Sn-Sb-Se based binary and ternary alloys for phase change

202 Pages·2008·21.28 MB·English

Sn-Sb-Se based binary and ternary alloys
for phase change memory applications
Von der Fakult(cid:127)at fu(cid:127)r Mathematik, Informatik und
Naturwissenschaften der Rheinisch-Westf(cid:127)alischen Technischen
Hochschule Aachen zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften genehmigte Dissertation
vorgelegt von
Kyung-Min Chung
M.Sc.
aus Seoul, Korea
Berichter: Universit(cid:127)atsprofessor Dr. Matthias Wuttig
Universit(cid:127)atsprofessor Dr. Gero von Plessen
Tag der mu(cid:127)ndlichen Pru(cid:127)fung: 28 October 2008
Diese Dissertation ist auf den Internetseiten
der Hochschulbibliothek online verfu(cid:127)gbar

Contents
List of Tables V
List of Figures VI
Abstract X
Zusammenfassung XIII
1 Introduction 1
1.1 Modern computer data storage . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Memory technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Emerging non-volatile memory technologies . . . . . . . . . . . . . . . . . 6
1.3.1 MRAM (Magnetic Random Access Memory) . . . . . . . . . . . . . 6
1.3.2 FeRAM (Ferroelectric Random Access Memory) . . . . . . . . . . . 7
1.3.3 PCRAM (Phase Change Random Access Memory) . . . . . . . . . 8
1.4 Challenges in PCRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.5 Development of phase change materials . . . . . . . . . . . . . . . . . . . . 14
1.6 Goals of this study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2 Theoretical background 17
2.1 Thermal Evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.1 The Hertz-Knudsen equation. . . . . . . . . . . . . . . . . . . . . . 19
2.1.2 The Knudsen cell and the cosine law of emission . . . . . . . . . . . 21
2.1.3 Applications of the cosine law . . . . . . . . . . . . . . . . . . . . . 25
I
Contents
2.1.4 Evaporation of alloys . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 Crystallization kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.2.1 Phase transformation . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2.2 Nucleation kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.2.3 Growth kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.2.4 Johnson-Mehl-Avrami (JMA model) . . . . . . . . . . . . . . . . . 43
2.3 X-ray analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.3.1 X-ray Di(cid:11)raction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.3.2 Laboratory X-ray methods . . . . . . . . . . . . . . . . . . . . . . . 52
2.3.3 X-ray Re(cid:13)ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3 Experimental Methods 62
3.1 Thermal Evaporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.1.1 Combinatorial material synthesis system . . . . . . . . . . . . . . . 62
3.1.2 The sample preparation chamber . . . . . . . . . . . . . . . . . . . 64
3.1.3 Secondary Neutral Mass Spectrometry . . . . . . . . . . . . . . . . 66
3.1.4 Control units and software . . . . . . . . . . . . . . . . . . . . . . . 69
3.2 Four-point probe method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.2.1 Activation energy for crystallization . . . . . . . . . . . . . . . . . . 74
3.3 X-ray analysis system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.3.1 X-ray di(cid:11)raction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.3.2 X-ray re(cid:13)ectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.4 Static tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.5 Atomic Force Microscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4 Results I : Sn-Se binary system 93
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.2 The SnSe alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.2.1 Temperature dependent electrical properties . . . . . . . . . . . . . 96
4.2.2 Investigation of structural properties . . . . . . . . . . . . . . . . . 98
II
Contents
4.2.3 Kinetics of the structural transformations . . . . . . . . . . . . . . 103
4.2.4 Density and thickness change upon crystallization . . . . . . . . . . 105
4.2.5 Static tester experiments . . . . . . . . . . . . . . . . . . . . . . . . 107
4.3 The SnSe alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
2
4.3.1 Temperature dependent electrical properties . . . . . . . . . . . . . 112
4.3.2 Investigation of structural properties . . . . . . . . . . . . . . . . . 114
4.3.3 Kinetics of the structural transformations . . . . . . . . . . . . . . 115
4.3.4 Density and thickness change upon crystallization . . . . . . . . . . 117
4.3.5 Static tester experiments . . . . . . . . . . . . . . . . . . . . . . . . 119
4.3.6 Comparison with sputtered SnSe alloy . . . . . . . . . . . . . . . . 122
2
4.4 The Sn Se alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
2 3
4.4.1 Temperature dependent electrical properties . . . . . . . . . . . . . 126
4.4.2 Investigation of structural properties . . . . . . . . . . . . . . . . . 129
4.4.3 Kinetics of the structural transformations . . . . . . . . . . . . . . 131
4.4.4 Density and thickness change upon crystallization . . . . . . . . . . 132
4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
5 Results II : Sn-Sb-Se ternary system 135
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
5.2 The MBE deposited and sputtered Sn Sb Se alloy . . . . . . . . . . . . . 140
1 2 4
5.2.1 Temperature dependent electrical properties . . . . . . . . . . . . . 140
5.2.2 Investigation of structural properties . . . . . . . . . . . . . . . . . 142
5.2.3 Kinetics of the structural transformations . . . . . . . . . . . . . . 144
5.2.4 Density and thickness change upon crystallization . . . . . . . . . . 146
5.2.5 Static tester experiments . . . . . . . . . . . . . . . . . . . . . . . . 148
5.3 The SnSe -Sb Se pseudobinary alloys . . . . . . . . . . . . . . . . . . . . 151
2 2 3
5.3.1 Temperature dependent electrical properties . . . . . . . . . . . . . 151
5.3.2 Investigation of structural properties . . . . . . . . . . . . . . . . . 153
5.3.3 Kinetics of the structural transformations . . . . . . . . . . . . . . 157
III
Contents
5.3.4 Density and thickness change upon crystallization . . . . . . . . . . 160
5.3.5 Static tester experiments . . . . . . . . . . . . . . . . . . . . . . . . 162
5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
Bibliography 170
Acknowledgements 183
Lebenslauf 185
IV
List of Tables
2.1 The X-ray wavelengths for selected material. . . . . . . . . . . . . . . . . . 53
3.1 Bulk densities and Z-values for common used materials.. . . . . . . . . . . 67
4.1 The XRD peak positions of the as-deposited SnSe alloy. . . . . . . . . . . . 99
4.2 The XRD peak positions of the annealed SnSe alloy. . . . . . . . . . . . . . 100
4.3 The XRD peak positions of the SnSe alloy. . . . . . . . . . . . . . . . . . 115
2
5.1 The XRD peak positions of Sn Sb Se alloy. . . . . . . . . . . . . . . . . . 143
1 2 4
5.2 The XRD peak positions of Sn Sb Se alloy. . . . . . . . . . . . . . . . . . 153
1 4 8
5.3 The XRD peak positions of Sn Sb Se alloy. . . . . . . . . . . . . . . . . . 155
1 2 5
5.4 The XRD peak positions of Sn Sb Se alloy. . . . . . . . . . . . . . . . . . 156
2 2 7
5.5 The data comparison for di(cid:11)erent SnSe -Sb Se pseudobinary alloys. . . . . 163
2 2 3
V
List of Figures
1.1 Various types of data storage. . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Principle of MRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Principle of FeRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 Principle of switching phase change materials. . . . . . . . . . . . . . . . . 9
1.5 Typical concepts of PCRAM cell design. . . . . . . . . . . . . . . . . . . . 12
2.1 The concept of physical vapor deposition. . . . . . . . . . . . . . . . . . . . 18
2.2 The Knudsen cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 The directional dependence of Knudsen cell. . . . . . . . . . . . . . . . . . 22
2.4 The directional dependence of condensation. . . . . . . . . . . . . . . . . . 25
2.5 Applications of the cosine law. . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.6 Comparisonof thickness pro(cid:12)leobtainedafterevaporationin the staticand
dynamic modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.7 The Gibbs free energy diagram for two phases, (cid:11) and (cid:12) of the same com-
pound as a function of the con(cid:12)gurational coordinates. . . . . . . . . . . . 34
2.8 The Gibbs free energy of formation of nuclei as a function of lattice size. . 36
2.9 The viscosity (cid:17) in various stability regimes. . . . . . . . . . . . . . . . . . . 39
2.10 Schematic representation of the growth of phase 1 into the phase 2 matrix. 40
2.11 The temperature dependence of nucleation and growth rate for a fast nu-
cleation and growth dominated materials. . . . . . . . . . . . . . . . . . . . 42
2.12 Basic features of a typical XRD experiment. . . . . . . . . . . . . . . . . . 47
2.13 Several atomic planes and theier d-spacings. . . . . . . . . . . . . . . . . . 48
VI
List of Figures
2.14 Schematic plot of characteristic X-ray spectrum. . . . . . . . . . . . . . . . 52
2.15 The Debye-Scherrer camera and an example of a powder di(cid:11)raction photo-
graph. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.16 X-ray powder di(cid:11)raction measurement using a focusing arrangement. . . . 56
2.17 Schematic diagram showing the re(cid:13)ection of x-rays at the interface of three
media with refractive indices, n , n and n . . . . . . . . . . . . . . . . . . 57
1 2 3
2.18 Schematic representation of a XRR spectra for thin (cid:12)lm deposited on a Si
Substrate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.1 Photos of the combinatorial material synthesis system. . . . . . . . . . . . 63
3.2 Scheme of the preparation chamber. . . . . . . . . . . . . . . . . . . . . . . 64
3.3 Sketch of the crucible used for the evaporation sources. . . . . . . . . . . . 65
3.4 Schematic representation of SNMS analysis. . . . . . . . . . . . . . . . . . 68
3.5 The control units and screenshot of the software for the preparation process. 70
3.6 Schematic representation of a four-point probe setup. . . . . . . . . . . . . 73
3.7 Overview of the Philips X’pert MRD system. . . . . . . . . . . . . . . . . . 77
3.8 Schematic representation of the focus and detector circle of the x-ray
di(cid:11)ractometer system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.9 Schematic illustration of the Bragg-Brentano geometry. . . . . . . . . . . . 81
3.10 Schematic representation of Seemann-Bohlin geometry. . . . . . . . . . . . 82
3.11 A schematic diagram illustrating the shape of the rocking curves for a
concave, convex and (cid:13)at sample [1] . . . . . . . . . . . . . . . . . . . . . . 85
3.12 Schematic illustration of the e(cid:11)ect of using the knife edge to improve the
pro(cid:12)le of the rocking curve [2]. . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.13 Schematic diagram of the far (cid:12)eld setup . . . . . . . . . . . . . . . . . . . 88
3.14 Visualization of the autofocus system with the knife edge method . . . . . 89
3.15 Basic schematic diagram of Atomic Force Microscope (AFM) . . . . . . . . 90
4.1 Phase diagram of the binary Sn-Se system. . . . . . . . . . . . . . . . . . . 94
4.2 The sheet resistance of SnSe alloy. . . . . . . . . . . . . . . . . . . . . . . . 97
VII
List of Figures
4.3 The XRD spectra of SnSe alloy. . . . . . . . . . . . . . . . . . . . . . . . . 99
4.4 The atomic distribution of SnSe alloy. . . . . . . . . . . . . . . . . . . . . . 101
4.5 The AFM measurement of SnSe alloy. . . . . . . . . . . . . . . . . . . . . . 102
4.6 The activation energy calculation of SnSe alloy. . . . . . . . . . . . . . . . 102
4.7 The X-ray re(cid:13)ectometry measurements of SnSe alloy. . . . . . . . . . . . . 105
4.8 Temperature dependence of the density and thickness for SnSe (cid:12)lm ob-
tained from XRR measurements. . . . . . . . . . . . . . . . . . . . . . . . 106
4.9 Re(cid:13)ectance measurements of SnSe alloy on as-deposited and annealed state.108
4.10 The PTE diagram for the amorphization of SnSe alloy. . . . . . . . . . . . 109
4.11 The PTE diagram for the recrystallization of SnSe alloy. . . . . . . . . . . 110
4.12 The sheet resistance of SnSe alloy. . . . . . . . . . . . . . . . . . . . . . . 112
2
4.13 The XRD spectra of SnSe alloy. . . . . . . . . . . . . . . . . . . . . . . . 114
2
4.14 The atomic distribution of SnSe alloy. . . . . . . . . . . . . . . . . . . . . 116
2
4.15 The AFM measurement of SnSe alloy. . . . . . . . . . . . . . . . . . . . . 117
2
4.16 The activation energy calculation of SnSe alloy. . . . . . . . . . . . . . . . 118
2
4.17 The X-ray re(cid:13)ectometry measurements of SnSe alloy. . . . . . . . . . . . . 119
2
4.18 Temperature dependence of the density and thickness for SnSe (cid:12)lm ob-
2
tained from XRR measurements. . . . . . . . . . . . . . . . . . . . . . . . 120
4.19 Re(cid:13)ectance measurements of SnSe alloy on as-deposited and annealed state.121
2
4.20 The PTE diagram for the amorphization of SnSe alloy. . . . . . . . . . . . 122
2
4.21 The PTE diagram for the recrystallization of SnSe alloy. . . . . . . . . . . 123
2
4.22 The sheet resistance of sputtered SnSe alloy. . . . . . . . . . . . . . . . . 124
2
4.23 The XRD spectra of sputtered SnSe alloy. . . . . . . . . . . . . . . . . . . 125
2
4.24 The grazing incidence XRD spectra of sputtered SnSe alloy. . . . . . . . . 126
2
4.25 The X-ray re(cid:13)ectometry measurements of sputtered SnSe alloy. . . . . . . 127
2
4.26 The sheet resistance of Sn Se alloy. . . . . . . . . . . . . . . . . . . . . . . 128
2 3
4.27 The XRD spectra of Sn Se alloy. . . . . . . . . . . . . . . . . . . . . . . . 129
2 3
4.28 The AFM measurement of Sn Se alloy. . . . . . . . . . . . . . . . . . . . . 130
2 3
4.29 The activation energy calculation of Sn Se alloy. . . . . . . . . . . . . . . 131
2 3
VIII