(A) study on the reduction of fluorine in SiOx thin films deposited by SiF₄-based PECVD

국문 초록 (Abstract)

본 연구에서는 SiF4를 전구체로 사용하여 PECVD(플라즈마 강화 화학 기상 증착) 방식으로 증착된 SiOx 박막 내의 불소(F) 및 수소(H) 불순물 제어 특성을 조사하였다. O2/SiF4 가스 비율, Bias Power, 그리고 Ar 유량이 박막의 화학적 조성 및 물리적 특성에 미치는 영향을 Ellipsometer, XPS, TOF-SIMS 및 OES를 통해 체계적으로 분석하였다.
분석 결과, O2/SiF4 비율은 산화 상태를 결정하는 주요 화학적 변수로 확인되었으나, 과도한 산소 공급이 반드시 불소 제거를 보장하지는 않는 것으로 나타났다. 오히려 과량의 산소 조건에서는 전구체의 해리가 촉진됨에 따라 막질 내 불소 유입이 증가하고, 결과적으로 굴절률이 감소하는 경향이 관찰되었다.
반면, Bias Power와 Ar 유량은 박막의 치밀화와 불순물 탈착을 유도하는 물리적 변수로 작용하였다. 이온 충돌은 수소 농도를 유의미하게 감소시켰으나, 고출력 Bias 조건에서는 불소 농도가 비선형적인 거동을 보였다. 이는 강한 이온 에너지에 의해 막질이 급격히 치밀화되는 과정에서 불소 원자가 구조적으로 포획되는 운동학적 트래핑(Kinetic trapping) 메커니즘의 가능성을 시사한다.
OES 분석을 통해 플라즈마 내 O 라디칼과 SiFx 종 사이의 균형이 막질 최적화의 핵심임을 확인하였다. 본 연구 결과는 화학적 산화 반응과 물리적 이온 충돌 에너지 사이의 정밀한 조절을 통해 SiF4 기반 PECVD 공정을 고신뢰성 SiOx 절연막 제조에 활용할 수 있음을 보여주며, 이는 저온 반도체 및 디스플레이 제조 공정을 위한 기초 자료로 활용될 것으로 기대된다.

다국어 초록 (Multilingual Abstract)

This study investigates the deposition of SiOx thin films via Plasma-Enhanced Chemical Vapor Deposition (PECVD) using SiF4 as a precursor, focusing on the systematic control of fluorine (F) and hydrogen (H) impurities. The effects of the O2/SiF4 gas ratio, bias power, and Ar flow rate on the film’s stoichiometry and physical properties were evaluated using Ellipsometry, XPS, TOF-SIMS, and OES.
The O2/SiF4 ratio was identified as a critical chemical variable, however, results suggest that an excessive oxygen supply may not unconditionally facilitate fluorine removal. Instead, higher O2 levels appeared to enhance precursor dissociation, leading to increased fluorine retention and a corresponding decrease in the refractive index.
Conversely, bias power and Ar flow functioned as physical variables that promoted film densification and impurity desorption. While ion bombardment significantly reduced hydrogen content, a non-linear trend in fluorine concentration was observed under high-bias conditions, suggesting a potential kinetic trapping mechanism where fluorine atoms become embedded within the rapidly densifying SiOx matrix.
OES analysis further confirmed that the balance between O radicals and SiFx species is essential for optimizing film quality. These findings demonstrate that SiF4-based PECVD can be effectively optimized for high-reliability SiOx dielectrics by precisely balancing chemical oxidation and physical bombardment energy, providing a foundational framework for low-temperature semiconductor manufacturing processes.

목차 (Table of Contents)

• Chapter 1. INTRODUCTION 1
• 1.1. Research Background 1
• 1.2. Review of SiF4-based SiOx Deposition and Its Limitations 2
• 1.3. Purpose and Scope of This Study 3
• Chapter 2. Theoretical Background 6
• 2.1 Fundamental Theory of Plasma-Based SiO2 Deposition 6
• 2.1.1 Basic Principles of PECVD 6
• 2.1.2 CCP Structure and Ion Energy Control 7
• 2.2 SiF4-based SiO2 Thin Film Formation Mechanism 7
• 2.2.1 Reaction Mechanism of SiF4-based SiO2 Deposition 7
• 2.2.2 Origins of Fluorine and Hydrogen and Their Impact on Film Properties 8
• 2.3 Correlation Between Process Parameters and Film Properties 9
• 2.3.1 Correlation Between Process Variables and Formation Mechanisms 9
• 2.3.2 Theoretical Approach of This Study 9
• Chapter 3. Experiment 11
• 3.1 Experimental Setup 11
• 3.2 Overview of SiO2 Thin Film Deposition Process 13
• 3.3 Process Parameter Design and Rationale 13
• 3.3.1 O2/SiF4 Gas Ratio 14
• 3.3.2 Bias Power 14
• 3.3.3 Ar Flowrate 15
• 3.4 Characterization Methods 15
• 3.5 Reproducibility and Data Processing 21
• Chapter 4. Results and Discussion 23
• 4.1 Deposition Behavior and Refractive Index Characteristics 23
• 4.1.1 Effect of O2/SiF4 Gas Ratio on Deposition Behavior and Refractive Index 23
• 4.1.2 Effect of Bias Power on Deposition Behavior and Refractive Index 24
• 4.2 XPS Analysis 27
• 4.2.1 Variation of O/Si Ratio with O2/SiF4 Gas Ratio 27
• 4.2.2 Variation of O/Si Ratio with Bias and Ar Conditions 27
• 4.2.3 Characteristics of Fluorine Concentration Variation 28
• 4.3 TOF-SIMS Analysis: Hydrogen Depth Profile Characteristics 31
• 4.4 OES Analysis: Behavior of Active Species in Plasma 34
• 4.5 Comprehensive Discussion 37
• Chapter 5. Conclusion 39
• References 41