Magnetic tunnel junction (mtj) stack with top magnetic pinning layer having strong perpendicular magnetic anisotropy

Abstract

A top pinned magnetic tunnel junction (MTJ) stack including a magnetic pinned layer structure having a second magnetic pinned layer with strong perpendicular magnetic anisotropy (PMA) is provided. The magnetic pinned layer structure includes a grain growth control layer between a first magnetic pinned layer having a body-centered cubic (BCC) texture and the second magnetic pinned layer. The presence of the grain growth control layer facilitates the formation of the second magnetic pinned layer having a face-centered cubic (FCC) texture or a hexagonal close-packed (HCP) texture, which in turn promotes the strong PMA for the second magnetic pinned layer in the magnetic pinned layer structure.

Description

Technical Field

[0001] This application relates to a magnetoresistive random access memory (MRAM). More specifically, this application relates to a top-pinned magnetic tunnel junction (MTJ) stack comprising a magnetic pinning layer structure including a second magnetic pinning layer having strong perpendicular magnetic anisotropy (PMA). Background Technology

[0002] Spin-transfer torque (STT) MRAM devices use a two-terminal device comprising an MTJ stack containing a magnetically pinned (reference) layer, a tunnel barrier layer, and a magnetically free layer. MTJ stacks can be classified into two types. The first type of MTJ stack is a bottom-pinned MTJ stack, such as that shown in Figure 1. The bottom-pinned MTJ stack shown in Figure 1 includes a magnetically pinned (or reference) layer 10, a tunnel barrier layer 12, and a magnetically free layer 14. An MTJ capping layer 16 is typically present on the magnetically free layer 14 in the bottom-pinned MTJ stack shown in Figure 1. In Figure 1, arrows within the magnetically pinned layer 10 indicate the possible orientation of that layer, and double-headed arrows in the magnetically free layer 14 illustrate that the orientation of that layer can be switched.

[0003] The second type of MTJ stack is the top-pinned MTJ stack, as shown in Figure 2. A top-pinned MTJ stack includes a magnetic free layer 20, a tunnel barrier layer 22, and a magnetically pinned (or reference) layer 24. An MTJ capping layer 26 is typically present on the magnetically pinned layer 24 in the top-pinned MTJ stack shown in Figure 2. In Figure 2, arrows within the magnetically pinned layer 24 indicate the possible orientations of the layer, and double-headed arrows in the magnetic free layer 20 illustrate that the orientation of the layer can be switched.

[0004] In STT MRAM, the MTJ stack requires a selection transistor because two currents in opposite directions perform the write operation on the MTJ stack. In a typical STT MRAM, the threshold voltage switching current I for the antiparallel configuration is... c (P(parallel state) → AP(antiparallel state)) is greater than the threshold voltage switching current I used for parallel configuration. c (AP→P). However, the drive power of the transistor also has an asymmetry that is incompatible with the write current asymmetry of conventional bottom-pinned MTJ (BP-MTJ) stacks, in which a pinned synthetic antiferromagnetic (SAF) reference layer is deposited below the tunnel barrier layer for improved material texturing from the metal seed layer.

[0005] STT MRAM devices with top-pinned MTJ (TP-MTJ) stacks address this asymmetry issue and thus improve the power efficiency of STT MRAM devices. However, fabricating stable TP-MTJ stacks compatible with high-temperature annealing cycles (the 400°C back-end process (BEOL) required for embedded memory applications) is challenging. This is due to uncontrolled texturing on top of the tunnel barrier layer after high-temperature processing, making it difficult to fabricate a 400°C-compatible top SAF reference layer. Summary of the Invention

[0006] A top-pinned magnetic tunnel junction (MTJ) stack with a magnetically pinned layered structure is provided, the magnetically pinned layered structure including a second magnetically pinned layer with strong perpendicular magnetic anisotropy (PMA). In this application, the magnetically pinned layered structure includes a grain growth control layer located between a first magnetically pinned layer having a body-centered cubic (BCC) texture and a second magnetically pinned layer. The presence of the grain growth control layer facilitates the formation of a second magnetically pinned layer having a face-centered cubic (FCC) texture or a hexagonal close-packed (HCP) texture, thereby promoting strong PMA for the second magnetically pinned layer in the magnetically pinned layered structure. "Strong PMA" refers to an in-field magnetic anisotropy greater than 4 kOe.

[0007] In one aspect of this application, a top-pinned MTJ stack is provided. In one embodiment, the top-pinned MTJ stack includes a magnetic free layer with a body-centered cubic (BCC) texture, a tunnel barrier layer with a BCC texture located on the magnetic free layer, and a magnetic pinning layer structure located on the tunnel barrier layer. According to this application, the magnetic pinning layer structure includes, from bottom to top, a first magnetic pinning layer with a BCC texture, a grain growth control layer, and a second magnetic pinning layer with a face-centered cubic (FCC) texture or a hexagonal close-packed (HCP) texture.

[0008] In some embodiments, the second magnetic pinning layer includes a lower magnetic pinning region and an upper magnetic pinning region, wherein the lower magnetic pinning region and the upper magnetic pinning region are separated by a synthetic antiferromagnetic coupling layer. In such embodiments, both the lower magnetic pinning region and the upper magnetic pinning region have an FCC texture or an HCP texture, and thus provide strong PMA.

[0009] In another aspect of this application, an STT MRAM device is provided. In one embodiment, the STT MRAM device includes a top-pinned MTJ stack located on the surface of a bottom electrode. In one embodiment, the top-pinned MTJ stack includes a magnetic free layer with a BCC texture, a tunnel barrier layer with a BCC texture located on the magnetic free layer, and a magnetic pinning layer structure located on the tunnel barrier layer. According to this application, the magnetic pinning layer structure includes, from bottom to top, a first magnetic pinning layer with a BCC texture, a grain growth control layer, and a second magnetic pinning layer with an FCC texture or an HCP texture.

[0010] In another embodiment of this application, a method for forming a top-pinned MTJ stack is provided. In one embodiment, the method includes forming a tunnel barrier layer with a body-centered cubic (BCC) texture on a magnetic free layer. Next, a first magnetic pinning layer with a BCC texture is formed on the tunnel barrier layer. Then, a grain growth control layer is deposited on the first magnetic pinning layer, wherein the grain growth control layer facilitates the formation of magnetic materials with face-centered cubic (FCC) or hexagonal close-packed (HCP) textures. Then, a second magnetic pinning layer with an FCC or HCP texture is formed on the grain growth control layer. According to this application, in-situ annealing is performed after the grain growth control layer is deposited.

[0011] In some embodiments of this application, in-situ annealing is performed after the grain growth control layer has been deposited but before the formation of the second magnetic pinning layer. In other embodiments of this application, in-situ annealing is performed after the grain growth control layer has been deposited and after at least a portion of the second magnetic pinning layer has been formed. Attached Figure Description

[0012] Figure 1 is a cross-sectional view of a prior art bottom-pinned MTJ stack, which includes a magnetic pinning (or reference) layer, a tunnel barrier layer, a magnetic free layer, and an MTJ capping layer from bottom to top.

[0013] Figure 2 is a cross-sectional view of a prior art top-pinned MTJ stack, which includes a magnetic free layer, a tunnel barrier layer, a magnetic pinning (or reference) layer and an MTJ capping layer from bottom to top.

[0014] Figure 3 This is a cross-sectional view of a top-pinned MTJ stack located on the surface of the bottom electrode according to this application.

[0015] Figure 4 This is a cross-sectional view of another top-pinned MTJ stack located on the surface of the bottom electrode according to this application.

[0016] Figures 5A-5CThis is a graph showing the out-of-plane hysteresis loop of the top-pinned MTJ stack after BEOL at 400°C according to this application.

[0017] Figures 6A-6C This is a graph showing the in-plane hysteresis loop of the top-pinned MTJ stack after BEOL at 400°C according to this application. Detailed Implementation

[0018] This application will now be described in more detail with reference to the following discussion and the accompanying drawings. It should be noted that the drawings provided in this application are for illustrative purposes only, and therefore are not drawn to scale. It should also be noted that identical and corresponding elements are referred to by the same reference numerals.

[0019] In the following description, numerous specific details, such as specific structures, components, materials, dimensions, processing steps, and techniques, are set forth in order to provide an understanding of different embodiments of this application. However, those skilled in the art will understand that various embodiments of this application can be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail to avoid obscuring the application.

[0020] It will be understood that when a component, as a layer, region, or substrate, is described as being "on" or "above" another component, it may be directly on the other component, or there may be intermediate components. Conversely, when a component is described as being "directly on" or "directly above" another component, there are no intermediate components. It should also be understood that when a component is described as being "below" or "under" another component, it may be directly below or under the other component, or there may be intermediate components. Conversely, when a component is described as being "directly below" or "directly under" another component, there are no intermediate components.

[0021] This application provides a top-pinned magnetic tunnel junction (MTJ) stack comprising a magnetic pinning layer structure, the magnetic pinning layer structure including a second magnetic pinning layer with a strong PMA (i.e., an in-field magnetic anisotropy greater than 4 kOe). In this application, the magnetic pinning layer structure includes a grain growth control layer located between a first magnetic pinning layer having a BCC texture and a second magnetic pinning layer. The presence of the grain growth control layer facilitates the formation of a second magnetic pinning layer having an FCC texture or an HCP texture, thereby promoting a strong PMA for the second magnetic pinning layer in the magnetic pinning layer structure, as defined above. The second magnetic pinning layer in the top-pinned magnetic tunnel junction (MTJ) stack maintains a strong PMA even after performing a BEOL annealing process at 400°C or above for embedded memory applications.

[0022] In this application, the term "face-centered cubic texture or FCC texture" refers to a crystal structure having a unit cell consisting of atoms at each corner of a cube and atoms at the center of each face; it is a close-packed plane, where it is assumed that the atoms on each face of the cube are in contact along the face diagonals. The term "body-centered cubic texture or BCC texture" refers to a crystal structure having a unit cell with one atom in the center and four other atoms arranged around it at the corners of the cube to form a cubic-shaped lattice. The term "hexagonal close-packed texture or HCP texture" refers to a crystal structure having a unit cell consisting of three layers of atoms, where the top and bottom layers contain six atoms at the corners of the hexagons and one atom at the center of each hexagon, and the middle layer contains three atoms located between the atoms of the top and bottom layers.

[0023] First refer to Figure 3-4 This illustrates different top-pinned MTJ stacks according to this application. Figure 3 and 4 As shown in each of them, the top-pinned MTJ stack is located on the bottom electrode 30. It should be noted that... Figure 3 The top-pinned MTJ stack shown includes a magnetic free layer 32 with a BCC texture, a tunnel barrier layer 34 with a BCC texture on the magnetic free layer 32, and a magnetic pinning layer structure 36 on the tunnel barrier layer 34. According to this application, the magnetic pinning layer structure 36 includes, from bottom to top, a first magnetic pinning layer 38 with a BCC texture, a grain growth control layer 40, and a second magnetic pinning layer 42 with an FCC texture or an HCP texture.

[0024] Figure 4 The illustrated top-pinned MTJ stack includes a magnetic free layer 32 with a BCC texture, a tunnel barrier layer 34 with a BCC texture on the magnetic free layer 32, and a magnetic pinning layer structure 36 on the tunnel barrier layer 34. According to this application, the magnetic pinning layer structure 36 includes, from bottom to top, a first magnetic pinning layer 38 with a BCC texture, a grain growth control layer 40, and a second magnetic pinning layer 42 with an FCC texture or an HCP texture. In this embodiment, the second magnetic pinning layer 42 includes a lower magnetic pinning region 44 and an upper magnetic pinning region 48, wherein the lower magnetic pinning region 44 and the upper magnetic pinning region 48 are separated by a synthetic antiferromagnetic coupling layer 46.

[0025] In any embodiment, the bidirectional arrows in the magnetic free layer 32 indicate that the orientation in that layer can be switched, while the unidirectional arrows in different magnetic layers or regions in the magnetic pinning layer structure 36 indicate that the orientation in those layers or regions is fixed. Furthermore, and in any embodiment, the grain growth control layer facilitates the formation of the second magnetic pinning layer 42 with FCC or HCP textures, thereby promoting strong PMA of the second magnetic pinning layer 42 in the magnetic pinning layer structure 36.

[0026] Now we will describe it in more detail. Figure 3-4 The various elements / components of the structure shown. As described above, Figure 3 and 4 The top-pinned MTJ stack shown is located on the bottom electrode 30. Commonly, for example, as... Figure 3-4 The bottom electrode 30 and top pinned MTJ stack shown in this application provide components / elements for an STT MRAM device. Figure 3-4 In the illustrated structure, the bottom electrode 30 is typically located on the surface of a conductive structure (not shown). The conductive structure is embedded in an interconnect dielectric material layer (also not shown). Another interconnect dielectric material layer (not shown) may be embedded... Figure 3-4 The example shown is a top-pinned MTJ stack. Another conductive structure and a top electrode (neither shown) may be located in... Figure 3-4 The example is shown above the top surface of the top-pinned MTJ stack. The bottom electrode 30 can be made of a conductive material, such as a conductive metal, a conductive metal alloy, or a conductive metal nitride. Examples of conductive metals that can be used to provide the bottom electrode 30 include, but are not limited to, copper (Cu), ruthenium (Ru), cobalt (Co), rhodium (Rh), tungsten (W), aluminum (Al), tantalum (Ta), or titanium (Ti). Examples of conductive metal alloys that can be used to provide the bottom electrode 30 include, but are not limited to, Cu-Al, and examples of conductive metal nitrides that can be used to provide the bottom electrode 30 include, but are not limited to, TaN or TiN. The bottom electrode 30 can be formed using techniques known to those skilled in the art. The conductive material providing the bottom electrode 30 can be formed using deposition processes such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), sputtering, or electroplating. The bottom electrode 30 can have a thickness from 10 nm to 200 nm; although other thicknesses are possible and can be used as the thickness of the bottom electrode 30. The bottom electrode 30 can be formed on a recessed or non-recessed surface of a conductive structure (not shown).

[0027] Although not shown in the accompanying drawings, the metal seed layer is typically, but not always, located between the bottom electrode 30 and the magnetic free layer 32. When present, the metal seed layer is formed on the physically exposed surface of the bottom electrode 30. The metal seed layer used in this application facilitates the growth of a magnetic free layer with a body-centered cubic (BCC) texture. In one embodiment, the metal seed layer may consist of a bilayer of tantalum (Ta) and ruthenium (Ru). In another embodiment, the metal seed layer may consist of a bilayer of Ta and platinum (Pt). The metal seed layer may have a total thickness from 1 nm to 50 nm. The metal seed layer may be formed using deposition processes including, for example, CVD, PECVD, physical vapor deposition (PVD), atomic layer deposition (ALD), or sputtering.

[0028] Then, a magnetic free layer 32 with a BCC texture is formed on the metal seed layer or the bottom electrode 30. The magnetic free layer 32 is composed of at least one magnetic material with magnetization, the orientation of which can be varied relative to the magnetization orientation of the magnetic pinning (i.e., reference) layer. Exemplary magnetic materials for the magnetic free layer 32 include alloys and / or multilayers of cobalt (Co), iron (Fe), cobalt-iron (Co-Fe) alloys, nickel (Ni), nickel-iron (Ni-Fe) alloys, and cobalt-iron-boron (Co-Fe-B) alloys. Typically, the magnetic free layer 32 consists of multilayers of Co or multilayers of Co alloys containing at least 50 atomic percent Co. The magnetic free layer 32 that can be used in this application can have a thickness of 1 nm to 3 nm; although other thicknesses can be used for the magnetic free layer 32. The magnetic free layer 32 can be formed using deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0029] The tunnel barrier layer 34 with a BCC texture is made of an insulating material and formed to a thickness that provides suitable tunneling resistance. Exemplary materials for the tunnel barrier layer 34 include magnesium oxide, aluminum oxide, and titanium oxide, or materials with high tunnel conductivity, such as semiconductors or low bandgap insulators. In one embodiment, magnesium oxide is used as the material to provide the tunnel barrier layer 34. The thickness of the tunnel barrier layer 34 can be from 0.5 nm to 1.5 nm; although other thicknesses can be used for the tunnel barrier layer 34, as long as the selected thickness provides the desired tunnel barrier resistance. The tunnel barrier layer 34 can be formed using deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0030] Then, a magnetically pinned layered structure 36 is formed on the tunnel barrier layer 34. Figure 3 In the illustrated embodiment, the magnetic pinning layer structure 36 includes, from bottom to top, a first magnetic pinning layer 38 with a BCC texture, a grain growth control layer 40, and a second magnetic pinning layer 42 with an FCC texture or an HCP texture. Figure 4 In the illustrated embodiment, the magnetic pinning layered structure 36 includes, from bottom to top, a first magnetic pinning layer 38 with a BCC texture, a grain growth control layer 40, a lower magnetic pinning region 44, and an upper magnetic pinning region 48, wherein the lower magnetic pinning region 44 and the upper magnetic pinning region 48 are separated by a synthetic antiferromagnetic coupling layer 46. Figure 4 In the illustrated embodiment, the lower magnetic pinning region 44, the synthetic antiferromagnetic coupling layer 46, and the upper magnetic pinning region 48 constitute a second magnetic pinning layer 42 having an FCC texture or an HCP texture. In any embodiment, the magnetic pinning layer structure 36 may be formed using deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0031] The first magnetic pinning layer 38 with a BCC texture used in this application has fixed magnetization. The magnetic material used to provide the first magnetic pinning layer 38 may be selected to optimize the barrier at the interface of the tunnel barrier layer 36. Examples of such optimization may include high tunnel magnetoresistance (TMR), high interface anisotropy, or good interface wetting. Thus, in some embodiments, the first magnetic pinning layer 38 may be composed of a metal or metal alloy comprising one or more metals exhibiting high spin polarization. In alternative embodiments, exemplary metals used to form the first magnetic pinning layer 38 include iron, nickel, cobalt, chromium, boron, and manganese. Exemplary metal alloys may include the metals listed above (i.e., iron, nickel, cobalt, chromium, boron, and manganese). In some embodiments, the first magnetic pinning layer 38 is composed of a multilayer stack of a cobalt-iron-boron (Co-Fe-B) alloy or a Co-Fe-B alloy containing additional iron. A metal intercalation layer may be present in the Co-Fe-B alloy multilayer stack, wherein the metal intercalation layer comprises tungsten (W), tantalum (Ta), iridium (Ir), or terbium (Tb). The first magnetic pinning layer 38 can be formed using deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering. The first magnetic pinning layer 38 can have a thickness of 3 nm to 20 nm; however, other thicknesses can be used for the first magnetic pinning layer 38.

[0032] Then, a grain growth control layer 40 is formed on the first magnetic pinning layer 38. The grain growth control layer 40 is composed of a metal that facilitates the formation of a magnetic material with FCC or HCP textures. Exemplary examples of metals that facilitate the formation of magnetic materials with FCC or HCP textures include rhodium (Rh), gadolinium (Gd), holmium (Ho), tantalum (Ta), hafnium (Hf), or tungsten (W). The thickness of the grain growth control layer 40 can be from 0.05 nm to 2 nm. In some examples, the grain growth control layer 40 includes an Rh layer with a thickness of 0.5 nm, an Rh layer with a thickness of 1 nm, or an Rh layer with a thickness of 1.5 nm.

[0033] The grain growth control layer 40 can be formed using deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering. In-situ annealing is performed after the grain growth control layer 40 is deposited. In-situ annealing is crucial for providing FCC or HCP texture for the subsequently formed second magnetic pinning layer 42. Without in-situ annealing, the second magnetic pinning layer has a BCC texture and therefore cannot achieve strong PMA.

[0034] In some embodiments, in-situ annealing is performed after the grain growth control layer 40 has been deposited but before the formation of the second magnetic pinning layer 42. In other embodiments, in-situ annealing is performed after the grain growth control layer 40 has been deposited and after at least a portion of the second magnetic pinning layer 42 has been formed. In this embodiment, in-situ annealing may be performed when only a portion or all of the second magnetic pinning layer 42 is formed.

[0035] In any embodiment, in-situ annealing is performed in an inert environment (i.e., the atmosphere) at a temperature of 300°C to 400°C for a period of 1 to 3 hours. Exemplary inert environments include, but are not limited to, helium, argon, or helium-argon mixtures.

[0036] exist Figure 3 In the embodiment shown, the second magnetic pinning layer 42 has fixed magnetization. In one embodiment, Figure 3 The second magnetic pinning layer 42 of the top-pinned MTJ stack shown may be composed of a metal or metal alloy comprising one or more metals exhibiting high spin polarization. In an alternative embodiment, for forming Figure 3 Exemplary metals of the second magnetic pinning layer 42 in the top pinned MTJ stack shown include iron, nickel, cobalt, chromium, boron, and manganese. Exemplary metal alloys may include the metals listed above (i.e., iron, nickel, cobalt, chromium, boron, and manganese). In some embodiments, Figure 3 The second magnetic pinning layer 42 of the top pinned MTJ stack shown is composed of a multilayer or superlattice of cobalt (Co) and platinum (Pt), a multilayer or superlattice of cobalt (Co) and palladium (Pd), or a multilayer or superlattice of cobalt (Co), nickel (Ni) and platinum (Pt). Figure 3 The second magnetic pinning layer 42 in the top pinned MTJ stack shown can be formed using deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering. Figure 3 The second magnetic pinning layer 42 in the top pinned MTJ stack shown may have a thickness of 3 nm to 20 nm; however, other thicknesses may be used for the second magnetic pinning layer 42.

[0037] In some embodiments, such as Figure 4As shown, the second magnetic pinning layer 42 can be a multilayer arrangement having (1) a highly spin-polarized region formed of a metal and / or a metal alloy using the aforementioned metals (i.e., iron, nickel, cobalt, chromium, boron, and manganese) and (2) regions composed of one or more materials exhibiting strong perpendicular magnetic anisotropy (strong PMA). Exemplary materials with strong PMA that can be used include metals such as cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), iridium (Ir), or ruthenium (Ru), and they can be arranged in alternating layers. The strong PMA region can also include alloys exhibiting strong PMA, wherein exemplary alloys include cobalt-iron-terbium, cobalt-iron-gadolinium, cobalt-chromium-platinum, cobalt-platinum, cobalt-palladium, iron-platinum, and / or iron-palladium. Alloys can be arranged in alternating layers. In one embodiment, a combination of these materials and regions may also be employed. Figure 4 In the illustrated embodiment, the second magnetic pinning layer 42 includes a lower magnetic pinning region 44 and an upper magnetic pinning region 48, wherein the lower magnetic pinning region 44 and the upper magnetic pinning region 48 are separated by a synthetic antiferromagnetic coupling layer 46. In such an embodiment, the lower magnetic pinning region 44 and the upper magnetic pinning region 48 may be composed of a multilayer or superlattice of cobalt (Co) and platinum (Pt), a multilayer or superlattice of cobalt (Co) and palladium (Pd), or a multilayer or superlattice of cobalt (Co), nickel (Ni) and platinum (Pt), and the synthetic antiferromagnetic coupling layer 46 is composed of a metal such as cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), iridium (Ir), or ruthenium (Ru). Figure 4 The second magnetic pinning layer 42 in the top pinned MTJ stack shown can be formed using one or more deposition processes, including, for example, CVD, PECVD, PVD, ALD, or sputtering. Figure 4 The second magnetic pinning layer 42 in the top pinned MTJ stack shown may have a thickness of 3 nm to 20 nm; however, other thicknesses may be used for the second magnetic pinning layer 42. The synthetic antiferromagnetic coupling layer 46 within the second magnetic pinning layer 42 may have a thickness of 0.2 nm to 0.8 nm.

[0038] MTJ capping (not shown) is typically formed on Figure 3 and Figure 4 The second magnetic pinning layer 42 shown in any of the above is used. The MTJ capping layer is preferably composed of magnesium oxide (MgO). Other materials used for the MTJ capping layer include aluminum oxide (Al2O3), calcium oxide (CaO), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), or, for example, Mg. y Ti( 1-y )O xThe MTJ capping layer can have a thickness of 0.3 nm to 2 nm; other thicknesses are possible and can be used as the thickness of the MTJ capping layer in this application. The MTJ capping layer can be formed using one or more deposition processes, including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0039] A hard mask (not shown) is typically formed over the MTJ overlay. The hard mask may be composed of a metal nitride such as tantalum nitride (TaN) or titanium nitride (TiN), or a metal such as titanium (Ti) or tantalum (Ta). In some embodiments, the hard mask may be used as the top electrode in an STT MRAM device. In other embodiments, a separate top electrode (composed of one of the conductive materials described above for the bottom electrode 30) may be formed on the hard mask. The hard mask may have a thickness from 50 nm to 1500 nm; although other thicknesses may be used for the hard mask in this application.

[0040] The top-pinned MTJ stack (and MTJ capping layer and hard mask) of this application can be formed by depositing different material layers that provide the specific top-pinned MTJ stack (and MTJ capping layer and hard mask) of this application, followed by patterning processes such as photolithography and etching. The top-pinned MTJ stack (and MTJ capping layer and hard mask) of this application may have a critical dimension (CD) less than or equal to the critical dimension (CD) of the bottom electrode 30. The deposition of the various material layers that provide the top-pinned MTJ stack (and MTJ capping layer and hard mask) of this application can be performed in the same deposition tool or different deposition tools.

[0041] The top-pinned MTJ stack of this application is stable during high-temperature annealing cycles (400°C back-end process (BEOL) required for embedded memory applications). This is due to the controlled texturing of the second magnetic pinning layer 42, which is obtained using the grain growth control layer 40 as described above and in-situ annealing.

[0042] This is observed Figure 5A , Figure 5B , Figure 5C , Figure 6A , Figure 6B and Figure 6C The data shown is used as an example. It is worth noting that... Figures 5A-5C This is a graph showing the out-of-plane hysteresis loop of a top-pinned MTJ stack according to this application after BEOL at 400°C, and... Figures 6A-6C This is a graph showing the in-plane hysteresis loop of a top-pinned MTJ stack according to this application after BEOL at 400°C. Used for generating Figure 5A , 5BThe top pinned MTJ stacks in the curves shown in 5C, 6A, 6B, and 6C are expected to have the same thickness for the rhodium (Rh) grain growth control layer. This is used to generate... Figure 5A , 5B In the top-pinned MTJ stacks shown in 5C, 6A, 6B, and 6C, the BCC texture is located below the grain growth control layer, while the FCC texture is located above the grain growth control layer. Each top-pinned MTJ stack includes a Ta metal seed, a Co-Fe-B magnetic free layer, a magnesium oxide tunnel barrier layer, a Co-Fe-B first magnetic pinning layer, an Rh grain growth control layer (with varying thicknesses), and a multilayered second magnetic free layer of Co and Pt. Figure 5A and 6A The data shown indicates that the Rh grain growth control layer has a thickness of 0.5 nm. Figure 5B and 6B The data shown indicates that the Rh grain growth control layer has a thickness of 1 nm, and for Figure 5C and 6C The data shown indicates that the Rh grain growth control layer has a thickness of 1.5 nm. Out-of-plane and in-plane hysteresis loops were generated using a vibrating sample magnetometer (VSM).

[0043] While this application has been specifically shown and described with respect to its preferred embodiments, those skilled in the art will understand that foregoing and other changes to form and detail may be made without departing from the scope of this application. Therefore, this application is intended not to be limited to the exact forms and details described and exemplified, but rather to fall within the scope of the appended claims.

Claims

1. A top pinned magnetic tunnel junction (MTJ) stack, comprising: a magnetic free layer having a body centered cubic (BCC) texture; a tunnel barrier layer having a BCC texture and located on the magnetic free layer; and a magnetic pinning stack located on the tunnel barrier layer, wherein the magnetic pinning stack comprises, from bottom to top, a first magnetic pinning layer having a BCC texture, a grain growth control layer, and a second magnetic pinning layer having a face centered cubic (FCC) texture or a hexagonal close packed (HCP) texture, wherein the grain growth control layer is composed of a metal that favors formation of a magnetic material having the FCC texture or the HCP texture, the metal comprising rhodium, gadolinium, or holmium, wherein the second magnetic pinning layer has an in-field magnetic anisotropy field greater than 4 kOe. the second magnetic pinning layer comprises a lower magnetic pinning region and an upper magnetic pinning region, wherein the lower magnetic pinning region and the upper magnetic pinning region are separated by a synthetic antiferromagnetic coupling layer.

2. The top pinned MTJ stack of claim 1, wherein, the grain growth control layer has a thickness of 0.05 nm to 2 nm.

3. The top pinned MTJ stack of claim 1, wherein, the first magnetic pinning layer is composed of a Co-Fe-B alloy or a Co-Fe-B alloy multilayer stack containing additional iron.

4. The top pinned MTJ stack of claim 1, wherein, a metal insertion layer is present in the Co-Fe-B alloy multilayer stack, wherein the metal insertion layer comprises tungsten, tantalum, iridium, or terbium.

5. The top pinned MTJ stack of claim 4, further comprising: the second magnetic pinning layer is composed of a multilayer or superlattice of cobalt and platinum, a multilayer or superlattice of cobalt and palladium, or a multilayer or superlattice of cobalt, nickel, and platinum.

6. The top pinned MTJ stack of claim 1, wherein, 7. A spin transfer torque magnetoresistive random access memory (STT MRAM) device, comprising: a top pinned magnetic tunnel junction (MTJ) stack located on a bottom electrode, wherein the top pinned MTJ stack comprises: a magnetic free layer having a body centered cubic (BCC) texture; a tunnel barrier layer having a BCC texture and located on the magnetic free layer; and a magnetic pinning stack located on the tunnel barrier layer, wherein the magnetic pinning stack comprises, from bottom to top, a first magnetic pinning layer having a BCC texture, a grain growth control layer, and a second magnetic pinning layer having a face centered cubic (FCC) texture or a hexagonal close packed (HCP) texture, wherein the grain growth control layer is composed of a metal that favors formation of a magnetic material having the FCC texture or the HCP texture, the metal comprising rhodium, gadolinium, or holmium, the second magnetic pinning layer has an in-field magnetic anisotropy field greater than 4 kOe. the second magnetic pinning layer comprises a lower magnetic pinning region and an upper magnetic pinning region, wherein the lower magnetic pinning region and the upper magnetic pinning region are separated by a synthetic antiferromagnetic coupling layer.

8. The STT MRAM device of claim 7, wherein, the grain growth control layer has a thickness of 0.05 nm to 2 nm.

9. The STT MRAM device of claim 7, wherein, the first magnetic pinning layer is composed of a Co-Fe-B alloy or a Co-Fe-B alloy multilayer stack containing additional iron.

10. The STT MRAM device of claim 9, wherein, a metal insertion layer is present in the Co-Fe-B alloy multilayer stack, wherein the metal insertion layer comprises tungsten, tantalum, iridium, or terbium.

11. The STT MRAM device of claim 10, further comprising: the second magnetic pinning layer is composed of a multilayer or superlattice of cobalt and platinum, a multilayer or superlattice of cobalt and palladium, or a multilayer or superlattice of cobalt, nickel, and platinum.

12. The STT MRAM device of claim 7, wherein, ​ 13. A method of forming a top-pinned magnetic tunnel junction (MTJ) stack, the method comprising: forming a tunnel barrier layer having a body-centered cubic (BCC) texture on a magnetic free layer having a BCC texture; forming a first magnetic pinned layer having a BCC texture on the tunnel barrier layer, depositing a grain growth control layer on the first magnetic pinned layer, wherein the grain growth control layer facilitates formation of a magnetic material having a face-centered cubic (FCC) texture or a hexagonal close-packed (HCP) texture, the grain growth control layer consisting of rhodium, gadolinium, or holmium; and forming a second magnetic pinned layer having the FCC texture or the HCP texture on the grain growth control layer, wherein an in-situ anneal is performed after depositing the grain growth control layer, wherein the second magnetic pinned layer has an in-field magnetic anisotropy field greater than 4 kOe.

14. The method of claim 13, wherein, the in-situ anneal is performed after depositing the grain growth control layer but before forming the second magnetic pinned layer.

15. The method of claim 13, wherein, the in-situ anneal is performed after depositing the grain growth control layer and after forming at least a portion of the second magnetic pinned layer.

16. The method of claim 13, wherein, the grain growth control layer has a thickness of 0.05 nm to 2 nm.

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