Depth Of Focus (Lithography) Calculator

Work out depth of focus (lithography) instantly with clear inputs, formula shown and shareable results.

About Depth Of Focus (Lithography) Calculator

Depth of focus falls with the square of numerical aperture: DOF = k2 x lambda x n / NA squared. That is the fundamental tension in lithography — every gain in resolution costs focus latitude, which is why wafer flatness and film stack thickness control became so demanding.

Formula

Depth of focus

DOF = k2 x lambda x n / NA^2

Worked example

With the default values below, Depth Of Focus (Lithography) Calculator returns Depth of focus of 91.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Exposure wavelength: 193 nm
Numerical aperture: 1.35
Process factor k2: 0.6
Immersion medium index: 1.44

Results

Depth of focus: 91.50 nm
Depth of focus in air: 63.54 nm
NA squared: 1.8225
Practical focus budget: 54.90 nm

Step by step

1Values used
2Depth of focus
3Depth of focus= 91.50 nm
4Depth of focus in air= 63.54 nm
5NA squared= 1.8225
6Practical focus budget= 54.90 nm

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does high NA hurt focus?

The steeper the cone of light, the faster the image blurs away from the focal plane. DOF at NA 1.35 is only tens of nanometres.

How is such tight focus maintained?

Real-time levelling, chemical mechanical planarisation to flatten each layer, and thin resist stacks. The wafer stage tracks focus continuously during the scan.