LOCOS, short for LOCal Oxidation of Silicon, is a

microfabrication Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as " semiconductor manufacturing ...

process where

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

is formed in selected areas on a silicon wafer having the Si-SiO₂ interface at a lower point than the rest of the silicon surface. As of 2008 it was largely superseded by

shallow trench isolation Shallow trench isolation (STI), also known as box isolation technique, is an integrated circuit feature which prevents electric current leakage between adjacent semiconductor device components. STI is generally used on CMOS process technology ...

. This technology was developed to insulate MOS transistors from each other and limit transistor cross-talk. The main goal is to create a

silicon oxide Silicon oxide may refer to either of the following: * Silicon dioxide or quartz, SiO2, very well characterized *Silicon monoxide Silicon monoxide is the chemical compound with the formula SiO where silicon is present in the oxidation state +2. In ...

insulating structure that penetrates under the surface of the wafer, so that the Si-SiO₂ interface occurs at a lower point than the rest of the silicon surface. This cannot be easily achieved by etching field oxide.

Thermal oxidation In microfabrication, thermal oxidation is a way to produce a thin layer of oxide (usually silicon dioxide) on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The ra ...

of selected regions surrounding transistors is used instead. The oxygen penetrates in depth of the wafer, reacts with silicon and transforms it into silicon oxide. In this way, an immersed structure is formed. For process design and analysis purposes, the oxidation of silicon surfaces can be modeled effectively using the Deal–Grove model.

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