Advances of tabletop electron storage rings for generating a brilliant extreme ultraviolet (EUV) or soft x-ray beam are discussed. An electron storage ring called MIRRORCLE-20SX currently provides a stored beam current with an average of 3 A, a 1-minute lifetime, 15 ms radiation damping time, and a beam size of about 3×3 mm2. We generate EUV by a thin-film target placed in the electron orbit. Photons in the wavelength around 13.9 nm is generated by an Si thin film, and 4.3 nm by a diamond-like carbon (DLC) film placed in the circulating electron beam. It is known from previous experimental studies that the mechanism of EUV emission is a synchrotron Cherenkov radiation (SCR). The observed photon power is 14 W/sr by the DLC film. We report that SCR is suitable for EUV lithography (EUVL) because the spectrum is monochromatic, the radiation angular spread is as narrow as 20×5 mrad2, and the emitter size can be 0.01×3 mm2. An optimized EUV source for lithography based on the tabletop synchrotron is proposed.
We present the conceptual design of a dispersive X-ray Absorption Fine Structure (XAFS) beamline for MIRRORCLE,
a new compact laboratory X-ray source. This machine accelerates electrons up to 1,4,6 or 20MeV
(depending upon the model) in a ring and produces X-rays when the electrons collide onto a thin target. The
radiation emitted has a white spectrum due to both synchrotron and bremsstrahlung emission. A substantial
part of the electrons are recovered after collisions, and the emitted light has high flux, wide energy spectrum
and a large angular dispersion.
We have opted for a simple beamline design using a collimator, slits, a curved crystal, the sample environment
and a CCD. The beamline parameters (position of the mirror, ray of curvature, slit aperture, reflecting angle, etc.)
have been optimized by defining and improving a figure of merit. This optimization allows for room constraints
(distances among elements), mechanical constraints (minimum curvature radii available) and optical constraints.
Further ray tracing simulations using SHADOW3 have been performed to check all the theoretical results, refine
the final parameters, quantitative flux calculations and for simulating the image on the CCD camera.
Advances of electron storage rings to beam currents of above 1 A and tabletop sizes make possible the development of a synchrotron-based source for EUV lithography (EUVL) at ~13.5-nm wavelength. The MIRRORCLE storage rings can provide on average 3-A electron beam current, 1-min lifetime, 15-ms radiation damping, and beam size ~3*3 mm2. MIRRORCLE-20SX, MIRRORCLE-6X, and MIRRORCLE-CV4 store electrons with energies of 20 MeV, 6 MeV, and 4 MeV, respectively. These machines can emit EUV from a tiny target, hit by the circulating beam, via transition radiation or diffusive radiation. Using a multilayer microelectromechanical system (MEMS) target allows enhancement and spectral purification of the emitted EUV. Aligning many such MEMS along the electron beam orbit and radiation collection by only one quasi-elliptical EUV mirror can provide EUV satisfying the joint requirements for an EUVL source.
MIRRORCLE is a noble hard X-ray source, which is quite different from either X-ray tubes or synchrotron light sources (SLS) in many regards. MIRRORCLE generates very parallel and high-density photons like SLS, but the source emitter size is much smaller than SLS as well as tube. The radiation angular spread is much wider than SLS and similar to tube. Thus diagnosis of human body size is possible. The X-ray spectrum is polychromatic peaking around 30-200 keV, which
is higher than SLS, while X-ray tube uses characteristic X-rays. The photon energy is selectable with MIRRORCLE by changing the target material and thickness. Because of these wonderful features the imaging by MIRRORCLE demonstrates 10 to 100 times magnifications, extremely sharp edge enhancement due to the phase contrast, and one
micron order spatial resolution without optical elements. Density mapping is demonstrated in a simple plane magnified imaging. When tomography is applied, density volume mapping is obtained.