Hector Medecki

Tunable coherent radiation in the soft X-ray and extreme ultraviolet spectral regions

Undulator radiation, generated by relativistic electrons traversing a periodic magnet structure, can provide a continuously tunable source of very bright and partially coherent radiation in the extreme ultraviolet (EUV), soft X-ray (SXR), and X-ray regions of the electromagnetic spectrum. Typically, 1-10 W are radiated within a 1/N relative spectral bandwidth, where N is of order 100. Monochromators are frequently used to narrow the spectral bandwidth and increase the longitudinal coherence length, albeit with a more than proportionate loss of power. Pinhole spatial filtering is employed to provide spatially coherent radiation at a power level determined by the wavelength, electron beam, and undulator parameters. In this paper, experiments are described in which broadly tunable, spatially coherent power is generated at EUV and soft X-ray wavelengths extending from about 3 to 16 nm (80-430-eV photon energies). Spatially coherent power of order 10 /spl mu/W is achieved in a relative spectral bandwidth of 9/spl times/10/sup -4/, with 1.90-GeV electrons traversing an 8-cm period undulator of 55 periods. This radiation has been used in 13.4-nm interferometric tests that achieve an rms wavefront error (departure from sphericity) of /spl lambda//sub euv//330. These techniques scale in a straightforward manner to shorter soft X-ray wavelengths using 4-5-cm period undulators at 1.90 GeV and to X-ray wavelengths of order 0.1 nm using higher energy (6-8 GeV) electron beams at other facilities.

At-wavelength interferometry for extreme ultraviolet lithography

A phase-shifting point diffraction interferometer is being developed for at-wavelength testing of extreme ultraviolet lithographic optical systems. The interferometer was implemented to characterize the aberrations of a 10× Schwarzschild multilayer-coated reflective optical system at the operational wavelength of 13.4 nm. Chromatic vignetting effects are observed and they demonstrate the influence of multilayer coatings on the wave front. A subaperture of the optic with a numerical aperture of 0.07 was measured as having a wave front error of 0.090 wave (1.21 nm) root mean square (rms) at a 13.4 nm wavelength. The wave front measurements indicate measurement repeatability of ±0.008 wave (±0.11 nm) rms. Image calculations that include the effects of the measured aberrations are consistent with imaging performed with the 10× Schwarzschild optic on an extreme ultraviolet exposure tool.

Characterization of an EUV Schwarzschild objective using phase-shifting point diffraction interferometry

We report wavefront measurement of a multilayer-coated, reflective optical system at 13.4-nm wavelength performed using a novel phase-shifting point-diffraction interferometer. Successful interferometric measurements of a 10x Schwarzschild objective designed for extreme ultraviolet projection lithography with 0.1-micrometer resolution demonstrate high- precision with sub-nanometer resolution. The goal of the interferometry is to achieve wavefront measurement accuracy beyond lambda/50 rms at EUV wavelengths. Preliminary measurements are discussed and the paths toward achieving the target accuracy are identified.

X-Ray Microscopy in Berkeley

A new high resolution soft X-ray microscope (XM-1) has been used in a variety of applications. It is a conventional transmission microscope with a zone plate condenser and objective. A mutual indexing system incorporates state-of-the-art visible light microscopy and precise positioning of samples. XM-1 has a spatial resolution of 43 nm, as measured with a knife edge object, using the 10% to 90% intensities. It is used in collaboration with other groups to investigate variety of mostly biological samples. In our most extensive study, the life cycle of malaria parasites (plasmodium falciparum) in intact human red blood cel1s was mapped. Abnormalities in the parasites development with protease inhibitor treatments and membrane protein deficiencies have been investigated and were linked to parasite mortality. New structures in green alga (Chlamydomonas), uniquely visible with soft X-rays, have been confirmed and analyzed in unfixed samples. In addition XM-1 is used to map the morphological variation of genetically altered sperm cells. We also give a brief introduction of the history of X-ray microscopy

Progress towards λ/20 extreme ultraviolet interferometry

Diffraction‐limited optical imaging systems for extreme ultraviolet (EUV) lithography require wave front aberrations to be limited to a fraction of the EUV wavelength. Surface figure metrology and wave front measurement at this level of accuracy represent key challenges in the development of EUV lithography. We have constructed and operated a wave front measuring interferometer at 12–13 nm wavelength. This interferometer is being used to measure the aberrations in 0.1 numerical aperture Fresnel zone plate lenses. Factors limiting the resolution and accuracy of the interferometer were studied. Substantial progress toward λ/20 wave front measurement accuracy has been made.

High flux undulator beamline optics for EUV interferometry and photoemission microscopy

A long undulator installed at a low emittance storage ring, generates quasi-monochromatic beams of high brightness and partial coherence properties; however, this also raises concerns regarding high heat loads on beam line components. There have been intensive research efforts to develop beam line optics to exploit brightness and coherence properties from undulators. These components must withstand high heat loads produced by intense synchrotron radiation beams impinging on their surface which could degrade beam line performance. The effects of high flux undulator radiation on beam line optics for EUV interferometry and photoemission microscopy will be discussed. Specifically, beam line schematics, design considerations of indirectly side cooled mirror and grating assemblies developed at the Center for X- Ray Optics and recent data of performance under undulator radiation load from beam line BL12.0 being commissioned at the ALS will be presented in this study.

Characterization of thermal distortion effects on beamline optics for EUV interferometry and soft x‐ray microscopy

This study analyzes synchrotron radiation heat loading effects on optical components of beamline BL12.0 for EUV interferometry and soft x‐ray microscopy at the Advanced Light Source (ALS). Newly developed indirect side‐cooled beamline optics were considered, and the resulting surface distortion of mirrors and grating indicates that there is no significant degradation of beamline performance in spectral resolution or throughput. Also analyzed are the effects of heat loading on end‐station components, such as Fresnel zone plates, transmission gratings, masks and membranes. Experimental results of heat loaded membranes are presented as well in this writing.

At-wavelength testing of optics for EUV

Optical systems for extreme ultraviolet (EUV) lithography require optical elements with wavefront aberrations limited to a fraction of an EUV wavelength to achieve diffraction-limited performance. Achieving wavefront and surface figure metrology at this level of accuracy is one of the key challenges in the development of EUV lithography. We have successfully built and operated a prototype EUV point diffraction interferometer which is capable of performing wavefront measurement of EUV optical elements at their operational wavelength. Initial experiments to characterize the interferometer, and to measure the optical wavefront diffracted from a Fresnel zone plate lens are discussed.

Interferometry using undulator sources (invited, abstract)

Optical systems for extreme ultraviolet (EUV) lithography need to use optical components with subnanometer surface figure error tolerances to achieve diffraction‐limited performance [M.D. Himel, in Soft X‐Ray Projection Lithography, A.M. Hawryluk and R.H. Stulen, eds. (OSA, Washington, D.C., 1993), 18, 1089, and D. Attwood et al., Appl. Opt. 32, 7022 (1993)]. Also, multilayer‐coated optics require at‐wavelength wavefront measurement to characterize phase effects that cannot be measured by conventional optical interferometry. Furthermore, EUV optical systems will additionally require final testing and alignment at the operational wavelength for adjustment and reduction of the cumulative optical surface errors. Therefore, at‐wavelength interferometric measurement of EUV optics will be the necessary metrology tool for the successful development of optics for EUV lithography. An EUV point diffraction interferometer (PDI) has been developed at the Center for X‐Ray Optics (CXRO) and has been already in operatio...

At-wavelength interferometry of extreme ultraviolet lithographic optics

A phase-shifting point diffraction interferometer (PS/PDI) has recently been developed to evaluate optics for extreme ultraviolet (EUV) projection lithography systems. The interferometer has been implemented at the Advanced Light Source at Lawrence Berkeley National Laboratory and is currently being used to test experimental EUV Schwarzschild objectives. Recent PS/PDI measurements indicate these experimental objectives to have wavefront errors on the order of 0.1 waves (∼1 nm at a wavelength of 13.4 nm) rms. These at-wavelength measurements have also revealed the multilayer phase effects, demonstrating the sensitivity and importance of EUV characterization. The measurement precision of the PS/PDI has been experimentally determined to be better than 0.01 waves. Furthermore, a systematic-error-limited absolute measurement accuracy of 0.004 waves has been demonstrated.