JPWO2009157479A1 - Switching element and method for manufacturing switching element - Google Patents

Abstract

The switching element of the present invention includes a resistance change layer (13) containing oxynitride, a first electrode (11) provided in contact with the resistance change layer (13), and a resistance change layer (13). And a second electrode (12) containing a material capable of supplying metal ions to the resistance change layer (13).

Description

  The present invention relates to a switching element using an electrochemical reaction and a manufacturing method thereof.

  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 thereof 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).

  FIG. 1 is a schematic cross-sectional view showing a configuration example of the switching element disclosed in Document 1. In FIG. 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 operation of the switching element shown in FIG. 1 will be described.

  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.

  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 off. Thereby, the electrical connection between the first electrode 31 and the second electrode 32 is cut, and the switch is turned off.

  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.

  The switching element can be used for a programmable device represented by an 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).

  Up to now, chalcogenides or metal oxides have been used in 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. Japanese Patent Application Laid-Open No. 2006-319028 discloses a switch in which a metal oxide is used for the resistance change layer. 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.

  The switching element is aimed to be formed in a 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.

  Furthermore, the maximum processing temperature when forming the wiring layer is 400 ° C., and most 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.

  The wiring layer can be roughly divided into three areas: a local wiring layer, a semi-global wiring layer, and a 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.

  In order to form a large number of switches, it is advantageous to form in a local wiring layer having 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.

  In general, 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.

  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.

  In order to mount the switching element on the wiring layer of the integrated circuit, the electrode is preferably made of a material that does not cause thermal diffusion of Cu or Ag to the resistance change layer 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.

  An example of the 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 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.

  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. .

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. 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.

(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.

  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 that is 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.

  The first electrode 11 may be any material that does not supply metal ions to the resistance change layer 13, such as platinum, at least at a site in contact with the resistance change layer 13. 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.

  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.

  The resistance change layer 13 may have a stacked structure of the oxynitride film and the 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.

  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.

  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.

  A part of the first electrode 21 is covered with an insulating layer 24 made of a silicon oxide film, and a part thereof is in contact with the resistance change layer 23 through an 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.

  With the above-described 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.

  Next, a method for manufacturing the switching element shown in FIG. 3 will be described.

  4A to 4D are cross-sectional views for explaining the method of 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).

  Subsequently, a silicon oxide film having a thickness of 40 nm is formed as the 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.

  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.

  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. Therefore, plasma nitriding is used when forming a switch in a wiring layer. 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. Here, the substrate temperature is about 350 ° C.

  After the tantalum oxynitride film is formed by the above method 1 or 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).

  Although the case where the variable resistance layer 23 is a single tantalum oxynitride film 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.

  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 above 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.

  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.

  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.

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.

  For 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.

  FIG. 6 is a graph showing 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.

  First, a positive voltage was applied to the second electrode 22 of the switching element of this example to gradually increase 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.

  Let's look at the characteristics of the sample switching elements for 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.

  Next, the results of the heat resistance test will be described.

  The switching element of this example and the sample switching element were subjected to a heat treatment at 350 ° C. for 1 hour 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.

  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.

(Second Embodiment)
The configuration of the switching element of this embodiment will be described with reference to FIG.

  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. The first electrode 11 only needs to be ruthenium at least in contact with the resistance change layer 13. 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.

  In this 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.

  The configuration of the switching element of this embodiment will be described with reference to FIG.

  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.

  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.

  Ruthenium was used for the 1st electrode 21 of the switching element of a present Example used as a measuring object. 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.

  FIG. 7 is a graph showing 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.

  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.

  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.

  As an example of the effect of the present invention, heat resistance to a heat process when forming a wiring is improved.

  While 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.

  Note that 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 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)

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.   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.   The switching element according to claim 2, wherein the deposition or removal of the metal ions occurs by applying a voltage or a current between the first and second electrodes.   The switching element according to claim 1, wherein the variable resistance layer includes tantalum or silicon.   2. The switching element according to claim 1, wherein a material of the second electrode is copper, and a portion of the first electrode that is in contact with the variable resistance layer is a material that does not supply the metal ions.   2. 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. 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. 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 variable resistance layer includes a process of forming an oxynitride film by plasma nitriding an oxide at 400 ° C. or lower.

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