The study asks how programmable maskless projection lithography can resolve dense nanoscale patterns under visible femtosecond illumination. Two cascaded spatial light modulators independently control amplitude and phase; alternating phase shifts suppress light between neighboring features, while two-photon exposure and photoresist thresholding refine linewidth. Optical simulations and scanning electron microscopy measurements support approximately 60 nm linewidths and 235 nm single-exposure pitch under 517 nm illumination. Two sequential interleaved exposures achieve approximately 158 nm pitc

Light: Advanced Manufacturing · 2026

Can cancelling light make smaller patterns?

At the nanoscale, blurred beams can fuse neighbouring lines. This paper gives those beams opposite phases—creating dark gaps that let tiny patterns stay separate.

Three experiments. One surprising role for darkness.

Pitch in a single exposurewith a phase-shift mask · Fig. 4

Linewidth at that same pitchwith a shorter exposure · Fig. S13

Pitch using two exposureswith ~100 nm linewidth · Fig. S19

The idea

The gap is the invention.

A digital mask chooses where light goes . A second mask chooses where each light wave is in its cycle . Give neighbouring bright regions a half-cycle difference, and their overlapping fields can cancel.

The resist then responds through a two-photon process: absorbing two photons in one excitation makes its exposure dose scale with intensity squared . A threshold decides which parts remain after development. Phase creates the contrast; exposure determines the material that survives.

Experiment with interference

First, make the gaps dark.

Start with a dense, three-pixel pattern. Turn the phase dial and watch light become a better patterning tool.

The 235 nm pattern merges. Give neighbouring waves different phases to recover dark gaps.

π is half a wave cycle. Where opposite fields meet, they cancel.

One projected pixel is approximately 78 nm. Try making the pattern denser.

Peaks and valleys have the same intensity.

Resolve the three-pixel pattern. Then test whether two pixels can pass through the same lens.

From the experiment

The same dense target. A different outcome.

At 235 nm pitch, the amplitude-only pattern loses its gaps. Adding the phase mask resolves separate lines. The source panel labels a 140 nm linewidth under this exposure condition.

Fig. 4a,c · scanning electron microscopy (SEM) Zhao et al. (2026), CC BY 4.0 · cropped and resized

Experiment with the material threshold

Then, choose what becomes material.

The phase-defined spacing stays fixed. Change exposure time to narrow the region that survives development.

75 seconds: ~100 nm linewidth. The measured pitch remains 235 nm.

An exposure is a choice

Less time. Less material.

Two-photon exposure favours the brightest parts of the image. With less dose, a smaller region reaches the resist threshold.

The authors measured 100, 80 and 60 nm linewidths at 75, 65 and 55 seconds, respectively. These three observations use the same 235 nm-pitch pattern and 2.4 mW power.

Switch from 75 to 55 seconds. Watch the line edges move inward while the line centres stay put.

Supplementary Fig. S13 · Zhao et al. (2026), CC BY 4.0. SEM panels displayed through a cropped view; resized.

Experiment with interleaving

One pattern. Two passes.

Make a dense target from two less dense subpatterns. Shift the second mask so it exposes the spaces left by the first.

Begin with the first exposure: a four-pixel-period subpattern.

Half a period gives evenly interleaved lines. After both passes, slide back to see what alignment changes.

The two exposures happen at different times. Their doses add in the resist.

Expose A, then B. With both present, move the second mask to zero shift: does another pass make another line?

From the supplementary experiment

158 nm pitch, measured after two passes.

The authors alternated two masks designed with a spacing of about 320 nm. Their combined exposure yielded a measured 158 nm pitch and approximately 100 nm linewidth , at 1.6 mW and 260 seconds.

The supplementary figure connects the two masks, their simulated dose profiles and the developed resist seen by SEM.

Supplementary Fig. S19 · Zhao et al. (2026), CC BY 4.0. Original figure, resized.

Why it matters

A mask that can change its mind.

These masks are digital. A new pattern is a new instruction to the spatial light modulators, rather than a newly manufactured physical mask. That makes phase control attractive for custom nanoscale patterning and small-batch fabrication.

Optics built in miniature

Dense nanostructures could support micro- and nano-optical components, including metasurfaces.

Programmable prototyping

The paper demonstrates resist patterns corresponding to representative circuit metal-layer layouts.

Parallel patterning

Projection exposes a whole patterned field at once. Digital phase expands the detail that can fit within it.

The research behind the experience

Read the full paper.

Digital phase-shift mask projection lithography enabling sub-diffraction-limit resolution for dense nanoscale patterning

Yuan-Yuan Zhao, Zi-Xin Liang, Jing-Tao Chen, Wen-Hui Li, Zhi-Cai Wu and Xuan-Ming Duan

Light: Advanced Manufacturing 7, 80 (2026)

Two cascaded liquid-crystal-on-silicon spatial light modulators independently set amplitude and phase. A 1:1 relay aligns their pixels. A 100×, NA 1.40 oil-immersion objective projects the masks with an approximately 102× measured reduction.

This is two-photon exposure in a thin photoresist film. The developed structures are measured by SEM; the isometric views here show the process conceptually.

Systems and principles; Methods; Supplementary Notes 7 and 14.

The first bench uses a coherent scalar Fourier model of rectangular bright stripes with alternating phases. Only spatial frequencies within NA/λ pass through the objective. The projected pixel width is 8 μm/102 ≈ 78.4 nm; stripe widths are two pixels, or one pixel in the two-pixel-pitch case.

Curves show normalized intensity I and dose I². A chosen normalized threshold of 0.35 determines the schematic retained regions. Negligible transmitted fields remain dark. Contrast is (Imax − Imin)/(Imax + Imin).

The two-exposure bench uses the same four-pixel periodic optical pattern, shifted for its second pass, and adds the sequential doses. Its threshold is 0.65 of the maximum single-pattern dose. The modeled pitch is ~314 nm per pass and ~157 nm when evenly interleaved; the paper reports 158 nm after development.

Optical curves and relief illustrate the mechanism. Measured pitches and linewidths are separately identified and come from Figs. 4, S13 and S19.

Paper figures and supplementary figures reproduced from Zhao et al. (2026), doi:10.37188/lam.2026.080, under Creative Commons Attribution 4.0 International. The comparison images and layout figure are cropped and resized. Supplementary SEM panels are presented through cropped views; the full figures below are resized.

The graphical abstract is an AI-generated conceptual illustration informed by Figs. 1, 4 and S19. The interactive diagrams are explanatory illustrations.

Explore the science. Try the idea.

Source figure

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