BRAGG-FRESNEL OPTICS FOR HARD X-RAY MICROSCOPY - DEVELOPMENT OF FABRICATION PROCESS AND X-RAY CHARACTERIZATION AT THE ADVANCED PHOTON SOURCE

Results are presented on development of processes for fabricating line ar and circular Bragg-Fresnel lenses (BFLs) on Si and III-V compound m aterial substrates, and on x-ray characterization of linear BFLs at th e Advanced Photon Source (APS). Processes were developed for fabricati ng long (zone length >5 mm) linear BFLs on Si with enhanced capability for focusing high-energy x rays. By stitching together 20 sequentiall y exposed 400-mu m-long linear BFLs, we were able to fabricate 8-mm-lo ng linear BFLs with 0.5-mu m finest zone width. BFLs were also fabrica ted on III-V compound semiconductor substrates GaAs and InP, with impr oved process control due to the substantially reduced zone thickness r equired (similar to 50% less than Si). Reduction of the zone aspect ra tio (thickness/width) lessens the demand on the process technology, an d may lead to higher lens resolution and pattern transfer accuracy. A process was explored to fabricate BFLs on a GaAs/AlGaAs heterostructur e incorporating a built-in ''etch stop'' layer to ensure uniform zone thickness. Experimental characterization of the focusing properties of a field-stitched 8-mm-long linear BFL on Si (zone aperture=150 mu m) was conducted at APS undulator beamline 1-ID-C using 10-keV x rays. Ba sed on measured focal plane intensity distribution, the focus was esti mated to be 1.2 mu m, comparable to the geometrically demagnified sour ce size of similar to 1 mu m. Lens efficiency was estimated to be simi lar to 30%. Work is underway to incorporate the BFL-microprobe in x-ra y microdiffraction and fluorescence microscopy experiments to study sp atially confined complex materials. (C) 1998 American American of Phys ics.