Gas Mixture Partial Pressure Calculator

Enter MFC flows and total pressure to obtain gas composition and partial pressures. Optionally apply a simple molecular-flow scaling to visualize conductance effects in high-vacuum lines.

Calculator

Given MFC flows and total pressure, compute gas composition (mole fraction) and partial pressures. Optionally apply a simple molecular-flow scaling (∝ 1/√M) to approximate conductance effects in high-vacuum lines.

Example: 5 mTorr = 5e-3 Torr.

Uses flows × 1/√M for an alternative composition, approximating conductance differences in molecular flow. Only affects the "scaled" fractions if molar masses are provided.

Gas mixture

GasFlow (sccm)M (g/mol)yi (simple)pi (simple)yi (scaled)
0.7692310.003846 Torr—
0.1538460.000769 Torr—
0.0769230.000385 Torr—

Simple mole fractions assume flows are proportional to molar throughput at a common STP. Scaled fractions use flows × 1/√M as a crude approximation of molecular-flow conductance effects.

Sum of simple mole fractions Σy_i ≈ 1.0000

Use simple y_i and p_i for recipe design and Dalton's law. Use scaled y_i only as a qualitative indicator when gas-dependent conductance might bias composition in the chamber compared to MFC setpoints.

Technical Explanation

Dalton's Law and Partial Pressure

In a non-reactive gas mixture, the total pressure is the sum of the partial pressures of each component: p_total = Σ p_i. For ideal gases, each partial pressure is given by p_i = y_i · p_total, where y_i is the mole (or volume) fraction of component i. This is the basis for computing partial pressures from composition and total pressure.

From MFC Flows to Composition

In semiconductor tools, gas composition is typically specified in terms of MFC setpoints (e.g., Ar 50 sccm, N₂ 10 sccm, O₂ 5 sccm). If all flows are referenced to the same standard conditions, the mole fraction y_i can be approximated as:

y_i ≈ F_i / ΣF_j

where F_i are the MFC flows in sccm. Partial pressures follow from p_i = y_i p_total. This is what the "simple" fraction in the tool represents.

Molecular-Flow Conductance Scaling (Advanced)

In high-vacuum lines, different gases may experience different conductances. In molecular flow, conductance scales like the mean molecular speed, roughly proportional to 1/√M, where M is molar mass. As a crude approximation, the tool offers a "scaled" composition using:

y_i,scaled ∝ F_i / √M_i

This does not replace a full flow/conductance model, but can indicate when very light gases (e.g., H₂, He) may be overrepresented at the gauge or chamber compared with heavier gases for the same MFC settings.

Practical Notes

Use the simple fractions and partial pressures for recipe design and basic Daltron's law analysis. The scaled fractions are intended as a qualitative indicator only. Real systems may deviate due to non-ideal gas behavior, temperature gradients, pumping configuration, and gas-phase reactions.