Tiny highways

Once the electronic components have been fabricated in the silicon, thin metallic and doped polysilicon films are added to form the interconnections among individual transistors and other devices. On some IBM logic chips, there may be up to six layers of these minute interconnecting wires joining together over four million circuits. A protective coating of polysilicon is then deposited on the wafers to protect the chips from moisture, corrosion, and atmospheric contamination.

A close up view

Low-angle scanning electron micrograph of a portion of a partially completed SRAM array containing six-device memory cells. The insulating oxide films have been removed, revealing the lower levels of the interconnection structure of the array.

The word lines (colored green) are salicided polysilicon lines (running horizontally). The local interconnections (tungsten; colored pink) provide cross-coupling for the n+ and p+ diffusion contacts and act as the lower portions of the contact studs to the first global interconnection level Ti/A1(Cu)/Ti/TiN; (colored yellow). The contact studs (tungsten; colored grey) constitute the upper portions of the contact paths to the global interconnections.