JP2011138954A - Method of manufacturing magnetic tunnel junction device using perpendicular magnetization of ferromagnetic layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MgO-based magnetic tunnel junction (MTJ) device with a perpendicular anisotropy, essentially including ferromagnetic pinned and free layers with perpendicular magnetization, separated by an MgO tunnel barrier, wherein a microstructure of the MgO tunnel barrier created by deposition of the metal Mg and a subsequent oxidization treatment or a reactive sputtering is amorphous or microcrystalline with an incomplete (001) plane-perpendicular structure. <P>SOLUTION: In the method of manufacturing the magnetic tunnel junction device, at least the ferromagnetic pinned layer alone or both the ferromagnetic pinned and free layers have a crystalline preferred grain growth promotion (PGGP) seed layer located between the tunnel barrier and the ferromagnetic pinned layer alone or between the tunnel barrier and both the pinned and free layers. The crystalline PGGP seed layer induces crystallization and preferred grain growth of the MgO tunnel barrier in annealing after the deposition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to the field of magnetic tunnel junction (MTJ) devices that are particularly relevant to magnetic random access memory (MRAM) using tunneling magnetoresistance. More particularly, the present invention relates to an MTJ device comprising a MgO tunnel barrier made by oxidation or reactive sputtering, and the microstructure is amorphous or incomplete (001) plane microstructure microcrystalline. . More particularly, the present invention relates to an MTJ device having a ferromagnetic layer with perpendicular anisotropy. More particularly, the present invention inserts a crystalline ferromagnetic layer adjacent to the MgO tunnel barrier and being a preferred grain growth promotion (PGGP) seed layer to enhance the crystallinity of the MgO tunnel barrier during post-deposition annealing. It relates to MTJ devices.

  The core element of a magnetic tunnel junction (MTJ) device is a three-layer structure of “ferromagnetic layer / tunnel barrier / ferromagnetic layer”. The change in resistance of the MTJ device is due to the difference in the tunneling probability of spin-polarized electrons through the tunnel barrier due to the bias voltage across the device, depending on the relative orientation of the magnetizations of the two ferromagnetic layers.

  The relative orientation of the magnetization of the two ferromagnetic layers sandwiching the tunnel barrier is realized by the difference in the magnetization reversal properties of the two ferromagnetic layers, while the magnetization of one ferromagnetic layer is not reversed by an external magnetic field during operation, The magnetization of the other ferromagnetic layer responds to an external magnetic field. Accordingly, parallel or antiparallel alignment of the magnetizations of the two ferromagnetic layers sandwiching the tunnel barrier during device operation is realized.

  The tunnel barrier is generally a dielectric material, must be extremely thin, and must be very uniform in thickness and composition. Any mismatch with respect to stoichiometric composition or thickness significantly reduces device performance.

  The most typically used structure of an MTJ device is shown schematically in FIG. 1A, which includes an antiferromagnetic pinning layer 103, synthetic antiferromagnetic (SAF) pinned layers 104, 105 and 106, a tunnel barrier 107, and a strong It consists of a magnetic free layer 108. The synthetic antiferromagnetic (SAF) pinned layer includes a ferromagnetic pinned layer 104, a nonmagnetic spacer 105, and a ferromagnetic reference layer 106. The key issues addressed for successful application to spin torque transfer MRAM (STT-MRAM) are scalability and the reduction in current (Jc) required to reverse the magnetization of the free layer. It is. However, STT-MRAM using in-plane magnetization is scalable and Jc because of the oval anisotropy to induce in-plane uniaxial anisotropy and the very strong demagnetizing field to overcome, respectively. Limits are shown for reduction. FIG. 1B shows a different type of MTJ device than that of FIG. 1A. The structure of the MTJ device shown in FIG. 1B includes a ferromagnetic pinned layer 203 having perpendicular anisotropy, a tunnel barrier 204, and a ferromagnetic free layer 205 having perpendicular anisotropy. Further, the ferromagnetic free layer 205 has a coercive force lower than that of the ferromagnetic pinned layer 203 so that the magnetization of the ferromagnetic free layer 205 can be switched more easily than the magnetization of the ferromagnetic pinned layer 203. Each STT-MRAM with this MTJ stack with perpendicular anisotropy must have an oval shape to induce in-plane uniaxial anisotropy and a demagnetizing field that actually supports the magnetization reversal of the free layer. Are expected to show greatly improved scalability and effectively reduced Jc.

Since its discovery, high TMR at room temperature is among the industry's latest topics for magnetic sensors such as spintronics applications such as non-volatile magnetoresistive random access memory (MRAM) and hard disk drive read heads It is one of. For conventional magnetic field switching MRAM applications, a 1 Mbit MRAM with a bit size of 300 × 600 nm ² provides a magnetoresistance (MR) ratio of 40% with a resistance-area (R × A) product with an MTJ of about 1 k to ² kΩ μm ^2. I need that. At a high density of 250 Mbits, the bit size is reduced to 200 × 400 nm ² and requires an MR ratio higher than 40% with an R × A product of about 0.5 kΩμm ² . Further reduction can be achieved with MRAM by applying magnetization reversal with spin transfer torque, but MTJ is required to provide MR ratios over 150% in the R × A product range of 10-30 Ωμm ² .

Initial efforts made to amorphous electrodes with amorphous AlO _x tunnel barriers and high spin polarization were not sufficient for the above requirements. Recently, single crystal Fe / MgO / Fe has been suggested by theoretical calculations (Butler et al., Phys. Rev. B 63, (2001) p0554416) and is as high as 6000% due to the excellent spin filtering effect of MgO. It is predicted that room temperature TMR can be obtained. This spin filtering effect, that is, the total reflection of minority spindown electrons in the antiparallel magnetization alignment of two ferromagnetic layers sandwiching the MTJ MgO tunnel barrier, is reflected in the minority spindown spin channel with Δl symmetry on the Fermi surface. This is essential because there is no Bloch eigenstate. This allows for coherent tunneling and even larger TMR ratios. There is a microstructural requirement to enable this coherent tunneling, which is the epitaxial growth of Fe (001) / MgO (001) / Fe (001), where the tunneling electrons are (001) atoms of Fe and MgO. This is because it passes through the surface. Experimental attempts to achieve this giant TMR based on single crystal (Fe / MgO / CoFe) growth using molecular beam epitaxy have demonstrated room temperature TMR up to 180%. (Yuasa et al., Appl. Phys. Lett. 87 (2005) p222508) A room temperature TMR of 220% has been reported using an MgO tunnel barrier with a polycrystalline CoFe ferromagnetic electrode (Parkin et al., Nat. Mater). 3 (2004) p862), even higher TMR was reported in MTJs made by practical magnetron sputtering on thermally oxidized Si wafers using amorphous CoFeB ferromagnetic electrodes. (Djayapraira et al., Appl. Phys. Lett. 86 (2005) p092502)

  Great efforts have been made to form MgO tunnel barriers in MTJs that are extremely thin and extremely uniform in thickness and composition. Furthermore, a similar great effort to achieve the crystallinity of MgO tunnel barriers with (001) plane normal organization was given by theoretical calculations and confirmed by the study of microstructure and thin film chemistry. It has been made to meet the microstructural requirement of (001) plane vertical epitaxy along with the sandwich ferromagnetic layer. (YS Choi et al., Appl. Phys. Lett. 90 (2007) p012505, YS Choi et al., J. Appl. Phys. 101 (2007) p013907)

  In a common method of making MTJ devices for mass production of MRAM or recording readheads, MgO tunnel barrier deposition is divided into direct deposition, metal deposition and subsequent oxidation treatment. Tunnel barrier deposition by rf-sputtering using a ceramic target or by reactive sputtering of a metal target in an atmosphere of a gas mixture of oxygen and inert gas is classified as a first group of direct depositions. Metal deposition and subsequent various types of oxidation treatments, such as natural oxidation, plasma oxidation, radical oxidation, or ozone oxidation, fall into the second group.

  One of the major bottlenecks in MTJ development is to control the tunnel barrier to a uniform thickness at very low thickness. If the tunnel barrier is too thin, there is a high risk of including pinholes and the leakage current will pass without spin-dependent tunneling. This significantly reduces the signal to noise ratio (S / N). Another bottleneck is the chemical heterogeneity of the tunnel barrier, which leads to excessive or incomplete oxidation and oxidation of the underlying ferromagnetic layer. These result in an asymmetric electrical property with respect to the sign of the applied bias, an unusual increase in the R × A product, and a decrease in the TMR ratio due to an increase in tunnel barrier thickness due to spin scattering in the surface oxidized underlying ferromagnetic layer. . (Park et al., J. Magn. Magn. Mat., 226-230 (2001) p926)

  In addition to the problem of uniform thickness control of ultra-thin MgO tunnel barriers and end-to-end chemical uniformity of MgO tunnel barriers, achieving large TMR ratios with low R × A products of MgO-based MTJs The most pressing problem for is the (001) plane normal texture and high crystallinity of the MgO tunnel barrier. FIG. 2 shows the relationship between MgO texture and crystallinity and magnetotransport properties of CoFeB / MgO / CoFeB MTJ, where MgO is deposited by rf sputtering. MTJs made with highly crystalline (001) textured MgO tunnel barriers induce the corresponding (001) texture of CoFe by crystallization of the CoFeB amorphous layer by annealing and thus CoFeB / MgO / CoFeB It is clearly shown in FIGS. 2A and 2B that the overall (001) organization is realized. Thus, as shown in FIG. 2C, it is possible to obtain a significantly increased MR ratio with a low R × A product. However, as can be further seen in FIG. 2C, the MTJ with the MgO tunnel barrier with imperfect crystallinity shows a very low MR ratio with an extremely high R × A product.

  Although the MgO tunnel barrier made by rf sputtering has made great progress on process optimization, the MR ratio and R × A product are very sensitive to the chamber conditions and particle generation inherent in rf-sputtering. There is a significant problem that is difficult to overcome for mass production to change (Oh et al., IEEE Trans. Magn., 42 (2006) p2642). Furthermore, the final R × A product uniformity (1σ) of MTJ devices with MgO tunnel barriers made by rf-sputtering is over 10%, but made by Mg deposition and subsequent oxidation treatment. It has been reported that the MgO tunnel barrier is less than 3%. (Zhao et al., US Patent Application No. 2007/0111332)

An alternative method of making the MgO tunnel barrier is reactive Mg sputtering in an atmosphere of Mg deposition followed by various oxidation treatments or a gas mixture of oxygen and inert gas. Plasma oxidation is used in the fabrication of AlOx tunnel barriers, but due to the high reactivity, it is extremely difficult to oxidize very thin metal layers, especially the rate of Mg oxidation for MgO formation is very high Fast and reliable oxidation to the interface of the underlying ferromagnetic layer. In this way, an MTJ with an AlOx tunnel barrier has yielded an R × A product and MR ratio of 10,000 Ωμm ² /45% by plasma oxidation treatment (Tehrani et al., IEEE Trans. Magn., 91 (2003)). On the other hand, an R × A product and an MR ratio of 1000 Ωμm ² /30% are obtained by ozone oxidation. (Park et al., J. Magn. Magn. Mat., 226-230 (2001) p926)

Therefore, an oxidation process with low energy has been proposed, which is radical oxidation and natural oxidation for forming an MgO tunnel barrier. In addition, reactive sputtering of Mg metal targets has been proposed to form MgO tunnel barriers in Ar and O ₂ atmospheres. FIG. 3 shows magnetotransport property measurements obtained from MTJs with MgO tunnel barriers made by various methods of MgO tunnel barrier deposition. The MTJ structure is the same except for the MgO tunnel barrier portion, and the lower layer / PtMn (15) / CoFe (2.5) / Ru (0.9) / CoFeB (3) / MgO (x) / CoFeB (3) / It is a cap layer. The thickness in parentheses is on the nanometer scale. Referring to the MR ratio and R × A product obtained from MTJ with MgO made by rf sputtering, the MR ratio of MTJ with MgO tunnel barrier made by oxidation and reactive sputtering is significantly lower It is clearly shown. For a given R × A product of 10 Ωμm ² , MTJ with MgO produced by rf sputtering gives an MR ratio of 180%, while MgO deposited by radical oxidation gives 100% and spontaneous oxidation is 60 MgO made by reactive sputtering gives 135%.

  Microstructural analysis was performed with a high resolution transmission microscope (HREM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). As shown in FIGS. 4A and 4B, it is clearly compared that the difference in magnetotransport properties is due to the difference in crystallinity of the MgO tunnel barrier and the lack of epitaxy in the CoFeB / MgO / CoFeB layer. 4A and 4B are cross-sectional HEEM images taken from an MTJ with a MgO tunnel barrier made by rf-sputtering and radical oxidation, respectively. Choi et al. Appl. Phys. 101 (2007) p013907, a CoFeB / MgO / CoFeB based MTJ made by rf sputtering is a Butler that MgO is highly crystalline and has good intergranular epitaxy with the CoFe layer. Satisfies the microstructural requirements given in the theoretical calculation by J. et al. The CoFe layer is crystallized by post-deposition annealing based on crystalline MgO as a crystallization template, and thus intergranular epitaxy is realized in the CoFe / MgO / CoFe layer. However, the MgO tunnel barrier produced by radical oxidation exhibits incomplete crystallinity mixed with amorphous, and it is difficult to confirm pseudoepitaxy at the interface with the CoFe layer.

  FIG. 4C shows a clear comparison of MgO crystallinity and texture with respect to deposition methods, ie, rf-sputtering and spontaneous oxidation. The MgO tunnel barrier deposited on the amorphous CoFeB layer by rf-sputtering by plane perpendicular theta-2 theta scan is highly crystalline in the as-grown state and is evident at 2 theta = 42.4 ° It is confirmed that the MgO (002) peak is highly organized in a preferred orientation in the direction perpendicular to the (001) plane. However, MgO produced by metal deposition and subsequent natural oxidation does not show an obvious peak, indicating that the MgO layer is almost amorphous.

  4D and 4E are XPS spectra obtained from MTJ with MgO tunnel barriers made by rf-sputtering and reactive sputtering, respectively. Choi et al., Appl. Phys. Lett. 90 (2007) p012505, for MgO crystallinity, higher MR ratio of MTJ and lower R × A product, it has a dominant quantity of oxygen ions at the MgO lattice point of NaCl structure. It is essential. As shown in FIG. 4D, the number of oxygen ions (its binding energy is about 531 eV) occupying the lattice point of MgO with NaCl structure is very high in MgO deposited by rf sputtering, but by reactive sputtering. In the deposited MgO, there is a significant amount of impurity oxygen ions (its binding energy is about 533.3 eV) which is almost 1/3 of the number of oxygen ions at the lattice points, as shown in FIG. 4E. Is clear. Therefore, it can be inferred that this high density of impurity oxygen ions in the MgO barrier is related to the incomplete crystallinity of MgO and is responsible for the incomplete MR ratio.

  In order to achieve good crystallinity of the MgO tunnel barrier produced by the oxidation method, a single crystalline ferromagnetic reference layer is used instead of two layers, and the MTJ structure is lower layer / PtMn (15) / CoFe (2.5) / Ru (0.9) / CoFe (3) / MgO (x) / CoFeB (3) / cap layer. As shown in FIG. 5A, an MTJ with a fully crystalline CoFe single reference layer significantly reduces the MR ratio from 130% to 35% with a CoFeB amorphous reference layer. Also, the shape of the entire hysteresis loop of FIG. 5B from a MTJ with a fully crystalline CoFe single reference layer after annealing immediately after deposition at 360 ° C. for 2 hours under a magnetic field of 10 kOe is insufficient or destroyed. The shape of the entire hysteresis loop of the MTJ shown in FIG. 5C with an amorphous CoFeB single reference layer after post-deposition annealing under the same conditions is shown in the circle mark. Clear SAF coupling is shown. Body-centered cubic CoFe has a tendency to sequentially grow (110) atomic planes parallel to the interface with Ru for lattice matching with the hexagonal close-packed Ru (0001) bottom surface. The (110) plane normal texture of the ferromagnetic reference layer is undesirable for the giant TMR from theoretical calculations by Butler et al. For MgO-based MTJ. Furthermore, the thermal stability of SAF (CoFeB / Ru / CoFe) is much worse than SAF (CoFeB / Ru / CoFeB), so that MTJ is a CoFeB / Ru / CoFe SAF after annealing and after annealing. When structured, it is not possible to guarantee a clear separation of the magnetization separation between the component ferromagnetic layers. Thus, it can be seen that the crystalline CoFe single reference layer is not effective in achieving good crystallinity of the MgO tunnel barrier.

  Thus, it is understood that the incomplete crystallinity of MgO tunnel barriers deposited by oxidation methods or reactive sputtering cannot serve as a crystallization template for crystallizing amorphous CoFeB to CoFe at the CoFeB / MgO interface. can do. Therefore, intergranular pseudoepitaxy cannot be expected in a CoFe / MgO / CoFe layer, which results in incomplete magnetotransport properties.

  Unlike MTJ devices that use in-plane magnetization of a ferromagnetic layer, MTJ devices that use perpendicular magnetization of a ferromagnetic layer have no problem of precession of magnetization during reversal due to spin transfer torque, and thus Jc Can be expected to decrease significantly. Furthermore, STT-MRAM using vertical anisotropy does not require in-plane shape anisotropy with respect to the uniaxial axis, thus allowing further expandability and thus increasing its density.

T.A. Zhao et al., US Patent Application No. 2007/0111332. S. Miura et al., US Patent Application No. K. Nishimura et al., Patent Application No. 2008-103661

W. H. Butler et al., Phys. Rev. B 63, 054416 (2001) S. Yuasa et al., Appl. Phys. Lett. 87, 222508 (2005) S. S. P. Parkin et al., Nat. Mater. 3, 862 (2004) D. Djayapraira et al., Appl. Phys. Lett. 86, 092502 (2005) Y. S. Choi et al., Appl. Phys. Lett. 90, 012505 (2007) Y. S. Choi et al. Appl. Phys. 101, 013907 (2007) B. Park et al. Magn. Magn. Mat. 226-230, 926 (2001) S. C. Oh et al., IEEE Trans. Magn. , 42, 2642 (2006) S. Tehrani et al., IEEE Trans. Magn. 91, 703 (2003)

  An object of the present invention is to provide a sufficiently high MR ratio with a low R × A product to apply an MgO-based MTJ using perpendicular magnetization of a ferromagnetic layer to a spin transfer torque MRAM, and MgO Can be made by metal deposition followed by various oxidation methods or by reactive sputtering, the microstructure of which is an amorphous or microcrystalline tunnel barrier with an incomplete (001) plane normal texture.

  According to the first aspect of the present invention, MgO tunnel barriers produced by metal deposition and subsequent various oxidation methods or produced by reactive sputtering are crystallized or induced in its preferred grain growth. It is important to do.

  According to the second aspect of the present invention, the crystallization or preferred grain growth of the MgO tunnel barrier, which is amorphous or microcrystalline with an imperfect (001) plane normal structure in the state immediately after growth, is achieved by the MgO tunnel. It can be achieved during post-deposition annealing by using a body-centered cubic crystalline ferromagnetic PGGP seed layer under or sandwiching the barrier.

  When using crystalline ferromagnetic pins or free layers, crystallization or preferred grain growth of MgO tunnel barrier, which is amorphous or microcrystalline with imperfect (001) plane normal structure in the as-grown state, is MgO. It can be achieved during post-deposition annealing by using a body-centered cubic crystalline ferromagnetic PGGP seed layer under or sandwiching the tunnel barrier.

  In the presence of a crystalline ferromagnetic PGGP seed layer, as shown schematically in FIG. 6, after post-deposition annealing, microcrystalline with an amorphous or incomplete (001) plane normal structure in the as-deposited state. Crystallization and suitable grain growth of the MgO tunnel barrier, which is the tunnel barrier of this, is caused.

  Thus, with this resulting MTJ microstructure of the present invention, it is possible to achieve a significant increase in MR ratio as well as a significant reduction in R × A product, as shown in FIG.

1 is a schematic diagram of a typical structure of a magnetic tunnel junction. 1 is a schematic diagram of a typical structure of a magnetic tunnel junction using perpendicular magnetization of a ferromagnetic layer. FIG. FIG. 3 shows that an MTJ fabricated using a highly crystalline (001) textured MgO tunnel barrier contains a corresponding (001) texture of CoFe by crystallization of a CoFeB amorphous layer by annealing. FIG. 3 shows that an MTJ fabricated using a highly crystalline (001) textured MgO tunnel barrier contains a corresponding (001) texture of CoFe by crystallization of a CoFeB amorphous layer by annealing. FIG. 3 shows that an MTJ with an MgO tunnel barrier with imperfect crystallinity exhibits a very low MR ratio with a very high R × A product. It is a figure which shows the magnetotransport characteristic measurement result obtained from MTJ provided with the MgO tunnel barrier produced by the various methods of MgO tunnel barrier deposition. It is a figure which shows the result of the fine structure and thin film chemical analysis from MgO produced by various methods, and is a photograph of the cross-sectional HREM image from MTJ with MgO produced by rf-sputtering. It is a figure which shows the result of the fine structure and thin film chemical analysis from MgO produced by various methods, and is a photograph of the cross-sectional HREM image from MTJ with MgO produced by radical oxidation. FIG. 7 shows the results of microstructure and thin film chemical analysis from MgO produced by various methods, comparing the crystallinity and structure of MgO tunnel barriers produced by rf-sputtering and natural oxidation. It is a theta scan. It is a figure which shows the result of the microstructure and thin film chemical analysis from MgO produced by various methods, and is the XPS 0 1s spectrum obtained from MgO produced by rf-sputtering. It is a figure which shows the result of the fine structure and thin film chemical analysis from MgO produced by various methods, and is an XPS 0 1s spectrum obtained from MgO produced by reactive sputtering. FIG. 6 shows a comparison of magnetotransport properties and hysteresis loop of MTJ with CoFe or CoFeB ferromagnetic single reference layer, MR ratio versus R × A product from MTJ with CoFe or CoFeB reference layer. FIG. 6 shows a comparison of magnetotransport properties and hysteresis loops of an MTJ with a CoFe or CoFeB ferromagnetic single reference layer, a total hysteresis loop from an MTJ with a CoFe reference layer. FIG. 6 shows a comparison of magnetotransport properties and hysteresis loops of an MTJ with a CoFe or CoFeB ferromagnetic single reference layer, a total hysteresis loop from an MTJ with a CoFeB reference layer. FIG. 4 is a schematic comparison of MTJ crystallization and preferred grain growth treatment after post-deposition annealing. It is a figure which illustrates an MTJ device manufacturing apparatus. It is the schematic of MTJ of this invention. It is the schematic of MTJ of the 1st Embodiment of this invention. It is the schematic of MTJ of the 2nd Embodiment of this invention. It is the schematic of MTJ of the 3rd Embodiment of this invention. It is the schematic of the magnetic moment of the PGGP seed layer of this invention. FIG. 6 is a schematic diagram of the influence of the magnetic moment of a thick PGGP layer on a perpendicular anisotropic ferromagnetic layer. It is a figure which shows the relationship between PGGP seed layer thickness and anisotropy. It is the schematic for analyzing the cross-sectional image obtained by the high-resolution transmission electron microscope (HRTEM) and the cross-sectional HRTEM image from MTJ immediately after the growth of 2nd Embodiment, respectively, and was pinched | interposed by the MgO tunnel barrier and the CoFeB layer CoFe PGGP seed layer. It is the schematic for analyzing the cross-sectional image each obtained by the high-resolution transmission electron microscope (HRTEM) and the cross-sectional HRTEM image from MTJ immediately after the growth of 2nd Embodiment, CoFe PGGP with a (001) plane perpendicular direction It represents the growth of the seed layer. It is the schematic for analyzing the cross-sectional image each obtained by the high-resolution transmission electron microscope (HRTEM) and the cross-sectional HRTEM image from MTJ immediately after the growth of 2nd Embodiment, (011) CoFe PGGP with a plane perpendicular direction It represents the growth of the seed layer. It is a figure which shows the cross-sectional HREM image of MTJ immediately after the growth of 2nd Embodiment. It is a figure which shows the cross-sectional HREM image of annealed MTJ of 2nd Embodiment. It is a figure which shows the diffraction pattern of the area | region selected from the area | region enclosed by the frame of the cross-sectional HREM image of FIG. 12A.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Where an alloy is described without a number implying an element ratio, it means in this document that the alloy contains each element in any ratio rather than the same ratio. FIG. 7 illustrates an MTJ device manufacturing apparatus in a preferred embodiment. FIG. 7 is a schematic plan view of a vacuum processing system 700 for fabricating a magnetic tunnel junction device. The vacuum processing system shown in FIG. 7 is a clustered system with multiple thin film deposition chambers that use physical vapor deposition techniques. The plurality of deposition chambers in the vacuum processing system are attached to a vacuum transfer chamber 701 (not shown) having a robot loader at a central position. The vacuum processing system 700 includes two load lock chambers 702 and 703 for loading / unloading substrates. The vacuum processing system includes a degas chamber 704 and a pre-etch / etch chamber 705. The vacuum processing system includes an oxidation chamber 706 and a plurality of metal deposition chambers 707, 708, and 709. Each of the chambers of the vacuum processing system is connected through a gate valve to open and close a passage between the chambers. Note that each chamber of the vacuum processing system includes a pump system, a gas introduction system, and a power supply system. Further, the gas introduction system includes a flow rate adjusting means, and the pump system includes a pressure adjusting means. By operating the flow rate adjusting means and the pressure adjusting means, the pressure in the chamber can be controlled to be constant for a certain period. Further, the chamber pressure can be controlled to be constant for a certain period by an operation based on the combination of the flow rate adjusting means and the pressure adjusting means.

  In each of the metal deposition chambers 707, 708, and 709 of the vacuum processing system 700, each of the magnetic layer and the non-magnetic metal layer is deposited on the substrate one by one by a sputtering method. In the metal deposition chambers 707, 708, and 709, for example, the target material is “CoFe”, the target material is “CoFeB”, and the target material is “Mg”. Furthermore, the target material is a “lower layer material” and the target material is a “cap material”. Pre-etching and etching are performed in a pre-etch / etch chamber. Oxidation takes place in oxidation chamber 706. In addition, each metal deposition chamber includes a sputtering apparatus capable of performing dc-sputtering. Procedures such as gas introduction into each chamber, valve switching, power ON / OFF, gas exhaust, and substrate transfer are performed by a system controller (not shown).

  FIG. 8D shows an MTJ stack structure 100 using the perpendicular magnetization of a ferromagnetic layer for a tunneling magnetoresistive (TMR) memory cell. Most advantageously, on the lower layer 120 and the Si wafer 110, the MTJ comprises a ferromagnetic pinned layer 130 with perpendicular anisotropy, a first ferromagnetic preferred grain growth promoting (PGGP) seed layer 140, a tunnel barrier 150, It comprises a second ferromagnetic preferred grain growth promoting (PGGP) seed layer 160 and a ferromagnetic free layer 170 having perpendicular anisotropy. A cap layer 180 (such as Pt) to which the upper electrode is attached is formed on the free layer 170.

  The MTJ device of the present invention is formed by fabricating a core element in an MTJ device, where the core is “crystalline ferromagnetic pinned layer 130 with perpendicular anisotropy / first crystalline ferromagnetic PGGP seed layer 140 / tunnel barrier. 150 / ferromagnetic PGGP seed layer 160 / ferromagnetic free layer 170 with perpendicular anisotropy "multilayer structure, and in a preferred embodiment, a combination of materials selected from the following group is used.

Group 1:
Selection for Ferromagnetic Preferred Grain Growth Promotion (PGGP) Seed Layer a. Crystal single layer b. Bilayered amorphous layer / Crystal layer Group 2:
Method of MgO tunnel barrier deposition c. Mg xÅ / Oxidation treatment * / Mg yÅ
d. Mg xÅ / Oxygen surfactant / Mg xÅ / Oxidation treatment * / Mg yÅ
e. Mg xÅ / oxidation treatment * / Mg yＭｇ / oxidation treatment * / Mg zÅ
f. Reactive sputtering MgOx / Oxidation treatment * / Mg y
g. Mg xÅ / reactive sputtering MgOx / oxidation treatment * / Mg yÅ
Oxidation treatment * includes plasma, nature, radicals, and ozone oxidation.
Group 3:
Location of the ferromagnetic PGGP seed layer h. Pinned layer only i. Free layer only j. Reference and free layer group 4:
Selection of ferromagnetic pin or free layer with perpendicular anisotropy k. Amorphous ferromagnetic layer l. Crystalline ferromagnetic layer m. Multi-layer (multiple repetitions of two layers)
Group 5:
Material selection for crystalline layer of crystalline ferromagnetic PGGP seed layer or double-layered ferromagnetic PGGP seed layer n. CoxFe100-x, where 0 <x atomic% <90
o. (CoxFe100-x) yB100-y, where 0 <x atomic% <90 and 90 <y atomic% <100
p. Fe

First Embodiment Referring to FIG. 8A showing the configuration of the stack of the first embodiment, one of the important aspects of the first embodiment is that the amorphous ferromagnetic pin and the free layer 133 have perpendicular anisotropy. , 173. Another important aspect of the first embodiment is the insertion of a crystalline ferromagnetic PGGP seed layer under or sandwiching the MgO tunnel barrier 153. Figures 8A-8C show the MgO tunnel barrier prior to the annealing step. By the annealing step, the layer sandwiched between the ferromagnetic PGGP seed layers is transformed into an MgO tunnel barrier 153 having an overall (001) plane normal texture.

The ferromagnetic pinned layer 133 and the free layer 173 having perpendicular anisotropy can be an amorphous rare earth / transition metal alloy (RE _x TM _1-x ), where RE = Y, Nd, Gd, Tb, Dy , Ho, Er, and Lu, and TM = Co, Fe, and CoFe alloys. Alternatively, the ferromagnetic pinned layer 133 and the free layer 173 having perpendicular anisotropy may be a rare earth / transition metal / corrosion resistant element alloy (RE _x TM _1-x ) _y CR _1-y , where CR = Cr. These layers can be formed by sputtering of an alloy target or co-sputtering of a multi-metal target. Other vapor deposition methods can be used. The ferromagnetic free layer 173 has a lower coercive force than the ferromagnetic pinned layer 133. It can be fabricated with a different material and / or element ratio than the ferromagnetic pinned layer 133.

The first and second crystalline ferromagnetic PGGP seed layers 143 and 163 can be crystalline layers having a bcc structure. Therefore, the first and second crystalline ferromagnetic PGGP layers 143 and 163 include Co _x Fe _1-x (0 ≦ x ≦ 0.9), (Co _x Fe _1-x ) _y B _1-y (0 ≦ x ≦ 0.9 and 0.9 ≦ y <1), Fe and the like. Furthermore, it can be deposited with a thickness (t) of 0.5 nm ≦ t ≦ 2 nm. The anisotropy induced in the ferromagnetic PGGP seed layer by a ferromagnetic pin or free layer with perpendicular anisotropy is due to the consideration of the associated energy because the uniaxial anisotropy field competes with the shape anisotropy. Can be determined.
Uniaxial anisotropy = 2K _u / M _s
Shape anisotropy = 4πM _s ,
Here, Ku is an anisotropy constant, and M _s is saturation magnetization. As shown in FIG. 9C, when the thickness of the crystalline ferromagnetic PGGP seed layer is increased, there is a transition thickness in which the shape anisotropy overcomes the uniaxial anisotropy. Thus, below this transition thickness of the crystalline ferromagnetic PGGP seed layer, the perpendicular anisotropy of the ferromagnetic PGGP seed layer is induced and all magnetic moments are aligned perpendicular to the film surface as shown in FIG. 9A. . However, beyond the transition thickness of the ferromagnetic PGGP seed layer, the shape anisotropy dominates and therefore all the magnetic moments align with the film surface, which in turn causes the ferromagnetic pin or free layer interface A magnetic moment is induced and the vertical anisotropy tilts from the vertical axis as shown in FIG. 9B. Therefore, the thickness of the ferromagnetic PGGP seed layer needs to be carefully controlled to be less than the critical transition thickness. On the other hand, if the thickness is less than 0.5 nm, it is too thin to be PGGP.

  For example, in the first embodiment of FIG. 8A, the lower layer 120 / TbCoFe133 / CoFe (1.5) 143) / Mg (1.1) / R—Ox x sec / Mg (0.3) / CoFe (1. 5) 163 / GdCoFe173 / cap layer 180, where the number in parentheses is the thickness on the nanometer scale, and "R-Ox x seconds" means a radical oxidation treatment of x seconds. In this example, the core element of the MTJ is formed by a combination of (a + c + i + k + n) or (a + c + j + k + n) from groups 1, 2, 3, 4 and 5 described above.

The method of forming the MgO tunnel barrier 153 is as follows:
Depositing a first metal Mg layer having a thickness of 1.1 nm on the first crystalline ferromagnetic PGGP seed layer 143;
The oxidation of the first metal layer by radical oxidation performed in the oxidation chamber. In the oxidation chamber, an electrically grounded “shower plate” is disposed between the upper ionization electrode and the substrate. An oxygen plasma is generated by applying 300 W rf power to the ionization electrode using an oxygen flow rate of 700 sccm. The oxygen radical shower flows through the shower plate, but charged particles such as ionized species and electrons cannot pass due to the electrical ground of the shower plate, and the first oxidized by radical oxidation is oxidized. A metal Mg cap having a thickness of 0.3 nm is deposited on the metal Mg layer.

  Further, a second crystalline ferromagnetic Co (70 atomic%) Fe (30 atomic%) PGGP seed layer 163 is deposited on the metallic Mg cap layer with a thickness of 1.5 nm.

  Post-deposition magnetic field annealing is performed. The purpose of post-deposition annealing is the preferred grain growth of microcrystalline MgO tunnel barrier 153 with an amorphous or incomplete (001) plane normal structure. This crystallization and preferred grain growth is thus finalized as adjacent crystallization or preferred grain growth during annealing using the first and second crystalline CoFe ferromagnetic PGGP seed layers 143, 163. The entire (001) plane perpendicular structure of the MgO tunnel barrier 153 is realized.

  The magnetotransport properties of MTJs made by the method of the present invention are both MTJs with MgO tunnel barriers made by rf sputtering and the same oxidation method made by rf sputtering without using a crystalline CoFe PGGP seed layer. It can be compared with an MTJ with a barrier. Referring to the MR ratio and R × A product obtained from MTJ with MgO made by the same oxidation method but without the insertion of a crystalline PGGP seed layer, MTJ using crystalline PGGP layer has a significant MR ratio An increase is obtained with a significant decrease in the R × A product, which shows a much improved magnetotransport property that is comparable or even better than that from an MTJ with a MgO tunnel barrier made by rf sputtering. Can be expected.

Second Embodiment Referring to FIG. 8B showing the configuration of the stack of the second embodiment, one of the important aspects of the second embodiment is the crystalline ferromagnetic pin and free layer 131 with perpendicular anisotropy. , 171. Furthermore, another important aspect of the second embodiment is the insertion of a two-layered ferromagnetic PGGP seed layer under or sandwiching the MgO tunnel barrier 151.

The crystalline ferromagnetic pin and free layer 131, 171 with perpendicular anisotropy can be a crystalline transition metal / refractory metal alloy (TM _x RM _1-x ) with chemical order, where TM = Co or Fe, and RM = Pt or Pd. The ferromagnetic free layer 171 having perpendicular anisotropy has a lower coercive force than the ferromagnetic pinned layer 131. It can be fabricated with a different material and / or element ratio than the ferromagnetic pinned layer 131.

  The first two-layered ferromagnetic PGGP seed layer 141 is a two-layered amorphous layer / bcc structure crystal layer, where the amorphous layer separates the ferromagnetic pinned layer 131 and the bcc structure crystal PGGP layer. In a similar manner, the second two-layered ferromagnetic PGGP seed layer 161 is a two-layered amorphous layer / bcc structure crystal layer, where the amorphous layer is a ferromagnetic free layer 171 and a bcc structure crystal PGGP layer. And are separated.

  The amorphous layers of the two-layered ferromagnetic PGGP seed layers 141 and 161 can be made of CoFeB (B> 10 atomic%). Instead of or in addition to B, materials that can change the crystalline ferromagnetic material into an amorphous material, such as Zr, Hf, Nb, Ta, Ti, Si, or P can be used. The amorphous layer of the double-layered ferromagnetic PGGP seed layer 141 prevents the crystal structure from being transmitted from the crystalline ferromagnetic pinned layer 131 to the crystal layer of the double-layered ferromagnetic PGGP seed layer 141, and thus the double-layered ferromagnetic PGGP seed layer 141. The crystal layer of the PGGP seed layer 141 can be formed with a preferable bcc structure. By forming an amorphous layer of the second ferromagnetic PGGP seed layer on the crystal layer in a similar manner, the ferromagnetic free layer can be formed with a preferred crystal structure.

The thickness (t ₁ ) of the crystal layer having the bcc structure and the thickness (t ₂ ) of the amorphous layer in the first and second ferromagnetic PGGP seed layers 141 and 161 are 0.5 nm ≦ t ₁ ≦ 1.5 nm. And 0.5 nm ≦ t ₂ ≦ 1.5 nm.

  For example, in the second embodiment of FIG. 8B, the lower layer 120 / CoPt131 / CoFeB (1.5) / CoFe (1.5) / Mg (1.1) / N—Ox x sec / Mg (0.3) /CoFe(1.5)/CoFeB(1.5)/FePt171/cap layer 180, where the number in parentheses is the thickness on the nanometer scale, "N-Ox x sec "Means a natural oxidation treatment of x seconds. In this example, the core element of the MTJ is formed by a combination of (b + c + i + l + n) or (b + c + j + l + n) of groups 1, 2, 3, 4 and 5 described above.

The method of forming the MgO tunnel barrier 151 is as follows:
Depositing a first metal Mg layer having a thickness of 1.1 nm on the ferromagnetic PGGP seed layer 141;

This is the oxidation of the first metal Mg layer by natural oxidation performed in the oxidation chamber. The natural oxidation treatment advantageously applied to the thinly formed metal Mg layer is to purify the oxidation chamber with oxygen gas at a pressure of about 6.5 × 10 ⁻¹ Pa and to flow oxygen gas at a flow rate of 700 sccm. And then leaving the as-deposited metal Mg layer in contact with the oxygen gas stream for a given exposure time and a thickness of 0.3 nm on the first metal Mg layer oxidized by natural oxidation. Depositing a metal Mg cap layer having a thickness.

  Still referring to FIG. 8B, the crystal layer of the second ferromagnetic PGGP seed layer 161 made of Co (70 atomic%) Fe (30 atomic%) is deposited on the metallic Mg cap layer to a thickness of 1.5 nm. . Next, an amorphous layer of a second ferromagnetic PGGP seed layer made of Co (60 atomic%) Fe (20 atomic%) B (20 atomic%) is deposited on the crystalline layer to a thickness of 1.5 nm.

Referring to FIGS. 10A to 10C and FIG. 11, the microstructure of the crystalline CoFe layer immediately after growth on the amorphous CoFeB layer of the first PGGP layer 141 is a body-centered cubic structure and a (001) plane perpendicular structure crystal. It is clear. FIGS. 10A to 10C are obtained with a high-resolution transmission electron microscope to confirm whether the crystalline CoFe layer of the ferromagnetic PGGP seed layer 141 grows in the (001) plane perpendicular direction or (011) plane perpendicular direction. A method for analyzing the obtained cross-sectional image will be described. When the crystalline CoFe layer deposited on the amorphous CoFeB layer of the first ferromagnetic PGGP seed layer 141 grows in the (001) plane perpendicular direction as shown in FIG. 10B, in FIG. 10A, the MgO tunnel barrier and the first ferromagnetic PGGP first ferromagnetic PGGP atomic spacing of the crystal CoFe layer of the seed layer 141 sandwiched between the amorphous CoFeB layer of the seed layer 141 (d) Although it is _{d 110,} first ferromagnetic PGGP seed If crystalline CoFe layer deposited on the amorphous CoFeB layer of the layer 141 is grown as (011) plane perpendicular shown FIG. 10C, atomic spacing (d) is a _{d 200.} The inter-atomic spacing (d ₁₁₀ ) of the (110) atomic plane of CoFe having a body-centered cubic structure is 2.02 、, and d ₂₀₀ is 1.41 Å. Referring to FIG. 11, the overall crystallinity of the crystalline CoFe layers of the ferromagnetic PGGP layers 141 and 161 is confirmed. The interatomic spacing of the crystalline CoFe layers of the ferromagnetic PGGP seed layers 141, 161 is measured using a 2.08Å d ₁₁₁ of the Cu layer as a reference for the length reference (not shown here). Using this criterion, the interatomic spacing of the crystalline CoFe layers of the PGGP seed layers 141, 161 was measured by averaging six atomic planes, according to which the interatomic spacing is 2.02 cm. Therefore, it can be confirmed that the crystalline CoFe layer on the amorphous CoFeB layers of the ferromagnetic PGGP seed layers 141 and 161 grows in the (001) plane perpendicular direction. Further, clear boundaries between the amorphous CoFeB layers and the crystalline CoFe layers of the ferromagnetic PGGP layers 141 and 161 can be confirmed.

  Post-deposition magnetic field annealing is performed. The purpose of post-deposition annealing is the crystallization of the amorphous layer of the first ferromagnetic PGGP layer 141 and / or the amorphous layer of the second ferromagnetic PGGP layer 161, and the amorphous or incomplete (001) plane normal texture. This is a preferred grain growth of a microcrystalline MgO tunnel barrier 151 having This crystallization and preferred grain growth can be achieved by using the crystalline CoFe layer of the first ferromagnetic PGGP layer 141 and / or the crystalline CaFe layer of the ferromagnetic PGGP layer 161 during adjacent annealing or preferred grain growth. Thus, finally, the entire (001) plane perpendicular structure of the ferromagnetic PGGP layer is realized.

  Referring to FIGS. 12A and 12B, the microstructure of the bilayered amorphous layer (CoFeB) / crystalline (CoFe) ferromagnetic PGGP seed layer is a complete structure of a single-layer structure with a body-centered cubic structure and a (001) plane perpendicular structure. It is clear that a crystalline CoFe PGGP seed layer is formed. The same rationale for analyzing cross-sectional images (FIGS. 10A to 10C) obtained by high-resolution transmission electron microscopy is that the annealed single layer CoFe PGGP seed layer is a (001) plane perpendicular crystal or (011) It is applied to confirm whether the crystal is perpendicular to the plane. With reference to FIG. 12A, it is confirmed that the single layer structure of the ferromagnetic PGGP seed layer 151 is formed by combining a crystalline CoFe layer and an amorphous CoFeB layer. This formation of a single layer ferromagnetic PGGP seed layer is illustrated by crystallization of an amorphous CoFeB layer based on crystalline CoFe as a preferred grain growth promoting seed layer. By using the same length criterion used in FIG. 11, the interatomic spacing of the single-layered ferromagnetic PGGP seed layer after annealing averages seven atomic planes from the region bounded by the frame in FIG. 12B. According to it, the interatomic spacing is 2.0 cm. In addition, the interatomic spacing of the MgO tunnel barrier was measured and was 2.13 cm based on the length criteria. Due to their interatomic spacing from the annealed single layer ferromagnetic PGGP seed layer and the MgO tunnel barrier, both the MgO tunnel barrier and the ferromagnetic PGGP seed layer are perfect crystals with a (001) plane normal structure Is confirmed. Furthermore, the diffraction pattern of the selected region shown in FIG. 12B from the region enclosed by the frame in FIG. 12A by Fast Fourier Transform using a Gatan Digital micrograph reveals the [001] crystal axis of the single layer CoFe ferromagnetic PGGP seed layer. Is parallel to the [011] crystal axis of the MgO tunnel barrier, confirming the inter-grain pseudo-epitaxy of 45 ° rotation epitaxy between the MgO tunnel barrier and the ferromagnetic PGGP seed layer. The diffraction pattern indicated by the underline is from a single layer CoFe ferromagnetic PGGP seed layer, and the diffraction pattern without the underline is from an MgO tunnel barrier. This intergranular pseudoepitaxy of CoFe / Mg0 / CoFe based magnetic tunnel junctions is described by Choi et al. Appl. Phys. 101, 013907 (2007), a decisive requirement for obtaining a giant TMR.

  The magnetotransport properties of MTJs made by the method of the present invention are both MTJs with MgO tunnel barriers made by rf sputtering and the same oxidation method made by rf sputtering without using a crystalline CoFe PGGP seed layer. It can be compared with an MTJ with a barrier. Referring to the MR ratio and R × A product obtained from MTJ with MgO produced by the same oxidation method but without the insertion of a crystalline PGGP seed layer, MTJ using crystalline PGGP layer has a significant MR ratio A significant increase is obtained with a significant decrease in the R × A product, which has a much improved magnetotransport property that is comparable or even better than that from an MTJ with a MgO tunnel barrier made by rf sputtering. It can be expected to show.

Third Embodiment Referring to FIG. 8C showing the configuration of the stack of the third embodiment, one important aspect of the third embodiment is that a multilayer with perpendicular anisotropy (multiple repetitions of two layers). ) Use of ferromagnetic pins and free layers 132, 172. Furthermore, another important aspect of the third embodiment is the insertion of a two-layered ferromagnetic PGGP seed layer under or sandwiching the MgO tunnel barrier 152.

  The ferromagnetic pins and free layers 132, 172 having perpendicular anisotropy can be multilayered by repeating magnetic metal layer / nonmagnetic metal layer (M / NM) with or without chemical order, where M = Co, Fe, CoFe or CoPt, and NM = Pt, Pd, Ag or Au. The ferromagnetic free layer 172 having perpendicular anisotropy has a lower coercive force than the ferromagnetic pinned layer 132. It can be fabricated with a different material and / or element ratio than the ferromagnetic pinned layer 132.

  For example, in the third embodiment of FIG. 8C, the lower layer 120 / Co / Pt132 / CoFeB (1.5) / CoFe (1.5) / Mg (0.43) / oxygen surfactant layer 30 Langmuir / Mg ( 0.67) / R-Ox x sec / Mg (0.3) / CoFe (1.5) / CoFeB (1.5) / Co / Pt172 / cap layer 180, where The rounded number is the thickness on the nanometer scale. This example is a method of forming a tunnel barrier of an MTJ device by use of a surface active material layer and subsequent radical oxidation. In addition, the core element of the MTJ is formed by a combination of (a + d + j + m + n) of the groups 1, 2, 3, 4 and 5 described above.

The method of forming the MgO tunnel barrier 152 is:
Depositing a first metal Mg layer having a thickness of 0.43 nm on the crystalline layer of the ferromagnetic PGGP seed layer 141;
Formation of an oxygen surfactant layer in a vacuum chamber by exposing a 0.43 nm metallic Mg layer to an oxygen atmosphere, the exposure being controlled to be 30 Langmuir depending on the exposure time and the oxygen flow rate through the chamber. Forming and

Depositing a second metal Mg layer having a thickness of 0.67 nm on the oxygen surfactant layer;
Oxidation of the first and second metal layers by radical oxidation performed in the oxidation chamber, in which an electrically grounded “shower plate” is disposed between the upper ionization electrode and the substrate With oxidation. The oxygen plasma is generated by applying 300 W rf power to the ionization electrode at an oxygen flow rate of 700 sccm. Oxygen radical shower flows through the shower plate, but charged particles such as ionized species and electrons cannot pass through due to the electrical grounding of the shower plate,

  A metal Mg cap having a thickness of 0.3 nm is deposited on the first and second metal Mg layers oxidized by radical oxidation.

  Referring to FIG. 8C, a crystal layer of a second ferromagnetic PGGP seed layer 161 made of Co (70 atomic%) Fe (30 atomic%) is deposited on the metal Mg cap layer to a thickness of 1.5 nm. Next, an amorphous layer of a second ferromagnetic PGGP seed layer made of Co (60 atomic%) Fe (20 atomic%) B (20 atomic%) is deposited on the crystalline layer to a thickness of 1.5 nm. Next, a ferromagnetic free layer 172 having perpendicular anisotropy is deposited on the amorphous layer of the second ferromagnetic PGGP seed layer 161.

  Post-deposition magnetic field annealing is performed. The purpose of post-deposition annealing is to crystallize the amorphous layers of the ferromagnetic PGGP seed layers 141 and 161 and to select suitable grains of the microcrystalline MgO tunnel barrier 152 having the amorphous or incomplete (001) plane perpendicular structure. With growth. This crystallization and preferred grain growth can be achieved by using the ferromagnetic CoPG layer of the ferromagnetic PGGP seed layer 141, 161 as an adjacent crystallization or preferred grain growth seed layer during annealing in this way. This is realized as an overall (001) plane perpendicular structure of the magnetic PGGP seed layers 141 and 161 and the MgO tunnel barrier 152.

  The magnetotransport properties of MTJs made by the method of the present invention are both MTJs with MgO tunnel barriers made by rf sputtering and the same oxidation method made by rf sputtering without using a crystalline CoFe PGGP seed layer. It can be compared with an MTJ with a barrier. Referring to the MR ratio and R × A product obtained from MTJ with MgO produced by the same oxidation method but without the insertion of a crystalline PGGP seed layer, MTJ using crystalline PGGP layer has a significant MR ratio A significant increase is obtained with a significant decrease in the R × A product, which has a much improved magnetotransport property that is comparable or even better than that from an MTJ with a MgO tunnel barrier made by rf sputtering. It can be expected to show.

  Again, based on previous studies related to magnetotransport properties and crystallinity and pseudo-epitaxy of MTJ, strong adjacent to the MgO tunnel barrier, which is amorphous or microcrystalline with incomplete (001) plane normal texture. It can be intuitively assumed that insertion of a magnetic PGGP seed layer induces crystallization of the MgO tunnel barrier and preferred grain growth during post-deposition annealing.

As another method of forming the MgO tunnel barrier, reactive sputtering can be used. For example, it
Deposition of a first metal Mg layer having a thickness of 0.6 nm on the ferromagnetic PGGP seed layer;
MgO layer with a thickness of 0.6 nm on the first metal Mg layer by reactive sputtering of Mg in a mixed gas of argon and oxygen by flowing argon at a flow rate of 40 sccm and oxygen at a flow rate of 4 sccm The formation of

The oxidation of the first metal layer and the MgO layer by natural oxidation performed in the oxidation chamber. Advantageously, the natural oxidation treatment applied to the thinly formed metal Mg layer and MgO layer comprises purifying the oxidation chamber with oxygen gas at a pressure of about 6.5 × 10 ⁻¹ Pa and at a flow rate of 700 sccm. Flowing oxygen, then leaving the metal Mg layer and MgO layer immediately after deposition in contact with the oxygen gas flow for a given exposure time, the MgO layer oxidized by natural oxidation and the first Depositing a metal Mg cap layer having a thickness of 0.3 nm on the metal Mg layer.

  In another embodiment, CoFeB (B <10 atomic%) can be used as the crystal layer of the bilayered ferromagnetic PGGP seed layer. The microstructure of CoFeB with boron content of 5.1 atomic% and 2.9 atomic% is crystalline immediately after deposition, while the microstructure of CoFeB with boron content of 20 atomic% is amorphous, It is clear that it is confirmed by XRD Theta-2 Theta Scan from a CoFeB monolayer deposited on a thermally oxidized Si wafer. The intensity is normalized by the thickness of the CoFeB single film. The grain size calculated using Scherrer's equation shows that the grain size of CoFeB (B: 2.9 atomic%) is larger than CoFeB (B: 5.1 atomic%), which is This can be reconfirmed by a significant decrease in resistivity. The resistivity of CoFeB varies significantly with crystallinity corresponding to the boron content. Furthermore, the XRD peak shift from 45.35 ° for CoFeB (B: 2.9 atomic%) to 45.02 ° for CoFeB (B: 5.1 atomic%) is at the interstitial position of the body-centered cubic structure. The lattice expansion of CoFe by containing boron is shown.

Claims (14)

A method of manufacturing a magnetic tunnel junction device using perpendicular magnetization of a ferromagnetic layer,
Forming a ferromagnetic pinned layer with perpendicular anisotropy;
Forming a tunnel barrier containing Mg and O by an oxidation method;
Forming a ferromagnetic free layer with perpendicular anisotropy having a lower coercivity than the ferromagnetic pinned layer;
Forming a ferromagnetic preferred grain growth promoting seed layer in contact with a surface of at least one of the tunnel barriers. The ferromagnetic pin and free layer can be an amorphous rare earth / transition metal alloy (RE _x TM _1-x ), where RE = Y, Nd, Gd, Tb, Dy, Ho, Er, and Lu, And TM = Co, Fe, and CoFe alloys. The ferromagnetic pin and free layer can be an amorphous rare earth / transition metal / corrosion resistant element alloy (RE _x TM _1-x ) _y CR _1-y , where CR = Cr. the method of.   The method of claim 1, wherein the ferromagnetic preferred grain growth promoting seed layer of claim 1 can be a bcc crystal layer.   The method of claim 1, wherein the ferromagnetic preferred grain growth promoting seed layer can be deposited with a thickness (t) of 0.5 nm ≦ t ≦ 2 nm. The ferromagnetic pin and free layer can be a crystalline transition metal / heat resistant metal alloy (TM _x RM _1-x ) with chemical order, where TM = Co or Fe and RM = Pt or The method of claim 1, which is Pd.   7. The method of claim 6, wherein the ferromagnetic preferred grain growth promoting seed layer can be a bilayered amorphous layer / crystal layer, wherein the bcc crystal layer is in contact with a tunnel barrier.   The stacking order of the two-layered PGGP is different on the free layer side and the pinned layer side, and the amorphous layer in the two-layered PGGP separates the crystal layer and the crystal free and pinned layer in the two-layered PGGP. Item 8. The method according to Item 7. Said crystal layer and amorphous layer of ferromagnetic preferred grain growth promoting bcc structure of the seed layer, respectively _{Co x Fe 1-x (0} ≦ x ≦ 0.9) or _{(Co x Fe 1-x)} y B 1 _8. The method of claim 7, wherein _-y (0≤x≤0.9 and 0.9≤x <1) and CoFeB (B> 10 atomic%). The thickness (t ₁ ) of the crystal layer of the bcc structure and the thickness (t ₂ ) of the amorphous layer in the ferromagnetic suitable crystal grain growth promoting seed layer are 0.5 nm ≦ t ₁ ≦ 1.5 nm and 0, respectively. The method of claim 7, wherein 0.5 nm ≦ t ₂ ≦ 1.5 nm.   The ferromagnetic pin and the free layer having perpendicular anisotropy according to claim 1 can be multilayered by repeating a magnetic metal layer / nonmagnetic metal layer (M / NM) having chemical order, wherein , M = Co, Fe, CoFe or CoPt, and NM = Pt, Pd, Ag or Au, ferromagnetic pins and free layers with perpendicular anisotropy.   12. The first ferromagnetic suitable crystal grain growth promoting seed layer according to claim 1, comprising a ferromagnetic pin having perpendicular anisotropy according to claim 11 and a free layer, and a double-layered amorphous layer / bcc structure crystal A first ferromagnetic preferred crystal, wherein the amorphous layer in the two-layered PGGP separates the ferromagnetic pin and free layer from the bcc crystal layer in the two-layered PGGP Grain growth promoting seed layer. In the crystal layer and the amorphous layer of the bcc structure in the first and second ferromagnetic suitable crystal grain growth promoting seed layers according to claim 12, Co _x Fe _1-x (0 ≦ x ≦ 0.9) or ( _{Co x Fe 1-x) y} B 1-y (0 ≦ x ≦ 0.9 and 0.9 ≦ x <1) and CoFeB (B> 10 atomic%), the crystalline layer and an amorphous layer of bcc structure. The thickness (t1) of the bcc structure and the thickness (t2) of the amorphous layer in the first and second ferromagnetic suitable crystal grain growth promoting seed layers according to claim 12 and 13 are 0.5 nm ≦ The thickness of the crystal layer (t ₁ ) and the thickness of the amorphous layer (t ₂ ) of the bcc structure, which can satisfy t ₁ ≦ 1.5 nm and 0.5 nm ≦ t ₂ ≦ 1.5 nm.