Spin coating thickness and spin speed calculator
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KEY POINTS
Spin-coated thickness is roughly inversely proportional to the square root of spin speed (t ∝ ω^−0.5): quadrupling the speed about halves the thickness. In practice spin speed can adjust thickness by about a factor of two; beyond that, a product with different solids content (viscosity) is used. More than 95% of the dispensed liquid is flung off, so coating efficiency is also a material cost issue.
Inputs
The power law is an empirical fit to datasheet spin curves. Real thickness also depends on temperature, humidity, exhaust, cup shape, acceleration and prewet (RRC), so replace the reference point with a value measured on your own tool. Coating efficiency counts the dry film volume; actual material utilization after multiplying by the solids fraction is lower still.
Spin curve
Thickness by spin speed
| Spin speed | Thickness | Relative to 3000 rpm |
|---|---|---|
| 1000 rpm | 2000 nm | 173 % |
| 1500 rpm | 1633 nm | 141 % |
| 2000 rpm | 1414 nm | 122 % |
| 3000 rpm | 1155 nm | 100 % |
| 4000 rpm | 1000 nm | 87 % |
| 5000 rpm | 894 nm | 77 % |
| 6000 rpm | 816 nm | 71 % |
Why thickness scales with the inverse square root of speed
In spin coating, liquid dispensed at the wafer center flows outward under centrifugal force and thins, while solvent evaporates and raises the viscosity until flow stops and the thickness is fixed. The balance between centrifugal thinning and evaporation makes the final thickness roughly inversely proportional to the square root of spin speed (α ≈ 0.5): quadrupling the speed about halves the thickness.
In practice spin speed can adjust thickness by about a factor of two; beyond that, a product with different solids content or viscosity is chosen. More than 95% of the dispensed liquid is flung off as waste, so reducing dispense volume is a major material cost issue. Coater/developers cut dispense volume sharply by prewetting the wafer with solvent before coating (RRC).
FAQ
How much does doubling the spin speed change thickness?
With the usual exponent of 0.5, thickness falls to about 1/√2, or roughly 71%.
Why not just spin faster for thinner films?
Practical spin speeds span roughly 1,000 to 5,000 rpm, and uniformity suffers at the extremes. Larger thickness changes are made with a different viscosity or dilution.
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Last updated: October 23, 2026