JP3817068B2 - Laminated thin film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated thin film including a metal thin film.
[0002]
[Prior art]
An electronic device has been devised in which various functional films such as a superconducting film, a dielectric film, a ferroelectric film, and a piezoelectric film are formed and integrated on a Si substrate which is a semiconductor crystal substrate. For example, in the combination of a semiconductor and a superconductor, SQUID, Josephson element, superconducting transistor, electromagnetic wave sensor, superconducting wiring LSI, and the like can be cited. In the combination of a semiconductor and a dielectric, an LSI with a higher degree of integration, Dielectric isolation LSI based on SOI technology is listed. In combination with semiconductor and ferroelectric, non-volatile memory, infrared sensor, optical modulator, optical switch, OEIC (Opto-Electronic Integrated Circuit: OPTO-ELECTRONIC INTEGRATED CIRCUITS) etc. Is mentioned.
[0003]
In these electronic devices, in order to ensure optimum device characteristics and reproducibility, it is desirable that the functional film be an epitaxial film that is as close to a complete single crystal as possible. In polycrystalline materials, it is difficult to obtain good device characteristics due to disturbance of physical quantities due to grain boundaries.
[0004]
Incidentally, an electrode film is usually provided between the Si substrate and the functional film. In order to obtain a functional film with good crystallinity, it is necessary to form the electrode film as an epitaxial film close to a single crystal. In response to such a requirement, the present inventors disclosed in Japanese Patent Application Laid-Open No. 9-110592, (001) -oriented ZrO on a Si single crystal substrate.₂A buffer layer including a thin film, a stabilized zirconia thin film, a rare earth element oxide thin film, and the like is provided, and BaTiO is formed on the buffer layer._ThreeIt has been proposed to form a (001) -oriented perovskite layer composed of, for example, and to form a metal thin film composed of Pt or the like on the perovskite layer as an electrode film. The perovskite layer is provided by ZrO₂This is because when a Pt thin film is directly formed on a (001) thin film, Pt becomes (111) oriented or polycrystalline, and a Pt (100) single oriented film cannot be formed. This is ZrO₂Due to the large lattice mismatch between the (001) plane and the Pt (100) plane, Pt has an energy stable (111) plane rather than growing epitaxially, that is, using the (100) plane as a growth plane. This is because it grows as a growth surface.
[0005]
However, it takes time to form the perovskite layer. In particular, it is difficult to form a perovskite layer that is homogeneous and has a composition as designed. Specifically, BaTiO is formed on the buffer layer containing Zr._ThreeWhen forming a thin film, BaZrO_ThreeSuch a (110) -oriented substance is easily formed. Japanese Patent Laid-Open No. 9-110592 uses a vapor deposition method in which a metal vapor is supplied to the surface of a substrate in an oxidizing gas as a method for forming a uniform thin film having a large area._ThreeWhen forming a thin film, it is necessary to accurately control the evaporation amounts of Ba and Ti so that Ba: Ti = 1: 1 when deposited as an oxide on the substrate surface.
[0006]
Therefore, if a (100) -oriented metal thin film having good crystallinity can be formed without providing a perovskite layer, it will be a great advance in terms of cost reduction, quality improvement, and yield improvement.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a laminated thin film including a single-oriented metal thin film having good crystallinity.
[0008]
[Means for Solving the Problems]
Such an object is achieved by the present inventions (1) to (6) below.
(1) Cubic crystal (100) single-oriented epitaxial thin film and a {111} facet at the interface in contact with the thin metal filmAnd the ratio of facet surfaces at the interface is 80% or more.A laminated thin film having a buffer layer.
(2) The laminated thin film according to (1), wherein the buffer layer contains a rare earth element oxide, zirconium oxide, or zirconium oxide in which a part of Zr is substituted with a rare earth element or an alkaline earth element.
(3) The laminated thin film according to (2), wherein when the rare earth element and the alkaline earth element are represented by R, the atomic ratio R / (Zr + R) is 0.2 to 0.75 in the buffer layer.
(4) An underlayer is provided on the opposite side of the metal thin film with the buffer layer in between, and the underlayer contains zirconium oxide or zirconium oxide in which a part of Zr is substituted with a rare earth element or an alkaline earth element. When the rare earth element and the alkaline earth element are represented by R, the atomic ratio R / (Zr + R) in the underlayer is smaller than the atomic ratio R / (Zr + R) in the buffer layer. .
(5) The laminated thin film according to any one of (1) to (4), wherein the metal thin film contains at least one of Pt, Ir, Pd, and Rh.
(6) The laminated thin film according to any one of (1) to (5), wherein the surface is present on a substrate composed of Si (100) single crystal.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The laminated thin film of the present invention is formed on a substrate made of Si single crystal or the like, has a buffer layer on the substrate side, and has a metal thin film in contact with the buffer layer.
[0010]
Buffer layer
The buffer layer is provided between the metal thin film and the substrate. Note that the buffer layer also functions as an insulator.
[0011]
The buffer layer is characterized in that the interface with the metal thin film includes a {111} facet plane. FIG. 1A is a schematic diagram of the facet surface on the buffer layer surface. FIG. 1B shows the facet surface in an enlarged manner. Since the buffer layer is an epitaxial film having a cubic (100) orientation, a tetragonal (001) orientation, or a monoclinic (001) orientation, this facet plane is a {111} facet plane. The metal thin film is epitaxially grown as a {111} oriented film on the {111} facet surface of the buffer layer. As the metal thin film grows, the concave portion constituted by the facet surface is filled, and finally the surface of the metal thin film becomes flat as shown in FIG. 1C, and this surface is parallel to the substrate surface. Become. This surface is a cubic (100) plane, but may be a tetragonal (001) plane due to distortion of the crystal lattice.
[0012]
Conventionally, when a facet surface is present on the surface of the buffer layer and a metal thin film made of a cubic metal is formed on the facet surface, the metal thin film becomes an epitaxial film having a cubic (100) orientation. It has not been reported and is the first discovery in the present invention. As described above, ZrO has also been conventionally used.₂Although it has been known to use a thin film or a rare earth element oxide thin film as a buffer layer, when a metal thin film is formed directly on a flat buffer layer, a good cubic (100) oriented epitaxial film has not been obtained.
[0013]
The size of the facet surface is not particularly limited, but if the height of the facet surface, that is, the size when projected onto a plane orthogonal to the plane of the buffer layer is too small, the effect of providing the facet surface on the buffer layer surface Therefore, the projected dimension is preferably 5 nm or more. On the other hand, when the projected dimension is large, the surface of the metal thin film cannot be flat unless the metal thin film is increased accordingly. However, if the metal thin film is thickened, cracks are likely to occur. Therefore, the projected dimension is preferably 30 nm or less. The projected dimension is determined from a transmission electron micrograph of the buffer layer cross section.
[0014]
The ratio of the facet surface at the interface is preferably 80% or more, more preferably 90% or more. If the ratio of the facet plane is too low, it is difficult to grow the metal thin film as a good quality epitaxial film. In addition, the ratio of the facet surface in this specification is an area ratio calculated | required as follows from the transmission electron micrograph of a buffer layer cross section. When the length of the measurement target region on the buffer layer surface (length in the in-plane direction) is B, and the total length of surfaces parallel to the in-plane (other than the facet plane) is H, the ratio is [1- ( H / B)²]× 100It is represented by The length B of the measurement target region is 1 μm or more.
[0015]
In order to form the {111} facet surface on the surface, the buffer layer is mainly composed of rare earth element oxide, zirconium oxide as a major component, or part of Zr is composed of rare earth element or alkaline earth element. It is preferable to use substituted zirconium oxide as a main component. In addition, the rare earth element in this specification shall contain Sc and Y. When such a buffer layer is cubic (100) or monoclinic (001) oriented, a facet plane can appear on the surface.
[0016]
When the rare earth element and the alkaline earth element are represented by R, the composition of the buffer layer is Zr_1-xR_xO_2-It can be represented by δ. Zirconium oxide (ZrO) where x = 0₂) Causes a phase transition from high temperature to room temperature from cubic to tetragonal to monoclinic, but the addition of rare earth elements or alkaline earth elements stabilizes the cubic. ZrO₂An oxide obtained by adding a rare earth element or an alkaline earth element to is generally called stabilized zirconia. In the present invention, ZrO₂It is preferable to use a rare earth element as an element for stabilization.
[0017]
In the present invention, if the facet surface can be formed, Zr_1-xR_xO_2-x in δ is not particularly limited. However, in Jpn.J.Appl.Phys.27 (8) L1404-L1405 (1988), in the rare earth element stabilized zirconia, x becomes less than 0.2 in the composition range and becomes a tetragonal or monoclinic crystal. In addition, J. Appl. Phys. 58 (6) 2407-2409 (1985) has an orientation plane other than the one to be obtained in the composition range of tetragonal or monoclinic crystals. It has been reported that a mono-oriented epitaxial film cannot be obtained due to contamination. However, as a result of repeated studies by the present inventors, it has been found that by using the vapor deposition method described later, epitaxial growth is possible even with a composition having x less than 0.2, and good crystallinity can be obtained. High purity ZrO₂The film has a high insulation resistance and a small leak current, and thus is preferable when an insulation characteristic is required. However, x is preferably 0.2 or more in order to facilitate the formation of the facet surface.
[0018]
On the other hand, when the buffer layer is formed in contact with the Si single crystal substrate, in the composition range where x exceeds 0.75, although it is cubic, it is difficult to obtain (100) single orientation, and (111) oriented crystals. Or (111) single orientation. Therefore, when the buffer layer is directly formed on the Si single crystal substrate, Zr_1-xR_xO_2-In δ, x ≦ 0.75 or less, particularly 0.50 or less is preferable.
[0019]
However, by forming a buffer layer on a Si single crystal substrate through an appropriate underlayer, the buffer layer can be in a cubic (100) single orientation even when x is large. As such an underlayer, a cubic (100) -oriented, tetragonal (001) -oriented or monoclinic (001) -oriented thin film made of zirconium oxide or stabilized zirconia is preferable. In the underlayer, x is set to a smaller value than the buffer layer.
[0020]
The rare earth elements contained in the stabilized zirconia thin film may be appropriately selected according to the lattice constant of the thin film in contact with the stabilized zirconia thin film or the substrate and the lattice constant of the stabilized zirconia thin film. If x is changed while fixing the type of rare earth element, the lattice constant of stabilized zirconia can be changed, but if only x is changed, the matching adjustable region is narrow. However, if the rare earth element is changed, the lattice constant can be changed relatively large, so that matching can be optimized easily. For example, if Pr is used instead of Y, the lattice constant can be increased.
[0021]
Zirconium oxide containing no oxygen defects is represented by the chemical formula ZrO.₂In the stabilized zirconia, the amount of oxygen changes depending on the kind, amount and valence of the added stabilizing element, and Zr_1-xR_xO_2-δ in δ is usually 0 to 1.0.
[0022]
The buffer layer may have a gradient composition structure in which the composition changes continuously or stepwise. In the case of a gradient composition structure, Zr_1-xR_xO_2-It is preferable that x in δ increase from the back surface side to the front surface side (metal thin film side) of the buffer layer. When the above-described underlayer is provided, it can be said that the composition of the buffer layer changes stepwise if the underlayer is considered to be part of the buffer layer.
[0023]
The rare earth element used for the buffer layer may be selected from at least one of Sc, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Since some oxides tend to be hexagonal rare earth a-type structures, it is preferable to select an element that stably forms a cubic oxide. Specifically, at least one of Sc, Y, Ce, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu is preferable. What is necessary is just to select suitably according to these conditions.
[0024]
An additive may be introduced into the buffer layer to improve the characteristics. For example, Al and Si have an effect of improving the resistivity of the film. Furthermore, transition metal elements such as Mn, Fe, Co, and Ni can form a level due to impurities (trap level) in the film, and the conductivity can be controlled by using this level. Become.
[0025]
ZrO used as an underlayer and buffer layer₂In the thin film, the upper limit of the Zr ratio is currently about 99.99 mol%. In addition, with the current high-purity technology,₂And HfO₂Is difficult to separate from ZrO₂The purity of generally indicates the purity at Zr + Hf. Therefore, ZrO in this specification₂The purity of HfO is a value calculated by regarding Hf and Zr as the same element.₂Is ZrO in the present invention.₂ZrO in thin films₂Because it works in exactly the same way, there is no problem. This also applies to the stabilized zirconia.
[0026]
The thickness of the buffer layer is not particularly limited, and may be set as appropriate so as to form a facet surface having an appropriate dimension, but is preferably 5 to 1000 nm, more preferably 25 to 100 nm. If the buffer layer is too thin, it is difficult to form a uniform facet surface, and if it is too thick, cracks may occur in the buffer layer. The thickness of the underlayer may be appropriately determined so that the underlayer becomes a homogeneous epitaxial film, the surface is flat, and no cracks are generated, but it is usually preferably 2 to 50 nm.
[0027]
Metal thin film
The reason for providing the metal thin film is as follows. When the laminated thin film of the present invention is used as a component of an electronic device, the metal thin film mainly functions as an electrode. If a piezoelectric thin film or the like is formed as a functional film on a metal thin film having good crystallinity and surface properties obtained by the present invention, various electronic devices such as a thin film bulk resonator having good characteristics can be realized. Further, in a light emitting element such as an LED or a laser diode, it is important to increase the brightness. However, if a function of reflecting emitted light is provided in the element, the increase in brightness may be easily achieved. For example, a thin film serving as a reflective layer can be placed at an appropriate position in the device to promote emission of light emitted to the outside of the device. The metal thin film in the present invention can also function as such a reflective layer. Moreover, since the metal thin film plays a role of absorbing stress in the thin film laminate, it also has an effect of preventing the occurrence of cracks in the thin film formed on the metal thin film.
[0028]
As described above, the metal thin film provided on the surface where the facet surface of the buffer layer exists grows while filling the concave portion constituted by the facet surface, and finally the metal thin film surface becomes flat and parallel to the substrate surface. It becomes. At this time, the metal thin film is usually a cubic epitaxial film in which the (100) plane is oriented parallel to the film surface, but the crystal is deformed by stress and becomes, for example, a tetragonal (001) oriented epitaxial film. Sometimes.
[0029]
The metal thin film is preferably composed mainly of at least one of Pt, Ir, Pd and Rh, and is preferably composed of a simple substance of these metals or an alloy containing these metals. Moreover, the metal thin film may be comprised from 2 or more types of thin films from which a composition differs.
[0030]
Although the thickness of a metal thin film changes with uses, Preferably it is 10-500 nm, More preferably, it is 50-150 nm, and it is preferable that it is thin to such an extent that crystallinity and surface property are not impaired. More specifically, in order to fill the unevenness formed by the facet surface of the buffer layer, the thickness is preferably 30 nm or more. If the thickness is 100 nm or more, sufficient surface flatness can be obtained. In order to sufficiently function as an electrode, the thickness is preferably 50 to 500 nm.
[0031]
The specific resistance of the metal thin film is preferably 10^-7-10^ThreeΩcm, more preferably 10^-7-10^-2Ωcm.
[0032]
Crystallinity and surface properties
The crystallinity of the buffer layer, the metal thin film, and the underlayer can be evaluated by the half-value width of the rocking curve of the reflection peak in XRD (X-ray diffraction) and the pattern of the RHEED image. The surface property can be evaluated with a pattern of RHEED image and a transmission electron microscope. Here, RHEED is reflection high energy electron diffraction (Reflction High Energy Electron Diffraction).
[0033]
Specifically, in X-ray diffraction, the full width at half maximum of the reflection rocking curve of (200) plane or (002) plane ((400) plane in the rare earth c-type buffer layer) is 1.50 ° or less. It is preferable to have a certain degree of crystallinity. The lower limit value of the half-value width of the rocking curve is not particularly limited and is preferably as small as possible. However, at present, the lower limit value is generally about 0.7 °, particularly about 0.4 °. In RHEED, when the image is spot-like, the surface has irregularities, and when it is streak-like, the surface is flat. In either case, if the RHEED image is sharp, the crystallinity is excellent.
[0034]
In the laminated thin film of the present invention, the buffer layer, the metal thin film, and the underlayer are epitaxial films. First, the epitaxial film in this specification needs to be a single alignment film. In this case, the single alignment film means that when measured by X-ray diffraction, the peak intensity of reflection from other than the target surface is 10% or less, preferably 5% or less of the maximum peak intensity of the target surface. It is a film. For example, in the (k00) single alignment film, that is, the a-plane single alignment film, the intensity of the reflection peak other than the (k00) plane in the 2θ-θX-ray diffraction of the film is 10 which is the maximum peak intensity of the (k00) plane reflection. % Or less, preferably 5% or less. In this specification, (k00) is a display that collectively refers to equivalent surfaces such as (100) and (200). The second condition of the epitaxial film in this specification is that when the film plane is the xy plane and the film thickness direction is the z axis, the crystals are aligned in the x axis direction, the y axis direction, and the z axis direction. It is oriented. Such orientation can be confirmed by showing a spot-like or streak-like sharp pattern in RHEED evaluation. For example, when the crystal orientation is disturbed in a buffer layer having irregularities on the surface, the RHEED image does not have a sharp spot shape but tends to extend in a ring shape. If the above two conditions are satisfied, it can be said to be an epitaxial film.
[0035]
substrate
The substrate used in the present invention is Si, MgO, SrTiO._ThreeA substrate having a Si (100) single crystal surface is most preferable. When the Si single crystal substrate is used, it is preferable that the axes of the substrate and the laminated thin film are in parallel with each other.
[0036]
Production method
The formation method of the buffer layer, the metal thin film, and the underlayer is not particularly limited, and may be appropriately selected from methods capable of forming these as an epitaxial film on the substrate, particularly on the Si single crystal substrate. In particular, it is preferable to use a vapor deposition method disclosed in Japanese Patent Application Laid-Open No. 9-110592 and Japanese Patent Application No. 9-106776 by the present applicant.
[0037]
Hereinafter, formation of a buffer layer made of stabilized zirconia will be described as a specific example of the manufacturing method.
[0038]
In carrying out this manufacturing method, it is desirable to use, for example, a vapor deposition apparatus 1 configured as shown in FIG.
[0039]
The vapor deposition apparatus 1 has a vacuum chamber 1a provided with a vacuum pump P, and a holder 3 for holding the substrate 2 is disposed in the lower portion of the vacuum chamber 1a. The holder 3 is connected to a motor 5 via a rotating shaft 4 and is rotated by the motor 5 so that the substrate 2 can be rotated in the plane. The holder 3 includes a heater 6 for heating the substrate 2.
[0040]
The vapor deposition apparatus 1 includes an oxidizing gas supply device 7, and the nozzle 8 of the oxidizing gas supply device 7 is disposed immediately below the holder 3. As a result, the partial pressure of the oxidizing gas is increased in the vicinity of the substrate 2. Below the holder 3, a Zr evaporation part 9 and a rare earth element evaporation part 10 are arranged. In each of these evaporation sections, in addition to the respective evaporation sources, energy supply devices (electron beam generator, resistance heating device, etc.) for supplying energy for evaporation are arranged.
[0041]
First, a substrate is set in the holder. In this manufacturing method, a homogeneous thin film is formed on a large area substrate, for example, 10 cm.²It can be formed on a substrate having the above area. Thereby, the electronic device having the laminated thin film of the present invention can be made extremely inexpensive as compared with the prior art. There is no particular upper limit for the area of the substrate, but currently it is 400 cm.²Degree. Current semiconductor processes mainly use 2 to 8 inch Si wafers, particularly 6 inch type wafers, but this method can cope with this. It is also possible to form a laminated thin film by selecting partly with a mask or the like instead of the entire wafer surface.
[0042]
When a Si single crystal substrate is used, it is preferable to subject the substrate to surface treatment before forming the buffer layer. For the surface treatment of the substrate, it is preferable to use, for example, a treatment method described in Japanese Patent Application Laid-Open No. 9-110592 or Japanese Patent Application No. 9-106776 by the present applicant.
[0043]
After such surface treatment, the Si crystal on the substrate surface is covered and protected by the Si oxide layer. The Si oxide layer is reduced and removed by a metal such as Zr supplied to the substrate surface when the buffer layer is formed.
[0044]
Next, the substrate is heated in a vacuum, and a buffer layer is formed by supplying Zr, a rare earth element, and an oxidizing gas to the substrate surface. The heating temperature may be appropriately set so that good crystallinity is obtained and a facet surface is formed. Specifically, the temperature is preferably 400 ° C. or higher for crystallization, and a film having excellent crystallinity can be obtained at 750 ° C. or higher. Further, the size of the facet surface can be controlled by the heating temperature. The upper limit of the heating temperature is usually about 1300 ° C., although it depends on the heat resistance of the substrate. Examples of the oxidizing gas used here include oxygen, ozone, atomic oxygen, and NO.₂In the following description, oxygen is taken as an example.
[0045]
In forming the buffer layer, oxygen gas is continuously supplied into the vacuum deposition tank while the vacuum tank is continuously evacuated with a vacuum pump. The oxygen partial pressure in the vicinity of the substrate is 10^-3-10^-1It is preferably about Torr. The upper limit of oxygen partial pressure is 10^-1The reason for the Torr is to keep the evaporation rate constant without deteriorating the metal in the evaporation source in the vacuum chamber. When oxygen gas is introduced into the vacuum evaporation tank, it is preferable to inject gas from the vicinity of the substrate surface to create an atmosphere with a high oxygen partial pressure only in the vicinity of the substrate, thereby reducing the amount of gas introduced on the substrate. The reaction can be further promoted. At this time, since the inside of the vacuum chamber is continuously evacuated, most of the vacuum chamber is 10%.^-Four-10^-6The pressure is low at Torr. The supply amount of oxygen gas is preferably 2 to 50 cc / min, more preferably 5 to 25 cc / min. By controlling the oxygen gas supply amount, the facet surface can be easily formed, and the size of the facet surface can be changed. Since the optimum supply amount of oxygen gas is determined by the volume of the vacuum chamber, the pumping speed of the pump, and other factors, an appropriate supply amount is obtained in advance.
[0046]
Each evaporation source is heated and evaporated by an electron beam or the like and supplied to the substrate. In order to form a uniform thin film having a facet surface, the film formation rate is preferably 0.05 to 1.00 nm / s, particularly preferably 0.10 to 0.500 nm / s. By controlling the film formation rate, the facet surface can be easily formed, and the size of the facet surface can be changed.
[0047]
Deposition area is 10cm²In the case of film formation on the surface of a substrate having a diameter of 2 inches, for example, when the film is formed on the surface of the substrate, the substrate is rotated as shown in FIG. The oxidation reaction can be promoted throughout. This makes it possible to form a large area and homogeneous film. At this time, the number of rotations of the substrate is preferably 10 rpm or more. When the rotational speed is low, a film thickness distribution is likely to occur within the substrate surface. Although there is no upper limit on the number of rotations of the substrate, it is usually about 120 rpm because of the mechanism of the vacuum apparatus.
[0048]
A thin film made of a rare earth element oxide or a thin film made of zirconium oxide may be formed according to the case of the stabilized zirconia thin film described above. Also, for example, when forming a rare earth element oxide thin film on a zirconium oxide thin film, if the same rare earth element is used in both thin films, when the zirconium oxide thin film is formed to a predetermined thickness, By stopping the supply and continuing to supply only the rare earth element, both thin films can be formed in succession. Further, when the buffer layer has a gradient composition structure, the supply amount of Zr is gradually reduced, and finally it is set to zero, so that the formation of the rare earth element oxide thin film may be performed.
[0049]
The above-described manufacturing method can be carried out under operating conditions that are easy to control without room for the presence of impurities, as is particularly clear in comparison with conventional vacuum deposition methods, sputtering methods, laser ablation methods, etc. It is suitable for obtaining an object having high reproducibility and high integrity in a large area.
[0050]
Even when the MBE apparatus is used in this method, the target thin film can be obtained in exactly the same manner.
[0051]
Method for forming metal thin film
The metal thin film is preferably formed by vapor deposition. The substrate temperature during vapor deposition is preferably 500 to 750 ° C. If the substrate temperature is too low, it is difficult to obtain a film with high crystallinity, and if the substrate temperature is too high, irregularities on the surface of the film tend to be large. In addition, crystallinity can be further improved by introducing Rf plasma while flowing a small amount of oxygen in the vacuum chamber during vapor deposition. Specifically, for example, in the Pt thin film, there is an effect of preventing the (111) oriented crystal from being mixed into the (100) oriented crystal.
[0052]
In the present invention, the flatness of the metal thin film surface is generally good, but sufficient flatness may not be obtained depending on the thickness of the metal thin film and the forming method. In such a case, the metal thin film surface can be polished and planarized. For polishing, chemical polishing using an alkaline solution or the like, mechanical polishing using colloidal silica, or the like, combined use of chemical polishing and mechanical polishing, or the like may be used.
[0053]
When the surface of the laminated thin film is polished, polishing strain may remain. When it is necessary to remove the polishing strain, it is preferable to anneal the laminated thin film. The annealing is preferably performed at 300 to 850 ° C., more preferably 400 to 750 ° C., preferably 1 second to 30 minutes, more preferably 5 to 15 minutes.
[0054]
【Example】
Hereinafter, specific examples of the present invention will be shown to describe the present invention in more detail.
[0055]
Example 1
On a Si (100) single crystal substrate, ZrO₂Thin film, Y₂O_ThreeA laminated thin film in which a thin film and a Pt thin film were laminated in this order was formed by the following procedure.
[0056]
First, a Si single crystal wafer (disk shape having a diameter of 2 inches and a thickness of 250 μm) was prepared by cutting the surface so as to be a (100) plane and mirror polishing. The wafer surface was etched and cleaned with a 40% aqueous ammonium fluoride solution.
[0057]
Next, using the vapor deposition apparatus 1 shown in FIG. 8, the single crystal substrate 2 is fixed to the substrate holder 3 provided with the rotation and heating mechanism installed in the vacuum chamber 1a, and the vacuum chamber is set to 10%.^-6After evacuating to Torr with an oil diffusion pump, in order to protect the substrate cleaning surface with Si oxide, the substrate was rotated at 20 rpm and oxygen was introduced into the vicinity of the substrate from the nozzle 8 at a rate of 10 cc / min. Heated to ° C. As a result, the substrate surface was thermally oxidized, and a Si oxide film having a thickness of about 1 nm was formed on the substrate surface.
[0058]
The substrate was then heated to 900 ° C. and rotated. The rotation speed was 20 rpm. At this time, oxygen gas is introduced from the nozzle at a rate of 10 cc / min, and metal Zr is evaporated from the evaporation source and supplied to the substrate surface to reduce the Si oxide formed in the previous step and to form a thin film. It was. The supply amount of metal Zr is ZrO.₂In terms of the film thickness, the thickness was 10 nm. This thin film is found to be ZrO in X-ray diffraction.₂(002) peak is clearly observed, and (001) single-oriented and highly crystalline ZrO₂It was confirmed to be a thin film. This ZrO₂As shown in FIG. 2, the thin film showed a complete streak pattern in RHEED, and it was confirmed that the surface was flat at the molecular level and was a highly crystalline epitaxial film.
[0059]
Next, this ZrO₂A single crystal substrate on which a thin film is formed is used as a substrate, and metal Y is supplied to the substrate surface under the conditions of a substrate temperature of 900 ° C., a substrate rotation speed of 20 rpm, and an oxygen gas introduction rate of 10 cc / min.₂O_ThreeA thin film was formed. The supply amount of metal Y is Y₂O_ThreeConverted to 40 nm. This Y₂O_ThreeThe RHEED image of the thin film was a sharp spot as shown in FIG. From this, this Y₂O_ThreeIt can be seen that the thin film is an epitaxial film with good crystallinity and has irregularities on the surface. This Y₂O_ThreeWhen the cross section of the thin film was observed with a transmission electron microscope, a facet surface having a height of 10 nm was present, and the ratio of the facet surface was 95% or more.
[0060]
Next, Y₂O_ThreeA Pt thin film having a thickness of 100 nm was formed on the thin film. The substrate temperature was 700 ° C. and the substrate rotation speed was 20 rpm. The RHEED image of this Pt thin film had a sharp streak shape as shown in FIG. This indicates that this Pt thin film is an epitaxial film with good crystallinity and the surface is flat at the molecular level.
[0061]
Further, when the 10-point average roughness Rz (reference length 1000 nm) according to JIS B 0610 was measured on the surface of the Pt thin film, it was 1.1 to 1.8 nm, and it was confirmed directly that the flatness was excellent. .
[0062]
Pt / Y obtained in this way₂O_Three/ ZrO₂An X-ray diffraction chart of the / Si (100) laminated structure is shown in FIG. In FIG. 5, only the peak of the plane equivalent to (100) and the peak of the plane equivalent to (001) are recognized for each thin film, and from this, each thin film has (100) single orientation or (001) single orientation. I know that there is. In FIG. 5, the full width at half maximum of the rocking curve of Pt (200) reflection was 1.1 °, and it was confirmed that the orientation was excellent.
[0063]
Example 2
ZrO₂Thin film and Y₂O_ThreeA Pt / stabilized zirconia / Si (100) laminated structure was produced in the same manner as in Example 1 except that a stabilized zirconia thin film was formed instead of the thin film. The composition of the stabilized zirconia thin film is Zr_0.7Y_0.3O_2-The substrate temperature, the number of substrate rotations, and the amount of oxygen introduced when forming the stabilized zirconia thin film are ZrO in Example 1.₂The same as in the case of thin film formation.
[0064]
The RHEED image of this stabilized zirconia thin film was a sharp spot as shown in FIG. From this, it can be seen that this stabilized zirconia thin film is an epitaxial film with good crystallinity and has irregularities on the surface. A transmission electron micrograph of the cross section of the stabilized zirconia thin film is shown in FIG. In FIG. 7, the right side is the Si single crystal substrate side. It can be seen that the interface between the buffer layer and the metal thin film has almost no plane parallel to the substrate surface (a plane perpendicular to the figure), and most of the interface consists of facet planes. The ratio of the facet surface of this stabilized zirconia thin film was 90% or more.
[0065]
【The invention's effect】
In the present invention, a buffer layer containing at least one of Zr oxide and rare earth element oxide is provided, and a facet surface is present on the surface of the buffer layer. When a metal thin film is formed directly on the surface of the buffer layer, the metal thin film becomes a film having a (100) single orientation and good crystallinity, and the surface of the metal thin film becomes flat at the molecular level. Further, since the contact area between the buffer layer and the metal thin film is increased due to the presence of the facet surface, peeling of the metal thin film can be suppressed.
[0066]
Further, in the present invention, unlike the above-mentioned Japanese Patent Laid-Open No. 9-110592, the BaTiO is interposed between the buffer layer and the metal thin film._ThreeSince it is not necessary to provide a perovskite layer made of, etc., the manufacturing process is simplified. In addition, since the buffer layer in the present invention can stably obtain higher crystallinity than the perovskite layer, the buffer layer has a high function as a buffer layer. In the present invention, the buffer layer is made of BaTiO._ThreePinholes are less likely to occur than layers.
[0067]
By laminating a functional film made of a ferroelectric, piezoelectric, superconductor, etc. on a substrate provided with the laminated thin film of the present invention, a nonvolatile memory, an infrared sensor, an optical modulator, an optical switch, an OEIC, a SAW Elements, convolvers, collimators, memory elements, image scanners, thin film bulk resonators, filters, SQUIDs, Josephson elements, superconducting transistors, electromagnetic wave sensors, superconducting wiring LSIs, and the like can be manufactured.
[Brief description of the drawings]
FIG. 1A is a schematic view of a {111} facet surface on a buffer layer surface, FIG. 1B is an enlarged view thereof, and FIG. 1C is a diagram showing a metal thin film formed on the facet surface. It is a schematic diagram which shows a state.
FIG. 2 is a drawing-substituting photograph showing a crystal structure, which is ZrO formed on a Si single crystal substrate.₂It is a RHEED image of a thin film.
FIG. 3 is a drawing-substituting photograph showing a crystal structure, and shows a ZrO image showing an RHEED image in FIG.₂Y formed on thin film₂O_ThreeIt is a RHEED image of a thin film.
4 is a drawing-substituting photograph showing a crystal structure, and FIG. 3 shows a RHEED image Y₂O_ThreeIt is a RHEED image of the Pt thin film formed on the thin film.
[Figure 5] Pt / Y₂O_Three/ ZrO₂3 is an X-ray diffraction chart of a / Si (100) laminated structure.
FIG. 6 is a drawing-substituting photograph showing a crystal structure, which is a RHEED image of a stabilized zirconia thin film formed on a Si single crystal substrate.
FIG. 7 is a drawing-substituting photograph showing a crystal structure, which is a transmission electron micrograph of a cross section of a stabilized zirconia thin film formed on a Si single crystal substrate.
FIG. 8 is an explanatory view showing an example of a vapor deposition apparatus used for forming the laminated thin film of the present invention.
[Explanation of symbols]
1 Vapor deposition equipment
1a Vacuum chamber
2 Substrate
3 Holder
4 Rotating shaft
5 Motor
6 Heater
7 Oxidizing gas supply device
8 nozzles
9 Zr evaporation section
10 Rare earth element evaporation section

Claims (6)

A metal thin film that is an epitaxial film of cubic (100) single orientation , and a buffer layer having a {111} facet surface at an interface in contact with the metal thin film , and a ratio of the facet surface at the interface is 80% or more ; A laminated thin film.  The laminated thin film according to claim 1, wherein the buffer layer contains a rare earth element oxide, zirconium oxide, or zirconium oxide in which a part of Zr is substituted with a rare earth element or an alkaline earth element.  The laminated thin film according to claim 2, wherein when the rare earth element and the alkaline earth element are represented by R, the buffer layer has an atomic ratio R / (Zr + R) of 0.2 to 0.75.  An underlayer on the opposite side of the metal thin film across the buffer layer, the underlayer containing zirconium oxide or zirconium oxide in which a part of Zr is substituted with a rare earth element or an alkaline earth element; The multilayer thin film according to claim 2, wherein when the element and the alkaline earth element are represented by R, the atomic ratio R / (Zr + R) in the underlayer is smaller than the atomic ratio R / (Zr + R) in the buffer layer.  The laminated thin film according to claim 1, wherein the metal thin film contains at least one of Pt, Ir, Pd, and Rh.  The laminated thin film according to any one of claims 1 to 5, wherein the surface is present on a substrate composed of Si (100) single crystal.

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