Tetragonal phase in Ge doped HfO 2 films on Si investigated by X-ray Absorption Spectroscopy
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1194-A01-02
Tetragonal phase in Ge doped HfO2 films on Si investigated by X-ray Absorption Spectroscopy Leonardo Miotti1, Karen P. Bastos1, Cláudio Radtke2, and Gerald Lucovsky1 North Carolina State University, Department of Physics, Box 8202, Raleigh, NC 27695-8202, USA 2 Instituto de Química, Universidade Federal do Rio Grande do Sul, 91509-900 Porto Alegre, Brazil 1
ABSTRACT The stabilization of the tetragonal phase of 5 nm thick HfO2 films by Ge doping is investigated using x-ray absorption spectroscopy around O and Ge Kedges and by Rutherford backscattering spectrometry. We show that Ge concentrations higher than ~5at.% are not stable during rapid thermal anneal at temperatures as low as 750oC and that the tetragonal phase of HfO2 is achieved at this Ge concentration.
INTRODUCTION The most important high-k dielectric investigated for high performance metal-oxidesemiconductor field effect transistors (MOSFET) devices is HfO2. Its polymorphism includes a monoclinic phase stable at room temperature, a tetragonal phase stable above 1700oC, and a cubic phase stable above 2200oC [1]. The ability to stabilize the tetragonal phase of HfO2 at room temperature is of technological interest because this phase has a significantly higher dielectric constant (k>30) as compared to the monoclinic and cubic phases (k~16-25) [2,3]. The stabilization of the tetragonal phase can be achieved by reducing the size of the nanograins, strain, and by doping (alloying) the dielectric [3-5]. In this work we investigate the stabilization of the tetragonal phase of nanometric thin HfO2 films on Si by doping with Ge, i.e, a tetravalent impurity with ionic radius smaller than Hf. This kind of impurity is expected to stabilize the tetragonal and not the cubic phase, and also does not have associated oxygen vacancies as trivalent impurities have [3,6]. Since x-ray diffraction cannot determine the phase in very thin films as those of technological interest and the film thickness can play an important role in the stabilization of the different phases, we used here x-ray absorption spectroscopy to probe the local symmetries of nanometric thin HfO2 films on Si.
EXPERIMENT HfO2 films were deposited on HF-last Si(100) by remote plasma enhanced chemical vapor deposition (REPCVD) at 300oC using Hf-t-butoxide, GeH4, and O2 as reactive gases. Prior to the dielectric deposition a thin SiOxNy interfacial layer, ~ 1 nm thick, was grown by remote plasma oxidation followed by a nitridation step. 5 nm thick HfO2 films were deposited with Ge atomic concentration ranging from 0 to 15at.%, as determined by in-situ Auger electron
spectroscopy. After deposition, the samples were submitted to rapid thermal annealing (RTA) in Ar flow at 750 or 1000oC. X-ray absorption spectroscopy of the O and Ge Kedge were performed in beam line 10-1 of the Stanford Synchrotron Radiation Lightsource (SSRL) and beamline 20ID-B of the Advanced Photon Source (APS), respectively. Rutherford backscattering spectrometry (RBS) using 2 MeV He+ ions was performed in a Tandem Accelerator
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