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Diamond OSAtlas

LT-LAB-1 · 365 nm

Gate, not a result

Hard contact, one formula.

The earlier page used the bare square root for proximity and the fuller form for contact. That is why it computed about 2.7 µm and then said a 5 µm line was impossible. One expression covers every gap.

R ≈ 1.5 × √( λ × (g + t/2) )

Wavelength, gap, and resist thickness in the same units. Here, micrometres. λ is 0.365.

On paper

4.15 µm

This bench

10.4 µm

Gap along the bottom, in micrometres. The light line is the paper limit. Copper is this bench, after the factor.

Teaching-lab territory. A 20 µm line should pass. A 10 µm line is allowed to fail. A 5 µm line wants contact, not this gap.

Chrome mask — consumable in contact
Gap 20 µm
Resist 2.0 µm
Wafer

What a bench actually prints

Paper column assumes 365 nm and a 2 µm resist.

  • 20 µm proximity

    4.2 µm

    20 µm reliable. 10 µm is a test. No force control, poor collimation.

  • Soft contact

    Between the two

    About 10 µm, sometimes 5. The gap is whatever the clamp gave.

  • Hard contact

    0.9 µm

    5 µm is the right gate. 2 µm is a stretch and wears the mask.

  • Vacuum contact

    Near 1 µm on a real aligner

    Not this tool. Needs a seal, a regulated force, and a flat chuck.

The floor for this tool

Gate 2 stays a 5 µm line in hard contact, photographed, measured against the mask, inside 20 percent. It sits at the good end of what this bench can do and above the 2 µm line where particles and bow take over. Zhou, Chen, Shu, Fan, Hu, and Duan (International Journal of Extreme Manufacturing, 2025) state that conventional hard contact is generally limited to about 2 µm. With a dry transferable resist they printed about 300 nm at 365 nm. That is a clean-room result. It is not a breadboard and a hood.

Source: Yu Zhou et al., International Journal of Extreme Manufacturing 7 (2025) 065101.

Why TMA is not on this bench

Pyrophoric

Trimethylaluminum is the aluminum source for both alumina atomic-layer deposition and sequential infiltration synthesis into PMMA. Same molecule. The difference is where it reacts: on a surface, or inside a film. It ignites in air and reacts violently with water. Fires are fought with dry powder, sand, or Met-L-X — not water or CO₂. It belongs in a qualified ALD chamber with interlocks.

PMMA’s ester carbonyl binds it. Polystyrene has no carbonyl, so it stays empty. That selectivity is the lithography value. It does not write 2 nm gates. It loads alumina into one polymer domain so the other can be etched.