MTJ stacks containing a top magnetic pinning layer with strong perpendicular magnetic anisotropy

Abstract

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

Description

[Technical Field]

[0001] This application relates to magnetoresistive random access memories (MRAMs). More particularly, this application relates to top-pinned magnetic tunnel junction (MTJ) stacks that include a magnetic pinned layer structure that includes a second magnetic pinned layer with strong perpendicular magnetic anisotropy (PMA). [Background technology]

[0002] Spin-transfer torque (STT) MRAM devices use two-terminal devices that include an MTJ stack, which includes a magnetic pinned (or reference) layer, a tunnel barrier layer, and a magnetic free layer. MTJ stacks can be classified into two types. The first type of MTJ stack is a bottom-pinned MTJ stack, as shown in FIG. 1. The bottom-pinned MTJ stack shown in FIG. 1 includes a magnetic pinned (or reference) layer 10, a tunnel barrier layer 12, and a magnetic free layer 14. An MTJ capping layer 16 typically resides on the magnetic free layer 14 of the bottom-pinned MTJ stack shown in FIG. 1. In FIG. 1, an arrow in the magnetic pinned layer 10 indicates the possible orientations of that layer, and a double-headed arrow in the magnetic free layer 14 indicates that the orientation of that layer can be switched.

[0003] A second type of MTJ stack is a top-pinned MTJ stack, for example, as shown in Figure 2. A top-pinned MTJ stack includes a magnetic free layer 20, a tunnel barrier layer 22, and a magnetic pinned (or reference) layer 24. An MTJ capping layer 26 typically resides on the magnetic pinned layer 24 of the top-pinned MTJ stack shown in Figure 2. In Figure 2, an arrow in the magnetic pinned layer 24 indicates the possible orientations of that layer, and a double-headed arrow in the magnetic free layer 20 indicates that the orientation of that layer can be switched.

[0004] In STT MRAM, select transistors are required for the MTJ stack to perform write operations with two different current directions. In a typical STT MRAM, the threshold voltage switching current Ic (P (parallel state) → AP (antiparallel state)) for the antiparallel configuration is larger than the threshold voltage switching current Ic (AP → P) for the parallel configuration. However, the transistor drive strength also has an asymmetry, which is incompatible with the write current asymmetry of a conventional bottom-pinned MTJ (BP-MTJ) stack, which deposits a pinned synthetic antiferromagnetic (SAF) reference layer below the tunnel barrier layer to improve the material texturization from the metal seed layer.

[0005] STT MRAM devices using top-pinned MTJ (TP-MTJ) stacks can solve this asymmetry problem and therefore improve the power efficiency of STT MRAM devices. However, it is difficult to fabricate stable TP-MTJ stacks compatible with high-temperature annealing cycles (400 °C back-end-of-line (BEOL) processes required for embedded memory applications). The reason is related to the uncontrollable texture formation of the top of the tunnel barrier layer after high-temperature processing, which makes it difficult to fabricate a top SAF reference layer compatible with 400 °C. Summary of the Invention

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

[0007] In one aspect of the present application, a top-pinned MTJ stack is provided. In one embodiment, the top-pinned MTJ stack includes a magnetic free layer having a body-centered cubic (BCC) texture, a tunnel barrier layer having a BCC texture located on the magnetic free layer, and a magnetic pinned layer structure located on the tunnel barrier layer. According to the present application, the magnetic pinned layer structure includes, from bottom to top, a first magnetic pinned layer having a BCC texture, a grain growth control layer, and a second magnetic pinned layer having 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, the lower magnetic pinning region and the upper magnetic pinning region being separated by a synthetic antiferromagnetic coupling layer. In such embodiments, the lower magnetic pinning region and the upper magnetic pinning region both have FCC or HCP texture, thereby providing a strong PMA.

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

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

[0011] In some embodiments of the present application, the in-situ annealing occurs after deposition of the grain growth control layer but before formation of the second magnetic pinning layer. In other embodiments of the present application, the in-situ annealing occurs after deposition of the grain growth control layer and after formation of at least a portion of the second magnetic pinning layer. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view of a prior art bottom-pinned MTJ stack including, from bottom to top, a magnetic pinned (or reference) layer, a tunnel barrier layer, a magnetic free layer, and an MTJ capping layer. [Figure 2] 1 is a cross-sectional view of a prior art top-pinned MTJ stack including, from bottom to top, a magnetic free layer, a tunnel barrier layer, a magnetic pinned (or reference) layer, and an MTJ capping layer. [Figure 3] 1 is a cross-sectional view of a top-pinned MTJ stack according to the present application located on top of a bottom electrode. [Figure 4] FIG. 10 is a cross-sectional view of another top-pinned MTJ stack according to the present application located on top of a bottom electrode. [Figure 5A] 1 is a graph showing the out-of-plane hysteresis loop of a top-pinned MTJ stack after BEOL at 400° C. according to the present application. [Figure 5B] 1 is a graph showing the out-of-plane hysteresis loop of a top-pinned MTJ stack after BEOL at 400° C. according to the present application. [Figure 5C] 1 is a graph showing the out-of-plane hysteresis loop of a top-pinned MTJ stack after BEOL at 400° C. according to the present application. [Figure 6A] 1 is a graph showing the in-plane hysteresis loop of a top-pinned MTJ stack after BEOL at 400° C. according to the present application. [Figure 6B] 1 is a graph showing the in-plane hysteresis loop of a top-pinned MTJ stack after BEOL at 400° C. according to the present application. [Figure 6C] 1 is a graph showing the in-plane hysteresis loop of a top-pinned MTJ stack after BEOL at 400° C. according to the present application. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present application will now be described in more detail by reference to the following discussion and the drawings accompanying this application. It should be noted that the drawings in this application are provided for illustrative purposes only, and as such, the drawings are not drawn to scale. It should also be noted that like and corresponding elements are referred to by like reference numerals.

[0014] In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps, and techniques, to provide an understanding of various embodiments of the present application. However, it will be understood by those skilled in the art that various embodiments of the present application can be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order to avoid obscuring the present application.

[0015] When an element, such as a layer, region, or substrate, is referred to as being "on" or "above" another element, it will be understood that it can be directly on the other element, or that intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or "directly above" another element, there are no intervening elements present. Also, when an element is referred to as being "below" or "below" another element, it will be understood that it can be below or beneath the other element, or that intervening elements may be present. In contrast, when an element is referred to as being "directly below" or "directly below" another element, there are no intervening elements present.

[0016] The present application provides a top-pinned magnetic tunnel junction (MTJ) stack including a magnetic pinning layer structure including a second magnetic pinning layer with a strong PMA (i.e., an in-field magnetic anisotropy field greater than 4 kOe). In the present application, the magnetic pinning layer structure includes a grain growth control layer located between a first magnetic pinning layer and a second magnetic pinning layer with a BCC texture. The presence of the grain growth control layer facilitates the formation of the second magnetic pinning layer with an FCC texture or an HCP texture, which in turn promotes the strong PMA, as defined above, for the second magnetic pinning layer of the magnetic pinning layer structure. The second magnetic pinning layer of the top-pinned magnetic tunnel junction (MTJ) stack maintains its strong PMA even after back-end annealing processes at temperatures above 400°C, which are used in embedded memory applications.

[0017] 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 an atom at the center of each face of the cube, where each face of the cube is a close-packed plane considered to be a contact point along the diagonal of the face within the cube. The term "body-centered cubic texture or BCC texture" refers to a crystal structure having a unit cell in which one central atom is surrounded by eight other atoms located at the corners of the cube, forming a cubic 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, with the upper and lower layers containing six atoms at the corners of a hexagon and one atom at the center of each hexagon, and the middle layer containing three atoms located between the atoms in the upper and lower layers.

[0018] 3-4, various top-pinned MTJ stacks according to the present application are shown. As shown in each of FIGS. 3 and 4, the top-pinned MTJ stack is located on a bottom electrode 30. In particular, the top-pinned MTJ stack shown in FIG. 3 includes a magnetic free layer 32 having a BCC texture, a tunnel barrier layer 34 having a BCC texture located on the magnetic free layer 32, and a magnetic pinned layer structure 36 located on the tunnel barrier layer 34. According to the present application, the magnetic pinned layer structure 36 includes, from bottom to top, a first magnetic pinned layer 38 having a BCC texture, a grain growth control layer 40, and a second magnetic pinned layer 42 having an FCC or HCP texture.

[0019] 4 includes a magnetic free layer 32 having a BCC texture, a tunnel barrier layer 34 having a BCC texture located on the magnetic free layer 32, and a magnetic pinned layer structure 36 located on the tunnel barrier layer 34. According to the present application, the magnetic pinned layer structure 36 includes, from bottom to top, a first magnetic pinned layer 38 having a BCC texture, a grain growth control layer 40, and a second magnetic pinned layer 42 having an FCC or HCP texture. In this embodiment, the second magnetic pinned layer 42 includes a lower magnetic pinned region 44 and an upper magnetic pinned region 48, which are separated by a synthetic antiferromagnetic coupling layer 46.

[0020] In either embodiment, the double-headed arrow in the magnetic free layer 32 represents a switchable orientation in that layer, and the single-headed arrow in the various magnetic layers or regions of the magnetic pinned layer structure 36 represents a fixed orientation in those layers or regions. Also, in either embodiment, the grain growth control layer facilitates the formation of the second magnetic pinned layer 42 with an FCC or HCP texture, which in turn promotes strong PMA for the second magnetic pinned layer 42 of the magnetic pinned layer structure 36.

[0021] Various elements / components of the structure shown in FIGS. 3-4 will now be described in more detail. As mentioned above, the top-pin MTJ stack shown in FIGS. 3 and 4 is located on a bottom electrode 30. The bottom electrode 30, e.g., as shown in FIGS. 3-4, and the top-pin MTJ stack of the present application collectively provide a component / component of an STT MRAM device. The bottom electrode 30 of the structure shown in FIGS. 3-4 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 embed the top-pin MTJ stack shown in FIGS. 3-4. Another conductive structure and a top electrode (neither of which are shown) may be located on the top surface of the top-pin MTJ stack shown in FIGS. 3-4. The bottom electrode 30 may be composed of a conductive material such as, for example, 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. 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 well known to those skilled in the art. The conductive material that provides the bottom electrode 30 can be formed using a deposition process, such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), sputtering, or plating. The bottom electrode 30 can have a thickness of 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).

[0022] Although not shown in the drawings, a metal seed layer is typically, but not necessarily, disposed 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 that can be used in the present application facilitates the growth of a magnetic free layer having a body-centered cubic (BCC) texture. In one embodiment, the metal seed layer can be composed of a bilayer of tantalum (Ta) and ruthenium (Ru). In another embodiment, the metal seed layer can be composed of a bilayer of Ta and platinum (Pt). The metal seed layer can have a total thickness of 1 nm to 50 nm. The metal seed layer can be formed using a deposition process including, for example, CVD, PECVD, physical vapor deposition (PVD), atomic layer deposition (ALD), or sputtering.

[0023] A magnetic free layer 32 having a BCC texture is then formed on the metal seed layer or the bottom electrode 30. The magnetic free layer 32 is composed of at least one magnetic material whose magnetization direction can be changed relative to the magnetization direction 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 is composed of a multilayer of Co or a multilayer of a Co alloy containing at least 50 atomic % Co. The magnetic free layer 32 that can be used in the present application can have a thickness of 1 nm to 3 nm, although other thicknesses for the magnetic free layer 32 can also be used. The magnetic free layer 32 can be formed using a deposition process including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0024] The tunnel barrier layer 34 having a BCC texture is composed of an insulating material and formed to a thickness that provides an appropriate tunneling resistance. Exemplary materials for the tunnel barrier layer 34 include magnesium oxide, aluminum oxide, and titanium oxide, or materials with higher electrical tunneling conductance, such as semiconductors or low-bandgap insulators. In one embodiment, magnesium oxide is used as the material providing the tunnel barrier layer 34. The thickness of the tunnel barrier layer 34 can be 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 tunneling barrier resistance. The tunnel barrier layer 34 can be formed using a deposition process, including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0025] A magnetic pinning layer structure 36 is then formed on the tunnel barrier layer 34. In the embodiment shown in Figure 3, 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 or HCP texture. In the embodiment shown in Figure 4, the magnetic pinning layer structure 36 includes, from bottom to top, the first magnetic pinning layer 38 with a BCC texture, the grain growth control layer 40, a lower magnetic pinning region 44, and an upper magnetic pinning region 48, which are separated by a synthetic antiferromagnetic coupling layer 46. In the embodiment shown in Figure 4, the lower magnetic pinning region 44, the synthetic antiferromagnetic coupling layer 46, and the upper magnetic pinning region 48 constitute the second magnetic pinning layer 42 with an FCC or HCP texture. In either embodiment, the magnetic pinning layer structure 36 may be formed using a deposition process including, for example, CVD, PECVD, PVD, ALD, or sputtering.

[0026] The first magnetic pinning layer 38 having a BCC texture used in this application has a fixed magnetization. The magnetic material used in providing the first magnetic pinning layer 38 can be selected to optimize the barrier at the interface with the tunnel barrier layer 34. Examples of such optimizations would include high tunneling magnetoresistance (TMR), high interface anisotropy, or good interface wettability. Thus, in some embodiments, the first magnetic pinning layer 38 can be composed of a metal or metal alloy including one or more metals that exhibit high spin polarization. In alternative embodiments, exemplary metals for forming the first magnetic pinning layer 38 include iron, nickel, cobalt, chromium, boron, and manganese. Exemplary metal alloys can include the metals exemplified above (i.e., iron, nickel, cobalt, chromium, boron, and manganese). In some embodiments, the first magnetic pinning layer 38 is composed of a cobalt-iron-boron (Co—Fe—B) alloy or a Co—Fe—B alloy multilayer stack including additional iron. A metal insert layer may be present in the Co-Fe-B alloy multilayer stack, and the metal insert layer may include tungsten (W), tantalum (Ta), iridium (Ir), or terbium (Tb). The first magnetic pinning layer 38 may be formed using a deposition process including, for example, CVD, PECVD, PVD, ALD, or sputtering. The first magnetic pinning layer 38 may have a thickness of 3 nm to 20 nm, although other thicknesses may be used for the first magnetic pinning layer 38.

[0027] A grain growth control layer 40 is then 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 an FCC or HCP texture. Illustrative examples of metals that facilitate the formation of a magnetic material with an FCC or HCP texture include rhodium (Rh), gadolinium (Gd), holmium (Ho), tantalum (Ta), hafnium (Hf), or tungsten (W). The grain growth control layer 40 can have a thickness of 0.05 nm to 2 nm. In some examples, the grain growth control layer 40 includes Rh having a thickness of 0.5 nm, Rh having a thickness of 1 nm, or Rh having a thickness of 1.5 nm.

[0028] The grain growth control layer 40 can be formed using a deposition process including, for example, CVD, PECVD, PVD, ALD, or sputtering. After deposition of the grain growth control layer 40, an in-situ anneal is performed. The in-situ anneal is important for imparting an FCC or HCP texture to the subsequently formed second magnetic pinning layer 42. Without the in-situ anneal, the second magnetic pinning layer would have a BCC texture, which would not result in a strong PMA.

[0029] In some embodiments, the in-situ anneal occurs after deposition of the grain growth control layer 40 but before the formation of the second magnetic pinning layer 42. In other embodiments, the in-situ anneal occurs after deposition of the grain growth control layer 40 and after the formation of at least a portion of the second magnetic pinning layer 42. In this embodiment, the in-situ anneal can occur when only a portion or the entire second magnetic pinning layer 42 is formed.

[0030] In either embodiment, the in-situ annealing is carried out in an inert environment (i.e., ambient) at a temperature of 300° C. to 400° C. for a time period of 1 to 3 hours. Exemplary inert environments include, but are not limited to, helium, argon, or a helium-argon mixture.

[0031] In the embodiment shown in FIG. 3 , the second magnetic pinned layer 42 has a fixed magnetization. In one embodiment, the second magnetic pinned layer 42 of the top-pinned MTJ stack shown in FIG. 3 can be composed of a metal or metal alloy including one or more metals that exhibit high spin polarization. In an alternative embodiment, exemplary metals for forming the second magnetic pinned layer 42 of the top-pinned MTJ stack shown in FIG. 3 include iron, nickel, cobalt, chromium, boron, and manganese. Exemplary metal alloys can include the metals exemplified above (i.e., iron, nickel, cobalt, chromium, boron, and manganese). In some embodiments, the second magnetic pinned layer 42 of the top-pinned MTJ stack shown in FIG. 3 is composed of a cobalt (Co) and platinum (Pt) multilayer or superlattice, a cobalt (Co) and palladium (Pd) multilayer or superlattice, or a cobalt (Co), nickel (Ni), and platinum (Pt) multilayer or superlattice. The second magnetic pinning layer 42 of the top-pinned MTJ stack shown in Figure 3 can be formed using a deposition process including, for example, CVD, PECVD, PVD, ALD, or sputtering. The second magnetic pinning layer 42 of the top-pinned MTJ stack shown in Figure 3 can have a thickness of 3 nm to 20 nm, although other thicknesses for the second magnetic pinning layer 42 can also be used.

[0032] In some embodiments, and as shown in FIG. 4 , the second magnetic pinning layer 42 can be a multilayer arrangement having (1) high spin polarization regions formed from metals and / or metal alloys using the metals described above (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 having strong PMA that can be used include metals such as cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), iridium (Ir), or ruthenium (Ru), which may be arranged as alternating layers. The strong PMA regions can include alloys exhibiting strong PMA, with exemplary alloys including cobalt-iron-terbium, cobalt-iron-gadolinium, cobalt-chromium-platinum, cobalt-platinum, cobalt-palladium, iron-platinum, or iron-palladium, or combinations thereof. The alloys may be arranged as alternating layers. 4, the second magnetic pinning layer 42 includes a lower magnetic pinning region 44 and an upper magnetic pinning region 48, with the lower magnetic pinning region 44 and the upper magnetic pinning region 48 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 comprised of a cobalt (Co) and platinum (Pt) multilayer or superlattice, a cobalt (Co) and palladium (Pd) multilayer or superlattice, or a cobalt (Co), nickel (Ni) and platinum (Pt) multilayer or superlattice, and the synthetic antiferromagnetic coupling layer 46 is comprised of a metal such as cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), iridium (Ir), or ruthenium (Ru). The second magnetic pinning layer 42 of the top-pinned MTJ stack shown in Figure 4 can be formed using one or more deposition processes including, for example, CVD, PECVD, PVD, ALD, or sputtering. The second magnetic pinning layer 42 of the top-pinned MTJ stack shown in Figure 4 can have a thickness of 3 nm to 20 nm, although other thicknesses for the second magnetic pinning layer 42 can be used.The synthetic antiferromagnetic coupling layer 46 in the second magnetic pinned layer 42 may have a thickness of 0.2 nm to 0.8 nm.

[0033] An MTJ capping layer (not shown) is typically formed on the second magnetic pinning layer 42 shown in either Figure 3 or Figure 4. The MTJ capping layer is preferentially composed of magnesium oxide (MgO). Other materials for the MTJ capping layer include aluminum oxide (Al2O3), calcium oxide (CaO), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), or other oxides such as Mg y Ti (1-y) O x and ternary oxides such as . The MTJ capping layer can have a thickness of 0.3 nm to 2 nm, although other thicknesses are possible and can be used as the MTJ capping layer thickness 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.

[0034] A hard mask (not shown) is typically formed over the MTJ capping layer. The hard mask can 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 can be used as the top electrode of the STT MRAM device. In other embodiments, a separate top electrode (composed of one of the conductive materials described above for the bottom electrode 30) can be formed on the hard mask. The hard mask can have a thickness of 50 nm to 1500 nm, although other thicknesses for the hard mask can also be used in this application.

[0035] The top-pin MTJ stack (and MTJ capping layer and hard mask) of the present application can be formed by deposition of various material layers that provide a particular top-pin MTJ stack (and MTJ capping layer and hard mask) of the present application, followed by a patterning process, such as lithography and etching. The top-pin MTJ stack (and MTJ capping layer and hard mask) of the present application can have a critical dimension (CD) that is smaller than or equal to the critical dimension (CD) of the bottom electrode 30. The deposition of the various material layers that provide the top-pin MTJ stack (and MTJ capping layer and hard mask) of the present application can be performed in the same deposition tool or different deposition tools.

[0036] The top-pinned MTJ stack of the present application is stable in high temperature annealing cycles (400° C. back-end-of-line (BEOL) processes required for embedded memory applications) due to the controlled texturing of the second magnetic pinning layer 42 achieved by utilizing the grain growth control layer 40 and in-situ annealing, as described herein above.

[0037] This is illustrated by examining the data shown in Figures 5A, 5B, 5C, 6A, 6B, and 6C. In particular, Figures 5A-5C are graphs showing out-of-plane hysteresis loops of top-pin MTJ stacks according to the present application after BEOL at 400°C, and Figures 6A-6C are graphs showing in-plane hysteresis loops of top-pin MTJ stacks according to the present application after BEOL at 400°C. The top-pin MTJ stacks used to generate the graphs shown in Figures 5A, 5B, 5C, 6A, 6B, and 6C were identical except for the thickness of the rhodium (Rh) grain growth control layer. In the top-pin MTJ stacks used to generate the data shown in Figures 5A, 5B, 5C, 6A, 6B, and 6C, the BCC texture was located below the grain growth control layer and the FCC texture was located above the grain growth control layer. Each top-pinned MTJ stack included 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, a Rh grain growth control layer (various thicknesses), and a Co and Pt multilayer second magnetic pinning layer. For the data shown in Figures 5A and 6A, the Rh grain growth control layer had a thickness of 0.5 nm. For the data shown in Figures 5B and 6B, the Rh grain growth control layer had a thickness of 1 nm. For the data shown in Figures 5C and 6C, the Rh grain growth control layer had a thickness of 1.5 nm. Both the out-of-plane and in-plane hysteresis loops were generated by vibrating sample magnetometry (VSM).

[0038] While the present application has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the scope of the present application. It is therefore intended that the present application not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.

Claims

1. a magnetic free layer having a body-centered cubic (BCC) texture; a tunnel barrier layer having a BCC texture and positioned on the magnetic free layer; a magnetic pinning layer structure located on the tunnel barrier layer, the magnetic pinning layer structure including, 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 whose crystal growth is controlled from the BCC texture of the first magnetic pinning layer via the grain growth control layer; Including, the grain growth control layer is composed of a metal that facilitates the formation of a magnetic material having the FCC texture or the HCP texture, the metal being selected from the group consisting of rhodium (Rh), gadolinium (Gd), holmium (Ho), and hafnium (Hf); the second magnetic pinning layer has a perpendicular magnetic anisotropy field greater than 4 kOe; Top-pinned magnetic tunnel junction (MTJ) stack.

2. 10. The top-pinned MTJ stack of claim 1, wherein the second magnetic pinning layer includes a lower magnetic pinning region and an upper magnetic pinning region, the lower magnetic pinning region and the upper magnetic pinning region being separated by a synthetic antiferromagnetic coupling layer.

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

4. 2. The top-pinned MTJ stack of claim 1, wherein the first magnetic pinning layer is composed of a cobalt-iron-boron (Co-Fe-B) alloy or a Co-Fe-B alloy multilayer stack with additional iron.

5. 5. The top-pinned MTJ stack of claim 4, further comprising a metal insert layer present in the Co—Fe—B alloy multilayer stack, the metal insert layer comprising tungsten (W), tantalum (Ta), iridium (Ir), or terbium (Tb).

6. 10. The top-pinned MTJ stack of claim 1, wherein the second magnetic pinning layer comprises a cobalt (Co) and platinum (Pt) multilayer or superlattice, a cobalt (Co) and palladium (Pd) multilayer or superlattice, or a cobalt (Co), nickel (Ni) and platinum (Pt) multilayer or superlattice.

7. a top-pinned magnetic tunnel junction (MTJ) stack located on the bottom electrode, the top-pinned MTJ stack comprising: a magnetic free layer having a body-centered cubic (BCC) texture; a tunnel barrier layer having a BCC texture and positioned on the magnetic free layer; a magnetic pinning layer structure located on the tunnel barrier layer, the magnetic pinning layer structure including, 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 whose crystal growth is controlled from the BCC texture of the first magnetic pinning layer via the grain growth control layer; Including, the grain growth control layer is composed of a metal that facilitates the formation of a magnetic material having the FCC texture or the HCP texture, the metal being selected from the group consisting of rhodium (Rh), gadolinium (Gd), holmium (Ho), and hafnium (Hf); the second magnetic pinning layer has a perpendicular magnetic anisotropy field greater than 4 kOe; Spin-transfer torque magnetoresistive random access memory (STT MRAM) devices.

8. 8. The STT MRAM device of claim 7, wherein the second magnetic pinning layer includes a lower magnetic pinning region and an upper magnetic pinning region, the lower magnetic pinning region and the upper magnetic pinning region being separated by a synthetic antiferromagnetically coupled layer.

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

10. 8. The STT MRAM device of claim 7, wherein the first magnetic pinning layer is composed of a cobalt-iron-boron (Co-Fe-B) alloy or a Co-Fe-B alloy multilayer stack with additional iron.

11. 11. The STT MRAM device of claim 10, further comprising a metal insertion layer present within the Co—Fe—B alloy multilayer stack, the metal insertion layer comprising tungsten (W), tantalum (Ta), iridium (Ir), or terbium (Tb).

12. 8. The STT MRAM device of claim 7, wherein the second magnetic pinning layer comprises a cobalt (Co) and platinum (Pt) multilayer or superlattice, a cobalt (Co) and palladium (Pd) multilayer or superlattice, or a cobalt (Co), nickel (Ni) and platinum (Pt) multilayer or superlattice.

13. 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 pinning layer having a BCC texture on the tunnel barrier layer; depositing a grain growth control layer on the first magnetic pinning layer that facilitates the formation of a magnetic material having a face-centered cubic (FCC) texture or a hexagonal close-packed (HCP) texture; forming a second magnetic pinning layer having an FCC texture or an HCP texture on the grain growth control layer, the second magnetic pinning layer being annealed in-situ after deposition of the grain growth control layer; 1. A method for forming a top-pinned magnetic tunnel junction (MTJ) stack, comprising:

14. 14. The method of claim 13, wherein the in-situ annealing occurs after depositing the grain growth control layer but before forming the second magnetic pinning layer.

15. 14. The method of claim 13, wherein the in-situ annealing occurs after deposition of the grain growth control layer and after forming at least a portion of the second magnetic pinning layer.

16. 14. The method of claim 13, wherein the grain growth control layer is composed of rhodium (Rh), gadolinium (Gd), holmium (Ho), tantalum (Ta), hafnium (Hf), or tungsten (W) and has a thickness of 0.05 nm to 2 nm.

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