Shallow Trench Isolation (STI)

The purpose of device isolation is to isolate one electrically active region from the other. The performance of isolation is measured by the leakage current between the two regions. Figure 1 shows a top-down view of two silicon metal-oxide-semiconductor field effect transistors (MOSFET). The active regions (junctions) are surrounded by isolation (commonly referred to as field oxide, or FOX, as almost all isolation of silicon semiconductor devices consists of some form of silicon oxide). The gate conductors (often referred to simply as "gates") of these transistors straddle across the active regions and are usually surrounded by insulator material called spacers. The patterning of gates and spacers and formation of junctions, all essential parts of MOSFET fabrication, will not be discussed here. Instead, this essay will concentrate on isolation, specifically the most advanced isolation structure for ultra-large scale integration (ULSI) manufacturing of MOSFET today - shallow trench isolation (STI).