As EUV approaches high volume manufacturing, reticle defectivity becomes an even more relevant topic for further investigation. Current baseline strategy for EUV defectivity management is to design, build and maintain a clean system without pellicle. In order to secure reticle front side particle adders to an acceptable level for high volume manufacturing, EUV pellicle is being actively investigated. Last year ASML reported on our initial EUV pellicle feasibility. In this paper, we will update on our progress since then. We will also provide an update to pellicle requirements published last year. Further, we present experimental results showing the viability and challenges of potential EUV pellicle materials, including, material properties, imaging capability, scalability and manufacturability.
EUV defectivity has been an important topic of investigation in past years. Today, the absence of a pellicle raises concerns for particle adders on reticle front side. A desire to improve defectivity on reticle front side via implementation of a pellicle could greatly assist in propelling EUV into high volume manufacturing. In this paper, we investigate a set of pellicle requirements and potential EUV pellicle materials. Further, we present experimental results of pellicle performance results and imaging results.
Failure of the receding meniscus during immersion lithography is one of the well known problems. A thin
liquid film left behind on the wafer during scanning may generate imaging defects. Liquid loss occurs at the
receding meniscus when the smooth substrate is accelerated beyond a critical velocity of approximately 1 m/s.
Nanotexturing the surface with average roughness values even below 10 nm results in critical velocity larger
than 2.5 m/s, the upper limit of our apparatus. This unexpected increase in critical velocity is observed for
both sticky rough hydrophobic and slippery superhydrophobic surfaces. We attribute this large increase in
critical velocity to the increased static receding contact angle, air extraction and in increased slip length for
such nanotextured surfaces. We have also presented the experimental proof of the hypothesis which shows
that the slip length and static receding contact angle as a significant parameters for the enhanced performance
of sticky surface. Further the dynamic contact line behavior on surface with regions of varying wetting
behaviour was studied. The preliminary result shows that the water droplet retains its meniscus shape as soon
as it transits from hydrophobic to superhydrophobic region. The secondary thin streak of entrained water on
the hydrophobic region is formed which can be controlled with higher extraction.
The method of electrophoretic deposition of charged polymer (polystyrene) microspheres on topologically patterned substrates is discussed. Surface patterning with different symmetries and structure periodicity in the sub-micrometer range over large surface areas was realized by laser interference lithography. Growth of colloidal crystals on patterned and bare electrode surfaces was compared. Surface patterning predetermined the colloidal crystal structure and orientation. Fcc colloidal crystals with (111), (100) and (110) crystal plane orientations parallel to the electrode surfaces were successfully grown on patterned electrodes with the corresponding pattern symmetry. The growth of colloidal crystals with (111) and (100) crystal plane orientations parallel to the electrode surface was easily controlled by patterned surfaces, while only two layers of colloidal crystals having the (110) plane orientation parallel to the electrode surface were grown in a controlled way. The growth of thick colloidal crystals in the non-close-packed  direction generated a mixture of small domains of different orientations, where domains with (111) and (100) orientations dominated. The thickness of the colloidal crystals was controlled by varying the deposition parameters. Thickness increased with increasing the applied voltage, deposition time, concentration of colloidal particles and with decreasing the withdrawal speed of the electrodes from the colloidal suspension. A threshold voltage of 3.36 V was determined, beyond which a significant increase in the thickness of the colloidal crystals with applied voltage was observed. A gradient in the thickness of the colloidal crystals was obtained across the electrode surface at low withdrawal speed (0.04 mm/s). Colloidal crystals with a homogeneous thickness over the electrode area were formed at withdrawal speeds of 0.07 - 0.1 mm/s.