Chapter 1: Introduction
1.2. Motivation
Titanium oxynitride and titanium oxycarbide are of relatively new compositions.
Therefore, they still need many works and characterizations to explore an accomplished knowledge on their properties. One of the most interesting properties is the effects of oxygen on structure, electrical and mechanical properties of TiNxOy and TiCxOy. In fact, there have been large amounts of scientific studies on the optical and electrical properties, and chemical compositions of titanium oxynitride and titanium oxycarbide. However, most of those studies focused on polycrystalline TiNxOy and TiCxOy films in contrast with epitaxial TiNxOy and TiCxOy films that has been rarely reported. This is due to the fact that TiNxOy and TiCxOy are very hard materials and are difficult to synthesize in bulk by several common deposition methods such as chemical vapor deposition (CVD), magnetron sputtering, and evaporation. Moreover, in order to obtain high-quality, especially epitaxial TiNxOy and TiCxOy films, those methods require a relatively high substrate temperature which may lead to serious problems for many applications. For hard materials such as TiN, TiC, TiNxOy and TiCxOy, mechanical properties are very important. The difficulty in deposition of epitaxial TiNxOy and TiCxOy also limited the chance to study mechanical properties of TiNxOy and TiCxOy due to the fact that mechanical properties depend on not only chemical composition but also microstructure, whereas microstructure of polycrystalline TiNxOy and TiCxOy films varies widely and is often uncharacterized. The deposition of epitaxial TiNxOy also can improve electrical conductivity and overcome the problem of fast grain boundary diffusion of dopants and
10
impurities along the columnar grains of the polycrystalline films [1.79-82]. Furthermore, study of epitaxial films can improve our understanding of basic properties of TiNxOy and TiCxOy. Growth of epitaxial TiNxOy and TiCxOy films is also helpful for etching study due to it can avoid the complicated etch effects from grain boundaries and orientations in polycrystalline films.
TiN, TiC, TiNxOy and TiCxOy films have been widely applied in hydrogen environment; but there is still a lack of understanding about the effect of hydrogen on those materials. Furthermore, studying the etching of those materials by pure hydrogen plasma could be helpful for the first understanding about the role of hydrogen in the patterning process using plasma containing atomic hydrogen such as Cl2/CHF3, Cl2/Ar/CHF3, Cl2/N2/CHF3, Ar/CHF3, and CH4/H2 [1.83, 84]. Moreover, hydrogen plasma treatment can be applied to the revelation of dislocation etch pits in TiN, TiC, TiNxOy and TiCxOy.
This thesis reports the successful growth of epitaxial titanium oxynitride and titanium oxycarbide films on MgO (001) substrates using pulsed laser deposition. The crystallinity, microstructure, chemical composition, and morphology of titanium oxynitride and titanium oxycarbide were investigated. The effect of oxygen on the lattice parameter, microstructure, electrical, and mechanical properties of TiNxOy was especially investigated. Mechanical properties of TiNxOy films were characterized by using nanoindentation. The nanoindentation data was then analyzed and simulated to exclude the substrate effect and then extract the accurate hardness and Young’s modulus of the films. The study of the effects of hydrogen microwave plasma on the stability and etching of titanium oxynitride films as function of gas pressure and treating time was also studied.
1.3. Structure of the thesis
The thesis consists of five chapters and is organized as follows: Chapter 2 presents experimental methods and procedures for growth of epitaxial TiNxOy and TiCxOy on MgO (001) substrates; surface morphology, chemical composition, microstructure, and electrical properties of TiNxOy and TiCxOy are also described. Chapter 3 shows the nanoindentation studies of epitaxial TiNxOy and TiCxOy films including the basic theory of nanoindentation, models to solve substrate effects, experimental procedures, and results. Chapter 4 shows the stability and etching of TiNxOy depending on the hydrogen
11
plasma treatment conditions. Finally, Chapter 5 presents conclusions of the present study as well as the future works.
12 References
[1.1] H.O. Pierson, Handbook of Refractory Carbides and Nitrides: Properties,
Characteristics, Processing and Applications, Noyes Publication, Westwood, New Jersey, USA, 1996.
[1.2] A. Czyzniewski, W. Precht, Deposition and some properties of nanocrystalline, nanocomposite and amorphous carbon-based coatings for tribological applications, J Mater Process Tech, 157 (2004) 274-283.
[1.3] S.H. Jhi, S.G. Louie, M.L. Cohen, J. Ihm, Vacancy hardening and softening in transition metal carbides and nitrides, Phys Rev Lett, 86 (2001) 3348-3351.
[1.4] A. Mani, P. Aubert, F. Mercier, H. Khodja, C. Berthier, P. Houdy, Effects of residual stress on the mechanical and structural properties of TiC thin films grown by RF sputtering, Surf Coat Tech, 194 (2005) 190-195.
[1.5] W. Precht, A. Czyzniewski, Deposition and some properties of carbide/amorphous carbon nanocomposites for tribological application, Surf Coat Tech, 174 (2003) 979-983.
[1.6] K.E. Tan, A.M. Bratkovsky, R.M. Harris, A.P. Horsfield, D. NguyenManh, D.G.
Pettifor, A.P. Sutton, Carbon vacancies in titanium carbide, Model Simul Mater Sc, 5 (1997) 187-198.
[1.7] P.E. Schmid, M.S. Sunaga, F. Levy, Optical and electronic properties of sputtered TiNx
thin films, J Vac Sci Technol A, 16 (1998) 2870-2875.
[1.8] J.H. Kang, K.J. Kim, Structural, optical, and electronic properties of cubic TiNx compounds, J Appl Phys, 86 (1999) 346-350.
[1.9] P. Patsalas, S. Logothetidis, Optical, electronic, and transport properties of nanocrystalline titanium nitride thin films, J Appl Phys, 90 (2001) 4725-4734.
[1.10] V.N. Lipatnikov, A.I. Gusev, Dependence of the resistivity of nonstoichiometric titanium carbide TiCy on the density and distribution of carbon vacancies, Jetp Lett+, 70 (1999) 294-300.
[1.11] V.N. Lipatnikov, A. Kottar, L.V. Zueva, A.I. Gusev, Ordering effects in nonstoichiometric titanium carbide, Inorg Mater+, 36 (2000) 155-161.
[1.12] S.R. Barman, D.D. Sarma, Electronic-Structure of TiOx (0.8 < x < 1.3) with disordered and ordered vacancies, Phys Rev B, 49 (1994) 16141-16148.
[1.13] Y.O. Ciftci, Y. Unlu, K. Colakoglu, E. Deligoz, The structural, thermodynamical and elastic properties of TiO, Phys Scripta, 80 (2009) 025601.
13
[1.14] D.A. Andersson, P.A. Korzhavyi, B. Johansson, First-principles based calculation of binary and multicomponent phase diagrams for titanium carbonitride, Calphad, 32 (2008) 543-565.
[1.15] K. Frisk, A revised thermodynamic description of the Ti-C system, Calphad, 27 (2003) 367-373.
[1.16] S. Jonsson, Z. Metallkd., 87 (1996) 691–702.
[1.17] E. Etchessahar, J.P. Bars, J. Debuigne, The Ti-N system - Equilibrium between the delta-phase, epsilon-phase and alpha-phase and the conditions of formation of the Lobier and Marcon metastable phase, J Less-Common Met, 134 (1987) 123-139.
[1.18] B.-J.Lee, N.Saunders, Thermodynamic evaluation of the Ti-Al-O ternary system, Z.
Metallkd., 88 (1997) 152-161.
[1.19] D.S. Stone, K.B. Yoder, W.D. Sproul, Hardness and elastic-modulus of TiN based on continuous indentation technique and new correlation, J Vac Sci Technol A, 9 (1991) 2543-2547.
[1.20] N. Greenwood, A. Earnshaw, Chemistry of the Elements, Butterworth-Heinemann, 1997.
[1.21] J.F. Shackelford, W. Alexander, CRC Materials Science and Engineering Handbook, Taylor & Francis, 2010.
[1.22] C.S. Shin, D. Gall, N. Hellgren, J. Patscheider, I. Petrov, J.E. Greene, Vacancy hardening in single-crystal TiNx(001) layers, J Appl Phys, 93 (2003) 6025-6028.
[1.23] P.C. Kong, B. Pfender, Carbide, Nitride and Boride Materials Synthesis and Processing, Chapman and Hall, London, 1997.
[1.24] D. Caceres, I. Vergara, R. Gonzalez, Y. Chen, E. Alves, Nanoindentation on MgO crystals implanted with lithium ions, Nucl Instrum Meth B, 191 (2002) 154-157.
[1.25] K. Kurosaki, D. Setoyama, J.J. Matsunaga, S. Yamanaka, Nanoindentation tests for TiO2, MgO, and YSZ single crystals, J Alloy Compd, 386 (2005) 261-264.
[1.26] S. Nagao, K. Nordlund, R. Nowak, Anisotropic elasticity of IVB transition-metal mononitrides determined by ab initio calculations, Phys Rev B, 73 (2006) 144113.
[1.27] R.C. Weast, Handbook of Chemistry and Physics, CRC Press, Boca Raton, FL, 1990.
[1.28] P. Ettymayer, W. Lengauer, Carbides: Transition Metal Solid State Chemistry, Wiley, 1994.
[1.29] C.N.R. Rao, W.E. Wahnsiedler, J.M. Honig, Plasma resonance in TiO, VO and NbO, J Solid State Chem, 2 (1970) 315-317.
14
[1.30] A.D. Mazzonia, M.S. Conconib, Synthesis of group IVB metals oxicarbides by carboreduction reactions, Materials Research, 5 (2002) 459-466.
[1.31] G. Neumann, R. Kieffer, P. Ettmayer, Über das System TiC-TiN-TiO, Monatshefte für Chemie,, 103 (1972) 1130-1137.
[1.32] J. Graciani, J.F. Sanz, T. Asaki, K. Nakamura, J.A. Rodriguez, Interaction of oxygen with TiN(001): N <-> O exchange and oxidation process, J Chem Phys, 126 (2007) 244713.
[1.33] F. Vaz, P. Cerqueira, L. Rebouta, S.M.C. Nascimento, E. Alves, P. Goudeau, J.E.
Riviere, Preparation of magnetron sputtered TiNxOy thin films, Surf Coat Tech, 174 (2003) 197-203.
[1.34] M. Lazarov, P. Raths, H. Metzger, W. Spirkl, Optical-constants and film density of TiNxOy solar selective absorbers, J Appl Phys, 77 (1995) 2133-2137.
[1.35] F. Maury, F.D. Duminica, TiOxNy coatings grown by atmospheric pressure metal organic chemical vapor deposition, Surf Coat Tech, 205 (2010) 1287-1293.
[1.36] Y. Suda, H. Kawasaki, T. Ueda, T. Ohshima, Preparation of high quality nitrogen doped TiO2 thin film as a photocatalyst using a pulsed laser deposition method, Thin Solid Films, 453 (2004) 162-166.
[1.37] M. Braic, M. Balaceanu, A. Vladescu, A. Kiss, V. Braic, G. Epurescu, G. Dinescu, A.
Moldovan, R. Birjega, M. Dinescu, Preparation and characterization of titanium oxy-nitride thin films, Appl Surf Sci, 253 (2007) 8210-8214.
[1.38] A.C. Fernandes, P. Carvalho, F. Vaz, S. Lanceros-Mendez, A.V. Machado, N.M.G.
Parreira, J.F. Pierson, N. Martin, Property change in multifunctional TiCxOy thin films:
Effect of the O/Ti ratio, Thin Solid Films, 515 (2006) 866-871.
[1.39] L. Marques, H.M. Pinto, A.C. Fernandes, O. Banakh, F.V.M.M.D. Ramos, Optical properties of titanium oxycarbide thin film, Appl Surf Sci, 255 (2009) 5615-5619.
[1.40] A. Afir, M. Achour, N. Saoula, X-ray diffraction study of Ti-O-C system at high temperature and in a continuous vacuum, J Alloy Compd, 288 (1999) 124-140.
[1.41] J. Graciani, S. Hamad, J.F. Sanz, Changing the physical and chemical properties of titanium oxynitrides TiN1-xOx by changing the composition, Phys Rev B, 80 (2009) 184112-184122.
[1.42] D. Hull, D.J. Bacon, Introduction to dislocations, Butterworth-Heinemann, 2011.
[1.43] L. Karlsson, L. Hultman, M.P. Johansson, J.E. Sundgren, H. Ljungcrantz, Growth, microstructure, and mechanical properties of arc evaporated TiCxN1-x (0 ≤ x ≤ 1) films, Surf Coat Tech, 126 (2000) 1-14.
15
[1.44] D. Munteanu, R. Cozma, B. Borcea, F. Vaz, The influence of oxygen flow on the tribological behaviour and residual stress of TiCO thin-films, J Optoelectron Adv M, 8 (2006) 712-715.
[1.45] Y. Saito, M. Hirata, H. Tada, M. Hyodo, Electrically switchable window using a suspension of TiOxNy particles, Applied Physics Letters, 63 (1993) 1319-1321.
[1.46] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-light photocatalysis in nitrogen-doped titanium oxides, Science, 293 (2001) 269-271.
[1.47] Y.X. Leng, P. Yang, J.Y. Chen, H. Sun, J. Wang, G.J. Wang, N. Huang, X.B. Tian, P.K. Chu, Fabrication of Ti-O/Ti-N duplex coatings on biomedical titanium alloys by metal plasma immersion ion implantation and reactive plasma nitriding/oxidation, Surf Coat Tech, 138 (2001) 296-300.
[1.48] R.J. Koerner, L.A. Butterworth, I.V. Mayer, R. Dasbach, H.J. Busscher, Bacterial adhesion to titanium-oxy-nitride (TiNOX) coatings with different resistivities: a novel approach for the development of biomaterials, Biomaterials, 23 (2002) 2835-2840.
[1.49] D.-H. Kang, D.-H. Ahn, M.-H. Kwon, H.-S. Kwon, K.-B. Kim, K.S. Lee, B.-k.
Cheong, Lower voltage operation of a phase change memory device with a highly resistive TiON layer, Japanese Journal of Applied Physics, 43 (2004) 5243-5244.
[1.50] X.G. Yang, C. Li, B.J. Yang, W. Wang, Y.T. Qian, Optical properties of titanium oxynitride nanocrystals synthesized via a thermal liquid-solid metathesis reaction, Chem Phys Lett, 383 (2004) 502-506.
[1.51] N. Biunno, J. Narayan, S.K. Hofmeister, A.R. Srivatsa, R.K. Singh, Low-temperature processing of titanium nitride films by laser physical vapor-deposition, Applied Physics Letters, 54 (1989) 1519-1521.
[1.52] V. Craciun, D. Craciun, C. Ghica, L. Trupina, C. Flueraru, N. Nastase, Growth of thin transparent titanium nitride layers by reactive laser ablation, Appl Surf Sci, 138 (1999) 593-598.
[1.53] H.D. Gu, K.M. Leung, C.Y. Chung, X.D. Han, Room-temperature growth of high-purity titanium nitride by laser ablation of titanium in a nitrogen atmosphere, Surf Coat Tech, 110 (1998) 153-157.
[1.54] J.H. Huang, K.W. Lau, G.P. Yu, Effect of nitrogen flow rate on structure and
properties of nanocrystalline TiN thin films produced by unbalanced magnetron sputtering, Surf Coat Tech, 191 (2005) 17-24.
16
[1.55] J.M. Lackner, W. Waldhauser, R. Berghauser, R. Ebner, B. Major, T. Schoberl, Structural, mechanical and tribological investigations of pulsed laser deposited titanium nitride coatings, Thin Solid Films, 453 (2004) 195-202.
[1.56] N. Biunno, J. Narayan, A.R. Srivatsa, O.W. Holland, Laser deposition of epitaxial titanium nitride films on (100) MgO, Applied Physics Letters, 55 (1989) 405-407.
[1.57] J. Bottiger, J. Chevallier, J.H. Petersen, N. Schell, W. Matz, A. Mucklich, Observation of the growth mode of TiN during magnetron sputtering using synchrotron radiation, J Appl Phys, 91 (2002) 5429-5433.
[1.58] R. Chowdhury, X. Chen, J. Narayan, Pulsed-laser deposition of epitaxial Si/TiN/Si(100) heterostructures, Applied Physics Letters, 64 (1994) 1236-1238.
[1.59] T. Lee, H. Seo, H. Hwang, B. Howe, S. Kodambaka, J.E. Greene, I. Petrov, Fully strained low-temperature epitaxy of TiN/MgO(001) layers using high-flux, low-energy ion irradiation during reactive magnetron sputter deposition, Thin Solid Films, 518 (2010) 5169-5172.
[1.60] W.J. Meng, G.L. Eesley, Growth and mechanical anisotropy of TiN thin films, Thin Solid Films, 271 (1995) 108-116.
[1.61] J. Narayan, P. Tiwari, X. Chen, J. Singh, R. Chowdhury, T. Zheleva, Epitaxial growth of TiN Films on (100) silicon substrates by laser physical vapor deposition, Applied Physics Letters, 61 (1992) 1290-1292.
[1.62] N. Pryds, D. Cockburn, K. Rodrigo, I.L. Rasmussen, J. Knudsen, J. Schou, Growth of thin films of TiN on MgO(100) monitored by high-pressure RHEED, Appl Phys a-Mater, 93 (2008) 705-710.
[1.63] P. Tiwari, T. Zheleva, J. Narayan, Epitaxial growth of TiN Films on (100) silicon substrates by laser physical vapor deposition, Laser Ablation in Materials Processing : Fundamentals and Applications, 285 (1993) 349-354.
[1.64] T. Zheleva, K. Jagannadham, J. Narayan, Epitaxial growth in large-lattice-mismatch systems, J Appl Phys, 75 (1994) 860-871.
[1.65] G. Leggieri, A. Luches, M. Martino, A. Perrone, G. Majni, P. Mengucci, I.N.
Mihailescu, Laser reactive ablation deposition of titanium carbide films, Thin Solid Films, 258 (1995) 40-45.
[1.66] P. Lin, C. Deshpandey, H.J. Doerr, R.F. Bunshah, N. Kaufherr, R. Nielsen, G. Fenske, Detailed characterization of TiC and TiN coatings prepared by the activated reactive
evaporation process, J Vac Sci Technol A, 5 (1987) 2732-2736.
17
[1.67] Y. Suda, H. Kawasaki, K. Doi, S. Hiraishi, Formation and properties of TiC thin films by pulsed Nd/YAG laser deposition, Thin Solid Films, 374 (2000) 282-286.
[1.68] J.K. Tang, J.S. Zabinski, J.E. Bultman, TiC coatings prepared by pulsed laser deposition and magnetron sputtering, Surf Coat Tech, 91 (1997) 69-73.
[1.69] A.K. Chaddha, J.D. Parsons, G.B. Kruaval, Thermally stable, low specific resistance (130 × 10-5 Ωcm2) TiC ohmic contacts to n-type 6Hα-SiC, Applied Physics Letters, 66 (1995) 760-762.
[1.70] H. Hogberg, J. Birch, M.P. Johansson, U. Jansson, L. Hultman, Strain relaxation of low-temperature deposited epitaxial titanium-carbide films, J Cryst Growth, 219 (2000) 237-244.
[1.71] L. Norin, H. Hogberg, J. Lu, U. Jansson, J.O. Malm, Deposition of transition metal carbide superlattices using C60 as a carbon source, Applied Physics Letters, 73 (1998) 2754-2756.
[1.72] L. Norin, S. McGinnis, U. Jansson, J.O. Carlsson, Low temperature deposition of epitaxial titanium carbide on MgO(001) by co-evaporation of C60 and Ti, J Vac Sci Technol A, 15 (1997) 3082-3085.
[1.73] W.H. Sheu, S.T. Wu, Epitaxial growth of TiC (002) on Si (001) by reactive magnetron sputtering at low temperatures, Jpn J Appl Phys 1, 37 (1998) 6094-6097.
[1.74] O. Diwald, T.L. Thompson, T. Zubkov, E.G. Goralski, S.D. Walck, J.T. Yates, Photochemical activity of nitrogen-doped rutile TiO2(111) in visible light, J Phys Chem B, 108 (2004) 6004-6008.
[1.75] G. Georgiev, N. Feschiev, D. Popov, Z. Uzunov, Titanium carbide thin-films obtained by reactive magnetron sputtering, Vacuum, 36 (1986) 595-597.
[1.76] J.E. Sundgren, B.O. Johansson, S.E. Karlsson, Mechanisms of reactive sputtering of titanium nitride and titanium carbide. 1. Influence of process parameters on film composition, Thin Solid Films, 105 (1983) 353-366.
[1.77] A.C. Fernandes, P. Carvalho, F. Vaz, N.M.G. Parreira, P. Goudeau, E. Le Bourhis, J.P.
Riviere, Correlation between processing and properties of titanium oxycarbide, TiCxOy, thin films, Plasma Process Polym, 4 (2007) S83-S88.
[1.78] A.C. Fernandes, L. Cunha, C. Moura, F. Vaz, P. Carvalho, E. Le Bourhis, P. Goudeau, J.P. Riviere, N.M.G. Parreira, The effect of bombarding conditions on the properties of
multifunctional Ti-C-O thin films grown by magnetron sputtering, Surf Coat Tech, 202 (2007) 946-951.
18
[1.79] N. Kumar, M.G. Fissel, K. Pourrezaei, B. Lee, E.C. Douglas, Growth and properties of TiN and TiOxNy diffusion-barriers in silicon on sapphire integrated-circuits, Thin Solid Films, 153 (1987) 287-301.
[1.80] W. Sinke, G.P.A. Frijilink, F.W. Saris, Oxygen in titanium nitride diffusion-barriers, Applied Physics Letters, 47 (1985) 471-473.
[1.81] N. Kumar, J.T. Mcginn, K. Pourrezaei, B. Lee, E.C. Douglas, Transmission electron-microscopy studies of brown and golden titanium nitride thin-films as diffusion-barriers in very large-scale integrated-circuits, J Vac Sci Technol A, 6 (1988) 1602-1608.
[1.82] R. Chowdhury, R.D. Vispute, K. Jagannadham, J. Narayan, Characteristics of titanium nitride films grown by pulsed laser deposition, J Mater Res, 11 (1996) 1458-1469.
[1.83] S.C. Abraham, C.T. Gabriel, J. Zheng, Performance of different etch chemistries on titanium nitride antireflective coating layers and related selectivity and microloading
improvements for submicron geometries obtained with a high-density metal etcher, J Vac Sci Technol A, 15 (1997) 702-706.
[1.84] J. Tonotani, T. Iwamoto, F. Sato, K. Hattori, S. Ohmi, H. Iwai, Dry etching characteristics of TiN film using Ar/CHF3, Ar/Cl2, and Ar/BCl3 gas chemistries in an inductively coupled plasma, J Vac Sci Technol B, 21 (2003) 2163-2168.
19
Chapter 2
Epitaxial growth of titanium oxynitride and titanium oxycarbide films on MgO substrate
2.1. Introduction
Titanium oxynitride and titanium oxycarbide films have been deposited by many methods such as CVD, MOCVD, magnetron sputtering, evaporation, and PLD. Among those methods, PLD has been widely used over the past decade and has been considered as an attractive alternative for the deposition of high-quality thin films because of its unique advantages. The main advantages of PLD are [2.1]:
(i) Conceptually simple: a laser beam vaporizes a target surface, producing a film with the same composition as the target.
(ii) Non-volatile targets (iii) Multi-component target.
(iv) Multi-target or multi-layer or alloy films.
(v) Operated under any ambient gas over a broad range of gas pressure (from 0 – 1 Torr).
(vi) Easy of thickness control.
(vii) Generally of lower substrate temperature.
(viii) Cost-effective: one laser can serve many vacuum systems.
(ix) Fast: high quality samples can be grown reliably in 10 or 15 minutes.
(x) Scalable: as complex oxides move toward volume production.
As shown in Fig. 2.1, the PLD process consists of three regimes:
(i) Regime I: Laser-target interaction.
(ii) Regime II: Target to substrate gas phase transportation.
(iii) Regime III: Deposition and film growth process.
20 Figure 2.1: The PLD process.
The regime II of gas transportation contains high ion/neutral ratio and many ionized species with high kinetic energy (about 10-100 eV). Therefore, PLD is particularly capable of deposition of many materials that are difficult to synthesize in bulk and by other deposition methods such as ceramics (YBCO, PZT, SBN), complex oxides, hard materials (including diamond/diamond like films, TiN, TiC, TiNxOy, TiCxOy, SiC…), and exotic alloys and multi-component films (Fe16N2, La1-xSrxMnO3). The film’s structure and growth mechanism are strictly related to the conditions of plasma obtained by the interaction between targets and laser beam. Authors in ref. [2.2] have shown that in the plume produced from TiC targets, there is the presence of a large amount of ions with high kinetic energy including Ti+, Ti2+, and C+ ions. The neutral Ti was also obtained in the TiC plasma plume. In case of pulsed laser deposition of TiN by the irradiation Ti target in nitrogen gas, the plasma plume contains high-density of reactive species and high-energy ions such as Ti and Ti+, Ti2+, N+ , and N2+ [2.3, 4].
In this chapter, we present the detailed description of the experimental procedures for epitaxial growth of titanium oxynitride and titanium oxycarbide films on MgO (001) substrate using PLD. The crystallinity, microstructure, chemical composition, and morphology of titanium oxynitride and titanium oxycarbide are also studied. The effect of oxygen on the lattice parameter, microstructure, and electrical properties of TiNxOy was especially investigated. The residual strain and stress tensors of TiNxOy and TiCxOy films were also calculated.
21 2.2. Experimental
2.2.1. Pulsed laser deposition system
The deposition of titanium oxynitride and titanium oxycarbide films was carried out in a PLD system. The base pressure in this PLD system can reach 1x10-6 Torr. Figure 2.2 presents a schematic view of the PLD system. The basic structure of the PLD system consists of the following parts:
(i) The substrate stage can be heated up to 700oC.
(ii) A 2-inch target is placed opposite to a substrate stage at a distance of 14 cm. The target can be rotated to avoid pitting during deposition.
(iii) KrF (λ = 248 nm) laser beam is incident at an angle of 45o with respect to the target.
(iv) The PLD reactor chamber is made of stainless steel to sustain high temperature and pressure.
Figure 2.2: A schematic view of the PLD system.
2.2.2. Experimental flowcharts and parameters and material analysis methods
22
Figure 2.3 shows the experimental flowcharts of deposition and characterization of epitaxial of titanium oxynitride and titanium oxycarbide films on MgO (001) substrates.
Before titanium oxynitride and titanium oxycarbide films deposition, MgO substrates were heat-treated at 700oC for 30 minutes to obtain a smooth and clean surface. To obtain TiNxOy films with different chemical composition, a TiNO0.064 target was used, and the deposition process was carried out under base pressure of 1 × 10-6 Torr and under nitrogen ambient gas of 10-3-10-5 Torr. Detailed deposition parameters are shown in Table 2.1. A TiCO0.5 target was used to deposit TiCxOy films, and deposition parameters for the TiCxOy films are showed in Table 2.2. After the deposition process had been completed, the substrate was cooled down to room temperature in 90 minutes.
Figure 2.3: Experimental flowcharts of deposition and characterization of epitaxial of titanium oxynitride and titanium oxycarbide films on MgO (001) substrate.
23
Table 2.1: Deposition parameters for titanium oxynitride films by the PLD method.
Sample A B C D
Table 2.2: Deposition parameters for titanium oxycarbide films by the PLD method.
Sample 1
24
The deposited films were then analyzed by atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), x-ray diffraction pattern (XRD), transmission electron microscopy, Hall measurements, and nanoindenter. The results of nanoindentation as well as data analysis will be presented in Chapter 3.
2.2.3. Instruments:
2.2.3.1. X-ray photoelectron spectroscopy
X-ray photoelectron spectroscopy (XPS) is one of the most powerful techniques used in the surface, interface and thin film analysis. Of all the presently available instrumental techniques for surface analysis, XPS can generally do quantitative analysis with readily interpretable and the informative results of chemical analysis.
In an XPS experiment, the sample is irradiated by low energy X-rays in an ultra high vacuum environment. This causes photo-ionisation of the atoms at the specimen's surface:
photoelectrons are emitted from the atomic energy levels with very specific Binding Energies and, consequently, with a very accurate spectral signature/fingerprint for all the elements from the Periodic Table and their chemical compounds. Quantitative data can be obtained from peak heights or peak areas. The quantitative sensitivity is in the range of (10-2 - 10-4) of a monolayer and the surface sensitivity is in the range of (2-100) monolayers (<0.5 - 20nm). From the results of this analysis, it is possible to infer which elements are present on the specimen, what their chemical states are (due to chemical shifts of the binding energy of the electron shells), and in what quantities they are present.
The following quantitative results are obtained with errors <10% (and <5% for using well known standards): element relative concentrations, oxidation states relative
The following quantitative results are obtained with errors <10% (and <5% for using well known standards): element relative concentrations, oxidation states relative