Wet process semiconductor manufacturing lines use aggressive chemicals to clean and etch silicon wafers. When a cleaning or etching step is complete, the remaining chemicals have to be disposed of safely. Low pH acids such as hydrochloric acid have to be neutralized with high pH chemicals so that the pH of the mixture approaches the neutral value of seven. The acid neutralization can be carried out continuously or in batches and either process can be fully automated. Ideally an acid neutralization system acts reliably with a minimum of supervision and keeps records of chemical use and discharge to demonstrate compliance with environmental regulations.
Continuous Flow and Batch Neutralization Systems Fulfill Different Requirements
The choice of an acid neutralization system reflects the type of semiconductor manufacturing that takes place. Large scale continuous manufacturing lines produce a continuous flow of waste chemicals. The composition of the flow and its volume changes little and can be analyzed in detail. A continuous flow acid neutralization system can then be designed to automatically and reliably neutralize the out flow. Because small changes can easily be detected and the dosages of neutralizing chemicals can be automatically adjusted, the automation required for such a system is easily set up. The automated continuous flow acid neutralization system can keep records of its neutralization activity and the volume and pH of the waste flow.
The neutralization of waste chemicals used in batch manufacturing is usually more complicated. Batch manufacturing is used for prototypes, one-of-a-king components and small quantities of special parts. Each batch can be different and it makes sense to use a batch acid neutralization system for these processes.
Instead of adjusting chemical dosages of an established process as in the continuous flow systems, batch neutralization systems have to measure the pH of the waste chemicals and add specific neutralizers. Several stages of neutralization may be required before the discharge is acceptable. Once the neutralization process is finalized, the sequence can be fully automated and can run as the batch is processed.
Other Considerations When Choosing an Acid Neutralization System
Once the choice of continuous flow or batch system is made, the acid neutralization system has to fulfill a few basic requirements. The system capacity has to be sufficient for the proposed application, with capacities ranging from a few gallons to hundreds of gallons per minute. The system can be located indoors if there is space but it can also be designed for outdoor operation. If automated, the exact automatic functions have to be programmed and set up. Finally the monitoring and record-keeping functions have to be determined.
Operational characteristics have to be considered as well. If the system is fully automated, it may run without supervision but alarms will be required for situations such as low chemical supply or a pH level outside permissible limits. Recording of neutralization process parameters can be digital, with a log, or on a chart recorder. Containment of spills is important and depends on whether the installation is indoors or outdoors. Spill detection has to be incorporated into the alarm system and the whole operation has to comply with environmental regulations.
Modutek Can Supply Acid Neutralization Systems to Meet Customer Needs
Included in Modutek’s complete line of wet process equipment are compact acid neutralization systems that can be customized to meet specific needs. Systems can be designed to fit into the space available at a customer’s facility and Modutek can help select suitable automation and operating characteristics. The Modutek acid neutralization systems operate reliably to keep waste discharge parameters close to specified values and a digital chart recorder documents compliance with discharge regulations.