Thursday, April 14, 2016

Scientists from MIPT have succeeded in growing ultra-thin 25 Å HfO2 ferroelectric films

Scientists from MIPT have succeeded in growing ultra-thin (2.5-nanometre) ferroelectric films based on hafnium oxide that could potentially be used to develop non-volatile memory elements called ferroelectric tunnel junctions. The results of the study have been published in the journal ACS Appl. Mater. Interfaces.

"Since the structures of this material are compatible with silicon technology, we can expect that new non-volatile memory devices with ferroelectric polycrystalline layers of hafnium oxide will be able to be built directly onto silicon in the near future," says the corresponding author of the study and head of the Laboratory of Functional Materials and Devices for Nanoelectronics, Andrei Zenkevich.

The cross section of the non-volatile memory structure shows a polycrystalline fused film of hafnium and zirconium oxides grown on a highly doped silicon substrate (upper electrode, titanium nitride)
(Source: Moscow Institute of Physics and Technology (MIPT), as published in EE Times)

As for you following this blog this is a break trough in the sense that previous work by Globalfoundries, NaMLab and Fraunhofer IPMS-CNT on ferroelectric hafnium oxide has always been much thicker (~70Å ) than a standard HfO2 used in HKMG technology that is typically 17 to 20 Å or so. Thick HfO2 is difficult to pattern since the etch species are not that volatile and therefore you need an advanced chuck in the etch chamber that can etch at elevated temperatures where the Hf-species are volatile enough to go in the general direction of the pump line without condensation anywhere on the wafer.

Read the full story here and the abstract is posted below:

As for the deposition method they used the well known TEMAH-H2O and TEMAZ-H2O ALD processes. It would be nice for all of us ALD process guys if you also mentioned the reactor or at least type of reactor used. A deposition temperature of 240 C means one thing in a hot wall reactor and totally something different in a warm wall reactor for instance.  For some reason physics, device & integration guys typically leave out this information - it is top secret even that ALD is a standard method today! The ellipsometer or AFM tool used or the TEM is always over specified, over specified - yeah you know even the AFM tips are specified. In this case, the supporting information reveals that the ALD reactor is coupled to a photoelectron spectroscopy (XPS) analysis chamber so possibly it is a custom ALD chamber that has been used.

Ultrathin Hf0.5Zr0.5O2 Ferroelectric Films on Si

Anna Chernikova, Maksim Kozodaev, Andrei Markeev, Dmitrii Negrov, Maksim Spiridonov, Sergei Zarubin, Ohheum Bak, Pratyush Buragohain, Haidong Lu, Elena Suvorova§, Alexei Gruverman*, and Andrei Zenkevich*
Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region 141700, Russia
Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588-0299, United States
§ École Polytechnique Fédérale de Lausanne, Lausanne, CH-1015, Switzerland
A.V. Shubnikov Institute of Crystallography, Leninsky pr. 59, Moscow 119333, Russia
NRNU “Moscow Engineering Physics Institute”, Moscow 115409, Russia
ACS Appl. Mater. Interfaces, 2016, 8 (11), pp 7232–7237
DOI: 10.1021/acsami.5b11653
Because of their immense scalability and manufacturability potential, the HfO2-based ferroelectric films attract significant attention as strong candidates for application in ferroelectric memories and related electronic devices. Here, we report the ferroelectric behavior of ultrathin Hf0.5Zr0.5O2 films, with the thickness of just 2.5 nm, which makes them suitable for use in ferroelectric tunnel junctions, thereby further expanding the area of their practical application. Transmission electron microscopy and electron diffraction analysis of the films grown on highly doped Si substrates confirms formation of the fully crystalline non-centrosymmetric orthorhombic phase responsible for ferroelectricity in Hf0.5Zr0.5O2. Piezoresponse force microscopy and pulsed switching testing performed on the deposited top TiN electrodes provide further evidence of the ferroelectric behavior of the Hf0.5Zr0.5O2 films. The electronic band lineup at the top TiN/Hf0.5Zr0.5O2 interface and band bending at the adjacent n+-Si bottom layer attributed to the polarization charges in Hf0.5Zr0.5O2 have been determined using in situ X-ray photoelectron spectroscopy analysis. The obtained results represent a significant step toward the experimental implementation of Si-based ferroelectric tunnel junctions.

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