Title Page
ABSTRACT
국문 초록
PREFACE
Contents
NOMENCLATURE 24
CHAPTER 1. INTRODUCTION 27
1.1. Low-Temperature Polycrystalline Silicon 27
1.1.1. Excimer Laser Annealing 29
1.2. Laser-Induced Periodic Surface Structure 33
1.3. Mechanism of Laser-Induced Periodic Surface Structure 35
1.3.1. Surface Electromagnetic Waves Scattering Model 35
1.3.2. Surface Plasmon Polariton Interference Model 38
1.3.3. The Sipe Theory 39
1.4. Parameters for Laser-Induced Periodic Surface Structure 42
1.4.1. Effects of Oblique Incident Angle on LIPSS Formation 42
1.4.2. The Effect of Polarization Direction on LIPSS Formation 43
1.5. Laser Surface Structuring via UV Gaussian Spot Beam 45
CHAPTER 2. Surface-Textured of Si Induced UV Spot Beam 46
2.1. Experimental Details 46
2.2. The Characteristics of Surface Structuring by Gaussian Beam 49
2.3. The Crystallinity Analysis in Laser-Treated Si Thin Films 52
2.3.1. Raman Spectroscopy Measurements of μp-Si Thin Film 52
2.3.2. The Crystallinity under Gaussian Single Pulse Irradiation 52
2.4. Enhancement of UV Absorption by Surface Nanostructures 55
2.4.1. The Enhanced UV Absorption by Surface Nanostructures 55
2.4.2. The Simulation of UV Absorption Behavior Modulated by Surface Periodicity 59
CHAPTER 3. Periodic Surface Texturing with an Asymmetric Gaussian Beam 62
3.1. Laser Fluence-Dependent Surface Topography 62
3.1.1. Experimental Details 62
3.1.2. The Single Pulse Laser Irradiation of Thin Film a-Si 63
3.1.3. The Ripple Formations of the 2D Scanned Si Thin Film Layer 65
3.1.4. The Crystallinity of the 2D Scanned Si Thin Film Layer 69
3.1.5. Laser Fluence-Dependent Surface Ripple 70
3.2. Scan-Interval Dependent Surface Topography 71
3.2.1. Experimental Details 71
3.2.2. The Influence of Asymmetric Gaussian Beam Scanning Path 74
3.2.3. The Crystallinity Following Irradiation Number 77
3.2.4. Surface Structuring Following Irradiation Number 83
3.2.5. Scan-Interval Dependent Surface Ripple 86
CHAPTER 4. Two-Dimensional Self-Assembled Si Nanopillars Array Formation using Gaussian Beam Overlap 87
4.1. Experimental Details 87
4.2. Surface Structure Formation under Single Pulse 88
4.3. The Incubation Effect of Multi-Irradiation 90
4.4. Mechanism for Homogeneous 2D Structuring 92
4.4.1. The "Seed" Formation of Large-Area LIPSS 95
4.5. Self-Assembled Si Nanopillar Array in 2D 98
4.5.1. Si Nanopillar Array with below 100 mJ/cm² 103
4.5.2. Si Nanopillar Array with 100-150 mJ/cm² 104
4.5.3. Si Nanopillar Array with 150-260 mJ/cm² 105
4.5.4. Si Nanopillar Array with above 260 mJ/cm² 106
4.5.5. The Crystallinity of Si Nanopillars 108
CHAPTER 5. CONCLUSION 109
REFERENCES 111
Table 3.1. Values of laser power, a pulse energy, average laser fluence (energy density), and maximum laser fluence for laser annealing experiments. 65
Table 3.2. Maximum laser fluence, effective lengths of the long (L) and short (S) axes are listed. Four different △x and △y are chosen for discrete laser scanning and... 73
Table 4.1. List of laser processing conditions. The two-axes scan interval △x, △y and the range and rate of Iacc of the four structural types of each Io. Each condition is[이미지참조] 102
Figure 1.1. The characteristics of amorphous Si (a-Si), poly-crystalline Si (p-Si), and single crystal Si (c-Si) and LCD and LTPS-AMOLED back panel comparison diagrams. 27
Figure 1.2. (a) Comparison of energy band and optical transition energy at the Γ point in Si [12], (b) Transmittance (T), absorption (A), and reflectance (R) of 45-nm... 28
Figure 1.3. The laser with a wavelength of 772 nm and pulse duration of 150 fs treated the crystalline silicon, resulting in (a) a treated surface and (b) a cross-section of a... 29
Figure 1.4. A schematic diagram of LTPS process equipment and an image of the silicon film surface after laser crystallization. 30
Figure 1.5. (a) A principle sketch of a Vyper/LineBeam-1300 LTPS production system with an integrated annealing chamber, and (b) the formation of the polysilicon layer... 30
Figure 1.6. Comparison between the melting and growth model and the LIPSS model. 31
Figure 1.7. A schematic diagram of melting and solidification in ELA. 31
Figure 1.8. Schematic diagram of the formation of LIPSS structure by laser irradiation with repetitive scans. 33
Figure 1.9. (a) A conceptual diagram of the wave vectors (ko: incident light wave vector, kg: grating wave vector, ks: scattered wave vector) when the incident angle is θ. (b)...[이미지참조] 36
Figure 1.10. Interference of a p-polarized electromagnetic wave by laser radiation under (a) normal incidence and (b) oblique incidence with angle θ. 37
Figure 1.11. Scheme of the SPP interference model: The initial roughness of the material is crucial for the formation of initial scattering, which may lead to the excitation... 38
Figure 1.12. (a) SEM images of the a-Si surface modified by femtosecond laser pulses with fluence of 0.15 J/cm² and number of laser pulses with 50 pulses. (b) 2D... 39
Figure 1.13. SEM images of the Secco-etched Si films crystallized at (a) θ=0° and 10 pulses, (b) θ=0° and 100 pulses, (c) θ=25° and 10 pulses, (d) θ=25° and 100 pulses. 42
Figure 1.14. The surface structures on the silicon after an irradiation sequence of 100 pulses at an energy Eo=48 μJ with different spatially inhomogeneous state of... 44
Figure 2.1. (a) Schematic of the laser-scanning system for nanosecond laser annealing with Gaussian beam profile. Nomarski microscope images of a single pulse applied to an a-Si... 46
Figure 2.2. The local surface images of a single pulse applied to an a-Si film with Eo of 300 μJ. Five positions, (I)-(V)are compared with the Nomarski optical microscope (NOM), AFM,... 50
Figure 2.3. Nomarski optical microscope images of a single pulse applied to an a-Si film with Eo of 300 μJ, and SEM images at localized positions (I)-(V). 51
Figure 2.4. Raman spectra of (a) amorphous-Si, (b) polycrystalline-Si, and (c) crystalline-Si. 52
Figure 2.5. Raman spectra of local surfaces at (I)-(V) in Fig. 2. Inset is the enlarged plot of black-dashed square. 53
Figure 2.6. Raman intensity and Raman shift for the vertical (a) and horizontal cross-section (b), indicated by white dotted lines in Figure 2.2. 54
Figure 2.7. Experimental setup for fiber-optic spectroscopic measurements. 55
Figure 2.8. Reflection (R), transmission (T), and absorption (A) spectra of the five local positions, indicated by the white boxes of (I)-(V) are plotted, where the area of diameter, 50... 57
Figure 2.9. Reflection (R), transmission (T), and absorption (A) spectra of the five local positions, indicated by the white boxes of (I)-(V) are plotted, where the area of diameter, 50... 58
Figure 2.10. Schematic of model surface, where the Si hemisphere with radius of 100 nm is on the Si surface with square symmetry of period, Λ, which is varied from 210 to 1000 nm. 59
Figure 2.11. Spectra changes with period, Λ for reflectance in (a), transmittance in (b), and absorption in (c). Spectra curves are plotted for Λ=1000 nm in (d), 500 nm in (e) and 210... 61
Figure 3.1. (a) Gaussian spatial profile of a single pulse beam and cross-sectional profiles of the laser beam (solid line) and Gaussian fitted curves (dotted lines) at horizontal... 63
Figure 3.2. Optical microscope images of a single pulse applied to an a-Si thin film with laser energies, Eo (maximum fluence, Io) of (a) 76 μJ, (b) 83 μJ, (c) 89 μJ, and (d) 94... 64
Figure 3.3. Photographs of Si thin film, scanned on 20 mm × 20 mm by laser spot beam with laser energy per pulse of (a) 76 μJ, (b) 83 μJ, (c) 89 μJ, and (d) 94 μJ. The images... 66
Figure 3.4. AFM images of the annealed Si surfaces with laser energies of (a) 76 μJ, (b) 83 μJ, (c) 89 μJ, and (d) 94 μJ. The arrow indicates the polarization direction. 68
Figure 3.5. 2-dimensional Fourier transformed images corresponding to Figures 3.4(a)-(d) and (e) horizontal cross-sectional profiles. 68
Figure 3.6. Raman spectra of the surface of a-Si film applied with various laser powers. The laser pulse energies for S1-S4 are used as listed in Table 3.1. 69
Figure 3.7. (a) An image of a single laser beam. (b) Gaussian profiles of laser beam with maximum intensities, Io of 55 and 90 mJ/cm², aligned along the y-axis image of... 71
Figure 3.8. the two-dimensional laser scan paths, where the lateral (LS) and vertical scan (VS) directions are illustrated. 74
Figure 3.9. (a) Photographs and enlarged optical micrographs of Si surfaces, irradiated by laser with an asymmetric Gaussian beam of the maximum fluence, 55 mJ/cm².... 75
Figure 3.10. (a) Photographs and optical micrographs of Si surfaces, irradiated by laser with an asymmetric Gaussian beam of the maximum fluence, 90 mJ/cm² . The... 76
Figure 3.11. Raman spectra measured at the local areas of Si surfaces irradiated by a laser for different effective pulse number Neff values with maximum fluence, 55...[이미지참조] 78
Figure 3.12. Raman intensity and Raman shift of laser treated Si surface for irradiation numbers, Neff (lower axis) and scan interval to y axis (upper axis) with the...[이미지참조] 80
Figure 3.13. TEM images of Si thin layers irradiated 400 pulses (Neff) with maximum laser fluences of (a) 55 mJ/cm² and (b) 90 mJ/cm². The inset figures are the 2D-FT...[이미지참조] 82
Figure 3.14. AFM results of Si surfaces irradiated by a laser with maximum laser fluence of 55 mJ/cm² in (a)-(d) and 90 mJ/cm² in (e)-(h). The vertical z-axis scale is... 84
Figure 3.15. SEM results of Si surfaces applied by a laser for different pulse number Neff with maximum laser fluence, 55 mJ/cm² in (a)-(d) and 90 mJ/cm² in (e)-(h). The white arrow...[이미지참조] 85
Figure 3.16. SEM results (upper) and their 2D-FT images (lower) of laser treated Si surfaces for different Neff values with maximum laser fluence, 55 mJ/cm² in (a)–(d) and...[이미지참조] 85
Figure 4.1. (a) OM image of a single pulse applied to an a-Si thin film with maximum fluence of 300 mJ/cm². (b) Gaussian beam profile at cross section of a center position.... 88
Figure 4.2. (a) Comparison of incubation effects between single pulse and 1D scanned samples for Io=100, 150, and 200 mJ/cm² with different pitches of 0.2 and 30... 91
Figure 4.3. OM images of Si surface scanned with a 1D scan along the x-axis direction of △x=0.55, 1.1, and 1.4 μm with maximum fluences of Io=(a) 80, (b) 120, (c)... 94
Figure 4.4. (a) 3D Gaussian beam profile with Io〉 Iro, where the beam is scanned in the x-axis direction and superimposed with Io (red) and Iro (blue). Lx is the length of... 95
Figure 4.5. (a) Schematic of two 1D line scans performed with a maximum fluence of Io=80 mJ/cm² and vertical separation of 5.5 μm. The first- and second-line beam... 97
Figure 4.6. (a) Schematic of a 2D raster scan of a Gaussian spot beam. The blue color regions indicate regions of periodic ripples are formed. (b) SEM images of a Si surface... 98
Figure 4.7. The map of the LIPSS types categorized into five types (I-V) based on the overlapping rate (OL) on the y-axis, for Nx=15. The red dots on the map... 101
Figure 4.8. Normal and 15° tilted SEM surface images of laser processed area in Io=90 mJ/cm². The I-V in the top left corner indicate the structure types presented in... 103
Figure 4.9. Normal and 15° tilted SEM surface images of laser processed area in Io=120 mJ/cm². The I-V in the top left corner indicate the structure types presented in... 104
Figure 4.10. Normal and 15° tilted SEM surface images of laser processed area in Io=170 mJ/cm². The I-V in the top left corner indicate the structure types presented in... 105
Figure 4.11. Normal SEM images of laser treated Si surface in Io=220 and 270 mJ/cm². 107
Figure 4.12. Raman spectra of laser treated a-Si surface in Io=80 mJ/cm², △x=△y=5.5 μm. 108