JP5517034B2 - Electronic device substrate - Google Patents

Description

  The present invention relates to an electronic element substrate having an oxide film on a metal substrate surface.

A thin oxide film is useful as a material for an excellent tunnel barrier layer or field effect element, or as a material for a semiconductor element such as a memory depending on the size of the band gap.
Among them, it has an electron emission source having a metal-tunnel barrier layer-metal (MIM structure) and a structure of metal-tunnel barrier layer-sensor layer (MIS), and transmits and receives electrons in the sensor layer to the metal layer through the tunnel barrier layer. We have applied for a patent for an alumina film and its manufacturing method that can be applied to a type of sensor, a magnetic device having a MIM / MIS structure and a material having a spin (see Patent Document 1).
In this method, the interface is terminated with metal atoms constituting the oxide film (FIG. 1A), and when the substrate is copper or nickel, the valence band offset (Schottky barrier height with respect to holes) is large. There was a problem.

  When the interface is terminated with an oxygen atom, this valence band offset is expected to decrease (according to first-principles calculation), but there is nothing that specifically achieves it. , Aimed to realize.

  The electronic device substrate of the present invention is characterized in that the interface between the oxide film and the metal substrate is terminated by oxygen atoms.

The inventors have succeeded in producing an alumina ultrathin film in which the interface with the metal substrate is terminated by oxygen atoms (FIG. 1B).
This is a new electronic device substrate obtained as a result of finding a rule for determining the type of interface termination atom and enabling it to be used as a method for producing an oxide film in which a metal substrate and an interface are terminated by oxygen atoms.

The schematic diagram of the interface termination | terminus of a metal substrate and an alumina film interface. (A) Aluminum atom termination, (b) Oxygen atom termination. The photoelectron spectrum of the alumina film ultrathin film on the copper substrate which has an aluminum atom termination shown in nonpatent literature 1. The photoelectron spectrum of the alumina film before the heat treatment of Experiment No. 11. The photoelectron spectrum of the alumina film after the heat treatment of Experiment No. 11. The photoelectron spectrum of the alumina film of experiment number 1. The photoelectron spectrum of the alumina film of experiment number 2. The photoelectron spectrum of the alumina film of experiment number 3. The photoelectron spectrum of the alumina film of experiment number 4. A high-speed reflection electron diffraction pattern of the alumina film of Experiment No. 5. A scanning secondary electron image of the alumina film of Experiment No. 5. The photoelectron spectrum of the alumina film of Experiment No. 6. The photoelectron spectrum of the alumina film of Experiment No. 7. The photoelectron spectrum of the alumina film of Experiment No. 8. The photoelectron spectrum of the alumina film of experiment number 9. The photoelectron spectrum of the alumina film of experiment number 10. A scanning secondary electron image of the alumina film of Experiment No. 10. The photoelectron spectrum of the alumina film | membrane before the heat processing of the experiment number 12. The photoelectron spectrum of the alumina film after the heat treatment of Experiment No. 12. The photoelectron spectrum of the alumina film after the heat treatment of Experiment No. 13.

The materials of the substrate of the present invention are copper (111) and nickel (111) in the examples. Based on the knowledge of the examples, metal elements having the same crystal surface structure, particularly fcc, for the following reasons. It can be applied to the (111) face of metal and the (0001) face of hcp metal.
The present invention is based on the fact that the interface between the metal substrate (M) and the oxide (AxOy) is terminated by oxygen atoms by thermodynamically satisfying the following relational expression.
The fact that the oxide interface is terminated by oxygen atoms means that the polar surface of the oxide grows on the metal substrate. In many cases, the oxygen termination surface of the oxide has a structure in which oxygen is closely packed, and in this case, the surface has two-dimensional symmetry in two dimensions. Therefore, if the following relational expression is satisfied thermodynamically, in addition to the copper (111) and nickel (111) mentioned as examples, the fcc metal (111) and the hcp metal ( 0001) plane.

In the production method used to produce the present invention, it is important that oxygen is present in the atmosphere during the deposition of the metal element to be oxidized on the substrate, and the appropriate range of the oxygen partial pressure is as follows. Can be determined.
Oxygen partial pressure: In the above chemical equilibrium (2), satisfies the following formula 2 conditions, and the oxygen partial pressure range alumina film to film growth in a state in which the metal element of the oxide is fully oxidized 5x10 ^{- 8} mbar to 6.6 × 10 ⁻⁷ mbar. Although the embodiment is ^2x10 -7 mbar and ^5x10 -7 mbar, the documents cited in the known document ^B, and the oxygen partial pressure range of 5x10 -8 mbar~6.6x10 ^-7 mbar the oxygen in the chemical equilibrium It is shown to be stable at the end side.

The oxygen partial pressure is different for each oxide film, and is the above-described chemical equilibrium equation. The oxygen partial pressure is such that the film grows in a state where the condition of the chemical formula 2 is satisfied and the metal element of the oxide is sufficiently oxidized. It becomes a range. By satisfying the condition of the chemical equilibrium formula (2) and in an oxygen partial pressure range in which the film grows in a state where the metal element of the oxide is sufficiently oxidized, a metal element that can be deposited other than aluminum (for example, Magnesium, tin, zinc, hafnium, zirconium, cerium, chromium, nickel, etc.) can be used.
The alumina film, not only ^2x10 -7 mbar and ^5x10 -7 mbar listed in Example ^believed to be in the range of 5x10 -8 mbar~6.6x10 ^-7 mbar.

If the growth temperature interface is above the temperature at which atomic migration necessary for thermodynamic equilibrium is possible and the oxide film does not sublime, it can be deposited as an oxide film on the substrate.
For an alumina film, the temperature is 500 ° C. or more and 830 ° C. or less. It is necessary that the interface be at or above the temperature at which atom transfer necessary for thermodynamic equilibrium is possible. From the examples, it can be seen that a thermodynamic equilibrium is not reached at 400 ° C., but a thermodynamic equilibrium interface is formed at 500 ° C. The upper limit of the temperature is limited by the temperature range in which the alumina film does not sublime, and the temperature is 830 ° C. or less based on the literature.
The growth temperature is different for each oxide film and is in a range not less than the temperature at which atom transfer is possible and not more than the temperature at which the oxide film does not sublime.
For example, it is 500 ° C. or higher and 830 ° C. or lower for an alumina film.

Film thickness: 0.4 nm to 8 nm
An oxide thin film having a polar surface as an interface has properties as an oxide film only when the (metal surface-oxygen surface) is one unit and has a thickness of at least 3 units. The thickness for 3 units is approximately 0.4 nm, which is the minimum film thickness. Although the maximum film thickness depends on the magnitude of the strain generated in the oxide thin film, it has been shown in the Examples that a film having a thickness of 5 nm or more can be produced epitaxially. It turns out that the film thickness can be increased even though it becomes a body. Since it is considered that a film having a thickness of less than 10 nm is used from the viewpoint of exhibiting the function of the MIS or MIM structure, the maximum film thickness is set to 8 nm.

In this example, Al is deposited on the (111) surface of various metal substrates in an oxygen atmosphere.
The surface of the substrate, the deposition conditions, and the obtained aluminum oxide thin film are as detailed in Table 1.
The thickness of the alumina thin film was estimated from the photoelectron spectrum.
Whether it is epitaxial or amorphous was judged by whether low-energy electron diffraction was clear.
In Experiment No. 13, low-energy electron diffraction was obtained, but it was found to be a polycrystal because it was not a spot pattern but a ring pattern.
The step interval refers to the width of a terrace existing between atomic steps appearing due to the polishing accuracy of the substrate surface, and the longer this interval, the higher the polishing accuracy.
In Experiment No. 5, in the scanning secondary electron image of the alumina film, as shown in FIG. 10 , a flat terrace and atomic steps are observed at an atomic level as wide as about 200 nm, and the flat alumina film at the atomic level is observed. It can be seen that is obtained.
Further, in Experiment No. 10, as shown in FIG. 16, on the polishing accurate clean nickel single crystal (111), the flat surface of 1000nm of the step interval was obtained.
As shown in FIG. 2, when the interface is an aluminum atom, the Al 2p photoelectron spectrum shows a peak due to the Al component at the interface between the Al and metal Al peaks in the oxide film (the intensity is weak and Is often observed).
As can be seen in FIG. 3, the unoxidized Al component gives a spectrum consisting of two sharp peaks, and the Al component in the alumina film gives a broad peak. It is discriminated whether it is a peak due to metal Al.
When the heat treatment in FIG. 3 is performed in oxygen, most of the metal Al is oxidized, and as shown in FIG. 4, the intensity of the two sharp peaks seen in FIG. 3 decreases, and the intensity of the peak due to Al in the alumina film. increased. In both FIG. 3 and FIG. 4, the Al component at the interface was observed as a bump. However, this bump is weaker than that in FIGS. 2, 18 and 19, and the interface elements are considered to be both aluminum atoms and oxygen atoms.
As shown in FIG. 17, when aluminum is deposited at a high deposition rate at an oxygen partial pressure of 1 × 10 −7 mbar and 200 ° C., the reaction between the deposited Al and oxygen does not proceed sufficiently, and the metal is not oxidized. A spectrum consisting of two sharp peaks with high intensity remained and a high intensity was observed. An interface Al component was also observed. By annealing this sample at an oxygen partial pressure of 1 × 10 −6 mbar and 200 ° C., the oxidation reaction progressed, and most of the remaining metal Al was oxidized. As shown in FIG. 18, the peak intensity of the metal Al component was It drastically decreased and the strength of the Al component in the alumina film greatly increased. Further, the interface Al component is observed with the same strength as in FIG. 2, and it can be seen that the interface element is an aluminum atom.
Note that the experiment numbers 11, 12, and 13 are reference examples for showing the limits of the present embodiment.
Thus, in this example, it is considered that heating to 50 × 10 ° C. or more at 3/4 hr or more is an appropriate range for the oxygen termination.

WO2007 / 029754

J. et al. Applied Physics, 103, 033707 (2008)

Claims (3)

An electronic device substrate having a flat epitaxial oxide film at an atomic level on the surface of the metal substrate, wherein an interface between the oxide film and the metal substrate is terminated by oxygen atoms , the metal substrate is made of copper or nickel, An electronic element substrate, wherein the epitaxial oxide film is made of alumina .   2. The electronic device substrate according to claim 1, wherein a film thickness of the flat epitaxial oxide film at the atomic level is in a range of 0.4 to 8 nm. The electronic element substrate according to claim 1, wherein the epitaxial oxide film flat at the atomic level is an alumina film.