Damage formation and annealing studies of low energy ion implants ...

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Pulsed lasers can produce rapid heating of the surface layers, with times of 10 -11 to 10 -6 s. This is known as the adiabatic regime, and affects only the near surface. It is possible with pulsed lasers to either regrow the surface region through liquid phase epitaxy or through solid phase epitaxy in the sub melt region (36). In device production it is currently most common to use RTA or SA but as the need for shallower junctions becomes greater, different types of annealing methods, including laser annealing, are being increasingly considered (37). The annealing of ion implanted amorphous Si produces a variety of effects, depending strongly on the initial state of the implanted region. Effects include epitaxial crystallisation, random nucleation and growth, dopant segregation and defect enhanced diffusion, which are described in this chapter. Regrown layers contain fewer defects when the starting point is amorphous Si compared to initially highly damaged layers. 3.3.2 Solid phase epitaxial regrowth (SPER) Solid phase epitaxial regrowth (SPER) is a process whereby amorphised Si is recrystallised upon thermal annealing from temperatures above half that of the melting temperature of the crystal, i.e. for Si from approximately 500 °C, to approximately 1350 °C. The underlying Si crystal acts as a template for the amorphised Si to be arranged upon (epitaxy). This occurs while the Si is still a solid, hence the term solid phase epitaxial regrowth (14, 38, 39). During SPER the amorphous Si rearranges itself on the underlying crystalline substrate starting from the amorphous / crystalline (a/c) interface and proceeds to the surface in a layer-by-layer fashion. Since crystalline Si has lower free energy there is always a driving force towards rearrangement to the crystal structure. During SPER, the implanted dopants take up substitutional lattice sites as the crystal-amorphous interface passes through their location. Time resolved reflectivity (TRR) (38) is the main technique that has been used for measuring SPER rates. It has been observed that impurities (dopants) affect the regrowth behaviour and the rate of SPER. Intrinsic (undoped) Si will be described first and then the addition of impurities is considered. 3.3.2.1 Intrinsic Si It has been shown for intrinsic amorphous layers, produced by self ion implantation, that the regrowth velocity is temperature and orientation dependant. The orientation dependence is related to the density of atomic packing on the different planes. The regrowth rate on (100) Si is approximately 2.5 times greater than (110) Si 43
and is approximately 25 times faster than (111) Si (40). Regrown (111) substrates have been observed to contain high levels of defects compared to (100) and (110) orientated substrates. In this thesis all experiments were carried out on (100) Si. A model for recrystallisation shows that bonds can be broken and reformed to produce the crystalline phase. To be considered a part of the crystal each atom should have at least two undistorted bonds to already aligned atoms of the crystal. For the (100) surface, a single atom can simply attach to any other atom of the crystal but for (110) and (111) planes two and three adjacent atoms, respectively, must attach simultaneously, to atoms of the crystal, which is less probable, accounting for the differences in rate and defects observed (39). The regrowth velocity is also temperature dependent and is shown to follow an Arrhenius type expression. ⎛ E A ⎞ v = v 0 exp⎜− ⎟ (nms ⎝ kT ⎠ -1 ) (3.3) where v is the growth velocity, k is the Boltzmann constant (8.617E-5 eV/K), T the temperature at which regrowth is occurring and EA the activation energy. v0 and EA can both be obtained from a plot of regrowth rates against temperature. Values obtained for intrinsic (100) Si are EA = 2.68 eV, and v0 = 3.07 × 10 15 nms -1 (39), although various studies have produced values for the activation energy from 2.3 to 2.9 eV (41). Doping changes the regrowth rate. For 2 × 10 14 cm -2 As implanted Si, the values for EA and v0 are 2.76 eV and 3.68 × 10 15 respectively (39). Figure 3.6 shows the trend in regrowth rate with temperature for ion implanted Si. Values for (110) and (111) have been inferred from the (100) values. Values for SPER rates of intrinsic and doped Si using equation 3.3 are given in Table 3.1 below. 44
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Damage formation and annealing stud
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3.2.2.6 Other models 40 3.2.3 Other
Page 5 and 6:
Chapter 7 Interaction between Xe, F
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List of Figures Figure 1.1 a) Schem
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Figure 4.13 Variation in the kinema
Page 11 and 12: Figure 6.10 MEIS energy spectra for
Page 13 and 14: Figure 7.8 Combined MEIS Xe depth p
Page 15 and 16: Abbreviations and Symbols a/c amorp
Page 17 and 18: Abstract The work described in this
Page 19 and 20: Chapter 7 5 M. Werner, J.A. van den
Page 21 and 22: terminal (Vg), current cannot flow
Page 23 and 24: This is an approximate average leve
Page 25 and 26: the active channel, adjacent to the
Page 27 and 28: To continue to improve devices ther
Page 29 and 30: produces a device quality regrown l
Page 31 and 32: technique of channelling Rutherford
Page 33 and 34: 22 J.S Williams. Solid Phase Recrys
Page 35 and 36: and the probability of scattering t
Page 37 and 38: importance for many atomic collisio
Page 39 and 40: M1, V0, E0 Figure 2.2 Elastic scatt
Page 41 and 42: 2.3.1 Models for inelastic energy l
Page 43 and 44: dE/dx (ev/Ang) 10 1 Inelastic Energ
Page 45 and 46: dE/dx (eV/Ang) 125 100 75 50 25 0 2
Page 47 and 48: Figure 2.5 Results of TRIM simulati
Page 49 and 50: Chapter 3 Damage and Annealing proc
Page 51 and 52: the Si/SiO2 interface, consuming th
Page 53 and 54: On the basis that by creating an in
Page 55 and 56: Figure 3.4 Structure of crystalline
Page 57 and 58: a Si atom will suffer little angula
Page 59 and 60: 3.2.2.5 Homogeneous model (Critical
Page 61: Sputtering and atomic mixing play a
Page 65 and 66: elevant dopants later. For equal co
Page 67 and 68: nearest neighbour distance (52). By
Page 69 and 70: Category I defects are produced whe
Page 71 and 72: thermal annealing (600 - 700 °C an
Page 73 and 74: Figure 3.11 Relationship between im
Page 75 and 76: defect pairs due to Coulomb attract
Page 77 and 78: ⎛ 〈 C ⎞ ⎛ ⎞ I 〉 〈 C V
Page 79 and 80: 27 R.D. Goldberg, J. S. Williams, a
Page 81 and 82: 67 H. Bracht. Diffusion Mechanism a
Page 83 and 84: Hall effect measurements were carri
Page 85 and 86: energy than one scattered from an a
Page 87 and 88: epresents a small improvement over
Page 89 and 90: (dE/dx)out multiplied by the path l
Page 91 and 92: they are small compared to the diff
Page 93 and 94: ackscattering (27). This fact forms
Page 95 and 96: Figure 4.7 a) Plot of a Gaussian di
Page 97 and 98: similar to the width of the error f
Page 99 and 100: UP Ion Beam SPIN Rotation Sample Sc
Page 101 and 102: Kinematic factor (K) 1.0 0.8 0.6 0.
Page 103 and 104: Figure 4.14 Illustration of the dou
Page 105 and 106: 4.2.2.4 Interpretation of spectra A
Page 107 and 108: with are comparatively small, ~ 0.5
Page 109 and 110: Inelastic energy loss (eV/Ang) 32 2
Page 111 and 112: iterative procedure is carried out
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Yield (couts per 5µC) 300 250 200
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SIMS experiments were also carried
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MEIS, using the scattering conditio
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4.5 Sample production Samples have
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an N2/O2 environment to maintain an
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38 M. Anderle, M. Barozzi, M. Bersa
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damage evolution behaviour observed
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Yield (counts per 5 µC) 250 200 15
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essentially a “zero dose” profi
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no longer “visible” in MEIS has
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yield (cts / 5µC) 500 400 300 200
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5.4 Conclusion MEIS analysis with a
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Chapter 6 Annealing studies 6.1 Int
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6.2.2.2 Results and Discussion Figu
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theory predictions and X-ray fluore
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implantation conditions are those u
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a) b) c) Yield (counts per 5 µC) Y
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greater than MEIS. SIMS is not sens
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attributed to the interference betw
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The as-implanted sample, with a bro
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a) b) Yield (counts per 5 µC) Yiel
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interface, as evidenced by the high
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duration, is observed. MEIS results
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Yield (counts per 5µC) 500 400 300
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ack edges of the Si peaks are very
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underneath the SiO2 layer, iii) it
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R s (Ω/sq) 950 900 850 800 750 60
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As concentration (at/cm 3 ) 1E22 1E
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R s (Ω/sq) 950 900 850 800 750 70
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Following annealing it was observed
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∆a/a (x 10 -3 ) 4,0 epi550 3,5 3,
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Yield (counts per 5 uC) 350 300 250
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(FWHM). Concomitantly, As in the re
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The higher temperature anneals carr
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ecomes steeper for the sample annea
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Figure 6.28 Schematic illustrations
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and the 2D picture in Figure 6.31b)
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6.5 Conclusion In summary, in this
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20 L. Capello, T. H. Metzger, M. We
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egarding B profiles relevant to the
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TRIM AU 0.04 0.03 0.02 0.01 TRIM si
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a) F profile PAI 3 keV BF2 b) F pro
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Yield (counts per 5 µC) 20 15 10 5
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the corresponding PAI sample, yield
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amorphous matrix, (16) i.e. local c
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21 M. Anderle, M. Bersani, D. Giube
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stopped at depths beyond the observ
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the role of each individual element
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