Your own mask, then six questions.

The built-in patterns are a start. Everything in litopc also runs on a mask you draw: the simulation, the correction and the studies. One drawn example and six recorded studies below.

Any mask, from rectangles

Draw your own

Add rectangles, cut a gap, correct.

Drawn, 2 rectangles and a cut

Printed

Corrected, 5 rounds

5.4 → 1.0 nm in 5 rounds (↓81 %). EUV 13.5 nm, NA 0.33: 2 rectangles and one cut drawn as the target, 212 nm field. The cut splits the two bars into two line ends facing each other; the correction pulls the ends out and keeps the gap open.

Draw: Edit ▸ Target. Add drags a rectangle onto the canvas; Cut removes one from the shape. Free accounts draw up to 5 rectangles, Pro up to 48.
Correct: Correct reshapes the mask edge by edge against your target: 3 rounds per run on Free, 5 on Pro, then more. The mask starts as a copy of the target.
Open it: This example in the simulator

One click each

Six studies

One variable swept, every print overlaid, the answer in a line.

1
Simulate any pattern, built-in or drawn.
2
Open the Studies tab beside Set-up in the left panel (on a phone, tap Set-up first) and pick a question.
3
Click a point on the chart, or a row: that print lights up on the canvas.

Recorded simulator output, 2026-11-01. Each caption names the tool and the pattern; Mask bias and MEEF read the same sweep two ways.

Free and Pro

Mask bias

Which single bias fits best?

Recorded example

edge error (nm)

0 nmmask bias24 nm

the reading

What printed

what printedbest bias +12 nm

300 × 200 nmprints at every bias13 prints

mask
print, every point
the reading
target
Correct's mask

Best bias +12 nm: 27.5 → 6.5 nm. DUV 193 nm · 110 nm square · Correct, edge by edge, reaches 6.7 nm.

Grows or shrinks every edge of the combined design by the same amount and measures the miss against the target: rule-based correction in one number, side by side with the model-based result.

Sweep: Every edge of the combined mask moves by the same amount, from shrink to grow.
Reads: Edge placement error against the target; the best bias is marked.
Set-up: DUV 193 nm dry, NA 0.93 · Custom, 110 nm square · τ 0.30 · every edge moved 0 to +24 nm · 1024 nm field
Run it: Studies tab ▸ Mask bias, after Simulate.

Free and Pro

MEEF (CD linearity)

How much of the mask reaches the wafer?

Recorded example

wafer CD (nm)

78 nmmask CD126 nm

wafer = mask

What printed

what printed102 nm mask

330 × 220 nmthe contact at every mask CD13 prints

mask
print, every point
the reading

MEEF ≈ 1.8 from 98 to 126 nm on the mask. DUV 193 nm · isolated 102 nm contact · 86 nm on the mask prints nothing, 90 nm prints 53 nm.

The same uniform edge move as Mask bias, read as wafer CD against mask CD; the slope is the mask error enhancement factor, and the plot shows where the line stops printing.

Sweep: The same uniform edge move as Mask bias, written as mask CD.
Reads: Printed CD against mask CD; the slope is MEEF, and the plot shows where the line stops printing.
Set-up: DUV 193 nm dry, NA 0.93 · isolated 102 nm contact · τ 0.19, its dose-to-size · mask CD 78 to 126 nm
Run it: Studies tab ▸ MEEF, after Simulate.

Free and Pro

Threshold latitude

How far can the dose drift?

Recorded example

CD (nm)

0.13threshold τ0.25

±10 % of target
target

What printed

what printedτ 0.19, dose-to-size

944 × 629 nmthe print at every threshold13 prints

mask
print, every point
the reading
target

In spec from τ 0.18 to 0.21. DUV 193 nm · 3 × 3 contact array, 102 nm holes at a 204 nm pitch · CD of the centre hole within ±10 % of 102 nm.

Steps the intensity threshold, the model's stand-in for exposure dose, and reports the span over which CD stays within ±10 % of the target.

Sweep: Intensity threshold τ, the model's stand-in for exposure dose.
Reads: Printed CD and EPE at each τ; the span that stays within ±10 % of the target.
Set-up: DUV 193 nm dry, NA 0.93 · 3 × 3 contact array, 102 nm holes at a 204 nm pitch (Pro pattern) · τ 0.13 to 0.25 around dose-to-size 0.19 · CD of the centre hole
Run it: Studies tab ▸ Threshold latitude, after Simulate.

Free and Pro

Focus latitude

How much defocus is allowed?

Recorded example

CD (nm)

-90 nmdefocus+90 nm

±10 % of target
target

What printed

what printedbest focus

180 × 120 nmthe print through focus13 prints

mask
print, every point
the reading
target

In spec from −45 to +45 nm of defocus. EUV 13.5 nm · L-shape, 14 nm lines at τ 0.25 · CD of the vertical arm within ±10 %.

A Bossung curve at the current threshold: printed CD through the tool's depth of focus, with the Rayleigh scale marked.

Sweep: Physical defocus through the tool's depth of focus, at the current threshold.
Reads: Printed CD per focus step (a Bossung curve); the span that stays in spec.
Set-up: EUV 13.5 nm, NA 0.33 · L-shape, 14 nm lines · τ 0.25, its dose-to-size · defocus −90 to +90 nm · CD of the vertical arm
Run it: Studies tab ▸ Focus latitude, after Simulate.

Free and Pro

Through pitch

How does CD change with pitch?

Recorded example

CD (nm)

220 nmpitch292 nm

target

What printed

what printed220 nm pitch

764 × 509 nm3 lines at every pitch13 prints

mask
print, every point
the reading

8.5 nm of pitch bias before correction. DUV 193 nm · three 100 nm lines, 400 nm long: 114 nm at a 220 nm pitch, 105 nm at 292 nm.

Sweeps the pitch of the dense-line pattern to show the iso-dense bias OPC has to absorb and the densest pitch that still resolves.

Sweep: Pitch of the dense line pattern, at fixed line width.
Reads: Printed CD per pitch: the iso-dense bias and the densest pitch that still resolves.
Set-up: DUV 193 nm dry, NA 0.93 · Dense lines, three 100 nm lines, 400 nm long · τ 0.30 · pitch 220 to 292 nm · CD of the middle line · 1024 nm field
Run it: Studies tab ▸ Through pitch, after Simulate.

Pro

Process window

Where do dose and focus both hold?

Recorded example

threshold τ 0.26–0.35

-180 nmdefocus+180 nm

in spec
largest window

τ 0.30–0.35 across 360 nm of focus. DUV 193 nm · 150 nm isolated line · the largest block of in-spec cells.

A threshold × defocus grid; the largest rectangle of in-spec cells is the window, read as depth of focus at a given threshold latitude.

Sweep: Threshold and defocus together, as a grid.
Reads: Which cells keep CD in spec; the largest rectangle of them is the window.
Set-up: DUV 193 nm dry, NA 0.93 · 150 nm isolated line · τ 0.26 to 0.35 × defocus −180 to +180 nm · in spec within ±10 %
Run it: Studies tab ▸ Process window (Pro), after Simulate.

Open litopc simulator How the print is simulated