JP2008306094A - Magnetic memory and manufacturing method of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic memory capable of writing and reading of stable information by blocking an unnecessary magnetic field ranging from circumference to a memory array, and having high reliability of holding record for a long period. <P>SOLUTION: The memory array including a magnetic storage element is coated with a dielectric layer, and a ferromagnetic body is arranged inside of this dielectric layer so as to surround a side direction parallel to a wafer surface of the memory array. Then, the ferromagnetic body is arranged on an upper surface of the memory array. With this structure, an influence of an external magnetic field of an operation of the magnetic storage element can be prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic memory, and more specifically, an external magnetic field that affects recording write operation and retention in a memory in which cells having magnetoresistive elements such as a ferromagnetic tunnel junction and a giant magnetoresistive element are integrated. Relates to a magnetic shield to prevent

  A magnetic random access memory (MRAM) is a non-volatile memory that can be written at high speed and has an infinite number of rewrites in principle. FIG. 1 is a schematic diagram of a ferromagnetic tunnel junction used in an MRAM. In the ferromagnetic tunnel junction, the magnetization direction is fixed by the tunnel barrier layer 5 and two ferromagnetic layers sandwiching the tunnel barrier layer, that is, the free layer 6 and the antiferromagnetic layer whose magnetization direction is changed by an external magnetic field. The magnetization fixed layer 4, the antiferromagnetic layer 3 that fixes the magnetization of the magnetization fixed layer 4, the underlayer 2, the electrode layer 7, and the like. In addition, the code | symbol 1 of FIG. 1 shows a wafer.

  In general, writing in the MRAM is performed by making the magnetization of the free layer parallel or antiparallel to the magnetization of the magnetization fixed layer by a write magnetic field generated by a write wiring current. The junction resistance of the ferromagnetic tunnel junction is minimum when the spontaneous magnetization of the two ferromagnetic layers is parallel, and is maximum when the two ferromagnetic layers are antiparallel, and therefore the level of the junction resistance corresponds to the written information. Since the relationship between the magnetization directions of the free layer and the magnetization fixed layer is maintained even after the write magnetic field is removed, the ferromagnetic tunnel junction can be used as a nonvolatile memory.

  Also, recently, the spin injection type that reverses the magnetization of the free layer by passing a spin-polarized current through the free layer, and the direction of magnetization by driving the domain wall formed in the free layer with a spin-polarized current There has been proposed a domain wall motion type storage element that changes the angle.

  In any type of MRAM, information is recorded by the magnetization state of the ferromagnetic material. Therefore, if an unnecessary magnetic field, that is, a disturbance magnetic field is applied from the outside during recording holding, the magnetization state of the free layer may change and the recording may be lost. In addition, the presence of an external magnetic field lowers the resistance to disturbance due to heat in the magnetization state of the ferromagnetic material. Therefore, the recording state may be lost while the magnetization state of the free layer changes during long-term recording retention. Further, if an unnecessary magnetic field is applied during the write operation, the magnetization of the free layer is not normally reversed, and erroneous information may be written.

  The MRAM can be used not only as a single memory but also as a mixed memory of a system LSI. When used as a mixed memory, since a logic circuit and an analog circuit are mounted on the same chip, there is a possibility of receiving a magnetic field from these circuits, for example, a magnetic field generated by a power supply line. Moreover, in the use mixed with the chip | tip which transmits / receives a high frequency like an IC card or RF tag, it receives to the influence of a high frequency.

  In order to prevent the influence of an external magnetic field, it is effective to use a magnetic shield. The magnetic shield is made of a ferromagnetic material, and has a function of deflecting from a memory array by passing a magnetic field through the shield against a direct current or low frequency magnetic field. In addition, a high frequency magnetic field is absorbed as heat energy, thereby showing a shielding effect.

  As an example of a magnetic shield, Patent Document 1 discloses a technique in which an MRAM chip 9 formed on a lead frame 8 is surrounded by a magnetic continuous magnetic shield member 11 formed of a soft magnetic material as shown in FIG. It is disclosed. In FIG. 2, reference numeral 10 denotes a wire for connecting the MRAM chip 9 and the lead frame 8. In Patent Document 2, as shown in FIG. 3, a magnetic shield film 17 is formed on the upper and lower surfaces of a package formed by sealing an MRAM chip 13 and another element 14 formed on a die pad 12 with a sealant 16. And a technique for suppressing the influence of the stray magnetic field on the MRAM chip 13 by guiding the stray magnetic field to the inside of the magnetic shield film 17 is disclosed. In FIG. 3, reference numeral 15 denotes an external lead 15. In Patent Document 3, as shown in FIG. 4, by mixing magnetic particles 20 inside a package 19 formed by sealing a semiconductor chip 18 formed on a die pad 12 of a lead frame 8 with a molding material, A technique for suppressing the influence of an external magnetic field is disclosed. In Patent Document 4, as shown in FIG. 5, a technique is disclosed in which the memory array block 21 is covered with a dielectric layer 22, the auxiliary shield layer 23 is patterned thereon, and a main shield layer 24 is further provided thereon. .

Japanese Patent No. 3879576 JP 2004-200195 A JP 2004-349476 A JP 2007-27757 A

  However, as in Patent Document 1 and Patent Document 2, a method of placing individual chips in a structure having a magnetic shield effect or providing a ferromagnetic plate serving as a shield for each individual package is Cost increases. In the technique of Patent Document 2, since the distance between the shield and the MRAM is increased, the ferromagnetic material used for the shield needs to be thick and large in order to obtain a sufficient magnetic shielding effect.

  In the technique of mixing magnetic particles in the mold material of Patent Document 3, since the density of the magnetic material is low, it is difficult to obtain a sufficient magnetic shield effect. In addition, if the magnetic material is included at a high density, the properties of the molding material itself change.

  In addition, since the techniques shown in Patent Document 1 to Patent Document 3 are provided with a magnetic shield outside the chip in units of chips, there is no effect in the use of an embedded memory in which MRAM and other circuits are mounted on the same chip.

  In the technique of Patent Document 4, since the magnetic shield is formed on the dielectric covering the MRAM in a state where the MRAM is formed on the wafer, the cost is lower than the technique of providing the magnetic substance for each packaging. Further, a shield can be added to the MRAM even when the MRAM is used as an embedded memory. However, since there is no shield in the side surface direction of the array, a sufficient magnetic shielding effect cannot be obtained depending on the arrival direction of the magnetic field. In particular, it is insufficient for shielding a magnetic field generated by a short distance, for example, an element mounted on the same chip.

  The object of the present invention is to solve these problems related to the magnetic shield of the conventional MRAM, sufficiently shield unnecessary magnetic fields applied to the MRAM array, and enable stable writing of information and long-term recording retention. And a method of manufacturing the same.

  The MRAM according to the present invention has a structure in which a ferromagnetic material is provided in the side surface direction of a magnetic memory array composed of a plurality of magnetic memory cells. This ferromagnetic material is provided so as to surround the memory array. An external magnetic field is induced in the ferromagnet to escape the memory array.

  The ferromagnet surrounding the memory array may be either a continuous structure in a plane parallel to the memory array or a discontinuous structure formed by a plurality of independent ferromagnets. In order not to create a path for the magnetic field to enter the inner region without being shielded by the magnetic material, it is preferable to have a structure in which the layers are not single but double or more layers are shifted while being shifted. Even in the case of a magnetic shield having a continuous structure, when it is difficult to form a thick single structure, a plurality of thin ferromagnetic structures separated by dielectrics can be superposed. For example, when an electromagnetic field simulation was performed, when a magnetic field having a component parallel to the shield plate of 796 A / m (10 Oe) was applied to a 100-nm-thick Ni—Fe alloy magnetic shield plate, the back side of the magnetic shield was shielded. The parallel magnetic field component was attenuated to 320 A / m (4 Oe) or less.

  This is because the direction of travel has changed due to the induction of a magnetic field in the shield. Further, by increasing the thickness of the shield or increasing the number of the shields, a high magnetic field shielding effect can be obtained. For example, in a structure in which Ni-Fe having a thickness of 100 nm is tripled, the magnetic field component parallel to the 796 A / m (10 Oe) shield outside the shield attenuates to about 40 A / m (0.5 Oe).

  When a magnetic field is incident perpendicularly to the side surface of a ferromagnetic material that is a magnetic shield, the effect of inducing the magnetic field inside the ferromagnetic material and diverting it from the memory array cannot be expected. By arranging the ferromagnetic body so as not to be perpendicular to the magnetic field from any direction, a magnetic shielding effect can be obtained from the magnetic field from any direction. For example, when the memory array is surrounded by a plurality of layers of magnetic materials that are not parallel to each other when viewed from the top surface of the wafer, there is a magnetic material that is not perpendicular to the magnetic field incident from any direction parallel to the wafer. become.

  The ferromagnetic material provided around the memory array preferably has a dimension in the direction perpendicular to the wafer larger than that of the magnetic material layer forming the magnetic recording cell in order to effectively shield the magnetism. Furthermore, when the dimension along the path surrounding the memory array is larger than the dimension in the direction perpendicular to the path surrounding the memory array and perpendicular to the path surrounding the memory array, the magnetic shape anisotropy causes an external magnetic field. Suitable for diverting from the memory array.

  In addition, the magnetic field shielding effect is improved by providing a ferromagnetic material not only in the lateral direction of the memory array but also above the memory array. The ferromagnetic material arranged above the memory array reduces the magnetic field reaching the memory array by attracting the magnetic field from the side surface of the memory array and passing it through itself. Further, the magnetic field from above the memory array is also deflected through the inside, so that the magnetic field reaching the memory array is reduced.

  The ferromagnetic material used as the magnetic shield is preferably a soft magnetic material having high magnetic permeability and saturation magnetic flux density. For example, a metal magnetic material such as a Ni—Fe alloy or soft ferrite is used.

  According to the present invention, it is possible to provide an MRAM that prevents a magnetic field that is harmful to the operation of the magnetic memory element from reaching the cell array, and that can perform long-term recording retention without malfunction. Further, since the shield is formed on a large number of chips in a wafer state, the cost can be kept low.

Embodiments of the present invention will be described below with reference to the drawings. Note that the process described below is performed on a wafer. That is, the following embodiment is performed on each chip in a state where a large number of the same chips are formed on the wafer. The wafer is cut into chips after the process according to the present invention and other predetermined processes are completed.
(First embodiment)
6 and 7 are schematic views for explaining the first embodiment of the present invention. 6 is a top view, and FIG. 7 is a cross-sectional view. For convenience of explanation, the ratio of dimensions and sizes of the memory array and the magnetic shield in the drawings is different from that of an actual device.

  The memory array 101 and other elements 102 on the wafer 100 are covered with a dielectric layer 103, for example, silicon oxide or a laminated film of silicon nitride and silicon oxide. A continuous ferromagnetic material 105 is provided on the dielectric layer 103 as a magnetic shield so as to surround the memory array 101.

  In FIG. 6, the shape viewed from above the magnetic shield is rectangular, but a part or all of the shape may be a curved surface.

  The structure shown in the first embodiment is formed by the following steps. First, as shown in FIG. 8A, the memory array 101 and other elements 102 formed on the wafer 100 are covered with a dielectric layer 103 such as silicon oxide. The dielectric layer 103 is formed by, for example, chemical vapor deposition (CVD). Next, as shown in FIG. 8C, a groove 106 for forming a ferromagnetic material serving as a magnetic shield is formed in the dielectric layer 103. The groove 106 is formed by reactive etching using, for example, a photoresist as a mask.

  Then, as shown in FIG. 8C, a ferromagnetic body 105 serving as a magnetic shield is embedded in the groove 106 formed in the previous step. The embedding of the ferromagnetic material 105 can be performed, for example, by sputtering. In the case of using a metal magnetic material such as a Ni—Fe alloy, the groove can be embedded by plating. The magnetic shielding effect can also be obtained by forming a ferromagnetic film on the inner wall surface of the groove without embedding the inside of the groove. However, since the volume of the ferromagnetic material becomes larger when embedded, the inner wall of the groove Compared with the case where a ferromagnetic film is formed on the surface, a greater effect can be expected.

  Next, as shown in FIG. 8D, the unnecessary ferromagnetic material 105 attached to the surface of the dielectric layer 103 is removed. At this time, the surface of the dielectric layer 103 can be removed and planarized. Unnecessary ferromagnetic and dielectric materials on the surface are removed by CMP (chemical mechanical polishing). Alternatively, it can be removed by etching or ion milling. Subsequently, as shown in FIG. 8E, when a metal magnetic material is used as the shield, a protective film 104 may be formed in order to protect the ferromagnetic material serving as the shield exposed on the surface. The protective film 104 is formed of a material having low reactivity with a ferromagnetic material, for example, silicon nitride. Alternatively, first, silicon nitride is deposited, and then silicon oxide is deposited.

In the structure shown in FIGS. 6 and 7, the magnetic shield is single. However, as shown in FIG. 9, the memory array 101 may be surrounded by double or more layers of the ferromagnetic material 105. As the magnetic shield is thicker, a higher magnetic shielding effect can be expected. However, when a thick shield is formed in a single layer, a wide and deep groove may not be embedded sufficiently, or the center of the groove may be recessed when the surface is polished by CMP. These problems can be solved by making the shield double or more and reducing the thickness of each shield layer. The process can be dealt with by forming a plurality of grooves formed in FIG.
(Second embodiment)
FIG. 10 is a schematic view for explaining the second embodiment, and is a view seen from above. The magnetic shield is composed of a plurality of independent ferromagnetic bodies 105A. Each of the ferromagnetic bodies 105A constituting the magnetic shield has a longer length in the direction surrounding the memory array when viewed from above than the direction perpendicular to the direction surrounding the memory array.

  A magnetic shield having a structure of a plurality of independent ferromagnets 105A can provide a magnetic shield effect even in a structure in which a single enclosure is formed as shown in FIG. 11, but a region surrounded by a shield as shown in FIG. The magnetic flux can be prevented from reaching the memory array directly by arranging the ferromagnetic bodies to overlap each other so that the path connecting the external areas with straight lines is blocked by the shield ferromagnetic body.

The magnetic shield of the second embodiment can be manufactured by the same method as that of the first embodiment. This embodiment may be used when it is difficult to form or fill a long groove or to perform CMP on the surface in the process.
(Third embodiment)
FIG. 12 is a schematic view for explaining the third embodiment of the present invention, and is a view seen from above.

  The magnetic shield is not a single layer, and is composed of two layers of ferromagnetic materials 105B and 105C having no parallel portions. With such a structure, there is a magnetic material whose surface is not perpendicular to a magnetic field incident from a direction such as parallel to the wafer surface. Therefore, it effectively exhibits a magnetic shielding effect against a magnetic field from any direction. In FIG. 12, the magnetic shield is double, but a higher magnetic shielding effect can be obtained by using three or more magnetic shields.

  The magnetic shield made of a discontinuous ferromagnetic material described in the second embodiment can be applied to the third embodiment.

The magnetic shield of the third embodiment can be manufactured by the same method as that of the first embodiment.
(Fourth embodiment)
FIG. 13 is a schematic diagram for explaining the fourth embodiment of the present invention, as viewed from the side of the wafer. FIG. 14 is a view as seen from above. Ferromagnetic materials 105 and 105D that function as magnetic shields are formed in the side direction and above the memory array, respectively. A higher magnetic shielding effect is expected when the shield in the lateral direction of the memory array and the upper shield are continuous than when the shield is discontinuous.

  The ferromagnetic material 105D disposed above the memory array shields the magnetic field from above the memory array. Also, the magnetic shield effect is shown by attracting and deflecting the magnetic field from the side surface direction of the memory array.

  A magnetic shield having a ferromagnetic material on the upper surface can be produced by the following steps. First, as shown in FIG. 15A, the memory array 101 and other elements 102 formed on the wafer 100 are covered with a dielectric layer 103 such as silicon oxide. The dielectric layer 103 is formed by, for example, a CVD method. Next, as shown in FIG. 15B, the surface of the dielectric layer 103 is flattened by CMP. Subsequently, as shown in FIG. 15C, the surface of the dielectric layer in the region where the magnetic shield having a ferromagnetic material is formed on the upper surface is recessed by etching or the like to form a recess 108. When a groove parallel to the surface of the wafer 100 is formed at the bottom of the concave portion 108, the ferromagnetic material above the memory array to be formed in FIGS. Along the magnetic anisotropy along. Giving magnetic anisotropy is effective for preferentially shielding a magnetic field from a specific direction.

  Next, as shown in FIG. 15D, a groove 106 for forming a shield surrounding the memory array 101 is formed by etching. At this time, if the groove 106 is formed inside the recess 108 formed in FIG. 15C, the ferromagnetic body 105 that forms a magnetic shield in the side surface direction of the memory array and the ferromagnetic body 105D above the memory array are continuous.

  Next, as shown in FIG. 15 (e), the grooves and the recesses formed on the surface are filled with the ferromagnetic material 109. Embedding is performed by sputtering or plating. Then, as shown in FIG. 15F, unnecessary ferromagnetic material 109 on the dielectric surface is removed by CMP. At this time, the ferromagnetic body 105D filling the recess remains without being removed by CMP, so that a structure covering the upper side of the memory array can be formed. Next, as shown in FIG. 15G, a protective film 104 is formed to protect the surface of the ferromagnetic body 105D.

  The steps of FIG. 15C and FIG. 15D can be reversed in order.

  Even if the steps after FIG. 15B are changed as follows, the magnetic shield structure according to the fourth embodiment can be formed.

  That is, as shown in FIG. 16A, the surface of the dielectric layer 103 is flattened by CMP. This step can be omitted. Next, as shown in FIG. 16B, a groove 106 for forming a shield surrounding the memory array is formed by etching. Subsequently, as shown in FIG. 16C, the surface of the dielectric layer 103 excluding the region above the memory array is covered with a resist 110. At this time, the groove 106 formed in the previous step is not covered.

  Next, as shown in FIG. 16D, a ferromagnetic material 109 is formed in the groove 106 and on the surface of the dielectric layer 103. The ferromagnetic material 109 is formed by sputtering or plating. Next, as shown in FIG. 16E, the resist 110 and the ferromagnetic material 109 formed thereon are removed by lift-off, and then the surface of the ferromagnetic material 105D is removed as shown in FIG. In order to protect, a protective film 104 is formed.

  In the fourth embodiment, a ferromagnetic material is disposed in the lateral direction and above the memory array. Here, the magnetic shield structure in the lateral direction of the memory array can be combined with any of the magnetic shields of the first, second, and third embodiments already described.

  In FIG. 13 and FIG. 14, the ferromagnetic material is arranged above the memory array and the ferromagnetic material is not arranged above the other circuits. However, by forming a magnetic shield such as communicating with the outside. Except for the case where inconvenience occurs, a ferromagnetic material may be disposed in a region other than above the memory array. In this case, for example, a pad part for connecting to the outside, such as a pad part, where it is inconvenient to place a ferromagnetic material, is not strongly recessed in the process before forming the ferromagnetic material. In the CMP process after forming the magnetic body, the ferromagnetic body can be removed. Alternatively, a region where the ferromagnetic material is not formed is covered with a resist before forming the ferromagnetic material, and the ferromagnetic material can be removed by lift-off after the ferromagnetic material is formed.

It is a cross-sectional schematic diagram of a ferromagnetic tunnel junction. It is a cross-sectional schematic diagram which shows one of the magnetic shields of the conventional MRAM. It is a cross-sectional schematic diagram which shows one of the magnetic shields of the conventional MRAM. It is a cross-sectional schematic diagram which shows one of the magnetic shields of the conventional MRAM. It is a cross-sectional schematic diagram which shows one of the magnetic shields of the conventional MRAM. It is the schematic diagram which looked at the magnetic memory by 1st Embodiment of this invention from the upper surface. 1 is a schematic cross-sectional view of a magnetic memory according to a first embodiment of the present invention. It is a figure explaining the manufacturing process of the magnetic memory by 1st embodiment of this invention. It is the schematic diagram which looked at the other example of the magnetic memory by 1st embodiment of this invention from the upper surface. It is the schematic diagram which looked at the magnetic memory by 2nd embodiment of this invention from the upper surface. It is the schematic diagram which looked at the other example of the magnetic memory by 2nd embodiment of this invention from the upper surface. It is the schematic diagram which looked at the magnetic memory by 3rd embodiment of this invention from the upper surface. It is the schematic diagram which looked at the magnetic memory by the 4th embodiment of this invention from the upper surface. It is a cross-sectional schematic diagram of the magnetic memory by 4th embodiment of this invention. It is a figure explaining the manufacturing process of the magnetic memory by the 4th embodiment of this invention. It is a figure explaining the example of a change of the manufacturing process of the magnetic memory by the 4th embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100 Wafer 2 Underlayer 3 Antiferromagnetic layer 4 Magnetization fixed layer 5 Tunnel barrier layer 6 Free layer 7 Electrode layer 8 Lead frame 9 MRAM chip 10 Wire 11 Magnetic shield member 12 Die pad 13 MRAM chip 14, 102 Other elements DESCRIPTION OF SYMBOLS 15 External lead 16 Sealant 17 Magnetic shield film 18 Semiconductor chip 19 Package 20 Magnetic particle 21 Memory array block 22, 103 Dielectric layer 23 Auxiliary shield layer 24 Main shield layer 101 Memory array 104 Protective film 105, 105A, 105B, 105C, 105D, 109 Ferromagnetic material 106 Groove 108 Recess 110 Resist

Claims (9)

A memory array including a magnetic storage element and a dielectric layer covering the memory array, and a ferromagnetic material surrounding the memory array is disposed around the memory array of the dielectric layer. And magnetic memory. The magnetic memory according to claim 1, wherein the ferromagnetic material surrounding the memory array is continuous along a path surrounding the memory array. The magnetic memory according to claim 1, wherein the ferromagnetic material surrounding the memory array is discontinuous along a path surrounding the memory array. When the outside of the region surrounded by the ferromagnetic material surrounding the memory array and the memory array is connected by an arbitrary straight line parallel to the surface of the memory array, the straight line intersects the ferromagnetic material surrounding the memory array. The magnetic memory according to claim 3. A ferromagnetic material that intersects the memory array and an area surrounded by the ferromagnetic material surrounding the memory array with an arbitrary straight line parallel to the surface of the memory array at an angle that is not perpendicular to the straight line. The magnetic memory according to claim 1, wherein the magnetic memory is provided. 6. The second ferromagnetic material according to claim 1, wherein a second ferromagnetic material is disposed in a region above the memory array of the dielectric layer covering the memory array. Magnetic memory. The magnetic memory according to claim 6, wherein the second ferromagnetic material arranged in a region above the memory array is continuous with the ferromagnetic material surrounding the memory array. A step of covering a memory array including a magnetic memory element with a dielectric layer; a step of forming a groove surrounding the memory array in the dielectric layer; and forming a ferromagnetic material in the groove formed in the dielectric layer The manufacturing method of the magnetic memory characterized by including the process to do. Covering a memory array including a magnetic storage element with a dielectric layer; forming a region of the dielectric layer above the memory array in a region whose surface is lower than the surroundings; and a groove surrounding the memory array Forming a dielectric, and forming a ferromagnetic material in a region where the surface formed above the memory array of the dielectric is lower than the surroundings and in the groove formed in the dielectric layer. A method of manufacturing a magnetic memory.

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