Patent Publication Number: US-2023136097-A1

Title: ReRAM Device and Method for Manufacturing the Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority to Chinese Patent Application No. 202111292129.0, filed on Nov. 3, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present application relates to a semiconductor technology, in particular to a Resistive RAM (ReRAM) device and a method for manufacturing the same. 
     BACKGROUND 
     Flash memory has been widely used as the best choice for nonvolatile memory applications because of its advantages of high density, low price, and electrical programmability and erasability. At present, flash memory cells are mainly at 65 nm technology node. With the requirement for high-capacity flash memories, the number of chips on each silicon chip will be reduced by using the existing technology node. At the same time, the floating gate based flash memory cell (NOR flash) will encounter problems in continuous reduction, including balance between the hot electron effect for programming in the channel direction and the leakage of subsequent cells, the voltage and current instability caused by the active region with smaller width, and the subsequent tolerance for data retention and endurance, which have a serious influence. With the development of technology, many alternatives have followed, including Resistive Random Access Memory (ReRAM) based on the change of resistance due to film properties, Magnetoresistive Random Access Memory (MRAM) based on the change of magnetoresistance, Ferroelectric Random Access Memory (FeRAM) based on ferroelectricity, and Parameter Random Access Memory (PRAM) based on the change of polymer properties, all of which are actively researched and developed to replace the position of floating gate in the existing node. Among these technologies, ReRAM based on the change of resistance due to film properties is the most promising structure, which has the advantages of low power consumption, fast writing speed and good endurance. 
     A simple ReRAM device, as illustrated in  FIG.  1   , is a Metal-Insulator-Metal (MIM) structure formed by sandwiching a resistance switching layer capable of realizing resistance switching between a top electrode and a bottom electrode. This MIM structure cell can realize the reversible switching between at least two different resistance states after applying certain voltage, namely, High Resistance State (HRS) and Low Resistance State (LRS). When the voltage is applied for the first time, due to the existence of the dielectric layer, the initial state is HRS. When the voltage is scanned to a certain condition, the resistance of the dielectric layer switches from FIRS to LRS. This process is called forming. Forming process is the process that the resistance of the device changes for the first time. When the voltage is applied again, the resistance of the dielectric layer returns to FIRS again from LRS, which is called reset. The subsequent resistance switching from FIRS to LRS is called set. The set process implements the writing function of data (from ‘0’ to ‘1’), and the reset process implements the clearing function of data (from ‘1’ to ‘0’), thus completing the basic function of storage. 
     Tantalum oxide thin films have attracted extensive attention due to their excellent endurance. The good endurance of tantalum oxide is due to its two stable states, TaO 2  (more conductive) and Ta 2 O 5  (more insulative). The data retention capability of the ReRAM device refers to whether the resistance of the resistance state can remain unchanged after the resistance of the device changes, which represents the length of the service life of the device. 
     A memory array structure consisting of ReRAM devices is as illustrated in  FIG.  2   . A memory cell structure consisting of a ReRAM device is as illustrated in  FIG.  3   . One component is a transistor and the other is a ReRAM device, which form a 1T1R structure. A gate of the transistor is used to connect a word line WL, a source is used to connect a source line SL, a drain is connected to the bottom electrode of the ReRAM device, and the top electrode of the ReRAM device is used to connect a bit line BL. 
     The resistance of the ReRAM device is operated by the current of the transistor. The principle of its resistance change is as illustrated in  FIG.  4   . The resistance change of the ReRAM is mainly explained according to the conductive film channel. There are oxygen vacancies and oxygen ions affected by the electric field in the film. After first forming, there will be a Conductive Filament (CF), similar to the UV of NOR flash. In the set process, oxygen ions leave their original positions, leaving oxygen vacancies (Vo) in the film, forming a low resistance state that can allow large current to pass through. When reverse voltage is applied, these oxygen ions recombine with oxygen vacancies (Vo) to form oxygen atoms, thus forming a state of high resistance and low current, and completing resetting. For the low resistance state, oxygen vacancies in the conductive thin layer are filled with the original oxygen ions after a long time, and on the other hand, it is vulnerable to the influence of nearby free oxygen to reduce the density, so that the resistance increases and the current decreases. In order to improve the stability, the relationship between the dimension of the conductive thin layer and the data retention capability is studied. It is found that the dimension of the smaller CF has a larger number N of oxygen vacancies (Vo) under the same conductivity, which has better reliability. 
     BRIEF SUMMARY 
     The technical problem to be solved by the present application is to provide a Resistive RAM (ReRAM) device, which can maintain the stability of the central conductive filament in the low resistance state. 
     In order to solve the technical problem, the ReRAM device provided by the present application includes a first resistance switching layer  5 , a second resistance switching layer  6 , a bottom electrode  1  and a top electrode  2 ; 
     a bottom surface of the first resistance switching layer  5  is connected with the bottom electrode  1 , and a first groove is formed in a center of a top surface; 
     the second resistance switching layer  6  is formed on the first resistance switching layer  5 , a center of a bottom surface of the second resistance switching layer  6  is filled downwards into the first groove in the center of the top surface of the first resistance switching layer  5 , and a top surface of the second resistance switching layer  6  is connected with the top electrode  2 ; 
     the material of the second resistance switching layer  6  is more conductive than the material of the first resistance switching layer  5 . 
     Further, the first resistance switching layer  5  is SrTiO 3 , SrZrO 3 , NiO, TiO 2 , TaO, TaO 2 , Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O; 
     the second resistance switching layer  6  is SrTiO 3 , SrZrO 3 , NiO, TiO 2 , TaO, TaO 2 , Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O. 
     Further, a second groove is formed in a center of the top surface of the second resistance switching layer  6 ; 
     the transverse dimension of the second groove is smaller than the transverse dimension of the first groove and the second groove is located right above the first groove; 
     the top electrode  2  is filled downwards into the second groove in the center of the top surface of the second resistance switching layer  6 . 
     Further, the first resistance switching layer  5  is Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O; 
     the second resistance switching layer  6  is TaO 2  or TaO. 
     Further, the depth of the first groove is ½-⅘ of the thickness H 1  of the first resistance switching layer  5 ; 
     the thickness H 2  of the part outside the first groove of the second resistance switching layer  6  is 1-1.5 times the depth of the first groove. 
     Further, the depth of the second groove is ½-⅘ of the thickness H 2  of the second resistance switching layer. 
     Further, the transverse dimension of the second groove is ⅓-⅔ of the transverse dimension of the first groove. 
     Further, the thickness of the first resistance switching layer is 3 nm-30 nm. 
     Further, the material of a surface of the top electrode  2  in contact with the top surface of the second resistance switching layer  6  is Ag, Pt, Ta, Ti or TiN; 
     the material of a surface of the bottom electrode  1  in contact with the bottom surface of the first resistance switching layer  5  is Ag, Pt, Ta, Ti or TiN. 
     In order to solve the technical problem, the present application further provides a method for manufacturing the ReRAM device, which includes the following steps: 
     step 1: performing a metal layer process to form a metal layer  11  of a bottom electrode  1  of the ReRAM device on a wafer  9 , the wafer  9  outside a central area of the metal layer  11  of the bottom electrode  1  of the ReRAM device being covered with an isolation dielectric layer  3 ; 
     step 2: sequentially depositing a bottom electrode contact surface layer  12  and a first resistance switching layer  5  on the metal layer  11  of the bottom electrode  1  of the ReRAM device and the isolation dielectric layer  3 , a first groove being formed in the first resistance switching layer  5  right above the bottom electrode  1 ; 
     step 3: depositing a second resistance switching layer  6 ; 
     step 4: performing etching to remove the second resistance switching layer  6 , the first resistance switching layer  5  and the bottom electrode contact surface layer  12  which cover the isolation dielectric layer  3  outside the metal layer  11  of the bottom electrode  1  and an adjoining area thereof, and reserve the second resistance switching layer  6 , the first resistance switching layer  5  and the bottom electrode contact surface layer  12  which cover positions right above the metal layer  11  of the bottom electrode  1  and the adjoining area thereof; 
     step 5: depositing a top electrode contact surface layer  22 ; 
     step 6: performing etching to remove the top electrode contact surface layer  22  on outer sides of the second resistance switching layer  6 , the first resistance switching layer  5  and the bottom electrode contact surface layer  12 . 
     Further, after step  2 , the first resistance switching layer  5  in the center right above the metal layer  11  of the bottom electrode  1  is etched firstly to widen the transverse dimension of the first groove and/or deepen the depth of the first groove, and then step 3is performed. 
     Further, the isolation dielectric layer  3  is SiN; 
     the first resistance switching layer  5  is Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O; 
     the second resistance switching layer is TiO 2  or TaO; 
     the bottom electrode contact surface layer  12  is formed of Ta, Ti or TiN; 
     the top electrode contact surface layer  22  is formed of Ta, Ti or TiN. 
     In the ReRAM device provided by the present application, the second resistance switching layer is formed on the first resistance switching layer, and the center of its bottom surface extends downwards and is filled into the first groove in the center of the top surface of the first resistance switching layer; the material of the second resistance switching layer is more conductive than the material of the first resistance switching layer. Starting from the structural aspect to improve the stability of the low resistance state, by forming the “concave” first resistance switching layer, the area most likely to form the conductive filament is in the central area of the resistance switching layer, which is not vulnerable to the influence of surrounding ions. The first resistance switching layer surrounds the downwards extending part of the center of the bottom surface of the second resistance switching layer. Since the first resistance switching layer is less conductive and the thickness of the surrounding part is larger than that of the central part, the surrounding part of the first resistance switching layer is difficult to be conducted completely, but it can effectively adsorb the surrounding ions. Therefore, each set can form incompletely conducted vacancies around the conductive filament, which can continuously adsorb the surrounding ions, thus maintaining the stability of the central conductive filament in the low resistance state, and solving the problem that the conductive thin layer (resistance switching layer) of the existing ReRAM device is vulnerable to the influence of surrounding ions, which makes the low resistance state unstable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly describe the technical solution of the present application, the drawings required for the present application will be briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the present application. Those skilled in the art may obtain other drawings based on these drawings without contributing any inventive labor. 
         FIG.  1    illustrates a schematic diagram of a structure of a common ReRAM device. 
         FIG.  2    illustrates a schematic diagram of a structure of a memory array formed by ReRAM. 
         FIG.  3    illustrates a schematic diagram of a structure of a memory cell formed by a ReRAM device. 
         FIG.  4    illustrates a schematic diagram of resistance change of a common ReRAM device. 
         FIG.  5    illustrates a schematic diagram of a structure of a ReRAM device according to an embodiment of the present application. 
         FIG.  6    illustrates a schematic diagram of a structure of a ReRAM device in a low resistance state according to an embodiment of the present application. 
         FIG.  7    illustrates a schematic diagram of a metal layer of a bottom electrode formed by adopting a method for manufacturing a ReRAM according to an embodiment of the present application. 
         FIG.  8    illustrates a schematic diagram in a step of sequentially depositing a bottom electrode contact surface layer and a first resistance switching layer in a method for manufacturing a ReRAM according to an embodiment of the present application. 
         FIG.  9    illustrates a schematic diagram in a step of depositing a second resistance switching layer in a method for manufacturing a ReRAM according to an embodiment of the present application. 
         FIG.  10    illustrates a schematic diagram in a step of forming a resistance switching layer in a method for manufacturing a ReRAM according to an embodiment of the present application. 
         FIG.  11    illustrates a schematic diagram in a step of forming a top electrode contact surface layer in a method for manufacturing a ReRAM according to an embodiment of the present application. 
     
    
    
     DESCRIPTION OF REFERENCE SIGNS 
       5 —first resistance switching layer;  6 —second resistance switching layer;  1 —bottom electrode;  2 —top electrode;  3 —isolation dielectric layer;  9 —wafer;  11 —bottom electrode metal layer;  12 —bottom electrode contact surface layer;  22 —top electrode contact surface layer. 
     DETAILED DESCRIPTION 
     The technical solution of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present application, not all of them. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without contributing any inventive labor still fall within the scope of protection of the present application. 
     Embodiment 1 
     Referring to  FIG.  5    and  FIG.  6   , a Resistive RAM (ReRAM) device includes a first resistance switching layer  5 , a second resistance switching layer  6 , a bottom electrode  1  and a top electrode  2 ; 
     a bottom surface of the first resistance switching layer  5  is connected with the bottom electrode  1 , and a first groove is formed in a center of a top surface; 
     the second resistance switching layer  6  is formed on the first resistance switching layer  5 , a center of a bottom surface of the second resistance switching layer  6  is filled downwards into the first groove in the center of the top surface of the first resistance switching layer  5 , and a top surface of the second resistance switching layer  6  is connected with the top electrode  2 ; 
     the material of the second resistance switching layer  6  is more conductive than the material of the first resistance switching layer  5 . 
     Further, the first resistance switching layer  5  is SrTiO 3 , SrZrO 3 , NiO, TiO 2 , TaO, TaO 2 , Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O. 
     Further, the second resistance switching layer  6  is SrTiO 3 , SrZrO 3 , NiO, TiO 2 , TaO, TaO 2 , Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O. 
     In the ReRAM device according to embodiment 1, the second resistance switching layer is formed on the first resistance switching layer, and the center of its bottom surface extends downwards and is filled into the first groove in the center of the top surface of the first resistance switching layer; the material of the second resistance switching layer is more conductive than the material of the first resistance switching layer. Starting from the structural aspect to improve the stability of the low resistance state, by forming the “concave” first resistance switching layer, the area most likely to form the conductive filament is in the central area of the resistance switching layer, which is not vulnerable to the influence of surrounding ions. The first resistance switching layer surrounds the downwards extending part of the center of the bottom surface of the second resistance switching layer. Since the first resistance switching layer is less conductive and the thickness of the surrounding part is larger than that of the central part, the surrounding part of the first resistance switching layer is difficult to be conducted completely, but it can effectively adsorb the surrounding ions. Therefore, each set can form incompletely conducted vacancies around the conductive filament, which can continuously adsorb the surrounding ions, thus maintaining the stability of the central conductive filament in the low resistance state, and solving the problem that the conductive thin layer (resistance switching layer) of the existing ReRAM device is vulnerable to the influence of surrounding ions, which makes the low resistance state unstable. 
     Embodiment 2 
     Based on the ReRAM device according to embodiment 1, a second groove is formed in a center of the top surface of the second resistance switching layer  6 ; 
     the transverse dimension of the second groove is smaller than the transverse dimension of the first groove and the second groove is located right above the first groove; 
     the top electrode  2  is filled downwards into the second groove in the center of the top surface of the second resistance switching layer  6 . 
     In the ReRAM device according to embodiment 2, the center of the bottom surface of the second resistance switching layer  6  extends downwards and is filled into the first groove in the center of the top surface of the first resistance switching layer  5 , and the top electrode  2  is filled downwards into the second groove in the center of the top surface of the second resistance switching layer  6 . By forming the “concave” first resistance switching layer  5  and second resistance switching layer  6 , it is ensured that the area most likely to form the conductive filament is in the center of the resistance switching layer, thus avoiding the influence of surrounding ions. 
     Embodiment 3 
     Based on the ReRAM device according to embodiment 2, referring to  FIG.  5   , the first resistance switching layer  5  is Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O; 
     the second resistance switching layer  6  is TaO 2  or TaO. 
     Further, the depth of the first groove is ½-⅘ of the thickness H 1  of the first resistance switching layer  5 ; 
     the thickness H 2  of the part outside the first groove of the second resistance switching layer  6  is 1-1.5 times the depth of the first groove. 
     Further, the depth of the second groove is ½-⅘ of the thickness H 2  of the second resistance switching layer. 
     Further, the transverse dimension of the second groove is ⅓-⅔ of the transverse dimension of the first groove. 
     Further, the thickness of the first resistance switching layer is 3 nm-30 nm. 
     Further, the material of a surface of the top electrode  2  in contact with the top surface of the second resistance switching layer  6  is Ag, Pt, Ta, Ti or TiN; 
     the material of a surface of the bottom electrode  1  in contact with the bottom surface of the first resistance switching layer  5  is Ag, Pt, Ta, Ti or TiN. 
     In the ReRAM device according to embodiment 3, the first resistance switching layer  5  surrounds the downwards extending part of the center of the bottom surface of the second resistance switching layer  6 . Since the first resistance switching layer  5  is less conductive and the thickness of the surrounding part is larger than that of the central part, the surrounding part of the first resistance switching layer  5  is difficult to be conducted completely, but it can effectively adsorb the surrounding ions. Therefore, referring to  FIG.  6   , each set can form incompletely conducted vacancies around the conductive filament, which can continuously adsorb the surrounding ions, thus maintaining the stability of the central conductive filament in the low resistance state, and solving the problem that the conductive thin layer of the existing ReRAM device is vulnerable to the influence of surrounding ions, which makes the low resistance state unstable. 
     Embodiment 4 
     A method for manufacturing the ReRAM device according to any one of embodiments 1-3 includes the following steps: 
     step 1: performing a metal layer process to form a metal layer  11  of a bottom electrode  1  of the ReRAM device on a wafer  9 , the wafer  9  outside a central area of the metal layer  11  of the bottom electrode  1  of the ReRAM device being covered with an isolation dielectric layer  3 , as illustrated in  FIG.  7   ; 
     step 2: sequentially depositing a bottom electrode contact surface layer  12  and a first resistance switching layer  5  on the metal layer  11  of the bottom electrode  1  of the ReRAM device and the isolation dielectric layer  3 , a first groove being formed in the first resistance switching layer  5  right above the bottom electrode  1 , as illustrated in  FIG.  8   ; 
     step 3: depositing a second resistance switching layer  6 , as illustrated in  FIG.  9   ; 
     step 4: performing etching to remove the second resistance switching layer  6 , the first resistance switching layer  5  and the bottom electrode contact surface layer  12  which cover the isolation dielectric layer  3  outside the metal layer  11  of the bottom electrode  1  and an adjoining area thereof, and reserve the second resistance switching layer  6 , the first resistance switching layer  5  and the bottom electrode contact surface layer  12  which cover positions right above the metal layer  11  of the bottom electrode  1  and the adjoining area thereof, as illustrated in  FIG.  10   ; 
     step 5: depositing a top electrode contact surface layer  22 ; 
     step 6: performing etching to remove the top electrode contact surface layer  22  on outer sides of the second resistance switching layer  6 , the first resistance switching layer  5  and the bottom electrode contact surface layer  12 , as illustrated in  FIG.  11   . 
     Further, after step 2, the first resistance switching layer  5  in the center right above the metal layer  11  of the bottom electrode  1  is etched firstly to widen the transverse dimension of the first groove and/or deepen the depth of the first groove, and then step 3 is performed. 
     Further, the isolation dielectric layer  3  is SiN. 
     Further, the first resistance switching layer  5  is Ta 2 O 6 , Ta 2 O 5 , Ta 2 O 4 , Ta 2 O 3 , Ta 2 O 2  or Ta 2 O; 
     the second resistance switching layer is TiO 2  or TaO. 
     Further, the bottom electrode contact surface layer  12  is formed of Ta, Ti or TiN; 
     the top electrode contact surface layer  22  is formed of Ta, Ti or TiN. 
     What are described above are only preferred embodiments of the present application, which, however, are not used to limit the present application. Any modification, equivalent replacement, improvement and the like made within the essence and principle of the present application shall be included in the scope of protection of the present application.