High-Reliability SiO2 Barrier Films Enabled by Effective Thickness and Interfacial Oxygen Reaction Layers = 유효두께 및 계면 산소반응층을 적용한 고신뢰성 SiO2 배리어 박막 형성에 관한 연구

다국어 초록 (Multilingual Abstract)

The modern electronics industry is rapidly transitioning from conventional rigid silicon-based devices toward flexible next-generation electronic technologies, driven by increasing demands for digitalization, hyper-connectivity, light-weighting, and portability. This transition is not limited to a simple evolution of form factors but is also closely linked to global challenges such as carbon neutrality, improved energy efficiency, and the reduction of the digital divide. In this context, the reliability of flexible electronic devices is critically determined by the performance of inorganic thin-film barrier layers that effectively suppress the ingress of moisture and oxygen from the external environment. However, low-temperature PECVD-deposited SiO2 films, which are widely employed as barrier layers, inherently suffer from structural limitations including residual carbon incorporation, incomplete oxidation, and accumulated residual stress. These limitations simultaneously degrade moisture barrier performance, mechanical stability, and long-term durability. To overcome these challenges, this study systematically investigates the correlations among process conditions, structure, and properties of low-temperature PECVD SiO2 films through a two-stage research approach. In the first stage, the effects of surface oxygen reactions on film composition, residual stress, refractive index, and water vapor transmission rate (WVTR) were quantitatively analyzed as a function of film thickness. Oxygen reactions resulted in a significant reduction in carbon content of approximately 53%, accompanied by increased refractive index, enhanced surface densification, and mitigated residual stress, confirming clear structural and chemical improvements. Nevertheless, WVTR improvement exhibited saturation behavior at a single-layer thickness of approximately 300 nm. This observation indicates that the formation of the inorganic SiO2 network in PECVD films is not governed by continuous thickness growth, but rather by a segment-limited behavior, determined by the oxygen penetration depth and the limited range of network rearrangement. To address the intrinsic limitations of single-layer structures, films with identical total thickness were comparatively analyzed between conventional single-layer deposition and segmented deposition with repeated 60 nm layers, where oxygen reactions were introduced at each interface. The segmented deposition structure exhibited higher film densification and superior moisture barrier performance. The thickness of 60 nm was identified as the effective thickness, defined as the minimum thickness required for SiO2 films to exhibit intrinsic inorganic network characteristics and to maximize barrier performance through surface oxygen reactions. Based on this effective thickness concept, a novel single-layer film design incorporating periodically introduced oxidation reaction layers (ORLs) via oxygen plasma was proposed. In the second stage, the optimal oxygen reaction conditions were systematically evaluated by varying the oxygen treatment time at each effective-thickness interface under a total film thickness of 300 nm. Unlike conventional post-deposition oxygen plasma treatments, the ORL functions as an interface-driven chemical transition layer that removes residual carbon and reconstructs the Si-O-Si network at each effective-thickness interface during film growth. By varying the oxygen reaction time from 20 to 120 s, the ORL-80 condition was identified as optimal, yielding enhanced refractive index, minimized residual stress, and improved structural stability. Furthermore, strengthened Si-O-Si asymmetric stretching vibration at 1063 cm-1 and a pronounced reduction in residual carbon verified by TEM-EDS analysis confirmed the optimized chemical structure. Notably, a 300 nm thick ORL-80 SiO2 film achieved WVTR performance equivalent to that of a conventional 700 nm single-layer SiO2 film, representing a significant achievement by reducing film thickness by approximately 57% without sacrificing barrier performance. Overall, this study clearly demonstrates that the barrier performance of SiO2 thin films is not dictated by absolute thickness alone, but is fundamentally governed by inorganic network rearrangement and defect suppression within each growth segment and at interfacial regions. This finding transcends the limitations of conventional thickness-based design strategies and provides a structural and chemical framework for understanding the intrinsic performance determinants of SiO2 barrier films. Moreover, the effective-thickness-based segment control and periodic ORL oxidation strategy simultaneously achieve carbon removal, densification, and stress relaxation within the deposition process, thereby establishing a new thin-film design paradigm capable of systematically overcoming the structural vulnerabilities of low-temperature PECVD SiO2 films. In particular, the ORL–80 architecture validates a practical pathway toward high-reliability flexible barrier design. The outcomes of this work offer concrete design guidelines for meeting the stringent requirements of low-temperature processing, ultra-thin film thickness, and long-term reliability demanded by next-generation flexible electronic devices, including flexible displays, wearable sensors, and electronic skin (e-skin). Furthermore, the proposed segment-based inorganic conversion and ORL mechanism can be extended beyond SiO2 to other low-temperature plasma-deposited films such as SiNx and Al2O3, positioning this approach as a foundational technology for future large-area, low-damage, and high-durability barrier processes.

목차 (Table of Contents)

• Content
• List of Figure ⅲ
• List of Table ⅵ
• Abstract ⅶ
• Chapter 1. Introduction
• 1.1 Background and Necessity of the Study 1
• 1.1.1 Expansion of the Flexible Electronics Market and the Need for
• High-Performance Barrier Technologies 1
• 1.1.2 Definition of Barriers and Technological Evolution 4
• 1.1.3 Changes in Substrate Types and the Resulting Requirements for
• Barrier Performance 10
• 1.1.4 Classification of Barrier Materials 13
• 1.1.5 Deposition Processes for Barrier Film Formation 19
• 1.1.6 Classification of Silicon Precursors for Barrier Film Deposition 23
• 1.1.7 Plasma Polymerization Theory 29
• 1.2 Previous Research Trends and Technical Limitations 33
• 1.3 Research Objective and Strategic Approach 35
• 1.4 References 37
• Chapter 2. Experimentals
• 2.1 Experimental setup 42
• 2.1.1 PECVD system 42
• 2.1.2 Substrate Cleaning 45
• 2.1.3 Depostion of SiO2 Thin Film 46
• 2.2 O2 plasma treatment for ORL formation 49
• 2.3 Analysis Method 51
• 2.3.1 Surface Molphology Analysis 51
• 2.3.2 Structure & Chemical Analysis 53
• 2.3.3 Mechanical Reliability Anaysis 59
• 2.3.4 Barrier Performance Evaluation 62
• Chapter 3. Cyclic Deposition with Controlled Effective
• Thickness for High-Performance SiO2 Films
• 3.1 Introduction 65
• 3.2 Experimental section 69
• 3.3 Results and discussion 73
• 3.4 Conclusion 86
• 3.5 Reference 88
• Chapter 4. Interfacial Oxidation-Enabled SiO2 Films with
• Enhanced Moisture Barrier without Increasing Thickness
• 4.1 Introduction 93
• 4.2 Experimental Section 97
• 4.3 Results and Discussion 101
• 4.4 Conclusion 112
• 4.5 Reference 114
• Chapter 5. Summary 120
• Abstract (in Korean) 123