Srivatsan Seshadri

Absolute efficiency measurement of high-performance zone plates

An absolute efficiency measurement technique for Fresnel zone plates using an electron impact micro-focus laboratory X-ray source (Lα line of Tungsten at 8.4 KeV) is demonstrated. A quasi-monochromatic x-ray image of a zone plate was obtained employing a pair of copper and cobalt filters. Applying this method to zone plates optimizes the zone plate fabrication process and provides the ability to explore zone geometry to achieve the best possible efficiency. Several zone plate parameters were tested with first order efficiency measuring from 1% to 29%.

Advances toward submicron resolution optics for x-ray instrumentation and applications

Sigray’s axially symmetric x-ray optics enable advanced microanalytical capabilities for focusing x-rays to microns-scale to submicron spot sizes, which can potentially unlock many avenues for laboratory micro-analysis. The design of these optics allows submicron spot sizes even at low x-ray energies, enabling research into low atomic number elements and allows increased sensitivity of grazing incidence measurements and surface analysis. We will discuss advances made in the fabrication of these double paraboloidal mirror lenses designed for use in laboratory x-ray applications. We will additionally present results from as-built paraboloids, including surface figure error and focal spot size achieved to-date.

Sub-80 nm Resolution X-Ray Fluorescence Imaging Spectrometer for Semiconductor Applications

Electron or x-ray excited X-ray fluorescence analysis is a widely deployed technique in various fields such as materials science, semiconductor manufacturing and defect review for thin film characterization. Layer thicknesses with sub nanometer accuracy and elemental composition to below a weight percent can be measured. With electron beam instruments such as SEMs, spatially resolved fluorescence maps are obtained by raster scanning a finely focused electron beam using energy or wavelength dispersive spectrometers (EDS/WDS) to collect elemental distribution and concentration information. The spatial resolution for these maps is fundamentally limited for thick (>1um) samples by the electron interaction volume to the order of one micrometer. This restriction can be overcome by the use of high-resolution Fresnel zone plate lenses as x-ray imaging optics. Based on this concept we have designed an x-ray fluorescence imaging spectrometer which combines the elemental identification capabilities of a spectrometer with the high spatial resolution (sub-80nm) of zone plate imaging optics. Such a spectroscopic imaging system can potentially be employed advantageously in many semiconductor applications. As a first application we demonstrate sub-surface imaging of copper interconnects and identification of manufacturing problems and failures.