KR20020026664A - Method of fabricating Sm-Fe-N magnetic thin films by nitriding - Google Patents

Abstract

PURPOSE: A method for manufacturing a Sm-Fe-N permanent magnet thin film through the nitriding treatment is provided to improve the coercivity and the remanence density by employing the laser ablation. CONSTITUTION: In an evaporator, a thin film of Sm2Fe17 is deposited on a substrate with a thickness of 10-300 nm, by irradiating the laser beam on a target of Sm2Fe17. The evaporator has the vacuum level of 10¬-5-10¬-7 Torr. The laser beam has a beam energy density of 100-250 J/cm¬2 and a pulse frequency of 10-50 Hz(Hertz). The substrate provided with the deposited thin film of Sm2Fe17 is processed by the heat treatment with 2-5 pressure of N2 at 450-550 °C, to thereby form a thin film of Sm2Fe17Nx(x<=3). The substrate and the target rotate at the speed of 3-5 RPM(Revolution Per Minute).

Description

Method of Fabricating Samarium-Iron-Nitrogen Permanent Magnet Thin Film by Nitriding {Method of fabricating Sm-Fe-N magnetic thin films by nitriding}

The present invention relates to a method for producing a Sm ₂ Fe ₁₇ N _x -based permanent magnet thin film used in micromachining devices, micro-sensors, and the like, and more specifically, bulk permanent by a simple method by laser ablation and nitriding treatment. The present invention relates to a method for producing a ferromagnetic Sm ₂ Fe ₁₇ N _x based thin film having magnetic properties comparable to that of a magnet.

Recently, the development of ferromagnetic permanent magnet thin films has been vigorous while a biasing field is required for MEMS, such as a micro motor and a micro actuator. The research is mainly focused on the development of rare earth magnetic thin films of SmCo-based composition, and the manufacturing method is using a general sputtering deposition technique (FJ Cadieu: J. Vac. Sci. Technol., A6 (3), 1668). (1988), FJ Cadieu, H. Hedge and K. Chen: IEEE Trans.Mag.MAG-25, 3783 (1989)).

However, the sputtering method is relatively complicated because the energy source is present in the deposition chamber, and the sputtering yield of each element constituting the target is different, which makes it difficult to control the composition of the magnetic thin film. have. In addition, since expensive Co elements are used, there is a disadvantage of lack of productivity in terms of economy. On the other hand, although Sm ₂ Fe ₁₇ N _x (x≤3) -based permanent magnets are known to be cheaper than SmCo-based, the technology for manufacturing thin films has not been developed.

The present invention applies a laser ablation method instead of the conventional sputtering method, and is less expensive than the Sm-Co system, but has a high coercive force, high residual magnetic flux density, and excellent magnetic direction anisotropy in the plane direction. To provide, for that purpose.

1 is an example of a laser ablation apparatus according to the present invention.

2 is a graph showing the effect of partial pressure of N ₂ gas on Sm ₂ Fe ₁₇ N _x in the nitriding heat treatment process

3 is a graph showing the change in magnetic properties according to the thin film thickness of Sm ₂ Fe ₁₇ N _x .

4 is a graph showing the magnetic properties measured in the plane direction and the direction perpendicular to the plane in the thin film of Sm ₂ Fe ₁₇ N _x .

* Description of the symbols for the main parts of the drawings *

1 ..... Target holder 2 ..... Lens

3 ..... Laser Beam 4 ..... Substrate

5 ..... Substrate holder 6 ..... Deposition chamber

7 ..... KrF laser gun

A method for producing a Sm-Fe-N-based permanent magnet thin film of the present invention for achieving the above object, by irradiating a laser beam to the target of Sm ₂ Fe ₁₇ in a vacuum deposition chamber to form a thin film of Sm ₂ Fe ₁₇ on the substrate Depositing to a thickness of 10-300 nm;

A step of obtaining a nitride magnetic thin film of Sm ₂ Fe ₁₇ Nx (x ≦ 3) by subjecting the substrate on which the thin film of Sm ₂ Fe ₁₇ is deposited to a temperature of 450 to 550 ° C. at a N ₂ partial pressure of ₂ to 5 atmospheres; It is composed.

Hereinafter, the present invention will be described in detail.

In order for a magnetic thin film to be essentially a ferromagnetic and to function as a permanent magnet, the following characteristics are required.

First, the coercivity and residual magnetic flux density must be high enough to be practically used. Second, the economic characteristics and magnetic properties must be excellent to the extent possible for permanent magnets. In view of this, magnetic anisotropy should be exerted in the plane direction.

The present inventors have used the laser ablation method (SB Krupannidhi, N. Maffei) of Sm ₂ Fe ₁₇ N _x (x≤3) -based permanent magnets in the process of developing thin-film permanent magnets satisfying the characteristics of such permanent magnets. , D. Roy and CJ Peng: J. Vac. Sci. Technol., A10 (4), 1815 (1992), R. Seed and C. Vittoria: IEEE Trans.Mag.MAG28, 3216 (1992)) The present invention has been completed in view of the fact that the thin film type can overcome the limitations of the conventional sputtering thin film manufacturing method.

According to the study of the present invention, the most important factor in the technology for producing a Sm ₂ Fe ₁₇ N _x (x≤3) -based permanent magnet thin film by the laser ablation method is to increase the composition of x in the composition of Sm ₂ Fe ₁₇ N _x Control of process conditions. It is known that the maximum composition value of N in this composition system is three. Furthermore, the magnetic anisotropy is to be exerted in the plane direction in consideration of the practical application of the permanent magnet thin film. From this point of view, the production method of the present invention will be described.

Sm ₂ Fe ₁₇ is attached to the target holder 1 in the vacuum deposition chamber shown in FIG. 1 as an example. Sm ₂ Fe ₁₇ is preferably prepared by repeated melting by arc melting and homogenized heat treatment to have a single phase. It is recommended to use a single crystal or polycrystal of (001) Si, Al ₂ O _{3 as} the substrate. The (001) Si substrate is easily available while being inexpensive among the substrates, and has an advantage of easy cutting of the substrate because it has a 4-axis lamination property. In addition, various micromachined components are the most suitable substrates in view of the silicon semiconductor process and compatibility with the components. Meanwhile, since Al ₂ O ₃ single crystal or polycrystalline substrates are actually used as various computer recording / reproducing heads or recording media substrates of the present, the permanent magnet thin film of the present invention may be used in actual situations. It makes sense in terms of using a suitable substrate.

The initial degree of vacuum in the evaporation chamber (6) is good or higher in consideration of the economical efficiency 10 ^-5 to

It is okay to set it to 10 ^-7 Torr. If the degree of vacuum is less than 10 ^-5 , not only the N content is small in the composition of Sm ₂ Fe ₁₇ N _x but also oxides may be formed. When the degree of vacuum is higher than 10 ^-7 Torr, the magnetic properties of the Sm ₂ Fe ₁₇ N _x thin film are Good, but the deposition rate is too slow, and also the production capacity is low, which is a problem of economic efficiency. In addition, the energy source of the laser is KrF or Nd-YAG laser is recommended because it is easy to control the thickness of the nano-scale thin film and advantageous technology for controlling the alloy composition.

And, the energy density of the laser beam (beam energy dencity) is preferably in the range of 100-250 J / ㎠, the reason is that when the laser specific energy of 100 J / cm ² or less, the growth of the magnetic thin film is slow and there is no productivity, 250 If J / cm ² or more may be difficult to practical use because the surface roughness of the grown thin film is poor.

In addition, the laser pulse frequency is mainly used in the range of 10-50 Hz, the reason is that the composition of the magnetic thin film does not match when using less than 10 Hz, the composition and surface roughness of the magnetic thin film is poor. In order to prevent the laser beam from being irradiated to only a portion of the laser deposition, the target and the substrate are preferably rotated during deposition. The rotational speed is preferably 3 to 5rpm. If the rotational speed is less than 3rpm, the composition of the growing thin film is heterogeneous by region, and if it is faster than 5rpm, it is difficult to control the growth rate of the thin film.

When depositing Sm ₂ Fe ₁₇ on the substrate, it is preferable to form an N ₂ gas atmosphere in the deposition chamber in order to increase the composition of N in Sm ₂ Fe ₁₇ during the deposition process. At this time, the N ₂ gas partial pressure is preferably 0.5-0.9 atm. The reason is that when the partial pressure of N ₂ gas is less than 0.5 atm, there is no gain in N content at all. It is difficult to maintain vacuum. The temperature of the substrate during the deposition is preferably deposited at room temperature in order to form the optimum texture of the magnetic material.

Sm ₂ Fe ₁₇ is deposited on the substrate as described above and then nitrided. The nitriding treatment is heated at 500 to 700 ° C. in an N ₂ gas atmosphere. If the heat treatment temperature is less than 500 ° C., the diffusion of N ₂ gas is insufficient, so that the composition of N is insufficient to obtain optimum magnetic properties. If the heat treatment temperature is higher than 700 ° C., the grains in the magnetic body grow excessively, and the coercive force decreases. In the nitriding process of the present invention, an easy magnetization axis of Sm ₂ Fe ₁₇ Nx (x≤3) crystal grains present in the magnetic thin film is arranged and grown in a magnetic field direction by externally loading a magnetic field. Magnetic anisotropy can be obtained in an in-plane arrangement. As such, the magnetic grains are magnetically loaded from the outside during the heat treatment process in order to have the aggregate structure. The external magnetic field is applied in parallel with the plane direction of the thin film, and the magnetic field force is higher than 3 KOe. Do. On the other hand, it is possible to apply an external magnetic field in the deposition process.

The strong magnetic field generated in the plane direction of the thin-film permanent magnet can be used for biasing such as a micro motor, a micro sensor, and a high density recording magnetic head.

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

Example 1

A target of Sm ₂ Fe ₁₇ composition was mounted in a vacuum target holder and the Si (001) substrate was rotated at a rotational speed of 3.5 rpm while maintaining a distance of 5 cm from the target. The vacuum degree of the deposition chamber was maintained at 3 × 10 ⁻⁵ Torr before laser deposition, and then N ₂ gas was blown into the deposition chamber to maintain the pressure of the deposition chamber at 0.9 atm. The laser pulse was fixed at 10 Hz so that the Sm ₂ Fe ₁₇ thin film was grown to 50 nm in thickness while maintaining the temperature of the Si (100) substrate. The thin films of Sm ₂ Fe ₁₇ grown as described above were fixed in a vacuum furnace at 500 ° C. to be nitrided in a vacuum heat treatment furnace, and nitrogen gas having a purity of 99.99% or higher was blown into the heat treatment furnace, respectively, 0.75, 1, 1.5, 2.5, and Heat treatment was performed for 1 hour at 5 atmospheres. During the heat treatment, the magnetic field was applied parallel to the plane direction of the specimen outside the heat treatment furnace, and the magnetic field force used was 4 kG. Each nitriding specimens were examined with magnetic properties in the plane direction of the specimen at a maximum magnetic field of 19kG using a Vibrating sample magnetometer. The measured results are summarized in FIG. 2.

FIG using 0.75, and N ₂ partial pressure of 1 atmosphere, as in the second specimen, the degree of nitriding nitride mimihayeo yet Sm ₂ Fe ₁₇ N _x, did not produce a. Therefore, Coercivity (Hc) is a weak magnetic property of Sm ₂ Fe ₁₇ phase shows 200-300 Oe level, saturation magnetization (4πMs) is believed to 7kG level. However, when the N ₂ partial pressure increases to 1.5, 3 atm, etc., it can be seen that the Sm ₂ Fe ₁₇ phase is completely converted to the Sm ₂ Fe ₁₇ N _x phase to become ferromagnetic. Thus, it can be seen that the coercive force rises to the 500 Oe range and the saturation magnetization force is maintained above 10 kG.

Example 2

The target of Sm ₂ Fe ₁₇ composition was mounted in a vacuum target holder in a vacuum deposition chamber, and the Si (001) substrate was rotated at a rotational speed of 3.5 rpm while maintaining a distance of 5 cm from the target. . Before the laser deposition, the vacuum of the deposition chamber was maintained at 3 × 10 ⁻⁵ Torr, and N ₂ gas was blown into the deposition chamber to maintain the pressure of the deposition chamber at 0.9 atm. The laser pulse was fixed at 10 Hz while maintaining the temperature of the Si (100) substrate at room temperature. The thin film of Sm ₂ Fe ₁₇ grown by fixing the deposition conditions as described above and dividing the thickness of the thin film into 50, 120, 190 and 300 nm, respectively, fixed the temperature in the vacuum furnace at 500 ° C. for nitriding in the vacuum heat treatment furnace. Nitrogen gas with a purity of 99.99% or more was blown into the heat treatment furnace, and the N ₂ partial pressure was fixed at 5 atmospheres, followed by heat treatment for 1 hour. During the heat treatment, the magnetic field was applied parallel to the plane direction of the specimen outside the heat treatment furnace, and the magnetic field force used was 4 kG. Each of the specimens subjected to nitriding treatment was measured in the same manner as in Example 1, and the results are summarized in FIG. 3.

As shown in FIG. 3, when the N ₂ partial pressure was set to 5 atmospheres at 500 ° C. and heat treated for 1 hour, it was confirmed that the composition was completely changed to Sm ₂ Fe ₁₇ N _x . However, as the deposition time increases and the thickness of the thin film becomes thicker, the saturation magnetization and residual magnetic flux density of the Sm ₂ Fe ₁₇ N _x thin film continue to increase, increasing from 10 to 13 kG and 2.5 to 11.5 kG, respectively. On the contrary, the coercive force gradually decreases with thickness and drops to 500 Oe. This is evidence that the magnetization biaxial axis (or magnetic anisotropy axis) of Sm ₂ Fe ₁₇ N _x magnetic thin film lies in the plane direction when the thickness is less than 50 nm, but as the thickness increases, the axis of magnetization changes in the vertical direction in the plane direction. to be. Therefore, it can be seen that it is necessary to appropriately control the thickness of the magnetic thin film in order to manufacture the thin film having the magnetic anisotropy held in the plane direction, which is one of the objectives of the present invention.

Example 3

Magnetic measurements of the specimens obtained in Example 2 were carried out in the plane and vertical directions of the specimens, respectively, and the results are summarized in FIG. 4.

As shown in FIG. 4, as the thickness of the magnetic thin film increases from 50 nm to 300 nm, the coercivity measured in the plane direction decreases rapidly and decreases from 550 Oe to 100 Oe or less, while the coercive force measured in the vertical direction remains 450 Maintain a level of 550 Oe. Therefore, it can be seen that the Sm ₂ Fe ₁₇ N _x nitrided permanent magnet thin film of the nanoscale should use the thickness of the thin film below 50 nm if necessary for magnetic anisotropy in the plane direction.

The invention various micro meosaen and Application Part, and various micro-motors, micro-sensors and high-density as a read permanent magnet thin film material for Bahia Singh _{(biasing) head Sm 2 Fe 17} N x magnetic material thin film of the composition as described above for the next It is expected to be used in advanced information communication and driving parts.

Claims (8)

Irradiating a laser beam on a target of Sm ₂ Fe ₁₇ in a vacuum deposition chamber to deposit a thin film of Sm ₂ Fe ₁₇ on a substrate with a thickness of 10-300 nm; A step of obtaining a nitride magnetic thin film of Sm ₂ Fe ₁₇ Nx (x ≦ 3) by subjecting the substrate on which the thin film of Sm ₂ Fe ₁₇ is deposited to a temperature of 450 to 550 ° C. at a N ₂ partial pressure of ₂ to 5 atmospheres; A method for producing a Sm-Fe-N based permanent magnet thin film by nitriding treatment. The method of claim 1, wherein the vacuum degree of the deposition chamber is 10 ^-5 to 10 ^-7 Torr. The method of claim 1, wherein the deposition chamber has a N ₂ partial pressure of 0.5-0.9 atm, wherein the Sm-Fe-N-based permanent magnet thin film is manufactured by nitriding treatment. The method of claim 1, wherein the energy density of the laser beam is 100 ~ 250J / Cm ^{2 The} method of manufacturing a Sm-Fe-N-based permanent magnet thin film by the nitriding treatment. The method according to claim 1, wherein the pulse frequency of the laser is 10 to 50 Hz. The method of claim 1, wherein the substrate and the target is rotated at 3 to 5rpm, characterized in that the Sm-Fe-N-based permanent magnet thin film by the nitriding treatment. The method of claim 1, wherein the substrate is (001) Si, Al ₂ O ₃ single crystal or polycrystalline method of producing a Sm-Fe-N-based permanent magnet thin film by the nitriding treatment. 8. The Sm-Fe-N system according to claim 1, wherein the heat treatment is performed while applying an external magnetic field of ₃ KOe or more in parallel with the surface direction of the substrate on which the Sm ₂ Fe ₁₇ thin film is deposited. Method for manufacturing permanent magnet thin film.