Photo Lithography Applying Photo Resist – scale: wafer level (mm / 12 inch) The liquid (blue here) that’s poured onto the wafer while it spins is a photo resist finish similar as the one known from film photography. The wafer spins during this step to allow very thin and even application of this photo resist layer. Exposure – scale: wafer level (mm / 12 inch) The photo resist finish is exposed to ultraviolet (UV) light. The chemical reaction triggered by that process step is similar to what happens to film material in a film camera the moment you press the shutter button. The photo resist finish that’s exposed to UV light will become soluble. The exposure is done using masks that act like stencils in this process step. When used with UV light, masks create the various circuit patterns on each layer of the microprocessor. A lens middle) reduces the mask’s image. So what gets printed on the wafer is typically four times smaller linearly than the mask’s pattern. Exposure – scale: transistor level ( 50-200nm) Although usually hundreds of microprocessors are built on a single wafer, this picture story will only focus on a small piece of a microprocessor from now on – on a transistor or parts thereof. A transistor acts as a switch, controlling the flow of electrical current in a computer chip. Intel researchers have developed transistors so small that about 30 million of them could fit on the head of a pin.