JP4560847B2 - Magnetoresistive random access memory - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetoresistive random access memory, and more particularly to a magnetoresistive random access memory using a magnetic tunnel resistance element.
[0002]
[Prior art]
A magnetoresistive random access memory (hereinafter referred to as MRAM) is a memory that determines 0 or 1 of information based on the spin direction of a magnetic film. Various materials have been proposed for use in this memory. Among them, the magnetic tunnel material has a large magnetoresistance change and electrical resistance, so that current flows in the magnetic film deposition direction of the magnetic tunnel resistance element. It is advantageous when used for a type of MRAM array.
[0003]
This magnetic tunnel resistance element has a structure in which an insulating film is sandwiched between two magnetic films. The magnitude of the magnetic field acting on these magnetic tunnel resistance elements is detected by using the fact that the magnitude of the magnetic tunnel current flowing between these two magnetic films changes depending on the angle formed by the spins of these two magnetic films. To do.
[0004]
When this magnetic tunnel resistance element is used for information recording, one layer is in the operating range (applied magnetic field range) of the magnetic tunnel resistance element, and its spin direction does not change. The other layer is configured such that the direction of the magnetic spin can be changed according to the direction of the magnetic field applied to the magnetic tunnel resistance element. The magnitude of resistance between the two magnetic layers corresponding to the parallel and antiparallel magnetic spin directions of the two magnetic films obtained as a result corresponds to 0 or 1 of information.
[0005]
When manufacturing a high-density memory using this magnetic tunnel resistance element, the magnetic tunnel resistance element can be processed to a size of around 1 μm. In order to obtain the magnetic stability of each magnetic layer, It has been reported that the ratio of the long side to the short side (hereinafter referred to as aspect ratio) of the magnetic tunnel resistance element is 3 or more. This is particularly important when the lower magnetic layer is a fixed layer (the direction of magnetic spin is fixed). Further, as the structure of the magnetic tunnel resistance element, as proposed by IBM, stable magnetic tunnel resistance characteristics can be obtained in a structure in which one of the two magnetic layers is changed in size. It has been reported.
[0006]
[Problems to be solved by the invention]
However, of the two magnetic films mentioned above, one of the case where the changed size structure of the magnetic film, taking the aspect ratio sufficient, a problem that the bit density per unit area is decreased There is.
[0007]
In addition, since it is necessary to provide a gap between the magnetic tunnel resistance elements, there is also a problem that the bit density per unit area is lowered when the aspect ratio is sufficiently high.
[0008]
The present invention has been made in view of such problems, and provides a high-density magnetoresistive random access memory by using a configuration in which a lower magnetic layer is common to a magnetic tunnel resistance element of 2 bits or more. For the purpose.
[0009]
[Means for Solving the Problems]
The magnetoresistive random access memory according to the present invention is:
A magnetic tunnel resistance element comprising a lower magnetic layer, a barrier film formed on the lower magnetic layer, and a plurality of upper magnetic layers formed on the barrier film;
An upper electrode connected to the upper surface of the magnetic tunnel resistance element;
A lower electrode connected to the lower surface of the magnetic tunnel resistance element;
A Cr film or a FeCo single film formed between the lower magnetic layer and the lower electrode;
It is characterized by having.
[0012]
In the present invention, it is preferable that the lower magnetic layer in contact with the barrier film has a composition including one or all selected from the group consisting of Ni, Co, and Fe.
[0013]
In the present invention, the bit density of the magnetoresistive random access memory can be determined only by the packing density of the upper magnetic layer by forming a plurality of upper magnetic layers in one lower magnetic layer. For this reason, a significant increase in density can be realized as compared with the conventional structure. In addition, since the lower magnetic layer can have a sufficient aspect ratio, magnetic stability can be obtained simultaneously with the increase in density.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1A is a schematic diagram of a magnetoresistive random access memory according to an embodiment of the present invention. (B) is a typical sectional view by an AA line of Drawing 1 (a). FIG. 2 is a circuit diagram showing an equivalent circuit of the magnetoresistive random access memory according to the embodiment of the present invention. FIG. 3 is a cross-sectional view taken along line BB in FIG.
[0015]
In the MRAM 1 of this embodiment, the magnetic tunnel resistance element 2 is formed on the lower electrode 3, respectively. Each magnetic tunnel resistance element 2 is provided with a word line 19. That is, as shown in FIG. 2, four diodes 12 and four magnetic tunnel resistance elements 2 connected in series to one lower electrode 3 are connected. The magnetic tunnel resistance elements 2 on different lower electrodes 3 are connected to each other by the upper electrode 4.
[0016]
Next, the configuration of the MRAM 1 will be described in detail. As shown in FIGS. 1B and 3, a lower electrode 3 composed of a first conductive film 6 made of, for example, Ti and a second conductive film 7 made of, for example, Cu is formed on a substrate 5. Is formed. On the lower electrode 3, for example, an antiferromagnetic film 8 made RhMn is made form. A lower magnetic layer 9 made of, for example, Co is formed on the antiferromagnetic film 8, and a barrier film 10 formed on the lower magnetic layer 9 by oxidizing an Al film, for example, is formed. Is provided. An upper magnetic layer 11 made of, for example, NiFe is formed on the barrier film 10. The anti-ferromagnetic film 8, the lower magnetic layer 9, the barrier film 10, and the upper magnetic layer 11 form the magnetic tunnel resistance element 2. That is, the same lower portion electrode 3, on the lower magnetic layer 9 and the barrier film 10, a plurality of (illustrated in FIG. 3, two) magnetic tunnel resistance element 2 is formed.
[0017]
Further, a Schottky film 13 made of, for example, Pt is formed on the upper magnetic layer 11. On the Schottky film 13, for example, a semiconductor film 14 made of Si doped with P is formed. On the semiconductor film 14, for example, an ohmic film 15 made of Ti is formed so as to be in ohmic contact with the semiconductor film 14. The diode 12 is formed by the Schottky film 13, the semiconductor film 14, and the ohmic film 15.
[0018]
Further, an interlayer insulating film 16 made of, for example, SiO ₂ is formed so as to cover the substrate 5, the lower electrode 3 , the barrier film 10, and the diode 12. In the interlayer insulating film 16, a contact hole 17 is opened on the magnetic tunnel resistance element 2. For example, the upper electrode 4 made of Cu is formed so as to bury the contact hole 17. In this way, the MRAM 1 is formed.
[0019]
As described above, a plurality of magnetic tunnel resistance elements 2 are formed on the lower electrode 3 , the lower magnetic layer 9 and the barrier film 10 , that is, a plurality of magnetic tunnel resistance elements 2 form one lower portion. By adopting a configuration in which the electrode 3 and the lower magnetic layer 9 are also used, the lower magnetic layer 9 can have a sufficient aspect ratio. For this reason, magnetic stability can be obtained, and the bit density of the MRAM 1 is determined only by the packing density of the upper magnetic layer 11, so that a significant increase in density can be realized as compared with the conventional structure.
[0020]
Further, as described above, by forming the antiferromagnetic film 8, the reversal magnetic field is generated by sufficient coercive force and exchange coupling so that the lower magnetic layer 9 is not reversed within the applied magnetic field range where the upper magnetic layer 11 is reversed. Can be shifted to the high magnetic field side.
[0021]
Next, a method for manufacturing the MRAM 1 of this embodiment will be described with reference to FIGS. 4A to 4D and FIGS. 5A and 5B are cross-sectional views showing a method of manufacturing a magnetoresistive random access memory according to an embodiment of the present invention in the order of steps.
[0022]
As shown in FIG. 4A, first, a previously cleaned substrate 5 made of, for example, a silicon substrate is set in a sputtering apparatus. The chamber of this sputtering apparatus is evacuated to 1 × 10 ⁻⁷ Torr or less. Then, for example, Ar gas having a purity of 99.9999% is introduced into the chamber until the pressure reaches 4 mTorr. For example, a direct current of 200 W is applied to the sputter gun installed in the chamber, a target of Ti and Cu having a target size of 126 mm in diameter is used, and the film formation rate is 12 nm / min. A Ti film having a thickness of 15 nm is formed on the substrate 5 as the film 6. On the first conductive film 6, for example, a Cu film having a film thickness of 300 nm is formed as the second conductive film 7 at a film formation rate of 25 nm / min.
[0023]
Subsequently, for example, in an Ar gas atmosphere of 4 mTorr, a DC power of 100 W is applied to a sputtering gun having a target size of 126 mm in diameter to form the antiferromagnetic film 8 at a film formation rate of 6.5 nm / min. A RhMn film having a thickness of 50 nm is formed. On the antiferromagnetic film 8, for example, the diameter of the target size by applying a DC power of 100W to sputter cancer 126 mm, as the lower magnetic layer 9 deposition rate at 6 nm / min, the film thickness is 30nm of A Co film is formed.
[0024]
Next, on the lower magnetic layer 9 , for example, a direct current power of 20 W is applied to a sputter gun having a target size of 126 mm in diameter, and the film formation rate is 2 nm / min and the film thickness is 1.8 nm using Al. An Al film is formed. After forming the Al film, the substrate 5 is moved to the processing chamber without breaking the vacuum, and, for example, pure oxygen is introduced until the pressure in the chamber reaches 100 Torr and left for 20 minutes. Perform oxidation treatment. Thereby, the barrier film 10 made of aluminum oxide is obtained.
[0025]
Next, on the barrier film 10, for example, the diameter of the target size by applying a DC power of 100W to sputter cancer 126 mm, as the upper magnetic layer 11 deposition rate at 65nm / min, the film thickness is 65nm of NiFe A film is formed.
[0026]
Next, the chamber of this sputtering apparatus is evacuated to 1 × 10 ⁻⁷ Torr or less, for example. Then, for example, Ar gas is introduced into the chamber until the pressure reaches 4 mTorr. For example, a DC power of 100 W is applied to a sputter gun equipped in the chamber, a Pt target having a target size of 126 mm in diameter is used, and a deposition rate is 9.8 nm / min. 13, a Pt film having a thickness of 30 nm is formed on the upper magnetic layer 11.
[0027]
Next, for example, the source gas is SiH ₄ + PH ₃ , the substrate temperature is 420 ° C., and P-doped Si having a film pressure of 500 nm is formed on the Schottky film 13 as the semiconductor film 14 by the CVD method. . Then, P is implanted 5 × 10 ¹⁵ into the semiconductor film 14 using an ion plating apparatus. Next, for example, Ar gas is introduced into the vacuum chamber until the pressure reaches 3.6 mTorr, 100 W DC power is applied to a sputtering gun having a target size of 126 mm in diameter, and the film formation rate is 11 nm / min. As the film 15, a Ti film having a thickness of 200 nm is formed.
[0028]
Next, as shown in FIG. 4B, a resist is patterned into the shape of the lower electrode 3. Then, for example, the lower electrode 3 is etched by ion milling with an input power of 500 V and 400 mA, a gas pressure of 0.2 mTorr, an etching rate of 70 nm / min. After the etching is completed, the resist is removed with acetone.
[0029]
Next, as shown in FIG. 4C, a resist is patterned into the shape of the magnetic tunnel resistance element 2. Next, for example, the magnetic tunnel resistance element 2 is etched by ion milling with an etching condition of, for example, an input power of 500 V and 400 mA, a gas pressure of 0.2 mTorr, an etching rate of 20 nm / min, and a beam angle of 0 degree. . Etching stops when the upper magnetic layer 11 is patterned, that is, when the barrier film 10 is slightly scraped. Next, in order to remove a so-called side wall deposit attached to the side wall of the workpiece after performing a predetermined etching, the beam angle is set to 60 degrees, and other than that, under the same etching conditions as the magnetic tunnel resistance element 2, Scrape off. Then, after the etching is completed, the resist is removed with acetone. The magnetic tunnel resistance element 2 has a short side of 2 μm and a long side of 8 μm.
[0030]
Next, the substrate 5 is again placed in the vacuum chamber of the sputtering apparatus after the etching is completed. Next, for example, after evacuating the vacuum chamber to 2 × 10 ⁻⁶ Torr or less, 5 mTorr of Ar gas is introduced. As shown in FIG. 4D, for example, by applying a power of 900 W and a frequency of 13.56 MHz to a target of SiO ₂ having a diameter of 126 mm, the film formation rate is 13 nm / min. A SiO ₂ film having a thickness of 1000 nm is formed.
[0031]
Next, as shown in FIG. 5A, patterning for processing the contact hole 17 is performed on the formed interlayer insulating film 16, and as the etching conditions, for example, the input power is 500 V, 400 mA, and the gas pressure is set. The contact hole 17 is opened by ion milling at 0.2 mTorr, the etching rate is 30 nm / min, the beam angle is 0 degree. Next, after the ion milling is completed, the resist is removed using, for example, acetone.
[0032]
Next, after the formation of the contact hole 17 is completed, it is set in a vacuum chamber. For example, the inside of the vacuum chamber is evacuated to 2 × 10 ⁻⁶ Torr or less, and then 5 mTorr of Ar gas is introduced. Then, as shown in FIG. 5B, for example, by applying a power of 200 W and a frequency of 13.56 MHz to a Cu target having a diameter of 126 mm, the film formation rate is 30 nm / min. A Cu film having a thickness of 300 nm is formed.
[0033]
Next, the upper electrode 4 is patterned with a resist. Then, for example, the upper electrode 4 is etched by ion milling with an input power of 500 V, 400 mA, a gas pressure of 0.2 mTorr, an etching rate of 70 nm / min, and the notch 18 is formed. Next, after the ion milling is completed, the resist is removed using, for example, acetone. Thereby, the MRAM 1 shown in FIG. 1 is formed.
[0034]
After this, the etched product is set in a vacuum chamber and evacuated to 2 × 10 ⁻⁶ Torr or less. Next, Ar gas is introduced until the pressure reaches 5 mTorr. For example, by applying a high frequency power of 900W is the SiO ₂ targets 126mm diameter, a second interlayer insulating film at a deposition rate of 13 nm / min (not shown), thickness 100nm of SiO ₂ film A film is formed on the upper electrode 4.
[0035]
Next, a second contact hole (not shown) is opened in the second interlayer insulating film. It is set in a vacuum chamber and evacuated to 2 × 10 ⁻⁶ Torr or less. Next, Ar gas is introduced until the pressure reaches 5 mTorr. For example, a direct current power of 200 W is applied to a Cu target having a diameter of 126 mm, and a Cu film having a film thickness of 300 nm is formed as the second contact hole as the word line 19 (not shown) at a film formation speed of 30 nm / min. The film is formed so as to be embedded. A wiring pad may be formed as necessary after the word line is formed.
[0036]
FIG. 6 is a graph showing the magnetoresistance change of the magnetoresistive random access memory according to the embodiment of the present invention, with the cell voltage on the vertical axis and the applied magnetic field on the horizontal axis. The MRAM 1 configured as described above generates a current when a voltage of 0.25 V is applied. Further, as shown in FIG. 6, the cell voltage changes according to the magnitude and direction of the applied magnetic field.
[0037]
FIGS. 7A and 7B are schematic diagrams showing current waveforms applied to the word lines. FIG. 7C shows the cell voltage on the vertical axis and the number of data write repetitions on the horizontal axis. It is a graph which shows the data writing characteristic of the magnetoresistive random access memory based on the Example of this. While a current of 10 mA is passed between the upper electrode 4 and the lower electrode 3 of the MRAM 1 configured as described above, a peak current height of 80 mA is applied to the word line 19 as shown in FIGS. When a pulse current is applied for 10 nsec, a response pulse of 2.2 mV is generated between the upper electrode 4 and the lower electrode 3 according to the direction of the pulse, as shown in FIG. Thus, it can be seen that information can be written.
[0038]
In this embodiment, the final resistance of one element is 20 kΩ · μm ² due to the oxidation treatment of the Al film. However, the resistance can be increased to about 200 kΩ · μm ² by extending the processing time. In addition, after the Al film is formed, oxygen is introduced into the vacuum chamber at 100 mTorr, oxygen plasma is generated at a high frequency of 13.56 MHz, and the Al film is exposed to oxygen plasma for 1 minute to form one final element. The resistance can be increased to 1 MΩ · μm ² .
[0039]
Further, the method for producing the barrier film 10 uses a method using pure oxygen. However, the present invention is not particularly limited to this, and the oxygen ion beam is changed to an Al film by changing to a natural oxidation method or oxygen plasma. For example, a method of irradiating and oxidizing the substrate can be used.
[0040]
In this embodiment, Cu is used as the lower electrode 3. However, the present invention is not particularly limited to this, and a conductive nonmagnetic metal or alloy such as W, Ta, Au, Mo and Cr. Can be used. Further, when the distance between the two magnetic tunnel resistance elements 2 formed is short, a part or all of the lower magnetic layer 9 may be used for the two magnetic tunnel resistance elements without using the nonmagnetic lower electrode 3. 2 can be used as the lower electrode 3 connected to the second electrode 3. Further, instead of the lower electrode 3, an antiferromagnetic film 8 or a laminated film of the lower magnetic layer 9 and Co can be used as the lower electrode 3.
[0041]
Furthermore, a dummy film for protecting the upper magnetic layer 11 when the contact hole 17 is processed can be formed on the upper magnetic layer 11. In this case, it is preferable to use a nonmagnetic metal or alloy as used for the lower electrode 3 as the material of the dummy film.
[0042]
In this embodiment, RhMn, which is a diamagnetic material, is used as the antiferromagnetic film 8, but the present invention is not particularly limited to this, and other antiferromagnetic materials such as FeMn or PtMn are used. Material can be used. Further, instead of the antiferromagnetic film 8, a Cr film or a FeCo single film having a sufficiently large coercive force can be used.
[0043]
Further, in this example, the lower magnetic layer is NiFe, but the present invention is not particularly limited to this, and the composition includes one or all selected from the group consisting of Ni, Co and Fe. Things can be used.
[0044]
Furthermore, in this embodiment, the semiconductor film 14 and the Schottky film 13 and the ohmic film 15 formed above and below the semiconductor film 14 are made of Si, Pt, and Ti, respectively. The present invention is not limited, and it is only necessary that the Schottky film 13 and the ohmic film 15 be formed above and below the semiconductor film 14. The semiconductor film 14 can also use other semiconductor materials such as GaAs. In the present invention, the magnetic tunnel resistance element 2 may be provided in series with two or more bits for the same lower electrode 3 and lower magnetic layer 9 , and the present invention is not limited to this embodiment.
[0045]
【The invention's effect】
In the present invention as described above, a plurality of upper magnetic layer, by the structure of forming the barrier film and Shita磁 layer, bit density of a magnetoresistive random access memory only packing density of the upper magnetic layer Can be determined. For this reason, a significant increase in density can be realized as compared with the conventional structure. Further, since the lower magnetic layer can have a sufficient aspect ratio, the magnetic stability of the lower magnetic layer can be obtained simultaneously with the increase in density.
[Brief description of the drawings]
FIG. 1A is a schematic diagram of a magnetoresistive random access memory according to an embodiment of the present invention. (B) is a typical sectional view by an AA line of Drawing 1 (a).
FIG. 2 is a circuit diagram showing an equivalent circuit of a magnetoresistive random access memory according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view taken along line BB in FIG.
4A to 4D are cross-sectional views showing a method of manufacturing a magnetoresistive random access memory according to an embodiment of the present invention in the order of steps.
FIGS. 5A and 5B are cross-sectional views showing a method of manufacturing a magnetoresistive random access memory according to an embodiment of the present invention in the order of steps. FIGS.
FIG. 6 is a graph showing the magnetoresistance change of the magnetoresistive random access memory according to the embodiment of the present invention, where the vertical axis represents the cell voltage and the horizontal axis represents the applied magnetic field.
FIGS. 7A and 7B are schematic diagrams showing current waveforms applied to word lines, and FIG. 7C shows the cell voltage on the vertical axis and the number of data write repetitions on the horizontal axis. It is a graph which shows the data writing characteristic of the magnetoresistive random access memory based on the Example of this.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1; Magnetoresistive random access memory (MRAM), 2; Magnetic tunnel resistive element, 3; Lower electrode, 4; Upper electrode, 5; Substrate, 6; First conductive film, 7: Second conductive film, 8; Magnetic film, 9; Lower magnetic layer, 10; Barrier film, 11; Upper magnetic layer, 12; Diode, 13; Schottky film, 14; Semiconductor film, 15; Ohmic film, 16; Interlayer insulating film, 17; , 18; notch, 19; word line

Claims (2)

A magnetic tunnel resistance element comprising a lower magnetic layer, a barrier film formed on the lower magnetic layer, and a plurality of upper magnetic layers formed on the barrier film;
An upper electrode connected to the upper surface of the magnetic tunnel resistance element;
A lower electrode connected to the lower surface of the magnetic tunnel resistance element;
A Cr film or a FeCo single film formed between the lower magnetic layer and the lower electrode;
A magnetoresistive random access memory. 2. The magnetoresistive random access memory according to claim 1 , wherein the lower magnetic layer in contact with the barrier film has a composition including one or all selected from the group consisting of Ni, Co, and Fe.

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