Effect of Post Metallization Annealing for La 2 O 3 Thin Film

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Figure 1-6 shows the candidates of rare earth materials for gateinsulators and their physical properties. Figure 1-6 (a) shows the value ofband gap for rare earth oxides. This figure describes that each element hasutterly different value and La2O3, Gd2O3 and Lu2O3 has the highest band gapof 5.4 eV. And most of rare earth oxides have the enough value of band gaparound 5 eV. Figure 1-6 (b) shows the value lattice energy for rare earthoxides. Lattice energy means the energy which is required to separatesingle atom from the state of a crystal, namely the oxides having large latticeenergy tend to show easy crystallization. As shown in Figure 1-6 (b), thelattice energy of rare earth oxides become larger with an atomic number.Unfortunately, rare earth metal oxides also have several problems tobe a alternative replacement as the gate insulator. One of them is thepositive fixed charge in the rare earth oxides. This charge would make theflat band voltage (VFB) shift to negative side and degrade the mobility owingto Coulomb scattering as explained in former section. This unacceptableproblem must be solved in order to replace SiO2 for sub 100nm CMOStechnology.Candidates for gate insulator in Rare earthLaCePrNdSmEuGdTbDyHoErTmYbLuBand Gap (eV)65432-14000Lu 2O LuLa 32O 2O3Gd 32 O 3 -13800Sm 2 O 3 Yb 2 O 3-13600Yb 2 O 3Dy 2O -13400 Gd 2 O Dy 2O 33 3Eu 2 O 3 Pr -132002O Sm 2O 33 Eu 2 O 3-13000Pr 2 O 3-12800La 2 O 3Lattice Energy (kJ/mol)-12600La 2 O 3 Pr 2 O 3 Sm 2 O 3 Gd 2 O 3 Dy 2 O 3 Er 2 O 3 Yb 2 O 3La 2 O 3 Pr 2 O 3 Sm 2 O 3 Gd 2 O 3 Dy 2 O 3 Er 2 O 3 Yb 2 O 3Ce 2 O 3 Nd 2 O 3 Eu 2 O 3 Tb 2 O 3 Ho 2 O 3 Tm 2 O 3 Lu 2 O 3 Ce 2 O 3 Nd 2 O 3 Eu 2 O 3 Tb 2 O 3 Ho 2 O 3 Tm 2 O 3 Lu 2 O 3Band Gap of Rare Earth OxidesLattice Energy of Rare Earth OxidesFigure 1-6: Physical Properties of Rare Earth Oxides(a) Band Gap of Rare Earth Oxide (b) Lattice Energy of Rare Earth Oxides- 10 -
1.3 Purpose of My StudyIt is considered and concerned that one of the serious problems in allof high-k materials is the degradation of mobility. And one of the reasonswhy using high-k material degrades mobility is the fixed charges in high-kfilms as explained in former section. The fixed charges, moreover, wouldmake VFB shift and this effect would bring serious problems to electricalcharacteristics on MOSFET.Figure 1-7 shows that the C-V characteristics for MIS capacitor withLa2O3 films fabricated by post deposition annealing (PDA) and as-deposition(no annealing), and ID-VD characteristics for MOSFET with La2O3 filmsfabricated by PDA process. From C-V characteristics shown in Figure 1-7(a), VFB shift toward negative side around -0.7V was observed despite ofas-deposition. This result means that formed La2O3 thin films containpositive fixed charges in the state of as-deposition. Moreover, although theannealing process has a role as the improvement in electrical characteristics,a huge VFB shift more than 1V toward negative side was observed after PDAprocess. And it was also confirmed from ID-VD characteristics thatMOSFET with La2O3 thin films fabricated by PDA process has normally-oncharacteristics resulting from that enormous VFB shift. Normally-oncharacteristics on MOSFET would prevent from realizing the low powerconsumption.From the aforementioned, this thesis focuses on the problem aboutVFB shift, and will report the results of another way of annealing, postmetallization annealing (PMA), and its optimization for rare earth oxides,mainly La2O3 thin films for the purpose of the suppression of VFB shift.-11 -
Page 2: CONTENTSChapter 1 Introduction-----
Page 5 and 6: Chapter 1Introduction-1 -
Page 7 and 8: Miniaturization with a scaling fact
Page 9 and 10: Table 1-2: Electrical Properties fo
Page 11 and 12: LSI fabrication, such as activation
Page 13: Table 1-4 shows the properties of t
Page 17 and 18: Chapter 2FabricationAndCharacteriza
Page 19 and 20: 2.1.1 1 Wet Cleaning Method of Sili
Page 21 and 22: 2.1.3 Molecular Beam Deposition (MB
Page 23 and 24: 2.1.4 Rapid Thermal Annealing (RTA)
Page 25 and 26: 2.1.5 Vacuum Evaporation MethodAlum
Page 27 and 28: 1 1 1 t 1 kTC = C + C = εε+ q ε
Page 29 and 30: In C-V curve, the two type of hyste
Page 31 and 32: 2.2.2 Leakage Current Density-Volta
Page 33 and 34: 2.2.3 Ellipsometry MethodEllipsomet
Page 35 and 36: 3.1 IntroductionIn this chapter, th
Page 37 and 38: 3.3 Electrical Characteristics in t
Page 39 and 40: Capacitance (µF/cm 2 )21Al/La O /
Page 41 and 42: Current Density [A/cm 2 ]10 2 10 1A
Page 43 and 44: 3.3.2 Effects of Chemical Oxidation
Page 45 and 46: 3.3.3 Dependence on the Annealing T
Page 47 and 48: Capacitance (µF/cm 2 )210Al_As-dep
Page 49 and 50: Capacitance (µF/cm 2 )210Al/La O /
Page 51 and 52: Al/La O / n-Si(100)/Al2 3 250 o C d
Page 53 and 54: As the summary of this sub-section,
Page 55 and 56: Current Density[A/cm 10 2 PDAAs-de
Page 57 and 58: Equivalent Oxide thickness [nm]32.5
Page 59 and 60: Figure 3-29 shows the plots of VFB
Page 61 and 62: 3.4.1.4 Dependence on the Ambience
Page 63 and 64: V Shift [V]FB0.60.40.20-0.2-0.4-0.6
Page 65 and 66:
Capacitance (µF/cm 2 )21PDA 300 o
Page 67 and 68:
case of aluminum electrodes as comp
Page 69 and 70:
3.4.2.2 Effects of Chemical Oxidati
Page 71 and 72:
V Shift [V]FB-0.4-0.5-0.6-0.7-0.8-0
Page 73 and 74:
2.62.5EOT [nm]2.42.3As-depo.2.2PDA_
Page 75 and 76:
Capacitance (µF/cm 2 )21Au_PMA_N2_
Page 77 and 78:
3.4.2.5 The comparison with the cas
Page 79 and 80:
3.4.3 Effects of PMA for Platinum U
Page 81 and 82:
4Pt/La O / n-Si(100)/Al2 3EOT [nm]3
Page 83 and 84:
EOT [nm]2.82.62.42.221.81.6Pt/La O
Page 85 and 86:
On the other hand, there was almost
Page 87 and 88:
V Shift [V]FB0.2Pt/La O / n-Si(100)
Page 89 and 90:
Capacitance (µF/cm 2 )21Pt/La O /
Page 91 and 92:
Capacitance (µF/cm 2 )21Pt_As-depo
Page 93 and 94:
Chapter 4Conclusions- 89 -
Page 95 and 96:
4.1.2 Summary of the Investigation
Page 97 and 98:
Table 4-2: Summary of my investigat
Page 99 and 100:
esults. The second is the time when
Page 101 and 102:
AluminumAl 2 O 3 or LaAlO 3Al Al Al
Page 103 and 104:
AcknowledgementIn the first place,
Page 105 and 106:
Reference[1] International Technolo
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Effect of Post Metallization Annealing for La 2 O 3 Thin Film

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