Metal oxide resists (MORs) have become one of the most attractive photoresist platforms that allow for high resolution and etch bias of small features while having a robust lithography performance. In this work, we present our study about improving line fidelity and reducing the dose of MOR for line space EUV lithography by applying spin-on underlayers (ULs). It is known that MOR patterning is induced by the activation during exposure and condensation of the active sites. Herein, we discuss the influence of ULs on MOR performance. A series of ULs with various chemistry, thickness, or process conditions were screened with MOR using NXE3400 EUV exposure system to print 14-nm HP line-space features. The results show that the nanobridges and scum can be alleviated, while the remaining resist thickness after development can be improved by up to 20% along with 5 to 10% dose reductions. A comprehensive assessment of the ULs encompassing various chemistries examines coating quality, uniformity, and surface energy. The discussion delves into the correlation between the surface properties including morphology, interaction, etc., and their respective impacts on lithography performance. Lastly, some spin-on ULs produce up to 75% reduction of metal diffusion from the MOR into the underlying layers.
Spin-on glass (SOG) underlayers to enhance extreme ultraviolet (EUV) lithography for patterning below 28-nm pitch require an in-depth understanding of the required adhesion forces necessary for good lithography. Here, we proposed a fundamentally new SOG underlayer platform composed of polymer blends that can achieve superior uniformity to improve line fidelity and provide a design path for underlayer materials. The structure and property of elemental composition and surface energy can be controlled easily and precisely by varying the combination of polymer, and consequently understanding and tuning the lithographic performance. The lithographic performance of SOG blends was evaluated using NXE3400 EUV exposure system to print 13-nm and 14-nm HP line-space features and contact hole features with CD of 20-nm. The results show that the polymer blends expand the process window for EUV resist for line-space with printable CD >11 nm and biased LWR to 3.6-nm without impact on dose when compared to conventional copolymers. In the case of CH patterning, CDU and DOF improvements were observed when compared to conventional SOG copolymers. Systematic studies on polymer blends based on functional groups and formulation compositions are in progress to establish a better understanding of enhancement of EUV lithography.
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