Photolithography

Photolithography, also called optical lithography or UV lithography, is a process used in microfabrication to pattern parts on a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern to a photosensitive (that is, light-sensitive) chemical photoresist on the substrate. A series of Chemical processing step then either etches the exposure pattern into the material or enables deposition of a new material in the desired pattern upon the material underneath the photoresist. In complex integrated circuits, a CMOS wafer may go through the photolithographic cycle as many as 50 times.

Photolithography shares some fundamental principles with photography in that the pattern in the photoresist etching is created by exposing it to light, either with an optical mask or with a projected image using some form of micro mirror device chip or laser scanning. This procedure is comparable to a high precision version of the method used to make printed circuit boards. Subsequent stages in the process have more in common with etching than with lithographic printing. This method can create extremely small patterns, down to a few tens of nanometers in size. It provides precise control of the shape and size of the objects it creates and can create patterns over an entire surface cost-effectively. Its main disadvantages are that it requires a flat substrate to start with, it is not very effective at creating shapes that are not flat, and it can require extremely clean operating conditions. Photolithography is the standard method of printed circuit board (PCB) and microprocessor fabrication.