Underlayer optimization method for EUV lithography

The combination photoresist-underlayer fulfills a central role in EUVL for patterning. Moreover, future high numerical aperture (NA) and tight pitches will require very thin layers in the lithography stack, which will increase the impact of chemical interactions at the photoresist-underlayer interface. Adhesion between these layers will be critical to overcome pattern collapse at high aspect ratios whereas at the same time the impact of interfacial effects, such as intermixing, on the lithography performance must be minimized. A fine balance must be found between several chemical interactions, which is a complex exercise with many unknown parameters. In this paper we present how the polar and dispersive components of the surface energy can be used to optimize EUV underlayers in order to achieve the best lithography performance. Subtle changes in the underlayer composition can have a large effect on the lithography performance. A PTD CAR photoresists test case will be used to demonstrate that the photoresist profile, scum formation, line width roughness, pattern collapse and stochastic defects can all be tuned into a certain direction just by tweaking the surface energies of the underlayer. The simplicity of the methodology in this study will be a powerful knob to understand and optimize underlayers for EUV photoresist-underlayer interactions.