Analysis of plasma-treated sapphire surface and its effect on crystallized Al2O3 quality
플라즈마 처리가 사파이어 기판 표면과 결정화된 알루미나의 결정성에 미치는 영향 분석

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dc.description학위논문 (석사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2018. 2. 윤의준.-
dc.description.abstractGaN-based LEDs, which are a group III-nitride compound semiconductors, are emerging as next-generation lighting technologies due to their superior energy efficiency and loger luminescent life than conventional incandescent lamps and fluorescent lamps. Generally, a GaN-based compound semiconductors are grown on a sapphire substrate by a hetero-epiaxy. However, there are problem of high threading dislocation density due to lattice constant mismatch, wafer bow due to difference in the thermal expansion coefficients between substrate and GaN film, and the low light extraction efficiency due to difference in the refractive index. In order to improve these problems, researches have been carried out to insert a patterns on the sapphire substrate surface to enable lateral overgrowth of GaN film and increase diffuse reflection. Our research group has also developed a CES (cavity-engineered sapphire substrate) which inserts an air cavity arrays on a sapphire substrate surface. When GaN film is grown on a CES, the threading dislocation density decreased due to lateral overgrowth, and the light extraction efficiency increased because of the diffuse reflection. Also, the air cavity arrays reduce the stress inside the thin film, thereby reducing the wafer bow phenomenon.
The CES is fabricated by crystallization of alpha-alumina through thermal treatment of amorphous-alumina deposited on a sapphire substrate. Therefore, in order to obtain a high-quality GaN film, the crystallinity of alumina layer is important. During the CES fabrication process, plasma treatment is performed before depositing the amorphous-alumina layer to remove the PR residue after the photolithography process and to obtain the desired shape pattern. This study was conducted to analyze the effect of plasma treatment on the surface of the sapphire substrate and the crystallinity of the crystallized alumina.
Plasma treatment was performed by adjusting parameters. In this study, plasma treatment was carried out using oxygen (O2) and argon (Ar) gas. Also, experiments were conducted by controlling the power applied to the plate which the substrate is placed. Fluorine (F) impurities were detected in both the oxygen and argon plasma treatment and about 1% of argon impurities were detected in the case of argon plasma treatment. The oxygen ratio on the surface of the sapphire substrate was increased during the oxygen plasma treatment, and the opposite result was obtained in the case of the argon plasma treatment. Also, as the plate power increases, the stoichiometry of the sapphire substrate surface became more broken. As a result of analysis using AFM technique, the surface morphology and roughness of plasma-treated samples did not much change much, but the crystallized samples showed that nano-sized grains appeared on the surface, and the surface roughness also increased greatly. As a result of the crystallinity analysis, the crystallinity of both gamma-alumina and alpha-alumina was degraded in comparison with the samples that not plasma-treated. Therefore, this study can be used to experminetally examine the effect of plasma treatment on the sapphire substrate surface and the crystallized alumina.
dc.description.tableofcontentsChapter 1. Introduction 1
1.1. Background theory 1
1.1.1. GaN-based LEDs 1
1.1.2. Technical issues in GaN-based LEDs 4

1.2. Cavity Engineered Sapphire substrate (CES) 9
1.2.1. Advantages of CES 9
1.2.2. Fabrication process of CES 11
1.2.3. Necessity of plasma treatment 13
1.2.4. Solid-phase-epitaxy (SPE) of alumina 15

1.3. Purpose of the study 17

Chapter 2. Experimental and analysis tools 19
2.1 CES fabrication techniques 19
2.1.1 Atomic layer deposition (ALD) 19
2.1.2 Inductively coupled plasma etcher (ICP-etcher) 21

2.2 Characterization techniques 23
2.2.1 Atomic force microscopy (AFM) 23
2.2.2 X-ray photoelectron spectroscopy (XPS) 23
2.2.3 High resolution X-ray diffraction (HR-XRD) 23
Chapter 3. Experimental results and discussion 25
3.1. Experimental setup 25
3.1.1 Plasma treatment 25
3.1.2 Amorphous alumina deposition 27
3.1.3 Thermal treatment 29

3.2. AFM analysis (roughness, morphology) 31
3.2.1 Bare sapphire surface 31
3.2.2 Amorphous alumina 31
3.2.3 Crystallized alumina (gamma-phase, alpha-phase) 34
3.2.4 Summary 37

3.3. XPS analysis (stoichiometry, impurities) 39
3.3.1 Oxygen plasma treated 39
3.3.2 Argon plasma-treated 41
3.3.3 Summary 43

3.4. XRD analysis (crystalline quality) 44
3.4.1 Crystallized gamma-phase alumina 44
3.4.2 Crystallized alpha-phase alumina 46
3.4.3 Summary 50

Chapter 4. Conclusion 51
Reference 52
dc.format.extent3844268 bytes-
dc.publisher서울대학교 대학원-
dc.subjectLight emitting diode (LED)-
dc.subjectCavity-engineered sapphire substrate (CES)-
dc.subjectalumina (Al2O3)-
dc.subjectSoild-phase-epitaxy (SPE)-
dc.subjectPlasma treatment-
dc.titleAnalysis of plasma-treated sapphire surface and its effect on crystallized Al2O3 quality-
dc.title.alternative플라즈마 처리가 사파이어 기판 표면과 결정화된 알루미나의 결정성에 미치는 영향 분석-
dc.contributor.AlternativeAuthorGiwoong Kim-
dc.contributor.affiliation공과대학 재료공학부-
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Material Science and Engineering (재료공학부) Theses (Master's Degree_재료공학부)
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