Bottom free layer magnetic tunnel junction and method of making the same

Abstract

Bottom free layer magnetic tunnel junctions (BMTJs) and methods of fabricating the same are provided. The BMTJs include a composite metal oxide seed layer and a free layer including boron (B) on the composite metal oxide seed layer. The composite metal oxide seed layer includes a first metal layer, a metal oxide layer on the first metal layer, and a second metal layer on the metal oxide layer. The second metal layer has been oxygen treated.

Description

Technical Field

[0001] This disclosure generally relates to semiconductor devices, and more specifically, to a vertical bottom free-layer spin-transfer torque magnetic random access memory (STT-MRAM) cell having a composite metal oxide seed layer and a method for manufacturing the vertical bottom free-layer STT-MRAM cell. Background Technology

[0002] Magnetic memories, particularly magnetic random access memories (MRAM), offer the potential for high read / write speeds, high endurance, non-volatility (e.g., persistence), and low power consumption. MRAM utilizes magnetic materials as the information recording medium to store information. One type of MRAM is spin-transfer torque magnetic random access memory (STT-MRAM). STT-MRAM utilizes a magnetic tunnel junction (MTJ), which is at least partially written to by a current driven through the magnetic junction and has a tunneling barrier stacked between free magnetic layers and pinned (or secured) magnetic layers. The current affects the magnetic moment of the free layer to align or dealign with the magnetic moment of the pinned layer (which is unaffected by the current). Since the alignment of the magnetic moments remains unchanged in the absence of a charging current, the MTJ stack behaves as a bistable system suitable for memory storage.

[0003] Depending on the location of the free layer, MTJs include top free layer MTJs (TMTJs) and bottom free layer MTJs (BMTJs).

[0004] Figure 1 A comparative bottom free layer (or top pinned layer) magnetic tunnel junction (BMTJ) 10 is illustrated. The comparative BMTJ 10 typically comprises a seed layer stack 12, a free layer 13, a main tunneling barrier layer 14, a synthetic antiferromagnetic pinned layer (SAF-PL) stack 15, and a capping layer 16 disposed on a bottom electrode 11. A top electrode 17 may contact the capping layer 16. The top electrode 17 and the bottom electrode 11 may be coupled to a selection device (e.g., a transistor). The SAF-PL stack 15 may include a top pinned layer (PL) 15-1, a spacer layer 15-2, a bottom pinned layer 15-3, and a polarization enhancement layer (PEL) 15-4. The spacer layer 15-2 provides antiferromagnetic coupling between the top pinned layer 15-1 and the bottom pinned layer 15-3 / PEL 15-4.

[0005] In a comparative BMTJ, the free layer 13 is typically formed of a boron (B)-containing material such as FeCoB, and the seed layer stack 12 is typically formed of a thin layer of amorphous metal 12-1 and magnesium oxide (MgO) 12-2 stacked on the amorphous metal 12-1. The thin layer of MgO 12-2 is typically about a monolayer, partially crystallized or amorphous, and has many pinholes, which results in lower thermal robustness in terms of diffusion and a lower resistivity-area product (RA) compared to the main tunneling barrier layer 14. It also has a relatively low boron (B) affinity for boron in the free layer, which leads to more boron accumulation at the MgO-free layer interface, thus contaminating the MgO-free layer interface. Furthermore, improvements in tunneling magnetoresistance (TMR) and factor of quality (FOM) are needed for BMTJs.

[0006] The information disclosed in this background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art. Summary of the Invention

[0007] One aspect of the present invention is for a bottom free-layer STT-MRAM cell with improved tunnel magnetoresistance (TMR) and factor of quality (FOM) as well as improved process margins for wafer uniformity in TMR and RA.

[0008] Another aspect of the present invention relates to a method for forming a bottom free layer STT-MRAM cell.

[0009] According to one embodiment of the present disclosure, a bottom free layer magnetic tunnel junction includes a composite metal oxide seed layer and a boron (B)-containing free layer on the composite metal oxide seed layer, wherein the composite metal oxide seed layer includes a first metal layer, a metal oxide layer on the first metal layer and a second metal layer on the metal oxide layer, wherein the second metal layer has been oxygen-treated.

[0010] In one embodiment, the metal oxide layer may include MgO, MgAlO, MgAl2O4 and / or (MgAl)3O4.

[0011] In one embodiment, the second metal layer may include Nb, Ta, Hf, Zr or Zr-X, wherein X may be Nb, Ta or Hf.

[0012] In one embodiment, the second metal layer may include metal-Ox, where x represents the molar ratio between oxygen atoms and metal atoms in the second metal layer, and x is less than the value Y, which is obtained by dividing the valence of the metal atoms by 2.

[0013] In one implementation, x can be greater than 0 and less than Y.

[0014] In one implementation, x can be 80% or less of Y.

[0015] In one embodiment, the second metal layer may include a metal, and the metal of the second metal layer may be partially oxidized.

[0016] In one embodiment, the metal oxide layer may include MgO, and the second metal layer may include Nb, Ta, or Hf.

[0017] In one embodiment, the metal oxide layer may include MgAl2O4, and the second metal layer may include Ta, Zr, or Zr-X, wherein X may be Nb, Ta, or Hf.

[0018] In one embodiment, the thickness of the second metal layer can be approximately Or smaller.

[0019] In one embodiment, the free layer may include one or more layers selected from FeB, FeB-X, FeCoB, FeCoB-X, Fe, Fe-X, FeCo, and FeCo-X, wherein X may be Be, Ni, Mo, Mg, Zr, Ta, V, Cr, W, Hf, Nb, or Tb.

[0020] In one embodiment, the first metal layer may include one or more layers selected from Ta, W, Mo, Hf, NiW, NiTa, NiCrW, FeCo-Y, FeCoB, FeCoB-Y, FeB-Y, and CoB-Y, wherein Y may be one or more elements selected from Ta, Zr, Mo, W, V, and Ni.

[0021] According to one embodiment of the present disclosure, a vertical bottom free layer STT-MRAM cell includes a bottom free layer magnetic tunnel junction according to an embodiment of the present disclosure.

[0022] According to one embodiment of the present disclosure, a method for manufacturing a bottom free-layer magnetic tunnel junction includes depositing a composite metal oxide seed layer on a bottom electrode and depositing a free layer containing boron (B) on the composite metal oxide seed layer, wherein the deposition of the composite metal oxide seed layer includes depositing a first metal layer on the bottom electrode, depositing a metal oxide layer on the first metal layer, depositing a second metal layer on the metal oxide layer, and performing an oxygen treatment on the second metal layer.

[0023] In one embodiment, the oxygen treatment may include a natural oxidation process or a free radical oxidation process.

[0024] In one embodiment, the oxygen treatment can be performed at ambient temperature.

[0025] In one embodiment, the oxygen treatment may include exposing the metal oxide layer to oxygen prior to the deposition of the second metal layer. In another embodiment, the method may further include performing annealing after the deposition of the second metal layer to allow oxygen to migrate from the metal oxide layer to the second metal layer.

[0026] In one embodiment, the oxygen treatment may include exposing the metal oxide layer to oxygen before the deposition of the second metal layer, and exposing the second metal layer to oxygen after the deposition of the second metal layer. In one embodiment, the method may further include performing annealing to allow oxygen to migrate from the metal oxide layer to the second metal layer.

[0027] In one embodiment, the method may further include performing annealing at a temperature of 350°C to 400°C after deposition of the main tunneling barrier layer, polarization enhancement layer, or bottom pinned layer.

[0028] This summary is provided to introduce the selection of features and concepts further described below in the detailed description of embodiments of this disclosure. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. One or more of the described features may be combined with one or more other described features to provide a functional device. Attached Figure Description

[0029] These and additional features and advantages of embodiments of the present disclosure will become more apparent when considered in conjunction with the following accompanying drawings and with reference to the following detailed description. Throughout the drawings, the same reference numerals are used to refer to the same features and components. These drawings are not necessarily drawn to scale.

[0030] Figure 1 A comparative bottom free layer (or top pinned layer) magnetic tunnel junction (BMTJ)10 was plotted.

[0031] Figure 2 This is a schematic illustration of a bottom free layer (or top pinned layer) magnetic tunnel junction (BMTJ) 20 according to an embodiment of the present disclosure.

[0032] Figure 3 This is a flowchart illustrating a method for manufacturing a BMTJ according to an embodiment of the present disclosure.

[0033] Figure 4 This is a flowchart illustrating a method for depositing a composite metal oxide seed layer according to an embodiment of the present disclosure.

[0034] Figure 5 Comparative Example 1, as well as the RA and TMR of Example 1 and Example 2, are shown.

[0035] Figure 6 The comparison examples RA and TMR of Example 2, as well as Examples 3 and 4, are shown.

[0036] Figure 7 The RA and TMR of Comparative Example 3 and Example 5 are shown.

[0037] Figure 8 The comparison examples RA and TMR of Example 4 and Example 6 are shown. Detailed Implementation

[0038] In the following description, exemplary embodiments will be illustrated with reference to the accompanying drawings, in which the same reference numerals refer to the same elements throughout. However, the invention may be embodied in a variety of different forms and should not be construed as being limited to the embodiments shown herein. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey to those skilled in the art aspects and features of the invention. Therefore, processes, elements, and techniques unnecessary for a full understanding of the aspects and features of the invention may not be described. Unless otherwise stated, the same reference numerals denote the same elements throughout the drawings and written description, and thus their description need not be repeated.

[0039] In the accompanying drawings, for clarity, the relative dimensions of elements, layers, and regions may be enlarged and / or simplified. For ease of interpretation, spatial relational terms such as “below,” “under,” “lower,” “below,” “above,” “upper,” etc., are used herein to describe the relationship of one element or feature as shown to other elements(s) or features(s). It will be understood that, in addition to the orientations depicted in the figures, the spatial relational terms are intended to also cover different orientations of the device in use or operation. For example, if the device in the figure is flipped, the element described as “below,” “under,” or “below” other elements or features will be oriented “above” said other elements or features. Thus, the example terms “below” and “below” can cover both vertical and horizontal directions. The device may be otherwise oriented (e.g., rotated 90 degrees or in other orientations), and the spatial relational descriptions used herein should be interpreted accordingly.

[0040] It will be understood that although the terms "first," "second," "third," etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, the first element, component, region, layer, or portion described below may be referred to as the second element, component, region, layer, or portion without departing from the spirit and scope of the invention.

[0041] It will be understood that when an element or layer is referred to as being "on," "connected to," or "attached to" another element or layer, it may be directly on, directly connected to, or attached to the other element or layer, or there may be one or more intermediary elements or layers. Furthermore, it will be understood that when an element or layer is referred to as being "between" two elements or layers, it may be the only element or layer between the two elements or layers, or there may be one or more intermediary elements or layers.

[0042] The terminology used herein is for the purpose of describing particular embodiments and is not intended to limit the invention. As used herein, the singular form “a” is intended to also include the plural form unless the context clearly indicates otherwise. It will also be understood that, when used in this specification, the terms “comprising,” “including,” “containing,” and “comprising…” indicate the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. As used herein, the term “and / or” includes any and all combinations of one or more associated listed items. Expressions such as “at least one of…” modify the entire list of elements when following a list of elements, without modifying any individual element in that list.

[0043] As used herein, the terms “substantially,” “approximately,” and similar terms are used as approximations rather than terms of degree, and are intended to account for inherent variations in measured or calculated values ​​that will be recognized by those skilled in the art. Furthermore, when describing embodiments of the invention, the use of “may” refers to “one or more embodiments of the invention.” As used herein, the terms “use,” “using…,” and “being used” can be considered synonymous with the terms “utilize,” “using…,” and “being utilized,” respectively. Moreover, the term “exemplary” is intended to indicate an example or instance.

[0044] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will also be understood that terms such as those defined in general dictionaries shall be interpreted as having the same meaning as they have in the relevant field and / or the context of this specification, and shall not be interpreted in an idealized or overly formal sense, unless expressly so defined herein.

[0045] Example embodiments are described in the context of specific magnetic junctions and magnetic memories having certain components. Those skilled in the art will readily recognize that embodiments of the invention are consistent with the use of magnetic junctions and magnetic memories having additional and / or extra components and / or additional features that do not contradict embodiments of the invention. Methods and systems are also described in the context of current understanding of spin-orbit interactions, spin transfer phenomena, magnetic anisotropy, and other physical phenomena. Consequently, those skilled in the art will readily recognize that theoretical explanations of the behavior of methods and systems are based on current understanding of spin-orbit interactions, spin transfer, magnetic anisotropy, and other physical phenomena. However, the methods and systems described herein do not depend on any particular physical explanation. Those skilled in the art will also readily recognize that methods and systems are described in the context of structures having a specific relationship with a substrate. However, those skilled in the art will readily recognize that the methods and systems are consistent with other structures. Furthermore, methods and systems are described in the context of certain layers being synthetic and / or simple. However, those skilled in the art will readily recognize that these layers can have a different structure. Additionally, methods and systems are described in the context of magnetic junctions with specific layers, spin-orbit interaction active layers, and / or other structures. However, those skilled in the art will readily recognize that magnetic junctions, spin-orbit interaction active layers, and / or other structures having additional and / or different layers that do not contradict the methods and systems described herein can also be used. Furthermore, certain components are described as magnetic, ferromagnetic, and ferrimagnetic. As used herein, the term magnetic can include ferromagnetic, ferrimagnetic, or similar structures. Therefore, as used herein, the terms "magnetic" or "ferromagnetic" include, but are not limited to, ferromagnets and ferrimagnets. The methods and systems are also described in the context of a single magnetic junction. However, those skilled in the art will readily recognize that the methods and systems are consistent with the use of magnetic memories having multiple magnetic junctions. Furthermore, as used herein, "in-plane" refers substantially to or parallel to the plane of one or more layers of the magnetic junction. Conversely, "perpendicular" corresponds to a direction substantially perpendicular to one or more layers of the magnetic junction.

[0046] According to one embodiment of this disclosure, a vertical bottom free-layer STT-MRAM cell includes a BMTJ, which includes a composite metal oxide seed layer on a bottom electrode and a boron (B)-containing free layer on the composite metal oxide seed layer. The composite metal oxide seed layer includes: a first metal layer on the bottom electrode, the first metal layer being amorphous; a metal oxide layer on the first metal layer; and a second metal layer on the metal oxide layer, the second metal layer being oxygen-treated.

[0047] Figure 2This is a schematic illustration of a bottom free layer (or top pinned layer) magnetic tunnel junction (BMTJ) 20 according to an embodiment of the present disclosure.

[0048] Reference Figure 2 The BMTJ 20 has a composite metal oxide seed layer 22, a free layer 23, a main tunneling barrier layer 24, a synthetic antiferromagnetic pinned layer (SAF-PL) stack 25, and a capping layer 26 disposed on the bottom electrode 21. The SAF-PL stack 25 may include a top pinned layer (PL) 25-1, a spacer layer 25-2, a bottom pinned layer 25-3, and a polarization enhancement layer (PEL) 25-4 including a texture disruption layer (TBL).

[0049] The main tunneling barrier layer 24 may include MgO. The free layer 23 may be a boron (B) layer. In one embodiment, the free layer may include one or more layers selected from iron boron (FeB), FeB-X, iron cobalt boron (FeCoB), FeCoB-X, iron (Fe), Fe-X, iron cobalt (FeCo), and FeCo-X, wherein X is selected from beryllium (Be), nickel (Ni), molybdenum (Mo), magnesium (Mg), zirconium (Zr), tantalum (Ta), vanadium (V), chromium (Cr), tungsten (W), hafnium (Hf), niobium (Nb), and terbium (Tb). For example, the free layer 23 may include iron cobalt boron / iron (FeCoB / Fe).

[0050] The composite metal oxide seed layer 22 includes: a first metal layer 22-1, which is amorphous; a metal oxide layer 22-2; and a second metal layer 22-3 that has been oxygen-treated. The metal oxide layer 22-2 may include MgO or magnesium aluminum oxide (MgAlO) (e.g., MgAl2O4, (MgAl)3O4, spinel oxides having various proportions of Mg and Al, etc.). The metal oxide layer 22-2 may be a partially crystalline or amorphous layer.

[0051] The first metal layer 22-1 is amorphous. In one embodiment, the first metal layer 22-1 may include one or more layers selected from Ta, W, Mo, Hf, NiW, NiTa, NiCrW, FeCo-Y, FeCoB, FeCoB-Y, FeB-Y, and CoB-Y, wherein Y is one or more elements selected from Ta, Zr, Mo, W, V, and Ni.

[0052] In one embodiment, the first metal layer 22-1 may include tantalum / FeCoB (Ta / FeCoB).

[0053] The second metal layer 22-3 may comprise a metal with a high affinity for oxygen and boron. For example, the second metal layer 22-3 may comprise niobium (Nb), tantalum (Ta), hafnium (Hf), or zirconium (Zr). The second metal layer 22-3 has a metal content of less than 5 angstroms. (e.g., less than) A thin layer with a thickness of approximately [missing information]. In one embodiment, the second metal layer 22-3 has approximately [missing information]. The thickness.

[0054] The second metal layer 22-3 can be oxygen-treated. Oxygen treatment can be exposure to an oxygen source (e.g., pure oxygen or an argon / oxygen mixture) without causing complete oxidation of the metal atoms in the second metal layer 22-3. For example, exposure to the oxygen source can be carried out for only a short period of time (e.g., less than 1 minute or less than 50 seconds) at a temperature (e.g., ambient temperature) that does not cause complete oxidation. It can be carried out by a natural oxidation process or a free radical oxidation process. As a result, the second metal layer 22-3 is an amorphous layer having an oxygen-rich interface with the free layer 23. Unlike the metal oxide layer 22-2, the second metal layer 22-3 can be a partially oxidized layer, rather than a completely oxidized layer. In one embodiment, the second metal layer 22-3 comprises both unoxidized metal atoms and metal atoms bonded to oxygen atoms.

[0055] Through oxygen treatment, oxygen atoms adhere to the metal atoms of the second metal layer 22-3 due to the high affinity of the metal atoms of the second metal layer 22-3 for oxygen. The composition of the second metal layer can be represented by metal-Ox. The oxygen atoms retained in the second metal layer 22-3 have a high affinity for boron. This overcomes the low boron affinity of the metal oxide layer 22-2 and pulls boron to the second metal layer 22-3, which attracts boron. Therefore, boron is introduced from the free layer 23 into the composite metal oxide seed layer 22.

[0056] In the second metal layer 22-3, the amount of oxygen atoms is less than the amount of oxygen atoms required to completely oxidize the metal atoms in the second metal layer 22-3. In other words, the metal atoms in the second metal layer 22-3 are only partially oxidized and not completely oxidized. For example, "x" in metal-Ox represents the molar ratio between oxygen atoms and metal atoms in the second metal layer 22-3. "x" can be less than the value "Y". "Y" is obtained by dividing the valence of the metal atom by the valence of the oxygen atom (i.e., dividing the valence of the metal atom by 2). In one embodiment, x is about 80% or less, 60% or less, 50% or less, or 30% or less of the value Y.

[0057] In one embodiment, the second metal layer 22-3 comprises Nb-Ox, and x is less than 1. For example, x is less than or equal to 0.7, 0.5, or 0.3, but greater than 0. In one embodiment, the second metal layer 22-3 comprises Ta-Ox, and x is less than 5 / 2. For example, x is less than or equal to 2, 1.5, or 1, but greater than 0. In one embodiment, the second metal layer 22-3 comprises Zr-Ox, and x is less than 2. For example, x is less than or equal to 1.5, 1, or 0.5, but greater than 0. That is, the amount of oxygen atoms in the second metal layer 22-3 is insufficient to completely oxidize the metal atoms in the second metal layer 22-3, and the second metal layer 22-3 is a partially oxidized layer.

[0058] Due to the oxygen-rich interface, the second metal layer 22-3 can also reduce or block the diffusion of metal from the first metal layer 22-1 to the free layer 23.

[0059] In the BMTJ according to embodiments of the present disclosure, and as described above, the composite metal oxide seed layer 22 enhances boron migration from the free layer 23 to the composite metal oxide seed layer 22 during in-situ annealing and / or post-annealing processes. Furthermore, the inclusion of a second metal layer 22-3 that has been oxygen-treated reduces or prevents the diffusion of metals (e.g., Ta) from the first metal layer 22-1 to the free layer 23. Consequently, better interface quality between the main tunneling barrier layer 24 and the free layer 23 is also achieved.

[0060] The uniformity of the entire seed layer 22 is improved by including an amorphous second metal layer 22-3 (which has been oxygen-treated). For example, compared to a conventional pinhole-containing seed layer in which a metal oxide layer (e.g., an MgO layer) contacts the free layer, the amorphous second metal layer 22-3 improves the uniformity of the interface between the seed layer and the free layer, and also provides an amorphous seed layer at the interface with the free layer instead of a conventional partially crystallized or amorphous MgO seed layer. As a result of the better seed layer quality, a higher TMR is achieved. Moreover, as a result of the better free layer quality, a lower current density Jc (measured parallel to the reference layer) is achieved. 50nm PAP This leads to a higher FOM (which is related to Jc) 50nm PAP (Inversely proportional) represents higher device performance or efficiency.

[0061] In one embodiment, the metal oxide layer 22-2 comprises MgO, and the second metal layer comprises Nb, Ta, or Hf.

[0062] In one embodiment, the metal oxide layer 22-2 comprises MgAl2O4, and the second metal layer comprises Ta, Zr, or Zr-X, wherein X is Nb, Ta, or Hf.

[0063] In one embodiment, the thickness of the second metal layer 22-3 is approximately Or smaller. In one embodiment, the thickness of the second metal layer is approximately...

[0064] According to one embodiment of this disclosure, a method for manufacturing a bottom free-layer magnetic MTJ (BMTJ) includes depositing a composite metal oxide seed layer on a bottom electrode and depositing a free layer comprising boron (B) on the composite metal oxide seed layer. The deposition of the composite metal oxide seed layer includes: depositing a first metal layer, the first metal layer being amorphous; depositing a metal oxide layer on the first metal layer; depositing a second metal layer on the metal oxide layer; and performing an oxygen treatment.

[0065] Figure 3 This is a flowchart illustrating the method for manufacturing a BMTJ. (See attached diagram) Figure 3 The method includes: in action 301, depositing a composite metal oxide seed layer on a bottom electrode; and in action 303, depositing a free layer including boron (B) on the composite metal oxide seed layer. Figure 4 This is a flowchart illustrating a method for depositing a composite metal oxide seed layer. (Refer to...) Figure 4 The method includes: in action 401, depositing a first metal layer on a bottom electrode, the first metal layer being amorphous; in action 403, depositing a metal oxide layer on the first metal layer; in action 405, depositing a second metal layer on the metal oxide layer; and in action 407, performing an oxygen treatment.

[0066] The deposition of the first metal layer, the metal oxide layer, the second metal layer, and the free layer can be achieved using any suitable method, such as chemical vapor deposition, physical vapor deposition, spin coating, etc.

[0067] The free layer may be a boron (B)-containing layer. In one embodiment, the free layer may include one or more layers selected from iron boron (FeB), FeB-X, iron cobalt boron (FeCoB), FeCoB-X, iron (Fe), Fe-X, iron cobalt (FeCo), and FeCo-X, wherein X is selected from beryllium (Be), nickel (Ni), molybdenum (Mo), magnesium (Mg), zirconium (Zr), tantalum (Ta), vanadium (V), chromium (Cr), tungsten (W), hafnium (Hf), niobium (Nb), and terbium (Tb). For example, the free layer may include iron cobalt boron / iron (FeCoB / Fe).

[0068] The metal oxide layer may include MgO or magnesium aluminum oxide (MgAlO) (e.g., MgAl2O4, (MgAl)3O4, spinel oxides having various proportions of Mg and Al, etc.). The first metal layer is amorphous. In one embodiment, the first metal layer may include one or more layers selected from Ta, W, Mo, Hf, NiW, NiTa, NiCrW, FeCo-Y, FeCoB, FeCoB-Y, FeB-Y, and CoB-Y, wherein Y is one or more elements selected from Ta, Zr, Mo, W, V, and Ni.

[0069] In one embodiment, the first metal layer may include tantalum / FeCoB (Ta / FeCoB).

[0070] The second metal layer may include a metal with a high affinity for oxygen and boron. For example, the second metal layer may include niobium (Nb), tantalum (Ta), hafnium (Hf), or zirconium (Zr). The second metal layer has a density less than [missing information]. (e.g., less than) A thin layer with a thickness of approximately [missing information]. In one embodiment, the second metal layer has approximately [missing information]. The thickness of the second metal layer. The second metal layer can be oxygen-treated. Oxygen treatment is exposure to an oxygen source (e.g., pure oxygen or an argon / oxygen mixture) for a short period (e.g., less than two minutes, less than one minute, or less than 50 seconds). It can be performed through natural oxidation or free radical oxidation.

[0071] Oxygen treatment can be performed through either natural oxidation or free radical oxidation. Natural oxidation can be performed in airflow mode, gas-confined mode, etc.

[0072] In one embodiment, the oxygen treatment is performed at ambient temperature (e.g., room temperature, such as about 25°C).

[0073] In one embodiment, the oxygen treatment may include: exposing the metal oxide layer to oxygen prior to the deposition of the second metal layer, such that oxygen atoms (e.g., additional oxygen atoms besides those already bonded to the metal during the formation of the metal oxide layer) adhere to the metal oxide layer; and annealing the BMTJ stack to allow the additional oxygen atoms to migrate from the metal oxide layer to the second metal layer. The annealing temperature may be from about 350°C to about 400°C. In one embodiment, the annealing may be performed after the deposition of the main tunneling barrier, PEL, or bottom PL.

[0074] In one implementation, oxygen treatment can be performed after the deposition of the second metal layer to provide an oxygen-rich metal interface with the free layer.

[0075] In one implementation, the oxygen treatment can be performed both before and after the deposition of the second metal layer.

[0076] In one embodiment, the oxygen treatment may include: exposing the metal oxide layer to oxygen prior to the deposition of the second metal layer, such that additional oxygen atoms are adsorbed onto the metal oxide layer; exposing the second metal layer to oxygen after the deposition of the second metal layer; and annealing the BMTJ stack to allow additional oxygen adsorbed in the metal oxide layer to migrate to the second metal layer.

[0077] Through oxygen treatment, oxygen atoms adhere to the metal atoms in the second metal layer due to the high affinity of the metal atoms in the second metal layer for oxygen. The second metal layer is amorphous and has an oxygen-rich interface with the free layer, and includes metal-Ox. The oxygen atoms retained in the second metal layer have a high affinity for boron. This overcomes the low boron affinity of the metal oxide layer and pulls boron to the second metal layer, which attracts boron. Thus, boron is introduced from the free layer into the composite metal oxide seed layer. However, the amount of oxygen atoms in the second metal layer is less than the amount of oxygen required to completely oxidize the metal atoms in the second metal layer. In other words, the metal atoms in the second metal layer are only partially oxidized and not completely oxidized. For example, x in metal-Ox represents the molar ratio between metal atoms and oxygen atoms in the second metal layer, and x is less than the ratio of the valence of the metal atom to the valence of the oxygen atom.

[0078] Example

[0079] Comparative Example 1

[0080] During the formation of the seed layer, it is deposited on the silicon wafer. Ta, FeCoBTa and FeCoB (hereinafter referred to as "FeCoB") The first metal layer is formed by sputtering MgO at a constant power for 400 seconds (s) while rotating to provide a uniformly deposited MgO layer, followed by a further 325 seconds without rotation, thereby forming a seed layer with a wedge-shaped MgO layer. This wedge-shaped MgO layer has a thickness that varies from thick to thin across 55 mm on each side of the wafer center. The average thickness of the MgO seed layer is approximately... Deposition on seed layer Iron cobalt boron (FeCoB) with 30% boron and Iron is used to form a free layer.

[0081] Example 1 and Example 2

[0082] Example 1 and Example 2 were manufactured similarly to Comparative Example 1, except that MgO was deposited for 250 s under rotation and for 250 s without rotation, and except that an oxygen-treated metal layer was included between the MgO and the free layer. In Example 1, the metal layer included having The thickness of Nb, in Example 2, the metal layer includes Nb with a thickness of [missing information]. The thickness of Ta was [missing information]. In each case, the oxygen treatment was performed for 30 seconds. Because the time for depositing the MgO layer was shortened in Examples 1 and 2 compared to that in Comparative Example 1, a thinner MgO layer was deposited in each case.

[0083] Comparative Example 2

[0084] In addition to sputtering MgO under rotating conditions for 725 s during seed layer formation and depositing a cobalt-iron-boron layer (with 30% boron and approximately 10% iron-boron) on the seed layer during free layer formation, the process also involves... Apart from the thickness of the iron layer, Comparative Example 2 was manufactured similarly to Comparative Example 1. A wedge-shaped iron layer was formed by sputtering an iron layer without rotation, the wedge-shaped iron layer having a cross-sectional area of ​​55 mm on each side of the wafer's center. Change to The thickness.

[0085] Example 3 and Example 4

[0086] Examples 3 and 4 were manufactured similarly to Comparative Example 2, except that the time for depositing MgO under rotation was shortened to 430 s and an oxygen-treated metal layer was included between the MgO and the free layer. In Example 3, the metal layer included In Example 4, the Nb metal layer includes The Ta. In each case, the oxygen treatment was performed for 30 seconds. For Comparative Example 2, the MgO thickness was approximately For Examples 3 and 4, the MgO thickness is approximately

[0087] Figure 5 Comparative Example 1, as well as the RA and TMR of Example 1 and Example 2, are shown. Figure 6 The comparison examples RA and TMR of Example 2, as well as Examples 3 and 4, are shown. (As can be seen from...) Figure 5-6As observed, the composite MgO and oxygen-treated Nb or Ta (hereinafter referred to as "MgO / (Nb,Ta) / OT") seed layers in the examples improve the intrinsic TMR by 30-40% compared to the corresponding comparative examples (representing conventional MgO seed layers) with similar RA. Furthermore, it can be observed that the composite MgO / (Nb,Ta) / OT seed layers in the examples significantly improve the uniformity of both TMR and RA when the thickness of the MgO layer or free layer varies.

[0088] Comparative Example 3

[0089] Comparative Example 3 was manufactured similarly to Comparative Example 1, except that MgAlO (instead of MgO) was first uniformly sputtered at a fixed power for 210 s while rotating and then for 180 s without rotation, thereby forming a MgAlO seed layer with a thickness varying from thick to thin across 55 mm on each side of the wafer's center. The average thickness of the MgAlO layer was approximately Deposition on seed layer Iron cobalt boron (FeCoB) with 30% boron was deposited. Iron is used to form a free layer.

[0090] Example 5

[0091] In addition to the deposition of MgAlO for 200 s without rotation, and in addition to the deposition between MgAlO and the free layer, Example 5 was manufactured similarly to Comparative Example 3, except for the thick oxygen-treated Zr metal layer. The oxygen treatment was performed for 30 seconds.

[0092] Comparative Example 4

[0093] In addition to uniformly sputtering MgAlO (instead of MgO) at a constant power for 390 s under rotating conditions to form a seed layer and deposit it. Comparative Example 4 was fabricated similarly to Comparative Example 1, except that a 30% boron FeCoB layer and an iron layer were used to form a free layer. The iron layer was deposited as a wedge-shaped iron layer without rotation, the wedge-shaped iron layer having a cross-sectional area of ​​55 mm on each side of the wafer center. Change to The thickness.

[0094] Example 6

[0095] In addition to the deposition of MgAlO under rotation lasting 200s and including between MgAlO and the free layer Example 6 was manufactured similarly to Comparative Example 4, except for the thick oxygen-treated Zr metal layer. The oxygen treatment was performed for 30 seconds.

[0096] Figure 7 The RA and TMR of Comparative Example 3 and Example 5 are shown. Figure 8 The RA and TMR of Comparative Example 4 and Example 6 are shown. (As can be seen from...) Figure 7-8 As observed, compared to the corresponding comparative example (representing a conventional MgAlO seed layer), the composite MgAlO / Zr / OT (MgAlO and oxygen-treated Zr layer) seed layer in the example improved the intrinsic TMR by 17-60% under similar RA conditions. Furthermore, it can be observed that when the thickness of the MgAlO layer or the free layer varies, the composite MgAlO / Zr / OT seed layer in the example significantly improves the uniformity of both TMR and RA.

[0097] Compare Example 5-6 and Example 7-11

[0098] Comparative Examples 5-6 and Examples 7-11 shown in Table 1 are additional examples that illustrate the differences in parameters between a seed layer without an oxygen-treated second metal layer (referred to as "MgO only") and a seed layer including an oxygen-treated second metal layer according to embodiments of the present disclosure.

[0099] Table 1

[0100]

[0101]

[0102] In Table 1, the time in seconds following MgO indicates the duration for depositing the MgO layer, and the time in seconds following OT indicates the duration for oxygen treatment. The thickness of the Nb layer is...

[0103] Table 1 also shows the film-level parameters. HkFL (effective perpendicular magnetic anisotropy field in the free layer), Alpha (damping constant, α), and ΔH0 (inhomogeneous linewidth broadening) were each measured using ferromagnetic resonance spectroscopy. Negative values ​​of HkFL indicate perpendicular anisotropy. As can be seen from Table 1, compared to a comparative seed layer with only MgO, the composite MgO / Nb-Ox seed layer improves HkFL and Kut (product of effective magnetic anisotropy constant and free layer thickness) and significantly reduces ΔH0 under similar RA conditions, indicating less magnetic inhomogeneity while maintaining a similar damping constant (α).

[0104] As can also be observed from Table 1, the MgO thickness decreases from Example 7 to Example 11 due to the reduced time spent depositing the MgO layer. The effect of MgO thickness in the MgO / Nb-Ox composite seed layer shows the trade-off between Hk FL and ΔHo.

[0105] Comparative Example 7

[0106] Deposition on the bottom electrode A first metal layer is formed by depositing a layer of MgO on the first metal layer to form a metal oxide layer, and then depositing another layer of MgO on the metal oxide layer. Layers are formed to create a free layer, and approximately [amount missing] are deposited on the free layer. A thick MgO layer is formed to create the main tunneling barrier layer, and approximately [amount missing] MgO is deposited on the main tunneling barrier layer. A thick FeCoB layer is used to form a PEL layer. Ta is deposited on the PEL layer to form a texture disruption layer (TBL). Co / Pt multilayers are deposited on the TBL to form a bottom pinned layer. Ir is deposited on the bottom pinned layer to form a spacer layer. Co / Pt multilayers are deposited on the spacer layer to form a top pinned layer. Ta / Ru is deposited on the top pinned layer to form a capping layer, thereby fabricating a BMTJ device.

[0107] Example 12

[0108] Except for depositing an Nb layer on the MgO seed layer before the deposition of the free layer and performing an oxygen treatment for 30 seconds (referred to as "MgO / Nb / OT"), the device was fabricated similarly to Comparative Example 7. The device was annealed at 350 to 400 °C after the Nb layer was deposited.

[0109] Table 2 compares Comparative Example 7 (device with conventional MgO seed layer) and Example 12 (device with composite oxide MgO / Nb / OT seed layer).

[0110] Table 2

[0111]

[0112] As can be seen from Table 2, compared with devices using conventional MgO seed layers, by reducing Jc 50ns PAP Device data with a critical size (CD) of approximately 40 nm, featuring a composite MgO / Nb-Ox seed layer, clearly demonstrates improved TMR (as shown in the full-film data) and improved FOM (= Delta85℃ / Jc). 50ns PAP It also exhibits excellent thermal stability at 85°C (expressed as delta).

[0113] Although the invention has been described in detail with reference to exemplary embodiments thereof, the exemplary embodiments described herein are not intended to be exhaustive or to limit the scope of the invention to the exact forms disclosed. Those skilled in the art will understand that changes and modifications to the described structures and methods of assembly and operation may be practiced without substantially departing from the principles, spirit, and scope of the invention as set forth in the appended claims.

[0114] This application claims priority and interest in U.S. Provisional Application No. 62 / 859,598, filed June 10, 2019, and U.S. Non-Provisional Application No. 16 / 535,933, filed August 8, 2019, the entire contents of which are incorporated herein by reference.

Claims

1. A bottom free-layer magnetic tunnel junction, comprising: Composite metal oxide seed layer, and A free layer containing boron (B) on the composite metal oxide seed layer, The composite metal oxide seed layer includes: First metal layer; A metal oxide layer on the first metal layer; and A second metal layer on the metal oxide layer, wherein the second metal layer has been oxygen-treated. The second metal layer comprises Nb, Zr, or Zr-X, where X is Nb, Ta, or Hf. The first metal layer comprises tantalum / iron cobalt boron (Ta / FeCoB).

2. The bottom free-layer magnetic tunnel junction according to claim 1, wherein the thickness of the second metal layer is 2.2 Å.

3. The bottom free layer magnetic tunnel junction according to claim 1, wherein the metal oxide layer comprises MgO, MgAlO, MgAl2O4 and / or (MgAl)3O4.

4. The bottom free-layer magnetic tunnel junction according to claim 1, wherein the second metal layer comprises Nb, Zr or Zr-X, wherein X is Nb or Hf.

5. The bottom free-layer magnetic tunnel junction according to claim 1, The second metal layer comprises metal -Ox. Where x represents the molar ratio between oxygen atoms and metal atoms in the second metal layer, and x is less than the value Y, which is obtained by dividing the valence of the metal atoms by 2.

6. The bottom free layer magnetic tunnel junction according to claim 5, wherein x is greater than 0 and less than Y.

7. The bottom free layer magnetic tunnel junction according to claim 5, wherein x is 80% or less of Y.

8. The bottom free-layer magnetic tunnel junction of claim 1, wherein the second metal layer comprises a metal, and the metal of the second metal layer is partially oxidized.

9. The bottom free-layer magnetic tunnel junction according to claim 1, wherein the metal oxide layer comprises MgO, and the second metal layer comprises Nb.

10. The bottom free-layer magnetic tunnel junction according to claim 1, wherein the metal oxide layer comprises MgAl2O4, and the second metal layer comprises Zr or Zr-X, wherein X is Nb, Ta, or Hf.

11. The bottom free-layer magnetic tunnel junction according to claim 1, wherein the free layer comprises one or more layers selected from FeB, FeB-X, FeCoB, FeCoB-X5, Fe, Fe-X, FeCo, and FeCo-X, wherein X is Be, Ni, Mo, Mg, Zr, Ta, V, Cr, W, Hf, Nb, or Tb.

12. A vertical bottom free layer spin-transfer torque magnetic random access memory cell, comprising the bottom free layer magnetic tunnel junction according to claim 1.

13. A method for manufacturing a bottom free-layer magnetic tunnel junction, the method comprising: A composite metal oxide seed layer is deposited on the bottom electrode, and A free layer containing boron (B) is deposited on the composite metal oxide seed layer; The deposition of the composite metal oxide seed layer includes: A first metal layer is deposited on the bottom electrode; A metal oxide layer is deposited on the first metal layer; Depositing a second metal layer on the metal oxide layer; and Oxygen treatment is performed on the second metal layer. The second metal layer comprises Nb, Zr, or Zr-X, where X is Nb, Ta, or Hf. The first metal layer comprises tantalum / iron cobalt boron (Ta / FeCoB).

14. The method of claim 13, wherein the oxygen treatment comprises a natural oxidation process or a free radical oxidation process.

15. The method of claim 13, wherein the oxygen treatment is performed at ambient temperature.

16. The method of claim 13, wherein the oxygen treatment is performed by exposing the metal oxide layer to oxygen prior to the deposition of the second metal layer.

17. The method of claim 16, further comprising performing annealing after deposition of the second metal layer to allow oxygen to migrate from the metal oxide layer to the second metal layer.

18. The method of claim 13, wherein the oxygen treatment comprises: Prior to the deposition of the second metal layer, the metal oxide layer is exposed to oxygen; as well as After the deposition of the second metal layer, the second metal layer is exposed to oxygen.

19. The method of claim 18, further comprising performing annealing to allow oxygen to migrate from the metal oxide layer to the second metal layer.

20. The method of claim 13, further comprising performing annealing at a temperature of 350°C to 400°C after deposition of the main tunneling barrier layer, polarization enhancement layer, or bottom pinned layer.

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