What is TEOS?
As shown in the image, TEOS (Tetraethyl Orthosilicate) has the molecular formula Si(OC₂H₅)₄. It is an organosilicon compound commonly used as a silicon source in Low-Pressure Chemical Vapor Deposition (LPCVD) or Plasma-Enhanced Chemical Vapor Deposition (PECVD) to form silicon dioxide (SiO₂) thin films.
Reaction Equation of PECVD TEOS Process
The PECVD TEOS process follows this chemical reaction:
Si(OC2H5)4+O2→SiO2+volatile by-productsSi(OC₂H₅)₄ + O₂ \rightarrow SiO₂ + \text{volatile by-products}
This reaction occurs at around 400°C, making it ideal for low-temperature deposition.
Why Use TEOS for Thin Film Deposition?
- Replacement for Silane (SiH₄): TEOS is used as an alternative to silane in SiO₂ deposition.
- Better Step Coverage: TEOS provides excellent step coverage, enabling uniform deposition on complex surface features such as trenches and holes.
- Fewer Side Reactions: Compared to silane, TEOS results in fewer unwanted side reactions, improving the quality of the deposited film.
Doping in PECVD TEOS
The PECVD TEOS process can be used to create different types of silicon dioxide films, such as:
- USG (Undoped Silicate Glass): Pure SiO₂ without doping.
- PSG (Phosphosilicate Glass): SiO₂ doped with phosphorus.
- BPSG (Boron Phosphosilicate Glass): SiO₂ doped with both boron and phosphorus.
- FSG (Fluorosilicate Glass): SiO₂ doped with fluorine.
Doping is achieved by introducing the following precursors:
- Phosphorus Source: TMP (P(OCH₃)₃) or TEPO
- Boron-Phosphorus Source: TMB
- Fluorine Source: SiF₄ or FTES
These films are widely used in semiconductor manufacturing and microelectronics due to their excellent electrical and mechanical properties.
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