JP4805865B2 - Variable resistance element - Google Patents

Description

The present invention comprises one electrode, the other electrode, and a variable resistor, wherein the variable resistor exists in a region sandwiched between the one electrode and the other electrode, and a voltage pulse is applied between the two electrodes. It relates applied to the variable resistive element whose electrical resistance varies by.

  In recent years, various devices such as next-generation non-volatile random access memory (NVRAM: Nonvolatile Random Access Memory) that can replace high-speed flash memory, such as FeRAM (Ferroelectric RAM), MRAM (Magnetic RAM), and PRAM (Phase Change RAM) A structure has been proposed, and intense development competition has been conducted from the viewpoint of high performance, high reliability, low cost, and process consistency. However, each of these current memory devices has advantages and disadvantages, and it is still far from the ideal realization of a “universal memory” having the advantages of SRAM, DRAM, and flash memory.

  For these existing technologies, a resistive non-volatile memory RRAM (Resistive Random Access Memory) (registered trademark) using a variable resistive element whose electric resistance reversibly changes by applying a voltage pulse has been proposed. This configuration is shown in FIG.

  As shown in FIG. 20, the variable resistance element has a configuration in which the variable resistor 4 is sandwiched between two electrodes (first electrode 2 and second electrode 3). In particular, the case where the variable resistor 4 is sandwiched in the vertical direction by both electrodes (2 and 3) formed in the upper and lower layers is shown. And it has the property which can change a resistance value reversibly by applying a voltage pulse between these both electrodes. A novel nonvolatile semiconductor memory device can be realized by reading a resistance value that changes by this reversible resistance change operation (hereinafter referred to as “switching operation”).

  In this nonvolatile semiconductor memory device, a plurality of memory cells including variable resistance elements are arranged in a matrix in the row direction and the column direction to form a memory cell array, and data is written to each memory cell in the memory cell array. Peripheral circuits for controlling erase and read operations are arranged. As the memory cell, a memory cell is composed of one selection transistor T and one variable resistance element R (referred to as “1T / 1R type”) because of the difference in its constituent elements. There are cells, memory cells composed of only one variable resistance element R (referred to as “1R type”), and the like.

By the way, as a material constituting the variable resistor 4, the electrical resistance is reversibly changed by applying a voltage pulse to a perovskite material known for its giant magnetoresistive effect by, for example, Shanguing Liu and Alex Ignatiev of the University of Houston, USA The method to make is disclosed in the following Patent Document 1 and Non-Patent Document 1. Although this method uses a perovskite material known for its giant magnetoresistive effect, this method is extremely epoch-making in that a resistance change of several orders of magnitude appears even at room temperature without applying a magnetic field. In the element structure exemplified in Patent Document 1, a crystalline praseodymium / calcium / manganese oxide Pr _1-X Ca _X MnO ₃ (PCMO) film, which is a perovskite oxide, is used as a variable resistor material. Yes.

  FIG. 21 is a schematic cross-sectional structure diagram of a conventional variable resistance element when the variable resistor 4 is configured using the PCMO film 91. A conventional variable resistance element 90 shown in FIG. 21 has a base insulating film 12, a second electrode 3, a PCMO film 91 (corresponding to the variable resistor 4), a first electrode 2, Interlayer insulating film 14 and conductive films (metal wirings) 23 and 24 are formed. The conductive films 23 and 24 are formed so as to fill the contact holes 25 and 26 previously formed in the interlayer insulating film 13, respectively, and thereby the electric power to the first electrode 2 and the second electrode 3 is respectively formed. Contact is being made.

  Under such a configuration, by appropriately controlling the voltage to be applied to the metal wirings 23 and 24, the voltage applied to the first electrode 2 and the second electrode 3 is controlled, whereby the variable resistor 4 (PCMO The resistance value of the film 91) can be changed, and a function as a variable resistance element is exhibited.

The material of the variable resistor 4 is a transition metal oxide, such as a titanium oxide (TiO ₂ ) film, a nickel oxide (NiO) film, a zinc oxide (ZnO) film, or niobium oxide (Nb ₂ O _5). It is known from Non-Patent Document 2, Patent Document 2, and the like that the film also exhibits a reversible resistance change. In particular, titanium oxide or nickel oxide has a locally reduced resistivity region (hereinafter referred to as “filament path” as appropriate) in the oxide due to heat rise due to current flowing into the variable resistance element, It is considered that a resistance change occurs due to decomposition.

Further, the material of the variable resistor 4 is an oxide of a transition metal element such as a titanium oxide (TiO ₂ ) film, a nickel oxide (NiO) film, a zinc oxide (ZnO) film, or a niobium oxide (Nb ₂ O ₅ ) film. Also, it is known from Non-Patent Document 2, Patent Document 2, and the like that reversible resistance change is exhibited. Among these, the phenomenon of the switching operation using titanium oxide is reported in detail in Non-Patent Documents 3 to 6, and the nickel oxide is reported in detail in Non-Patent Document 7.

US Pat. No. 6,204,139 Liu, S .; Q. In addition, “Electrical-pulse-induced reversible resistance change effect in magnetosensitive films”, Applied Physics Letter, Vol. 76, pp. 2749-2751, 2000 H. Pagna, et al., “Bistable Switching in Electroformed Metal-Insulator-Metal Devices”, Phys. Stat. Sol. (A), vol. 108, pp. 11-65, 1988 JP 2002-537627 A G. Taylor et al., "RF Relaxation Oscillations in Polycrystalline TiO2 Thin Films", Solid-State Electrics, 1976, vol. 19, pp. 669-674 F. Argal et al., “Switching Phenomena in Titanium Oxide Thin Films”, Solid-State Electronics, Pergamon Press 1968, vol. 11, pp. 535-541 Beam et al., Proc. IEEE, 52, 300-1, 1964 F. Argall, Solid State Electronics Pergamon Press 1968, vol. 11, pp. 535 S. Seo et al., Applied Physics Letters 86,093509,2005

  When the perovskite oxide is used as the material of the variable resistor 4 whose resistance is changed by the voltage pulse, the crystallization temperature is as high as 500 ° C. to 700 ° C. and cannot be formed after the LSI wiring is formed. In addition, most of the constituent elements of perovskite are currently not used in LSI processes, and these elements may affect device characteristics, so it is necessary to verify and take measures against contamination of these elements. It becomes.

  For example, when PCMO is used as the perovskite type oxide, the resistance value can be increased with an applied pulse of one polarity and the resistance can be decreased with a pulse of the opposite polarity, but even with a combination of completely opposite polarities There is a characteristic that the resistance can be similarly varied. For this reason, when the polarity pulse applied when lowering the resistance is repeatedly applied to the variable resistance element, the resistance may increase.

  On the other hand, when titanium oxide or nickel oxide is used as the material of the variable resistor 4, titanium or nickel element is widely used in the LSI process, so there is no possibility of affecting the device characteristics. However, the resistance change of the variable resistance element of titanium oxide or nickel oxide, which has been studied in the past, is based on the phenomenon that the filament path is formed or decomposed depending on the voltage pulse application condition and becomes low resistance or high resistance. . In order to obtain this switching operation, it is necessary to first apply a specific voltage to form a filament path (hereinafter referred to as “forming process”).

  Also, the resistance value fluctuates due to the change in the filament path diameter and filament density due to the increase in the number of switching operations, and the resistance value is determined by the filament, so the element in the low resistance state has an area dependency. There are problems such as not being available, and it has not been put into practical use as a device.

  The present invention has been made in view of the above-described problems, has good LSI process consistency, can perform resistance switching operation without forming a filament path, and can exhibit a stable resistance value and holding characteristics. An object is to provide a resistance element.

In order to achieve the above object, in the variable resistance element according to the present invention, a variable resistor is sandwiched between the first electrode and the second electrode, and a voltage pulse is applied between the first electrode and the second electrode. The variable resistance element is configured to change the electric resistance between the two electrodes, and the variable resistor is made of a transition metal oxide or a transition metal oxynitride and is in contact with the first electrode. 1 the contact surface toward the second contact surface in contact with the second electrode, the oxygen concentration being contained configured to decrease,
By applying a pulse voltage between the two electrodes so that the first electrode is positive with respect to the second electrode, the resistance characteristic of the variable resistance element transitions from a low resistance state to a high resistance state,
The resistance characteristic of the variable resistance element is changed from a high resistance state to a low resistance state by applying a pulse voltage between the electrodes so that the first electrode is negative with respect to the second electrode. First feature.

  According to the first characteristic configuration of the variable resistance element according to the present invention, the oxygen contained in the material constituting the variable resistor has a high oxygen concentration in the region near the first contact surface in contact with the first electrode. It is the structure which is shown and the density | concentration falls toward the 2nd contact surface which contacts a 2nd electrode. Accordingly, there are few oxygen defects near the first contact surface where the oxygen concentration is high, and there are many oxygen defects from the first contact surface toward the second contact surface. In a region where there are no or few oxygen vacancies, the concentration of carriers (electrons) is lower than in a region where there are many oxygen vacancies. For this reason, in the initial state before the pulse voltage is applied, the resistance state is somewhat higher than that of a conventional variable resistance element having a variable resistor having a uniform oxygen concentration.

  At this time, when a pulse voltage is applied so that the voltage of the first electrode with respect to the second electrode becomes positive, electrons are injected into the region near the second contact surface, which is a region with a low oxygen concentration, and one of the electrons is injected. As a result, the oxygen ions are generated. Since this oxygen ion has a negative polarity, after being attracted to the first electrode to which a positive voltage is applied, it is trapped by oxygen defects existing in the vicinity of the first contact surface. As described above, the vicinity of the first contact surface is configured so that the amount of oxygen defects is small to some extent in the initial state. However, since the amount of oxygen defects is further reduced by applying the pulse voltage, In the vicinity, the resistance is further increased.

  Conversely, when a pulse voltage is applied so that the voltage of the second electrode with respect to the first electrode is positive, oxygen ions in the variable resistor move to the second electrode to which the positive voltage is applied. Therefore, the amount of oxygen defects increases in the region near the first contact surface, and the resistance characteristics in the region near the region are reduced.

By the way, since it can be considered that the variable resistor is configured by connecting the region formed in the region near the first contact surface and the other region in series, the region near the first contact surface. If the resistance characteristic of the variable resistor is high, the variable resistor as a whole exhibits a high resistance state. Conversely, if the resistance characteristic in the vicinity of the first contact surface is low, the variable resistor as a whole is low Indicates. Therefore, by switching the polarity of the polarity of the pulse voltage as described above, switching of the resistance characteristics can be performed.
That is, when a positive voltage is applied to the first electrode side with a high oxygen concentration and a small amount of oxygen defects in the initial state, a negative voltage is applied to generate the variable electrode on the second electrode side. As a result of oxygen ions being attracted to the first electrode side, the amount of oxygen defects can be further reduced, and a high resistance state can be realized in the region near the first electrode, and the high resistance state can also be realized as the entire variable resistance element. it can. On the contrary, when a negative voltage is applied to the first electrode side, it is generated inside the variable resistor on the first electrode side and attracted to the second electrode side. As a result, oxygen vacancies in the region near the first electrode side The amount increases, a low resistance state can be realized in the region near the first electrode, and the low resistance state can also be realized as the entire variable resistance element.

That is, according to this configuration, for changing the resistance characteristic by controlling the amount of oxygen defects in the contact surface near the electrode, it is not necessary to form a filament path as in the conventional configuration. Therefore, unlike the conventional configuration, problems such as fluctuations in the resistance value due to an increase in the number of switching operations do not occur, and a variable resistance element exhibiting a stable resistance value and holding characteristics can be realized.

  In addition to the first characteristic configuration, the variable resistance element according to the present invention may further include the transition metal oxide or the transition metal oxynitride constituting the variable resistor from the first contact surface. The second feature is that the oxygen concentration contained in the position advanced by 10 nm in the direction of the two contact surfaces is reduced by 15% or more compared to the first contact surface.

  According to the second characteristic configuration of the variable resistance element according to the present invention, it is possible to reliably realize the transition of the resistance characteristic with respect to the variable resistance element in the initial state without performing the forming process.

  In addition to the first or second characteristic configuration, the variable resistance element according to the present invention may be configured such that the transition metal oxide or the transition metal oxynitride constituting the variable resistor has the first contact surface. The third feature is that the volume density of the microcrystals is decreased from the first to the second contact surface.

In general, the higher the volume density of transition metal oxide or transition metal oxynitride microcrystals, the smaller the amount of oxygen defects, and the lower the volume density, the greater the amount of oxygen defects. Therefore, according to the third characteristic configuration of the variable resistance element according to the present invention, since the amount of oxygen defects can be reduced in the region near the first contact surface, the polarity of the applied voltage is changed to change the region near the region. By controlling the amount of oxygen defects, the resistance characteristics of the variable resistance element can be changed without forming a filament path.

Moreover, the variable resistance element according to the present invention has a protruding portion in which the second electrode protrudes toward the formation surface of the first electrode in addition to any one of the first to third characteristic configurations. The variable resistor is a layered transition metal oxide or transition metal oxynitride polycrystal formed at the tip of the protrusion of the second electrode so as to be connected to the first electrode, A fourth feature is that the angle formed by the crystal growth direction of the polycrystalline body and the interface of the first contact surface is not less than 0 ° and not more than 22 °.

  Further, the variable resistance element according to the present invention is characterized in that, in addition to any one of the first to fourth characteristic configurations, the variable resistor is made of an oxide or oxynitride of Ti or Ni. The fifth feature.

  The variable resistor may be composed of an oxide or oxynitride of a transition metal material other than the above materials, for example, Cu, Nb, Zn, Co, W, V, or the like.

  In order to achieve the above object, a variable resistance element manufacturing method according to the present invention is a variable resistance element manufacturing method having the first characteristic configuration, wherein the second electrode is formed on a substrate. One step, a second step of exposing a part of the second electrode after completion of the first step, and a step of exposing the variable resistor so as to contact the exposed surface of the second electrode after completion of the second step. A third step of forming, and a fourth step of forming the first electrode so as to come into contact with the variable resistor after completion of the third step, wherein the third step comprises the step of forming the second electrode. The first feature is that the variable resistor is formed under a condition in which the concentration of oxygen contained in the predetermined direction increases or decreases from the vicinity of the exposed surface.

  According to the first feature of the method of manufacturing a variable resistance element according to the present invention, the variable resistor provided in the manufactured variable resistance element has a high oxygen concentration in a region near the first contact surface in contact with the first electrode. It has shown and becomes the structure that the density | concentration falls toward the 2nd contact surface which contacts a 2nd electrode. Therefore, by changing the positive / negative polarity of the applied pulse voltage and adjusting the amount of oxygen defects present in the region near the first contact surface, a variable resistance element capable of changing resistance characteristics without forming a filament path is provided. Manufacture is possible.

  In addition, according to the present method, since a conventional manufacturing process of a semiconductor device can be used, a new dedicated device is not required and a stable switching characteristic is exhibited using the conventional manufacturing apparatus. A variable resistance element can be manufactured.

  In the variable resistance element manufacturing method according to the present invention, in addition to the first feature, the third step includes the variable resistance element extending from an exposed surface of the second electrode toward an inner direction of the second electrode. The second feature is that the oxidation treatment is performed under such a condition that the oxygen concentration inside the body is lowered.

  According to the second feature of the variable resistance element manufacturing method of the present invention, by controlling the oxidation time and the temperature condition during oxidation, the oxygen concentration in the region near the exposed surface and the region near the exposed surface It is possible to easily adjust the degree of shading with the oxygen concentration at the position advanced in the inner direction.

  The variable resistance element manufacturing method according to the present invention is characterized in that, in addition to the second feature, the third step is a step of performing an oxidation treatment while changing the reaction temperature in two or more stages. Features.

  According to the third feature of the method of manufacturing a variable resistance element according to the present invention, the oxygen concentration contained can be adjusted according to the position in the variable resistance body without performing complicated control.

  In addition, as the oxidation treatment according to the third step, plasma oxidation treatment in which oxidation is performed by oxygen radicals generated by exciting oxygen or a gas containing oxygen with plasma, or ozone oxidation treatment in which oxidation is performed in an ozone atmosphere. Ordinary thermal oxidation treatment in which oxidation is performed in an atmosphere of oxygen or a gas containing oxygen can be employed. In such a case, the oxygen concentration contained can be adjusted according to the position in the variable resistor body by changing the reaction temperature in two or more steps.

  In the variable resistance element manufacturing method according to the present invention, in addition to the second or third feature, the first step deposits a first conductive film patterned in a predetermined shape on the substrate. And after that, after depositing the first interlayer insulating film, forming a predetermined region to open an opening that exposes a part of the upper surface of the first conductive film, and then completely opening the opening. A step of depositing a second conductive film on the entire surface including the bottom surface and the inner side surface of the opening so as to be in contact with the first conductive film in a film thickness range that does not fill, and then a second interlayer insulating film is deposited A step of forming the second electrode by combining the first conductive film and the second conductive film, wherein the second step is a step of forming the first interlayer insulating film. Removing the second interlayer insulating film and the second conductive film until the upper surface is exposed; The door and the fourth characteristic.

  In the variable resistance element manufacturing method according to the present invention, in addition to the fourth feature, the third step is performed in a direction of 68 ° or more and 90 ° or less with respect to the crystal growth direction of the second conductive film. A fifth feature is that the second conductive film is oxidized.

  According to the fifth feature of the variable resistance element manufacturing method of the present invention, since the resistance ratio between the resistance value in the low resistance characteristic and the resistance value in the high resistance characteristic can be increased, the resistance characteristic in a steady state. Therefore, it is possible to manufacture a variable resistance element that can realize stable switching characteristics.

  For example, when the second conductivity type is TiN, the crystal growth direction refers to the normal direction of the (1,1,1) preferential orientation plane of the NaCl type crystal structure. On the other hand, the second conductive film is oxidized in a direction of 68 ° or more and 90 ° or less.

  Further, in the variable resistance element manufacturing method according to the present invention, in addition to the second or third feature, the first step includes depositing a first conductive film and a first interlayer insulating film on the substrate. The second electrode is formed by patterning the first conductive film by patterning both into a predetermined shape, and the second step is the step of forming the first conductive film patterned in the first step. A sixth feature is a step of exposing the side wall portion.

  In the variable resistance element manufacturing method according to the present invention, in addition to the sixth feature, the third step is performed on the side wall portion of the first conductive film exposed in the second step. A seventh feature is that the oxidation treatment is performed in a direction orthogonal to the crystal growth direction of one conductive film.

  According to the seventh feature of the variable resistance element manufacturing method according to the present invention, the resistance ratio between the resistance value in the low resistance characteristic and the resistance value in the high resistance characteristic can be increased. Therefore, it is possible to manufacture a variable resistance element that can realize stable switching characteristics.

In addition to the first feature described above, the variable resistance element manufacturing method according to the present invention is characterized in that, in the first step, the first conductive film is deposited on the substrate and then patterned into a predetermined shape. Forming the second electrode with the first conductive film formed, and the second step comprises:
After the first interlayer insulating film is deposited on the entire surface, a predetermined region is opened to form an opening that exposes a part of the upper surface of the second electrode, and the third step is a transition metal oxide or transition metal The variable resistor film made of oxynitride is formed under the condition that the concentration of oxygen contained upward from the vicinity of the exposed surface of the second electrode located on the bottom surface of the opening is increased. The eighth feature is that the step of depositing the entire surface so as to fill the portion.

  According to the eighth feature of the method of manufacturing a variable resistance element according to the present invention, the variable resistor deposited in the opening has a high oxygen concentration in the region near the upper surface and is contained toward the bottom of the opening. The film is formed under such a condition that the oxygen concentration is lowered. Therefore, by subsequently depositing the first electrode on the upper surface of the variable resistor, the oxygen concentration in the region near the contact surface with the first electrode is increased, and the oxygen concentration is lowered toward the contact surface with the second electrode. Therefore, a filament path can be formed by adjusting the amount of oxygen defects present in the vicinity of the first contact surface by changing the positive / negative polarity of the applied pulse voltage. Thus, it becomes possible to manufacture a variable resistance element capable of changing the resistance characteristics.

  In addition to the eighth feature, the variable resistance element manufacturing method according to the present invention includes an ALD method in which the third step changes the oxygen flow rate or oxygen partial pressure while changing the oxygen flow rate or oxygen partial pressure by two or more steps. The ninth feature is that the deposition is performed by the CVD method or the reactive sputtering method.

  According to the ninth feature of the method of manufacturing a variable resistance element according to the present invention, the oxygen concentration contained can be adjusted according to the position in the variable resistor without performing complicated control.

  According to the configuration of the present invention, a resistance switching operation can be performed without forming a filament path. Thereby, the resistance characteristic after switching can be stabilized as compared with the conventional configuration in which the resistance characteristic changes based on the formation state of the filament path. Therefore, by providing the variable resistance element according to the present invention, it is possible to realize a nonvolatile semiconductor memory device with good data retention characteristics.

  Hereinafter, each embodiment of a variable resistance element according to the present invention (hereinafter appropriately referred to as “the present invention element”), a manufacturing method thereof, and a driving method thereof (hereinafter appropriately referred to as “the present invention method”) will be described. Will be described with reference to FIG.

[First Embodiment]
A first embodiment (hereinafter referred to as “this embodiment” as appropriate) of an element of the present invention, a method for manufacturing the same, and a driving method will be described with reference to the following FIGS.

  FIG. 1 is a schematic cross-sectional structure diagram of an element of the present invention according to this embodiment. In the element 1 of the present invention, the second electrode 3 made of the conductive materials 13 and 16 and the first electrode 2 made of the conductive material 21 are formed on the semiconductor substrate 11 on which the substrate base insulating film 12 is formed. A variable resistor 20 is formed between the second electrode 3 (the conductive material 16 constituting the electrode) and the first electrode 2. Further, a first interlayer insulating film 14 and a second interlayer insulating film 17 are formed between the conductive material 13 and the conductive material 21, and the conductive material 21 (first electrode 2) is the third interlayer. Covered with an insulating film 22. A contact hole is formed in a predetermined region of the first interlayer insulating film 14 and the second interlayer insulating film 22, and the first electrode 2 and the conductive material (metal wiring) 23 and 24 are filled in the contact hole. Electrical connection to the second electrode 3 is possible.

  Below, with reference to each figure of FIG.1 and FIGS.2-4, the manufacturing process of this invention element 1 is demonstrated. 2 (a) to 2 (e) and 3 (a) to 3 (d) below are schematic cross-sectional structural diagrams in one process when the element 1 of the present invention is manufactured (convenient on paper). It is divided into the above two drawings). FIG. 4 is a flowchart showing the manufacturing process of the element 1 of the present invention, and each step in the following sentence represents one step of the flowchart shown in FIG.

  Each schematic cross-sectional structure diagram shown in each of FIGS. 1 to 3 is merely schematically illustrated, and therefore, the scale of the actual structure does not necessarily match the scale of the drawing. Absent. The numerical values of the thickness of each film deposited in each process and the diameter of the opening and the like are merely examples, and are not limited to these values. The same applies to the following embodiments.

  First, as shown in FIG. 2A, a first conductive film 13 (hereinafter referred to as a TiN film), which is a conductive material, is formed on a semiconductor substrate 11 on which a base insulating film 12 is formed by, for example, a sputtering method. Deposited with a thickness of about 200 nm. Thereafter, patterning is performed in a predetermined shape by photolithography and etching (step # 1).

Next, as shown in FIG. 2B, a first interlayer insulating film 14 (hereinafter referred to as an SiO ₂ film), which is an insulating material, is deposited to a thickness of about 500 nm by, for example, a CVD (Chemical Vapor Deposition) method. Thereafter, the surface is planarized by a CMP (Chemical Mechanical Polishing) method (step # 2). The film thickness of the first interlayer insulating film 14 formed on the first conductive film 13 after planarization is about 200 nm.

  Next, as shown in FIG. 2C, the upper surface of the first conductive film 13 is exposed in a part of the region where the first conductive film 13 is formed in the lower layer by the photolithography method and the etching method. Then, an opening 15 having a diameter of about 400 nm is formed in the first interlayer insulating film 14 (step # 3).

  Next, as shown in FIG. 2D, the second conductive film 16 is deposited on the entire surface of the substrate by sputtering so as not to completely fill the opening 15 (step # 4). The second conductive film 16 is made of the same material as that of the first conductive film 13, and here is a TiN film. At this time, for example, if the film thickness of the second conductive film 16 is about 50 nm, the second conductive film 16 having a film thickness of about 20 nm is deposited on the outer side wall of the opening 15, and the inside remains open. It becomes.

Next, as shown in FIG. 2E, as in step # 2, a second interlayer insulating film 17 (referred to as SiO ₂ film) is deposited to a film thickness of about 400 nm by, for example, CVD (step # 5).

  Next, as shown in FIG. 3A, the second interlayer insulating film 17 and the second conductive film 16 are removed to such an extent that the upper surface of the first interlayer insulating film 14 is exposed, and the opening 15 is formed in step # 4. The upper surface of the second conductive film 16 deposited along the outer side wall is exposed (step # 6). Through this process, the upper surface of the second conductive film 16 is exposed in an annular shape. At this time, the second interlayer insulating film 17 deposited in step # 5 is formed on the inner side of the second conductive film 16 exposed in the annular shape, and the outer side of the second conductive film 16 exposed in the annular shape. The first interlayer insulating film 14 deposited in step # 2 is formed.

  Next, as shown in FIG. 3B, the second conductive film 16 is oxidized from the exposed surface toward the first conductive film 13 (step # 7). Due to the oxidation treatment, a part of the second conductive film 16 formed of the TiN film is changed to a titanium oxynitride such as TiON (hereinafter simply referred to as “TiON”), thereby forming the variable resistor 20. Is done. At this time, step # 7 is performed under such a condition that the oxygen concentration contained in TiON constituting the variable resistor 20 decreases from the vicinity of the exposed surface toward the formation position direction of the first conductive film 13 (downward in the drawing). Such oxidation treatment is performed.

  Specifically, for example, the exposed surface of the second conductive film 16 is subjected to an oxidation treatment in an ozone atmosphere of about 250 ° C., and then the reaction temperature is continuously or intermittently divided into two or more stages. It is assumed that oxidation treatment is performed while the temperature is raised, and the temperature is finally raised to about 450 ° C. Note that this reaction temperature value is an example, and in the initial stage, the oxidation treatment is performed under a temperature condition of about 200 ° C. to 300 ° C., and the temperature rises, and finally the temperature of about 250 ° C. to 450 ° C. The oxidation treatment may be performed under conditions. By this step, the volume density occupied by the microcrystals of TiON constituting the variable resistor 20 becomes high in the region near the exposed surface and decreases toward the region where the first conductive film 13 is formed.

  Next, as shown in FIG. 3C, the third conductive film 21 (here, the first conductive film 13 and the second conductive film) is formed on the upper surface so as to contact the variable resistor 20 formed in Step # 7. The TiN film is deposited in the same manner as in step 16 (step # 8).

  By passing through this step # 8, the variable resistor 20 is constituted by the second electrode 3 formed by integrating the second conductive film 16 and the first conductive film 13, and the third conductive film 21. The first electrode 2 is sandwiched between the first electrode 2 and the same configuration as the conceptual configuration shown in FIG.

Next, as shown in FIG. 3D, a third interlayer insulating film 22 (hereinafter referred to as an SiO ₂ film), which is an insulating material, is deposited by a CVD method to a thickness of about 500 nm (step # 9).

  Thereafter, the third interlayer insulating film 22 located above the formation region of the third conductive film 21, and the first interlayer insulating film 14 and the third interlayer insulation film 22 located above the formation region of the first conductive film 13 are formed. A contact hole is formed so that the upper surface of the lower conductive film is exposed, and a conductive material (for example, an Al—Si—Cu film having a thickness of 400 nm and a TiN film having a thickness of 50 nm is laminated in the contact hole. By filling with (structure), metal wirings 23 and 24 are formed (step # 10, see FIG. 1). As a result, voltage can be applied to the second conductive film 21 (first electrode 2) via the metal wiring 23, and voltage can be applied to the first conductive film 13 (second electrode 3) via the metal wiring 24. Application is possible.

  FIG. 5 is a graph showing resistance characteristics of the element of the present invention manufactured based on the manufacturing method of the present embodiment described above. For comparison, in step # 7, the resistance characteristics of variable resistance elements manufactured by performing a conventional oxidation process that performs an oxidation process under uniform conditions are displayed side by side. FIG. 5A is a graph showing the resistance characteristics when the oxidation treatment is performed without changing the temperature condition, and FIG. 5B is the resistance when the oxidation treatment is performed while changing the temperature condition. It is a graph which shows a characteristic. That is, FIG. 5A shows resistance characteristics of a variable resistance element having a uniform oxygen concentration in the variable resistor 4, and FIG. 5B shows that the oxygen concentration in the variable resistor 4 varies depending on the position. It is a resistance characteristic about the variable resistance element set to (2). In FIG. 5B, the variable resistance element in which the concentration of contained oxygen is reduced by 30% at a position advanced 10 nm from the first contact surface in contact with the first electrode 2 toward the second electrode 3. Measurement was performed using

  In FIGS. 5A and 5B, the horizontal axis indicates the magnitude of the applied pulse voltage, and the vertical axis indicates the resistance value of the variable resistance element measured after the pulse voltage is applied. Is defined by the polarity of the polarity of the first electrode 2 with respect to the second electrode 3. A method for measuring the resistance characteristic of the variable resistance element after applying the pulse voltage will be described later.

  In order to change the resistance characteristic of the variable resistance element manufactured based on the conventional method from the initial state, it is necessary to perform the forming process for forming the desired filament path as described above. In FIG. 5A, in order to change the resistance characteristics from the initial state A0 to the low resistance state A1, the forming process is executed by applying a pulse voltage having a sufficiently large absolute value (−7 V in the graph). Has been. After the filament path is formed by executing this forming process, the switching of the resistance characteristics can be realized by alternately applying positive and negative polarities whose absolute values are smaller than the pulse voltage applied during the forming process. In FIG. 5A, transition between a high resistance state and a low resistance state is possible by alternately applying a pulse voltage of + 2.2V and a pulse voltage of −1.8V.

  On the other hand, in the case of the element of the present invention manufactured by the manufacturing method based on the present embodiment, as shown in FIG. 5B, the resistance characteristic of the variable resistance element after changing the resistance characteristic once is changed. Voltage to be applied (a voltage of about −1.8V required to change the resistance characteristics from B1 to B2 or a voltage of about + 2.2V required to change the resistance characteristics from B2 to B3) By applying a voltage of the same level as the absolute value in the initial state B0, the resistance characteristic can be changed. In FIG. 5B, by applying the same pulse voltage + 2.2V as the pulse voltage necessary for changing the variable resistance element after changing the resistance characteristics to the high resistance characteristics from the initial state. It can be seen that the transition is made to the resistance characteristic B1. This can be said to suggest that the forming process, which has been conventionally required, is unnecessary when changing the resistance characteristics of the element of the present invention manufactured by the manufacturing method according to the present embodiment. The reason for this will be discussed below.

  In step # 7, the oxidation progress of the second conductive film 16 is changed by performing the oxidation treatment while changing the reaction temperature. Under a certain processing time, the oxidation of the second conductive film 16 progresses as the reaction temperature is higher than when the reaction temperature is low. That is, as the reaction temperature is higher than when the reaction temperature is low, oxidation proceeds more from the exposed surface of the second conductive film 16 toward the formation position of the first conductive film 13 within the same time. Become.

  As a result, the exposed surface vicinity of the second conductive film 16 that can be oxidized even at a low reaction temperature is subjected to a long-time oxidation treatment, whereas the oxidation does not proceed at a low reaction temperature, For the region where the oxidation is performed at a reaction temperature equal to or higher than a predetermined temperature, the time during which the oxidation is performed is shorter than that in the vicinity of the exposed surface. Therefore, in the vicinity of the exposed surface, the second conductive film 16 (TiN) is oxidized for a long time, and as a result, the oxygen concentration contained in the variable resistor 20 (TiON or the like) generated by the oxidation increases. On the other hand, in the region that advances from the vicinity of the exposed surface in the direction of the formation position of the first conductive film 13 (internal direction), the time during which the oxidation treatment is performed is shorter than that in the vicinity of the exposed surface. The oxygen concentration contained in the resistor 20 (TiON or the like) is lowered. That is, the variable resistor 20 generated in Step # 7 has a high oxygen concentration contained in the vicinity of the exposed surface, and the oxygen concentration decreases from the vicinity of the exposed surface toward the formation position of the first conductive film 13. It will be.

  By the way, the variable resistor 20 has oxygen vacancies in the initial state, and the number of oxygen vacancies is affected by the concentration of oxygen contained therein. That is, there are few oxygen defects in the vicinity of the exposed surface where the oxygen concentration is high, that is, in the vicinity of the contact surface with the second conductive film 21 (first electrode 2), and from the first contact surface to the formation direction of the first conductive film 13. The number of oxygen defects increases. In a region where there are no or few oxygen vacancies, the concentration of carriers (electrons) is lower than in a region where there are many oxygen vacancies.

  FIG. 6 is a schematic diagram for explaining a resistance state change when a pulse voltage is applied to the element of the present invention. In the following description, in order to facilitate understanding of the description, the description will be made using the same reference numerals as those used in FIG.

  As described above, the variable resistor 4 (corresponding to the variable resistor 20) has a high oxygen concentration in the vicinity of the contact surface with the first electrode 2 (corresponding to the third conductive film 21), and the second electrode 3 (first electrode). It is formed so that the oxygen concentration decreases in the direction of the conductive film 13 and the unoxidized second conductive film 16) (see FIG. 6A).

  Here, as shown in FIG. 6B, a pulse voltage (or pulse current) in which the first electrode 2 side having a high oxygen concentration becomes positive with respect to the second electrode 3 having a low oxygen concentration. Apply "pulse voltage". At this time, electrons are injected into the variable resistor 4 from the second electrode 3 side where the oxygen concentration is low by the applied pulse. A part of the injected electrons are captured by a defect level of oxygen atoms existing in the variable resistor 4, and the oxygen atoms are ionized into oxygen ions. Since the oxygen ions are negative, they move to the first electrode 2 to which a positive voltage is applied, and are trapped by oxygen defects present inside the variable resistor 4 on the first electrode 2 side. As a result, the amount of oxygen vacancies is further reduced on the first electrode 2 side, and the region becomes a high resistance state (see FIG. 6C). The variable resistor 4 is formed on the first electrode 2 side because it can be considered that the region formed on the first electrode 2 side and the other region are connected in series. As a result, the variable resistor 4 exhibits a high resistance state as a whole.

  On the other hand, as shown in FIG. 6 (d), a pulse voltage having a polarity opposite to that described above, that is, a pulse in which the second electrode 3 side having a low oxygen concentration becomes positive with respect to the first electrode 2 having a high oxygen concentration. When a voltage is applied, oxygen ions in the variable resistor 4 move to the second electrode 3 side to which a positive voltage is applied. Oxygen defects are generated in oxygen atoms due to the movement of oxygen ions. Since many oxygen ions exist on the first electrode 2 side that is in a high resistance state, many oxygen defects are generated in the region on the first electrode 2 side when the pulse voltage is applied. As a result, since the resistance state on the first electrode 2 side is lowered, the resistance of the variable resistor 4 is lowered as a whole.

  In the present embodiment, in step # 7, the oxidation treatment is performed while changing the temperature, so that the oxygen concentration of the variable resistor 4 varies depending on the region, and the vicinity of the region in contact with the first electrode 2 is variable. The resistor 4 is subjected to oxidation treatment under temperature conditions within a sufficiently oxidizable range. As a result, the oxygen concentration of the variable resistor 4 in the vicinity of the region in contact with the first electrode 2 becomes a high concentration state, and the amount of oxygen defects in the initial state after manufacture can be reduced. Therefore, by applying a pulse voltage having a polarity as shown in FIG. 6B, sufficient oxygen ions are compensated for the amount of oxygen defects existing in the vicinity of the region in contact with the first electrode 2. Thus, the high resistance region can be easily formed.

  In the element of the present invention, the oxygen concentration of the variable resistor 4 in the vicinity of the first electrode 2 side, which is the destination of oxygen ions when the resistance of the variable resistor 4 is increased, is increased. The more oxygen ions that contribute to the resistance state transition, that is, the lowering of resistance, can be formed closer to the first electrode 2 side, and these oxygen ions can be reduced until a voltage for lowering resistance is applied. Since the movement becomes difficult, the high resistance state can be stably maintained.

  Further, in the element of the present invention, when the electric resistance of the variable resistor 4 is changed from the high resistance state to the low resistance state, the first electrode 2 to which a pulse voltage is applied so as to be negative with respect to the other electrode. Since the oxygen concentration of the variable resistor 4 in the vicinity of the region in contact with the side is increased and the oxygen concentration is decreased toward the second electrode 3 which is the other electrode, the oxygen concentration toward the second electrode 3 is reduced. Ion migration is facilitated, and resistance can be reduced more efficiently by generating oxygen defects. Further, since the oxygen concentration of the variable resistor 4 in the vicinity of the region in contact with the first electrode 2 side is lowered to increase the amount of oxygen defects in the initial state, it is compensated by oxygen ions moving from the second electrode 3 side. A low resistance state can be stably maintained until a pulse voltage for transitioning to a high resistance state is applied while avoiding a decrease in the amount of oxygen defects.

  In particular, referring to FIG. 5, in the case of a variable resistance element (FIG. 5A) in which the oxygen concentration is substantially uniform throughout the variable resistor 4 by manufacturing without changing the temperature condition, While a forming process is required, the oxygen concentration contained in the variable resistor 4 is changed from the first contact surface in contact with the first electrode 2 to the second electrode 3 by manufacturing by changing the temperature condition. In the case of the variable resistance element (FIG. 5 (b)) in which the oxygen concentration contained is reduced by 30% at the position advanced by 10 nm, it can be seen that the forming process is unnecessary. By changing the temperature condition variously and changing the oxygen concentration contained in the variable resistor, it is contained at a position advanced 10 nm from the first contact surface in contact with the first electrode 2 toward the second electrode 3. It was confirmed that the forming process becomes unnecessary if the oxygen concentration is lower by 15% or more.

  One of the objects of the present invention is to use it for information storage based on a resistance value indicated by a variable resistance element including a variable resistor whose resistance value varies depending on the pulse voltage. The problem of whether or not the resistance value of the variable resistance element to be maintained is stably held until after the next pulse voltage application is important. This point will be verified below with reference to the drawings.

  FIG. 7 shows 10 hours, 100 hours, and 1000 hours with the variable resistance element maintained at a high temperature (150 ° C.) after several switching operations for the element of the present invention manufactured by the above method. It is a graph which shows the result of having read out resistance value suitably under room temperature later. FIG. 7A shows a case where the variable resistance element is held in a low resistance state, and FIG. 7B shows a case where the variable resistance element is held in a high resistance state.

  As shown in FIGS. 7A and 7B, the element of the present invention manufactured by the above method is in a low resistance state even after 1000 hours have passed under a high temperature state. It was confirmed that it was possible to maintain its own resistance state regardless of whether it was in a high resistance state.

  The measurement results in FIG. 7 suggest that the element of the present invention can maintain a good resistance value even in a high temperature state and exhibits a stable resistance characteristic. That is, it means that the element of the present invention can be applied as a nonvolatile memory device that can rewrite data repeatedly by applying a voltage pulse and has good data retention characteristics even in a high temperature environment.

  The switching characteristics are improved by improving the ratio of the resistance value in the low resistance state of the element 1 of the present invention to the resistance value in the high resistance state (hereinafter abbreviated as “resistance ratio of the element 1 of the present invention” as appropriate). In order to achieve this, it is also useful to perform the oxidation treatment in step # 7 under a predetermined angle condition.

  8 and 9 are schematic diagrams for explaining desirable oxidation conditions in the oxidation treatment according to Step # 7. FIG. 8 is a conceptual schematic diagram in a state immediately before the execution of the oxidation process according to Step # 7. FIG. 9 is a state where the third conductive film 21 is deposited after the oxidation process according to Step # 7 is completed (Step # 8). FIG.

  As shown in FIG. 8, in step # 7, the exposed surface of the second conductive film 16 deposited in step # 4 is oxidized from above. Incidentally, since the second conductive film 16 is formed by depositing TiN by the sputtering method in step # 4, the film 16 is composed of a layered polycrystalline body. In step # 7, it is preferable to oxidize the exposed surface from an angle of 68 ° or more and 90 ° or less with respect to the interface direction formed by the second conductive film 16, that is, the crystal growth direction.

  At this time, in the step of forming the opening 15 in Step # 3, the opening 15 is tapered with a predetermined angle, and the crystal growth direction of the second conductive film 16 is adjusted by adjusting this angle. As a result, the angle formed by the crystal growth direction and the oxidation direction (hereinafter referred to as “oxidation angle” as appropriate) can be adjusted (contained within the above range).

  After forming the opening 15 having a tapered shape in step # 3, the second conductive film 16 is deposited in step # 4, so that the second conductive film 16 filled in the opening 15 has an interface corresponding to the taper angle. Direction (crystal growth direction). Therefore, after passing through steps # 5 and # 6, the second conductive film 16 can be oxidized at an oxidation angle corresponding to the taper angle by performing an oxidation process from above the exposed surface of the second conductive film 16. . In step # 3, a tapered opening 15 having a predetermined taper angle is formed so that the oxidation angle falls within the range of 68 ° to 90 °.

  When the oxidation treatment is performed under such an angle condition, as shown in FIG. 9, the interface direction (crystal growth direction) of TiON constituting the variable resistor 20 formed by the oxidation treatment, and step # 8 is in the range of 0 ° to 22 ° with the contact interface of TiN constituting the third conductive film 21 deposited in FIG.

  FIG. 10 is a graph showing the relationship between the oxidation angle in Step # 7 and the resistance ratio of the device 1 of the present invention after manufacture, and is graphed with the oxidation angle on the horizontal axis and the resistance ratio on the vertical axis. It is.

  Referring to FIG. 10, if the angle formed by the TiN crystal direction and the oxidation direction is 65 ° or less, the resistance ratio generally shows a value of about 40 times or less, but the range is 68 ° or more. Within the range, a high resistance ratio of 120 times or more is realized. As the resistance ratio is higher, the distinction between the high resistance state and the low resistance state becomes more prominent, so that the resistance characteristic does not transition in the steady state, and stable switching characteristics can be realized. Therefore, the more stable switching characteristics can be realized by oxidizing the second conductive film 16 at an angle in the range of 68 ° to 90 °.

  Hereinafter, a measurement method for measuring the resistance characteristic of the variable resistance element as shown in FIG. 5 or FIG. 7 will be described.

  FIG. 11 shows a configuration of a measuring apparatus for applying a voltage pulse to a variable resistance element and measuring an IV characteristic. The measurement apparatus 30 includes a variable resistance element R (present invention element 1) to be measured, a pulse generator 34, a digital oscilloscope 31, a parameter analyzer 32, and a changeover switch 33. The parameter analyzer 32 is, for example, a model number 4156B manufactured by Agilent Technologies, and used as a current / voltage measuring device.

  At the time of measurement, one terminal of the variable resistance element R is connected to the ground of the digital oscilloscope 31 and the other terminal is connected to the fixed end of the changeover switch 33. Further, one terminal of the digital oscilloscope 31 and one terminal of the pulse generator 34 are connected. Then, one of the movable terminals of the changeover switch 33 is connected to the other terminal of the digital oscilloscope 31 and the other terminal of the pulse generator 30 to form one circuit. Further, the other terminal of the movable end of the changeover switch is connected to the parameter analyzer 32 to form the other circuit. In this way, both circuits can be switched by the switching operation of the movable end of the changeover switch 33 to form a measurement system.

  When applying the voltage pulse, the selector 33 is operated to electrically connect the pulse generator 34 and the variable resistance element R to apply the voltage pulse. The voltage pulse generated at this time is observed with the digital oscilloscope 31. Subsequently, the changeover switch 33 is connected to the parameter analyzer 32 (disconnected from the pulse generator 34), and the IV characteristic of the variable resistance element R is measured.

  When measuring the resistance characteristics of the element 1 of the present invention, first, +2.2 V (positive polarity pulse with a voltage amplitude of 2.2 V) and pulse width (pulse application time) 50 ns on the first electrode 2 side of the element 1 of the present invention. Then, a voltage pulse is generated from the pulse generator 34 so that a voltage is applied, and the resistance value after the application is obtained by measuring the IV characteristic with the parameter analyzer 32. After the measurement, a voltage pulse is applied from the pulse generator 34 so that a voltage is applied to the first electrode 2 side of the element 1 of the present invention at a voltage of −1.8 V (negative pulse with a voltage amplitude of 1.8 V) and a pulse width of 35 nsec. The resistance value after application is obtained by measuring the IV characteristic with the parameter analyzer 32.

  The IV characteristic is measured every time the voltage pulse is applied, and the current value when a voltage of +0.5 V is applied is measured. From the result, the resistance value of the variable resistance element after application of the voltage pulse is derived. The element 1 of the present invention manufactured based on the above-described method of the present invention changes its resistance value by applying a voltage pulse of about ± 2.0 V, but applies a relatively low voltage of ± 0.5 V. However, since the resistance value hardly changes, the resistance value of the variable resistance element after the voltage pulse application can be measured without affecting the subsequent voltage pulse application.

  In addition, about the measuring method which measures the resistance characteristic of this manufactured element of this invention, it is the same also as this embodiment also in each embodiment mentioned later.

  In step # 7, the oxidation process using ozone is performed. However, the oxidation process may be performed in an atmosphere of oxygen or a gas containing oxygen, and a gas containing oxygen or oxygen may be used. The second conductive film 16 may be oxidized by generating oxygen radicals by excitation with plasma.

  In step # 7, the oxygen concentration contained in the variable resistor 20 to be formed is changed from the region near the exposed surface of the second conductive film 16 by performing oxidation treatment while appropriately changing the temperature condition. Although it is configured to decrease toward the formation position of one conductive film 13, it is not necessarily required to be accompanied by a change in temperature condition as long as the oxidation treatment is performed under a condition that causes a difference in oxygen concentration. For example, under the reaction rate-determining state, even when the temperature is the same, the oxygen concentration is different as the distance from the region near the exposed surface increases. The same effect as the element 1 of the present invention can be obtained. In the following embodiments, the same applies to the oxidation treatment.

  Moreover, in the manufacturing method of the element 1 of the present invention described above, each step of applying, exposing, and developing a photoresist executed when performing a photolithography method, a step of removing the photoresist after etching, a post-etching step In addition, general processes such as a cleaning process performed after resist removal are omitted. The same applies to the following embodiments.

[Second Embodiment]
A second embodiment (hereinafter referred to as “this embodiment” as appropriate) of the element of the present invention, its manufacturing method, and driving method will be described with reference to the following FIGS.

  FIG. 12 is a schematic cross-sectional structure diagram of the element of the present invention according to this embodiment. Compared to the inventive element 1 according to the first embodiment, the inventive element 1a is different from the inventive element 1 in that the variable resistor 20 is formed in a direction perpendicular to the substrate surface. The element 1a of the present invention according to the embodiment is different in that the variable resistor 20 is formed in a direction parallel to the substrate surface.

  The element 1a of the present invention shown in FIG. 12 includes a second electrode 3 made of a conductive material 13 and a first electrode 2 made of a conductive material 21 on a semiconductor substrate 11 on which a substrate base insulating film 12 is formed. The variable resistor 20 is formed between the conductive material 13 (second electrode 3) and the conductive material 21 (first electrode 2). A first interlayer insulating film 14 is formed between the conductive material 13 and the conductive material 21, and the conductive material 21 (first electrode 2) is covered with the third interlayer insulating film 22. Yes. A contact hole is formed in a predetermined region of the first interlayer insulating film 14 and the third interlayer insulating film 22, and the first electrode 2 and the conductive material (metal wiring) 23 and 24 are filled in the contact hole. Electrical connection to the second electrode 3 is possible.

  Below, with reference to each figure of FIGS. 12-16, the manufacturing process of this invention element 1a is demonstrated. In addition, each figure of the following FIG. 13 (a)-(e) is a schematic sectional structure figure in one process at the time of manufacturing this invention element 1a. FIG. 14 is a flowchart showing the manufacturing process of the element 1a of the present invention, and each step in the following sentence represents one step of the flowchart shown in FIG.

  First, as shown in FIG. 13A, a first conductive film 13 (hereinafter referred to as a TiN film), which is a conductive material, is formed on a semiconductor substrate 11 on which a base insulating film 12 is formed by, for example, a sputtering method. Deposition is performed with a thickness of about 40 nm (step # 21).

Next, as shown in FIG. 13B, a first interlayer insulating film 14 (hereinafter referred to as an SiO ₂ film), which is an insulating material, is deposited by a CVD method, for example, to a thickness of about 500 nm (step # 22).

  Next, as shown in FIG. 13C, the first conductive film 13 and the first interlayer insulating film 14 are patterned by the photolithography method and the etching method to expose the side wall portions of the first conductive film 13 (steps). # 23). At this time, the upper surface of the first conductive film 13 is covered with the first interlayer insulating film 14.

  Next, as shown in FIG. 13D, oxidation treatment is performed on the first conductive film 13 from the exposed surface toward the inside of the first conductive film 13 (step # 24). Due to the oxidation treatment, a part of the first conductive film 13 formed of the TiN film is changed to a titanium oxynitride such as TiON (hereinafter simply referred to as “TiON”), thereby forming the variable resistor 20. Is done. At this time, step # 24 is performed under such a condition that the oxygen concentration contained in TiON constituting the variable resistor 20 decreases from the vicinity of the exposed surface toward the internal direction of the first conductive film 13 (leftward in the drawing). Apply oxidation treatment.

  Specifically, for example, oxygen radicals are generated by exciting an oxygen gas at about 250 ° C. with plasma to oxidize the exposed surface of the first conductive film 13, and then continuously or in two or more stages. The oxidation treatment is performed while intermittently increasing the reaction temperature in a plurality of stages, and finally the temperature is increased to about 450 ° C. In the present embodiment, unlike the first embodiment, the direction in which the oxidation treatment is performed is a direction perpendicular to the crystal direction of TiN constituting the first conductive film 13 (see FIG. 15). By this step, the volume density occupied by the microcrystals of TiON constituting the variable resistor 20 becomes high in the vicinity of the exposed surface, and in the internal direction of the first conductive film 13 (leftward in the drawing, away from the exposed surface). It becomes the structure which falls toward.

  In addition, the above reaction temperature value is an example. In the initial stage, oxidation treatment is performed under a temperature condition of about 200 ° C. to 300 ° C., and the temperature is increased, and finally the temperature is about 250 ° C. to 450 ° C. The oxidation treatment may be performed under temperature conditions. In addition, as described above in the first embodiment, the oxidation treatment may be performed using an oxidation method in an ozone atmosphere.

  Next, as shown in FIG. 13E, the third conductive film 21 is formed so as to be in contact with the variable resistor 20 (step # 25). Specifically, for example, Pt is deposited with a film thickness of about 150 nm by a sputtering method, and then patterned into a shape as shown in FIG. 13E by a photolithography method and an etching method. In this embodiment, since the oxidation direction in step # 24 is a direction orthogonal to the crystal direction of TiN constituting the first conductive film 13, the third crystal direction of the TiON constituting the variable resistor 20 and the third direction. The angle formed by the contact interface of Pt constituting the conductive film 21 is about 0 ° (see FIG. 16).

Thereafter, a third interlayer insulating film 22 (hereinafter referred to as an SiO ₂ film), which is an insulating material, is deposited by CVD to a thickness of about 500 nm, and metal wirings 23 and 24 are formed by the same method as in the first embodiment. (Step # 26, see FIG. 12). As a result, voltage can be applied to the second conductive film 21 (first electrode 2) via the metal wiring 23, and voltage can be applied to the first conductive film 13 (second electrode 3) via the metal wiring 24. Application is possible.

  Also in the present embodiment, as in the first embodiment, the variable resistor 20 (4) included in the element 1a of the present invention in the initial state after manufacture is in contact with the third conductive film 21 (first electrode 2). A configuration in which the concentration of oxygen contained is high and the oxygen concentration is decreased toward the formation region of the first conductive film 13 (second electrode 3) is shown. Therefore, also in the element 1a of the present invention according to the present embodiment, similarly to the element 1 of the present invention according to the first embodiment, the first conductive film 13 having a low oxygen concentration can be formed without performing the forming process with respect to the initial state. The resistance is increased by applying a pulse voltage such that the third conductive film 21 having a high oxygen concentration becomes positive, and conversely, the oxygen concentration is lower than that of the third conductive film 21 having a high oxygen concentration. The resistance can be reduced by applying a pulse voltage that makes the first conductive film 13 side positive.

  In step # 24, the oxidation process is performed using plasma. However, as in the first embodiment, the oxidation process is performed by heating in an atmosphere of ozone or oxygen or a gas containing oxygen. It is good as a thing.

[Third Embodiment]
A second embodiment (hereinafter referred to as “this embodiment” as appropriate) of the element of the present invention, its manufacturing method, and driving method will be described with reference to the following FIGS.

  FIG. 17 is a schematic sectional view of the element of the present invention according to this embodiment. The element 1b of the present invention has a configuration in which the variable resistor 20 included in the element 1 of the present invention in the first embodiment has an annular shape when viewed from above and has an insulating film 17 on the inside thereof. The variable resistor 20 provided in the element 1b of the present invention is different in that the inside is completely filled with the variable resistor 20 and the insulating film 17 is not provided.

  The element 1b of the present invention shown in FIG. 17 includes a second electrode 3 made of a conductive material 13 and a first electrode 2 made of a conductive material 21 on a semiconductor substrate 11 on which a substrate base insulating film 12 is formed. The variable resistor 20 is formed between the conductive material 13 (second electrode 3) and the conductive material 21 (first electrode 2). A first interlayer insulating film 14 is formed between the conductive material 13 and the conductive material 21, and the conductive material 21 (first electrode 2) is covered with the third interlayer insulating film 22. Yes. A contact hole is formed in a predetermined region of the first interlayer insulating film 14 and the third interlayer insulating film 22, and the first electrode 2 and the conductive material (metal wiring) 23 and 24 are filled in the contact hole. Electrical connection to the second electrode 3 is possible.

  Below, with reference to each figure of FIGS. 17-19, the manufacturing process of this invention element 1b is demonstrated. In addition, each figure of the following FIG. 18 (a)-(e) is a schematic sectional structure figure in one process at the time of manufacturing this invention element 1b. FIG. 19 is a flowchart showing the manufacturing process of the element 1b of the present invention, and each step in the following sentence represents one step of the flowchart shown in FIG.

First, a first conductive film 13 (hereinafter referred to as a Pt film), which is a conductive material, is deposited on the semiconductor substrate 11 on which the base insulating film 12 is formed by a sputtering method, for example, to a thickness of about 200 nm, and then photolithography is performed. Patterning is performed in a predetermined shape by the method and the etching method (step # 31). Then, as shown in FIG. 18A, after depositing a first interlayer insulating film 14 (hereinafter referred to as an SiO ₂ film), which is an insulating material, by a CVD method, for example, by a CVD method, the surface is deposited by a CMP method. Flatten (step # 32). The film thickness of the first interlayer insulating film 14 formed on the first conductive film 13 after planarization is about 100 nm.

  Next, as shown in FIG. 18B, the upper surface of the first conductive film 13 is exposed in a part of the region where the first conductive film 13 is formed in the lower layer by photolithography and etching. Then, an opening 15 having a diameter of about 275 nm is formed in the first interlayer insulating film 14 (step # 33).

  Next, as shown in FIG. 18C, a transition metal oxide film or a transition metal oxynitride film (hereinafter referred to as a NiO film) constituting the variable resistor 20 by an ALD method (Atomic Layer Deposition) method is used. A film thickness of about 200 nm is deposited, and the opening 15 is filled with the variable resistor film 20 (step # 34). At this time, the oxygen concentration contained in the variable resistor film 20 filled in the opening 15 is high in the region near the uppermost surface of the opening 15 and is directed toward the position of the upper surface of the first conductive film 13. The film formation related to Step # 34 is performed under the condition that the oxygen concentration is lowered.

  Specifically, when the NiO film is formed, the film is formed in a state where oxygen gas is added. In the initial stage of the film forming process, the flow rate of the added oxygen gas is set to be small, and then continuously. Alternatively, the film formation process is performed while the flow rate of oxygen gas is intermittently increased in two or more stages. As a result, the NiO film to be formed has a higher oxygen concentration as it is closer to the upper surface, and the oxygen concentration is lower as it is farther from the upper surface, that is, closer to the exposed surface (upper surface) of the first conductive film 13.

In this step, in addition to the film formation by the ALD method, the variable resistor film may be formed by the CVD method or the reactive sputtering method. When the film is formed based on the CVD method, the variable resistor film is formed by changing the film forming condition by changing the flow rate of the added oxygen gas as in the case of the ALD method. It is possible to give a gradient to the oxygen concentration of 20. In the case of the reactive sputtering method, sputtering is performed under Ar / O ₂ gas, and the film forming conditions are changed by changing the partial pressure of O ₂ gas, so that the variable resistor film is formed. It is possible to give a gradient to the oxygen concentration of 20. In this case, for example, in the initial stage, the sputtering process is performed at an Ar flow rate of about 90 to 100 sccm and an O ₂ flow rate of about 0 to 10 sccm, and thereafter, intermittently divided into a plurality of stages of continuous or two or more stages. ₂ minutes performing sputtering while increasing the pressure, eventually 40～60Sccm about the Ar flow rate, the _{O 2} flow rate can be made to perform the sputtering process in order 40～60Sccm.

  Next, as shown in FIG. 18D, the variable resistor film 20 deposited outside the opening 15, that is, the variable resistor 20 deposited on the upper surface of the first interlayer insulating film 14 is removed by CMP. And flattening (step # 35).

  Next, as shown in FIG. 18E, the third conductive film 21 is deposited on the upper surface so as to be in contact with the variable resistor 20 formed in Step # 35 (Step # 36). Specifically, for example, Pt is deposited with a film thickness of about 150 nm by a sputtering method, and then patterned into a shape as shown in FIG. 18E by a photolithography method and an etching method.

Thereafter, a third interlayer insulating film 22 (hereinafter referred to as an SiO ₂ film), which is an insulating material, is deposited by CVD to a thickness of about 500 nm, and metal wirings 23 and 24 are formed by the same method as in the first embodiment. (Step # 37, see FIG. 17). As a result, voltage can be applied to the second conductive film 21 (first electrode 2) via the metal wiring 23, and voltage can be applied to the first conductive film 13 (second electrode 3) via the metal wiring 24. Application is possible.

  Also in the present embodiment, as in the first and second embodiments, the variable resistor 20 (4) included in the element 1b of the present invention in the initial state after manufacture is connected to the third conductive film 21 (first electrode 2). A configuration in which the oxygen concentration contained in the contact surface is high and the oxygen concentration is decreased toward the formation region of the first conductive film 13 (second electrode 3) is shown. Therefore, also in the element 1b of the present invention according to the present embodiment, as in the above embodiments, the first conductive film 13 with a low oxygen concentration has a high oxygen concentration without performing the forming process with respect to the initial state. The resistance is increased by applying a pulse voltage such that the third conductive film 21 side is positive, and conversely, the first conductive film 13 side having a lower oxygen concentration than the third conductive film 21 having a higher oxygen concentration is provided. The resistance can be reduced by applying a pulse voltage that is positive.

  In the first and second embodiments, TiN is used as the second electrode 3, but the oxide generated by the oxidation treatment is a material having variable resistance characteristics (switching characteristics). It is not limited to TiN. That is, in addition to TiN, it may be composed of transition metal materials such as Cu, Ni, Ti, Nb, Zn, Co, W, and V, or nitrides thereof, and further composed of these composite films. It may be a thing. At this time, in the first and second embodiments, a transition metal oxide or a transition metal oxynitride generated by oxidizing a material used as the second electrode 3 is used as the variable resistor 4.

  The material of the first electrode 2 in the first and second embodiments and the material of the first electrode 2 and the second electrode 3 in the third embodiment may be conductive materials that generally function as electrodes. In addition to the above-described TiN and Pt, transition metal materials such as Ir, Os, Ru, Rh, Pd, Ti, Al, Cu, Zn, Mn, Zr, Ni, V, W, and Co, or nitriding thereof It may be composed of a material, or may be composed of a composite film of these.

  In addition to the NiO film described above, the material of the variable resistor 4 in the third embodiment may be any material (for example, a transition metal oxide or a fiber metal oxynitride having variable resistance characteristics (switching characteristics)). CuO, NiO, TiON, etc.).

1 is a schematic sectional view of a variable resistance element according to a first embodiment of the present invention. Schematic cross-sectional structure diagram for each manufacturing step showing the variable resistance element manufacturing method according to the first embodiment of the present invention (1). Schematic cross-sectional structure diagram for each manufacturing process showing the variable resistance element manufacturing method according to the first embodiment of the present invention (2) The flowchart which shows the manufacturing method of the variable resistance element of 1st Embodiment which concerns on this invention. The graph which shows the resistance characteristic of the variable resistive element of 1st Embodiment which concerns on this invention. The schematic diagram for demonstrating the change of a resistance state by having applied the pulse voltage with respect to the variable resistance element which concerns on this invention The graph which shows the retention characteristic of the resistance state of the variable resistive element which concerns on this invention Schematic (1) for demonstrating desirable oxidation angle conditions in the oxidation process which concerns on 1 process of the manufacturing method of the variable resistance element of 1st Embodiment which concerns on this invention. Schematic (2) for demonstrating desirable oxidation angle conditions in the oxidation process which concerns on 1 process of the manufacturing method of the variable resistance element of 1st Embodiment which concerns on this invention. The graph which shows the relationship between an oxidation angle and the resistance ratio of the variable resistance element which concerns on this invention after manufacture Schematic configuration diagram showing the configuration of a measurement system for measuring the resistance characteristics of a variable resistance element Schematic cross-sectional structure diagram of a variable resistance element according to a second embodiment of the present invention Schematic cross-sectional structure diagram for each manufacturing process showing a variable resistance element manufacturing method of a second embodiment according to the present invention The flowchart which shows the manufacturing method of the variable resistance element of 1st Embodiment which concerns on this invention. Schematic (1) for demonstrating desirable oxidation angle conditions in the oxidation process which concerns on 1 process of the manufacturing method of the variable resistance element of 2nd Embodiment which concerns on this invention. Schematic (2) for demonstrating desirable oxidation angle conditions in the oxidation process which concerns on 1 process of the manufacturing method of the variable resistance element of 2nd Embodiment which concerns on this invention. Schematic sectional structural view of a variable resistance element according to a third embodiment of the present invention. Schematic cross-sectional structure diagram for each manufacturing process showing a variable resistance element manufacturing method of a third embodiment according to the present invention The flowchart which shows the manufacturing method of the variable resistance element of 3rd Embodiment which concerns on this invention. Conceptual configuration diagram of variable resistance element Schematic sectional view of a conventional variable resistance element using a PCMO film

Explanation of symbols

1: Variable resistance element according to the first embodiment of the present invention 1a: Variable resistance element according to the second embodiment of the present invention 1b: Variable resistance element according to the third embodiment of the present invention 2: First electrode 3: First Two electrodes 4: Variable resistor 11: Semiconductor substrate 12: Base insulating film 13: First conductive film 14: (First) interlayer insulating film 16: Second conductive film 17: Second interlayer insulating film 20: Variable resistor 21 : Third conductive film 22: third interlayer insulating film 23: conductive film (metal wiring)
24: Conductive film (metal wiring)
25: Contact hole 26: Contact hole 30: Resistance characteristic measuring device 31: Pulse generator 31a: Output terminal of pulse generator 32: Digital oscilloscope 32a, 32b: Input terminal of digital oscilloscope 32g: Ground terminal of digital oscilloscope 33: Parameter analyzer 34 : Changeover switch 34a: fixed end of changeover switch 34b, 34c: movable end of changeover switch 90: conventional variable resistance element 91: PCMO film

Claims (5)

A variable resistance element in which a variable resistor is sandwiched between a first electrode and a second electrode, and an electric resistance between the two electrodes is changed by applying a voltage pulse between the first electrode and the second electrode. Because
The variable resistor is
It is composed of transition metal oxides excluding iron or transition metal oxynitrides,
The oxygen concentration contained is reduced from the first contact surface in contact with the first electrode toward the second contact surface in contact with the second electrode,
By applying a pulse voltage between the two electrodes so that the first electrode is positive with respect to the second electrode, the resistance characteristic of the variable resistance element transitions from a low resistance state to a high resistance state,
The resistance characteristic of the variable resistance element is changed from a high resistance state to a low resistance state by applying a pulse voltage between the electrodes so that the first electrode is negative with respect to the second electrode. A variable resistance element.   The oxygen concentration contained in the transition metal oxide or the transition metal oxynitride constituting the variable resistor at a position advanced by 10 nm from the first contact surface toward the second contact surface. The variable resistance element according to claim 1, wherein the variable resistance element is reduced by 15% or more as compared with one contact surface.   The transition metal oxide or the transition metal oxynitride constituting the variable resistor reduces the volume density of microcrystals from the first contact surface toward the second contact surface. The variable resistance element according to claim 1 or 2. The second electrode has a protrusion protruding toward the formation surface of the first electrode;
The variable resistor is a layered transition metal oxide or transition metal oxynitride polycrystal formed at the tip of the protruding portion of the second electrode so as to be connected to the first electrode, The variable according to any one of claims 1 to 3, wherein an angle formed by a crystal growth direction of a crystal body and an interface between the first contact surfaces is not less than 0 ° and not more than 22 °. Resistance element. The variable resistance element according to any one of claims 1 to 4, wherein the variable resistor is made of an oxide or oxynitride of Ti or Ni.

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