Magnetic tunnel junction (MTJ) is a core component in several applications including read-heads of hard disk drives, sensors and magneto-resistive random-access memory (MRAM). Among them, MRAM is an emerging non-volatile memory that is advantageous in terms of ultra-low power consumption and easy integration with logic circuit. The discovery of perpendicularly magnetized MTJ (p-MTJ) has attracted more attention than MTJ with in-plane magnetization, because the p-MTJ relies on interfacial perpendicular magnetic anisotropic (PMA) instead of magneto-static shape anisotropy, such that the size of p-MTJ can be further reduced while retaining sufficient thermal stability. Thermal stability, which is positively related to PMA, and tunneling magnetoresistance (TMR) ratio are key parameters for evaluating the performance of the p-MTJ. However, strong PMA and high TMR ratio are not easy to be achieved simultaneously during optimization of the p-MTJ. Hence, p-MTJ is continuously developed to achieve a high thermal stability and a high TMR ratio in order to obtain good data retention and read margin of memory cells in non-volatile magnetic memory.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “on,” “above,” “top,” “bottom,” “upper,” “lower,” “over,” “beneath,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
The present disclosure is directed to a magnetic tunnel junction (MTJ) element with improved thermal stability and a method for manufacturing the same. The MTJ element may be incorporated in various magnetic devices, such as magneto-resistive random-access memory (MRAM), sensor, biosensor, spin-transfer torque MRAM (STT-MRAM), spin-orbit torque MRAM (SOT-MRAM), spintronic devices (e.g., spin-torque oscillator (STO) or microwave-assisted magnetic recording (MAMR)), or various design of perpendicular magnetic anisotropic (PMA) spin valve, but are not limited thereto. Other suitable applications for the MTJ element are within the contemplated scope of disclosure. Furthermore, the dimension of the MTJ element is able to be adjusted, so that the MTJ element is permitted to be integrated in varieties of semiconductor technology nodes or generations, such as 65 nm, 85 nm, but is not limited thereto.
In some embodiments, as shown in
In some embodiments, the semiconductor substrate 2 may be made of an elemental semiconductor material, or an alloy semiconductor material, but is not limited thereto. Other suitable materials for the semiconductor substrate 2 are within the contemplated scope of disclosure. In some embodiments, a peripheral circuit (not shown) may be formed over the semiconductor substrate 2, and may include active devices (for example, transistors, or the like), passive devices (for example, capacitors, resistors, or the like), decoders, amplifiers, and combinations thereof. In some embodiments, through the interconnecting layers 32, each of the magnetic devices 4 can be electrically connected to the peripheral circuit or other suitable devices located above the magnetic devices 4. Other suitable peripheral circuits and routing for controlling the magnetic devices 4 are within the contemplated scope of disclosure.
In some embodiments, as shown in
The tunnel barrier layer 53 includes a first insulating material for electrons to tunnel therethrough. In some embodiments, the first insulating material of the tunnel barrier layer 53 includes oxide, nitride, or oxynitride, or combinations thereof, so as to induce a spin dependent tunneling effect between the reference layer 52 and the free layer 54. In some embodiments, the first insulating material of the tunnel barrier layer 53 includes, for example, but is not limited to, magnesium oxide (MgO), aluminum oxide (AlOx), silicon oxide (SiOx), titanium oxide (TiOx), tantalum oxide (TaOx), chromium oxide (CrOx), hafnium oxide (HfOx), zinc oxide (ZnO), or combinations thereof. Other suitable materials for the tunnel barrier layer 53 are within the contemplated scope of disclosure. In some embodiments, the tunnel barrier layer 53 is made of MgO having a (001) texture. In some embodiments, the tunnel barrier layer 53 has a thickness ranging from about 1 Å to about 30 Å.
In some embodiments, the reference layer 52 includes a first ferromagnetic material, such as cobalt (Co), iron (Fe), nickel (Ni), cobalt-iron alloy (CoFe), cobalt-iron-nickel alloy (CoFeNi), cobalt-boron alloy (CoB), iron-boron alloy (FeB), cobalt-iron-boron alloy (CoFeB), or combinations thereof. In some embodiments, the reference layer 52 may be formed as a single layer structure or a multi-layered structure, such as (Co/X)n, where X may be Ni, platinum (Pt), palladium (Pd), etc., and n is an integer greater than two. In some embodiments, the reference layer 52 exhibits perpendicular magnetic anisotropy (PMA) with a fixed magnetic orientation in a direction perpendicular to the plane of the semiconductor substrate 2. In some embodiments, the reference layer 52 further includes a non-magnetic coupling layer (not shown), such as ruthenium (Ru) or iridium (Ir), which is stacked with the ferromagnetic material and which serves as a moment diluting layer. In some embodiments, the reference layer 52 further includes a transition layer (not shown) which is in contact with the tunnel barrier layer 53 so as to induce or enhance interfacial PMA of the reference layer 52 by forming, for example, but not limited to, a ferromagnetic metal/oxide interface. Other suitable materials for the reference layer 52 are within the contemplated scope of disclosure. In some embodiments, the reference layer 52 has a thickness ranging from about 30 Å to about 160 Å.
In some embodiments, the free layer 54 includes a second ferromagnetic material, such as Fe, Co, Ni, CoFe, CoB, FeB, CoFeB, cobalt-iron-nickel-boron alloy (CoFeNiB), or combinations thereof. In some embodiments, the free layer 54 may be formed as a single layer structure or a multi-layered structure having alternatively stacked ferromagnetic and non-magnetic sub-layers. In some embodiments, the free layer 54 has a thickness ranging from about 10 Å to about 30 Å. In some embodiments, the tunnel barrier layer 53 and the free layer 54 together induce an interfacial PMA by forming electronic bonds between the second ferromagnetic material (e.g., CoFeB) and the first insulating material (e.g., MgO), for example, an iron-oxygen (Fe—O) bond (i.e., a bonding between an iron ion in the free layer 54 and an oxygen ion in the tunnel barrier layer 53).
The dusting layer 58 includes a non-magnetic metal. In some embodiments, the non-magnetic material of the dusting layer 58 includes molybdenum (Mo), tungsten (W), or a combination thereof. In some embodiments, the dusting layer 58 has a predetermined thickness to permit the interfacial PMA to be established between the tunnel barrier layer 53 and the free layer 54. That is to say, although the dusting layer 58 is interposed between the tunnel barrier layer 53 and the free layer 54, the dusting layer 58 does not completely separate the tunnel barrier layer 53 from the free layer 54, and a plurality of interfacial regions (not shown) are formed between the tunnel barrier layer 53 and the free layer 54 for inducing the interfacial PMA. In some embodiments, the dusting layer 58 has a body center cubic (bcc) crystalline structure, while in some alternative embodiments, the dusting layer 58 may have an amorphous structure. It is known to those in the art that there are several annealing steps performed at a temperature of up to 400° C. for several hours in back-end-of-line (BEOL) processes, and thus impurities (e.g., boron from the reference layer 52 or the free layer 54) will be inevitably diffused among the layers of the MTJ element 5 during annealing steps. Without being limited to any one theory, it is considered that less impurities at the interfacial regions between the tunnel barrier layer 53 (for example, MgO) and the free layer 54 (for example, CoFeB) may enable more Fe—O bonds to be established, thereby inducing a higher interfacial PMA. In the disclosure, it is believed that the dusting layer 58 serves as a diffusion barrier that is able to reduce impurities at the interfacial regions between the tunnel barrier layer 53 and the free layer 54 because vacancies between the second ferromagnetic material and the first insulating material have been occupied by the non-magnetic metal (i.e., Mo and/or W atoms), thereby enhancing the interfacial PMA effect of the free layer 54. The predetermined thickness of the dusting layer 58 has an optimizable value. Excess thickness of the first dusting layer 58 may interfere Fe—O bonds to be established, and causes reduction of interfacial PMA. On the contrary, if the dusting layer 58 is too thin, the dusting layer 58 may loss its function as a barrier layer. In some embodiments, the predetermined thickness of the dusting layer 58 is greater than 0 Å and less than about 3 Å. In some embodiments, when the dusting layer 58 is made of W, the predetermined thickness of the dusting layer 58 may range from about 0.3 Å to about 1.1 Å. In some embodiments, when the dusting layer 58 is made of Mo, the predetermined thickness of the dusting layer 58 may range from about 0.73 Å to about 2.64 Å.
In some embodiments, as shown in
In some embodiments, the MTJ element 5 further includes a seed layer 51 and a buffer layer 56, as shown in
In some embodiments, the seed layer 51 includes Ni, Ru, Pt, tantalum (Ta), chromium (Cr), nitride thereof, alloy thereof, or combinations thereof. In some embodiments, the seed layer 51 may be formed as a single layer structure or a multi-layered structure having a plurality of sub-layers. In some embodiments, the sub-layers of the seed layer 51 may be an amorphous film, a crystalline film, or a combination thereof. Other suitable materials or configuration for the seed layer 51 are within the contemplated scope of disclosure. In some embodiments, the seed layer 51 has a thickness ranging from about 30 Å to about 100 Å.
In some embodiments, the buffer layer 56 includes Ru, Ta, Mo, alloy thereof, or combinations thereof. In some embodiments, the buffer layer 56 may be formed as a single layer structure or a multi-layered structure. Other suitable materials or configuration for the buffer layer 56 are within the contemplated scope of disclosure. In some embodiments, the buffer layer 56 has a thickness ranging from about 30 Å to about 100 Å.
In some alternative embodiments, the MTJ element 5 may further include additional features, and/or some features present in the MTJ element 5 may be modified, replaced, or eliminated without departure from the spirit and scope of the present disclosure.
In step 61, the reference layer 52 is formed on the seed layer 51 using a deposition process, such as physical vapor deposition (PVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), and electron beam physical vapor deposition (EBPVD). Other suitable techniques for forming the reference layer 52 are within the contemplated scope of disclosure.
In step 62, the tunnel barrier layer 53 is formed on the reference layer 52 using, for example, a deposition process similar to those mentioned in step 61. Other suitable techniques for forming the tunnel barrier layer 53 are within the contemplated scope of disclosure.
In step 63, the dusting layer 58 is formed on the tunnel barrier layer 53 using, for example, a deposition process similar to those mentioned in step 61. In some embodiments, the dusting layer 58 is formed in a PVD chamber, in which a PVD target may be Mo, W, or a combination thereof, and in which a carrier gas (e.g., argon, nitrogen, helium, or the like) for generation of plasma has a flow rate ranging from about 0 sccm to about 1000 sccm. Other suitable techniques for forming the dusting layer 58 are within the contemplated scope of disclosure.
In step 64, the free layer 54 is formed on the dusting layer 58 using, for example, a deposition process similar to those mentioned in step 61. Other suitable techniques for forming the free layer 54 are within the contemplated scope of disclosure.
In step 65, the dusting layer 57 is formed on the free layer 54 using, for example, a deposition process similar to those mentioned in step 63. Other suitable techniques for forming the dusting layer 57 are within the contemplated scope of disclosure.
In step 66, the capping layer 55 is formed on the dusting layer 57 using, for example, a deposition process similar to those mentioned in step 61. Other suitable techniques for forming the capping layer 55 are within the contemplated scope of disclosure.
In step 67, the buffer layer 56 is formed on the capping layer 55 using, for example, a deposition process similar to those mentioned in step 61. Other suitable techniques for forming the buffer layer 56 are within the contemplated scope of disclosure.
In step 68, an annealing process is performed. In some embodiments, the annealing process is performed at a temperature ranging from about 300° C. to about 500° C. (for example, about 400° C.).
Details regarding the seed layer 51, the reference layer 52, the tunnel barrier layer 53, the free layer 54, the capping layer 55, the buffer layer 56, and the dusting layers 57, 58 are similar to those as described above, and thus details thereof are omitted for the sake of brevity.
In some embodiments, some steps in the method 6 may be modified, replaced, or eliminated without departure from the spirit and scope of the present disclosure. For example, when step 63 is omitted and the free layer 54 is formed on the tunnel barrier layer 53 in step 64, the MTJ element 5 shown in
In this disclosure, a MTJ element is provided with at least one dusting layer for enhancing thermal stability and keeping TMR ratio of the MTJ element. The dusting layer interposed between a ferromagnetic layer (e.g., a free layer) and an oxide layer (e.g., a capping layer or a tunnel barrier layer) is considered to act as a barrier layer to prevent diffusion of impurities (e.g., boron) to interfacial regions between the ferromagnetic layer and the oxide layer, so as to induce stronger interfacial PMA between the ferromagnetic layer and the oxide layer, thereby obtaining a MTJ element with a higher interfacial PMA and a higher thermal stability. Furthermore, in the case that the dusting layer is interposed between the free layer and the capping layer, coercive field (Hc) of the MTJ element is significantly enhanced and TMR ratio is kept at the same time, and other magnetic properties (e.g., canting) and electrical properties (e.g., read voltage, write voltage, and RA) are not significantly changed. Additionally, the dusting layer(s) can be suitably introduced in the MTJ element regardless of whether it is designed as a top spin valve configuration or a bottom spin configuration. Therefore, the structure of the MTJ element of the disclosure provides a flexible strategy for MTJ optimization.
In accordance with some embodiments of the present disclosure, a magnetic tunnel junction (MTJ) element includes a reference layer, a tunnel barrier layer, a free layer, and a dusting layer. The reference layer has a fixed magnetic orientation. The tunnel barrier layer is disposed on the reference layer, and includes an insulating material. The free layer has a changeable magnetic orientation, and includes a first surface and a second surface. The second surface is disposed to confront the tunnel barrier layer and opposite to the first surface. The dusting layer is formed on one of the first and second surfaces of the free layer, and includes a non-magnetic metal.
In accordance with some embodiments of the present disclosure, the non-magnetic metal of the dusting layer includes molybdenum (Mo), tungsten (W), or a combination thereof.
In accordance with some embodiments of the present disclosure, the dusting layer is formed on the second surface of the free layer and interposed between the tunnel barrier layer and the free layer, and has a predetermined thickness to permit an interfacial perpendicular magnetic anisotropy (PMA) to be established between the tunnel barrier layer and the free layer.
In accordance with some embodiments of the present disclosure, the predetermined thickness of the dusting layer is greater than 0 Å and less than 3 Å.
In accordance with some embodiments of the present disclosure, the insulating material of the tunnel barrier layer includes oxide, nitride, oxynitride, or combinations thereof.
In accordance with some embodiments of the present disclosure, a magnetic tunnel junction (MTJ) element includes a reference layer, a tunnel barrier layer, a free layer, a capping layer, and a dusting layer. The reference layer has a fixed magnetic orientation. The tunnel barrier layer is disposed on the reference layer, and includes a first insulating material. The free layer has a changeable magnetic orientation, and includes a first surface and a second surface. The second surface is disposed to confront the tunnel barrier layer and opposite to the first surface. The capping layer is disposed on the second surface of the free layer, and includes a second insulating material. The dusting layer is formed on one of the first and second surfaces of the free layer, and includes a first non-magnetic metal.
In accordance with some embodiments of the present disclosure, the dusting layer is formed on the first surface of the free layer and is interposed between the free layer and the capping layer.
In accordance with some embodiments of the present disclosure, the MTJ element further includes an additional dusting layer which is formed on the second surface of the free layer, which is interposed between the tunnel barrier layer and the free layer, and which includes a second non-magnetic metal.
In accordance with some embodiments of the present disclosure, each of the first and second non-magnetic metals independently includes molybdenum (Mo), tungsten (W), or a combination thereof.
In accordance with some embodiments of the present disclosure, the dusting layer has a predetermined thickness to permit an interfacial perpendicular magnetic anisotropy (PMA) to be established between the free layer and the capping layer. The additional dusting layer has a predetermined thickness to permit an interfacial PMA to be established between the tunnel barrier layer and the free layer.
In accordance with some embodiments of the present disclosure, the predetermined thickness of each of the dusting layer and the additional dusting layer is greater than 0 Å and less than 3 Å.
In accordance with some embodiments of the present disclosure, each of the first and second insulating materials independently includes metal oxide, metal nitride, metal oxynitride, or combinations thereof.
In accordance with some embodiments of the present disclosure, a method for manufacturing a magnetic tunnel junction (MTJ) element includes: forming a tunnel barrier layer on a reference layer which has a fixed magnetic orientation, the tunnel barrier layer including a first insulating material; forming a free layer on the tunnel barrier layer, the free layer having a changeable magnetic orientation; and forming a dusting layer to be in contact with the free layer, the dusting layer including a first non-magnetic metal.
In accordance with some embodiments of the present disclosure, the dusting layer is interposed between the tunnel barrier layer and the free layer.
In accordance with some embodiments of the present disclosure, the method further includes forming a capping layer on the free layer. The capping layer includes a second insulating material. The dusting layer is interposed between the free layer and the capping layer.
In accordance with some embodiments of the present disclosure, each of the first and second insulating materials independently includes metal oxide, metal nitride, metal oxynitride, or combinations thereof.
In accordance with some embodiments of the present disclosure, the method further includes forming an additional dusting layer between the tunnel barrier layer and the free layer. The additional dusting layer includes a second non-magnetic metal.
In accordance with some embodiments of the present disclosure, each of the first and second non-magnetic metals independently includes molybdenum (Mo), tungsten (W), or a combination thereof.
In accordance with some embodiments of the present disclosure, the dusting layer has a predetermined thickness to permit an interfacial perpendicular magnetic anisotropy (PMA) to be established between the free layer and the capping layer. The additional dusting layer has a predetermined thickness to permit an interfacial PMA to be established between the tunnel barrier layer and the free layer.
In accordance with some embodiments of the present disclosure, the dusting layer is formed by physical vapor deposition.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes or structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.