JPH03132911A - Inspection method for thin film magnetic head - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding the inspection method of thin-film magnetic heads used in magnetic disk drives, the quality of the head is determined at an intermediate stage of the manufacturing process by determining the inductance depending on the amount of magnetic flux generated in the head pole layer. In order to be able to make a judgment, we calculated the value by subtracting the head inductance measured in a strong magnetic field from the coil inductance measured in the absence of a strong magnetic field, and estimated the amount of magnetic flux generated in the head pole layer from this value. It is configured to inspect whether it is good or bad.

[Industrial Field of Application] The present invention relates to a method for inspecting a thin film magnetic head used in a magnetic disk drive.

A thin-film magnetic head is made by forming two thin magnetic pole layers (upper and lower) on a slider substrate with a coil layer sandwiched between them, and narrowing the magnetic pole layers on the tip side of the head to form a gap section in which they are brought close to each other via a gap layer. Writing on the medium is performed using leakage magnetic flux from the magnetic field, and during reading, the medium magnetic flux flowing in from the gap portion is converted into a signal voltage by coil linkage.

However, because thin-film magnetic heads have thin magnetic poles, a large proportion of the magnetic flux leaks to the outside, and even when the coil inductance is measured to inspect the head, the proportion of inductance due to leaked magnetic flux is large, and the inductance component in the magnetic pole layer is large. It does not show the inherent inductance of the head due to the magnetic flux passing through it.

Therefore, there is a need for an inspection method that determines the quality of the electromagnetic conversion characteristics of a thin-film magnetic head by determining the inductance that is dependent on the magnetic flux passing through the magnetic pole layer of the thin-film magnetic head.

[Prior Art] Conventionally, in a thin-film magnetic head, two thin magnetic pole layers (upper and lower) are formed on a slider substrate with a coil layer sandwiched between them. During writing, the magnetic flux generated in the magnetic pole layer is controlled by the current flowing through the coil layer. A portion of the information leaks to the medium through the gap at the tip of the head, magnetizing the medium and recording. In addition, during successive recording, magnetic flux from the medium surface flows into the magnetic pole layer through the gap portion, and reading is performed by inducing a voltage in the coil layer interlinking with the magnetic pole layer.

Therefore, the magnetic properties of the magnetic pole are very important in terms of the electromagnetic conversion characteristics of a thin film magnetic head, and in particular, since the magnetic pole layer of a thin film magnetic head is thin, the state of formation of the magnetic pole layer has a large effect on the electromagnetic conversion characteristics of the head.

In such thin-film magnetic heads, multiple head elements are made by laminating each layer on a wafer, and after the head elements are formed, the wafer is cut into individual heads (chip cutting), and grooves are cut into the air bearing surface of the slider. It is manufactured by applying Inspection of thin-film magnetic heads manufactured using this type of manufacturing process involves measuring the inductance and resistance of the head during head element formation on the wafer and after cutting out the chips. At the completion stage, the electromagnetic conversion characteristics are inspected.

[Means for solving the problem] However, in such conventional thin-film magnetic head inspection methods, inspections at the time of wafer formation and chip cutting are difficult to detect defects such as coil short circuits and breaks. This is an inspection for removal, and an inspection of electromagnetic characteristics for evaluating the performance of a thin-film magnetic head depends on the inspection at the time of completion.

However, when inspecting the electromagnetic conversion characteristics of a completed product, if a defective product is found that does not have the specified conversion characteristics, such as output voltage, the finished product itself must be rejected as a defective product, or
It is necessary to take measures such as replacing the entire head mechanism, and there is a problem in that the yield of the magnetic head is directly linked to the yield of the product.

Of course, inductance is measured during wafer formation and chip cutting, but with thin-film magnetic heads,
Since the inherent inductance of the head cannot be measured, it is not possible to evaluate the quality of the head from the measurement results.

FIG. 8 schematically shows a magnetic circuit of a bulk head and a thin film magnetic head having a structure in which a coil is wound around a magnetic pole core.

In the bulkhead shown in Fig. 8(a), the magnetic core is sufficiently large, so that most of the magnetic flux generated when the coil is energized, for example, passes through the magnetic pole core as shown by the broken line and is transmitted to the outside. Leakage flux is negligible. Therefore, the measured inductance of the coil depends on the amount of magnetic flux generated in the magnetic core, and the electromagnetic conversion characteristics of the head can be evaluated by looking at the measured inductance value, and inspection to eliminate defective products can be performed by measuring the inductance. It is possible.

However, thin film magnetic heads have a thin magnetic pole layer, so the eighth
This corresponds to a magnetic core with a small cross-sectional area as shown in Figure (b), and for example, of the magnetic flux generated when the coil is energized, the ratio of the magnetic flux passing through the core and the magnetic flux leaking to the outside is approximately the same. In inductance measurement, the inductance due to the overall magnetic flux including leakage magnetic flux is measured, so it is not possible to evaluate the electromagnetic conversion characteristics of the thin film magnetic head from the measured inductance value, and in the end, it is not possible to evaluate the electromagnetic conversion characteristics of the thin film magnetic head. There was a problem that I had no choice but to rely on.

The present invention has been made in view of these conventional problems, and an object of the present invention is to provide a method for inspecting a thin-film magnetic head in which the quality of the head can be determined by determining the inductance depending on the magnetic flux generated in the magnetic pole layer. shall be.

[Means to solve the problem] FIG. 1 is a detailed explanatory diagram of the present invention.

First, in the present invention, a pair of magnetic pole layers 20-1 and 20-2 are formed on the slider substrate 16 with at least the coil layer 18 sandwiched therebetween. The present invention is directed to a thin-film magnetic head 10 having a laminated structure in which a gap portion 24 is formed by disposing the thin-film magnetic head 10 in close proximity to each other.

In the present invention, as a method for testing such a thin film magnetic head 10, first, an inductance measuring means 12 and a strong magnetic field generating means 14 are prepared.

The inductance L1 at both ends of the coil of the thin film magnetic head 10 is measured by the inductance measuring means 12 in the absence of a strong magnetic field generated by the strong magnetic field generating means 14, and the inductance L2 at both ends of the coil is measured in the strong magnetic field generated by the strong magnetic field generating means 14.
is measured by the inductance measuring means 12.

In this way, the inductance L without a strong magnetic field and in a strong magnetic field
Once L and L2 have been measured, the inductance LO that depends on the amount of magnetic flux generated in the magnetic pole layer of the thin-film magnetic head 10 is obtained by subtracting the inductance L2 in a strong magnetic field from the inductance L1 without a strong magnetic field. That is, Lo=L1-L2. Then, the finally determined inductance L
By estimating the amount of magnetic flux generated in the magnetic pole layer from the value of o, it is possible to judge whether the electromagnetic conversion characteristics are good or bad, and reject the product as a defective product at an intermediate stage of the manufacturing process.

[Function] According to the method for testing a thin film magnetic head according to the present invention having such a configuration, when a strong magnetic field sufficient to saturate the head pole layer is externally applied, the magnetic permeability μ in the head pole layer increases. is μ=1, which is the same as the state where no magnetic pole layer exists, that is, the state where there is only leakage magnetic flux.Using this fact, the inductance L2 that depends on the leakage magnetic flux is measured, and the inductance L2 that depends on this leakage magnetic flux is set to the normal state. By subtracting it from the inductance L1 measured by , it is possible to obtain an inductance Lo that depends only on the amount of magnetic flux passing through the magnetic pole layer excluding the influence of leakage magnetic flux.

The value of inductance L that depends on the amount of magnetic flux in this magnetic pole layer
O can be determined at intermediate stages of the manufacturing process, such as during wafer formation and chip cutting, so if the inductance Lo is less than the specified value, the specified electromagnetic conversion characteristics cannot be obtained even when inspecting the finished product. Therefore, the head is rejected as a defective product, and by improving the helding yield, it is possible to prevent the occurrence of defective products due to head defects during inspection of the finished product.

Also, the original inductance L exceeds the specified value.

In cases where this cannot be achieved, the yield can be improved by taking measures such as adjusting the depth of the gap portion by polishing, for example.

[Example] FIG. 2 is an explanatory diagram of an example showing an example of an apparatus configuration for carrying out the measuring method of the present invention.

In FIG. 2, reference numeral 26 denotes a measurement table, and on the measurement table 26, for example, a wafer 28 on which a plurality of thin film magnetic head elements are stacked is placed as a test object.

Bolm-Hertz type coils 141 and 142 are arranged on both sides of the measurement stand 26, and each coil 141 and 142 is connected in series to a drive circuit 140, and by passing a drive current from the drive circuit 140 through the coils, the measurement stand 26 is A strong magnetic field is applied to the mounted wafer 28.

12 is an inductance measuring device, and a pair of stylus 30
By bringing the stylus 30 into contact with the coil terminal of the thin film magnetic head element formed on the wafer 28, the inductance of the coil can be measured.

FIG. 3 is an overall configuration diagram of a thin film magnetic head to be inspected by the present invention. A pair of thin film magnetic head elements 32 are formed on the end face of a slider substrate 16, and a pair of thin film magnetic head elements 32 are formed from each thin film magnetic head element 32. Coil terminals 34, 36 are pulled out. Therefore, inductance can be measured by bringing the stylus 30 of the inductance measuring device 12 shown in FIG. 2 into contact with the coil terminals 34,36.

Two grooves are formed in the track forming direction on the surface of the slider substrate 16 facing the medium side, and an air bearing surface 42 is formed in which the surface between the grooves is lower than the surfaces on both sides.

FIG. 4 is an enlarged cutaway diagram showing the thin film magnetic head element 32 shown in FIG. be done.

First, FIG. 5 is a stacked cross-sectional view showing a portion from the upper magnetic pole layer 20-2 to the gap portion 24 at the tip of the head in the enlarged broken explanatory view of FIG. 4.

In FIG. 5, a protective film layer 38-1 is formed following the bottom slider substrate 16, and a lower magnetic pole layer 20-1 is formed on the protective film layer 38-1.

The lower magnetic pole layer 20-1 is made thinner on the head magnetic pole portion 24 side at the tip of the head. 0.5 on the bottom pole layer 20-1
A gap layer 22 having a thickness of about 1.0 μm is formed.

Furthermore, an insulating layer 40-1 is formed following the gap layer 22, and a first phase coil layer 18-1 is formed on the insulating layer 40-1.
After forming the insulating layer 40-2, the second phase coil layer 18-2 is formed, and then the insulating layer 40-2 is buried.
3 and bury it.

On the insulating layer 40-3, an upper magnetic pole layer 20 is disposed to surround the entire insulating layer 40-3.
-2 is formed, and the upper magnetic pole layer 20-2 is formed on the gap layer 22 over the gap depth D on the head tip side,
Lower magnetic pole layer 20-1 and gap layer 2 at the head tip
2 and the upper magnetic pole layer 20-2 form a gap portion 24. In other words, as shown in FIG.
The narrowed tips of -1, 20-2 are brought together to form a gap for magnetic coupling with the medium side. Here, the gap width W is, for example, about 10 to 20 μm.

FIG. 6 is an explanatory view of the coil layer of the head shown in FIG. 4.5, showing a state where the second phase coil layer 18-2 located under the upper magnetic pole layer 20-2 is visible. As is clear from FIG. 5, the first phase coil layer 20-1 is arranged below the second phase coil layer 20-2 with an insulating layer interposed therebetween.

To form the coil layers 20-1 and 20-2, first connect the coil terminal 34 to one end of the first phase coil layer 20-1 located below, and then connect the first phase coil layer 20-1 to the outside. The coil layer 20-2 of the second phase is formed in a spiral shape inward from the top and is connected to the second phase coil layer 20-2 disposed above by contacting in the thickness direction at the center position. As is clear from the figure, it is formed in a spiral shape from the center outward, and is taken out to the coil terminal 36.

FIG. 7 is an explanatory diagram of the wafer 28 to be inspected placed on the measurement table 26 in FIG.
is divided into a plurality of parts to constitute a slide substrate of the head, and on the surface of each divided position, as shown in the figure, a thin film magnetic head element having a laminated structure shown in Figures 4 to 6 is shown in Figure 3. They are formed in pairs like this.

When the thin film magnetic head elements are thus formed on the wafer 28, as shown in FIG. 2, the wafer 28 is placed on the measuring table 26 and each head element is inspected.

As shown in FIG. 7, the wafer 28 that has been inspected has unnecessary parts cut off from the four corners around it, and chips are cut out in units of heads. The chip-cut head member is subjected to polishing on the air bearing surface 42 as shown in FIG. 3, and the inspection of the present invention is carried out again either after this polishing is completed or after it is cut out from the wafer 28. It is done.

Next, the inspection method of the present invention will be explained with reference to FIG.

First, as shown in FIG. 2, the wafer 28 is placed on the measuring table 26, and the coil terminal of a specific thin film magnetic head element in the wafer 28, that is, the thin film magnetic head element 32 shown in FIG.
A pair of stylus 30 is brought into contact with the coil terminals 34 and 36 taken out from the coil terminals 34 and 36, respectively, and the inductance measuring device 1 is first set in a state in which no current is passed through the Bolm-Hertz coils 141 and 142 by the drive circuit 140, that is, in a state in which there is no strong magnetic field.
2 to measure the inductance L1 of the coil.

Next, a strong magnetic field is applied to the wafer 28 by turning on the drive circuit 140 and causing a drive current to flow through the Bolm-Hertz coils 141 and 142. Bolm Hertz type coil 141.142
The thin film magnetic head element on the wafer 28 receives a strong magnetic field due to the energization.The magnetic pole layer 20-1.20-2 in the head is saturated by the application of the strong magnetic field, and the magnetic pole layer 20-1.20-2 is saturated by the application of the strong magnetic field.
The magnetic permeability μ in 2 becomes μ=1, and the magnetic pole layer 20-1.20
The same situation will occur if -2 does not exist.

The inductance L2 is measured by the inductance measuring device 12 while applying such a strong magnetic field. The inductance L2 measured in this strong magnetic field is the magnetic pole layer 20-
The inductance depends on the leakage magnetic flux that does not pass through 1.20-2.

If the inductance L1 without a strong magnetic field and the inductance L2 in a strong magnetic field can be measured in this way, the inductance LO as the difference between the two is determined as LO=LL-L2. The inductance LO obtained in this way is an inductance that depends on the amount of magnetic flux that passes only through the magnetic pole layer 20-1 and 20-2, where the inductance component L2 due to leakage magnetic flux is removed from the inductance L1 that depends on the overall magnetic flux. It will be shown. Therefore, if the value of inductance LO, which depends on the amount of magnetic flux passing through the magnetic pole layer, is greater than or equal to the specified value, sufficient electromagnetic conversion characteristics are guaranteed; It can be rejected as a defective product that cannot achieve the desired performance.

The measurement results obtained using the inspection method of the present invention are shown in the following table.

As is clear from this measured data, the electromagnetic conversion characteristics of head A are 0.5 mVpp, and the electromagnetic conversion characteristics of head B are 0.4 mVpp, and there is almost no difference from 840 mH and 830 mH of inductance L1 without a strong magnetic field. . However, the inductance L2 in a strong magnetic field
Head A has a difference of 320 mH and Head B has a difference of 400 mH, and the final inductance LO of the head magnetic pole is 520 mH for Head A and 400 mH for Head B.
mH, and due to this inductance LO, the electromagnetic conversion characteristics of heads A and B, that is, the output, becomes 0. It can be seen that there is a difference of 1 mVpp. In this way, the electromagnetic conversion characteristics of the head can be estimated from the value of the original inductance LO of the head magnetic pole determined by the present invention, and the electromagnetic conversion characteristics expected in the intermediate stages of wafer formation and chip cutting can be estimated. Heads that cannot be obtained can be rejected as defective products.

On the other hand, if the value of inductance LO measured by the present invention is slightly lower than the specified value, the head is not rejected as a defective product, but the characteristics can be improved by adjusting the head. Specifically, the electromagnetic conversion characteristics can be improved by reducing the gap depth D of the gap portion 24 in the laminated cross-sectional view of the head shown in FIG. Therefore, if the inductance LO measured by the present invention is slightly lower than the standard value, it is possible to improve the performance by controlling the gap depth, etc., rather than rejecting it as a defective product, and as a result, the yield of the head itself can be improved. can.

[Effects of the Invention] As described above, according to the present invention, it is possible to inspect the magnetic properties of the pole layer during the manufacturing process of a thin-film magnetic head, which improves the yield in manufacturing the head and improves the completion rate. This prevents the occurrence of defective products due to head defects at this stage, and as a result can greatly contribute to reducing device costs.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention; Fig. 2 is an explanatory diagram of an embodiment for carrying out the inspection method of the present invention; Fig. 3 is an overall configuration diagram of a thin-film magnetic head; Fig. 4 is an enlarged view of the head section. Broken explanatory diagram; Fig. 5 is a cross-sectional view of the laminated layers of the thin film magnetic head; Fig. 6 is an explanatory diagram of the coil layer of the thin film magnetic head; Fig. 7 is an explanatory diagram of the wafer that is the measurement target of the present invention; Fig. 8 is the head magnetic pole It is an explanatory diagram. In the figure, 10: Thin film magnetic head 12: Inductance measuring means (device) 14; Strong magnetic field generating means 140: Drive circuit 141.142: Bolm-Hertzian coil 16: Slider substrate 18.18-1.18-2: Coil layer 20 -1.20-2: Coil layer (lower, upper) 22: Gap layer 24: Gap portion 26: Measuring table 28: Ueno\- 30: Stylus 32: Thin film magnetic head element 34.36: Coil terminal 38- 1.38-2+protective film layer 40-1 to 40-3: insulating layer 42: air bearing surface 50: wafer chip

Claims (1)

[Claims] (1) At least a coil layer (
A pair of magnetic pole layers (20-1, 20-2) sandwiching 18)
A thin film magnetic head ( In the inspection method of 10), an inductance measuring means (12) and a strong magnetic field generating means (1) are used.
4), and an inductance (
L1) and the inductance (L2) in a strong magnetic field generated by the strong magnetic field generating means (14) are each measured by the inductance measuring means (12), and the inductance (L2) in the strong magnetic field is calculated from the inductance (L1) without a strong magnetic field. ) minus the inductance (
A method for inspecting a thin film magnetic head, characterized in that the suitability of the head is determined by estimating the amount of magnetic flux generated in the magnetic pole layer of the thin film magnetic head (10) from the value of Lo).