Modeling of charge collection efficiency degradation in semiconductor devices induced by MeV ion beam irradiation

Modeling of charge collection efficiency degradation in semiconductor devices induced by MeV ion beam irradiation Ettore Vittone Physics Department University of Torino - Italy 1

IAEA Coordinate Research Programme (CRP) F1116 (211-215) Utilization of ion accelerators for studying and modeling of radiation induced defects in semiconductors and insulators Leipzig Univ. COOPERATION AND MUTUAL UNDERSTANDING LEAD TO GROWTH AND GLOBAL ENRICHMENT NUS Torino Univ. Surrey Univ. SANDIA Helsinki Univ. Delhi Univ. CAN Malesian Nuclear Agency Ruđer Bošković Inst. ANSTO JAEA-Kyoto Univ. 2

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 3

Radiation damage is the general alteration of the operational properties of 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 (oxides), 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. 4

M. Bruzzi, M. Moll, RD5, 21 Frank Hartmann, Silicon tracking detectors in high-energy physics Nuclear Instruments and Methods in Physics Research A 666 (212) 25 46 5

Modeling radiation degradation in solar cells extends satellite lifetime Robert J. Walters, Scott Messenger, Cory Cress, Maria Gonzalez and Serguei Maximenko A physics-based model of the effect of radiation on the performance of solar cells in space may enhance the on-orbit lifetime of Earth-orbiting spacecraft. SPIE 211 Space environment wide spectrum of ions (protons) and electrons. To understand the performance of a solar cell in the space radiation environment, it is necessary to know how cell degradation depends on the energy of the irradiating particle. http://spie.org/x43655.xml 6

Characterization of radiation induced damage: Device characteristic after irradiation Y Y 1 K 1 K ed D d Device characteristics 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 7

IBIC: Ion Beam Induced Charge Incoming radiation V out Deposited Energy Q Free charge generation and transport V Output Electrical Signal V out V out F(Deposited Energy, FreeCarrier Transport) Measured Well known Material Characterization 8

Characterization of radiation induced damage: Induced Charge after irradiation Induced Charge before irradiation CCE Q Q 1 Particle Fluence K 1 K ed Equivalent damage factor D d Displacement dose MeV Ion beams to induce the damage DIB=DAMAGING IONS And to probe the damage PIB=PROBING IONS 9

CCE degradation induced by ion irradiation Is a function of the damaging ion fluence 1, Hamamatsu photodiode Vbias = 1 V Y Y 1 K 1 K ed D d,95 CCE,9,85 DIB= Cl 11 MeV PIB= He 1.4 Cl MeV 11 1 1 1 1 Fluence (m -2 ) 1

CCE degradation induced by ion irradiation Is a function of the ion energy and mass 1, Hamamatsu photodiode Vbias = 1 V Y Y 1 K 1 K ed D d,95 O 4 MeV He 1.4 MeV CCE,9,85 PIB= He 1.4 MeV Cl 11 MeV Li 2.15 MeV 1 1 1 1 Fluence (m -2 ) 11

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 ) 12

CCE degradation induced by ion irradiation Is a function of the polarization state of the device 1, Hamamatsu photodiode Vbias = 1 V Y Y 1 K(V bias ) 1 K ed D d CCE,95,9 He 1.4 MeV V bias 1 V 5 V 2 V,85 1 V 1 1 1 Fluence (m -2 ) 13

CCE degradation induced by ion irradiation Is a function of the probing ions (PIB) 1, n-type Fz silicon diode Vbias = 5 V Y Y 1 K(V bias, PIB ) 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 ) 14

Summary CCE degradation DIBs(12 MeV and 8 MeV He) PIBs (1, 2, 4.5 H; 8, 12 MeV He) Different bias voltages (1,2,5 V) 15

Goals To correlate the effect of different kinds of radiation on the properties of materials and devices 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) 17

Model for charge pulse formation (IBIC theory) Formalism based on the Shockley-Ramo-Gunn theorem Adjoint equation method: the CCE is the solution of the Adjoint Equation T.H.Prettyman, Nucl. Instr. and Meth. in Phys. Res. A 422 (1999) 232-237. 18

Pulse shapes calculation Shockley-Ramo theorem I -q v 1 d Gunn theorem Gunn s theorem I -q v E V Weighting field 19

Boundary conditions Formalism based on the Gunn s theorem Solve the boundary n t p t continuity potential equations defined by using conditions, space charge n n n Dn n Gn n p p p Dp p Gp p the r Initial conditions For mapping charge pulses G n,p (r r ) (t) Generation point at t Evaluate the Gunn's weighting field by solving the Poisson s E E V The potentials of all the other conductors are held constant i equation Evaluate the induced charge Q (t) i t q dt' drn(r,t';r ) v n (r) p(r,t';r ) v p (r) E(r) V i V 2

is Adjoint equation Method the Q in t (t) q dt' dr Green's Charge function Induced n( r, t';r for the from ) v electron electrons n ( r) E( r) V continuity i V Short-cut equation The continuity equation involves linear operators The charge induced from electrons can be evaluated by solving a single, time dependent adjoint equation. n t n n D n n G * n n n n G n Q in n E V i 22

Model for charge pulse formation (IBIC theory) 1D Ionization profile Gunn s weighting field Fully depleted device No diffusion Q S q d dx x d x x F dy V F dy V y S y S exp exp y x x y dz dz v v p n 1 1 p n Holes Electrons Ramo Theorem Drift lengths 23

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 24

The experimental protocol Z. Pastuovic et al., IEEE Trans on Nucl. Sc. 56 (29) 2457; APL (98) 9211 (211) 25

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 26

Experimental protocol C-V characteristics Depletion width-voltage Experimental protocol Electrical characterization 27

Experimental protocol Experimental protocol hole drift velocity profiles Gunn s weighting potential Electrical characterization Electrostatic modeling Gunn s weighting field Electron drift velocity profiles 28

MeV scanning ion microbeam Spot size < 3 m PROBING THE PRISTINE SAMPLE 29

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) 3

Ion microbeams Different ion mass/energy Spot size < 3 m DAMAGING SELECTED AREAS 1X1 m 2 31

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 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) 32

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 33

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 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) 34

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 f Counts 1 5 1 V Fluence 5 m Electrical characterization IBIC map on pristine sample Irradiation of 9 regions at different fluences IBIC map of irradiated regions IBIC spectra (bias voltage = 1 V and 1 V) from the central regions of four of the areas shown in Fig. c Counts 1 5 1 V 42 44 46 48 Pulse Height (Channels) 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) 35

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 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) 36

DIB: Vacancy profiles PIB = Probing ion beam DIB = Damaging ion beam PIB: Ionization profiles Different bias voltages 37

CCE 1..9.8.7.6.5.4.3.2 DIB=8 MeV He V bias = 5 V PIB 8 MeV He 12 MeV He.1.. 2.x1 12 4.x1 12 6.x1 12 Fluence (cm -2 ) 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 38

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) DIB P+ N N+ 39

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) 4

1,,9,8 PIB=1 MeV H DIB=8 MeV He,7 CCE,6,5,4,3,2,1, PIB 2 4 6 8 1 Fluence (x1 12 cm -2 ) Hole motion Electron motion P+ N N+ Ionization energy loss (kevm) 1 5 Generation profile Electric field 1 2 3 4 5 Depth (m) 41

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 42

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) DIB P+ N N+ 43

Vacancy/ion/m 1 8 6 4 2 Vacancy profile 1 2 3 4 5 Depth (m) PIB N P+ 6 3 Ionization energy loss (kevm)9 Generation profile 1 2 Depth (m) N+ Long range PIB 44

1,,9,8 CCE,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+ 6 3 Ionization energy loss (kevm)9 Generation profile 1 2 Depth (m) N+ 45

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) 46

Short range PIB Long range PIB Bias Voltage = 5 V n =17 m 3 /s p =13 m 3 /s 47

P-type N-type n-type Fz silicon diode Damaging ions: 8 MeV He Probing ions: 1,2,4.5 MeV H, 12 MeV He Bias Voltages: 1,2 5 V 48

Fz silicon diode Capture coefficient n-type n = (25±3) m 3 /s p = ( 21±16) m 3 /s p-type n = (131± 9) m 3 /s p = (22±3) m 3 /s 49

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 1-3 Vacancy Marlowe di-vacancy Marlowe Vacancy SRIM 5 1 15 2 25 3 35 4 45 5 55 6 Depth (m) C. R. Crowell, Appl. Phys. 9, 79-81, 1976 Vth= 1.8 1 7 m/s n =v th σ n σ n (3.6±.4) 1-15 cm 2 5

51 d d x y x n n S x x y p p S S Vac(x) 1 v 1 dz exp V y F dy Vac(x) 1 v 1 dz exp V y F dy x dx q Q Solution of the adjoint equations For very low level of radiation Linearization vs. Effective fluence *

Very low level of damage E. Vittone et al. / Nuclear Instruments and Methods in Physics Research B 372 (216) 128 142 52

Derivation of the Non Ionizing Energy Loss (NIEL) displacement damage formula Constant vacancy profile Low displacement damage CCE 1 K D ed d K ed y R d z z d eff F eff F dz k n n (z) dy dx x k p p (z) dy M V z S V S z y dx x K ed = equivalent damage factor depends on Electrostatics of the device Carrier transport and recombination Ion probe ionization profile 53

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 54

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. The capture coefficient is directly related to the radiation hardness of the material 55

Characterization of radiation induced damage: Induced Charge after irradiation Induced Charge before irradiation CCE Q Q 1 Particle Fluence K 1 K ed Equivalent damage factor D d Displacement dose 58

n t n n D n n G * n n n Excess carrier lifetime Trap density N 1 trap v th Thermal velocity Capture cross section N trap N Trap density induced by radiation trap k Trap density in pristine material 1 1 K 59

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 = (25±3) m 3 /s p = (21±16) m 3 /s 6