**3.1 Photolithography**

Photolithography is one of the earliest and still one of the most popular methods for fabricating LoCs. The photolithography and etching method for fabricating mask and LoCs relies on the traditional photo developing method. The process involves using negative or positive photoresists. Photoresists are exposed to high intensity UV-wavelengths through masks and spin coated. In photolithography, there are mask and mask-less methods. Mask-less photolithography can be achieved by methods whereby light is spatially modulated and light patterns can be manipulated at every pixel. In photolithography, before etching with chemicals, a UV resist can be used to spin coat chemicals and focused UV light can be beamed onto the photoresist [34].
