KR100345300B1 - Fabrication Method of SmCo Hard Magnetic Film - Google Patents

Abstract

The present invention relates to a method for producing a SmCo-based hard magnetic thin film, and an object thereof is to apply a laser ablation method of manufacturing a thin film by irradiating a laser beam to a target mounted inside a reaction chamber. It is intended to form a SmCo-based thin film exhibiting good magnetic properties by appropriately changing the parameters on a Si single crystal substrate which can be most commonly used at low cost in mass production of thin films.

The present invention for achieving the above object is a step of mounting a SmCo-based target composition of Sm _100-X Co _X (at.%) In a vacuum reaction chamber, and heating a single crystal Si substrate; After rotating the SmCo-based target and the Si substrate, the target is irradiated with Nd-YAG laser light in fixed Q mode with a pulse width of 100-250 μs by optically extending the oscillation time. Depositing an SmCo-based thin film on the substrate; The present invention relates to a method for producing a SmCo-based hard magnetic thin film comprising the step of cooling a Si substrate on which a thin film is deposited at a cooling rate of 3 to 5 ^° C. per minute.

Description

Fabrication Method of SMC-based Hard Magnetic Thin Films {Fabrication Method of SmCo Hard Magnetic Film}

The present invention relates to a method for manufacturing a SmCo-based thin film applicable to various electronic fields, including a magnetic recording device, and more particularly to a method for manufacturing a SmCo-based hard magnetic thin film by a laser ablation method will be.

Since the 1970s, extensive research has been conducted on the magnetic properties of rare earth-transition metal intermetallic compounds with CaCu ₅ structure. Among these intermetallic compounds, the excellent properties exhibited by several kinds of compounds are enormous light magnetic properties. For example, in the compounds such as Sm (Co-Ni) ₅ and Sm (Co-Cu) ₅ , the anisotropic magnetic field measured at cryogenic temperature shows an order of 100 T, and the coercive force has a large light magnetic property of more than 20 T reported [S . Foner, EJ McNiff, H. Oesterreicher, FT Parker and M. Misroch: J. Appl. Phys., 49 , 2061 (1979)], and it is well known that it is the best material for use as a permanent magnet. In fact, Sm ₂ Co ₇ and SmCo ₅ bulk permanent magnets are commercially available for high temperature.

On the other hand, according to the progress of computer technology, the magnetic recording device requires an increase in recording density and a study on the thinning of the rare earth-transition metal compound whose main phase is SmCo ₅ as a material to satisfy this [Y. Liu, DJ Sellmyer, BW Robertson, SS Shan and SH Liou: IEEE Trans. Magn. MAG-31 , 2740 (1995), EMT Velu and DN Lambeth: IEEE Trans. MAG-28 , 3949 (1992)], as microwave equipment becomes smaller and lighter, as a magnet for bias magnetic field or micromotor for efficient microwave and millimeter wave monolithic integrated circuits (MMIC). Thinning of permanent magnets in anticipation of applications in micromechanics and microelectronics such as microactuators and microactuators [S. Yamashita and J. Yamasaki: J. Appl. Phys. 70 , 6627 (1991), DD Stancil: Microwave Opt. Technol. Lett. 2 (3) , 53 (1989)].

As a conventional SmCo-based thin film manufacturing method, sputtering method has been mainly used [FJ Cadieu: J. Vac. Sci. Technol., A6 (3) , 1668 (1988), FJ Cadieu, H. Hegde and K. Chen: IEEE Trans. Mag., 25 , 3783 (1989), K.-H Muller, Lei CaO, NM Dempsey and PAP Wendhausen: J. Appl. Phys. 79 , 5045 (1996). However, these methods are relatively complex due to the presence of energy sources inside the reaction chamber, and the sputtering yields of the individual elements to be targeted are different. Therefore, precise compositional control in the production of alloy thin films such as SmCo is somewhat difficult in the manufacturing process. It is difficult.

Accordingly, an object of the present invention is to produce a thin film by irradiating a laser beam to a target mounted inside a reaction chamber in which the method is recently developed, which is relatively advantageous for solving the problem of the thin film manufacturing method. Laser ablation method [SB Krupanidhi, N. Maffei, D. Roy and CJ Peng: J. Vac. Sci. Technol. A10 (4), p. 1815 (1992), K. Tanaka, Y. Omata, Y. Nishikawa, Y. Yoshida K. Nakamura: IEEE Trans. Journal on Magnetics in Japan. 6 , 11, p. 1001 (1991), R. Seed and C. Vittoria: IEEE Trans. Mag. 28 , p.3216 (1992)] is used to form SmCo thin films on Si single crystal substrates that can be used at low cost in mass production. have.

1 is a graph showing coercive force and squareness ratio according to substrate temperature of an SmCo-based thin film

2 is a graph showing the coercive force and the angular ratio according to the Co concentration of the SmCo-based thin film

The present invention for achieving the above object is a step of mounting a SmCo-based target composition of Sm _100-X Co _X (at.%) In a vacuum reaction chamber, and heating a single crystal Si substrate;

After rotating the SmCo-based target and the Si substrate, the target is irradiated with Nd-YAG laser light in fixed Q mode with a pulse width of 100-250 μs by optically extending the oscillation time. Depositing an SmCo-based thin film on the substrate;

The present invention relates to a method for manufacturing a SmCo-based magnetic thin film comprising the step of cooling the Si substrate on which the thin film is deposited at a cooling rate of 3-5 ^° C. per minute.

Hereinafter, the present invention will be described in detail.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film using a laser ablation method. First, a SmCo-based target is mounted in a vacuum reaction chamber, and a single crystal Si substrate is heated.

The SmCo-based target is selected to have a composition suitable for the thin film to be formed. In particular, the composition of the target used in the ablation using a fixed Q mode laser light is preferably Sm _100-X Co _X (73 ≦ _X ≦ 83.3). It is because the angle and coercivity property is good when it is less than 73at.%, But it requires a large amount of expensive rare earth elements, which makes the target difficult to manufacture due to the increase in brittleness of the target, and it is disadvantageous economically. It can decrease and adversely affect the magnetic properties.

The target can be produced by plasma arc melting with Sm _100-X Co _X (73≤X≤93) alloy target, the diameter of the target is preferably 20 to 50 mm, the higher the purity of the element is more than 99.9% purity It is preferable to have.

The Si substrate is heated by applying a laser ablation method. At this time, the heating is preferably heated to a temperature of at least 660 ^° C. The reason is that when heated to a temperature of less than 660 ℃, the ablated particles from the target is quenched on the substrate, the SmCo amorphous phase (amorphous phase) is the mainstream This is because the thin film exhibits soft magnetic propertes, which adversely affects the hard magnetic properties of the thin film, such as coercivity being significantly reduced. In addition, the heating of the Si substrate is more preferably at a temperature of 700 ^o C or less, because the Sm ₁ Co ₅ , Sm ₂ Co ₁₇ hard magnetic grains in the SmCo-based thin film formed when it exceeds 700 ^o C Rather, it may adversely affect the characteristics of the light magnetic field.

The Si substrate is a single crystal, and can be applied to various single crystals. In particular, when the Si single crystal substrate of the (100) plane is applied, the Si substrate has an excellent effect.

In addition, in the present invention, after rotating the SmCo-based target and the Si substrate, the Nd-YAG laser light of the fixed Q mode (Fixed Q mode) with a pulse width of 100-250μs by optically extending the oscillation time The target is irradiated to deposit a SmCo thin film on the substrate.

It is preferable to rotate the substrate holder on which the Si substrate is placed to achieve uniform use of the SmCo-based target and the thin film deposited to obtain economical use of the target and uniform plume during the laser ablation. The speed is 3 to 4 rpm.

The Nd-YAG laser beam irradiated to the SmCo target rotated as described above has a pulse width of 100-250 µs. This is because if the pulse width is less than 100 μs, there is little effect of shortening the deposition time, and if it exceeds 250 μs, it is too fast to control the deposition time.

In addition, the Nd-YAG laser light is a fixed Q mode (Fixed Q mode) is a high energy density range of 1x10 ⁵ ~ 2x10 ⁵ J / cm ² is preferred, because the 1x10 ⁵ J / cm ² or less target surface It is impossible to form a thin film because there is no plume at. In case of more than 2x10 ⁵ J / cm ² , it is very difficult to control the deposition time at a fast deposition rate, especially the crystallization of SmCo thin film is not active and the surface of thin film This is because the number of droplets rapidly increases, adversely affecting the magnetic properties and the surface shape of the thin film.

In addition, in the present invention, the Si substrate on which the thin film is deposited is cooled at a cooling rate of 3 to 5 ^° C. per minute.

The deposited Si substrate to cool at a cooling rate per minute of 3~5 ^o C, The reason is that the peeling and cracks of the thin film on the substrate surface when the cooling rate exceeds 5 ^o C and induced, slow cooling than 3 ^o C This is because it takes too much time and is unnecessary.

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

Example 1

After the initial vacuum of the reaction chamber of the laser ablation apparatus is 4x10 ^-6 Torr or less, the substrate temperature is reached at room temperature, 640, 660, 680, 700 ^o C, and fixed Q mode at each temperature. The thin film was produced using the laser beam. In the laser ablation, a Sm _16.7 Co _83.3 target having a purity of 99.9% and a diameter of 50 mm was positioned at an angle of 45 ^° from the laser beam incident direction, and the rotation speed was 3.3 rpm. The substrate used a (100) Si single crystal having a size of 10 x 10 x 1 mm, and the distance from the target center to the center of the substrate was fixed at 5 cm and the rotation speed was 3 rpm. At this time, a device for generating an Nd-YAG laser light having a wavelength of 1064 nm was used. The laser light energy density at the target surface is fixed at 50Hz pulse frequency (repetition rate) of the laser light, and then the laser output is 1x10 ⁵ J / cm ² by combining two convex lenses having a focal length of 50 cm. The size was adjusted.

After the thin film formation was completed for 1 minute by the laser ablation as described above, the temperature was lowered at a cooling rate of 3 to 5 ^o C / min to 300 ^o C and then cooled in the chamber to room temperature.

Various properties of the SmCo thin film prepared by the above method were evaluated and the results are shown in Table 1 and FIG. 1. Among the properties, the film thickness was measured by "alpha-step" (α-step), and the surface shape was observed by scanning electron microscope (SEM). The crystal phase of the thin film was evaluated by X-ray diffraction analysis, and the magnetic properties were evaluated by using a vibrating sample magnetometer (VSM).

Example Target composition (at.%) Substrate temperature ( ^o C) Laser Light Energy Density (J / cm ² ) Square ratio (4πM _r / 4πM _s ) Coercive force (Oe) ／／ ⊥ ／／ ⊥ Comparative Example 1 Sm _16.67 Co _83.3 Room temperature 1 x 10 ⁵ 0.3 0.21 393 818 Comparative Example 2 " 640 " 0.60 0.3 1756 1789 Inventive Example 1 " 660 " 0.63 0.27 2231 1844 Inventive Example 2 " 680 " 0.77 0.33 3438 1840 Inventive Example 3 " 700 " 0.8 0.37 4070 1985

[Rectangle ratio and coercive force in Table 1 are measured values in the magnetic field of 16 kOe //, ⊥ indicates that the magnetic field was applied in parallel or vertical direction with respect to the thin film surface at the time of measurement, respectively]

As shown in Table 1 and FIG. 1, as the substrate temperature increases, particularly when the magnetic field is applied in parallel to the thin film surface (Inventive Examples 1, 2, and 3), the angular ratio and the coercive force are at most 0.8 and 4070 Oe, respectively. The good value until is shown. The cause of this characteristic was confirmed by X-ray diffraction experiments because the crystallization is increased with increasing temperature, and a large amount of hard magnetic phases such as Sm ₁ Co ₅ and Sm ₂ Co ₁₇ are generated in the thin film. The magnetic properties of Inventive Examples 1, 2 and 3 are required for in-plane magnetic recording media [DN Lambeth, DE Laughlin, S. Charp, L.-L. Lee, P. Harllee and L. Lang, Nanomagnetism, edited by GC Hadjipanayis (1996), p. 49].

Example 2

As can be seen in Example (1), when the substrate temperature was 640 ^° C. or more, good hard magnetic properties were exhibited. In order to understand the effect of composition on hard magnetic properties, Sm _100-X Co _X (73≤X≤93) target was used and the substrate temperature was 680 ^o C, followed by irradiation with laser light energy density of 1x10 ⁵ . After the thin film was prepared in the same manner as in Example (1), the characteristics were analyzed and evaluated, and the magnetic properties are shown in Table 2 and FIG. 2.

Example Target composition (at.%) Substrate temperature ( ^o C) Laser Light Energy Density (J / cm ² ) Square ratio (4πM _r / 4πM _s ) Coercive force (Oe) ／／ ⊥ ／／ ⊥ Comparative Example 3 Sm ₇ Co ₉₃ 680 1 x 10 ⁵ 0.32 0.08 430 405 Comparative Example 4 Sm ₁₃ Co ₈₇ 680 " 0.56 0.2 1288 1266 Inventive Example 2 Sm _16.67 Co _83.3 680 " 0.63 0.27 3489 1840 Inventive Example 4 Sm ₂₂ Co ₇₈ 680 " 0.91 0.59 6113 2454 Inventive Example 5 Sm ₂₇ Co ₇₃ 680 " 0.87 0.54 6288 2052

In Table 2, the angular ratio and coercive force are the values measured in the magnetic field of 16 kOe.

As shown in Table 2 and Figure 2, when the magnetic field is applied in parallel to the thin film surface as X decreases in the range of Co concentration X 73 ≤ X ≤ 83.3 in Sm _100-X Co _X (Invention Example 2, The square ratio and the coercive force of 4 and 5) increase and show very good values up to 0.9 and 6288 Oe. The reason for this characteristic is that in the X-ray diffraction experiment, the diffraction lines of the Sm ₅ Co ₂ compounds are observed as the main diffraction lines, and the diffraction lines of the hard magnetic phases Sm ₁ Co ₅ and Sm ₂ Co ₁₇ are observed and the simultaneous EPMA It was found that the Sm concentration was higher than the target in the average composition of the thin film through micro analysis, and the particle contribution of the thin film surface which is almost the same as the target component was also very high. That is, as the X decreases, the hard magnetic properties are improved, which is closely related to the concentration of Sm in the average composition of the thin film. When X is large, compounds of Sm ₅ Co ₂ , Sm ₁ Co ₅ , and Sm ₂ Co ₁₇ are present. However, the amount of Sm ₅ Co ₂ produced was insufficient to actively generate Sm ₁ Co ₅ and Sm ₂ Co ₁₇ , which are light magnetic phases. On the other hand, when X is small, the production of Sm ₅ Co ₂ compound is Sm ₁ Co ₅ , Sm _2. It is thought to be due to promoting the production of Co ₁₇ phase. This characteristic also satisfies the characteristics required for in-plane magnetic recording media and is expected to be used in micromechanics and microelectronics as a bias magnetic field magnetic thin film for MMIC.

According to the present invention as described above, the SmCo-based hard magnetic thin film that can be usefully applied to a variety of electronic fields, including magnetic recording elements and magnets for bias magnetic field, micro motors and micro actuators that require an increase in recording density. The effects that can be obtained through the ablation method are provided.

Claims (5)

Mounting a SmCo-based target having a composition of Sm _100-X Co _X (at.%) In a reaction chamber in a vacuum state and heating a single crystal Si substrate; After rotating the SmCo-based target and the Si substrate, the target is irradiated with Nd-YAG laser light in fixed Q mode with a pulse width of 100-250 μs by optically extending the oscillation time. Depositing an SmCo-based thin film on the substrate; Method for producing a SmCo-based light magnetic thin film comprising the step of cooling the Si substrate on which the thin film is deposited at a cooling rate of 3 ~ 5 ^o C per minute The method of claim 1, The Si substrate is a manufacturing method of SmCo-based hard magnetic thin film, characterized in that the (100) Si substrate The method of claim 1, The heating method of the Si substrate is a method for producing a SmCo-based hard magnetic thin film, characterized in that the temperature range of 660 ^~ 700 ^° C. The method of claim 1, The Nd-YAG laser light manufacturing method of SmCo-based magnetic thin film, characterized in that the energy density is 1x10 ⁵ ~ 2x10 ⁵ J / cm ² The method according to any one of claims 1 to 4, The target has a composition of Sm _100-X Co _X (73≤X≤83.3) method for producing a SmCo-based light magnetic thin film, characterized in that