Physical and electrical characterization of polysilicon vs. TiN gate electrodes for HfO 2 transistors

Abstract

The effects of pre-deposition substrate treatments and gate electrode materials on the properties and performance of high- k gate dielectric transistors were investigated. The performance of O 3 vs. HF-last/NH 3 pre-deposition treatments followed by either polysilicon (poly-Si) or TiN gate electrodes was systematically studied in devices consisting of HfO 2 gate dielectric produced by atomic layer deposition (ALD). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) using X-ray spectra and Electron Energy Loss Spectra (EELS) were used to produce elemental profiles of nitrogen, oxygen, silicon, titanium, and hafnium to provide interfacial chemical information and to convey their changes in concentration across these high- k transistor gate-stacks of 1.0–1.8 nm equivalent oxide thickness (EOT). For the TiN electrode case, EELS spectra illustrate interfacial elemental overlap on a scale comparable to the HfO 2 microroughness. For the poly-Si electrode, an amorphous reaction region exists at the HfO 2/poly-Si interface. Using fast transient single pulse (SP) electrical measurements, electron trapping was found to be greater with poly-Si electrode devices, as compared to TiN. This may be rationalized as a result of a higher density of trap centers induced by the high- k/poly-Si material interactions and may be related to increased physical thickness of the dielectric film, as illustrated by HAADF-STEM images, and may also derive from the approximately 0.5 nm larger EOT associated with polysilicon electrodes on otherwise identical gate stacks.