sccm → Pumping Speed Calculator

Calculate required pumping speed (S) from gas flow and chamber pressure. Q = S × P → S = Q / P. Useful for cryo capacity checks, throttle interpretation, and chamber pressure troubleshooting.

Calculator

Required Pumping Speed (S = Q / P)

126.67 L/s

Q (throughput) = 1.27 Torr·L/s  |  P = 0.0100 Torr

Technical Explanation

Throughput and Pumping Speed

In vacuum systems, throughput (Q) is the gas load pumped per unit time, expressed as pressure × volumetric flow (e.g. Torr·L/s). Pumping speed (S) is the volume of gas removed per unit time (L/s). At steady state, the fundamental relationship is:

Q = S × P

Therefore, the required pumping speed is S = Q / P. Given gas flow (e.g. sccm from MFC) and chamber pressure, you can calculate the minimum pump speed needed to maintain that pressure.

Conversion: sccm → Q (Torr·L/s)

At STP (760 Torr, 0°C): 1 sccm = 760 × (10⁻³/60) ≈ 0.01267 Torr·L/s. For 1 slm: Q ≈ 12.67 Torr·L/s. The tool uses these conversion factors to compute Q from sccm or slm input.

Practical Applications

  • Cryo capacity — Compare required S with cryo pump capacity to judge if cryo capacity is sufficient for the gas load.
  • Throttle opening — With conductance-limited flow, effective S depends on throttle. Use S = Q/P to infer effective pump speed or throttle conductance.
  • Chamber pressure not dropping — If pressure stays high despite pumping, compare actual Q (from MFC, leaks, outgassing) with pump capacity. If Q > S × P at target pressure, the pump cannot reach that pressure.

References & Disclaimer

Conversion uses STP (760 Torr, 0°C). For critical applications, verify calculations and pump specifications independently.

Engineering Guide

Why this calculation matters

When MFC process gas flows into a pumped chamber, steady-state pressure satisfies Q = S × P. Engineers need S to judge cryo capacity, throttle settings, and whether pressure problems are pump-limited or load-limited.

In semiconductor equipment work: RIE/CVD pressure troubleshooting, cryo sizing checks, comparing required S with S_eff from conductance analysis, and validating throttle valve strategy.

Input parameters

Flow (throughput)
Gas load in sccm or slm at STP.
Chamber pressure
Steady-state P in Torr, mTorr, mbar, or Pa.

Output interpretation

Required S (L/s)
S = Q / P at the stated pressure point.
Q (Torr·L/s)
Intermediate throughput for audit trail.

If required S exceeds installed S_eff, the chamber cannot hold target pressure at that flow. If required S is modest but pressure is high, look for excess Q (leak, outgassing, wrong MFC).

Assumptions

  • Steady state: gas inflow equals pump removal.
  • Q from sccm uses STP conversion (760 Torr reference volume flow).
  • S is effective speed at the chamber unless stated otherwise.

Limitations

  • Transient startup or pulsed gas not modeled.
  • Does not include conductance — compare result with S_eff from piping analysis.
  • Multi-gas mixtures use total volumetric flow approximation.

Worked example

RIE — 150 sccm total at 12 mTorr target

  1. Flow: 150 sccm, Pressure: 12 mTorr.
  2. Required S ≈ 158 L/s.
  3. If conductance tool gives S_eff = 90 L/s, equilibrium P ≈ 21 mTorr — cannot hold 12 mTorr until conductance improves.