P. Ilinski

Performance of a high-resolution x-ray microprobe at the Advanced Photon Source

We have developed a x-ray microprobe in the energy region from 6 to 20 keV using undulator radiation and zone-plate optics for microfocusing-based techniques and applications at a beamline at the Advanced Photon Source (APS). The performance of the beamline was shown to meet our design objectives, including preservation of the source brilliance and coherence, selectable transverse coherence length and energy bandwidth, high angular stability, and harmonic suppression of the beam. These objectives were achieved by careful thermal management and use of a novel mirror and crystal monochromator cooling geometry. All beamline optical components are water cooled, and the x-ray beam in the experiment station is stable in beam intensity, energy, and position over many days with no active feedback. Using a double-crystal Si(111) monochromator, we have obtained a focal spot size (FWHM) of 0.15 μm(v)×1.0 μm(h), and a photon flux of 4×109 photons/sec at the focal spot, and thus a photon flux density gain of 15,000. A...

Measurement of strain in Al–Cu interconnect lines with x-ray microdiffraction

We report measurement of strain in patterned Al–Cu interconnect lines with x-ray microdiffraction technique with a ∼1 μm spatial resolution. Monochromatized x rays from an undulator were focused on the sample using a phase fresnel zone plate and diffracted light was collected by an area detector in a symmetric, angle dispersive x-ray diffraction geometry. Measurements were made before and after the line sample was stressed for electromigration. Results show an increase in inter- and intra-grain strain variation after the testing. Differences in strain behavior of grains with (111) and (200) crystallographic planes parallel to the substrate surface were observed. A position dependent variation of strain after the testing was measured whereas no such dependence was found before the testing.

Optimization of the design for the LCLS undulator line

The Linac Coherent Light Source (LCLS) undulator line will consist of undulator segments separated by breaks of various lengths. Focusing quadrupoles, in a FODO lattice, and electron-beam diagnostics will be located in the breaks, and every third break will be longer to also accommodate photon diagnostics. The electron-beam beta function and the undulator period were selected to minimize the saturation length. The FEL simulation code RON has been used to optimize parameters such as the length of the undulators and the break lengths between undulators. Different break lengths after the first three undulators have been found to help reduce the overall undulator line saturation length. Tolerances for individual undulators have also been determined. r 2001 Elsevier Science B.V. All rights reserved. PACS: 41.60. Cr

X-ray microdiffraction study of Cu interconnects

We have used x-ray microdiffraction to study the local structure and strain variation of copper interconnects. Different types of local microstructures have been found in different samples. Our data show that the Ti adhesion layer has a very dramatic effect on Cu microstructure. Strain measurement was conducted before and after electromigration test, Cu fluorescence was used to find the mass variations around voids and hillocks, and x-ray microdiffraction was used to measure the strain change around that interested region.

APS undulator radiation—first results

The first undulator radiation has been extracted from the Advanced Photon Source (APS). The results from the characterization of this radiation are very satisfactory. With the undulator set at a gap of 15.8 mm (K=1.61), harmonics as high as the 17th were observed using a crystal spectrometer. The angular distribution of the third-harmonic radiation was measured, and the source was imaged using a zone plate to determine the particle beam emittance. The horizontal beam emittance was found to be 6.9 {plus_minus} 1.0 nm-rad, and the vertical emittance coupling was found to be less than 3%. The absolute spectral flux was measured over a wide range of photon energies, and it agrees remarkably well with the theoretical calculations based on the measured undulator magnetic field profile and the measured beam emittance. These results indicate that both the emittance of the electron beam and the undulator magnetic field quality exceed the original specifications.

Photon diagnostics for the X-ray FELs at TESLA

An X-ray diagnostic station will be installed for each of the XFEL undulator beamlines at TESLA. Primary purpose of the X-ray diagnostics is to provide an additional tool for alignment and commissioning of the numerous undulator cells along an XFEL beamline independently from electron-beam-based alignment procedures. Both methods will complement one another. The X-ray diagnostic station will be a sensitive instrument generating essential input for the undulator control system. The diagnostic station will be located about 120 m downstream from the last undulator cell. Total flux measurements will verify the XFELs gain. Analysis of the spectral and spatial distribution of the spontaneous radiation of individual or several consecutive undulator segments will be used to optimize angle and position of the electron beam trajectory, to verify the magnetic gap, and to adjust the phase match between two undulator segments. The two latter purposes cannot be served by electron-beam-based alignment.

X-ray zone plate fabrication using a focused ion beam

An x-ray zone plate was fabricated using the novel approach of focused ion beam (FIB) milling. The FIB technique was developed in recent years, it has been successfully used for transmission electron microscopy (TEM) sample preparation, lithographic mask repair, and failure analysis of semiconductor devices. During FIB milling, material is removed by the physical sputtering action of ion bombardment. The sputter yield is high enough to remove a substantial amount of material, therefore FIB can perform a direct patterning with submicron accuracy. We succeeded in fabricating an x-ray phase zone plate using the Micrion 9500HT FIB station, which as a 50 kV Ga+ column. Circular Fresnel zones were milled in a 1.0-micrometer-thick TaSiN film deposited on a silicon wafer. The outermost zone width of the zone plate is 170 nm at a radius of 60 micrometer. An achieved aspect ratio was 6:1.

MEASUREMENTS OF X-RAY SPECTRAL FLUX OF HIGH BRIGHTNESS UNDULATORS BY GAS SCATTERING

Absolute radiation flux and polarization measurements of the Advanced Photon Source (APS) undulators may have to be made under high thermal loading conditions. A method that may circumvent the high‐heat‐load problem was tested during a recent APS/CHESS undulator run. The technique makes use of a Si(Li) energy‐dispersive detector to measure 5–35 keV x rays scattered from a well‐defined He gas volume at controlled pressure.

Phase‐space measurement of stored electron beam at the Cornell Electron Storage Ring using a combination of slit array and CCD detector

A new technique for fast phase‐space measurement has been developed and tested during a recent APS/CHESS undulator run. A measurement time of a few seconds was obtained by using a slit array and a high‐resolution position sensitive detector system. The detector system consists of a CdWO4 scintillation crystal, an optical imaging system, and a CCD detector. The short measurement time increases the measurement accuracy by reducing the effects from the instabilities of the electron beam in storage ring. The vertical emittance at the Cornell Electron Storage Ring in single‐bunch and low‐current mode was measured, and reasonable agreement with the expected values for both source size and source divergence were obtained (σy=75 μm and σy’=12 μrad). The effects of the finite size of the first slit on the measurement results are discussed, and a comprehensive data analysis procedure is described.

Predicted performance of the LCLS x-ray diagnostics

An x-ray diagnostics concept is proposed for the Linac Coherent Light Source (LCLS). X-ray diagnostics will provide spectral and spatial measurements of the spontaneous and SASE radiation along the undulator line, and will be complimentary to an electron beam diagnostics. Main goal of the x-ray diagnostics is to measure the radiation gain along the undulator line. Diagnostics setup consists of diamond crystal monochromator and silicon PIN diode and CCD camera detectors. Accuracy and dynamic ranges of x-ray diagnostics are discussed.