C. Capasso

High-Resolution X-Ray Microscopy Using an Undulator Source, Photoelectron Studies with Maximum

We present the first results of high‐spatial resolution x‐ray imaging studies with an upgraded version of the scanning photoemission multiple application x‐ray imaging undulator microscope. The microscope is a multilayer coated Schwarzschild objective that focuses undulator radiation onto the sample. The recent upgrade improved the spatial resolution by a factor six reaching a full width at half maximum value of 0.5 μm. Highly polished mirrors reduced the diffuse background by almost two orders of magnitude and drastically improved the contrast. The improved microscope was used to perform a series of tests on microgrids and reverse Fresnel zone plates. The microscope capability to detect chemical and topological contrast was verified by using patterned metal overlayers on Si and GaAs substrates. Further improvements to increase the flux and the spatial resolution are underway; this includes the installation of a new undulator beamline.

First results of microspectroscopy from a scanning photoemission microscope with a submicron probe size

Utilizing a Mo–Si multilayer coated Schwarzschild objective to focus 95 eV photons, we have recently demonstrated better than 0.1 μm resolution as a scanning x‐ray transmission microscope. Operating as a scanning photoemission microscope with submicron resolution, we have demonstrated its chemical mapping capabilities by studying a patterned Al/AlOx test structure. In addition, we have also studied the cleaved GaAs(110) surface and have identified lateral variations in the surface band bending on the scale of 100 meV. In both experiments, core level microspectroscopy was performed at selected points on the sample to elucidate the image contrast mechanisms.

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.

Photoelectron Microscopy in the Life Sciences - Imaging Neuron Networks

Photoemission techniques like electron spectroscopy for chemical analysis are the leading electronic probes in materials science—but their impact in the life sciences has been minimal. A critical problem is that the lateral resolution in ordinary photoemission does not exceed a few tenths of a millimeter. This space‐averaged probe is nearly useless for most of the fundamental problems in biophysics and biochemistry, which deal with microstructures in the submicron range or smaller. This limit is being overcome with photoemission microscopes, such as our scanning instrument maximum. The first scanning photoelectron micrographs of a cellular system with submicron resolution are presented. Minute details of neuron networks are imaged on maximum, thereby opening the way to novel applications of photoemission in the life sciences. The details include individual neurons, axons, dendrites, and synapses, and composite large‐area scanning micrographs were routinely produced with a lateral resolution of 0.5 μm.

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.

Comparative study of x-ray lithography process optimization using theoretical and empirical tools

This paper presents the results of a simple orthogonal matrix experiment testing photoresist performance as a function of post exposure bake temperature and time. The dose latitude of quarter micron line/space pairs is found under these conditions. These empirical results are compared against those produced under identical process conditions but utilizing simulated images based on resist dissolution rate data. The matrix responses of the empirical and simulated data sets are compared. Also, these linewidth results are compared against resist characteristic data produced under identical process conditions. The matrix responses of the three data sets are compared.

Spectral effects on x-ray lithography

The actinic spectra of two beamlines of the University of Wisconsins Center for X-ray Lithography (CXrL) at the Aladdin storage ring were studied in three configurations. Some beamlines optimized for particular bandwidths are presented and their impact on mask making, aerial image quality, printed image quality, and device damage discussed. Resist performance dependence on the actinic spectrum is investigated. The exposure-gap tree response of 0.25 micron features is presented for different spectra. Resist characteristic curve data were collected for these conditions and are compared.

Micropositioning in MAXIMUM: Photoemission microscopy with normal incident optics (abstract)

We discuss the two critical micropositioning systems implemented on the latest version of MAXIMUM at the Wisconsin Synchrotron Radiation Center. MAXIMUM is an undulator‐based x‐ray photoelectron microscope. The microscope utilizes a set of multilayer‐coated normal incident Schwarzchild objective to produce a submicron focus spot. The sample is rastered across the spot and photoelectrons emitted from the sample are collected to form an image. The Schwarschild objective is mounted such that it is vibrationally isolated from the vacuum chamber. The two mirrors are mounted on a three axis flexural pivot stage actuated by inchworm motors. This system allows in situ fine alignment of the objective and it is totally decoupled from any vacuum forces. The inchworm motors will also act as clamps when the objective is aligned. The sample scanning is done by a flexural hinge stage actuated by an in‐house design PZT stack. The stage has a range of 100 μm×100 μm×5 μm with a resolution of 100 A. The system is totally UH...