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[ The PC Guide | Systems and Components Reference Guide | The Processor | Processor Physical Characteristics | Processor Manufacturing ]

Semiconductor Materials and Wafer Manufacture

Processors are manufactured from semiconductor material. Semiconductors are materials that transmit electricity only under certain conditions, and therefore are ideal for making the ultra-small, high-speed transistors that implement the modern processor.

Only certain materials are suitable for use in semiconductors. To be suitable, the material must be (at the very least):

  • Able to be made into a semiconductor. A chemical process called "doping" is used to introduce small impurities into a pure material, which enables the material to act electrically as a semiconductor.
  • Able to be manufactured into large pieces of uniform composition and high quality.
  • Of the appropriate hardness so that it can be cut into thin slices without being so brittle that it cracks.
  • Readily available and relatively inexpensive, to ensure supply and keep costs down.

The most famous, and widely used material for semiconductors is of course silicon. It is used for processors, memory, and most other mainstream chips. Another popular material for use in semiconductors is gallium arsenide (GaAs), which is not nearly as widely encountered, and is generally used for specialty applications.

Silicon has several great advantages that make it ideal for use for semiconductors. Obviously it is a semiconductive material. It also has several manufacturing advantages that make it the material of choice: it is plentiful and hence cheap in its raw form (regular sand is silicon dioxide). But most importantly, it can be grown into large, uniform crystals. The first step in the manufacture of a chip is growing these large crystals of silicon. This is similar in concept to how you can grow sugar crystals in a cup of water, although of course, special techniques are used.

These crystals are very large--the common current size is 8 inches in diameter, and this will probably actually increase to 12 inches very soon! The larger the crystal, the more chips that can be manufactured at the same time, and the less waste material, thus saving money. Despite being made from a cheap raw material, these crystals are expensive due to the precise technology used to make them, and the extremely high quality standards required to make a crystal suitable for use in chip making. A single, high-quality crystal will be used to make many thousands of processors.

These large crystals are cut into wafers by high-precision saws. These thin slices of semiconductor material then undergo the process that transforms them into actual integrated circuits. Each crystal is cut into several hundred wafers, each less than 1 mm thick (one fortieth of an inch) and 8 inches in diameter. The thinner the wafers, the more that can be made from a single crystal, but the more fragile they are and the harder they are to manipulate. The wafers undergo several more steps before being ready for use, including precision polishing and chemical treatment.

Next: Logic Design

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