Semiconductor exposure tools project a reduced image of the photomask, the original circuit pattern, onto the silicon wafer, which is coated in a photosensitive layer called a photoresist. Projecting the circuit pattern onto the photoresist leaves an image of the circuit on the photoresist in much the same way that illuminating light through a film negative leaves a latent image on photo printing paper. After exposure, the wafer is subjected to developing, etching, doping and other processes that leave just the circuit on the wafer. Developing involves the immersion of the wafers in developer to dissolve and remove unexposed, unnecessary photoresist, while etching removes the surface membrane of silicon dioxide through a chemical reaction, and doping adds conductive impurities through ion irradiation. This series of processes is repeated over 30 times to complete a single IC chip.
The diagram below shows the steps involved in manufacturing a simple transistor.