SILICIDE-TO-SILICON SPECIFIC CONTACT RESISTANCE CHARACTERIZATION TEST STRUCTURES AND MODELS Natalie Stavitski The graduation committee consists of: Chairman: prof.dr.ir. J. van Amerongen University of Twente Secretary: prof.dr.ir. J. van Amerongen University of Twente Promoter: prof.dr.ir. R.A.M. Wolters NXP Semiconductors/ University of Twente Assistant promoter: dr. A.Y. Kovalgin University of Twente Referee: dr.ir. J.H. Klootwijk Philips Research Internal members: prof.dr.ir. A.J. Mouthaan University of Twente prof.dr. J. Schmitz University of Twente External members: prof.dr. K. Maex KU Leuven prof.dr.ir. J.W. Slotboom NXP Semiconductors/ TUDelft This research was funded by NXP Semiconductors. PhD thesis: University of Twente, The Netherlands. Title: SILICIDE-TO-SILICON SPECIFIC CONTACT RESISTANCE CHARACTERIZATION TEST STRUCTURES AND MODELS Author: Natalie Stavitski, M.Sc. ISBN: 978-90-365-2937-2 Copyright © 2009 by Natalie Stavitski, Enschede, the Netherlands All rights reserved. No part of this publication may be adapted in whole or in part without the prior written permission of the author. Printed at: Printservice Technical University of Eindhoven, the Netherlands ii SILICIDE-TO-SILICON SPECIFIC CONTACT RESISTANCE CHARACTERIZATION TEST STRUCTURES AND MODELS DISSERTATION to obtain the doctor’s degree at the University of Twente, on the authority of the rector magnificus, prof.dr. H. Brinksma on account of the decision of the graduation committee, to be publically defended on Thursday 3rd of December 2009 at 15.00 by Natalie Stavitski born on 15 March 1979 in Kemerovo (Soviet Union) iii This dissertation is approved by the promoter prof. dr. ir. R. A. M. Wolters and the assistant promoter dr. A. Y. Kovalgin iv To my mother Tatiana, my husband-to-be Mark and our lovely son Daniel v vi Contents 1 Introduction ......................................................................................... 1 1.1 Motivation of this work ................................................................ 2 1.1.1 Low resistance contacts for MOS devices............................ 2 1.1.2 Silicides are the materials of choice..................................... 2 1.1.3 The purpose of this work ...................................................... 5 1.2 Silicide-to-silicon contacts............................................................ 6 1.2.1 The Schottky barrier formation............................................ 6 1.2.2 Conduction mechanisms....................................................... 8 1.2.3 Ohmic contact and specific contact resistance .................. 10 1.3 Methods to obtain ρc ................................................................... 11 1.3.1 Shockley method................................................................. 12 1.3.2 Transmission line model by Scott....................................... 15 1.3.3 Cross-bridge Kelvin resistor .............................................. 18 1.4 Dopant concentration profiling ................................................... 20 1.4.1 Secondary ion mass spectrometry ...................................... 21 1.4.2 Spreading resistance profiling ........................................... 22 1.5 Outline of this thesis ................................................................... 23 1.6 References................................................................................... 24 2 TLM structures evaluation ............................................................... 27 2.1 Motivation................................................................................... 28 2.1.1 Background ........................................................................ 28 2.1.2 Preliminary experiments .................................................... 29 2.2 Test structures optimization........................................................ 30 2.3 Fabrication of optimized test structures...................................... 32 2.4 Results and discussion ................................................................ 34 2.4.1 TEM analysis...................................................................... 34 2.4.2 Verification for different silicide widths............................. 37 2.4.3 Fitting with the Scott method ............................................. 37 2.4.4 Deviating RcW values of NiSi-to-n-HDD contacts............. 40 2.4.5 Non-linearity of the I-V curves for low dopant levels ........ 41 2.4.6 RcW values at different temperatures ................................. 42 2.4.7 Measurement limits in terms of dopant concentration....... 43 2.5 Conclusions................................................................................. 44 2.6 Acknowledgements......................Error! Bookmark not defined. 2.7 References................................................................................... 45 3 Low ρc of NiSi and PtSi to Si............................................................. 47 3.1 The ρc of NiSi and PtSi to Si in a broad doping range................ 48 3.1.1 Motivation .......................................................................... 48 3.1.2 Experimental approach...................................................... 48 3.1.3 Results ................................................................................ 50 3.1.4 Discussion .......................................................................... 50 3.1.5 Conclusion.......................................................................... 54 3.2 Active dopant segregation........................................................... 55 3.2.1 Motivation .......................................................................... 55 3.2.2 Experimental approach...................................................... 56 3.2.3 Results and discussion........................................................ 56 3.2.4 Conclusion.......................................................................... 58 3.3 Impact of interface ...................................................................... 58 3.3.1 Motivation .......................................................................... 58 3.3.2 Experimental approach...................................................... 58 3.3.3 Results and discussion........................................................ 60 3.3.4 Conclusion.......................................................................... 61 3.4 Acknowledgments........................Error! Bookmark not defined. 3.5 References................................................................................... 62 4 The extraction of ρc using metal-to-metal CBKR structures......... 65 4.1 Motivation................................................................................... 66 4.2 Test structures description .......................................................... 67 4.3 Experimental............................................................................... 67 4.3.1 Test structures fabrication ................................................. 67 4.3.2 Measurement description ................................................... 69 x 4.4 Measurement results and discussion........................................... 70 4.4.1 Rk for square contacts with δU = δL................................... 70 4.4.2 Rk for square contacts with δU ≠ δL ................................... 71 4.4.3 Rk for round contacts......................................................... 72 4.5 ρc extraction using 1D- and 2D-model........................................ 74 4.6 ρc extraction by our approach...................................................... 76 4.6.1 Definition of general parameters ....................................... 77 4.6.2 Model description............................................................... 77 4.6.3 Model application .............................................................. 85 4.6.4 Comparison with a standard simulator.............................. 87 5 Silicide-to-silicon CBKR structures ................................................. 93 5.1 Motivation................................................................................... 94 5.2 Experimental approach............................................................... 94 5.3 Test structures fabrication........................................................... 96 5.4 Measurement results and discussion........................................... 98 5.5 Modeling................................................................................... 104 5.6 Conclusions............................................................................... 108 5.7 References................................................................................. 109 6 Summary and conclusions .............................................................. 111 Samenvatting ............................................................................................ 117 Acknowledgements................................................................................... 121 About the Author ..................................................................................... 127 xi xii 1 Introduction This chapter provides the relevant theoretical background for further reading. Silicide-silicon contacts and their technological importance are discussed. The motivation of this research is presented. The principle of metal-semiconductor contact formation based on generally-accepted conduction mechanisms is illustrated. The specific contact resistance, which is the important parameter for contact