UCLA UCLA Electronic Theses and Dissertations Title Kinetic Modeling of Halogen-Based Plasma Etching of Complex Oxide Films and its Application to Predictive Feature Profile Simulation Permalink https://escholarship.org/uc/item/8bs858h7 Author Marchack, Nathan Publication Date 2012 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA Los Angeles Kinetic Modeling of Halogen-Based Plasma Etching of Complex Oxide Films and its Application to Predictive Feature Profile Simulation A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Chemical Engineering by Nathan Philip Marchack 2012 ABSTRACT OF THE DISSERTATION Kinetic Modeling of Halogen-Based Plasma Etching of Complex Oxide Films and its Application to Predictive Feature Profile Simulation by Nathan Philip Marchack Doctor of Philosophy in Chemical Engineering University of California, Los Angeles, 2012 Professor Jane P. Chang, Chair In this work, a comprehensive framework for predicting etching behavior is developed using the test case of hafnium lanthanate (HfxLayOz) in Cl2/BCl3 chemistry, starting from detailed thermodynamic analysis in the form of volatility diagrams. Through these calculations, it was predicted that at typical plasma reactor operating pressures, the reactions of molecular Cl2 and Cl radicals with La2O3 and HfO2 could generate sufficiently high partial pressures of OxCly for measurable material removal to occur. The etch rate of Hf0.25La0.12O0.63 as a function of ion energy was characterized in situ using a quartz crystal microbalance. The etch rate data was found to exhibit a dual ion energy dependence with a maximum etch rate of ~27 Å/min at Eion = 175 eV. The overall etch rate was found to be approximately half that of a pure HfO2 film etched at the same conditions, due to the formation of non-volatile LaClx compounds. ii QMS measurements of HfLaO in Cl2 chemistry showed LaOCl and LaCl as the primary La-containing etch products. XPS analysis of pure La2O3 films provided further evidence of this hypothesis, showing significant Cl retention (~10%) compared to HfLaO and also revealing the presence of Cl-O-La bonding. A kinetics-based bulk scale (TML) model was fit to the aforementioned experimental data and good agreement was shown between the TML model’s simulated results and etch rate data. An additional degree of validation was provided through a comparison of the model's predicted composition of the surface mixing layer and the XPS- measured film compositions after plasma exposure. The final validation of this approach was to assess the fitted kinetic parameters for complex oxide etching in Cl-based chemistry (such as reaction rate coefficients, threshold energies and sticking probabilities) at feature scale levels. The results from the TML model were coupled to a Monte Carlo based feature profile simulator and used to predict the variation of the etched feature profiles of Hf0.25La0.12O0.63 films for varying aspect ratios (1.5, 3 and 6) and ion energies (75, 100 and 175 eV). In order to compare to experimental results, features of varying aspect ratio were achieved using an e-beam tool to pattern a ZEP520A photoresist mask on HfLaO followed by etching in Cl2. Good agreement was achieved with the etched profile at 100 eV and AR = 5. As a test of the model's ability to handle variations in gas chemistry with a material system besides that of high-k dielectrics, this methodology was also applied to the shallow trench isolation process (Si etching in Cl2/O2 chemistry). The model showed good fitting of the major process parameters (etch rate, etch product ratios and surface composition) and showed an ability to predict the profile variation with 0, 2, 6 and 8% oxygen addition to a pure Cl2 plasma for the etching of Si. iii The dissertation of Nathan Philip Marchack is approved. Puneet Gupta Robert F. Hicks Yunfeng Lu Jane P. Chang, Committee Chair University of California, Los Angeles 2012 iv TABLE OF CONTENTS CHAPTER 1: INTRODUCTION ............................................................................................. 1 1.1 Motivation ........................................................................................................................ 2 1.2 Complex Materials and Architecture ............................................................................. 12 1.3 Halogen-Based Plasma Etching of Oxide Materials ...................................................... 22 1.4 Shallow Trench Isolation (STI) ...................................................................................... 27 1.5 Thermodynamic Assessment.......................................................................................... 29 1.6 Plasma Modeling ............................................................................................................ 33 1.7 Kinetic-Based Modeling of the Plasma/Surface Interactions ........................................ 35 1.8 Cell-Based Monte Carlo Feature Profile Simulation ..................................................... 42 1.9 Scope and Organization ................................................................................................. 46 CHAPTER 2: EXPERIMENTAL SETUP ............................................................................. 48 2.1 UHV Transfer Tube and Load Lock .............................................................................. 48 2.2 ICP Plasma Etcher .......................................................................................................... 50 2.3 Material Systems For Logic Applications ...................................................................... 53 2.4 Plasma Diagnostics ........................................................................................................ 57 2.5 Surface Characterization ................................................................................................ 69 2.6 Theoretical Methods ....................................................................................................... 78 CHAPTER 3: IN-SITU ETCH STUDY OF HfxLayOz IN Cl2/BCl3 PLASMA .................... 105 3.1 Etch Rate Quantification .............................................................................................. 106 3.2 Etch Rate of HfLaO/La2O3 as a Function of Ion Energy in Cl2 Plasma ...................... 113 3.3 Comparison with Etch Rate of HfLaO/La2O3 in BCl3 Chemistry ................................ 120 3.4 Comparison with Ex-Situ Measurements ..................................................................... 124 3.5 Etch Products of La2O3 in Cl2 and BCl3Plasmas ......................................................... 127 3.6 Surface Composition of HfxLayOz and La2O3 Post- Cl2 /BCl3 Exposure ..................... 132 3.7 Summary and Analysis of HfxLayOz Etch Rate and Mechanisms ............................... 143 CHAPTER 4: KINETICS-BASED MODELING OF COMPLEX OXIDE FILMS ............ 145 4.1 Phenomenological Modeling of HfLaO Etch Behavior ............................................... 145 4.2 Translating Mixed Layer Model Adaptation ................................................................ 155 4.3 Summary of TML Modeling of Cl2 Etching ................................................................ 166 CHAPTER 5: EXTENSION TO FEATURE SCALE MODELING ................................... 168 5.1 Patterning Features on HfxLayOz/La2O3 Films ............................................................. 168 5.2 MC Predictions of HfxLayOz Aspect Ratio and Ion Energy Dependence .................... 171 5.3 Comparison of Different Material Systems - HfO2 vs. HfLaO .................................... 177 5.4 Comparison of MC Modeling with Experimental Profiles .......................................... 179 5.5 Application to Shallow Trench Isolation (STI) ............................................................ 180 5.6 Summary of Feature Profile Modeling......................................................................... 189 CHAPTER 6: SUMMARY................................................................................................... 190 APPENDICES ............................................................................................................................ 193 BIBLIOGRAPHY ....................................................................................................................... 297 v LIST OF FIGURES Figure 1.1 (a) A simplified cross-sectional view of a metal-oxide semiconductor field-effect transistor (MOSFET); key parameters are labeled along with their constant-field scaling factor (λ). L, W, tox, and xj are the gate length, width, dielectric thickness, and junction depth, respectively. VGS, VDS, and IDS are the gate voltage, drain voltage, and drain current, respectively, and N(A/D) is dopant concentration. A shallow trench isolation (STI) is also shown with labeled features: top and bottom sidewall angles (SWA), trench width (D) and trench depth (tx) . (b) The material evolution and (c) the geometric advancement of a 3D tri-gate structure to further enable device scaling. ................................................................................................................................. 3 Figure 1.2 (a) High aspect ratio trenches in relation to one of the world’s tallest freestanding structures, Taipei 101, (b) a schematic of high-aspect ratio holes for 3D flash memory technology showing the complexity