Nanomechanical Prpoerties and Stress-induced Graphitization of Diamond-like Amorphous Carbon Film

Owing to the miniaturization of electron devices and the demand of high strength for machinery tools, interconnects and protective coatings with high electrical and thermal conductivity as well as an excellent mechanical performance are required for next-generation applications. Carbonaceous materials have been widely studied in recent years because of their variety of forms, mature processes and special properties (low friction coefficient, graphitization, and high electrical and thermal conductivity). By changing processing parameters, carbonaceous materials present many different properties including: (1) diamond-like carbon films with a high sp3 bond ratio has very good mechanical properties, and (2) carbon films with a high sp2 ratio have good electrical conductivity (anisotropic). To prepare high-quality carbonaceous films and to clarify the graphitization mechanism can extend the lifetime of tools and benefit the fabrication of textured graphite. Therefore in this study, first, a cathodic vacuum arc system without a magnetic filter was adopted for depositing diamond-like amorphous carbon (a-C) films, by introducing a periodic deposition process. Experimental results indicated that the multilayered a-C films obtained by the periodic deposition exhibited much smaller surface roughness with much fewer microparticles, and the mechanical properties of the films were effectively enhanced. Under scratching stresses, graphitic nanocrystallites with a (002) lattice parallel to maximum resolved shear stresses were found to form in a shear zone at a-C film surface. During in-situ compression of a-C nanopillars in a transmission electron microscope, the amorphous structure in pillar surface region clearly transformed into an ordered graphite structure. The calculated temperature rises under scratching and in-situ compression are much lower than the temperature required for the thermal graphitization of a-C, verifying that stresses can effectively induce the transformation of a-C into crystalline graphite in the absence of heat. Last, combining thermal annealing, the stress-induced graphitization was applied to assist the localized formation of oriented graphitization. By using low-temperature annealing processes, a textured and patterned crystalline graphitic structure could be successfully obtained from mechanically stressed a-C films.由於電子產品的微小化以及工具強度要求的提高，現今許多產品皆需要導電與導熱效率更高且機械性能更為優異的內連線材料及保護塗層，以滿足下一個世代應用上的需求。碳基材料因其種類多樣性、製程技術成熟度以及薄膜特殊性 (低摩擦係數與石墨化現象以及高導電與導熱等)，近年來受到許多學者及工業應用的注意與研究。藉由改變製程參數，碳基材料可具有許多不同類型與特性，如：(1) 高 sp3鍵結比例的類鑽薄膜結構擁有極佳的機械性質，以及 (2) 高 sp2鍵結比例的碳膜擁有極佳的導電性質 (方向性)，分別可應用在不同的領域。如何以現有設備生產出更高品質之碳基薄膜，並釐清碳基薄膜在使用中的石墨化現象，將有助於提升工具使用壽命，並可應用於方向性石墨結構之製造與應用。因此，本研究首先嘗試利用不外加磁濾管之陰極真空電弧鍍膜系統、配合週期性沉積製程以沈積類鑽非晶碳膜；結果顯示，週期性沉積製程可大幅移除電漿氣氛中的懸浮微粒，並達到降低薄膜表面粗糙度之成果，且所沉積之多層膜結構有效提升薄膜之機械性質。而在石墨化研究上結果顯示，在刮痕應力作用下，薄膜表層形成含有奈米石墨晶粒之剪變層，其 (002) 晶格平面沿最大分解剪應力方向排列；於穿透式電子顯微鏡臨場觀測中發現，非晶碳膜奈米柱表層區域在應力作用下，其非晶結構明顯轉變為有序排列之石墨晶格結構。經計算，刮痕測試及穿透式電子顯微鏡臨場壓縮測試時之溫度變化遠低於一般熱誘發非晶碳膜石墨化之溫度，可證實應力可有效誘發非晶碳轉變為結晶石墨結構。最後，透過應力誘發石墨化之發現，可進一步結合退火製程而達到應力輔助局部方向性石墨化之效果，成功以低溫退火將非晶質碳膜轉變為方向性排列並可圖案化之結晶石墨結構。Table of Contents 誌謝............................................................................................................. I 摘要...........................................................................................................III Abstract.....................................................................................................V Table of Contents ..................................................................................VII List of Figures......................................................................................... XI List of Tables......................................................................................XXIII Chapter 1 Introduction..........................................................................1 Chapter 2 Literature Review ................................................................3 2-1 Hard Coatings and Vacuum Technology .......................................3 2-1-1 Hard Coatings......................................................................3 2-1-2 Carbon Base Coating Materials.........................................10 2-1-3 Vacuum Manufacture Process Via CVD and PVD process .....................................................................................................12 2-1-4 Issue and solutions of Cathodic Vacuum Arc Deposition .17 2-2 Amorphous Carbon......................................................................22 2-2-1 Amorphous Carbon and Development ..............................22 2-2-2 Comparison of Deposition Methods .................................27 2-2-3 Structure Identification by Raman Analysis......................31 2-3 Graphitization Phenomenon of Amorphous Carbon ...................38 2-3-1 Unique Tribological Properties .........................................38 2-3-2 Self-lubricate Transformation Layer .................................42 2-3-3 Heat-induced Graphitization Process................................46 VIII 2-3-4 Stress-induced Graphitization Process ..............................48 2-4 Stress-assisted Patterned Texture Graphite Structure..................52 2-4-1 Next Generation Interconnection Materials ......................52 2-4-2 Application of Patterned Texture Graphite........................54 2-4-3 Mechanism of Stress-assisted Textured Graphitization ....60 2-4-4 Manufacture Process of Patterned Texture Graphite.........64 2-5 Goals and Frameworks of This Thesis ........................................69 Chapter 3 Reduce Roughness and Enhanced Mechanical Properties of Multilayered Diamond-like Carbon Films by Periodic Arc Deposition .........................................................................................71 3-1 Introduction..................................................................................71 3-2 Experiment Procedures................................................................73 3-3 Results and Discussion ................................................................77 3-3-1 Surface Roughness and Particles.......................................77 3-3-2 Structure Characterization.................................................84 3-3-3 Mechanical Properties and Interface Adhesion.................90 3-4 Summary......................................................................................96 Chapter 4 Nanoscopic observations of stress-induced formation of graphitic nanocrystallites at amorphous carbon surfaces ...........97 4-1 Introduction..................................................................................97 4-2 Experiment Procedures................................................................99 4-3 Results and Discussion ..............................................................101 4-3-1 Micro-Raman Analysis....................................................101 4-3-2 TEM Analysis of Surface Graphitization ........................108 4-3-3 Friction Heat and Flash Temperature ..............................111 4-3-4 In-situ TEM Observation Under Compression ...............113 IX 4-3-5 Criterion and Mechanism for Shear Stress-induced Graphitization............................................................................116 4-4 Summary....................................................................................120 Chapter 5 Stress-assisted Patterned Texture Graphitization of Amorphous Carbon Films.............................................................121 5-1 Introduction................................................................................121 5-2 Experiment Procedures..............................................................123 5-3 Results and Discussion ..............................................................125 5-3-1 Micro-Raman Analysis....................................................125 5-3-2 TEM Analysis of Stress-assisted Textured Graphitization ...................................................................................................136 5-3-3 Mechanism for Stress-assisted Textured Graphitization.148 5-4 Summary....................................................................................154 Chapter 6 Conclusions.......................................................................155 References..............................................................................................157 Vita and Publication List......................................................................183 X XI List of Figures Fig. 2-1 The TiN coated cutting tools [8]. ..................................................6 Fig. 2-2 Typical dependence of machining coast on machining speed [14]. .............................................................................................................6 Fig. 2-3 TEM micrograph of the WC/C multilayer structure [8]. ..............7 Fig. 2-4 Hardness as a function of the lattice period for multilayer coatings [8, 21-22] ..............................................................................7 Fig. 2-5 Idealized nanostructured coatings suggested by Veperk et al. and schematic of the nc-TiN/a-Si3N4/nc-TiSi2 structure [20, 25].............8 Fig. 2-6 Hardness of nc-TiN/a-Si3N4 nanocomposites as a function of the silicon content [8]. ..............................................................................8 Fig. 2-7 Schematic representation of material hardness as a function of grain size [25]. ....................................................................................9 Fig. 2-8 Sheet resistance of as-deposited and 600, 700, 800, and 900 oC-annealed Si/QHEA/Cu and Si/SHEA/Cu film stacks. [40]...........9 Fig. 2-9 Hardness of FCVA produced ta-C film [44]. ..............................11 Fig. 2-10 overview of the main categories of hard carbon materials [43]. ...........................................................................................................11 Fig. 2-11 The mechanism schematic diagram of CVD process [63]........15 Fig. 2-12 The mechanism schematic diagram of PVD process [68]........15 Fig. 2-13 (a) Magnetic field applied to the cathode. (b) Electric field distribution of the vacuum arc and retrograde motion of cathode spot. (c) Sample photograph of steered Cu cathode spot. [74]. ................16 Fig. 2-14 (a), (b) SEM image of CVA deposit DLC film surface [75].....19 XII Fig. 2-15 The schematic of droplets emission from cathodic target surface [74]....................................................................................................19 Fig. 2-16 The methods to reduce droplet generation. (a) Distributed arc using electron beam. (b) Distributed arc using preionized gas flow. (c) Shunting arc [74]. ........................................................................20 Fig. 2-17 Shielded arcs. (a) Simple shielded arc. (b) Superconductor shielded arc under magnetic field [74]. ............................................20 Fig. 2-18 The schematic of FCVA deposition system [74].......................21 Fig. 2-19 The schematic of different types of FCVA deposition system [74]....................................................................................................21 Fig. 2-20 The atomic structure of a hydrogenated DLC film [93]. ..........24 Fig. 2-21 Different carbon hybridised bonding [90]. ...............................24 Fig. 2-22 Ternary phase diagram of bonding in a-C films [90]. ..............25 Fig. 2-23 The SEM image of a-C:H coatings [97]. ..................................25 Fig. 2-24 The hardness of ta-C coatings [98]. ..........................................26 Fig. 2-25 The schematic of ion deposition system [90]. ..........................29 Fig. 2-26 The schematic of sputter and ion beam assisted deposition system [90]...............................................................................................29 Fig. 2-27 The schematic of CVA deposition system [90].........................30 Fig. 2-28 The schematic of FCVA deposition system [90].......................30 Fig. 2-29 Phonon and electron band structure of the resonant Raman shift effect in graphitic carbons [90, 121].................................................34 Fig. 2-30 Phonon and electron band structure of the resonant Raman shift effect in graphitic carbons [90].........................................................35 Fig. 2-31 Eigenvectors of the Raman G and D modes in graphite and amorphous carbons [90, 121]. ..........................................................35 XIII Fig. 2-32 Variation of Raman ID/IG ratio with in-plane correlation length La [90]. ..............................................................................................36 Fig. 2-33 Schematic of the three stages variation of G peak position, FWHM and ID/IG ratio [90, 121].......................................................36 Fig. 2-34 The factors affecting the position and intensity of the Raman G and D peaks of non-crystalline carbons [90]. ...................................37 Fig. 2-35The schematic of the tribological contact mechanism [123]. ....40 Fig. 2-36 The relation of hardness, COF and various kinds of hard coatings [125]. ..................................................................................40 Fig. 2-37 Friction coefficient of a-C:H films prepared with CH4 and H2 gas [131]............................................................................................41 Fig. 2-38 Effect of moist air on the frictional behavior of a ta-C film [125]..................................................................................................41 Fig. 2-39 The number of paper publish for studying a-C especially for tribological properties [125]. ............................................................43 Fig. 2-40 The build of transfer layer between two counterpart [144]. .....43 Fig. 2-41 The variation of Raman spectrum of a-C film, wear track, wear debris and transfer film [126]. ..........................................................44 Fig. 2-42 The Raman spectrum of transfer film and graphite [145]. .......44 Fig. 2-43 The TEM image and the diffraction pattern of short ordered structure from transfer film [146]. ....................................................45 Fig. 2-44 The a-C Raman spectrum at different annealing temperature [147]..................................................................................................47 Fig. 2-45 The calculation temperature as a function of the percentage of apparent contact area. [149]..............................................................47 Fig. 2-46 The schematic of the stress-induced graphitization process XIV [126]..................................................................................................49 Fig. 2-47 The simulation of diamond tip sliding against a-C film [151]. 49 Fig. 2-48 The simulation result of diamond tip sliding against a-C film with obvious graphitization process occurred [151]. .......................50 Fig. 2-49 The simulation result of a-C film intrinsic stress variation after test [151]. ..........................................................................................50 Fig. 2-50 The simulation result of diamond tip sliding against a-C film with obvious graphitization process occurred [152]. .......................51 Fig. 2-51 The simulation result of diamond tip sliding against a-C film with obvious graphitization process occurred [152]. .......................51 Fig. 2-52 TEM image of carbon nanotube [156]......................................53 Fig. 2-53 The SEM image of graphehe on Ni substrate [157]. ................53 Fig. 2-54 Cross section TEM image of nanocrystialline carbon film with preferred orientation [153]................................................................53 Fig. 2-55 The fast pathway for electrons at graphite basal plane [166]. ..56 Fig. 2-56 Thermal conductivity of various carbonaceous materials and the transportation pathways [165]. .........................................................56 Fig. 2-57 The schematic and TEM image of textured graphite for Li-Ion battery [167]......................................................................................57 Fig. 2-58 The variation of capacity (as percentage of maximum capacity) between two different structures [167]. ............................................57 Fig. 2-59 The schematic picture of carbon based materials for applications [168]. ............................................................................58 Fig. 2-60 Raman spectrum of as-deposited and annealed films with various sp3 content [168]. .................................................................58 Fig. 2-61 Cross section TEM image of as-deposited and annealed films XV carbon film with preferred orientation [168]....................................59 Fig. 2-62 Three different types of conceivable models for atomistic graphitization process enhance by electron simulation [169]. .........62 Fig. 2-63 Calculation of the potential energy as a function of the compression of graphite structure [173]...........................................63 Fig. 2-64 The HRTEM cross section image of (a) deposit at 150 oC and (b) deposit at 400 oC [175]. ....................................................................63 Fig. 2-65 Summary of techniques for the formation of textured carbon [153]..................................................................................................66 Fig. 2-66 Plane view TEM image of carbon film prepared at 240 oC with different ion energies indicated [176]...............................................66 Fig. 2-67 Plane view TEM image of carbon film prepared at 640 oC with different ion energies indicated [176]...............................................67 Fig. 2-68 A schematic structural phase diagram for noncrystalline carbon films in the ion energy-substrate temperature plane. [176]. .............67 Fig. 2-69 THRTEM image of dark field TEM micrograph (a) SAD showing two bright spots at the (002) fringe indicating a high degree of orientation is present in the film. (b) High magnification micrograph on the aligned region of the film showing alignment of graphitic planes [177]. ......................................................................68 Fig. 2-70 Schematic cross-section of a-C film before and after modified. (a) a-C film before modification. (b) The lateral volumetric increase compressive on the boundary (denoted by the arrows) together with the thermal energy from the pulse will lead to the growth vertically ordered the graphitic planes [177]. ...................................................68 Fig. 3-1 The overall experiment procedure of chapter 3. .........................75 XVI Fig. 3-2 SEM surface morphologies of single- and multilayered DLC films: (a) S100, (b) S200, (c) S400, (d) S800, (e) M400-1A, (f) M400-5A, (g) M400-5N; (h) magnified images of S400 (left) and M400-5A (right)................................................................................80 Fig. 3-3 SEM surface morphologies of single- and multilayered DLC films: (a) S400 (left) and M400-5A (right), (b) magnified images of S400 (left) and M400-5A (right).......................................................81 Fig. 3-4 (a) Surface roughness and (b) numbers of different-sized surface particles on single- and multilayered DLC films..............................82 Fig. 3-5. Schematic illustrations of arc deposition system and the processes of particle emission, suspension and removal..................83 Fig. 3-6 XRD patterns of single- and multilayered DLC films................87 Fig. 3-7 (a) Bright-field and (b) high-resolution TEM images (with corresponding SAD pattern) of multilayered DLC film (M400-5A). ...........................................................................................................88 Fig. 3-8 (a) Raman spectra of single- and multilayered DLC films and micro-Raman spectrum of surface microparticles; (b) curve fitting of Raman spectrum of multilayered DLC film (M400-5A). ................89 Fig. 3-9 Hardness and elastic modulus of single- and multilayered DLC films, as measured by nanoindentation.............................................94 Fig.3-10 (a) SEM surface fractography and (b) cross-sectional TEM image of multilayered DLC film (M400-5A) along scratch track after nanoscratch test; magnified TEM images around the regions of (c) delamination and crack origin at TiC/DLC interface and (d) crack front in DLC film..............................................................................95 Fig. 4-1 (a) Schematic plots of the samples and detections of a-C film XVII (left), thin foil (center) and nanopillars (right) for micro-Raman analyses, TEM characterizations and in-situ TEM compressions, respectively. ....................................................................................100 Fig. 4-1(b) The overall experiment procedure of chapter 4. ..................100 Fig. 4-2 (a) Optic micrograph of a-C film along a nanoscratch track, marked with micro-Raman detecting locations (A: a-C film; B: beginning stage of nanoscratch track, C: central stage, E: end stage, F: end stage near film fracture); (b) micro-Raman spectra of a-C film at the different stages of the nanoscratch track; (c) micro-Raman spectrum and peak fittings of microcrystalline graphite (Gr; Raw: raw data, Sum: sum of peak fittings; DGr and GGr: sharp D and G peak fittings)..................................................104 Fig. 4-3 Micro-Raman spectra and peak fittings of (a) a-C film and (b) the central stage of nanoscratch track, (c) end stage and (d) end stage near film fracture (Raw: raw data, Sum: sum of all peak fittings; D and G: broad D and G band fittings, D+G: su