An Introduction to mems (Micro-electromechanical Systems)
tải về 1.48 Mb. Chế độ xem pdf
|
| 3.1 Photolithography
Photolithography is the photographic technique to transfer copies of a master pattern, usually a circuit layout in IC applications, onto the surface of a substrate of some material (usually a silicon wafer).
The substrate is covered with a thin film of some material, usually silicon dioxide (SiO 2 ), in
the case of silicon wafers, on which a pattern of holes will be formed (Figure 17). A thin layer of an organic polymer, which is sensitive to ultraviolet radiation, is then deposited on the oxide layer; this is called a photoresist. A photomask, consisting of a glass plate (transparent) coated with a chromium pattern (opaque), is then placed in contact with the photoresist coated surface. The wafer is exposed to the ultraviolet radiation transferring the pattern on the mask to the photoresist which is then developed in a way very similar to the process used for developing photographic films. The radiation causes a chemical reaction in the exposed areas of the photoresist of which there are two types; positive and negative. Positive photoresist is strengthened by UV radiation whereas negative photoresists are
|