A device for detecting magnetism

Abstract: According to this invention, a device for detecting magnetism comprises; a substrate, an interposed insulating layer containing impurities therein, formed on the substrate, and a ferromagnetic magnetoresistive element formed on the interposed layer, wherein at least a portion of the interposed layer on which the ferro­ magnetic magnetoresistive element is formed has a concentration of impurities of less than a predetermined value. Further, in the device of this invention, the surface of the layer interposed between the substrate and the ferromagnetic magnetoresistive element has a surface roughness of less than 120 and an angle between a contacting surface of a conductive wiring and the ferromagnetic magnetoresistive element and the surface of the interposed layer is less than 78 degrees. There­ fore, a device wherein a deterioration of the quality film of the ferromagnetic magnetoresistive element can be avoided and a reduction of the ratio of the resis­ tance variation of the ferromagnetic magnetoresistive element can-be maintained at less than 10% can be obtained, and further, a device wherein the generation of noise can be effectively suppressed so that the device is highly sensitive to magnetism and has a high S/N ratio, and further, the breakdown ratio caused by wiring breakages is effectively reduced, can be obtained.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a device for detecting magnetism, which device comprises a thin film of a ferromagnetic magnetoresistive element mounted on a substrate as a magnetism detecting means. 2. Description of the Related Art A device for detecting magnetism which comprises a thin film of a ferromagnetic magnetoresistive element consisting mainly of a ferromagnetic body and mounted on a substrate as a magnetism detecting means is known. A device for detecting magnetism is generally constructed such that a variation of magnetism can be detected, for example, as a variation in an electric voltage, utilizing the phenomenon that a value of the resistance of the ferromagnetic magnetoresistive element is changed in the presence of magnetism. The output signal obtainable from such a device for detecting magnetism as described above is usually so weak that these output signals must be amplified by a separate device, for example, an amplifying IC or the like, produced in a separate production process. Nevertheless, the device is easily affected by the influence of noise, and therefore, a highly sensitive device for detecting magnetism is still required. As described above, since the output signal from such a device is usually very weak, the output signal from the ferromagnetic magnetoresistive element 101 is amplified by an IC 100, such as an amplifier circuit, a waveform shaping circuit or the like, as shown in Figure 2, in which leads 102 and a molded case 103 are also shown. Recently, a demand has arisen for such an aforementioned IC and ferromagnetic magnetoresistive element to be integrated as one body. Hereafter, one example of a manufacturing process of a device for detecting magnetism having such an IC and the ferromagnetic magnetoresistive element integrated as one body, which the inventors of this invention had tried to make and to use for experiments and tests, will be explained with reference to Figure 3. Figure 3 is a cross sectional view of an example of the construction of a device for detecting magnetism in which the ferromagnetic magnetoresistive element and IC are integrated into one package. The steps for manufacturing the device for detecting magnetism will be explained hereunder with reference to Figure 5. First, in step 200, a P type silicon (Si) wafer 1 is obtained, then in step 201, a thermal oxide film is formed on the P type silicon (Si) wafer by a thermal oxidation process and openings are provided in a predetermined region of the thermal oxide film. Then, in step 202, an N⁺ type buried layer 2 is formed by diffusing antimony (Sb) or arsenic (As) into the wafer 1 from the opening, and in step 203, the thermal oxide film is removed and an N⁻ type epitaxial layer 3 having a low concentration of impurities is formed on the P type silicon wafer. Then, in step 204, a thermal oxidation process is applied to the surface of the epitaxial layer 3 to form a thermal oxide film, openings are provided in the film at the position corresponding to the position in the epitaxial layer 3 in which the isolating regions will be formed, and then in step 205, an isolating region 4 is formed by a diffusion of boron (B). Next, in step 206, an insulating film consisting of SiO₂ is formed by a thermal oxidation process, and then in step 207, a P⁺ type diffusion layer 6, which is used as a base region, is formed by diffusing the boron (B) into the N⁻ type epitaxial layer 3, and successively, in step 208, N⁺ type diffusion layers 7, which are used as an emitter region and a contact region with the collector (the epitaxial layer 3), respectively, are formed by diffusing P (phosphorus) into the respective layer in the same way as for forming the P⁺ type diffusion layer 6. Further, in step 209, a contacting portion is provided by selectively forming an opening in the insulating film 5. The insulating film 5 thus produced is shown in Figure 3. Then, in step 210, the contacts are completed by depositing A1 thereon to form wiring 9, and in step 211 a thermal-treatment is carried out. Thereafter, in step 212, the ferromagnetic body including Ni as a main component thereof, and further including Fe and/or Co, for example, an alloy of Ni-Fe or Ni-Co, is deposited on the surface thereof by a vacuum deposition method to form a thin film of the ferromagnetic magnetoresistive element 10 having a thicKness of 20 to 200nm (200 to 2000 Å), and then, the thin film is etched to form a predetermined pattern thereon. Further, in step 213, a surface protecting film 11 which protects the bipolar IC and the ferromagnetic magnetoresistive element thus produced is formed on the surface thereof, and then an opening 12 is formed by removing a portion of the surface protecting film 11 which corresponds to the position at which a terminal of an electrode will be mounted and then, in step 214, the terminals of the electrodes are formed at that portion. Finally, at step 215, a thermal treatment for recovering the characteristics of the transistor varied due to the formation of the ferromagnetic magnetoresistive element 10 and the surface protecting film 11, and to improve the quality of the film of the ferromagnetic magnetoresistive element 10, is applied to the thus-produced device. In this manufacturing process, the step 208 for forming the N⁺ type diffusion layers 7 of the bipolar IC is carried out by a vapour diffusion method, usually by employing POCl₃ gas, but in the above process, the diffusion source P is also diffused into the interposed insulating film 5 to form a layer 8 in the surface portion of the interposed insulating film 5, in which the concentration of the impurities is higher than that of the rest of the portion of the film 5. Namely, the layer 8 is not formed as a separate film to the film 5, but is a layer containing a high concentration of impurities therein and is similar to a Phospho Silicate Glass film (PSG film), and accordingly this layer 8 is referred to as a PSG layer hereinafter. On the other hand the interposed insulating film 5 may be referred to as the interposed layer or only simply to the layer hereafter. This PSG layer 8 has a gettering function, and therefore, in an ordinary IC, usually remains on the surface thereof without change. But, in the device for detecting magnetism as mentioned above, it was found that, when the ferromagnetic magnetoresistive element 10 is formed on the surface of the PSG layer 8, the quality of the film thus formed, in relation to the electromagnetic characteristics, for example, is remarkably deteriorated when compared with the film of the ferromagnetic magnetoresistive element deposited on the surface of the SiO₂ film formed on the surface of the silicon (Si) wafer only by applying the thermal oxidation process to the surface thereof, without forming a bipolar IC or the like on the surface or on the surface of a glass substrate. According to experiments by the inventors, it was found that the closer the portion of the ferromagnetic magnetoresistive element 10 is to the insulating film or the layer 5 of the IC, the greater the deterioration of the quality of the film of the ferromagnetic magnetoresistive element. It was also found that this deterioration is caused by the chemical reaction of P (phosphorous) contained as impurities in the PSG layer 8 formed in the surface portion of the insulating film or layer 5 of the IC with the ferromagnetic magnetoresistive element, due to the thermal treatment carried out in step 215. It was further found that this phenomenon applies to an insulating film 5 containing only As as the impurities, and not containing P as mentioned above. According to further experiments concerning the factors causing the generation of noise, depending upon the mechanical construction of the device for detecting magnetism per se, by the inventors of this invention, it was found that, for example, Barkhausen noise is generated when a surface roughness of the surface of an interposed layer of the ferromagnetic magnetoresistive element is coarse. EP-A-0271018 falling under Article 54(3) EPC relates to a thin film solid state device. The integrated device is for detecting magnetism and comprises a silicon substrate, a continuous silicon dioxide layer formed thereon and a continuous electrically conductive thin film of permalloy formed on the silicon dioxide layer. A resistive layer is formed on the permalloy layer and an insulating layer is formed thereon. The top insulating layer is etched to expose sites on the resistive layer at which electrical contacts are formed. This invention as defined in the claims is based upon the above findings, and the object of the invention is to provide a device for detecting magnetism having a ferromagnetic magnetoresistive element formed on a substrate, wherein the film quality thereof is not deteriorated even when a thermal treatment is carried out after the ferromagnetic magnetoresistive element is formed. Another object of the invention is to provide a device for detecting magnetism having a high sensitivity by controlling the surface roughness thereof. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view of one example of the device for detecting magnetism, of this invention; Fig. 2 shows a construction of a conventional device for detecting magnetism; Fig. 3 is a cross sectional view of a prototype of the device for detecting magnetism according to the present invention, and used for tests or experiments carried out by the present inventors; Fig. 4 is a graph indicating the relationship between the phosphorous concentration of the interposed insulating layer and the ratio of change in the resistance of the ferromagnetic magnetoresistive element; Fig. 5 is a flow chart of a manufacturing process of the device for detecting magnetism, of this invention; Fig. 6 is a graph indicating the relationship between the arsenic concentration of the interposed insulating layer and the ratio of change in the resistance of the ferromagnetic magnetoresistive element; Fig. 7 is a characteristics chart indicating the relationship between the surface roughness and generation ratio of Barkhausen noise; Fig. 8 is a chart indicating the relationship between the inclination angle  and the breakdown ratio caused by a wiring breakage in the ferromagnetic magnetoresistive element; Fig. 9 shows a method for measuring the characteristic as shown in Fig. 8; and, Fig. 10 is a graph indicating the relationship between the magnetic field intensity and the value of the value of the resistance. DESCRIPTION OF THE PREFERRED EMBODIMENT According to the invention there is provided a device for detecting magnetism which comprises, a substrate, a thin film ferromagnetic magnetoresistive element, and an insulating layer interposed between said substrate and said magnetoresistive element, said insulating layer having an upper impurity layer portion and a lower remaining layer portion adjacent to said substrate, said impurity layer portion containing impurities at a higher concentration than that of the remaining layer portion, wherein said impurity layer portion has an opening where the remaining layer portion is exposed, and the magnetoresistive element is located on said exposed remaining layer portion in said opening. In this invention, the substrate may be a semiconductor, preferably silicon, and the impurities contained in the remaining layer portion may be phosphorus (P) having a concentration of less than 5 P₂O₅ mol% and/or arsenic (As) having a concentration of less than 1 x 10¹⁷ cm⁻³. Further, in this invention, the interposed selected insulating layer may be silicon based and preferably is made of a substance selected from silicon dioxide (SiO₂) and silicon nitride (Si₃N₄) and the ferromagnetic magnetoresistive element may be made of a substance containing Ni as a main component and preferably further containing Fe and/or Co. The surface of at least said remaining layer portion on which said ferromagnetic magnetoresistive element is formed preferably has a surface roughness of less than 12nm (120 Å). A conductive wiring consisting of a thin film may be formed on said insulating layer and the ferromagnetic magnetoresistive element may extend onto said conductive wiring to make electrical contact, the angle between the contacting surface at the lateral edge of said conductive wiring and the surface of said insulating layer being less than 78 degrees. The impurities in the insulating layer preferably consist of a substance selected from phosphorus (P), boron (B) and arsenic (As). In a preferred embodiment, at least a processing circuit consisting of a bipolar integrated circuit for processing signals output from said ferromagnetic magnetoresistive element is included in the same substrate on which said ferromagnetic magnetoresistive element is formed and said insulating layer is extended to at least the place located over said processing circuit to serve as an insulating film and contains therein the same impurities as contained in a diffusion region forming a collector region in said circuit. EXAMPLE The invention will be described by way of an example, with reference to the accompanying drawings. Figure 1 is a cross sectional view indicating one example of this invention in which a bipolar IC portion A for processing signals from the ferromagnetic magnetoresistive element 10, a portion of a ferromagnetic magnetoresistive element B, and a terminal portion of the electrode C, are provided. Namely, in the device for detecting magnetism of this invention, at least a ferromagnetic magnetoresistive element 10 and a processing circuit for processing signals from the ferromagnetic magnetoresistive element 10, for example, a bipolar IC, a MOSIC including an amplifier, or a waveform shaper or the like, are integrately mounted on the same substrate, and can be simultaneously produced by the same process. And in this manufacturing process, the impurities such as P or As are introduced into the insulating film or layer of the IC. The manufacturing process of this device for detecting magnetism is basically the same as that of the process explained above, with reference to Figure 5, to obtain the device shown in Figure 3, which was used for experiments and tests by the inventors, and consequently, a PSG layer 8 containing a high concentration of P (phosphorus) as impurities, caused by diffusing the diffusion source P when the N⁺ type diffusion layers 7 of the bipolar IC were formed, is formed in a upper portion of the insulating film 5 consisting of silicon dioxide (SiO₂). According to the example of this invention, in the manufacturing flow as shown in Figure 5, a new step of removing the PSG layer 8, in step 300, is performed after step 208 in which the N⁺ type diffusion layers 7 are formed. In step 300, a part of the PSG layer 8 corresponding to the predetermined region on which the ferromagnetic magnetoresistive element 10 of the ferromagnetic magnetoresistive element portion B will be formed, is partially removed to make an opening 13, and accordingly, the lower portion of the insulating film 5 containing P (phosphorus) at a low concentration or containing little P, is exposed. Namely, the PSG layer 8 containing a high concentration of P is selectively removed by using a liquid composed of a mixture of ammonium fluoride, hydrofluoric acid, and water, as an etchant, utilizing the phenomenon of a difference of the etching speed of the portion containing P at a higher concentration and that of the portion containing P at a lower concentration. In such a case, the total etching speed can be reduced by decreasing the content ratio of hydrofluoric acid in the etchant, to improve the control thereof. After steps 209 to 211 are completed, a pattern of the ferromagnetic magnetoresistive element 10 is formed at the opening 13. Figure 4 shows the relationship between the phosphorus concentration of the insulating film or layer 5 and the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10, when using a film of Ni-Co alloy as the ferromagnetic magnetoresistive element 10. Generally, when the N⁺ type diffusion layer 7 which is an emitter region of the bipolar IC, is formed, the PSG layer 8 having a phosphorus concentration of 10 to 20 P₂O₅ mol% is formed, and therefore, the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10 is less by 20 to 50% than the same ratio measured when the film of Ni-Co formed on the surface of the silicon dioxide film does not contain impurities therein (i.e., the phosphorus concentration of 0 P₂O₅ mol%). But, in this invention, as a part of the PSG layer 8 having a high phosphorus concentration is removed, and the phosphorus concentration of a portion of insulating film 5 corresponding to the predetermined region on which the ferromagnetic magnetoresistive element 10 will be formed is reduced to less than 5 P₂O₅ mol%, the chemical reaction of P (phosphorus) contained in the PSG layer 8 with the ferromagnetic magnetoresistive element 10 is suppressed. Accordingly, the reduction of the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10 can be, in practice, maintained at less than 10% even after the thermal treatment at step 215, and a ferromagnetic magnetoresistive element having a superior film quality and electromagnetic characteristics such that no problem will arise during the practical usage thereof, can be obtained. Further, as the rest of the portions of the PSG layer 8 provided on the other portions of the IC, remain unchanged, the deterioration of the IC characteristics thereof can be effectively avoided due to the gettering function thereof. Next, another example of this invention will be described hereunder. In this example, As (arsenic) is used as a diffusing source in the step of forming the N⁺ type diffusion layers of the bipolar IC in the above mentioned example. The manufacturing process of the device for detecting magnetism in this example is basically the same as that explained with reference to Figure 5 above, and accordingly, an explanation of each step used in this example, which is the same as used in the previous example, will be omitted. As in this example, when As (arsenic), which is known to be a dangerous substance in a gaseous condition, is used, the process for making the N⁺ type diffusion layers 7 in step 208 is carried out by the ion implantation method. After step 208 is completed, the PSG layer 8 in which the As is highly concentrated is formed on the surface of the insulating film 5, and in step 300, a part of the PSG layer 8 of the insulating film 5, corresponding to the predetermined region on which the ferromagnetic magnetoresistive element 10 will be formed, is partially removed by etching the surface thereof by a thickness of about 100nm (1000 Å), using an etchant having as a main component thereof, hydrofluoric acid, and accordingly, a lower portion of the insulating film 5 containing little As is exposed. Figure 6 shows the relationship between the As (arsenic) concentration at the surface of the insulating film 5 and the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10 when using a film of Ni-Co alloy as the ferromagnetic magnetoresistive element 10. Generally, when the N⁺ type diffusion layer 7, which is an emitter region of the bipolar IC, is formed in the surface portion of the insulating film 5, As is diffused at a concentration of about 1 x 10²¹ (1/cm³) to form a PSG layer 8, and therefore, the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10 is reduced by 40% compared to the same ratio when the Ni-Co film formed on the surface of the silicon dioxide film does not contain impurities therein. But, as shown in Figure 6, in this example, by controlling the surface concentration of As of the insulating film 5, exposed by the etching operation at step 300, to less than 1 x 10¹⁷ (1/cm³), the reduction of the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10 can be maintained, in practice, at less than 10%, and therefore, the ferromagnetic magnetoresistive element having a superior film quality and having electromagnetic characteristics such that no problem arises during the practical usage thereof, can be obtained. In this example, when As is implanted into the silicon dioxide film, it is not usually introduced deeply into the silicon dioxide film and, generally, is implanted to about 50 nm (500 Å) in depth from the surface of the film, when the accelerating energy of the ion implantation is 130 KeV. Further, from the view point of the present technical level, even if the accelerating energy of the ion implantation is set to an upper limit of 160 KeV, the depth of the implantation will be at most around 70 nm (700 Å). Accordingly, as mentioned above, when the surface of the insulating film 5 is etched by about 100nm (1000 Å), almost all of the As contained in the film or layer 5 can be eliminated, and consequently, a reduction of the ratio of the resistance variation of the ferromagnetic magnetoresistive element 10 can be effectively avoided. The concentration of impurities used in this invention is measured by a known measurement method such as an atomic absorption spectro photometry method or a fluorescent X ray spectroscopy method. When the impurities are As, the amount of As represented by the unit of 1/cm³, contained in the film or layer 5 is measured by that method and such amount thereof is directly used as the concentration of impurities. While when the impurities are P, the amount of P is measured by that method and such amount thereof is then converted to the amount of P₂O₅ in mol% by an ordinary calculating method and the amount of the number thus converted is used as the concentration of impurities. Although this invention is described above by one example thereof, it is not restricted thereto, since it is apparent that this invention can be applied to the many variables as shown hereunder as long as they do not fall outside of the scope of this invention as defined by the claims. (1) The impurities contained in the silicon dioxide layer may be Boron (B) or the like, other than P (phosphorus) and As (arsenic), and accordingly, the ferromagnetic magnetoresistive element may be formed on the surface of the layer, as a PSG layer or BPSG layer containing the impurities (B and/or P) therein at a concentration less than a predetermined value. Further, the film used as the ferromagnetic magnetoresistive element may be Ni-Fe film. Although, the value of the ratio of the resistance variation of the Ni-Fe film is smaller than that of the Ni-Co film, the same characteristics can be obtained because the configuration of the magnetic domain of both films is the same. As described above, any substance can be selected as the impurities contained in the silicon dioxide layer and the ferromagnetic magnetoresistive element. Note, any of the substances which can be diffused into the silicon dioxide film as impurities in the thermal treatment at step 215 can be used in this invention. It is a basic conception of this invention that the ratio of the resistance variation will be reduced in accordance with this diffusion. (2) The IC constructed inside of the substrate need not be a bipolar IC, and can be a MOSIC or the like. As described above, as a result of an experiments, the present inventors found that Barkhausen noise is generated when a surface roughness of the surface of an interposed layer, i.e., an insulating film interposed between the ferromagnetic magnetoresistive element and the substrate, is coarse, and further found that the breakdown ratio caused by a wiring breakage mainly depends upon the condition of the contacting surface formed between the ferromagnetic magnetoresistive element and the wiring. To overcome the above drawbacks in accordance with this invention, the device for detecting magnetism is further characterized in that the surface of at least the remaining layer portion on which the ferromagnetic magnetoresistive element is formed has a surface roughness of less than 12nm (120 Å). Another feature of this invention lies in a technical construction such that the device for detecting magnetism is further characterized in that a conductive wiring consisting of a thin film electrically connected to the ferromagnetic magnetoresistive element is formed on the insulating interposed layer, and the angle formed between contacting surfaces of the conductive wiring and the ferromagnetic magnetoresistive element and the surface of the interposed insulating layer is less than 78 degrees. In this invention, the film of the ferromagnetic magnetoresistive element may be composed of a substance having Ni as the main component thereof. According to the technical construction explained above, magnetic domains of the ferromagnetic magnetoresistive element can move continuously in accordance with variations in the magnetism measured, and therefore, the generation of Barkhausen noise caused by an irregular movement of the magnetic domains can effectively suppressed. Furthermore, when the inclination angle  of the contacting surface of the conductive wiring 9 to the ferromagnetic magnetoresistive element 10 is less than 78° (degrees), the ratio of breakdowns caused by wiring breakages is effectively reduced. Accordingly, the device for detecting magnetism of this invention does not require the separate device required in the current technology, and thus the packaging area of the device can be reduced accordingly and the wiring arrangement, including the bonding wiring for connecting each component or the like, can be simplified. Further, in this invention, since the surface roughness of the interposed layer, i.e., the silicon dioxide layer 5 in this example, of the ferromagnetic magnetoresistive element 10 has a thickness of 10nm (100 Å), the generation of Barkhausen noise can be decreased to almost 0%, as shown in Figure 7, indicating the importance of the relationship between the surface roughness and the generation of Barkhausen noise, and therefore, the sensitivity of the magnetism is increased and the S/N ratio is improved. The characteristic shown in Figure 7 is obtained by a measuring method wherein first the ferromagnetic magnetoresistive element 10 is formed into a strip having a linear pattern as shown in Figure 9, and thereafter, the resistance value of the ferromagnetic magnetoresistive element 10 is measured by applying the magnetic field H thereto transversely to the direction of the current flowing in the element while a predetermined voltage is applied to both ends thereof. This measuring operation was carried out by using an XY recorder; YEW provided by YOKOGAWA ELECTRIC CO. LTD., and under conditions of room temperature (25 ±2°C) and a current I of 1 mA. The resultant data are shown in Figure 10 as a solid line. But, when Barkhausen noise is generated, a noise component A shown by a dotted line, which is slightly apart from the solid line, can be seen in Figure 10, and the noise generation ratio is finally obtained by detecting the frequency of the existence or nonexistence of the noise component A. In Figure 7, the 0% noise generation ratio is based on the fact that the XY recorder used in this measurement has a limited resolution of less than 0.5% of a maximum output pulse (100%). As apparent from Figure 7, the generation of Barkhausen noise can be effectively suppressed when the surface roughness is less than 12nm (120 Å), as shown in the above example. The lower limit of the surface roughness of this invention can not be defined at a critical value, but the lower limit thereof may be determined as the minimum value of the surface roughness at which the present processing technology can provide a surface roughness on the surface of the film. Further, the reason why Barkhausen noise is generated when the surface roughness thereof is more than 12nm (120 Å), is considered to be because, when the surface roughness of the insulating interposed layer is coarse, the under surface of the ferromagnetic magnetoresistive element facing the interposed insulating layer becomes coarse, reflecting the coarseness of the surface of the insulating interposed layer, and thus the magnetic domain of the ferromagnetic magnetoresistive element 10 is deformed to generate an inner distortion therein. Accordingly, the extent of the anisotropic dispersion of the ferromagnetic body will be increased so that the domain wall of the magnetic domain is moved irregularly in accordance with the variation of the magnetism measured and therefore, the noise is rapidly increased to cause a distortion of the output of the ferromagnetic magnetoresistive element 10. Therefore, to suppress the generation of Barkhausen noise, preferably the coarseness of the undersurface of the ferromagnetic magnetoresistive element 10 is controlled since, as described above, the surface roughness of the interposed insulating layer must be controlled because the coarseness of the under surface of the ferromagnetic magnetoresistive element 10 is substantially reflected by the surface roughness of the interposed insulating layer. Figure 7 shows the characteristics of the ferromagnetic magnetoresistive element 10 made of Ni-Fe alloy. Almost the same characteristics as that obtained by the Ni-Fe alloy can be obtained by using Ni-Co alloy. This is supported by the fact that the composition ratio of Ni-Fe alloy is 83:17 but the same ratio of Ni-Co alloy is 76:24 (in both cases, the unit thereof is wt% and the allowance for error is ±2%), both alloys contain Ni having a strong ferromagnetic characteristics as a main component, and further, both films have the same magnetic domain construction. Further, in this example, since the inclination angle  at the contacting portion of the conductive wiring 9 with the ferromagnetic magnetoresistive element 10, is 50 degrees, the breakdown ratio caused by wiring breakages can be reduced to almost 0%, as shown in Figure 8, which shows the relationship between the inclination angle  and the breakdown ratio caused by wiring breakage. Generally, the thin film of the ferromagnetic magnetoresistive element 10 has a thickness of 50-100nm (500 - 1000 Å), at most around 200nm (2000 Å) even in the thickest case, i.e., this film is an extremely thin film, and consequently, it is easily broken at a step-like portion formed at the portion connecting with the conductive wiring 9. But, in this invention, as shown in Figure 8, the breakdown ratio can be effectively reduced by making the inclination angle  of the conductive wiring 9 less than 78 degrees. Any of Al containing Cu or Si as an impurity therein, Au, and Cu or the like can be used as the material of the conductive wiring 9, other than A1 per se, and will provide the same effect as when A1 is used. Although, this invention is described above by one example thereof, it is not restricted thereto, since it is apparent that this invention can be applied to the many variables as shown hereunder as long as they do not fall outside of the scope of this invention as defined by the claims. (1) As the interposed insulating layer 5, insulating film other than silicon dioxide may be used. This is shown by the results of an experiment utilizing a film made of silicon nitride, for example, Si₃N₄ , or a glass (#7059 provided by CORNING GLASS), wherein the characteristics shown in Figure 7 did not shown any change when compared with the previous results. As the substrate used in this invention, an insulating substrate other than the semiconductor substrate can be used. (2) In the example mentioned above, an electric circuit other than the amplifier circuit may be used as the signal processing circuit formed in the same substrate. For example, a hysteresis circuit comprising a Schmitt trigger circuit or the like may be formed as the signal processing circuit, when the device for detecting magnetism of this invention is used to control the rotation of a magnetic body, for example, in an encoder or the like. (3) In the above example, the control of the surface roughness of the silicon dioxide film 5 was carried out by controlling the deposition speed, but this control also can be carried out by grinding. In this case, the surface of the semiconductor substrate before the silicon dioxide film 5 is formed thereof, may be ground to a surface roughness Ra of, for example, 2-3nm (20-30 Å), and thereafter, the silicon dioxide film 5 may be formed on the surface by a thermal oxidization method. In this method, the surface of the silicon dioxide film 5 can be controlled to have a surface roughness Ra of around 10nm (100 Å), due to a reflecting of the surface roughness of the semiconductor substrate. When manufacturing the device for detecting magnetism of this invention, in which the PSG layer is removed from the surface of the silicon dioxide film for example, the grinding method can be applied to the portion of the film from which the PSG layer had been removed. The removal of the PSG layer should be carried out with great care, to ensure a surface roughness of less than 10nm (100 Å). As described above, in accordance with the invention, the ferromagnetic magnetoresistive element is formed on a region of a interposed insulating layer such as a silicon dioxide film, in which the concentration of impurities thereof is less than a predetermined value, and thus a deterioration of the quality film of the ferromagnetic magnetoresistive element can be avoided. Moreover, a reduction of the ratio of the resistance variation of the ferromagnetic magnetoresistive element can be maintained at less than 10% in practice. Furthermore, according to this invention, the surface roughness of the interposed layer between the substrate and the ferromagnetic magnetoresistive element is less than 12nm (120 Å), and accordingly, the generation of noise can be effectively suppressed, and therefore, the device for detecting magnetism according to this invention has a high sensitivity and a high S/N ratio. Further, since the inclination of angle  of the contacting surface of the conductive wiring 9 with the ferromagnetic magnetoresistive element 10 is less than 78° (degrees), the breakdown ratio caused by wiring breakages is effectively reduced.

Claims: A device for detecting magnetism comprising, a substrate (1), a thin film ferromagnetic magnetoresistive element (10), and an insulating layer (5) interposed between said substrate and said magnetoresistive element, said insulating layer having an upper impurity layer portion (8) and a lower remaining layer portion adjacent to said substrate, said impurity layer portion (8) containing impurities at a higher concentration than that of the remaining layer portion, wherein said impurity layer portion (8) has an opening (13) where the remaining layer portion is exposed, and the magnetoresistive element (10) is located on said exposed remaining layer portion in said opening (13). A device for detecting magnetism according to claim 1, wherein the substrate (10) is a silicon substrate. A device for detecting magnetism according to claim 1 or 2, wherein said impurities include phosphorous (P), and said concentration of impurities of said remaining layer portion is a phosphorus concentration of less than 5 P₂O₅ mol%. A device for detecting magnetism according to claim 1 or 2, wherein said impurities include arsenic (As), and said concentration of impurities of said remaining layer portion is an arsenic concentration of less than 1 x 10¹⁷ cm⁻³. A device for detecting magnetism according to any one of claims 1 to 4, wherein the surface of at least said remaining layer portion on which said ferromagnetic magnetoresistive element is formed has a surface roughness of less than 12nm (120 Å). A device for detecting magnetism according to any one of claims 1 to 5, wherein a conductive wiring (9) consisting of a thin film is formed on said insulating layer (5) and the ferromagnetic, magnetoresistive element extends onto said conductive wiring to make electrical contact, the angle between the contacting surface at the lateral edge of said conductive wiring (9) and the surface of said insulating layer (5) being less than 78 degrees. A device for detecting magnetism according to any one of claims 1, 2, 5 and 6, wherein said impurities contained in said insulating layer (5) consist of a substance selected from phosphorous (P), boron (B), and arsenic (As). A device for detecting magnetism according to any one of claims 1 to 7, wherein said insulating layer (5) is a film made of a substance selected from silicon dioxide and silicon nitride. A device for detecting magnetism according to any one of claims 1 to 8, wherein said ferromagnetic magnetoresistive element (10) is a thin film containing Ni as a main substance therein. A device for detecting magnetism according to claim 9, wherein said ferromagnetic magnetoresistive element (10) consists of a metallic alloy selected from Ni-Fe and Ni-Co. A device for detecting magnetism according to any one of claims 1 to 10, wherein at least a processing circuit consisting of a bipolar integrated circuit (IC) for processing signals output from said ferromagnetic magnetoresistive element (10) is included in the same substrate (1) on which said ferromagnetic magnetoresistive element (10) is formed and further wherein said insulating layer (5) is extended to at least the place located over said processing circuit to serve as an insulating film and contains therein the same impurities as contained in a diffusion region forming an emitter region (7) in said circuit.

Inventors: AO KENICHI, ARASUNA TOSHIKAZU, IZAWA ICHIRO, YOSHINO YOSHIMI, AO, KENICHI, ARASUNA, TOSHIKAZU, IZAWA, ICHIRO, YOSHINO, YOSHIMI
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1988
Main classification: H01L27
IPC codes: H01L43, G01R33, H01L27