What is a fab in semiconductors, and what does "going into the fab" mean?

A fab is a chip factory. The word is short for fabrication facility, or fabrication plant. In the semiconductor industry it means the factory where chips are built layer by layer on silicon wafers; people also say wafer fab or chip fab. It is where a finished design becomes a real thing.

In Taiwan's chip industry, people often use the English word even when they are speaking Chinese: "I work in the fab", "I have to go into the fab in a minute". This article starts from the word itself. Each section is short; if you want more on one part, follow its link.

What does fab stand for?

To fabricate means to make, and fabrication is the noun. A factory that makes chips is a fabrication plant or fabrication facility, and the short form keeps the first three letters: fab. More than one are fabs.

In everyday English, fab can also be short for fabulous, which has nothing to do with factories. The context tells you which one it is: a fab mentioned alongside chips, wafers or cleanrooms is a chip factory.

What does "going into the fab" mean?

It is everyday talk in Taiwan's chip industry, and it usually means one of two things:

• Walking onto the cleanroom floor. Fab engineers spend much of their time in offices outside the cleanroom, reading data and sitting in meetings; when they need to look at a tool or pick up wafers, they "go into the fab". First they put on a cleanroom suit that covers them from head to toe, then pass through an air shower: a small room where nozzles blow strong, clean air to knock particles off the suit. On the way out, they change back into their own clothes. Why they dress like this: What is a bunny suit, and why do chip fab workers wear one?
• Getting a job at a fab. "I want to go into a fab after I graduate" means wanting to work at a chip factory. For the jobs inside, see What jobs are there in the semiconductor industry?

So "I'm in the fab" can mean "I'm in the cleanroom right now", or "I work at a chip factory".

What is the difference between a fab and a foundry?

In one line: a fab is a place; a foundry is a business.

• A fab is the factory itself: the building, the cleanroom, the tools.
• A foundry is the business of making chips for other companies: the customer designs the chip, the foundry builds it, and it sells no chips of its own. The word foundry originally meant a metal-casting works, and later came to be used for this kind of company too.

Think of a kitchen. The fab is the kitchen. A foundry is like a central kitchen that takes orders from many food brands and cooks to their recipes. Every central kitchen has a kitchen, but not every kitchen is a central kitchen: a company that designs and makes its own chips (an IDM) also has its own fabs, but they make its own chips.

Some people use fab and foundry as if they meant the same thing. When reading the news, this is enough: "building a new fab" is about a factory; "foundry" is about the kind of business a company runs. How the foundry business works: The news says "foundry". What is it, and how does making chips for other companies work as a business?

What is inside a fab?

• The cleanroom: where chips are actually made, and the heart of a fab. Filtered air blows down from the ceiling and leaves through a floor full of holes, so the air is far cleaner than in an ordinary room (How clean is a cleanroom?).
• Seven process areas: litho, etch, thin film, CMP, furnace, ion implantation and wet clean. Tools that do the same job sit together, and wafers go back and forth between these areas through hundreds of steps, over weeks to months (What do the seven process areas of a chip fab do?, How are computer chips made?).
• Transport: wafers travel in sealed FOUPs, carried to the door of each tool by the OHT on rails in the ceiling (How do wafers move around a fab?).
• Measurement and testing: every important step is measured afterwards: how thick the film is, how wide the lines are, whether extra particles turned up. When a lot is finished, before it leaves the fab, there is also WAT (wafer acceptance test): it measures test keys, small structures placed between the chips just for measuring, to see whether the lot was made right (How does a chip fab know each step went right?). Wafer sort, which tests every single chip, is often done at a test-and-assembly house or at a separate test house.
• The subfab: the floor under the cleanroom. Many of the tools' vacuum pumps, exhaust treatment units, and gas and chemical lines are down here, placed as close as possible below the tool they serve upstairs. The power, ultrapure water, gases and chemicals the whole fab needs come from Facilities (What does a fab facilities engineer do?).

Outside the cleanroom there are also the engineers' offices, and the control room where Facilities watches the whole fab's water, power and gas. The tools are expensive and wafers take weeks to months, so a fab runs all year round, with people working in shifts (Why do chip fabs run 24 hours a day?).

How is a fab different from a test-and-assembly house or a chip design company?

A chip (its formal name is IC, integrated circuit) usually passes through three kinds of places:

	Chip design company	Fab (wafer fab)	Test-and-assembly house
What it does	Designs the circuit on computers and hands over the design	Builds the circuit on wafers, layer by layer, from that design	Tests the chips, cuts them apart, packages them, tests them again
What it handles	Design files	Whole wafers	Single chips
Where people work	Offices, at a computer	Between the office and the cleanroom	Between the office and the cleanroom; the cleanroom is usually less strict than a wafer fab's
Read next	VLSI design vs working in a fab: what's the difference?	How are computer chips made?	What is an OSAT, and what happens in a test-and-assembly house?

The order goes like this: the design company hands over its design, which becomes a set of photomasks for printing the circuit; the wafers are made in the fab, then go on to the test-and-assembly house. The industry often calls the fab part the "front end" and assembly & test the "back end".

What does fabless mean?

Fabless means "without a fab": a company that designs chips but has no wafer fab of its own. It hands its designs to a foundry to make, and the packaging and testing to a test-and-assembly house. Most of what people call chip design companies are this kind. In the kitchen picture, it is a food brand that designs the menu but has no kitchen of its own.

Why not build a fab? Because fabs are very expensive. Building one of the most advanced fabs and filling it with tools costs from several billion to more than ten billion dollars, and once it is built, it only pays off if it stays full of work. Without a fab, a company can put its money and people into design; the price is lining up time and capacity at a foundry.

The opposite of fabless is a company that designs its own chips and also owns its fabs: the IDM (integrated device manufacturer) mentioned above. How the three kinds of company split the work, and why, is explained with a restaurant in The news says "foundry". Outside semiconductors, fabless is also used for companies that build no factories of their own and only design and sell.

In fab24hr

The fab in fab24hr's name is a chip fab. The game is set in a made-up R&D line, production fab and test-and-assembly house: in A day in the fab you can pick any of the three, and the main story, The life of a chip, follows a made-up hearing-aid chip from the R&D line through the production fab to the test-and-assembly house. Walking from the office into the cleanroom always means putting on a cleanroom suit and passing the air shower, often several times a day; as the production fab's facilities engineer, you also go downstairs to the subfab. To spend a shift in the fab, tap "Clock in", choose "A day in the fab", then on the "Your role today" card tap "R&D line", "Production fab" or "Test-and-assembly house", swipe to the job, and tap an area if the job has them. How an R&D line differs from a production fab: How is an R&D line different from a production fab? What the air shower and the subfab look like inside: Chip fab machines, taken apart. The companies, people, tool IDs and figures in the game are fictional; what a fab is and what is inside one come from public, general sources. For other jargon, see Chip fab jargon in plain English.