Quantitative Low Current Ion Beam Characterization by Beam Profiling and Imaging via Scintillation Screens

Transcription

1 Quantitative Low Current Ion Beam Characterization by Beam Profiling and Imaging via Scintillation Screens , Mühlleithen XIII. Erfahrungsaustausch: Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen, Dr. Susette Germer

2 Motivation Requirements for a perfect guinea pig: fits the specific scientific problem maximum gain in information Story behind the use of test animals: C. Darwin: birth of modern science E. Schrödinger: most popular cat

3 Outline 1. Ion beam diagnostics via scintillator screens for low energy beams Setup and method Results and discussion 2. Summary 3. Outlook RF ion beam source Scintillator screen (inorganic crystals, YAG:Ce) IOM, Group of Prof. Arnold Development and characterization of ion and plasma based technologies for ultra precision machining of surfaces IOM, Leipzig

4 1. Ion beam diagnostic setup and method Ion beam diagnostics setup Scintillator screen (Y 3 Al 5 O 12 :Ce YAG:Ce, λ = 550 nm) Faraday cup RF ion beam source: Ar +, U B = 1 kv, U A = 200 V, I B = 2 ma, p = 2.5e 5 mbar Scintillator + CCD camera: neutralized beam imaging via luminescence process by ionizing radiation light output Faraday cup: electrical measurements of non neutralized beam ion current density Wafer: test etching etching rate Cooling system and CCD camera 4 Wafer SiO 2 /Si RF ion beam source

5 1. Ion beam diagnostic setup and method Ion beam diagnostics method Imaging and characterization of the neutralized ion beam via scintillator screen for the identification of the tool function Comparison of the results obtained by Faraday scans and test etchings Footprints, 4 Wafer SiO 2 /Si Correlation between the light output and the ion current density as well as the etch rate! Scintillator image of the neutralized beam Faraday cup FWHM Ion current density

6 1. Ion beam diagnostics results and discussion RF ion beam source parameters: aperture S = 2.0 mm, wd = 35 mm, α S = 45 and U B = 1 kv Scintillation screen: imaging of neutralization with and without ion beam in scanning mode (v = 0.5 mm/sec) to reduce signal scattering through surface contaminations Difference image analysis: achievement / evaluation of horizontal and vertical beam profiles Horizontal cross section Tool function information: Light output FWHM Beamlet structure Difference image Vertical cross section Grid of the ion source Low Pass Filter

7 1. Ion beam diagnostics results and discussion Comparison of obtained beam profiles for Scintillator (YAG:Ce), Faraday scan and test etching 3.51 mm (SE 2.3%) 3.21 mm (SE 3.9%) 4.02 mm (SE 3.7%) 3 beam profiles fit quite well YAG:Ce contaminations result in minor profile deviations Faraday scan missing neutralization and excitation of secondary electrons Parameter: working distance, normalized to 25 mm Strong correlation between the light output and the current density as well as the etch rate Scintillation method achieves a detailed characterization of the neutralized ion beam (error 8%)

8 1. Ion beam diagnostics results and discussion Estimations of beam divergence via scintillator method Good correlation of full divergence angle (2ϴ) between YAG:Ce method, Faraday cup and test etching Parameter: pulse width modulation, working distance of 45 mm Light output and etch rate follow expected trend toward increasing pulse width

9 2. Summary/ 3. Outlook Ion beam diagnostic setup: scintillation method as a powerful tool for neutralized ion beam characterization in the low energy range and identification of the tool function Limitations: contaminations, temperature, surface charges Further research: development and characterization of a subaperture ion beam source (beam diameter < 0.5 mm) using adjustable electrostatic lenses parlament der tiere.de/

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