slm vs sccm: choosing flow units in semiconductor recipes
When to specify standard liters per minute vs standard cubic centimeters per minute, and how to avoid order-of-magnitude errors in gas panels.
By Semiconductor Tools Editorial Team · Last updated: 2026-06-14
1 slm = 1000 sccm at the same standard conditions. The choice is human-factors engineering: sccm for precision at low flow, slm for readability at high flow. Software that allows unit toggling without clear labeling has caused production incidents.
Selection guidelines
- sccm: MFC setpoints below ~1000 sccm; ALD pulses; dopant blends.
- slm: Purge >10 slm; vent manifolds; abatement dilution air.
Worked example — Purge step documentation (MFC Gas Flow Unit Converter)
Recipe author writes "N₂ purge 8 slm for 60 s." Tool software accepts sccm only.
- Converter: 8000 sccm (not 8 sccm—three-order error), gas N₂, To: kg/hr → ≈ 0.60 kg/hr for abatement mass loading check.
- Conversely, 8 sccm entered by mistake instead of 8 slm delivers 1000× less purge—verify by kg/hr sanity check (0.0006 kg/hr vs 0.60 kg/hr).
Worked example — Throttle process at slm scale
H₂ carrier 2.5 slm at 5 Torr in polysilicon deposition.
- Pumping Speed Calculator: flow = 2.5 slm (= 2500 sccm), P = 5 Torr → S ≈ 6.34 L/s required.
- MFC Converter: 2.5 slm H₂ → 0.0135 kg/hr mass flow for consumption logs.