Resistive RAM and method of manufacturing the same

A resistive RAM and a method of manufacturing the same are provided. The resistive RAM includes a first electrode, a second electrode, a transition metal oxide (TMO) layer between the first and second electrodes, an activated metal layer between the first electrode and the TMO layer, and a metal oxynitride layer formed on a surface of the activated metal layer in the gas environment containing oxygen and nitrogen elements.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

This invention relates to a technique for a resistive RAM (RRAM), and more particularly to a RRAM and a method of manufacturing the same.

2. Description of Related Art

In general, an RRAM includes a transition metal oxide (TMO), a top electrode (TE) and a bottom electrode (BE), and is connected to the outside via a top wire and a bottom wire. The RRAM switches a resistance state from 0 to 1 or from 1 to 0 by means of an external operating voltage/current. Since the conductive path is controlled by means of oxygen vacancies under a low resistance state (LRS), once oxygen ions diffuse into a TMO layer due to high temperature, the oxygen vacancies inside the conductive path would be reduced, so that operation of the RRAM becomes unstable.

Therefore, there have been a variety of techniques for reducing diffusion of the oxygen ions into the TMO, such as increasing a Set power, which, however, affects the yield for Reset. Moreover, there is a technique of using an oxide layer to block the diffusion of the oxygen ions, but it may impact on the conductivity of the memory as a whole.

Among various RRAMs, an RRAM having hafnium oxide as the TMO layer receives much attention due to excellent durability and high switching speed. However, it is often hard to retain a Ti/HfO2RRAM currently employed in LRS in high temperature, leading to deterioration in the so-called “high-temperature data retention” (HTDR). Thus, there is necessity for research and improvement in the RRAM.

SUMMARY OF THE INVENTION

An RRAM is provided to improve data retention and to enhance conductivity.

A method of manufacturing the RRAM is also provided, which manufactures a memory having a good yield for data retention and a low operating voltage.

One of exemplary embodiments comprises an RRAM including a first electrode, a second electrode, a TMO layer between the first and second electrodes, an activated metal layer between the first electrode and the TMO layer, and a metal oxynitride layer formed on a surface of the activated metal layer in the gas environment containing oxygen and nitrogen elements.

Another of exemplary embodiments comprises a method of manufacturing the RRAM. The method includes forming a first electrode, forming a TMO layer on the first electrode, forming a second electrode on the TMO layer, forming an activated metal layer, and forming a metal oxynitride layer on a surface of the activated metal layer in the gas environment containing oxygen and nitrogen elements.

DESCRIPTION OF EMBODIMENTS

The concept of the invention may be more sufficiently understood with reference to the drawings that show the embodiments of the invention. However, the invention may be realized in many different fours and should not be explained to be limited to the embodiments described below. In fact, the embodiments provided below serve merely to elaborate the invention more completely and in detail, and to fully convey the scope of the invention to persons having ordinary skills in the art.

In the drawings, the size and relative size of each layer and area may be illustrated in exaggeration for the sake of clarity.

FIGS. 1A,1B,1C,1D and1E are respectively cross-sectional schematic views of five RRAMs according to an embodiment of the invention.

Referring toFIG. 1A, an RRAM100includes a second electrode serving as a bottom electrode (BE)102, a first electrode serving as a top electrode (TE)104, and a transition metal oxide (TMO) layer106between the first and second electrodes104and102. The TE104(first electrode) and the BE102(second electrode) may respectively be a layer made of materials such as Ti, Ta, TiN, TaN or the like, while a material of the TMO layer106may be HfOxor other adequate metal oxides. Thicknesses of the TE and BE104and102are respectively, for example but not limited to, 10 nm to 100 nm. On the other hand, the thickness of the TMO layer106is, for example but not limited to, 3 nm to 11 nm.

InFIG. 1A, the RRAM100further includes an activated metal layer107and a metal oxynitride layer108, wherein the activated metal layer107is between the TE104(first electrode) and the TMO layer106, while the metal oxynitride layer108is formed on a surface107aof the activated metal layer107in the gas environment containing oxygen and nitrogen elements for blocking oxygen ions in the activated metal layer107from diffusing to the TE104(first electrode). In this embodiment, the material of the activated metal layer107is, for example, Ti, Ta, W, Hf, Ni, Al, V, Co, Zr or Si; the thickness of the activated metal layer107is between about 5 nm to 45 nm; the material is preferably Ti or Ta. Because this metal oxynitride layer108is not formed by deposition, a thinner film layer can be obtained than a traditional deposition process such as sputtering and so on. For example, a thickness “t” of the metal oxynitride layer108is between about 1 nm to 20 nm. A ratio of oxygen to total atoms in the metal oxynitride layer108is between about 10% and 60%, while a ratio of nitrogen to the total atoms is between about 15% and 60%, for instance.

Next, referring toFIG. 1B, an RRAM110as shown herein takes the BE102as the first electrode and the TE104as the second electrode. Furthermore, in the condition that the material of the BE102(first electrode) is identical with the material of the activated metal layer, the metal oxynitride layer108may be formed on a surface102aof the BE102. That is, the BE102inFIG. 1Bmay be deemed as both the first electrode and the activated metal layer, and therefore the activated metal layer is not shown in the figure. In the RRAM110, the metal oxynitride layer108is used to block diffusion of oxygen ions in the TMO layer106to the BE102(first electrode). For parameters such as materials and thicknesses of other film layers, please also refer toFIG. 1A.

The features ofFIGS. 1A and 1Bare combined in an RRAM120ofFIG. 1C. That is, a metal oxynitride layer122is disposed between the TE104and the TMO layer106, and a metal oxynitride layer124is also disposed between the BE102and the TMO layer106. Herein, the metal oxynitride layer122is formed on a surface126aof an activated metal layer126in the gas environment containing oxygen and nitrogen elements, and the metal oxynitride layer124is also formed on the surface102aof the BE102made of an identical material with the activated metal layer in the gas environment containing oxygen and nitrogen elements. Therefore, the TMO layer106of the RRAM120is protected by the metal oxynitride layers122and124thereon and thereunder and has a more preferable effect thanFIGS. 1A and 1Bwith respect to HTDR in LRS.

As regards an RRAM130ofFIG. 1D, similar to the structure inFIG. 1B, the RRAM130has a metal oxynitride layer132formed on the surface102aof the BE102in the gas environment containing oxygen and nitrogen elements. But the difference lies in that a first buffer layer134is disposed between the TMO layer106and the metal oxynitride layer132. The material of the first buffer layer134may be identical with the material of the BE102, so that the TMO layer106obtains more preferable electric and thermal conductive characteristics upon deposition.

The features ofFIGS. 1A and 1Dare combined in an RRAM140ofFIG. 1E. That is, a metal oxynitride layer142is disposed between the TE104and the TMO layer106, and a metal oxynitride layer144is also disposed between the BE102and the TMO layer106. Furthermore, a first buffer layer148is disposed between the TMO layer106and the metal oxynitride layer144. Since the metal oxynitride layer142is formed on a surface146aof an activated metal layer146in the gas environment containing oxygen and nitrogen elements, and the metal oxynitride layer144is also formed on the surface102aof the BE102in the gas environment containing oxygen and nitrogen elements, data retention of the RRAM140is excellent.

The metal oxynitride layers in the above drawings are all formed in the gas environment containing oxygen and nitrogen elements. Therefore, to elaborate the manufacturing process of the metal oxynitride layer concisely, the embodiment below merely takes the structure ofFIG. 1Afor example, and the embodiment may be applied to manufacturing the structures ofFIGS. 1B to 1E.

FIGS. 2A to 2Care cross-sectional views illustrating a process of manufacturing an RRAM according to another embodiment of the invention.

Referring toFIG. 2A, after forming a first electrode200and a TMO layer202in sequence, an activated metal layer204is formed. The first electrode200is a material layer of Ti, Ta, TiN, TaN, or the like, while the material of the TMO layer202is HfOx or other adequate metal oxide. The material of the activated metal layer204is, for example, Ti, Ta, W, Hf, Ni, Al, V, Co, Zr or Si; the material is preferably Ti or Ta.

Referring toFIG. 2Bthen, a metal oxynitride layer208is formed on a surface204aof the activated metal layer204in an environment of gas206containing oxygen and nitrogen elements. In this embodiment, the gas206is, for example, at least one selected from the group consisting of N2O, NO2, NO, N2O2, N2/O2, N2/O3, N2, NH3, O2, H2O, H2O2and O3, wherein the slash “/” means containing both gases. For instance, one single gas206containing oxygen and nitrogen elements may be used to form the metal oxynitride layer208, or different gases206may be inputted simultaneously, such as oxygen (O2) and nitrogen (N2), but it is not limited thereto. Different gases206may also be inputted in sequence. The process of inputting the gas206may be with or without plasma. Due to the plasma, a reaction time may be shortened or a thicker metal oxynitride layer may be formed.

Next, referring toFIG. 2C, a second electrode210is formed on the metal oxynitride layer208, so that an RRAM as inFIG. 1Ais obtained.

To manufacture the RRAM ofFIG. 1B, an activated metal layer needs to be formed after the step of forming the first electrode (200). Furthermore, when the first electrode and the activated metal layer are made of the same material, the two layers may be deemed as one layer of the same material, and the step as in the aboveFIG. 2Bis performed to form a metal oxynitride layer. Subsequent steps are available in the prior art and are not repeated herein.

To manufacture the RRAM ofFIG. 1D, a first buffer layer is formed on the metal oxynitride layer after framing a metal oxynitride layer. Other steps are available in the above techniques and are not repeated herein.

However, the method of the invention is not limited to above steps. Before foaming the metal oxynitride layer, a second buffer layer300may be formed on a surface204aof an activated metal layer204, as shown inFIG. 3. Then, a metal oxynitride layer302is formed in a gas206environment containing oxygen and nitrogen elements. Therefore, the second buffer layer300is disposed on the surface204aand contacts the metal oxynitride layer302directly. The second buffer layer300is, for example, an extra-thin TiN layer, TiOxlayer (x<2), TiNxOylayer (x and y are not 0 and x+y<2) manufactured by sputtering deposition, etc. The second buffer layer300may mitigate a reaction rate of the metal oxynitride layer302.

Several experiments are provided below to verify the effects of the invention, but the experiments do not serve to limit the scope of the invention.

Experiment Example 1

An RRAM as inFIG. 1Ais manufactured, wherein a metal oxynitride layer is made of titanium oxynitride, and the titanium oxynitride layer is formed by activating metallic Ti under 300° C. for 5 minutes in the gas environment containing oxygen and nitrogen elements and has a thickness of 5 nm.

Comparative Example 1

An RRAM as in the Experiment Example 1 is manufactured, but the metal oxynitride layer is omitted.

Comparative Example 2

An RRAM as in the Experiment Example 1 is manufactured, wherein the metal oxynitride layer is replaced with an aluminum oxide layer having a thickness of about 1.5 nm.

Result 1: Data Retention

After high-temperature thermal treatment (i.e. baking), a yield of data retention is measured, and the results are shown inFIGS. 4 and 5.

It is learned fromFIG. 4that the yield of data retention in the Experiment Example 1 of the invention is obviously higher than that in the Comparative Example 1.

It is learned fromFIG. 5that the yield of original data retention in the Experiment Example 1 of the invention is obviously higher than that in the Comparative Example 2.

Result 2: standard deviation percentages of current in high resistance state (HRS), wherein a lower standard deviation percentage means less noise during high-temperature reading.

After high-temperature thermal treatment (i.e. baking), the current in HRS is measured for 21 times, and the results are shown in terms of standard deviation percentages inFIG. 6.

It is learned fromFIG. 6that the standard deviation percentages of the current in HRS in the Experiment Example 1 of the invention is obviously lower than the Comparative Examples 1 and 2.

In view of the above, by means of the metal oxynitride layer formed on the surface of the activated metal layer, not only the diffusion of the oxygen ions in the activated metal layer to the electrode is blocked, which thereby enhances data retention, but the impact on electric conduction of the memory is also reduced by means of the extra-thin metal oxynitride layer.