Delivering Semiconductor Manufacturing Cleanroom Fire Safety
As semiconductor nodes become smaller and fire risks continue to increase, the industry is using very early detection fire safety devices to protect sensitive tools and processes from smoke contamination
Matt Wyman and Khaleel Rehman
View full PDF here
For semiconductor fabricators, there is a critical need to protect the cleanroom environment from fires, as well as from the associated contamination from smoke particulate that can cause catastrophic product and process equipment damage.
For this reason, the National Fire Protection Association (NFPA) 318 Standard for the Protection of Semiconductor Fabrication Facilities stipulates requirements for smoke detection in semiconductor fabs. There is a significant fire risk within such environments due to the high volume of electrical equipment, continuous air supply, operation of fully automated processes, and presence of flammable and explosive substances.
Air at these facilities requires significant monitoring for the presence of even minute amounts of smoke or aerosol particles, as do the individual fabrication tools used for deposition, resist, photolithography, etching, and ionization. In the industry, a “tool” refers to any workstation, process machine, or support cabinet located in the fab manufacturing cleanroom environment. Most are quite costly, enclosed systems, including all electrical power, chemical storage, and delivery systems such as piping, robotics, and instrumentation.
This equipment can pose a significant fire risk due to the use of combustible plastic materials, flammable and pyrophoric chemicals, and the presence of high-voltage electrical power. The industry is also increasing its use of pyrophoric materials used in the process, which can spontaneously ignite when exposed to oxygen. Given these risks, highly sensitive smoke detection equipment is vital to protect both tools and the facility.
Photo Curtesy of Honeywell
If there is a fire in a fab, the most expensive part is the loss of production and cleanup. The micro contamination from smaller particulates can be as extensive as large particulates in significant fires. Contaminated equipment may even need to be replaced, as it cannot be brought back to the purity level required for the manufacturing process.
Smoke contamination can significantly lower product yields when fabs need to be in the high 90%. With semiconductor chips, the manufacturing processes take days, weeks, or months as many layers are formed. One small incident can ruin a large batch of chips, resulting in a scrap of the products and starting over.
One concern at the tool level is the proximity of combustible materials to high-voltage equipment, such as high-powered lasers used in metrology and photolithography processes and plasma-based systems used in ion implanters. As a result, all systems must meet the safety standards outlined in the National Electrical Code® and by organizations such as NFPA and SEMI. Insurers may also have specific requirements for fire protection for any given type of tool.
In equipment with higher-than-normal risks, especially from electrical hazards, it is fairly common for the fab tool OEM (original equipment manufacturer) to integrate high-sensitivity smoke detection systems at the equipment level.
Generally, OEMs outsource the fire detection or suppression systems design, installation, and validation testing, with work completed before the tool is shipped to the semiconductor manufacturing fab. For electrical hazards, the fire safety system includes fully integrating high-sensitivity smoke detection systems like very early smoke detection devices. The fire safety system includes flame detectors with suppression systems for flammable liquid or combustible plastic hazards.
It is becoming more common to install and integrate an economical, miniature, very early smoke detection unit within each tool. The unit is designed to protect small tool manufacturing environments. Since semiconductor tools are essentially small rooms, the miniature unit is well suited to the application. Covering up to 5,000 sq. ft., the detector works by continually drawing air into sampling holes in a pipe network. The air is filtered and passed into a detection chamber where light scattering technology detects the presence of very small amounts of smoke. The miniature unit supports a number of pre-engineered pipe network designs to simplify installation.
At the same time, there are considerable airflow issues to manage given all the equipment within a tool, so the fire protection equipment must also properly mount and route the air sampling piping to enable it to reach all the critical areas. Before the tool is shipped to a fab, “wire burn” testing should be completed to validate that the unit properly detects the specified fire size or incipient thermal event and alarms.
Matt Wyman is with Koetter Fire Protection International, LLC (KFPI)
Khaleel Rehman is with Honeywell Inc.,