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Fabrication and Characterization of thin D E-Detector for Spectroscopic Application

Fabrication and Characterization of thin D E-Detector for Spectroscopic Application. Göran Thungström 1 , Lars Westerberg 2 , Reimar Spohr 3 , C. Sture Petersson 1 ,4

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Fabrication and Characterization of thin D E-Detector for Spectroscopic Application

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  1. Fabrication and Characterization of thin DE-Detector for Spectroscopic Application Göran Thungström1, Lars Westerberg2, Reimar Spohr3, C. Sture Petersson1,4 1ITM, Mid-Sweden University, Sundsvall, Sweden, 2The Svedberg Laboratory, Uppsala, Sweden, 3GSI, Darmstadt, Germany, 4Royal Institute of Technology, Department of Electronics, Electrum, Kista, Sweden Department of Information Technology and Media Sensor Technology

  2. Outline • Introduction • Detector fabrication • Processing Remarks • Characterisation • Conclusion Department of Information Technology and Media Sensor Technology

  3. Introduction Department of Information Technology and Media Sensor Technology

  4. Department of Information Technology and Media Sensor Technology

  5. CHICSi ”CELSIUS Heavy-Ion Collision Silicon Detector System” CHICSi—a compact ultra-high vacuum compatible detectorsystem for nuclear reaction experiments at storage rings. I. General structure, mechanics and UHV compatibility, L. Westerberg et.al., Nuclear Instruments and Methods in Physics Research A 500 (2003) 84–95 Department of Information Technology and Media Sensor Technology

  6. O N C B 9Be Li 7Be Department of Information Technology and Media Sensor Technology

  7. Detector fabrication • Silicon Wafer • FZ • <100> • 1000 to 5000 Wcm • 380 mm, diameter 100 mm • N-type • Double side polished • Processing • Growth of 0.5 mm SiO2 • Doping at 900 C for 30 min using solid phosphorus-oxide source in N2 ambient + n Si n - type <100> SiO 2 Department of Information Technology and Media Sensor Technology

  8. Processing • Re-growth of SiO2 • Opening of detector window 2x2 mm2 + n Si n - type <100> SiO 2 Department of Information Technology and Media Sensor Technology

  9. Processing • Etching in 25 w% TMAH at 80 C for 14 h. + n SiO 2 Department of Information Technology and Media Sensor Technology

  10. Processing • Doping of detector window by using a solid boron-oxide source at 950 C for 30 min in N2 followed by annealing 30 min in O2 • Oxide in the detector window is removed by 5% hydro-fluoric-acid + n + p SiO 2 Department of Information Technology and Media Sensor Technology

  11. + n Al + p SiO 2 • Processing • Electron beam evaporation of Aluminium. • 0.1 mm • Detector window metallization is patterned • Forming Gas Annealing 400 C in 5% H2 and 95% N2 for 30 min. Department of Information Technology and Media Sensor Technology

  12. Processing remarks • Aligning marks • Wet etching undercut Solution ! Etch the oxide until 1/3 of the oxide thickness remain. Cover the aligning marks with resist. After baking, continue to etch the detector windows. Department of Information Technology and Media Sensor Technology

  13. Processing remarks Si Si Department of Information Technology and Media Sensor Technology

  14. 0 -10 -5 10 -9 -1 10 -9 -1,5 10 -9 -2 10 -15 -10 -5 0 Reverse Bias Voltage (V) Characterization • IV characterization • 8.8mm DE-detector Department of Information Technology and Media Sensor Technology

  15. CV-characterization c1 + n Al + p c2 2 ++++++ ++++++ SiO c4 c3 Ctotal=c1+c2+c3+c4 =310pF (oxide cap.) “decrease rapidly” Department of Information Technology and Media Sensor Technology

  16. Experimental setup • DE Bias: 7V • E detector 300 mm thickness, 200 mm2, 19000 Wcm, Bias: 40V, Ileak=8 nA • Pressure: 2*10-2 torr • Preamplifiers: Ortec 142 A,B • Shaping Amp.: Ortec 570, 1 ms • Two parameter MCA  2 mm a 20 mm DE E 12 mm  1.5 mm Vacuum chamber Department of Information Technology and Media Sensor Technology

  17. 6288 keV 5684 keV 5341 keV 6777 keV 8785 keV • Irradiation with alfa source • Calibration of the E-detector • Energy/channel=10 keV • E=10*ch+134 ( keV) Department of Information Technology and Media Sensor Technology

  18. Resolution of the E detector • 2*s2=d2 (ch2) • Rfwhm=2.355*s (ch) • Efwhm=66 keV Department of Information Technology and Media Sensor Technology

  19. Measurement of the DE-E detector telescope, E-detector • 1) ch: 153 result in an E=1664 keV • 2) ch: 317 result in an E=3304 keV • 3) ch: 404 result in an E=4174 keV • 4) ch: 468 result in an E=4814 keV 3 1 2 4 Department of Information Technology and Media Sensor Technology

  20. Calibration of DE-Detectors • DE-detectors with different thickness, irradiated with 241Am • 1) ch: 645 and DE= 3817keV • 2) ch: 350 and DE= 2176 keV • 3) ch: 186 and DE=1263 keV • 4) ch: 71 and DE=625 keV • Result in a cal. Eq. • DE=5.57*ch+227 (keV) 3 2 1 4 Department of Information Technology and Media Sensor Technology

  21. Estimation of DE-detector thickness • DX=-0.0347+7.558*E-0.441*E2-0.00565*E3 1) DE=3817 result in DX=22 um 2) DE=2176 result in DX=14.3 um 3) DE=1263 result in DX=8.8 um 4) DE=625 result in DX=4.5 um Department of Information Technology and Media Sensor Technology

  22. Measured DE-E plot of a 241Am source, for different DE thicknesses 4 22 um 3 DE-Detector (MeV) 14.3 um 2 8.8 um 1 4.5 um 0 (ch.) 0 E-detector (MeV) 0 2 4 6 Department of Information Technology and Media Sensor Technology

  23. Energy Straggling • W2=Wd2+Wres2+Wstrag2 • Wres=66 keV • Wstrag=”SRIM-2003.26” • Wd= ”thickness variation” • Wd1= 204 keV (22 um) • Wd2=102 keV (14.3 um) • Wd3=70 keV (8.8 um) • Wd4=117 keV (4.5 um) • DXDE1=0.62 um • DXDE2=0.31 um • DXDE3=0.22 um • DXDE4=0.36 um Department of Information Technology and Media Sensor Technology

  24. Channeling a • Channeling DE-detector (ch) E-detector (ch) Department of Information Technology and Media Sensor Technology

  25. Conclusion • Ultra thin DE-detectors for spectroscopic applications has been fabricated and characterized down to a thickness of 4.5 um. • The fabrication was in use of a common one side mask aligner. • The detector display low leakage current and the resulting capacitance is close to the detector window capacitance below a threshold voltage • The detector telescope should be slightly tilted to reduce the probability for channeling • However, even better thickness uniformity is needed to improve the resolution in the DE-E detector telescope Department of Information Technology and Media Sensor Technology

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