Gerd Schoenhense

Actinic extreme ultraviolet lithography mask blank defect inspection by photoemission electron microscopy

A new method for the actinic inspection of defects inside and on top of extreme ultraviolet (EUV) lithography multilayer-coated mask blanks is presented. The experimental technique is based on photoemission electron microscopy supported by the generation of a standing wave field inside and above the multilayer mask blank when illuminated near the resonance Bragg wavelength at around 13.5nm. Experimental results on programed defect samples based on electron beam lithographic structures or silica balls overcoated with an EUV multilayer show that buried defects with a lateral size down to 50nm are detectable. Furthermore, phase structures as shallow as 6nm in height on a programed phase grating sample have been detected by this technique. The contrast of the phase defect structures has shown to be strongly dependent on and controlled by the phase of the standing wave field at the mask blank surface, and thus can be optimized by tuning the inspection wavelength.

At-wavelength inspection of sub-40 nm defects in extreme ultraviolet lithography mask blank by photoemission electron microscopy

A new at-wavelength inspection technology to probe nanoscale defects buried underneath Mo/Si multilayers on an extreme ultraviolet (EUV) lithography mask blank has been implemented using EUV photoemission electron microscopy (EUV-PEEM). EUV-PEEM images of programmed defect structures of various lateral and vertical sizes recorded at an ~13.5 nm wavelength show that 35 nm wide and 4 nm high buried line defects are clearly detectable. The imaging technique proves to be sensitive to small phase jumps, enhancing the edge visibility of the phase defects, which is explained in terms of a standing wave enhanced image contrast at resonant EUV illumination.

Photoemission microscopy with microspot-XPS by use of undulator radiation and a high-throughput multilayer monochromator at BESSY

Abstract We present a new experiment for photoelectron microspectroscopy by use of undulator radiation, which has been set up at the beamline U2 at the Berlin electron storage ring BESSY 1. This approach employs a non-imaging simulated hemispherical electron energy analyser attached to an imaging photoemission electron microscope (FOCUS IS-PEEM) with integrated microarea selector. The photoemission microscope exhibits a lateral resolution of 25 nm (with 4.9 eV UV-excitation), while the resolution with incident synchrotron radiation in the soft X-ray range is about 100–120 nm (mainly due to chromatic aberrations). Photoemission microscopy as well as photoelectron microspectroscopy of selected areas on the sample surface were performed by using the third harmonic of the direct undulator beam which was monochromatized and refocused by a two-element multilayer optic in the 70–95 eV energy range. The multilayer monochromator operating at near-normal incidence consists of a concave spherical multilayer mirror ( r =650 mm) and a plane multilayer grating (blazed grating 1221 L/mm, blaze angle 0.8 deg). Both elements were coated with a Mo/Si multilayer of equal d -spacing (20 doublelayers, d =10.5 nm) to enhance the reflectivity for EUV radiation at near-normal incidence angles. The characterization of the individual optical components by EUV reflectometry shows a peak reflectance of about 47% at a photon energy of 95 eV in the case of the focusing multilayer mirror while the first order diffraction efficiency of the multilayer blaze grating was measured to be up to 32%. The evaluation of the photoelectron spectra measured with this set-up displays that the spectral resolution of the incident radiation is better than 0.7 eV, while it is about 2–4 eV in the case of a two-multilayer-mirror configuration. Analysis of the surface topography and the chemical composition of inhomogeneities of thin evaporated layers on a mesoscopic scale are the main applications of this experiment.

Actinic EUVL mask blank defect inspection by EUV photoelectron microscopy

A new method for the actinic at-wavelength inspection of defects inside and ontop of Extreme Ultraviolet Lithography (EUVL) multilayer-coated mask blanks is presented. The experimental technique is based on PhotoElectron Emission Microscopy (PEEM) supported by the generation of a standing wave field inside and above the multilayer mask blank when illuminated near the resonance Bragg wavelength at around 13.5 nm wavelength. Experimental results on programmed defect samples based on e-beam lithographic structures or PSL equivalent silica balls overcoated with an EUV multilayer show that buried defects scaling down to 50 nm in lateral size are detectable with further scalability down to 30 nm and smaller due to the PEEMs instrumental performance. Furthermore, phase structures as shallow as 6 nm in height on a programmed phase grating sample has been detected by this technique. The visibility of the phase defect structures has been shown to be strongly dependent on and controlled by the phase of the standing wave field at the mask blank surface and thus can be optimized by tuning the illumination wavelength between 12.5 nm and 13.8 nm.

Actinic inspection of sub-50 nm EUV mask blank defects

A new actinic mask inspection technology to probe nano-scaled defects buried underneath a Mo/Si multilayer reflection coating of an Extreme Ultraviolet Lithography mask blank has been implemented using EUV Photoemission Electron Microscopy (EUV-PEEM). EUV PEEM images of programmed defect structures of various lateral and vertical sizes recorded at around 13 nm wavelength show that 35 nm wide and 4 nm high buried line defects are clearly detectable. The imaging technique proves to be sensitive to small phase jumps enhancing the visibility of the edges of the phase defects which is explained in terms of a standing wave enhanced image contrast at resonant EUV illumination.

Miniaturized objective lens for a photoelectron emission microscope

Photoemission electron microscopy (PEEM) has turned out to be one of the most promising methods for surface analysis in the recent years. It is a full field imaging technique based on the emission of secondary electrons by far ultraviolet light or X-rays. The emission intensity of secondary electrons is critically dependent upon the acceptance angle of the incident radiation. However, the size of the microscope restricts this angle substantially. Miniaturizing the objective lens of the microscope reduces the restriction of the acceptance angle and improves the performance of the PEEM considerably. We report on the fabrication of a miniaturized objective lens containing the extraction electrode, the electron column, the contrast aperture and the electron optical correction system for a PEEM. The extraction electrode as well as the electron column have been manufactured using precision milling techniques and electron discharge micromachining. For the fabrication of the correction system (stigmator / bending unit), a process combining aligned photolithography into a thick SU-8 resist and electroforming has been used. All electrodes were made in gold with a height of 150 (mu) m. After attaching a FOTURAN substrate to the electrode and etching under the electrodes, free standing apertures in an octupole and quadruple arrangement were obtained. The outer diameter of the electrodes is 5 mm and the inner diameter is 1 mm, respectively. Each electrode is connect individually to the external power supply which controls their operation. The overall size of the miniaturized objective lens is 23 mm, which has reduced the size of the lens by one order of magnitude when compared to commercially available instruments.