10.1.7 Conductors and Resistors

In order to connect the single components of an integrated circuit metal interconnects must be produced. Metal layers, usually aluminum and copper, are deposited, patterned, and etched until the interconnect lines remain. The metal traces must be wide enough to avoid the problem of electro-migration which is the movement of atoms caused by current flow. When a certain amount of electro-migration occurs, the integrated circuit fails. Electro-migration can be avoided by keeping the peak current density under a certain threshold.

Although non-metallic conductors are generally worse conductors than metal, they are used as well. Poly-silicon, which is composed of lots of non-aligned, randomly oriented small silicon crystals is an example of a frequently used non-metallic conductor. The size of the small crystals it consists of is called grain size and determines its properties. Although poly-silicon consists of silicon atoms as does crystal silicon, its electrical characteristics are very different. Poly-silicon is a good conductor when heavily doped and a good resistor when lightly doped and it is often used for gates of field effect transistors and as an electrode for capacitors.