How are computer chips made? The semiconductor manufacturing process, step by step

Computer chips are made like this: silicon from sand is refined until it is extremely pure and made into thin, round wafers; in a chip factory, called a fab, circuits are "printed" and "etched" onto the wafer one layer at a time, dozens of times over; then the chips are tested, cut apart, put into packages and tested again, and only the good ones ship. What gets built on the wafer is a huge number of tiny switches (transistors) and the wires that connect them. The whole road takes hundreds of steps, and the fab part alone takes weeks to months.

Below are the steps in order: what each one does and why. Each step has its own article for the details.

What are the steps of making a chip?

Order	Step	Where	What happens
1	Make the wafer	A wafer maker	Silicon is purified, grown into an ingot and sliced into wafers
2	Design and photomasks	A design company, a mask shop	The circuit is designed on computers and turned into a set of photomasks for printing it
3	Build the circuit layer by layer	The fab	Clean, oxidize, deposit film, litho, etch, implant, polish; repeated dozens of times
4	Wafer test	A test-and-assembly house or a test house	Every chip is tested once before the wafer is cut
5	Dicing and packaging	A test-and-assembly house	The wafer is cut into chips, and each one goes into a protective package
6	Final test	A test-and-assembly house	Each packaged chip is tested again; only the good ones ship
7	Into a product	The customer's assembly plant	Soldered onto circuit boards, built into phones and computers, into someone's hands

Steps 1 and 2 don't come one after the other: different places prepare them separately, and step 3 starts once both the wafers and the photomasks have reached the fab. The industry often calls step 3 the "front end" and steps 4 to 6 the "back end", or assembly and test.

Step 1: Where do wafers come from?

Sand and quartz are mostly silicon dioxide, which is silicon combined with oxygen (why silicon is used at all: What is a semiconductor?). First, carbon in a very hot furnace pulls the oxygen away, leaving silicon that is about 98 to 99 percent pure. Then chemical refining purifies it again and again: silicon for chips has to be at least 99.9999999 percent pure, which people call "nine nines".

Next it is melted. A small piece of silicon with its atoms lined up perfectly is dipped in as a seed, then pulled up slowly while it turns, and a long, round crystal grows, called an ingot. The ingot is sliced thin and polished mirror-flat, and that is a wafer. The most common size today is 30 cm (12 inches) across, and it is less than a millimeter thick. Why it's round: Why are wafers round?

Step 2: Why design the chip and make photomasks first?

Because the fab builds from a drawing. Engineers design the circuit on computers: which switches go where and how they connect, simulated and checked many times. When it's final, the design is handed over; this is called tape-out. The design is then made into a set of photomasks, one for each layer's pattern and often dozens in a set, like negatives for printing the circuit.

The same chip design is laid out across the whole wafer like a chessboard, so one wafer holds anywhere from dozens to more than ten thousand chips, all made at the same time (how a chip differs from a wafer: What is a chip?).

Step 3: What happens inside the fab?

When a lot, a batch of wafers, goes onto the production line, that is called a wafer start. From then on, the wafers go back and forth between these kinds of steps:

1. Wet clean: chemicals and ultrapure water wash off particles, organic residue and metals too small to see. Wafers are cleaned before and after almost every major step, so it is one of the most repeated steps. (What is wafer cleaning?)
2. Furnace (oxidation): more than a hundred wafers at a time go into a very hot tube, where the silicon surface grows a layer of silicon dioxide that doesn't conduct, or the heat puts atoms that were knocked out of place back in order. (What does a furnace do in a chip fab?)
3. Thin film: a new layer of material is laid on the wafer, insulating or conducting, usually just a few nanometers to a few hundred nanometers thick. (What is thin film deposition?)
4. Lithography: the wafer is coated with light-sensitive photoresist, exposed through a photomask and developed, which prints this layer's pattern. (What is photolithography?)
5. Etch: following the resist pattern, the material the resist doesn't cover is cut away, so the pattern is really built into the wafer. (What is etching?)
6. Ion implantation: atoms such as boron or phosphorus are shot into the silicon, deciding which small regions conduct and how well; areas that shouldn't be hit are covered with photoresist first. (What is ion implantation?)
7. CMP (polishing): every new layer leaves the surface uneven; once it's polished flat, the next layer's pattern prints sharply. (What is CMP?)

After important steps, a few wafers are pulled aside and measured: film thickness, line width, how well each layer lines up with the one below, and whether any extra particles landed. When a number drifts, work stops until someone finds out why (How does a chip fab know each step went right?). Each of these seven jobs has its own area in the fab: see What do the seven process areas of a chip fab do?

Why are the same steps repeated dozens of times?

Because a chip is like a tall building. The ground floor is the transistors, the switches, built into the silicon itself. Above them, layer after layer of very fine metal wires connect the switches, and the most advanced chips have more than ten of these layers.

Each layer has a different shape, so each one needs its own round: add a layer of material, print its pattern with litho, etch or implant through it, clean, polish flat, then move on to the next. Simple chips have around ten layers and complex ones have dozens. A wafer comes back to the litho area dozens of times, and it all adds up to hundreds of steps. Inside a fab, people also often split the work into two halves: building the transistors first, then the wiring.

Why are chips made in a cleanroom?

Because the lines on a chip are packed so tightly: on the most advanced chips, the densest lines sit only a few tens of nanometers apart. A speck of dust too small to see lands on the circuit like a boulder. It can break a line or join two lines together, and that chip is dead.

So chips are made in a cleanroom. Filtered air blows from the ceiling straight down, people wear a cleanroom suit that covers them head to toe, and wafers travel around the fab in sealed boxes. How clean it is: How clean is a cleanroom?

What happens after the wafer is finished?

The wafer leaves the fab for a test-and-assembly house (or a dedicated test house). From there, roughly:

1. Wafer test: before the wafer is cut, very fine needles touch the contacts of every chip, power it up and test it, and the good and bad chips are recorded as a wafer map. This is called wafer sort: bad chips are caught early, so no one pays to package them. (How are chips tested?)
2. Dicing: the wafer is ground thinner from the back, then cut along the narrow gaps between chips into separate pieces.
3. Packaging: a common way is to attach the chip to a small substrate, connect its contacts with metal wires thinner than a hair (What is wire bonding?), then seal everything in plastic. The package protects the thin, brittle chip, brings its contacts to the outside and helps it shed heat. (What is chip packaging?)
4. Final test: each packaged chip is tested again, because packaging can damage it too. Some products are also run powered at high temperature for a while before shipping, so the weak ones fail first and get caught. (What is burn-in?)
5. Shipping: the good parts often go into small pockets on a long tape wound onto a reel and travel to the customer's factory, where machines solder them onto circuit boards one by one. Then they go into products and into someone's hands.

How long does it take to make a chip?

Going from wafer start to a finished wafer usually takes weeks to months, and longer for more advanced chips with more layers (What is a wafer start?). Most of that time isn't spent being processed but waiting in line at the tools. The tools are expensive and every wafer stays in the line that long, which is why fabs run 24 hours a day (Why do chip fabs run 24 hours a day?). After the wafer is finished, assembly and test take more time before anything ships.

In fab24hr

fab24hr's main story, The life of a chip, follows a made-up hearing-aid chip, "Glowmere", along this whole road. In the prologue, "Tape-out", Glowmere's design goes to the fab and becomes a set of photomasks. Act one is on the R&D line, and chapter 2, "Station by Station", covers the first five days after wafer start: you follow the first 12 wafers through seven areas (wet clean, furnace, thin film, litho, etch, CMP and implant) and do one step by hand in each. In act two, at the production fab, you are the etch process engineer, and the hot lot H-2417, carrying Glowmere, is stuck in an etch tool. Act three, at the test-and-assembly house, runs from wafer test to the night before shipping. In the finale, the chip goes into a hearing aid and into Mr. Shen's hands. The page The life of a chip matches each stage to its chapter.

To spend a day in one area, tap "Clock in", choose "A day in the fab", then on the "Your role today" card tap "Production fab" or "R&D line", swipe to the job, and tap an area if the job has them. The companies, chip, people, lot numbers and figures in the game are fictional; how chips are made and why each step is done come from public, general sources. For other jargon, see Chip fab jargon in plain English.