Royal Institute of Technology Low Temperature Epitaxy Growth and Kinetic Modeling of SiGe for BiCMOS Application Arash Salemi Master Thesis Supervisor: Docent Henry Radamson Co-Supervisor: Dr. Mohammadreza Kolahdouz Examiner: Prof. Mikael Östling KTH, Royal Institute of technology Department of Integrated Devices and Circuits Stockholm, Sweden 2011 Abstract There is an ambition of continuously decreasing thermal budget in CMOS and BiCMOS processing, thus low temperature epitaxy (LTE) (350-650°C) with chemical vapor deposition (CVD) technique in order to have faster process with low cost. One of the growth issues at low temperatures is gas quality where the oxygen and moisture contamination becomes critical for the epilayers quality. If the level amount of contamination is not controlled, the silicon dioxide islands are formed and the oxygen level in the film will be high. This thesis is focused on two different aspects of “LTE”. The first focus of this thesis was to identify the effect of contamination on the strain and quality of the SiGe epilayers (prior and during epitaxy). The samples in this study were exposed to different oxygen and moisture partial pressures (2ppb-250 ppm range) at different exposure temperatures (350-650°C). The results revealed that presence of contamination even at low ranges (2-100 ppb) is not negligible and affects the strain. Parameters such as O2 exposure temperature and partial pressure, and SiGe layer’s growth temperature impacted the oxygen level and strain in the films. For oxygen levels below 100 ppb, High Resolution Scanning Microscopy (HRSEM) could not detect very small oxide island. By increasing the O2 partial pressure well above 100 ppb, the oxide islands are saturated at 0.08 µm2. The second focus of this thesis was to model the Si2H6/Ge2H6-based epitaxial growth of SiGe. The model can predict the number of free sites on Si surface, growth rate of Si and SiGe, and the Ge content at low temperature. A good agreement between the model and the experimental data is found. This model can provide the required growth parameters for certain layer profile which is vital to decrease the total number of growth runs for calibration and cause to reduce the total fabrication cost. ii To Mana, my beloved wife iii Contents Abstract ...................................................................................................................................... ii Acknowledgments ..................................................................................................................... vi Acronyms and Symbols ........................................................................................................... vii Chapter 1 .................................................................................................................................... 1 1.1 Introduction .................................................................................................................. 1 Chapter 2 .................................................................................................................................... 3 2.1 Chemical Vapor deposition (CVD) .............................................................................. 3 2.2 Si-SiGe Strained Layer Epitaxy ................................................................................... 4 2.3 Heteroepitaxy Modes .................................................................................................... 7 2.4 Low Temperature SiGe Epitaxy ................................................................................... 8 2.5 Kinetics of Silane, Disilane, Germane, and Digermane ............................................... 9 2.5.1 The Silane .............................................................................................................. 9 2.5.2 The Disilane ........................................................................................................ 10 2.5.3 The Germane and Digermane ............................................................................. 11 2.6 Hydrogen Coverage .................................................................................................... 11 2.7 Wafer Cleaning ........................................................................................................... 11 2.8 Oxygen and Moisture Contamination......................................................................... 11 Chapter 3 .................................................................................................................................. 13 3.1 Result and Discussion ................................................................................................. 13 3.2 Effect of temperature on SiGe Epitaxy ....................................................................... 13 3.3 Oxygen Contamination ............................................................................................... 15 3.4 Exposing O2 prior to the SiGe Epitaxy ....................................................................... 15 3.5 Exposing O2 during the SiGe Epitaxy ........................................................................ 19 Chapter 4 .................................................................................................................................. 23 4.1 Kinetic Model for Si2H6/Ge2H6 Based Epitaxy Growth of SiGe ............................... 23 4.2 Adsorption Kinetics .................................................................................................... 24 4.3 Sticking Coefficient .................................................................................................... 24 4.4 Surface coverage ......................................................................................................... 24 4.5 The Langmuir Isotherm .............................................................................................. 25 4.6 Hydrogen Desorption ................................................................................................. 25 4.7 Activation energy ....................................................................................................... 26 4.8 Modeling of non-selective epitaxy growth of SiGe .................................................... 28 4.9 Composition Model .................................................................................................... 30 iv Chapter 5 .................................................................................................................................. 33 5.1 Conclusions and Future Outlook ................................................................................ 33 References ................................................................................................................................ 34 Appendix .................................................................................................................................. 37 v Acknowledgments I would like to express my deep gratitude to my supervisor Docent Henry Radamson for his continues support, excellent guidance and motivation me in this thesis. He helped and supported me in different parts and I learned a lot of things in our discussions in semiconductor technologies. I am deeply grateful to Prof. Mikael Östling, head of the integrated device and circuits (EKT) department, dean of the ICT School at KTH who accepted me as a diploma worker in the EKT department. His ideas were so useful not only in this thesis but also for my daily life. I would never have been able to finish this thesis without helping and supporting my co- supervisor Dr. Mohammadreza Kolahdouz, who worked with me side by side and guided me during this period. I learned so many experimental and theoretical things, and our discussions were so useful I would like to thank to Dr. Rick Wise in Texas Instruments for the discussions and financial support through the SRC program. I am so thankful to Prof. Carl-Mikael Zetterling for his kind support. Also thanks to Docent Margareta Linarsson for the SIMS results. During my education at KTH, Sam Vaziri was my best friend and colleague, and I have many sweet memories with him. Our discussions during that time encouraged me to work harder. I am thankful to Mahdi Moeen who was my co-worker, and also Dr. Reza Ghandi my friend who kindly helped me. All of my teachers and friends are thanked for providing a nice working atmosphere at KTH. Last but not least, I would like to express my deepest gratitude to my beloved wife and our families who helped and supported me to be where I am now. Thank you all Arash Salemi Stockholm, June 2011 vi Acronyms and Symbols As Arsenide B Boron C Carbon CMOS Complementary Metal Oxide Semiconductor CVD Chemical Vapor Deposition DLTS Deep Level Transient Spectroscopy FWHM Full With Half Maximum GaAs Gallium Arsenide Ge Germanium GeH4 Germane Ge2H6 Digermane HBT Heterojunction Bipolar Transistor HCl Hydrogen chloride HH Heavy Hole HRSEM High-Resolution Scanning Electron Microscopy HRXRD High-Resolution X-Ray Diffraction LH Light Hole ML Mono Layer N2 Nitrogen O2 Oxygen ppb Parts-per billion ppm Parts-per million RPCVD Reduced Pressure CVD Si Silicon SiGe/Si1-xGex Silicon Germanium alloy (subscript ~ fraction of constituent) SiGe(B) Silicon Germanium Boron alloy SiGe(C) Silicon Germanium Carbon alloy Si2H2Cl2 Dichloro Silane SiH4 Silane Si2H6 Disilane Si3H8 Trisilane vii SIMS Secondary Ion Mass Spectroscopy XRD X-Ray Diffraction Ea Activation Energy of Adsorption Ed Activation Energy of Desorption