Paper NS+NC-FrM10
Etch Stop Control and Low-Damage Atomic-Layer Etching of HfO2₂ using BCl₃ and Ar Neutral Beam

Friday, October 24, 2008, 11:20 am, Room 311

The downscaling of metal-oxide-semiconductor field-effect transistors (MOSFETs) has created the need for high-dielectric-constant k materials to replace SiO₂ for reducing the gate-leakage current while maintaining the gate-dielectric capacitance. Therefore, there have been many studies on the dry etching of HfO₂ using halogen-based plasma etching for applications to MOSFET devices. A precise etch rate is required in the plasma etching for HfO₂ instead of a high etch rate due to the low thickness of the material. Moreover, an extremely high etch selectivity over the under layer material is required. In addition, the damage on the etched surface is intolerable. However, the conventional plasma-etching processes tend to physically damage the surface of the devices by creating surface defects, including structural disruption, an intermixing layer, or stoichiometry modification, and increasing surface roughness, due to use of energetic reactive ions to achieve vertical etch profiles. In addition, these halogen-based plasma etchings showed finite etch selectivity between HfO₂ and the under lying materials. These problems decrease the device performance. Atomic-layer etching (ALET) may be the most suitable method for etching HfO₂ in next-generation MOSFET devices because it may etch HfO₂ with no physical damage and with atomic-scale etch controllability. The etch characteristics of HfO₂ by ALET were investigated using a BCl₃./Ar neutral beam. The effect of ALET on surface modification and etch-depth control was also examined. Self-limited etching of HfO₂ could be obtained using BCl₃ ALET. This was attributed to the absorption of BCl₃ by the Langmuir isotherm during the absorption stage and the vaporization of hafnium-chlorides/boron oxychlorides formed on the surface during the desorption stage. In addition, the surface composition of HfO₂ was not altered by etching during ALET.