JP5689932B2 - Method for manufacturing tunnel magnetoresistive element - Google Patents

Description

  The present invention relates to a magnetic reproducing head of a magnetic disk drive device, a storage element of a magnetic random access memory, and a magnetic sensor.

  A tunnel magnetoresistive element using crystalline MgO as a tunnel barrier layer exhibits a huge MR ratio (magnetoresistive change rate) of 200% or more at room temperature. Therefore, a magnetic reproducing head of a magnetic disk drive device or a magnetic random access memory Application to (MRAM) storage elements and magnetic sensors is expected. In a conventional magnetoresistive element using MgO as a tunnel barrier layer, an RF magnetron sputtering method using an MgO sintered target has been used to form the MgO tunnel barrier layer (Patent Document 1, Non-Patent Document). 1-5). However, the method of forming MgO by RF magnetron sputtering using an MgO sintered target has a problem that the normalized tunnel resistance value (RA) is likely to vary, and there is a possibility that the yield at the time of device manufacture is significantly reduced.

  In order to avoid such a problem, several methods for forming an MgO tunnel barrier layer without using an MgO sintered target are known.

As a method for forming the MgO tunnel barrier layer, Tsann et al. Firstly formed a metal Mg layer, secondly laminated an oxygen-doped metal Mg layer, and thirdly, oxidized the laminated body. A three-stage formation method has been proposed (Patent Document 2).
As a method for forming the MgO tunnel barrier layer, the first Mg layer is formed, the first Mg layer is formed into a MgO layer by a natural oxidation method, and the second Mg layer is formed on the MgO layer. And a three-stage formation method in which a first Mg layer is formed, an MgO layer is formed on the first Mg layer by reactive sputtering, and a second Mg layer is formed on the MgO layer. (Patent Document 3).

  Hong et al., As a method of forming the MgO tunnel barrier layer, formed a first Mg layer, converted the first Mg layer into a first MgO layer by radical oxidation, and annealed the first MgO layer to give (001) crystal orientation. A five-stage formation method is proposed in which a second Mg layer is formed on the first MgO layer, and the second Mg layer is naturally oxidized to form a second MgO layer. Hong et al. Also formed a first Mg layer, converted the first Mg layer into a first MgO layer by radical oxidation, formed a second Mg layer on the first MgO layer, and radically oxidized the second Mg layer. A five-stage formation method has also been proposed in which a second MgO layer is formed and a third Mg layer is formed on the second MgO layer (Patent Document 4).

  Miura et al., As a method for forming an MgO tunnel barrier layer, formed a first Mg layer, naturally oxidized the first Mg layer, formed a second Mg layer on the first Mg layer, and formed the second Mg layer on the first Mg layer. A four-stage formation method has been proposed in which natural oxidation is performed at an oxygen pressure lower than that during oxidation of the first Mg layer (Patent Document 5).

  Dave et al. Used MgO tunnel barrier layer formation method by plasma oxidation of metal Mg, radical oxidation of metal Mg, reactive sputtering with Ar: oxygen ratio of 5: 3, and MgO sintered target. Four types of RF sputtering methods are introduced (Non-Patent Document 6). Oh et al. Also introduced a method for radical oxidation of metallic Mg as a method for forming an MgO tunnel barrier layer (Non-patent Document 7).

JP 2006-080116 A US Pat. No. 6,841,395 JP 2007-142424 A JP 2007-173843 A JP 2007-305768 A

D. D. Djayapraira et al. “Applied Physics Letter”, 86, 092502 (2005). J. et al. Hayagawa et al., “Japan Journal of Applied Physics”, 44, L587 (2005). K. Tsunekawa et al., "Applied Physics Letter", 87, 072503 (2005). S. Ikeda et al., “Japan Journal of Applied Physics”, 44, L1442 (2005). Y. Nagamine et al., "Applied Physics Letter", 89, 162507 (2006). R. W. Dave et al., “IEEE Transactions on Magnetics”, 42, 1935 (2006). S. C. Oh et al., “IEEE Transactions on Magnetics”, 42, 2642 (2006).

If an attempt is made to form an MgO tunnel barrier layer by simply oxidizing metal Mg, it is difficult to obtain an RA of several hundred Ω · μm ² or less, as introduced in Non-Patent Document 6 and Non-Patent Document 7. This is considered to be because when Mg metal is exposed to an oxygen atmosphere, a passive film is formed on the surface and oxidation is less likely to proceed deeper than that.

  Therefore, Patent Document 4 and Patent Document 5 propose a method for solving the above problem by repeating film formation and oxidation of metal Mg twice. However, the method of repeating the film formation and oxidation of metal Mg twice has a problem that the production throughput is remarkably lowered by going back and forth between the film formation chamber and the oxidation treatment chamber. Alternatively, in order to avoid a decrease in throughput due to repeated conveyance, a method of providing two metal Mg film forming chambers and two oxidation treatment chambers is conceivable. In that case, however, device production is increased due to an increase in apparatus cost and an increase in installation area. The problem of increasing the cost arises.

  In the methods of Patent Document 2 and Patent Document 3, the number of processes is relatively small, and the problems of throughput and production cost are solved. However, the MR ratio in the low RA region is 40% or less, and the performance of the tunnel magnetoresistive element using the MgO tunnel barrier layer is not sufficiently exhibited. Further, since there is no example of RA variation that greatly affects the yield, it is unclear whether the process is suitable for production.

  An object of the present invention is to provide a method and an apparatus for manufacturing a tunnel magnetoresistive element that has a relatively small number of steps and has excellent characteristics of RA uniformity and a high MR ratio at low RA. To do.

In order to achieve such an object, one aspect of the present invention is a method of manufacturing a tunnel magnetoresistive element having a first ferromagnetic layer, a tunnel barrier layer, and a second ferromagnetic layer, the tunnel barrier layer being Forming a first metal layer on the first ferromagnetic layer by sputtering the metal target by applying power to the metal target to form plasma, among the early stage and late stage of deposition, without introducing either stage by oxygen gas, as engineering of forming a first metal layer which is an oxygen-doped by introducing the other stages only oxygen gas have a step of forming the first metal layer is characterized to be in the metal target in the same chamber successively performed in a state which supplied power.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing apparatus of a tunnel magnetoresistive element which have few dispersion | variations in RA and can obtain a high MR ratio in low RA can be provided.

It is a top view which shows typically the structure of the sputtering device which can be used for manufacture of the tunnel magnetoresistive element of this invention. It is a cross-sectional schematic diagram of the tunnel magnetoresistive element which concerns on this embodiment. It is a film | membrane block diagram of the tunnel magnetoresistive element produced using the manufacturing method and manufacturing apparatus of this invention. It is a formation flow of the tunnel barrier layer by a present Example. 5a and 5b are graphs in which the MR ratio and RA of the present tunnel magnetoresistive element are plotted with respect to the oxidation time. This is a flow of forming a tunnel barrier layer when oxygen gas mixing is stopped at the beginning and end of film formation when oxygen is doped during film formation of the first metal layer. 6 is a schematic time chart of input power, shutter opening / closing, Ar gas introduction, and oxygen gas introduction when forming a metal Mg layer. It is the graph which showed the relationship between RA and MR ratio of the tunnel magnetoresistive element produced by this method. In the tunnel magnetoresistive element which concerns on Example 3, it is the graph which showed the board | substrate surface distribution of RA when only the oxidation time of radical oxidation was 100 second. 10 is a graph showing variations between RA substrates when the oxidation time of radical oxidation is only 20 seconds in the tunnel magnetoresistive element according to Example 4. FIG. 6 is a graph showing the MR ratio when the thickness of the second metal Mg layer is changed in the magnetic tunnel element of Example 1.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view schematically showing the configuration of a sputtering apparatus that can be used for manufacturing the tunnel magnetoresistive element of the present invention. In such an apparatus, a vacuum transfer chamber 20 in which two robots 28 for substrate transfer are mounted, sputtering chambers 21 to 24 connected to the vacuum transfer chamber 20, a substrate pretreatment chamber 25, an oxidation treatment chamber 26, and a load. The lock chamber 27 is configured. All the rooms except the load lock chamber 27 are vacuum chambers of 2 × 10 ⁻⁶ Pa or less, and the movement of the substrate between the vacuum chambers is performed in a vacuum by the vacuum transfer robot 28.

  A substrate for forming a spin-valve type tunnel magnetoresistive thin film is placed in a load lock chamber 27 which is first brought to atmospheric pressure. After the load lock chamber 27 is evacuated, it is transferred to a desired vacuum chamber by a vacuum transfer robot 28. Is done.

As an example, a case where a bottom type spin-valve type tunnel magnetoresistive thin film having a laminated ferrimagnetic pinned layer as a pinned magnetic layer produced in an example described later will be described.
FIG. 2 is a schematic cross-sectional view of the tunnel magnetoresistive element according to this embodiment.

  A specific configuration of each layer will be described with reference to FIG. The lower electrode layer 2 has a stacked structure of Ta (5 nm) / CuN (20 nm) / Ta (3 nm) / CuN (20 nm) / Ta (3 nm). The antiferromagnetic layer 3 is a laminated ferrimagnetic fixed layer made of PtMn (15 nm), the magnetization fixed layer 4 is made of CoFe (2.5 nm) / Ru (0.85 nm) / CoFeB (3 nm), and 4b CoFeB is the first strong. Corresponds to the magnetic layer. The tunnel barrier layer 6 is MgO (1.5 nm). The magnetization free layer 7 is CoFeB (3 nm) and corresponds to the second ferromagnetic layer. As the protective layer 8, a stacked structure of Ta (8 nm) / Cu (30 nm) / Ta (5 nm) / Ru (7 nm) is used. In addition, () shows the film thickness.

  The PtMn layer has a Pt content of 47 to 51 (atomic%) by adjusting the composition of the sputtering target and the film formation conditions (gas type, gas pressure, input power) so as to be ordered by annealing and to exhibit antiferromagnetism. ) To form a PtMn layer.

In order to efficiently form the film configuration as described above, a sputtering target is disposed in each sputtering chamber as follows. The sputtering chamber 21 is Ta (tantalum) and Cu (copper), and the sputtering chamber 22 is Co ₇₀ Fe ₃₀ (cobalt-iron), PtMn (platinum-manganese), Ru (ruthenium), Co ₆₀ Fe ₂₀ B _20. (Cobalt-iron-boron) and Mg are arranged in the sputtering chamber 23 as sputtering targets 21a to 21b, 22a to 22d, and 23a, respectively. Further, the sputtering chamber 24 to place _{Ta, Co 60 Fe 20 B 20} , Mg, Ru, Cu as the sputtering target 24 a to 24 e.

The spin valve tunnel magnetoresistive thin film having the laminated ferrimagnetic structure which is the most complicated film structure in the present invention is formed as follows.
First, the substrate 1 is transferred to the substrate pretreatment chamber 25, and about 2 nm of the surface layer contaminated in the atmosphere is physically removed by reverse sputter etching. Thereafter, the substrate 1 is transferred to the sputtering chamber 21 to form the lower electrode layer 2 having a laminated structure of Ta / CuN / Ta / CuN / Ta. At this time, CuN is formed by adding a small amount of nitrogen in addition to Ar as a sputtering gas, using a Cu target when forming a CuN film. Thereafter, the substrate is moved to the sputtering chamber 22 to form an antiferromagnetic layer 3 made of PtMn / CoFe / Ru and a magnetization fixed layer 4 (first ferromagnetic layer) made of CoFeB. Here, IrMn (iridium-manganese) may be used as the antiferromagnetic layer 3 instead of PtMn. In that case, it is preferable to use a Ru layer as the underlying layer 9 of the IrMn layer. In such a case, the film configuration formed in the sputtering chamber 22 is Ru / IrMn / CoFe / Ru / CoFeB.

  Next, a method for forming a tunnel barrier layer will be described. After forming the film up to CoFeB as the first ferromagnetic layer in the sputtering chamber 22, the substrate 1 is moved to the sputtering chamber 23, and metal Mg is formed while doping oxygen. As an example of the oxygen doping method, Ar and oxygen are used as the sputtering gas. Here, the oxygen gas to be mixed is preferably 30% or less of the sputtering gas. This is to suppress the surface oxidation of the Mg target.

  Individual gas inlets are provided in the vacuum chamber, and gas is introduced while individually controlling the flow rates of Ar and oxygen. The oxygen gas introduction timing at the time of oxygen doping need not always be the same as the Ar introduction timing of the sputtering gas, and may be delayed from the Ar introduction timing or earlier than the Ar stop timing.

  Next, the substrate 1 is moved to the oxidation treatment chamber 26 and oxidation treatment is performed. As the method of oxidation treatment, either natural oxidation or radical oxidation may be used. In the case of natural oxidation, the pressure in the oxygen atmosphere is maintained at 0.01 to 10 Torr and left for a predetermined time. In the case of radical oxidation, a high frequency is applied to an electrode in an oxygen atmosphere to generate oxygen plasma, and the charge in the plasma is passed through a shower plate having a plurality of holes having a length of about 10 mm and a diameter of about 1 mm. The substrate is irradiated with particles (active oxygen species and oxygen) other than the particles.

  Next, the substrate 1 is moved to the sputtering chamber 24 to form a film of Mg / CoFeB / Ta / Cu / Ta / Ru. The thickness of Mg is preferably 0.1 nm or more and 0.6 nm or less. By doing so, as will be described later with reference to FIG. 11, an MR ratio of 100% or more can be expressed.

  Thereafter, the produced tunnel magnetoresistive thin film is put in an annealing furnace in a magnetic field, and is annealed at a desired temperature and time in a vacuum while applying a magnetic field parallel to one direction with a strength of 8 kOe or more. Empirically, the temperature is 250 ° C. or higher and 360 ° C. or lower. A long time of 5 hours or more is preferable at a low temperature, and a short time of 2 hours or less is preferable at a high temperature.

  In the above-described embodiment, Ar (argon) is a main component as a sputtering gas. However, the present invention is not limited to this. For example, He (helium), Ne (neon), Kr (krypton), A sputtering gas mainly containing at least one of Xe (xenon) may be used.

  Next, embodiments of the present invention will be described with reference to the drawings.

Example 1
FIG. 3 is a film configuration diagram of a tunnel magnetoresistive element manufactured by using the manufacturing method and manufacturing apparatus according to the present invention. The film configuration is the same as that shown in FIG. 2 except that IrMn having a thickness of 7 nm is used as the antiferromagnetic layer 3 and a Ru layer having a thickness of 5 nm is used as the underlayer 9.

With reference to FIG. 4, the formation method of the tunnel barrier layer according to the present embodiment will be described.
FIG. 4 is a flow chart for forming a tunnel barrier layer according to this embodiment.
In step S401, the layers up to the first ferromagnetic layer were formed in the same manner as in the above-described embodiment.
In step S403, a film of 1.2 nm metal Mg was deposited on the CoFeB layer serving as the first ferromagnetic layer in an atmosphere into which 15 sccm of Ar gas and 5 sccm of oxygen were independently introduced (the mixed oxygen concentration was 25%). Next, in step S405, the substrate was oxidized by being left in an oxygen atmosphere of 0.1 Torr or 1 Torr for 60 to 600 seconds in an oxidation treatment chamber.
Finally, in step S407, a 0.2-nm metallic Mg film was formed in an atmosphere into which only Ar gas was introduced at 15 sccm. After that, in step S409, the film formation of the tunnel magnetoresistive element was completed by forming the film up to CoFeB / Ta / Cu / Ta / Ru.

  The tunnel magnetoresistive element was placed in an annealing furnace in a magnetic field after film formation, and annealed in a magnetic field at 360 ° C. for 2 hours while applying a 1 T magnetic field in a vacuum.

5a and 5b are graphs in which the MR ratio and RA of the present tunnel magnetoresistive element are plotted with respect to the oxidation time. As shown in FIG. 5a, it can be seen that an MR ratio exceeding 100% is obtained under any oxidation conditions. As shown in FIG. 5b, for RA, the RA increases as the oxidation time increases under any oxidation condition, but the value of 0.1 Torr is about half that of the low pressure condition of 1 Torr compared to the high pressure condition of 1 Torr. It is low. The lowest RA was obtained when an oxidation treatment of 0.1 seconds was performed for 60 seconds, and an MR ratio of 121% was achieved with 2.6 Ωμm ² of RA.

  The MR ratio and RA were measured by the Current-In-Plane-Tunneling (CIPT) method using a 12-terminal probe. The measurement principle of the CIPT method is D.C. C. Worledge, P.M. L. Troilloud, “Applied Physics Letters”, 83 (2003), 84-86.

(Example 2)
FIG. 6 shows a flow of forming a tunnel barrier layer when oxygen gas mixing is stopped at the beginning and the end of film formation when oxygen is doped during film formation of the first metal layer. At this time, radical oxidation was used as a method of oxidizing the first metal layer. The film configuration of FIG. 2 was used as the film configuration of the tunnel magnetoresistive element.

Hereinafter, the flow of forming the tunnel barrier layer will be described with reference to FIG.
In step S601, the layers up to the first ferromagnetic layer were formed in the same manner as in the above-described embodiment.
In step S603, the first metal layer was formed on the first ferromagnetic layer through the following three steps. That is, in the initial stage of film formation of the first metal layer, the first metal layer was formed in an Ar gas atmosphere without introducing oxygen gas (lower layer of the first metal layer). In the middle stage of film formation, the first metal layer was formed in an atmosphere into which Ar gas and oxygen gas were introduced (intermediate layer of the first metal layer). Further, in the latter stage of film formation, the first metal layer was formed in an Ar gas atmosphere without introducing oxygen gas (upper layer of the first metal layer). By doing so, it is possible to prevent the first ferromagnetic layer and the second ferromagnetic layer from being oxidized.

Hereinafter, step S603 will be described in more detail.
First, in the sputtering chamber 23, a 1.2 nm-thick metal Mg (first metal layer) is formed on the CoFeB layer serving as the first ferromagnetic layer.
FIG. 7 shows a schematic time chart of the input power, shutter opening / closing, Ar gas introduction, and oxygen gas introduction during the deposition of the 1.2 nm metal Mg layer. First, power is supplied to the cathode with the Mg target and Ar gas is introduced into the vacuum chamber almost simultaneously to generate plasma. The power to be input is DC 50 W, and the flow rate of Ar gas to be introduced is 100 sccm. In this pre-sputtering time, the shutter disposed between the target and the substrate is closed, so that no film adheres to the substrate.

  Next, the shutter is opened and film formation is started. When the film thickness reaches 0.6 nm (corresponding to the lower layer of the first metal layer), 5 sccm (oxygen concentration = 4.76%) of oxygen gas is introduced, and the Mg layer is doped with a small amount of oxygen. When the thickness of the Mg layer reaches 1.0 nm (corresponding to the intermediate layer of the first metal layer), the introduction of oxygen is stopped. Subsequently, the remaining 0.2 nm Mg layer is deposited in an Ar atmosphere (corresponding to the upper layer of the first metal layer), and the deposition of the 1.2 nm first metal layer is completed.

  In this embodiment, the first metal layer is formed in an Ar atmosphere without introducing oxygen in the initial stage and the late stage of forming the first metal layer. There is no need, and a method of forming the first metal layer in an Ar atmosphere without introducing oxygen only in one of the film forming steps may be adopted.

  Next, in step S605, the substrate is moved to the oxidation treatment chamber 26 and radical oxidation is performed. During radical oxidation, 700 sccm of oxygen gas was introduced into the vacuum chamber, and 300 W of RF power was applied to the electrodes. The oxidation time was 10 seconds.

  Finally, also in step S607, the substrate is moved to the sputtering chamber 24, and 0.3 nm of metal Mg (corresponding to the second metal layer) is formed. Next, in step S609, the second and subsequent ferromagnetic layers were formed in the same manner as in the previous embodiment.

FIG. 8 is a graph showing the relationship between the RA and MR ratio of a tunnel magnetoresistive element manufactured by this method. For comparison, data when oxygen was not introduced during the formation of the first metal Mg layer was also plotted. By introducing oxygen at the time of forming the first metal Mg layer and doping the metal Mg layer with oxygen, a high MR ratio of 86% was achieved with a low RA of 2.5 Ωμm ² .

(Example 3)
FIG. 9 shows the substrate surface of the RA when only the oxidation time of radical oxidation is set to 100 seconds in the tunnel magnetoresistive element similar to the film configuration of the tunnel magnetoresistive element used in Example 2 and the MgO tunnel barrier forming method. It is the graph which showed internal distribution. The horizontal axis is the distance from the center of the 300 mm diameter wafer. For comparison, an RA distribution of a tunnel magnetoresistive element in which an MgO tunnel barrier is directly formed from an MgO sintered target by RF sputtering is also shown. According to this, the RA distribution of the tunnel magnetoresistive element formed by the method of the present invention is 1.6%, which is clearly better than the RA distribution of 9.4% by the RF sputtering method of the MgO sintered target. I know that there is.

Example 4
FIG. 10 is also a tunnel magnetoresistive element similar to the film configuration of the tunnel magnetoresistive element used in Example 2 and the method of forming the MgO tunnel barrier, and the RA resistance when only the oxidation time of radical oxidation is set to 20 seconds. It is the graph which showed the variation between board | substrates. The horizontal axis represents the number of substrates processed continuously. For comparison, the RA variation of the tunnel magnetoresistive element in which the MgO tunnel barrier is directly formed by RF sputtering from the MgO sintered target is also shown. According to this, the RA variation between the substrates of the tunnel magnetoresistive element formed by the method of the present invention is 1.3%, which is clearly better than the RA variation of 6.7% of the method by RF sputtering of the MgO sintered target. It turns out that it is a result.

(Example 5)
FIG. 10 is a graph showing the MR ratio when the thickness of the second metal Mg layer is changed in the magnetic tunnel element of Example 1. It was found that the MR ratio was remarkably increased by forming the second metal Mg layer. From this result, the thickness of the metal Mg layer formed as the second metal layer is preferably 0.1 nm or more and 0.6 nm or less. By doing so, an MR ratio of 100% or more can be realized.

Claims (9)

A method of manufacturing a tunnel magnetoresistive element having a first ferromagnetic layer, a tunnel barrier layer, and a second ferromagnetic layer,
The step of producing the tunnel barrier layer comprises
Forming a first metal layer on the first ferromagnetic layer by sputtering the metal target by applying power to the metal target to form a plasma, Of the latter stages, the process includes forming an oxygen-doped first metal layer by introducing oxygen gas only in the other stage without introducing oxygen gas only in one stage,
The step of forming the first metal layer is continuously performed in a state where electric power is supplied to the metal target in the same chamber.   2. The method of manufacturing a tunnel magnetoresistive element according to claim 1, wherein the first metal layer is Mg (magnesium).   The first metal layer is formed by sputtering using at least one of He (helium), Ne (neon), Ar (argon), Kr (krypton), and Xe (xenon) as a main component of the sputtering gas. The method of manufacturing a tunnel magnetoresistive element according to claim 1, wherein: 4. The method of manufacturing a tunnel magnetoresistive element according to claim 3 , wherein the sputtering gas is mixed with oxygen gas of 30% or less as a method of doping oxygen during the formation of the first metal layer. 5.   As a method of doping oxygen during the formation of the first metal layer, a sputtering gas inlet and an oxygen gas inlet are provided separately, and the flow rate of the sputtering gas and the flow rate of the oxygen gas are controlled independently. 2. The method of manufacturing a tunnel magnetoresistive element according to claim 1, wherein The step of forming the tunnel barrier layer further includes a step of oxidizing the oxygen-doped first metal layer to form a metal oxide layer,
2. The method of manufacturing a tunnel magnetoresistive element according to claim 1, wherein the oxygen-doped first metal layer is exposed to an oxygen pressure atmosphere in a range of 0.01 to 10 Torr as a method of oxidizing the first metal layer. The step of forming the tunnel barrier layer further includes a step of oxidizing the oxygen-doped first metal layer to form a metal oxide layer,
2. The method of manufacturing a tunnel magnetoresistive element according to claim 1, wherein the method of oxidizing the oxygen-doped first metal layer is radical oxidation using active oxygen species. The step of producing the tunnel barrier layer comprises
Oxidizing the oxygen-doped first metal layer to form a metal oxide layer;
The method of manufacturing a tunnel magnetoresistive element according to claim 1, further comprising: forming a second metal layer on the metal oxide layer.   9. The method of manufacturing a tunnel magnetoresistive element according to claim 8, wherein the second metal layer is Mg and the film thickness is 0.1 nm or more and 0.6 nm or less.

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