Imprint the electronic circuit design onto the wafers through a process known as photolithography. First, wafers are coated with photosensitive chemicals that harden when exposed to UV light. In sealed dark rooms light is shone through the image of the design through a miniaturising lens and on to the coated wafer. When the chemical is washed off the design remains. The wafers are built up layer by layer, repeating the photo etching process in each new layer. Some layers are cooked, some layers ionised by plasma, and some are baked in metal. Each treatment changes the properties for that layer.