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Chip fab machines, taken apart

25 machines, in the order a wafer meets them

Chips are made one machine at a time. Every machine below is one you meet in the fab24hr game, and the text is the same as in the game's "Take it apart" view. Press "Take it apart" to open its 3D model in your browser: it assembles, comes apart, and you read about each part; then press "See it work" to watch one full run. It works on phones too.

OHT · stocker · Air shower · Cluster tool · Batch wet bench · Spin clean chamber · Vertical furnace · CVD chamber · PVD chamber · Coater/developer · Scanner · Plasma etch chamber · Ion implanter · Chemical mechanical polishing · Measuring electron microscope · Subfab · Gas cabinet · Wafer prober · Wafer dicing saw · Die bonder · Wire bonder · Molding machine · X-ray inspection · Final test · Reliability oven

OHT

AMHS · Transport

In the fab, wafer pods mostly aren't pushed around by people: a whole network of track hangs under the ceiling, and OHT vehicles hang from it and run along it, carrying pods from one tool to the next, or to places like a stocker. Right above a tool, the OHT lowers the pod on belts and sets it on the tool's load port. The model shows a stretch of track, one OHT and the front of one tool.

Take it apart · See it work → · Read more: How do wafers move around a fab? FOUPs and the overhead hoist transport

stocker

STOCKER · Transport

While a wafer pod waits between two steps for a tool, it's kept for a while in an automated store like this one. Inside are shelves divided into slots, and in the middle a crane runs along the aisle, rising and lowering, and uses a fork to put pods into slots and take them out again. The OHT and people both drop off and pick up lots at the load ports. The system keeps track of which pod is in which slot and which tool it's waiting for. The enclosure turns see-through when the model is taken apart.

Take it apart · See it work → · Read more: How do wafers move around a fab? FOUPs and the overhead hoist transport

Air shower

AIR SHOWER · Entrance

A small room between the gowning room and the cleanroom. Once suited up, you walk in, and nozzles on both sides blast strong, clean air that blows some of the loose particles off the surface of your suit. The dust that comes off is drawn away by the return vents near the floor, goes through a filter and is blown out again. The two doors are interlocked, so they never open at the same time. Here the room's walls are see-through.

Take it apart · See it work → · Read more: What is a bunny suit, and why do chip fab workers wear one?

Cluster tool

COMMON · Skeleton

The wafer's trip begins at the pod on the front. A robot arm in the front-end module puts it into the load lock. Once that is pumped to vacuum, the arm in the transfer chamber in the middle carries it into one of the process chambers around it. When it's done, it goes back the same way to its pod. Etch tools and thin-film tools all share this "skeleton". What differs is what happens inside the process chambers.

Take it apart · See it work →

Batch wet bench

WET BENCH · Wet clean

Wet clean uses chemicals to wash wafers clean, removing organic matter, particles and the thin oxide layer on the surface. A batch tool cleans a whole batch at once (typically about 50 wafers): pods go on the load station on the left, a robot arm grips the whole batch and dips it into each chemical tank in turn, and after each chemical it goes into a rinse tank to be rinsed with pure water. Finally it's dried in the dryer and comes out on the right. When the tool comes apart, the enclosure turns see-through, the tanks slide apart to the left and right, and the plumbing cabinet drops lower.

Take it apart · See it work → · Read more: What is wafer cleaning, and why are wafers cleaned so many times?

Spin clean chamber

SINGLE WAFER CLEAN · Wet clean

The wafer lies flat on a spin chuck and is sprayed with chemicals from above as it turns; the chemical flung off is caught by the splash cups around it. Then it's rinsed clean with pure water, and finally the water stops and it spins at high speed under blowing nitrogen until it's dry. One wafer at a time: every wafer gets the same conditions, and it comes out cleaner than in a batch tank, but it's slower, so one tool often stacks several, even a dozen or more, of these chambers working together. Here a quarter of one chamber is cut away.

Take it apart · See it work → · Read more: What is wafer cleaning, and why are wafers cleaned so many times?

Vertical furnace

FURNACE · Thermal

An upright "oven": over a hundred wafers are stacked in a quartz boat that rises from below into a quartz tube, and the heater around it heats the tube to anywhere from a few hundred to over 1,000°C. Let oxygen in and an oxide layer grows on the wafer surfaces; pump it to low pressure and let in other gases, and films such as polysilicon and silicon nitride grow (low-pressure CVD). When the run is done, the boat lowers back into the loading area below, and a robot arm puts the wafers back into their pods. A quarter of the tube is cut away.

Take it apart · See it work → · Read more: What does a furnace do in a chip fab? Oxidation and annealing explained

CVD chamber

CVD · Thin film

CVD (chemical vapor deposition) "grows" a thin film on the wafer: gases shower evenly out of the showerhead above and react chemically on the heated wafer surface, leaving a solid layer behind, such as silicon oxide or silicon nitride. This kind gets help from a plasma (PECVD), so the film can grow without such high temperatures. Here a quarter of one process chamber is cut away.

Take it apart · See it work → · Read more: What is thin film deposition? How chips are built up layer by layer

PVD chamber

PVD · Thin film

PVD (physical vapor deposition) coats the wafer with a layer of metal (aluminum, copper, titanium and so on); in the fab it's usually called "sputtering". The chamber is pumped to high vacuum and a little argon is let in. The target gets a negative voltage of a few hundred volts, and the argon turns into plasma. Argon ions are pulled into the target and knock metal atoms loose like billiard balls; the atoms land on the wafer below and build up into a film. Behind the target, a rotating plate of magnets keeps the plasma close to the target's surface. Here a quarter of one chamber is cut away.

Take it apart · See it work → · Read more: What is thin film deposition? How chips are built up layer by layer

Coater/developer

TRACK · Litho

In the coater/developer, a wafer is first coated with photoresist and baked, then sent out the far end into the scanner. When it comes back from exposure, it's baked again and soaked in developer to bring out the pattern. The two tools are joined into one line, with wafers running through one after another. The lights in the lithography area are yellow because photoresist is sensitive to blue and ultraviolet light. Real tools have more modules, stacked higher; here it's simplified to two levels.

Take it apart · See it work → · Read more: What is photolithography? How do chip patterns get printed?

Scanner

SCANNER · Litho

The most expensive tool in lithography. Laser light passes through the illumination system and becomes a long, thin strip of light that shines through the photomask. The projection lens below shrinks the pattern on the mask (typically by 4 times) and projects it onto the photoresist on the wafer. During exposure, the mask and the wafer travel in opposite directions at the same time, so the strip of light sweeps across one whole field; then it's on to the next field. Each wafer needs anywhere from a few dozen to over a hundred fields. The most advanced tools use extreme ultraviolet light, with mirrors instead of lenses and the whole tool under vacuum. The model is not to scale.

Take it apart · See it work → · Read more: What is photolithography? How do chip patterns get printed?

Plasma etch chamber

ETCH · Etch

Etching removes the parts of the wafer that are not covered by photoresist. The chamber is pumped to vacuum and gas is let in, and the coil on top turns the gas into plasma. The electrode underneath adds a voltage that pulls the ions in the plasma downward so they strike the wafer straight on, digging deep, straight holes or trenches. Here a quarter of one process chamber is cut away.

Take it apart · See it work → · Read more: What is etching? How are dry and wet etching different?

Ion implanter

IMPLANT · Doping

Transistors only work once a tiny amount of boron, phosphorus or arsenic is added to the silicon (doping). The implanter turns a gas containing these atoms into ions and pulls them into an ion beam with an electric field. The analyzer magnet bends the beam, and only ions of the right mass make the turn. Then they're accelerated, swept across, and driven evenly into the wafer surface. How many go in depends on the current and the time; how deep, on the voltage. The model leaves out the vacuum pipes: the purple line is the ion beam, and it's not to scale.

Take it apart · See it work → · Read more: What is ion implantation, and how does a fab shoot atoms into silicon?

Chemical mechanical polishing

CMP · Planarization

CMP is like sanding a surface flat, except the sandpaper is a polishing pad, the sand is the fine grains in the slurry, and chemicals soften the surface so it polishes more easily. The polishing head grips the wafer and presses its front side against a spinning pad, and the wafer is polished on three discs in turn. Afterward it goes to the cleaning section on the right to be scrubbed, rinsed and spun dry before it returns to its pod: wet slurry must never leave the tool. This is called "dry in, dry out."

Take it apart · See it work → · Read more: What is CMP, and why do wafers need to be polished flat?

Measuring electron microscope

CD-SEM · Metrology

After lithography and etch, a few wafers are pulled to check that the line width is right. The lines are only tens of nanometers wide, but the wavelength of light is several hundred nanometers, too coarse to see them clearly, so electrons are used instead. An electron gun fires electrons, magnetic lenses squeeze them into a tiny spot, scan coils sweep the spot back and forth, and a detector turns the electrons that bounce off into a black-and-white image. The line width is measured from that image. The whole thing must be under vacuum and protected from vibration. Here the column and the vacuum chamber have a section cut away.

Take it apart · See it work → · Read more: How does a chip fab know each step went right? Metrology vs inspection

Subfab

SUBFAB · The level under the tools

The tool you see in the cleanroom is only half of it. Below the floor is a whole other level: here each tool has its own vacuum pumps, exhaust treatment unit and chiller, and some even keep their power racks downstairs. Cooling water, pure water, dry air and nitrogen also come up through the floor from here. The people on this level look after water, power and gases, so the tools can run. Here the equipment under one tool is spread out around it.

Take it apart · See it work →

Gas cabinet

GAS CABINET · Subfab

Specialty gases that are toxic, flammable or corrosive are shut away cylinder by cylinder in steel cabinets like this one. The cabinet is always under exhaust and has a detector inside. Gas leaving a cylinder passes through a whole gas panel that lowers its pressure and controls it, then goes out through a line to a valve box that branches it out to each tool. Here the cabinet door is see-through.

Take it apart · See it work → · Read more: What does a fab facilities engineer do?

Wafer prober

PROBER · Assembly & test

Once a wafer is finished, and before it's cut apart, every die on it is tested. The prober handles the wafers and the positioning: the chuck raises the wafer so the fine needles on the probe card land exactly on a die's metal pads. The test head above and the tester behind send signals in and check the response. Good and bad are recorded on a wafer map, and bad dies aren't packaged after the wafer is cut. Often each wafer is also tested once at a high temperature and once at a low one.

Take it apart · See it work → · Read more: How are chips tested, and how is wafer sort (CP) different from final test (FT)?

Wafer dicing saw

DICING SAW · Assembly & test

After testing, the wafer gets a sheet of tape on its back, stretched inside a metal frame, and goes into the dicing saw. A camera first finds the scribe lines between the dies. The spindle spins a very thin diamond blade at high speed, and a table carries the wafer back and forth under it, cutting through the wafer one line at a time. The tape is not cut through, so the separated dies stay neatly stuck in place. Afterward the wafer is washed and blown dry. Lasers are also used for cutting. The parts around the blade are enlarged in the model.

Take it apart · See it work → · Read more: What is chip packaging, and why does a finished chip still need a package?

Die bonder

DIE BONDER · Assembly & test

The cut wafer is still stuck to its tape. Going by the wafer test results, the die bonder picks only the good chips: an ejector pin underneath pushes one chip up, a pickup nozzle above lifts it away with suction and carries it to a spot on the board where glue has already been dispensed, then presses it there so it sticks. Chip after chip, and when the whole strip is done, it goes off to be baked so the glue hardens. The area around the work table is enlarged in the model.

Take it apart · See it work → · Read more: What is chip packaging, and why does a finished chip still need a package?

Wire bonder

WIRE BONDER · Assembly & test

Once the cut dies are glued onto a lead frame, very fine metal wire connects the metal pads on each chip to the leads outside, so electricity can get in and out. The capillary at the tip of the bond head first presses a tiny ball onto a pad, draws a loop of wire over to a lead and presses it off there, using heat, pressure and ultrasonic vibration. It can bond more than ten wires a second. The parts around the bond head are greatly enlarged in the model.

Take it apart · See it work → · Read more: What is wire bonding, and how does a chip connect to the outside?

Molding machine

MOLDING · Assembly & test

The whole wire-bonded board strip goes into a hot mold, and the top and bottom halves close and clamp it tight. A pellet of molding plastic in the pot softens in the heat, and a plunger pushes it upward, squeezing it along narrow runners into every cavity until the chips and wires are completely covered. Once it has set firm in the mold, the mold opens and the strip comes out; it then goes into an oven for a while to harden completely, and after that it's cut into single modules.

Take it apart · See it work → · Read more: What is chip packaging, and why does a finished chip still need a package?

X-ray inspection

X-RAY · Assembly & test

You can't see inside a sealed module from the outside. X-rays pass through plastic, but metal blocks some of them. Send X-rays up through the module from below, catch them with the detector above, and you get a black-and-white image that shows the fine wires: whether any have been pushed out of place, whether any are touching. The cabinet walls have lead sheets inside, and X-rays come on only when the door is closed and locked.

Take it apart · See it work → · Read more: What is chip packaging, and why does a finished chip still need a package?

Final test

FINAL TEST · Assembly & test

Once modules are sealed and cut, each whole module is tested again. The handler's arm places the modules one at a time into the test socket and presses them in (many machines place several at once and test them together to save time), so every pin touches a tiny probe beneath it; the test head below and the tester behind send signals in and measure the response. After testing, modules are sorted by result: good ones into one tray, bad ones into different trays by the reason they failed.

Take it apart · See it work → · Read more: How are chips tested, and how is wafer sort (CP) different from final test (FT)?

Reliability oven

RELIABILITY · Assembly & test

Some modules are sampled before shipping, plugged into burn-in boards and slid into the oven. The door closes and the heat goes up; the modules bake while running under voltage, for several days straight, so they "age" a little faster, to see whether any fail. How many fail by the end shows whether this batch's "fails when brand new" stretch (the far left end of the bathtub curve) is high.

Take it apart · See it work → · Read more: What is burn-in, and why are chips "burned in" before they ship?

In the classroom

Each "Take it apart" link opens that machine directly, so you can put it in a handout, a slide or a course page and students land on it without hunting through the game. In the game, the codex has a "Machines" page too. A lesson for each of the seven process areas is in fab24hr in the classroom.

What's real and what's simplified

The structure and movements follow public textbooks and university course notes and show only the general shape; sizes, numbers and parts are simplified. They are not any manufacturer's machines and are not operating training. Where the content comes from is explained under "Where this comes from" on the About page.

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