Patent Publication Number: US-2022216160-A1

Title: Semiconductor structure and formation method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/CN2021/108908, filed on Jul. 28, 2021, which is based on and claims priority to Chinese Patent Application No. 202110003498.7, filed on Jan. 4, 2021. The entire contents of International Patent Application No. PCT/CN2021/108908 and Chinese Patent Application No. 202110003498.7 are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present application relate to the field of semiconductors, and in particular, to a semiconductor structure and a formation method thereof. 
     BACKGROUND 
     A Dynamic random access memory (DRAM) is a semiconductor memory widely used in multi-computer systems. With the rapid development of a semiconductor integrated circuit device, requirements on a contact effect between structures of the semiconductor integrated circuit device are becoming higher and higher. 
     A metallic copper layer plays an important role in interconnection between integrated circuits. In the prior art, a barrier layer is formed on a surface of the metallic copper layer to prevent diffusion of the metallic copper layer to other regions. However, a contact effect between the metallic copper layer and the barrier layer is poor, and the metallic copper layer easily diffuses along a contact surface with the barrier layer to form an air gap or a projection in the semiconductor structure. 
     How to improve the contact effect between the metallic copper layer and the barrier layer becomes an urgent problem to be solved by those skilled in the art. 
     SUMMARY 
     The embodiments of the present application provide a semiconductor structure and a formation method thereof, which help solve the problem of the poor contact effect between the metallic copper layer and the barrier layer. 
     According to some embodiments, in a first aspect, the present application provides a method of forming a semiconductor structure, including: providing a substrate, a dielectric layer on the substrate, the dielectric layer having a trench; forming a metallic copper layer filling the trench; forming a contact layer on an upper surface of the metallic copper layer, a material of the contact layer containing cuprous ions; and forming a barrier layer on an upper surface of the contact layer, a material of the barrier layer containing a same element as the material of the contact layer. 
     According to some embodiments, in a second aspect, the present application further provides a semiconductor structure, including: a substrate, the substrate having a dielectric layer, the dielectric layer having a metallic copper layer, and the dielectric layer exposing an upper surface of the metallic copper layer; a contact layer, the contact layer being located on the upper surface of the metallic copper layer, and a material of the contact layer containing cuprous ions; and a barrier layer, the barrier layer being located on an upper surface of the contact layer, and a material of the barrier layer containing a same element as the material of the contact layer. 
     The embodiments of the present application may have the following advantages. 
     In the semiconductor structure formation method according to the first aspect of the embodiments of the present application, a contact layer is formed between a metallic copper layer and a barrier layer, a material of the contact layer contains cuprous ions, and the material of the contact layer contains same elements as a material of the barrier layer. The contact layer contains cuprous ions, which has similar chemical properties to the metallic copper layer; therefore, the contact layer formed on the upper surface of the metallic copper layer has good adhesion with the metallic copper layer, and no gap exists between the metallic copper layer and the contact layer. At the same time, since the material of the contact layer contains same elements as the material of the barrier layer, the contact layer and the barrier layer also have similar chemical properties and good adhesion therebetween. Based on the above, two opposite sides of the contact layer are closely bonded with the metallic copper layer and the barrier layer respectively, and no air gap or projection exists between the metallic copper layer and the barrier layer, which improves the contact performance of the metallic copper layer and the barrier layer. 
     In the semiconductor structure formation method according to the second aspect of the embodiments of the present application, a buffer layer is formed between a dielectric layer and a barrier layer, and an upper surface of the buffer layer is flush with an upper surface of the contact layer. The contact layer contains cuprous ions; in order to prevent contact of the two sides of the contact layer with other structures in the semiconductor structure to conduct electricity, the buffer layer is formed on the two sides of the contact layer to achieve isolation and insulation effects, which helps improve the security of the semiconductor structure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       One or more embodiments are exemplarily described by using figures that are corresponding thereto in the accompanying drawings; the exemplary descriptions do not constitute limitations on the embodiments. Elements with same reference numerals in the accompanying drawings are similar elements. Unless otherwise particularly stated, the figures in the accompanying drawings do not constitute a scale limitation. 
         FIG. 1  is a schematic structural diagram of a semiconductor structure; 
         FIG. 2  to  FIG. 11  are schematic structural diagrams corresponding to steps of a method of forming a semiconductor structure according to a first embodiment of the present application; and 
         FIG. 12  is a schematic structural diagram of a semiconductor structure according to a second embodiment of the present application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     It can be known from the Background that the contact effect between the metallic copper layer and the barrier layer in the prior art is poor. 
     Referring to  FIG. 1 , a semiconductor structure includes: a substrate  200 , a dielectric layer  201 , a metallic copper layer  203 , a barrier layer  207  and a metal layer  209 . 
     The barrier layer  207  is located on an upper surface of the dielectric layer  201  and an upper surface of the metallic copper layer  203 . Due to a poor contact effect between the metallic copper layer  203  and the barrier layer  207 , a gap exists between the metallic copper layer  203  and the barrier layer  207 . After a metal layer  209  electrically connected to the metallic copper layer  203  is formed, flow of electrons causes a physical form of the metallic copper layer  203  to become active, and the metallic copper layer  203  flows between the gaps. Portion of the metallic copper layer  203  is raised, forming an air gap  210  between the metallic copper layer  203  and the barrier layer  207 , which reduces the performance of the semiconductor structure. 
     In order to solve the above problem, in a method of forming a semiconductor structure according to an embodiment of the present application, a contact layer is formed between a metallic copper layer and a barrier layer, a material of the contact layer contains cuprous ions, and the material of the contact layer contains same elements as a material of the barrier layer, which improves a contact effect between the metallic copper layer and the barrier layer in the semiconductor structure. 
     In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, various embodiments of the present application will be described below in details with reference to the drawings. However, those of ordinary skill in the art may understand that, in the embodiments of the present application, numerous technical details are set forth in order to enable a reader to better understand the present application. However, the technical solutions claimed in the present application can be implemented without these technical details and various changes and modifications based on the embodiments below. 
       FIG. 2  to  FIG. 11  are schematic structural diagrams corresponding to steps of a method of forming a semiconductor structure according to a first embodiment of the present application. The semiconductor structure formation method according to the first embodiment of the present application is described in detail below with reference to the accompanying drawings. 
     Referring to  FIG. 2 , the semiconductor structure formation method according to the first embodiment of the present application includes: providing a substrate  100 , a dielectric layer  101  on the substrate  100 , and the dielectric layer  101  having a trench  102 . 
     The substrate  100  may be made of sapphire, silicon, silicon carbide, gallium arsenide, aluminum nitride, zinc oxide or the like. In this embodiment, the substrate  100  is made of a silicon material. 
     The dielectric layer  101  is formed on a surface of the substrate  100 . The dielectric layer  101  may be formed by a chemical vapor deposition process. In other embodiments, the dielectric layer may also be formed by an atomic layer deposition process. 
     The dielectric layer  101  may be silicon oxide or a high dielectric material. The high dielectric material is specifically a ferroelectric ceramic material, a barium titanate based material or a lead titanate based material. 
     In this embodiment, the trench  102  is formed in the dielectric layer  101 . The trench  102  may be formed by a dual damascene process, and the dual damascene process includes a via first trench last method and a via last trench first method. 
     Referring to  FIG. 3 , a metallic copper layer  103  filling the trench  102  (refer to  FIG. 2 ) is formed. The metallic copper layer  103  may be formed by a chemical vapor deposition process. In other embodiments, the metallic copper layer may also be formed by an atomic layer deposition process. 
     Referring to  FIG. 4 , a buffer layer  104  is formed on an upper surface of the dielectric layer  101  and an upper surface of the metallic copper layer  103 . 
     The buffer layer  104  is formed between the dielectric layer  101  and the barrier layer. The contact layer contains cuprous ions; in order to prevent contact of the two sides of the contact layer with other structures in the semiconductor structure to conduct electricity, the buffer layer  104  is formed on the two sides of the contact layer to achieve isolation and insulation effects, which helps improve the security of the semiconductor structure. 
     The buffer layer  104  may be formed by an atomic layer deposition process. The buffer layer  104  of a uniform thickness can be formed on the dielectric layer  101  and the metallic copper layer  103  through the atomic layer deposition process. In other embodiments, the buffer layer may also be formed by a chemical vapor deposition process. 
     The buffer layer  104  has isolation and insulation functions. The buffer layer  104  may be made of silicon nitride, silicon oxide or the like. 
     In this embodiment, the buffer layer  104  has a thickness ranging from 5 nm to 10 nm, which may specifically be 6 nm, 7 nm or 8 nm. The buffer layer  104  is required to have only isolation and insulation functions. Therefore, the formed buffer layer  104  has a smaller thickness, which helps save manufacturing costs of the semiconductor structure. 
     Referring to  FIG. 5  and  FIG. 6 , portion of the buffer layer  104  located on the upper surface of the metallic copper layer  103  is removed to expose at least the upper surface of the entire metallic copper layer  103 . 
     In this embodiment, the step of etching to remove a portion of the buffer layer  104  located on the upper surface of the metallic copper layer  103  includes the following steps. 
     A photoresist  105  is formed on portion of the buffer layer  104  located on the upper surface of the dielectric layer  101 , which may be divided into a negative photoresist and a positive photoresist according to its chemical reaction mechanism and development principle. In this embodiment, the portion of the buffer layer  104  located on the upper surface of the metallic copper layer  103  is removed using the positive photoresist. 
     An exposure and development step is performed to remove the portion of the buffer layer  104  located on the upper surface of the metallic copper layer  103 . The photoresist  105  is etched by oxygen-containing plasma, and the photoresist  105  is removed. 
     Referring to  FIG. 7  and  FIG. 8 , after the portion of the buffer layer  104  located on the upper surface of the metallic copper layer  103  is removed, a contact layer  106  is formed on the exposed upper surface of the entire metallic copper layer  103 , and the upper surface of the contact layer  106  is flush with an upper surface of a remaining portion of the buffer layer  104 . 
     In this embodiment, the step of forming a contact layer  106  involves: forming an initial contact layer by a Spin-On-Dielectric (SOD) process. In the SOD process, firstly, the substrate  100 , the dielectric layer  101  and the metallic copper layer  103  are rotated at a certain speed; at the same time, a fluid precursor is provided for the upper surface of the metallic copper layer  103 , and the precursor is subjected to a centripetal force of rotation on the upper surface of the metallic copper layer  103 , and under the centripetal force, diffuses in all directions to form a uniform initial contact layer of fluid that fills an air gap between the metallic copper layer  103  and the buffer layer  104 ; subsequently, a solid contact layer  106  is formed by sintering in an aerobic environment. 
     The initial contact layer is formed by an SOD process. Due to the centripetal force of rotation, the formed initial contact layer uniformly fills the air gap between the metallic copper layer  103  and the buffer layer  104 . 
     In other embodiments, the initial contact layer may also be formed by a Flowable Chemical Vapor Deposition (FCVD) process. 
     In this embodiment, the spin-on-dielectric process includes: the substrate  100 , the dielectric layer  101  and the metallic copper layer  103  rotating at a rate of  500  to  3000  revolutions per minute during the formation of the initial contact layer by spin-on-dielectric, which may specifically be  1000  revolutions per minute,  1500  revolutions per minute or  2000  revolutions per minute. 
     After the initial contact layer is formed, the initial contact layer is thermally treated to form the contact layer  106 . The thermal treatment involves sintering the initial contact layer in an aerobic environment to form the solid contact layer  106 . 
     In this embodiment, the thermal treatment process includes: a process temperature ranging from 70° C. to 80° C. during the thermal treatment to the initial contact layer, which may specifically be 73° C., 76° C. or 79° C.; and a process duration ranging from 10 minutes to 20 minutes, which may specifically be 13 minutes, 16 minutes or 19 minutes. 
     The material of the contact layer  106  contains cuprous ions, which may specifically be cuprous thiocyanate. The contact layer  106  contains cuprous ions, which has similar chemical properties to the metallic copper layer  103 ; therefore, the contact layer  106  formed on the upper surface of the metallic copper layer  103  has good adhesion with the metallic copper layer  103 , and no gap exists between the metallic copper layer  103  and the contact layer  106 . 
     Referring to  FIG. 7 , the formed contact layer  106  is not only on the upper surface of the metallic copper layer  103  but also on the upper surface of the buffer layer  104 , and the upper surface of the contact layer  106  is higher than an upper surface of a remaining portion of the buffer layer  104 ; in order to make the upper surface of the contact layer  106  flush with the upper surface of the remaining portion of the buffer layer  104 , Chemical Mechanical Polishing (CMP) is required to be performed on the contact layer  106 . 
     The contact layer  106  located on the upper surface of the buffer layer  104  is removed by the chemical mechanical polishing, so that the upper surface of the contact layer  106  after the chemical mechanical polishing is flush with the upper surface of buffer layer  104 , and the upper surface of the contact layer  106  after the chemical mechanical polishing is flatter. When the barrier layer is subsequently formed on the contact layer  106 , since the upper surface of the contact layer  106  is relatively flat, no gap may be generated between the contact layer  106  and the barrier layer due to the roughness of the upper surface of the contact layer  106 . 
     During the removal of portion of the contact layer  106  by the chemical mechanical polishing, a polishing time may specifically be 10 s to 50 s, such as 20 s, 30 s or 40 s. 
     The contact layer  106  is cleaned after the chemical mechanical polishing. A cleaning liquid used in the cleaning may be made of ammonia and pure water in a ratio of 4:1 to 1:1, which may specifically be 2:1. 
     The contact layer  106  formed after the chemical mechanical polishing has a thickness of 5 nm to 10 nm, which may specifically be 6 nm, 7 nm or 8 nm. 
     The contact layer  106  has a same thickness as the buffer layer  104 . The upper surface of the contact layer  106  and the upper surface of the buffer layer  104  form a uniform and flat surface, which facilitates subsequent formation of a barrier layer by deposition. Moreover, the contact layer  106  is required to only play a role of connecting the metallic copper layer  103  and the barrier layer. Therefore, the formed contact layer  106  has a smaller thickness, which helps save manufacturing costs of the semiconductor structure. 
     Referring to  FIG. 9 , a barrier layer  107  is formed on the upper surface of the contact layer  106 . 
     In this embodiment, the step of forming a barrier layer  107  includes: forming the barrier layer  107  on the upper surface of the contact layer  106  and the upper surface of the remaining portion of the buffer layer  104 . The barrier layer  107  may be formed by a chemical vapor deposition process. In other embodiments, the barrier layer may also be formed by an atomic layer deposition process. 
     In this embodiment, the material of the barrier layer  107  contains a same element as the material of the contact layer  106 . Specifically, the material of the barrier layer  107  may be silicon carbon nitride. In other embodiments, the material of the barrier layer may also be tantalum nitride and other tantalum compounds. 
     Since the material of the contact layer  106 contains a same element as the material of the barrier layer  107 , the contact layer  106  and the barrier layer  107  also have similar chemical properties and good adhesion therebetween, and no gap exists between the barrier layer  107  and the contact layer  106 . It can be obtained that two opposite sides of the contact layer  106  are closely bonded to the metallic copper layer  103  and the barrier layer  107  respectively, and no air gap or projection exists between the metallic copper layer  103  and the barrier layer  107 , which improves the contact performance of the metallic copper layer  103  and the barrier layer  107 . 
     Referring to  FIG. 10  and  FIG. 11 , subsequent to the step of forming a barrier layer  107 , the method further includes: forming a metal layer  109  passing through the barrier layer  107  and the contact layer  106 , the metal layer  109  being in contact with the upper surface of the metallic copper layer  103 . The metal layer  109  is in contact with the metallic copper layer  103 , and the two are electrically connected to form a conductive path. 
     In this embodiment, the step of forming a metal layer  109  includes: etching to remove a portion of the barrier layer  107  and portion of the contact layer  106  to expose the upper surface of portion of the metallic copper layer  103  to form a via  108 ; and forming the metal layer  109  on the exposed upper surface of the portion of the metallic copper layer  103 . 
     The via  108  may be formed by a dry etching process. The via  108  formed by the dry etching process has a more regular shape, which facilitates the subsequent formation of the metal layer with a regular shape in the via  108 . In other embodiments, the via may also be formed by a wet etching process. 
     The metal layer  109  may be formed by a chemical vapor deposition process. In other embodiments, the metal layer may also be formed by an atomic layer deposition process. 
     The metal layer  109  is made of tin, copper, aluminum, gold, silver or other materials. Gases used in the metal layer  109  formed by tungsten include silane and tungsten hexafluoride. In other embodiments, tungsten may also be prepared from diboron hexahydride and tungsten hexafluoride. 
     In the semiconductor structure formation method according to this embodiment, a contact layer is formed between a metallic copper layer and a barrier layer, a material of the contact layer contains cuprous ions, and the material of the contact layer contains a same element as a material of the barrier layer. The contact layer contains cuprous ions, which has similar chemical properties to the metallic copper layer; therefore, the contact layer formed on the upper surface of the metallic copper layer has good adhesion with the metallic copper layer, and no gap exists between the metallic copper layer and the contact layer. At the same time, since the material of the contact layer contains a same element as the material of the barrier layer, the contact layer and the barrier layer also have similar chemical properties and good adhesion therebetween. Based on the above, two opposite sides of the contact layer are closely bonded with the metallic copper layer and the barrier layer respectively, and no air gap or projection exists between the metallic copper layer and the barrier layer, which improves the contact performance of the metallic copper layer and the barrier layer. 
     A second embodiment of the present application provides a semiconductor structure. The semiconductor structure may be a semiconductor structure formed according to the semiconductor structure formation method in the first embodiment. The semiconductor structure according to the second embodiment of the present application is described in detail below with reference to the accompanying drawings. 
       FIG. 12  is a schematic structural diagram of a semiconductor structure according to a second embodiment of the present application. 
     Referring to  FIG. 12 , the semiconductor structure according to this embodiment includes: a substrate  300 , the substrate  300  having a dielectric layer  301 , the dielectric layer  301  having a metallic copper layer  303 , and the dielectric layer  301  exposing an upper surface of the metallic copper layer  303 ; a contact layer  306 , the contact layer  306  being located on the upper surface of the metallic copper layer  303 , and a material of the contact layer  306  containing cuprous ions; and a barrier layer  307 , the barrier layer  307  being located on an upper surface of the contact layer  306 , and a material of the barrier layer  307  containing a same element as the material of the contact layer  306 . 
     The substrate  300  may be made of sapphire, silicon, silicon carbide, gallium arsenide, aluminum nitride, zinc oxide or the like. In this embodiment, the substrate  300  is made of a silicon material. 
     The dielectric layer  301  may be silicon oxide or a high dielectric material. The high dielectric material is specifically a ferroelectric ceramic material, a barium titanate based material or a lead titanate based material. 
     The metallic copper layer  303  is a conductive layer and may act as a gate of the semiconductor structure. 
     The semiconductor structure according to this embodiment further includes: a buffer layer  304 , the buffer layer  304  being located between the dielectric layer  301  and the barrier layer  307 . 
     The buffer layer  304  is formed between the dielectric layer  301  and the barrier layer  307 . The contact layer  306  contains cuprous ions; in order to prevent contact of the two sides of the contact layer  306  with other structures in the semiconductor structure to conduct electricity, the buffer layer  304  is formed on the two sides of the contact layer  306  to achieve isolation and insulation effects, which helps improve the security of the semiconductor structure. 
     The buffer layer  304  may be made of silicon nitride, silicon oxide or the like. The buffer layer  304  has a thickness ranging from 5 nm to 10 nm, which may specifically be 6 nm, 7 nm or 8 nm. The buffer layer  304  is required to have only isolation and insulation functions. Therefore, the formed buffer layer  304  has a smaller thickness, which helps save manufacturing costs of the semiconductor structure. 
     The material of the contact layer  306  contains cuprous ions, which may specifically be cuprous thiocyanate. The contact layer  306  contains cuprous ions, which has similar chemical properties to the metallic copper layer  303 ; therefore, the contact layer  306  formed on the upper surface of the metallic copper layer  303  has good adhesion with the metallic copper layer  303 , and no gap exists between the metallic copper layer  303  and the contact layer  306 . 
     In this embodiment, the contact layer  306  has a thickness of 5 nm to 10 nm, which may specifically be 6 nm, 7 nm or 8 nm; and an upper surface of the buffer layer  304  is flush with the upper surface of the contact layer  306 . 
     This indicates that the contact layer  306  has a same thickness as the buffer layer  304 . The upper surface of the contact layer  306  and the upper surface of the buffer layer  304  form a uniform and flat surface, which facilitates subsequent formation of a barrier layer by deposition. Moreover, the contact layer  306  is required to only play a role of connecting the metallic copper layer  303  and the barrier layer. Therefore, the formed contact layer  306  has a smaller thickness, which helps save manufacturing costs of the semiconductor structure. 
     The material of the barrier layer  307 contains a same element as the material of the contact layer  306 . Specifically, the material of the barrier layer  307  may be silicon carbon nitride. In other embodiments, the material of the barrier layer may also be tantalum nitride and other tantalum compounds. 
     Since the material of the contact layer  306 contains same elements as the material of the barrier layer  307 , the contact layer  306  and the barrier layer  307  also have similar chemical properties and good adhesion therebetween, and no gap exists between the barrier layer  307  and the contact layer  306 . It can be obtained that two opposite sides of the contact layer  306  are closely bonded to the metallic copper layer  303  and the barrier layer  307  respectively, and no gap or projection exists between the metallic copper layer  303  and the barrier layer  307 , which improves the contact performance of the metallic copper layer  303  and the barrier layer  307 . 
     In this embodiment, the semiconductor structure further includes: a metal layer  309 , the metal layer  309  passing through the barrier layer  307  and the contact layer  306 , and the metal layer  309  being in contact with the upper surface of the metallic copper layer  303 . 
     The metal layer  309  is made of tin, copper, aluminum, gold, silver or other materials. Gases used in the metal layer  309  formed by tungsten include silane and tungsten hexafluoride. In other embodiments, tungsten may also be prepared from diboron hexahydride and tungsten hexafluoride. 
     In the semiconductor structure according to this embodiment, a contact layer is provided between the metallic copper layer and the barrier layer, a material of the contact layer contains cuprous ions, and the material of the contact layer contains same elements as a material of the barrier layer. The contact layer contains cuprous ions, which has similar chemical properties to the metallic copper layer; therefore, the contact layer on the upper surface of the metallic copper layer has good adhesion with the metallic copper layer, and no gap exists between the metallic copper layer and the contact layer. At the same time, since the material of the contact layer contains same elements as the material of the barrier layer, the contact layer and the barrier layer also have similar chemical properties and good adhesion therebetween. Based on the above, two opposite sides of the contact layer are closely bonded with the metallic copper layer and the barrier layer respectively, and no air gap or projection exists between the metallic copper layer and the barrier layer, which improves the contact performance of the metallic copper layer and the barrier layer. 
     Those of ordinary skill in the art may understand that the above implementations are specific embodiments for implementing the present application. However, in practical applications, various changes in forms and details may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art can make respective changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims.