Optimization of multilayer reflectors for extreme ultraviolet lithography

Bal, Matthieu F.; Singh, Mandeep; Braat, Joseph J. M.

doi:10.1117/1.1793171

Cited by 14 publications

(4 citation statements)

References 11 publications

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“…Liang et al, 2001 used a ray tracing model to show that laterally grading multilayer coatings for reflective lenses can improve reflectance over large angular ranges while reducing aberration [1]. Similar analysis by Bal et al, 2004 found that laterally graded multilayers can be designed to sharpen the point spread function by reduction of angularly dependent focus shifts [2].…”

Section: Introductionmentioning

confidence: 87%

Genetic optimization of aperiodic multilayer masks for high and hyper-NA EUV lithography

Maguire,

Smith

2024

Optical and EUV Nanolithography XXXVII

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To achieve higher resolution extreme ultraviolet lithography targeted toward sub-10nm, reflective projection scanner image numerical apertures (NA i ) are being increased beyond the current value of 0.33 to 0.55, and upwards of 0.75 as a desirable target. Bragg reflectors using alternating silicon and molybdenum that have heretofore been coated as periodic multilayers cannot achieve desired reflected amplitudes as corresponding 0.25X mask numerical apertures (NA m ) are accordingly increased. Additionally, TM polarized image modulation decreases with NA, which becomes significant at 0.55 and above. We present here the optimization of non-regular alternating, or aperiodic, silicon-molybdenum multilayer reflective coatings that can achieve improved amplitude and polarization performance through angle as higher-NA EUVL lithography is pursued. Through the use of rigorous EM computation paired with a genetic optimization method, we show that amplitude apodization can be recovered to 60% peak reflectance for NA m values up to 0.2 (corresponding to NA i values of 0.8), while at the same time achieve a TE degree of polarization (DOP) exceeding 40%.

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Section: Introductionmentioning

confidence: 87%

Genetic optimization of aperiodic multilayer masks for high and hyper-NA EUV lithography

Maguire,

Smith

2024

Optical and EUV Nanolithography XXXVII

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“…Such EUV sources and corresponding beam steering optics are currently being developed with tremendous effort. [2][3][4][5][6][7][8][9][10][11][12][13] Besides semiconductor microlithography, there are also other applications of EUV radiation, which can strongly profit from the EUVL source and optics developments. For instance, Bonfigli et al demonstrated the generation of surfacenear color centers in LiF crystals positioned in the vicinity of a laser-produced EUV plasma.…”

Section: Introductionmentioning

confidence: 99%

Compact EUV source and Schwarzschild objective for modification and ablation of various materials

et al. 2007

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In recent years technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far, intense light sources based on discharge or laser plasmas, light guiding and imaging optics, as well as detection devices are already available. Currently, the application of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis comes more and more into focus. The aim is to make use of the strong interaction between soft x-ray radiation and matter for surface-near probing, modification or structuring techniques. In this contribution, we demonstrate the surface-near direct structuring of different polymeric materials as well as lithium fluoride crystals using EUV radiation with a wavelength of 13.5 nm. The setup consists of a table-top EUV source based on a laser-induced plasma and a modified Schwarzschild objective with a resolution down to 130 nm. The mirrors of the employed objective were coated with Mo/Si multilayers, providing a transmittance of around 42 % (reflectivity ~65 % @ 13.5 nm per mirror). With a demagnification factor of 10 small foci are generated, leading to spot diameters of 30 µm in plasma imaging mode and down to 1 µm in mask imaging mode, respectively. The EUV energy density of ~100 mJ/cm² obtained in the focus is sufficient to observe direct photo-etching of polymers, e.g. PMMA. Thus, material interaction studies are currently in progress. The investigations revealed already that in contrast to common excimer laser ablation there are no incubation pulses when using EUV radiation. For lower energies the ablation rate is found to be linear with respect to the applied dose, whereas for higher energies a saturation behavior is observed. By EUV irradiation of LiF samples surface-near defects within the crystal lattice are formed. These color-centers (mainly F 2 -and F 3 + -color centers) are known to be stable at room temperature. They are able to emit characteristic radiation in the visible range after optical excitation with a wavelength around 450 nm. In the future structured areas of such color centers could be used as laser-active gain medium in distributed feedback lasers. For measuring the radiation resistence of Mo/Si mirrors, the setup was used as a top-illuminated microscope at 13.5 nm. By placing the analyzing Mo/Si mirror into the image plane of the objective, the change in reflectivity due to irradiation at a fluence of 20mJ/cm 2 could be observed.

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“…The choice of an adequate initial design plays a significant role in obtaining a highquality EUV lithographic objective. 11,12 However, for an EUV objective system, the large number of variables and design requirements make the optical design difficult. A grouping design method is generally applied for designing a complicated optical system.…”

Section: Strategy Of Grouping Designmentioning

confidence: 99%

Designing projection objectives for 11-nm node of extreme ultraviolet lithography

Cao

Liu

2014

J. Micro/Nanolith. MEMS MOEMS

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Abstract. Extreme ultraviolet (EUV) lithography is a promising candidate for next-generation lithography. To achieve an 11-nm node, a six-mirror EUV projection objective with a numerical aperture (NA) of 0.5 is designed with the grouping design method. In this design, pupil obscuration is introduced to decrease the angular spread on the mirrors, which still makes the six-mirror objective with aspheric surfaces sufficient for aberration correction. The grouping design allocates the complexity of designing a whole system to each of the mirror groups and could compatibly apply to designing EUV projection objectives with obscuration. The ×8 reduction design serves as an example for illustrating the grouping design principles for this type of system. In addition, the specific design forms with different reductions are presented and discussed. Design of these six-mirror objective systems provides potential solutions for 11-nm node EUV lithography.

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Optimization of multilayer reflectors for extreme ultraviolet lithography

Cited by 14 publications

References 11 publications

Genetic optimization of aperiodic multilayer masks for high and hyper-NA EUV lithography

Genetic optimization of aperiodic multilayer masks for high and hyper-NA EUV lithography

Compact EUV source and Schwarzschild objective for modification and ablation of various materials

Designing projection objectives for 11-nm node of extreme ultraviolet lithography

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