JPH04331795A - Production of polycrystalline thin film - Google Patents

Abstract

PURPOSE:To produce a polycrystal layer having excellent orientation of crystal. CONSTITUTION:In depositing constituent particles beaten and driven out from a target by sputtering on a substrate, the constituent particles are deposited on the substrate while slantingly applying the substrate ions generated from an ion gun. The angle of irradiation is most preferably about 45 degrees and a mixed ion of argon ion and oxygen ion is preferable as the ion. By this method, each crystal particle of polycrystal layer is orientated rectangularly to the c-axis on a film-forming face of the substrate and a thin film of crystal particles orientated in the a-axis and the b-axis is obtained.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a polycrystalline thin film with uniform crystal orientation. [0002] Oxide superconductors discovered in recent years are excellent superconductors that exhibit a critical temperature exceeding the liquid nitrogen temperature. In order to use it as a superconductor, there are various problems that must be solved. One of the problems is that the critical current density of oxide superconductors is low. The problem of the low critical current density of the oxide superconductor is largely due to the existence of electrical anisotropy in the crystal itself of the oxide superconductor. It is known that it is easy to conduct electricity in the a-axis and b-axis directions of the crystal axes, but it is difficult to conduct electricity in the c-axis direction. From this point of view, in order to form an oxide superconductor on a base material and use it as a superconductor, it is necessary to form an oxide superconductor with good crystal orientation on the base material, and to It is necessary to orient the a-axis or b-axis of the crystal of the oxide superconductor in the direction in which electricity is to flow, and to orient the c-axis of the oxide superconductor in the other direction. [0004] Conventionally, therefore, various methods have been tried to form an oxide superconducting layer with good crystal orientation on a base material such as a substrate or a metal tape. One method is to use a single crystal base material such as MgO or SrTiO3, which has a similar crystal structure to that of the oxide superconductor, and form an oxide superconducting layer on these single crystal base materials by a film formation method such as sputtering. method is implemented. [0005] When a film forming method such as sputtering is performed using the single crystal base material of MgO or SrTiO3, the crystal orientation of the oxide superconducting layer grows based on the crystal of the single crystal base material. The oxide superconducting layer formed on these single crystal substrates can exhibit a sufficiently high critical current density of several hundred thousand to several million A/cm2. It has been known. Problems to be Solved by the Invention By the way, in order to use an oxide superconductor as a conductor, it is necessary to form an oxide superconducting layer with good crystal orientation on a long base material such as a tape. There is a need to. However, when forming an oxide superconducting layer directly on a base material such as a metal tape, the metal tape itself is polycrystalline and its crystal structure is significantly different from that of an oxide superconductor. It is impossible to form layers. Furthermore, there is a problem that the heat treatment performed when forming the oxide superconducting layer causes a diffusion reaction between the metal tape and the oxide superconducting layer, causing the crystal structure of the oxide superconducting layer to collapse and deteriorating the superconducting properties. Therefore, conventionally, on a base material such as a metal tape,
It has been practiced to coat an intermediate layer such as MgO or SrTiO3 and form an oxide superconducting layer on this intermediate layer. However, an oxide superconducting layer formed on this type of intermediate layer has a much lower critical current density (for example, several thousand to ten thousand A/cm2) than an oxide superconducting layer formed on a single crystal substrate.
The problem was that it only showed the degree. This is considered to be due to the reasons explained below. FIG. 16 shows a cross-sectional structure of an oxide superconducting conductor in which an intermediate layer 2 is formed on a base material 1 such as a metal tape, and an oxide superconducting layer 3 is formed on this intermediate layer 2. Here, in the structure shown in FIG. 16, the oxide superconducting layer 3
is in a polycrystalline state, in which a large number of crystal grains 4 are bonded together in a disordered manner. When looking at each of these crystal grains 4 individually, the c-axis of each crystal grain 4 is oriented perpendicular to the base material surface, but the a-axis and b-axis are oriented in random directions. It is thought that When the directions of the a- and b-axes become disordered for each crystal grain in the oxide superconducting layer, the quantum connectivity of the superconducting state is lost at the grain boundaries where the crystal orientation is disordered, and as a result, the superconducting properties, especially This is thought to cause a decrease in critical current density. Further, the reason why the oxide superconductor is in a polycrystalline state in which the a-axis and b-axis are not oriented is because the intermediate layer 2 formed thereunder is in a polycrystalline state in which the a-axis and b-axis are not oriented. This seems to be because, when forming the oxide superconducting layer 3, the oxide superconducting layer 3 grows to match the crystal of the intermediate layer 2. By the way, in fields other than the application of the oxide superconductor, techniques for forming various alignment films on polycrystalline substrates are used. Examples include the field of optical thin films, magneto-optical disks, wiring boards, high-frequency waveguides, high-frequency filters, and cavity resonators. The challenge is to form a good polycrystalline thin film. In other words, if the crystal orientation of a polycrystalline thin film is good, the quality of the optical thin film, magnetic thin film, wiring thin film, etc. formed thereon will improve, and furthermore, if the crystal orientation is good on the base material, It would be even more preferable if good optical thin films, magnetic thin films, wiring thin films, etc. could be directly formed. Furthermore, magnetic thin films such as permalloy or sendust, which have high magnetic permeability and are thermally stable, have been put into practical use as core materials for magnetic heads used in high frequency bands. These magnetic thin films are conventionally formed on a predetermined substrate by vapor deposition or sputtering, but if the crystal orientation of these magnetic thin films is low, it is difficult to control the magnetic anisotropy of the magnetic thin film. There was a problem that the orientation of the crystal grains became disordered within the film plane, impairing the high frequency characteristics of magnetic permeability. Additionally, if the axial directions of the crystal axes within the film plane are disordered, local fluctuations called skews and ripples will occur in the in-plane magnetization, which will impair the high-frequency characteristics of magnetic permeability as described above. . The present invention has been made to solve the above-mentioned problems, and the crystal axis c
At the same time, the a-axis and b-axis of the crystal axes of the polycrystalline thin film can be aligned along the plane parallel to the film formation surface, forming a polycrystalline thin film with excellent crystal orientation. The purpose is to provide a method that can be used. Means for Solving the Problems In order to solve the above problems, the invention according to claim 1 deposits constituent particles of a target ejected by sputtering on a base material, and forms polycrystalline particles on the base material. In a method for forming a thin film, when depositing the constituent particles on a base material, ions generated by an ion source are irradiated obliquely to the film-forming surface of the base material. [0013] In order to solve the above problem, the invention according to claim 2 sets the irradiation angle when irradiating the base material according to claim 1 with ions to 40 to 60 degrees with respect to the film-forming surface of the base material. The range shall be as follows. In order to solve the above problem, the invention according to claim 3 uses an inert gas ion, or a reactive gas containing at least one of an inert gas and a polycrystalline thin film constituent element, as the ion according to claim 1. A method for producing a polycrystalline thin film, characterized by using a mixed ion of. [Operation] When the constituent particles ejected from the target by sputtering are deposited on the film-forming surface of the base material, ions are also irradiated from an oblique direction at the same time, so that the constituent particles are efficiently activated. In addition to c-axis orientation, a-axis orientation and b-axis orientation are also improved with respect to the film-forming surface of the base material. As a result, even in polycrystalline thin films with many grain boundaries formed, the a-axis, b-axis, and c-axis orientations of each grain are all improved, resulting in improved polycrystalline film quality. A crystal thin film is obtained. Furthermore, in order to form such a polycrystalline thin film with good orientation, it is most preferable to set the ion irradiation angle to 45 degrees. Furthermore, to activate the constituent particles,
Argon and oxygen ions are preferred. [Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of an apparatus used when carrying out the method of the present invention, and the apparatus of this example has a configuration in which a sputtering apparatus is provided with an ion source for ion beam assist. The apparatus of this embodiment includes a substrate holder 11 that holds a substrate A, a plate-shaped target 12 that is disposed diagonally above the substrate holder 11 and facing each other at a predetermined interval, and the substrate holder 11. The main components are: an ion source 13 that faces obliquely upward at a predetermined interval and is placed apart from the target 12; and a sputter beam irradiation device 14 that is placed below the target 12 toward the lower surface of the target 12. It is configured. In addition, reference numeral 1 in the figure
5 indicates a target holder holding the target 12. Further, the apparatus of this embodiment is housed in a vacuum container (not shown), so that the surroundings of the base material A can be maintained in a vacuum atmosphere. Furthermore, an atmospheric gas supply source such as a gas cylinder is connected to the vacuum container, and the interior of the vacuum container is kept in a low pressure state such as vacuum, and an atmosphere of argon gas or other inert gas, or an inert gas containing oxygen is connected to the vacuum container. It allows you to enjoy the atmosphere. [0020] The base material A has various shapes such as a plate material, a wire material, and a tape material. It is made of various ceramics, etc. In addition, when using a long metal tape (tape made of Hastelloy or stainless steel) as the base material A, a feeding device and a winding device for the metal tape are installed inside the vacuum container, and the tape is continuously drawn from the feeding device. It is preferable to configure so that a polycrystalline thin film can be continuously formed on a tape-shaped base material by feeding the base material A into the material holder 11 and then winding it up with a winding device. [0021] The substrate holder 11 is equipped with a heater inside, so that the substrate A placed on the substrate holder 11 can be heated to a desired temperature. Said target 1
2 is for forming the target polycrystalline thin film, and a film having the same composition or a similar composition to the target polycrystalline thin film is used. Specifically, the target 12 is zirconia stabilized with MgO or Y2O3 (
YSZ), MgO, SrTiO3, etc., but the target is not limited thereto, and any target suitable for the polycrystalline thin film to be formed may be used. The ion source 13 is constructed by housing an evaporation source inside a container and having an extraction electrode near the evaporation source. This device ionizes some of the atoms or molecules generated from the evaporation source, and irradiates the ionized particles as an ion beam by controlling them with an electric field generated by an extraction electrode. There are various methods for ionizing particles, such as a direct current discharge method, a high frequency excitation method, a filament method, and a cluster ion beam method. The filament method is a method in which a tungsten filament is heated with electricity to generate thermoelectrons, which collide with evaporated particles in a high vacuum to ionize them. Furthermore, in the cluster ion beam method, clusters of aggregated molecules that come out into a vacuum from a nozzle provided in the opening of a crucible containing raw materials are bombarded with thermal electrons, ionized, and emitted. In this embodiment, an ion source 13 having an internal structure shown in FIG. 2 is used. The ion source 13 includes an extraction electrode 17, a filament 18, and an introduction tube 19 for Ar gas, etc., inside a cylindrical container 16, and can irradiate parallel beams of ions from the tip of the container 16. It is something. As shown in FIG. 1, the ion source 13 is opposed to the substrate A with its central axis S inclined at an inclination angle θ with respect to the upper surface (film forming surface) of the substrate A. This inclination angle θ
is preferably in the range of 40 to 60 degrees, most preferably around 45 degrees. Therefore, the ion source 13 is arranged so as to be able to irradiate the upper surface of the base material A with ions at an angle of inclination θ. Note that the ions irradiated onto the base material A by the ion source 13 include He+, Ne+, Ar+, Xe+, and Kr+.
Ions of rare gases such as ions, or mixed ions of these and oxygen may be used. The sputter beam irradiation device 14 has the same configuration as the ion source 13, and is capable of irradiating the target 12 with ions to knock out constituent particles of the target 12. In addition, in the method of the present invention, it is important to be able to knock out the constituent particles of the target 13, so the configuration is such that the constituent particles of the target 12 can be knocked out by applying a voltage to the target 12 with a high frequency coil or the like. The sputter beam irradiation device 14 may be omitted. Next, Y is deposited on the base material A using the apparatus having the above configuration.
A method for forming a polycrystalline thin film of SZ will be explained. To form a polycrystalline thin film on the base material A, a YSZ target is used, and the inside of the container housing the base material A is evacuated to create a reduced pressure atmosphere. And ion source 1
3 and the sputter beam irradiation device 14 is activated. When the target 12 is irradiated with ions from the sputter beam irradiation device 14, constituent particles of the target 12 are knocked out and fly onto the base material A. Then, target 1 is placed on base material A.
At the same time as the constituent particles ejected from 2 are deposited, mixed ions of Ar ions and oxygen ions are irradiated from the ion source 13. The irradiation angle θ during this ion irradiation is most preferably 45 degrees, and preferably in the range of 40 to 60 degrees. If θ is 90 degrees, the c-axis of the polycrystalline thin film is oriented perpendicular to the film formation surface of base material A, but the (111) plane stands on the film formation surface of base material A, which is not preferable. . Also,
When θ is set to 30 degrees, the polycrystalline thin film does not even have c-axis orientation. If ion irradiation is performed at the above angle, the (100) crystal plane of the polycrystalline thin film will stand up. By performing sputtering while performing ion irradiation at such an irradiation angle, the a-axis and b-axis of the crystal axes of the YSZ polycrystalline thin film formed on the base material A can be oriented. This seems to be due to the fact that the sputtered particles that were being deposited were efficiently activated by ion irradiation at an appropriate angle. FIG. 3 shows a substrate A on which a polycrystalline thin film B of YSZ has been deposited by the method described above. Polycrystalline thin film B shown in Figure 3
The fine crystal grains 20 having a cubic crystal structure are
A large number of crystal grains 20 are joined together through grain boundaries, and the c-axis of the crystal axis of each crystal grain 20 is oriented at right angles to the upper surface (film formation surface) of the base material A. The a-axes and the b-axes are oriented in the same direction and in-plane. Further, the c-axis of each crystal grain 20 is oriented at right angles to the (upper) film-forming surface of the base material A. The a-axes (or b-axes) of each crystal grain 20 are joined together so that the angle they form (grain boundary inclination angle K shown in FIG. 2) is within 30 degrees. Once the polycrystalline thin film B of YSZ is formed on the base material A as described above, an oxide superconducting layer is formed on this polycrystalline thin film B. To form an oxide superconducting layer on polycrystalline thin film B, sputtering is performed in an oxygen gas atmosphere using a target with a composition similar to or the same as that of the target oxide superconductor, and oxidation is applied onto polycrystalline thin film B. A physical superconducting layer may be formed, or a laser vapor deposition method may be used in which the target is irradiated with a laser beam to scoop out constituent particles for vapor deposition. In the polycrystalline thin film B, the c-axis is oriented in a direction perpendicular to the film-forming surface of the base material A, and the a-axes and b-axes are aligned along a plane parallel to the film-forming surface. Since it has good orientation, the oxide superconducting layer laminated on the polycrystalline thin film B by sputtering or laser evaporation also deposits and grows crystals so as to match the orientation of the polycrystalline thin film B. Therefore, the oxide superconducting layer formed on the polycrystalline thin film B becomes a polycrystalline oxide superconducting layer, but in each crystal grain of this oxide superconducting layer,
The c-axis, which is difficult to conduct electricity, is oriented in the thickness direction of the base material A, and the a-axes or b-axes are oriented in the longitudinal direction of the base material A. Therefore, the obtained oxide superconducting layer has excellent quantum connectivity at the grain boundaries, and there is little deterioration of the superconducting properties at the grain boundaries, so it is easy to conduct electricity in the longitudinal direction of the base material A, and it has an excellent critical current density. You can get something. (Manufacturing Example) An apparatus having the configuration shown in FIG. 1 was used, and the inside of a container housing this apparatus was evacuated to 3.0×10 -4 Torr using a vacuum pump. The base material has a width of 1
Hastelloy C of 0mm, thickness 0.5mm, length 10cm
276 tape was used. The target is made of YSZ (stabilized zirconia) and the sputtering voltage is 1000V.
, the sputtering current was set to 100 mA, the ion source beam irradiation angle was set to 45 degrees or 90 degrees, the ion source assist voltage was set to 300 V, 500 V, and 700 V, and the ion source current was set to 15 to 50 mA. A film-like YSZ layer with a thickness of 0.3 μm was formed on the base material by performing sputtering and ion irradiation simultaneously. Regarding each YSZ polycrystalline thin film obtained, C
An X-ray diffraction test was conducted using the θ-2θ method using uKα radiation. 5 to 7 are diagrams showing the diffraction intensities of samples measured at an incident angle of 45 degrees of the ion source while changing the ion beam voltage and ion beam current as appropriate. From the results shown in Figures 5 to 7, a peak of the (200) or (400) plane of YSZ was observed, indicating that the (100) plane of the YSZ polycrystalline thin film was oriented along a plane parallel to the substrate surface. It was found that the YSZ polycrystalline thin film was formed with its C axis oriented perpendicularly to the upper surface of the substrate. Furthermore, from the comparison of the magnitude of each peak shown in FIGS. 5 to 7, the c of the polycrystalline thin film increases when the beam current is larger and the beam voltage is smaller, that is, when a large amount of ions are irradiated at a lower rate. It was found that the axial orientation can be improved. FIGS. 8 to 10 show the angle of incidence 90 of the ion source.
FIG. 3 is a diagram showing the diffraction intensity of a sample measured by changing the ion beam voltage and ion beam current as appropriate. Figures 8 to 1
From the results shown in 0, sufficient c-axis orientation was observed even when the incident angle of the ion source was set to 90 degrees. Next, in the c-axis oriented sample as described above, it was determined whether the a-axis or b-axis of the YSZ polycrystalline thin film was oriented. For that measurement, Figure 11
As shown in Figure 2, a polycrystalline thin film of YSZ formed on base material A is irradiated with X-rays at an angle of θ, and at a position at an angle of 2θ with respect to the incident X-rays in the vertical plane containing the incident X-rays. By installing the X-ray counter 25 and appropriately changing the value of the horizontal angle φ with respect to the vertical plane containing the incident X-rays, that is, by rotating the base material A by the rotation angle φ as shown by the arrow in FIG. The orientation of the a-axes or b-axes of the polycrystalline thin film B was measured by measuring the diffraction intensity. The results are shown in FIGS. 12 and 13. In the case of a sample manufactured by setting the incident angle of the ion beam to 45 degrees as shown in FIG. A peak of the (311) plane of YSZ appears. This corresponds to the (011) peak of YSZ in the plane of the substrate, and it is clear that the a-axes or b-axes of the YSZ polycrystalline thin film are oriented with respect to each other. On the other hand, as shown in Figure 13, in the case of the sample manufactured with the ion beam incident angle set at 90 degrees, no special peaks are observed, and the directions of the a- and b-axes are disordered. found. From the above results, it is clear that the polycrystalline thin film of the sample produced by the method of the present invention has not only the c-axis orientation, but also the a-axis orientation and the b-axis orientation. Therefore, it has been revealed that by implementing the method of the present invention, it is possible to produce a polycrystalline thin film of YSZ or the like with excellent orientation. On the other hand, FIG. 14 shows the results of testing the crystal orientation of each crystal grain in the polycrystalline layer of the sample of the YSZ polycrystalline thin film used in FIG. 12. In this test, when performing X-ray diffraction using the method explained earlier based on Figure 11, the diffraction peaks were measured when the angle of φ was set in 5-degree increments from -10 degrees to 45 degrees. be. Figure 14
From the results shown in , it is clear that the diffraction peak of the obtained YSZ polycrystalline thin film appears within a grain boundary inclination angle of 30 degrees, but disappears at a grain boundary inclination angle of 45 degrees. Therefore, it was found that the grain boundary angle of the crystal grains of the obtained polycrystalline thin film was within 30 degrees, and it was revealed that the polycrystalline film had good orientation. FIG. 15 shows another example of an apparatus suitable for use in carrying out the method of the present invention. In the apparatus of this example, the same components as those of the apparatus shown in FIG. 1 are given the same reference numerals, and their explanation will be omitted. The difference between this example device and the device shown in FIG. 1 is that the target 1
2 are provided, three sputter beam irradiation devices 14 are provided, and a high frequency power source 30 is connected to the base material A and the target 12. In the device of this example, three targets 12
, 12, and 12, and can form a composite film on the base material A by knocking out different types of particles, respectively. Therefore, it has the feature that even a polycrystalline film with a more complicated composition can be manufactured. Alternatively, sputtering can be performed from the target 12 by operating the high frequency power source 30. When the method of the present invention is carried out using the apparatus of this example, a polycrystalline thin film with excellent orientation can be obtained as in the case of the apparatus shown in FIG. By the way, if the method of the present invention is carried out using the apparatus having the configuration shown in FIG. 1 or 15, an optical thin film with good orientation, a magnetic thin film of a magneto-optical disk with good orientation,
Any thin film for fine wiring for integrated circuits with good orientation, or a dielectric thin film used for high frequency waveguides, high frequency filters, cavity resonators, etc. can be formed. That is,
If these thin films are formed on polycrystalline thin film B with good crystal orientation by a film forming method such as sputtering, laser evaporation, vacuum evaporation, or CVD (chemical vapor deposition), they will have good consistency with polycrystalline thin film B. As these thin films are deposited or grown, the orientation becomes good. By manufacturing these thin films by the method of the present invention, high-quality thin films with good orientation can be obtained, so optical thin films have excellent optical properties, magnetic thin films have excellent magnetic properties, and are suitable for wiring. In the case of a thin film, no migration occurs, and in the case of a dielectric thin film, a thin film with good dielectric properties can be obtained. As explained above, according to the present invention, when the constituent particles ejected from the target by sputtering are deposited on the film forming surface of the base material, the ion beam is irradiated from an oblique direction. As a result of being able to efficiently activate the constituent particles, it is possible to improve not only the c-axis orientation but also the a-axis orientation and the b-axis orientation on the film-forming surface of the base material. Therefore, by implementing the method of the present invention, even in a polycrystalline thin film in which many grain boundaries are formed, all of the a-axis orientation, b-axis orientation, and c-axis orientation of each grain can be improved. A polycrystalline thin film can be formed. Furthermore, if the angle of ion irradiation is set at 45 degrees and the irradiated ions are mixed ions of argon and oxygen, a polycrystalline thin film with the most suitable orientation can be obtained. .

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of an apparatus used when carrying out the method of the present invention.

FIG. 2 is a cross-sectional view showing an example of an ion source used to implement the present invention.

FIG. 3 is an explanatory diagram showing a polycrystalline thin film obtained by carrying out the method of the present invention.

FIG. 4 is an enlarged plan view of the polycrystalline thin film shown in FIG. 3;

FIG. 5 is a graph showing the X-ray diffraction results of a sample of the present invention manufactured at a beam voltage of 300V.

FIG. 6 is a graph showing the X-ray diffraction results of a sample of the present invention manufactured at a beam voltage of 500V.

FIG. 7 is a graph showing the X-ray diffraction results of a sample of the present invention manufactured at a beam voltage of 700V.

FIG. 8 is a graph showing the X-ray diffraction results of a comparative example sample manufactured at a beam voltage of 300V.

FIG. 9 is a graph showing the X-ray diffraction results of a comparative example sample manufactured at a beam voltage of 500V.

FIG. 10 is a graph showing the X-ray diffraction results of a comparative example sample manufactured at a beam voltage of 700V.

FIG. 11 is a configuration diagram for explaining a test method conducted to examine a-axis orientation.

FIG. 12 shows (311) a polycrystalline thin film according to an example of the present invention.
It is a graph which shows the diffraction peak of a surface.

FIG. 13 shows (31
1) is a graph showing the diffraction peak of the surface.

FIG. 14 shows (311) a polycrystalline thin film of an example of the present invention.
It is a graph showing the results of measuring the diffraction peak of the surface at every 5 degrees of rotation angle.

FIG. 15 is a configuration diagram showing another example of an apparatus suitable for use in carrying out the method of the present invention.

FIG. 16 is a block diagram showing a polycrystalline thin film manufactured by a conventional method.

[Explanation of symbols]

Claims (3)

[Claims] 1. In a method for forming a polycrystalline thin film on a base material by ejecting constituent particles of a target by sputtering and depositing them on a base material, an ion source is used when depositing the constituent particles on the base material. 1. A method for producing a polycrystalline thin film, which comprises depositing ions while obliquely irradiating the film-forming surface of a base material with ions generated by the method. 2. The irradiation angle when irradiating the base material according to claim 1 with ions is 40 to 6
A method for manufacturing a polycrystalline thin film, characterized in that the temperature is within a 0 degree range. 3. A polycrystalline thin film characterized in that the ions according to claim 1 are inert gas ions or mixed ions of an inert gas and a reactive gas containing at least one element constituting the polycrystalline thin film. manufacturing method.