Your first pattern on a maskless tool

1 · Choose a resist

Start by picking a photoresist that matches the job, because that single choice sets almost everything downstream — how thick a film you can coat, what developer you need, and whether the sidewall comes out straight or undercut. Rather than guess, narrow the recipe library with its filters, in this order: thickness (the film your process actually needs), application (etch mask, lift-off, electroplating, MEMS structural, grayscale, and so on), then tone.

If you want to understand the families before you filter, each resist class has its own explainer: DNQ–novolak positive resists are the general-purpose workhorse for etch masking; image-reversal resists and lift-off underlayers give the undercut profile that lift-off needs; epoxy negative resists such as SU-8 build thick, high-aspect-ratio structures; and chemically amplified resists trade sensitivity for tighter process control. Any resist in the library is exposable at 365 and 405 nm — the two lines a maskless UV tool provides.

For a first run, favour a forgiving, well-documented positive resist and a modest film thickness. A resist with a wide process window and a full datasheet is far easier to get right than a specialised one, and you can move to the demanding process once the flow is familiar.

2 · Prepare and coat

Whatever ends up on the surface at coat time prints as a defect, so begin with a clean, dry substrate. A standard clean followed by a dehydration bake — and, for many resists on oxide, an HMDS adhesion prime — gives the resist a surface it will actually stick to through development. The processing guidelines cover why each of these matters.

Next, spin-coat the resist: a few drops are dispensed onto the substrate, which then spins so centrifugal force spreads a uniform film while solvent flashes off. Film thickness falls as spin speed rises, so you read your target thickness off the resist's spin curve — published on every recipe page — and set the speed to match. Read from a plotted point rather than guessing between two.

Finally, soft-bake the coated film on a hotplate to drive out the casting solvent so the film is dry and stable before exposure. The exact temperature and time scale with thickness and are on the recipe page; the soft-bake section of the guidelines explains the balance — underbake leaves solvent that scums, overbake can desensitise the resist.

Sources: Cornell CNF — Photolithography Manual

3 · Expose your design directly

This is the step a maskless tool reinvents. On a conventional aligner you would first pay for and wait on a photomask, then shine UV through it. A maskless (direct-write) system instead writes your design straight onto the resist — you load a layout file and the tool exposes the pattern point by point, with the dose set in software per layer. There is no mask, so a design change is a file change, not a new mask order. How that projection works — DMD patterning, direct write, grayscale — is covered in how maskless lithography works.

The quantity that matters is dose — the energy per unit area delivered to the film. Too little leaves scum and unresolved features; too much widens or rounds them. Each resist has a characteristic dose-to-clear, and datasheets usually quote a working dose at 365 nm; where the 405 nm value is unpublished it cannot be inferred, so the honest first move is a short dose array — a row of identical features exposed at stepped doses — to find what clears cleanly on your own tool. Doses live on the recipe pages; the exposure section of the guidelines explains the trade-offs.

Some resists then need a post-exposure bake before developing — essential for a chemically amplified resist, and a sidewall-smoothing step for a conventional DNQ resist. Check whether your resist calls for one.

Sources: MicroChemicals — Exposure of Photoresists

4 · Develop the pattern

Development dissolves the soluble regions and leaves your pattern behind — the exposed areas for a positive resist, the unexposed areas for a negative one. Most conventional resists develop in an aqueous, metal-ion-free base (TMAH); epoxy resists such as SU-8 are the exception and develop in an organic solvent. The developer, its strength and the time are all on the recipe page — don't improvise them.

Develop for the time the recipe specifies and no longer: under-development leaves scum in areas that should be clear, while over-development thins and rounds features. A gentle rinse and dry finishes the step. The development section of the guidelines covers puddle versus immersion and why the timing is tight.

5 · Inspect the result

Before you commit the pattern to an etch, deposition or plating step, look at it under a microscope. A good result has crisp, fully-cleared features at the right dimension with clean sidewalls. Most first-run problems announce themselves as a recognisable defect that points straight back at a step above — and each is defined in the glossary.

• —Scum or residue in areas that should be clear → underexposure or under-development. Increase dose or develop time within the recipe's window, or refresh the developer.
• —Features too small, or missing → over-development or over-dose. Back off the time or dose.
• —Ragged or lifting edges → an adhesion problem: revisit the clean, dehydration bake and HMDS prime.
• —Rounded or bridged features → over-exposure, or a soft-bake that was too hot or too long.

A dose array from the exposure step earns its keep here: comparing the same feature across stepped doses shows you exactly which one clears cleanly, and that becomes your working dose. Don't expect a perfect first exposure — expect a good second one. Note what you changed, and iterate; because there's no mask, each iteration costs only a fresh coat.

Common questions

Where to next

1. Cornell NanoScale Science & Technology Facility (CNF). Photolithography Techniques Manual. https://www.cnfusers.cornell.edu/sites/default/files/Area-Resources/PhotolithTechniquesManual20.pdf
2. MicroChemicals GmbH. Exposure of Photoresists (application note). https://www.microchemicals.com/dokumente/application_notes/exposure_photoresist.pdf