JP2997497B2 - Magnetic information detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a scanning magnetic force microscope that obtains information on the surface morphology or magnetic properties of a sample by using a magnetic force or a tunnel current generated when a magnetic probe and a sample such as a magnetic material are brought close to each other. The present invention relates to a magnetic information detecting device such as a scanning tunnel microscope or an atomic force microscope.

[Prior art]

The scanning tunneling microscope, which is a conventional technique, applies a voltage between the probe and the sample, and utilizes the tunnel current and the field emission current obtained when the distance between the probe and the sample is reduced, to change the surface morphology of the sample. It is a device to check. On the other hand, a scanning magnetic force microscope is an apparatus that uses a magnetic material as a probe and uses a magnetic force when the magnetic probe approaches a magnetic sample to check the magnetization state of the sample. Conventionally, a method of acquiring magnetic information of a sample in a scanning magnetic force microscope using a magnetic force obtained by bringing a magnetic probe and a sample close to each other is described in Journal of Vacuum.
It is discussed in Science Technology A6 (1988) pp. 279-282, or Applied Physics Letters 50 (1987) pp. 1455--1457.

[Problems to be solved by the invention]

A magnetic force microscope is a device that detects a magnetic field generated by interaction between a leakage magnetic field on a magnetic sample surface and a magnetic probe. The magnetic probe used in the above-mentioned conventional technology is a magnetic probe in which the entire surface of the cantilever is simply coated with a magnetic material, or a magnetic probe in which the tip of a magnetic wire such as Ni or Fe is bent into an L shape. Was used. A magnetic probe formed simply by coating the surface of a cantilever with a magnetic material has a drawback that the axis of easy magnetization of the magnetic material is irregularly formed and the magnetic force sensitivity between the sample and the magnetic probe is low. In addition, conventional magnetic probes using Ni, Fe, etc. have a small coercive force of 80 A / m or less, so when the magnetic probe comes close to the sample surface, the magnetic field leaks from the sample surface. However, there is a disadvantage that the direction of the magnetization changes, and a highly sensitive magnetic force cannot be detected. Further, there is a disadvantage that the magnetic domain structure cannot be observed at a high resolution because the sample and the magnetic probe cannot be sufficiently close to each other due to the same reason. In addition, in the prior art, since errors due to changes in the gap between the probe and the sample are included, accurate magnetic force cannot be obtained even if surface morphology information is removed from the measured magnetic force (including surface morphology information). There were drawbacks. A first object of the present invention is to provide a magnetic information detecting device capable of detecting a magnetic force due to a leakage magnetic field perpendicular or parallel to a sample surface with high sensitivity. It is a second object of the present invention to provide a magnetic information detecting device capable of preventing deterioration of the surface of a magnetic probe and measuring a magnetic force and a tunnel current between the sample and the probe with good reproducibility.

[Means for Solving the Problems]

In order to achieve the first object, according to the present invention, a magnetic thin film is formed on a surface of a tip portion of a cantilever having a sharp tip and a crystal orientation control layer, and a magnetic thin film is formed on this layer. Use a probe. In order to achieve the second object, an oxidation-resistant protective film is formed on the surface of the magnetic thin film.

[Action]

The easy axis of magnetization of the magnetic thin film formed on the surface of the cantilever differs depending on the growth direction of the crystal grains constituting the magnetic thin film.
In order to control the direction of the axis of easy magnetization, an underlayer for controlling the growth direction of crystal grains of the magnetic thin film is provided on the surface of the cantilever, and the magnetic thin film is formed thereon by vacuum evaporation or sputtering. The growth direction of the crystal grains of the magnetic thin film can be arbitrarily changed by controlling the material of the underlayer and the incident direction of the vapor-deposited particles. A magnetic probe oriented in a specific direction can be formed. Magnetic materials for magnetic probes are Co and Fe
Can be used as an alloy or a multilayer film in which Ni, Cr, Pt, Zr, C, N, etc. are added as a main component. A polycrystalline film of Ge, Si, Tr, Cr, C or the like, an amorphous film, or an alloy film thereof is used as an underlayer material for controlling the axis of easy magnetization of the magnetic material. Magnetize a magnetic thin film with an easy axis of magnetization in any one of the directions perpendicular to and parallel to the surface of the cantilever along the easy axis, and then place the tip of the cantilever perpendicular to the sample surface Accordingly, it is possible to manufacture a magnetic probe capable of detecting a component in a vertical or parallel direction of a leakage magnetic field on a sample surface with high sensitivity. Furthermore, the radius of curvature at the tip is 100 nm
The use of a sharpened cantilever as described below makes it easy to control the curvature of the tip of the magnetic probe. The tip of the cantilever can be arbitrarily processed according to the etching conditions in the semiconductor lithography technique. Further, the cantilever alone or the cantilever on which the magnetic thin film is formed can be processed into an arbitrary shape by processing the tip portion using, for example, a focused ion beam (FIB). In addition, because the magnetic probe is thinner, the holding force is greater than that of a wire-shaped magnetic probe, and the magnetic field of the magnetic probe does not change due to the leakage magnetic field on the sample surface. Measurement can be performed in close proximity, and high-sensitivity, high-resolution magnetic force information can be obtained. This effect is further enhanced by selecting a material having a large coercive force as the magnetic probe thin film material. With this configuration, the cantilever is bent by the magnetic force acting between the magnetic probe and the magnetic sample. By detecting the amount of the deflection by a displacement detecting means (for example, a tunnel current, an optical method, or a change in capacitance) provided behind the cantilever, magnetic force information of the sample can be obtained. At the same time, by detecting the tunnel current between the sample and the magnetic probe, it is possible to obtain surface morphological information of the sample and more accurate magnetic force information. A similar measuring means, besides the magnetic force between the sample and the probe,
The present invention can be applied to a scanning tunnel microscope-like device that detects displacement between a sample and a probe due to sound, heat, light, or the like. In addition, since the protective film has a lower oxidizing power than the material of the magnetic probe, an altered layer such as an oxide film or a nitride film is formed on the surface of the magnetic probe to prevent a change in the magnetic properties of the magnetic probe. To act. Desirable materials for the protective film are Pt, Pd, Au, Ru, Rh,
An alloy containing Cr, C, and at least one of these elements. Desirable thickness of the protective film is less than 100 nm. As the material of the protective film, a material having electric conductivity is desirable. More preferably, a nonmagnetic material is used.

【Example】

Hereinafter, the present invention will be described with reference to examples. Embodiment 1 This embodiment will be described with reference to FIG. A cantilever 1 having a sharp and sharp tip as shown in FIG. As a material of the cantilever 1,
It is better to have high rigidity and low specific gravity. In this embodiment, Si,
A cantilever 1 having a similar configuration was manufactured using SiO ₂ , Si ₃ N ₄ , W, Mo, diamond-like carbon, or stainless steel, and the same effect was obtained. The cantilever 1 is supported by a support 2. The tip 3 of the cantilever 1 was machined into a sharp pointed form. The curvature of the tip 3 could be arbitrarily changed by, for example, appropriately selecting an etching rate and an etching solution in a photo process. After the photo process, it was processed into a sharp pointed shape by ion beam etching or the like. The curvature of the tip portion 3 of the cantilever 1 is less than 100 nm, which is suitable for obtaining high-resolution magnetic information on the order of submicrons. Next, a magnetic probe 4 is formed on the tip 3 of the cantilever 1 (FIG. 1 (b)). The magnetic probe 4 was formed of a magnetic material thin film. An underlayer 5 was provided below the magnetic thin film to control the direction of the axis of easy magnetization of the magnetic material thin film. The direction of the axis of easy magnetization of the magnetic thin film was arbitrarily controlled to be perpendicular or parallel to the surface of the tip 3 of the cantilever depending on the combination of the material of the underlayer 5 and the magnetic material thin film formed thereon. As a material of the underlayer 5, a polycrystalline film, an amorphous film, or an alloy film of Ge, Si, Ti, Cr, C, or the like was used. The magnetic thin film material is mainly composed of Co and Fe, and Ni, Cr, Pt,
An alloy or a multilayer film added to Zr, C, N, etc. was used.
Since the magnetic force acting between the sample and the magnetic probe depends on the magnitude of the magnetization at the tip of the magnetic probe, the saturation magnetization of the magnetic material thin film used as the magnetic probe must be 100 kA to improve the magnetic force sensitivity. / m or more is good. When the magnetic probe approaches the magnetic sample surface, the magnetic field of the magnetic probe changes due to the leakage magnetic field on the sample surface, and as a result, the magnetic force sensitivity decreases. Therefore, the coercive force of the magnetic thin film constituting the magnetic probe was set to 80 A / m or more. The underlayer 5 and the magnetic material thin film were formed by a vacuum evaporation method or a sputtering method. For example, as the underlayer 5
Using Cr or C, Co-Ni, Co-Ni-Pt, Fe-
By using Ni or the like, a magnetic probe 4 was manufactured in which the axis of easy magnetization of the magnetic material thin film was parallel to the surface 3 of the tip of the cantilever and highly oriented in the direction of the tip of the cantilever. Further, for example, Ge, Si, Ti or a multilayer film thereof is used as the underlayer 5 and a magnetic thin film such as Co—Cr or Co—Cr—Ni is formed thereon, so that the easy axis of magnetization of the magnetic thin film is A magnetic probe 4 highly oriented perpendicular to the surface of the tip 3 was produced. Further, when the underlayer and the magnetic thin film are formed, the tip surface of the cantilever is moved from 0 to the evaporation source.
By installing the magnetic thin film at an angle in the range of 90 degrees, the easy axis of magnetization of the magnetic thin film could be controlled in any direction within the range of 0 to 90 degrees with respect to the tip surface of the cantilever. The coercive force of the magnetic material thin film constituting the magnetic probe 4 and the crystal grain size of the thin film were arbitrarily controlled by changing the temperature at the time of forming the thin film, the pressure of the sputtering gas, and the like. For example, after forming a Cr underlayer with a thickness of 20 nm at a substrate temperature of 150 ° C. by a vacuum evaporation method, and then forming a magnetic thin film made of Co ₈₀ Ni ₂₀ thereon, the coercive force
A magnetic probe 4 having a magnetic characteristic of 16 kA / m and a saturation magnetization of 700 kA / m and having a magnetic easy axis highly oriented parallel to the surface of the tip 3 of the cantilever was obtained. To obtain magnetic force information with a resolution of 0.1 μm or less, the curvature of the tip of the magnetic probe must be 0.1 μm
It was necessary to: For this purpose, the crystal grain size of the magnetic material thin film constituting the magnetic probe should be at least 0.1μ.
m or less. The crystal grain size of the magnetic material thin film was controlled by the speed at which the thin film was formed, the substrate temperature, the pressure of the sputtering gas, and the type of underlayer when the magnetic material thin film was formed. The crystal grain size constituting the magnetic thin film when formed under the above conditions of the present embodiment is 20 to 50 nm.
Met. For comparison, a magnetic thin film made of Co ₈₀ Ni ₂₀ was directly formed without providing the underlayer 5 on the surface of the tip 3 of the cantilever. The magnetic properties of this thin film are coercive force 10 kA / m, saturation magnetization 690 kA
Although the characteristics were almost the same as those with the / m and Cr underlayers,
The direction of the axis of easy magnetization of the magnetic thin film constituting the magnetic probe 4 was randomly oriented with respect to the surface of the tip 3 of the cantilever. As a result of comparing the magnetic force sensitivity between the magnetic probe 4 and the magnetic sample in the direction perpendicular to the sample surface using the two types of magnetic probes, the underlayer 5 was provided on the surface of the tip 3 of the cantilever. The magnetic probe with the highly easy axis of magnetization of the film showed a value more than 10 times larger than the magnetic probe without the underlayer. Similarly, an amorphous Ge film is formed as a base layer 5 on the surface of the tip 3 of the cantilever, and a magnetic thin film made of Co-20 wt% Cr is formed thereon, and the axis of easy magnetization is perpendicular to the surface of the cantilever. A magnetic probe 4 highly oriented in the direction was produced. The magnetic probe in this case could detect the magnetic force of the component parallel to the sample surface with high sensitivity. It is a matter of course that the magnetic probe 4 having the same configuration may be made to adhere a magnetic material by an electric field plating method other than the vacuum evaporation method and the sputtering method. In this embodiment, the shape of the tip of the cantilever was described by a photo process, but the shapes of the cantilever and the tip of the magnetic probe could also be processed by irradiating an ion beam. For example, the first process
The tip of the cantilever fabricated as shown in FIG. 1A is processed into a sharper tip by a focused ion beam (FIB), and then a magnetic thin film is formed thereon. A needle was made. Also, after forming a magnetic thin film as shown in FIG. 1 (b), it was similarly processed by a focused ion beam to produce a magnetic probe having an arbitrary tip shape as shown in FIG. 1 (c). Embodiment 2 Another embodiment of the magnetic probe of the present invention will be described with reference to FIG. An underlayer 5 and a magnetic thin film 7 were formed in this order on one surface of a cantilever 1 having a sharp pointed tip made of SiO _{2 having a} thickness of 1 μm, a width of 20 μm, and a length of 180 μm. At this time, the cantilever 1 was curved so that the surface on which the magnetic thin film 7 was formed was concave. Subsequently, a protective film 6 was formed on the surface of the magnetic thin film 7 and the surface of the cantilever on the opposite side. The protective film 6 is preferably made of an electrically conductive material. The effect was the same even if the thickness of the protective film 6 formed on the surface of the magnetic thin film 7 was different from the thickness of the protective film formed on the back surface side. The displacement of the cantilever is
Tunnel current between the concave side of the cantilever and a metal probe (not shown) or an optical displacement detection method was used. For this purpose, the surface of the cantilever 1 is preferably a mirror surface, and is formed on this surface. The crystal grain size of the protective film was preferably 50 nm or less. If the crystal grain size of the protective film becomes larger than this, the undulation of the surface becomes large, causing an error in the displacement detection of the cantilever. The magnetic probe prepared as described above was used by setting the tip of the cantilever to be perpendicular to the sample surface. Embodiment 3 An example in which a magnetic probe manufactured according to the present invention is applied to a magnetic force microscope will be described with reference to FIG. A magnetic probe 4 was formed by sequentially forming an underlayer 5 and a magnetic thin film 7 on the surface of a cantilever 1 having a sharp tip. The magnetic probe was set such that the tip of the cantilever approached perpendicularly to the surface of the magnetic sample 8. That is, the magnetic thin film 7 formed on the surface of the cantilever 1 was set such that the axis of easy oxidation was perpendicular or parallel to the sample surface. The magnetic thin film 7 was used while being magnetized in the direction of the axis of easy magnetization of the magnetic thin film formed on the surface of the cantilever 1 and kept in a remanent magnetization state. An electrically conductive coating layer 6 of Au, Pt or the like was formed on both surfaces of the magnetic probe and the cantilever. On the opposite surface of the magnetic thin film 7, a metal probe 9 having a sharp tip is set close to the cantilever 1 and a tunnel current between the cantilever surface and the metal probe is detected, whereby the sample and the magnetic probe are detected. The displacement of the cantilever due to the magnetic force between the needles was detected. The metal probe 9 was formed of a sharply pointed W line or Pt line, but the same effect was obtained in each case. With the measurement configured as described above, the displacement of the cantilever due to the leakage magnetic field on the surface of the magnetic sample 8 was detected, and magnetic force information such as the magnetic domain structure of the magnetic sample 8 was obtained from the result.
At the same time, by detecting the tunnel current between the magnetic probe 4 and the sample 8, morphological information on the sample surface was obtained. By forming the protective film 6 on the surface of the magnetic probe, measurement with good reproducibility was possible even when the magnetic probe was operated for a long time in air, vacuum, or various gas atmospheres. The same effect was obtained by using Ru, Rh, Au, Pd and an alloy containing them in addition to Pt as the protective film 6. Embodiment 4 Another embodiment of the magnetic probe manufactured according to the present invention will be described with reference to FIG. A cantilever consisting of a tip 10 having a sharp tip was held by the support 2. The cantilever 11 was made of silicon oxide.
Similar effects can be obtained by using any of silicon nitride, diamond-like thin film, and non-magnetic metal foil.
Tip 10 is made of tungsten, platinum or cantilever 11
A non-magnetic material made of the same material as nickel or nickel,
A structure composed of a wire or a foil of a magnetic material such as iron or cobalt was manufactured. The tip 10 was fixed to the cantilever 11 with an adhesive or the like, and then the tip was etched and sharpened by electric field polishing or the like, or the tip 10 having a sharp tip was fixed to the cantilever 11 in advance. First, an underlayer (not shown) for controlling the crystal orientation of the magnetic thin film was formed on the surface of the chip 10 manufactured as described above, and then a magnetic thin film was formed thereon to manufacture the magnetic probe 4. In this case, in order to obtain the magnetic probe 4 having a sharp pointed tip, it is desirable that the thickness of the underlayer for controlling the crystal orientation and the thickness of the magnetic thin film are thin, and the thickness of each of them is appropriately 0.1 μm or less. By forming a magnetic thin film by providing an underlayer for controlling crystal orientation on the surface of the chip, a magnetic probe 4 in which the axis of easy magnetization of the magnetic thin film is highly oriented perpendicular or parallel to the surface of the chip 10 is manufactured. did. When using the magnetic probe 4, it was magnetized in a direction parallel or perpendicular to the tip of the sharp tip 10. The magnetized magnetic probe 4 is a tip 10
Was set so that the tip of the sample was perpendicular to the surface of the sample 8.
When the magnetic probe 4 is magnetized parallel to its tip, the vertical component of the leakage magnetic field of the magnetic sample 8 is detected, while when the magnetic probe 4 is magnetized perpendicular to its tip, the magnetic sample 8 is detected.
The horizontal component of the leakage magnetic field was detected. The magnetic force generated by the interaction between the magnetic probe 4 and the magnetic sample 8 causes the cantilever 11 to move.
Undergoes bending. The displacement due to the bending of the cantilever 11 was detected by a displacement detecting means provided behind the cantilever 11, for example, a metal probe 9 having a sharp tip, and a tunnel current between the metal probe 9 and the surface of the cantilever 11. By using a magnetic probe of this configuration, a magnetic force of the order of 10 ^-10 N and high-resolution magnetic information of the order of submicrons could be obtained with good reproducibility. In the present invention, since the axes of easy magnetization of the magnetic probe are aligned and the coercive force of the magnetic probe is large, the magnetization of the magnetic probe does not change due to the magnetic field from the sample as in the related art.
Therefore, if the surface morphology information is obtained by measuring the tunnel current between the sample and the magnetic probe, accurate magnetic information can be obtained from this and the magnetic information (including the surface morphology information) obtained by the magnetic force measurement. Can be

【The invention's effect】

As described above, the underlayer for controlling the crystal orientation is provided on the surface of the cantilever having a sharp tip, and the magnetic thin film is formed thereon, so that the axis of easy magnetization of the magnetic thin film is parallel to the surface of the cantilever from the direction perpendicular to the surface. A magnetic probe highly oriented in any direction within a range of various directions can be formed. The magnetic probe thus formed is magnetized along the axis of easy magnetization, and the tip of the cantilever is set so as to approach perpendicularly to the sample surface, so that the magnetic force in the direction perpendicular or parallel to the sample surface is obtained. Can be configured with high sensitivity and high resolution. In addition, the distance between the magnetic sample and the magnetic probe can be controlled with high precision by forming the magnetic information detecting device by covering the surface of the magnetic probe with a coating layer made of a conductive material. There is an effect that magnetic force information and morphological information on the sample surface can be obtained. In addition, by coating the surface of the magnetic probe with a coating layer made of a conductive material, it is possible to prevent changes in magnetic characteristics and electrical conductivity due to oxidation of the surface of the magnetic probe, and to provide information on magnetic force and sample surface morphology. This has the effect of obtaining information with good reproducibility.

[Brief description of the drawings]

1 (a) to 1 (c) are explanatory views of an embodiment of the present invention, FIG. 2 is an explanatory view showing an example of a method for manufacturing a magnetic probe of the present invention, and FIG. FIG. 4 is an explanatory diagram of an application example to a magnetic force microscope using the magnetic probe of the present invention. FIG. 4 is an explanatory diagram of another application example of the magnetic probe of the present invention. Explanation of symbols 1: cantilever, 2: support, 3: tip, 4: magnetic probe, 5: underlayer, 6: protective film, 7: magnetic thin film, 8: sample, 9: metal probe, 10: Tip, 11: Cantilever.

Continuation of the front page (72) Inventor Shigeyuki Hosoki 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-2-78006 (JP, A) JP-A-3-96854 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 37/00 G01R 33/10-33/12 G01N 27/72 G01B 7/34 H01J 37/28 JICST file (JOIS) WPI (DIALOG)

Claims (7)

(57) [Claims] 1. A cantilever having a sharp tip, a magnetic probe formed at the tip of the cantilever, and a displacement of the magnetic probe caused by a magnetic force generated between the magnetic probe and a magnetic sample. A magnetic information detecting device, wherein the magnetic probe is formed of a magnetic material thin film, and the easy axis of magnetization of the magnetic material thin film is oriented in one direction. 2. The magnetic information detecting device according to claim 1, wherein said magnetic material thin film is formed on a surface of said cantilever via a nonmagnetic underlayer. 3. The magnetic information detecting device according to claim 2, wherein the coercive force in the easy axis direction of the magnetic material thin film constituting the magnetic probe is 80 A / m or more. 4. The magnetic information detecting device according to claim 2, wherein said magnetic material thin film is magnetized in a direction parallel or perpendicular to a surface of said cantilever. 5. The magnetic information detecting device according to claim 2, wherein a protective film made of a conductive material is formed on surfaces of said magnetic probe and said cantilever. 6. The magnetic information detecting device according to claim 2, wherein said magnetic material thin film has a crystal grain size of 100 nm or less. 7. The curvature of the sharp tip of the cantilever is:
3. The magnetic information detecting device according to claim 2, wherein the magnetic information detecting device has a thickness of 100 nm or less.