Back End Variability

The back end of the IC fabrication process refers to the steps which form the interconnect or wiring for the circuit, as well as any passive devices such as integrated inductors or capacitors formed within the interconnect process layers. Because the back end process shares many technologies and tools with the front end, many of the variations affecting the front end are also operative here, particularly those related to lithography and etch. In addition, a number of process technologies are used heavily in the back end, such as copper electroplating and chemical-mechanical polishing, which generate additional types and sources of variation. The key impacts we are concerned with here are variations in the final interconnect or backend components of the chip, including variations in the geometry of the structures formed, and in the material properties of these structures.