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

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Figure 3.6 SPER rates for Si (100), (110) and (111). From (39). SPER rate (nms -1 ) Anneal temperature / °C Intrinsic Si As doped to 2 × 10 21 cm -3 550 0.12 0.047 600 1.04 0.43 650 7.18 3.1 700 40.5 18.7 800 797 402 900 9420 5120 1000 75600 43700 Table 3.1 Regrowth rates for intrinsic and 2 × 10 14 cm -2 As doped Si, for various temperatures. 3.3.2.2 Dopant and other impurity Atoms Implanted impurity atoms have been observed to alter the regrowth rate. The effects depend on species and concentration (42). Virtually all non doping impurities (e.g. O, N, F), at moderate to high concentration (0.1 to >1 atom %), have been seen to reduce the SPER rate (43). For group III and group V dopants such as B and As ions at low concentrations, ~ 1 × 10 19 cm -3 , an increase in the regrowth rate has been observed (42), with B exhibiting the largest rate enhancing effect. As dopant concentrations are increased, it has been observed that the regrowth rate reaches some maximum value and then slows down for increasing concentration (14) and this is described in more detail for specific 45
elevant dopants later. For equal concentration of n and p type dopants, the regrowth rate is reduced to that characteristic of intrinsic amorphous Si (38). For increasing dopant concentrations, of the order 1 × 10 20 cm -3 , processes such as impurity segregation and precipitation can occur, which alter the crystallisation kinetics. These processes are strongly influenced by the growth temperature and the rate at which dopant diffuse in the amorphous Si layer. Precipitation e.g. dopant clustering has been observed to retard the epitaxy. Segregation or “Push out” of the dopant occurs for slow diffusing species (As, Sb), which do not precipitate prior to epitaxy. Segregation occurs at the a/c interface and the effect is to “snowplough” excess dopant in front of the advancing a/c interface (14, 38). Segregation is not observed below a certain critical impurity concentration, which is species dependant and is always greater than the equilibrium solid solubility, i.e. the maximum concentration that can be accommodated through diffusion at a particular temperature. Note that the term solid solubility or just solubility is often used to refer to the concentration that can take up substitutional positions during SPER. At concentrations below the solid solubility all dopants present can take up substitutional positions. For higher concentrations above the solid solubility excess dopant segregates. At these concentrations the regrowth rate is observed to appreciably slow down. For much higher dopant concentrations polycrystalline growth has been observed, associated with random nucleation and growth (38), as described in section 3.3.3. B has the highest solid solubility of the elements in group III (36, 44). For concentrations from 2 × 10 19 cm -3 to 2 × 10 20 cm -3 B enhances the SPER rate (42). The amount of enhancement increases with increasing dose within this concentration range. Above 2 × 10 20 cm -3 a saturation in rate occurs. The saturation level can be increased with increasing annealing temperature. This effect is believed to be due to the limited solid solubility of B in Si, and the assumption that only dissolved B increases the SPER rate. BF2 is most commonly used to implant B. BF2 contains both rate enhancing B and rate retarding F in the same layer. The effect of BF2 is simply a combination of rate enhancement from B effects and retardation effects from F. F retardation is strongly temperature dependent therefore rate retardation due to F in BF2 sample should be less pronounced as the temperature is increased. During annealing F has been observed to both segregate to the surface and diffuse to the EOR region (45-48). When As is present in amorphous Si there is a temperature dependant interplay between processes such as SPER, random crystallisation, impurity diffusion, defect 46
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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
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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 and 62: Sputtering and atomic mixing play a
Page 63: and is approximately 25 times faste
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
Page 113 and 114: 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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