Wet Processing Application Capabilities Provided by Modutek

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

Standard Clean 1 (SC1 Clean)

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

RCA Clean

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

SPM Process Clean

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

KOH Etch

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

Nitride Etch

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

Aluminum Etch

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

Modutek Equipment That Supports These Wet Processing Applications

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

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

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

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

 

Isotropic and Anisotropic Silicon Wet Etching Processes

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

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

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

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

How Anisotropic Etching Works

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

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

Controlling the Etching Speed to Obtain Specific Structures

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

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

Differences between Isotropic and Anisotropic Silicon Wet Etching

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

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

 

Safely Controlling the Silicon Nitride Etching Process

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

The Silicon Nitride Wet Etching Process

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

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

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

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

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

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

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

The Benefits of the Modutek Silicon Nitride Etch Bath

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

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

How Quick Dump Rinsers Improve Silicon Wet Etching Results

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

How Quick Dump Rinsers Work

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

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

Modutek’s DR Series Quick Dump Rinser Features

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

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

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

How Modutek’s DR Series Rinsers Improve Silicon Etching Results

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

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

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

How Quartz Tube Stations Work and the Benefits They Provide

Among the many processing steps involved in the manufacture of semiconductor components are high-temperature operations such as diffusion of materials into the silicon wafers. Quartz tubes are an ideal vessel for these process steps because the tubes can withstand the temperatures required and are inert enough to minimize contamination.

Typically, the silicon wafers are placed into a horizontal quartz tube large enough to hold the wafers and their supports. The quartz tube cleaning station can heat the contents up to over 1000 degrees centigrade. In a diffusion process, impurities such as phosphorus are introduced into the quartz tube.

Once the process is complete, the quartz tube is contaminated and has to be cleaned for the next batch of wafers. Complete and reliable cleaning is essential for the semiconductor manufacturing process because contaminating particles can cause defects in the semiconductor components or result in inferior product quality.

How Quartz Tube Cleaning Works

Quartz tube cleaning is a custom-designed process because the dimensions and cleaning requirements of quartz tube furnaces can vary widely. Quartz tubes are mechanically delicate, so they have to be handled with care. At the same time the cleanliness requirements are rigorous so that all traces of the contaminating material have to be removed. Finally, the rinsing and drying process must not introduce any new particles into the quartz tube. The cleanliness of the tube directly impacts the performance of the semiconductor manufacturing facility.

In horizontal quartz tube cleaning stations, the tube is inserted into the cleaning enclosure and cleaned with an acid spray. The acid dissolves and removes the contaminant from the high-temperature furnace. A subsequent rinse cycle removes all traces of the acid from the tube surfaces. A drying cycle can speed up drying without introducing particles into the cleaning enclosure. Mechanical handling of the tubes reduces the possibility of breakage due to human error and minimizes opportunities for the entry of contaminating particles. Safety interlocks, exhaust fans and safety shields protect operators from the hazardous chemicals.

Modutek’s Quartz Tube Stations Offer Numerous Benefits

A key factor in effective customization of quartz tube cleaning stations is that the supplier has to design and build the stations so that they can make the required adjustments. Modutek designs and builds all process, etching and cleaning components in house at the company’s San Jose, California facility. Equipment is customized exactly according to the requirements of the specific application.

In addition to providing customized equipment, Modutek can supply the degree of automation required by the customer. Cleaning process steps can be initiated manually or the whole cycle can be completely automated. Different steps can initially be run and timed manually and then, when optimum performance is reached, automated operation can be locked in.

Full automation reduces human error and keeps operators safe by allowing them to monitor the cleaning process remotely. Automated quartz tube cleaning stations will run the same cleaning job exactly the same way, with identical timing and dosages. Results from an automated system are predictable and uniform and the system can be programmed for the best possible results.

Modutek’s horizontal quartz tube cleaning stations are an excellent solution for semiconductor manufacturers. Rugged and reliable with one-piece construction up to ten feet long, the basic units offer many options for additional features. Once the requirements of the cleaning application are satisfied, Modutek can offer design add-ons such as holding tanks, automation features, a T/C sheath cleaner or a bottle washer. Modutek is a leading semiconductor equipment manufacturer that provides continuous product innovations and improvements along with the highest degree of customer service and support.

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

Why High Temperature Quartz Baths Are Required for Silicon Wafer Cleaning

Silicon wafers undergo many process steps during the manufacture of semiconductor components and cleaning the wafers properly is an important factor in successful fabrication. Process steps include etching and diffusion, both of which involve coating the wafer with masking material to guide the etching chemicals or diffusion targets. Once a step is completed, the masking chemicals have to be completely removed. If traces remain or if other impurities are introduced, the quality of the final semiconductor product will be affected.

Silicon wafers are cleaned with aggressive chemicals to remove organic masking material and other possible contaminants. As a result, the cleaning solution container has to be able to resist the action of corrosive chemicals while remaining inert without becoming a source of contamination itself. Baths made of quartz are highly stable, resist corrosion and can be designed and built to avoid contamination. Quartz baths are an ideal solution to the challenges of silicon wafer cleaning and the maintaining of high levels of wafer cleanliness.

How Quartz Baths Clean Silicon Wafers

Quartz baths provide a clean and safe container for the chemical reactions that are used in silicon wafer cleaning. Depending on the materials used, the quartz bath may simply hold the wafers and the cleaning chemicals, but some processes require heating, circulating the solution or the addition of chemicals. In each case, the control actions must be accurate, reliable and easily duplicated.

For example, materials such as hydrochloric acid, sulfuric acid and hydrogen peroxide may be used for cleaning the silicon wafers. Quartz is impervious to these strong chemicals and the quartz tanks remain unaffected while the acids clean the silicon wafers. With SPM clean, sulfuric acid and hydrogen peroxide are mixed and maintained at a constant temperature of about 130 degrees centigrade. Periodic spiking with hydrogen peroxide is necessary because it decomposes in the solution. The mixture cleans wafers rapidly but can’t attack the quartz bath container.

Using bath containers that are inert and don’t contaminate is important because the electrical and physical structures making up modern semiconductor components are extremely sensitive to contaminating particles. As these structures become smaller and more tightly packed on a wafer, even a single particle can interfere with the etching or the diffusion process. Such interference from particles reduces the yield of semiconductor components and affects the productivity of the semiconductor manufacturing facility.

The Benefits of Using Modutek’s Quartz Baths

Modutek has over 30 years experience in quartz bath design and manufacture so that the company’s baths fulfill all the basic requirements for semiconductor processing and deliver additional benefits. Modutek can provide standard units where they satisfy customer requirements but can also design and build custom systems for special applications.

Modutek’s QFa series high temperature re-circulating quartz baths are safe and reliable with a low total cost of ownership. The semiconductor grade quartz of the baths is flame polished to reduce contamination and the vessels are designed for an especially long service life. Particle addition from re-circulating flow is kept to a minimum and remote control is available. Tank sizes range from an inner measurement of 7.75 x 7.75 inches and 9 inches high to 21.5 x 11.5 inches and 10.5 inches high. Custom sizes are available as well.

The QFa baths have an integrated heater that provides an operating range of 30 to 180 degrees centigrade. The heaters produce a temperature rise of 2 degrees per minute and control accuracy is plus/minus 1 degree centigrade, these variables depending on the operating conditions. The wide temperature range, fast thermal response and accurate temperature control make the Modutek quartz baths ideal for silicon wafer cleaning. The high precision guarantees excellent repeatability of the process between batches and the fast heating rate reduces process times. Overall, Modutek’s quartz baths can help improve the semiconductor production performance of manufacturing facilities and research labs. For a free quote or consultation on selecting the right equipment for your manufacturing process contact Modutek at 866-803-1533.

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

Ordering a Wet Bench Station for Your Specific Process Requirements

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

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

Physical Requirements Affect the Ordering Process

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

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

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

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

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

Equipment for specific wet bench processes can include the following:

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

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

Modutek Can Help

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

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

Selecting Silicon Wet Etching Equipment for Your Application

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

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

Getting the Right Tanks and Baths

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

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

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

Automation Can Improve Throughput and Yield

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

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

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

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

Modutek Provides Industry-Leading Silicon Wet Etching Equipment

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

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

How Chemical Delivery Systems Are Customized for Specific Applications

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

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

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

The Volume of Chemicals Needed Impacts the System

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

How Chemicals Are Used Influences Customized Controls

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

Facility Layout Affects System Design

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

Modutek Can Meet Customization Requirements

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

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

Improving Silicon Wafer Cleaning with the Piranha Etch Process

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

Modutek Quartz Baths for Piranha Etch

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

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

Improving Piranha Process Control

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

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

The Modutek “Bleed and Feed” Process Control Method

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

Benefits of the Process Change

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

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

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

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