RU2753803C1 - Method for creating self-oriented magnetic sensor - Google Patents

Abstract

FIELD: microelectronics.SUBSTANCE: the substance of the invention lies in the fact that the method for creating a self-aligning magnetic sensor contains the stages at which the use of an MTJ cell with shape anisotropy is carried out, which makes it possible to exclude the stage of annealing in an external magnetic field in the technological route, which is necessary for orienting the sensitive layer.EFFECT: acceleration of the technological production process for the manufacture of MTJ magnetic sensors.2 cl, 6 dwg

Description

FIELD OF TECHNOLOGY

[0001] The present technical solution relates to the field of microelectronics, in particular to a method for creating a self-orienting magnetic sensor.

LEVEL OF TECHNOLOGY

[0002] Magnetically sensitive devices or magnetic sensors are devices that respond to an external magnetic field. Such a field, as a rule, can be formed by various types of sources, for example, magnets, electric current, magnetic field of the earth, etc. Devices operating on the basis of a magnetic tunnel junction (MTJ - Magnetic Tunnel Junction) can act as magnetic sensors. consist of at least two ferromagnetic layers separated by a thin dielectric layer. MTJ magnetic sensors are often used to create MTJ cells, which are used to create magnetoresistive memory (MRAM).

[0003] When creating an MTJ sensor, one of the layers of the ferromagnet has a fixed direction of magnetization and is called the "reference layer". The second layer of the ferromagnet has a direction of magnetization corresponding to the action of an external magnetic field, and thus forms a "sensitive layer".

[0004] There are various types of MTJ sensors that have different configurations. One of the examples of such sensors are orthogonal sensors, in which the direction of magnetization of the reference layer is orthogonally directed to the magnetization of the sensitive layer. FIG. 1 shows an example of the structure of a standard MTJ stack (10) for creating an MTJ sensor, similar to which is disclosed, for example, in US patent application US 20120049843 A1 (Everspin Technologies Inc., 01.03.2012).

[0005] The direction of the magnetization of the ferromagnets in the reference and sensing layers of the stack (10) is fixed by using an antiferromagnet layer. As shown in FIG. 1, the generally known type of MTJ stack (10) contains a bottom electrode (PO) located on the substrate, a support layer (100), which consists of an antiferromagnet layer (101), two ferromagnet layers (102, 104), and a nonmagnetic conducting layer ( 103) separating the layers of the ferromagnet (102, 104).

[0006] The sensitive layer (120) is located above a thin dielectric layer (111) separating the reference (110) and sensitive layers (120), and contains layers of ferromagnet (121) and antiferromagnet (122). Above the sensitive layer (120) is a highly resistive electrically conductive layer (112), which plays the role of the upper electrode during the formation of a contact to the MTJ cell, as well as the role of a rigid mask in plasma-chemical etching for the subsequent formation of the MTJ cell.

[0007] To provide a blocking temperature of the support layer T _b1 different from the blocking temperature of the sensitive layer Th, the layers of ferromagnets (101, 122) are made of different materials or materials with different thicknesses. Blocking temperature is the temperature at which the energy of thermal motion becomes large enough to destroy the exchange interaction at the ferromagnet / antiferromagnet interface. If the temperature exceeds the blocking temperature, then the coupling of the magnetic moments at the ferromagnet / antiferromagnet interface is lost and the direction of magnetization of the ferromagnet layer is no longer fixed.

[0008] The prior art magnetic sensor manufacturing route employs two stages of annealing in an external magnetic field in order to fix the magnetization direction of the reference and sensing layers in the MTJ cell. The first annealing in an external magnetic field is performed at a temperature higher than the blocking temperature of the reference layer T _b1 (the direction of the magnetic field during annealing is shown by the red arrow). The second annealing in an external magnetic field is usually carried out at the end of the MTJ sensor manufacturing route in order to fix the direction of magnetization of the ferromagnet layer (121) of the sensitive layer (120) in the required orthogonal direction (Fig. 2), while the temperature during the second annealing should be higher than the temperature blocking the sensitive layer T _b2 (the direction of the magnetic field during annealing is shown by the green arrow), but below the blocking temperature T _b1 , so as not to destroy the connection of magnetic moments at the ferromagnet / antiferromagnet interface in the reference layer.

[0009] Thus, the existing process for the manufacture of magnetic sensors is rather laborious and time-consuming in terms of the need to carry out two stages of annealing in an external magnetic field.

SUMMARY OF THE INVENTION

[0010] The present solution is aimed at optimizing the route of manufacturing MTJ magnetic sensors in terms of simplifying, and thereby accelerating, the technological production process by implementing a method of self-orientation of the direction of the magnetic moments of the sensitive layer in the production of MTJ magnetic sensors.

[0011] The technical result achieved by the claimed method consists in accelerating the technological production process of manufacturing magnetic MTJ sensors by using an MTJ cell with shape anisotropy, which makes it possible to exclude the stage of annealing in an external magnetic field in the technological route necessary for orienting the sensitive layer.

[0012] The claimed result is achieved by a method of creating a self-orienting magnetic sensor, in which:

an MTJ stack is formed on the lower electrode located on a dielectric substrate, which contains:

a support layer containing an antiferromagnet layer with a blocking temperature T _b1 , a first ferromagnet layer, an interlayer of non-magnetic material and a second ferromagnet layer, with the direction of magnetization of the first and second ferromagnet layers being opposite;

a barrier layer applied over the support layer;

a sensitive layer applied over the barrier layer, wherein the sensitive layer contains a ferromagnet layer and an antiferromagnet layer with a blocking temperature T _b2 ;

applying a highly resistive conductive layer over the MTJ stack to form an upper electrode of the MTJ cell;

perform magnetic annealing in the presence of an external magnetic field at a temperature T> T _b1 ;

the process of plasma-chemical etching of the upper highly resistive layer and the MTJ stack is carried out, in which an MTJ cell with an upper electrode is formed, containing a form that provides the direction of the magnetization of the sensitive layer along its long axis;

contacts are formed to the upper electrode of the MTJ cell and subsequent levels of metal wiring using high-temperature processes with a temperature T _p , and T _b1 > T _p > T _b2 , while during this stage the direction of the magnetization of the sensitive layer is automatically set orthogonal to the direction of magnetization of the reference layer along the long axis of the MTJ cell.

[0013] In a particular embodiment of the method, the magnetic sensor has the shape of an ellipse, oval, or rectangle.

BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 illustrates a prior art example of an MTJ stack for the manufacture of magnetic sensors.

[0015] FIG. 2 illustrates a top view of an MTJ sensor with the direction of magnetization during the annealing steps in an external magnetic field.

[0016] FIG. 3 is a graph showing the change in electrical resistance as a function of the magnitude of an external magnetic field.

[0017] FIG. 4A-4E illustrate the steps of the present method for forming a magnetic sensor.

[0018] FIG. 5 illustrates a top view of an MTJ sensor with possible magnetization directions of the reference layer and the sensing layer.

[0019] FIG. 6A-6B illustrate a hysteresis loop reflecting the change in resistance for two possible cases of the direction of magnetization of the sensitive layer.

CARRYING OUT THE INVENTION

[0020] The tunnel magnetoresistance of the MTJ cell will change when the relative orientation of the magnetic moment of the two ferromagnetic layers changes, and this phenomenon is known as the tunnel magnetoresistance (TMR) effect. The magnetization direction of the reference layer is fixed, and the magnetization direction of the free layer can be adjusted according to the external magnetic field (H), so the electrical resistance of the MTJ cell will also change. An MTJ cell shows the lowest resistance when the direction of magnetization of the free layer is parallel to the reference layer and a strong current flows through the barrier. On the contrary, the resistance will increase significantly when the direction of magnetization is antiparallel, so a small current flows through the barrier. FIG. 3 is a graph showing the dependence of the resistance of the MTJ cell on the direction of the applied external magnetic field (H). In this case, the field is directed perpendicular to the direction of magnetization of the sensitive field (green arrow).

[0021] A further detailed disclosure of the present technical solution will be given with reference to FIG. 4A to FIG. 4D.

[0022] As shown in FIG. 4A, the creation of a magnetic sensor (20) is based on the formation of an MTJ stack containing a lower electrode (210) located on the substrate, a support layer (200), which consists of an antiferromagnet layer (201), at least two ferromagnet layers (202, 204) and a nonmagnetic conductive layer (203) separating the layers of the ferromagnet (202, 204). The sensitive layer (220) is located above the thin dielectric layer (211) separating the reference (210) and sensitive layers (220) and contains layers of a ferromagnet (221) and an antiferromagnet (222). Above the sensitive layer (220) is a highly resistive electrically conductive layer (212), which plays the role of the upper electrode in the formation of a contact to the MTJ cell, as well as the role of a rigid mask in plasma-chemical etching for the subsequent formation of the MTJ cell.

[0023] Layers of antiferromagnets (201, 222) are made from different materials or materials with different thicknesses, so that such layers have different blocking temperatures, in particular T _b2 for layer (201) and T b2 for layer (222).

[0024] The lower electrode (210) is located on a substrate (not shown), which can be made, for example, of silicon oxide or other semiconductor material such as: Si, SiC, SiGe, SiGeC, Ge, GaAs, InAs, InP or compounds materials from Groups III-IV and their combinations. The material for forming the lower electrode (210) and the layer (212) for forming the upper electrode and the MTJ cell may be a compound selected from the group of Ta, TaN, Ti, TiN, TaSi, TaSiN, etc.

. Для слоев ферромагнетиков (111, 122) может применяться материал на основе соединений таких как: NiFe, CoFeB, NiFeX, CoFeX и др. толщина слоев также может иметь различную величину с сохранением достижения требуемого эффекта при создании магнитного сенсора (20).[0025] The material for the support layer (200) can be, for example, a CoFe, CoFeB, or combinations thereof, or other useful compounds. The layer thickness can be different, for example, from 10 to 100

... For layers of ferromagnets (111, 122), a material based on compounds such as NiFe, CoFeB, NiFeX, CoFeX, etc. can be used.The thickness of the layers can also have different values while maintaining the achievement of the required effect when creating a magnetic sensor (20).

[0026] After applying the MTJ layers and the highly resistive electrically conductive layer as shown in FIG. 4B, the annealing process is carried out in the presence of an external magnetic field (H) at a temperature T> T _b1 (the direction of the magnetic field during annealing is shown by the red arrow). The temperature range during this stage can vary depending on the materials used for antiferromagnets and their thickness, for example, for PtMn, a temperature of T> 280 ° C is required, and for IrMn, T> 220 ° C. The upper limit of the temperature range is T <400 ° C, because at this temperature the dielectric layer between the reference and sensitive layers begins to collapse.

[0027] As shown in FIG. 4B, after the layers of the MTJ stack are deposited to form the MTJ cell, a topology transfer process from the photoresist mask is carried out by plasma-chemical etching through the upper layer (212) of the conductive rigid mask, which is also the upper electrode for the MTJ cell. The MTJ cell is manufactured in a shape that guides the magnetization along its long axis, such as rectangular, oval or elliptical. This effect is known as shape anisotropy and the principle of manufacturing such elements is known from the prior art (see, for example, RU 2705175 C2, RU 2716282 C1).

[0028] During the stage of annealing in an external magnetic field, the direction of magnetization is established for the layers of ferromagnets of the reference (202, 204) and sensitive layers (221), but the direction of magnetization of the sensitive layer (220) will be parallel to the direction of magnetization of the reference layer (200 ).

[0029] In the path of contacting to cell MTJ and subsequent levels of metal wiring, high temperature processes are applied with temperatures higher than the blocking temperature T _b2 (up to T _p = 300 ° C), but less than the blocking temperature T _b1 . This leads to a reorientation of the direction of magnetization of the sensitive layer (221) in the direction orthogonal to the direction of magnetization of the layers (202, 204) of the reference layer (200).

[0030] Due to the use of this temperature effect, there is no need for a second magnetic annealing, since due to the effect of anisotropy of the MTJ cell shape, the magnetization direction of the sensitive layer (210) is automatically set orthogonal to the magnetization direction of the support layer (200) along the easy magnetization axis of the formed MTJ cell as shown in FIG. 4G-4D and Fig. 5.

[0031] The direction can be directed in two possible orthogonal directions, which will be set automatically by the shape of the MTJ cell, but the total resistance of the magnetic sensor (20) will be unchanged, as shown in the graphs of FIG. 6A-6B. The graphs show that both possible variants of the direction of magnetization of the sensitive layer (210) under the influence of an external magnetic field (H) directed perpendicular to the direction of the sensitive layer (210) will give the same values of electrical resistance.

[0032] This allows you to significantly speed up the process of manufacturing such products, by eliminating the need for a second magnetic annealing to fix in the orthogonal direction of the magnetization of the sensitive layer (210).

[0033] The presented description of the claimed solution discloses only preferred examples of its implementation and should not be construed as limiting other, particular examples of its implementation, not going beyond the scope of legal protection, which are obvious to a specialist in the relevant field of technology.

Claims (11)

1. A method of creating a self-orienting magnetic sensor, in which: a) an MTJ stack is formed on the lower electrode located on a dielectric substrate, which contains: a support layer containing an antiferromagnet layer with a blocking temperature T _b1 , a first ferromagnet layer, an interlayer of non-magnetic material and a second ferromagnet layer, with the direction of magnetization of the first and second ferromagnet layers being opposite; a barrier layer applied over the support layer; a sensitive layer applied over the barrier layer, wherein the sensitive layer contains a ferromagnet layer and an antiferromagnet layer with a blocking temperature T _b2 ; b) applying a highly resistive conductive layer over the MTJ stack to form the top electrode of the MTJ cell; c) performing magnetic annealing in the presence of an external magnetic field at a temperature T> T _b1 ; d) the process of plasma-chemical etching of the upper highly resistive layer and MTJ stack is carried out, in which forming an MTJ cell with an upper electrode, containing a shape that guides the magnetization of the sensitive layer along its long axis; f) the formation of contacts to the upper electrode of the MTJ cell and subsequent levels of metal wiring is carried out using high-temperature processes with a temperature T _p , and T _b1 > T _p > T _b2 , while during stage e) the direction of the magnetization of the sensitive layer is automatically set orthogonal to the direction magnetization of the reference layer along the long axis of the MTJ cell. 2. The method of claim 1, wherein the MTJ cell is in the shape of an ellipse, oval, or rectangle.

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