2.2 Oxidation

Thermal oxidation is the process of silicon dioxide (SiO₂) extraction from pure silicon (Si) as a result of a chemical reaction of silicon and oxygen (O₂). There can be distinguished between two production techniques

• dry oxidation: the silicon wafer is settled to a pure oxygen atmosphere at a temperature above 900^oC. At the surface of the wafer a chemical reaction
  

  $$\Longrightarrow$$ (2.23)

  
  
  takes place. Because of a very low oxidation velocity (< 100 nm/h), this method is often used to generate high quality thin oxide layers.
• wet oxidation: the silicon wafer is settled to a water vapor atmosphere and the reaction equation can be written as
  

  $$\Longrightarrow$$ (2.24)

  
  
  This process has a rather high oxidation velocity (> 20 nm/min) and is therefore often used to produce oxide layers for insulation and passivation techniques.

Both have in common, that the grown oxide consumes the necessary silicon from the wafer substrate itself, where the ratio between the thickness of consumed silicon to the thickness of the grown oxide is a factor of 0.44 (Fig. 2.2).

Figure 2.2: Oxide growth by thermal oxidation