Paper PS-MoA9
Investigation of Surface Reactions for Chlorine-Based Plasma Etching of Nitrided Hafnium Silicates

Monday, October 15, 2007, 4:40 pm, Room 607

The development of plasma etching chemistries is necessary to pattern new gate dielectric materials, such as hafnium-based oxides, for sub-45nm CMOS devices. Nitrided hafnium silicates (HfSiON) are promising since they combine the high dielectric constant and improved interface state density of hafnium silicates with the beneficial properties of silicon oxynitrides. In this work, chlorine-based chemistries are used in an electron cyclotron resonance high density plasma reactor to etch Hf-rich and Si-rich nitrided hafnium silicates, with 0 to 15 at.% of nitrogen. The plasma density, electron temperature, and gas phase species are characterized by a Langmuir probe, optical emission spectroscopy, and quadrupole mass spectrometry. The etching of SiO₂ and HfO₂ was first studied in Cl₂ and BCl₃ plasmas, to allow for studies of the etching of HfSiON with well controlled and varying compositions of Si and N in HfO₂. The etch rates of nitrided hafnium silicates were found to increase with the square root of ion energy, and the etching rate of films increased with increasing nitrogen incorporation as well as SiO₂ percentage in the film. The surface chlorination was enhanced with increasing ion energy, ranging from 1 to 4 at.% of chlorine on the etched surfaces, demonstrating that the etching reaction is limited by the momentum transfer from the ions to the film surface. The measured etching threshold energies were higher than that of pure HfO₂, suggesting that Si and N incorporation modifies film structure/density. In addition, nitrogen was detected removed in the form of SiN₂Cl_x, and more nitrogen remains on the surface of the Hf-rich films than the Si-rich films. This suggests that the removal of N is related to its bonding within the film. Hafnium and silicon were removed as HfCl_x, SiCl_x, and SiO₂Cl_x, and increased with ion energy. A generalized phenomenological model will be presented to describe the effect of SiO₂ and N incorporation on the etching behavior of HfO₂.