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 Silicon Wet Etching Processes Are Improved with Specialized Equipment

how-silicon-wet-etching-processes-are-improved-with-specialized-equipmentWhile Modutek’s wet bench equipment supports all common wet etching processes, the continuous development of new wet bench technologies allows the company to offer specialized equipment that can improve performance for specific applications. Key factors for high output quality, fast processing, high yields and reliable outcomes are cleanliness, repeatability, tight control and precise dosages. Modutek’s standard line of silicon wet etching equipment already scores highly on these factors but the company’s specialized equipment can further improve performance for certain processes.

Buffered Oxide Etch (BOE)

The BOE process requires tight and precise temperature control while filtering lowers the particulate count and reduced acid consumption results in lower costs. Modutek’s F-series sub-ambient circulation bath is specially designed for BOE applications and addresses these factors. The temperature controller is accurate to less than plus/minus one degree centigrade in a range from 10 to 60 degrees centigrade with sub-ambient capability. The circulating bath includes 10.0 to 0.2 micron filtration and is designed for low acid consumption. Using a wet bench system specialized for the BOE process can reduce costs and defects in products while providing safe and reliable operation.

Piranha Etching

The sulfuric acid/hydrogen peroxide mixture of the Piranha solution is extremely corrosive, and the mixture is exothermic when first prepared. The Modutek QFa Series of Quartz High Temperature Recirculating Baths are ideal for withstanding the high temperatures, first of the initial heating after mixing and then during the process that is heated to preserve mixture reactivity. The baths have heaters that can raise the temperature of the mixture by two degrees Centigrade per minute and the temperature controller can maintain the temperature at plus/minus one degree centigrade over a range of 30 to 180 degrees centigrade. These Modutek quartz baths are characterized by the high degree of safety, reliable operation and low cost of ownership.

Potassium Hydroxide (KOH) Etching

Modutek Teflon tanks are ideal for use in KOH etching because they can be custom fitted to any wet bench configuration and come in three models to satisfy common heating and recirculating requirements. The TFa and TI series of Teflon tanks are temperature controlled to an accuracy of plus/minus 0.5 degrees centigrade over a range of 30 to 100 degrees centigrade. The TFa series are overflow re-circulating models while the TI series are static. The TT series are static ambient temperature models. All Teflon tanks are made from PFA Teflon with special welding techniques to minimize the presence of undesirable by-products in the process and to reduce contamination. Modutek’s Teflon tanks improve KOH process control, increasing reliability and reproducibility of process conditions.

Silicon Nitride Etching

Etching silicon nitride with a phosphoric acid deionized water mixture is challenging because the concentration changes as the deionized water evaporates and because adding water to the process can cause an explosion. Modutek’s silicon nitride wet etching bath is specially designed to address these issues and provide reliable and safe process control. The mixture is kept at the boiling point, which changes as the concentration increases. Depending on the temperature of the mixture, small amounts of deionized water are added to the boiling mixture to maintain the concentration at the required level. Using the boiling point temperature as an indication of the concentration and allowing the boiling mixture to immediately distribute small amounts of water lets Modutek control the process while maintaining safe operation.

With its extensive experience in silicon wet etching process technology, Modutek can deliver specialized equipment suited to a particular process and help customers select the right equipment for their applications. With equipment specially designed for the process used, customers obtain superior results while often saving money as well. Contact Modutek for a free consultation or quote on using the right silicon wet etching equipment for your application.

 

Why Teflon Tanks Are Used with the KOH Etching Process

KOH etching is a preferred silicon wafer fabrication method because it works rapidly and reliably while handling of the chemicals is relatively safe. The process relies on a contamination-free environment and uses the temperature and KOH concentration to control the etching speed. Teflon tanks are used in this process because the Teflon is stable and doesn’t degrade. The KOH etching process controls allow accurate and repeatable temperature control for reliable fabrication results and high-quality production. KOH etching in Teflon tanks with temperature control is an excellent process for silicon wafer nanostructure fabrication in both manufacturing facilities and research environments.

How KOH Etching Works

KOH or potassium hydroxide etches silicon quickly and at a constant rate that depends on the concentration of the solution and the temperature of the liquid. In addition to these controllable variables, silicon etching is influenced by the crystal planes of the silicon and the doping concentration. These factors can be used to direct etching in certain directions and to stop etching at given points. The result is that KOH etching can produce the precise nanostructures needed as long as the crystal planes and doping are used correctly.

The controllable variables have to be kept tightly to set values and variations have to be minimized. Important factors are the maintenance of the KOH solution at the desired concentration and temperature. The Teflon tanks have to be designed to support the consistent and accurate etching necessary for defect-free wafer fabrication.

Modutek Teflon Tank Features

Modutek Teflon tanks are designed to support KOH etching leading to wafer fabrication of the highest quality. The temperature-controlled tanks are available in re-circulating and static versions and come in standard sizes for single or double carrier capacities as well as in custom sizes when required. The re-circulating tanks have an all-Teflon fluid path, and in the available custom configurations, are easy to integrate into existing fabrication lines.

Modutek Teflon tanks eliminate contamination from the tanks or fluid paths by ensuring the KOH solution only comes into contact with Teflon, which in unaffected by the corrosive chemical. In addition, Teflon welding for the tanks is carried out with advanced PFA sheet welding techniques that reduce impurities and by-products. The result is that the KOH solution stays pure.

A key element of the KOH etching process control is the initial concentration of the KOH solution and keeping it constant throughout the process step. Modutek Teflon tanks have sealed lids that minimize water loss, even during lengthy etching. Water condensing systems and de-ionized water spiking systems are available if the application requires it.

The other variable affecting the etch rate is the temperature of the KOH solution. Modutek tanks have either inline heating or immersion heating in the overflow weir. Temperature can be controlled between 30 and 100 degrees Centigrade with an accuracy of plus/minus 0.5 degrees Centigrade. Heating is rapid with an average heat-up rate of 2 to 3 degrees Centigrade per minute depending on the details of the installation. Rapid heating and tight control result in superior etching performance and consistent output.

To make operation of the KOH etching flexible and convenient, the Modutek Teflon tanks systems have standard drain interlocks and low level, high limit, and high-temperature alarms. Temperature process controllers and remote operation timers are also available.

Modutek Teflon KOH tanks are designed specifically for applications such as KOH etching and Modutek can supply custom systems specially adapted to customer requirements. Tank sizes and controls can be designed to match customer applications. Modutek can rely on its experience and expertise to supply KOH etching systems that meet the highest quality standards and deliver the best output possible.

 

How the KOH Etching Process is Improved Using Modutek’s Teflon Tanks

Among the different approaches available to foundries that create intricate integrated circuitry on semiconductor chips, etching with potassium hydroxide (KOH) is frequently preferred for the error-free mass-production that it allows.

The improvement in precision that the KOH etching process brings to semiconductor fabrication is attributable in large part to the use of deionized water. When employed with high alkalinity in excess of pH 12, this process can be thermally adjusted for precise degrees of etching.

How does the use of potassium hydroxide improve the semiconductor etching process?

While dry semiconductor etching processes do exist, they tend to present challenges in process control. Semiconductor wafers etched in this way tend to suffer from quality control issues. Dry etching processes can be difficult to build and run, as well — toxic and explosive chemicals often seen as byproducts, after all.

Greater precision

Etching with potassium hydroxide offers greater precision, and lends itself to improved control, as well.

The fluids employed in the KOH etching process are stored in tanks built into the equipment. One of the most cost-effective and meaningful choices to make in KOH etching processes: to place Teflon tanks within the etching equipment in order to hold the fluids employed. Teflon tanks can make the KOH etching process safer than other options available.

It is possible to structure the KOH etching process in a way to easily create repeat manufacturing projects, as well. When such projects come in from different clients, fabrication units can focus their strengths on setting up the equipment, worrying as little as possible about safety or reliability.

Opting for fewer contaminants and greater cleanliness

Customization is one of the greatest most significant improvements that Modutek brings to the KOH etching equipment business — one where generic, mass-produced Teflon tanks are the norm. Modutek’s Teflon tanks are especially capable of bringing impurity quantities to levels that are impressively low. The result is greater reliability and consistency over an extended period of time.

Greater control

Modutek’s Teflon tanks come with highly customizable temperature settings. Temperature control is achieved either through in-line heating and cooling equipment installed, or through immersion in liquid tanks. It is precisely varied anywhere between 30°C to 100°C. Temperature changes dialed up our achieved at a fast rate of 2°C a minute, on average (although tank size does affect response rates).

Modutek brings customization to the table

Modutek designs Teflon tanks for the specific needs of each client installation. Whether a fabrication plant requires temperature controlled recirculating baths for their KOH etching processes or temperature controlled static baths, Modutek’s Teflon tanks deliver both freedom from water loss and freedom from concentration deficiency.

From dual heating Teflon tanks for fast and consistent water-based etching, to the installation of drains and valves that enable rapid cleanup, high-tech remote data interfaces, controllers and timers, Modutek’s clients have their choice of every advance in KOH etching.

 

Etching Silicon Wafers Without Using Hydrofluoric Acid

Etching Silicon Wafers Without Hydrofluoric AcidHydrogen fluoride is an excellent etching chemical for silicon wafer fabrication, etching rapidly to remove silicon oxide, for example after an initial RCA clean. While highly effective, hydrofluoric acid is extremely dangerous. Its vapor can cause death and it is toxic enough that even a small area of skin exposed to the chemical can cause cardiac arrest. As a result, storage and handling is difficult and disposal problematic. Safety and environmental considerations have resulted in a search for alternatives. Depending on the silicon wet etching application, other chemicals may be suitable for replacing hydrofluoric acid and Modutek can help customers make the change by recommending equipment that supports alternative chemical processes.

Why Hydrofluoric Acid is Especially Dangerous

Hydrofluoric acid is extremely toxic and penetrates the skin to cause secondary effects that require medical attention. Its vapor can cause lungs to fill up with liquid and exposure to even small amounts can cause death. Neutralization and disposal is difficult and any mistakes run the risk of severe environmental contamination. Given the dangers, silicon fabrication facility owners, managers and process engineers are looking for alternative process chemicals.

While hydrofluoric acid is dangerous as a corrosive chemical, its added danger comes from its absorption into the body. It affects the nerves at sites where the skin has been exposed to the acid and victims may initially feel little pain as a result, often delaying treatment. At the same time, hydrofluoric acid can penetrate deep into the body and attack underlying tissue and bones, causing lasting damage. It also disrupts the calcium chemistry of the blood, eventually leading to cardiac arrest. Exposure of as little as 25 square inches of skin can result in deep burns that are slow to heal and in death if medical treatment is delayed.

Bare skin and the eyes are the most common areas of exposure. Treatment starts with extensive rinsing, for about 15 minutes, of the exposure site. Repeated application of calcium gluconate gel helps mitigate the effect on blood calcium. Anyone with more than four square inches of skin exposed should be admitted to hospital for monitoring of blood chemistry. Normal safety measures to avoid contact with hydrofluoric acid are to cover all skin and wear eye protection.

Hydrofluoric acid is hazardous waste and its discharge is tightly regulated. The acid must first be neutralized and then discharge limits on fluoride and metals must be observed. A complete neutralization process often starts with adding a basic solution to the acid and then precipitating out other materials until they fall within discharge limits. After discharge, the resulting sludge represents an additional waste problem. While other chemicals may be subject to similar discharge procedures, hydrofluoric acid represents an additional risk if neutralization is not carried out properly.

Possible Alternative Etching Solutions

Depending on the particular silicon wet etching application, other etchants may be substituted for hydrofluoric acid. Potassium hydroxide (KOH) is a safer chemical and can be used for etching in many applications.  Tetramethylammonium hydroxide (TMAH) and nitride etch are other possible alternatives that may be used.

Modutek can help facilitate a switch from hydrofluoric acid where possible. The company has over 35 years experience with silicon wafer fabrication equipment and has the in house expertise to advise customers about possible alternatives.

In addition to analyzing customer process needs and making recommendations, Modutek can supply the equipment required from their complete line of wet bench and chemical delivery stations. Modutek’s equipment, while able to handle hydrofluoric acid, is also designed to work with other chemical processes that don’t use it. Modutek can offer standard or customized components such as Teflon tanks or quartz baths to help customers wishing to use other chemicals where they can. Contact Modutek for a free consultation and quote on selecting the right equipment to support the silicon wet etching process for your application.

Selecting Equipment for the KOH Wafer Etching Process

Selecting Equipment for the KOH Wafer Etching ProcessKOH etching is increasingly used for creating microscopic structures in silicon. The wafer etching process uses a 20 to 30 percent solution of potassium hydroxide to create cavities in the unmasked parts of a silicon wafer. KOH etching is comparatively safe and etching can be tightly controlled through regulation of the bath temperature and doping of the silicon. Semiconductor fabrication facilities favor this etching method because of its high precision, good repeatability and cost effectiveness.

How It Works

The silicon wafer is masked with a material impervious to KOH, usually silicon dioxide or silicon nitride. The mask is based on the layout of the structures and circuits of the final semiconductor product and determines where cavities will be etched. The silicon wafers are immersed in the KOH solution and the temperature is controlled to give the desired etch rate.

KOH etching is extremely sensitive to temperature variations at temperatures above 60 degrees centigrade, with the etch rate in microns per hour approximately doubling for every ten degree rise in temperature. A typical rate is 1 micron per minute for a bath at 80 degrees centigrade. Accurate control of the temperature is a key factor in precise etching results.

While varying the temperature can control the etch rate, the orientation of the crystal planes in the silicon and doping of the silicon with boron also influence the rate and direction of the etch. The anisotropic nature of the silicon crystal can be used to create slopes and shapes along the crystal planes and the etch can be stopped in specific locations with boron doping. This way KOH etching can create complex shapes and circuit paths for semiconductor products.

Modutek KOH Bath Equipment

Modutek supports KOH etching as one of its wafer etching process options in the company’s line of wet bench process equipment. The TFa and TT series Teflon heated tanks are ideal for the requirements of KOH etching. The tanks are available for standard carrier sizes for single or double capacity and Modutek can also build custom sizes if needed. The modular nature of the tanks means they can easily be integrated in any new or existing wet etching station.

The TFa series high temperature overflow tanks and the TT series static tanks are both PFA Teflon tanks with an all-Teflon fluid path. Heating can be inline or immersion heating in the overflow weir. The operating temperature range is from 30 to 100 degrees centigrade and the tanks can heat up at the rate of 2 to 3 degrees centigrade per minute. Temperature control accuracy is plus/minus 0.5 degrees centigrade and liquid levels and high temperatures are monitored. The high precision temperature control and the rapid heating rate ensure that heating is uniform throughout the bath.

Additional features and specifications of the Modutek KOH etching tanks include 360 degree overflow filtration through serration overflow, an optional condensing Teflon refluxor with Teflon cooling coils, a pneumatically actuated auto cover, an aspirator valve system and a Teflon gravity drain. An RS232 interface, temperature controllers and remote operation timer switches complete the remote operation capabilities.

Modutek can help customers considering KOH etching in their selection of the appropriate systems. The company has a complete range of wet bench process equipment, chemical handling systems and equipment repair capabilities. In addition to their standard lines, Modutek can customize components to meet the specific needs of their customers. Experienced company personnel can work with customers to design optimal configurations and layouts for their clean room facilities. The KOH etching tanks are the ideal solution for semiconductor fabricators that need to etch microstructures in silicon wafers.

Tips on Improving Your Silicon Wafer Etching Process

Tips on Improving Your Silicon Wafer Etching ProcessSemiconductor manufacturing facilities and research labs need silicon wafer etching equipment that delivers accurate and repeatable results in a safe and reliable environment. The structures on semiconductor wafers and for micro-electromechanical systems (MEMS) have to be produced to meet tight tolerances and with no contamination by impurities or stray particles. An improved silicon wafer etching process depends on selecting the right etching process and using high-quality equipment, which are key factors for consistent output with a low rate of defects.

Silicon Wafer Etching Processes

Wafer etching is a multi-stage fabrication process and different chemical baths are used to achieve specific purposes. Process steps include cleaning, masking and etching of the wafers themselves or deposited metal. These steps result in the production of microscopic structures in the silicon wafer and in electrical connections where required. Key factors for improved etching performance are control of etching speed and the cleanliness of the fabrication environment.

Silicon nitride is used as a masking material and is etched with hot phosphoric acid. Key factors for improved results are the accurate control of the acid concentration and temperature through the addition of de-ionized water.

Piranha etching is carried out with a mixture of sulfuric acid and hydrogen peroxide. The etching solution cleans organic residue from silicon wafers and is often used to remove photoresist. Cleaning with piranha etching can be appropriate at various stages of the semiconductor fabrication process, and its effective application depends on the correct mixture and accurate control of the process.

The KOH etching process creates microscopic structures in the silicon using a solution of potassium hydroxide. Variables controlling the etch rate include bath temperature, KOH concentration, silicon crystal orientation and impurities in the silicon. Improved etching performance means tightly controlling the etch rate to get the precise structures needed.

Buffered oxide etch (BOE) uses hydrofluoric acid and a buffering agent to etch thin masking films of silicon nitride or silicon dioxide. If properly controlled, it results in a highly consistent and repeatable process that is compatible with photoresist.

The key to improving silicon etch performance is to use wet process equipment from a supplier that has the required experience and who can deliver high-quality equipment designed for excellent etching performance. Modutek has over 35 years experience in the field, and can advise customers on which equipment best supports their particular wet processing requirements and can offer standard or customized equipment as needed.

Etching Equipment Design Features

Choosing the right wafer etching process for each stage of semiconductor fabrication is important, but it is the design characteristics of the equipment that ensure improve etching results. Critical design features of Modutek’s etching equipment include the following:

  • Filtration and flow control. Filtered etch baths feature continuous filtration in the 10- to 0.2-micron range and reduced acid consumption.
  • Temperature control. Temperature controlled circulators can heat or cool an etching bath and keep the temperature at the required levels. Operating range is 10 to 60 degrees centigrade with an accuracy of plus/minus 1 degree.
  • Tank design. Teflon tanks for KOH etching are available in many configurations and in standard carrier sizes for single or double capacity. Quartz baths for a variety of etching applications including piranha clean are available in a range of sizes.

Modutek helps customers improve their silicon etching performance by advising them on the right equipment for their specific etching applications and by ensuring the equipment delivers accurate performance in a consistent way. When silicon etching processes are carried out reliably with repeatable results, facility productivity increases and output quality improves.

Commercial Market Opportunities for MEMS Technology

Using KOH Etching for Batch ProcessingMicro-electro-mechanical systems (MEMS) is a technology that incorporates the use of microscopic devices ranging in size from several millimeters to less than one micron. They usually have both electrical and mechanical functions and often include parts that can move in response to process conditions, commands from outside the structure or commands from integrated electronics. Typical miniaturized MEMS devices include sensors, actuators and other microscopic structures manufactured on silicon wafers using similar techniques as for semiconductors. They are popular because they are inexpensive to fabricate and are easily integrated into systems containing electronic controls, often on the same silicon wafer.

MEMS Applications

MEMS were first used in the automotive industry and then found increased application in the medical and optical fields. Typical macroscopic functions that were taken over by MEMS counterparts were pressure sensors, inertial sensors and chemical sensors. The MEMS sensors were less expensive to manufacture and performed better than the corresponding large sensors. In addition, different sensors could be placed on one silicon wafer along with signal processing electronics. For example, one unit could measure chemical pressure, detect impurities and generate alarm signals.

As MEMS fabrication methods became more sophisticated, the systems were able to take on additional functions and include different structures. For example, today’s MEMS can include mirrors, gears, pumps, nozzles and valves. Associated electronics can evaluate the signals, perform complex analysis and send results to external receivers via radio frequency elements. Such devices are found in the automotive industry in car airbags, tires and fuel systems. Technical products such as ink jet printers, digital projectors, bar code readers and display screens use MEMS to reduce costs and miniaturize components. Medical systems and devices use the miniature MEMS for diabetic evaluation, insulin delivery, blood analysis and needle less injectors. As the number of applications increases, the market for MEMS continues to grow as does the interest in inexpensive, reliable and rapid fabrication methods.

How MEMS are Produced

To create the microscopic structures that make up MEMS, manufacturers use technology similar to that used to produce microelectronics. For silicon wafer based MEMS, the wafers are masked, etched and cleaned in multiple steps. Silicon wet etching is one method that offers a number of advantages.

Wet etching with potassium hydroxide, or KOH etching, is inexpensive and reliable. KOH is safe and etches quickly. Repeatability is good and the process can be controlled by changing the temperature, the concentration of KOH, the crystal plane orientation of the silicon and the doping concentration. The KOH process allows for very precise etching and it can be automated. Other methods of creating microscopic structures on silicon wafers are more expensive, more risky or not as reliable.

Modutek’s Support for the KOH Etching Process

Modutek offers a variety of wet bench processing options including KOH etching. The company’s KOH silicon etching tank is designed and manufactured in house and can be built to customer specifications to satisfy specific wet process requirements. Its design emphasizes cleanliness with an all-PFA construction and consistency in the process to deliver accurate etching results.

The tanks are manufactured to reduce impurities and contaminants to a minimum with the PFA sheet material welded together using advanced welding techniques. The resulting process tanks deliver excellent performance and high quality output. Custom installations to work with existing wet bench equipment are available. Modutek uses its experience in the wet bench process to ensure that customer needs are met and the equipment functions as expected. If you have challenging wet processing applications contact Modutek for a free quote or consultation on solutions that will address your requirements.

Using KOH Etching for Batch Processing

Using KOH Etching for Batch ProcessingEtching baths with varying concentrations of potassium hydroxide (KOH) and controlled temperatures are used in creating microscopic structures on silicon wafers. Modutek can supply equipment such as PFA Teflon tanks, circulation and filtering systems and cassette handling equipment that supports KOH etching. The company designs and builds individualized systems for customers who want to use KOH etching and the resulting systems deliver accurate control, high repeatability, consistent performance and superior output quality.

The KOH Etching Process
The KOH etching process is well understood and is a preferred method for creating silicon wafer nano structures for semiconductor manufacturing and in research facilities. The process delivers controlled and uniform results with high precision and it is relatively safe.

The silicon surface is masked to allow etching and cavity creation in specific areas according to the layout of the final semiconductor product. The etch rate can be controlled by varying the concentration of KOH and the bath temperature. KOH etching is also impacted by the following:

  • The lattice planes of the crystalline silicon
  • Boron doping of the silicon
  • The presence of atomic defects in the silicon crystal
  • Natural impurities

Orienting the lattice planes in a particular direction can influence and control the direction of the etching and the shape of the cavities created in the silicon. Similarly, boron doping can be used to stop etching in a particular direction. Together with the mask, these factors permit the creation of cavities of the required shapes and orientations. Defects in the silicon crystal or natural impurities may reduce the quality of the final product and can result in defective items.

Advantages of KOH Etching
KOH etching provides excellent results and is used extensively because of the following advantages:

  • Safe and easy to handle
  • Rapid etching
  • Excellent reproducibility
  • Low cost
  • High precision when process variables are tightly controlled

Modutek can supply equipment that builds on the listed advantages to deliver corresponding benefits to the customer.

Modutek’s KOH Etching Process Equipment
Modutek’s wet bench technology supports KOH processing, and Modutek examines each request in detail before building the equipment for a particular application. This includes the KOH processing tank, the recirculating system and the silicon wafer handling. Sizes, capacities and control characteristics are adjusted for the customer’s requirements.

The systems supplied by Modutek use the latest technology to provide high accuracy and excellent output quality. Etch rates can be controlled precisely and etch uniformity is guaranteed. Even long etch times, such as up to 3 days, can be handled reliably and safely.

Modutek’s KOH processing tanks are PFA Teflon with all-Teflon fluid paths. The tanks are manufactured onsite using advanced PFA sheet welding techniques designed to minimize impurities and unwanted by-products. The tanks are available as static or as recirculating baths.

The static baths can be ambient temperature baths or temperature controlled from 30 to 100 degrees centigrade. The recirculating temperature controlled baths feature heat-up rates of 2 to 3 degrees centigrade per minute and a temperature control accuracy of plus/minus 0.5 degrees centigrade. The available semi automatic cassette handling reduces costs and increases reliability.

In each case Modutek makes sure that the equipment supplied fits into the existing or a new installation and is compatible with any other wet processing systems. Modutek’s specialists work to ensure the supplied equipment satisfies the customer’s requirements and meets or exceeds performance expectations.

Silicon Wafer Etching Processes for Wet Processing Applications

Silicon Wafer Etching Processes for Wet Processing ApplicationsThe manufacture of semiconductor components such as processors and integrated circuits relies heavily on the etching of silicon wafers with processes such as KOH etching to generate the required structures and connections. Modutek provides wet bench technology that can be used for a wide variety of these etching applications. Managers in charge of semiconductor manufacturing facilities, research centers or universities as well as process engineers working at these organizations can use wet bench equipment from Modutek to meet their silicon wafer etching needs.

KOH Etching

Etching silicon wafers with potassium hydroxide (KOH) is used to create microscopic structures in the silicon. The etch rate is impacted by the temperature of the etching bath, the concentration of KOH and the crystalline structure and impurities in the silicon. KOH etching is an inexpensive and repeatable process that etches rapidly. Modutek offers PFA Teflon tanks of their TFa or TT series for KOH etching applications.

Silicon Nitride Etch

Silicon nitride is used as a masking material in the fabrication of integrated circuits. It can be deposited on the silicon wafer as a thin film and is etched with hot phosphoric acid. The bath temperature is about 180 degrees Celsius, the boiling point of phosphoric acid. The Modutek series Nb nitride etch bath achieves precise temperature control by regulating the de-ionized water to phosphoric acid ratio. Modutek’s silicon nitride etch baths offer excellent repeatability, accurate process control and a high level of safety.

Piranha Etch

The piranha solution is made up of a mixture of sulfuric acid and hydrogen peroxide and is used to clean silicon wafers during the semiconductor manufacturing process. A common ratio used is 3 parts of concentrated sulfuric acid to one part of 30 percent hydrogen peroxide. The solution cleans organic compounds from substrates and oxidizes most metals. It is often used to clean photoresist from silicon wafers. Modutek can evaluate a customer’s silicon wafer cleaning requirements and propose suitable solutions from its extensive line of wet processing equipment.

Metal Etch

The conductors linking the microscopic electronic structures on a silicon wafer must be metallic to conduct the electric signals. Metals such as aluminum, copper and gold are deposited on the silicon wafer and must be etched. Etching metals can be challenging and effective etching depends on selecting the right chemicals and process.

For example, the Modutek vacuum metal etcher is designed for precise wet etching of aluminum layers. The process takes place under vacuum because the chemical reaction creates hydrogen bubbles that interfere with etching precision. In the vacuum, the bubbles are immediately removed by an evacuating pump. Modutek’s wet process equipment can use a variety of etchants to etch different metals.

Gallium Arsenide (GaAs) Etch

Gallium Arsenide is a semiconductor used in the manufacture of integrated circuits and other electric and electronic devices. It is etched with solutions containing hydrogen peroxide, usually in combination with sulfuric, hydrochloric or phosphoric acids. Modutek’s wet process solutions can handle such etching chemicals at lower cost than dry etching.

Modutek Wet Bench Solutions

As a premier provider of semiconductor manufacturing equipment for over 35 years, Modutek can offer wet processing equipment for a wide variety of semiconductor etching and cleaning applications. Modutek’s wet bench technology delivers reliable, repeatable results safely and accurately. The company can help customers in industry and research find solutions to their semiconductor manufacturing needs. For a free quote or consultation on selecting the right equipment for your silicon wafer etching process, contact Modutek at 866-803-1533 or email [email protected].