JPS62269305A - Thin film of magnetic material and manufacture thereof - Google Patents

Abstract

PURPOSE:To bring the axis of easy magnetization into a planar direction or a vertical direction as well as to contrive improvement in the corrosion-resisting property and the electric resistivity of the title thin film by a method wherein the thin film is formed with the cobalt nitride having a specific composition and magnetic coercive force. CONSTITUTION:The cobalt nitride in the state of thin film is formed in the composition indicated by the formula CoNx(0.005<=x<=0.6), and the magnetic coercive force of 100 Oe or more is given to the cobalt nitride thin film. To be more precise, said cobalt nitride thin film is formed by performing a sputtering metnod on the substrate at 350 deg.C in the inert gas containing N2 using Co or CoN as a target. As a result, the title magnetic thin film is composed of the epsilon-Co phase of hexagonal structure, alpha-Co phase of face-centered cubic crystal structure, gamma-Co3N phase of hexagonal structure, delta-Co2N phase of orthorhombic structure, or the mixture of the above-mentioned phases. Consequently, the magnetic thin film, having the axis of easy magnetization in a planar orientation or in vertical direction, high magnetic coercive force, high electric resistivity, and excellent abrasion-resisting property and corrosion- resisting property, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel magnetic thin film having a high coercive force, which is suitably used in thin film magnetic devices such as magnetic recording media, and a method for manufacturing the same.

BACKGROUND OF THE INVENTION With the development of an advanced information society, various thin film application devices have been developed, and it has become necessary to make the high coercive force permanent magnets used in these devices thinner. For example, as magnetoresistive elements become thinner, permanent magnets that apply bias magnetic fields need to be made thinner, and pattern formation is also required to be compatible with process technology. On the other hand, in magnetic recording technology, there is a strong demand for even higher recording densities. Therefore, great efforts are being made to develop or improve magnetic recording media such as magnetic disks and magnetic tapes, magnetic heads, and their drive mechanisms.

Among these, magnetic recording media are particularly required to have excellent magnetic properties such as coercive force and squareness, as well as excellent mechanical durability.

In order to meet the above requirements, magnetic disks have been changed from the conventional fine particle coating type such as 7-Fe2O3 to γ-Fe20.
3 thin films, high coercive force, high magnetization alloy thin films such as Co-Ni,
The development trend is shifting towards perpendicularly anisotropic Co-Cr alloy thin films, and magnetic tapes are moving from fine particle coating types such as T Fe2O3 to thin films made of high coercive force and high magnetization iron alloy powders, Co and their alloys, etc. Development is underway.

In these various devices, the magnetic properties of the magnetic thin film required for each device are slightly different, but all require magnetic properties of high coercive force and high residual magnetization, and the axis of easy magnetization is in-plane or perpendicular. It is required to be easy to manufacture, have excellent chemical and thermal stability, corrosion resistance, mechanical durability, etc.

However, conventional materials and various known high coercive force magnetic thin films currently under development have advantages and disadvantages, and for this reason, the development of new high coercive force magnetic thin films is desired.

Problems to be Solved by the Invention In view of the above-mentioned current situation, the present invention has a high coercive force suitable for magnetic thin film devices such as magnetic recording media, has an axis of easy magnetization in the in-plane direction or perpendicular direction, and has corrosion resistance. Excellent in
The purpose of this invention is to provide a novel magnetic thin film with high electrical resistivity and an easy method for manufacturing the same.

Means for Solving the Problems The present inventors have searched and studied thin film cobalt nitride from various angles, and as a result, have come up with the present invention. That is, according to the present invention, the compositional formula CoNx (
A magnetic thin film made of cobalt nitride is provided, which is expressed as 0,005≦x≦0.6) and has a coercive force of 100°e or more.

The cobalt nitride thin film of the present invention has an axis of easy magnetization within the film plane or in a direction perpendicular to the film plane.

Furthermore, the cobalt nitride thin film of the present invention has a hexagonal structure ε-Co phase or a face-centered cubic structure α-Co phase in the sputtered state, that is, as-depo state.
It consists of an o phase, a γ-Co3N phase with a hexagonal structure, a δ-Co□N phase with an orthorhombic structure, or a mixed phase thereof.

These phase structures can be formed in the as-sputtered state, i.e. as-dep, by controlling the N2 concentration in the inert gas, the temperature of the substrate and the bias voltage, for example in reactive sputtering.

In this state, the desired phase structure can be obtained.

Furthermore, according to the present invention, in an inert gas containing N2, C
Sputtering is performed on a substrate at 350° C. or lower using CoN or CoN as a target, and the composition formula is CoN,
A method for manufacturing a magnetic thin film is provided, which is characterized in that cobalt nitride, which is expressed as (0,005≦x≦0.6) and has a coercive force of 100 Oe or more, is formed on the substrate.

That is, sputtering according to the present invention is carried out while maintaining the substrate temperature at 350° C. or lower, more specifically at a temperature in the range from room temperature to 350° C., to obtain a crystalline cobalt nitride thin film.

Sputtering can be performed using various sputtering devices such as a radio frequency (RF) method and a magnetron method. In addition, as a target for sputtering, Co
A molded body made of N powder, a composite target made of Co and CoN powder, etc. can also be used.

Further according to a preferred embodiment of the present invention, the nitrogen content and crystal structure of cobalt nitride are controlled by adjusting the N2 concentration in the inert gas, the temperature of the substrate, and the bias voltage.

It goes without saying that the cobalt nitride thin film of the present invention can be manufactured by other generally known thin film forming methods such as vacuum evaporation, ion blating, etc. in addition to sputtering.

FIG. 1 is a diagram showing the relationship between the nitrogen concentration X in a CoN thin film and the crystal structure obtained as a result of the inventors' research on cobalt nitride thin films.

As shown in Figure 1, as X, that is, the amount of nitrogen,
α phase of cc), T phase of hexagonal structure (h, cp), δ phase of orthorhombic structure, and changes to ζ phase of face-centered cubic structure (fcc) when X is around 1. It was also revealed that these phases can be obtained stably and that there is a miscible region between each phase.In particular, it was revealed that there is a miscible region between each phase. It has been discovered that a face-centered cubic α phase can be stably obtained at room temperature when X is in the range of about 0.01 to 0.3.

Figure 2 shows N2 and
The cobalt nitride film obtained by performing reactive sputtering while maintaining the total gas pressure of the mixed gas consisting of r at 5 mTorr and changing the N2 partial pressure ratio r (nitrogen gas pressure PN2/total gas pressure P total) In-plane coercive force (Hal+
) and the N2 partial pressure ratio r.

As shown in FIG. 2, a cobalt nitride thin film having a high coercive force of 100 Oe or more is obtained except when r is around 0.05 and around 0.2. More specifically, when 0.08<r<0.1, a thin film assumed to be made of Co and N is obtained;
It is an in-plane magnetized film or an isotropic film that has a relatively large in-plane coercive force as well as a thin film obtained in the range of 2<r<0.25. Furthermore, perpendicular anisotropy appears in a thin film obtained with 0.3<r<1.0, and in particular, a δ-phase thin film has an axis of easy magnetization completely perpendicular to the film surface.

Figure 2 shows the relationship between a specific nitrogen partial pressure ratio r, which is one of the sputtering conditions, and magnetic properties, that is, in-plane coercive force, but other sputtering conditions, such as substrate temperature, substrate bias, input power, etc. The magnetic properties change significantly by changing the conditions. As a result of analyzing the cobalt nitride thin films obtained under these various conditions using X-ray diffraction, an
A coercive force of 0 Oe or more, and a coercive force of 0. All cobalt nitride thin films simultaneously having a saturation magnetic flux density of IKG or higher are hexagonal ε phase, face-centered cubic α phase, hexagonal r phase, orthorhombic δ phase, or a mixture thereof, and X is from 0.005 to 0. It became clear that the value was in the range of .6.

Regarding the substrate temperature, the smaller r and the higher the substrate temperature, the more difficult it is for nitrogen atoms to be incorporated into the thin film. On the other hand, the orientation between crystals changes greatly depending on the difference in substrate temperature. For example, in the case of r-0,5, the thin film obtained at a substrate temperature of 200°C or less is γ(101), and further 2
At 30° C., the orientation changes to the r (002) plane, and from this point the orientation changes to the α phase.

In particular, the reason why the substrate temperature is limited to 350°C or less in the present invention is that at temperatures higher than this, cobalt nitride decomposes, making it difficult for nitrogen to be incorporated into the thin film. This is because the cobalt nitride thin film has a hexagonal crystal structure containing almost no ε-Co, and a cobalt nitride thin film having the magnetic properties targeted by the present invention cannot be obtained.

Furthermore, a multiphase coexistence state can be obtained by substrate bias.

When a bias is applied in the region r<Q, 5, as the bias voltage increases, nitrogen content: 1. Whereas a phase with a small amount of nitrogen appears, when a bias is applied in the region of r>Q, 5, a phase with a large nitrogen content appears as the bias voltage increases.

In the present invention, when the nitrogen content The range of X was limited to 0.005 to 0.6. In order to obtain a cobalt nitride thin film with an easy axis of magnetization in the film plane within this composition range, X is 0.005 to 0.3.
In order to obtain a perpendicularly magnetized film having an axis of easy magnetization with respect to the film surface, X is preferably in the range of 0.2 to 0.6.

Furthermore, the cobalt nitride thin film in which When used as a magnetic recording medium, it has the advantage of low eddy current loss and, as a result, excellent high frequency characteristics.

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

Example 1 In an rf two-pole sputtering device, the degree of vacuum is IX 1
After reaching O-6 Torr, a mixed gas of N2 and N2 was introduced, and the total gas pressure was 5 mTorr, and the N2 gas partial pressure ratio r-
0.2, reactive sputtering was performed using a Co target, and about 0.5 was placed on a glass substrate heated to 230°C.
A cobalt nitride thin film with a thickness of μm was formed.

When this thin film was examined by X-ray diffraction, it was found to be an α phase with an fcc structure, as shown in FIG. 3(a). In addition, magnetic measurements using a vibrating magnetometer revealed that the axis of easy magnetization was in the in-plane direction, and the magnetic properties in the in-plane direction had a saturation magnetic flux density of 4πM
s is 6.5KG, squareness ratio Sl+ is 0.82, coercive force H8
11 is 420 Oe and has an electrical resistivity of 440 μΩcm
It was a high coercive force magnetic thin film.

Example 2 In an rf two-pole sputtering device, the degree of vacuum is IXl,
After reaching 0-6 Torr, total gas pressure 5 mTorr
A cobalt nitride thin film of about 1 μm was formed on a quartz substrate heated to 340° C. by performing reactive sputtering using a Co target with the SN2 partial pressure ratio r=0.8.

As shown in FIG. 3(b), the thin film in this state is a mixed phase of an ε phase with an HCP structure and an α phase with an FCC structure, and its magnetic properties are 4 yrMs, 15.6KG, and a squareness ratio of 5II0.
64, Hc++ 520 Oe, the axis of easy magnetization was in the in-plane direction, and the film was a high coercive force magnetic thin film with an electrical resistivity of 85 μΩcm. FIG. 4 shows the M-8 curve of the obtained thin film.

Example 3 Under the same conditions as Example 2, a cobalt nitride thin film with a thickness of about 0.8 μm was formed on a quartz substrate heated to 180° C. The thin film in this state has a mixed phase of a γ phase with an hcp structure and a δ phase with an orthorhombic structure, as shown in FIG.
HCL 580Oe, horizontal coercive force Hel+320
A high coercive force magnetic thin film having an electrical resistivity of 205 μΩcm and an axis of easy magnetization perpendicular to the film surface was obtained.

Example 4 In an rf two-pole sputtering device, the degree of vacuum is lXl0
After reaching -6 Torr, a mixed gas of 8r and N2 was introduced, the total gas pressure was 5 mTorr, and the N2 partial pressure ratio r = 0.
5, the substrate bias (8) was varied from 0 to -150, and reactive sputtering was performed using a Co target.
In particular, a cobalt nitride thin film was formed on an unheated (room temperature) glass substrate. The magnetic properties of this thin film are shown in FIG.

In Figure 5, ■When 5=0, 4 πMs0.25K
G.

This shows that it is an in-plane easily magnetized film having magnetic properties of Hc++220 Oe and Hct 120 Oe. Further, this thin film phase state was a cobalt nitride thin film consisting of a γ phase with an hcp structure.

Furthermore, in Fig. 5, when V, -50V, 4πM
s Q, 9KGXHcz 335Oe, Hct 76
This indicates that the film is a perpendicularly anisotropic film with magnetic properties of 0 Oe.

FIG. 6 shows the M-11 curve of the obtained thin film. The phase state of this thin film was a cobalt nitride thin film consisting of a mixture of a γ phase with an hcp structure and a δ phase with an orthorhombic structure. moreover,
In the case of VS - 100V, it is also a perpendicularly anisotropic film with the axis of easy magnetization in the vertical direction, and its phase state consists of a mixture of α phase of fcc structure, γ phase of hcp structure, and δ phase of orthorhombic crystal. It was a cobalt nitride thin film.

Furthermore, in the case of vs −150V in Fig. 4, 4π
ts 1.2KG, Hcz400Oe, Hct
This shows that it is an isotropic magnetized film having magnetic properties of 460 Oe.

In addition, the phase states are the ζ phase of the hcp structure and the α phase of the fcc structure.
It was a cobalt nitride thin film consisting of a mixed phase of a γ phase with an hcp structure.

Next, the hardness of the 1 μm thick cobalt nitride thin film prepared under the conditions of a substrate bias voltage Vs of −50 V was measured using a 1ζ micro Vickers hardness tester. As a result, the average value of 10 measurement points was 1270, and the hardness of a normal alloy thin film, for example, a Co-Cr alloy thin film, was 50.
It was found that the hardness was much higher than that of 0 to 600. This shows that the cobalt nitride thin film according to the present invention has excellent wear resistance.

Furthermore, the same cobalt nitride thin film and cobalt thin film were left in an atmosphere with a temperature of 60°C and a humidity of 80% for 5 days,
Corrosion resistance was investigated. In the cobalt thin film containing no N, five or more corroded parts were observed per 1 mm2, whereas in the cobalt nitride thin film according to the present invention, almost no corroded parts were observed.

This investigation revealed that cobalt nitride thin films have superior oxidation and corrosion resistance compared to metal and alloy thin films.

As described in detail, the cobalt nitride thin film according to the present invention comprises:
It is a new magnetic thin film that has easy axes in the plane and in the vertical direction, has high coercive force and high electrical resistivity, and has excellent wear resistance and corrosion resistance. Suitable for thin film magnetic devices such as magnetic recording media.

[Brief explanation of the drawing]

Figure 1 is a phase diagram showing the relationship between the nitrogen concentration FIG. 3 is an X-ray diffraction pattern showing the phase state of cobalt nitride obtained in Examples 1, 2, and 3; The figure is a diagram showing the M-8 curve of the thin film obtained in Example 2. Figure 5 is a diagram showing the relationship between the substrate bias voltage (■) and magnetic properties in RF bipolar sputtering, and (b) Figure 6 shows the M-8 curve of a cobalt nitride thin film obtained at a substrate bias voltage of 50 V. (Main reference numbers) Hel+... Coercive force in the direction parallel to the film surface, HCL
・Coercive force in the direction perpendicular to the film surface, 4πMs...Saturation magnetic flux density

Claims (7)

[Claims] (1) A magnetic thin film made of cobalt nitride, represented by the compositional formula CoN_x (0.005≦x≦0.6), and characterized by having a coercive force of 100 Oe or more. (2) The magnetic thin film according to claim 1, wherein the cobalt nitride has an axis of easy magnetization within the film plane. (3) The magnetic thin film according to claim 1, wherein the cobalt nitride has an axis of easy magnetization in a direction perpendicular to the film surface. (4) The cobalt nitride has a hexagonal structure ε-Co phase, a face-centered cubic structure α-Co phase, a hexagonal structure γ-Co_3N phase, or an orthorhombic structure δ-Co_2
The magnetic thin film according to any one of claims 1 to 3, characterized in that it is an N-phase or a mixture thereof. (5) Co or CoN in an inert gas containing N_2
Sputtering was performed on a substrate at 350°C or lower using CoN as a target, and the composition formula CoN_x (0.005≦x≦0
．． 6) A method for manufacturing a magnetic thin film, characterized in that cobalt nitride having a coercive force of 100 Oe or more is formed on the substrate. (6) The above-mentioned cobalt nitride may be an ε-Co phase with a hexagonal crystal structure, an α-Co phase with a face-centered cubic structure, a γ-Co_3N phase with a hexagonal structure, or a δ-Co_2 phase with an orthorhombic structure.
6. The method for producing a magnetic thin film according to claim 5, wherein the magnetic thin film is an N phase or a mixed phase thereof. (7) Claim 5, characterized in that the nitrogen content and crystal structure of cobalt nitride are controlled by adjusting at least one of the N_2 concentration in the inert gas, the temperature of the substrate, and the bias voltage. Or the method for producing a magnetic thin film according to item 6.