KR100693409B1 - Nonvolatile Memory Device Based on Resistance Switching of Oxide ? Method Thereof - Google Patents

Abstract

The present invention relates to a nonvolatile memory device using a resistance change of an oxide film and a method of manufacturing the same. More specifically, in order to implement a ReRAM device using a change in resistance, a large amount of oxygen does not match the composition ratio (stoichiometry), and therefore, the first layer (bottom oxide) having high conductivity and the second layer having high composition ratio and high resistance ( The present invention relates to a nonvolatile semiconductor memory device and a manufacturing method characterized in that an oxide film having a multi-layer composition ratio consisting of a top oxide) is formed.

In order to fabricate a ReRAM device, a thin film of metal oxide having a thickness of about 50 to 100 nm is deposited on a silicon wafer or a conductive electrode by using various metal oxides and deposition methods. By minimizing the amount of oxygen at high temperatures during deposition, it forms metal oxides with significantly lower oxygen composition than metal oxides. An oxide film having high conductivity is formed. The oxide film is oxidized at a low temperature in an oxygen atmosphere at low temperature to form an oxide film layer having a high resistance of about 10 to 30 nm on the surface.

The ReRAM device of the present invention not only has a 10-year data retention characteristic, which is essential as a nonvolatile memory, but also the electrical characteristics of the device exhibit a significant change in the drain current of the MOSFET due to a change in resistance, thereby providing a good quality memory. It may be provided as an element.

Description

Nonvolatile Memory Device and its Manufacturing Method Using Resistance Change of Oxide Film {Nonvolatile Memory Device Based on Resistance Switching of Oxide & Method Thereof}             

Figure 1 is a cross-sectional SEM photograph of the ZrO _x oxide film of the present invention showing a cross-sectional structure having two layers of oxide.

Figure 2 shows the composition of ZrO _x using XPS (a) surface oxide layer, (b) shows a bulk oxide layer.

Figure 3 shows the current and resistance change characteristics according to the switching cycle of a typical ReRAM device.

4 shows data retention characteristics of a typical ReRAM device.

FIG. 5A illustrates a cross-sectional structure of a 1T-1R ReRAM device, and FIG. 5B illustrates On / Off characteristics of a 1T-1R device.

The present invention relates to a nonvolatile memory device using a resistance change of an oxide film and a method of manufacturing the same. More specifically, the composition ratio (stoichiometry) does not match due to the lack of oxygen, and thus the composition ratio of the multilayer composed of the first conductive layer having high conductivity and the second layer having high resistance and high resistance is different. A nonvolatile semiconductor memory device and a manufacturing method characterized by forming an oxide film.

Flash memory, which has been commercially available as a non-volatile memory, has been used to store or remove electrons in floating polysilicon or silicon nitride to change the threshold voltage (V _th ) to the storage device. I use it. On the contrary, recently studied PRAM (phase change memory) and MRAM (magnetic memory) generate resistance change by using externally applied heat / magnetic field and use them as memory devices.

The present invention is similar to the above two next-generation memory devices in terms of the use of resistance change, but it is characterized by causing the resistance change of the insulating film using a voltage pulse, so that a simpler structure and a manufacturing process than a PRAM / MRAM can be realized. Can be.

The ReRAM device using the resistance change of the oxide of the present invention has been studied in the 1960s and 1970s, and has recently been actively studied. Based on the research results published so far, the basic switching characteristics have been studied for various oxide materials, but the specific characteristics of the switching mechanism are insufficient. Due to this nonuniformity, the number of switching, set / reset voltage, and reset current have many problems to commercialize the next generation Giga / Tera-bit memory.

The present invention discloses the structure and process of an ideal ReRAM device based on a physical understanding of the switching mechanism of ReRAM oxide. Formation of two layers of oxide is essential for optimal operating conditions of ReRAM devices. That is, due to the lack of oxygen, the composition ratio (stoichiometry) does not match, which results in the formation of an oxide film having a different composition ratio of a multilayer composed of a highly conductive first oxide and a second oxide having a high resistance and a high resistance. Let's do it.

According to the present invention, a conductive filament is formed to locally flow an appropriate level of current through a high-resistance oxide insulator thin film by applying a high voltage pulse to a memory device, and then a voltage pulse of an appropriate level is applied to the memory device. The electrons are trapped in the conductive oxide film so that the current flows low, or the trapped electrons disappear and the current flows largely. This resistance change characteristic is used as a nonvolatile memory device.

In other words, the commercialization of ReRAM requires the need for a new oxide manufacturing process with stable, high switching frequency and low power operation characteristics using oxide, and systematic research and understanding of device switching and conduction mechanism. .

In the related art related to the present invention, U.S. Patent No. 3,336,514 (Bistable metal-niobium oxide-Bismuth thin film device) is to confirm the ReRAM characteristics using a Nb ₂ O ₅ single oxide film on the Nb-metal electrode, C. Rossel et al. al., Electrical current distribution across a metal-insulator-metal structure during bistable switching, JOURNAL OF APPLIED PHYSICS VOLUME 90, NUMBER 6, 15 SEPTEMBER 2001, p.2892, IBM). The characteristics of the ReRAM using doped SrZrO ₃ oxide (Oxide) are confirmed, and it is understood that chromium (Cr) ions present in the oxide trap / detrap electrons as a switching mechanism. In this case, the single thin film process is considered to be relatively unstable switching characteristics, the technical configuration is different from the present invention.

The present invention implements an optimal device structure and process based on a systematic understanding of the conduction / switching mechanism of a ReRAM device. As a result, oxygen is insufficient in the composition of the stoichiometry and thus the first layer (bottom) has high conductivity. and a method of manufacturing a nonvolatile semiconductor memory device characterized in that an oxide film having a different composition ratio of a multilayer composed of a second layer (top oxide) having a high composition ratio and a high resistance is formed.

In other words, by forming an oxide layer having a different composition ratio and having different resistances, a NDR (negative differential resistance) effect is induced, and thus it can be used as a resistance change memory. After applying a high voltage pulse to the memory device to form a conductive filament so that an appropriate level of current flows in the oxide thin film having a high resistance, an appropriate level of voltage pulse is applied to the device to trap electrons in the conductive oxide film. trapped to make the current flow low, or the trapped electrons disappear to control the current to flow large. This resistance change characteristic is used as a nonvolatile memory device.

According to the present invention, a conductive filament is formed to apply a high voltage pulse to a memory device, so that an appropriate level of current flows in an oxide insulator thin film having a high resistance, and then a voltage pulse of an appropriate level is applied to the memory device. The electrons are trapped in the current so that the current flows low, or the trapped electrons disappear so that the current flows largely. Using the resistance change characteristics, a device for ReRAM is manufactured by using the following steps.

According to the present invention, there is a lack of oxygen, so that the composition ratio (stoichiometry) does not match, and thus the oxide layer having a different composition ratio of a multilayer composed of a first oxide having a high conductivity and a second oxide having a high resistance and a high resistance. A nonvolatile semiconductor memory device and a method for manufacturing the same are formed.

* 1st layer (Bottom Oxide) deposition process

Thin films were deposited with ZrO _x with a thickness of about 50-100 nm using reactive sputtering during various deposition processes on silicon wafers or conductive electrodes. In addition to the reaction sputtering, the deposition method may be selected from among pulsed-laser deposition (PLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), molecular beam epitaxy (MBE), and e-beam evaporation.

In sputtering, the process conditions are as follows: the deposition temperature is 400 to 500 ° C., and the mixing ratio of argon and oxygen is 30: 1 to minimize the amount of oxygen, thereby forming ZrO _x having a significantly lower composition of oxygen than ZrO ₂ . An oxide film of a high conductivity first layer (Bottom Oxide) is formed.

Various metal oxides can be used as the oxide thin film material. Examples of such metal oxides in the present invention include ZrO _x , NiO _x , HfO _x , TiO _x , Ta ₂ O _x , Al ₂ O _x , La ₂ O _x , Nb ₂ O _x , SrTiO _x , Cr-doped SrTiO _x , Any one selected from Cr-doped SrZrO _x may be used.

In the metal oxide of the oxide thin film material, an appropriate composition ratio x is 1.5 to 1.9. That is, the case where it is about 5 to 25% smaller than 2 which is a stoichiometric composition of oxygen can be used.

* 2nd layer (Top Oxide) deposition process

The highly conductive oxide film formed as described above is oxidized at a temperature of 200 to 300 ° C. in an oxygen atmosphere to form a second oxide (Top Oxide) oxide film having a high resistance of about 10 to 30 nm on the surface. For example, when ZrO _x is deposited as the oxide film of the first layer, the oxide film of the _second layer forms a ZrO ₂ layer.

Hereinafter, the present invention will be described by the following examples. However, these are only one embodiment of the present invention to explain the description of the present invention more easily, and the scope of the present invention is not limited to these embodiments.

<Example 1>

In the deposition of ZrO ₂ thin films with metal oxides on the silicon wafer by reactive sputtering, the process conditions during sputtering are deposition temperature of 400 ° C., and the mixing ratio of argon and oxygen is 30: 1, minimizing the amount of oxygen, so that the thickness is about 50-100 nm. ZrO _x thin films were deposited. ZrO _x , which is an oxide film of the first layer (Bottom Oxide), is significantly lower than that of ZrO _2. An oxide film with high conductivity was obtained. At this time, the appropriate composition ratio x is 1.5 to 1.9. That is, it is about 5 to 25% smaller than 2 which is a stoichiometric composition of oxygen.

The oxide film of the first layer was oxidized at a low temperature of 300 ° C. in an oxygen atmosphere to form a ZrO ₂ layer, which is an oxide film of a second layer (Top Oxide) having a high resistance of about 10 to 30 nm on the surface.

<Example 2>

In the same manner as in Example 1, reactive sputtering was carried out to form ZrO _x , which is an oxide film of the first layer. An oxide film with high conductivity was obtained. On the oxide film of the first layer, the mixing ratio of argon and oxygen was 4: 1, which significantly increased the partial pressure of oxygen to form a ZrO ₂ layer, which is an oxide film of the second layer having a high resistance of about 10 to 30 nm, on the surface.

<Example 3>

In the same manner as in Example 1, reactive sputtering was carried out to form TiO _x , an oxide film of the first layer. An oxide film with high conductivity was obtained. The oxide film of the first layer was oxidized at a low temperature at 300 ° C. in an oxygen atmosphere to form a TiO ₂ layer, which is an oxide film of a second layer having a high resistance of about 10 to 30 nm in thickness on the surface.

<Example 4>

In the same manner as in Example 1, reactive sputtering was carried out to form NiO _x , which is an oxide film of the first layer. An oxide film with high conductivity was obtained. The oxide film of the first layer was oxidized at a low temperature of 300 ° C. in an oxygen atmosphere to form a NiO ₂ layer, which was an oxide film of a second layer having a high resistance of about 10 to 30 nm in thickness on the surface.

<Example 5>

In the same manner as in Example 1, deposition was carried out using PLD to form SrTiO _x , which is an oxide film of the first layer. An oxide film with high conductivity was obtained. The oxide film of the first layer was oxidized at a low temperature of 300 ° C. in an oxygen atmosphere to form an SrTiO ₃ layer, which is an oxide film of a second layer having a high resistance of about 10 to 30 nm in thickness, on the surface.

It can be seen that the cross-sectional electron microscope (SEM) photograph of the oxide film formed through the process of Example 1 of the present invention is composed of two layers of oxide films as shown in FIG. 1.

Figures 2a and 2b is the result of x-ray photoelectron spectroscopy (XPS) on the surface of Figure 2a, while forming a ZrO ₂ of the composition ratio, while in the case of Figure 2b observed in bulk, the composition ratio does not fit, in the metal Zr The XPS peak usually observed is seen. That is, it can be seen that the surface and the bulk are formed of oxide films having different compositions.

The electrical characteristics of the nonvolatile memory device fabricated using the deposition process of the multilayer oxide thin film implemented in the present invention are shown in FIG. 3. It can be seen that the resistance forms two different states according to the applied voltage.

After the formation of the oxide thin films having different resistances in the multilayer, when a high voltage pulse is applied, most of the voltages are applied to the high resistance thin films, whereby local conductive filaments are formed in the high resistance oxide films. At this time, by applying a current level of compliance (current compliance) of the appropriate level is determined the physical size of the filament and the maximum value of the current that can flow through it.

A large amount of trap states exist in the oxide thin film having a poor composition ratio. In particular, the existing oxygen vacancies can be induced into positively charged oxygen pores and electrons as follows.

^{_{ZrO 2-X Vo ↔Vo +2 +}} 2e -

That is, the electric field applied from the outside moves electrons present in the oxide film, so that a positive charge remains in the oxide film, which causes an increase in the effective electric field in the oxide film, and a large amount of current flows even at a low electric field applied from the outside. This allows the resistance to remain low.

However, if a voltage is applied above the threshold of current, further increase of current is prevented by the high-resistance oxide film having a filament on top, and electrons are collected in the conductive insulating film, so that oxygen and positively charged oxygen pores To form neutral oxygen vacancies. In other words, the amount of the electric charge present in the oxide film is eliminated, so that the effective electric field is reduced, and the resistance of the insulating film is relatively increased under the low voltage applied from the outside.

Data retention characteristics of the ReRAM device fabricated through the present invention are shown in FIG. 4. It has been confirmed that it has 10 years of data retention characteristics that are essential for nonvolatile memory.

In addition, the schematic and the electrical characteristics of the 1Tr-1R unit device fabricated using the present invention is shown in FIG. FIG. 5A illustrates a cross-sectional structure of a 1T-1R ReRAM device, and FIG. 5B illustrates On / Off characteristics of a 1T-1R device. It can be used as a memory device by showing a significant change in the drain current of the MOSFET due to the change in resistance.

The ReRAM device fabricated from the multilayer oxide thin film implemented in the present invention not only has the essential ten-year data retention characteristic of the nonvolatile memory by inducing a negative differential resistance (NDR) effect, but also the electrical characteristics of the device are changed by resistance change. Due to the significant change in the drain current of the MOSFET can be provided to a good memory device.

Claims (12)

delete delete delete delete Reducing a supply amount of oxygen as a reactant to form a first layer composed of a metal oxide having a composition which lacks oxygen stoichiometrically; And oxidizing the metal oxide of the first layer in an oxygen atmosphere to form a second layer comprising a metal oxide satisfying the stoichiometry. delete 6. The oxide film according to claim 5, wherein in forming the oxide thin film of the first layer, the amount of oxygen is deposited at a thickness of 50 to 100 nm at a mixture ratio of argon and oxygen of 30: 1 at 400 to 500 占 폚. Manufacturing method of nonvolatile memory device using resistance change The method of claim 5, wherein in forming the oxide thin film of the second layer, the oxide film is oxidized at a low temperature of 200 to 300 DEG C in an oxygen atmosphere and deposited on the surface at a thickness of 10 to 30 nm. Manufacturing method of volatile memory device The method of claim 5, wherein in forming the oxide thin film of the second layer, a mixture of argon and oxygen in the deposition process is adjusted to 4: 1 to deposit a thin film of about 10 to 30 nm having a high resistance to match the composition ratio. Method for manufacturing nonvolatile memory device using change in resistance of oxide film The oxide thin film material of claim 5, wherein the oxide thin film material is ZrO _x , NiO _x , HfO _x , TiO _x , Ta ₂ O _x , Al ₂ O _x , La ₂ O _x , Nb ₂ O _x , SrTiO _x , Cr-doped SrTiO _x , Or Cr-doped SrZrO _x is a method of manufacturing a nonvolatile memory device using a change in resistance of the oxide film, characterized in that In the above thin film material, x is 1.5 to 1.9. delete delete

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