Patent Publication Number: US-2022216401-A1

Title: Resistive random access memory and method of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 110100451, filed on Jan. 6, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to a memory and a method of fabricating the same, and in particular to a resistive random access memory (RRAIVI) and a method of fabricating the same. 
     Description of Related Art 
     A resistive random access memory (RRAIVI) has advantages of fast operational speed, low power consumption, etc., so it has become a non-volatile memory that has been widely studied in recent years. A positive voltage is applied to the RRAM when it is performing a SET operation. Oxygen ions in a variable resistance layer will enter an oxygen exchange layer after being attracted by the positive voltage to leave the variable resistance layer. The variable resistance layer generates oxygen vacancies, forms filaments, and presents a conductive state. At this time, the variable resistance layer converts from a high resistance state (HRS) to a low resistance state (LRS). A negative bias voltage is applied to the RRAM when a RRAM unit  10  performs a RESET operation, and the oxygen ions in the oxygen exchange layer return to the variable resistance layer, causing the filaments to break and presenting a non-conductive state. At this time, the variable resistance layer converts from LRS to HRS. However, when the oxygen vacancies generated in the variable resistance layer are insufficient, a current in the low resistance state (LRS) will be insufficient too. In addition, some of the filaments in the variable resistance layer are likely to be damaged in the subsequent baking process, causing the resistive random access memory to have insufficient current during operation. Applying a higher operating voltage to the resistive random access memory may drive more oxygen vacancies, but it will cause greater power consumption. 
     SUMMARY 
     This disclosure provides a resistive random access memory and a method of fabricating the same, which may enable the resistive random access memory to have sufficient current and prevent an excessively large operating voltage being used, so as to reduce power consumption. 
     An embodiment of the disclosure provides a resistive random access memory including a first electrode layer and a second electrode layer disposed opposite to each other, a variable resistance layer located between the first electrode layer and the second electrode layer, an oxygen exchange layer located between the variable resistance layer and the second electrode layer, a vacancy-supplying layer surrounding a middle sidewall of the oxygen exchange layer, and a vacancy-driving electrode layer located on the vacancy-supply layer and surrounding an upper sidewall of the oxygen exchange layer. 
     An embodiment of the disclosure also provides a method of fabricating a resistive random access memory, which includes the following steps. A variable resistance layer is formed on the first electrode layer. A vacancy-supply layer is formed on the variable resistance layer. A vacancy-driving electrode layer is formed on the vacancy-supply layer. A first opening is formed in the vacancy-driving electrode layer. A first oxygen barrier layer is formed in the first opening. A second opening is formed in the first oxygen barrier layer and the vacancy-supply layer. An oxygen exchange layer is formed in the second opening. A second oxygen barrier layer is formed on the vacancy-driving electrode layer and the oxygen exchange layer. And, a second electrode layer is formed on the second oxygen barrier layer. 
     Based on the above, the disclosure provides a resistive random access memory and a method of fabricating the same. Oxygen vacancies may be increased by the disposition of the vacancy-driving electrode layer and the vacancy-supply layer, to enable the resistive random access memory to have sufficient current and prevent an excessively large operating voltage being used, so as to reduce power consumption. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1G  are schematic cross-sectional views of a fabrication process of a resistive random access memory according to an embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     With reference to  FIG. 1G  a resistive random access memory (RRAM) unit  10  includes a first electrode  102 , a variable resistance layer  104 , a second electrode  120 , a vacancy-barrier layer  106 , a vacancy-supply layer  108 , and a vacancy-driving electrode layer  110 , an oxygen exchange layer  116   a,  a first oxygen barrier layer  114   a,  and a second oxygen barrier layer  118 . 
     The first electrode  102  may be connected to a conductive feature below, such as a via plug  100 . The via plug  100  is, for example, any via plug in a dielectric layer  99  of the metal interconnection structure formed on the substrate. The via plug  100  is, for example, a via plug of a same height as a first layer via plug in contact with a first metal layer closest to the substrate. 
     The first electrode layer  102  and the second electrode  120  are disposed correspondingly. Materials of the first electrode layer  102  and the second electrode  120  may include metal, metal nitride, other materials, or a combination thereof. The materials of the first electrode layer  102  and the second electrode  120  are, for example, titanium nitride (TiN), tantalum nitride (TaN), titanium aluminum nitride (TiAlN), titanium tungsten (TiW) alloy, platinum (Pt), iridium (Ir), ruthenium (Ru), titanium (Ti), tungsten (W), tantalum (Ta), aluminum (Al), zirconium (Zr), hafnium (Hf), nickel (Ni), copper (Cu), cobalt (Co), iron (Fe), gamma (Gd), manganese (Mo), graphite, or a combination thereof. The first electrode layer  102  and the second electrode  120  may be a single layer or multiple layers. Thicknesses of the first electrode layer  102  and the second electrode  120  are not specifically limited, but is usually between 5 nanometers (nm) and 500 nm. 
     The variable resistance layer  104  is located between the first electrode layer  102  and the second electrode  120 . The variable resistance layer  104  may have the following characteristics. Oxygen ions are attracted by a positive voltage away from the variable resistance layer  104  to generate oxygen vacancies, form filaments, and present a conductive state when the positive voltage is applied to the resistive random access memory. At this time, the variable resistance layer  104  converts from a high resistance state (HRS) to a low resistance state (LRS). The oxygen ions enter the variable resistance layer  104 , causing the filaments to break and presenting a non-conductive state when a negative bias is applied to the resistive random access memory. At this time, the variable resistance layer  104  converts from LRS to HRS. In general, the conversion of the variable resistance layer  104  from FIRS to LRS is called a set (hereinafter referred to as SET) operation and the conversion of the variable resistance layer  104  from LRS to FIRS is called a reset (hereinafter referred to as RESET) operation. A material of the variable resistance layer  104  is not specifically limited, and any material that may change its own resistance through application of a voltage may be used, the material of the variable resistance layer  104  includes metal oxides, such as hafnium oxide (HfO 2 ), tantalum oxide (Ta 2 O 5 ), titanium oxide (TiO 2 ), magnesium oxide (MgO), nickel oxide (NiO), niobium oxide (Nb 2 O 5 ), aluminum oxide (Al 2 O 3 ), vanadium oxide (V 2 O 5 ), tungsten oxide (WO 3 ), zinc oxide (ZnO), or cobalt oxide (CoO), oxygen content of the variable resistance layer  104  may be about 75 atomic percent (at %) to about 100 atomic percent. A thickness of the variable resistance layer  104  is, for example, 2 nm to 10 nm. 
     The oxygen exchange layer  116   a  is located between the variable resistance layer  104  and the second electrode  120 . A top surface area of the oxygen exchange layer  116   a  is less than a surface bottom area of the second electrode  120 , and a surface bottom area of the oxygen exchange layer  116   a  is less than a top surface area of the variable resistance layer  104 . The oxygen exchange layer  116   a  may be formed from a material likely to bond with oxygen than the vacancy-driving electrode layer  110  and the variable resistance layer  104 . The material of the oxygen exchange layer  116   a  may include an incompletely oxidized metal oxide. In other words, the oxygen exchange layer  116   a  may be a metal layer containing oxygen ions, the material of the oxygen exchange layer  116   a  may include TiO 2-x , HfO 2-x , or TaO 2-x , where x is 0.2 to 0.7. 
     The first oxygen barrier layer  114   a  and the second oxygen barrier layer  118  surround the top surface and an upper sidewall of the oxygen exchange layer  116   a.  The first oxygen barrier layer  114   a  laterally surrounds the upper sidewall of the oxygen exchange layer  116   a,  and is located between the second oxygen barrier layer  118  and the vacancy-supply layer  108 , and between the upper sidewall of the oxygen exchange layer  116   a  and the vacancy-driving electrode layer  110 . The second oxygen barrier layer  118  covers the top surface of the oxygen exchange layer  116   a,  a top surface of the first oxygen barrier layer  114   a,  and a top surface of the vacancy-driving electrode layer  110 , the first oxygen barrier layer  114   a  and the second oxygen barrier layer  118  may block oxygen ions in the oxygen exchange layer  116   a  from diffusing to the second electrode  120  and the vacancy-driving electrode layer  110  when the RRAM unit  10  is performing the RESET operation. The first oxygen barrier layer  114   a  and the second oxygen barrier layer  118  may include a dielectric material layer with a high dielectric constant greater than 3, such as aluminum oxide (Al 2 O 3 ), hafnium oxide (HfO 2 ), or zirconium oxide (ZrO 2 ), or a combination thereof. 
     The vacancy-supply layer  108  laterally surrounds a middle sidewall of the oxygen exchange layer  116   a,  which may provide vacancies to the oxygen exchange layer  116   a.  A material of the vacancy-supply layer  108  may include an incompletely oxidized metal oxide. In other words, the vacancy-supply layer  108  may be a metal layer containing oxygen ions. The material of the vacancy-supply layer  108  may include TiO x , TaO x , HfO x , Ta 2 O 5-x , or TaO 2-x , where x is 0.2 to 1.8. A thickness of the vacancy-supply layer  108  is, for example, 5 nm to 50 nm. 
     The vacancy-driving electrode layer  110  is located above the vacancy-supply layer  108  and below the second electrode  120 . The vacancy-driving electrode layer  110  laterally surrounds the upper sidewall of the oxygen exchange layer  116   a,  and the first oxygen barrier layer  114   a  is sandwiched between the vacancy-driving electrode layer  110  and the upper sidewall of the oxygen exchange layer  116   a.  The vacancy-driving electrode layer  110  may drive vacancies in the vacancy-supply layer  108  below to enter the oxygen exchange layer  116   a  through the middle sidewall of the oxygen exchange layer  116   a.  The vacancy-driving electrode layer  110  is less likely to bond with oxygen as compared with the oxygen exchange layer  116   a  and the vacancy-supply layer  108 . The vacancy-driving electrode layer  110  may also be called an inert vacancy-driving electrode layer  110 . The vacancy-driving electrode layer  110  may be a single layer or multiple layers. The vacancy-driving electrode layer  110  includes a conductive material. The conductive material may be a metal or a metal nitride, such as platinum, iridium, ruthenium, rhodium, tungsten, titanium, hafnium, tantalum, hafnium nitride, tantalum nitride, titanium nitride, tungsten nitride, or a combination thereof, the top surface of the vacancy-driving electrode layer  110  is coplanar with the top surface of the first oxygen barrier layer  114   a  and the top surface of the oxygen exchange layer  116   a.  A bottom surface of the vacancy-driving electrode layer  110  is coplanar with a bottom surface of the first oxygen barrier layer  114   a.  A thickness of the vacancy-driving electrode layer  110  is, for example, 10 nm to 100 nm. 
     The vacancy-barrier layer  106  is located below the vacancy-supply layer  108  and above the variable resistance layer  104 , and laterally surrounds a lower sidewall of the oxygen exchange layer  116   a.  The vacancy-barrier layer  106  may prevent the vacancies in the vacancy-supply layer  108  from diffusing downward, and limit a path of the vacancies in the vacancy-supply layer  108 . The path of the vacancies of the vacancy-supply layer  108  is to enter the oxygen exchange layer  116   a  through the middle sidewall of the oxygen exchange layer  116   a,  and then travel down to the variable resistance layer  104 . A material of the vacancy-barrier layer  106  includes a dielectric material. A dielectric constant of the vacancy-barrier layer  106  is greater than  4  and less than dielectric constants of the first oxygen barrier layer  114   a  and the second oxygen barrier layer  118 . The dielectric material is, for example, a dielectric material containing silicon. The silicon-containing dielectric material is, for example, silicon nitride, silicon carbide, silicon carbonitride (SiCN), silicon carbon oxynitride (SiCON), or a combination thereof. 
     A positive voltage is applied to the second electrode  120  to enable the oxygen ions in the variable resistance layer  104  to enter the oxygen exchange layer  116   a  after being attracted by the positive voltage to leave the variable resistance layer  104 , and generate oxygen vacancies in the resistance layer  104  generates to form a filament current when the RRAM unit  10  is performing a forming operation. In addition, the vacancy-driving electrode layer  110  also drives the vacancies in the vacancy-supply layer  108  below to enter the oxygen exchange layer  116   a  through the middle sidewall of the oxygen exchange layer  116   a,  and then travels down to the variable resistance layer  104  to form an additional filament current when the positive voltage is applied to the second electrode  120 . In other words, a current of the RRAM unit  10  not only comes from the vacancies formed by the oxygen ions leaving the variable resistance layer  104 , but also from the vacancies in the vacancy-supply layer  108 . Therefore, the RRAM unit  10  has sufficient current. 
     With reference to  FIGS. 1A to 1G  a method of fabricating the RRAM unit  10  is described as follows. 
     With reference to  FIG. 1A , the first electrode layer  102 , the variable resistance layer  104 , the vacancy-barrier layer  106 , the vacancy-supply layer  108 , and the vacancy-driving electrode layer  110  are sequentially formed on a substrate (not shown) on which the via plug  100  and the dielectric layer  99  have been formed. 
     With reference to  FIG. 1B , photolithography and an etching process is performed to pattern the vacancy-driving electrode layer  110 , and then an opening  112  is formed in the vacancy-driving electrode layer  110 . A bottom surface of the opening  112  exposes the vacancy-supply layer  108 . 
     With reference to  FIG. 1C , the first oxygen barrier layer  114  is formed in the opening  112 . A formation method of the first oxygen barrier layer  114  is, for example, forming a first oxygen barrier material layer on the vacancy-driving electrode layer  110  and in the opening  112 , and then performing a planarization process to remove the first oxygen barrier material layer except for the first oxygen barrier material layer in the opening  112 . 
     With reference to  FIG. 1D , an opening  115  is formed in the first oxygen barrier layer  114 , the vacancy-supply layer  108 , and the vacancy-barrier layer  106 , and a first oxygen barrier layer  114   a  is left behind on an upper sidewall of the opening  115 . The opening  115  may be formed by photolithography and etching, so as to pattern the first oxygen barrier layer  114 , the vacancy-supply layer  108 , and the vacancy-barrier layer  106 . The opening  115  may also be formed by the following method. An anisotropic etching process is performed on the first oxygen barrier layer  114  to form an oxygen barrier spacing wall, that is, the first oxygen barrier layer  114   a.  Afterwards, an etching process is performed by using the oxygen barrier spacing wall (the first oxygen barrier layer  114   a ) and the vacancy-driving electrode layer  110  as a hard mask, so as to remove a portion of the vacancy-supply layer  108  and a portion of the vacancy-barrier layer  10  to form the opening  115 . 
     With reference to  FIGS. 1E and 1F , the oxygen exchange layer  116  is formed on the vacancy-driving electrode layer  110  and the first oxygen barrier layer  114   a,  and in the opening  115 . Then, a planarization process is performed to remove the oxygen exchange layer  116  except for the oxygen exchange layer  116  in the opening  115 , leaving behind the oxygen exchange layer  116  in the opening  115 , and exposing the vacancy-driving electrode layer  110  and the first oxygen barrier layer  114   a.    
     With reference to  FIG. 1G  the second oxygen barrier layer  118  and the second electrode layer  120  are formed on the vacancy-driving electrode layer  110  and the first oxygen barrier layer  114   a.  Afterwards, the second electrode layer  120 , the second oxygen barrier layer  118 , the vacancy-driving electrode layer  110 , the vacancy-supply layer  108 , the vacancy-barrier layer  106 , the variable resistance layer  104 , and the first electrode layer  102  are patterned to form the resistive random access memory unit  10 . 
     In the resistive random access memory and the method of fabricating the same according to the embodiment of the disclosure, the vacancies of the variable resistance layer may be increased by the disposition of the vacancy-driving electrode layer and the vacancy-supply layer, thereby increasing the current of the resistive random access memory and prevent an excessively large operating voltage being used, so as to reduce power consumption. In addition, since the resistive random access memory has a high current in the initial stage, even if some of the filaments are damaged in the subsequent baking process, the resistive random access memory can still have enough current during operation. 
     Although the disclosure has been disclosed with the foregoing exemplary embodiments, they are not intended to limit the disclosure. Any person skilled in the art can make various changes and modifications within the spirit and scope of the disclosure. Accordingly, the scope of the disclosure is defined by the claims appended hereto and their equivalents.