Introduction

The chemical reactions describing the thermal oxidation of silicon in oxygen or water vapor are given by the following equations:

Si(solid) + O₂ ® SiO₂ (solid) -------------------DRY OXIDATION

Si(solid) + 2H₂O ® SiO₂(solid) +2H₂ -----------WET OXIDATION

For growth of an oxide of thickness d, a layer of silicon with thickness of 0.44d is consumed. Oxidation proceeds by the diffusion of the oxidizing species through the oxide to the Si-SiO₂ interface, where the oxidation reaction occurs.

When bare silicon is exposed to the atmosphere, it reacts almost immediately with oxygen or moisture present in the air and forms a thin (about 10 to 20°A) layer of silicon dioxide, called the native oxide. The thickness of the native oxide is sufficient to stop further oxidation of the silicon at room temperature. [1]

Fig. 1 Silicon Oxidation Process [2]

Uses of silicon dioxide

• It serves as a mask against implant or diffusion of dopant into silicon. The thickness of the oxide needed to mask is about 500°A.

• It provides surface passivation.

• It is used to isolate one device from another.

• It is used as a gate dielectric for MOSFETs.

• It provides electrical isolation of multi-level metallization systems.

• Silicon oxide is used as a screen oxide for ion implantation process in order to prevent silicon contamination.[2] [1]