The relationships between polymer molecular weight, surface roughness measured by Atomic Force Microscopy (AFM), and EUV (Extreme UltraViolet, 13.4 nm) line edge roughness (LER), were studied in four separate rounds of experiments. In Round 1 , EUV-2D (XP98248B) was prepared with seven levels of added base. These seven resists were patterned using EUV lithography; the LER was determined using 100 nm dense lines. The LER of the seven resists dramatically decreases with increasing level of base. These LER results were compared with the surface roughness of these resists after development for unexposed and DUV (248 nm) exposed surfaces. In Rounds 2-4, we evaluated three sets of EUV-2D type resists prepared with polymers having M of 2.9, 4.9, 6. 1, 9.1, 16. 1, and 33.5 Kg/mole. EUV LER and surface roughness were determined for each resist. In Round 2, the polymers were substituted into the EUV-2D resist matrix with no other formulation changes. In Round 3, the PAG level was decreased with increasing polymer M to obtain a constant unexposed film thickness loss (UFTL) for all six resists. In Round 4, both PAG level and base level were modified to yield six resists with similar sensitivity and UFTL. These experiments have led to conclusions about the impact of polymer molecular weight on imaging LER and AFM surface roughness, as well as elucidating the relationship between all three.

The extreme ultraviolet (EUV) Engineering Test Stand (ETS) is a step-and-scan lithography tool that operates at a wavelength of 13.4 nm. It has been developed to demonstrate full-field EUV imaging and acquire system learning for equipment manufacturers to develop commercial tools. The initial integration of the tool is being carried out using a developmental set of projection optics, while a second, higher-quality, projection optics is being assembled and characterized in a parallel effort. We present here the first lithographic results from the ETS, which include both static and scanned resist images of 100 nm dense and isolated features throughout the ring field of the projection optics. Accurate lithographic models have been developed and compared with the experimental results.

Photospeed is a prime consideration for wafer throughput of extreme ultraviolet ͑EUV͒ lithography. Faster photoresists additionally provide system advantages such as less thermal management of the mirrors and mask, and potentially increased component lifetimes. However, there are some predicted detrimental considerations when using fast photoresists such as shot noise. In this article, we report details of the formulation of photoresists exposed at 248 nm and identical formulations exposed at 13.4 nm. Compositions typically contained co-or terpolymers of poly-4-hydroxystyrene, t-butyl acrylate and as an option, styrene, a photoacid generator of bis-t-butylphenyl iodonium camphorsulfonate or perfluoroxbenzensulfonate and tetrabutyalummonium or triphenylsulphonium hydroxide base. With these formulations, the EUV photospeed was varied from 34 to 2.7 mJ/cm 2 . Scanning electron microscope analysis was done for all wafers at Sandia using GORA software to determine the line-edge roughness ͑LER͒. Identical formulations were exposed at photon dense deep UV ͑DUV͒ wavelengths and comparatively photon-sparse EUV wavelengths. Therefore, ratioing the LER of identical formulations exposed at DUV minimizes the confounding effects of formulation changes that affect dissolution, resolution, etc. A plot of the line-edge roughness ratio of LER EUV /LER DUV as a function of the photospeed was used to gain insight into the effect of shot noise on the LER of dense lines. If shot noise effects were dominating the LER for EUV, then the ratio would increase above the nominal value as the dose to size was decreased. It is clear that the current generation of DUV resists, with the invention of no new material required, can be reformulated to satisfy the photospeed specification of 5 mJ/cm 2 for EUV lithography and no shot noise effects have been observed.

We demonstrate direct flare measurements of 4-mirror projection optics in the Engineering Test Stand (ETS) using a conventional resist clearing method (the Kirk method). Two extreme ultraviolet (EUV) lithographic projection optics, one with higher flare than the other, have been characterized and the results compared. The measured results have also been compared to analytical calculations based on measured mirror roughness and the extended point spread function (PSF). Full-field flare across the 24 mm field width has been measured, and we have verified that flare is constant across the field for EUV lithography as predicted. Horizontal (H) and vertical (V) flare bias has been observed and the cause of the H-V flare bias has been investigated. The main cause has been identified to be anisotropic mirror polishing. Simulations with the 2 dimensional Power Spectral density (PSD) function have confirmed the experimental results.

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