JP2010147428A - Variable resistance element and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable resistance element that stably exhibits desired electrical characteristics, and to provide a method for manufacturing such a variable resistance element.
In a variable resistance element, a first barrier film (15a) is formed in a direction perpendicular to the substrate surface of a semiconductor substrate at the boundary between a sidewall insulating film and a first insulating film. . A first barrier film 15 (15b) is also formed on the bottom surface of the sidewall insulating film 16. These barrier films are made of a material having a diffusion preventing property for preventing diffusion of reducing species such as hydrogen, oxidizing species such as oxygen, or both. The first electrode 17a is formed on the bottom surface of the opening 30, and the second electrode 17b is formed on the upper surface of the insulating film 13 and a partial upper surface of the sidewall insulating film 16 on the insulating film 13 side. A variable resistor 18 is formed so as to straddle.
[Selection] Figure 1

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. The present invention relates to a method for manufacturing a variable resistance element that changes its electrical resistance when applied.

  In recent years, various devices such as FeRAM (Ferroelectric RAM), MRAM (Magnetic RAM), PRAM (Phase Change RAM), etc. as next-generation non-volatile random access memory (NVRAM) capable of high-speed operation instead of flash memory 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.

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

  As shown in FIG. 6, the variable resistance element of the conventional configuration has a structure in which a lower electrode 103, a variable resistor 102, and an upper electrode 101 are sequentially stacked, and a voltage is applied between the upper electrode 101 and the lower electrode 103. By applying a pulse, the resistance value can be reversibly changed. 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 this memory cell, one memory cell is composed of one select transistor T and one variable resistance element R (1T / 1R type) or one variable because of the difference in the components. There is a (1R type) memory cell composed only of the resistance element R. Among these, FIG. 7 shows a configuration example of a 1T / 1R type memory cell.

  FIG. 7 is an equivalent circuit diagram showing a configuration example of a memory cell array including 1T / 1R type memory cells. The gate of the selection transistor T of each memory cell is connected to the word lines (WL1 to WLn), and the source of the selection transistor T of each memory cell is connected to the source lines (SL1 to SLn) (n is a natural number). . One electrode of the variable resistance element R for each memory cell is connected to the drain of the selection transistor T, and the other electrode of the variable resistance element R is connected to the bit lines (BL1 to BLm) (m is a natural number). ). Each word line WL1 to WLn is connected to the word line decoder 106, each source line SL1 to SLn is connected to the source line decoder 107, and each bit line BL1 to BLm is connected to the bit line decoder 105. In response to an address input (not shown), specific bit lines, word lines, and source lines for writing, erasing and reading operations to specific memory cells in the memory cell array 104 are selected.

  FIG. 8 is a schematic cross-sectional view of one memory cell constituting the memory cell array 104 in FIG. In this configuration, the select transistor T and the variable resistance element R form one memory cell. The selection transistor T includes a gate insulating film 113, a gate electrode 114, a drain diffusion region 115, and a source diffusion region 116, and is formed on the upper surface of the semiconductor substrate 111 on which the element isolation region 112 is formed. The variable resistance element R includes a lower electrode 118, a variable resistor 119, and an upper electrode 120.

  The gate electrode 114 of the transistor T forms a word line, and the source line wiring 124 is electrically connected to the source diffusion region 116 of the transistor T through the contact plug 122. The bit line wiring 123 is electrically connected to the upper electrode 120 of the variable resistance element R through the contact plug 121, while the lower electrode 118 of the variable resistance element R is connected to the transistor T through the contact plug 117. The drain diffusion region 115 is electrically connected.

  As described above, the selection transistor T and the variable resistance element R are arranged in series, so that the transistor of the memory cell selected by the change in the potential of the word line is turned on, and the memory selected by the change in the potential of the bit line. Only the variable resistance element R of the cell can be selectively written or erased.

  FIG. 9 is an equivalent circuit diagram illustrating a configuration example of a 1R type memory cell. Each memory cell includes only the variable resistance element R, and one electrode of the variable resistance element R is connected to the word lines (WL1 to WLn) and the other electrode is connected to the bit lines (BL1 to BLm). Each word line WL1 to WLn is connected to a word line decoder 133, and each bit line BL1 to BLm is connected to a bit line decoder 132. A specific bit line and word line for writing, erasing and reading operations to specific memory cells in the memory cell array 131 are selected in accordance with an address input (not shown).

  FIG. 10 is a schematic perspective view showing an example of a memory cell constituting the memory cell array 131 in FIG. As shown in FIG. 10, the upper electrode wiring 143 and the lower electrode wiring 141 are arranged so as to cross each other, one of which forms a bit line and the other forms a word line. In addition, the variable resistor 142 is arranged at the intersection (usually referred to as “cross point”) of each electrode. In the example of FIG. 10, for convenience, the upper electrode 143 and the variable resistor 142 are processed into the same shape. It becomes the area of crossing points.

Here, as the variable resistor material used for the variable resistor 119 in FIG. 8 or the variable resistor 142 in FIG. 10, the super giant magnetoresistive effect is obtained by Shangquing Liu, Alex Ignatiev, etc. of the University of Houston, USA. A method of reversibly changing the electrical resistance by applying a voltage pulse to a known perovskite material 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.

As another variable resistor material, titanium oxide (TiO ₂₎ film, a nickel oxide (NiO) film, a zinc oxide (ZnO) film, an oxide of a transition metal element such as niobium oxide _(Nb 2 _{O 5)} film It is known from Non-Patent Document 2 and Patent Document 2 that reversible resistance change is exhibited. Among these, the phenomenon of the switching operation using NiO is reported in detail in Non-Patent Document 3.

US Pat. No. 6,204,139 JP 2002-537627 A JP 2007-27537 A Japanese Patent Laid-Open No. 11-135736 Liu, S.Q. and others, “Electric-pulse-induced reversible resistance change effect in magnetoresistive films”, Applied Physics Letter, Vol.76, pp.2749-2751,2000 H. Pagnia et al., “Bistable Switchingin Electroformed Metal-Insulator-MetalDevices”, Phys.Stat.Sol. (A), vol.108, pp.11-65, 1988 Baek, I.G., et al., “Highly Scalable Non-volatile Resistive Memory using Simple Binary Oxide Driven by Asymmetric Unipolar Voltage Pulses”, IEDM 04, pp. 587-590, 2004

  For example, when manufacturing a memory cell having a structure as shown in FIG. 8, after forming the variable resistance element R, it is exposed to a reducing atmosphere such as hydrogen in each process such as a wiring forming process.

  For example, in the manufacturing process of a MOSFET constituting a peripheral circuit (logic circuit) of a memory cell, in order to finally adjust transistor characteristics such as an interface state of a gate electrode, a fixed charge, an on-current value, and a threshold current, a metal After forming the wiring structure and before forming a passivation film, a hydrogen annealing treatment of about several tens of minutes is performed in a hydrogen atmosphere with a hydrogen concentration in the range of several to 50% in a temperature range of 400 ° C. to 450 ° C. Is given to.

  At this time, the variable resistor is exposed to a hydrogen atmosphere, and there is a problem that the characteristics (particularly resistance characteristics) of the variable resistor fluctuate due to the influence of the hydrogen atmosphere (reducing atmosphere).

  Even if hydrogen annealing is not performed, for example, when a silicon oxide film is formed as an interlayer insulating film by a plasma CVD method, hydrogen is generated during the film forming process. There may be an influence on the characteristics of the variable resistor.

Further, a W (tungsten) film excellent in embedding coverage is generally used as a material for the contact electrode embedded in the contact hole, and the W film is usually thermal CVD by thermal reaction between WF ₆ and SiH _4. The film is formed by the method, and hydrogen is generated under the thermal reaction during the film formation. The characteristics of the variable resistor may be affected by hydrogen generated in such a contact electrode formation process.

  A nonvolatile semiconductor memory device using a variable resistor is configured to store information associated with each resistance characteristic by reversibly changing the resistance characteristic by applying an electrical pulse. Therefore, the resistance characteristic of the variable resistor is an element representing the information written in the memory cell at the present time. However, when the generation of hydrogen has an influence on the characteristics (resistance characteristics) of the variable resistor, information is erroneously read at the time of reading, or a problem that correct rewriting processing cannot be performed is caused.

  Therefore, it is possible to manufacture variable resistance elements that exhibit stable resistance characteristics by using a hydrogen barrier film in a stack-structure RRAM in order to prevent a reducing atmosphere such as hydrogen generated during the process from flowing into the variable resistance body. Has been filed by the present applicant (see Patent Document 3 above).

  By the way, in the above-mentioned Patent Document 3, the description is limited to a variable resistance element (a structure shown in FIG. 8 is an example) showing a stack structure formed by sandwiching a variable resistor between two upper and lower electrodes. Similarly, in Patent Document 4 described above, the content of avoiding hydrogen damage by forming a hydrogen barrier film in the case of FeRAM is described, but in this document, only a memory element having a stack structure is assumed. Yes.

  In the conventional stack structure, the surface of the electrode and the variable resistor is exposed to a gas, a chemical solution, or the like used in the machining process, and thus cannot always be said to have a clean surface. Further, there is a problem that the contact resistance is not stable due to the influence of natural oxidation after the lower electrode and variable resistor are formed and the influence of the film forming process atmosphere of the film deposited on the upper layer.

  Therefore, the present inventor has come up with the idea of realizing a variable resistance element showing another structure (hereinafter referred to as “contact structure” as appropriate) in which the surface of the electrode and the variable resistor is not exposed as compared with the stack structure.

  FIG. 11 is a schematic structural diagram of a variable resistance element conceived as a process leading to the present invention. 11 includes a semiconductor substrate 11, a wiring layer 12, an insulating film 13 (hereinafter referred to as “first insulating film 13”), a sidewall insulating film 16, a first electrode 17a, and a second electrode. 17b, a variable resistor 18, a barrier film 19, an insulating film 20, and contact electrodes 23a and 23b.

  That is, the variable resistance element 10 shown in FIG. 11 has a sidewall insulating film 16 formed so that the film thickness increases toward the bottom surface in the insulating film 13 provided with the opening 30, and further the sidewalls. A first electrode 17 a is provided inside the insulating film 16. The variable resistor 18 is in contact with the upper surface of the first electrode 17a and is also in contact with the upper surface of the side wall of the sidewall insulating film 16, and further above the side wall of the side wall insulating film 16 on the first insulating film 13 side. In addition, the first insulating film 13 is in contact with the upper surface of the second electrode 17b. That is, the variable resistor 18 is in contact with both the divided first electrode 17a and second electrode 17b. As a result, similarly to the stack type structure, it is possible to exhibit variable resistance characteristics that reversibly change the resistance value by applying an electric pulse.

  The variable resistance element 10 as shown in FIG. 11 can be formed through the following process. That is, after forming the wiring layer 12 on the semiconductor substrate 11, the insulating film 13 is formed on the upper surface of the substrate 11. Thereafter, after forming an opening 30 in the insulating film 13 so that a part of the upper surface of the wiring layer 12 is exposed, the insulating film is formed again under a film thickness condition within a range not completely filling the opening 30. Form a film. Thereafter, the insulating film is etched back so that the upper surface of the wiring layer 12 is exposed, and the sidewall insulating film 16 is formed.

  Next, an electrode film as a material for the first electrodes 17a and 17b is formed. Also at this time, the electrode film is formed under a film thickness condition within a range that does not completely fill the opening 30 (and the region surrounded by the sidewall insulating film 16). Thereby, a thin electrode film region (hereinafter referred to as “local thin film region” as appropriate) is formed on a part of the upper surface of the side wall of the sidewall insulating film 16. When the oxidation treatment is performed under this condition, the variable resistor 18 is formed in the region where the electrode film is oxidized. At this time, in the local thin film region, the oxidation treatment is performed under such a condition that the portion corresponding to the film thickness of the electrode film formed is oxidized. As a result, the variable resistor 18 formed by oxidizing the electrode film existing in the local thin film region causes the electrode film to be positioned on the bottom surface side of the opening 30 and the upper surface of the first insulating film 13. It will be divided into the second electrode 17b located on the side. As a result, the variable resistor 18 is sandwiched between the first electrode 17 a and the second electrode 17 b in the region surrounded by the sidewall insulating film 16 in the opening 30.

  After that, after patterning the second electrode 17b and the variable resistor 18 as necessary, a barrier film 19 is formed on the entire surface so as to cover the upper surface and side surfaces of the variable resistor 18. Then, after the insulating film 20 is formed, contact plugs 23a and 23b are formed by a normal process to obtain the configuration shown in FIG.

  In the case of a normal stack type structure, after forming the lower electrode, an oxidation treatment is performed to change a portion from the upper surface of the lower electrode downward to a variable resistor, and then an electrode film is formed on the upper surface of the variable resistor. The upper electrode is formed by forming a film. Therefore, the upper surface of the variable resistor before the upper electrode is formed is exposed to the process atmosphere, and the upper electrode is formed by forming an electrode film on the upper surface. Therefore, the interface between the variable resistor and the upper electrode is formed. Impurities that occur during the process adhere to the surface. Moreover, since the variable resistor is formed by oxidizing a part of the lower electrode, the electrical characteristics between the variable resistor and the lower electrode are adjusted by the process conditions during oxidation. On the other hand, since the upper electrode is formed by forming an electrode film on the upper surface of the variable resistor, the electrical characteristics between the upper electrode and the variable resistor are adjusted by the process conditions at the time of electrode film formation. . That is, the electrical characteristics of the variable resistance element composed of the upper electrode, the variable resistor, and the lower electrode are determined in accordance with two conditions: a process condition during oxidation and a process condition during electrode film formation. It becomes. For this reason, the electrical characteristics of the variable resistance element are easily affected by process conditions, and it is difficult to stably manufacture an element that satisfies the electrical characteristics at the time of design.

  On the other hand, when the variable resistance element 10 having the structure shown in FIG. 11 is formed through the process as described above, the contact surface between the variable resistor and the electrode is not exposed to the atmosphere. Then, the first electrode 17a, the second electrode 17b, and the variable resistor 18 are formed from the electrode film by oxidizing a part of the electrode film formed in one process in one oxidation process. . As a result, the interface between the first electrode 17a and the variable resistor 18 and the interface between the second electrode 17b and the variable resistor 18 are both formed under the same process conditions. Therefore, by maintaining the oxidation treatment at a predetermined process condition, the contact resistance at both interfaces is stabilized, and the electrical characteristics of the variable resistance element can be stabilized between the elements.

  FIG. 11 illustrates a state in which the barrier film 19 is formed using the method described in Patent Document 3 so that a reducing atmosphere such as hydrogen does not flow into the variable resistor 18. By forming the barrier film 19 on the upper surface and the side surface of the variable resistor 18, the reducing atmosphere is prevented from flowing in from above and from the side of the variable resistor 18.

  However, as apparent from FIG. 11, a reducing atmosphere can flow into the variable resistor 18 from the direction of the arrow D <b> 1 through the first insulating film 13 and the sidewall insulating film 16. Since Patent Documents 3 and 4 do not originally assume a variable resistance element having a contact structure, there is no disclosure or suggestion of means for solving this problem peculiar to the contact structure.

  For example, as one countermeasure, another barrier film may be formed between the sidewall insulating film 16 and the second electrode 17b. However, in this method, since the barrier film is in direct contact with the interface between the variable resistor 18 and the second electrode 17b, characteristic fluctuation occurs, and a variable resistance element exhibiting desired electrical characteristics is stably manufactured. It becomes difficult. In addition, when a barrier film is actually formed between the sidewall insulating film 16 and the second electrode 17b, the barrier film material is sputtered over the entire surface after the sidewall insulating film 16 is formed. At this time, the exposed upper surface of the wiring layer 12 is covered with the barrier film. Therefore, in order to ensure conduction between the first electrode 17a and the wiring layer 12 to be formed later, it is necessary to expose the wiring layer 12 by etching the barrier film in the region sandwiched between the sidewall insulating films 16. There is. However, this etching process also etches the side wall portion of the sidewall insulating film 16, which may reduce the film thickness or cause etching damage. Such an action on the sidewall insulating film 16 is not desirable because it may change the characteristics of the variable resistance element.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a variable resistance element that stably exhibits desired electrical characteristics, and to provide a method for manufacturing such a variable resistance element.

  In order to achieve the above object, a variable resistance element according to the present invention includes a first insulating film formed on a semiconductor substrate having an opening penetrating in a direction perpendicular to the substrate surface, and in the opening. A first barrier film provided with a first barrier part formed in contact with the side wall of the first insulating film, and a second barrier part formed in an annular shape from the outer periphery toward the inside on the bottom surface of the opening; A sidewall insulating film formed so as to be in contact with the upper surface of the second barrier section and the side wall of the first barrier section on the inner side of the opening and to increase in thickness toward the bottom; and on the bottom of the opening A first electrode formed so as to be at least partially surrounded by the second barrier portion, a partial upper surface of the sidewall insulating film located on the first barrier portion side, and an upper surface of the first barrier portion And the above A second electrode formed over the upper surface of the insulating film; an upper surface of the first electrode; a partial upper surface of the sidewall insulating film where the second electrode is not formed; and an upper surface of the second electrode. Thus, a variable resistor for separating the first electrode and the second electrode, and a second barrier film formed on an upper surface of the variable resistor, the first electrode and the second electrode are provided. The electrical resistance between the two electrodes is changed by applying a voltage pulse therebetween, and the first barrier film and the second barrier film are subjected to a reduction reaction with a reducing species of the variable resistor, and the variable resistance. In order to suppress at least one of the oxidation reactions with the oxidized species of the body, the reduced species or the oxidized species or both of them are made of a film that prevents diffusion to the variable resistor. Features.

  According to the characteristics of the variable resistance element according to the present invention, first, since the barrier film is formed at the boundary between the sidewall insulating film and the first insulating film, the outside of the sidewall insulating film (on the first insulating film side). Therefore, it is possible to suppress the diffusion of reducing species and oxidizing species into the variable resistor through the sidewall insulating film. Further, since the barrier film is also formed on the bottom surface of the sidewall insulating film, it is possible to suppress the diffusion of reducing species and oxidizing species into the variable resistor through the sidewall insulating film from below.

  Unlike the conventional stack structure, the first electrode is formed on the bottom surface in the opening, the second electrode is formed outside the first electrode, and the upper surface of the first electrode and the second electrode are formed. A variable resistance element is realized by forming a variable resistor over the upper surface of a part of the sidewall insulating film that is not formed and the upper surface of the second electrode. Therefore, with such a structure, a part of the electrode film is changed into a variable resistor by oxidizing the formed electrode film, and thereby the variable resistance element is realized by dividing the electrode into two. it can. That is, the variable resistance element can be manufactured without exposing the interface between the variable resistor and the electrode to the atmosphere. Accordingly, since impurities do not adhere to the interface between the electrode and the variable resistor, it is possible to manufacture a variable resistance element that exhibits a desired resistance characteristic as compared with the conventional stack structure.

  At this time, the first barrier film and the second barrier film may be made of an oxide containing Al or Ti.

  In the variable resistance element according to the present invention, in addition to the above features, the second electrode is formed on a partial upper surface of the first insulating film, and the second barrier film is formed on the second electrode. It is formed over the upper surface and the outer surface of the variable resistor located on the upper surface, the outer surface of the second electrode, and the upper surface of the first insulating film on which the second electrode is not formed. Features.

  A variable resistance element manufacturing method according to the present invention is a variable resistance element manufacturing method having the above characteristics, wherein the first insulating film is formed by forming the opening after forming the insulating film. And preventing diffusion of the reducing species or the oxidizing species or both under a film thickness condition that does not completely fill the opening so as to cover the bottom surface and the inner surface of the opening. Forming a barrier film having diffusion preventing property, and then forming an insulating film on the upper surface of the barrier film under a film thickness condition that does not completely fill the opening, and then opening the opening. Etching back the insulating film and the barrier film until a partial bottom surface of the portion appears, forming the first barrier film and the sidewall insulating film, and then the sidewall insulating film The area surrounded by Forming an electrode film over the exposed bottom surface of the opening, the side wall of the sidewall insulating film on the inside of the opening, and the top surface of the first insulating film under a film thickness condition that does not fill; A step of forming an electrode film having a local thin film region on at least a part of the side wall of the sidewall insulating film on the inside of the opening, and then performing an oxidation treatment to oxidize at least the local thin film region, The local thin film region that has been oxidized and changed to the variable resistor divides the electrode film formed on the bottom surface side of the opening and the electrode film formed in a region outside the local thin film region. Forming the first electrode and the second electrode, and then forming a barrier film having anti-diffusion properties so as to cover at least the upper surface of the variable resistor. And having a step of forming a second barrier film.

  The variable resistance element manufacturing method according to the present invention, in addition to the above feature, includes a step of patterning the electrode film after forming the electrode film and before performing the oxidation process, After completion of the oxidation treatment, a barrier film having the diffusion preventing property is formed over the upper surface and side surface of the variable resistor, the side surface of the first electrode, and the upper surface of the first insulating film where the first electrode is not formed. Another feature is that the second barrier film is formed by forming a film.

  According to the configuration of the present invention, the interface between the variable resistor and the electrode is not exposed to the atmosphere, and reducing species and oxidizing species can be prevented from flowing into the variable resistor. Therefore, a variable resistance element that stably exhibits desired electrical characteristics can be realized.

  Hereinafter, embodiments of a variable resistance element and a method for manufacturing the same according to the present invention will be described with reference to FIGS.

  In addition, each schematic structure drawing shown below is typically shown, and the dimensional ratio on the drawing does not necessarily coincide with the actual dimensional ratio. Further, the same components as those in FIG. 11 described above are denoted by the same reference numerals.

  FIG. 1 is a schematic structural diagram of a variable resistance element according to the present invention. The variable resistance element 1 according to the present invention includes a semiconductor substrate 11, a wiring layer 12, a first insulating film 13, a barrier film 15 (hereinafter referred to as “first barrier film 15”), a sidewall insulating film 16, and a first electrode 17a. The second electrode 17b, the variable resistor 18, the barrier film 19 (hereinafter referred to as “second barrier film 19”), the second insulating film 20, and the contact electrodes 23a and 23b.

  That is, according to the variable resistance element 1, the first barrier film 15 is formed in the direction orthogonal to the substrate surface of the semiconductor substrate 11 at the boundary between the sidewall insulating film 16 and the first insulating film 13. A first barrier film 15 is also formed on the bottom surface of the sidewall insulating film 16. Hereinafter, the first barrier film 15 formed at the boundary between the sidewall insulating film 16 and the first insulating film 13 is referred to as a “first barrier portion 15 a”, and the first barrier film 15 formed on the bottom surface of the sidewall insulating film 16. One barrier film is referred to as a “second barrier portion 15b”.

  Each of the first barrier film 15 and the second barrier film 19 is made of a material having a diffusion preventing property for preventing diffusion of reducing species such as hydrogen, oxidizing species such as oxygen, or both. AlOx can be used. These barrier films are not limited to AlOx as long as they have the above-described diffusion preventing properties, and may be composed of, for example, an oxide containing Al or an oxide containing Ti.

  Similar to the variable resistance element 10 shown in FIG. 11, the variable resistance element 1 shown in FIG. 1 has a second barrier in order to prevent reduction species and oxidation species from flowing into the variable resistor 18 from above or from the side. A membrane 19 is provided. The variable resistance element 1 shown in FIG. 1 differs from the variable resistance element 10 in that a first barrier film 15 is further provided in addition to the second barrier film 19.

  The variable resistance element 1 includes the first barrier film 15 (particularly, the first barrier portion 15a), so that reduced species and oxidized species are diffused from the first insulating film 13 side (arrow X1 in FIG. 1). Even if it exists, it has the effect of shielding the diffusion at the interface with the sidewall insulating film 16 (arrow X2 in FIG. 1). For this reason, it is possible to prevent the reducing species and oxidizing species from flowing into the variable resistor 18 through the sidewall insulating film 16. Further, the first barrier film 15 (second barrier portion 15 b) is also provided on the bottom surface of the sidewall insulating film 16, so that even when reducing species or oxidized species are diffused from below the sidewall insulating film 16. , Has the effect of suppressing the flow into the sidewall insulating film 16.

  FIG. 2 is a graph comparing the switching characteristics of the variable resistance element 1 shown in FIG. 1 and the variable resistance element 10 shown in FIG. 11, and is graphed with the resistance value of the variable resistance element as a vertical axis (logarithmic scale). is there.

  FIG. 2 shows a first pulse voltage (voltage −2.6 [V], pulse width 35 [nsec], expressed as “Pulse1” in the drawing) and a second pulse voltage for both variable resistance elements 1 and 10. (Voltage +2.0 [V], pulse width 35 [nsec]. Indicated as “Pulse2” in the drawing) The range of the measurement result of the resistance value (readout resistance value) measured after each voltage application Is displayed on the graph. In the reading process, a resistance value measured by applying a voltage of 0.5 [V] is shown.

  In FIG. 2, the transition of the resistance value after the change to the low resistance state is indicated by dotted lines for both elements 1 and 10 (V1, V2). According to this, it can be seen that the fluctuation of the dotted line V1 is smaller than that of the dotted line V2. That is, according to FIG. 2, it can be seen that the variable resistance element 1 shown in FIG. 1 has more stable resistance characteristics than the variable resistance element 10 shown in FIG.

  Then, when both the elements 1 and 10 are compared, only the difference in whether or not the first barrier film 15 is present remains. In other words, this means that the resistance characteristics of the variable resistance element can be stabilized by forming the first barrier film 15.

  According to the above, even for a variable resistance element having a so-called contact structure as shown in FIG. 1, it is possible to prevent inflow of reducing species and oxidizing species into the variable resistor 18, thereby providing stable resistance characteristics. Can be realized.

  And the variable resistance element 1 shown in this FIG. 1 can be manufactured through the process of step # 1- # 10 mentioned later. Through these steps, unlike the stack structure described above, the variable resistance element can be manufactured without exposing the interface between the variable resistor and the electrode to the atmosphere. Therefore, it is possible to realize a variable resistance element that exhibits more stable resistance characteristics than the variable resistance elements described in Patent Documents 3 and 4.

  Hereinafter, a method for manufacturing the variable resistance element 1 will be described with reference to the drawings. 3 and 4 are schematic cross-sectional views showing a manufacturing process when manufacturing the variable resistance element 1, and each process is divided into FIGS. 3 (a) to 3 (f) and FIGS. 4 (a) to 4 (e). (It is divided into two drawings for the sake of space). FIG. 5 is a flowchart showing the manufacturing process of the method of the present invention, and steps # 1 to # 10 in the following sentence represent steps of the flowchart shown in FIG.

First, as shown in FIG. 3 (a), a transistor circuit or the like (not shown) and an insulating film (first insulating film) of SiO ₂ film or the like wiring layer 12 on the semiconductor substrate 11 which is suitably formed 13 by CVD For example, the film is deposited on the entire surface with a thickness of about 400 nm (step # 1).

  Next, as shown in FIG. 3B, the resist layer formed by a known photolithography technique is used as a mask, and a predetermined hole diameter of about 400 nm is formed in the first insulating film 13 by a known etching technique. Opening 30 is formed so that the upper surface of the part is exposed (step # 2).

  Next, as shown in FIG. 3C, an AlOx film as the barrier film 15 is deposited on the entire surface by a sputtering method with a film thickness that does not completely fill the opening 30 (for example, about 10 nm) (step). # 3).

Next, as shown in FIG. 3D, the insulating film 16 such as a SiO ₂ film for forming the sidewall insulating film is formed with a film thickness that does not completely fill the opening 30 (for example, about 170 nm). Deposit on the entire surface (step # 4).

  Next, as shown in FIG. 3E, the entire surface is etched back by a known etching technique until a part of the upper surface of the wiring layer 12 is exposed (step # 5). At this time, the insulating film 16 and the barrier film 15 on the first insulating film 13 are removed by etching, and the upper surface of the first insulating film 13 is exposed.

  By this step # 5, the sidewall insulating film 16 is formed in the opening 30 so as to increase in film thickness toward the bottom surface. Further, the barrier film 15 remains on the boundary between the sidewall insulating film 16 and the first insulating film 13 and on the bottom surface of the sidewall insulating film 16. A barrier film 15 formed at the boundary between the sidewall insulating film 16 and the first insulating film 13 is a first barrier portion 15a, and a barrier film 15 formed in an annular shape on the bottom surface of the sidewall insulating film 16 is a second barrier portion. It corresponds to 15b.

  Next, as shown in FIG. 3F, a TiN film as an example of the electrode film 17 is deposited on the entire surface of the semiconductor substrate 11 to a thickness of about 60 nm, for example, by sputtering (step # 6). At this time, in step # 5, the sidewall insulating film 16 formed so that the film thickness increases toward the bottom surface is formed, so that the electrode film 17 is deposited on the upper surface of the sidewall of the sidewall insulating film 16. A thin electrode film region (hereinafter referred to as “local thin film region” as appropriate) is formed on a part of the upper surface of the side wall of the sidewall insulating film 16. Also in this step # 6, the electrode film 17 is formed with a film thickness within a range in which the opening 30 is not completely filled. By this step # 6, the electrode film 17 is formed on the bottom surface of the opening 30 where the wiring layer 12 is exposed.

  Next, as shown in FIG. 4A, the electrode film 17 is patterned as necessary by a known etching technique using a resist formed by a known photolithography technique as a mask.

Next, as shown in FIG. 4B, for example, the electrode film (TiN film) 17 is oxidized by thermal oxidation in an atmosphere containing oxygen at 250 to 450 ° C. to form the variable resistor film 18. A TiO ₂ film is formed (step # 7). At this time, at least in the local thin film region, a portion corresponding to the film thickness of the electrode film formed is oxidized. Due to the variable resistor 18 formed in this step # 7, the electrode film 17 has a first electrode 17a located on the bottom surface side of the opening 30 and a second electrode 17b located on the top surface side of the first insulating film 13. Will be divided. As a result, the variable resistor 18 is sandwiched between the first electrode 17 a and the second electrode 17 b in the region surrounded by the sidewall insulating film 16 in the opening 30. The first electrode 17a is configured to be at least partially surrounded by the second barrier portion 15b.

  In order to realize the variable resistance element 1, it is necessary to leave the first electrode 17a on the bottom surface of the opening 30 as a matter of course at the end of step # 7. Therefore, in this step # 7, the oxidation process is performed under predetermined conditions of the pressure condition, the temperature condition, and the processing time, thereby forming the bottom surface position of the opening 30 (that is, the upper surface position of the wiring layer 12). The electrode film 17 is not completely oxidized, and a partially unoxidized electrode film 17 remains in the region. That is, an unoxidized electrode film 17 is formed on the bottom surface of the opening 30 in contact with the upper surface of the wiring layer 12, and the variable resistor formed by oxidizing the electrode film 17 on the upper region thereof. The body membrane 18 is present. As an example of this step # 7, thermal oxidation treatment may be performed for about 40 minutes at 300 ° C. under normal pressure (760 Torr).

  Next, as shown in FIG. 4C, an AlOx film as the second barrier film 19 is deposited on the entire surface by sputtering for about 10 nm (step # 8). When the patterning process is performed after step # 6, the second barrier film 19 covers the upper surfaces and side surfaces of the second electrode 17b and the variable resistor 18, and the upper surface of the first insulating film 13. It is formed. The second barrier film 19 has a function of preventing inflow of reducing species and oxidizing species from above and from the side of the variable resistor 18.

Next, as shown in FIG. 4D, an insulating film such as SiO ₂ as the second insulating film 20 is formed by a CVD method, for example, about 700 nm (step # 9), and flattened by a known CMP method or the like. Flattening with the technology).

  Next, as shown in FIG. 4E, a contact electrode 23a that communicates with the wiring layer 12 and a contact electrode 23b that communicates with the second electrode 17b are formed by a known contact technique (step # 10). Thereafter, an upper wiring layer is formed.

  In the above description, general steps such as a step of applying, exposing, and developing a photoresist, a step of removing the photoresist after etching, and a cleaning step after etching and removing the resist are omitted. is doing.

  In the variable resistance element 1 manufactured through the above steps # 1 to # 10, as in the method described in Patent Document 3 or 4, after forming the lower electrode and the variable resistor, the electrode film as the upper electrode is changed to the variable resistance element. This can be realized without going through a process of forming a film so as to be in contact with the upper surface of the body. That is, the first electrode 17a, the second electrode 17b, and the variable resistor 18 are formed from one electrode film by one oxidation treatment according to Step # 7. That is, by adjusting the conditions for the oxidation treatment, the electrical characteristics between the variable resistor 18 and the first electrode 17a and the electrical characteristics between the variable resistor 18 and the second electrode 17b can be controlled. Further, the interface between the variable resistor and each electrode is not exposed to the atmosphere. This makes it possible to stably manufacture the variable resistance element 1 having desired electrical characteristics.

  As described above, since the first barrier film 15 is formed on the boundary between the sidewall insulating film 16 and the first insulating film 13 and on the bottom surface of the sidewall insulating film 16, the reduction into the variable resistor 18 is performed. Inflow of seeds and oxidized species can be prevented, and resistance characteristics can be stabilized. This effect is as seen in FIG.

  In step # 1, the semiconductor substrate 11 is appropriately formed with a transistor circuit or the like. However, the circuit does not necessarily have to be formed.

  Further, in the film forming process of the electrode film 17 according to Step # 6, the film thickness of the electrode film 17 (that is, the film thickness in the local thin film region) formed on the side wall upper surface of the sidewall insulating film 16 is set to the opening 30. Directional sputter deposition methods such as collimated sputtering, long throw sputtering, and ionization sputtering in order to make the film thickness sufficiently thinner than the electrode film 17 formed on the upper surface of the bottom surface (wiring layer 12) and the upper surface of the first insulating film 13. It is preferable to form a film using Furthermore, the film thickness of the variable resistor 18 may be controlled by using a laminated film of a CVD method and a sputtering method.

In addition, as an oxidation process according to Step # 7, in addition to a thermal oxidation method using molecules containing oxygen such as O ₂ , O ₃ , H ₂ O, N ₂ O, and NO, a plasma oxidation method or an ion An injection method or the like may be used.

  In Step # 6, a TiN film is used as an example of the electrode film 17, but it is formed of a transition metal such as Cu, Ni, V, Zn, Nb, Ti, W, Co, or a transition metal nitride. Is also possible. At this time, the variable resistor film 18 is made of a metal oxide or metal oxynitride formed by oxidizing the material used as the electrode film 17.

Schematic structure diagram of variable resistance element according to the present invention The graph for demonstrating the effect of the variable resistance element which concerns on this invention Part of a process cross-sectional view when manufacturing a variable resistance element according to the present invention Another part of process sectional drawing at the time of manufacturing the variable resistance element which concerns on this invention The flowchart which shows the manufacturing process of the variable resistance element based on this invention in order. Schematic structure diagram of variable resistance element with conventional configuration Equivalent circuit diagram showing one configuration example of 1T / 1R type memory cell Cross-sectional schematic diagram of a 1T / 1R type memory cell Equivalent circuit diagram showing one configuration example of 1R type memory cell Cross-sectional schematic diagram of 1R type memory cell Schematic structural diagram of a variable resistance element for explaining the problem of the present invention

Explanation of symbols

1: Variable resistance element according to the present invention 10: Variable resistance element 11: Semiconductor substrate 12: Wiring layer 13: Insulating film (first insulating film)
15: Barrier film (first barrier film)
15a: first barrier part 15b: second barrier part 16: sidewall insulating film 17a: first electrode 17b: second electrode 18: variable resistor 19: barrier film (second barrier film)
20: Insulating film (second insulating film)
23a, 23b: contact electrode 30: opening 101: upper electrode 102: variable resistor 103: lower electrode 104: memory cell array 106: word line decoder 107: source line decoder 111: semiconductor substrate 112: element isolation region 113: gate insulation Film 114: Gate electrode 115: Drain diffusion region 116: Source diffusion region 117: Contact plug 118: Lower electrode 119: Variable resistor 120: Upper electrode 121: Contact plug 123: Bit line wiring 124: Source line wiring 131: Memory cell array 132: Bit line decoder 133: Word line decoder 141: Lower electrode wiring 142: Variable resistor 143: Upper electrode wiring BL1 to BLm: Bit line R: Variable resistance element SL1 to SLn: Source line T: Selection Transistors WL1-WLn: Word line

Claims (5)

A first insulating film formed on the semiconductor substrate and having an opening penetrating in a direction perpendicular to the substrate surface;
A first barrier portion formed in contact with the side wall of the first insulating film in the opening, and a second barrier portion formed in an annular shape from the outer periphery toward the inside on the bottom surface of the opening. A barrier film;
A sidewall insulating film formed so as to be in contact with the upper surface of the second barrier section and the side wall of the first barrier section on the inner side of the opening and to increase in thickness toward the bottom surface;
A first electrode formed on the bottom surface of the opening so as to be at least partially surrounded by the second barrier;
A second electrode formed over a partial upper surface of the sidewall insulating film located on the first barrier portion side, an upper surface of the first barrier portion, and an upper surface of the first insulating film;
The first electrode and the second electrode are formed over the upper surface of the first electrode, the partial upper surface of the sidewall insulating film where the second electrode is not formed, and the upper surface of the second electrode. A variable resistor that divides
A second barrier film formed on the upper surface of the variable resistor,
By applying a voltage pulse between the first electrode and the second electrode, the electrical resistance between the electrodes changes,
The first barrier film and the second barrier film are:
In order to suppress at least one of the reduction reaction of the variable resistor with the reducing species and the oxidation reaction of the variable resistor with the oxidizing species, the reducing species or the oxidizing species or both of the above A variable resistance element comprising a film that prevents diffusion to a variable resistor.   The variable resistance element according to claim 1, wherein the first barrier film and the second barrier film are made of an oxide containing Al or Ti. The second electrode is formed on a partial upper surface of the first insulating film,
The second barrier film includes an upper surface and an outer surface of the variable resistor located on an upper surface of the second electrode, an outer surface of the second electrode, and the first electrode on which the second electrode is not formed. The variable resistance element according to claim 1, wherein the variable resistance element is formed over an upper surface of the insulating film. It is a manufacturing method of the variable resistance element according to claim 1,
Forming the first insulating film by forming the opening after forming the insulating film;
Thereafter, a diffusion preventing property for preventing diffusion of the reducing species or the oxidizing species or both of them under a film thickness condition that does not completely fill the opening so as to cover the bottom surface and the inner surface of the opening. Forming a barrier film provided; and
Thereafter, an insulating film is formed on the upper surface of the barrier film under a film thickness condition that does not completely fill the opening, and then the insulating film and the barrier film are formed until a partial bottom surface of the opening appears. Performing etch back on the first barrier film and the sidewall insulating film; and
Thereafter, under a film thickness condition that does not completely fill the region surrounded by the sidewall insulating film, the exposed bottom surface of the opening, the sidewall of the sidewall insulating film on the inside of the opening, and the Forming an electrode film over the upper surface of the first insulating film, thereby forming an electrode film having a local thin film region on at least a part of the side wall of the sidewall insulating film on the inside of the opening;
Thereafter, an oxidation treatment is performed to oxidize at least the local thin film region, and the electrode film formed on the bottom surface side of the opening by the local thin film region that has been oxidized and changed into the variable resistor; Dividing the electrode film formed in a region outside the local thin film region to form the first electrode and the second electrode;
And subsequently forming the second barrier film by forming the barrier film having the diffusion preventing property so as to cover at least the upper surface of the variable resistor. Manufacturing method. After forming the electrode film, before performing the oxidation treatment, having a step of patterning the electrode film,
After completion of the oxidation treatment, a barrier film having the anti-diffusion property over the upper surface and side surface of the variable resistor, the side surface of the first electrode, and the upper surface of the first insulating film where the first electrode is not formed. The method of manufacturing a variable resistance element according to claim 4, wherein the second barrier film is formed by forming a film.

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