Tunable Anti-Reflective Coatings with Built-in Hard Mask Properties Facilitating Thin Resist Processing

摘要

Patterning sub-150 nm features in dielectric stacks using single layer resist processes in conjunction with organic anti-reflective coatings (ARCs) is becoming very difficult. Typical organic ARC-open etch processes suffer from poor ARC-to-resist selectivities (～0.7), and are accompanied by critical dimension (CD) losses. The resist remaining is often not sufficient to prevent artifacts such as substrate 'microcrevicing' during subsequent etches. PECVD-deposited titanium nitride and silicon oxynitride films have been investigated as ARC layers but their basic nature has caused residue formation at the resist/ARC interface. We have developed a PECVD-deposited material, TERA (Tunable Etch-Resistant ARC) that acts as an ARC at 248 nm and 193 nm wavelengths and provides excellent etch selectivity to resist surpassing those attained with organic ARCs~+. In addition, this material demonstrates excellent hard mask properties for subsequent dielectric etch steps. The optical properties of these films can be easily tuned to minimize substrate reflectance at either imaging wavelength by controlling the precursor composition and deposition conditions. The films are compatible with 248 nm and 193 nm resists - no footing, undercut or residue is observed during patterning. The films can be etched selectively to resist (selectivity ～2.5) that translates to less resist consumption during the ARC-open etch. Compared to resists, TERA demonstrates better etch resistance while patterning dielectric stacks ―the silicon oxide-to-TERA selectivity exceeds 8. In this paper, the excellent optical tunability and substrate reflectivity control achieved with TERA are discussed. Clean lithography using 248 nm, 193 nm and e-beam resists is shown. The etch characteristics of TERA in fluorocarbon and halogen-based plasma chemistries are discussed. Finally, the formation of 135 nm and 120 nm deep trench patterns in thick dielectric stacks using TERA in conjunction with commercial 248 nm and 193 nm resists, respectively is demonstrated. The extendibility of this approach to pattern silicon without roughening or 'microcrevicing' using sub-200 nm thick resists is motivated.