Micron manufactures memory — Here's how
Memory chips are integrated circuits with various components (transistors, resistors, and capacitors) formed on the same chip. These integrated circuits begin as silicon, which is basically extracted from sand. Turning silicon into memory chips is an exacting, meticulous procedure involving engineers, metallurgists, chemists and physicists.
Memory is produced in a very large facility called a fab, which contains many cleanroom environments. Semiconductor memory chips are manufactured in cleanroom environments because the circuitry is so small that even tiny bits of dust can damage it. Micron's Boise facility covers over 1.8 million square feet and has class 1 and class 10 cleanrooms. In a class 1 cleanroom, there is no more than 1 particle of dust in a cubic foot of air. In comparison, a clean, modern hospital has about 10,000 dust particles per cubic foot of air. The air inside a cleanroom is filtered and recirculated continuously, and employees wear special clothing such as dust-free gowns, caps, and masks to help keep the air particle-free. This special clothing is commonly referred to as a bunny suit.
The first step from silicon to integrated circuit is the creation of a pure, single-crystal cylinder, or ingot, of silicon six to eight inches in diameter. These cylinders are sliced into thin, highly polished wafers less than one-fortieth of an inch thick. Micron uses six- and twelve-inch wafers in its fabrication processes. The circuit elements (transistors, resistors, and capacitors) are built in layers onto the silicon wafer.
Most chip designs are developed with the help of computer systems or computer-aided design (CAD) systems. Circuits are developed, tested by simulation, and perfected on computer systems before they are actually built. When the design is complete, glass photomasks are made—one mask for each layer of the circuit. These glass photomasks are used in a process called photolithography.
In the sterile cleanroom environment, the wafers are exposed to a multiple-step photolithography process that is repeated once for each mask required by the circuit. Each mask defines different parts of a transistor, capacitor, resistor, or connector composing the complete integrated circuit and defines the circuitry pattern for each layer on which the device is fabricated.