Is working in a chip fab dangerous? How fabs protect people

Working in a chip fab does involve real hazards, but the fab shuts them in and keeps them under control, layer by layer. Safety doesn't rest on "everyone be careful". Design keeps the hazards shut away first, rules cover the moments they are opened, and then come personal protection, training and drills. No job is completely free of risk; this article is about what the hazards are and how a fab protects people, not a verdict on whether any particular fab is safe. Whether the work is hard is a different question: see "Is working in a semiconductor fab hard?".

What are the hazards in a chip fab?

• Chemicals: strong acids, strong bases and solvents, used to clean wafers and to etch. They burn skin and eyes.
• Specialty gases: some are toxic, some corrosive, some catch fire on contact with air, and for many of them your nose is no warning (see "What gases does a chip fab use, and why so much care?").
• High voltage and heavy current: in the tools and the power panels. Touching them can mean an electric shock.
• Things that move: the robot arms that carry wafers inside a tool, a chamber lid that rises and lowers. If a hand is inside when they start, it gets pinched.
• Energy you can't see: lithography scanners use very strong ultraviolet light, and some inspection tools use lasers; the high voltage in an ion implanter can give off X-rays. All of these are kept inside the tools; direct exposure can hurt people.
• Heat: furnaces, and a chamber that has only just stopped, are still very hot.

Is a cleanroom dangerous on an ordinary day?

Most of the time these hazards are shut away. Chemicals and gases travel in sealed pipes, processing happens inside closed tools, and wafers ride in sealed pods moved by machines, so people seldom touch any of it directly.

The time to be most careful is when things get opened: opening a tool's chamber for maintenance, changing a gas cylinder, repairing a pipe, wiring something up. Many of the rules below are built around those moments. For the everyday rules of the cleanroom, see "What are the rules for entering a cleanroom?".

How does a fab protect people? Layer by layer

Workplace safety has a well-known order: removing the hazard is best; if you can't, use design to separate people from it; then rules; personal protective equipment comes last. The higher up the list, the less it depends on people remembering every single time.

Layer 1: design that shuts the hazard in

• What: chemicals and gases run in sealed pipes, the dangerous ones often in double-walled pipe; cylinders sit in gas cabinets that are always being exhausted; every tool is exhausted all the time (see "Where does the air in a cleanroom come from?"); gas detectors sniff nonstop, and when one reads a leak the valve closes by itself. On many tools the doors and covers are interlocked: open one, and the robot arm, the laser or the high voltage stops. Tools that produce X-rays are enclosed in shielding.
• Why: design doesn't get tired and doesn't forget.
• Without it: a small leak goes straight into the air people breathe, and with many gases your nose gives no warning.

Layer 2: rules for the moments things get opened

• What: before anything is repaired, it goes through lockout/tagout (step by step below). Changing a toxic gas cylinder or working a chemical valve is often a two-person job: one does it, one watches. For work such as welding or going into a cramped space, you first get a work permit that says who is doing what, where, and someone responsible signs it before work starts. Nobody handles something they haven't been trained for.
• Why: opening a tool or a pipe means taking away part of layer 1 first, and procedure has to make up for it.
• Without it: someone who doesn't know a person is inside presses start; someone gets into trouble with no one nearby to help.

Layer 3: personal protection, the last line

• What: with chemicals, acid- and alkali-resistant gloves, a face shield or goggles, and an apron; when changing toxic gas, respiratory protection that supplies air from somewhere other than the room. A cleanroom suit mainly protects the wafers (see "What is a bunny suit, and why do chip fab workers wear one?"); it is not there to stop chemicals.
• Why it comes last: it only protects the person wearing it, and only if it is the right gear, worn properly.
• Without it: whatever slips past the earlier layers lands on skin or in the eyes.

Layer 4: training, drills, and what to do when something goes wrong

• What: before starting work, people are trained: what the chemicals can do, where the emergency showers and eyewash stations are. Evacuation drills happen regularly, and some fabs drill for earthquakes too. If a chemical splashes on you, you rinse with water right away, and for a long time. When an alarm goes off, people leave first and the lots wait: you put down what you're doing, follow the evacuation route to the assembly point for a roll call, and go back only once it has been checked.
• Why: in the few seconds when something happens there is no time to think; only moves you have practiced come out right.
• Without it: people panic and can't find the shower; someone is still inside and nobody knows.

"People first, lots later" is also where the interview question "a tool goes down, what do you do first?" starts (see "What do chip fab engineer interviews ask, and how do you prepare?"); problems that can't hurt anyone follow a procedure written in advance (see "What does OCAP mean in a chip fab?").

What is lockout/tagout? Step by step

The procedure before a repair is called lockout/tagout, often shortened to LOTO: the switches and valves that could send energy in are shut and locked, and a tag with a name hangs on them. "Energy" here means more than electricity: it also covers the pressure of gases and chemicals, moving parts and heat. Each fab writes it a little differently; a common order is:

1. Tell people, then shut down the normal way: let the control room and the people scheduling lots know, so they can move work elsewhere. If you don't, someone is still waiting on the tool or using it.
2. Cut the energy sources: pull the circuit breaker (the switch for that circuit) and close the gas and chemical valves. Pressing "stop" on the tool leaves power and gas connected, and one signal could start it again.
3. Lock and tag: put on your own lock and keep the key on you, then hang a tag with your name; if several people are working, each puts on a lock of their own. The lock means no one else can open it, and the tag tells them who is inside; without a tag, someone may think it was simply left off.
4. Release the energy that is left: pressure and gas in the lines, electricity stored in capacitors, hot parts are all still there after the sources are shut. So the lines are depressurized, the gas pushed out with nitrogen (a purge), and the parts left to cool; otherwise, what stayed inside can still hurt someone the moment it is opened.
5. Prove there is no energy: press start once to make sure nothing moves; for electricity, measure with a meter, trying the meter on something you know is live both before and after. "I thought it was off" doesn't count, only a measurement does; if the wrong switch was turned off, this is the step that catches it.
6. Only then start work, and take off your own lock when done: put the tools away, make sure no one is inside, each person removes their own lock, everyone is told, and only then does power come back and the valves open. Only the person who put on a lock knows whether they have finished.

In fab24hr

Tap "Clock in", choose "A day in the fab", then on the "Your role today" card tap "Production fab", swipe to the Facilities engineer, and under the name tap "Gases & chemicals". On the late-night shift, "Night watch", you and Zheng put on face shields, aprons and acid-resistant gloves and go downstairs to put an acid refill valve that was left on manual back to auto; the first step is checking the valve for a lock and tag. On the morning shift, "Cylinder change", you and Hui-Ju, both in respiratory protection, change a specialty gas cylinder, and any step you skip comes back to find you later. On the evening shift, "A Trace in the Cabinet", the detector picks up a trace, and you leave the cabinet door shut and sniff through the small window.

In the "Power" area of Facilities, before wiring you pull the circuit breaker, put on your own lock and test for voltage. On the etch equipment engineer's morning shift, "Chamber open", you lock and tag first, wait for the chamber to cool, then open it with a face shield on, and the inside gives off a little acid vapor; if you skip the lockout/tagout, you will see why it can't be skipped. Some roles in the production fab may also get a gas detector alarm; if you take the pod in your hands back to the stocker before leaving, the chief says, "Lots can be made again. People can't."

The fab, people, tool numbers and events in the game are fictional. What the hazards are, how a fab protects people and how lockout/tagout works come from public, general sources and do not describe any company's practice; in reality every fab has its own procedures and training. For other jargon, see Chip fab jargon in plain English.