Patent Application
20190280186
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2018-044525, filed on Mar. 12, 2018, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to magnetic memories.
Magnetic memories (hereinafter also referred to as MRAMs (Magnetic Random Access Memories)) generally have a magnetic tunnel junction (MTJ) element that serves as a storage element. The MTJ element is formed on an electrode disposed on a substrate. The MTJ element has a multilayer structure including a first magnetic layer disposed above the electrode, a second magnetic layer disposed between the first magnetic layer and the electrode, and a nonmagnetic layer (“tunnel barrier layer”) disposed between the first magnetic layer and the second magnetic layer.
In order to avoid the degradation of characteristics of the MTJ element, side faces of the MTJ element are covered by a protective film of an insulating material such as Si3N4. The protective film covers an upper face of the electrode except for a region where the MTJ element is disposed, and a n of a lower insulating film disposed on the substrate.
Before embodiments of the present invention are described, how the present invention has been reached will be described.
A protective film of an insulating material such as Si3N4 is formed on side faces of an MTJ element, an upper face of an electrode other than a region where the MTJ element is formed, and an upper face of a lower insulating film disposed on a substrate. Both of the protective film and the lower insulating film are formed of a ceramic material, which is an insulating material. The ceramic materials are mainly bonded by ionic bonds, covalent bonds, or van der Waals bonds. The protective film may easily adhere to the upper face of the lower insulating film since the ceramic materials may easily form bonds at the interface.
However, the electrode and a part of the side faces of the MTJ element are mainly formed of a metal material. The metal materials are bonded by metal bonds. The protective film of a ceramic material thus is not easily bonded to the part of the side faces of the MTJ element and the upper face of the electrode since it is difficult to form bonds at the interface. Therefore, the protective film does not easily adhere to the part of the side faces of the MTJ element, and to the upper face of the electrode. Therefore, the characteristics of the MTJ element may degrade, and further the reliability of the magnetic memory may degrade.
A metal-ceramic reaction layer may be disposed between the metal material and the ceramic material in order to improve the degree of adhesion between the metal material and the ceramic material. However, the metal-ceramic reaction layer disposed on the side faces of the MTJ element may degrade characteristics of the MTJ element. The reason for this is that in the first place, the material of the protective film is chosen from those that are difficult to react with a material exposed on the side faces of the MTJ element so that no reaction such as oxidation is caused on the side faces of the MTJ element. Therefore, formation of the metal-ceramic reaction layer on the side faces of the MTJ element may cause a problem.
As the pitch of arranged MTJ elements decreases, the area in which the protective film is in contact with the lower insulating film decreases. Therefore, the area in which the protective film has good adhesion is decreased. On the other hand, as the pitch decreases, the area in which the protective film is in contact with the side faces of the MTJ element and the upper face of the electrode increases. Therefore, the area in which the protective film is difficult to adhere increases.
Thus, if the pitch of the arranged MTJ elements decreases, the adhesion of the protective film to the substrate degrades. This may increase the probability of the protective film coming off during the manufacture or the operation of the device. If the protective film comes off during the manufacture or the operation of the device, oxygen, water, or corrosive gases may enter the interface between the MTJ element and the protective film, and degrade the characteristics of the MTJ element. This in turn degrades the reliability of the magnetic memory. For example, if the pitch of the arranged MTJ elements is equal to 40 nm or less, the above-described problem becomes marked. If a sum of a length along a stacked direction of a multilayer structure of the MTJ element 10 and a thickness of the cap layer 20 is more than a half of the pitch of the arranged MTJ elements the above-described problem becomes marked.
The inventors of the present invention studied hard to obtain a magnetic memory that may solve the problem. Embodiments of such a magnetic memory will be described below.
A magnetic memory according to an embodiment includes: an electrode including a lower face, an upper face opposed to the lower face, and a side face that is different from the lower face and the upper face; a magnetoresistive element disposed on the upper face of the electrode, including a multilayer structure including a first magnetic layer disposed above the upper face of the electrode, a second magnetic layer disposed between the upper face of the electrode and the first magnetic layer, and a nonmagnetic layer disposed between the first magnetic layer and the second magnetic layer; a first insulating film disposed on the side face of the electrode; and a second insulating film including a first portion disposed on a side face of the multilayer structure of the magnetoresistive element, and a second portion, the first insulating film being disposed between the second portion and the side face of the electrode.
A contact plug 4i that is electrically connected to a part of a lower face of each electrode 6i (i=1, 2, 3) is disposed to be electrically connected to one of a source terminal and a drain terminal of a selection transistor 40i for selecting a corresponding MTJ element 101. The state “A is electrically connected to B” herein means that A may be directly connected to B or that A may be indirectly connected to B via a conductive material. A gate of the selection transistor 40i (i=1, 2, 3) is electrically connected to a wiring 50.
A cap layer 20i is disposed on each MTJ element 10i (i=1, 2, 3). The MTJ element 10i (i=1, 2, 3) and the cap layer 20i are included in a multilayer structure disposed on a corresponding electrode 6i.
An insulating film 100 containing, for example, silicon oxide is disposed to cover side faces of each contact plug 4i (i=1, 2, 3), side faces of each electrode 6i, and a region of the lower face of each electrode 6i that is not connected to the contact plug 4i. In other words, the contact plugs 41 to 43 that are electrically connected to the selection transistors 401 to 403, respectively, are disposed within the insulating film 100, and the electrode 6i that is electrically connected to a corresponding contact plug 4i (i=1, 2, 3) is embedded in the insulating film 100. The thickness of the insulating film 100 disposed on each side face of the electrode 6i (i=1, 2, 3) increases from the upper face of the electrode 6i downward. Therefore, the cross-sectional area, which is parallel to the upper face of the electrode 6i, of the insulating film 100 disposed on the side face of the electrode 6i (i=1, 2, 3) increases from the upper face to the lower face of the electrode 6i (i=1, 2, 3). The insulating film 100 has a recessed portion between adjacent two MTJ elements.
A protective film 24 containing, for example, silicon nitride is disposed to cover side faces of the insulating film 100 and side faces of the multilayer structure including the MTJ element 10i (i=1, 2, 3) and the cap layer 20i. The protective film 24 also covers the region of the upper face of the electrode 6i (i=1, 2, 3) where the MTJ element 101 is not disposed. The protective film 24 is disposed along side faces and a bottom of each recessed portion of the insulating film 100 between adjacent two MTJ elements.
An interlayer insulating film 26 is disposed to cover side faces of the protective film 24 but not to cover the upper face of the protective film 24 and the upper face of the cap layer 20i (i=1, 2, 3). In
A wiring 30i that is electrically connected to the upper face of the cap layer 20i (i=1, 2, 3) is disposed on the interlayer insulating film 26.
A method of writing data to each MTJ element 10i (i=1, 2, 3) in the magnetic memory according to the first embodiment including the above-described configuration will be described below. An example will be described, in which the magnetic layer 12 is a reference layer where a direction of magnetization is fixed, and the magnetic layer 16 is a storage layer where a direction of magnetization direction may be changed. If the magnetization direction of the magnetic layer 16 needs to be changed from antiparallel (opposite) to parallel (the same) relative to the magnetization direction of the magnetic layer 12, a write current is caused to flow from the magnetic layer 16 to the magnetic layer 12. As a result, spin-polarized electrons flow from the magnetic layer 12 to the magnetic layer 16 via the nonmagnetic layer 14, act on the magnetization of the magnetic layer 16, and change the magnetization direction of the magnetic layer 16 from antiparallel (opposite direction) to parallel (the same direction).
If the magnetization direction of the magnetic layer 16 needs to be changed from parallel to antiparallel relative to the magnetization direction of the magnetic layer 12, a write current is caused to flow from the magnetic layer 12 to the magnetic layer 16. As a result, spin-polarized electrons flow from the magnetic layer 16 to the magnetic layer 12 via the nonmagnetic layer 14. Electrons with spin that is in the same direction as the magnetization direction of the magnetic layer 12 pass through the magnetic layer 12. However, electrons with spin that is in the opposite direction to the magnetization direction of the magnetic layer 12 are reflected at the interface between the magnetic layer 12 and the nonmagnetic layer 14, and the reflected electrons act on the magnetization of the magnetic layer 16 to change the magnetization direction of the magnetic layer 16 from parallel to antiparallel.
If the magnetic layer 12 is a storage layer and the magnetic layer 16 is a reference layer, the direction of the current in each case is opposite to the above descriptions.
A method of reading data from the magnetic memory according to the first embodiment will be described, taking the case of the MTJ element 101 as an example. A voltage is applied to the wiring 50 to turn on the selection transistor 40i (i=1, 2, 3). Subsequently, a read current is caused to flow between one of the source terminal and the drain terminal of the selection transistor 401 and the wiring 301 via the MTJ element 101 to determine whether the magnetization direction of the magnetic layer 12 is parallel or antiparallel to the magnetic layer 16 in the MTJ element 101 based on the read current. As a result, data stored in the MTJ element 101 is read.
With the above-described configuration, the magnetic memory according to the first embodiment may have an increased contact area between the protective film 24 and the insulating film 100, which are bonded well with each other, even if the pitch of arranged MTJ elements is narrow. This may prevent the degradation of adhesion. As a result, the protective film may be prevented from coming off during the manufacture or the operation of the device. This in turn improves reliability of the magnetic memory.
Although each MTJ element 101 (i=1, 2, 3) is disposed on a region of the upper face of the electrode 6i in this embodiment, it may be disposed on the entire upper face of the electrode 6i. This means that the diameter of the electrode 6i (i=1, 2, 3) is the same as the diameter of the MTJ element 10i. In this case, the protective film 24 have a first portion arranged on each side face of the MTJ element 10i (i=1, 2, 3), and a second portion arranged on each side face of the electrode 6i, and the first portion and the second portion are continuously connected to each other.
Although the magnetoresistive elements 101 to 103 in this embodiment are magnetic tunnel junction (MTJ) elements in which the nonmagnetic layer 14 contains an insulating material, they may be giant magneto-resistance (GMR) elements in which the nonmagnetic layer 14 is a metal layer.
The magnetic layers 12 and 16 in this embodiment may be formed of CoFe or CoFeB. The magnetic layers 12 and 16 may have a synthetic multilayer structure.
The magnetic layers 12 and 16 in this embodiment may be magnetic layers of a material other than CoFeB or CoFe. The magnetic layers 12 and 16 in this embodiment may be formed a material having a magnetization that is perpendicular to the faces of the magnetic layers.
The magnetic layers 12 and 16 may be layers of a magnetic material such as a metallic element such as Ni, Fe, or C, an alloy such as Ni—Fe, Co—Fe, Co-Ni, or Co—Fe-Ni, an amorphous material such as (Co, Fe, Ni)—(Si, B), (Co, Fe, Ni)—(Si, B)—(P, Al, Mo, Nb, Mn), or Co—(Zr, Hf, Nb, Ta, Ti), or a Heusler alloy, or layers having a multilayer structure including layers of materials selected from the above-described materials. The expression (Co, Fe, Ni), for example, means that at least one of Co, Fe, and Ni is included. The Heusler alloys have a composition expressed as X2YZ where X is Co, Y is at least one of V, Cr, Mn, and Fe, and Z is at least one of Al, Si, Ga, and Ge.
The magnetic layers 12 and 16 may also be layers of a magnetic material that is a perpendicular magnetization material such as an alloy including any of FePt, CoPt, CoCrPt, and (Co, Fe, Ni)—(Pt, Ir, Pd, Rh)—(Cr, Hf, Zr, Ti, Al, Ta, Nb), or a material (Co, Fe)/(Pt, Ir, Pd). The magnetic layers 12 and 16 may also have a multilayer structure including stacked layers of these perpendicular magnetization materials.
A nonmagnetic element such as silver (Ag), copper (Cu), gold (Au), aluminum (Al), ruthenium (Ru), osmium (Os), rhenium (Re), tantalum (Ta), boron (B), carbon (C), oxygen (O), nitrogen (N), palladium (Pd), platinum (Pt), zirconium (Zr), iridium (Ir), tungsten (W), molybdenum (Mo), or niobium (Nb) may be added to the above-described magnetic materials to adjust magnetic characteristics, and also physical characteristics such as crystallinity, mechanical characteristics, and chemical characteristics.
The nonmagnetic layer 14 may be formed of an insulating material such as aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), aluminum nitride (AlN), silicon nitride (SiN), bismuth oxide (Bi2O3), magnesium fluoride (MgF2), calcium fluoride (CaF2), strontium titanate (SrTiO3), lanthanum aluminate (LaAlO3), aluminum oxinitride (Al—N—O), or hafnium oxide (HfO), or a composite material including a combination of the insulating materials.
The nonmagnetic layer 14 may also be formed of at least one nonmagnetic metal such as copper, silver, gold, vanadium, chromium, or ruthenium, or at least one of the above materials containing an insulating material for current constriction.
A method of manufacturing a magnetic memory according to a second embodiment will be described with reference to
As shown in
Next, a resist pattern 7i having the same size as each electrode 6i (i=1, 2, 3) is disposed on each electrode 6i (i=1, 2, 3), as shown in
Subsequently, the insulating film 100 is etched at portions between the electrodes, using the resist patterns 7i (i=1, 2, 3) as masks, by reactive ion etching (RIE), for example, to form recessed portions 102. Each recessed portion 102 has a tapered shape, and the opening area of each recessed portion 102 is decreased from the top to the bottom (
Etching conditions are selected in a manner that physical etching acts stronger than chemical etching, so that redeposition 100a caused by the etching of the insulating film 100 is attached to each side face of the electrode 6i (i=1, 2, 3). The redeposition 100a contains the same material as the insulating film 100 (
An embedded layer 8 is then formed to fill into each recessed portion 102, as shown in
Next, as shown in
Next, as shown in
The hard mask layer 17 is then patterned by anisotropic etching (for example, RIE), using the resist patterns 18a as masks, to form hard mask patterns 17a. Subsequently, the material layer 10 is patterned by anisotropic etching, using the hard mask patterns 17a as masks. As a result, MTJ elements 101 to 103 are formed (
Next, the embedded layer 8 is removed as shown in
Next, as shown in
Next, as shown in
Subsequently, as shown in
Next, as shown in
If the hard mask patterns 17a are formed of a conductive material, an upper wiring material layer is disposed to cover the upper faces of the hard mask patterns 17a, the upper face of the protective film 24, and the upper face of the interlayer insulating film 26. If the hard mask patterns 17a are formed of an insulating material, the hard mask patterns 17a are removed by selective etching, and then an upper wiring material layer that fills openings formed by the removal of the hard mask patterns 17a is disposed to cover the upper face and a part of the side faces of the protective film 24 and the upper face of the interlayer insulating film 26. Subsequently, the upper wiring material layer is patterned to form a wiring 30i connecting to the MTJ element 101 (i=1, 2, 3), thereby completing the magnetic memory shown in
The magnetic memory manufactured according to the manufacturing method of the second embodiment may have an increased contact area between the protective film 24 and the insulating film 100, which a bonded well with each other, even if the pitch of arranged MTJ elements is narrow. This may prevent the degradation of adhesion. As a result, the protective film may be prevented from coming off during the manufacture or the operation of the device. This in turn improves reliability of the magnetic memory.
In the drawings of the first and second embodiments, the side faces of each of the MTJ elements 10i (i=1, 2, 3) and the electrodes 6i are perpendicular to an upper face of the semiconductor substrate. The side faces of each of the MTJ elements 10i (i=1, 2, 3) and the electrodes 6i may have forward tapered shapes depending on manufacturing conditions. In this case, an area and a diameter of the lower face of the MTJ element 10i (i=1, 2, 3) is greater than an area and a diameter of the upper face of the MTJ element 10i respectively, an area and a diameter of the lower face of the electrode 6i (i=1, 2, 3) is greater than an area and a diameter of the upper face of the electrode 6i respectively.
The side faces of each of the MTJ elements 10i (i=1, 2, 3) and the electrodes 6i may have inverse tapered shapes depending on manufacturing conditions. In this case, the area and the diameter of the lower face of the MTJ element 10i (i=1, 2, 3) is smaller than the area and the diameter of the upper face of the MTJ element 10i respectively, the area and the diameter of the lower face of the electrode 6i (i=1, 2, 3) is smaller than the area and the diameter of the upper face of the electrode 6i respectively.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-044525 | Mar 2018 | JP | national |
