<title>Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology</title>

Abstract

EUVL, i.e. projection lithography, utilizing actmic wavelengths in the range of 21 1-13 nm, appears to be the natural extension of optical lithography into the NGL-regime. All-reflective imaging systems, utilizing aspherical, multilayer coated, near normal incidence mirrors with reflectivities around 70%, were designed to enable diffraction limited imaging from 7Onm down to 3Onm feature sizes at high throughput. However, diffraction limited performance of optical systems calls for surface figures of typically 2J50to 2/1OO. Considering the operation wavelength of 2l 1-13 nm, this demand corresponds to unprecedented requirements for figure metrology and fabrication technology. Simultaneously, low flare levels and high reflectivities of the mirrors have to be ensured for proper system operation. These properties are related to the substrate roughness in the mid spatial (typically ljim-lmm) and high spatial (typically <1 jim) frequency ranges respectively. Accordingly these quantities have to be generated and controlled on a few-A-level.In this paper, the metrology and fabrication concepts at CARL ZEISS will be reviewed. The present status in the fabrication of specific EUVL mirrors will be reported as well.

<title>Progress of the EUVL alpha tool</title>

“…The potential of blassical'approaches, based on refractive compensation systems was assessed in the framework ofthe Micro Exposure Tool (MET) mirror fabrication system as reported previously [9]. In this MET project, Carl Zeiss is building a projection optics box in collaboration with Lawrence Livermore National Labs [10].…”

Projection optics for extreme ultraviolet lithography (EUVL) micro-field exposure tools (METs) with a numerical aperture of 0.5

“…These PSD curves are used to guide the polishing of the optical surfaces. This strategy has been described in earlier literature [7]. A technological challenge of the MET5 program is adapting the polishing and metrology techniques used to achieve the results above on aspheres with greater aspheric departure.…”

Manufacturing and Investigating Objective Lens for Ultrahigh Resolution Lithography Facilities

“…Now this method is widely used for substrate form correcting and even for final ion-beam polishing in optical industry (Allen et al, 1991;Chason & Mayer, 1993;Ghigo et al, 2007). Recently an intensive literature has evolved which is devoted to the application of this method for the precision correction of substrates for projection EUV lithography (Dinger et al, 2000;Murakami, 2007). For the ion beams, applied for the surface shape correction of substrates for EUV and soft Xray optical elements, a number of requirements are imposed, the basic of which is the preservation of the surface roughness at an initial (supersmooth) level even when the removed layer depth reaches a few hundreds of nanometers.…”