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Overview: In many applications the combination of optical/structural and analytical imaging of the same target at the same time is desirable. In an electron microscope a focused electron beam is used for optical imaging. For nano-scale surface processing and advanced structural imaging a primary focused ion beam (FIB) is used. The FIB produces a small amount of secondary ions, which can be used for spatially resolved mass spectrometry. Challenges: • Limited space • Low secondary ion beam currents (typical 1 … 5 pA) • Broad kinetic energy distribution of the secondary ions • Difficult vacuum conditions Approach: • Helium cooling section to minimize energy distribution width • Extraction lens configuration [1] • Axial segmented linear quadrupole trap made in planar technology [2] for ion transfer • Pressure stage incorporating a quadrupole ion wave guide for ion transfer between different pressure regions • 3D-Ion trap used in Fourier Transform mode as mass analyzer Introduction 3D-Ion Trap Principle of Operation Metrological Characterization of a Sensitive Secondary Ion Mass Spectrometer for Electron Microscopes to Combine Optical/Structural and Analytical Imaging Alexander Laue , Albrecht Glasmachers, Albrecht Brockhaus; University of Wuppertal, Germany Michel Aliman, Hubert Mantz; Carl Zeiss NTS GmbH, Oberkochen, Germany Cross Section of the SIMS Device References Preikszas, D.; Aliman M.; Mantz, H.; Laue, A.; Brockhaus, A.; Glasmachers, A. Optimization of the collection efficiency of secondary ions for spartially resolved SIMS in Crossbeam devices, 12 th International seminar on Recent Trends in Charged Particle Optics and Surface Physics Instrumentation, 2010 Glasmachers, A.; Laue, A.; Brockhaus, A.; Puwey, A.; Aliman, M. Planar technologies for optimized realizations of quadrupole ion guides and quadrupole ion wave guides, 58 th ASMS Conference, 2010 Laue, A.; Glasmachers, A. New Design of a Compact Fourier-Transform Quadrupole Ion Trap for High Sensitivity Applications, 57 th ASMS Conference, 2009 Patent application EP11152379.1 – 1232: Apparatus for focusing and for storage of ions and for separation of pressure areas, 2011 Patent application EP11152420.3 – 2208: Apparatus for transmission of energy and/or for transportation of an ion as well as particle beam device having an apparatus such as this, 2011 IonGuide IonGuide Compact and fully integrated SIMS-device Methods for Stage-by-Stage Characterization • System dimensioning of the complete transfer chain using SimIon • Hard sphere model to simulate collisions and cooling efficiency I. Secondary ions are continuously generated by the FIB II. Secondary ions are accelerated into the SIMS orifice [1] III. Ions are cooled and bunched in the IonGuide IV. Ions are accumulated and sequentially transferred/pulsed into the mass analyzer (3D-trap) V. Ions are analyzed by measuring their influence charge on the cap electrodes [3] WaveGuide Ionization: electron beam ionization (tungsten filament) of Argon/Krypton outside the SIMS device. IonGuide used for ion transfer to WaveGuide Ion detection: Cup electrode of 3D-trap used as Faraday-Cup 3D-Trap Ionization: 266nm UV Laser for in-situ ion generation of vapor phase converted aromatic hydrocarbons Ion detection: Measuring the influence charge of trapped ions IonGuide Ionization: electron beam ionization (tungsten filament) of Argon/Krypton outside the SIMS device Ion detection: WaveGuide electrode used as Faraday-Cup WaveGuide WaveGuide Mass Analyzer Conclusions Transient signal and spectrum of in- situ generated benzene-ions • WaveGuide: Enables transfer of cooled and bunched ions between different pressure regions • IonGuide: Kinetic energy equilibrium depends on DC ramp of the IonGuide • IonGuide: High helium pressure minimizes kinetic energy distribution of ions • 3D trap: Compact and highly efficient wideband mass analyzer • SIMS: Complete chain tested under typical lab conditions → proof of concept adduced Future work: • Improve and extend low mass range • Improve pressure stages to enable high resolution measurements (longer signal transients) • Improve dynamic mass range mass spectrum of FIB sputtered ions (complete transfer chain) HV amplifier charge amplifier valve Sequence Control System UV-Laser sample gas bend-voltage: +12 V WaveGuide control unit System potentials extract cool transfer analyze FIB target microscope chamber P < 5×10 -6 mbar analysis chamber P < 5×10 -6 mbar cooling stage (Helium) P = 1×10 -2 … 5×10 -3 mbar pump pump pump University of Wuppertal, Germany Institute for Pure and Applied Mass Spectrometry athmosphere • Ions are shifted and pulsed into the 3D-trap • High pulse amplitudes → strong signals • Ions are transferred with different shift frequencies • Shift frequency does not affect transfer efficiency • DC ramp affects kinetic energy equilibrium • High DC ramps → high kinetic energy • Low helium pressure causes broad kinetic energy distributions • Measurements show higher kinetic energy than numerical simulations • Difficult to determine field distortion- and RF-effects 0 10 20 50 30 40 60 70 80 90 100 200 300 100 0 -100 200 300 400 Transient signal [mV] Time [ms] 0 10 20 50 30 40 60 70 80 90 100 Frequency [kHz] Arbitrary unit 30 40 50 80 60 70 90 100 110 Frequency [kHz] Arbitrary unit Noise signal Ion signal Charge amplifier Electrometer DC-bias (variable) DC-offset DC-ramp IonGuide WaveGuide 0 50 100 250 150 200 300 350 z-axis [mm] Kinetic energy [eV] -1 V DC ramp <E kin,z > = 0.12 eV <collisions> = 92 -15 V DC ramp <E kin,z > = 2.1 eV <collisions> = 48 5 × 10 -3 mbar 1 × 10 -2 mbar Measurement Simulation Kinetic energy at IonGuide outlet [eV] Kinetic energy at IonGuide outlet [eV] 0 5 10 Arbitrary unit 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 80 90 Cooling efficiency at constant pressure (P He = 1 × 10 -2 mbar) Kinetic energy distribution at different pressures Comparison of kinetic energy distributions 400 15 100 60 0 10 20 30 40 50 Arbitrary unit -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 0.5 1.0 2.5 1.5 2.0 3.0 3.5 time [ms] 0 0.5 1.0 2.5 1.5 2.0 3.0 3.5 time [ms] -100 -50 50 0 100 150 time [μs] -100 -50 50 0 100 150 time [μs] Different pulse amplitudes Different shift frequencies -8 -7 -6 -2 -5 -3 -1 2 time [ms] -4 0 1 -8 -7 -6 -2 -5 -3 -1 2 time [ms] -4 0 1 1 0 -1 -5 -3 -4 -2 -6 Voltage [V] 200 100 -300 -100 -200 0 -400 Voltage [mV] 200 100 -300 -100 -200 0 -400 Voltage [mV] 200 100 -500 -200 -400 -100 -600 Voltage [mV] 300 0 -300 200 100 -500 -200 -400 -100 -600 Voltage [mV] 300 0 -300 0 -5 -20 -15 -10 -25 Voltage [V] [1] [2] [3] [4] [5]
