JPS6412112B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a magnetic thin film for a magnetoresistive element, and in particular, the present invention relates to a method for manufacturing a magnetic thin film for a magnetoresistive element.
This invention relates to a method for manufacturing a magnetic thin film for a magnetoresistive element manufactured by a sputtering method mainly made of Co. Magnetoresistive elements using magnetic thin films are used in magnetic heads,
It is widely used in magnetic thin film memory detectors, magnetic field sensors, magnetic bubble detectors, Magnescale detectors, VTR tape cue detectors, rotary encoder signal detectors, and others. Ni--Fe thin films and Ni--Co thin films are used as magnetic thin films for magnetoresistive elements used in these various sensors, and these thin films are mainly produced by vacuum evaporation method, but sputtering method is also used. It can also be produced by By the way, with the vacuum evaporation method, the content of impurities in the thin film is lower than that with the sputtering method, and the magnetoresistive effect ΔR/R of the thin film is lower.
(However, R is the resistance of the element, and ΔR is the change in resistance due to the magnetic field.) Because it has the advantage of being large, vacuum evaporation has conventionally been used exclusively to produce magnetic films for magnetoresistive elements. However, it is known that the vacuum evaporation method has the following drawbacks (1), (2), and (3) compared to the sputtering method. (1) It is difficult to control the film thickness. (2) The film adhesion strength is weak. (3) There is an incident angle effect. (4) There is a large composition deviation from the master alloy. The present invention eliminates the above-mentioned defects of thin films produced by vacuum evaporation method or sputtering method.
It is an object of the present invention to provide an improved method for manufacturing a magnetic thin film for a magnetoresistive element, and the above object can be achieved by providing the thin film and the method for manufacturing the same as described in the claims. That is, in the present invention, a thin film consisting of 10 to 50% by weight of Co and the remainder substantially Ni is produced by a sputtering method, and then the thin film is heated in a temperature range of 200 to 500°C either in vacuum or in a hydrogen atmosphere. The present invention relates to a method of manufacturing a magnetic thin film for a magnetoresistive element, characterized in that annealing is performed in a step. Next, the present invention will be explained in detail. The present inventors have conducted various studies to eliminate and improve the above-mentioned drawbacks of thin films produced by vacuum evaporation or sputtering methods. We have come up with a method for producing thin films that eliminates and improves the defects of thin films produced by the neglected sputtering method, and also eliminates and improves the defects of thin films produced by vacuum evaporation. The present inventors fabricated Ni by sputtering method.
- The magnetoresistive effect of the Co magnetic thin film is significantly improved by subjecting the thin film to either vacuum annealing or hydrogen atmosphere annealing. A thin film that has a magnetoresistive effect comparable to that of a magnetoresistive element film, and does not have the drawbacks of conventional vacuum deposition methods, such as difficulty in controlling film thickness, weak film adhesion strength, and unavoidable incidence angle effects. The present invention was completed based on the new finding that it is possible to obtain the following. Next, the present invention will be explained in detail using experimental data. By the sputtering method used in the experiments of the present invention
A Ni—Co thin film was prepared as follows. The sputtering device is a common RF two-pole sputtering device. The substrates used were three ordinary glass slides measuring 26 mm x 76 mm x 0.7 mm. After heating at approximately 300° C. for 2 hours for the purpose of removing strain from the substrate and degassing the sputtering chamber, the substrate was cooled and returned to room temperature. 4×
After exhausting to 10 ^-5 Pa., apply normal Ar gas 5x.
The pressure inside the sputtering chamber was set by introducing up to 10 ^-3 Pa. and adjusting the conductance using a high-pressure gas valve (main valve). The distance between the target and the substrate was 46 mm. The target is a 10mm x 10mm Ni (purity 99.9%) on a 125mm Co (purity 99.9%) plate.
It is a composite form of pieces lined up. To remove impurities from the target, press sputtering was performed for 30 minutes at an input power of 100 W, and then a film was formed. The sputtering conditions are as shown in Table 1, except for the experiment to investigate film thickness dependence.

[Table] The substrate temperature in the table is the temperature of the stainless steel substrate holder 20 minutes after opening the shutter and starting sputtering. The composition of the sample was determined by measuring EPMA and saturation magnetization Ms. The magnetization curve of the sample was measured using a VSM (vibrating sample magnetometer). The film thickness was measured using a repeated reflection interference microscope, and the specific resistance of the sample was measured using the four-probe method and the magnetoresistive effect (hereinafter referred to as this effect) described below.
(referred to as MR effect) was measured using a two-terminal method. The MR effect of the sample was measured using an apparatus shown in the circuit diagram in Figure 1. The outline of this device is described below. The two Helmholtz coils HC1 and HC2 are arranged orthogonal to each other. C1, R1, L2, and R2 connected to these coils adjust the current value flowing through each coil, so that HC1 and HC2 always generate magnetic fields of the same strength, and the phase of both magnetic fields is
It is now shifted by 90 degrees. In other words, a rotating magnetic field with constant strength is generated near the sample stage.
This makes it possible to easily measure the vertical and horizontal MR effects simultaneously, and there is no need to change the direction of the sample current with respect to the measurement magnetic field. For measurement, first set the sample, apply an alternating magnetic field to demagnetize it, apply a current, and read the voltage V across the sample with a DMM (digital multimeter). Next, a rotating magnetic field (60Hz) is applied, and the voltage change (120Hz) across the sample due to the MR effect is read using an oscilloscope. At this time, a voltage (60Hz) induced by the lead wire of the sample is also applied, so a compensation coil (Compe Coil) is installed to create a differential configuration between the voltage from this coil (60Hz) and the voltage from the sample (60Hz + 120Hz). to cancel the induced voltage. The voltage ΔV at this time was measured, and the MR effect was measured as ΔV/V=ΔR/R. The shape of the sample is 8 mm x 10 mm, and we believe that the effect of shape can be ignored. We compared the characteristics of Ni--Co thin films produced by vacuum evaporation and sputtering. Figure 2 shows the Ni-Co thin film.
It is a diagram showing the relationship between Ni content wt% and MR effect ΔR/R, where curve a shows the relationship obtained for a thin film made by vacuum evaporation method (hereinafter referred to as vacuum evaporation thin film) with a film thickness of 2000 Å. , curve b shows the relationship obtained for a thin film produced by the sputtering method (hereinafter referred to as a sputtered thin film). From the same figure, Ni is 60-70wt%
Curve a shows a relatively large value of ΔR/R of 2.5 to 3.0% in the vicinity, and the composition dependence is evident, while curve b shows ΔR/R of 0.8 to 1.0 within the above Ni content range. % and composition dependence is relatively small, and the MR effect shows only about 1/3 of the value. Further, the specific resistance ρ of both types of thin films was 20 to 26 μΩcm, and the coercive force Hc was 10 to 30 Oe. Therefore, the inventors of the present invention, in a vacuum of 1.3×10 ^-3 Pa
Alternatively, the sputtered film can be annealed in a hydrogen atmosphere.
We investigated the MR effect. As a result, we newly discovered that annealed sputtered films exhibit as large an MR effect as vacuum-deposited thin films. Figure 3 shows that when a sputtered film with a thickness of 2000 Å is annealed using the vacuum method, the curve a corresponds to the annealing temperature Ta.
The curve b shows the relationship between the MR effect ΔR/R and the annealing temperature Ta and the specific resistance ρ. Note that the component composition of the thin film in this case is Ni65 and Co35. As described with reference to FIG. 2, the above composition is included in the composition region where the value of ΔR/R is the largest. As is clear from curve a showing the relationship between annealing temperature Ta and MR effect ΔR/R in this figure, when Ta is around 300℃, ΔR/R
shows the largest value, which is more than three times the value of ΔR/R before annealing. On the other hand, it can be seen that the effect of annealing is extremely small at an annealing temperature of less than 200°C or higher than 400°C. Also, according to curve b showing the relationship between specific resistance ρ and annealing temperature Ta, Ta is
ρ becomes the smallest around 300℃, and this ρ
The value of ρ has decreased to about 1/3 of that before annealing, and is comparable to the value of ρ for the vacuum-deposited film. Figure 4 is a diagram showing the relationship between annealing temperature Ta and coercive force Hc. When annealing temperature Ta is 300°C, coercive force
Hc is the minimum, and its value has decreased to less than 1/5 of the value before annealing. The large MR effect ΔR/R and small specific resistance ρ and coercive force Hc are all suitable characteristics for a magnetoresistive element for a magnetic sensor, and conventional magnetoresistive elements have been unused due to drawbacks in their characteristics. The present inventors were able to newly discover that even a sputtered film can be made into a magnetic thin film for a magnetoresistive element by annealing according to the present invention. By the way, in the above experiment, the degree of vacuum was 1.3×
Although the annealing time was 10 ^-3 Pa and 1 hour, it was found that better magnetic properties could be obtained by increasing the degree of vacuum to a higher degree of vacuum. In addition, when the MR effect of the vacuum-deposited film (Ni ₇₀ Co ₃₀ ) by vacuum annealing was investigated, no significant improvement was observed as shown in FIG. 5. Next, the present inventors investigated the relationship between annealing temperature, MR effect, and resistivity ρ in a hydrogen atmosphere.
FIG. 6 is a diagram showing the above relationship, and the composition and thickness of the thin film were Ni ₇₀ Co ₃₀ and 2000 Å, the same as those in FIGS. 3 and 4, respectively. As is clear from Figure 6, the MR effect shown by curve a is 400% in hydrogen.
It was found that the MR effect reached 5% by annealing at °C, which is 5 times higher than before annealing, and is almost the same as the value of the MR effect conventionally known for vacuum-deposited films. Further, the specific resistance ρ shown by curve b in the same figure becomes approximately 10 μΩcm after annealing at 400° C. in hydrogen, which is found to be lower than 1/4 of the value before annealing.
The specific resistance value of 10 μΩcm is even smaller than the specific resistance value obtained in a vacuum-deposited film. Figure 7 is a diagram showing the relationship between annealing temperature Ta and coercive force Hc in a hydrogen atmosphere. Coercive force Hc is the smallest at an annealing temperature of 300°C, and is 1/4
It can be seen that it has decreased. Ni thus annealed within the temperature range of 250-500℃ in hydrogen atmosphere
- It has been revealed that the Co sputtered film is superior to the sputtered film annealed in vacuum as a magnetic film for magnetoresistive elements, and has properties that are at least as good as those of the vacuum-deposited film. As a result of annealing Ni-Co sputtered films with different Ni contents, it was found that the relationship between the MR effect and the Ni content showed almost the same tendency as curve a in Figure 2. Fabricated by sputtering method as explained above.
It has become clear that by annealing a Ni-Co thin film in vacuum or in a hydrogen atmosphere, it has an MR effect that is close to or comparable to that of a vacuum-deposited film, and that it is possible to maintain an MR effect suitable for a magnetic sensor. Ni should be in the range of 50~90wt%, and the annealing temperature when annealing in vacuum should be in the range of 200~400℃,
Among these, the MR effect is large at 250 to 350°C, and an element with low resistivity ρ and coercive force Hc can be obtained.
In addition, when annealing is performed in a hydrogen atmosphere, 250 to 500
A magnetic film excellent as a magnetoresistive element can be obtained within the temperature range of 300°C, and the most excellent magnetic film is obtained especially when annealing is performed within the range of 300 to 500°C. Next, in the present invention, the reason why the component composition of the thin film and the annealing temperature of the thin film are limited will be explained. If Co is less than 10% by weight or more than 50% by weight, the MR effect ΔR/R will be too small to produce a thin film suitable for magnetoresistive elements, so Co should be in the range of 10 to 50% by weight. There is a need to. In addition, if the annealing temperature is lower than 200℃ or higher than 500℃, the MR effect of the thin film, specific resistance,
Since the coercive force makes it unsuitable for use in magnetoresistive elements, the annealing temperature must be within the range of 200 to 500°C. Next, the present invention will be explained with reference to Examples and Comparative Examples. Example A sputtered film having a composition of Ni ₆₅ Co ₃₅ and a film thickness of 2000 Å was annealed at 300°C in vacuum and at 400°C in hydrogen for 60 minutes, respectively. The properties of the thin film obtained in this way are described in the second section below.
Shown in the table.

[Table] Comparative Example 1 A vacuum-deposited thin film having a composition of Ni ₇₀ Co ₃₀ and a thickness of 2000 Å was annealed in vacuum at 400°C for 60 minutes. Table 3 shows the properties of the thin film thus obtained and the thin film before annealing.

[Table] As can be seen from the table, annealing the deposited film slightly increases the MR effect, but no significant improvement in the soft magnetic properties was expected. Comparative Example 2 A sputtered film having a composition of Ni ₆₅ Co ₃₅ and a thickness of 2000 Å was prepared. Its properties are shown in Table 4 below.

[Table] According to the table, it can be seen that there is no superiority in terms of soft magnetic properties and MR effect compared to permalloy thin films. The following is clear from the above experimental data of the present invention, Examples, and Comparative Examples. (1) The ρ of the sputtered film is approximately
About 1.2 to 2.5 times larger. (2) The MR effect of vapor deposited films is 2.5-3.0%, and that of sputtered films is 0.8-1.0%. (3) When a deposited film is vacuum annealed, the MR effect increases to 3.3%, and in the case of a sputtered film, it increases to 3.5%. (4) When the sputtered film is annealed in hydrogen,
MR effect increases to 5.1%. As described above, the present invention provides a magnetic film suitable as a magnetoresistance element for various magnetic sensors, which has an MR effect comparable to that of conventional vacuum-deposited films, and eliminates and improves the various drawbacks of vacuum-deposited films. I can do it.

[Brief explanation of drawings]

Figure 1 is the circuit diagram of the MR effect measuring device, Figure 2 is the circuit diagram of the MR effect measurement device.
A diagram showing the relationship between the Ni content and the MR effect of a Ni-Co thin film. Figure 3 shows the relationship between the annealing temperature Ta of the thin film and the MR effect,
Figure 4 shows the relationship between thin film annealing temperature Ta and coercive force Hc, and Figure 5 shows the relationship between vacuum annealing temperature Ta and MR effect of vacuum deposited film, MR effect, and resistivity. Figure 6 is a diagram showing the relationship between the annealing temperature Ta of a sputtered film in a hydrogen atmosphere, MR effect, and resistivity, and Figure 7 is a diagram showing the relationship between the annealing temperature Ta of a sputtered film in a hydrogen atmosphere and coercive force. FIG.

Claims (1)

[Claims] 1. 10 to 50% by weight of Co produced by sputtering method,
1. A method for manufacturing a magnetic thin film for a magnetoresistive element, comprising annealing the thin film, the remainder of which is essentially Ni, within a temperature range of 200 to 500° C. either in vacuum or in a hydrogen atmosphere. 2. In a vacuum, the sputtered thin film is
A method according to claim 1, characterized in that the annealing is carried out within a temperature range of 200 to 400°C. 3. The method according to claim 1, wherein the sputtered thin film is annealed in a hydrogen atmosphere within a temperature range of 250 to 500°C.