Throughput, leak rate, and the rate-of-rise method
Using throughput units and the pressure rise test to quantify leaks and gas loads.
By Semiconductor Tools Editorial Team · Last updated: 2026-06-14
Throughput Q quantifies gas load in pressure×volume/time units: Pa·m³/s (SI), mbar·L/s (European practice), or Torr·L/s (US vacuum tradition). Leak rates, outgassing loads, permeation, and continuous MFC process gas can all be expressed as throughput—enabling direct comparison on a single scale.
Converting MFC flow to throughput
At STP (0°C, 101.325 kPa), our tools use:
- 1 sccm ≈ 1.689×10⁻³ Pa·m³/s ≈ 0.01689 mbar·L/s ≈ 0.01267 Torr·L/s
- 1 slm = 1000 × above
Rate-of-rise (pressure rise) test
With the pump isolated, chamber volume V, and measured pressure rise from p₁ to p₂ over Δt:
qL = V · (Δp / Δt)
qL in mbar·L/s when V is in liters and Δp in mbar. At steady state with pump connected: pult ≈ qL / Seff.
Worked example — MFC load in throughput units (Throughput & Leak Rate Converter)
A chamber receives 30 sccm N₂ process gas continuously. Express Q in mbar·L/s and Torr·L/s for comparison with a leak-check spec of 0.01 mbar·L/s.
- In Throughput Converter, enter 30, unit sccm.
- Read: ≈ 0.507 mbar·L/s and ≈ 0.380 Torr·L/s.
- Process gas load exceeds the 0.01 mbar·L/s leak spec by ~50×—the spec applies only when MFCs are closed; document test conditions accordingly.
Worked example — Rate-of-rise leak quantification
Post-PM leak check: chamber V = 150 L, isolated from pump. Pressure rises from 2×10⁻⁶ Torr to 8×10⁻⁶ Torr in 10 min (600 s).
- In the Rate-of-Rise section: V = 150 L, p₁ = 2e-6, p₂ = 8e-6 Torr, Δt = 600 s.
- Δp = 6×10⁻⁶ Torr → qL ≈ 1.5×10⁻⁶ Torr·L/s (≈ 2.0×10⁻⁶ mbar·L/s).
- If Seff = 80 L/s (from conductance tool), predicted ultimate pressure p ≈ q/S ≈ 1.9×10⁻⁸ Torr—if actual base is 5×10⁻⁷ Torr, additional gas load (outgassing) dominates over true leak.