7.3 Depositing metals and alloys
Metal layers are used extensively in device fabrication: to carry current for both power and signals, to apply the voltages that control transistors and generate forces for MEMS, as mirrors and optical coatings, and in magnetic devices for recording media. Different applications might require a continuous film, a long track, multiple thin layers or a plug filling a ‘via hole’ through to a buried layer. The electrical properties resulting from micro structure and composition must be controlled, diffusion into under- and overlying layers must be curbed, and uniformity is, as always, an issue.
To deposit a metal layer, there are several techniques to choose from.