JP4869140B2 - Tunnel magnetoresistive element manufacturing apparatus and manufacturing method - Google Patents

Description

  The present invention relates to a tunnel magnetoresistive effect element manufacturing apparatus and method, and more particularly to a technique for improving practicality and stability.

  A TMR (Tunnel Magnetic Resistor) magnetic device is a device using a ferromagnetic tunnel junction (hereinafter referred to as MTJ) having a ferromagnetic layer / insulator layer / ferromagnetic layer as a basic configuration. An example of such a device is a magnetic random access memory (hereinafter referred to as MRAM).

  In MTJ, the value of the tunnel current flowing in the insulator layer differs depending on the magnetization direction of both ferromagnetic layers. Normally, a tunnel that passes through an insulating film at an angle formed by two ferromagnetic layers while fixing the magnetization direction of one ferromagnetic layer (hereinafter pinned layer) and changing the other magnetization direction freely (hereinafter free layer) The current is changed and the change is read as a change in electric resistance. Utilizing this characteristic, it is applied to a magnetic sensor, a magnetic head for recording (for example, Patent Document 1) and an MRAM (for example, Patent Document 2).

  A general method for forming an MTJ in manufacturing a TMR magnetic device is as follows. First, a pinned layer made of permalloy, Fe, Co, Ni, and a ferromagnetic material containing them is formed on a wafer using a sputtering film forming apparatus. Next, a free layer made of the above-described ferromagnetic material is formed on the insulator layer, and a film structure of a pin layer made of a ferromagnetic material / insulator layer / free layer made of a ferromagnetic material is formed. Among them, the insulator layer is formed by forming an aluminum or magnesium metal film and oxidizing it by any of the following methods.

  One is a method in which the metal film surface is exposed to an oxygen atmosphere and is naturally oxidized, but has a drawback that the oxidation rate is slow. On the other hand, there is a method of actively oxidizing the metal film with oxygen or nitrogen plasma. Recently, there is a technique of oxidizing a metal film with radicals of oxygen or nitrogen so that charged particles in plasma do not damage the insulating film.

  In the TMR magnetic device, since the junction resistance needs to be reduced, the insulator layer is required to be formed with a very thin film thickness of about 1 nm, and to be smooth and oxidized to a desired thickness. Since the electrical characteristics of the TMR device are strongly influenced by the oxidation state of the insulator layer, a high MR (Magneto Resistive) ratio and magnetoresistance effect can be obtained if it is sufficiently oxidized.

  However, there is a problem in controllability and reproducibility because a thin film is required to form an aluminum or magnesium metal thin film as an insulator layer in a desired oxidation state, that is, with a desired oxidation thickness and degree of oxidation. In order to know the oxidation state, the monitor substrate was taken out from the film forming apparatus, and the electrical and magnetic characteristics of the MTJ were measured and judged.

  As means for solving this problem, Patent Document 3 discloses a method for optically grasping the surface of an insulator layer. In FIG. 2 of Patent Document 3, a processing chamber 51 for producing a tunnel insulating film by oxidizing the surface of a substrate 40 with a plasma 56 and an infrared light source 60 for optically evaluating the surface state of the substrate 40. And a detector of a reflective infrared spectrophotometer, a control analysis system that analyzes an output signal from the detector, and an oxidation control system that controls oxidation based on the analysis signal.

  In the above-described configuration, in the oxidation step, the metal film serving as the tunnel insulating film is irradiated with light from the light source, and the reflected light is detected by a reflective infrared spectrophotometer. Since the reflected light changes depending on the surface state of the metal film, the oxidation state can be controlled and managed by monitoring the detector signal.

JP 2002-237628 A JP 2001-144345 A JP 2004-235223 A

  However, the infrared light source and the reflective infrared spectrophotometer used in Patent Document 3 are not practical because they are larger than the processing chamber because they are precision analytical instruments, and the operability in the mass production line is poor. It was. In addition, the infrared light incident window 57 and the light receiving window 58 shown in FIG. 2 of Patent Document 3 can detect the oxidation state stably because the surface becomes dirty and the transmittance decreases when used for a long time. was difficult. Therefore, there is a problem that the characteristics of the manufactured tunnel magnetoresistive element vary.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a tunnel magnetoresistive element manufacturing apparatus and method that can reduce variations in characteristics in manufacturing.

  The method of manufacturing a tunnel magnetoresistive effect element according to the present invention includes a step of preparing a substrate having a first ferromagnetic film and a metal film sequentially formed on a surface, and subjecting the metal film to an oxidation process or a nitridation process. An insulator film forming step of forming an insulator film having a predetermined thickness and a step of forming a second ferromagnetic film on the insulator film, the insulator film forming step including the predetermined step A thickness detecting step of detecting the thickness of the metal film by obtaining a transmission characteristic of a high frequency signal in the metal film.

  The tunnel magnetoresistive element manufacturing apparatus and method according to the present invention detects the thickness of an insulating film formed from a metal film by determining the transmission characteristics of a high-frequency signal in the metal film. Can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.

<Embodiment 1>
FIG. 1 is a cross-sectional view showing a schematic configuration of a metal film oxidation treatment apparatus which is a part of a tunnel magnetoresistive element (TMR device) manufacturing apparatus according to Embodiment 1 of the present invention. 2 and 3 are cross-sectional views showing a detailed configuration of the metal film oxidation treatment apparatus of FIG. FIGS. 4 to 5 are a perspective view and a cross-sectional view showing the configuration of the model used for the simulation of the metal film oxidation treatment apparatus of FIG. 1, respectively, and FIGS. 6 to 7 are graphs showing the simulation results described above. It is.

  In the present embodiment, a method for detecting the oxidation state of the metal film in the step of forming the insulator film of the tunnel magnetoresistive effect element will be described. The insulator film is not limited to the oxidation of the metal film, but may be formed by nitriding the metal film.

  In FIG. 1, a wafer 3 made of a silicon substrate placed on a stage 2 is vacuum-sealed and subjected to an oxidation treatment of a metal film in an oxidation treatment chamber 1 (insulator film formation chamber). The exhaust port 4 evacuates the oxidation processing chamber 1 with a vacuum pump (not shown).

  The radical generator 8 includes a radical generation chamber 5 that is a space for generating radicals, a gas supply port 6 for supplying gas to the radical generation chamber 5, and an RF power source 7 for generating radicals in the radical generation chamber 5. Including.

  The radicals generated in the radical generator 8 are guided to the oxidation treatment chamber 1 through the introduction pipe 9 and supplied onto the wafer 3 as indicated by arrows.

  The film forming apparatus 13 is an apparatus for sequentially forming a first ferromagnetic film and a metal film that becomes an insulator film by oxidation treatment on the wafer 3 so as to be adjacent to the oxidation treatment chamber 1. Is arranged. The wafer 3 is transferred between the oxidation processing chamber 1 and the film forming apparatus 13 via the gate shutter 12.

  Further, the stage 2 and the RF power source 7 are connected to the outside of the oxidation processing chamber 1 via a network analyzer 14 for measuring transmission characteristics of a high frequency signal and an oxidation state monitoring means 15. As will be described later, the stage 2, the network analyzer 14, and the oxidation state monitoring means 15 function as thickness detection means for detecting the thickness of the insulator film formed by the oxidation treatment in the oxidation treatment chamber 1. is there.

  In the following, with reference to FIG. 1, a method for forming an insulator film in the manufacture of a TMR device will be described.

  First, in the film forming apparatus 13, a ferromagnetic film and a metal film are stacked on the wafer 3.

  Next, the wafer 3 is transferred to the oxidation processing chamber 1 through the gate shutter 12 and placed on the stage 2.

  Next, radicals generated by the radical generator 8 are supplied to the surface of the wafer 3 and the metal film is oxidized, whereby an insulator film made of an oxide film is formed on the wafer 3. As a gas supplied to the radical generation chamber 5 through the gas supply port 6, oxygen gas or the like is used (in the case of performing nitriding instead of oxidation, nitrogen gas or the like is used).

  Next, the wafer 3 on which a desired insulator film is formed is transferred to the processing chamber for the next process via the gate shutter 12 and the film forming apparatus 13.

  Below, with reference to FIGS. 2-3, the detection method of the oxidation state in manufacture of a TMR device is demonstrated.

  Referring to FIG. 2, the stage 2 includes a wafer placement unit 23 on which the wafer 3 is placed and a wafer presser 20 for pressing the wafer 3 from above. The wafer retainer 20 is made of an insulating material such as quartz or ceramic, and has a ring shape to retain the peripheral portion of the wafer 3 surface. A part of the wafer holder 20 is inserted into the wafer mounting portion 23 and can be driven in the vertical direction with respect to the wafer mounting portion 23 by a driving means (not shown).

  In the wafer retainer 20, a pair (two places) of contact fingers 21 and 22 having excellent electrical continuity are disposed on a part of the surface that contacts the peripheral portion of the wafer 3 surface. The contact fingers 21 and 22 are connected to measurement terminals of the network analyzer 14 via high-frequency cables 24 and 25, respectively.

  Referring to FIG. 1, the high frequency transmission characteristic measured by network analyzer 14 is monitored by oxidation state monitoring means 15. When it is determined that the desired oxidation state has been reached, the RF power source 7 is stopped, and the oxidation treatment process (insulating film formation process) ends.

  Referring to FIG. 3, in wafer 3, base oxide film 34, ferromagnetic film 33 serving as a pinned layer, and metal film 31 are formed in this order on silicon substrate body 35.

  The base oxide film 34 is formed with a film thickness of about several hundreds of nanometers on the silicon substrate body 35 except for the periphery of the wafer 3.

  The material of the ferromagnetic film 33 is not particularly limited, and Ni—Fe alloys represented by permalloy, Fe, Co, Ni exhibiting ferromagnetism, and ferromagnetic materials containing them can be used. The ferromagnetic film 33 is formed by laminating these materials with a film thickness of about several tens of nanometers.

  On the other hand, the metal film 31 forms a very thin film of about 1 nm that becomes a tunnel barrier, that is, an insulator film by oxidation or nitridation, and aluminum, magnesium, a rare earth element, or an alloy containing these elements can be used. . Normally, a lower electrode layer is formed on the MTJ pinned layer on the silicon substrate body 35 side, but is omitted in FIG.

  When the insulator film is formed with the above-described film structure, an MTJ is formed by forming a second ferromagnetic film (not shown) serving as a free layer thereon.

  Referring to FIG. 3, in wafer holder 20, contact fingers 21 and 22 are made of a highly conductive material such as gold, silver, or copper, and signal ends 211 and 221 that are in contact with metal film 31 and silicon, respectively. It has earthing ends 212 and 222 in contact with the surface of the substrate body 35.

  The signal terminal 211 is connected to the S terminal of the high frequency cable 24, the ground terminal 212 is connected to the G terminal of the high frequency cable 24, the signal terminal 221 is connected to the S terminal of the high frequency cable 25, and the ground terminal 222 is connected to the G terminal of the high frequency cable 25. And connected to the network analyzer 14.

  Thereby, the high frequency transmission characteristic between the signal end 211 of the contact finger 21 and the signal end 221 of the contact finger 22 can be easily measured using the silicon substrate body 35 as the earth ground.

  Hereinafter, a method for detecting the oxidation state of the metal film 31 will be described with reference to FIG.

  In the film forming apparatus 13, the wafer 3 on which the metal film 31 is formed on the ferromagnetic film 33 serving as the pinned layer is transferred to the oxidation processing chamber 1 and placed on the stage 2. Then, the wafer 3 is oxidized to the metal film 31 while being fixed to the stage 2 by the wafer presser 20.

  In order to detect the oxidation state in the metal film 31, first, the electrical high-frequency characteristics of the wafer 3 are measured by the network analyzer 14 in the initial state where oxidation is not performed, that is, in the state where radicals are not supplied. This measurement is performed by the two-port transmission method of the network analyzer 14 and the transmission characteristics between the contact fingers 21 and 22 are measured. In this case, since the base oxide film 34 is sufficiently thicker than the ferromagnetic film 33 and the metal film 31, it becomes an electrical insulator. Therefore, the network analyzer 14 measures the high-frequency signal transmission characteristics of the portion where the ferromagnetic film 33 and the metal film 31 are combined.

  Next, when radicals are supplied and oxidation starts, oxidation proceeds gradually from the surface of the metal film 31 and an oxide layer 32 is formed as an insulator film (oxide film). At this time, the metal film 31 in the periphery of the wafer 3 is not oxidized because it is covered with the wafer retainer 20. Therefore, the signal end 211 of the contact finger 21 and the signal end 221 of the contact finger 22 maintain electrical continuity with the surface of the metal film 31 in the periphery of the wafer 3.

  In such a state, the transmission characteristic of the high frequency signal in a state where the surface of the metal film 31 is oxidized is measured by the method described above. This measurement is performed continuously or intermittently during the period of oxidation treatment, so that a change in transmission characteristics corresponding to the oxidation treatment time can be obtained.

  In order to verify the above method, the relationship between the oxidation state of the surface of the metal film 31 and the high-frequency transmission characteristics was calculated by the following simulation. FIG. 4 is a perspective view showing the configuration of the model used for the simulation, and FIG. 5 is a cross-sectional view taken along the line A-A ′ of FIG. 4. On the base oxide film 34 as the insulator film, a structure in which 40 nm of Ni as the ferromagnetic film 33 is stacked and 2 nm of aluminum as the metal film 31 is stacked. In addition, the ferromagnetic film 33 and the metal film 31 were each set such that the width W of the input end of the high-frequency signal was 400 nm and the length L was 1 mm. 4 to 5, the transmission direction of the high-frequency signal is indicated by an arrow.

  FIG. 6 is a graph showing the simulation result. In FIG. 6, the horizontal axis represents the frequency, and the vertical axis represents the S parameter [1, 2] indicating the transmission characteristic of the high-frequency signal, depending on the thickness of the oxide layer 32 corresponding to the oxidation state of the metal film 31. The simulation results under the three conditions are shown. That is, the state in which the metal film 31 is not oxidized at all and remains aluminum (when the oxide layer 32 is 0 nm) is a solid line, and the metal film 31 is oxidized halfway from the surface (when the oxide layer 32 is 1 nm). ) Is a wavy line, and the case where the metal film 31 is entirely oxidized to become an insulator film (when the oxide layer 32 is 2 nm) is shown by a one-dot chain line. In FIG. 6, transmission characteristics corresponding to frequencies from 20 MHz to 100 MHz are shown, and S parameter [1,2] = 1.0 represents no transmission loss.

  As shown in the simulation results of FIG. 6, the transmission loss is small under any oxidation condition near the frequency of 20 MHz, but the S parameter [1,2] decreases and the transmission loss increases as the frequency increases. . Further, this transmission characteristic is lowered depending on the thickness of the oxide layer 32. When the entire metal film 31 becomes the oxide layer 32, that is, when the oxide layer 32 is 2 nm, the loss corresponding to the frequency of 100 MHz is 1. 0.0-0.4 = 0.6. The reason why the transmission loss increases in the high frequency region is considered to be due to the presence of an inductive component and a capacitive component in the transmission path composed of the ferromagnetic film 33 and the metal film 31.

  FIG. 7 shows the simulation result, with the frequency fixed at 100 MHz, the thickness of the oxide layer 32 on the horizontal axis, and the S parameter [1, 2] on the vertical axis. As shown in FIG. 7, as the thickness of the oxide layer 32 increases, the S parameter [1, 2] decreases. From the above, it can be seen that the transmission characteristics of the TMR device composed of the ferromagnetic film 33 and the metal film 31 change corresponding to the depth at which the surface of the metal film 31 is oxidized, that is, the oxidation state.

  Therefore, as shown in FIG. 2, in the oxidation treatment process of the metal film 31 in manufacturing the TMR device, if high-frequency transmission characteristics are measured from the contact fingers 21 and 22 provided on the wafer holder 20 on the stage 2, the metal Information corresponding to the progress of oxidation of the film 31 is obtained. Accordingly, the change of the transmission characteristics shown in FIG. 7 is monitored in real time by the oxidation state monitoring means 15 during the oxidation treatment process, and the RF power supply 7 is stopped if a predetermined oxide film thickness, that is, the end point of oxidation is determined. Thus, the oxidation treatment process can be completed.

  Thus, in the present embodiment, the thickness of the oxide layer 32 formed by subjecting the metal film 31 to oxidation or nitridation is detected by determining the transmission characteristics of the high-frequency signal. Therefore, it is possible to reduce variation in characteristics of the manufactured TMR magnetic device as compared with Patent Document 3 using a precision analysis instrument such as an infrared light source or a reflective infrared spectrophotometer. Therefore, the yield in manufacturing the TMR magnetic device can be increased.

  Moreover, said effect can be made remarkable by using a signal with a frequency of 20-100 MHz as a high frequency signal.

  In the above description, the case where only one pair (two locations) of the contact fingers 21 and 22 are provided on the surface of the wafer retainer 20 that contacts the peripheral portion of the surface of the wafer 3 is described. It may be provided. Thereby, more information on the progress of oxidation can be obtained, so that the characteristic variation in the manufacture of the TMR magnetic device can be further reduced.

  In the above description, the case where the S parameter is used as the transmission characteristic of the high-frequency signal has been described.

1 is a cross-sectional view showing a schematic configuration of a metal film oxidation treatment apparatus according to a first embodiment. 1 is a cross-sectional view illustrating a detailed configuration of a metal film oxidation treatment apparatus according to a first embodiment. 1 is a cross-sectional view illustrating a detailed configuration of a metal film oxidation treatment apparatus according to a first embodiment. 1 is a perspective view showing a configuration of a model used for simulation of a metal film oxidation processing apparatus according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view showing a configuration of a model used for simulation of the metal film oxidation treatment apparatus according to the first embodiment. 4 is a graph showing a simulation result of the metal film oxidation treatment apparatus according to the first embodiment. 4 is a graph showing a simulation result of the metal film oxidation treatment apparatus according to the first embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Oxidation processing chamber, 2 stage, 3 wafer, 4 exhaust port, 5 radical generating chamber, 6 gas supply port, 7 RF power supply, 8 radical generator, 9 introduction pipe, 12 gate shutter, 13 film-forming apparatus, 14 network analyzer , 15 Oxidation state monitoring means, 20 Wafer holder, 21, 22 Contact finger, 23 Wafer mounting part, 24, 25 High-frequency cable, 31 Metal film, 32 Oxide layer, 33 Ferromagnetic film, 34 Base oxide film, 35 Silicon Board body, 211, 221 Signal end, 212, 222 Ground end.

Claims (7)

Preparing a substrate on the surface of which a first ferromagnetic film and a metal film are sequentially formed;
An insulator film forming step of forming an insulator film having a predetermined thickness by subjecting the metal film to oxidation treatment or nitriding treatment;
Forming a second ferromagnetic film on the insulator film,
The method of manufacturing a tunnel magnetoresistive effect element, wherein the insulator film forming step includes a thickness detecting step of detecting the predetermined thickness by obtaining a transmission characteristic of a high frequency signal in the metal film. It is a manufacturing method of the tunnel magnetoresistive effect element according to claim 1,
The thickness detection step is a method of manufacturing a tunnel magnetoresistive element using a signal having a frequency of 20 to 100 MHz as the high frequency signal. A stage on which a substrate on which a first ferromagnetic film and a metal film are sequentially formed is placed;
An insulator film forming chamber in which the stage is disposed in a room and an insulator film having a predetermined thickness is formed by performing an oxidation process or a nitriding process on the metal film;
An apparatus for manufacturing a tunnel magnetoresistive effect element, comprising: thickness detecting means for detecting the predetermined thickness by obtaining a transmission characteristic of a high frequency signal in the metal film of the substrate placed on the stage. It is a manufacturing apparatus of the tunnel magnetoresistive effect element according to claim 3,
The said thickness detection means is a manufacturing apparatus of the tunnel magnetoresistive effect element which uses a signal with a frequency of 20-100 MHz as said high frequency signal. A tunnel magnetoresistive effect element manufacturing apparatus according to claim 3 or 4,
The apparatus for manufacturing a tunnel magnetoresistive effect element, wherein the thickness detecting means includes a conductor that is in electrical contact with a predetermined portion of the substrate surface. A tunnel magnetoresistive element manufacturing apparatus according to claim 5,
The apparatus for manufacturing a tunnel magnetoresistive effect element, wherein the thickness detection means further includes substrate pressing means for pressing the substrate with the conductor. A tunnel magnetoresistive effect element manufacturing apparatus according to claim 5 or 6,
An apparatus for manufacturing a tunnel magnetoresistive effect element, wherein a plurality of the predetermined locations are provided on the substrate surface.

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