Measurement and adjustment of resist SWA in EUV lithography

EUV Lithography is in production for multiple years now and this gave us significant learning. Absorption of the high energy photons is a key aspect, which leads to the challenge of carefully tuning the resist thickness. For thin resists there is little absorption which is not beneficial for photon stochastics. On the other hand if resist thickness is large this might have detrimental patterning consequences like pattern collapse. High absorbing resists always lead to sloped profiles after resist development. This has impact on the achievable Depth of Focus. We will show experimental validation of SWA through focus and LCDU through resist stack, both for 0.33NA and 0.55NA. It might be advantageous to try and adjust the profile and SWA, especially in negative defocus condition. This can be done applying micro focus-drilling. With micro focus drilling the imaging properties are more homogenous across the resist stack, especially on the negative defocus side. We will show experimental validation of this concept of Micro Focus Drilling.