ADDITIVES SCREENING TECHNIQUES AND PROCESS CHARACTERIZATION FOR ELECTROPLATING OF SEMICONDUCTOR INTERCONNECTS by LINDSAY ERIN BOEHME Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Dissertation Advisor: Professor Uziel Landau Department of Chemical Engineering CASE WESTERN RESERVE UNIVERSITY August, 2014 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Lindsay Erin Boehme candidate for the Doctor of Philosophy degree*. (signed) Prof. Uziel Landau (chair of the committee) Prof. Rohan Akolkar Prof. Heidi Martin Prof. Daniel Scherson Prof. Robert Preisser (Date) April 21, 2014 *We also certify that written approval has been obtained for any proprietary material contained therein. Dedicated to my loving husband, Aleks, for standing by my side through this adventure and being my biggest supporter. Table of Contents List of Tables………………………………………………………………………………………………………………... iv List of Figures……………………………………………………………………………………………………………….. v Acknowledgements……………………………………………………………………………………………………. xvi List of Symbols…………………………………………………………………………………………………………... xvii Abstract…………………………………………………………………………………………………………………….… xx Chapter 1: Introduction……………………………………………………………………………………………. 1 Chapter 2: Experimental Methodology .......................................................................... 8 2.1 Experimental Set-up ............................................................................................. 8 2.2 Electrochemical Characterization Techniques ................................................... 10 2.2.1 The Polarization Study ................................................................................ 10 2.2.2 The Injection Study ..................................................................................... 11 2.2.3 Coupon Plating ............................................................................................ 15 2.3 Materials Characterization Techniques ............................................................. 17 2.3.1 Focused Ion Beam (FIB) .............................................................................. 17 2.3.2 Scanning Electron Microscopy (SEM) ......................................................... 18 2.3.3 Four-Point Probe Resistivity Measurement ................................................ 18 Chapter 3: New and Improved Screening Techniques for Identifying Effective Additives for Bottom-up Fill .............................................................................................. 22 3.1 New Screening Technique .................................................................................. 27 3.2 Extending the Polarization Test to Via Fill Capability ......................................... 30 3.2.1 Developing an Expression for Via Fill Capability ......................................... 30 3.2.2 Predicting Via Fill Capability ........................................................................ 36 3.2.3 Effect of Trench Aspect Ratio and Feature Loading on Via Fill ................... 40 i 3.2.4 Comparison of Predicted Trench Fill to Experimental Data ....................... 41 3.3 Polarization Required by a Suppressor for Via Fill ............................................. 43 3.4 Conclusions......................................................................................................... 46 Chapter 4: The Effect of Transport and Electrolyte Circulation on Bottom-up Fill ..... 49 4.1. Co-injection Model ............................................................................................. 52 4.1.1. Transport and Adsorption of Additives onto a Flat Copper Surface .......... 52 4.1.2. Conversion of Surface Coverage into Voltage Transient ............................ 60 4.1.3. Results and Discussion of Co-injection Model ............................................ 61 4.2. Effect of Flow on Bottom-Up Fill ........................................................................ 68 4.2.1. Transport and Adsorption of Additives Inside a Via ................................... 68 4.2.2. Modeling Additives Distribution Inside a Via using Literature Parameters 72 4.2.3. Modeling Additives Distribution Inside a Large (0.1 µm diameter) Via with Co-injection Parameters ............................................................................................. 79 4.2.4. Modeling Additives Distribution Inside a Small (40 nm diameter) Via with Co-injection Parameters ............................................................................................. 84 4.3. Conclusions......................................................................................................... 87 Chapter 5: Temperature Effects on Additives Induced Polarization in Copper Electroplating of Interconnects ........................................................................................ 92 5.1. Results and Discussion ....................................................................................... 94 5.1.1 Potential Transient in Copper Plating in the Presence of PEG with Increasing Temperature ............................................................................................. 94 5.1.1. Plating Kinetics for Copper and PEG ......................................................... 105 5.2. Conclusions....................................................................................................... 112 Chapter 6: The Impact of Electrolyte Acidity on Bottom-Up Metallization of Copper Interconnects .................................................................................................................. 116 6.1 Results and Discussion ..................................................................................... 117 ii 6.2.1. Electrochemical Behavior ......................................................................... 117 6.2.2. Predicted Bottom-up Fill Capability .......................................................... 122 6.2.3. Gap-fill Performance ................................................................................. 123 6.2.4. Seed Layer Stability ................................................................................... 125 6.2.5. Current Distribution Across A Wafer ........................................................ 128 6.2 Conclusions....................................................................................................... 132 Chapter 7: Dependence of Suppressor Inhibition on the Halogen Ion ...................... 135 7.1 Results and Discussion ..................................................................................... 137 7.1.1 Substitution for Chloride Ion .................................................................... 137 7.1.2 Halogen Concentration Effects ................................................................. 142 7.2 Conclusions....................................................................................................... 145 Chapter 8: Characterizing the Effects of PEG Molecular Weight ............................... 148 8.1 Results and Discussion ..................................................................................... 151 8.1.1 Electrochemical Characterization Studies ................................................ 151 8.2 Conclusions....................................................................................................... 154 Chapter 9: Identification and Characterization of Commercially Available Compounds... .................................................................................................................. 156 9.1. Results and Discussion ..................................................................................... 158 9.1.1. Injection Studies ........................................................................................ 158 9.2. Conclusions....................................................................................................... 161 Chapter 10: Conclusions and Suggestions for Future Work ......................................... 163 10.1 Conclusions....................................................................................................... 163 10.2 Suggestions for Future Work ........................................................................... 165 Bibliography…………………………………………………………………………………………………….……..….168 iii List of Tables Table 2.1. Electrolyte details for acidity effect studies…………………………………………………. 9 Table 3.1. Predicted smallest via size that can be filled with the corresponding additive assuming a via + trench depth of 250 nm......................................................................... 38 Table 3.2. Predicted trench size that can be filled with the tested commercial suppressor. ........................................................................................................................ 43 Table 3.3. Predicted via diameter, D, that can be filled at a given feature loading, f. ..... 46 Table 4.1. Dimensionless parameters used to non-dimensionalize all equations for the co-injection simulation. .................................................................................................... 58 Table 4.2. Parameters used to simulate additive distribution for co-injection ............... 63 Table 4.3. Dimensionless parameters used for transport and adsorption equations for bottom-up fill simulation. ................................................................................................. 70 Table 4.4. Literature