SpectroscopicEllipsometry AnalysisofNanoporous LowDielectricConstantFilms ProcessedviaSupercriticalCO2forNext-generationMicroelectronicDevices _____________________________________ Adissertation PresentedtotheFaculty oftheGraduateSchool UniversityofMissouri-Columbia _____________________________________ InPartialFulfillment OftheRequirementsfor theDegree DoctorofPhilosophy _____________________________________ By MaslinaT.Othman Dr.ShubhraGangopadhyay, DissertationSupervisor May2007 The undersigned, appointed by the dean of the Graduate School, have examined the dissertation entitled Spectroscopic Ellipsometry Analysis of Nanoporous Low Dielectric Constant Films Processed via Supercritical CO2 for Next-generation Microelectronic Devices presented by Maslina Tasrin Othman, a candidate for the degree of Doctor of Philosophy in Electrical and Computer Engineering, and hereby certify that, in their opinion it is worthy of acceptance. ____________________________________ Professor Shubhra Gangopadhyay ____________________________________ Professor Lex A. Akers ________________________________ Professor Suchismita Guha _________________________________ Professor Ping Yu ________________________________ Professor Rajesh Shende Acknowledgements First and foremost I would like to thank my dissertation supervisor, Professor Shubhra Gangopadhyay, who is supported me in every possible way being her guidance and ideas.Thank you for guiding me through out my PhD’s studies.Without her I would nothaveaccomplishedthis.Whatshetaughtmeisfarbeyondthisresearch itself. It is also a pleasure to acknowledge the assistance of Dr.Jorge Lubguban and his family throughoutmyPhDprogram. My gratitude also goes to the faculty and staff in the Department of Electrical Engineering at the University of Missouri-Columbia for contributing in one way or another to my studies.I would also like to thank to Tami Beatty and Betty Barfield for helpingmeinmanywaysthroughmyundergraduate,master andPh.Dstudies. Last but not least,I am very grateful to my family for supporting me in many ways. I am extremely thankful to my many friends who supported me through difficulties Iencounteredduringmyresearchand studies. ii Table of Contents Acknowledgements…………………………………………………………………..…...ii Listof Figures ………………………………………………………………………….....v ListofTables………………………………………………………………………….....vii Abbreviations……………………………………………………………………………viii Abstract………………………………………………………………………..…………..x Chapter1............................................................................................................................. 1 1.1 THE NEED FOR LOW-K MATERIALS.............................................................................................. 1 1.2 POSSIBLE MATERIAL USED AS INSULATOR LAYER ........................................................................ 3 1.3 INTRODUCING POROSITY TO LOWER K-VALUE.............................................................................. 5 1.4 SCCO2 TO GENERATE PORES ....................................................................................................... 6 1.5 SCCO2 PROCESS TO SOLVE LOW-K INTEGRATION ISSUES ........................................................... 7 1.6 PROBLEMS IN POROUS FILM CHARACTERIZATION ....................................................................... 8 1.7 VASE™ AS A GOOD MEASURING TECHNIQUE TO POROUS FILM................................................. 9 1.8 OBJECTIVE OF THE DISSERTATION ............................................................................................. 10 1.9 DISSERTATION ORGANIZATION.................................................................................................. 16 Chapter2........................................................................................................................... 18 2.1 SUPERCRITICAL CO2 PROCESS TO GENERATE POROUS FILM ..................................................... 18 2.2 SUPERCRITICAL OR VAPOR TREATMENT WITH HMDS TO REPAIR POROUS FILM ...................... 24 2.3 SUPERCRITICAL OR VAPOR TREATMENT WITH TMCS TO REPAIR POROUS FILM ....................... 28 2.4 OTHER APPLICATIONS USING SUPERCRITICAL FLUID TECHNOLOGY............................................ 30 Chapter3........................................................................................................................... 32 3.1 OVERVIEW ................................................................................................................................. 32 3.2 VARIABLE ANGLE SPECTROSCOPIC ELLIPSOMETRY................................................................... 33 3.2.1 Basic concepts: How do ellipsometers work? ...................................................................... 33 3.2.2 Ellipsometer Configuration .................................................................................................. 35 3.2.3 Reflection/refraction atthe planar interface ........................................................................ 36 3.2.4 Variable Angle Spectroscopic Ellipsometry (VASE™) Measurementand Analysis............. 43 3.3 ANALYTICAL METHOD USING SPECTROSCOPY ELLIPSOMETRY TO CHARACTERIZE THIN FILM..... 47 3.3.1 Cauchy layer......................................................................................................................... 47 3.3.2 Bruggeman Effective Medium Approximation (BEMA) layer .............................................. 47 3.3.3 Graded layer......................................................................................................................... 49 3.3.4 Surface roughness................................................................................................................. 49 3.3.5 Silicon substrate ................................................................................................................... 50 3.4 ELLIPSOMETRY MODELING FOR POROUS FILM .......................................................................... 50 3.5 FOURIER TRANSFORM INFRARED (FT-IR).................................................................................. 51 3.5.1 Absorbance, LambertBeer’s Law ........................................................................................ 52 iii 3.5.2 Quantitative spectralanalysis .............................................................................................. 55 3.6 CAPACITANCE-VOLTAGE (C-V) ELECTRICAL MEASUREMENT.................................................... 59 Chapter4........................................................................................................................... 60 4.1 OVERVIEW ................................................................................................................................. 60 4.1.1 Fabrication ofsacrificialporogen approach ....................................................................... 62 4.1.2 Description ofsamples used in this research ....................................................................... 63 4.2 THERMAL ANNEALING PROCESS................................................................................................. 64 4.3 SUPERCRITICAL CO2 PROCESS.................................................................................................... 65 4.3.1 High Pressure SCCO2 ExperimentalSystem ........................................................................ 65 4.3.2 SCCO2 treatmentprocedure................................................................................................. 67 4.4 EXPERIMENT PARAMETERS ........................................................................................................ 69 Chapter5........................................................................................................................... 70 5.1 OVERVIEW ................................................................................................................................. 70 5.2 IMPLEMENTED SPECTROSCOPIC ELLIPSOMETRY ANALYTICAL METHOD FOR CHARACTERIZING POROUS THIN FILM.................................................................................................................................... 71 5.3 SCCO2 WITH PULSING MODE TO REMOVE POROGEN EFFECTIVELY .......................................... 82 5.3.1 Overview............................................................................................................................... 82 5.3.2 ExperimentalProcedure....................................................................................................... 82 5.3.3 Results and Discussions........................................................................................................ 83 5.4 POROGEN AND WATER REMOVAL VIA SCCO2 ........................................................................... 85 5.4.1 Overview............................................................................................................................... 85 5.4.2 ExperimentalProcedure....................................................................................................... 86 5.4.3 Results and Discussions........................................................................................................ 86 5.5 SILYLATION (TMCS) TO RESTORE HYDROPHOBICITY IN POROUS FILM VIA SCCO2.................. 93 5.5.1 Overview............................................................................................................................... 93 5.5.2 ExperimentalProcedure......................................................................................................