Magnetic sensor and method of manufacturing the same

The magnetic sensor includes a semiconductor substrate having Hall elements on a front surface of the semiconductor substrate, an adhesive layer formed on a back surface of the semiconductor substrate, and a magnetic flux converging plate formed on the adhesive layer. The magnetic flux converging plate is formed on the back surface of the semiconductor substrate through formation of the magnetic flux converging plate by electroplating on a base conductive layer formed on a plating substrate prepared separately from the semiconductor substrate, application of an adhesive for forming the adhesive layer onto a surface of the magnetic flux converging plate so that the magnetic flux converging plate adheres to the back surface of the semiconductor substrate, and peeling off of the plating substrate afterward from the base conductive layer formed on the magnetic flux converging plate.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-051498 filed on Mar. 15, 2016, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic sensor using Hall elements, and to a method of manufacturing the magnetic sensor, in particular, relates to a magnetic sensor, which includes a magnetic flux converging plate, and is configured to detect vertical and horizontal magnetic fields, and to a method of manufacturing the magnetic sensor.

2. Description of the Related Art

Hall elements are used in various applications since non-contact position detection and non-contact angle detection can be made by Hall elements as magnetic sensors.

First, the principle of magnetic detection with the Hall elements is described. When a magnetic field is applied vertically to a current flowing through a substance, an electric field (Hall voltage) is generated in a direction vertical to both the current and the magnetic field. Typical Hall elements are thus configured to detect a vertical magnetic field component with a current caused to flow on a surface of a semiconductor substrate or a wafer made of silicon or other materials.

In addition, it is known that the Hall elements can detect not only a vertical magnetic field but also a horizontal magnetic field in combination with a magnetic thin film made of a material having high magnetic permeability, with use of the magnetic thin film as a magnetic flux converging plate configured to change a direction of a magnetic flux to guide the magnetic flux to the Hall elements (see, for example, Japanese Patent Application Laid-open No. 2002-071381).

The magnetic sensor including the magnetic flux converging plate may be manufactured as follows. For example, the Hall elements are formed on the silicon substrate, and then the magnetic flux converging plate is formed on the silicon substrate by electroplating. Alternatively, a protective film made of polyimide or other materials is formed on a front surface of the silicon substrate, and the magnetic flux converging plate is formed on the protective film by electroplating (for example, see WO 07/119569 A1).

When the magnetic flux converging plate is formed on the silicon substrate having the Hall elements formed thereon, large stress is generated on the silicon substrate because the thermal expansion coefficients of a metal magnetic body and the silicon substrate or the protective film made of polyimide or other materials are significantly different from each other. The stress affects the magnetic sensor, increasing shift and fluctuations in the magnetic characteristics.

SUMMARY OF THE INVENTION

In view of this, the present invention has made to provide a magnetic sensor capable of suppressing an influence due to stress to achieve less shift or fluctuations in magnetic characteristics, and to provide a method of manufacturing the magnetic sensor.

According to one embodiment of the present invention, there is provided a magnetic sensor, including: a semiconductor substrate including Hall elements on a front surface of the semiconductor substrate; an adhesive layer formed on a back surface of the semiconductor substrate; and a magnetic flux converging plate formed on the adhesive layer.

According to one embodiment of the present invention, there is provided a method of manufacturing a magnetic sensor, the method including: forming Hall elements on a front surface of a semiconductor substrate; forming a base conductive layer on a plating substrate; forming, on the base conductive layer, a resist having an opening for forming a magnetic flux converging plate; forming a magnetic flux converging plate in the opening by performing electroplating under a state in which the resist is formed; removing the resist; removing a part of the base conductive layer by etching with use of the magnetic flux converging plate as a mask; applying an adhesive onto the magnetic flux converging plate; bonding a back surface of the semiconductor substrate and the magnetic flux converging plate formed on the plating substrate to each other with use of the adhesive; and peeling off the plating substrate from the base conductive layer.

According to one embodiment of the present invention, the magnetic flux converging plate is formed on the back surface of the semiconductor substrate including the Hall elements on the front surface thereof. Thus, stress generated due to a difference in coefficient of thermal expansion between the semiconductor substrate and the magnetic flux converging plate is applied to the semiconductor substrate from the back surface side. As a result, stress to be applied to the Hall elements formed on the front surface side of the semiconductor substrate can be suppressed by the amount of the thickness of the semiconductor substrate. Time-dependent change or fluctuations in the magnetic characteristics of the magnetic sensor can thus be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description is now given of an embodiment of the present invention with reference to the drawings.

FIG. 1is a sectional view for illustrating the structure of a magnetic sensor according to the embodiment of the present invention.

As illustrated inFIG. 1, the magnetic sensor according to this embodiment includes a semiconductor substrate1, a pair of Hall elements2, which is formed on a front surface of the semiconductor substrate1, and is formed so as to be separated from each other, a protective film3covering the front surface of the semiconductor substrate1including the Hall elements2, an adhesive layer40formed on a back surface of the semiconductor substrate1, a magnetic flux converging plate10mounted on the back surface of the semiconductor substrate1through intermediation of the adhesive layer40, and a conductive layer11formed on a surface of the magnetic flux converging plate10on the opposite side of the adhesive layer40.

In this embodiment, the semiconductor substrate1is a P-type semiconductor substrate, and each of the Hall elements2is a horizontal Hall element including a square or cross-shaped vertical magnetic field sensing portion having a four-fold rotational axis, and, at respective vertices and end portions thereof, vertical magnetic field detection control current input terminals and vertical magnetic field Hall voltage output terminals corresponding to surface N-type highly-doped regions having the same shape.

The positional relationship between the Hall elements and the magnetic flux converging plate is important in order to achieve a magnetic sensor having small fluctuations in characteristics. The magnetic flux converging plate10is formed so as to overlap with at least a part of each of the pair of Hall elements2in plan view.

With this configuration, stress generated due to a difference in coefficient of thermal expansion between the semiconductor substrate1and the magnetic flux converging plate10is applied to the semiconductor substrate1from the back surface side. As a result, stress to be applied to the Hall elements2formed on the front surface of the semiconductor substrate1may be suppressed by the amount of the thickness of the semiconductor substrate1. In this manner, the magnetic sensor having small temporal change or fluctuations in the magnetic characteristics may be obtained.

In this case, when the thickness of the semiconductor substrate1is excessively large, the distance between the magnetic flux converging plate10and the Hall elements2formed on the front surface of the semiconductor substrate1increases, and thus the sensitivity of the magnetic sensor may not be sufficient. Further, when the thickness of the semiconductor substrate1is excessively small, the stress applied to the Hall elements2formed on the front surface of the semiconductor substrate1increases. The thickness of the semiconductor substrate1is thus preferred to be from about 100 μm to about 400 μm.

Further, when the thickness of the magnetic flux converging plate10is excessively small, the sensitivity of the magnetic sensor decreases. Further, when the thickness of the magnetic flux converging plate10is excessively large, the influence due to stress increases. The thickness of the magnetic flux converging plate10is thus preferred to be from about 20 μm to about 50 μm.

Next, a method of manufacturing the magnetic sensor illustrated inFIG. 1is described with reference toFIG. 2AtoFIG. 4B.

FIG. 2AtoFIG. 4Bare sectional views for illustrating steps of the method of manufacturing a magnetic sensor according to this embodiment.FIG. 2AandFIG. 2Bare illustrations of a process of manufacturing the Hall elements,FIG. 3AtoFIG. 3Eare illustrations of a process of manufacturing the magnetic flux converging plate, andFIG. 4AandFIG. 4Bare illustrations of a process of bonding the semiconductor substrate and the magnetic flux converging plate to each other.

First, as illustrated inFIG. 2A, on the front surface of the P-type semiconductor substrate1, the Hall elements2and a peripheral circuit (not shown), for example, a control circuit for the Hall elements2, are formed by a normal semiconductor manufacturing process.

Then, as illustrated inFIG. 2B, the back surface of the semiconductor substrate1, which has the Hall elements2and the peripheral circuit formed thereon, is ground, to thereby reduce the thickness of the semiconductor substrate1to from about 100 μm to about 400 μm.

Next, as illustrated inFIG. 3A, separately from the semiconductor substrate1, a plating substrate30for forming the magnetic flux converging plate is prepared, and a base conductive layer11for the magnetic flux converging plate10is formed on the plating substrate30. In this case, the base conductive layer11for the magnetic flux converging plate10serves as an electrode for electroplating. Further, the plating substrate30is peeled off from the base conductive layer11in the subsequent process, and hence adhesiveness between the plating substrate30and the base conductive layer11is preferred to be weak. It is therefore suitable to use copper as the base conductive layer11and a silicon wafer or an acrylic plate as the plating substrate30. Further, the thickness of the base conductive layer11is preferred to be from about 0.3 μm to about 1.0 μm in order to suppress stress.

Then, as illustrated inFIG. 3B, a resist20having an opening20a(hereinafter also referred to as “opening for forming the magnetic flux converging plate”) with a shape of the magnetic flux converging plate10to be formed is formed by photolithography. In this case, the thickness of the resist20is required to be larger than the thickness of the magnetic flux converging plate10to be formed, and hence the thickness of the resist20is desired to be from about 30 μm to about 60 μm.

Next, as illustrated inFIG. 3C, the magnetic flux converging plate10having a thickness of from about 20 μm to about 50 μm is formed in the opening20aof the resist20by electroplating. The magnetic flux converging plate10is desired to be made of a soft magnetic material having low coercive force and high magnetic permeability, for example, permalloy or supermalloy.

Then, as illustrated inFIG. 3D, the resist20is removed to obtain the magnetic flux converging plate10having a desired shape.

Further, as illustrated inFIG. 3E, unnecessary part of the base conductive layer11is removed by etching with use of the magnetic flux converging plate10as a mask.

In this embodiment, the magnetic flux converging plate10is made of a soft magnetic material having low coercive force and high magnetic permeability, for example, permalloy or supermalloy, and hence it is desired to perform, after the plating, high-temperature annealing treatment at a temperature of from 800° C. to 1,000° C. in a hydrogen atmosphere. With this, the soft magnetic property may be improved, and a magnetic flux converging plate having good performance may be obtained. In contrast, in the related-art method involving forming the magnetic flux converging plate on the semiconductor substrate by plating as described in the “Description of the Related Art” section, such annealing treatment cannot be performed because the elements formed on the semiconductor substrate may be affected. In this embodiment, a magnetic flux converging plate can thus be formed to have better performance than that of the magnetic flux converging plate formed by the related-art manufacturing method.

Even in this embodiment, the annealing treatment cannot be performed when an acrylic plate is used as the plating substrate30, and hence a silicon wafer is used as the plating substrate30when annealing treatment is required to obtain a desired soft magnetic property.

Next, as illustrated inFIG. 4A, an adhesive (adhesive layer)40is applied onto the magnetic flux converging plate10formed on the plating substrate30in the steps illustrated inFIG. 3AtoFIG. 3E. The adhesive40is required to have stronger adhesiveness to the semiconductor substrate1than to the base conductive layer11or the plating substrate30. For example, an epoxy adhesive may be suitably used.

Then, the magnetic flux converging plate10formed on the plating substrate30is bonded to the back surface of the semiconductor substrate1, which is formed in the steps illustrated inFIG. 2AandFIG. 2B, and has the Hall elements2formed on the front surface thereof, with use of the adhesive40.

As described above, when the annealing treatment is performed after the magnetic flux converging plate10is formed, the magnetic flux converging plate10may warp or other strains may be caused in the magnetic flux converging plate10. The semiconductor substrate1, however, adheres to the magnetic flux converging plate10through intermediation of the adhesive40, and hence the semiconductor substrate1and the magnetic flux converging plate10may be bonded to each other without a gap therebetween by adjusting the thickness of the adhesive40.

Further, when a large strain is caused in the magnetic flux converging plate10by the annealing treatment, there may be added a step of performing polishing after the annealing treatment to planarize the surface of the magnetic flux converging plate10. A peripheral edge of the magnetic flux converging plate10may be chipped and tapered when the polishing is performed after the resist20is removed, but this situation leads to improvement in sensitivity due to concentrated magnetic flux on the tapered portion, and hence there is no particular problem.

In this case, as the plating substrate30, a silicon wafer that is the same or has the same shape and the same dimension as the silicon wafer used as the semiconductor substrate1, or an acrylic plate having the same shape or the same dimension as the silicon wafer used as the semiconductor substrate1may be used, and an alignment mark may be formed on each of the semiconductor substrate1and the plating substrate30. In this manner, only by aligning the semiconductor substrate1and the plating substrate30, positional fluctuations between the Hall elements2and the magnetic flux converging plate10may be reduced, and thus a magnetic sensor having small fluctuations in characteristics may be manufactured.

After the adhesive40is cured, as illustrated inFIG. 4B, the plating substrate30is peeled off from the base conductive layer11. In this manner, the magnetic flux converging plate10is formed in a desired region as illustrated inFIG. 1. At this time, as described above, the adhesiveness between the plating substrate30and the base conductive layer11is weak, and hence the plating substrate30may be easily peeled off from the base conductive layer11.

As described above, with this embodiment, the magnetic sensor having small fluctuations or shift in magnetic characteristics due to stress, and the method of manufacturing the magnetic sensor may be provided. Further, the magnetic flux converging plate may be formed by photolithography and electroplating, and hence the manufacturing cost may also be reduced.

The embodiment of the present invention has been described above, but the present invention is not limited to the above-mentioned embodiment, and various modifications can be made thereto without departing from the gist of the present invention.

For example, in the above-mentioned embodiment, the protective film3is formed, but the protective film3may be omitted.

Further, in the above-mentioned embodiment, an example in which the P-type semiconductor substrate is used as the semiconductor substrate1is described, but an N-type semiconductor substrate may be used.