4. Spacers

A spacer is an important element in the structure of a CMOS transistor. It is used to protect the transistors' flanks during the manufacture of the sources and drains, and during the manufacture of the contact areas between the silicon and the first metal level. It is manufactured in two phases: the first corresponds to the deposition of a silicon nitride film, followed by anisotropic etching without a mask, leaving the film only on the transistors' walls, as shown in figure 11 . Spacers must be resistant to gas-phase and liquid-phase etching processes, to oxidizing treatments used, for example, to shrink resins, and sometimes to the gaseous phases of epitaxy processes used to raise sources and drains. The aim is...