Extreme ultraviolet lithography (EUVL) at 13.5nm is the next generation lithography technique capable of printing sub-50nm structures. With decreasing feature sizes to be printed, the requirements for the lithography mask also become more stringent in terms of defect sizes and densities that are still acceptable and the development of lithography optics has to go along with the development of new mask defect inspection techniques that are fast and offer high resolution (preferable in the range of the minimum feature size) at the same time. We report on the development and experimental results of a new 'at wavelength' full-field imaging technique for defect inspection of multilayer mask blanks for EUV lithography. Our approach uses a photoemission electron microscope (PEEM) in a normal incidence illumination mode at 13nm to image the photoelectron emission induced by the EUV wave field on the multilayer mask blank surface. We show that by these means, buried defects in the multilayer stack can be probed down to a lateral size of 50nm, which was the smallest pre-defined structure size under study so far. The PEEMs spatial resolution has been proven to be as small as 29nm edge slope width in measurements with 250nm radiation. Therefore, the capability of this technique for actinic measurements at 13nm radiation is anticipated to be well below 50nm.

We report on the development and first experimental results of a "at wavelength" full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet (EUV) lithography. According to the International Semiconductor Roadmap by Sematech, less than 5x10(-3) defects per cm(2) should be present on such multilayer mask blank to enable mass production of microelectronics using EUV lithography, thus fast high-resolution methods for mask defect inspection and localization are needed. Our approach uses a photoemission electron microscope in a normal incidence illumination mode at 13 nm to image the photoelectron emission induced by the EUV wave field on the multilayer mask blank surface. We show that by these means, buried defects in the multilayer stack can be probed down to a lateral size of 50 nm. (c) 2006 American Institute of Physics.

The energy dependence of the circular dichroism in the angular distribution of photoelectrons (CDAD) was investigated from the shallow Cs 5p core levels. Cesium was prepared in a hexagonal ordered monolayer on W(110). The results are mainly influenced by scattering of the photoelectrons within the adlayer. At low energies, the behavior observed is described by means of a model that treats only the back-scattering of photoelectrons at the potential step between the adlayer and the substrate. It leads to a simple method determining the position of the monolayer with respect to the substrate. In this approach, the back-scattering model is matched with the measured energy dependence of the CDAD between hν = 21 eV and hν = 33 eV . This procedure yields reliable results already for a single observation angle of the photoelectron. The distance between cesium and tungsten was determined to be (2.2 ± 0.1) Å, which corresponds to the effective distance between the center of the adsorbed layer and the potential step between the layer and the substrate. Finally, the fitted result was proven to meet the complete angular dependence of the CDAD at different photon energies.

The observation of magnetic circular dichroism in the angular distribution of photoelectrons (MCDAD) from alkali and rare-gas films adsorbed on a thin remanently magnetized Co layer is reported. The observation of an antisymmetric MCDAD near normal emission for Co(0001)–Cs 5p semi core level is shown. The reversed magnetization leads to a mirror-image-like distribution. The second system under investigation, physisorbed Co(0001)–Xe 5p, does not give such an but shows significant differences in the MCDAD signal for both directions of magnetization, in particular in the |m j | substates of the p 3/2 level. A magnetic coupling between Xe and Co is evident when we take results of spin-resolved photoemission into account.

We present a new method for momentum-selective imaging by means of a time-of-flight (TOF) technique. The instrument employs a time- and space-resolving delayline detector in combination with a parabolic electrostatic field and a drift space. We use this kind of spectrometer, to raise the efficiency of experiments, which are total momentum resolved. The main difference to conventional photoemission experiments using a rotatable spectrometer is the simultaneous detection of all emitted photoelectrons. In addition to this feature, the angular distribution should be directly visible, to observe solid state symmetries. In order to facilitate these requirements, we use a delayline detector as a position and time sensitive device with a versatile user interface. First results obtained at BESSY I are presented.

A method for microspectroscopy and energy-selective imaging using a special photoemission electron microscope (PEEM) is presented. A modified commercial PEEM was combined with a delay line device as x, y, t detector serving as the basic arrangement for spectromicroscopy. One can measure the time of flight of the electrons passing a drift section in order to analyze the energy distribution of photoelectrons in PEEM. The time of flight is referenced to the time structure of the synchrotron radiation from an electron storage ring. At electron kinetic energies of less than 20 eV within the drift region a spatial resolution of about 100 nm has been obtained. Fast counting electronics (instead of a camera) delivers an image for real-time monitoring on an oscilloscope screen or for image acquisition by a computer. A time resolution of about 500 ps has been obtained with the potential of further improvement. The spatial resolution of the delay line detector is about 50 μm in the image plane corresponding to 1000 pixels in the image diagonal. Direct photoemission from the W-4f core level of a W(110) single-crystal sample was observed at several photon energies. The W-4f fine-structure splitting of 2.3 eV could be well resolved at a pass energy around 40 eV through the drift region.

In the present study, spin polarisation and dichroism were investigated in angular resolved VUV photoemission ARUPS from magnetised as well as paramagnetic rare earth surfaces. Thin Gd(0001) films were prepared epitaxially on W(110). The photoelectrons were excited by polarised synchrotron radiation from the BESSY I synchrotron radiation source. A SPLEED detector attached to an electron spectrometer mounted on a single axis goniometer was used for angular resolved spin analysis. The main part of this work focused on the characteristic surface state of Gd(0001) which shows a splitting, as previously observed by linear magnetic dichroism and spin polarised photoemission. The spin analysis shows that the two observed states have opposite spin characters. Additionally, the non-magnetic circular dichroism suggests j =3/2 character for the surface state. The experimental findings are compared to atomic models and one-step photoemission calculations.

The dichroic effects of photoemission excited by polarised light depend on the angle of photon incidence. Measurements of the difference in the angle-resolved photoemission intensities from Cs 5p semi-corelevels excited by photons of opposite helicity, or of orthogonal linear polarisation are reported. It was thought that the dependence of dichroism on the angle of incidence cannot be described using equations omitting metal optics. A complete consideration of the vector potential of the exciting light is needed, including the phase shift between it's parallel and perpendicular components. The phase shift is produced by the complex index of refraction. Using the Fresnel equations for structureless media, one finds that the second and the third components of the Stokes vector both change their sign, if only the initial helicity or linear polarisation are reversed. The complex index of refraction of a Cs-covered W(110) surface is determined from measurements using the quantitative knowledge of the dichroism effects, that is, CDAD and LDAD.

We report on the dependence of dichroic photoemission excited by polarised light on the angle of photon incidence. We measured the difference in the angle-resolved photoemission intensities from Cs-5p semi-corelevels excited by photons of opposite helicity, known as CDAD and of orthogonal linear polarisation—LDAD. We found that the dependence of dichroism on the angle of incidence can not be described by the equations used in the photoemission model for free atomic states. A complex consideration of the parallel and perpendicular components of the vector potential of the exciting light is needed, including the phase shift between these components. The phase shift is produced by the complex index of refraction. Using the Fresnel-equations for structureless media, one finds that in CDAD measurements not only the third component of the Stokes vector is responsible for the differences in the excitation process, but also the second component and vice versa for LDAD. Both Stokes components change the sign if the initial helicity or linear polarisation is reversed resulting in an additional dichroism just of the other kind.

We report on the dependence of dichroic photoemission excited by circularly polarised light on the angle of photon incidence. We measured the difference in the angle-resolved photoemission intensities from Cs 5p semi-core levels excited by photons of opposite helicity, which is known as CDAD. We found that the dependence of the measured differences on the angle of light incidence deviates strongly from the model of CDAD for free atoms, as expected. Using the Fresnel equations and a complex index of refraction, one finds that not only the third component but also the second component of the Stokes vector is responsible for the excitation process. Both Stokes components change sign if the initial helicity is reversed, resulting in an additional linear dichroism.

We investigated circular dichroism in photoemission from Kr and Xe adsorbed on Pt(111). A large CDAD has been observed in emission from the p states of both rare gases depending on the observation angle and the photon energy. Special interest was put on the CDAD in emission from the near-threshold region. Strong CDAD was found in constant final state mode spectra for very low kinetic energies of the photoelectrons. Our results show, that in a completed monolayer the Xe 5p states cannot be treated as atom-like.