Droplet impact phenomena in nanolithography

Sten Arjen Reijers

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Extreme ultraviolet lithography (EUVL) is the next generation of photo-lithography technology used by the semiconductor industry for the manufacturing of integrated circuits. Fundamental understanding of the fluid dynamics inside this machine is crucial to optimize and stabilize the EUV light used in this machine. In this thesis we therefore study, both numerically and analytically, two types of droplet impact phenomena: the deformation dynamics of a droplet after laser impact and the splashing and cavity dynamics after oblique droplet impact onto a deep liquid pool.

In the first part of this thesis we present a numerical and analytic framework to study the propagation of pressure waves inside the droplet as function of a pressure pulse acting on the illuminated side of the droplet after laser impact. We show that compressible flow effects strongly alter the early droplet deformation when the momentum transfer to the droplet is increased and the pressure pulse duration is short compared to the acoustic timescale. Furthermore, we present and experimentally validate a model for the tilt angle sensitivity, i.e. when the laser impacts the droplet with a relative misalignment to the center-line. We validate this model for three different experimental settings and we analytically show that the tilt angle sensitivity is minimized when the laser spot size is large compared to the effective size of the droplet.

In the second part of this thesis we numerically study the ejecta sheet formation, splashing threshold, cavity formation, cavity evolution and the maximum cavity dimensions after oblique droplet impact onto a deep liquid pool. We are able to recover all experimental splashing regimes: an omni-directional, a single-sided crown splash and deposition regime for a broad range of impact parameters. Finally, we introduce a semi-analytical solving method for the Burgers' equation to study nonlinear flows. We proof that a sequence transformation allows to write the non-linear equation as a recursive integral equation for all initial value problems. The method could potentially be used to get a deeper understanding of the non-linear flow regimes inside the droplet after laser impact or after oblique droplet impact, which we leave for future work.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
  • Lohse, Detlef, Supervisor
  • Gelderblom, Hanneke , Co-Supervisor
Award date17 Oct 2019
Place of PublicationEnschede
Print ISBNs978-90-365-4871-7
Publication statusPublished - 17 Oct 2019


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