Understand the cleanroom concentration proxy

The cleanroom inputs in Design to wafer connect ISO class and downflow to defect-density and yield estimates. In Cloud and the Windows app, the linked sliders use the reference fab environment; imported layout previews have a separate environment. See the reference-fab guide to open the example.

From concentration to deposition

The calculation uses Cn = 10^N × (0.1/D)^2.08 particles/m³. N is the ISO class. D is the particle-size threshold in µm: Cn represents particles with diameter at least D. It uses one cumulative threshold, so overlapping threshold populations are not added together.

Deposited particles/cm² = Cn × (downflow + settling speed) × exposure × deposition fraction ÷ 10,000. Both speeds are in m/s and exposure is in seconds. The divisor converts square metres to square centimetres.

Environment D0 = deposited particles/cm² × killer fraction. The model adds this contribution to User D0 (defects/cm²) · Assumption to obtain Total D0 (defects/cm²).

Read the inputs and estimates

The linked controls allow whole ISO classes 1–9 and downflow 0–1 m/s. Independent ISO-class inputs can include fractional values within 1–9. Threshold D (µm) accepts 0.1–5 µm. Settling speed and exposure are nonnegative; deposition and killer fractions range from 0 to 1.

The Poisson, Murphy and negative-binomial probabilities use active die area in cm² and total D0 in defects/cm². Expected good dies equal completed wafers × dies per wafer × each yield probability.

Interpret environment changes

Changing a linked slider recalculates these estimates over the same simulated lots. Their cycle and completion times stay the same.

The reference fab and its environmental values are illustrative assumptions. ISO class supplies a concentration proxy, not a measured particle distribution or certification. The environment-to-D0 mapping is uncalibrated; yield probabilities and expected good dies are estimates, not measured production results.