishing gases because the firefighting gas displaces oxygen and could cause suffocation.

Many solvents are harmful when workers are exposed to them over extended periods, either through direct contact or through breathing the vapors. A complete enclosure of the solvent processing tanks along with effective exhausts and leak detection limits the amount of solvent to which workers can be exposed.

Disposal of used solvents has to be carried out safely and according to environmental regulations. The disposal can be on-site if the facility has the corresponding capability, or the waste can be stored in a carboy for pick-up by a specialized disposal company.

Modutek Stainless Steel Wet Bench Stations are Safe and Customizable

Modutek stainless steel stations are made from 304 stainless steel and are available in fully automatic, semi-automatic, or manual versions. Dry to dry and fume hood designs are possible, and the stations feature casters and leg levelers. SolidWorks simulation software calculates the process flow characteristics and all design, assembly, and testing are carried out in-house. The stations can be built to the size and length required and extensive customization is available to exactly match customer requirements.

On the safety side, all stations are wired to the NFPA 70 & 79 standards and designed with fire suppression. Safety interlocks with emergency power off buttons are included. The station tanks have a one-inch lip exhaust and a continuous flow deionized water manifold. PVC safety shields are included and the stations have a nitrogen head case purge with Photohelic pressure interlocks. A Teflon nitrogen gun and deionized water hand spray are also included.

As a leading wet bench manufacturer, Modutek works closely with customers to determine how best to help them meet their objectives. Careful wet bench design can increase productivity and output while reducing costs. Modutek is focused on delivering wet bench equipment such as stainless-steel solvent stations using the best available materials and safe, high-quality designs.

With over 40 years of experience in the manufacture of wet benches and with the ability to carry out all design, assembly, and testing work in the company’s San Jose facility, Modutek is the ideal partner for semiconductor fabrication facilities and research labs. Modutek’s in-house experience allows for easy customization and safe execution of wet process semiconductor manufacturing projects of all kinds. Contact Modutek for a free consultation to discuss your specific solvent processing requirements.

How Teflon Tanks Improve the KOH Etching Process

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How Teflon Tanks Improve the KOH Ethcing ProcessEtching silicon wafers with potassium hydroxide (KOH) is a popular process for semiconductor manufacturing because it is relatively safe compared to other etching methods and because it features good control of the etch rate. When carried out in Teflon tanks, contamination is reduced and the etch rate can be controlled.

A key factor for successful etching is to determine the required etch rate. If the rate is too fast, the KOH may etch too far into the silicon, while if the rate is too slow, the etched holes might be too shallow. Improving the KOH etching process means applying several control methods to the etch rate to ensure the resulting etched shapes are exactly correct.

Process Factors that Affect the KOH Etch Rate

The KOH etch rate in silicon wafers is influenced by the following factors:

  • Process temperature. The higher the temperature of the KOH solution, the faster KOH will etch the silicon.
  • Solution concentration. A higher concentration increases the etch rate. Normally the concentration of the KOH solution is about 30 percent, but it can vary from 10 to 50 percent, with a corresponding effect on the etch rate.
  • Doping. Doping means adding impurities to the silicon crystal. When boron is placed into the silicon crystal lattice at a specific location, etching stops in that direction. Boron doping can influence the shapes to be etched in this way.
  • Crystal lattice orientation. The silicon crystal atoms are arranged in a cubic lattice that has a greater atom density in some directions than in others. Etching is slower in directions with a higher atom density.

All four factors have to be taken into account when designing the mask to obtain the microscopic structures in the silicon. The silicon wafer has to be oriented correctly to give the different etch rates along with the different lattice directions. Doping has to be in a place where etching is required to stop and the correct KOH solution concentration has to be mixed. These are initial conditions that are established before the process starts. A target temperature can be set as well but the temperature can be varied to adjust the etch rate during processing. The ability to vary the etch rate by changing the temperature results in excellent control of the KOH etching process.

Modutek Teflon Tanks Feature Rapid Heating and Precise Temperature Control

Modutek’s Teflon tanks for KOH processing are available in a circulating or a static design. The heat source is either inline or immersed in the overflow weir. An all-Teflon liquid path reduces the possibility of contamination. The heated tanks can improve the KOH etching process with short heat-up times and precise temperature control. As a result, Modutek Teflon tanks can keep the etch rate steady by maintaining an accurate temperature set point or can allow the etch rate to be adjusted with fast and reliable controlled temperature changes.

Both models of Teflon tanks feature uniform heating throughout the baths, level and temperature limit settings, and a drain interlock. Heat up rates are 2 to 3 degrees centigrade per minute and the temperature is controlled with a precision of plus/minus 0.5 degrees centigrade. The operating temperature is from 30 to 100 degrees centigrade and a cooling refluxor with Teflon cooling coils is included.

Modutek’s Teflon tanks are available in standard sizes but can work with customers to design and build systems with custom sizes and special requirements. With their high-quality materials, precise temperature controls, and customization capabilities, Modutek’s Teflon tanks can improve the KOH etching process to deliver better semiconductor manufacturing results. Contact Modutek for a free consultation to discuss your specific process requirements.

How Process Controls Are Improved with Automated Wet Bench Equipment

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how-process-controls-are-improved-with-automated-wet-bench-equipmentWhen semiconductor manufacturing is automated, tight process control can improve overall facility performance. An optimized manufacturing process can reduce consumption of consumables and production results are more uniform. Once a batch has run successfully, an automated process ensures that it will run the same way for subsequent batches. With good design, automation reduces silicon wafer handling and particle contamination. A wet process equipment provider has to be able to customize the automated functions to meet the needs of the application, but once it is set up, the process can run with a minimum of amount of monitoring from an operator.

Automation Can Reduce Chemical Use

An optimized automated process uses the least amount of chemicals required to carry out the etching or cleaning function and it continues to do so reliably. Spills and human error are eliminated while chemical use is tracked. Chemical treatment prior to disposal is closely monitored and neutralizing chemical use is reduced to a minimum while still ensuring compliance with environmental regulations. When overall chemical use is reduced, the cost savings can be substantial.

Output Quality is Improved with Automation

As semiconductor components and micro-structures become more tightly packed, they are more sensitive to dosage variations and process parameter inaccuracies. Processes such as etching are often dependent on temperature and chemical concentration. The timing of the process steps is critical in obtaining exactly the required etched pattern. Fully automated wafer fabrication equipment has these variables programmed in and runs the process accurately and the same way each time. Semiconductor component output is consistent with fewer defects and rejections.

Automated Neutralization Reduces Environmental Impact

Using an automated system to treat, neutralize and discharge chemical waste has several advantages. Waste from wet process manufacturing can be toxic and hazardous so human error during neutralization can have severe consequences for the environment and surrounding communities. Automation can ensure that acid and solvent chemical waste is neutralized and an automated system can block discharge if the output pH is not within predefined limits. Because all chemical use and discharge is tracked, compliance with environmental regulations can easily be demonstrated.

An Experienced Provider Can Customize Both Equipment and Automation

Depending on what kind of semiconductor components are being produced, a manufacturing or research facility may require highly customized equipment to carry out the process steps required. The automation has to flexible enough to accommodate custom process steps and the equipment provider has to be able to program the automation accordingly. Ideally, an experienced provider will work with customers to exactly define what is needed and then build the wafer fabrication equipment with the required automation. Such cooperation can result in equipment and controls designed and built for the specific purpose and delivering exceptional performance for the customer.

Modutek Designs and Builds Its Own Equipment with Automation

Modutek designs and builds its own equipment in-house based on extensive experience in wet process technology. This leaves Modutek in an ideal position to customize wafer processing equipment as needed to meet customer requirements. Because the expertise is in-house, Modutek engineers and technicians can adjust designs to reflect customer needs. This ability extends to the wet bench stations as well as to the automation that runs them.

Modutek’s SolidWorks Simulation software calculates precise dosages and process parameters and is also developed and supported in-house. Modutek can offer assistance for custom design of process stations, supporting equipment, and software to ensure customers get the systems they need. After the process line is built, installed, and tested, Modutek can provide full support with their own in-house specialists to make sure the automated semiconductor manufacturing process continues to operate as expected.

How Chemical Carts Provide Safe Handling and Disposal of Chemicals

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How Chemical Carts Provide Safe Handling and Disposal of ChemicalsChemical handling equipment is an important part of a semiconductor manufacturing operation because the aggressive chemicals used in etching and cleaning semiconductor wafers have to be stored, delivered to the process, and disposed of safely. Chemical carts, also referred to as chemical pump carts or chemical collection carts, are a convenient way to remove waste chemicals from process tanks and ready them for disposal. These carts are compact units that can be rolled up to the processing line to pump out processing tank contents. Carts have to be designed for safe pumping and containment of the chemicals and for moving them to a safe location for further treatment.

Chemical Cart Design Features

Modutek’s chemical carts allow operators to quickly remove used chemicals from a process line and let the process continue to the next step with a minimum of delay. The carts are easily rolled up to the process tank that contains the used chemicals and operators can safely transfer even toxic or corrosive chemicals. Modutek’s chemical carts have the following features:

  • Compact profile at 36 inches long, 18 inches wide, and 42 inches high
  • Made of white polypropylene resistant against acids; also available in stainless steel for solvent applications
  • Mounted on swivel casters that can be locked
  • Suction wand for emptying process tanks
  • Independent discharge tube for transfer of waste chemicals to a neutralization system
  • Pneumatic pump, three-eighths inch
  • On-cart five-gallon chemical tank with double containment that is Department of Transport approved
  • High-level sensor interlocked with pump for additional safety
  • All-Teflon piping

Once operators have pumped waste chemicals into the cart tank, the cart can be rolled out to a neutralization area or the waste can be shipped off-site for neutralization and disposal by a specialized company. In either case, the amount of chemicals and the treatment are recorded to ensure compliance with local environmental regulations.

Chemical Handling Equipment Increases Workplace Safety

Chemical handling equipment such as chemical carts allows operators to receive, store, deliver and discharge dangerous chemicals safely. Well-designed chemical handling equipment can reduce waste, deliver accurate dosages to the process and track chemical use. Containment of spills is an important safety and environmental issue that can be addressed by good design practices. Modutek’s extensive experience with wet process technology and the acids used to ensure that the company’s chemical handling systems operate in a completely safe and reliable manner.

Chemical Handling Functions Require Different Types of Equipment

While chemical carts used for the disposal of used chemicals fulfill one particular role, similar units can take on other functions. Chemical delivery systems handle chemical reception, storage, and delivery to the process. They can include remote bulk storage such as in large tote chemical containers that can supply high volumes of chemicals or 55-gallon drums located at the process. Chemical delivery systems can include software for dosage control and software can control the mixing of chemicals as well.

Chemical lift stations can fulfill a role similar to chemical carts but the units are permanently installed. They are sometimes located behind the wet process station they are serving, but Modutek has developed a space-saving design that allows an integration of the lift station in the process line. When chemical waste or waste water enters the lift station tank, the liquids are pumped to a neutralization area for further treatment.

Modutek’s product line of chemical handling equipment allows manufacturers to make their workplaces safer and save money. Chemical carts and other chemical handling equipment can be customized in terms of flow, capacity, and functionality to respond exactly to customer needs. Modutek can leverage its experience in semiconductor manufacturing equipment to help customers choose the right systems and ensure that the chosen systems perform as needed.

How Specialized Equipment Improves Silicon Wet Etching Processes

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Results from common wet etching processes such as KOH and Piranha etch can be improved with the use of specialized equipment. Depending on the process, key parameters can be controlled especially well and innovative procedures can reduce particle counts. When specialized equipment is used in silicon wet etching processes, wafer output can increase, defects can be reduced and output quality can improve. Equipment such as temperature controls, recirculating baths, and special control strategies can optimize specific processes and positively impact overall facility performance.

KOH Etching is Reliable and Easy to Control

Etching with potassium hydroxide (KOH) is a favorite process for applications requiring tight control of the etch rate. The KOH etch speed depends on the concentration of the bath and the temperature. A base etch rate can be attained by using an appropriate concentration and the rate can then be varied by controlling the temperature.

Modutek Teflon tanks are specially suited for KOH etching because they minimize contamination and feature tight temperature control. The TI static tanks and the TFa recirculating tanks are temperature-controlled models while the TT series of tanks operate at ambient temperature. The TI and TFa models operate over a temperature range of 30 to 180 degrees centigrade and temperature control is within plus/minus 0.5 degrees centigrade. Modutek Teflon tanks with KOH etching feature excellent output quality with low defects and high reproducibility.

Piranha Etch Works Quickly

Piranha etch uses a mixture of sulfuric acid and hydrogen peroxide to quickly remove organic residue such as photoresist from silicon wafer surfaces. The mixture has to be handled carefully because it is highly exothermic when first prepared. Normal operation is often at around 130 degrees centigrade so the process requires tanks that can withstand high temperatures and can be heated.

Modutek quartz baths are ideal tanks for Piranha etching. The QFa series high temperature circulating baths can withstand the initial temperature spike from mixture preparation and the subsequent heating to operating temperature. The quartz tanks heat at a rate of two degrees centigrade per minute and temperature accuracy is plus/minus one-degree centigrade. Modutek quartz baths with Piranha etch represent an inexpensive, safe and reliable etching process.

Buffered Oxide Etch (BOE) Etches Silicon Dioxide

Buffered oxide etch uses buffered hydrofluoric acid to etch thin films of silicon dioxide or silicon nitride. The Modutek F-series sub-ambient circulating baths reduce consumption of acid and filter out contaminating particles. Temperatures of 10 to 60 degrees centigrade are maintained within plus/minus 1-degree centigrade and the sub-micron particle filter reduces the particle count and improves yields. Modutek has designed the F-series baths especially for BOE applications and delivers a safe and reliable process with low-cost operation.

Silicon Nitride Etching Requires Special Control Measures

A phosphoric acid and de-ionized water mixture etches silicon nitride in a process that requires special stabilizing controls. The mixture usually operates at its boiling point of about 160 degrees centigrade. As the etching proceeds, de-ionized water evaporates, leaving an increasing concentration of acid behind. The higher concentration increases the boiling point and the etch rate. To keep the process working consistently, the concentration has to be restored to the lower level.

Adding enough water to restore the concentration risks an explosive reaction when the water mixes with the acid. Modutek has designed a control system that frequently adds small quantities of water to the silicon nitride wet etching baths whenever the temperature rises. The small amount of water is mixed in immediately and the concentration remains steady. Modutek’s specialized control system ensures improved stability and safe operation.

Modutek’s extensive experience in wet process fabrication allows the company to design and build specialized equipment to meet the needs of its silicon wet etching process customers. Such special equipment can improve output quality, reduce costs, and increase yields.