WO2009157479A1 - Switching element and switching element manufacturing method - Google Patents

Switching element and switching element manufacturing method Download PDF

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Publication number
WO2009157479A1
WO2009157479A1 PCT/JP2009/061495 JP2009061495W WO2009157479A1 WO 2009157479 A1 WO2009157479 A1 WO 2009157479A1 JP 2009061495 W JP2009061495 W JP 2009061495W WO 2009157479 A1 WO2009157479 A1 WO 2009157479A1
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Prior art keywords
electrode
switching element
layer
resistance change
change layer
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PCT/JP2009/061495
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French (fr)
Japanese (ja)
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利司 阪本
憲幸 井口
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日本電気株式会社
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Priority to JP2010518039A priority Critical patent/JPWO2009157479A1/en
Publication of WO2009157479A1 publication Critical patent/WO2009157479A1/en

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/20—Multistable switching devices, e.g. memristors
    • H10N70/24—Multistable switching devices, e.g. memristors based on migration or redistribution of ionic species, e.g. anions, vacancies
    • H10N70/245—Multistable switching devices, e.g. memristors based on migration or redistribution of ionic species, e.g. anions, vacancies the species being metal cations, e.g. programmable metallization cells
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/011—Manufacture or treatment of multistable switching devices
    • H10N70/021—Formation of switching materials, e.g. deposition of layers
    • H10N70/026—Formation of switching materials, e.g. deposition of layers by physical vapor deposition, e.g. sputtering
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/821—Device geometry
    • H10N70/826—Device geometry adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/841—Electrodes
    • H10N70/8416—Electrodes adapted for supplying ionic species
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/881—Switching materials
    • H10N70/883—Oxides or nitrides
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/881—Switching materials
    • H10N70/883—Oxides or nitrides
    • H10N70/8833—Binary metal oxides, e.g. TaOx
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/881—Switching materials
    • H10N70/884—Switching materials based on at least one element of group IIIA, IVA or VA, e.g. elemental or compound semiconductors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
    • H10B63/30—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices comprising selection components having three or more electrodes, e.g. transistors

Definitions

  • the present invention relates to a switching element using an electrochemical reaction and a manufacturing method thereof.
  • a switching element using an electrochemical reaction As a resistance change type switch, a switching element using an electrochemical reaction (hereinafter referred to as a switching element) has been proposed.
  • a switching element is known to have a smaller size and lower on-resistance than a semiconductor switch such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
  • MOSFET Metal Oxide Semiconductor Field Effect Transistor
  • FIG. 1 is a schematic cross-sectional view showing a configuration example of the switching element disclosed in Document 1.
  • the switching element includes a first electrode 31, a second electrode 32, and a resistance change layer 33 provided in contact with these two electrodes.
  • the resistance change layer 33 is also an ion conductive layer that conducts metal ions.
  • the low resistance state (ON state) and the high resistance state (OFF state) transition from one to the other or the other to one by the positive voltage or the negative voltage applied between the first and second electrodes, and the voltage application is stopped. The state after the transition is retained.
  • the metal of the second electrode 32 becomes metal ions and dissolves in the resistance change layer 33. Then, metal ions in the resistance change layer 33 are deposited on the surface of the first electrode 32 as a metal, and a metal dendrite that connects the first electrode 31 and the second electrode 32 is formed by the deposited metal.
  • the metal dendrite is a metal deposit in which metal ions in the resistance change layer 33 are deposited.
  • the metal dendrite is dissolved in the resistance change layer 33, and a part of the metal dendrite is cut. Thereby, the electrical connection between the first electrode 31 and the second electrode 32 is cut, and the switch is turned off.
  • the first electrode 31 is desirably a material that does not supply metal ions into the resistance change layer when a voltage is applied. In order to switch from the off state to the on state, a negative voltage may be applied to the first electrode 31 again.
  • the switching element can be used for a programmable device typified by FPGA (Field Programmable Gate Array) and a memory.
  • Programmable logic switches are currently composed of semiconductor transistors, but if the above switching elements are used, the switch area can be reduced (1/30) and the switch resistance (1/30) compared to switches composed of semiconductor transistors. 50)
  • the switching element can be built in the wiring layer. Therefore, reduction of the chip area and improvement of wiring delay can be expected. In addition, the degree of integration can be improved by using the memory.
  • Document 2 Journal of Solid State Circuits, Vol. 40, No. 1, pp. 168-176, 2005
  • chalcogenides or metal oxides have been used for the resistance change layer of metal deposition type switches.
  • a switch in which chalcogenide is used for the resistance change layer is disclosed in Document 2.
  • a switch in which a metal oxide is used for the resistance change layer is disclosed in Japanese Patent Application Laid-Open No. 2006-319028.
  • Cu and Ag and chalcogen compounds such as CuS, AgS, and AgGeS are used as chalcogenides.
  • TaO, GdO, WO, etc. are used as a metal oxide.
  • the aim is to form the switching element in the wiring layer of an integrated circuit.
  • Integrated circuits can be broadly divided into a semiconductor substrate surface where transistors are formed and a region where wirings are formed. Since the wiring layer has a laminated structure of about 10 layers, a large number of switches can be formed three-dimensionally, and there is an advantage that the area penalty of the switch can be reduced by forming between the wiring layers.
  • the processing temperature when forming the wiring layer is at most 400 ° C., and most of the processing steps are as low as 350 ° C. or less.
  • the temperature and heating time required to form one wiring layer are about 350 ° C. and about 30 minutes.
  • the formation of the transistor requires a high temperature of 1000 ° C. or higher. If the switching element is formed after the formation of the transistor, the resistance to the temperature of the switch need not be 1000 ° C., but may be 400 ° C. Thus, (1) a large number of switches can be formed, (2) the area penalty is small by forming between the wiring layers, and (3) the temperature applied after the switch is formed is relatively low, 400 ° C. or less. These are the merits of forming in the wiring layer.
  • the wiring layer can be roughly divided into three areas: local wiring layer, semi-global wiring layer, and global wiring layer.
  • the local wiring layer is a wiring layer directly above the transistor, and the wiring pitch is equal to the minimum processing dimension and is fine and complicated.
  • the global wiring is formed with a wiring pitch of several tens to several hundred times the minimum processing dimension, and the wiring width is also widened so as to reduce the resistance.
  • Cu and Ag which are the first electrode constituent metals of the switching element, easily diffuse into the metal oxide due to heat.
  • heat of 350 ° C. or more is applied by bringing TaO, SiO and Cu into contact with each other, neutral Cu atoms diffuse into TaO and SiO to deteriorate the insulation characteristics, and a large leakage current is observed.
  • a trap level is formed at a deep band gap, and a leak current appears through the trap.
  • the electrode is preferably made of a material that does not cause thermal diffusion to the resistance change layer of Cu or Ag during the heat treatment in the manufacturing process.
  • the electrode in order to change the resistance and operate as a switch, it is necessary for Cu ions or Ag ions to move through the resistance change layer according to the voltage.
  • An example of an object of the present invention is to provide a switching element having improved heat resistance against a thermal process when forming a wiring, and a method for manufacturing the same.
  • a switching element includes a resistance change layer containing an oxynitride, a first electrode provided in contact with the resistance change layer, and provided in contact with the resistance change layer. And a second electrode containing a material capable of supplying the same.
  • the method for manufacturing a switching element includes a variable resistance layer, a first electrode in contact with the variable resistance layer, and a material in contact with the variable resistance layer and capable of supplying metal ions to the variable resistance layer.
  • a step of forming the resistance change layer includes a process of forming an oxynitride film by plasma nitriding an oxide at 400 ° C. or lower. .
  • FIG. 1 is a schematic cross-sectional view showing a configuration example of a related switching element.
  • FIG. 2 is a schematic cross-sectional view illustrating a configuration example of the switching element according to the first embodiment.
  • FIG. 3 is a schematic cross-sectional view illustrating a configuration example of the switching element according to the first embodiment.
  • FIG. 4A is a cross-sectional view for explaining the method for manufacturing the switching element of the first embodiment.
  • 4B is a cross-sectional view for explaining the method for manufacturing the switching element of Example 1.
  • FIG. 4C is a cross-sectional view for explaining the method for manufacturing the switching element of Example 1.
  • FIG. FIG. 4D is a cross-sectional view for explaining the method for manufacturing the switching element of the first embodiment.
  • FIG. 4A is a cross-sectional view for explaining the method for manufacturing the switching element of the first embodiment.
  • 4B is a cross-sectional view for explaining the method for manufacturing the switching element of Example 1.
  • FIG. 4C is a cross
  • FIG. 5 is a diagram illustrating a configuration of a circuit for measuring the characteristics of the switching element according to the first embodiment.
  • FIG. 6 is a diagram illustrating current / voltage characteristics of the switching element according to the first embodiment.
  • FIG. 7 is a graph showing current / voltage characteristics of the switching element of Example 2. In FIG.
  • FIG. 2 is a cross-sectional view showing a configuration example of the switching element of the present embodiment.
  • the switching element of the present embodiment has a configuration including a first electrode 11, a second electrode 12, and a resistance change layer 13 in contact with both electrodes.
  • the resistance change layer 13 includes oxynitride as a material.
  • the material of the first electrode 11 is platinum (Pt)
  • the material of the second electrode 12 is copper.
  • the 1st electrode 11 should just be a material which does not supply a metal ion to the resistance change layer 13 at least the site
  • the 2nd electrode 12 should just be a material which can supply a metal ion to the resistance change layer 13 at least the site
  • tantalum oxynitride (TaON) is used as the resistance change layer 13, but the same effect can be obtained with silicon oxynitride (SiON) or tantalum oxynitride silicate (TaSiON). Further, in tantalum oxynitride silicate, silicon (Si) is mixed into tantalum oxynitride, thereby adding an effect of suppressing leakage current that increases due to heat treatment.
  • the resistance change layer 13 may have a laminated structure of the above oxynitride film and oxide film. Specifically, it has a laminated structure of tantalum oxide and tantalum oxynitride, and tantalum oxynitride is in contact with the second electrode 12.
  • FIG. 3 is a schematic cross-sectional view showing a configuration example of the switching element of this example.
  • the switching element is provided on the silicon substrate 25 covered with the silicon oxide film 26, and the first electrode 21, the second electrode 22, and the resistance provided in contact with these two electrodes.
  • This is a structure having a change layer 23.
  • the resistance change layer 23 is made of tantalum oxynitride having a thickness of 15 nm
  • the first electrode 21 is made of platinum having a thickness of 40 nm
  • the second electrode 22 is made of copper having a thickness of 100 nm.
  • Part of the first electrode 21 is covered with an insulating layer 24 made of a silicon oxide film, and part of the first electrode 21 is in contact with the resistance change layer 23 through the opening of the insulating layer 24.
  • the side surface of the first electrode 21 and a part of the upper surface are covered with the insulating layer 24.
  • a portion of the upper surface of the first electrode 21 that is not covered with the insulating layer 24 is in contact with the resistance change layer 23 through an opening provided in the insulating layer 24.
  • the switching element is formed in the opening of the insulating layer 24, and the junction area of the switch corresponding to the contact area between the first electrode 21 and the resistance change layer 23 is as large as the opening. Since the insulating layer 24 separates the second electrode 22 and the first electrode 21 other than the switch portion, it is possible to suppress the leakage current at the off time.
  • 4A to 4D are cross-sectional views for explaining a method for manufacturing the switching element of this embodiment.
  • a silicon oxide film 26 having a thickness of 300 nm is formed on the surface of the silicon substrate 25. Platinum is formed on the silicon oxide film 26 by sputtering, and the formed platinum is processed into a desired pattern by etching to form the first electrode 21 (FIG. 4A).
  • a silicon oxide film having a thickness of 40 nm is formed as an insulating layer 24 on the silicon oxide film 26 so as to cover the first electrode 21 by a sputtering method. Openings 41 are formed in the insulating layer 24 by lithography and etching techniques (FIG. 4B). In the opening 41, a part of the upper surface of the first electrode 21 is exposed.
  • the insulating layer 24 is a silicon oxide film, but other insulating films such as silicon oxynitride may be used.
  • a resist is spin coated on the opening 41 and the insulating layer 24.
  • Resist patterning is performed by a lithography technique to form a resist mask 42 shown in FIG. 4C.
  • Oxygen plasma treatment is performed on the first electrode 21 exposed in the opening of the resist mask 42 to remove organic substances such as resist residues from the surface of the first electrode 21 and clean the surface.
  • a tantalum oxynitride film is formed on the resist mask 42 and on the opening. The following method 1 or method 2 is used for forming the tantalum oxynitride film.
  • Method 1 A tantalum oxide film is formed on a substrate by a sputtering method, and plasma nitridation is performed on the formed tantalum oxide film to form a tantalum oxynitride film.
  • the processing temperature of plasma nitriding is at most about 400 ° C., usually 350 ° C. or lower and 200 ° C. or higher, which is lower than that of thermal nitriding. It is advantageous.
  • Method 2 A tantalum oxide target is sputtered in a mixed gas atmosphere of an inert gas such as a nitrogen gas and an argon gas, so that the tantalum oxide protruding from the target and the nitrogen in the mixed gas atmosphere are formed on the substrate. accumulate. In this manner, a tantalum oxynitride film is formed on the substrate by a sputtering method.
  • the substrate temperature is about 350 ° C.
  • the tantalum oxynitride film After forming the tantalum oxynitride film by the above method 1 or method 2, copper having a thickness of 100 nm is deposited on the tantalum oxynitride film by vacuum evaporation or sputtering. Thereafter, the tantalum oxynitride film and copper formed on the resist mask 42 together with the resist mask 42 are removed to form the resistance change layer 23 and the second electrode 22 (FIG. 4D).
  • the resistance change layer 23 is a single layer of tantalum oxynitride
  • a laminated structure of tantalum oxynitride and tantalum oxide may be used.
  • This laminated structure can be formed by the following method 3 or method 4. In any method, the laminated structure is formed so that the tantalum oxynitride is in contact with the second electrode 22.
  • Method 3 A method of forming the laminated structure by combining sputtering and plasma nitriding.
  • a tantalum oxide film is formed by a sputtering method, a plasma nitriding process is performed on the formed tantalum oxide film to form a tantalum oxynitride film, and a tantalum oxide film is formed on the tantalum oxynitride film by a sputtering method.
  • Method 4 A method of forming the laminated structure by a sputtering method. Using a tantalum oxide target, a tantalum oxide film is formed by a sputtering method in which the growth atmosphere is a mixed gas of oxygen and argon. Subsequently, a tantalum oxynitride film is formed on the tantalum oxide film by a sputtering method using a mixed atmosphere of nitrogen and argon without changing the target.
  • the opening 41 is formed smaller than the pattern of the first electrode 21, and the pattern of the second electrode 22 and the resistance change layer 23 is formed larger than the opening 41, thereby joining the switch.
  • the area is determined by the size of the opening 41.
  • the opening 41 may be formed on the first electrode 21, and the resistance change layer 23 may cover the exposed surface of the first electrode 21 in the opening 41.
  • FIG. 5 is a diagram showing the configuration of a circuit for measuring the characteristics of the switching element.
  • a MOSFET 27 is connected in series to the switching element SW.
  • the drain electrode D of the MOSFET 27 is connected to the first electrode 21 of the switching element SW, and the source electrode S is grounded.
  • the voltage V G of 5V is applied to the gate electrode G, the measurement of the current flowing through the switching element SW when changing the voltage applied to the second electrode 22 of the switching element SW.
  • the MOSFET 27 serves to control the current flowing through the switching element in order to control the maximum current.
  • the resistance change layer 23 of the switching element of this example to be measured a tantalum oxynitride film having a thickness of 15 nm formed by the method 2 was used.
  • the materials of the first electrode and the second electrode were the same as in this example, and a sample using tantalum oxide having a film thickness of 15 nm for the variable resistance layer was also prepared. Platinum is used for the first electrode. Below, the measurement result of a switching element is demonstrated.
  • FIG. 6 is a graph showing the current / voltage characteristics of the switching element.
  • the horizontal axis indicates the voltage applied to the second electrode, and the vertical axis indicates the current flowing through the switching element.
  • the current flowing through the switching element was controlled to be 2 mA or less.
  • the solid line in the graph shows the current / voltage characteristics when tantalum oxynitride is used for the resistance change layer, and the broken line shows the current / voltage characteristics when tantalum oxide is used for the resistance change layer.
  • a positive voltage was applied to the second electrode 22 of the switching element of this example, and the voltage was gradually increased from 0V to 6V, and then gradually returned to 0V.
  • the initial state of the switching element is in the off state, and when the applied voltage becomes around 5 V, the state is changed to the on state. Thereafter, the current / voltage characteristics of the MOSFET 27 are observed until the applied voltage changes from 5V to 6V and then returns to 0V.
  • a negative voltage is applied to the second electrode 22. The applied voltage was changed from 0V to -2.5V, and then returned to 0V.
  • the heat treatment at 350 ° C. for 1 hour was performed on the switching element of this example and the sample switching element to verify how the current / voltage characteristics in FIG. 6 change.
  • tantalum oxynitride was used for the resistance change layer 23
  • the current / voltage characteristics did not change greatly.
  • tantalum oxide is used for the resistance change layer 23
  • the OFF state is changed to the ON state by the heat treatment, and even if a negative voltage is applied, the OFF state cannot be changed.
  • the use of the metal oxynitride as the variable resistance layer can improve the heat resistance against the thermal process when forming the wiring.
  • the material of the second electrode 12 is copper as in the first embodiment, but the material of the first electrode 11 is ruthenium (Ru), and the resistance change layer 13 is made of an oxide. It is a material that contains.
  • the 1st electrode 11 should just be a ruthenium the site
  • the 2nd electrode 12 should just be a material which can supply a metal ion to the resistance change layer 13 like the copper at least the site
  • tantalum oxide (TaO) is used as the resistance change layer 13, but the same effect can be obtained with silicon oxide (SiO) or tantalum oxide silicate (TaSiO). Similar to the first embodiment, the effect of suppressing the leakage current that is increased by the heat treatment is added by mixing silicon (Si) into tantalum oxide.
  • the switching element of the present embodiment has the configuration shown in FIG. 3, wherein the resistance change layer 23 is a tantalum oxide film and the material of the first electrode 21 is ruthenium. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.
  • the manufacturing method is the same as that of Example 1 except that the material of the first electrode 21 of Example 1 is ruthenium and the tantalum oxynitride of the resistance change layer 23 is tantalum oxide. The detailed explanation is omitted.
  • the circuit used for the measurement of the switching element is the same as the circuit shown in FIG. 5 and the measurement method is the same as that of the first embodiment, and detailed description thereof is omitted.
  • Ruthenium was used for the first electrode 21 of the switching element of this example to be measured.
  • the materials of the second electrode and the resistance change layer were the same as in this example, and a sample using platinum for the first electrode was also prepared. Tantalum oxide is used for the resistance change layer, and the film thickness is greater than 15 nm.
  • FIG. 7 is a graph showing the current / voltage characteristics of the switching element.
  • the horizontal axis indicates the voltage applied to the second electrode, and the vertical axis indicates the current flowing through the switching element.
  • the current flowing through the switching element was controlled to be 5 mA or less.
  • the solid line shown in the graph is the current / voltage characteristic when ruthenium is used for the first electrode 21, and the broken line is the current / voltage characteristic when platinum is used for the first electrode 21.
  • the switching element of this example has the same characteristics as platinum indicated by the broken line, and it can be seen that ruthenium can be used for the first electrode 21. Even when the switching element of this example was heat-treated, there was no significant change in the switching voltage. Ruthenium has advantages such as exhibiting metal properties even when oxidized, and being easier to etch than platinum.
  • the switching element of the present embodiment uses a metal oxide as the variable resistance layer and uses ruthenium for the first electrode, so that not only the same effect as in the first embodiment is obtained but also the first electrode is oxidized. Even if it has the property of a metal, the effect that it is easy to process compared with platinum is acquired. Note that ruthenium may be used for the first electrode of the first embodiment.
  • the thermal resistance to the thermal process when forming the wiring is improved.

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Abstract

A switching element is provided with a variable resistance layer (13) containing an oxynitride, a first electrode (11) arranged in contact with the variable resistance layer (13), and a second electrode (12) which is arranged in contact with the variable resistance layer (13) and contains a material which can supply metal ions to the variable resistance layer (13).

Description

スイッチング素子およびスイッチング素子の製造方法Switching element and method for manufacturing switching element
　本発明は、電気化学反応を利用したスイッチング素子およびその製造方法に関する。 The present invention relates to a switching element using an electrochemical reaction and a manufacturing method thereof.
　抵抗変化型のスイッチとして、電気化学反応を利用したスイッチング素子（以下、スイッチング素子と呼ぶ）が提案されている。その一例が特表２００２－５３６８４０号公報（以下では、文献１と称する）に開示されている。このスイッチング素子は、ＭＯＳＦＥＴ（Metal　Oxide　Semiconductor　Field　Effect　Transistor）などの半導体スイッチよりもサイズが小さく、オン抵抗が小さいことが知られている。 As a resistance change type switch, a switching element using an electrochemical reaction (hereinafter referred to as a switching element) has been proposed. One example of this is disclosed in JP-T-2002-536840 (hereinafter referred to as Document 1). This switching element is known to have a smaller size and lower on-resistance than a semiconductor switch such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
　図１は文献１に開示されたスイッチング素子の一構成例を示す断面模式図である。スイッチング素子は、第１電極３１と、第２電極３２と、これら２つの電極に接して設けられた抵抗変化層３３とを有する構成である。抵抗変化層３３は金属イオンが伝導するイオン伝導層でもある。 FIG. 1 is a schematic cross-sectional view showing a configuration example of the switching element disclosed in Document 1. The switching element includes a first electrode 31, a second electrode 32, and a resistance change layer 33 provided in contact with these two electrodes. The resistance change layer 33 is also an ion conductive layer that conducts metal ions.
　低抵抗状態（オン状態）と高抵抗状態（オフ状態）は、第１と第２電極間に印加する正電圧または負電圧によって一方から他方、または他方から一方に遷移し、電圧の印加を止めると、遷移後の状態が保持される。 The low resistance state (ON state) and the high resistance state (OFF state) transition from one to the other or the other to one by the positive voltage or the negative voltage applied between the first and second electrodes, and the voltage application is stopped. The state after the transition is retained.
　図１に示したスイッチング素子の動作について説明する。 The operation of the switching element shown in FIG. 1 will be described.
　第２電極３２を接地して、第１電極３１に負電圧を印加すると第２電極３２の金属が金属イオンになって抵抗変化層３３に溶解する。そして、抵抗変化層３３中の金属イオンが第１電極３２の表面に金属になって析出し、析出した金属により第１電極３１と第２電極３２を接続する金属デンドライトが形成される。金属デンドライトは抵抗変化層３３中の金属イオンが析出した金属析出物である。金属デンドライトで第１電極３１と第２電極３２が電気的に接続することで、スイッチがオン状態になる。 When the second electrode 32 is grounded and a negative voltage is applied to the first electrode 31, the metal of the second electrode 32 becomes metal ions and dissolves in the resistance change layer 33. Then, metal ions in the resistance change layer 33 are deposited on the surface of the first electrode 32 as a metal, and a metal dendrite that connects the first electrode 31 and the second electrode 32 is formed by the deposited metal. The metal dendrite is a metal deposit in which metal ions in the resistance change layer 33 are deposited. When the first electrode 31 and the second electrode 32 are electrically connected with a metal dendrite, the switch is turned on.
　一方、上記オン状態で第２電極３２を接地して、第１電極３１に正電圧を印加すると、金属デンドライトが抵抗変化層３３に溶解し、金属デンドライトの一部が切れる。これにより、第１電極３１と第２電極３２との電気的接続が切れ、スイッチがオフ状態になる。 On the other hand, when the second electrode 32 is grounded in the ON state and a positive voltage is applied to the first electrode 31, the metal dendrite is dissolved in the resistance change layer 33, and a part of the metal dendrite is cut. Thereby, the electrical connection between the first electrode 31 and the second electrode 32 is cut, and the switch is turned off.
　なお、電気的接続が完全に切れる前の段階から第１電極３１および第２電極３２間の抵抗が大きくなったり、電極間容量が変化したりするなど電気特性が変化し、最終的に電気的接続が切れる。電気特性の変化は、抵抗変化層内への金属析出により第１および第２電極の間の電気伝導度が大きかったのが、析出した金属の一部が取り除かれることにより電気伝導度が小さくなることによるものである。第１電極３１は、電圧を印加した際に、抵抗変化層中に金属イオンを供給しない材料であることが望ましい。また、上記オフ状態からオン状態にするには、再び第１電極３１に負電圧を印加すればよい。 Note that the electrical characteristics change from the stage before the electrical connection is completely cut off, such as the resistance between the first electrode 31 and the second electrode 32 is increased, or the capacitance between the electrodes is changed. The connection is lost. As for the change in electrical characteristics, the electrical conductivity between the first and second electrodes was large due to metal deposition in the variable resistance layer, but the electrical conductivity was reduced by removing a part of the deposited metal. It is because. The first electrode 31 is desirably a material that does not supply metal ions into the resistance change layer when a voltage is applied. In order to switch from the off state to the on state, a negative voltage may be applied to the first electrode 31 again.
　上記スイッチング素子は、ＦＰＧＡ（Ｆｉｅｌｄ　Ｐｒｏｇｒａｍｍａｂｌｅ　Ｇａｔｅ　Ａｒｒａｙ）に代表されるプログラマブルデバイスや、メモリに用いることができる。プログラマブルロジックのスイッチは現在、半導体トランジスタで構成されているが、上記スイッチング素子を用いれば、半導体トランジスタで構成されるスイッチに比べてスイッチ面積の縮小（１／３０）、スイッチ抵抗の低減（１／５０）、スイッチング素子の配線層への作り込みが可能となる。そのため、チップ面積の縮小と配線遅延の改善が期待できる。また、メモリに用いることで、集積度を向上させることができる。その一例が「ジャーナル・オブ・ソリッド・ステート・サーキッツ、４０巻、１号、１６８頁～１７６頁、２００５年」（以下では、文献２と称する）に開示されている。 The switching element can be used for a programmable device typified by FPGA (Field Programmable Gate Array) and a memory. Programmable logic switches are currently composed of semiconductor transistors, but if the above switching elements are used, the switch area can be reduced (1/30) and the switch resistance (1/30) compared to switches composed of semiconductor transistors. 50) The switching element can be built in the wiring layer. Therefore, reduction of the chip area and improvement of wiring delay can be expected. In addition, the degree of integration can be improved by using the memory. One example is disclosed in “Journal of Solid State Circuits, Vol. 40, No. 1, pp. 168-176, 2005” (hereinafter referred to as Document 2).
　これまで、金属析出型のスイッチの抵抗変化層にカルコゲナイドまたは金属酸化物が用いられている。抵抗変化層にカルコゲナイドが用いられているスイッチが文献２に開示されている。また、抵抗変化層に金属酸化物が用いられているスイッチが、特開２００６－３１９０２８号公報に開示されている。具体的には、カルコゲナイドとしてＣｕＳ、ＡｇＳ、ＡｇＧｅＳ等のＣｕおよびＡｇとカルコゲンとの化合物が用いられる。また、金属酸化物としてはＴａＯ、ＧｄＯ、ＷＯ等が用いられる。 So far, chalcogenides or metal oxides have been used for the resistance change layer of metal deposition type switches. A switch in which chalcogenide is used for the resistance change layer is disclosed in Document 2. A switch in which a metal oxide is used for the resistance change layer is disclosed in Japanese Patent Application Laid-Open No. 2006-319028. Specifically, Cu and Ag and chalcogen compounds such as CuS, AgS, and AgGeS are used as chalcogenides. Moreover, TaO, GdO, WO, etc. are used as a metal oxide.
　上記スイッチング素子を集積回路の配線層中に形成することを目指している。集積回路はトランジスタが形成される半導体基板表面と、配線が形成される領域に大きく分けることができる。配線層は１０層程度の積層構造のためスイッチを３次元的に多数形成できることと、配線層間に形成することでスイッチの面積ペナルティを少なくできるメリットがある。 The aim is to form the switching element in the wiring layer of an integrated circuit. Integrated circuits can be broadly divided into a semiconductor substrate surface where transistors are formed and a region where wirings are formed. Since the wiring layer has a laminated structure of about 10 layers, a large number of switches can be formed three-dimensionally, and there is an advantage that the area penalty of the switch can be reduced by forming between the wiring layers.
　さらに、配線層を形成する際の加工温度が最高でも４００℃あり、大半の加工工程は３５０℃以下の低温である。配線層の１層を形成するのに必要な温度、加熱時間はおおよそ３５０℃、３０分程度である。一方、トランジスタの形成には１０００℃以上の高温が必要となっている。トランジスタの形成後に上記スイッチング素子を形成するのであれば、スイッチの温度への耐性は、１０００℃の必要はなく、４００℃あればよい。このように、（１）スイッチを多数形成できること、（２）配線層間へ形成することで面積ペナルティが少ないこと、（３）スイッチ形成後に印加される温度が４００℃以下と比較的低温であること、などが配線層に形成するメリットである。 Furthermore, the processing temperature when forming the wiring layer is at most 400 ° C., and most of the processing steps are as low as 350 ° C. or less. The temperature and heating time required to form one wiring layer are about 350 ° C. and about 30 minutes. On the other hand, the formation of the transistor requires a high temperature of 1000 ° C. or higher. If the switching element is formed after the formation of the transistor, the resistance to the temperature of the switch need not be 1000 ° C., but may be 400 ° C. Thus, (1) a large number of switches can be formed, (2) the area penalty is small by forming between the wiring layers, and (3) the temperature applied after the switch is formed is relatively low, 400 ° C. or less. These are the merits of forming in the wiring layer.
　配線層は大きくローカル配線層、セミグローバル配線層、グローバル配線層の３つの領域に分けることができる。ローカル配線層はトランジスタ直上の配線層で、その配線ピッチは最小加工寸法に等しく、微細かつ複雑である。一方、グローバル配線は、最小加工寸法の数十から数百倍の配線ピッチで形成されており、低抵抗となるように配線幅も太くなっている。 The wiring layer can be roughly divided into three areas: local wiring layer, semi-global wiring layer, and global wiring layer. The local wiring layer is a wiring layer directly above the transistor, and the wiring pitch is equal to the minimum processing dimension and is fine and complicated. On the other hand, the global wiring is formed with a wiring pitch of several tens to several hundred times the minimum processing dimension, and the wiring width is also widened so as to reduce the resistance.
　多数のスイッチを形成するには、配線ピッチの小さいローカル配線層に形成するのが有利である。ローカル配線層にスイッチを形成した場合、スイッチより上層のセミグローバル配線やグローバル配線を形成する際の加熱工程に耐える熱耐性が必要となる。上述したように、配線層１層には３５０℃、３０分の熱が加わることから、スイッチが９層の配線層の形成に耐えるには、３０分を９回サイクルさせる際の熱履歴への耐性が必要となる。 In order to form a large number of switches, it is advantageous to form a local wiring layer with a small wiring pitch. When a switch is formed in the local wiring layer, heat resistance is required to withstand a heating process when forming a semi-global wiring or a global wiring above the switch. As described above, heat is applied to one wiring layer at 350 ° C. for 30 minutes. Therefore, in order for the switch to withstand the formation of the nine wiring layers, the heat history when cycling 30 minutes nine times is added. Tolerance is required.
　一般に、熱によってスイッチング素子の第１電極構成金属であるＣｕやＡｇが容易に金属酸化物内部に拡散することが知られている。例えば、上記ＴａＯ、ＳｉＯおよびＣｕを接触させて３５０℃以上の熱を加えると、ＴａＯおよびＳｉＯ中へ中性のＣｕ原子が拡散して絶縁特性が劣化し、大きなリーク電流が観測されるようになる。重金属が酸化物中に固溶すると、バンドギャップの深い位置にトラップ準位を形成され、そのトラップを介したリーク電流が現れる。 Generally, it is known that Cu and Ag, which are the first electrode constituent metals of the switching element, easily diffuse into the metal oxide due to heat. For example, when heat of 350 ° C. or more is applied by bringing TaO, SiO and Cu into contact with each other, neutral Cu atoms diffuse into TaO and SiO to deteriorate the insulation characteristics, and a large leakage current is observed. Become. When the heavy metal is dissolved in the oxide, a trap level is formed at a deep band gap, and a leak current appears through the trap.
　一方、３５０℃以上の熱を上記の抵抗変化材料のカルコゲナイドに加えた場合、カルコゲナイドを構成する金属イオンの拡散が活発となり、カルコゲナイドの変形や組成変化などが起こってしまう。カルコゲナイドは金属酸化物と比較しても熱耐性が低い。 On the other hand, when heat of 350 ° C. or higher is applied to the chalcogenide of the resistance change material, diffusion of metal ions constituting the chalcogenide becomes active, and chalcogenide deformation or composition change occurs. Chalcogenides are less heat resistant than metal oxides.
　集積回路の配線層にスイッチング素子を実装するには、電極は、製造過程の熱処理でＣｕやＡｇの抵抗変化層への熱拡散が起こらない材料が好ましい。一方、抵抗が変化してスイッチとして動作するためには、電圧によってＣｕイオンやＡｇイオンが抵抗変化層を移動する必要がある。 In order to mount the switching element in the wiring layer of the integrated circuit, the electrode is preferably made of a material that does not cause thermal diffusion to the resistance change layer of Cu or Ag during the heat treatment in the manufacturing process. On the other hand, in order to change the resistance and operate as a switch, it is necessary for Cu ions or Ag ions to move through the resistance change layer according to the voltage.
　本発明の目的の一例は、配線を形成する際の熱工程に対する熱耐性が向上したスイッチング素子およびその製造方法を提供することである。 An example of an object of the present invention is to provide a switching element having improved heat resistance against a thermal process when forming a wiring, and a method for manufacturing the same.
　本発明の一側面のスイッチング素子は、酸窒化物を含む抵抗変化層と、抵抗変化層に接して設けられた第１の電極と、抵抗変化層に接して設けられ、抵抗変化層に金属イオンを供給可能な材料を含む第２の電極と、を有する構成である。 A switching element according to one aspect of the present invention includes a resistance change layer containing an oxynitride, a first electrode provided in contact with the resistance change layer, and provided in contact with the resistance change layer. And a second electrode containing a material capable of supplying the same.
　また、本発明の一側面のスイッチング素子の製造方法は、抵抗変化層と、抵抗変化層に接する第１の電極と、抵抗変化層に接し、抵抗変化層に金属イオンを供給可能な材料を含む第２の電極と、を有するスイッチング素子の製造方法であって、抵抗変化層を形成する工程は、酸化物に対して４００℃以下でプラズマ窒化することにより酸窒化膜を形成する処理を含むものである。 The method for manufacturing a switching element according to one aspect of the present invention includes a variable resistance layer, a first electrode in contact with the variable resistance layer, and a material in contact with the variable resistance layer and capable of supplying metal ions to the variable resistance layer. And a step of forming the resistance change layer includes a process of forming an oxynitride film by plasma nitriding an oxide at 400 ° C. or lower. .
図１は関連するスイッチング素子の一構成例を示す断面模式図である。FIG. 1 is a schematic cross-sectional view showing a configuration example of a related switching element. 図２は第１の実施形態のスイッチング素子の一構成例を示す断面模式図である。FIG. 2 is a schematic cross-sectional view illustrating a configuration example of the switching element according to the first embodiment. 図３は実施例１のスイッチング素子の一構成例を示す断面模式図である。FIG. 3 is a schematic cross-sectional view illustrating a configuration example of the switching element according to the first embodiment. 図４Ａは実施例１のスイッチング素子の製造方法を説明するための断面図である。FIG. 4A is a cross-sectional view for explaining the method for manufacturing the switching element of the first embodiment. 図４Ｂは実施例１のスイッチング素子の製造方法を説明するための断面図である。4B is a cross-sectional view for explaining the method for manufacturing the switching element of Example 1. FIG. 図４Ｃは実施例１のスイッチング素子の製造方法を説明するための断面図である。4C is a cross-sectional view for explaining the method for manufacturing the switching element of Example 1. FIG. 図４Ｄは実施例１のスイッチング素子の製造方法を説明するための断面図である。FIG. 4D is a cross-sectional view for explaining the method for manufacturing the switching element of the first embodiment. 図５は実施例１のスイッチング素子の特性を測定するための回路の構成を示す図である。FIG. 5 is a diagram illustrating a configuration of a circuit for measuring the characteristics of the switching element according to the first embodiment. 図６は実施例１のスイッチング素子の電流・電圧特性を示す図である。FIG. 6 is a diagram illustrating current / voltage characteristics of the switching element according to the first embodiment. 図７は実施例２のスイッチング素子の電流・電圧特性を示す図である。FIG. 7 is a graph showing current / voltage characteristics of the switching element of Example 2. In FIG.
　（第１の実施形態）
　本実施形態のスイッチング素子の構成を説明する。図２は本実施形態のスイッチング素子の一構成例を示す断面図である。 (First embodiment)
The configuration of the switching element of this embodiment will be described. FIG. 2 is a cross-sectional view showing a configuration example of the switching element of the present embodiment.
　図２に示すように、本実施形態のスイッチング素子は、第１電極１１と、第２電極１２と、これら両方の電極に接触する抵抗変化層１３とを有する構成である。そして、抵抗変化層１３は材料に酸窒化物を含んでいる。本実施形態では、第１電極１１の材料は白金（Ｐｔ）であり、第２電極１２の材料は銅である。 As shown in FIG. 2, the switching element of the present embodiment has a configuration including a first electrode 11, a second electrode 12, and a resistance change layer 13 in contact with both electrodes. The resistance change layer 13 includes oxynitride as a material. In the present embodiment, the material of the first electrode 11 is platinum (Pt), and the material of the second electrode 12 is copper.
　なお、第１電極１１は、少なくとも抵抗変化層１３と接する部位が白金のように抵抗変化層１３に金属イオンを供給しない材料であればよい。第２電極１２は、少なくとも抵抗変化層１３と接する部位が銅のように抵抗変化層１３に金属イオンを供給可能な材料であればよい。 In addition, the 1st electrode 11 should just be a material which does not supply a metal ion to the resistance change layer 13 at least the site | part which contact | connects the resistance change layer 13 like platinum. The 2nd electrode 12 should just be a material which can supply a metal ion to the resistance change layer 13 at least the site | part which contact | connects the resistance change layer 13 like copper.
　本実施形態では、抵抗変化層１３として酸窒化タンタル（ＴａＯＮ）を用いるが、酸窒化シリコン（ＳｉＯＮ）または酸窒化タンタルシリケート（ＴａＳｉＯＮ）についても同様の効果が得られる。さらに、酸窒化タンタルシリケートでは、酸窒化タンタルにシリコン（Ｓｉ）を混入することにより、熱処理によって増大するリーク電流を抑制する効果が追加される。 In this embodiment, tantalum oxynitride (TaON) is used as the resistance change layer 13, but the same effect can be obtained with silicon oxynitride (SiON) or tantalum oxynitride silicate (TaSiON). Further, in tantalum oxynitride silicate, silicon (Si) is mixed into tantalum oxynitride, thereby adding an effect of suppressing leakage current that increases due to heat treatment.
　抵抗変化層１３は、上記の酸窒化膜と酸化膜の積層構造でもよい。具体的には、酸化タンタルと酸窒化タンタルの積層構造であり、酸窒化タンタルが第２電極１２と接する。 The resistance change layer 13 may have a laminated structure of the above oxynitride film and oxide film. Specifically, it has a laminated structure of tantalum oxide and tantalum oxynitride, and tantalum oxynitride is in contact with the second electrode 12.
　本実施例のスイッチング素子の構成を説明する。図３は本実施例のスイッチング素子の一構成例を示す断面模式図である。 The configuration of the switching element of this embodiment will be described. FIG. 3 is a schematic cross-sectional view showing a configuration example of the switching element of this example.
　図３に示すように、スイッチング素子は、シリコン酸化膜２６で覆われたシリコン基板２５上に設けられ、第１電極２１と、第２電極２２と、これら２つの電極に接して設けられた抵抗変化層２３とを有する構造である。抵抗変化層２３は膜厚１５ｎｍの酸窒化タンタルで形成され、第１電極２１は膜厚４０ｎｍの白金で形成され、第２電極２２は膜厚１００ｎｍの銅で形成されている。 As shown in FIG. 3, the switching element is provided on the silicon substrate 25 covered with the silicon oxide film 26, and the first electrode 21, the second electrode 22, and the resistance provided in contact with these two electrodes. This is a structure having a change layer 23. The resistance change layer 23 is made of tantalum oxynitride having a thickness of 15 nm, the first electrode 21 is made of platinum having a thickness of 40 nm, and the second electrode 22 is made of copper having a thickness of 100 nm.
　第１電極２１の一部はシリコン酸化膜から成る絶縁層２４で覆われ、一部は絶縁層２４の開口部を介して抵抗変化層２３と接している。本実施例では、図３に示すように、第１電極２１の側面と、上面の一部が絶縁層２４で覆われている。そして、第１電極２１の上面のうち絶縁層２４で覆われていない部位が、絶縁層２４に設けられた開口部を介して抵抗変化層２３と接している。 Part of the first electrode 21 is covered with an insulating layer 24 made of a silicon oxide film, and part of the first electrode 21 is in contact with the resistance change layer 23 through the opening of the insulating layer 24. In the present embodiment, as shown in FIG. 3, the side surface of the first electrode 21 and a part of the upper surface are covered with the insulating layer 24. A portion of the upper surface of the first electrode 21 that is not covered with the insulating layer 24 is in contact with the resistance change layer 23 through an opening provided in the insulating layer 24.
　上述の構成により、絶縁層２４の開口部にスイッチング素子が形成され、第１電極２１と抵抗変化層２３の接触面積に相当する、スイッチの接合面積が開口部程度の大きさになっている。スイッチ部分以外の第２電極２２と第１電極２１との間が絶縁層２４で分離されているので、オフ時のリーク電流を抑制できる。 With the above configuration, the switching element is formed in the opening of the insulating layer 24, and the junction area of the switch corresponding to the contact area between the first electrode 21 and the resistance change layer 23 is as large as the opening. Since the insulating layer 24 separates the second electrode 22 and the first electrode 21 other than the switch portion, it is possible to suppress the leakage current at the off time.
　次に、図３に示したスイッチング素子の製造方法について説明する。 Next, a method for manufacturing the switching element shown in FIG. 3 will be described.
　図４Ａから図４Ｄは本実施例のスイッチング素子の製造方法を説明するための断面図である。 4A to 4D are cross-sectional views for explaining a method for manufacturing the switching element of this embodiment.
　シリコン基板２５の表面に膜厚３００ｎｍのシリコン酸化膜２６を形成する。白金をスパッタリング法によりシリコン酸化膜２６の上に形成し、形成した白金をエッチングにより所望のパターンに加工して第１電極２１を形成する（図４Ａ）。 A silicon oxide film 26 having a thickness of 300 nm is formed on the surface of the silicon substrate 25. Platinum is formed on the silicon oxide film 26 by sputtering, and the formed platinum is processed into a desired pattern by etching to form the first electrode 21 (FIG. 4A).
　続いて、絶縁層２４として膜厚４０ｎｍのシリコン酸化膜を、第１電極２１を覆ってシリコン酸化膜２６の上にスパッタリング法により形成する。リソグラフィおよびエッチング技術により開口部４１を絶縁層２４に形成する（図４Ｂ）。開口部４１においては第１電極２１の上面の一部が露出している。ここでは、絶縁層２４をシリコン酸化膜としたが、シリコン酸窒化物などの他の絶縁性膜でもよい。 Subsequently, a silicon oxide film having a thickness of 40 nm is formed as an insulating layer 24 on the silicon oxide film 26 so as to cover the first electrode 21 by a sputtering method. Openings 41 are formed in the insulating layer 24 by lithography and etching techniques (FIG. 4B). In the opening 41, a part of the upper surface of the first electrode 21 is exposed. Here, the insulating layer 24 is a silicon oxide film, but other insulating films such as silicon oxynitride may be used.
　開口部４１と絶縁層２４の上にレジストをスピンコートする。リソグラフィ技術によりレジストのパターニングを行い、図４Ｃに示すレジストマスク４２を形成する。レジストマスク４２の開口に露出した第１電極２１に対して酸素プラズマ処理を行い、第１電極２１の表面からレジスト残渣などの有機物等を取り除いてその表面をクリーニングする。酸素プラズマ処理の後、レジストマスク４２の上および開口に酸窒化タンタル膜を形成する。酸窒化タンタル膜の形成には、次に示す方法１または方法２を用いる。 A resist is spin coated on the opening 41 and the insulating layer 24. Resist patterning is performed by a lithography technique to form a resist mask 42 shown in FIG. 4C. Oxygen plasma treatment is performed on the first electrode 21 exposed in the opening of the resist mask 42 to remove organic substances such as resist residues from the surface of the first electrode 21 and clean the surface. After the oxygen plasma treatment, a tantalum oxynitride film is formed on the resist mask 42 and on the opening. The following method 1 or method 2 is used for forming the tantalum oxynitride film.
　方法１：酸化タンタル膜をスパッタリング法により基板上に形成し、形成した酸化タンタル膜に対してプラズマ窒化を行って酸窒化タンタル膜を形成する。プラズマ窒化の処理温度は、高くても４００℃程度、通常、３５０℃以下２００℃以上であり、熱窒化と比較して低温であることから、プラズマ窒化は配線層にスイッチを形成する際には有利である。 Method 1: A tantalum oxide film is formed on a substrate by a sputtering method, and plasma nitridation is performed on the formed tantalum oxide film to form a tantalum oxynitride film. The processing temperature of plasma nitriding is at most about 400 ° C., usually 350 ° C. or lower and 200 ° C. or higher, which is lower than that of thermal nitriding. It is advantageous.
　方法２：酸化タンタルのターゲットに対して、窒素ガスとアルゴンガス等の不活性ガスの混合ガス雰囲気でスパッタリングを行うことで、ターゲットから飛び出した酸化タンタルと混合ガス雰囲気中の窒素とが基板上に堆積する。このようにして酸窒化タンタル膜をスパッタリング法により基板上に形成する。ここで、基板温度は３５０℃程度とする。 Method 2: A tantalum oxide target is sputtered in a mixed gas atmosphere of an inert gas such as a nitrogen gas and an argon gas, so that the tantalum oxide protruding from the target and the nitrogen in the mixed gas atmosphere are formed on the substrate. accumulate. In this manner, a tantalum oxynitride film is formed on the substrate by a sputtering method. Here, the substrate temperature is about 350 ° C.
　上記方法１または方法２で酸窒化タンタル膜を形成した後、真空蒸着法またはスパッタリング法により膜厚１００ｎｍの銅を酸窒化タンタル膜の上に堆積させる。その後、レジストマスク４２とともにレジストマスク４２の上に形成された酸窒化タンタル膜と銅を除去し、抵抗変化層２３および第２電極２２を形成する（図４Ｄ）。 After forming the tantalum oxynitride film by the above method 1 or method 2, copper having a thickness of 100 nm is deposited on the tantalum oxynitride film by vacuum evaporation or sputtering. Thereafter, the tantalum oxynitride film and copper formed on the resist mask 42 together with the resist mask 42 are removed to form the resistance change layer 23 and the second electrode 22 (FIG. 4D).
　なお、抵抗変化層２３が酸窒化タンタル膜単層の場合を説明したが、酸窒化タンタルと酸化タンタルの積層構造でもよい。この積層構造は、次に示す方法３または方法４で形成することが可能である。いずれの方法でも酸窒化タンタルが第２電極２２に接するように積層構造を形成する。 Although the case where the resistance change layer 23 is a single layer of tantalum oxynitride has been described, a laminated structure of tantalum oxynitride and tantalum oxide may be used. This laminated structure can be formed by the following method 3 or method 4. In any method, the laminated structure is formed so that the tantalum oxynitride is in contact with the second electrode 22.
　方法３：スパッタリング法とプラズマ窒化処理を組み合わせて上記積層構造を形成する方法である。酸化タンタル膜をスパッタリング法により形成し、形成した酸化タンタル膜に対してプラズマ窒化処理を行って酸窒化タンタル膜とし、酸窒化タンタル膜の上に酸化タンタル膜をスパッタリング法により形成する。 Method 3: A method of forming the laminated structure by combining sputtering and plasma nitriding. A tantalum oxide film is formed by a sputtering method, a plasma nitriding process is performed on the formed tantalum oxide film to form a tantalum oxynitride film, and a tantalum oxide film is formed on the tantalum oxynitride film by a sputtering method.
　方法４：スパッタリング法により上記積層構造を形成する方法である。酸化タンタルのターゲットを用い、成長雰囲気を酸素とアルゴンの混合気体とするスパッタリング法で酸化タンタル膜を形成する。続いて、ターゲットを変えずに、成長雰囲気を窒素とアルゴンの混合気体とするスパッタリング法で酸窒化タンタル膜を酸化タンタル膜の上に形成する。 Method 4: A method of forming the laminated structure by a sputtering method. Using a tantalum oxide target, a tantalum oxide film is formed by a sputtering method in which the growth atmosphere is a mixed gas of oxygen and argon. Subsequently, a tantalum oxynitride film is formed on the tantalum oxide film by a sputtering method using a mixed atmosphere of nitrogen and argon without changing the target.
　また、上述の製造方法では、開口部４１を第１電極２１のパターンよりも小さく形成し、第２電極２２および抵抗変化層２３のパターンを開口部４１よりも大きく形成することで、スイッチの接合面積が開口部４１の大きさで決まる。第１電極２１、第２電極２２および抵抗変化層２３のパターンについては、開口部４１のパターンとの余裕を設けておけばよく、加工精度を高くする必要はない。第１電極２１の上に開口部４１が形成され、開口部４１の第１電極２１の露出面を抵抗変化層２３が被覆すればよい。複数のスイッチング素子を作製する場合、各スイッチング素子の開口部４１を精度よく形成すれば、複数のスイッチング素子の特性を均一にすることができる。 Further, in the manufacturing method described above, the opening 41 is formed smaller than the pattern of the first electrode 21, and the pattern of the second electrode 22 and the resistance change layer 23 is formed larger than the opening 41, thereby joining the switch. The area is determined by the size of the opening 41. About the pattern of the 1st electrode 21, the 2nd electrode 22, and the resistance change layer 23, what is necessary is just to provide allowance with the pattern of the opening part 41, and does not need to make processing precision high. The opening 41 may be formed on the first electrode 21, and the resistance change layer 23 may cover the exposed surface of the first electrode 21 in the opening 41. When producing a plurality of switching elements, the characteristics of the plurality of switching elements can be made uniform if the openings 41 of the respective switching elements are accurately formed.
　次に、図３に示したスイッチング素子の動作について説明する。図５はスイッチング素子の特性を測定するための回路の構成を示す図である。 Next, the operation of the switching element shown in FIG. 3 will be described. FIG. 5 is a diagram showing the configuration of a circuit for measuring the characteristics of the switching element.
　図５に示すように、測定回路は、スイッチング素子ＳＷにＭＯＳＦＥＴ２７が直列に接続されている。ＭＯＳＦＥＴ２７のドレイン電極Ｄがスイッチング素子ＳＷの第１電極２１に接続され、ソース電極Ｓが接地されている。ゲート電極Ｇに５Ｖの電圧ＶＧを印加し、スイッチング素子ＳＷの第２電極２２に印加する電圧を変化させたときにスイッチング素子ＳＷに流れる電流を測定した。ＭＯＳＦＥＴ２７は、最大電流を制御するためにスイッチング素子に流れる電流を制御する役割を果たす。 As shown in FIG. 5, in the measurement circuit, a MOSFET 27 is connected in series to the switching element SW. The drain electrode D of the MOSFET 27 is connected to the first electrode 21 of the switching element SW, and the source electrode S is grounded. The voltage V G of 5V is applied to the gate electrode G, the measurement of the current flowing through the switching element SW when changing the voltage applied to the second electrode 22 of the switching element SW. The MOSFET 27 serves to control the current flowing through the switching element in order to control the maximum current.
　測定対象となる本実施例のスイッチング素子の抵抗変化層２３には、膜厚１５ｎｍの酸窒化タンタルを上記方法２により形成したものを用いた。また、特性比較のために、第１電極および第２電極のそれぞれの材料は本実施例と同じで、抵抗変化層に膜厚１５ｎｍの酸化タンタルを用いたサンプルも準備した。第１電極に白金を用いている。以下に、スイッチング素子の測定結果を説明する。 As the resistance change layer 23 of the switching element of this example to be measured, a tantalum oxynitride film having a thickness of 15 nm formed by the method 2 was used. For comparison of characteristics, the materials of the first electrode and the second electrode were the same as in this example, and a sample using tantalum oxide having a film thickness of 15 nm for the variable resistance layer was also prepared. Platinum is used for the first electrode. Below, the measurement result of a switching element is demonstrated.
　図６はスイッチング素子の電流・電圧特性を示すグラフである。横軸は第２電極に印加する電圧を示し、縦軸はスイッチング素子に流れる電流を示す。スイッチング素子に流れる電流が２ｍＡ以下になるように制御した。グラフに示す実線は抵抗変化層に酸窒化タンタルを用いた場合の電流・電圧特性であり、破線は抵抗変化層に酸化タンタルを用いた場合の電流・電圧特性である。 FIG. 6 is a graph showing the current / voltage characteristics of the switching element. The horizontal axis indicates the voltage applied to the second electrode, and the vertical axis indicates the current flowing through the switching element. The current flowing through the switching element was controlled to be 2 mA or less. The solid line in the graph shows the current / voltage characteristics when tantalum oxynitride is used for the resistance change layer, and the broken line shows the current / voltage characteristics when tantalum oxide is used for the resistance change layer.
　まず、本実施例のスイッチング素子の第２電極２２に正電圧を印加して、０Ｖから６Ｖまで徐々に高くし、その後、０Ｖまで徐々に戻した。そのときの電流値の変化を図６で見ると、スイッチング素子の初期状態はオフ状態であり、印加電圧が５Ｖ付近になったところでオン状態に遷移している。その後、印加電圧が５Ｖから６Ｖに変化し、さらに０Ｖに戻るまでの間は、ＭＯＳＦＥＴ２７の電流・電圧特性が観測されている。一方、第２電極２２に負電圧を印加してみる。印加電圧を０Ｖから－２．５Ｖに変化させ、その後、０Ｖに戻した。そのときの電流値の変化を図６でみると、－０．８Ｖ付近でオフ状態に遷移していることがわかる。 First, a positive voltage was applied to the second electrode 22 of the switching element of this example, and the voltage was gradually increased from 0V to 6V, and then gradually returned to 0V. When the change of the current value at that time is seen in FIG. 6, the initial state of the switching element is in the off state, and when the applied voltage becomes around 5 V, the state is changed to the on state. Thereafter, the current / voltage characteristics of the MOSFET 27 are observed until the applied voltage changes from 5V to 6V and then returns to 0V. On the other hand, a negative voltage is applied to the second electrode 22. The applied voltage was changed from 0V to -2.5V, and then returned to 0V. When the change of the current value at that time is seen in FIG. 6, it can be seen that the state is shifted to the OFF state in the vicinity of −0.8V.
　特定比較のためサンプルのスイッチング素子の特性について見てみる。このサンプルでは、上述したように、本実施例の素子の抵抗変化層と同じ膜厚の酸化タンタルを抵抗変化層に用いている。抵抗変化層が酸化タンタルの場合、図６の破線に示すように、オフからオン状態に遷移する電圧は３Ｖであった。この結果から、抵抗変化層２３を酸化タンタルから酸窒化タンタルにすることにより、スイッチング電圧が高くなっていることがわかる。スイッチング電圧の高電圧化は、銅イオンの拡散速度が小さくなっていることに起因する。 ¡Look at the characteristics of the sample switching element for a specific comparison. In this sample, as described above, tantalum oxide having the same thickness as that of the variable resistance layer of the element of this example is used for the variable resistance layer. When the variable resistance layer was tantalum oxide, the voltage for transition from the off state to the on state was 3 V, as indicated by the broken line in FIG. From this result, it is understood that the switching voltage is increased by changing the resistance change layer 23 from tantalum oxide to tantalum oxynitride. The higher switching voltage is due to the lower diffusion rate of copper ions.
　次に、熱耐性試験を行った結果を説明する。 Next, the results of the heat resistance test will be described.
　本実施例のスイッチング素子とサンプルのスイッチング素子に対して、３５０℃で１時間の熱処理を行い、図６の電流・電圧特性がどのように変化するかを検証した。その結果、抵抗変化層２３に酸窒化タンタルを用いた場合は、スイッチング電圧にわずかな変化があったものの、電流・電圧特性が大きく変わることはなかった。一方、抵抗変化層２３に酸化タンタルを用いた場合には、オフ状態が熱処理によってオン状態へ遷移し、負の電圧を印加してもオフ状態へ遷移させることはできなかった。 The heat treatment at 350 ° C. for 1 hour was performed on the switching element of this example and the sample switching element to verify how the current / voltage characteristics in FIG. 6 change. As a result, when tantalum oxynitride was used for the resistance change layer 23, although there was a slight change in the switching voltage, the current / voltage characteristics did not change greatly. On the other hand, when tantalum oxide is used for the resistance change layer 23, the OFF state is changed to the ON state by the heat treatment, and even if a negative voltage is applied, the OFF state cannot be changed.
　以上のことから、本実施形態のスイッチング素子によれば、抵抗変化層として金属酸窒化物を用いることより、配線を形成する際の熱工程に対する熱耐性を向上させることができる。 From the above, according to the switching element of the present embodiment, the use of the metal oxynitride as the variable resistance layer can improve the heat resistance against the thermal process when forming the wiring.
　（第２の実施形態）
　本実施形態のスイッチング素子の構成を、図２を参照して説明する。 (Second Embodiment)
The configuration of the switching element of this embodiment will be described with reference to FIG.
　本実施形態のスイッチング素子では、第２電極１２の材料は第１の実施形態と同様に銅であるが、第１電極１１の材料はルテニウム（Ｒｕ）であり、抵抗変化層１３は酸化物を含む材料である。なお、第１電極１１は、少なくとも抵抗変化層１３と接する部位がルテニウムであればよい。第２電極１２は、少なくとも抵抗変化層１３と接する部位が銅のように抵抗変化層１３に金属イオンを供給可能な材料であればよい。 In the switching element of this embodiment, the material of the second electrode 12 is copper as in the first embodiment, but the material of the first electrode 11 is ruthenium (Ru), and the resistance change layer 13 is made of an oxide. It is a material that contains. In addition, the 1st electrode 11 should just be a ruthenium the site | part which contact | connects the resistance change layer 13 at least. The 2nd electrode 12 should just be a material which can supply a metal ion to the resistance change layer 13 like the copper at least the site | part which contact | connects the resistance change layer 13. As shown in FIG.
　本実施形態では、抵抗変化層１３として酸化タンタル（ＴａＯ）を用いるが、酸化シリコン（ＳｉＯ）または酸化タンタルシリケート（ＴａＳｉＯ）についても同様の効果が得られる。酸化タンタルにシリコン（Ｓｉ）を混入することにより、熱処理によって増大するリーク電流を抑制する効果が追加されるのは、第１の実施形態と同様である。 In the present embodiment, tantalum oxide (TaO) is used as the resistance change layer 13, but the same effect can be obtained with silicon oxide (SiO) or tantalum oxide silicate (TaSiO). Similar to the first embodiment, the effect of suppressing the leakage current that is increased by the heat treatment is added by mixing silicon (Si) into tantalum oxide.
　本実施例のスイッチング素子の構成を、図３を参照して説明する。 The configuration of the switching element of this embodiment will be described with reference to FIG.
　本実施例のスイッチング素子は、図３に示した構成で、抵抗変化層２３を酸化タンタル膜とし、第１電極２１の材料をルテニウムとしている。その他の構成は実施例１と同様であるため、その詳細な説明を省略する。 The switching element of the present embodiment has the configuration shown in FIG. 3, wherein the resistance change layer 23 is a tantalum oxide film and the material of the first electrode 21 is ruthenium. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.
　なお、製造方法については、実施例１の第１電極２１の材料をルテニウムとし、抵抗変化層２３の酸窒化タンタルを酸化タンタルとしていることを除いて、実施例１と同様であるため、その詳細な説明を省略する。 The manufacturing method is the same as that of Example 1 except that the material of the first electrode 21 of Example 1 is ruthenium and the tantalum oxynitride of the resistance change layer 23 is tantalum oxide. The detailed explanation is omitted.
　次に、本実施例のスイッチング素子の動作を説明する。スイッチング素子の測定に用いた回路は図５に示した回路と同様であり、測定方法も実施例１と同様であり、その詳細な説明を省略する。 Next, the operation of the switching element of this embodiment will be described. The circuit used for the measurement of the switching element is the same as the circuit shown in FIG. 5 and the measurement method is the same as that of the first embodiment, and detailed description thereof is omitted.
　測定対象となる本実施例のスイッチング素子の第１電極２１には、ルテニウムを用いた。また、特性比較のために、第２電極および抵抗変化層のそれぞれの材料は本実施例と同じで、第１電極に白金を用いたサンプルも準備した。抵抗変化層には、酸化タンタルを用いており、膜厚は１５ｎｍよりも厚くしている。 Ruthenium was used for the first electrode 21 of the switching element of this example to be measured. For comparison of characteristics, the materials of the second electrode and the resistance change layer were the same as in this example, and a sample using platinum for the first electrode was also prepared. Tantalum oxide is used for the resistance change layer, and the film thickness is greater than 15 nm.
　図７はスイッチング素子の電流・電圧特性を示すグラフである。横軸は第２電極に印加する電圧を示し、縦軸はスイッチング素子に流れる電流を示す。スイッチング素子に流れる電流が５ｍＡ以下になるように制御した。グラフに示す実線は第１電極２１にルテニウムを用いた場合の電流・電圧特性であり、破線は第１電極２１に白金を用いた場合の電流・電圧特性である。 FIG. 7 is a graph showing the current / voltage characteristics of the switching element. The horizontal axis indicates the voltage applied to the second electrode, and the vertical axis indicates the current flowing through the switching element. The current flowing through the switching element was controlled to be 5 mA or less. The solid line shown in the graph is the current / voltage characteristic when ruthenium is used for the first electrode 21, and the broken line is the current / voltage characteristic when platinum is used for the first electrode 21.
　実施例１で説明した測定方法と同様にして、第２電極２２に電圧を印加してスイッチング素子に流れる電流を測定した。その結果、図７に示すように、本実施例のスイッチング素子は、破線に示す白金と同様な特性が得られており、第１電極２１にルテニウムを用いることが可能であることがわかる。本実施例のスイッチング素子に熱処理を行ってもスイッチング電圧に大きな変化はなかった。なお、ルテニウムは、酸化しても金属の性質を示すこと、エッチングが白金と比較して容易であるなどの利点がある。 In the same manner as the measurement method described in Example 1, a voltage was applied to the second electrode 22 to measure a current flowing through the switching element. As a result, as shown in FIG. 7, the switching element of this example has the same characteristics as platinum indicated by the broken line, and it can be seen that ruthenium can be used for the first electrode 21. Even when the switching element of this example was heat-treated, there was no significant change in the switching voltage. Ruthenium has advantages such as exhibiting metal properties even when oxidized, and being easier to etch than platinum.
　本実施形態のスイッチング素子は、抵抗変化層として金属酸化物を用い、第１電極にルテニウムを用いることより、第１の実施形態と同様な効果が得られるだけでなく、第１電極が酸化しても金属の性質を有し、かつ、白金に比べて加工をしやすいという効果が得られる。なお、第１の実施形態の第１電極にルテニウムを用いてもよい。 The switching element of the present embodiment uses a metal oxide as the variable resistance layer and uses ruthenium for the first electrode, so that not only the same effect as in the first embodiment is obtained but also the first electrode is oxidized. Even if it has the property of a metal, the effect that it is easy to process compared with platinum is acquired. Note that ruthenium may be used for the first electrode of the first embodiment.
　本発明の効果の一例として、配線を形成する際の熱工程に対する熱耐性が向上する。 As an example of the effect of the present invention, the thermal resistance to the thermal process when forming the wiring is improved.
　以上、実施形態および実施例を参照して本願発明を説明したが、本願発明は上記実施形態および実施例に限定されるものではない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。 Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.
　なお、この出願は、２００８年６月２６日に出願された日本出願の特願２００８－１６７３３３の内容が全て取り込まれており、この日本出願を基礎として優先権を主張するものである。 This application incorporates all the contents of Japanese Patent Application No. 2008-167333 filed on June 26, 2008, and claims priority based on this Japanese application.
　１１、２１　　第１電極
　１２、２２　　第２電極
　１３、２３　　抵抗変化層
　２４　　絶縁層
　２５　　シリコン基板
　２６　　シリコン酸化膜
　２７　ＭＯＳＦＥＴ 11, 21 First electrode 12, 22 Second electrode 13, 23 Variable resistance layer 24 Insulating layer 25 Silicon substrate 26 Silicon oxide film 27 MOSFET

Claims (8)

  1. 　酸窒化物を含む抵抗変化層と、
    　前記抵抗変化層に接して設けられた第１の電極と、
    　前記抵抗変化層に接して設けられ、前記抵抗変化層に金属イオンを供給可能な材料を含む第２の電極と、
    を有するスイッチング素子。     A resistance change layer containing oxynitride;
    A first electrode provided in contact with the variable resistance layer;
    A second electrode including a material provided in contact with the variable resistance layer and capable of supplying metal ions to the variable resistance layer;
    A switching element.
  2. 　前記金属イオンが前記抵抗変化層内に析出することにより、前記第１および第２の電極の間の電気伝導度が大きくなり、析出した金属の一部が取り除かれることによって前記電気伝導度が小さくなる、請求項１記載のスイッチング素子。 When the metal ions are deposited in the resistance change layer, the electrical conductivity between the first and second electrodes is increased, and by removing a part of the deposited metal, the electrical conductivity is decreased. The switching element according to claim 1.
  3. 　前記金属イオンの析出または除去が、前記第１および第２の電極間に電圧または電流を印加することによって起こる、請求項２記載のスイッチング素子。 The switching element according to claim 2, wherein the metal ions are deposited or removed by applying a voltage or a current between the first and second electrodes.
  4. 　前記抵抗変化層がタンタルまたはシリコンを含む請求項１記載のスイッチング素子。 The switching element according to claim 1, wherein the variable resistance layer includes tantalum or silicon.
  5. 　前記第２の電極の材料が銅であり、前記第１の電極の前記抵抗変化層に接する部位が前記金属イオンを供給しない材料である、請求項１記載のスイッチング素子。 The switching element according to claim 1, wherein the material of the second electrode is copper, and the portion of the first electrode that contacts the variable resistance layer is a material that does not supply the metal ions.
  6. 　前記抵抗変化層が酸窒化膜および酸化膜の積層構造からなり、該酸窒化膜が前記第２の電極と接する、請求項１に記載のスイッチング素子。 The switching element according to claim 1, wherein the variable resistance layer has a laminated structure of an oxynitride film and an oxide film, and the oxynitride film is in contact with the second electrode.
  7. 　酸化物を含む抵抗変化層と、
    　前記抵抗変化層に接して設けられたルテニウムを含む第１の電極と、
    　前記抵抗変化層に接して設けられ、前記抵抗変化層に金属イオンを供給可能な材料を含む第２の電極と、
    を有するスイッチング素子。     A variable resistance layer including an oxide;
    A first electrode containing ruthenium provided in contact with the variable resistance layer;
    A second electrode including a material provided in contact with the variable resistance layer and capable of supplying metal ions to the variable resistance layer;
    A switching element.
  8. 　抵抗変化層と、該抵抗変化層に接する第１の電極と、前記抵抗変化層に接し、該抵抗変化層に金属イオンを供給可能な材料を含む第２の電極と、を有するスイッチング素子の製造方法であって、
    　前記抵抗変化層を形成する工程は、酸化物に対して４００℃以下でプラズマ窒化することにより酸窒化膜を形成する処理を含むものである、スイッチング素子の製造方法。     Manufacturing of a switching element having a resistance change layer, a first electrode in contact with the resistance change layer, and a second electrode in contact with the resistance change layer and including a material capable of supplying metal ions to the resistance change layer A method,
    The step of forming the resistance change layer includes a process of forming an oxynitride film by plasma nitriding an oxide at 400 ° C. or lower.
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