Upon loading and unloading wafers in nanolithography machines, friction occurs between the wafer and its support. While some friction is required to fixate the wafer, inhomogeneous deformations and stresses that occur during these positioning processes can affect the accuracy of the illumination process. The goal of this project is to investigate the potential of using mechanical metamaterials on the wafer support to passively control and guide the wafer flattening process, as part of a general suite of positioning and aligning problems in high-tech systems.

Metamaterials are materials that derive their properties from their structure, not only from their chemical composition. The internal structure of these materials is specifically designed to create new functionalities not found in nature. While most of the properties of these metamaterials are fixed, compliance, resulting from the use of soft or relatively thin materials, can be used as a paradigm to design mechanical metamaterials that exhibit tunable functionality. Applications range from materials with adaptive auxetic behavior, tunable stiffness, or ad-hoc optical, phononic, and acoustic properties, to tunable surface properties such as the drag coefficient, wettability, and chemistry. A particularly interesting and promising avenue that is being explored at AMOLF is to harness mechanical instabilities in the design of reconfigurable metamaterials, as a way to incorporate increasingly non-linear mechanical behavior that can be used for more complex interactions with the material’s environment.

While a range of mechanical metamaterials with unique properties have been developed, up till now their application remains limited. Given that the mechanics that govern the response of these metamaterials are scale invariant, most of the metamaterials being developed at AMOLF are built and tested at the macroscale (typical mm-scale to cm-scale features), and depend on fabrication strategies involving 3D printing, lasercutting and manual assembly. However, depending on the required materials, additional fabrication constraints exist at the micro- and nanoscale, and in order to explore the potential practical use of metamaterials at these scales, this project, that is a new collaboration between ARCNL, ASML and AMOLF, could prove essential.

To explore this connection, we have identified a possible problem at ASML for which mechanical metamaterials could potentially provide a solution. In DUV and EUV lithography systems, wafers are placed on wafer supports, aligned and exposed. In both cases the wafer support surface comprises an array of pillars termed burls. The wafers are not completely flat, and during loading the wafer is flattened against the burls either by applying air pressure differences (DUV) or electrostatically (EUV), and later released during unloading. The non-flatness of the wafers during the loading and unloading processes leads to the occurrence of friction between the wafer and the burls of the wafer support. This friction varies with number of wafer passes, from wafer to wafer and from burl to burl, because of wear and differences between wafer back-side material, surface condition, contamination and local environment. The large number of factors affecting friction means that the friction variations are largely unpredictable. The friction results in stresses and deformations in the wafer and in the support. Although the friction forces are transmitted at the bottom side of the wafer, the deformations that result from these friction forces are ‘visible’ at the top of the wafer. Friction - and the unpredictable changes in the friction forces - thus limit the accuracy and repeatability with which the wafer can be positioned.

In this project you will explore how wafer loading can be improved by the use of mechanical metamaterials. By tuning the nonlinear mechanical response of the metamaterial, our aim is to deform the curved wafer into a flat (or significantly flatter) state without exerting (large) tangential forces on the wafer that would cause inplane deformations. The height and stress/strain relation of the mechanical metamaterials can in principle be designed, so that the effect is independent of the original flatness profile of the wafer. We will start approaching this problem through a combination of analytical (e.g. simple spring models), numerical optimization (e.g. machine learning) and 'table-top' experimental work.

At the start of the PhD the candidate meets the requirements for an MSc-degree, to ensure eligibility for a Dutch PhD examination. The position is open to candidates from a range of backgrounds, including Physics, Engineering, Mathematics, Computer Science or a related field. We are looking for a highly motivated candidate with a go-getter mentality. Preferably, the candidate has a strong theoretical/numerical background, in combination with a sound appetite for experimental work. Excellent verbal and written communication skills (in English) are essential.

The position is intended as full-time (40 hours / week, 12 months / year) appointment in the service of the Netherlands Foundation of Scientific Research Institutes (NWO-I) for the duration of four years, with a starting salary of € 2,441 and a range of employment benefits. After successful completion of the PhD research a PhD degree will be granted at the University of Amsterdam. Several courses are offered, specially developed for PhD-students. AMOLF assists any new foreign PhD-student with housing and visa applications and compensates their transport costs and furnishing expenses.

Soft Robotic Matter

Besides being embedded in the Soft Robotic Matter group of Overvelde, the project is a collaboration between other groups at AMOLF (van Hecke), ARCNL (Weber) and ASML.

The Soft Robotic Matter group (See also: www.overvelde.com) combines concepts from soft robotics and architected materials, to provide new and exciting opportunities in the design of compliant structures and devices with highly non-linear behaviour. To this end, the Soft Robotic Matter group uses a combination of computational and experimental tools. The Contact Dynamics group at ARCNL researches fundamental aspects of friction and wear with a relevance to positioning challenges in nanolithography. For this project, your lab work will be primarily stationed at AMOLF, as employee of the AMOLF-ARCNL joint research programme, you will work closely with the ARCNL team, as well as with expert industrial contacts from ASML. 

AMOLF performs leading research on the fundamental physics and design principles of natural and man-made complex matter, with research in 4 interconnected themes: nanophotonics, nanophotovoltaics, designer matter, and biophysics. AMOLF leverages these insights to create novel functional materials, and to find solutions to societal challenges in renewable energy, green ICT, and health care. AMOLF is one of the NWO-I national research institutes located at the Amsterdam Science Park, Amsterdam, The Netherlands. It has approximately 130 scientist and a total size of ca. 200 employees. Furthermore it hosts the Amsterdam NanolabNL clean room, which is part of the national NanoLabNL cleanroom network. See also www.amolf.nl

ARCNL The Advanced Research Center for Nanolithography (ARCNL) focuses on the fundamental physics and chemistry involved in current and future key technologies in nanolithography, primarily for the semiconductor industry. ARCNL is a public-private partnership between the Dutch Research Council (NWO), the University of Amsterdam (UvA), the VU University Amsterdam (VU) and the semiconductor equipment manufacturer ASML. ARCNL is located at the Amsterdam Science Park, Amsterdam, The Netherlands, and is currently building up towards a size of approximately 100 scientists and support staff. See also www.arcnl.nl