JP4845301B2 - Method for manufacturing spin tunnel magnetoresistive film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of etching a composite formed by contacting at least a conductor and an insulator, and a workpiece.
[0002]
[Prior art]
In recent years, semiconductor memories, which are solid-state memories, are widely used in information equipment, and there are various types such as DRAM, FeRAM, and flash EEPROM. These semiconductor memories have advantages and disadvantages, and there is no memory that satisfies all of the specifications required for current information equipment. For example, DRAM has a high recording density and a large number of rewritable times, but it is volatile and information is lost when the power is turned off. In addition, the flash EEPROM is non-volatile, but the erasure time is long and is not suitable for high-speed information processing.
[0003]
In contrast to the current state of semiconductor memory as described above, memory (MRAM) using the magnetoresistive effect has specifications required by many information devices in terms of recording time, reading time, recording density, number of rewritable times, power consumption, etc. It is promising as a memory that fills everything. In particular, MRAM using the spin tunnel magnetoresistance (TMR) effect is advantageous for high recording density or high-speed reading because a large read signal can be obtained, and recent research reports have demonstrated its feasibility as MRAM. Yes.
[0004]
The basic configuration of a magnetoresistive film used as an MRAM element is a sandwich structure in which a magnetic layer is formed adjacent to a nonmagnetic layer. Cu and Al ₂ O ₃ are examples of materials often used as the nonmagnetic film. A magnetoresistive film using a conductor such as Cu as a nonmagnetic layer is called a giant magnetoresistive film (GMR film), and a film using an insulator such as Al ₂ O ₃ is a spin tunnel film ( TMR film). Since the TMR film exhibits a larger magnetoresistance effect than the GMR film, it is preferable as an MRAM memory element.
[0005]
As shown in FIG. 4A, when the magnetization directions of the two magnetic layers are parallel, the electric resistance of the magnetoresistive film is relatively small, and as shown in FIG. 4B, the magnetization directions are antiparallel. If so, the electrical resistance is relatively large. Therefore, information can be read by using one of the magnetic layers as a recording layer and the other as a reading layer and utilizing the above properties. For example, the magnetic layer 11 located below the nonmagnetic layer 12 is the readout layer, the magnetic layer 13 located above is the recording layer, and the magnetization direction of the recording layer is rightward, `` 1 '', and the leftward direction is `` 0 '' And As shown in FIG. 5 (a), when the magnetization directions of both magnetic layers are rightward, the electric resistance of the magnetoresistive film is relatively small, and as shown in FIG. 5 (b), the magnetization direction of the readout layer is rightward. When the magnetization direction of the recording layer is leftward, the electric resistance is relatively large. Further, as shown in FIG. 5C, when the magnetization direction of the reading layer is leftward and the magnetization direction of the recording layer is rightward, the electric resistance is relatively large. As shown in FIG. When the magnetization direction of the layer is leftward, the electrical resistance is relatively small. That is, when the magnetization direction of the readout layer is fixed to the right, if the electrical resistance is large, “0” is recorded in the recording layer, and if the electrical resistance is small, “1” is recorded. Will be. Alternatively, when the magnetization direction of the readout layer is fixed to the left, if the electrical resistance is large, “1” is recorded in the recording layer, and if the electrical resistance is small, “0” is recorded. Will be.
[0006]
In order to create a MRAM having a high recording density by arranging a plurality of magnetoresistive elements, it is necessary to collectively process a desired shape and size after forming a magnetoresistive film. An etching process is generally used for microfabrication, and various etching techniques have been established in the semiconductor process.
[0007]
An aluminum alloy used as a wiring material of a semiconductor element is generally etched by adding boron trichloride to chlorine gas. Aluminum reacts easily with chlorine and is removed as a gas. Similarly, tungsten used as a wiring material can be etched with both a fluorine-based gas and a chlorine-based gas. A fluorocarbon gas is used to etch silicon oxide used as an insulating film.
[0008]
As described above, all of the etching techniques used in the semiconductor process gasify and remove the material, and the etched substance hardly reattaches to the workpiece.
[0009]
[Problems to be solved by the invention]
The magnetic material used for the magnetoresistive film is a transition metal such as Co, Fe, or Ni, or an alloy thereof, or an alloy of a rare earth metal such as Tb, Dy, or Gd and the transition metal. In order to finely process these materials by dry etching, it is preferable to react with an etching gas and vaporize and remove as in an etching method used in a semiconductor process. In recent studies, various etching gases have been studied using various etching gases. However, at present, the magnetic material has not been gasified and removed, and the magnetic material knocked out by the etching gas easily reattaches to the side wall of the element.
[0010]
A TMR film obtains a magnetoresistive effect by spin tunneling of electrons through a thin insulator, but when processed by physical etching, a magnetic material that is a conductor on the side wall of the TMR element as described above. Therefore, there is a problem that the magnetic material disposed on the upper and lower portions of the insulator is electrically short-circuited and a large magnetoresistive effect cannot be obtained.
[0011]
In view of this point, the present invention aims to increase the electric resistance of a substance reattached to a processed cross section in a method for etching a composite formed by contacting a conductor and an insulator, and in particular, etching a TMR film. It aims at preventing the short circuit of the element which arises by processing.
[0012]
[Means for Solving the Problems]
The present invention is a method of manufacturing a spin tunnel magnetoresistive film that performs dry etching of a multilayer structure in which an insulator is sandwiched between at least two magnetic materials ,
The magnetic body is an alloy composed of at least one element selected from Co, Fe, and Ni and at least one element selected from rare earth metals,
In the dry etching, a spin tunnel magnetoresistive film characterized in that after etching one magnetic body with only an inert gas, the other magnetic body is etched by switching to a gas containing at least nitrogen and no oxygen It relates to the manufacturing method .
[0018]
Includes alloys that exhibit perpendicular magnetization.
[0023]
Includes those where the inert gas is argon.
[0024]
The nitrogen partial pressure ratio in the gas containing at least nitrogen and not containing oxygen is 0.02 or more and less than 1.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0030]
FIG. 1 schematically shows the basic configuration of the TMR film and the shape at each stage when the TMR film is processed by an embodiment of the etching method of the present invention.
[0031]
As shown in FIG. 1 (a), the basic configuration of the TMR film is formed by sequentially forming a first magnetic layer 101, a nonmagnetic layer, and a second magnetic layer 103, and the nonmagnetic layer 102 is an insulator. is there. After such a TMR film is formed by a film forming apparatus, a resist is applied by a spinner and exposed to light to form a resist 200 in a desired shape as shown in FIG. 1 (b). After this is mounted on an etching apparatus and evacuated, for example, argon gas is introduced into the apparatus to perform dry etching. In the etching process, the second magnetic layer 103 is first etched, and then the nonmagnetic layer 102 and the first magnetic layer 101 are etched. At this time, as shown in FIG. 1 (c), a fence 100 made of redeposits is formed on the processed cross section, that is, on the element side wall. The TMR film shows a large resistance value because current flows through the insulating layer, but the reattachment is mainly made of a magnetic material that is a conductor, and has a very small resistance value compared to the resistance value of the TMR film. Have. Therefore, most of the current flows through the redeposition material having a low resistance value and does not tunnel through the insulating layer, so that the original magnetoresistance effect cannot be obtained.
[0032]
As described above, there is not yet a sufficient method for vaporizing and removing a magnetic material by reactive etching, so it is difficult to avoid the formation of a fence due to redeposits on a processed cross section. Therefore, in this embodiment, the electric resistance of the reattachment is increased, and the decrease in the magnetoresistance effect of the TMR film is reduced by reducing the electrons flowing in the reattachment, and the etching gas is formed using nitrogen. This problem was solved by making the re-deposited material a mixture containing nitride or nitrogen.
[0033]
In this embodiment mode, nitrogen is used as an etching gas. However, even if oxygen is used, the electric resistance of the redeposits is increased. However, since oxygen chemically reacts with the resist for pattern formation, there is a problem that the resist is burned out during etching and a desired processed shape cannot be obtained. Therefore, it is not preferable to use oxygen as an etching gas. The object of the present invention can also be achieved by using a mixed gas of an inert gas and nitrogen as an etching gas. In addition, as a result of elemental analysis by Rutherford backscattering analysis on the re-deposited material formed on the processing side surface when etching with an inert gas and nitrogen mixed gas or nitrogen gas as an etching gas, all of the nitrogen elements When existence was confirmed and etching was performed only with an inert gas such as argon or xenon, nitrogen was not detected in the redeposits.
[0034]
Fig. 2 shows that a first magnetic layer, alumina, and a second magnetic layer are sequentially formed on a silicon wafer and etched to a size of 20μm x 20μm using gases with different partial pressure ratios of inert gas and nitrogen. The resistance value between the first magnetic layer and the second magnetic layer is shown. However, the first magnetic layer and the second magnetic layer were made of magnetic materials having the same composition, and the etching depth was set such that the etching depth of the first magnetic layer was constant at 5 nm. The magnetic materials used are Co, Ni ₈₀ Fe ₂₀ , Gd ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ , and Tb ₂₀ (Fe ₆₀ Co ₄₀ ) ₈₀ . From this graph, it is understood that the element resistance can be kept high by setting the partial pressure ratio of nitrogen to the mixed gas of inert gas and nitrogen to 0.02 or more.
[0035]
FIG. 3 is a graph showing the relationship between the partial pressure ratio of nitrogen to the mixed gas of argon and nitrogen and the etching rate. According to this result, the etching rate when using a mixed gas or nitrogen is significantly lower than when using pure argon. This phenomenon occurred similarly even when an element other than argon such as xenon was used as the inert gas. Therefore, when it is desired to shorten the etching time as much as possible, it is not a good idea to perform etching using a mixed gas or nitrogen. Therefore, in such a case, it is preferable to perform etching only with an inert gas until immediately before penetrating the insulator by etching, and then etch with nitrogen or a mixed gas, because the etching processing time can be shortened.
[0036]
【Example】
Next, examples of the present invention will be described.
[0037]
(Example-1)
In order to form Co 20 nm and Al _x O _100-x 2.2 nm continuously on a silicon wafer with low electrical resistance, and then turn the Al _x O _100-x film into an Al ₂ O ₃ film Oxygen gas was introduced into and plasma oxidation treatment was performed. Further, after the inside of the film forming chamber was sufficiently evacuated, Ni ₈₀ Fe ₂₀ was formed to a thickness of 40 nm to form a TMR film. Both the Co film and the Ni ₈₀ Fe ₂₀ film are in-plane magnetization films. A 10 μm × 10 μm square pattern was formed on the obtained TMR film with a resist, and this was etched to the interface between the Co film and the silicon wafer by plasma etching using nitrogen gas.
[0038]
The resistance value between the Ni ₈₀ Fe ₂₀ film of the obtained workpiece and the silicon wafer was about 4.5 kΩ, and the magnetoresistance change rate was about 18%. Here, the rate of change in magnetoresistance is obtained from a value obtained by dividing the amount of change in resistance of the TMR film that occurs when a magnetic field is applied in the in-plane direction and the magnitude and direction thereof are changed by the minimum value of resistance.
[0039]
(Example-2)
The TMR film used in Example-1 was plasma etched in the same manner as in Example-1 by using a mixed gas of argon gas 0.50 Pa and nitrogen gas 0.35 Pa. The resistance value between the Ni ₈₀ Fe ₂₀ film of the workpiece thus obtained and the silicon wafer was about 4.7 kΩ, and the magnetoresistance change rate was about 18%.
[0040]
(Example-3)
The TMR film used in Example-1 was subjected to plasma etching using argon gas until the processed surface reached the interface between the Ni ₈₀ Fe ₂₀ film and the Al ₂ O ₃ film, and then to the interface between the Co film and the silicon wafer using nitrogen gas. Etching was performed. The resistance value between the Ni ₈₀ Fe ₂₀ film of the workpiece thus obtained and the silicon wafer was about 4.9 kΩ, and the magnetoresistance change rate was about 19%.
[0041]
(Example-4)
The TMR film used in Example-1 was subjected to plasma etching using argon gas until the processed surface reached the interface between the Ni ₈₀ Fe ₂₀ film and the Al ₂ O ₃ film, and then mixed with argon gas 0.50 Pa and nitrogen gas 0.35 Pa. Etching was performed to the interface between the Co film and the silicon wafer by gas. The resistance value between the Ni ₈₀ Fe ₂₀ film of the workpiece thus obtained and the silicon wafer was about 4.8 kΩ, and the magnetoresistance change rate was about 19%.
[0042]
(Example-5)
The Ni ₈₀ Fe ₂₀ was deposited by 2.2nm continuously 40nm and Al _x O _100-x on the low electric resistivity silicon wafer, then the Al _x O _100-x film in order to the Al ₂ O ₃ film formed Plasma oxidation was performed by introducing oxygen gas into the film chamber. Further, after the inside of the film formation chamber was sufficiently evacuated, a Co film was formed to a thickness of 20 nm to form a TMR film. A 10 μm × 10 μm square pattern was formed on the obtained TMR film with a resist, and this was etched to the interface between the Ni ₈₀ Fe ₂₀ film and the silicon wafer by plasma etching using nitrogen gas. The resistance value between the Co film and the silicon wafer of the workpiece thus obtained was 5.2 kΩ, and the magnetoresistance change rate was about 19%.
[0043]
(Example-6)
The TMR film used in Example-5 was plasma etched in the same manner as in Example-1 by using a mixed gas of argon gas 0.50 Pa and nitrogen gas 0.35 Pa. The resistance value between the Co film and the silicon wafer of the workpiece thus obtained was about 5.0 kΩ, and the magnetoresistance change rate was about 19%.
[0044]
(Example-7)
The TMR film used in Example-5 was subjected to plasma etching using argon gas until the processed surface reached the interface between the Co film and the Al ₂ O ₃ film, and then to the interface between the Ni ₈₀ Fe ₂₀ film and the silicon wafer using nitrogen gas. Etching was performed. The resistance value between the Co film and the silicon wafer of the workpiece thus obtained was 5.4 kΩ, and the magnetoresistance change rate was about 19%.
[0045]
(Example-8)
The TMR film used in Example-5 was plasma etched using argon gas until the processed surface reached the interface between the Co film and the Al ₂ O ₃ film, and then Ni was mixed with a mixed gas of argon gas 0.50 Pa and nitrogen gas 0.35 Pa. Etching was performed up to the interface between the ₈₀ Fe ₂₀ film and the silicon wafer. The resistance value between the Co film and the silicon wafer of the workpiece thus obtained was about 5.3 kΩ, and the magnetoresistance change rate was about 19%.
[0046]
(Example-9)
Gd ₂₀ (Fe ₆₀ Co ₄₀ ) ₈₀ 10 nm and Al _x O _100-x 2.2 nm are continuously formed on a silicon wafer with low electrical resistance, and then Al _x O _100-x film is Al ₂ O ₃ film. In order to achieve this, an oxygen gas was introduced into the film formation chamber and a plasma oxidation treatment was performed. Further, after the inside of the film forming chamber was sufficiently evacuated, Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ was formed to a thickness of 10 nm to form a TMR film. These magnetic films have an easy axis of magnetization in the direction perpendicular to the film surface. A 10 μm × 10 μm square pattern was formed on the obtained TMR film by resist, and this was etched to the interface between the Gd ₂₀ (Fe ₆₀ Co ₄₀ ) ₈₀ film and the silicon wafer by plasma etching using nitrogen gas. . The resistance value between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film of the workpiece thus obtained and the silicon wafer was 0.3 MΩ, and the magnetoresistance change rate was about 22%.
[0047]
(Example-10)
The TMR film used in Example-9 was plasma etched in the same manner as in Example-9 by using a mixed gas of argon gas 0.50 Pa and nitrogen gas 0.35 Pa. The resistance value between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film of the workpiece thus obtained and the silicon wafer was about 0.3 MΩ, and the magnetoresistance change rate was about 21%.
[0048]
(Example-11)
The TMR film used in Example-9 was subjected to plasma etching using argon gas until the processed surface reached the interface between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film and the Al ₂ O ₃ film, and then Gd ₂₀ ( Etching was performed up to the interface between the Fe ₆₀ Co ₄₀ ) ₈₀ film and the silicon wafer. The resistance value between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film of the workpiece thus obtained and the silicon wafer was about 0.3 MΩ, and the magnetoresistance change rate was about 24%.
[0049]
(Example-12)
The TMR film used in Example-9 was plasma etched using argon gas until the processing surface reached the interface between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film and the Al ₂ O ₃ film, and then argon gas 0.50 Pa and nitrogen were used. Etching was performed up to the interface between the Gd ₂₀ (Fe ₆₀ Co ₄₀ ) ₈₀ film and the silicon wafer with a mixed gas of 0.35 Pa. The resistance value between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film of the workpiece thus obtained and the silicon wafer was about 0.3 MΩ, and the magnetoresistance change rate was about 24%.
[0050]
(Comparative Example-1)
The TMR film used in Example-1 was plasma-etched in the same manner as in Example-1 by using a mixed gas of argon gas 0.60 Pa and nitrogen gas 0.01 Pa. The resistance value between the Ni ₈₀ Fe ₂₀ film of the workpiece thus obtained and the silicon wafer was about 160Ω, and no change in magnetoresistance was confirmed.
[0051]
(Comparative Example-2)
The TMR film used in Example-1 was plasma-etched with argon gas in the same manner as in Example-1. The resistance value between the Ni ₈₀ Fe ₂₀ film of the workpiece thus obtained and the silicon wafer was about 30Ω, and no change in magnetoresistance was confirmed.
[0052]
(Comparative Example-3)
The TMR film used in Example-9 was plasma-etched in the same manner as in Example-9 using a mixed gas of argon gas 0.60 Pa and nitrogen gas 0.01 Pa. The resistance value between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film of the workpiece thus obtained and the silicon wafer was about 110Ω, and no change in magnetoresistance was confirmed.
[0053]
(Comparative Example-4)
The TMR film used in Example-9 was subjected to plasma etching in the same manner as in Example-9 with argon gas. The resistance value between the Tb ₂₁ (Fe ₆₀ Co ₄₀ ) ₇₉ film of the workpiece thus obtained and the silicon wafer was about 50Ω, and no change in magnetoresistance was confirmed.
[0054]
【The invention's effect】
As described above, the dry etching method of the present invention can increase the electrical resistance by using a nitriding or nitrogen-containing substance as the re-deposited material formed on the processing side surface. The processed object, which is a composite of a conductor such as a TMR film and an insulator, can be produced without an electrical short circuit due to the reattachment.
[Brief description of the drawings]
1 (a), (b) and (c) schematically show the basic configuration of a TMR film and the shape at each stage when the TMR film is processed according to an embodiment of the etching method of the present invention; It is sectional drawing shown.
FIG. 2 is a graph showing the resistance value of the TMR film with respect to the partial pressure ratio of nitrogen and argon used as an etching gas, (a) is a graph plotted against a partial pressure ratio range of 0 to 1, and (b) is a partial pressure ratio. Is a graph plotted against the range 0 to 0.1.
FIG. 3 is a graph showing the etching rate of each conductor material with respect to the partial pressure ratio of nitrogen and argon used as an etching gas, where (a) is a graph plotted against a partial pressure ratio ranging from 0 to 1, and (b) is a partial graph. 3 is a graph plotted with respect to a pressure ratio range of 0 to 0.1.
FIG. 4 is a diagram for explaining the magnetization direction of a magnetic layer of a magnetoresistive effect film and the magnitude of electric resistance.
FIG. 5 is a diagram illustrating a relationship between a magnetization direction of a magnetic layer and a read signal when a magnetoresistive film is used as a memory element.
[Explanation of symbols]
11 Magnetic material (reading layer)
12 Non-magnetic material
13 Magnetic material (recording layer)
001 board
101 First magnetic body
102 Non-magnetic material
103 2nd magnetic body
110 Fence (reattachment)
200 resists

Claims (4)

A method of manufacturing a spin tunnel magnetoresistive film that performs dry etching of a multilayer structure in which an insulator is sandwiched between at least two magnetic materials ,
The magnetic body is an alloy composed of at least one element selected from Co, Fe, and Ni and at least one element selected from rare earth metals,
In the dry etching, a spin tunnel magnetoresistive film characterized in that after etching one magnetic body with only an inert gas, the other magnetic body is etched by switching to a gas containing at least nitrogen and no oxygen Manufacturing method . 2. The method of manufacturing a spin tunnel magnetoresistive film according to claim 1 , wherein the alloy exhibits perpendicular magnetization. The method for manufacturing a spin tunnel magnetoresistive film according to claim 1 or 2 , wherein the inert gas is argon. 4. The spin tunnel magnetoresistive film according to claim 1, wherein a partial pressure ratio of nitrogen in the gas containing at least nitrogen and not containing oxygen is 0.02 or more and less than 1. 5. Manufacturing method .

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