In Framework of CERN RD50 Collaboration J.Hrknen, 10th ESSD, Wildbad - PowerPoint PPT Presentation

Thermal donor generation in Czochralski silicon particle detectors M.Bruzzi 1) , J.Härkönen 2) , Z. Li 3) , P.Luukka 2) , D. Menichelli 1 ) , E. Tuovinen 1) 1) University of Florence 2) Helsinki Institute of Physics, CERN/PH, Switzerland 3) Brookhaven National Laboratory, Upton, NY11973-5000, USA In Framework of CERN RD50 Collaboration J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

OUTLINE • Motivation •Thermal Donors (TD) in oxygen rich silicon •Processing of MCz-Si detectors with TDs •Introduction of TDs •DLTS spectra •Annealing of p-type MCz-Si with TDs •Conclusions J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Motivation • n+/p-/p+ detector signal comes from electrons having three times higher mobility than the holes •The detectors used in particle tracking systems must be fully depleted at reasonably low operating voltage •By introduction of TDs, the V fd of detectors can be adjusted in wide range J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Thermal Donors in Cz-Si •TDs are oxygen complexes that form shallow states in Si band gap below the conduction band. •High O content leads to Thermal Donor (TD) formation at temperatures 400 0 C – 600 0 C. •TD formation can be enhanced if H is present. •Typical process steps at 400 0 C – 600 0 C - Aluminum sintering (e.g. 30min @ 450 0 C) - Passivation insulators over metals (LTO,TEOS etc ~600 0 C + H 2 from Si 3 H 4 process gas) D.J. Chadi, Phys. Rev. Lett. 77, 861–864 (1996) J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Thermal Donor generation •TD formation depends on - O concentration in silicon - Temperature - Amount of H in detector processing Cz-Si, O i ≈ 8*10 17 cm -3 685V MCz-Si, O i ≈ 4,9*10 17 cm -3 68V Oxygenated Fz-Si, O i ≈ 1*10 17 cm -3 J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Sample processing •n + /p - /p + diodes with p-stops •p + /p - /p + diodes •TD generation 35 and 45 minutes •TD generation 60,70 and 80 minutes •5 mask levels •4 mask levels •TD induced type-inversion J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Thermal Donor generation (experimental results) •O concentration from FTIR measurements •Thick reference wafer •Center 4,95*10 17 cm -3 •Right 4,89*10 17 cm -3 •Left 4,93*10 17 cm -3 •Right 4,93*10 17 cm -3 J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Thermal Donor generation (experimental results) 9E+12 8E+12 7E+12 6E+12 Ntd(cm^-3) 5E+12 4E+12 3E+12 2E+12 1E+12 0 0 1000 2000 3000 4000 5000 6000 Time (s) J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Thermal Donor generation (experimental results) 6E+12 5E+12 4E+12 3E+12 2E+12 1E+12 0 0 1000 2000 3000 4000 5000 6000 7000 -1E+12 -2E+12 -3E+12 -4E+12 J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Leakage current 4,5E-09 4,0E-09 no TD 3,5E-09 no TD TD 45min at 430C 3,0E-09 TD 45min at 430C Current [A] 2,5E-09 2,0E-09 1,5E-09 1,0E-09 5,0E-10 0,0E+00 -300 -250 -200 -150 -100 -50 0 Voltage [V] J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Deep Level Transient Spectroscopy •Sample heated at 430C 45 minutes •Sample heated at 370C 45 minutes J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Annealing of proton irradiated detectors 450 •1,5*10 14 cm -2 1MeV n Cz-Si 400 neutron equivalent. TD's 60min 350 TD's 70min 300 TD's 80min Vfd (V) 250 200 150 100 50 0 1 10 100 1000 Heating time at 80C (min) J.Härkönen, 10th ESSD, Wildbad Kreuth June 20

Conclusions •Thermal Donors can be introduced into MCz-Si detectors at 430 ° C during the aluminum sintering. •It is low temperature, low cost process, no additional process complexity >> feasible solution for large scale experiments ? •Effective resistivity range is very wide in TD-process 500 Ω cm < σ < ∼ 10 k Ω cm •No increase of leakage current •With this method it is possible to adjust the V fd of p-type MCz-Si n+/p-/p+ detectors J.Härkönen, 10th ESSD, Wildbad Kreuth June 20