Atomistic simulations of H2 and He plasmas modification of thin-films materials for advanced etch processes Vahagn Martirosyan To cite this version: Vahagn Martirosyan. Atomistic simulations of H2 and He plasmas modification of thin-films materi- als for advanced etch processes. Micro and nanotechnologies/Microelectronics. Université Grenoble Alpes, 2017. English. NNT : 2017GREAT101. tel-01803013 HAL Id: tel-01803013 https://tel.archives-ouvertes.fr/tel-01803013 Submitted on 30 May 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. 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THÈSE Pour obtenir le grade de DOCTEUR DE LA COMMUNAUTÉ UNIVERSITÉ GRENOBLE ALPES Spécialité : NANO ELECTRONIQUE ET NANO TECHNOLOGIES Arrêté ministériel : 25 mai 2016 Présentée par Vahagn MARTIROSYAN Thèse dirigée par Olivier JOUBERT, CNRS et codirigée par Emilie DESPIAU-PUJO, UJF préparée au sein du Laboratoire Laboratoire des Technologies de la Microélectronique dans l'École Doctorale Electronique, Electrotechnique, Automatique, Traitement du Signal (EEATS) Modification de matériaux en couches minces par plasmas H2 ou He : Simulations atomistiques pour procédés de gravure innovants Atomistic simulations of H2 and He plasmas modification of thin-films materials for advanced etch processes Thèse soutenue publiquement le 15 décembre 2017, devant le jury composé de : Monsieur Olivier JOUBERT Directeur de Recherche, CNRS, Directeur de thèse Monsieur Remi DUSSART Professeur, Université d'Orléans, Président Monsieur Jonathan MOUGENOT Maître de Conférences, Université Paris 13 , Examinateur Madame Emilie DESPIAU-PUJO Maître de Conférences, Université Grenoble Alpes, Co-directeur de thèse Monsieur Vasco GUERRA Professeur, IST Lisbonne, Portugal , Rapporteur Monsieur Gilles CARTRY Professeur, Université Aix-Marseille, Rapporteur Table of abbreviations ……………………………………………………………………………………….…………… 4 1. General introduction ……………………………………………………………………………………………… 5 1.1. The evolution of Microelectronics …………………………………………………………………………. 6 1.2. Low-temperature reactive plasmas ……………………………………………………………………….. 9 1.2.1. Structure of radio-frequency (RF) glow discharges ………………………………………… 10 1.2.2. Plasma sheath and directional ion bombardment …………………………………………. 12 1.3. Low-pressure plasmas for material processing in Microelectronics ………………………. 14 1.3.1. Surface reactions and Etching mechanisms …………………………………………………… 14 1.3.2. How to transfer a pattern into a material stack? …………………………………………… 15 1.4. Technological challenges of advanced plasma etching processes for next-generation transistors …………………………………………………………………………….. 18 1.4.1. Structure of advanced transistors (FinFET and FDSOI) ………………………………….. 18 1.4.2. Limitations of conventional plasma processes (CW-ICP and CCP) …………………. 21 1.4.3. Alternative plasma technologies for advanced etching processes ………………… 25 1.5. Light gases (H2/He) material modification for nanoscale precision etching .…..…….. 29 1.5.1. The Smart CutTM technology for SOI substrates preparation ……………………….. 29 1.5.2. The Smart Etch concept ………………………………………………………………………………. 30 1.5.2.1. Principle of the Smart Etch ……………………………………………………….. 31 1.5.2.2. Experimental implementation of the Smart Etch concept ………… 32 1.6. Molecular Dynamics simulations to assist process development …………………………. 35 1.7. Purpose of the study and organization of the PhD manuscript ……………………………. 36 2. Molecular dynamics simulations ………………………………………………………………………….. 38 2.1. MD: General principles ………………………………………………………………………………………… 39 2.1.1. Atomic motion ……………………………………………………………………………………………. 39 2.1.2. Interatomic potentials, ab-initio and classical MD ………………………………………. 40 2.1.3. Statistical physics ………………………………………………………………………………………… 41 2.1.4. Numerical integration …………………………………………………………………………………. 41 2.2. MD for modeling plasma-surface interaction ………………………………………………...……. 42 2.2.1. General concept of the model ……………………………………………………………...……. 43 2.2.2. Simulation of plasma species impacts …………………………………………………...…… 43 2.2.3. Simulation cell and periodic boundary conditions ………………………………………. 44 2.2.4. Thermalization ……………………………………………………………………………………………. 45 2.2.5. Timescale related problems ………………………………………………………………………… 46 2.2.6. Etch products ……………………………………………………………………………………………… 47 2.3. Modeling of Si-H-He and SiN-H-He interactions …………………………………………………… 48 2.3.1. Choice of the Si-H interatomic potential …………………………………………………….. 48 2.3.2. Choice of the Si-N-H interatomic potential …………………………………………………. 48 2.3.3. Choice of the Si/SiN-He interatomic potential ……………………………………..…….. 49 2.4. Preparation of the initial Si and SiN substrates ……………………………………………………. 49 2.4.1. Crystalline Si (100) substrate ……………………………………………………………..………. 49 2.4.2. Amorphous SiN substrate ……………………………………………………………..…………… 50 2.5. Encountered issues related to H2 and He interactions with Si and SiN ………………... 52 2.5.1. Timestep and cell size ………………………………………………………………………………… 52 2.5.2. Adequate runtime and capture of He and H2 desorption phenomena ……….. 53 2.6. Computational details and simulation parameters ……………………………………………… 56 2.6.1. Input plasma parameters …………………………………………………………………………… 57 1 2.6.2. Analysis of the substrate modification …………………………………………………..….. 60 3. Helium plasma modification of Si/Si3N4 thin films ……………………………...……………………... 63 3.1. Motivation and objectives of the study …………………………………………………...................... 63 3.2. Computational details …………………………………………………………………..…………………………... 64 3.2.1. Preliminary statistical studies ………………………………………………………...........………… 64 3.2.2. Conditions of simulation ………………………………………………………………………………….. 66 3.3. Surface evolution with the ion dose and self-limited ion implantation ……………..………. 68 3.4. Structure and composition of the modified layers at steady state ……………..……………… 70 3.5. Helium trapping and clusters formation in both materials ………………………………………... 72 3.5.1. Mechanisms of He implantation and storage …………………………………………..………. 72 3.5.2. Temperature-dependent desorption of He ……………………………………..……………….. 74 3.6. Influence of the ion energy on the substrate modification …………………………………..……. 76 3.7. Comparison with experimental data ……………………………………………………………....………… 77 3.8. Technological potential of helium plasmas for the Smart Etch process …………………..…. 81 3.9. Conclusion ………………………………………………………………………………………………..…………….... 82 4. Hydrogen plasmas modification of Si thin films ……………………………………………………..…… 84 4.1. Motivation and objectives of the study ………………………………………………………………………. 84 4.2. Computational details ………………………………………………………………………………………........... 86 + 4.3. Hx (x=1-3) ion implantation in Si ………………………………………………………………………………… 87 4.3.1. Surface evolution with the ion dose and self-limited ion implantation ………………… 87 4.3.2. Structure of the H-implanted Si layer at steady state …………………...…………………..… 89 4.3.3. Influence of ion type and ion energy on the substrate modification ………………..….. 92 4.3.4. Effect of the surface temperature and application to the Smart-Cut technology …. 94 + 4.4. Mixed Hx ion/ H radical bombardment of silicon (H2 plasma exposure) ……………………… 96 4.4.1. Surface evolution with the ion dose and etching ……………………………………………..….. 96 4.4.2. Structure and composition of the [a-Si:H] modified layer at steady state …………….. 98 4.4.3. Influence of the ion energy (Eion) ………………………………………………………………………….. 99 4.4.4. Influence of the radical-to-ion flux ratio (Γ= ΓH/ ΓHx+) …………………………………………….. 100 4.4.5. Influence of the ion composition ………………………………………………………………………….. 102 4.4.6. Limitations of hydrogen plasmas for the Smart Etch of silicon substrates …………….. 103 4.5. Conclusion ……………………………………………………………………………………………………………..……. 104 5. Modification of SiN by a H2 plasma ………………………………………………………………………………. 106 5.1. Motivation and objectives of the study ………………………………………………………………………… 106 5.2. Computational details ………………………………………………………………………………………………….. 107 + 5.3. Pure Hx (x=1-3) ion implantation in SiN ……………………………………………………………………….. 108 5.3.1. Evolution of the surface with the ion dose …………………………………………………………… 109 5.3.2. Structure of the H-implanted material at steady state …………………………………………. 110 5.3.3. Influence of the ion energy and ion type on the substrate modification ………………. 111 5.3.4. Conclusive remarks ………………………………………………………………………………………………. 115 + 5.4. Mixed Hx ion/H radical bombardment of SiN (H2 plasma exposure) ……………………………… 116 5.4.1. Evolution of the surface with the ion dose ………………………………………………..…………. 117 5.4.2. Structure and composition of the modified layer at steady state …………………………. 118 5.4.3. Influence of the ion energy (Eion) ………………………………………………………………………….. 119 5.4.4. Influence of the radical-to-ion flux ratio (Γ= ΓH/ ΓHx+) ………………………………………….... 121 5.4.5. Influence of the ion composition …………………………………………………………..…………….. 122 2 5.4.6. Comparison with experiments …………………………………………………………………..………... 123 5.4.7. Stochastic effects of ion implantation at low doses ……………………………………………… 127 5.4.8. Key parameters for the Smart Etch of SiN in hydrogen plasmas ………………………….. 130 5.5. Conclusion ……………………………………………………………………………………………………………..…….. 134 6. General conclusion ………………………………………………………………………………………………..…….