The front end of line (FEOL) is the first portion of IC fabrication where the individual components (transistors, capacitors, resistors, etc.) are patterned in a semiconductor substrate. FEOL generally covers everything up to (but not including) the deposition of metal interconnect layers.

Steps

For the CMOS process, FEOL contains all fabrication steps needed to form isolated CMOS elements: Finally, the surface is treated to prepare the contacts for the subsequent metallization. This concludes the FEOL process, that is, all devices have been built. Following these steps, the devices must be connected electrically as per the nets to build the electrical circuit. This is done in the back end of line (BEOL). BEOL is thus the second portion of IC fabrication where the individual devices are connected.