Measurement of Adhesion Using the Island Blister Test by Scott Anthony Skorski B.S., Metallurgy, Columbia University 1987) M.S., Materials Engineering, M.I.T. 1989) Submitted to the Department of Materials Science and Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Materials Science and Engineering at the Massachusetts Institute of Technology May 1994 (D 1994 Massachusetts Institute of Technology All rights reserved / Signature of A uthor ................................................ 5(cid:1) ....................................... f ..................... Department of Materials Science and Engineering April 29, 1994 Ce rtified b y ................................................................................ ... ........ . ......... r erick J. McGarry Professor of Polymer Engineering Thesis Supervisor Ce rtified b y .................................................................. ... . .................I. ......................... C/ Stephen D. Senturia. Barton L. Weller Professor of Electrical Engineering Thesis Sunervisor A ccep ted b y ............................................................. ................................ ...... Carl V T ompson 11 Professor of Electronic Materials Chair, Department Committee on Graduate Students MASSACHOSMS INSTITUTF I AUG 1 8 1994 Measurement of Adhesion Using The Island Blister Test by Scott Anthony Sikorski submitted to the Department of Materials Science and Engineering on April 29, 1994 in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Materials Engineering Abstract This thesis focuses on the refinement and application of the island blister test (IBT) initially proposed and demonstrated by Allen and Senturia. to the measurement of the specific interfacial fracture energy of polyimides (hexafluorodianhydride- aminophenoxybiphenylin (HFDA-APBP), pyromellitic dianhydride-oxydianiline (PMDA-ODA), and biphenyldianhydride-phenyldiamine (BPDA-PDA)) to metals (Cr and Al). A finite element model developed by Margaritis using the modified crack closure technique provides an analysis of the debonding process. The mode I and mode 11 contributions along with the plastic dissipation are separately calculated through the model. A new sample fabrication process was developed to produce circular blister sites at yields approaching I 0%. Refinements in the testing methodology increase testing reproducibility and testing yield. Reproducibility is 13%, in close agreement with the ± 15% predicted based on an error analysis of the test. The mode I component of the specific fracture energy is found to provide a criterion for the onset of fracture. This result, found long ago for elastic fracture in homogeneous bodies, is original for the case of interfacial decohesion in the presence of extreme plastic dissipation. The error analysis resulted in a numerically derived relationship that describes they,, in terms of the experimental parameters and elastic constants of the adhered film. Adhesion to Cr ,vas found in all cases to be superior than to Al. X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning electron microscopy were used to explored the nature of the fracture surfaces. The locus of failure of all the polyimides studied on Cr was cohesive in the polymer. When debonded from an Al adherend, the locus of failure was a combination of cohesive in the polyimide and adhesive at the interface between the polyimide and oxidized aluminum. This combination is consistent with the lower measured debond energies. It was found that processing effects can strongly influence , The locus of failure produced by the peel testing the same systems was nearly identical to those described above for the IBT. An attempt was made to evaluate the measured peel energies in terms of the plastic analysis of Kim and Avaras. An exploratory study of the application of the IBT to metal on polymer systems is reported. Thesis Supervisors: Dr. Frederick J. McGarry Professor of Polymer Engineering Dr. Stephen Senturia Barton L. Weller Professor of Electrical Engineering 2 Table of Contents Abstract .......................................................................................................................... 2 Table of Contents ........................................................................................................... 3 List of Figures ................................................................................................................ 5 List of Tables .................................................................................................................. 8 Acknowledgm ents ........................................................................................................ 10 1. Introduction ............................................................................................................. 12 1 I Advantages and Challenges of Thin-Film Multichip Packaging .................. 12 1.2 Me thods of Adhesion Testing ..................................................................... 16 1.3 Blister Tests ............................................................................................... 20 1.4 Objectives and Scope of Thesis .................................................................. 25 2. Experim ental M ethods ............................................................................................. 27 2.1 M echanical Properties ................................................................................ 27 2.1.1 Constitutive Behavior .................................................................. 27 2.1.2 Residual Stress M easurem ent ....................................................... 3 2.2 The Island Blister Test ................................................................................ 35 2.2.1 Samp le Fabrication Process. ........................................................ 35 2.2.2 Testing M ethodology ................................................................... 43 2.3 The Peel Test .............................................................................................. 48 3. Analysis of the Island Blister Test ............................................................................ 5 1 3.1 Introduction ................................................................................................ 51 3.2 The Finite Elem ent M odel .......................................................................... 57 3.3 Error Analysis ............................................................................................ 66 3.4 Test'Lim itations ......................................................................................... 68 4. Me asurem ent of Specific Fracture Energy ................................................................ 74 4.1 Island Blister Test Results .......................................................................... 74 4. 1.1 Criterion for Fracture ................................................................... 75 4.1.2 Film Stress During Testing .......................................................... 78 4.1.3 The Dependency of y,,,o n the Inner Radius .................................. 85 4.2 Peel 'rest Results. ....................................................................................... 92 3 4.3 M etal on Polym er System s ....................................................................... 100 4.4 Discussion ................................................................................................ 104 5. Locus of Failure Analysis ...................................................................................... III 5.1 Introduction .............................................................................................. 112 5.2 HFDA-APBP on M etals ........................................................................... 116 5.2.1 HFDA-APBP Reference Spectra ................................................ 116 5.2.2 HFDA-APBP on Chromi um ...................................................... 118 5.2.3 HFDA-APBP on Alumi num ...................................................... 130 5.3 PM DA-ODA on M etal ............................................................................. 138 5.3.1 PM DA-ODA Reference Spectra ................................................ 138 5.3.2 PM DA-ODA on Chrom ium ....................................................... 143 5.3.3 PMD A-ODA on Alumi num ....................................................... 147 5.4 BPDA-PDA on M etal ............................................................................... 162 5.4.1 BPDA-PDA Reference Spectra .................................................. 162 5.4.2 BPDA-PDA on Chrom ium ........................................................ 164 5.4.3 BPDA-PDA on Alum inum ........................................................ 168 5.5 Sum m ary .................................................................................................. 174 6. Conclusions and Sum m ary ..................................................................................... 176 Appendix A : IBT Samp le Fabrication Details ............................................................. 183 Appendix B: Polyim ide Cure Schedules ...................................................................... 185 Appendix C: IBT Testing Procedure ........................................................................... 186 Appendix D : C Program for Creating ABAQUS Input Decks ..................................... 189 Appendix E: Sample Xess Spreadsheet for Calculating Specific Fracture Energies ..... 193 Bibliography ............................................................................................................... 194 4 List of Figures 1.1.1 One possible variation of the thin film multi-chip module ................................ 12 1.1.2 Interfaces typical in thin film structures ........................................................... 13 1.2.1 Illustration of adhesion testing techniques applied to thin flm systems ............ 17 1.3.1 Illustrations of the geometries of various blister tests ....................................... 21 2.1.1 Stress strain curves for P12545, PI261 1, and LJD4212 ...................................... 30 2.1.2 Geometry of load deflection samples ................................................................ 3 2.2.1 Fabrication process for polymer-on-metal IBT samples. ................................... 37 2.2.2 Fabrication process for metal-on-polymer IBT samples .................................... 38 2.2.3 Photograph of IBT wafer after completion of PD2721 backside processing ..... 42 2.2.4 Photograph of Teflon fixture for HF-based backside etching process ............... 42 2.2.5 Photograph of completed polymer-on-metal IBT sample ready for testing ....... 42 2.2.6 Schem atic of IBT testing apparatus .................................................................. 44 2.2.7 Photographs of IBT testing apparatus ............................................................... 45 2.2.8 Schem atic of retaining pin concept ................................................................... 46 2.2.9 Example of automated pressure control ............................................................ 47 2.3.1 Schem atic of peel test apparatus ....................................................................... 49 3.2.1 Schem atic of tw o crack tip elem ents ................................................................ 58 3.2.2 Stress-strain behavior for polyimides with piecewise-linear representation ....... 61 3.2.3 Displacement versus reaction force at first node released ................................. 63 3.2.4 Vertical deflection as a function of radial position ............................................ 65 3.3.1 Behavior of UD4212 film under uniaxial tension ............................................. 69 3.4.1 Design space for UD4212 on Cr and ACr ....................................................... 72 3.4.2 Design space for P12611 and P12545 on ACr .................................................. 73 4.1.1 Stresses and strains versus radial position in UD4212-Cr IBT sample .............. 79 4.1.2 Peel angle as a function of film thickness ......................................................... 80 5 4.1.3 Stress contours from P12545 on Cr and on Al .................................................. 81 4.1.4 M ises stress in UD 4212-Cr sam ple ................................................................... 84 4.1.5 Calculated Mode I specific fracture energy as a function of inner radius for several system s ................................................................................................. 86 4.1.6 Stress-strain behavior of UD4212 under cyclic loading beyond its initial yield point ................................................................................................................. 88 4.1.7 Modified model of constitutive relationship for UD4212 ................................. 89 4.2.1 Schematic of peel test geometry showing peel angleeB 93 .................................... 4.2.2 Breakdown of measured peel energy into plastic and specific fracture energy contributions for U D 4212-Cr ........................................................................... 96 4.2.3 Specific fracture energies from peel test data with film plasticity ..................... 97 4.3.1 Schematic of metal-on-polymer IBT with polyimide backing layer ................ 101 4.3.2 Alternate structure of metal-on-polymer IBT with polyimide backing layer ... 102 5.1.1 Schematic of fracture surface terminology ..................................................... 114 5.2.1 Chemical repeat units of the polyimides investigated ..................................... 117 5.2.2 H FD A -A PBP reference spectra ...................................................................... 119 5.2.3 Carbon (Is) spectra of HFDA-APBP on "high quality" Cr ............................. 121 5.2.4 Carbon (Is) spectra of HFDA-APBP on "low quality" Cr ............................... 125 5.2.5 Carbon (Is) spectra of HFDA-APBP on Cr peel fracture surfaces .................. 128 5.2.6 Carbon (Is) spectra of HFDA-APBP on Al Cr IBT fracture surfaces .............. 131 5.2.7 Aluminum (2p) spectra of HFDA-APBP on A]Cr fracture surfaces ............... 134 5.2.8 Carbon (Is) spectra of HFDA-APBP on AlCr peel fracture surfaces ............... 135 5.2.9 SEM micrographs of adherend side of HFDA-APBP on AlCr fractures ......... 136 5.3.1 PM DA- ODA reference spectra ....................................................................... 142 5.3.2 Carbon (Is) spectra of PMDA-ODA on Cr IBT fracture surfaces ................... 144 5.3.3 Oxygen (Is) spectra of PMDA-ODA on Cr fracture surfaces ......................... 145 5.3.4 Carbon (I s) spectra of PMDA-ODA on Cr peel fracture surfaces ................... 148 6 5.3.5 Fluorine and aluminum spectra of PMDA-ODA on Al IBT fracture surfaces. 150 5.3.6 Carbon (I s) spectra of PMDA-ODA on Al-containing metallurgies ............... 153 5.3.7 SEM micrographs of PMDA-ODA on AlCr fracture surfaces ........................ 156 5.3.8 AES depth profile of PMDA-ODA on AlCr "feature. . .................................... 157 5.3.9 AES depth profile of PMDA-ODA on AlCr matrix ........................................ 158 5.4.1 BPD A-PDA reference spectra ........................................................................ 165 5.4.2 Carbon (Is) spectra of BPDA-PDA on Cr fracture surfaces ............................ 166 5.4.3 Carbon (Is) spectra of BPDA-PDA on AlCr IBT fracture surfaces. ................ 169 5.4.4 SEM micrographs of substrate side of BPDA-PDA on AlCr peel fracture su rfaces .......................................................................................................... 17 1 5.4.5 Carbon (Is) spectra of BPDA-PDA on ACr peel fracture surfaces ................ 172 7 List of Tables 1.1.1 Summary of relationships used to evaluate standard blister test data ................. 22 2.1.1 Mechanical properties of polyimide films ........................................................ 29 2.1.2 Residual stresses in films as a function of flm thickness and substrate m etallization .................................................................................................... 34 3.3.1 Estimated errors in experimental parameters .................................................... 67 3.4.1 Table of constants for materials under investigation ......................................... 71 4.1.1 Summary of IBT data as a function of film thickness ....................................... 76 4.1.2 Demonstration of the reproducibility of the IBT ............................................... 77 4.1.3 Maximum von Mises stress at element centroids in adhered films for polym er-on-m etal systems ................................................................................ 83 4.1.4 The effect of mechanical properties assumptions on the FEA calculated specific fracture energies for representative systems. ..................................................... 85 4.2.1 Com pilation of peel test adhesion data ............................................................. 94 5.1.1 Summary of polyimide to metal adhesion data ............................................... III 5.1.2 X PS scan param eter set .................................................................................. 115 5.2.1 Peak assignments and energy levels for HFDA-APBP reference spectra ........ 118 5.2.2 Peak assignments and energy levels for HFDA-APBP on Cr .......................... 122 5.2.3 Stoichiornetry of HFDA-APBP systems ......................................................... 124 5.2.4 Peak assignments and energy levels for HFDA-APBP on Cr peel fracture su rfaces ........................................................................................................... 12 9 5.2.5 Peak assignments and energy levels for HFDA-APBP on AlCr ...................... 132 5.3.1 Theoretical bond assignments and energy levels for PMDA-ODA ................. 140 5.3.2 Summary of XPS results for PMDA-ODA systems ........................................ 141 5.3.3 Peak assignments and energy levels for PMDA-ODA on Cr ........................... 146 5.3.4 Peak assignments and energy levels for PMDA-ODA on Al ........................... 151 5.3.5 Summary, of peak positions and relative intensities for PM D A O D A on A lCr .............................................................................. 159 8 5.4.1 Theoretical bond assignments and energy levels for BPDA-PDA ................... 163 5.4.2 Summary of film stoichiometries for BPDA-PDA systems. ............................ 164 5.4.3 Peak assignments and energy levels for BPDA-ODA on Cr ........................... 167 5.4.4 Peak assignments and energy levels for BPDA-PDA on ACr ........................ 170 6.1.1 Relative rankings of adhesion in the material systems studied based on the IBT and the peel test .............................................................................................. 18 1 9 Acknowledgments Several people and organizations contributed greatly to the success of this work. First, my advisors Prof. S.D. Senturia and Prof. F.J. McGarry are warmly acknowledged for their support and guidance over the past several years. The encouragement of Prof. McGarry during the difficult early years instilled the confidence in myself necessary to complete this work and is deeply appreciated. This work was completed through the Resident Work Study program of my employer, the IBM Corp., who provided financial support in the form of tuition and stipend payment. I would like to thank the management team at IBM who supported my application to this program. Especially appreciated are the efforts of Pete Hayunga without whose persistent support none of this would have been possible. Also recognized are Dr. Thomas Redmond, Linda Herman-Spiro, and Dr. John Knickerbocker for their continued support. The financial assistance provided by the Electronics Packaging Program in the form of laboratory and computer usage fees is also greatly appreciated. George Margaritis has been both a great friend and a tremendous source of information to me who started this work with little understanding of the world of fracture mechanics. George also developed the finite element analysis of the island blister test, without which none of the subsequent understanding would have been possible. Mark Brillhart and Ed Shaffer will be warmly remembered not only for their stimulating comments but also for their friendship which created a amiable work environment. David Volfson provided much technical assistance in the early days, especially with regard to mask design and the IBT fabrication process. Fred Trusell trained me in the use of much of the laboratory equipment and assisted with modification of the testing apparatus. As a 10