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Investigation of Post-Plasma Etch Fluorocarbon Residue

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Investigation of Post-Plasma Etch Fluorocarbon Residue INVESTIGATION OF POST-PLASMA ETCH FLUOROCARBON RESIDUE CHARACTERIZATION, REMOVAL AND PLASMA-INDUCED LOW-K DAMAGE FOR ADVANCED INTERCONNECT APPLICATIONS Tamal Mukherjee, B.Sc., M.Sc. Dissertation Prepared for the Degree of DOCTOR OF PHILOSOPHY UNIVERSITY OF NORTH TEXAS May 2016 APPROVED: Oliver M. R. Chyan, Major Professor William E. Acree, Jr., Committee Member Francis D’Souza, Committee Member LeGrande Slaughter, Committee Member Michael Richmond, Chair of the Department of Chemistry Costas Tsatsoulis, Dean of the Toulouse Graduate School Mukherjee, Tamal. Investigation of Post-Plasma Etch Fluorocarbon Residue Characterization, Removal and Plasma-induced Low-k Damage for Advanced Interconnect Applications. Doctor of Philosophy (Chemistry-Analytical Chemistry), May 2016, 135 pp., 8 tables, 64 figures, references, 54 titles. Modern three-dimensional integrated circuit design is rapidly evolving to more complex architecture. With continuous downscaling of devices, there is a pressing need for metrology tool development for rapid but efficient process and material characterization. In this dissertation work, application of a novel multiple internal reflection infrared spectroscopy metrology is discussed in various semiconductor fabrication process development. Firstly, chemical bonding structure of thin fluorocarbon polymer film deposited on patterned nanostructures was elucidated. Different functional groups were identified by specific derivatization reactions and model bonding configuration was proposed for the first time. In a continued effort, wet removal of these fluorocarbon polymer was investigated in presence of UV light. Mechanistic hypothesis for UV- assisted enhanced polymer cleaning efficiency was put forward supported by detailed theoretical consideration and experimental evidence. In another endeavor, plasma-induced damage to porous low-dielectric constant interlayer dielectric material was studied. Both qualitative and quantitative analyses of dielectric degradation in terms of increased silanol content and carbon depletion provided directions towards less aggressive plasma etch and strip process development. Infrared spectroscopy metrology was also utilized in surface functionalization evaluation of very thin organic films deposited by wet and dry chemistries. Palladium binding by surface amine groups was examined in plasma-polymerized amorphous hydrocarbon films and in self-assembled aminosilane thin films. Comparison of amine concentration under different deposition conditions guided effective process optimization. A time- and cost-effective method such as current FTIR metrology that provides in-depth chemical information about thin films, surfaces, interfaces and bulk layers can be increasingly valuable as critical dimensions continue to scale down and subtle process variances begin to have a significant impact on device performance. © Copyright 2016 By Tamal Mukherjee All Rights Reserved ii ACKNOWLEDGEMENTS Looking back in time, I am grateful to all the influential people who have played key roles in my extraordinary journey at UNT graduate school. Without their invaluable advice, direction and support, this dissertation would not have been possible. Firstly, my deepest gratitude goes to Dr. Oliver Chyan for his excellent guidance, caring, patience, and providing me with an excellent atmosphere for doing research. His constant encouragement towards developing analytical mind and improving critical thinking served me grow both academically and professionally. His constructive criticism helped me recover when my steps wavered. I am thankful to work with a truly diverse and talented group of fellow graduate students in IEMR laboratory. Special acknowledgement extends to the ‘team IR’. Every past and present member of IEMR lab have contributed to my overall scientific training and skill development. I am privileged to have worked in high-impact research projects supported by leading semiconductor corporations. Hearty appreciation goes to the wonderful personnel at the stockroom and administrative office for always being super-helpful. Department of Chemistry at UNT deserves special gratitude for continued financial assistance in the form of teaching assistantships. My committee members also supported and encouraged me throughout the progress of this research. I cordially thank Samantha Tan and Alex Kabansky for their excellent supervision during my summer internship at Lam Research. I specially thank my hardworking parents for remaining patient, supportive and cheerful during my long graduate school venture. The final words go to my wonderful wife – Dipanwita – my support pillar who unconditionally stood by me during good and bad times. Thank you everyone again for your friendship, counsel and inspiration. May God bless you all. iii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS …………………………………………………………………...... iii LIST OF TABLES ……………………………………………………………………………... vii LIST OF ILUSTRATIONS ………………………………………………………………….... viii CHAPTER 1: INTRODUCTION ………………………………………………………...… 1 1.1 Development of Cu/Low-k Interconnects ……………………………………………. 1 1.2 Low Dielectric Constant Materials ………………………………………………...… 4 1.3 Principles of Plasma Etching ……………………………………………………...…. 6 1.4 Cu/Low-k Integration Challenges …………………………………………………... 11 1.5 References …………………………………………………………………………... 14 CHAPTER 2: INSTRUMENTATION …………………………………………………..… 18 2.1 Introduction ………………………………………………………………….……...... 18 2.2 Fourier Transform Infrared (FTIR) Spectroscopy ……………………….…….…..… 19 2.3 X-ray Photoelectron Spectroscopy (XPS) ………………………………………….... 28 2.4 Contact Angle ……………………………………………………………………........ 30 2.5 Scanning Electron Microscopy (SEM) ……………………………………….…….… 31 2.6 Fluoropolymer Deposition …………………………………………………….….…... 32 2.7 UV Irradiation and Wet Clean ……………………………………………….…….…. 32 2.8 Chemicals ……………………………………………………………………….…...... 33 2.9 References ………………………………………………………………………..…… 34 CHAPTER 3: CHARACTERIZATION OF MODEL FLUOROCARBON POLYMER .… 38 3.1 Introduction ……………………………………………………………………….…. 38 iv 3.2 Experimental ………………………………………………………………………… 40 3.3 Results …………………………………………………………………………….…. 41 3.4 Summary ………………………………………………………………………….…. 60 3.5 References ………………………………………………………………………....… 61 CHAPTER 4: UV-ASSISTED WET REMOVAL OF MODEL FLUOROCARBON POLYMER FILM ……………………………………………………………………….… 65 4.1 Introduction ……………………………………………………………………….…. 65 4.2 Experimental ………………………………………………………………………… 67 4.3 Results …………………………………………………………………………….,… 67 4.4 Summary ………………………………………………………………………….…. 81 4.5 References ………………………………………………………………………..,.… 82 CHAPTER 5: LOW-K DAMAGE ASSESSMENT OF ETCH, STRIP AND CLEAN PROCESES …..…………………………………………………………………………… 85 5.1 Introduction …………………………………………………………………………. 85 5.2 Evaluation of plasma process-induced dielectric damage of low-k trench structures 87 5.2.1 Experimental ……………………….………………………………………..… 87 5.2.2 Results ……..……………………….………………………………………..… 89 5.3 Development and Optimization of Various Strip Processes by MIR-IR Metrology 101 5.3.1 Experimental ………………………………………………………………...... 101 5.3.2 Results ……………………………………………………………………...…. 101 5.4 Correlation studies of electrical and infrared characterization of dielectric damage … 105 5.4.1 Experimental ………………………………………………………………….. 105 5.4.2 Results ………………………………………………………………………… 106 v 5.5 Summary …………………………………………………………………………….. 111 5.6 References …………………………………………………….…………………….. 111 CHAPTER 6: IR CHARACTERIZATION OF VARIOUS FUNCTIONALIZED THIN FILMS FOR IC FABRICATION APPLICATIONS ……………………………………… 114 6.1 Characterization of APTES thin films for Pd-loading application …………………. 114 6.1.1 Introduction …………………………………………………………….……... 114 6.1.2 Experimental ………………………………………………………………….. 116 6.1.3 Results ………………………………………………………………………… 117 6.2 Characterization of Hydrocarbon Thin Films for Diffusion Barrier Application …….. 125 6.2.1 Introduction …………………………………………………………………… 125 6.2.2 Experimental ………………………………………………………………….. 126 6.2.3 Results ………………………………………………………………………… 127 6.3 Summary ……………………………………………………………………………… 132 6.4 References …………………………………………………………………………….. 132 vi LIST OF TABLES Table 1.1. Representative list of varieties of low dielectric materials with reported k values and preferred deposition method ……………………………………………………………………... 5 Table 2.1. Infrared absorption bands from O impurity in silicon. FWHM = full width at half maxima …………………………………………………………………………………………. 25 Table 2.2. Potential applications of FTIR-assisted chemical bonding transformation mapping in IC fabrication process/material development …………………………………………………… 27 Table 3.1. Vibrational assignments of observed absorption band frequencies of MFP film …… 43 Table 3.2. Vibrational assignments of observed absorption band frequencies in differential spectrum of DNPH-derivatized MFP film ……………………………………………………… 47 Table 4.1. Comparison of atomic percentage concentration of MFP film before and after progressive UV/air irradiation ………………………………………………………………….. 71 Table 5.1. List of blanket wafers and plasma process descriptions inducing different degrees of dielectric damage ………………………………………………………………...……………. 106 Table 6.1. List of functionalized HC film samples and corresponding process descriptions ... 126 vii LIST OF ILLUSTRATIONS Figure 1.1. Illustration of hierarchical scaling of Cu-based BEOL in a typical multi-level chip cross section. Features not necessarily to scale ………….……………………………………….. 2 Figure 1.2. Schematic cross-section of interconnect RC circuit with parasitic capacitance ….…. 3 Figure 1.3. Schematic overview of lithographic etching
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