Oxygen concentration in silicon (Oi) converter
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KEY POINTS
Interstitial oxygen in CZ silicon is found by multiplying the FTIR absorption coefficient at 1107 cm⁻¹ by a conversion factor, but the factor differs by standard: Old ASTM is about twice New ASTM, and New ASTM is about 1.6 times JEIDA. When someone quotes "15 ppma oxygen," always check which standard it uses.
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The absorption coefficient α is the measured quantity and does not depend on the standard. The table below converts the same α with each standard's coefficient; when comparing specifications, convert back to α first and then reinterpret.
Conversion by standard (same sample)
| Standard | Coefficient K (atoms/cm³ per cm⁻¹) | atoms/cm³ | ppma | |
|---|---|---|---|---|
| New ASTM (ASTM F121-83) | 4.81×10¹⁷ | 7.492×10¹⁷ | 15.00 | ← Reference |
| Old ASTM (ASTM F121-79) | 9.63×10¹⁷ | 1.500×10¹⁸ | 30.03 | |
| JEIDA | 3.03×10¹⁷ | 4.720×10¹⁷ | 9.45 | |
| IOC-88 (SEMI MF1188) | 3.14×10¹⁷ | 4.891×10¹⁷ | 9.79 | |
| DIN 50438 | 2.45×10¹⁷ | 3.816×10¹⁷ | 7.64 |
Why wafer oxygen concentration matters
Czochralski (CZ) silicon contains roughly 10¹⁷ to 10¹⁸ atoms/cm³ of interstitial oxygen dissolved from the quartz crucible. Heat treatment turns this oxygen into precipitates (BMDs) that act as gettering sites for metal impurities inside the wafer, but too much oxygen also creates defects in the device region near the surface. Interstitial oxygen also pins dislocations, strengthening the wafer and preventing slip during heat treatment.
Oxygen concentration is measured by FTIR absorption at 1107 cm⁻¹, but the coefficient converting absorption to concentration differs by standard: Old ASTM is about twice New ASTM, and New ASTM is about 1.6 times JEIDA. Whenever someone quotes "15 ppma oxygen," always confirm which standard the value is based on.
FAQ
Why do oxygen values differ between specifications?
Each standard uses a different coefficient to turn the measured FTIR absorption into concentration, so the same wafer gives different ppma values.
Why does wafer oxygen matter?
Oxygen precipitates act as gettering sites for metal contamination and interstitial oxygen strengthens the wafer, but too much oxygen creates defects near the device surface.
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Last updated: October 23, 2026