JP2009069005A - Magnetic field calibration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic field calibration method for accurately and stably implementing a magnetic field calibration in comparison with a calibration using a hall element and a probe. <P>SOLUTION: The magnetic field calibration method of the invention is sequentially provided with: a first process for measuring a magnetic field characteristic of a magnetoresistive element, and obtaining a first magnetic field characteristic; a second process for placing the magnetoresistive element on a stage of a magnetic field applying means; a third process for adjusting a height of the stage so as to match a surface height of the magnetoresistive element with a surface height of a to-be-measured wafer during a normal measurement; and a fourth process for causing the magnetic field applying means to apply a magnetic field to the magnetoresistive element in the in-plane direction, and obtaining a second magnetic field characteristic. In the fourth process, the magnetic field applied to the magnetoresistive element is adjusted so as to match substantially the first magnetic field characteristic with the second magnetic field characteristic. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic field calibration method for accurately measuring the characteristics of various magnetic sensors arranged on a substrate such as a wafer.

A sensor using a ferromagnetic magnetoresistive element (MR element) is known as a sensor for detecting a magnetic field, and is widely used in the field of a magnetic switch integrated with an IC.
In order to measure the characteristics of this type of magnetic sensor at the wafer level, a magnetic field prober equipped with a magnetic field application mechanism is used (for example, Patent Document 1). An outline of the measurement is shown in FIG.

  The magnetic field prober is made of a nonmagnetic material in order to suppress the influence of an external magnetic field except for the magnetic field applying means. The accuracy of the magnetic field application mechanism is extremely important for guaranteeing the characteristic value, and the calibration thereof needs to be performed periodically. The magnetic field application mechanism is normally driven by a current source, and calibration is to obtain a relational expression between the current value and the magnetic field value.

An overview of a conventional magnetic field calibration method is shown in FIG.
(1) Lower the prober stage 100 to such an extent that the gauss meter probe 101 can be installed.
(2) Install the probe 101 of the gauss meter. (3) Apply a magnetic field from the magnetic field applying means 102 and read the value of the applied magnetic field from the value of the gauss meter.

However, the following problems occur at this time.
First, since a gauss meter usually uses a Hall element, its sensitivity is low, and the error is relatively large particularly in a low magnetic field region (see Non-Patent Document 1, for example).

  Also, when measuring a magnetic field with a gauss meter, a probe is usually used. However, it is difficult to align the probe and the magnetic field, and the position and inclination of the Hall element installed in the probe has a certain range. Therefore, it is difficult to detect an accurate magnetic field in a minute region (for example, see Non-Patent Document 2). For this reason, it is difficult to align the probe, and the position and inclination of the magnetic field sensor in the probe cannot be accurately determined. In addition, since the Hall sensor is large in size, the measurement magnetic field has an average value, and an accurate value is not known.

Further, since the Hall element installed in the Gauss meter probe has a thickness of about several millimeters in the Z direction, the measurement magnetic field has an average value in the Z direction (see, for example, Non-Patent Document 2). For this reason, when measuring a device whose magnetosensitive direction is the XY direction, such as a magnetoresistive element, the value of the magnetic field including the variation in the Z direction does not show an accurate value.
Japanese Patent No. 3054458 http://wwwsoc.nii.ac.jp/jsndi/bulletin/J_02_sep.html http://www.toyo.co.jp/bell/probe/bell03.html

  The present invention has been devised in view of such a conventional situation, and provides a magnetic field calibration method capable of stably performing more accurate magnetic field calibration as compared with the case of using a Hall element or a probe. The purpose is to do.

According to a first aspect of the present invention, there is provided a magnetic field calibration method for measuring a magnetic field characteristic of a magnetoresistive element to obtain a first magnetic field characteristic, and placing the magnetoresistive element on a stage of a magnetic field applying means. A second step, a third step of adjusting the height of the stage so that the surface height of the magnetoresistive element and the surface height of the wafer to be measured during normal measurement are substantially the same, and the magnetic field applying means A magnetic field calibration method comprising at least a fourth step of obtaining a second magnetic field characteristic by applying a magnetic field in an in-plane direction of the magnetoresistive element, wherein the first magnetic field characteristic in the fourth step The magnetic field applied to the magnetoresistive element is adjusted so that the second magnetic field characteristics are substantially the same.
The magnetic field calibration method according to a second aspect of the present invention is the magnetic field calibration method according to the first aspect, wherein the first step includes a step of arranging the magnetoresistive element in a Helmholtz coil, and an in-plane of the magnetoresistive element by the Helmholtz coil. And a step of applying a magnetic field in the direction.

  In the present invention, the magnetic field calibration using the magnetoresistive element as a calibration sample can be performed by adjusting the magnetic field applied to the magnetoresistive element so that the first magnetic field characteristic and the second field characteristic are substantially the same. . By using a magnetoresistive element as a calibration sample, the resolution is higher than when a Hall element used in a gauss meter is used. In addition, since the magnetoresistive element has sensitivity in the in-plane direction, it is not easily affected by variations in the distribution of the magnetic field in the vertical direction. Thus, the present invention can provide a magnetic field calibration method capable of performing more accurate magnetic field calibration stably as compared with the case of using a Hall element or a probe.

  Hereinafter, an embodiment of a magnetic field calibration method according to the present invention will be described with reference to the drawings.

  The magnetic field calibration method of the present invention includes a first step of measuring a magnetic field characteristic of a magnetoresistive element to obtain a first magnetic field characteristic, a second step of placing the magnetoresistive element on a stage of a magnetic field applying means, A third step of adjusting the height of the stage so that the surface height of the magnetoresistive element and the surface height of the wafer to be measured at the time of normal measurement are substantially the same, and the magnetoresistive element by the magnetic field applying means And a fourth step of obtaining a second magnetic field characteristic by applying a magnetic field in the in-plane direction, wherein the first magnetic field characteristic and the second magnetic field characteristic in the fourth step Are adjusted so that the magnetic field applied to the magnetoresistive element is substantially the same.

In the present invention, the magnetic field calibration using the magnetoresistive element as a calibration sample can be performed by adjusting the magnetic field applied to the magnetoresistive element so that the first magnetic field characteristic and the second field characteristic are substantially the same. . By using a magnetoresistive element as a calibration sample, the resolution is higher than when a Hall element used in a gauss meter is used. In addition, since the magnetoresistive element has sensitivity in the in-plane direction, it is not easily affected by variations in the distribution of the magnetic field in the vertical direction. Thereby, in this invention, compared with the case where a Hall element and a probe are used, more accurate magnetic field calibration can be performed stably.
Hereinafter, each step will be described in detail. In addition, the numerical value quoted in the following description is an example to the last, and it cannot be overemphasized that it is not limited to this.

(1) First, a bridge structure including four sets of resistors is formed using a magnetoresistive element (hereinafter referred to as “calibration sample”).
1A and 1B are diagrams illustrating an example of a calibration sample configured using a magnetoresistive element, where FIG. 1A is a plan view and FIG. 1B is a cross-sectional view.
The calibration sample 10 has a magnetoresistive element 12 formed on a substrate 11 made of silicon or the like. The magnetoresistive element 12 of the calibration sample 10 preferably forms a bridge structure consisting of four sets of resistors. By using a calibration sample made of a magnetoresistive element, the resolution is higher than that of a Hall element used in a gauss meter. In addition, since the magnetoresistive element has sensitivity in the plane direction, it is not easily affected by variations in the magnetic field distribution in the Z direction.
The input resistance of the calibration sample 10 is, for example, 10 kΩ, and the saturation magnetic field is, for example, about 8 mT.

(2) Then, the magnetic field characteristic of the magnetoresistive element 12 is measured to obtain the first magnetic field characteristic [first step].
The first step is a step of placing the magnetoresistive element 12 (calibration sample 10) in the Helmholtz coil 20, a step of applying a magnetic field in the in-plane direction of the magnetoresistive element 12 by the Helmholtz coil 20, (See FIG. 2).
The Helmholtz coil 20 is known as a device capable of applying an accurate magnetic field in proportion to an electric current. By using the Helmholtz coil 20, an accurate magnetic field can be applied to the magnetoresistive element, and an accurate first magnetic field characteristic can be obtained.
An example of the first magnetic field characteristic obtained from the current-magnetic field characteristic and the current-voltage characteristic of the magnetoresistive element 12 (calibration sample 10) is shown in FIG.

The Helmholtz coil 20 shown in FIG. 2 has a current-magnetic field dependency of 2.918 mT / A, for example. Using this Helmholtz coil 20, sweeping the applied magnetic field to 8 mT → 0 mT, it was measured the calibration sample 10, and its output was changed by about 37m V (see FIG. 4).

(3) Next, the magnetoresistive element 12 is placed on the stage 31 of the magnetic field applying means 30 [second step]. Further, the height of the stage 31 is adjusted so that the surface height of the magnetoresistive element 12 and the surface height of the wafer 32 to be measured during normal measurement are substantially the same [third step].
As shown in FIG. 5, the calibration sample 10 is placed on a stage 31 of a prober (magnetic field applying means 30), and the surface height of the calibration sample 10 (that is, the surface height of the magnetoresistive element 12) is measured during normal measurement. In step (3), the height of the wafer to be measured 32 is adjusted to be the same as the measurement height. By placing the calibration sample 10 on the stage 31 and adjusting the stage height, the sample position (X, Y, Z) can be accurately defined.

  In FIG. 5, the film thickness of the wafer 32 to be measured was 625 μm, and the thickness of the calibration sample 10 was 1600 μm. Therefore, if the stage 31 is lowered by 975 μm from the normal level, the height of the surface of the calibration sample 10 and the surface of the wafer 32 to be measured are the same.

(4) Next, the magnetic field applying means 30 applies a magnetic field in the in-plane direction of the magnetoresistive element 12 to obtain a second magnetic field characteristic [fourth step].
As shown in FIG. 6, the magnetic field applying means 30 applies a magnetic field in the in-plane direction of the magnetoresistive element 12, and measures the bridge voltage at that time. The value obtained at this time is used as the second magnetic field characteristic, and the second magnetic field characteristic is compared with the first magnetic field characteristic value, whereby the magnetic field value can be calibrated.

Specifically, the magnetic field applied to the magnetoresistive element 12 is adjusted so that the first magnetic field characteristic and the second magnetic field characteristic are substantially the same.
FIG. 7 shows an example of the second magnetic field characteristic obtained from the current-magnetic field characteristic and the current-voltage characteristic of the magnetoresistive element 12, and a comparison between the first magnetic field characteristic and the second magnetic field characteristic.
Thus, by adjusting the magnetic field applied to the magnetoresistive element 12 so that the first magnetic field characteristic and the second field characteristic are substantially the same, magnetic field calibration using the magnetoresistive element as a calibration sample can be performed. it can.
By comparing the value (second magnetic field characteristic) obtained by re-measurement of the calibration sample 10 by the magnetic field applying means 30 of the prober with the value (first magnetic field characteristic) obtained by the Helmholtz coil, the magnetic field applying means It is possible to accurately measure the output magnetic field.

  In the state shown in FIG. 6, the output magnetic field of the magnetic field applying means 30 was swept from 8 mT to 0 mT, and the calibration sample 10 was measured. A comparison of the outputs is shown in FIG. As is apparent from FIG. 8, a result almost identical to the result measured in the Helmholtz coil was obtained.

  As described above, in the present invention, a magnetoresistive element is used as a calibration sample, so that the resolution is higher than when a Hall element used in a gauss meter is used. In addition, since the magnetoresistive element has sensitivity in the in-plane direction, it is not easily affected by variations in the distribution of the magnetic field in the vertical direction. Thereby, in this invention, compared with the case where a Hall element and a probe are used, more accurate magnetic field calibration can be performed stably.

  The magnetic field calibration method of the present invention has been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the spirit of the invention.

  The present invention can be applied as a magnetic field calibration method that can accurately and stably measure the characteristics of a plurality of magnetic sensors or the like arranged on a substrate such as a wafer.

The figure which shows an example of the calibration sample comprised using the magnetoresistive element. The figure which shows typically a mode that the 1st magnetic field characteristic of a magnetoresistive element is measured using a Helmholm coil. The figure which shows an example of the 1st magnetic field characteristic calculated | required from the current-magnetic field characteristic and current-voltage characteristic of a magnetoresistive element. The figure which shows an example of the 1st magnetic field characteristic of a magnetoresistive element. The figure which shows a mode that the height of a stage is adjusted so that the surface height of a calibration sample and the surface height of a to-be-measured wafer may become substantially the same. The figure which shows typically a mode that the magnetic field characteristic of a magnetoresistive element is measured using a magnetic field application means. The figure which shows an example of the 2nd magnetic field characteristic calculated | required from the electric current-magnetic field characteristic and electric current-voltage characteristic of a magnetoresistive element, and a comparison with a 1st magnetic field characteristic and a 2nd magnetic field characteristic. The figure which shows the comparison of the magnetic field dependence of a bridge voltage about the case where a prober and a Helmholtz coil are used. The figure which shows a mode that the characteristic of a magnetic sensor using a prober is measured. The figure which shows the outline | summary of the conventional magnetic field calibration method typically.

Explanation of symbols

  10 calibration sample, 11 substrate, 12 magnetoresistive element, 20 Helmholtz coil, 30 magnetic field applying means, 31 stage, 32 wafer to be measured

Claims (2)

A first step of measuring the magnetic field characteristics of the magnetoresistive element to obtain the first magnetic field characteristics;
A second step of placing the magnetoresistive element on the stage of the magnetic field applying means;
A third step of adjusting the height of the stage so that the surface height of the magnetoresistive element is substantially the same as the surface height of the wafer to be measured during normal measurement;
A magnetic field calibration method comprising at least a sequence of a fourth step of obtaining a second magnetic field characteristic by applying a magnetic field in an in-plane direction of the magnetoresistive element by the magnetic field applying means,
In the fourth step, a magnetic field calibration method characterized by adjusting a magnetic field applied to the magnetoresistive element so that the first magnetic field characteristic and the second magnetic field characteristic are substantially the same. The first step includes
Placing the magnetoresistive element in a Helmholtz coil;
The magnetic field calibration method according to claim 1, further comprising: applying a magnetic field in the in-plane direction of the magnetoresistive element by the Helmholtz coil.

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