DIRECT OBSERVATIONS OF NICKEL SILICIDE FORMATION ON (100) Si AND Si0.75Ge0.25 SUBSTRATES USING IN-SITU TRANSMISSION ELECTRON MICROSCOPY RAMESH NATH S/O PREMNATH (B.Sc.(Hons.), NUS) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF MATERIALS SCIENCE NATIONAL UNIVERSITY OF SINGAPORE 2004 Acknowledgements I would like to express my utmost gratitude and thanks to my supervisor Professor Mark Yeadon for this project accomplishment. Without his patient guidance, this work will not have been possible. From my early days of ignorance, he had been there to provide knowledge, mentorship and assistance whenever difficulties are encountered. I am also grateful for Prof. Yeadon’s invaluable coaching in the handling of his precious transmission electron microscope and the knowledge of the operating techniques and little tricks here and there that he transferred to the me. It is a joy to work with him in the laboratory and get to know him as a friend. I am also deeply indebted to Dr. Christopher Boothroyd for his mentorship and guidance in helping me better understand the principles of the transmission electron microscope and the Gatan Image Filter. The long discussions we had over tea have definitely helped shaped me to be a better microscopist. I would also like to thank Dr. Lap Chan (CSM) for being an excellent teacher and facilitator who has helped to put this project together. I must particularly express my most sincere gratitude to my colleagues and also my friends, Dr. Foo Yong Lim and Soo Chi Wen, for their advice, understanding and help along the way. I would also like to thank my loved ones who were very supportive of what could be a misadventure, but happily, turned out to be a great learning experience and project. Finally, I would like to thank Professor Chow Gan Moog, Professor Chua Soo Jin and Professor Alfred Huan for the provision of the laboratory facilities, which made this project possible. i Table of contents Acknowledgements………………………………………………………………… i Table of contents…………………………………………………………………… ii Summary…..……………………………………………………………………….. vi List of tables………………………………………………………………………...viii List of figures……………………………………………………………………......ix Nomenclature……………………………………………………………………… xvi List of publications...……………………………………………………………….xviii 1 Introduction................................................................................................. 1 2 Literature Review and Thin Films .............................................................. 5 2.1 Silicon-germanium technology........................................................... 5 2.1.1 Introduction to SiGe technology..................................................... 5 2.1.2 Si1-xGex growth issues..................................................................... 7 2.2 Silicide technology.............................................................................. 9 2.2.1 Introduction to silicides................................................................... 9 2.2.2 Formation of silicides for technological applications................... 11 2.2.3 Requirements for silicides in silicon integrated circuits............... 13 2.2.4 Comparison of nickel silicide with other silicides........................ 15 2.2.4.1 Titanium disilicide .............................................................. 15 2.2.4.2 Cobalt disilicide .................................................................. 16 2.2.4.3 Nickel monosilicide ........................................................... 19 2.2.4.4 Nickel silicidation on Si1-xGex substrates........................... 22 2.3 Principles of thin films...................................................................... 23 2.3.1 Mechanism for the formation of thin film nickel silicide phases . 24 ii 2.3.2 Agglomeration of thin films.......................................................... 27 References ....................................................................................................... 29 3 Principles of transmission electron microscopy ...................................... 32 3.1 Introduction to transmission electron microscopy............................ 32 3.2 Important electron interactions with the sample in TEM ................. 33 3.3 Diffraction......................................................................................... 36 3.3.1 Theory of electron diffraction....................................................... 36 3.3.2 Structure factor.............................................................................. 43 3.3.3 Selected area electron diffraction.................................................. 45 3.4 Bright and dark field imaging........................................................... 47 3.5 Basic optics operation of JEM 2000V TEM..................................... 49 References ....................................................................................................... 51 4 Experimental setup.................................................................................... 52 4.1 The MERLION system..................................................................... 52 4.2 Preparation of Si (100) substrates..................................................... 55 4.3 Preparation of Si0.75Ge0.25 (100) substrates....................................... 56 4.4 Nickel deposition .............................................................................. 58 4.5 Resistive annealing ........................................................................... 59 4.6 Observation and data collection........................................................ 60 4.6.1 Gatan DualView 780 digital camera............................................. 61 4.6.2 Gatan Image Filter ........................................................................ 61 4.6.2.1 Theory of operation............................................................. 62 iii 4.6.2.2 Basic concepts of EELS...................................................... 64 4.6.2.3 Uses of EELS Data ............................................................. 66 4.6.2.4 EFTEM................................................................................ 68 4.6.2.5 Selecting an energy loss...................................................... 68 References ....................................................................................................... 69 5 Results and discussion I: Ni on Si (100)................................................... 70 5.1 Ni on clean Si (100) .......................................................................... 71 5.1.1 Preliminary inspection of clean Si (100) ...................................... 71 5.1.2 Nickel deposition on clean Si (100).............................................. 72 5.1.3 Annealing of the 12nm Ni film on clean Si (100) ........................ 73 5.2 Ni on oxide-covered Si (100)............................................................ 87 5.2.1 Preliminary inspection of oxide-covered Si (100)........................ 87 5.2.2 Nickel deposition on oxide-covered Si (100) ............................... 88 5.2.3 Annealing of the 12nm Ni film on oxide-covered Si (100).......... 88 5.2 Summary of Chapter 5...................................................................... 92 References ....................................................................................................... 93 6 Results and discussion II: Ni on relaxed Si0.75Ge0.25 (100)...................... 95 6.1 Preliminary inspection of relaxed Si0.75Ge0.25 (100) ........................ 96 6.2 Nickel deposition on relaxed Si0.75Ge0.25 (100) ............................... 99 6.3 Annealing of the 12nm Ni film on relaxed Si0.75Ge0.25 (100) ........ 100 6.4 Summary of Chapter 6.................................................................... 112 References ..................................................................................................... 113 iv 7 Conclusion .............................................................................................. 115 Appendix: Indexing of SAED patterns......................................................... 118 A.1 Identification of major spots and calibration of SAED patterns..... 118 A.1.1 Step one....................................................................................... 118 A.1.2 Step two and three....................................................................... 120 A.2 Calibration and indexing of SAED pattern in Figure 5.1 (b).......... 121 A.3 Indexing of SAED pattern in Figure 5.2 (b) ................................... 124 A.4 Indexing of SAED pattern in Figure 5.4 (a) ................................... 125 A.5 Indexing of SAED pattern in Figure 5.4 (c) ................................... 128 A.6 Indexing of SAED pattern in Figure 5.15 (b) ................................. 131 v Summary Recent success in the growth technology of Si1-xGex epitaxial thin films has found its potential in high-speed electronic device applications for ultra large-scale integrated (ULSI) circuits, such as complementary metal-oxide semiconductor (CMOS) technology. One of the requirements for the device structures is to form a good ohmic contact that will not degrade the device performance, where metal silicides have played a key role. It is anticipated that they will continue to be used with strained-Si and Si1-xGex device technologies. There is considerable interest in the use of NiSi due to its lower silicon consumption and one-step low temperature of formation. A severe disadvantage