Jeff Roeder, age, 14, of Hamilton, Ohio, for his question:

HOW ARE INTEGRATED CIRCUITS MADE?

An integrated circuit is a tiny device that controls electric signals in such electronic equipment as computers and television sets. Many integrated circuits contain thousands of electronic parts on a paper thin chip of silicon. A chip may measure less than 0.15 square inch.

Silicon is a semiconductor, a material that can be doped or treated to control electric signals. Manufacturers use such substances as aluminum or boron as impurities to dope silicon.

A manufacturer.of an integrated circuit will begin with a wafer of silicon that has been doped with various impurities. The wafer measures from one to two inches in diameter.

A photographic process reduces a large master design for the circuit to microscopic size. Technicians use these microscopic designs to make hundreds of integrated circuit chips on one wafer.

A process called diffusion bakes more impurities into certain areas of the wafer, according to the designs.

After the wafer has been completed, a technician divides it into individual chips and adds wire connections to each one. The finished chips are mounted in ceramic, metal or plastic containers for installation in various kinds of electronic equipment.

The circuits may be tested by a computer to make sure they work properly.

An integrated circuit does many of the jobs performed by a conventional circuit, which consists of separate parts connected together. But integrated circuits are hundreds of times as small as conventional circuits and cost less to build and operate. They also work faster and more reliably.

Scientists developed integrated circuits during the early 1960s for guided missiles and satellites.

Integrated circuits enabled scientists to design more advanced computers than could be built with conventional circuits. The circuits also led to the development of electronic watches and pocket calculators as well.

The compact structure of an integrated circuit gives it many advantages over a conventional circuit. An integrated circuit, for example, works faster because electric signals travel shorter distances when going from one part of the circuit to another.

Integrated circuits also make electronic equipment more reliable and easier to service. These circuits have fewer connections that might fail.

In addition, a faulty part of a conventional circuit may be difficult to find and repair. If a part of an integrated circuit fails, a repairman simply replaces the entire circuit.