Shallow trench isolation (STI)
Beginner
Little trenches filled with glass that wall off each switch from its neighbors.
Novice
Trenches etched into the silicon around each transistor’s active area and filled with silicon dioxide, then polished flat. They stop current leaking between neighboring transistors.
Expert
Pad oxide and nitride hard mask, trench etch, liner oxide, oxide fill, CMP stopping on the nitride, nitride strip. Replaced LOCOS around 250 nm because it doesn’t encroach on the active area.
Explained in Making them (Transistors).
See also: Chemical-mechanical polishing (CMP), FEOL and BEOL.