Semiconductor device fabrication facts for kids

A special clean room where computer chips are made.

Making computer chips is the process used to build semiconductor devices. These are tiny electronic parts, usually integrated circuits (ICs), which are the brains of everyday electrical and electronic devices. Think of them as the tiny engines inside your computer, phone, or even your smart fridge!

These chips are made on thin, round slices called wafers, usually from super pure silicon. The process involves many steps, like using light to draw patterns (called photolithography) and adding or removing tiny layers of material. It's like building a super tiny city, layer by layer, on the wafer.

This whole process happens in very special factories called "fabs" or "foundries." The most important part of a fab is the "clean room." This room is kept incredibly clean, much cleaner than a hospital operating room! This is because even a tiny speck of dust can ruin a chip. Making advanced chips can take many weeks, and the whole process is often done by robots in a sealed, clean environment to make sure as many chips as possible work perfectly. Wafers travel in special sealed boxes called FOUPs, which also have a super clean inside.

How Small Can Chips Get?

Every new way of making chips has rules about how small the parts can be and how close they can be to each other. When parts get smaller, more of them can fit on a chip. This means chips can become more powerful, use less energy, and cost less to make.

For a long time, new chip-making methods were named after the smallest part they could make, measured in nanometers. A nanometer is super tiny – about 100,000 times smaller than a human hair! So, you might hear about a "90 nm process" or a "7 nm process."

However, these numbers aren't always the actual size of the smallest part anymore. They've become more like names for new generations of technology. For example, one company's "10 nm" chip might be similar in size and power to another company's "7 nm" chip. It's a bit like how different car models have different names, even if they're similar in size.

A Brief History of Chip Making

Making computer chips has come a long way!

The Start of Modern Chips

A very important type of chip technology called CMOS was invented in 1963. Companies like RCA started using CMOS chips in their products in the late 1960s. Back then, the parts on the chips were much bigger, around 20 micrometers (which is 20,000 nanometers!). Over time, they got smaller and smaller.

Chip manufacturing started in places like Texas and California in the 1960s. Now, it's a huge global business!

Chips Today

Today, big chip makers like Samsung Electronics, Intel, and TSMC have factories all over the world. Some companies, like Qualcomm and Broadcom, design chips but don't make them themselves. They pay other companies, like TSMC, to do the manufacturing.

Chip technology keeps getting smaller and more powerful. As of 2019, companies were making chips with parts as small as 14 nm, 10 nm, and even 7 nm. Some companies have even started making 5 nm chips, and plans for 3 nm chips are in the works! This constant shrinking of parts allows our electronic devices to become faster and more powerful every year.

How Chips Are Made: Step-by-Step

Making a computer chip involves many steps, repeated over and over. Here's a simplified look at some of the main things that happen:

• Wafer Processing: This is where the magic happens on the silicon wafer.

* Cleaning: Wafers are cleaned super carefully using special liquids and pure water. * Drawing Patterns (Photolithography): * A special liquid called "photoresist" is put on the wafer. * Light is shined through a "mask" (like a stencil) onto the photoresist. This light changes the photoresist where it hits. * A liquid developer then washes away the parts of the photoresist that were exposed (or not exposed, depending on the type). This leaves a pattern on the wafer. * Adding Materials (Deposition): New layers of different materials are added to the wafer. This can be done in many ways, like: * Chemical vapor deposition (CVD) * Atomic layer deposition (ALD) * Physical vapor deposition (PVD) * Changing Electrical Properties (Ion Implantation): Tiny particles called "ions" are shot into the wafer. This changes how well different parts of the silicon conduct electricity, creating the parts of the transistor. * Removing Materials (Etching): Parts of the wafer are removed using special chemicals or gases. This helps shape the tiny parts of the chip. * Heating (Thermal Treatments): Wafers are heated to very high temperatures to make the materials stronger or to activate the changes made by ion implantation. * Polishing (Chemical-mechanical polishing): The wafer surface is made perfectly flat and smooth. * Testing (Wafer Testing): Before the chips are cut, they are tested to make sure they work. Any bad chips are marked.

• Preparing the Chips (Die Preparation):

* The wafer is made thinner. * The wafer is then cut into individual chips, called "dies."

• Packaging the Chips (IC Packaging):

* Each good chip is attached to a small frame. * Tiny wires are connected from the chip to the pins on the package. These pins will connect the chip to other parts of an electronic device. * The chip is then sealed in a plastic or ceramic case to protect it.

• Final Testing (IC Testing): The packaged chips are tested again to make sure they still work perfectly after being put into their cases.

How much smaller computer chip parts have become over time, compared to other tiny things.

Keeping Chips Clean and Perfect

Making chips requires an incredibly clean environment. Even a tiny speck of dust can cause a chip to fail.

The Cleanroom Environment

• Super Filtered Air: Factories are filled with air that's filtered to remove even the smallest particles. Giant fans on the ceiling constantly push clean air down, sweeping any dust to the floor.
• Special Suits: Workers wear special "cleanroom suits" that cover them from head to toe. This is to stop tiny bits of skin or hair from falling onto the chips. Even with these suits, people still create dust, so robots do most of the work in the cleanest areas.
• Sealed Boxes: Wafers are moved around in special sealed boxes (FOUPs) that keep them safe from the air in the cleanroom, making sure they stay super clean.

All these steps help make sure that as many chips as possible work correctly.

What Are Wafers?

A wafer is the thin, round slice of material on which computer chips are built. Most wafers are made from super pure silicon. This silicon is grown into large, crystal cylinders, like a giant sausage, up to 300 mm (almost 12 inches) wide. These cylinders are then sliced into very thin wafers, about as thick as a fingernail, and polished to be incredibly smooth and flat.

How Chips Are Built: The Main Steps

Making a chip involves four main types of processes:

• Adding Material (Deposition): This is when new layers of material are grown or coated onto the wafer. Think of it like painting a new layer on a canvas.
• Removing Material (Removal): This is when parts of the material are taken off the wafer. This can be done by etching (using chemicals or gases) or by polishing.
• Creating Patterns (Patterning): This is like drawing the design for the chip. It usually involves lithography, where light is used to create patterns on the wafer.
• Changing Electrical Properties (Modification): This involves making parts of the chip conduct electricity differently. This is often done by adding tiny amounts of other elements (called "doping") or by heating the wafer.

Modern chips can have many layers, sometimes more than eleven, and involve hundreds of individual steps!

Building the Transistors (FEOL)

The first part of making a chip is called "Front-End-of-Line" (FEOL) processing. This is where the tiny transistors, which are the basic switches of a computer chip, are built directly into the silicon wafer. Sometimes, special tricks are used to make these transistors work even better, like adding a layer of silicon-germanium to improve how electricity flows.

Connecting the Transistors (BEOL)

Once the transistors are built, they need to be connected to each other to form the complete electronic circuits. This is called "Back-End-of-Line" (BEOL) processing.

• Metal Layers: This involves creating tiny metal wires that connect the transistors. These wires are separated by layers of insulating material, like glass.
• Connecting Wires: Historically, these wires were made of aluminum. Now, copper is often used because it conducts electricity better and faster. Tiny holes, called "vias," are made in the insulating layers to connect wires on different levels.

As chips get more complex, with many layers of wires, it's super important to keep each layer perfectly flat. This is done using polishing techniques.

Testing the Chips

After all the manufacturing steps, the chips are tested thoroughly.

Testing on the Wafer

The chips are tested while they are still on the wafer. A special machine uses tiny probes to touch each chip and check if it works. If a chip doesn't work, it might be marked with a tiny dot of ink. This helps save money because only the good chips will be packaged.

Final Testing

After the good chips are cut from the wafer and put into their protective packages, they are tested again. This makes sure they weren't damaged during packaging and that all the connections are correct. The chip's name and numbers are then etched onto its package.

How Many Chips Work? (Yield)

The "yield" is the percentage of chips on a wafer that work correctly. Manufacturers want this number to be as high as possible. If the yield is low, it means many chips failed, and the cost of the working chips goes up because they have to cover the cost of the failed ones.

• Contamination: Dust particles are a big problem. Even a particle 1/5 the size of a chip's feature can cause it to fail! That's why cleanrooms are so important.
• Process Variation: Sometimes, tiny differences in the manufacturing process can cause chips to fail.
• Chip Size: Smaller chips generally have a higher chance of working because there's less area for a defect to occur.

Engineers use special tools to inspect wafers during the process to predict if too many chips will fail. If so, the wafer might be stopped early to save money.

Hazardous Materials in Chip Making

Making computer chips uses many strong and sometimes dangerous chemicals. These include:

• Poisonous elements like arsenic and phosphorus.
• Highly reactive liquids like hydrofluoric acid.

It's very important that workers are not directly exposed to these materials. Factories use a lot of automation (robots!) to keep workers safe. They also have special systems to clean the air and water that leave the factory, protecting both workers and the environment.

See also

In Spanish: Fabricación de circuitos integrados para niños