Theory and practice of Materials Analysis for Microelectronics with a nuclear microprobe

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1 TUTORIAL Theory and practice of Materials Analysis for Microelectronics with a nuclear microprobe Ettore Vittone Physics Department University of Torino, Italy Ettore Vittone 1

2 IBIC for the functional characterization of semiconductor materials and devices Measurement of the their electronic properties and performances Main physical observable: current Current = F(carrier density; carrier transport) Free carriers (electron/hole) transport Two mechanisms: Drift and Diffusion Drift: by the electrical force v=μ E Diffusion: by a concentration gradient Recombination/trapping Carrier lifetime Ettore Vittone 2

3 Principles of radiation detection techniques Incoming radiation Q V out Deposited Energy Moving charge q V Induced charge Q Output Signal V out V out F(Deposited Energy, Free Carrier Transport) Nuclear spectroscopy Material characterisation Ettore Vittone 3

4 Stopping power (kev m -1 ) X-ray energy loss rate Using MeV ions to probe the electronic features of semiconductors H+ ion energy (MeV) IBIC long range low lateral scattering 1 5 a wide choice of ion range and electronic energy losses (kev\(mm s -1 ) 7 3x1 7 2x1 7 1x1 7 3 kev Photon current: 5* Depth ( m ) SRIM (Stopping and Range of Ion in Matter) Electrode energy loss very small ( 1%) photons/s XBIC analysis through thick surface layers charge pulses height spectra almost independent on topography. profiling Ettore Vittone 4

5 Electron/Hole pair generation N eh E ion eh 1 MeV in diamond generates about 77 e/h pairs Each high energy ion creates large numbers of charge carriers to be measured above the noise level. A. Lo Giudice et al. Applied Physics Letters 87, 2221 (25) Ettore Vittone 5

6 Physical Observable: Induced current/charge Shockley-Ramo Theorem v m E The current is induced by the motion of charges in presence of an electric field v Induced current I(t) q d Ettore Vittone 6

I Q Physical Observable: Induced current/charge 1..8.6.4.2. Q(t) T I(t)dt.75.5.25.

7 I Q Physical Observable: Induced current/charge Q(t) T I(t)dt Time I(t) q v d W. Shockley, J. Appl. Phys. 9 (1938) 635. S. Ramo, Proc. I.R.E. 27 (1939) 584. Ettore Vittone 7

8 I I Q Q CARRIER LIFETIME I(t) q v d exp t Time Induced current Ettore Vittone 8 Drift time=d/v Time

9 IIa diamond; resistivity about 1 15 Ω cm; dielectric constant =.5 pf/cm; Dielectric relaxation time = 5 s. Charge neutrality not maintained 4 mm thick natural diamond, biased at 4 RT C. Canali, E. Gatti, S.F. Koslov, P.F. Manfredi, C. Manfredotti, F. Nava, A. Quirini Nucl. Instr. Meth. 16 (1979) Ettore Vittone 9

10 V out d v V m ee CCE d Generation at the anode -> Hole collection Generation at the cathode -> Electron collection d exp m ee 1 K. Hecht, Z. Physik 77, (1932) 23 Ettore Vittone 1

11 C. Canali, E. Gatti, S.F. Koslov, P.F. Manfredi, C. Manfredotti, F. Nava, A. Quirini Nucl. Instr. Meth. 16 (1979) mm thick natural diamond, biased at 4 RT Electrons: Drift velocity; v me d/t R Mobility; md 2 /(T R *V Bias ) Ettore Vittone 11

12 Shockley-Ramo Theorem v m E The current is induced by the motion of charges in presence of an electric field v Induced current I(t) q d Ettore Vittone 12

13 Schottky electrode Energy Loss (kev/mm -1 ) Depletion Region 5 mm thick N-type epitaxial 4H-SiC layer Applied Bias Voltage (V) Frontal ion Irradiation MeV 2 MeV FAST DRIFT COMPLETE COLLECTION Depth (mm) DIFFUSION Bragg.opj Ettore Vittone 13

14 Energy Loss (kev/mm -1 ) Applied Bias Voltage (V) Frontal ion Irradiation 4H-SiC Schottky diode MeV 2 MeV Depth (mm) Bragg.opj Ettore Vittone 14

15 Energy Loss (kev/mm -1 ) Applied Bias Voltage (V) Frontal ion Irradiation 4H-SiC Schottky diode MeV 2 MeV Depth (mm) Bragg.opj Ettore Vittone 15

16 Energy Loss (kev/mm -1 ) Applied Bias Voltage (V) Frontal ion Irradiation 4H-SiC Schottky diode MeV 2 MeV Depth (mm) Bragg.opj Ettore Vittone 16

17 Energy Loss (kev/mm -1 ) Applied Bias Voltage (V) Frontal ion Irradiation 4H-SiC Schottky diode MeV 2 MeV Depth (mm) Bragg.opj Ettore Vittone 17

18 CCE Active region width 1,,8,6,4,2 1.5 MeV 2 MeV, Applied Bias Voltage (V) minority carrier diffusion length L p =(9..3) mm D p = 3 cm 2 /s p = 27 ns 4H-SiC Schottky diode Ettore Vittone 18

19 L p ( mm ) Temperature dependent IBIC (TIBIC) p ( mm-2 ) L ,5 (b),45,4,35,3,25,2,15 (a), T (K) L p T D T T p p Two trapping levels SRH recombination model A 2.5 Lp Dp D p (T) B T.5 B E t B T T exp ND kbt The fitting procedure provides a trapping level of about.163 ev which is close to the value found in similar 4H SiC Schottky diodes by DLTS technique (S1 level). Ettore Vittone 19

20 From Spectroscopy to micro-spectroscopy Use of focused ion beams Ettore Vittone 2

21 Trajectories One advantage of IBIC over other forms of charge collection microscopy is that it provides high spatial resolution analysis in thick layers since the focused MeV ion beam tends to stay focused through many micrometers of material. Electrons 1 kev 2 mm 2 mm 47 mm 9 mm 4 MeV H+ in Si 147 mm 4 mm Electrons 4 kev 2 MeV H+ in Si 3 MeV H+ in Si 6 mm 2 mm Abs#151-F. Watt: nuclear microprobe, towards nanometer spost sizes Ettore Vittone 21

22 Frontal IBIC MeV Ions V out V b Ettore Vittone 22

Frontal IBIC IBIC imaging with 2 MeV protons IBIC maps of

at electrode tips due to concentration of the electric field 5 2 V

Position (nm) Intra-crystallite charge transport M.B.H.

23 Frontal IBIC IBIC imaging with 2 MeV protons IBIC maps of polycrystalline diamond inter-digitated detectors show hot spots at electrode tips due to concentration of the electric field 5 2 V 37 V 4 Single grain IBIC line scan Counts Position (nm) Intra-crystallite charge transport M.B.H.Breese et al. NIM-B 181 (21), ; P.Sellin et al. NIM-B 26 (27), Ettore Vittone 23

24 Poster Session I (23/7/212) h Poster #75 Aleksandr Ponomarev Investigation of Cd1-xMnxTe Polycrystalline Thin Films Using Nuclear Microprobe Techniques Ettore Vittone 24

25 LATERAL IBIC-TRIBIC Ettore Vittone 25

26 Monocrystalline Diamond Schottky diode Ettore Vittone 26

27 Plateaux: Depletion region (active region) Vs. Bias voltage Induced charge (fc) V bias = X axis (mm) Exponential-like decay outside the highly efficient depletion region Electron diffusion length : Mobility lifetime : m e e L e D (2.57.3)V / cm e e ( ) mm Ettore Vittone 27

28 A high-speed imaging system for Time Resolved digital IBIC at Surrey Lateral TRIBIC CdZnTe radiation detector v m E Induced current I(t) q v d Ettore Vittone 28

29 Poster Session III (26/7/212) h Poster #171 Natko Skukan CVD diamond as a position sensitive detector using charge carrier transition time Ettore Vittone 29

30 Pulse shapes calculation Shockley-Ramo theorem I -q v 1 d Gunn s theorem I -q v E V Weighting field Ettore Vittone 3

31 Induced current into the sensing electrode I -q v w E V Weighting field E -q v E w w Weighting potential: V w V Equation of motion: v dr dt The induced charge Q into the sensing electrode Q q t t B A Idt w ( r B q t t B A ) v E w ( r A w ) dt q r B r A E q V w r B dr V r A is given by the difference in the weighting potentials between any two positions (r A and r B ) of the moving charge Ettore Vittone 31

32 To evaluate the total induced charge Evaluate by solving Evaluate the the the actual Poisson s potential Gunn' s weighting equation potential V V is the bias potential at the sensitive electrode Magnetic effects are negligible; Electric field propagates instantaneously Free carrier velocities much smaller than the light speed Excess charge does not significantly perturb the electric field Solve (continuit the y) transpo rt equations The induced charge Q into the sensing electrode is given by the difference in the weighting potentials between any two positions (r A and r B ) of the moving charge Q q V r V B r A Ettore Vittone 32

33 Weighting potential Weighting field Electric Field V bias Schottky barrier Depletion Region Neutral n-type Depth E w E V Depth w V 1 Depth Ettore Vittone 33

34 Weighting potential Electrostatics Electrons/holes Induced charge w V 1 Electric field h+ Q q V final position V initial position e- Transport properties Ettore Vittone 34 Depth

35 Weighting potential w 1 V Electric field h+ e- Ettore Vittone 35 x Depth

36 Weighting potential 1 Electric field w V h+ e- Ettore Vittone 36

37 Weighting potential CCE Q Q q V V final initial electrons collected position position Generated q x 1 Total Number of electrons w w 1 V Electric field h+ e- Ettore Vittone 37 x Depth

38 Weighting potential 1 Electric field w V h+ Ettore Vittone 38 x Depth

39 Weighting potential CCE Q Q q q V V final initial holes collected position position x Generated Total Number of holes w 1 Electric field CCE ToT electrons electrons collected Generated holes holes collected Generated x x 1 w w 1 w V h+ Ettore Vittone 39

4 MeV He ion probe,35,3,25,2,15,1 Cl Li O He,5, 1 1 2 3 4

40 Vacancy/Ion/mm Energy loss (kev/mm) ionization profile of the 1.4 MeV He ion probe,35,3,25,2,15,1 Cl Li O He,5, Depth (mm) Vacancy profiles generated by 11 MeV Cl, 4 MeV O, 2.15 MeV Li 1.4 MeV He Ettore Vittone 4

41 Weighting potential Effects of localized recombination centres w 1 V Electric field h+ e- Traps Recombination Centers Ettore Vittone 41 x Depth

42 Weighting potential 1 Electric field w V h+ e- Traps Recombination Centers Ettore Vittone 42 x Depth

43 Weighting potential CCE Q Q q q V V final initial electrons collected position position x Generated 1 Total Number of electrons w w 1 V Electric field h+ e- Traps Recombination Centers Ettore Vittone 43 x Depth

44 Weighting potential 1 Electric field w V h+ Traps Recombination Centers Ettore Vittone 44 x Depth

45 Weighting potential CCE Q Q q q V V final initial holes collected position position x Generated Total Number of holes w 1 Electric field w V Traps h+ Recombination Centers Ettore Vittone 45 x w Depth

46 Radiation Damage in 4H-SiC z 2 MeV 4+ C V out x V b = 1 V y Ettore Vittone 46

47 Transport equations Vacancy profille (from SRIM; PAS) Shockley-Read-Hall Recombination/trapping model Electrostatics of the device (TCAD) Trap cross section (DLTS) Shockley-Ramo-Gunn Theorem Low Level of damage Trap/vacancy ratio Radiation hardness Ettore Vittone 47

48 Oral Session 25/7/212, h 9:-1.3 #25: Milko Jaksic (invited) : Review of nuclear microprobe applications in material science Oral Session 25/7/212, h 11:-12.3 #198: Gyorgy Vizkelethy: Investigation of ion beam induced radiation damage in Si and GaAs diodes #92: Zeljko Pastuovic: Overview of radiation damage studies in silicon diodes exposed to focused ion beam irradiation-proposed template for further research of radiation damage studies in semiconducting materials and devices by IBIC Poster Session I (23/7/212) h Poster #141: Veljko Grilj: Comparison of sccvd diamond and silicon SB detectors irradiated by low energy protons Ettore Vittone 48

49 The induced charge Q into the sensing electrode is given by the difference in the weighting potentials between any two positions (r A and r B ) of the moving charge Q q V final V position initial position CHARGE SHARING IN MULTIELECTRODE DEVICES Ettore Vittone 49

50 Actual potential Weighting potential Ettore Vittone 5

51 CHARGE CURRENT Weighting potential 2,5 Actual potential 2, 1,5 1,,5 Q q V final V position initial position Ettore Vittone 51, time time

52 CHARGE CURRENT Weighting potential Actual potential Q q V final V position initial position Ettore Vittone time time

53 CHARGE CURRENT Weighting potential Actual potential,1, -,1 -,2 -,3 -,4 -,5 1 time q V final V position -3 Q -4 initial position Ettore Vittone time

54 CHARGE CURRENT Weighting potential Actual potential,4,2, -,2 time Q q V final V position initial position Ettore Vittone 54 -,4 1,,8,6,4,2, -,2 -,4 -,6 -,8-1, time

55 Poster Session I (23/7/212) h Poster #123: Jacopo Forneris: IBIC characterization of an ion beam micromachined multi electrode diamond detector Poster Session III (26/7/212) h Poster #16: Laura Grassi: Charge collection study in the interstrip region of DSSSD using proton microbeam Ettore Vittone 55

56 Horizontal electric field Q q V final V position initial position Ettore Vittone 56

57 CCE LEFT ELECTRODE 1, RIGHT ELECTRODE,8,6,4,2 A SUB-MICROMETER POSITION SENSITIVE DETECTOR, Position (mm) 2 MeV He+ Ettore Vittone 57

58 Oral Session 25/7/212, h 11:-12.3 #133: David Jamieson (invited): Addressing roadmap challenges: adapting nuclear microprobe technology to build engineered atom devices #124: Jacopo Forneris: Modeling of ion beam induced charge sharing experiments for design of high resolution position sensitive detectors. Ettore Vittone 58

59 I HOPE YOU ENJOY YOUR TIME AT THE Ettore Vittone 59

60 Ettore Vittone 6 SOLUTION OF THE EQUATIONS OF MOTION = TRAJECTORIES OF CHARGES Initial point (r A ) ; final point (r B ) ) ( ) ( q Q A w B w r r w -q V -q I E v E v

61 CHARGE CURRENT SOLUTION OF THE EQUATIONS OF MOTION = TRAJECTORIES OF CHARGES I -q Initial point (r A ) ; final point (r B ) Q q E v V w ( r B ) -q v E w ( r A ) w E w E w 2,5 2, 1,5 1,,5, time time Ettore Vittone 61

62 CHARGE CURRENT SOLUTION OF THE EQUATIONS OF MOTION = TRAJECTORIES OF CHARGES Initial point (r A ) ; final point (r B ) I E -q v V Q q w ( r B ) -q v E w ( r A w ) time time Ettore Vittone 62

63 CHARGE CURRENT SOLUTION OF THE EQUATIONS OF MOTION = TRAJECTORIES OF CHARGES Initial point (r A ) ; final point (r B ) I E -q v V Q q w ( r B ) -q v E w ( r A w ),1, -,1 -,2 -,3 -,4 -,5 1 time -1-2 time -3-4 Ettore Vittone 63

64 CHARGE CURRENT SOLUTION OF THE EQUATIONS OF MOTION = TRAJECTORIES OF CHARGES Initial point (r A ) ; final point (r B ) E w E w I E -q v V Q q w ( r B ) -q v E w ( r A w ),4,2, -,2 -,4 1,,8,6,4,2, -,2 -,4 -,6 -,8-1, time time Ettore Vittone 64

IBIC (Ion Beam Induced Charge Collection) Analytical technique suitable for the measurement of transport properties in semiconductor materials and devices Control of in-depth generation

65 IBIC (Ion Beam Induced Charge Collection) Analytical technique suitable for the measurement of transport properties in semiconductor materials and devices Control of in-depth generation profile Suitable for finished devices (bulk analysis). Micrometer resolution CCE profiles: Active layer extension; Diffusion length In-situ analysis of radiation damage Ettore Vittone 65

66 L p ( mm ) Temperature dependent IBIC (TIBIC) p ( mm-2 ) L ,5 (b),45,4,35,3,25,2,15 (a), T (K) Two trapping levels SRH recombination model A 2.5 Lp Dp D p (T) B T.5 B E t B T T exp ND kbt The fitting procedure provides a trapping level of about.163 ev which is close to the value found in similar 4H SiC Schottky diodes by DLTS technique (S1 level). E. Vittone et al., NIM-B 231 (25) 491. Ettore Vittone 66

67 CCE Time resolved IBIC (TRIBIC) Silicon Power diode Mesa Rectifier Proton beam (2-3-4 MeV) p + W n n + Mesa Rectifier 168 lifetime = (5 1) ms Electrodes (Ag-Ni-Cr) C Charge sensitive preamplifier V Shaping amplifier Passivation Mesa Glass ADC Digital oscilloscope IBIC TRIBIC V 1 V 5 V.5 p + n 3 mm 16 mm Experiment Theory n + 11 mm Time (ms) Ballistic deficit Ettore Vittone 67

68 Radiation Damage 17 μm 68 μm 145 μm Area 1:.. Area 2: 1,8 E1 Area 3: 6,1 E9 Area 4: 2, E9 Area 5: 6,1 E8 Area 6: 2, E8 Fluences (cm -2 ) Good Reproducibility Ettore Vittone 68

69 Lateral IBIC V b = 5 V Area 1 Area 2 Area 3 Area 4 Area 5 Area 6 CCE profiles Lifetime reduction Depletion region shrinking Ettore Vittone 69

70 Frontal IBIC Polycrystalline CVD diamond Under illumination CCE Dark Ettore Vittone conditions 7

71 N i =4 Uniformity (D.Meier, PhD thesis 1999, C.Manfredotti 2) N i =16 N i =32 a 4 A TOT a 16 a 32 s i 1 1 s Ni j1 s i, j N s N 1 i s s = overall average signal evaluated over the total scanned area A i, j TOT Ni j1 N i = Number of pixel of area a i : A TOT = a i N i s i,j = signal from the j-th pixel of area a i i 2 Ettore Vittone 71

72 IBIC maps with different pixel dimension Uniformity s i 1 1 s Ni j1 s i, j N s i mm pixel dimension (mm) The uniformity is between 8% and 1% on the length scale above 2 mm; at 1 mm the uniformity is 69% Ettore Vittone 72

73 Schottky electrode 5 mm thick N-type epitaxial 4H-SiC layer Frontal ion Irradiation Depletion region Fast drift transport Energy Loss (kev/mm -1 ) Complete collection 1 mm Neutral region Depth (mm) Diffusion transport Incomplete collection.7 MeV.9 MeV 1.1 MeV 1.3 MeV 1.5 MeV 1.7 MeV CCE 1,2,25,3,35,4,45,5,55,6,65,7,75,8,85,9,95 1, Ettore Vittone M. Jaksic et al.nim-b, 188 (22),

74 L p Numerical Simulations ( 4, 9, 3) mm p 8 ns 3 V 5 V 7 V V b Ettore Vittone 74

75 Diamond Schottky diode structure: homoepitaxial growth on HPHT substrates (type Ib, 44.4 mm 3 ) slightly B doped (Acceptor concentration cm -3 ) heavily B-doped buffer layer as back contact (Acceptor concentration cm -3 ) 25 μm thick intrinsic layer as active volume Schottky contact: frontal Al circular contact ( = 2 mm, 2 nm thick) on intrinsic layer Lateral IBIC of a diamond Schottky diode back contact on B-doped layer ohmic contact sample cleaved in order to expose its cross section for IBIC characterization ideality factor: n = (1.51.4) series resistance: R s = ( ) kω back B-doped contact shunt resistance: R sh = (9 6) 5 V -> I<5 pa S. Almaviva et al. Synthetic single crystal diamond dosimeters for conformal radiation therapy application Diamond & Related Materials 19 (21) Ettore Vittone 75

76 4H-SiC Schottky diode Starting Material: 36 mm n-type 4H-SiC by CREE (USA) Epitaxial layer from Institute of Crystal Growth (IKZ), Berlin, Germany Devices from Alenia Marconi System Si-face Ettore Vittone 76

Lateral IBIC measurements performed at the ion microbeam line of the AN2 accelerator of the National Laboratories of Legnaro (LNL-INFN) charge sensitive electronic chain and synchronous signal

77 Lateral IBIC measurements performed at the ion microbeam line of the AN2 accelerator of the National Laboratories of Legnaro (LNL-INFN) charge sensitive electronic chain and synchronous signal acquistition with microbeam scanning ion species and energy: H 2 MeV ion current: 1 3 ions s -1 no pile up or charging effects ion beam spot on the sample: FWHM = 3 μm raster-scanned area: S = 6262 μm 2 Ettore Vittone 77

78 4 MeV Protons (1 mm range) 4H SiC Schottky barrier Ettore Vittone 78

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