Non-destructive determination of local strain with 100-nanometre spatial resolution

Structure sizes of approximately 180 nm are now standard in microelectronics, and state-of-the-art fabrication techniques can reduce these to just a few tens of nanometres. But at these length scales, the strain induced at interfaces can locally distort the crystal lattice, which may in turn affect device performance in an unpredictable way. A means of non-destructively characterizing such strain fields with high spatial resolution and sensitivity is therefore highly desirable. One approach is to use Raman spectroscopy, but this is limited by the intrinsic approximately 0.5-microm resolution limit of visible light probes. Techniques based on electron-beam diffraction can achieve the desired nanometre-scale resolution. But either they require complex sample preparation procedures (which may alter the original strain field) or they are sensitive to distortional (but not dilational) strain within only the top few tens of nanometres of the sample surface. X-rays, on the other hand, have a much greater penetration depth, but have not hitherto achieved strain analysis with sub-micrometre resolution. Here we describe a magnifying diffraction imaging procedure for X-rays which achieves a spatial resolution of 100nm in one dimension and a sensitivity of 10(-4) for relative lattice variations. We demonstrate the suitability of this procedure for strain analysis by measuring the strain depth profiles beneath oxidized lines on silicon crystals.

Morphological and Functional Modifications of Optical Thin Films for Space Applications Irradiated with Low-Energy Helium Ions.

Future space missions will operate in increasingly hostile environments, such as those in low-perihelion solar orbits and Jovian magnetosphere. This exploration involves the selection of optical materials and components resistant to the environmental agents. The conditions in space are reproduced on ground through the use of ion accelerators. The effects of He particles coming from the solar wind impinging on a gold thin film have been systematically investigated, considering absorbed doses compatible with the duration of the European Space Agency Solar Orbiter mission. Structural and morphological changes have been proved to be dependent not only on the dose but also on the irradiation flux. A predictive model of the variation of thin film reflectance has been developed for the case of lower flux irradiation. The results are discussed regarding reliability and limitations of laboratory testing. The outcomes are important to address the procedures for the space qualification tests of optical coatings.

Potential use of V-channel Ge(220) monochromators in X-ray metrology and imaging.

While channel-cut crystals, in which the diffracting surfaces in an asymmetric cut are kept parallel, can provide beam collimation and spectral beam shaping, they can in addition provide beam compression or expansion if the cut is V-shaped. The compression/expansion ratio depends in this case on the total asymmetry factor. If the Ge(220) diffraction planes and a total asymmetry factor in excess of 10 are used, the rocking curves of two diffractors will have a sufficient overlap only if the second diffractor is tuned slightly with respect to the first one. This study compares and analyses several ways of overcoming this mismatch, which is due to refraction, when the Cu Kα1 beam is compressed 21-fold in a V21 monochromator. A more than sixfold intensity increase was obtained if the matching was improved either by a compositional variation or by a thermal deformation. This provided an intensity gain compared with the use of a simple slit in a symmetrical channel-cut monochromator. The first attempt to overcome the mismatch by introducing different types of X-ray prisms for the required beam deflection is described as well. The performance of the V-shaped monochromators is demonstrated in two applications. A narrow collimated monochromatic beam obtained in the beam compressing mode was used for high-resolution grazing-incidence small-angle X-ray scattering measurements of a silicon sample with corrupted surface. In addition, a two-dimensional Bragg magnifier, based on two crossed V15 channel monochromators in beam expansion mode and tuned by means of unequal asymmetries, was successfully applied to high-resolution imaging of test structures in combination with a Medipix detector.

Diffraction efficiencies for the higher orders of a reflection grating in the soft x-ray region: comparison between theory and experiment.

Diffraction efficiencies of a blazed grating measured in the soft x-ray region with photon energies between 60 and 925 eV are compared with calculations using the differential formalism of the exact electromagnetic theory. The parameters of the grating (gold coated with 1200 lines/mm and blaze angle 1.5 degrees ) are frequently used in soft x-ray monochromators. A quality check of this grating is made by investigating the total efficiency. Data for the -1, 0, +1, +2, and +3 orders are presented, so that the suppression capability for higher harmonics can be derived. Use of a blazed grating diffracting in 0. order is given.

Phase-retardation and full-polarization analysis of soft-x-ray synchrotron radiation close to the carbon K edge by use of a multilayer transmission filter.

We have produced a multilayer transmission filter with 100 periods of Cr/C to achieve a significant phase retardation while maintaining good transmission for photon energies just below the carbon K edge. This device was installed into a polarimeter behind the SX700/3 monochromator at the Berlin synchrotron radiation laboratory, BESSY. The phase-retardation properties were observed as theoretically predicted. Agreement between experiment and calculation could be obtained by introduction of a rather small interface roughness in the simulation code (σ = 0.65 nm rms). An observed phase retardation of 5° was sufficient to permit, for the first time we believe, a complete and unambiguous polarization analysis of soft-x-ray synchrotron radiation (265-eV photon energy) with primary standards.

Submicrometre beams from a hard X-ray waveguide at a third-generation synchrotron radiation source.

The use of an X-ray waveguide for scattering experiments at an undulator of a third-generation synchrotron radiation source is discussed. The performance with a perfect crystal monochromator, multilayer monochromator and focusing mirror is explored. A maximum flux of 8 x 109 photons s(-1) at lambda = 0.083 nm was obtained for a 0.15 (V) x 600 (H) micron(2) beam at the exit of the waveguide with a multilayer monochromator. The combination of an Si (111) monochromator and ellipsoidal mirror resulted in a flux of approximately 10(9) photons s(-1) but with a horizontal compression of the beam to approximately 30 micron. The use of the waveguide in diffraction experiments is addressed.

Precise measuring method for detecting the in situ distortion profile of a high-heat-load mirror for synchrotron radiation by use of a pentaprism long trace profiler.

A precise measuring method for detecting the in situ distortion profile of a high-heat-load mirror for synchrotron radiation by use of a pentaprism long trace profiler (LTP) is presented. A maximum distortion of 0.47 microm across a length of 180 mm was measured for an internally water-cooled mirror on an undulator beam line at ELETTRA while exposed to a total emitted power of 600 W. This first successfully tested in situ distortion profile points out the importance and need for this method. Two configurations for performing in situ LTP tests are discussed. For this measurement the configuration with all the equipment external to the vacuum chamber was used. The experiment has an accuracy and a repeatability of 0.04 microm. Suggestions for improving the accuracy and stability are presented.

Characterization of sputtered nickel/carbon multilayers with soft-x-ray reflectivity measurements.

Several sputtered Ni/C multilayer mirrors with periods between 3.8 and 6.0 nm were investigated with the HASYLAB reflectometer to determine the peak reflectivity and the internal structure of the multilayers. The enhanced reflectivity in the Bragg maximum, especially below 284 eV (carbon K edge), is interesting for practical applications. For both materials (Ni and C), the optical constants were previously obtained from angular-dependent reflectivity measurements. The layer thicknesses, interface roughnesses, and mean thickness errors of multilayer mirrors are obtained from least-squares fits of theoretical reflectivity curves. A model is presented to describe the influence of interface roughness on other parameters obtained from the analysis. All Ni/C multilayers, with Ar as the sputter gas, were produced in the low-pressure triode-assisted sputtering facility of Sincrotrone Trieste.

Optical constants of float glass, nickel, and carbon from soft-x-ray reflectivity measurements.

Angular-dependent reflectivity was measured with a dynamic range of 5-6 orders of magnitude at ~20 different photon energies in the range from 40 to 800 eV with the HASYLAB reflectometer with synchrotron radiation. Several float-glass substrates and a number of sputtered Ni and C films were investigated to improve the accuracy. The optical constants were obtained from least-squares fits of theoretical reflectivity curves, taking into account the influence of film thicknesses and surface and interface roughnesses. All samples with Ni and C films were produced on float-glass substrates, with Ar as the sputter gas, in the low-pressure triode-assisted sputtering facility of the Sincrotrone Trieste.

Submicrometre resolution phase-contrast radiography with the beam from an X-ray waveguide.

Experimental data with unprecedented submicrometre resolution obtained in a phase-contrast radiography experiment in a magnifying configuration are presented. The term 'phase contrast' here indicates that the phase retardation of coherent light in matter was utilized as the contrast mechanism. The coherent and divergent beam exiting an X-ray waveguide was used in a lensless configuration to magnify spatial variations in optical path length up to several hundred times. The defocused image of a nylon fibre was measured with a resolution of 0.14 micro m at the object. Sufficient contrast was found for exposure times of 0.1 s, i.e. in the regime for real-time studies.

Soft-x-ray polarimeter with multilayer optics: complete analysis of the polarization state of light.

The design of a versatile high-precision eight-axis ultrahigh-vacuum-compatible polarimeter is presented. This multipurpose instrument can be used as a self-calibrating polarization detector for linearly and circularly polarized UV and soft-x-ray light. It can also be used for the characterization of reflection or transmission properties (reflectometer) or polarizing and phase-retarding properties (ellipsometer) of any optical element. The polarization properties of Mo/Si, Cr/C, Cr/Sc, and Ni/Ti multilayers used in this polarimeter as polarizers in transmission and as analyzers in reflection have been investigated theoretically and experimentally. In the soft-x-ray range, close to the p edges of Sc, Ti, and Cr, resonantly enhanced phase retardation of the transmission polarizers of as much as 18 degrees has been measured. With these newly developed optical elements the complete polarization analysis of soft-x-ray synchrotron radiation can be extended to the water-window range from 300 to 600 eV.