Trench depth measurement system for VLSI DRAM's capacitor cells using optical fiber and michelson interferometer

A simple method to precisely measure the trench depth of VLSI DRAM's capacitor cells is presented. The measurement system uses a Michelson interferometer and a white light source. The trench depth is transformed into the optical path difference between the central peak and one of sideband peaks produced during one-way scan of a mirror in a Michelson interferometer. The measurement error was within
\pm0.2 \mu
m for trench depths of
2-5 \mu
m. The multimode fiber used in the system facilitates wafer setup so that the system can be introduced into an in-process measurement system.