Q. I have read that some computer chips being made today have millions of transistors on them. How is this possible?

Wednesday, August 27, 2014

A. The transistors on an IC are made by a process called “vapor deposition.”

In this process, the dopants that make the P- and N-type layers of the transistors are heated so that they vaporize. The vapors are mixed with hot gases and are introduced into a chamber holding the piece of silicon crystal which is to be the IC “chip”.

The surface of the silicon is coated with a material that can prevent the dopant vapor from affecting the silicon. But holes are formed in this coating by photographic methods. Where there are holes, the vapor “diffuses” into the silicon, kind of the way oil soaks into hard cement.

This allows selected parts of the surface ofthe silicon to become P- or N-type material. By repeating the process a number of times, the P and N layers for the transistors are built up.

The interconnections between them are made by depositing aluminum in strips, like the traces on a printed circuit board, but much, much smaller. When the circuit has been formed on the IC, it is coated with a layer of silicon dioxide, basically glass, which protects

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