I would like to thank my advisor, Dr. Toshikazu Nishida, for his guidance and encouragement. I also would like to

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  • INVESTIGATION OF PROCESS FABRICATION FOR LOW-NOISE P-TYPE DIFFUSED PIEZORESISTORS

    By

    ROBERT DIEME

    A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

    OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

    UNIVERSITY OF FLORIDA

    2009

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  • 2009 Robert Dim

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  • To my father and mother.

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  • ACKNOWLEDGMENTS

    I would like to thank my advisor, Dr. Toshikazu Nishida, for his guidance and

    encouragement. I also would like to express my gratitude to Dr. Mark Sheplak, Dr. Gijs

    Bosman, and Dr. Kevin Jones, for their ideas and encouragement. I would also like to thank Dr.

    Louis N. Cattafesta III for help with my experiments. I also thank Bryan L. Zachary, Nicholas

    G. Rudawski, Jack Y. Zhang, and all Interdisciplinary Microsystems Group (IMG) students for

    their help and support.

    I thank my father, mother, brother, sisters, and friends for their prayers, support, and

    encouragement through my study. Special thanks go to Rev. John D. Gillespie for his advice and

    all the people at St. Augustine Church. Finally, I thank God for all of the grace He gives me.

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  • TABLE OF CONTENTS page

    ACKNOWLEDGMENTS ...............................................................................................................4

    LIST OF TABLES...........................................................................................................................9

    LIST OF FIGURES .......................................................................................................................11

    ABSTRACT...................................................................................................................................17

    CHAPTER

    1 INTRODUCTION ..................................................................................................................19

    1.1 Motivation.....................................................................................................................19 1.2 Objective and Outline ...................................................................................................20

    2 BACKGROUND ....................................................................................................................22

    2.1 Test Vehicle: Piezoresistor............................................................................................22 2.1.1 Computation of Piezoresistor Resistance under Non-Degenerate

    Approximation ..................................................................................................23 2.1.1.1 Resistance computation with uniform carrier concentration under

    non-degenerate approximation ...........................................................24 2.1.1.2 Resistance computation with non-uniform carrier concentration

    under non-degenerate approximation .................................................24 2.2 MEMS Piezoresistive Microphone ...............................................................................26

    2.2.1 MEMS piezoresistive Microphone Voltage Output..........................................26 2.2.2 MEMS Piezoresistive Microphone Sensitivity .................................................27 2.2.3 MEMS Piezoresistive Microphone Minimum Detectable Signal.....................27

    2.3 Noise and Noise Power Spectral Density......................................................................28 2.4 Noise Sources in Piezoresistor ......................................................................................29

    2.4.1 Electrical Thermal Noise...................................................................................29 2.4.2 Mechanical Thermal Noise ...............................................................................30 2.4.3 Low Frequency Noise .......................................................................................30

    2.4.3.1 Hooges model....................................................................................31 2.4.3.2 McWhorters model............................................................................32

    2.4.4 Shot Noise .........................................................................................................33 2.5 Defects in Semiconductors............................................................................................34

    2.5.1 Bulk Defects......................................................................................................34 2.5.2 Interface Traps ..................................................................................................35

    2.6 Process Dependence of 1/f Noise..................................................................................36 2.7 Summary .......................................................................................................................38

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  • 3 PIEZORESISTOR DESIGN ..................................................................................................41

    3.1 Introduction...................................................................................................................41 3.1.1 Piezoresistor Design with Uniform Doping Concentration ..............................41 3.1.2 Piezoresistor Design with Gaussian Non-Uniform Doping Concentration ......42 3.1.3 Fabrication Non-Idealities.................................................................................43

    3.1.3.1 Transient enhanced diffusion (TED) ..................................................43 3.1.3.2 Oxidation enhanced diffusion (OED).................................................44 3.1.3.3 Impurity segregation...........................................................................44

    3.1.4 Fundamental Physics That Affect Electrical Activation of Impurities .............45 3.2 Piezoresistor Design Parameters ...................................................................................47

    3.2.1 Piezoresistor Impurity Profile ...........................................................................47 3.2.2 Piezoresistor Resistance ....................................................................................47 3.2.3 Piezoresistor Surface Area ................................................................................48 3.2.4 Piezoresistor Volume ........................................................................................48

    3.3 Test Structures Design ..................................................................................................48 3.4 Boron Profile Simulations.............................................................................................49

    3.4.1 Analytical Calculation.......................................................................................49 3.4.2 Limited Source Diffusion: Ion Implantation.....................................................49 3.4.3 Annealing After Ion implantation .....................................................................50 3.4.5 Florida Object Oriented Process Simulator (FLOOPS) ....................................51

    3.4.5.1 Simplest FLOOPS (Fermi model) ......................................................52 3.4.5.2 More accurate FLOOPS (Pair model) ................................................52

    3.5 P-type Piezoresistor Implant and Annealing Condition................................................52 3.5.1 Piezoresistor Generation 1 (PG1)......................................................................52 3.5.2 Piezoresistor Generation 2 (PG2)......................................................................54

    3.5.2.1 Boron implanted piezoresistors at 20 keV with a dose 7x1014 cm-2...55 3.5.2.2 Boron implanted piezoresistors at 40 keV with a dose 7x1014 cm-2

    through SiO2 .......................................................................................56 3.5.2.3 Boron solid source diffused piezoresistors for 25 min at 950 C.........56 3.5.2.4 Boron solid source diffused piezoresistors for 25 min at 950 C

    followed by phosphorus solid source diffusion for 5 min at 800 C....57 3.6 Additional Test Structures.............................................................................................57

    3.6.1 P-type Capacitor................................................................................................57 3.6.2 P/N Diode..........................................................................................................58 3.6.3 Van der Pauw Structure ....................................................................................59 3.6.4 Carrier Concentration Test Structures...............................................................59

    3.6.4.1 Spreading resistance technique...........................................................60 3.6.4.2 Secondary ion mass spectroscopy (SIMS) technique.........................60 3.6.4.3 Capacitance-voltage technique ...........................................................60 3.6.4.4 Hall measurement technique...............................................................61

    3.7 Summary .......................................................................................................................62

    4 EXPERIMENTAL METHOD................................................................................................78

    4.1 Piezoresistor Experimental Methods.............................................................................78 4.1.1 Piezoresistor I-V Measurement.........................................................................78

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  • 4.1.2 Piezoresistor No