Exposure machines (Mask Aligner/Stepper) are widely used in lithography processes for structures in the micrometer range, such as advanced semiconductor packaging (bump/RDL), micro-optical components, high-end passive components, LEDs, MEMS, and more. In exposure systems, the light source is crucial for producing high-quality lines and patterns. Factors such as the uniformity of irradiation, the angular distribution of radiation, and the intensity of exposure all significantly impact the exposure quality, while the irradiation intensity determines the exposure time.

Traditionally, mercury lamp sources have been used in the 350-450 nm wavelength range. However, these sources have many drawbacks, making them outdated, such as their large size, mercury content (not environmentally friendly), low electrical-to-optical power conversion efficiency, the need for a 30-minute warm-up time, and short lamp life (about 1000 hours).

With the advancement of LED technology, high-power LEDs in the relevant wavelength range have emerged in recent years, opening new possibilities for achieving better exposure performance in exposure machines. However, since mercury lamp sources have been used for decades, a well-established industrial ecosystem has been built around them, including various optical components, photoresist (lithography ink) formulations, and process optimizations. As a result, concerns remain about the compatibility of new light source technologies with the existing ecosystem and supply chain.


LED Light Source Exposure Study

An article by Johana Bernasconi et al., published in Optics Express in 2018, shows that after upgrading the light source system of the MA-BA8 Gen.3 SUSS mask-aligner to an LED light source system, the uniformity of the light source reached 2.59%. The performance was found to be consistent with the original mercury lamp source system. Exposure tests at both contact mode and a 30μm proximity gap achieved resolutions of <1μm and 3μm, respectively, meeting the original specifications of the SUSS exposure machine.

LED Light Source Exposure Results: (a)&(b) - contact printing； (c)&(d) - proximity printing Source https://opg.optica.org/oe/fulltext.cfm?uri=oe-26-9-11503&id=385752

SUSS Report As a leading exposure equipment manufacturer, SUSS published a related research report in 2017, demonstrating that mask-aligner exposure systems using LED light sources achieve exposure results comparable to those of mercury lamp source systems. The image on the right shows the SEM images of linewidth/line pitch produced in 1.2 µm thick AZ4110 photoresist using LED light sources and traditional 1 kW mercury lamps. The tests were conducted under broadband spectrum and a 20 µm gap condition. The results show that the exposure outcomes from both light sources are very similar, including resolution, feature shapes, and side wall angles.		Comparison of exposure results using LED light source (a-c) and mercury lamp (d-f).
SUSS's research successfully applies UV LED light sources in SMILE This equipment is used for the production of microlens arrays, where imprint materials are shaped into the desired 3D form using a stamp. During this process, ultraviolet exposure triggers a crosslinking reaction in the imprint polymer, leading to its curing. The lens array shown in the image on the right was produced using DELO OM 6610 material on an 8-inch wafer. In this test, the results produced by the LED light source were comparable to those generated by traditional mercury lamps.		Imprinted microlens arrays produced using SMILE technology and LED light sources. Source: https://www.suss.com/cn/news/technical-publications/high-intensity-uv-led-mask-aligner-for-applications-in-industrial-research

The spectrum of a typical 1kW mercury lamp (blue), a typical LED light source (solid orange), and an example of a customized LED light source (dashed orange line) are shown.

SUSS's report also indicates that LED light sources offer flexibility in spectral composition and irradiance intensity customization. Generally, users prefer a light source that closely matches the existing process. To achieve this, the LED light source can adjust the intensity composition of the i, h, and g lines to align with the known mercury lamp spectrum (e.g., 350W or 1 kW mercury lamp spectrum). The dashed spectrum in the image on the left illustrates how the LED light source can be adjusted to closely match the 1 kW mercury lamp spectrum that is suitable for the AZ4110 photoresist response. The flexibility to adjust the wavelength composition (spectrum) and its relative intensity provides new opportunities for equipment or processes. It enables optimization of exposure conditions and photoresist material matching, and even allows for consistent lighting from machine to machine.

Energy Consumption Reduced by 60% with LED Light Source Through actual testing of the entire system, it has been shown that the energy consumption of LEDs is significantly lower than that of mercury lamps. The image on the right compares the energy consumption of a typical MA/BA Gen4 Pro mask aligner exposure system with a 1kW mercury lamp (left) and an LED light source (right). Under the same exposure intensity, the LED system consumes approximately 60% less energy during operation. Not only is the electrical power consumption reduced, but the need for a powerful exhaust system or special cooling airflow is eliminated. The consumption of Clean Dry Air (CDA) and nitrogen is also significantly reduced.

Comparison of energy consumption between MA/BA Gen4 Pro mask aligner exposure system with LED light source and equivalent 1 kW mercury lamp.

Primelite GmbH is a German startup specializing in UV LED light source solutions. From the outset, its product designs have been focused on the semiconductor application market. In addition to using the most advanced UV LED chips, its optical components are semiconductor-grade, and the company carefully selects key component suppliers. Primelite also upholds a commitment to high-quality assurance with German design and manufacturing standards.