Photoresist Spin Coating Thickness Calculator

Semiconductor wafer lithography & thin film processing: Calculate final dried photoresist film thickness, radial centrifugal flow, solvent evaporation dynamics, and spin speed scaling.

Resist Chemistry & Spin Chuck Settings

Spin Speed ω (RPM): Main spin plateau speed

Solid Content x_s (% wt): Polymer solids in solvent

Kinematic Viscosity ν (cSt): Resist viscosity (η/ρ in mm²/s)

Evaporation Rate Factor e (nm/s): Solvent volatilization rate (PGMEA)

Wafer Diameter (mm): Silicon substrate size

Resist Target Calibration Constant K: Empirical K factor (nm·RPM^0.5)

Dry Film Thickness & Film Uniformity

Dry Resist Thickness (h_dry)

Meyerhofer Model Thickness

Evaporation-viscosity balance

Edge Bead Removal (EBR) Width

Front/back edge bead solvent trim

Thickness vs Speed Sensitivity

dh/dω (nm per 100 RPM)

Wafer Edge Centrifugal Force

Radial acceleration (g-force)

Target 4000 RPM Thickness

Scaled to 4000 RPM reference

Recommended Tools & Equipment

Tested hardware and components for high reliability

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Frequently Asked Questions

Why does resist thickness scale inversely with the square root of RPM?

Hydrodynamic balance between centrifugal outflow force (proportional to ω² · r) and viscous shear drag (proportional to viscosity and velocity gradient) leads mathematically to an asymptotic liquid film thickness that decreases as 1/√ω.

What causes striations during spin coating?

Striations are radial wave-like thickness variations caused by Marangoni surface tension instability. As volatile solvents evaporate unevenly along the liquid surface, surface tension gradients pull fluid toward cooler regions, freezing radial ripples into the dried film.

What is the purpose of the post-apply softbake (PAB)?

After spin coating, the film still contains 10% to 15% residual solvent. The wafer is baked on a hotplate at 90°C to 130°C for 60 seconds to evaporate solvent, anneal film stress, and stabilize photoacid generator (PAG) chemistry.