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Hard X-ray nano-patterning

 

Hard x-ray lithography using Talbot effect

 

When a monochromatic light wave is incident on a periodic grating, the wave-field at the exit of the grating is replicated at the multiples of the 'Talbot distance', downstream of the grating. The sectioned multilayer mask composed of Si and WSi2 are used as a hard x-ray mask. Synchrotron hard x-rays usually used as a light source for making a sub 100nm nano-pattern. Also, Fresnel diffraction based simulation is conducted to specify the exact Talbot distance.

 

     pt1.png

 

                       < Schematic view of the Talbot effect. The grating image is replicated at the Talbot distance, ZT while its phase

                is reversed at ZT/2. The period of the wave-field intensity reduces to half the grating period at ZT/4 and 3ZT/4. >

 

                    pt2.jpg

                      < Wave-field intensity recorded on PR at 0.2 mm (a), 1.4 mm (b), 2.8 mm (c), 4.2 mm (d), 5.6 mm

                               (e) downstream of the grating. On the right is the simulated result for comparison. >

 

Hard x-ray lithography using focused beam

 

We focus coherent hard x-rays using Fresnel Zone Plate (FZP). The outermost zone width of FZP is approximately 400nm, and the focal length is 1.5m long at 7.5keV. The beam size is about 5mm * 35mm. The focused beam flux is estimated to be 1012 /mm2. We have another FZP of short focal length with a circular beam. The focused beam size is 40nm * 40m. Using these FZPs, the x-ray exposure time to make patterns can be dramatically reduced. So, we can develop x-ray beam writer such as e-beam writer.

 

                                                        pt3.jpg

                   < (a) Optical microscope image of the Fresnel zone plate fabricated on silicon used in this experiment. 

                                 (b) Schematic drawing of the focusing geometry using the zone plate. >

 

                                                              pt4.JPG

 

             < SEM images of the PR patterned by unfocused direct beam (a) and focused X-ray beam with exposure times of 4 s

                                                         (b) 5 s (c) and 10 s (d), respectively. >

XLNP Department of Physics and Photon Science , GIST , 123 Cheomdan-gwagiro(Oryong-dong), Buk-ku, Gwangju, 500-712 Republic of Korea Tel : +82-062-715-2352 Dasan building 606

Designed by J.M.Kim and D.H.Kang / X-ray Laboratory for Nano-scale Phenomena

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