Thin HfO2 Layers Research Articles

Study of HfO2 films deposited on strained Si1−xGex layers by atomic layer deposition

This paper focuses on the growth of HfO2 by atomic layer deposition (ALD) at 350°C on pseudomorphic Si1−xGex thin films (x=15% and 25%). Two different Si1−xGex surface preparations (chemical oxidation and HF “last” treatment) have been investigated to obtain the highest HfO2 film quality with the thinnest interfacial layer possible. The initial stages of the ALD growth on these different surfaces (i.e., hafnium adsorption and chlorine contamination) analyzed by total x-ray fluorescence show that HF last treated Si1−xGex surfaces are more convenient than chemically oxidized ones to grow high quality HfO2 layers. This result is confirmed by x-ray photoelectron spectroscopy investigations of the interfacial layer structure as a function of the surface treatment. As-deposited and annealed thin HfO2 layers (2.5, 3.5, 5, and 8nm) grown on HF last treated Si0.75Ge0.25 strained layers were analyzed by mercury probe. An equivalent oxide thickness as low as 0.7nm was obtained for a 2.5nm as-deposited HfO2 film. Mobility results show that a 22% mobility enhancement is obtained in the entire effective field range with HfO2∕SiGe compared to the HfO2∕Si reference.

Silicide formation at HfO2–Si and ZrO2–Si interfaces induced by Ar+ ion bombardment

The effect of ion bombardment with Ar+ at several keV energy ranges resulting in silicide formation at HfO2–Si and ZrO2–Si interfaces has been investigated in situ with x-ray photoelectron spectroscopy. The set of spectra recorded during the growth of thin HfO2 and ZrO2 layers on Si(100) was compared to those obtained during subsequent sputtering with an Ar+ beam. It is shown that the Ar+ ion beam affects the MeO2–Si (Me=Hf,Zr) interface at thickness ⩽3nm, inducing the formation of a silicide layer ∼2nm in thickness. The proposed mechanism of silicide formation including the depletion of the interface in oxygen due to its preferential sputtering and subsequent Hf–Si intermixing is corroborated by computer simulations.

Paramagnetic NO2 centers in thin γ-irradiated HfO2 layers on (100)Si revealed by electron spin resonance

Electron spin resonance (ESR) analysis reveals the incorporation of N in (100)Si/HfO2 structures with ultrathin amorphous HfO2 films deposited by chemical vapor deposition (CVD) using Hf(NO3)4 as precursor, through detection, after 60Co γ-irradiation, of NO2 radicals (density ≳55 at. ppm). The molecules are found to be stabilized and likely homogeneously distributed in the HfO2 network. Some network forming N entity is suggested as a precursor, transformed into ESR-active NO2 upon γ-irradiation. The interesting N incorporation aspect appears inherent to the particular CVD process.

On the Nature of Weak Spots in High-k Layers Submitted to Anneals

ABSTRACTIn the path to the introduction of high-k dielectric into IC components, a large number of challenges have still to be solved. Some of the major issues concern the low mobility of carriers and the reliability of the devices. Trapped charges in the stack have been identified as being the cause of these issues. With this in mind, we used Conducting Atomic Force Microscopy, combined with physical analysis to understand the nature of these charges. In this contribution, we have studied the uniformity of thin HfO2 layers, with and without anneal. The Conducting Atomic Force microscopy measurements show spots of higher conductivity. Recording local IV's in those ‘weak’ spots suggests that they consist of positive charge. On the other hand, XPS and ToFSIMS analysis show a diffusion of the interfacial SiO2 upwards into the high-k layer. Finally, the comparison of samples with differing high-k material and crystallinity indicates a strong correlation between the weak spots and the presence of silicon in the film.

Spin-dependent tunneling in HfO2 tunnel junctions

We identified reactively sputtered HfO2 as a particularly good material for making thin insulating barriers for spin-dependent tunnel junctions. This material allows one to form pinhole-free tunnel barriers with good transmission of the spin polarization of the tunneling electrons. Magnetic tunnel junctions consisting of a thin layer of HfO2 sandwiched between transition metal electrodes (Co and Fe, for instance) exhibit changes of tunnel resistance up to 30% at low temperature as a function of applied field. This effect can be used in a variety of magnetic field sensing applications or in magnetic random access memory.