Thermal oxidation

The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it.

Thermal oxide incorporates silicon consumed from the substrate and oxygen supplied from the ambient.

According to the commonly used Deal-Grove model, the time τ required to grow an oxide of thickness Xo, at a constant temperature, on a bare silicon surface, is: where the constants A and B relate to properties of the reaction and the oxide layer, respectively.

This model has further been adapted to account for self-limiting oxidation processes, as used for the fabrication and morphological design of Si nanowires and other nanostructures.

Solving the quadratic equation for Xo yields: Most thermal oxidation is performed in furnaces, at temperatures between 800 and 1200 °C.

A single furnace accepts many wafers at the same time, in a specially designed quartz rack (called a "boat").

Historically, the boat entered the oxidation chamber from the side (this design is called "horizontal"), and held the wafers vertically, beside each other.

However, many modern designs hold the wafers horizontally, above and below each other, and load them into the oxidation chamber from below.

Chlorine is often introduced by adding hydrogen chloride or trichloroethylene to the oxidizing medium.

This redistribution is governed by the segregation coefficient, which determines how strongly the oxide absorbs or rejects the dopant, and the diffusivity.