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- Rocca, J. J., et al.
(författare)
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Compact Soft X-ray Lasers for Imaging, Material Processing, and Characterization at the Nanoscale
- 2007
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Ingår i: 32nd IEEE/CPMT International Electronic Manufacturing Technology Symposium. - 9781424413355 ; , s. 72-73
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Konferensbidrag (refereegranskat)abstract
- As manufacturing of devices advances into the nanoscale, critical feature sizes have rapidly shrunk to below the wavelength of visible light. These advances in nanotechnology have created a need to develop better ways of accessing the nanoworld. The extreme ultraviolet (EUV)/ soft x-ray (SXR) region of the spectrum provides an opportunity to use coherent light at wavelengths that are 10- to 100-times shorter than visible light, at 1 to 100 nm. Given the diffraction limit in imaging resolution, these wavelengths allow us to "see" smaller features and "write" smaller patterns than would be possible with visible light. We have developed compact laser-pumped and discharge-pumped lasers operating at wavelengths of λ=13.2 nm [1] and λ=46.9 nm [2] respectively, and have used them in the demonstration of nanoscale full field imaging [3,4], nanopatterning [5], and nanoscale laser ablation [6]. The high brightness and short wavelength output from these lasers when combined with specialized EUV/SXR optics, offer unique opportunities for the implementation of table-top imaging, patterning and metrology tools with superior spatial resolution for applications in nanoscience and nanotechnology. Using these new compact short wavelength lasers we have built two microscopes, using λ=46.9 nm or λ=l 3.2 nm laser illumination. The compact λ=46.9 nm microscope (Fig. 1a and lb) condenses the light using a multilayer coated Schwarzschild mirror, and images the test object using a diffractive zone plate lens. The spatial resolution of this microscopes was assessed by imaging test samples consisting of dense line gratings of half-periods ranging from 200 down to 35 nm. Figure 2(a) and (b) show images of a 100 nm and 70 nm half-period gratings obtained with the λ =46.9 nm microscope. The lineout in the image of the 70 nm lines shows a modulation of ∼30% indicating that the features are fully resolved according to the Rayleigh criterion. By rearranging the optics, the λ=46.9 nm microscope can also image surfaces. An image of fully resolved dense metal lines, with half-period of 170 nm, patterned on the silicon wafer is shown in Figure 2 (c). The shorter wavelength λ= 3.2 nm microscope uses all zone plate optics to render images of transmissive test patterns with increased spatial resolution . An image of fully resolved 50 nm half-period dense lines acquired with a 20 seconds exposure is shown in Figure 2(d). From images like this one, the spatial resolution of the λ=13.2 nm table-top microscope was determined to be better than 38 nm [3]. The high coherence of these short wavelength lasers also allows for the printing of arrays of nanoscale features using interferometric lithography. We have demonstrated combined a λ=46.9 nm capillary discharge laser and a Lloyd's mirror to print arrays of cone-shaped nano-dots with ∼ 58 nm FWHM diameter (Fig 3a) [5]. The same arrangement was used to print arrays of nano-holes 120 nm FWHM and 100 nm in depth over areas in excess of 500 × 500 μm2 in different photoresists using exposure times as short as 80 s. Larger area patterns can be readily printed using precision translation stages and multiple exposures by overlay superposition. The ability to focus SXL laser light into near diffraction-limited spots also opens the possibility to develop new types of nanoprobes. We have demonstrated ablation of sub-100 nm diameter holes by directly focusing the output of a λ=46.9 nm laser onto a sample with a zone plate lens. Figure 3(b) shows an AFM image of a 82 nm diameter crater obtained ablating a 500 nm thick PMMA layer with a single laser shot. The holes were observed to have very clean walls and high reproducibility. We have recently added the capability to spectroscopically analyze the light emitted from the plasma created during the ablation, opening the possibility to develop analytic nanoprobles. All of these results illustrate the capabilities of compact short wavelength lasers for nanotechnology applications.
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