JP3642568B2 - Method for manufacturing magnetoresistive film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a magnetoresistive film whose electrical resistance changes with an external magnetic field.
[0002]
[Prior art]
Up to now, as a film using the magnetoresistive effect (MagnetoResistance effect), an anisotropic magnetoresistive film using a metal ferromagnetic layer, and two metal ferromagnets laminated via a metal nonmagnetic layer A giant magnetoresistive film including a layer and a tunnel magnetoresistive film including two metal ferromagnetic layers stacked via an insulating nonmagnetic layer (tunnel barrier layer) are known.
[0003]
The TMR film using the tunnel magnetoresistive effect (hereinafter referred to as TMR) is magnetic random access because of its non-volatility, high speed, and long-term reliability when applied to highly integrated memory devices. Studies are underway as memory (Magnetic Random Access Memory, hereinafter referred to as MRAM).
[0004]
This TMR film is required to have a submicron element size due to the demand for high integration, and a method for producing the TMR film by drawing using an electron beam (hereinafter referred to as EB) has been announced ( WJ Gallagher et al., J. Appl. Phys. 81, 3741 (1997)).
[0005]
In this method, first, as shown in the cross-sectional view of FIG. 5A, a lower electrode 52 mainly made of a metal ferromagnet, an Al oxide tunnel barrier layer 53, and mainly a metal ferromagnet are formed on a Si substrate 51. A laminated film of the upper electrode 54 is deposited by a magnetron sputtering apparatus.
[0006]
Next, as shown in the cross-sectional view of FIG. 5B, a pattern of a negative EB resist 55 is formed at the joint portion by EB drawing, and is used as a mask to form the upper electrode 54 and the oxide tunnel barrier layer. 53 ion milling is performed to form a submicron sized tunnel junction pattern. In this ion milling, the etching is controlled to stop at the upper surface of the lower electrode 52 after passing through the oxide tunnel barrier layer 53.
[0007]
Next, as shown in the cross-sectional view of FIG. 5C, a SiO ₂ insulating film 56 is deposited on the lower electrode 52 in which the EB resist 55 is formed at the junction by a magnetron sputtering apparatus.
[0008]
Next, a contact hole is exposed on the tunnel junction in a self-aligned manner by a lift-off process using an EB resist 55 under the SiO ₂ insulating film 56, and then the upper portion of Ag / Au is placed in the contact hole. The wiring 57 is formed by patterning using lift-off of a photoresist (not shown), and an upper wiring 57 that contacts the upper electrode 54 is formed as shown in the sectional view of FIG.
[0009]
[Problems to be solved by the invention]
As described above, a TMR film having a submicron junction size can be obtained by a manufacturing method using EB lithography. However, in this manufacturing method, several problems arise because EB writing is directly performed on the laminated film of the metal ferromagnetic layer 52 / oxide tunnel barrier layer 53 / metal ferromagnetic layer 54.
[0010]
This is presumably because a phenomenon as schematically shown in the cross-sectional view of FIG. 6 occurs during the patterning of the resist 55 shown in the cross-sectional view of FIG.
[0011]
That is, as shown in FIG. 6, when EB writing is performed on the EB resist 62 formed on the laminated film 61 of the metal ferromagnetic layer 52 / oxide tunnel barrier layer 53 / metal ferromagnetic layer 54, a relatively large mass is obtained. The reflection of the high energy incident EB 63 by the metal laminated film containing several metals becomes much larger than that of EB drawing of a semiconductor or the like.
[0012]
Accordingly, the scattering of the reflected electrons 64 spreads several times in the lateral direction as compared with the actual drawing region, and the same effect as when drawing is also performed around the irradiation region of the EB 63 occurs. Therefore, the fineness and controllability of the drawing pattern shape is lost.
[0013]
Also, in EB drawing that obtains a submicron fine shape, drawing is often performed with a beam energy as high as about 50 keV or more in order to improve the convergence of EB. However, most of the EBs at high energy easily penetrate the resist 62 and reach the underlying metal laminated film, and the metal laminated film is easily charged to cause electrostatic breakdown in the oxide tunnel barrier layer. This also causes a significant decrease in device manufacturing yield.
[0014]
As described above, in EB drawing for producing a TMR film having a submicron metal ferromagnetic layer / oxide tunnel barrier layer / metal ferromagnetic layer junction, formation of a fine pattern with a controlled shape is insufficient. In addition, charge-up due to a large amount of incident electron beams may cause electrostatic breakdown of the TMR film.
[0015]
An object of the present invention is to solve such problems and to provide a method for manufacturing a fine magnetoresistive film suitable for highly integrated memories.
[0016]
[Means for Solving the Problems]
In view of the above circumstances, the first of the present invention is an ion beam that is electrically neutralized in a laminated film provided on the first and second metal ferromagnetic layers laminated via a nonmagnetic layer. The manufacturing method of the magnetoresistive film which irradiates is provided.
[0017]
In view of the above circumstances, the second aspect of the present invention is an insulating layer or a laminated film formed on a laminated film comprising first and second metal ferromagnetic layers laminated via a nonmagnetic layer. A method of manufacturing a magnetoresistive film is provided which irradiates an electrically neutralized ion beam to a resist material layer formed in (1).
[0018]
In the first aspect of the present invention, a laminated film including a first metal ferromagnetic layer, a nonmagnetic layer, and a second metal ferromagnetic layer, or an insulating layer or a resist material layer formed on the laminated film In addition, by irradiating an ion beam that is electrically neutralized, a submicron fine magnetoresistive film capable of high integration can be easily manufactured at a high yield.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
In the first embodiment, implantation drawing is performed by using a focused ion beam of Ga (Focused Ion Beam, hereinafter referred to as FIB) on an inorganic resist containing Si (hereinafter, referred to as Si-based inorganic resist), and an F-based A method for manufacturing a TMR film using a mask pattern formed by dry etching will be described.
[0020]
First, as shown in the cross-sectional view of FIG. 1A, a laminated film 12 having a metal ferromagnetic layer / insulating nonmagnetic (tunnel barrier) layer / metal ferromagnetic layer is formed on a Si substrate 11. After that, the Si base inorganic resist thin film 13 is formed on the upper metal ferromagnetic layer by processing into the shape of the lower electrode including the lower metal ferromagnetic by photolithography and ion milling.
[0021]
Next, as shown in the cross-sectional view of FIG. 1B, a Ga ion beam 14 focused as an exposure process is applied to the Si-based inorganic resist on the surface of the laminated film 12 where the magnetoresistive effect film is to be left. 13 for injection drawing.
[0022]
Simultaneously with the implantation of the Ga ion beam 14, an electron beam 15 that electrically neutralizes the Ga ion beam 14 is irradiated to the vicinity of the irradiation region of the Ga ion beam 14 with low energy. Thereby, the Si-based inorganic resist 13 is irradiated with the Ga ion beam 14 as an electrically neutralized beam. Here, since the stopping power (energy lost per unit flight distance) of the Ga ion beam in the Si-based inorganic resist 13 is large, the incident Ga atoms remain in the vicinity of the surface of the Si-based inorganic resist 13.
[0023]
Next, when dry etching 16 using SF ₆ gas shown in FIG. 1C is performed on the entire surface of the Si-based inorganic resist 13, nonvolatile Ga fluoride is formed in the Ga ion beam irradiation region. As a result, the etching rate is greatly reduced, and volatile Si fluoride is formed in the region not irradiated with the Ga ion beam, and etching removal of the Si-based inorganic resist proceeds.
[0024]
As a result, as shown in the cross-sectional view of FIG. 1C, a fine structure 18 of an Si-based inorganic resist can be produced as a negative resist. By using this as a mask, the upper metal strength can be increased by ion milling. Fine processing of the upper electrode including the magnetic material can be performed.
[0025]
An arbitrary pattern, particularly a sub-micron fine pattern using the fineness of FIB can be formed on the Si-based inorganic resist by the FI FIB implantation exposure to the Si-based inorganic resist and the F-based dry etching.
[0026]
That is, in this method, the incident Ga atoms remain on the very surface of the Si-based inorganic resist, and because the chemical characteristics of the implanted Ga atom species are used instead of the energy of the ions, the beam is essentially a beam. In addition, the metal laminated film is hardly damaged.
[0027]
Further, unlike EB, the ion beam can be easily neutralized in order to irradiate the low-energy electron beam, and there is no need to worry about electrostatic breakdown due to the charged beam irradiation.
(Second Embodiment)
Next, a method for manufacturing a TMR film according to the second embodiment will be described.
[0028]
First, a stacked film including a lower electrode 22 having a metal ferromagnetic layer, an oxide tunnel barrier layer 23, and an upper electrode 24 having a metal ferromagnetic layer is formed on a Si substrate 21, and then, as shown in FIG. As shown in the sectional view, the lower electrode 22 is formed by photolithography and ion milling.
[0029]
Thereafter, a SiN _x layer is formed as an Si-based inorganic resist on the laminated film. Here, the SiN _x layer is deposited to a thickness of about 200 nm using a plasma CVD apparatus.
[0030]
Next, after performing FIB implantation drawing of Ga ions on the SiN _x layer, dry etching using SF ₆ gas is performed, thereby forming a resist pattern of a submicron junction as shown in FIG. Then, ion milling is performed using this as a mask to form a joint portion of the upper electrode.
[0031]
Here, FI ion implantation drawing of Ga ions is performed under conditions of a beam energy of about 30 keV and an implantation dose of about 5 × 10 ¹⁶ cm ⁻² . Since the FIB beam current at this time is about several tens of pA to several hundreds of pA, the ion beam can be easily neutralized by installing a filament as an electron beam emitter in the vicinity of the sample.
[0032]
Thereafter, when dry etching using SF ₆ as a reactive gas is performed using an electron cyclotron resonance type reactive ion beam etching apparatus, a SiN _x resist pattern 25 having a film thickness of about 150 nm can be formed. Using the SiN _x resist pattern 25 as a mask, the upper electrode 24 and the oxide film tunnel barrier layer 23 can be formed as a junction by Ar ion milling with a beam energy of about 400 eV.
[0033]
Next, as shown in the cross-sectional view of FIG. 2C, after the SiN _x resist pattern 25 is peeled off, a SiO ₂ insulating film 26 is deposited on the entire surface, and a photoresist 27 for an etch back process is further formed thereon. Is applied to the entire surface.
[0034]
Here, the SiN _x resist 25 is removed by isotropic plasma etching using an F-based reaction gas or a buffered hydrofluoric acid solution. The SiO ₂ insulating film is deposited to a thickness of about 100 nm using a sputtering apparatus. Furthermore, as a photoresist for the etch back process, for example, AZ5214E photoresist is applied to a thickness of about 1.2 μm. At this time, if the size of the junction is as small as about 2 μm or less, if the photoresist on the junction is made thinner than the other parts, the step of about 60 nm that can be formed in the junction after ion milling is almost eliminated on the upper surface of the photoresist. The
[0035]
Next, by performing an etch back process of the photoresist applied to the entire surface of the lower electrode 22, a resist opening is formed only on the junction, and then the SiO ₂ insulating film 26 is dried using the photoresist as a mask. Etching is performed to form a contact hole for the upper electrode as shown in FIG.
[0036]
Here, as an etch back process, dry etching of the photoresist is performed until the SiO ₂ insulating film 26 is exposed by reactive ion etching (RIE) using CF ₄ gas. Thereafter, a high selective etching of SiO ₂ with respect to the photoresist is performed by RIE in which H ₂ gas is added to CF ₄ gas, thereby forming a contact hole in the SiO ₂ insulating film using the photoresist as a mask.
[0037]
Next, after removing the photoresist mask 27 by O ₂ ashing, an upper wiring 28 made of Ti / Pt / Au is formed on the contact hole by photolithography lift-off as shown in FIG. Then, the manufacture of the TMR film is finished.
[0038]
As a method for producing the fine mask 25 at the tunnel junction, after applying an EB positive resist, FIB drawing is performed, and after development with a normal developer, a metal such as Ti or an oxide such as SiO ₂ is deposited or sputtered. A method of depositing and forming a hard mask using a registry shift-off is also possible. In other words, since the bond irradiation of the polymer in the resist and the polymerization reaction occur in the ion-irradiated region, it is possible to form a positive resist pattern or a negative resist pattern with a normal developer.
[0039]
Here, even in the case of a resist exposure process similar to EB writing, the ion beam hardly scatters in the substance, so that there is almost no proximity effect.
[0040]
Furthermore, since ions have a large stopping power in the substance, an exposure sensitivity that is two to three orders of magnitude higher than that of electrons can be obtained, and even a thin film resist has very little damage to the base.
(Third embodiment)
Next, a method for manufacturing a magnetoresistive film according to the third embodiment of the present invention will be described.
[0041]
As shown in the cross-sectional view of FIG. 3, a lower electrode 22 having a metal ferromagnetic layer is formed on a Si substrate 21, and an EB resist coated on the entire surface of the lower electrode 22 is irradiated with a Ga ion beam, and O _When dry etching of ₂ plasma is performed, the EB resist 31 remains only in the Ga ion irradiation region, so that the resist mask can be patterned into the shape of the junction.
[0042]
In this case, Ga oxide is formed on the surface of the EB resist 31 in the Ga ion beam irradiation region and functions as an etching stop layer, so that the EB resist 31 is patterned as a negative resist. After the upper electrode 24 is processed by ion milling using the resist 31, a SiO ₂ insulating film (not shown) is formed on the entire surface without peeling off the resist 31, and lift-off is performed to make the contact hole a tunnel junction. It can be formed in a self-aligning manner.
[0043]
This resist mask formation process also uses the dry etching selectivity of the ion beam implantation region and the non-implantation region as described in the first embodiment, so that a good processing shape can be obtained and the substrate damage is extremely high. There is little worry about electrostatic breakdown.
[0044]
In addition, a self-alignment process using a pattern forming method such as normal EB negative resist coating, ion beam irradiation exposure, and development with a normal developer is also possible. In this case, the same effect can be obtained.
(Fourth embodiment)
Next, a method for manufacturing a magnetoresistive film according to the fourth embodiment of the present invention will be described.
[0045]
First, in order to form a contact hole on the junction of the SiO ₂ insulating film 41 formed on the entire surface of the Si substrate 21 on which the lower electrode 22, the oxide tunnel barrier layer 23, and the upper electrode 24 are formed, FIG. As shown in the cross-sectional view of FIG. 4, when ion beam lithography using a positive EB resist 42 is applied, it is possible to avoid the problems of scattered electron scattering and charge-up, and to form fine contact holes satisfactorily.
[0046]
Further, as shown in FIG. 4B, if ion beam assisted etching is performed by spraying a reactive gas 44 on the region irradiated with the ion beam 43, an etching rate that is an order of magnitude higher than that of physical sputter etching can be obtained. Therefore, a contact hole can be formed directly in the SiO ₂ insulating film 45 without using an etching mask.
[0047]
Here, an F-based reaction gas such as SF ₆ may be used for ion beam assisted etching for the SiO ₂ insulating film. In this ion beam assisted etching, since there is no effect of re-deposition of the etched material, a trench shape having a very large aspect ratio can be formed with a very smooth side wall. It is valid.
[0048]
When a contact hole is formed by this method, there is a concern that the junction is damaged by ion irradiation. However, if a metal such as Au having a large mass number is formed as a passivation film on the upper portion of the junction, most of the ions are formed. Stays in the Au film and is less likely to damage the laminated film.
[0049]
The method for manufacturing a magnetoresistive film according to the embodiment described above can be applied to a method for manufacturing a magnetic memory device in which magnetoresistive films such as MRAM are integrated. The present invention can also be applied to a method for manufacturing a magnetic head equipped with a magnetoresistive film.
[0050]
In each of the above embodiments, the TMR film has been mainly described. However, a giant magnetoresistive composed of a spin valve in which two metal ferromagnetic layers are stacked via a metal nonmagnetic layer or an artificial lattice. It can also be applied to an effect film, and a good fine pattern can be formed.
[0051]
In addition, the present invention is not limited to the above-described embodiments, and can be appropriately changed within the scope of the claims.
[0052]
【The invention's effect】
As described above, according to the present invention, a fine magnetoresistive element can be manufactured with a simple process and with a high yield.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a method of manufacturing a magnetoresistive film according to a first embodiment of the invention.
FIG. 2 is a cross-sectional view for explaining a magnetoresistive film manufacturing method according to a second embodiment of the invention.
FIG. 3 is a cross-sectional view for explaining a magnetoresistive film manufacturing method according to a third embodiment of the present invention.
FIG. 4 is a sectional view for explaining a method for manufacturing a magnetoresistive film according to a fourth embodiment of the invention.
FIG. 5 is a cross-sectional view for explaining a conventional method for manufacturing a TMR film.
FIG. 6 is a cross-sectional view illustrating a problem related to a manufacturing method according to a conventional technique.
[Explanation of symbols]
11, 21, 51 ... Si substrate 12, 61 ... Metal ferromagnetic layer / insulating non-magnetic layer / metal ferromagnetic layer laminated film 13 ... Si-containing inorganic resist 14 ... Ga ion beam 15 ... electron beam 16 ... F-based dry etching 22, 52 ... lower electrode 23, 53 ... oxide tunnel barrier layers 24, 54 ... upper electrode 25 ... SiN _x resists 26, 41, 45, 56... SiO ₂ insulating film 27... photoresist 28, 57... upper wiring 31, 42, 55, 62. ..Reactive gas 45 ... SiO ₂ insulating film 63 ... EB
64 ... backscattered electrons

Claims (2)

The insulating layer formed on the laminated film including the first and second metal ferromagnetic layers laminated via the nonmagnetic insulating layer, or the resist material layer formed on the laminated film is electrically intermediated. And a step of irradiating the ionized beam, and a step of etching the laminated film into a predetermined shape by etching the laminated film using the insulating layer or resist material layer irradiated with the ion beam as a mask material. A method of manufacturing a magnetoresistive effect film. 2. The magnetoresistive film according to claim 1 , wherein an inorganic resist containing Si is used for the resist material layer, a Ga ion beam is used for the ion beam, and the laminated film is formed into a predetermined shape by F-based etching. Manufacturing method.

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