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sccm to kg/hr conversion in semiconductor processes

Practical guide to converting between volumetric (sccm) and mass flow (kg/hr) units for process recipes.

By Semiconductor Tools Editorial Team · Last updated: 2026-06-14

Process recipes in semiconductor manufacturing are often authored in sccm because MFCs are volumetric devices at standard conditions. Cost tracking, bulk gas inventory, chemical consumption audits, and cross-facility mass-balance models frequently require kg/hr. Converting correctly requires the gas-specific density at the same standard used by the MFC calibration.

Conversion chain

The conversion proceeds in two steps:

  1. Volumetric flow (L/min) = sccm ÷ 1000
  2. Mass flow (g/min) = L/min × ρSTP (g/L); then kg/hr = g/min × 0.06

ṁ [kg/hr] = (sccm / 1000) × ρ [g/L] × 0.06

ρSTP values on this site come from NIST Chemistry WebBook data: N₂ 1.2506 g/L, Ar 1.784 g/L, O₂ 1.429 g/L, H₂ 0.0899 g/L, He 0.1786 g/L.

Worked example — CVD silane carrier gas audit with MFC Gas Flow Unit Converter

A LPCVD process runs N₂ carrier at 800 sccm for 120 minutes per lot. You need hourly N₂ mass consumption for environmental reporting.

  1. In the converter: Flow Value 800, gas N2, From: sccm, To: kg/hr.
  2. Result: ≈ 0.0600 kg/hr (800 × 0.001 × 1.2506 × 0.06).
  3. For a 2-hour run: 0.0600 × 2 = 0.120 kg N₂ per lot.
  4. Compare with H₂ at the same 800 sccm: switch gas to H2 → only ≈ 0.0043 kg/hr, illustrating why gas species must be selected before converting.

Worked example — Oxidation step mass-flow check

Recipe calls for 50 sccm O₂. A mass-balance model expects g/min input.

  1. Converter: 50 sccm, gas O2, To: g/min.
  2. Result: ≈ 0.0715 g/min (50 × 0.001 × 1.429).
  3. If MFC full-scale accuracy is ±1% FS on a 5000 sccm device (±50 sccm), the absolute uncertainty at 50 sccm setpoint is larger than the entire flow—see MFC calibration basics.

Common pitfalls

  • Using NTP (20°C) density with STP-calibrated MFC readings (~7% error possible).
  • Applying N₂-calibrated K-factors to specialty gases without vendor correction.
  • Forgetting that sccm is volumetric: identical sccm for H₂ and Ar does not mean identical mass delivery.