JPS6180076A - Apparatus for inspecting mr element - Google Patents

Abstract

PURPOSE:To miniaturize and simplify an apparatus as a whole, in the wafer transferred by an X-Y table, by providing a coil and probe moving up and down with the respect to the inspection surface of the unit region of said wafer. CONSTITUTION:An alternating magnetic field generation means 1 applies a uniform magnetic field to the inspection surface corresponding to the MR element formed to the unit region on a wafer 16 and an X-Y table 15 moves the wafer 16 to an X-Y direction. A motor 5 for driving a probe 2 up and down performs the positional determination of a coil 1 and the probe 2 on the MR element to be inspected. The output voltage of the MR element detected by the probe 2 is applied to a computer 12 through a digital multimeter 9 and processed while the processed result is recorded on a disc recorder 13 and displayed on a CRT display apparatus 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a characteristic testing device for an MR element (ferromagnetic magnetoresistive element).

[Prior Art] An MR element has a characteristic that its resistance value changes under the influence of a magnetic field, and has good sensitivity. For this reason, it is used as a magnetic sensor in magnetic rotary encoders and the like.

A large number of magnetic sensors using this MR element are simultaneously formed on a wafer using thin film technology, and depending on the form of use as a magnetic sensor, four or more magnetic sensors are formed in a single layer for each region (Unit) II that constitutes the magnetic sensor. Alternatively, a plurality of them may be provided in close proximity to each other. An example of this magnetic sensor is one in which a bridge circuit is constructed of four MR elements mr as shown in FIG. 1(a). That is, the terminals T, T5 are grounded, and by applying a constant voltage (for example, 5V) to the terminal T3, the terminal T2 is grounded.
, T4 is detected according to the magnetic field strength, and this output voltage characteristic shows the output voltage characteristic as shown in Fig. 1(b) according to the change of the signal magnetic field. Even with each magnetic sensor, variations in characteristics that are difficult to avoid during manufacturing tend to occur, and for this reason, these characteristics must be inspected.The inspection is based on the output voltage V when an alternating magnetic field is applied.
This is done by measuring 1 to v6, etc.

Conventionally, after writing the above characteristic curve on recording paper, a value that is considered to well represent the characteristic, such as VPP"V2-■5, vp
p=v3-■6, His A=V2-V3. Hiss B =
V6 VS, DV O=Va −V,, VO
Characteristics were evaluated by measuring = (V, +Va)/2, etc., and conditions for these values were combined to determine pass/fail. However, such a method has the disadvantage that measurement and determination require time and manpower. Another drawback is that in order to write a defective product mark using a computer, the measurement results must be input into the computer again from the keyboard.

In addition, for each unit area formed in large numbers on the wafer, M
To continuously measure the characteristics of a sensor using an R element or the characteristics of a single MRJ element.

There was no satisfactory measurement device that was easy to manufacture and relatively small. The reason is that in order to apply a uniform magnetic field that is constant every time to the surface to be inspected (the part corresponding to the MR element), if we try to place the entire Uni-Hachi inside an ideal Helmholtz coil, that is, in a uniform magnetic field, As the coils became larger, the power supplies for them also became larger. On the other hand, it is extremely inefficient to insert chips that have been subdivided into unit areas into individual coils for measurement.

[Object of the Invention] An object of the present invention is to provide a comparatively small and simple testing device that can automatically test the characteristics of a sensor using an MR element or a single MR element in a short time. The purpose of the present invention is to provide a plurality of unit areas provided on a wafer, inspection surfaces corresponding to MR elements formed in each unit area, and a method for applying a uniform magnetic field to one of the inspection surfaces. An alternating magnetic field generating means, an X-Y table that carries a wafer and transports it in the X-Y direction in order to position one of the inspection surfaces in the magnetic field generated by the alternating magnetic field generating means, and an MR unit in a unit area. A probe connected to a terminal connected to the element, an L-lower conveying means for approaching and connecting the alternating magnetic field generating means and the probe to a selected unit area, and processing for determining characteristics from the output voltage taken out from the probe. This is achieved by an MR element inspection apparatus characterized by comprising means.

Furthermore, the present invention is achieved by an MR element inspection apparatus which further includes a mark means and records the determination result of the processing means in a unit area as required.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

Fig. 2 shows an apparatus for carrying out an embodiment of the characteristic testing method of the present invention, and in the figure, 1 is a signal magnetic field generating coil, and in the embodiment, an air-core coil is used. . A probe 2 detects the output voltage of a magnetic sensor placed in the magnetic field generated by the signal magnetic field generating coil. 8 is a coil driver for exciting the coil;
An excitation current is applied to the coil 1 under the control of the microcomputer 12. 3 and 4 are coils 1. probe 2
The arms 3 and 4 are moved up and down by a vertical drive motor 5. A solenoid 7 is supported by the arm 3 and is driven by a pen driver 10 to mark defective products with dot marks or the like. 7a is a pen body driven by a solenoid. 9 is a digital multimeter that converts the detected voltage of the probe 2 into a digital value and provides it to the microcomputer 12. 13 is a disk recording device for recording the measurement value processing results, and 14 is a CRT display device for displaying the data.

The above-mentioned probe vertical drive motor 5 moves the MR to be inspected in each magnetic sensor unit area on the wafer 16.
A coil 1 is placed on the area where the element exists (hereinafter referred to as the inspection surface 17).
Position the probe 2. The positioning of this coil will be described later, but generally speaking, it is to place a small gap G between the inspection surface 17 and the bottom surface of the coil I in a uniform magnetic field created by the coil I.

15 is a wafer 16 on which a large number of magnetic sensors have been formed.
This is an X-Y table for moving in the direction. This X
- Y table has X under the control of microcomputer.
A known device can be used that includes a rotational-linear motion conversion φ transmission positioning means for controlling the movement of the table in the Y direction and the Y direction and regulating the position, and a pulse motor as a driving means. Therefore, details will be omitted.

Next, embodiments of the present invention will be described in detail with reference to the 'isZ diagram and the figure numbers below.

Coil 1 is a rectangular air-core coil.

It has four (1-1 to 1-4) magnetic field generating surfaces.

Since each surface intersects so that the current direction intersects, the magnetic fields on the four sides interfere with each other near the four corners, making it impossible to obtain a uniform magnetic field.Therefore, a small inspection surface is placed on a surface where the magnetic field is uniform and stable, excluding the four corners. 17 is required between the coil 1 and the inspection surface 17. To achieve this relationship,
The mutual relationship is set as shown in FIGS. 3 and 4. That is, in the figure, G indicates the gap between the inspection surface 17 and the bottom of the air-core coil 1, T indicates the thickness of the coil 1, W indicates the width of the coil, and L indicates the length of one side of the rectangular coil. show.

In addition, considering the efficiency, it is desirable that the above G be as close to O as possible, so L/u-(1), G → 0, coil 1 is a single layer, and the influence of coils other than the bottom side is ignored and modeled. Then, W/w approaches l, but it is difficult to change G→0 in terms of positioning accuracy, and MR elements are generally long and thin, making positioning in the W direction difficult, so in practice W/w approaches 1. takes a value of 1.2 or more, preferably 1.5 or more. On the other hand, L/1 can be a value of 5 or more if modeled with other conditions as optimal conditions, but considering practicality, a value of 10 or more is desirable. From this point on, the upper limit will naturally be regulated. The details of calculating these numbers are omitted, but G = 0.01
~l ■, L/1=5 or more, W/w=1.5
If it is above, it has been confirmed that practicality is satisfied.0 For example, according to experiments, when G = 0.5 mm, L/
, Q, = 10 or more, and W/w = 2 or more, then
This is sufficient for practical use, and it is sufficient to reduce the size of the coil within this range.

In the example, W is 3 mm, L is 30 mm, and T
Although it depends on the wire diameter and the number of windings, it is desirable that the wire be thin, and although several layers are used in the embodiment, it is also possible to make it thinner. Also, although G depends on the balance with positioning accuracy,
The value is set to be as small as possible, and is 1 mm or less.

On the other hand, the lowercase letter W is the width of the inspection surface 17, which is 30 Bm in the example. 1 is also the length, which is 1■.

In order to satisfy this condition that a uniform magnetic field must be applied to each inspection surface 17 formed on the wafer 16, the length of one side of the inspection surface 17 is 1 compared to the length of one side of the coil 1. The relationship L>l is set, and the relationship vAW of the inspection surface 17 with respect to the width W of the coil 1 is set W>w. Inspection surface 1 is the positioning accuracy of coil 1 and inspection surface 17.
The relationship among the positioning accuracy ΔX in the longitudinal direction of 7, the positioning accuracy Δy in the width direction, and the positioning accuracy ΔZ of the distance G between the facing surfaces of the coil 1 and the inspection surface 17 are maintained at a constant accuracy. As a result, the magnetic field generated by the coil l with respect to the inspection surface 17 can be considered to have approximately the same conditions as when a parallel current is passed in the length direction of the infinite width hand plate, so the generated magnetic field is uniform and in the horizontal direction. become parallel.

FIG. 5 is an enlarged view of a large number of magnetic sensors (unit areas) S formed on the wafer 16, and each inspection surface 17 has one
Four MR elements indicated by 7' are provided in two layers with an insulating layer in between, and the lower surface of the coil 1 is accurately positioned with respect to the inspection surface 17. In addition, 20 in FIG. 5 is a lead electrode pattern 4.

Now, when the inspection surface 17 of the magnetic sensor is influenced by a magnetic field, the resistance value of the MR element changes, and an output voltage commensurate with the change in resistance value is output between the terminals T2 and T4. A power voltage detection circuit for this purpose can be configured as shown in FIG. 6, for example. That is, the probes 2 .
5 is grounded and a voltmeter 31 is connected between the terminals T2 and T4, it is possible to obtain an output voltage change as a magnetic sensor corresponding to a resistance value change of the MR element 17' depending on the magnetic field strength. Then, the extracted voltage is measured by a digital multimeter 9 and outputted to the microcomputer 12.

In addition, as the enlarged view in Figure 6 shows in detail, appropriate locations are used as marking areas for marking pass/fail judgments.
For example, a circle (dot) D indicating a defect is marked as shown by a broken line.

To test the output characteristics of the magnetic sensor, use Microcomputer 1.
2 is executed.

As shown in Figure 2, the microcomputer 12 has a microbe of 1m! -t! Tsusa MPU, RAM, ROM
The output voltage data converted by the digital multimeter 9 is stored in the RAM under the control of the microprocessor MPU.
The output data after a predetermined time is written to the RAM, and the microprocessor M
Each inspection process is executed under the control of a characteristic inspection program stored in the PU or ROM. Next, the control procedure for each inspection process will be executed in detail with reference to FIGS. 7 to 10.

First, in step S1 of the inspection process, the internal state of the processor and the X-Y table are initialized.Next, the process proceeds to step S2, where the microcomputer moves the X-Y table 5 in the X and Y directions. A drive pulse is applied to the illustrated pulse motor, and the first
The test surface 17 of the magnetic sensor to be tested is positioned with respect to the coil 1. Next, proceed to the probe movement step S3,
The probe 2 is connected to the terminal T, -75, and the coil 1 is brought close to the inspection surface 17 accordingly. This movement control is performed by the MPU controlling the probe vertical drive motor 5.Next, the control proceeds to step S4, and the power switch SW is turned on to apply a predetermined voltage, for example, a voltage of 5 cm, between the terminals of the magnetic sensor. ON, and then in step S5 an alternating signal magnetic field is applied to the magnetic sensor (MR element).
The residual magnetic field of is set to zero. (1) to (10) in Figure 8
is a graph showing the polarity, intensity, and rate of change per time of the signal magnetic field applied according to the time axis, and the time period in which the degaussing process is performed is the zero-order period shown by (1) on the time axis. Then, the process proceeds to step S6, where the output voltage v1 in the signal magnetic field O is measured, and is written to the disk in step S7.
), the signal magnetic field is increased in the positive direction at the rate of increase in time period (3), data is taken in one after another, unnecessary data is erased while comparing with the previous data, and (step S8
), when it is confirmed in step S9 that the captured data no longer increases, the maximum value of the stored data values is detected as the local maximum value V2. The detected v2 is written to the disk in step S10.Next, in step S11, the signal magnetic field is rapidly increased in the positive direction until the magnetic sensor is magnetically saturated, without taking in data [time period (4)
] After that, in step 512, the magnetic field is rapidly decreased to the vicinity of the magnetic field strength where v2 was detected, without importing data [time period (5)], and then the reduction rate of time period (6) is decreased. The data acquisition and comparison are started again (step 513), and the maximum value v3 when the signal magnetic field decreases is
, detects the output voltage v4 in the signal magnetic field O in time period (6), and writes to the disk (steps 514 to 5).
17), the signal magnetic field applied to the lil sensor continues to decrease further during time period (7), during which data is captured, and after the minimum value V is detected and written to the disk (step 518, 519), the data acquisition is stopped, and the signal magnetic field is rapidly decreased so that the magnetic sensor reaches magnetic saturation in step S20, and after reaching the saturation magnetic field, the data acquisition is also omitted in the following step S21. Then, the signal magnetic field is rapidly increased [time period (9)], and when the magnetic field increases to near the magnetic field strength at which v5 is detected, control proceeds to step S22. and step 32
2. In S23, the signal magnetic field is increased at an increasing rate of the time period (lO).

Data is taken in again, the minimum value v6 is detected while the signal magnetic field is rising in the positive direction, and after detection, writing to the disk is performed in step S24.

By performing the above-mentioned inspection process on each magnetic sensor on the wafer, inspection of the characteristics of each magnetic sensor, that is, the output voltages V and -V with respect to the signal magnetic field strength, is completed, and this data is stored on the disk 8. The information is written and used as quality determination information for the magnetic sensor, that is, the unit area S, or manufacturing reference information.

Following execution of the inspection process, it is necessary to evaluate the measured characteristics and determine whether the product is non-defective.

This determination is performed according to the determination processing flowchart shown in FIG.

In step 530, the previously measured ■1 to V6 (7
) using the data, VPI)-V2-Vs.

VPP-Va-v6, HisAmV2-V3,
HisBmV6-V5, nvo4-v4-v,, vow
(v I+V4)/2 is calculated, and in step S31
z'te vPP, vpp, Hiss A, Hiss B,
DVO and VO are compared with their respective reference values to determine pass/fail. If it is defective, proceed to NG and step S32.
Then, the solenoid 7 is driven to execute marking. 0 If the result is pass, the process goes to Go, and then the process goes to step S33. 6 Next, the result of pass or fail is written on the disk in step S33.

Note that the pass/fail determination in step 531 does not necessarily need to be made by all the comparisons mentioned above, and only the required data according to the specifications required for the magnetic sensor is compared with the reference value. It goes without saying that before comparing and examining the data of (1) to v6, short-circuit and disconnection tests are performed, and this is done at the time of initial voltage application to the magnetic sensor.

Furthermore, although the above-described embodiments have shown a method for measuring the characteristics of a magnetic sensor using an MR element, it goes without saying that the method can also be applied to testing the characteristics of a single MR element.

[Effects of the Invention] As described above, according to the present invention, the characteristics of a senna using an MR element or the MR element itself can be automatically tested in a short time, which can greatly contribute to labor saving. In addition, a coil and a probe that move up and down with respect to the inspection surface of the unit area are provided for the wafer transferred by the X-Y table, so that
The coil can be made smaller, and the entire device can be made relatively smaller and simpler.

Moreover, since it is possible to mark whether the product is good or not at the same time as the inspection, it is possible to prevent confusion between processing data and a unit area officer having characteristics based on the data.

[Brief explanation of the drawing]

FIG. 1(a) is an explanatory diagram of a magnetic sensor using an MR element,
Figure 2 (b) is a graph showing changes in signal magnetic field strength and the output voltage characteristics of a magnetic sensor using an MR element placed in the magnetic field. FIG. 3 is a block diagram of an inspection device that inspects the output voltage of a placed magnetic sensor. Figure 3 is a cross-sectional view with only the coil and inspection surface taken out to explain the dimensional relationship and position between the air-core coil and the inspection surface placed in the magnetic field generated by the coil. Figure 3 is a side view, Figure 5 is an explanatory diagram showing the configuration on the wafer, Figure 6 is an explanatory diagram showing the circuit configuration for applying voltage to the magnetic sensor, and Figure 7 is a magnetic sensor executed by a microcomputer. Fig. 8 is a graph showing the strength of the magnetic field generated by the coil and the change in unit time; Fig. 9 is a control flowchart of the characteristic testing process of FIG. 10 is a flowchart showing the process of determining whether the tested magnetic sensor passes or fails. Here, l...coil, 2...probe, 3...
Coil driver, 4...Digital multimeter, 16
... wafer, 17 ... inspection surface, 17' ... MR element. Figure 1 (d) Figure 1 (b) Figure 3
Figure 4 Figure 2 1J 14

Claims (2)

[Claims] (1) A large number of unit areas provided on a wafer, inspection surfaces corresponding to MR elements formed in each unit area, and alternating magnetic field generating means for applying a uniform magnetic field to one of the inspection surfaces; In order to position one of the inspection surfaces in the magnetic field generated by the alternating magnetic field generating means, an a probe to be connected to the selected terminal; a vertically moving conveying means for approaching and connecting the alternating magnetic field generating means and the probe to a selected unit area; and a processing means for determining characteristics from an output voltage taken out from the probe. An MR element inspection device characterized by comprising: (2) The MR element inspection apparatus according to claim 1, further comprising a mark means, and records the determination result of the processing means on the unit area as necessary.