KR100549858B1 - Method of producing half-metallic magnetic oxide - Google Patents

Abstract

The present invention not only improves the bonding of metal ions and oxygen generated from the metal target by disposing a conductor provided with at least one hole between the predetermined metal target and the substrate holder in the plasma sputtering apparatus, Provided is a method for producing a semimetal magnetic oxide that can obtain a magnetic thin film having excellent characteristics by applying a magnetic field larger than the coercive force on a substrate.

In a preferred embodiment, the secondary power can be generated by additionally supplying electric power by connecting the electric power supply for the electric conductor to the electric conductor. Such a plasma sputtering device not only provides high energy for oxygen decomposition, but also can generate metal ions having different ionic values at an exact composition ratio through additional power, which is very useful for preparing semimetal oxides at low process temperatures.

Plasma Sputtering Device, Semi-Metallic Oxide, Fe3O4 Thin Film, Magnetic Random Access Memory (MRAM), Secondary Plasma

Description

Method of manufacturing semi-metal magnetic oxide {METHOD OF PRODUCING HALF-METALLIC MAGNETIC OXIDE}

1 is a schematic cross-sectional view of a plasma sputtering apparatus used in the present invention.

2A and 2B are front and side views of a ring-shaped conductor employed in the plasma sputtering apparatus of FIG.

3A and 3B show an X-ray diffraction pattern of a Fe ₃ O ₄ bulk and a Fe ₃ O ₄ thin film according to an embodiment of the present invention.

3 is a magnetization curve of a magnetic thin film for explaining the influence on the magnetic field in the method for producing a semi-metal magnetic oxide of the present invention.

5A to 5D are photographs taken of a scanning electron microscope (SEM) of a Fe ₃ O ₄ thin film obtained by varying an applied voltage to a conductor as an embodiment of the present invention.

6 is a graph showing a specific resistance value of the Fe ₃ O ₄ thin film obtained by varying the flow rate of oxygen gas as an embodiment of the present invention.

<Code Description of Main Parts of Drawing>

10: process chamber 12: substrate holder

13: self-forming means 14: target

16: heating means 17: gas injection portion

19: power supply 20: conductor

29: power supply for the conductor

The present invention relates to a method for manufacturing a magnetic oxide, which is a kind of half-metallic oxide, and in particular, a method for manufacturing a high quality magnetic oxide such as Fe ₃ O ₄ by supplying additional RF power while applying a magnetic field to a substrate. And a plasma sputtering apparatus used therein.

In general, ferromagnetic oxides with semimetal properties have energy gaps for minority spin bands at Fermi energy levels, while energy gaps for majority spin bands. Not. That is, the formation of such spin dependent energy gaps causes the ferromagnetic oxide materials to have 100% spin-polarization. Materials having such semimetal properties show very high magnetoresistance values in devices having spin-tunneling structures.

Therefore, anti-metal magnetic oxide has been recognized for its applicability as a magnetic recording medium, and many studies have been conducted. In particular, a variety of magnetic random access memory devices, magnetic sensor devices, and next-generation spin devices It is attracting attention as a material that can be applied to high speed and high frequency devices.

Such representative semimetal magnetic oxide Fe ₃ O ₄ is composed of an inverse spinel structure (inverse spinel structure). In the inverse spinel structure, Fe (+ 3-valent) and Fe (+ 2-valent) are added to tetrahedral coordinates and octahedral coordinates in a face center cubic structure composed of oxygen. consist of. In particular, the composition ratio of Fe (+ trivalent): Fe (+ divalent) is exactly 2: 1. Minority spin electrons hopping between Fe (+ trivalent) and Fe (+ 2-valent) show excellent conductivity, and these hopping electrons have a Verwey temperature of about 125K. ) Shows a metal-insulator transition due to a hopping electron frozen effect. Thus, at room temperature, there is a small but limited range of density of states at the Fermi level.

In order to prepare a Fe ₃ O ₄ thin film, a semi-metal magnetic oxide having such characteristics, Fe (+ divalent) and Fe (+ _trivalent) having different electron values must be formed using Fe, the same material. The composition ratio is also required to be precisely adjusted. Further, the deposition process must apply high energy to decompose oxygen molecules.

Therefore, the process for producing a semi-metal magnetic oxide has not been commercialized due to the problem that the same material must be separated by electrons with different ions based on the correct composition ratio, and high energy is required.

Conventionally, in order to manufacture a semimetal magnetic oxide, a molecular beam epitaxy (MBE) device and a pulsed laser depostion (PLD) device have been used. Molecular beam epitaxial device has an advantage that can control the exact composition ratio, pulse laser deposition device has the advantage that can be suitably used as a method of manufacturing Fe oxide because it uses high energy when thin film deposition. However, the MBE process is difficult to commercialize due to the expensive equipment even though the accurate composition ratio can be realized. Instead of forming the Fe ₃ O ₄ thin film using the Fe target of the PLD process, an expensive Fe ₃ O ₄ target formed at a desired composition ratio is required. There is a problem to use, and the magnetic material grown through this process has a problem that the anti-ferromagnetic phase (antiferromagnetic phase) is present therein, the magnetization saturation state is not achieved.

Further, in the conventional process, due to the additional heat energy applied to raise the temperature of the substrate, the magnetism of the grown magnetic body may be lowered. This problem has a serious problem that the Fe ₃ O ₄ thin film loses the magnetic properties of other magnetic materials when manufacturing a device laminated with other magnetic materials and a multilayer thin film.

As such, in order to manufacture a semimetal oxide thin film, not only expensive experimental equipment is required, but also it is difficult to grow a magnetic thin film having excellent characteristics, and thus has not been applied to an actual industry.

Therefore, there is a strong demand in the art for a new semimetal oxide production method capable of producing a semimetal oxide such as Fe ₃ O ₄ having excellent characteristics while using a conventional thin film forming apparatus.

The present invention has been made to solve the above problems, the object is to improve the oxygen decomposition while using a conventional sputtering device, and furthermore, semi-metal magnetic oxide having excellent characteristics by appropriately adjusting the composition ratio of metal ions and oxygen ions To provide a method for producing a.

In order to achieve the above technical problem, the present invention provides a substrate holder for supporting a substrate, a metal target disposed at a position facing the substrate holder, a gas injection portion for supplying oxygen gas into the process chamber, a target and a substrate. In the method for producing a semi-metal magnetic oxide-based thin film on the substrate using a plasma sputtering device having a power supply unit for applying a voltage using a holder as an anode,

Disposing a conductor provided with at least one hole substantially parallel to the substrate between the substrate holder and the metal target;

Applying a magnetic field to a region where a thin film is to be formed on the substrate;

Injecting oxygen gas into the process chamber;

Applying a predetermined voltage to form a sputtering condition in the process chamber;

Forming a semi-metal magnetic oxide thin film on the substrate by combining ions emitted from the metal target with oxygen ions decomposed from the injected oxygen gas by sputtering conditions formed in the process chamber. Provided is a method for manufacturing a thin film.

In a specific embodiment of the present invention, the metal target is made of Fe, the semi-metal magnetic oxide thin film formed on the substrate may be a Fe ₃ O ₄ thin film. In addition, the conductor may be a ring shape, or may be a mesh shape in which a plurality of holes are arranged.

Furthermore, preferably, the magnetic field applied to the substrate is 100 Oe or more, more preferably 100 Oe to 2 kOe.

Further, in a preferred embodiment of the present invention, the flow rate of the oxygen gas injected into the process chamber can be adjusted in the range of about 0.1-10 sccm, and a predetermined activation gas can be injected as necessary. Such activating gas may be an argon gas.

When injecting argon gas, the flow rate is preferably adjusted in the range of about 10-50 sccm.

Further, in the present invention, in order to obtain a better magnetic thin film, it is preferable to apply a predetermined voltage to the conductor and apply an additional RF voltage.

In addition, preferably in the process of forming a magnetic thin film, the substrate holder can be rotated at a constant speed.

In addition, the substrate on which the magnetic thin film is formed may be heated to a predetermined temperature. At this time, the temperature of the heated substrate is preferably maintained at about 100 ° C-400 ° C so as not to damage the magnetism of the thin film to be formed.

Moreover, this invention provides the plasma sputtering apparatus used for the said manufacturing method. The apparatus includes a process chamber, a substrate holder formed on one side of the process chamber, a gas holder for supplying a reaction gas into the process chamber, and a position substantially opposite to the substrate. A metal target for discharging particles by sputtering set in the process chamber, a power supply for supplying electric power for generating a discharge between the substrate holder and the target, between the target and the substrate holder; And a conductor provided with at least one hole to allow particles emitted from the target to travel onto the substrate, and magnetic field forming means for forming a magnetic field on the substrate to be disposed in the substrate holder.

Hereinafter, with reference to the drawings, the present invention will be described in detail.

1 is a schematic cross-sectional view of a plasma sputtering apparatus according to an embodiment of the present invention.

Referring to FIG. 1, the plasma sputtering apparatus includes a substrate holder 12 for placing a substrate 11 in a process chamber 10 and a target 14 formed at a position substantially opposite to the substrate holder 12. Equipped. In addition, the process chamber 10 is provided with a gas inlet 17 for injecting a reactive gas or an activating gas, and is provided with a power supply unit 19 to discharge between the substrate holder 12 and the target 14. Supply power to induce

The power supply unit 19 is connected to one side of the target 14 to apply power through a negative electrode (not shown) that serves as a sputtering gun to release the ion particles from the target onto the substrate 11. At this time, the ion particles emitted from the target 14 are combined with the reaction gas injected through the gas inlet 17 to be formed on the substrate 11 as a thin film of a desired material.

In particular, in the present invention, a predetermined conductor 20 is additionally disposed between the target and the substrate holder. The conductor is characterized in that at least one hole is provided so that particles emitted from the target 14 can travel toward the substrate 11.

As in this embodiment, such a conductor may use the ring-shaped conductor 20 shown in FIG. Referring to FIG. 2, the ring-shaped conductor 20 is formed in a symmetrical shape and arranged at regular intervals so as to form a conductor region in a circular shape so as to uniformly affect the substrate and the target. The emitted ions are directed onto the substrate.

The conductor used in the present invention is not limited to the above ring. That is, the substrate may have a uniform effect, and may be used as long as it has a conductor having at least one hole so that the ion particles emitted from the target may proceed to the substrate under sputtering conditions. As another form of such a conductor, not only the ring-shaped conductor adopted in the present embodiment but also a mesh-shaped conductor in which a plurality of holes are uniformly arranged may be used.

The conductor 20 disposed between the substrate 11 and the target 14 has the same effect as supplying high energy by grounding electrons in the plasma state to increase the cation density of the activating gas in the plasma. Can be. Therefore, the oxygen can be effectively decomposed to improve the binding with Fe (+2) and Fe (+3) ions released from the target.

In addition, the plasma sputtering apparatus may include a separate power supply unit 29 for supplying power to the conductor 20. The power supply unit 29 for the conductor generates a secondary plasma by supplying additional power by applying a voltage to the conductor 20. This secondary plasma refers to an additional plasma state that is formed separately from the plasma by the normal power supply unit 19. As described above, when the secondary plasma is formed through the power supply unit 29 for the conductor, since the energy can be provided higher than the state in which the conductor voltage is not applied, the oxygen gas is brought into the ion state (O ^-1 ). It is more preferable to decompose and by controlling the power additionally supplied through the conductor 20, it is possible to control the Fe (+ 2) and Fe (+ 3) ions having different binding energies at an appropriate ratio. Do. Therefore, by supplying additional power to the conductor using the conductor power supply unit 29 to form a suitable ratio of Fe (+2) and Fe (+3) ions and oxygen ions generated in a sufficient amount, The Fe ₃ O ₄ magnetic thin film having a thin film can be formed. This effect is the same even if the shape of the conductor 20 is different. In the case of a mesh having a plurality of holes uniformly arranged, there is a difference that voltage can be applied more densely than a ring shape.

In addition, the plasma sputtering apparatus according to the present invention is characterized in that it comprises a magnetic forming means (13). The magnetic forming means 13 may further improve the spin alignment state of the atoms by applying a magnetic field larger than the coercive force of the thin film to be formed at least in the process of forming the magnetic thin film to be formed on the substrate 11. Accordingly, the magnetic thin film to be formed may have a magnetic axis formed in a predetermined direction to obtain a magnetic thin film having an improved square ratio of a hysteresis loop.

In the plasma sputtering apparatus shown in FIG. 1, a Fe ₃ O ₄ thin film could be formed on a substrate by injecting a predetermined amount of oxygen gas or oxygen gas and an activation gas (eg, Ar gas).

Furthermore, the substrate holder may further include a heating means 16 for heating the temperature of the arranged substrate or a rotating means (not shown) for rotating the substrate. The heating means 16 may be implemented by disposing a resistor in the substrate holder 12 and generating heat by using the resistor. In general, as the substrate 11 is heated to a higher temperature, the oxide crystals grown on the substrate 11 become better. However, as described above, in the case of the magnetic oxide, when the temperature is too high, the magnetic material may be lost. Therefore, it is used when no additional voltage is applied to the conductor 20, and the substrate temperature is preferably maintained at about 100 ° C to about 400 ° C. Meanwhile, the thin film on the substrate 11 may be more uniformly formed by rotating the substrate 11 during the thin film formation using the rotating means.

The present invention also provides a method for producing a semimetal oxide using the plasma sputtering apparatus.

According to the method for manufacturing a semi-metal magnetic oxide thin film of the present invention, a conductor provided with at least one hole in a plasma apparatus is disposed between the substrate holder and the metal target, and the thin film is formed in a region where the thin film is to be formed on the substrate. Form a magnetic field greater than the coercive force. Subsequently, oxygen gas is injected into the process chamber, and a predetermined voltage is applied to form a sputtering condition in the process chamber. Due to the sputtering conditions formed in the process chamber, ions emitted from the metal target and oxygen ions decomposed from the injected oxygen gas may be combined to form a semi-magnetic magnetic oxide thin film on the substrate.

In general, the gas injected into the process chamber may additionally inject argon gas, which is an activation gas, in addition to oxygen gas, which is a reaction gas. The role of the activating gas is to increase the cation density in the process chamber. Therefore, additional injection of argon gas is desirable to obtain a high quality Fe ₃ O ₄ thin film.

Hereinafter, it will be described in detail through an embodiment of a method for manufacturing a semimetal oxide thin film according to the present invention. In this example, a method of manufacturing a representative Fe ₃ O ₄ thin film among semimetal oxides is illustrated.

Example 1

First, a substrate is placed in a substrate holder in a process chamber of a conventional plasma sputtering apparatus, a ring-shaped conductor is disposed between the substrate holder and the metal target, and at least a region of the thin film to be formed at least in the region where the thin film is to be formed on the substrate. It formed a magnetic field larger than the coercive force. In order to form such a magnetic field, two permanent magnets of about 500 (Oe) were mounted on both sides of the outer peripheral portion of the substrate holder. In addition, the ring-shaped conductor used was the same as that shown in Figure 2, in order to produce a Fe ₃ O ₄ thin film, a metal target was used a Fe target.

Subsequently, argon gas and reactive gas are supplied at a flow rate of about 30 sccm and about 0.8 sccm, respectively, as an activation gas in the process chamber of the plasma sputtering device in which the ring-shaped conductor is disposed so that the total pressure in the process chamber is 2 mtorr. It was. Then, about 60W of power was supplied between the Fe target and the substrate holder to form a primary plasma under reactive sputtering conditions. In this state, pre-sputtering was performed for 3 minutes to remove impurities adhering to the process chamber, in particular, the target and the sputtering gun.

Next, the Fe ₃ O ₄ thin film manufacturing process was performed while continuing to supply the same power. At this time, the secondary plasma was formed by additionally supplying 200 W of power to the ring-shaped conductor.

As such, the X-ray diffractometer (XRD) pattern of the Fe ₃ O ₄ thin film obtained by applying an additional bias to the ring-shaped conductor was analyzed, and compared with other Fe ₃ O ₄ bulk samples and XRD patterns.

3A and 3B show XRD patterns of a general Fe ₃ O ₄ bulk sample and a Fe ₃ O ₄ thin film prepared through this example, respectively. In contrast to Figures 3a and 3b, the two materials have peaks at nearly equal angles (2Θ = 29.8, 35, 37.1, 56.8, 62), and this embodiment is a non-bulk thin film, thus affecting the effects of strain generation between gratings. In view of the above, the relative size of each peak is almost the same, it can be seen that the thin film prepared through the present example is a Fe ₃ O ₄ thin film.

Comparative example

In this comparative example, the Fe ₃ O ₄ thin film was formed under the same conditions as in the first embodiment except that the magnetic field was not formed on the substrate. In order to compare the thin film formed in the comparative example with the thin film formed in Example 1 in terms of magnetic properties, the magnetization curve of the thin film according to the change of the magnetic field is illustrated as shown in FIG. 4. In the graph of Fig. 4, the curve indicated by A is the result of the thin film of Example 1, and the curve indicated by B is the result of the comparative example in which the thin film was grown without applying a magnetic field. In the case of the example, it can be seen that the magnetization value changes from positive to negative or from negative to positive instantaneously when the magnetic field direction is switched, whereas the change gradually occurs in the comparative example.

That is, in the thin film obtained in Comparative Example 1, the spin reversal phenomenon of the thin film atoms did not occur instantaneously, and thus the magnetization saturation state was not reached in the interval between -5000 (Oe) and 5000 (Oe), and the magnetization value was changed by the change of the magnetic field. Appeared to be.

This is because, when the magnetic field is not formed on the substrate during the thin film formation process, the spin alignment state of the formed thin film atoms is poor, so that the magnetic axis for magnetization is not formed.

The magnetic field applied at this time must be at least greater than the coercive force of the thin film to be formed, in order to affect the spin alignment of the thin film. It is formed by (Oe)-2 (KOe).

Example 2

In this embodiment, another Fe ₃ O ₄ thin film was formed under the condition that only the magnitude of the voltage applied to the conductor was different from that of the first embodiment. In this embodiment, 250W, which is about 50W larger than the first embodiment, was supplied to the ring-shaped conductor.

Comparing the Fe ₃ O ₄ thin film obtained in Example 1 and the Fe ₃ O ₄ thin film obtained in this Example, the SEM pictures were examined to determine the effect of the power supplied to the ring-shaped conductor.

5a to 5d are SEM images of the Fe ₃ O ₄ thin film of Example 1 and the Fe ₃ O ₄ thin film prepared according to the present embodiment. In particular, FIGS. 5b and 5d show scale bars in FIGS. 5a and 5c, respectively. Same SEM picture.

5A to 5D, the Fe ₃ O ₄ thin film nanoscale structure is shown, but as shown in FIGS. 5C and 5D, it can be seen that the particles of the Fe ₃ O ₄ thin film obtained at higher power than Example 2 are finer. . As such, the Fe ₃ O ₄ thin film according to the present invention may have a nanoscale structure, and thus may be applied to a nanoscale spin device such as a quantum dot layer.

Example 3

In this embodiment, the same conditions as in Example 1 with a flow rate of the Fe ₃ O _4, oxygen gas was produced a thin film of about 0.7sccm, about 0.9sccm, about 1.0sccm, in contrast to about 4 1.2sccm of Fe ₃ O ₄ Thin films were further prepared.

The resistivity value (Ω · cm) for each of the Fe ₃ O ₄ thin films obtained in this example was measured. Figure 6 shows the specific resistance value of the Fe ₃ O ₄ thin film and the example 4 of this embodiment Fe ₃ O ₄ thin film of Example 1 in a graph. The resistivity value of the Fe ₃ O ₄ bulk is 4 × 10 ⁻³ Ω · cm, and is known to be approximately in the range of about 10 ⁻³ to about 10 ⁻² . As shown in Figure 6, although the properties appear in the range of about 10 ^-3 , since it is produced in the form of a thin film in the present embodiment, it is determined that it is increased by the strain between the lattice, considering this almost accurate Fe ₃ O ₄ It can be seen that it has the electrical properties of the material.

In addition, as a result of this embodiment, it can be seen that a suitable oxygen flow rate for producing the Fe ₃ O ₄ thin film ranges from about 0.7 to about 1.0 sccm.

The semimetal oxide thin film manufacturing method of the present invention may be implemented in other embodiments.

For example, when the semimetal oxide thin film is formed, the thin film may be uniformly grown on the substrate by additionally rotating the substrate holder at a constant speed.

In addition, although the method is possible at room temperature, the method may further include heating the substrate to a predetermined temperature to form a higher quality semimetal oxide thin film. If the temperature of the substrate is less than about 100 ° C., it is difficult to fully expect the effect of heating. If the temperature of the substrate is greater than about 400 ° C., as described above, the magnetic properties of other magnetic materials combined to form a specific device may be lost. In consideration of the fact that the Curie temperature of the Fe ₃ O ₄ thin film is 850 K, the temperature of the substrate during heating is preferably in the range of about 100 ° C to about 400 ° C.

The present invention described above is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims.

As described above, according to the semi-metal magnetic oxide-based thin film manufacturing method of the present invention, not only provides high energy for oxygen decomposition, but also can generate metal ions having different ionic values at an accurate composition ratio through additional power. It is very useful for manufacturing semimetal oxide at low process temperature, and it is possible to form a magnetic thin film suitable for multilayer thin film memory devices by applying a magnetic field in the process of forming a thin film to improve spin alignment state of the formed magnetic atoms. You can get it.

Claims (17)

A substrate holder for supporting a substrate, a metal target disposed at a position facing the substrate holder, a gas injection portion for supplying oxygen gas into the process chamber, and a power supply portion for applying voltage using the target and the substrate holder as anodes In the method for producing a semi-metal magnetic oxide-based thin film on the substrate using a plasma sputtering device, Disposing a ring-shaped conductor between the substrate holder and the metal target; Applying a magnetic field larger than the coercive force of the thin film to the thin film forming region of the substrate such that the semi-metal magnetic oxide thin film to be formed has a biaxial axis for magnetization in a predetermined direction; Applying an RF voltage to the process chamber to form a plasma between the substrate holder and the target; Injecting oxygen gas into the process chamber and applying an additional RF voltage to the ring-shaped conductor to decompose the oxygen gas into oxygen ions; And And forming a semi-metal magnetic oxide thin film on the substrate by combining the metal ions and the oxygen ions emitted from the metal target by the plasma. The method of claim 1, The metal target is made of Fe, The semimetal magnetic oxide thin film is a semi-metal magnetic oxide oxide thin film manufacturing method characterized in that the Fe ₃ O ₄ thin film. delete delete The method of claim 2, The magnetic field applied to the substrate is a semi-metal magnetic oxide oxide thin film manufacturing method characterized in that more than 100 Oe. The method of claim 5, The magnetic field applied to the substrate is a method of manufacturing a semi-metal magnetic oxide-based thin film, characterized in that 100 Oe ~ 2 kOe. The method of claim 1, The oxygen gas is a semi-metal magnetic oxide oxide thin film manufacturing method characterized in that the injection with other activation gas. The method according to claim 1 or 7, The flow rate of the oxygen gas injected into the process chamber is a method of manufacturing a semi-metal magnetic oxide oxide thin film, characterized in that 0.1 to 10 sccm. The method of claim 7, wherein The activation gas is a semi-metal magnetic oxide oxide thin film manufacturing method characterized in that the argon gas. The method of claim 9, The flow rate of the argon gas injected into the process chamber is a method of manufacturing a semi-metal magnetic oxide oxide thin film, characterized in that 10 to 50 sccm. delete The method of claim 1, Forming the semi-metal magnetic oxide thin film, Semi-metal magnetic oxide oxide thin film manufacturing method characterized in that it further comprises the step of rotating the substrate holder at a constant speed. The method of claim 1, The method of manufacturing a semi-metal magnetic oxide oxide thin film further comprising the step of heating the substrate to a predetermined temperature. The method of claim 13, The heating temperature of the substrate is a method for producing a semi-metal magnetic oxide-based thin film, characterized in that 100 ℃ ~ 400 ℃. delete delete delete

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