Outgassing in vacuum chambers: meaning and effect
What outgassing is, which materials dominate, and how Q_out limits base pressure after pumpdown.
By Semiconductor Tools Editorial Team · Last updated: 2026-06-14
Outgassing is the release of adsorbed and absorbed gas from surfaces and bulk materials when exposed to vacuum. It is often the dominant gas load at base pressure—not the pump catalog speed—especially after chamber vent, PM, or introduction of polymers and elastomers.
Material contributions
- Stainless steel: Water desorption from oxide layer; decreases with pump time and bake.
- Viton and elastomers: Often 10–100× higher q_A than conditioned metal.
- Shields, anodized parts, cables: Increase effective area and trap moisture.
- Deposited films: CVD/etch byproducts can alter subsequent outgassing.
Steady-state balance: S_eff × p ≈ Q_out → p ≈ Q_out / S_eff.
Worked example — Outgassing Load Estimator
Chamber internal area ~5000 cm² unbaked steel + 200 cm² Viton. S_eff = 120 L/s from Conductance Calculator.
- Steel preset (~10 h pump): q_A = 1e-9 → Q ≈ 5e-6 mbar·L/s.
- Viton preset: q_A = 1e-7 on 200 cm² → Q ≈ 2e-5 mbar·L/s.
- Total Q ≈ 2.5e-5 mbar·L/s → estimated base p ≈ 2e-7 mbar. If measured base is 5e-6 mbar, investigate leaks or underestimated elastomer area.