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Plasma etching of SiO2 using fluorinated alcohols and ethers as low-GWP alternatives to perfluorocarbons

  • 유상현 (You Sanghyun, 아주대학교 일반대학원)

초록/요약

In this dissertation, SiO2 contact-hole etching using low-GWP materials as environmentally sustainable alternatives to high-GWP perfluorocarbons (PFCs) was investigated. The etch characteristics of various low-GWP materials were systematically investigated, and their feasibility as PFC replacement was evaluated. In addition, an advanced cyclic etching (ACE) process using low-GWP materials was developed to enable contact-hole diameter reduction and etch profile improvement. SiO2 contact holes were etched using low-GWP materials, such as fluorinated alcohols (pentafluoropropanol and hexafluoroisopropanol), perfluoroalkyl vinyl ethers (perfluoropropyl vinyl ether and perfluoroisopropyl vinyl ether), and fluorinated ether (heptafluoropropyl methyl ether). Their etch characteristics were investigated by analyzing dissociation pathways, relative amounts of radicals, steady-state fluorocarbon film properties, and etch profiles, and compared with those of C4F8 to evaluate the feasibility of replacing PFCs with low-GWP materials for SiO2 etching. The effects of flow rate ratios on the etch profile of SiO2 contact holes were systematically investigated, and a 100-nm-diameter contact hole was successfully etched under optimal process conditions. The low-GWP materials demonstrated significantly reduced environmental impact while maintaining comparable or superior etch performance. An ACE process using HFE-347mcc3 was developed to achieve contact-hole diameter reduction and etch profile improvement. The ACE process consisted of pre-deposition of a protection layer on the mask followed by cyclic alternation of deposition and etching steps. The effects of flow rate ratio and duration in the pre-deposition step on mask profiles and contact-hole etch profiles were systematically investigated. The etch profiles obtained by the ACE process were compared with those from continuous and cyclic etching processes, demonstrating superior performance: the ACE process achieved reduced contact-hole diameters, complete suppression of sidewall bowing, and the smallest degree of non-verticality, confirming successful diameter control and profile optimization. In this study, SiO2 contact holes were etched using low-GWP materials, including fluorinated alcohols (pentafluoropropanol and hexafluoropropanol), perfluoroalkyll vinyl ethers (perfluoropropyl vinyl ether and perfluoroisopropyl vinyl ether), and fluorinated ethers (heptafluoropropyl methyl ether). By comparing their etch profiles, the feasibility of these fluorinated alcohols, perfluoroalkyl vinyl ethers and fluorinated ethers for high-aspect-ratio etching was demonstrated. Furthermore, we developed an ACE process utilizing one of these low-GWP materials and proposed a method capable of reducing PFC emissions while effectively suppressing pattern distortion and further increasing the aspect ratio through contact-hole diameter reduction.

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목차

Chapter 1. Introduction 1
1.1 SiO2 etching using fluorocarbon plasmas 1
1.2 Environmental issues in SiO2 etching using PFC plasmas 8
1.3 Objectives 13
Chapter 2. Plasma etching of SiO2 using low-GWP materials 16
2.1 Introduction 16
2.2 Experimental 21
2.2.1 Inductively coupled plasma system 21
2.2.2 Faraday cage system 23
2.2.3 Properties of low-GWP materials and C4F8 26
2.2.4 Materials and measurements 30
2.3 Plasma etching of SiO2 using fluorinated alcohols 34
2.3.1 SiO2 etch characteristics using fluorinated alcohols 35
2.3.2 SiO2 contact-hole etching using fluorinated alcohol 64
2.4 Plasma etching of SiO2 using perfluoroalkyl vinyl ethers 71
2.4.1 SiO2 etch characteristics using perfluoroalkyl vinyl ethers 72
2.4.2 Comparison of SiO2 etch mechanisms in PPVE and PIPVE 84
2.5 Effect of additive gas on plasma etching of SiO2 using heptafluoropropyl methyl ether 97
2.5.1 Etching of 200-nm-diameter SiO2 contact hole 98
2.5.2 Angular dependence of HFE-347mcc3/O2/Ar plasmas 105
2.5.3 Etching of 100-nm-diameter SiO2 contact hole 113
2.6 Comparative analysis of SiO2 etch behavior in low-GWP materials based on molecular structures 115
2.7 Summary 128
Chapter 3. Control of the diameter of SiO2 contact holes using low-GWP materials 137
3.1 Introduction 137
3.2 Experimental 146
3.3 Result and discussion 150
3.3.1 Comparison of SiO2 contact-hole etch profiles among low-GWP material plasmas 150
3.3.2 Continuous etching of SiO2 contact holes using HFE-347mcc3 154
3.3.3 Pre-deposition of a protection layer using HFE-347mcc3 157
3.3.4 Advanced cyclic etching of SiO2 contact holes using HFE-347mcc3 163
3.4 Summary 176
Chapter 4. Conclusions 179
4.1 Plasma etching of SiO2 using low-GWP materials 179
4.1.1 Fluorinated alcohols 179
4.1.2 Perfluoroalkyl vinyl ethers 181
4.1.3 Fluorinated ethers with additive gas control 182
4.2 Advanced cyclic etching for diameter control 182
4.3 Concluding remarks 184
References 186
Abstract (국문 초록) 209

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