4.7 Applying metal/sputtering

We now put the wafer in a sputter deposition system . In the sputter system, we coat the entire surface of the wafer with a conductor. Analuminum-silicon alloy is usually used, although other metals are employed as well.

A sputtering system is shown schematically in . A sputtering system is a vacuum chamber, which after it is pumped out, is re-filled with a low-pressureargon gas. A high voltage ionizes the gas, and creates what is known as the Crookes dark space near the cathode, which in our case, consists of a metal target made out of themetal we want to deposit. Almost all of the potential of the high-voltage supply appears across the dark space. (The glowdischarge consists of argon ions and electrons which have been stripped off of them. Since there are about equal number of ionsand electrons, the net charge density is about zero, and hence by Gauss' law, so is the field.)