MFC Gas Flow Unit Converter

Convert between sccm, slm, g/min, and kg/hr for process gases at STP (Standard Temperature and Pressure). Essential for semiconductor MFC specifications and recipe development.

Calculator

Result

0.007504 kg/hr

Gas: Nitrogen (MW: 28.013 g/mol, ρ: 1.2506 g/L at STP)

Formula

Mass flow = Volumetric flow × Density; Density(N2) at STP = 1.2506 g/L

Technical Explanation

What is sccm?

sccm (standard cubic centimeters per minute) is a volumetric flow rate unit commonly used in semiconductor manufacturing. It describes the volume of gas flowing per minute, corrected to standard conditions. One sccm equals one cubic centimeter of gas per minute at STP (Standard Temperature and Pressure: 0°C, 101.325 kPa). In semiconductor equipment, MFCs (Mass Flow Controllers) are often specified in sccm or slm (standard liters per minute), since volumetric flow is directly measurable and commonly used in process recipes.

STP Definition

STP (Standard Temperature and Pressure) is defined as 0°C (273.15 K) and 101.325 kPa (1 atm). At STP, one mole of an ideal gas occupies 22.414 liters. This standardization allows engineers to compare flow rates across different gases and conditions. Gas density at STP depends on molecular weight: density (g/L) = molecular weight (g/mol) ÷ 22.414 (L/mol). For example, N2 has a molecular weight of 28.013 g/mol and a density of approximately 1.25 g/L at STP.

Conversion Formulas

To convert between volumetric and mass flow, the key relationship is:

Mass flow (g/min) = Volumetric flow (L/min) × Density (g/L)

Since 1 slm = 1 L/min and 1 sccm = 0.001 L/min, we have: Mass flow (g/min) = slm × ρ, or Mass flow (g/min) = sccm × 0.001 × ρ, where ρ is the gas density at STP. To convert to kg/hr, multiply g/min by 0.06 (because 1 g/min = 0.001 kg/min = 0.06 kg/hr).

Importance in Semiconductor Processes

In semiconductor fabrication, gas flow control is critical for CVD (Chemical Vapor Deposition), etch, and other processes. MFC accuracy directly affects film thickness, stoichiometry, and device yield. Engineers often need to convert between sccm (common in equipment specs) and kg/hr or g/min (used in mass balance or cost calculations). Using the correct gas density for each species ensures accurate conversions and reliable process control.

FAQ

Why do different gases give different mass flow for the same sccm?
Because mass flow = volumetric flow × density. Heavier gases (e.g., Ar) have higher density at STP than lighter gases (e.g., H2), so the same sccm corresponds to a higher mass flow for heavier gases.
What is the relationship between sccm and slm?
1 slm = 1000 sccm. Both are volumetric flow units at STP.
Does temperature affect the conversion?
Yes. Our converter uses STP (0°C, 101.325 kPa). If your process runs at different conditions, gas density will differ. For precise applications, use the ideal gas law to adjust density for your actual T and P.

References & Disclaimer

  • NIST Chemistry WebBook (webbook.nist.gov) — gas properties
  • SEMI Standards — process control guidelines

This tool is for educational purposes. For critical applications, verify calculations independently and consult applicable standards. Gas data is from NIST at STP; actual process conditions may differ.

Engineering Guide

Why this calculation matters

MFC setpoints are usually in sccm or slm, but mass-balance spreadsheets, gas billing, and abatement loading often require g/min or kg/hr. Manual conversion with the wrong gas density or standard condition is a common source of recipe and cost errors.

In semiconductor equipment work: Used in CVD/etch recipe documentation, bulk gas consumption estimates, comparing MFC specs across vendors, and verifying mass-based dopant or carrier gas targets.

Input parameters

Flow value
Numeric flow rate to convert.
Gas type
N₂, Ar, O₂, H₂, or He — density at STP from NIST.
From / To unit
sccm, slm, g/min, or kg/hr at STP (0°C, 101.325 kPa).

Output interpretation

Converted flow
Equivalent flow in the selected output unit.
Formula line
Shows mass = volumetric × ρ at STP for traceability.

If two gases show very different kg/hr at the same sccm, that reflects density—not an error. For low-flow MFC accuracy impact, compare absolute mass error at your setpoint, not only volumetric tolerance.

Assumptions

  • STP: 0°C, 101.325 kPa (1 atm); molar volume 22.414 L/mol.
  • Ideal gas; gas densities from NIST Chemistry WebBook.
  • MFC calibration gas matches selected species (K-factor applied in hardware, not here).
  • Steady-state flow; no pressure/temperature correction for actual line conditions.

Limitations

  • Does not apply real-gas corrections at high line pressure.
  • Specialty gases (NF₃, SF₆, silanes) require vendor K-factors not modeled here.
  • NTP (20°C) or IUPAC STP (100 kPa) differ by ~1–7% from this STP.

Worked example

CVD N₂ carrier — 800 sccm to kg/hr

  1. Enter Flow: 800, Gas: N₂, From: sccm, To: kg/hr.
  2. Result ≈ 0.060 kg/hr (800 × 0.001 × 1.2506 × 0.06).
  3. For a 2-hour run: ~0.12 kg N₂ per lot for environmental or cost tracking.
  4. Compare with H₂ at 800 sccm → ~0.0043 kg/hr to see mass difference at equal volumetric flow.