Design and synthesis of novel metal complexes as volatile precursors for ALD-based processes

국문 초록 (Abstract)

금속 산화물 반도체는 높은 캐리어 이동도와 화학적 안정성으로 인해 차세대 디스플레이 및 전자소자용 소재로 큰 주목을 받고 있다. 특히 갈륨(Ga3+), 인듐(In3+), 아연(Zn2+) 등 금속 산화물은 투명 트랜지스터와 유연 소자에 적용 가능성이 높으며, 박막의 균질성과 전기적 특성은 증착 공정에 사용되는 금속 전구체의 구조적, 열적 특성에 의해 크게 좌우된다. 따라서 안정적이면서도 충분한 휘발성을 갖는 새로운 금속 전구체의 설계가 고성능 금속 산화물 반도체 구현의 핵심 요소로 인식되고 있다. 한편, 반도체 소자의 고집적화가 가속되면서 기존 ArF(193nm) 기반 리소그래피는 해상도의 물리적 한계에 직면하였다. 이에 따라 13.5nm 파장의 극자외선(EUV) 리소그래피가 차세대 미세 공정 기술로 부상하고 있다. EUV는 짧은 파장과 높은 광자 에너지를 통해 7nm 이하 초미세 패턴 형성을 가능하게 하며, 고집적 회로 구현과 공정 단순화 측면에서 혁신적인 대안으로 평가된다. EUV 공정에서는 특히 포토레지스트 소재의 흡광도와 구조적 안정성이 성능을 결정하는 핵심 요소로, 기존의 유기 고분자 기반 레지스트는 낮은 EUV 흡수율과 전자 산란에 따른 한계가 존재한다. 이러한 문제를 해결하기 위해 Zn2+, In3+, Sn4+, Sb5+, Hf4+, Bi3+ 등 d-오비탈 금속을 중심으로 한 건식 포토레지스트가 주목받고 있으며, 금속 전구체의 화학적 안정성, 휘발성, 제어된 반응성을 보장하는 분자 설계가 핵심 전략으로 부상하고 있다.
본 논문에서는 원자층 증착을 통한 금속 산화물 및 건식 포토레지스트 박막 제조를 위해 개발한 Ga3+, In3+, Sb3+, Yb3+, Zn2+, Hf4+ 전구체에 대해 소개한다. 금속 전구체의 반응성과 열적, 물리적 특성을 향상시키기 위해, 중심 금속에 이미노피롤리디네이트, 피롤라이드 이민, N-알콕시 카복스아마이드, 알콕시 알킬아마이드 계열의 리간드를 도입하고 그 특성을 평가하였다. 이미노피롤리디네이트 리간드가 도입된 Ga3+ 및 In3+ 전구체는 상온에서 액체이며, 증기압은 상용화된 전구체들과 유사하거나 그 보다 월등히 높게 나타났다 (Ga3+: T1torr= 41°C, In3+: T1torr= 39.6°C). 피롤라이드 이민 리간드를 도입한 In3+ 및 Zn2+ 전구체는 리간드 작용기의 큰 입체 장애 유발과 제한적인 킬레이트 물림각에 의해 단량체 구조를 형성하였으며, 이에 따라 녹는점이 낮아져 높은 휘발성을 보였다 (In3+: T1torr= 70.3°C, Zn2+: T1torr= 148°C). N-알콕시 카복스아마이드 리간드가 도입된 Sb3+ 전구체는 리간드의 큰 입체 부피로 인해 분자간 인력이 효과적으로 차단되어 단량체 구조를 형성하였고, 증기압은 상용화된 Sb3+ 전구체보다 높았다 (T1torr= 45°C). 흥미롭게도, Yb3+ 전구체는 리간드의 입체 부피에 따라 염 제거 반응에 사용된 알칼리 금속이 포함된 이핵 구조를 형성하기도 하였다. 리간드의 부피를 증가시키면 알칼리 금속의 삽입을 억제하여 동종 리간드 착물을 형성하고, 감압 승화를 통한 정제가 가능해진다 (160°C/0.9torr). 마지막으로, 알콕시 알킬아마이드 리간드가 도입된 Hf4+ 전구체는 N-치환기가 phenyl일 경우 대체로 상온에서 고체이며 열 안정성이 낮아 감압 정제 중 열분해가 발생하였다. 그러나 N-치환기를 tert-butyl로 치환하면 녹는점이 낮아지고 열 안정성이 향상되어 감압 정제 시 높은 수율로 정제가 가능해진다. 이러한 결과들은 금속-리간드 상호작용의 정밀한 제어를 통해 전구체의 열적 거동과 휘발성을 원하는 방향으로 조절할 수 있음을 보여주며, 차세대 금속 산화물 반도체 및 EUV 건식 포토레지스트용 고성능 무기 전구체로의 적용 가능성을 제시한다.

다국어 초록 (Multilingual Abstract)

Metal oxide semiconductors have gained significant attention as promising materials for advanced displays and electronic devices owing to their high carrier mobility and chemical stability. In particular, oxides containing gallium (Ga3+), indium (In3+), and zinc (Zn2+) show great potential for use in transparent and flexible transistors, where the structural and thermophysical properties of the metal precursors critically influence uniformity and electrical performance of thin films.
Driven by the continuous scaling of device dimensions, conventional ArF (193 nm) lithography has reached its resolution limit, and extreme ultraviolet (EUV, 13.5 nm) lithography has emerged as a next-generation technology enabling sub-7 nm patterning. In EUV lithography, the absorption and structural stability of photoresists are key performance factors. However, traditional organic resists exhibit low EUV absorption and electron scattering. To overcome these limitations, dry photoresists based on d-orbital metals such as Zn2+, In3+, Sn4+, Sb5+, Hf4+, and Bi3+ have attracted increasing interest. Thus, the design of metal precursors with optimized volatility, chemical stability, and reactivity has become a central strategy for the development of high-performance EUV photoresists.
In this study, novel Ga3+, In3+, Sb3+, Yb3+, Zn2+, and Hf4+ precursors were developed for vapor-phase deposition of metal oxide and dry photoresist thin films by introducing various ligand types-iminopyrrolidinate, pyrrolide imine, N-alkoxy carboxamidate, and alkoxy-alkylamido. The iminopyrrolidinate-based Ga3+ and In3+ precursors were liquids at room temperature with high vapor pressures (Ga3+: T1torr= 41°C, In3+: T1torr= 39.6°C). Pyrrolide imine-based In3+ and Zn2+ complexes formed monomeric structures due to high steric hindrance, resulting in high volatility (In3+: T1torr= 70.3°C, Zn2+: T1torr= 148°C). The Sb3+ precursors with an N-alkoxy carboxamide ligands were liquids at room temperature and exhibited excellent thermal behavior and high volatility (T1torr= 45°C). Interestingly, Yb3+ precursors formed either heterodinuclear or homodinuclear structures depending on the ligand size, and the homodinuclear complex could be purified by sublimation at 160°C under 0.9 torr. The heteroleptic Hf4+ precursors incorporating alkoxy-alkylamido ligands with tert-butyl group exhibited high volatility and thermal stability, enabling high yield purification by vacuum distillation. These results demonstrate that precise control of metal-ligand interactions enables the tailored design of highly volatile and thermally stable precursors, highlighting their potential as promising candidates for advanced metal oxide semiconductors and EUV dry photoresist materials.

다국어 초록 (Multilingual Abstract)

In this dissertation, we presented the design and synthesis of 36 novel metal precursors based on Ga3+, In3+, Sb3+, Yb3+, Zn2+, and Hf4+ ions. Furthermore, their thermophysical properties were systematically evaluated to assess suitability for atomic layer deposition (ALD) processes.
In chapter 2, we examined in detail the thermophysical properties of Ga and In complexes with amidinate-type imino-pyrrolidinate ligands. For gallium, increasing ring size reduces intermolecular interactions, resulting in a lower melting point and increased vapor pressure. In contrast, for indium, the thermophysical properties are more influenced by the presence of substituents that effectively saturate the coordination environment around the central metal than by ring size. These differences are attributed to the different metal ion sizes.
In chapters 3 and 6, we described the synthetic routes and thermophysical properties of heteroleptic monomeric In and Zn complexes bearing pyrrolide-imine ligands capable of forming chelate rings at fixed bite angles with the central metal. Surprisingly, both metals exhibit the highest vapor pressure and superior thermal behavior when the R group is tert-pentyl. These results refute the theory that increasing molecular weight leads to lower volatility.
In chapters 4 and 5, we introduced homoleptic Sb and Yb complexes formed by introducing oxygen-rich alkoxy-carboxamidate ligands. For Sb, the ground-state molecular structure was calculated and compared with the single crystal structure, confirming that the experimentally yielded solid-state structure closely matches the theoretical calculations. Interestingly, for the Yb complexes, increasing the functional group bulkiness effectively blocked the insertion of alkali metals into the structure, preventing the formation of bimetallic complexes. The thermophysical properties of the Sb and Yb complexes were found to improve as the R1 group increased from methyl to ethyl and as the R2 group increased from ethyl to tert-butyl. These results suggest that the large functional groups effectively reduces intermolecular forces by inducing steric hindrance.
Finally, in chapter 7, we reported heteroleptic monomeric hafnium amido complexes formed by incorporating alkoxy-alkylamide ligands into TDMAHf and TEMAHf. Ligands bearing flexible functional groups more effectively suppress intermolecular interactions than less flexible analogues, thereby enhancing volatility. In contrast, rigid groups such as phenyl group did not improve the thermal stability of the complexes and instead led to decomposition during vacuum purification. Overall, the most favorable thermal behavior and physicochemical properties were observed for the complex with N-tBu and O-Et groups.
These results demonstrate that deliberate modulation of metal-ligand interactions and ligand backbone provides a general strategy to tune precursor properties. Therefore, the precursor platforms developed herin are promising condidates for high-performance ALD processes targeting next-generation metal oxide semiconductors and EUV dry photoresists.

목차 (Table of Contents)

• Chapter 1. Introduction to Precursor Chemistry for Advanced Oxide Semiconductor and EUV Patterning Applications 1
• 1.1. Metal Oxide Semiconductors 1
• 1.2. Extreme Ultraviolet (EUV) Lithography and Photoresists 4
• 1.3. Precursor Chemistry 10
• Chapter 2. Synthesis of Highly Volatile Heteroleptic Gallium(Ⅲ) and Indium(Ⅲ) Amidinates with Imino-Pyrrolidinate Derivatives 20
• 2.1. Introduction 20
• 2.2. Experimental Section 26
• 2.3. Results and Discussion 34
• 2.4. Conclusion 57
• Chapter 3. Synthesis of Heteroleptic Monomeric Indium(Ⅲ) Precursors Bearing Pyrrolide-Imine Derivatives 59
• 3.1. Introduction 59
• 3.2. Experimental Section 64
• 3.3. Results and Discussion 71
• 3.4. Conclusion 87
• Chapter 4. High Volatile Antimony(Ⅲ) Precursors for Metal Oxide Thin Film Deposition 88
• 4.1. Introduction 88
• 4.2. Experimental Section 91
• 4.3. Results and Discussion 97
• 4.4. Conclusion 114
• Chapter 5. Synthesis of Novel Homoleptic Ytterbium(Ⅲ) Precursors with Alkoxy-Carboxamide Derivatives 115
• 5.1. Introduction 115
• 5.2. Experimental Section 119
• 5.3. Results and Discussion 122
• 5.4. Conclusion 135
• Chapter 6. Synthesis of Volatile Zinc(Ⅱ) Precursors with Pyrrolide-Imine Ligands 136
• 6.1. Introduction 136
• 6.2. Experimental Section 140
• 6.3. Results and Discussion 145
• 6.4. Conclusion 159
• Chapter 7. Synthesis of Novel Liquid Hafnium(Ⅳ) Precursors Bearing Alkoxy-Alkylamide Ligands 160
• 7.1. Introduction 160
• 7.2. Experimental Section 165
• 7.3. Results and Discussion 173
• 7.4. Conclusion 186
• Chapter 8. Summary 187
• References 189
• Appendix 227
• Appendix 1. 1H, 13C NMR, and FT-IR Spectral Data for the Complexes in Chapter 2 227
• Appendix 2. 1H, 13C NMR, and FT-IR Spectral Data for the Complexes in Chapter 3 239
• Appendix 3. 1H, 13C NMR, and FT-IR Spectral Data for the Complexes in Chapter 4 249
• Appendix 4. 1H, 13C NMR, and FT-IR Spectral Data for the Complexes in Chapter 6 259
• Appendix 5. 1H, 13C NMR, and FT-IR Spectral Data for the Complexes in Chapter 7 266
• 논문요약 282