A new protocol to evaluate the charge collection efficiency degradation in semiconductor devices induced by MeV ions

Session 12: Modification and Damage: Contribute lecture O-35 A new protocol to evaluate the charge collection efficiency degradation in semiconductor devices induced by MeV ions Ettore Vittone Physics Department University of Torino Aliz Simon IAEA - Vienna ATOMKI, Hungary On behalf of the IAEA coordinated research project CRP F1116 «Utilization of Ion Accelerators for Studying and Modelling Ion Induced Radiation Defects in Semiconductors and Insulators 1

Object of the research Study of the radiation hardness of semiconductors Tool Focused MeV Ion beams to induce the damage and to probe the damage 2

Radiation damage is the general alteration of the operational properties of a semiconductor devices induced by ionizing radiation Three main types of effects: - Transient ionization. This effect produces electron-hole pairs; particle detection with semiconductors is based on this effect. -Long term ionization. In insulators, the material does not return to its initial state, if the electrons and holes produced are fixed, and charged regions are induced. - Displacements. Dislocations of atoms from their normal sites in the lattice, producing less ordered structures, with long term effects on semiconductor properties. V.A.J. van Lint, The physics of radiation damage in particle detectors, Nucl. Instrum. Meth. A253 (1987) 453. 3

- Displacements. Dislocations of atoms from their normal sites in the lattice, producing less ordered structures, with long term effects on semiconductor properties http://holbert.faculty.asu.edu/eee56/radiationeffectsdamage.pdf 4

Characterization of radiation induced damage: Device characteristic after irradiation Y Y 1 K 1 K ed D d Device characteristic before irradiation Particle Fluence Equivalent damage factor Displacement dose First order: proportionality, independent of the particle, between the damage factor and the particle NIEL NIEL approach: measurement of K ed only for one particle (at one specific energy) K ed can be estimated for all the particles and energies 5

CCE degradation induced by ion irradiation 1, Is a function of the damaging ion fluence Hamamatsu photodiode Vbias = 1 V Y Y 1 K 1 K ed D d,95 CCE,9,85 Cl 11 MeV 1 1 1 1 Fluence (m -2 ) 6

CCE degradation induced by ion irradiation Is a function of the ion energy and mass Y Y 1 K 1 K ed D d 1, Hamamatsu photodiode Vbias = 1 V,95 O 4 MeV He 1.4 MeV CCE,9 Li 2.15 MeV,85 Cl 11 MeV 1 1 1 1 6/17/215, Fluence Opatija; (m -2 E. ) Vittone, A. Simon 7

CCE degradation induced by ion irradiation Is a function of the material and/or device 1, N-type Fz-Si Y Y 1 K 1 K ed D d CCE,95,9 4H-SiC Schottky diode Hamamatsu p-i-n diode,85 P-type Fz-Si,8 1 1 1 1 1 Fluence (m -2 ) 8

CCE degradation induced by ion irradiation Is a function of the polarization state of the device Hamamatsu photodiode Y Y 1 K(V bias ) 1 K ed D d 1, CCE,95,9 He 1.4 MeV V bias 1 V 5 V 2 V,85 1 V 1 1 1 Fluence (m -2 ) 9

CCE degradation induced by ion irradiation Is a function of the ion used to measure the CCE 1, n-type Fz silicon diode Vbias = 5 V Y Y 1 K(V bias, Ion probe) 1 K ed D d,9 CCE,8,7,6,5 Probing ions 1 MeV H 2 MeV H 4.5 MeV H 8 MeV He 12 MeV He,4,3 Damage induced by 8 MeV He 1 1 1 Fluence (m -2 ) 1

Summary 11

IAEA Coordinate Research Programme (CRP) F1116 (211-215) Utilization of ion accelerators for studying and modeling of radiation induced defects in semiconductors and insulators Ruđer Bošković Inst. Croatia Helsinki University Finland ANSTO Australia Leipzig University Germany JAEA & Kyoto University Japan SANDIA USA Delhi Univ. India Surrey University United Kingdom CNA Spain NUS Singapore MNA Malaysia Torino University Italy 12

Goals To correlate the effect of different kinds of radiation on the properties of materials and devices To predict the effects of one radiation relative to another To extract parameters directly correlated with the radiation hardness of the material Experimental protocol Model for charge pulse formation (IBIC theory) Model for CCE degradation (SRH model) 13

Model for charge pulse formation (IBIC theory) Formalism based on the Shockley-Ramo-Gunn theorem The charge induced by the motion of free carriers is the Green s function of the continuity equations Adjoint equation method: the CCE is the solution of the Adjoint Equation 1 1 T.H.Prettyman, Nucl. Instr. and Meth. in Phys. Res. A 422 (1999) 232-237. E. Vittone, A. Simon 14

15 6/17/215, Opatija d x x y n th,n n n n n S d x y x p th,p p p p p S S z v v V(z) k z v 1 dz exp V y F dy z v v V(z) k z v 1 dz exp V y F dy x dx q Q d x x y n n S d x y x p p S S v 1 dz exp V y F dy v 1 dz exp V y F dy x dx q Q Electrons Holes Gunn s weighting field Drift lengths Model for charge pulse formation (IBIC theory) Ionization profile Fully depleted device No diffusion Ramo Theorem 1D

Model for CCE degradation Shockley-Read-Hall model Basic assumption: 1) In the linear regime, the ion induced damage affects mainly the carrier lifetime 2) The ion induced trap density is proportional to the VACANCY DENSITY 1 1 Vac(x) Fluence Capture coefficient Vacancy Density Profile 16

The experimental protocol Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 17

Samples under study n- and p- type Fz p-i-n Si diodes Fabricated by the Institute of Physics, University of Helsinki 16 floating guard rings The frontal electrode and the guard rings are coated with Al (.5 µm]). The Al electrode has a hole in the center, 1 mm diameter. Different dimensions: 5 or 2.5 mm MeV ions E. Vittone, A. Simon 18

Experimental protocol C-V characteristics Depletion width-voltage Experimental protocol Electrical characterization 19

Experimental protocol Experimental protocol hole drift velocity profiles Gunn s weighting potential Electrical characterization Electrostatic modeling Gunn s weighting field Electron drift velocity profiles 2

MeV scanning ion microbeam Spot size < 3 m PROBING THE PRISTINE SAMPLE 21

IBIC map on a pristine diode probed with a scanning 1.4 MeV He microbeam; Experimental protocol Uniform CCE map Electrical characterization Electrostatic modeling IBIC map on pristine sample Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 22

Ion microbeams Different ion mass/energy Spot size < 3 m DAMAGING SELECTED AREAS 1X1 m 2 23 23

IBIC map on a pristine diode probed with a scanning 1.4 MeV He microbeam; ZOOM in view of the selected area for focused ion beam irradiation at different fluences 1 2 3 4 5 7 8 6 9 5 m 1 m Experimental protocol Commercial p-in diodes Electrical characterization IBIC map on pristine sample Irradiation of 9 regions at different fluences Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 24

He ion microbeam Energy 1.4 MeV Spot size < 3 m PROBING DAMAGED AREAS Normalized Ionizing Energy loss (1/m).3.2.1 1.4 MeV He in Si. 1 2 3 4 5 6 7 Depth (m) Data from SRIM 25

IBIC map on a pristine diode probed with a scanning 1.4 MeV He microbeam; 1 2 3 4 5 7 8 6 9 5 m 1 m Experimental protocol Commercial p-in diodes Electrical characterization IBIC map on pristine sample Irradiation of 9 regions at different fluences IBIC map of irradiated regions a measured 2D distribution of the IBIC signal amplitude after irradiation Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 26

IBIC map on a pristine diode probed with a scanning 1.4 MeV He microbeam; 1 2 3 4 5 7 8 6 9 1 m Experimental protocol IBIC spectra (bias voltage = 1 V and 1 V) from the central regions of four of the areas shown in Fig. c f Counts Counts 1 5 1 5 Fluence 1 V 1 V 42 44 46 48 Pulse Height (Channels) 5 m a measured 2D distribution of the IBIC signal amplitude after irradiation Commercial p-in diodes Electrical characterization IBIC map on pristine sample Irradiation of 9 regions at different fluences IBIC map of irradiated regions Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 27

IBIC map on a pristine diode probed with a scanning 1.4 MeV He microbeam; 1 2 3 4 5 7 8 6 9 1 m Experimental protocol CCE 1,,95,9 Hamamatsu photodiode He 1.4 MeV V bias 1 V 5 V 2 V 5 m Commercial p-in diodes Electrical characterization IBIC map on pristine sample Irradiation of 9 regions at different fluences IBIC map of irradiated regions,85 1 1 1 Fluence (m -2 ) 1 V a measured 2D distribution of the IBIC signal amplitude after irradiation Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 28

DIB: Vacancy profiles PIB = Probing ion beam DIB = Damaging ion beam PIB: Ionization profiles Different bias voltages 29

CCE 1..9.8.7.6.5.4.3.2.1 DIB=8 MeV He V bias = 5 V 8 MeV He 12 MeV He.. 2.x1 12 4.x1 12 6.x1 12 Fluence (cm -2 ) PIB 2 MeV H Fixed DIB Fixed V bias Variable PIBs Fixed DIB Fixed PIB Variable V bias CCE 1..9.8.7.6.5.4.3 DIB=8 MeV He PIB=2 MeV H V bias (V) 5 V 2 V 1 V. 2.x1 12 4.x1 12 6.x1 12 Fluence (cm -2 ) CCE 1..9.8.7.6.5.4.3 PIB=2 MeV H V bias = 5 V DIB 12 MeV He 8 MeV He. 2.x1 12 4.x1 12 6.x1 12 Fluence (cm -2 ) Variable DIB Fixed PIB FIXED V bias 3

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) DIB P+ N N+ 31

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) PIB P+ Ionization energy loss (kevm) 1 5 Short range PIB Generation profile N N+ 1 2 3 4 5 Depth (m) 32

1,,9,8 PIB=1 MeV H DIB=8 MeV He,7 CCE,6,5,4,3,2,1, 2 4 6 8 1 Fluence (x1 12 cm -2 ) Hole motion Electron motion PIB P+ N N+ Ionization energy loss (kevm) 1 5 Generation profile Electric field 1 2 3 4 5 Depth (m) 33

CCE 1,,9,8,7,6,5,4,3,2,1, PIB=1 MeV H DIB=8 MeV He 2 4 6 8 1 Fluence (x1 12 cm -2 ) Residual map n Free parameter d d y F y 1 1 dx x dy exp dz n Vac(x QS q ) V x S v x n 34

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) DIB P+ N N+ 35

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) PIB N P+ Ionization energy loss (kevm) 9 6 3 Generation profile 1 2 Depth ( m ) N+ Long range PIB 36

CCE 1,,9,8,7,6,5,4,3,2,1, Vacancy/ion/m 1 8 6 4 2 Vacancy profile PIB=4.5 MeV H DIB=8 MeV He 2 4 6 8 1 1 2 3 4 5 Fluence Depth (x1 (m) 12 cm -2 ) Hole motion Electron motion PIB N P+ Ionization energy loss (kevm) 9 6 3 Generation profile 1 2 Depth ( m ) N+ 37

CCE 1,,9,8,7,6,5,4,3,2,1, Vacancy/ion/m 1 8 6 4 2 Vacancy profile PIB=4.5 MeV H DIB=8 MeV He 2 4 6 8 1 1 2 3 4 5 Fluence Depth (x1 (m) 12 cm -2 ) Residual map Q S q d dx x x d x dy dy F V F V y S y S exp exp x y y x dz dz 1 v p 1 v n 1 1 p n Vac(x) Vac(x) 38

Short range PIB Long range PIB Bias Voltage = 5 V n =17 m 3 /s p =13 m 3 /s 39

Bias Voltage = 5 V n-type Fz silicon diode Bias Voltage = 2 V Damaging ions: 8 MeV He Probing ions: 1,2,4.5 MeV H, 12 MeV He Bias Voltages: 1,2 5 V Bias Voltage = 1 V CAPTURE COEFFICIENTS n = (23±6) m 3 /s p = (7±3) m 3 /s 4

Fz silicon diode Capture coefficient 41

N-type silicon DLTS measurements singly V2( /) negatively charged divacancy σ n 5 1-15 cm 2 1 2 8 MeV He From MARLOWE simulation 1 1 Vacancy/Ion/m 1 1-1 1-2 Vacancy Marlowe di-vacancy Marlowe Vacancy SRIM n =v th σ n 1-3 5 1 15 2 25 3 35 4 45 5 55 6 Depth (m) σ n (5.3±1.4) 1-15 cm 2 E. Vittone, A. Simon 42

Limits of applicability Basic Hypotheses DIB : low level of damage 1 e,h 1,e,h n,p Vac(x) 1,e,h v Vac(x) e,h th linear model Independent traps, no clusters Unperturbed electrostatics (i.e. doping profile) of the device PIB : ion probe CCE is the sum of the individual e/h contributions No plasma effects induced by probing ions 44

CONCLUSIONS An experimental protocol has been proposed to study the radiation hardness of semiconductor devices Under the assumption of low damage level, the CCE degradation of a semiconductor device induced by ions of different mass and energy can be interpreted by means of a model based on The Shockley-Ramo-Gunn theorem for the charge pulse formation The Shockley-Read-Hall model for the trapping phenomena If the generation occurs in the depletion region, an analytical solution of the adjoint equation can be calculated. Adjusted NIEL scaling can be derived from the general theory in the case of constant vacancy profile. The model leads to the evaluation of the capture coefficient. For n-type Fz-Si it is in good agreement with DLTS data The capture coefficient is directly related to the radiation hardness of the material 45