Physical characterization of hfo2 hfo2 al2o3 alloy thin films

Physical Characterization of HfO2 & HfO2-Al2O3 Alloy Thin Films Tok Kwee Lee (B.Sc.(Hons.), NUS) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE Department of Physics National University of Singapore 2005 Acknowledgements I would like to express my heartfelt thanks to my supervisor, A/Prof Andrew Wee for his invaluable guidance and for many helpful discussions during the course of this project I would also like to express special thanks to the following people: Dr Osipowicz, Mr Liu Rong and Mdm Liu Yanjiao for helping with the RBS, SIMS and XPS experiments respectively Finally, I would like to thank my husband Tianfu for his support and continuous encouragement during the course of this work i Contents Acknowledgements i Contents ii Summary v List of Tables vii List of Figures viii Introduction 1.1 Preliminaries: The MOSFET 1.2 Scaling and Improved performance 1.3 High κ Gate Dielectric 1.3.1 Organization of thesis Thin Film Deposition 2.1 Atomic Layer Chemical Vapour Deposition 2.2 Sample Preparation 10 2.2.1 HfO2 and HfO2 -Al2 O3 alloys 10 Composition of Thin Films 3.1 12 Rutherford Backscattering Spectrometry 12 3.1.1 Introduction 12 3.1.2 Experimental 13 ii 3.1.3 3.2 3.3 Results & Discussion 14 X-ray Photoelectron Spectroscopy 15 3.2.1 Introduction 15 3.2.2 Experimental 17 3.2.3 Results & Discussion 18 Conclusion 20 Thermal Stability of Thin Films 22 4.1 Introduction 22 4.2 Glancing Angle X-Ray Diffraction 24 4.3 4.4 4.2.1 Introduction 24 4.2.2 Experimental 25 Results & Discussion 26 4.3.1 Phase study of HfO2 26 4.3.2 HfO2 -Al2 O3 alloy samples 27 Conclusion 29 Diffusion Studies of HfO2 -Al2 O3 Alloy Thin Films 31 5.1 Introduction 31 5.2 Secondary Ion Mass Spectrometry 31 5.3 Bulk & Grain Boundary Diffusion 33 5.3.1 Bulk Diffusion 33 5.3.2 Grain Boundary Diffusion 34 5.4 Experimental 34 5.5 Results & Discussion 34 5.6 Conclusion 38 Conclusion 39 Bibliography 41 iii A XPS spectra 45 B SIMS 55 iv Summary The continued scaling of complementary metal-oxide-semiconductor (CMOS) device feature sizes have allowed the semiconductor industry to achieve unprecedented gains in productivity and performance This rapid scaling has caused the channel length and the thickness of the gate dielectric to decrease rapidly As a result, high gate leakage current across the thin gate dielectric now necessitate the introduction of alternative high κ gate dielectric materials in order that the stringent requirements for leakage current can be met Due to its high dielectric constant, HfO2 (κ ∼ 20) is a potential candidate for gate oxide replacement However, as HfO2 is thermally less stable and it crystallizes at about 400◦ C, Al2 O3 was co-deposited with HfO2 to obtain an alloy that is more resilient to crystallization In this work, we will investigate the physical characteristics of HfO2 and HfO2 -Al2 O3 alloy thin films (∼ 20 nm) prepared by ALCVD The samples were deposited on p-type Si(100) substrate at 300◦ C Their composition was first determined using RBS and XPS The HfO2 thin film was found to be in good stoichiometry For the HfO2 -Al2 O3 alloy thin films, the Hf to Al cation ratios obtained were much higher than the expected From the results, the films were also found to be of good compositional uniformity Glancing incidence XRD was then employed to study the microstructure and thermal stability of HfO2 and HfO2 -Al2 O3 alloy thin films that were annealed using RTP for temperature up to 1000◦ C As-deposited HfO2 was found to have a small degree of crystallization in mixed tetragonal and monoclinic phase Upon annealing at 1000◦ C, the tetragonal polymorphs transformed into monoclinic polymorphs and the thin film crystallizes fully in the monoclinic phase For the HfO2 -Al2 O3 alloy samples, crystallization was observed to be suppressed in the thin films up to an annealing temperature of 800◦ C At 1000◦ C, the HfO2 -Al2 O3 thin films crystallize in the monoclinic phase in the [111] direction The degree of crystallization and the crystallite size was found to decrease for increasing Al2 O3 content in the samples The effect of thermal annealing on precursor contamination and interdiffusion of silicon v in the thin films were then investigated using SIMS SIMS results indicate the presence of an interfacial layer between the thin film and the silicon substrate Chlorine contamination from precursor by-products was also found in the thin films and the interfacial region in the as-deposited films After the samples were annealed at 1000◦ C, it was observed that the chlorine contamination persists at the interface only Silicon out-diffusion from the substrate into the thin film was also observed in HfO2 -Al2 O3 samples that were annealed at 1000◦ C This is likely to be due to enhanced diffusion along grain boundaries when the samples crystallize during the annealing process vi List of Tables 1.1 Material properties of high κ candidate Table adapted from reference[8] 2.1 Precursors used in the deposition of the various types of films 11 2.2 Target composition and estimated thickness of thin films 11 3.1 Film composition in atomic fraction of the samples obtained by RBS 14 3.2 Film composition in atomic fraction of the samples obtained by XPS 20 4.1 Crystallite size for samples annealed at 1000◦ C 28 A.1 Sample peak parameters 46 A.2 Sample peak parameters 48 A.3 Sample peak parameters 50 A.4 Sample peak parameters 52 A.5 Sample peak parameters 54 vii List of Figures 1.1 (a) Schematic diagram of a MOSFET (b) Energy band diagram of a MetalInsulator-Semiconductor (MIS) capacitor under inversion condition 2.1 Deposition of Al2 O3 thin film 10 3.1 Setup used for RBS analysis 13 3.2 RBS spectra obtained for HfO2 -Al2 O3 samples Inset shows an enlarged view of the Hf peaks 14 3.3 RBS spectra for sample (red line indicates simulation of spectra) 15 3.4 Sampling depth of XPS experiment 16 3.5 Schematic Diagram of an XPS spectrometer 17 3.6 Hf4f, Al2p and O1s spectra obtained for the various HfO2 -Al2 O3 samples 18 3.7 XPS wide scan and Hf4f and O1s fitted core level spectra for sample 1, pure HfO2 19 4.1 Diffraction of X-ray by a crystal 24 4.2 Effect of crystallite size on diffraction curves 25 4.3 Sample 1(HfO2 ): XRD diffractograms of as-deposited and annealed samples 26 4.4 XRD patterns of HfO2 -Al2 O3 alloy samples: (a) as-deposited and (b) annealed at 800◦ C 27 4.5 XRD patterns of HfO2 -Al2 O3 alloy samples annealed at 1000◦ C 28 5.1 Schematic diagram showing the initiation of the collision cascade and the sputter removal of material from the sample surface[34] 32 viii 5.2 Schematic representation of the diffusion profile showing contributions from the bulk and grain boundary diffusion regimes.[35] 33 5.3 SIMS profiles obtained for sample 1, and before and after annealing at 1000 ◦ C The first row shows as-deposited sample profiles while the second row shows profiles of annealed samples 35 5.4 ClCs+ and SiCs+ curves for sample and sample 36 5.5 Bulk diffusion in sample annealed at 1000◦ C Linear fit to the data is indicated by red line 37 5.6 Grain boundary diffusion in sample annealed at 1000◦ C Linear fit to the data is indicated by red line 38 A.1 Sample Wide Scan 45 A.2 Sample high resolution scans for Hf4f, O1s and C1s 46 A.3 Sample Wide Scan 47 A.4 Sample high resolution scans for Hf4f, Al2p, O1s and C1s 47 A.5 Sample Wide Scan 49 A.6 Sample high resolution scans for Hf4f, Al2p, O1s and C1s 49 A.7 Sample Wide Scan 51 A.8 Sample high resolution scans for Hf4f, Al2p, O1s and C1s 51 A.9 Sample Wide Scan 53 A.10 Sample high resolution scans for Al2p, O1s and C1s 53 B.1 SIMS depth profiles for Sample at various annealing temperature 55 B.2 SIMS depth profiles for Sample at various annealing temperature 56 B.3 SIMS depth profiles for Sample at various annealing temperature 56 ix BIBLIOGRAPHY 42 Chapter [12] W.K Chu, W.M Mayer and M.A Nicolet Backscattering Spectrometry Academic Press, New York, (1978) [13] L.R Doolittle, Nucl Instr Meth., B9, 344, (1985) [14] R Kwok, XPSPEAK version 4.1, http://www.phy.cuhk.hk/∼surface/XPSpeak, (1999) [15] M Repoux, Surface and Interface Analysis,18, 567, (1992) [16] John Moulder et al Handbook of X-ray Photoelectron Spectra, Eden Prairie, Minn: Perkin Elmer Corporation, (1992) [17] NIST XPS database, http://www.srdata.nist.gov/xps Chapter [18] B.D Cullity and S.R Stock, Elements of X-ray Diffraction, 3rd edn, Prentice-Hall, London, (2001) [19] Powder Diffraction File, Newtown Square, Pa : International Centre for Diffraction Data, (2004) [20] S.V Ushakov et al, Phys Stat Sol B, 241, 2268, (2004) [21] Ed by Gernot Kostorz Phase Transformation in Materials, Wiley-VCH Verlag, Weinheim Germany, (2001) [22] J-P Maria et al, J Mater Res., 17, 1571, (2002) [23] J.Schaeffer, Journal of the Electrochemical Society, 150, F67-F74, 2003 [24] X Zhao and D Vanderbilt, Phys Rev B, 65, 233106, (2002) [25] A.I Kingon, J.P Maria and S.K Streiffer, Nature, 406, 1032 (2000) BIBLIOGRAPHY 43 [26] M.L Green, E.P Gusev, R Degraeve and E.L Garfunkel, J Appl Phys., 90, 2057, (2001) [27] H Kim, P.C McIntyre & K.C Saraswat, Appl Phys Lett., 82, 106, (2003) Chapter [28] R.G Wilson, F.A Stevie and C.W Magee, Secondary Ion Mass Spectrometry, John Wiley, New York, (1989) [29] Ed by J.C Vickerman, A Brown and N.M Reed, Secondary Ion Mass Spectrometry: Principles and Applications, Oxford University Press, New York, (1989) [30] Ed by J Nowotny, Science of Materials Interfaces, p227-309, Elsevier, Amsterdam, (1993) [31] Ed by J Nowotny, Science of ceramic interfaces II, p277-310, Elsevier, Amsterdam, (1994) [32] Ed by Graeme E Murch, Arthur S Nowick, Diffusion in Crystalline Solids, Academic Press, Orlando, (1984) [33] J Bennett et al, Appl Surf Sci.,203-204, 419, (2003) [34] Ed by B.G Yacobi et al, Microanalysis of Solids, Plenum Press, New York, (1994) [35] K Kowalski et al, J Phys Chem Solids, 57, 153, (1996) [36] Martin Glicksman, Diffusion in solids: field theory, solid-state principles, applications, John Wiley, New York, (2000) [37] I Kaur, Y.Mishin and W.Gust Fundamentals of Grain and Interphase Boundary Diffusion, John Wiley, (1995) [38] J.C Fisher, J Appl Phys., 22, 74, (1951) [39] R.T Whipple, Phil Mag A, 45, 1225,(1954) BIBLIOGRAPHY 44 [40] T Suzuoka, Phys Soc Jpn., 19, 839, (1964) [41] A.D Le Claire, J Appl Phys., 14, 351, (1963) [42] H De Witte, T Conard, W Vandervorst and R Gijbels, Appl Surf Sci., 203-204, 523, (2003) [43] C Huyghebaerta, T Conard and W Vandervorst, Appl Surf Sci., 231-232, 552, (2004) [44] W Vandervorst et al , Appl Surf Sci.,231-232, 569, (2004) [45] T Conard, C Huyghebaerta and W Vandervorst, Appl Surf Sci., 231-232, 574, (2004) [46] Tadeusz Bak et al, J Am ceram Soc., textbf85, 2244, (2002) [47] Matsuda et al, Solid State Ionics, 111, 301, (1998) Appendix A XPS wide scans and high resolution scans for Hf4f, Al2p, O1s and C1s spectra are contained in this appendix Curve fitting results were obtained using XPSpeak software[14] Each peak is numbered and the corresponding peak parameters are presented in tables according to sample number Sample Pure HfO2 Figure A.1: Sample Wide Scan 45 46 APPENDIX A XPS SPECTRA Sample Hf 4f 24.3 Sample 22.3 20.3 18.3 O1s B.E/eV 12.3 14.3 16.3 Sample C1s B.E/eV 536.3 534.3 532.3 530.3 528.3 526.3 290.3 288.3 286.3 284.3 282.3 B.E/eV 280.3 278.3 Figure A.2: Sample high resolution scans for Hf4f, O1s and C1s Element Peak Type Position Area FWHM %GL Hf4f 4f7/2 4f5/2 O-Hf O-C C C-O C-O 16.697 eV 18.353 eV 529.897 eV 531.523 eV 284.761 eV 286.863 eV 288.835 eV 13660.120 10245.090 12688.890 2513.050 2124.999 159.768 250.784 1.356 1.356 1.564 1.795 1.794 1.385 1.650 12% 4% 17% 0% 0% 0% 0% O1s C1s Table A.1: Sample peak parameters eV eV eV eV eV eV eV 47 APPENDIX A XPS SPECTRA Sample Figure A.3: Sample Wide Scan Sample Hf 4f Sample Al 2p 21.5 19.5 17.5 13.5 15.5 Sample B.E/eV 11.5 O1s 81.5 79.5 77.5 Sample 73.5 529.5 527.5 B.E/eV 69.5 C 1s B.E/eV 537.5 535.5 533.5 531.5 71.5 75.5 291.5 289.5 287.5 285.5 283.5 B.E/eV 281.5 279.5 Figure A.4: Sample high resolution scans for Hf4f, Al2p, O1s and C1s 48 APPENDIX A XPS SPECTRA Element Peak Type Position Area FWHM %GL Hf4f 4f7/2 4f5/2 Al O-Hf O-Al O-C C C-O C-O 16.951 eV 18.612 eV 73.949 eV 530.057 eV 530.867 eV 531.698 eV 284.750 eV 286.358 eV 288.426 eV 10915.840 8186.878 543.690 10768.650 1970.802 3116.890 2066.689 246.114 284.355 1.458 1.458 1.661 1.618 1.955 1.950 1.517 1.268 2.047 9% 3% 0% 17% 0% 2% 0% 0% 0% Al2p O1s C1s Table A.2: Sample peak parameters eV eV eV eV eV eV eV eV eV 49 APPENDIX A XPS SPECTRA Sample Figure A.5: Sample Wide Scan Sample Hf4f Sample B.E/eV 12.2 82.2 Al2p 24.2 22.2 20.2 18.2 16.2 Sample 14.2 O1s 80.2 78.2 76.2 74.2 72.2 Sample B.E/eV 70.2 C1s B.E/eV 538.2 536.2 534.2 532.2 530.2 B.E/eV 528.2 526.2 292.2 290.2 288.2 286.2 284.2 282.2 280.2 Figure A.6: Sample high resolution scans for Hf4f, Al2p, O1s and C1s 50 APPENDIX A XPS SPECTRA Element Peak Type Position Area FWHM %GL Hf4f 4f7/2 4f5/2 Al O-Hf O-Al O-C C C-O C-O 17.031 eV 18.682 eV 74.080 eV 530.193 eV 530.598 eV 531.800 eV 284.773 eV 286.330 eV 288.902 eV 8161.165 6120.874 1225.855 6713.265 6737.053 3675.144 2023.160 348.339 150.541 1.492 1.492 1.779 1.530 2.277 2.283 1.536 2.014 1.498 6% 0% 0% 21% 0% 0% 0% 0% 0% Al2p O1s C1s Table A.3: Sample peak parameters eV eV eV eV eV eV eV eV eV 51 APPENDIX A XPS SPECTRA Sample Figure A.7: Sample Wide Scan Sample Hf 4f Sample B.E/eV 11.6 81.6 Al 2p 23.6 21.6 19.6 17.6 15.6 Sample 13.6 O1s 79.6 77.6 75.6 Sample 73.6 71.6 B.E/eV 69.6 C 1s 535.6 533.6 531.6 529.6 B.E/eV 527.6 525.6 B.E/eV 291.6 289.6 287.6 285.6 283.6 281.6 279.6 Figure A.8: Sample high resolution scans for Hf4f, Al2p, O1s and C1s 52 APPENDIX A XPS SPECTRA Element Peak Type Position Area FWHM %GL Hf4f 4f7/2 4f5/2 Al O-Hf O-Al O-C C C-O C-O 17.144 eV 18.796 eV 74.224 eV 530.386 eV 530.867 eV 531.947 eV 284.757 eV 286.470 eV 288.677 eV 4637.897 3478.423 1875.533 4056.602 9760.918 3938.552 2441.257 325.793 228.040 1.518 1.518 1.750 1.553 2.342 2.453 1.630 1.600 1.500 5% 0% 0% 9% 4% 0% 0% 0% 0% Al2p O1s C1s Table A.4: Sample peak parameters eV eV eV eV eV eV eV eV eV 53 APPENDIX A XPS SPECTRA Sample Pure Al2 O3 Figure A.9: Sample Wide Scan Sample 83.2 Sample 81.2 Al2p 79.2 O1s 77.2 75.2 73.2 B.E/eV 71.2 Sample C1s 537.2 535.2 533.2 531.2 529.2 B.E/eV 527.2 525.2 291.2 289.2 287.2 285.2 283.2 Figure A.10: Sample high resolution scans for Al2p, O1s and C1s B.E/eV 281.2 54 APPENDIX A XPS SPECTRA Element Peak Type Position Area FWHM %GL Al2p O1s Al O-Al O-C C C-O C-O 74.458 eV 531.086 eV 532.210 eV 284.806 eV 286.460 eV 288.776 eV 2870.235 15126.690 4936.922 2152.695 286.402 276.168 1.714 2.108 2.318 1.535 1.685 1.800 2% 6% 8% 0% 0% 0% C1s Table A.5: Sample peak parameters eV eV eV eV eV eV Appendix B SIMS sputtering profiles for sample 1, and are contained in this appendix Each sample was annealed to 400◦ C, 600◦ C, 800◦ C, and 1000◦ C respectively Figure B.1: SIMS depth profiles for Sample at various annealing temperature 55 APPENDIX B SIMS Figure B.2: SIMS depth profiles for Sample at various annealing temperature Figure B.3: SIMS depth profiles for Sample at various annealing temperature 56 [...]... of the various types of films A series of HfO2 -Al2 O3 thin films of different compositions were prepared as shown in Table 2.2 The recipes prescribed to obtain the targeted composition for the HfO2 -Al2 O3 films were based on the HfCl4 :TMA pulse ratio in a cycle As such, the HfO2 -Al2 O3 alloy films obtained using such method are often not well characterized for its composition The thickness of films. .. composition of the material Sample No 1 2 3 4 5 Target Composition 100% HfO2 60% HfO2 - 40% Al2 O3 40% HfO2 - 60% Al2 O3 20% HfO2 - 80% Al2 O3 100% Al2 O3 Hf/Al Estimated thickness/nm 0.75 0.33 0.13 - 226 204 208 205 200 Table 2.2: Target composition and estimated thickness of thin films Chapter 3 Composition of Thin Films In this chapter, we set forth to determine the composition of the deposited thin films. .. 2.2.1 HfO2 and HfO2 -Al2 O3 alloys Precursors used for deposition are trimethyl aluminium (TMA, Al(CH3 )), hafnium tetrachloride (HfCl4 ) and water (H2 O) Table 2.1 shows the precursors used for deposition of HfO2 , Al2 O3 and HfO2 -Al2 O3 alloy films respectively Nitrogen was used as the carrier 11 CHAPTER 2 THIN FILM DEPOSITION and purge gas Thin Film Deposited Precursors Used HfO2 Al2 O3 HfO2 -Al2... HfO2 -Al2 O3 alloy thin films using glancing angle X-ray Diffraction (GIXRD) and examine its stability when subject to thermal treatment Interdiffusion of impurities in the thin film as a result of thermal treatment will be treated in the following chapter 24 CHAPTER 4 THERMAL STABILITY OF THIN FILMS 4.2 4.2.1 Glancing Angle X-Ray Diffraction Introduction Basic Principle of XRD When a beam of parallel,... interference occurs as a result of the periodicity of the lattice Consider the case where the path difference of the scattered x-rays between plane A and B differs slightly from an integral number of wavelength The plane of atoms scattering x-rays exactly out of phase with that in plane A will then be 25 CHAPTER 4 THERMAL STABILITY OF THIN FILMS deep within the crystal When the size of the crystal is too small,... the subject of high κ dielectric, chapter 2 on the method of thin film deposition and chapter 3 discusses the composition of the thin films obtained by Rutherford Backscattering and CHAPTER 1 INTRODUCTION 8 X-ray Photoelectron Spectroscopy In chapter 4, we will look at the effect of thermal treatment on the microstructure of the sample while in chapter 5 the diffusion of impurities into the thin film... studying is HfO2 -Al2 O3 alloy deposited using atomic layer CVD We will first look at the microstructure of the as-deposited thin films followed by the effect of thermal treatment on the films Following which, we will look at the effect of thermal annealing on the interdiffusion of impurities between the dielectric and silicon substrate The thesis is organized as follows: chapter 1 consists of a general... the sample surface The step size of 0.02◦ per step and a step time of 2s per step was used to collect the spectra CHAPTER 4 THERMAL STABILITY OF THIN FILMS 4.3 4.3.1 26 Results & Discussion Phase study of HfO2 Figure 4.3 shows the XRD results obtained for sample 1, HfO2 From the figure, we first note that the as-deposited sample is mainly amorphous with a slight degree of crystallization as indicated... suggests that the samples have uniform compositions throughout the films In addition, we note that the results using XPS, which has a shallower sampling depth, were well correlated and quite close to that obtained by RBS This further affirms the compositional uniformity of the samples Chapter 4 Stability of HfO2 and HfO2- Al2O3 Thin Films under Thermal Processing 4.1 Introduction Silicon dioxide, in... illustrates how an Al2 O3 thin film is obtained ALCVD is a deposition technique whereby highly conformal films with precise control of layer thickness can be obtained at low deposition temperature It offers potential for large area growth as it is integrable into existing manufacturing methods to obtain good composition control and high uniformity films[ 9, 10] As ALCVD of thin films is a relatively slow ... studied thin films of HfO2 and HfO2 -Al2 O3 alloy deposited on silicon substrate by ALCVD for gate dielectric replacement Using RBS and XPS, the composition of the films were determined The HfO2 thin. .. monoclinic HfO2 -Al2 O3 alloy thin films In the HfO2 -Al2 O3 thin films , suppressed crystallization was observed for films annealed up to 800◦ C However, the HfO2 -Al2 O3 alloy samples crystallize... achievable and offset the advantage of using a high κ material Hence, the feasibility of this solution will need to be investigated Chapter Diffusion Studies of HfO2- Al2O3 Alloy Thin Films 5.1 Introduction