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