Silicon
Purifying to electronic-grade polysilicon.
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At a glance
Inputs
- Metallurgical-grade silicon
- Hydrogen chloride / chlorine
- Hydrogen
Outputs
- Electronic-grade polysilicon (9N+)
What is it?
The refinement of metallurgical-grade silicon into electronic-grade silicon (EGS) — polycrystalline silicon pure to better than 99.9999999% ("nine nines", 9N).
Why is it needed?
Semiconductor devices depend on precisely controlled doping at parts-per-billion levels. Any uncontrolled impurity swamps the intentional dopants and ruins device behaviour.
How does it work?
The dominant route is the Siemens process: MGS is converted to trichlorosilane gas, distilled to extreme purity, then decomposed onto heated silicon rods to grow high-purity polysilicon.
The result is electronic-grade polysilicon — pure, but polycrystalline (many small crystals), so it still is not a usable wafer.
Critical parameters
- Impurity concentration (ppb)
- Distillation efficiency
- Deposition temperature
Typical defects
- Residual donors/acceptors (B, P)
- Carbon and metal contamination
Equipment involved
- Distillation columns
- Siemens deposition reactors
Materials involved
- Trichlorosilane
- Hydrogen
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Related research
- Fluidized-bed reactor (granular polysilicon)
- Energy-efficient purification