In the Lithocoat project, co-funded by ChemistryNL, TNO, together with ASML, is searching for a hydrophobic coating that can withstand extreme conditions and is not harmful to the environment. The project yields a great deal of generic knowledge regarding PFAS-free hydrophobic systems and degradation mechanisms, which can then be applied to other applications.
Hydrophobic coatings are important in many areas to prevent moisture from having an undesirable effect. Examples include outdoor clothing, food packaging, and industrial processes. Until recently, per- and polyfluoralkyl (PFAS)-like coatings were often used for this purpose. However, these are so strong that they are sometimes referred to as “forever chemicals” because they practically do not break down in nature and consequently accumulate in plants and animals. This situation has led to legislation and regulations prohibiting the use of PFAS. Consequently, a search has begun for alternative coatings that possess the same properties as PFAS but do not pose a burden to health or the environment.
Stable under extremely hard radiation
In the two-year Lithocoat project, TNO and ASML are collaborating on the development of such a hydrophobic coating for use in lithography machines, which is resistant to high intensity hard UV radiation. The production process utilizes UV light with an extremely short wavelength (deep UV) and very high intensity. Under these conditions, chemical bonds break easily and free radicals are formed. Only very strong materials do not degrade under these conditions. Therefore, for the coating ASML needs, one must look not only at the hydrophobic character but also at the robustness of the molecules.
There are various possibilities regarding the hydrophobic character. “If you do not want to use fluorine, as in PFAS, you first look at long alkyl chains that you fix to a surface, for example,” explains Daniel Mann, Senior Scientist from the Materials Solutions department at TNO.
Designing New Materials
“We started in September 2025. We spent the first few months working with ASML to thoroughly define the user requirements,” says Nicole Meulendijks, who is involved in this project as a project manager from the Materials Solutions department at TNO. “After selecting the promising approaches and materials, we are now conducting tests.” In the initial rapid screening, Mann and his team examine the hydrophobic nature of the new materials. Subsequently, the candidates proceed to more rigorous test conditions set up by ASML. Candidates that fail quickly are eliminated, while the promising ones enter a phase where they are further optimized, for example by adding additives or changing the structure. Finally, the researchers also examine the molecular structure by combining various analytical techniques. For instance, a thermogravimetric analysis (TGA), in which the material is heated to approximately 1000 degrees, allows for the study of mass loss and the moment water is released. This provides an indication of the ratio between organic and inorganic compounds and says something about the temperature stability of the material.
With other tests, the team examines which atoms are present, how they are linked, and what the oxidation state is. For nanomaterials, the microscopic structure of the material can even be visualized using an electron microscope. “Full characterization takes a lot of time, so we only do that for materials that we have determined, together with ASML, have interesting properties.”
Exploring different paths
Mann explains that they started with a number of materials, some of which did not work as well as expected. “We now have a candidate that actually works quite well. We are currently refining that material and further testing whether it actually meets all user criteria.” At the same time, Mann is also looking for other candidates to have alternatives in reserve in case the first candidate turns out not to meet the requirements.
