UV-LED light sources for mask aligners

Why convert a mask aligner to UV-LED

Most older contact and proximity aligners use a high-pressure mercury arc lamp. It works, but it has costs that a lab manager knows well: the lamp needs warm-up before the first exposure, intensity drifts as the lamp ages, lamps are changed regularly, and each one holds mercury that needs careful handling when it breaks or reaches end of life. The lamp also runs hot and needs its own power supply and cooling.

A UV-LED conversion replaces the mercury lamp house with an LED source. The source switches on when needed, drifts far less than a mercury lamp, though it still needs periodic intensity checks, and has no mercury. For teaching cleanrooms with many occasional users, the gain in day-to-day reliability is often the main reason to convert.

What changes with UV-LED

The mercury lamp emits strong lines at 365 nm (i-line), 405 nm (h-line) and 436 nm (g-line). A UV-LED source covers the part of that spectrum your resists need, using LEDs at or near the relevant lines; which channels are available depends on the source model. The relative intensity of each line can differ from what your mercury lamp delivered, and broadband resists may respond differently.

That means exposure doses change. After the conversion we measure intensity at the wafer plane and set exposure times from the measured dose. We then run test exposures with your resists so you can confirm resolution and sidewall profile before returning to production work. For a longer discussion, see mercury lamp to UV-LED on a mask aligner.

Scope

A typical conversion covers:

• Survey of the lamp house, condenser optics, shutter, exposure timer and lamp power supply
• Choice of LED source and wavelengths for your resists
• Mechanical fit of the LED source in place of the lamp house
• Connection to the aligner shutter and exposure controls, so the operator workflow stays familiar
• Intensity and uniformity mapping across the exposure field
• Test exposures and dose recommendations

The exact scope depends on the aligner model and its configuration. Common candidates include the SUSS MA6, the SUSS MJB4 and the EVG620.

Typical downtime

The aligner is out of service for the installation, mapping and test exposures. On a single aligner this is normally a short planned stop of a few days, depending on configuration and on how many resists you want requalified. The proposal states the planned downtime.

What we need from you

• Aligner model, configuration and the lamp power currently used
• The resists you expose and their target doses or exposure times
• Test wafers and a test mask you know well
• Time on the tool for test exposures after installation

Results and documentation

You receive the installed source, an intensity and uniformity map, dose recommendations from the test exposures and updated operating notes. The old lamp house is returned to you or disposed of as you choose. The upgrade applies to contact and proximity aligners in lithography.