J. Wallace

Microscopic-Scale Lateral Inhomogeneities of the Photoemission Response of Cleaved Gaas

Photoelectron energy distribution spectra taken for the first time on micrometer‐sized areas of cleaved GaAs(110) reveal rigid shifts from location to location in the photoemission core level peak energies, indicating band‐bending changes on a microscopic scale.

Feasibility tests of transmission x-ray photoelectron emission microscopy of wet samples

We performed feasibility tests of photoelectron emission spectromicroscopy of wet samples in the water window (285-532 eV) soft x-ray spectral region. Water was successfully confined in an ultrahigh vacuum compatible compartment with x-ray transparent sides. This water cell was placed in the MEPHISTO spectromicroscope in a transmission geometry, and complete x-ray absorption spectra of the water window region were acquired. We also show micrographs of test samples, mounted outside of the compartment, and imaged through the water. This technique can be used to study liquid chemistry and, at least to the micron level, the microstructure of wet samples. Possibilities include cells in water or buffer, proteins in solution, oils of tribological interest, liquid crystals, and other samples not presently accessible to the powerful x-ray photoelectron emission spectromicroscopy technique

Photoemission Spectromicroscopy with Maximum at Wisconsin

We describe the development of the scanning photoemission spectromicroscope MAXIMUM at the Wisoncsin Synchrotron Radiation Center, which uses radiation from a 30-period undulator. The article includes a discussion of the first tests after the initial commissioning.

A new beamline for EUV lithography research

We have recently completed construction of a new branch-line and exposure station for EUV lithography research at the Synchrotron Radiation Center. We use uniform area and interferometrically patterned exposures for the investigation of technologically relevant material properties under EUV exposure. Two multilayer mirrors are installed into an existing undulator beamline to extract the beam both before and after a spherical grating monochromator. Both beams are directed into a single experimental chamber by means of additional multilayer mirrors. In this way both the high flux raw undulator beam and the monochromatic beam are available for experiments.

SuperMAXIMUM: A Schwarzschild‐based, spectromicroscope for ELETTRA

X ray microscopy excels on high‐brightness sources, such as the Advanced Light Source and ELETTRA, where there is a good match between the source and optics phase spaces. In these conditions, diffraction‐limited operation becomes possible with large flux. We will discuss the development of a second‐generation x ray scanning spectromicroscope; an evolution of the MAXIMUM project at the University of Wisconsin. The new tool is called SuperMAXIMUM and will be installed on ELETTRA in Trieste, Italy.

The MAXIMUM Photoelectron Microscope at the University of Wisconsin’s Synchrotron Radiation Center

The Multiple Application X-Ray Imaging Undulator Microscope (or MAXIMUM) is a project being carried out jointly by the University of Wisconsin and the Lawrence Berkeley Laboratory. The principal mode of operation of the system is as a photoemission microscope. In this mode, the radiation from the 30-period undulator on the Aladdin 0.8 GeV storage ring is first passed through a monochromator and then focussed on a pinhole aperture. A 20X demagnified image of this pinhole is formed at the sample plane by a 2-clement microscope objective of the Schwarzschild design, whose surfaces are coated with multilayers to reflect soft x-rays (>77eV). While the diffraction limit of the microscope is around 300 A at a wavelength of 120 A, imperfections in the optics and intensity considerations limit the spatial resolution that can be obtained to about 1000 A. The sample to be studied is positioned at the focus of the microscope and the energy spectra of the emitted photoelectrons are analysed by a cylindrical mirror analyser. In this way it is possible to obtain detailed chemical maps of the specimen, with information on both its chemical components and their chemical status. In this paper we describe the design and operation of the the MAXIMUM beamline, and present some preliminary results obtained with solid state and biological samples.

Accelerated radiation damage testing of x-ray mask membrane materials

An accelerated test method and resulting metrology data are presented to show the effects of x- ray radiation on various x-ray mask membrane materials. A focused x-ray beam effectively reduces the radiation time to 1/5 of that required by normal exposure beam flux. Absolute image displacement results determined by this method indicate imperceptible movement for boron-doped silicon and silicon carbide membranes at a total incident dose of 500 KJ/cm2, while image displacement for diamond is 50 nm at 150 KJ/cm2 and silicon nitride is 70 nm at 36 KJ/cm2. Studies of temperature rise during the radiation test and effects of the high flux radiation, i.e., reciprocity tests, demonstrate the validity of this test method.

A new scanning photoemission microscope for ELETTRA: SuperMAXIMUM

High brightness, third‐generation synchrotrons allow diffraction‐limited performance and large flux for scanning photoemission microscopes. A new microscope, SuperMAXIMUM, is being developed at the University of Wisconsin Center for X ray Lithography in collaboration with the Sincrotrone Trieste. The beamline, being built in Trieste, uses a variable angle spherical grating monochromator (VASGM). A combination of rotation of a plane mirror and rotation of the spherical grating keeps the slit positions and beam directions fixed. The microscope objectives are normal‐incidence, multilayer‐coated Schwarzschild objectives. The project, which is nearing completion, utilizes novel designs for optics alignment, sample rastering mechanics, and software control. We will discuss the project status, new designs, and techniques.

New results from MAXIMUM: an x-ray scanning photoemission microscope

The scanning soft x-ray photoemission microscope (MAXIMUM) operating at the Synchrotron Radiation Center at the University of Wisconsin-Madison has been substantially upgraded. The major upgrades are: installation of a new beam line that is optimized for the microscope; new optical mount and alignment system for the Schwarzschild objective; a new scanning stage; installation of a cylindrical mirror analyzer; implementation of an ultrahigh vacuum sample preparation chamber and transfer system; a new window-driven data acquisition program that is more flexible and user-friendly. The new system had demonstrated better than 0.1 micrometers spatial resolution, and photoemission data with 350 meV energy resolution has been obtained.

Linear-Fresnel-Zone-Plate-Based Two-State Alignment Method for Sub-0.25 µm X-Ray Lithography System

In this paper, we present a linear-fresnel-zone-plate-based two-state alignment method developed at the Center for X-ray Lithography. The alignment system uses a linear Fresnel zone plate (LFZP) as a mask alignment mark and an array of dots as a wafer alignment mark. The alignment error signal extraction is based on a two-state modulation of the incident light. The optical system is arranged outside of the exposure X-ray path and alignment can be performed during X-ray exposures. In the experiment, we obtained an alignment signal depth of focus larger than 4 µm and the gap change between the mask and wafer did not affect the alignment position. The X-ray double-exposure experiment on the system demonstrated an alignment accuracy better than 0.035 µm (3σ) on both Al and silicon nitride marks.