Optical lithography

In many applications such as micro- and nano-electronics, -photonics, -mechanics, and –fluidics, one of the most important fabrication processes is lithography, which is used to produce the desired pattern (to be deposited or removed) on the surface of a substrate. Lithography uses resist materials (photoresists, polymers, etc.) to cover areas on the wafer that will not be subjected to material deposition or removal.

Optical Lithography refers to a lithographic process that uses visible or ultraviolet light to form patterns on the photoresist through printing. Printing is the process of projecting the image of the patterns onto the wafer surface using a light source and a photo mask.  There are three types of printing - contact, proximity, and projection printing. Equipment used for printing are known as printers or aligners. (source: siliconfareast.com)

Patterned masks, usually composed of glass or chromium, are used during printing to cover areas of the photoresist layer that shouldn't get exposed to light.  Development of the photoresist in a developer solution after its exposure to light produces a resist pattern on the wafer, which defines which areas of the wafer are exposed for material deposition or removal.

Optical lithography offers very fast and reproducible results. However, the minimum line width that can be achieved with standard contact lithography is around 1 µm.

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