RESPONDING TO SEMICONDUCTOR FACILITIES

RESPONDING TO SEMICONDUCTOR FACILITIES

Hazardous materials and computers may seem incongruous to most people. In reality, they are closely related. This article will take you on a tour of a typical semiconductor facility from the perspective of the many potential hazards such a facility can present for emergency responders. Semiconductor facilities generally manufacture computer chips, circuit boards, and panels.

Let’s begin with the processes involved in manufacturing computer chips.

• Epitaxial growth. During this process, chemical vapor deposition is used to grow a thin crystal layer on a silicon wafer. The wafer is heated by radio frequency to approximately 1,500°F and exposed to hydrogen gas, which cleans and etches the wafer. Additional gases, such as trichlorosilane, arsine, and tetrachlorosilanc, are introduced to the wafer and decompose to form a layer of crystals.
• Diffusion. In this step, the chip is heated by radio frequency in a tube furnace w ith temperatures ranging from 1,700°F to 2,300°F. Corrosive, flammable, and toxic chemicals are used, including arsenic trichloride, boron trioxide, phosphorous oxychloride, diborane, and phosphorous pentoxide.
• Metallization. During this process, the wafer is placed in a vacuum device and heated by radio frequency induction. Chrome, gold, silver, and titanium then are introduced to the wafer to form the chip’s electric circuits.
• Plating. In plating, chemical immersion tanks, usually made of PVC material, are used. The tanks are heated with electric heating elements, which introduce the risk of ignition should the liquid w ithin them evaporate. Ignition could damage the exhaust duct system as well as the tanks.
• Etching. During this process, selected portions of the chip are removed and the chip is prepared for additional processing.
• Chemicals used in this operation are hydrofluoric acid, ammonium fluoride, phosphoric acid, and nitric acid.
• Dry etching. This step completes the manufacturing process. Unlike the earlier etching process, it incorporates gases instead of chemical liquids. These gases include boron trichloride, nitrogen, oxygen, chlorine, trifluoromethane, and tetrafluorome thane.
• Cleaning. Most cleaning is performed at wet bench stations and uses sulfuric acid and hydrogen peroxide. In most high-tech semiconductor facilities, a system of belowfloor pipelines transfers used chemicals from wet bench stations to chemical holding tanks for storage until they can be treated. These pipelines, which are equipped with leak detectors, usually are the “pipe-withina-pipe.” combination type, to prevent chemical leakage from the carrier pipe.

TOXIC GASES

Numerous toxic gases are used in manufacturing computer chips. Gas cylinders involved in the manufacturing processes are stored in specially designed gas cabinets that feature sprinkler, exhaust, and leakdetection systems. The tubing used to supply the tooling used in the process is enclosed in a sealed jacket to prevent leakage. The jacket also contains leak-detection and overpressurization sensors. When a leak is detected within the system, the gas supply from the tool automatically is shut down.

All cabinets can be operated from a separate control room, adjacent to the cabinet storage room. Video cameras throughout the room give the operator a full view of any possible gas leaks w ithin the room.

Silane gas. a pyrophoric material that ignites spontaneously in air below 130°F, usually is stored outside the building in protected storage distribution centers. These areas feature dry-sprinkler deluge systems that are activated by UV detectors surrounding the storage areas. Storage can range from one or two to up to a dozen compressed gas cylinders, which are controlled by a distant control center w ithin the manufacturing building.

CRYOGENIC GASES

Cryogenic gases such as hydrogen, nitrogen. and oxygen are found in large quantities at semiconductor facilities. These gases are carried throughout the complex by overhead trestles. Some locations may have onsite compressed-gas manufacturing complexes operated by vendors. Most, if not all, hydrogen and oxygen is shipped in by tank truck; hydrogen tank farms usually are found in an isolated, restricted area enclosed by fencing and equipped with video cameras.

Portable dewars filled at a refill station within the building distribute nitrogen within the building. The extremely low temperatures of cryogenic gases make them a serious danger for firefighters, even those wearing turnouts.

FIRE DEPARTMENT RESPONSE

The super-clean buildings in which computer chips are manufactured can be located almost anywhere in a response area. These facilities, because of the nature of their product and clients, among them the military and other government agencies, feature elaborate security systems to protect themselves against theft and espionage.

As is true of all facilities within your response district, the first step in response to an emergency at a semiconductor facility should be preplanning. The high degree of security at these sites necessitates a high degree of cooperation between the facility’s on-site fire or safety representatives and the responding fire department. Some sites have 24-hour-a-day, seven-day-a-week, fully staffed industrial fire departments; others have emergency response teams (ERTs) trained to the level of OSHA hazardousmaterials responder level; and some smaller plants have no on-site response teams and rely completely on outside emergency responders.

It is advantageous for a small group of fire department representatives to perform a walk-through tour of the facility (due to the clean-room status of many areas, only a few fire department representatives can be taken through at a time). These individuals should review the facility layout as well as all hazards present and transfer this information to the preplan.

• Fire protection systems. Most complexes have fully sprinklered buildings and underground fire main systems with yard hydrants. These systems are inspected at
• least monthly and are reviewed annually by the manufacturer’s insurance company.

ARRIVING AT AN INCIDENT

Fire department personnel should meet with a facility representative immediately on arrival at the scene. They should not enter any building or chemical storage area without assistance from a facility representative.

What will be done (and, just as important, what will not be done) to control the incident must be determined. Have all procedures and equipment in place before commencing. In addition, the prevalence of hazardous materials necessitates using hazmat SOPs. Contamination of personnel must be a concern. EMS workers with appropriate haz-mat training should be on hand to treat injured plant personnel and firefighters.

Following is an overview of some of the problems firefighters may encounter when responding to a semiconductor plant, as well as other considerations regarding the sites.

• Compressed-air system failures. Compressed air is the blood that makes the facil-
• ity run. It is used to operate badge door locks, exhaust systems, and heating and airconditioning systems. Loss of wet-station exhaust will allow toxic vapors to flow through the station areas, exposing workers and responders. Since the drain valves on chemical wet stations also are air-operated, a loss of the compressed-air system would allow wet stations to dump their chemicals, overwhelming pipelines that were not designed to handle the extra volume of chemicals that would be introduced. In turn, tanks could back up and overflow, allowing chemicals to mix, creating additional

• unforeseen hazards.
• Roof operations. A common fircground occurrence, roof operations, poses additional dangers for firefighters at semiconductor facilities. Some locations may keep oversi/ed air-handler units on the roof. Fires within these structures should be extinguished as soon as possible, to avoid fire extension and possible failure of the roof. Exhaust ducts and roof fans from chemical wet stations, also commonly found on the roof, can present inhalation and skinabsorbing hazards for emergency responders working there.
• Chemical storage. Chemicals arrive at semiconductor facilities mainly by tractor trailers and tank trucks. Containers vary from small lecture toxic gas bottles to oneton chlorine and sulfur dioxide cylinders. Corrosives arrive in small, one-gallon jugs and 55-gallon drums, some of which are lined with plastic and constructed of stainless steel.

Chemical distribution systems within the complex can be as simple as hand-carrying one-gallon glass jugs to work stations and as complex as having computer-controlled overhead distribution pipeline systems. The computer-controlled type of system automatically supplies the wet stations from bulk storage areas ranging in size from several 55-gallon drums to storage tanks of 1,000 to 5,000 gallons. These bulk storage areas have built-in safety features such as deluge foam sprinkler systems, UV detectors. rate-of-rise temperature sensors, and leak-detection systems.

As a rule, most chemical spills at semiconductor plants are small—usually no more than a gallon. In many instances, they are contained to a wet station. Industrial waste treatment facilities found on site will contain large amounts of heavy metals and fluoride waste from the manufacturing processes. Treatment facilities also contain sulfuric acid and bulk storage of powdered lime used to neutralize chemical wastes.

• Gas leaks. Gas leaks also occur at semiconductor facilities. These gases may present multiple hazards, such as being pyrophoric and toxic. Determine the consequences of opening gas cabinets or shutting down gas-distribution systems.
• Confuted spaces. Confined space entry and rescue in semiconductor facilities are extremely hazardous. Numerous chemical
• storage tanks are present within the complex, and manholes and high-voltage electrical vaults dot the industrial landscape. Remember, OSHA 1910.146 requires facility managers to inform emergency responders of what is in or what was in the confined space they will enter.
• Power generators. These complexes require vast amounts of energy to operate. Some plants have their own power plants to provide heat, electricity, treated water, and air conditioning. Most use conventional fuels to operate their boilers, which produce high-pressure steam to supply heating and air conditioning. Large quantities of chemicals are used to treat in-house water systems. to prevent rust buildup.

As you can see, semiconductor facilities can present some unique challenges for emergency responders. Remember, therefore. that a good response begins with a good preplan. If a semiconductor site is within your response area, visit the site and become familiar with its hazards. Communicating with the facility’s fire chief or safety representative prior to an incident will help ensure a successful and safe operation should an emergency occur.