X-ray zone plates with 25 aspect ratio using a 2-μm-thick ultrananocrystalline diamond mold
- 356 Downloads
Hard X-ray phase zone plates are focusing optics used for X-ray microscopes at synchrotron radiation facilities. The resolution is determined by the outer-most zone width (OZW) and modern lithographic techniques are capable of patterning OZW less than 100 nm. Efficiency of a phase zone plate will peak when the zones have a thickness that provides a π-phase shift to the X-rays. Thus, a hard X-ray zone plate with ideal efficiency and sub-100-nm resolution requires fabricating high-aspect-ratio, dense-packed structures in materials suitable for exposure to synchrotron radiation. The fabrication method implemented involves an electroforming mold process where a top resist layer is lithographically patterned and used for pattern transfer into a bottom layer which acts as the electroform mold. The resulting mold is filled with Au by electroplating, and afterwards the mold is not removed but remains in place for mechanical support. Ultrananocrystalline diamond (UNCD) was used as the mold layer. UNCD is deposited by hot-filament chemical vapor deposition with well-controlled stress and thickness up to 2 μm. The top resist layer is hydrogen silsesquioxane, which is a high-contrast electron beam lithography resist and resistant to the oxygen reactive ion etching required for UNCD pattern transfer. Using this fabrication method, we successfully produced zone plates with OZW down to 80 nm and an aspect ratio up to 25 for a thickness of 2 μm. The efficiency of several fabricated zone plates were measured, demonstrating their functionality.
KeywordsOuter Zone Zone Plate Mold Material Pattern Transfer Electron Storage Ring
We acknowledge Daniel Rosenmann and Ross Harder for their assistance, Advanced Diamond Technologies for supplying UNCD films. Use of the Center for Nanoscale Materials and the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
- Naguib NN, Elam JW, Birrell J, Wang J, Grierson DS, Kabius B, Hiller JM, Sumant AV, Carpick RW, Auciello O (2006) Carlisle JA (2006) Enhanced nucleation, smoothness and conformality of ultrananocrystalline diamond (UNCD) ultrathin films via tungsten interlayers. Chem Phys Lett 430(4):345–350. doi: 10.1016/j.cplett.2006.08.137 CrossRefGoogle Scholar