(A) controlled growth of tungsten-based thin films prepared by atomic layer deposition = 원자층 증착법에 의해 제조된 텅스텐 기반 박막의 성장 제어

다국어 초록 (Multilingual Abstract)

Tungsten (W)-based thin films, such as tungsten (W), tungsten nitrides (WNx), tungsten carbonitrides (WNxCy) and tungsten carbides (WCx), have been extensively used for various applications, which includes hard coating materials for cutting tool [1], catalysts for hydrogen evolution [2] , thin film resistors [3], tribological applications [4], gate or diffusion barrier for Si-based semiconductor devices fabrication [5-6] etc. Among those applications, the most interesting industrially and fastest developing area nowadays is microelectronics [7]. W has been traditionally used as a contact and a via plug material and gathered recent interests as a gate or a bit line and a plug material for source/drain [8-12] due to chemical and thermal stability (Tm: 3422 oC), low resistivity (bulk resistivity: 5.6 µΩcm) and a moderate step coverage when it was deposited using conventional chemical vapor deposition (CVD). W-based nitrides, carbonitrides and carbides have also been investigated extensively for semiconductor microelectronic devices applications. Specifically, these materials are being intensively studied as a diffusion barrier [13], a metal gate electrode [14-15], and a glue layer at ultrahigh-aspect-ratio contact and via holes [8,16] in ultralarge-scale-integrated (ULSI) devices, because of their desirable material properties, including high melting temperatures (W2N: ~ 3500 oC, W2C: ~ 3049 oC, WC: ~ 2870 oC), relatively low resistivities (W2N: ~ 22 µΩcm, W2C: ~ 90 µΩcm, WC: ~ 188 µΩcm), chemical inertness and highly-dense rock-salt-based crystal structures.
Various thin film deposition methods including sputtering [17-18], CVD [19-20] and atomic layer deposition (ALD) [21-32] have been reported to prepare these W-based materials. Among them, ALD has been developed most recently and drawn much attention with an ever-continuous device scaling since ALD enables an atomic-scale control for the film thickness and composition as well as a perfect step coverage [33-34]. Generally, extensive researches on ALD processes for W or W-based binary and ternary nitride thin films have also been reported by using mainly halide precursor, WF6, and reactants in summarized table 1-1 however those trials have shown drawbacks and limitations [25-26, 29-31]. The use of F-containing inorganic precursor (WF6) has a potential problem of incorporating corrosive F impurities, resulting etching of underlying materials [12,26], degradation of adhesion [35], and defect formation due to an unwanted reaction with underlying materials [36].
In this study, we prepared and investigated phase-controlled W-based binary thin films grown by ALD using a new fluorine- and nitrogen-free W metallorganic precursor of tungsten tris(3-hexyne) carbonyl and various reactants such as NH3 and N2+H2 plasma. It was found that the use of N2+H2 mixture plasma could control a phase, microstructure and composition of films from those of WNx to WCx. In particular, ALD-WCx films deposited with higher H2 flow rates showed a relatively lower resistivity and had a nano-crystalline structure close to an amorphous. Such aspects would open a possibility of demonstrating a better performance in a view of the diffusion barrier and gate electrode materials.

국문 초록 (Abstract)

Transition metal 텅스텐을 기반으로 하는 이원계 및 삼원계 물질인 텅스텐-나이트라이드, 텅스텐-카본나이트라이드, 텅스텐-카바이드 박막은 hard coating, catalysts, resistors, tribological applications 및 실리콘 기반의 반도체 장치에서 gate 와 diffusion barrier 등에 광범위하게 적용되어 지고 있으며, 그 중에서도 초미세 microelectronic 분야에서 가장 활발하게 연구가 진행되고 있다. 특히나 이러한 물질들은 높은 열적 안정성, 비교적 낮은 비저항, 화학적 안정과 고밀도의 rock-salt 기반의 결정 구조의 장점 때문에 ULSI (ultralarge-scale-integrated) 장치에서 via hole 또는 고단차 (ultrahigh-aspect-ratio)의 구조물로서 diffusion barrier, metal gate electrode, glue layer로 적용되는 연구가 활발히 진행되고 있다.
기존의 텅스텐 기반의 물질들은 sputtering, CVD, 등 여러가지 방법으로 제조 되어 왔다. 그러나 반도체 소자의 집적화 기술이 발달함에 따라 구조가 복잡해지고 조밀해지면서 더욱 정교한 증착 기술이 요구되었고, 이에 따라 원자층 증착법 (Atomic Layer Deposition; ALD)과 같은 기술이 제시되었고 많은 연구가 진행되고 있다. 원자층 증착법은 자기제한적 성장특성을 통하여 대면적 및 복잡한 구조의 기판에 대하여 뛰어난 증착성을 가지며, 정밀한 두께 조절이 가능하다는 장점을 가지고 있다. 그럼에도 불구하고, 원자층 증착법을 이용한 텅스텐 기반의 물질들을 형성하는 데에도 큰 문제점이 발생하게 되었다. 기존에 일반적으로 텅스텐 화합물의 박막증착에는 tungsten (VI) fluoride (WF6)라는 inorganic 전구체를 사용해왔다. 하지만 WF6 전구체 내에 포함되어 있는 부식성이 강한 플루오린의 영향으로 인접한 물질들에 확산되어 Cu pitting 등과 같은 데미지를 입힐 뿐만 아니라 계면접착력에도 문제가 발생하게 되었다. 이를 해결하고자 플루오린이 포함되어 있지 않은 전구체들의 연구 및 개발이 이루어지고 있다.
그리하여 본 연구에서는 기존 연구에서의 한계점을 해결하기 위하여 플루오린이 포함되어 있지 않는 Tungsten tris(3-hexyne) carbonyl [W(CO)(CH3CH2C≡CCH2CH3)]가 새로운 유기금속 전구체로써 연구에 사용되었으며, 암모니아 (NH3) 및 질소(N2) 와 수소(H2) 환원가스의 다양한 조합을 통하여 텅스텐-나이트라이드 부터 텅스텐-카바이드 박막의 상, 미세구조, 조성과 같은 성장을 제어 할 수 있었으며, 이를 통하여 다양한 물성을 조절 할 수 있었다. 또한, 본 연구를 통해 단 하나의 전구체를 이용하여 플루오린의 영향을 받지 않고 성장 제어가 가능한 텅스텐기반의 물질을 선택적으로 제조하여 metal gate와 diffusion barrier 에서의 성능 및 가능성을 확인하였다.

목차 (Table of Contents)

• CHAPTER 1. Introduction 1
• 1.1 Introduction 2
• CHAPTER 2. Theoretical Background 5
• 2.1 Atomic layer deposition (ALD) 6
• 2.1.1 Principle of atomic layer deposition 6
• 2.1.2 Characteristic of atomic layer deposition 7
• 2.1.3 Plasma-enhanced atomic layer deposition 9
• 2.2 Applications of ALD metal and nitride thin films for semiconductor devices 12
• 2.2.1 Cu interconnect technology 12
• 2.2.1.1 ALD of diffusion barriers against Cu 12
• 2.2.1.2 Cu seed or direct plating materials 14
• 2.2.2 Contact, via plug and barrier 15
• 2.2.3 Metal gate electrode 17
• 2.3 Potential W-based materials for semiconductor device processing 19
• 2.3.1 Transition (3d-5d) metal nitrides and carbides 19
• 2.3.2 Application of ALD W-based nitride and carbide 21
• 2.3.3 Previous study on ALD W-based nitride and carbide 23
• CHAPTER 3. A growth of WNx thin films prepared by atomic layer deposition using W(CO)(CH3CH2C≡CCH2CH3) [tungsten tris(3-hexyne)carbonyl] precursor and NH3 24
• 3.1 Synthesis of tungsten precursor 25
• 3.2 Experimental ALD process using NH3 as a reactant 26
• 3.3 Analysis of the deposited WNx thin films 28
• 3.4 Results of the deposited ALD-WNx films 29
• 3.4.1 Growth kinetics of ALD-WNx 29
• 3.4.2 Properties of ALD-WNx 32
• 3.5 Application of ALD-WNx thin films 41
• 3.5.1 Diffusion barrier performances of ALD-WNx 41
• 3.6 Summary and conclusions 45
• CHAPTER 4. A controlled growth of WNx and WCx thin films prepared by atomic layer deposition using W(CO)(CH3CH2C ≡CCH2CH3) [tungsten tris(3-hexyne) carbonyl] precursor and N2+H2 mixture 46
• 4.1 Experimental ALD process using N2+H2 mixture as a reactant 47
• 4.2 Analysis of the deposited ALD-WNx and WCx thin films 49
• 4.3 Results of the controlled ALD-WNx and WCx films 50
• 4.3.1 Properties of the controlled ALD-WNx and WCx 50
• 4.4 Summary and conclusions 58
• CHAPTER 5. Atomic layer depsosited nanocrystalline WCx thin films as a metal gate and diffusion barrier for Cu metallization 59
• 5.1 Experimental ALD-WCx process using N2+H2 mixture as a reactant 60
• 5.2 Analysis of the deposited WCx thin films 61
• 5.3 Results of the deposited ALD-WCx process 62
• 5.3.1 Growth kinetics of ALD-WCx process 62
• 5.3.2 Properties of ALD-WCx 65
• 5.4 Application of ALD-WCx thin films 72
• 5.4.1 Metal gate electrode work function 72
• 5.4.2 Diffusion barrier performances of ALD-WCx 74
• 5.5 Summary and conclusion 78
• CHAPTER 6. Reference 79
• ABSTRACT (in Korean) 86