Introduction to photolithography
Photolithography is the process of using light to transfer a pattern to a substrate. It is typically used for rapid patterning of larger structures and areas.
The main types of lithography used to generate patterns for micro- and nanofabrication are photolithography and e-beam lithography . In photolithography, the pattern is transferred to the substrate by illuminating through a "mask". In all cases, the substrate should first be coated with a "resist" layer. Resist is a polymer that is sensitive to the radiation being used. In the case of photolithography, the polymer is sensitive to visible or UV-light. If the resist is "positive", it will be broken down into low molecular weight components by the radiation, and is then easily rinsed away during "development". There are also resists that become cross-linked by the radiation. In this case, rinsing leaves a pattern of crosslinked polymer that can't be rinsed away. Instead, the non-crosslinked part is rinsed away. This is referred to as a "negative resist". The principle is the same for e-beam lithography, but the polymers are now sensitive to electrons rather than UV-visible radiation, and the pattern is written directly into the resist. No mask is required.
The resolution limits of photolithography are in the range of the wavelength of the radiation used. In the Nanolab, we use standard wavelengths available from a mercury vapour lamp (ca 400nm-1). In practice, this means that it is mainly used to generate connecting circuits for e-beam generated nanostructures.
Introduction video - photolithography (external link)
For details of the projection camera, mask aligner, spin coaters, hot plates, resists, developers and other details, please refer to our technical site.