Influence of Yttrium Doping Into Hafnium Dioxide on Film Structure and Dielectric Properties

Thin films of Hafnium oxide serve as new high dielectric films with interesting application in semiconductor device fabrication – particularly as gate oxide layer in the transistor and the dielectric media of capacitive memory cell. Recently developments of such films have shown that the incorporation of other metal oxides such as yttrium oxide influences its post annealed crystalline structure and as predicted by theory increased dielectric is observed.                               

Previous studies showed that addition of yttrium in HfO₂ thin films would result in series desirable properties, such as, improved thermal stability and an increased effective permittivity due to the crystallization into the cubic phase at lower annealing temperature induced by yttrium doping. Those studies were mainly carried out by techniques like molecular pulsed laser deposition, chemical/physical vapor deposition, which have a moderate control of film composition and structure. While in cutting-edge microelectronics fabrication, it demands highly controls of composition and growth rate in manner of submonolayer, the Atomic Layer Deposition thereby has attracted much interest.

In this study different nanolaminated compositional structures of yttrium doped hafnium oxide films (with yttrium dopant from 2.5%—100%) are deposited on silicon (100) using tris(ethylcyclopentadienyl) yttrium, and tetrakis-diethylamino hafnium, with water vapor as the oxidant. This nanolaminated Yttrium doped HfO₂ (YDH) structure is achieved by atomic layer deposition (ALD) process, which utilizes a series of surface-limiting chemical reactions that makes it ideal for excellent control of film composition and structure. The resulting film composition and crystalline structural properties are investigated using X-ray Photoelectron Spectroscopy, Grazing Incidence X-ray Diffraction and Fourier Transformed Infrared Spectroscopy; the changes of surface morphologies film structures as well as interfacial layers of YDH films before and after annealing at 600 ºC (N₂ ambient, 5 minutes) were examined by Optical Profiler and Transmission Electron Microscopy; dielectric constants and leakage current densities of YDH films subjected to forming gas annealing were examined by Capacitance-Voltage and Current-Voltage. A strong compositional effect on the dielectric constant, which maximized at 14% of yttrium content, was observed. The leakage current densities of the studied films were less than 10^-5 A/cm² at 1V.