Patent Publication Number: US-2022216100-A1

Title: Manufacturing method of semiconductor structure and semiconductor structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Patent Application No. PCT/CN2021/112770, which claims priority to Chinese Patent Application No. 202110003495.3, filed with the Chinese Patent Office on Jan. 4, 2021 and entitled “MANUFACTURING METHOD OF SEMICONDUCTOR STRUCTURE AND SEMICONDUCTOR STRUCTURE.” International Patent Application No. PCT/CN2021/112770 and Chinese Patent Application No. 202110003495.3 are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate to the field of semiconductors, and in particular to a manufacturing method of a semiconductor structure and a semiconductor structure. 
     BACKGROUND 
     With the development of semiconductor manufacturing technologies, the critical dimension of the semiconductor process has shrunk to the order of deep submicron. Due to the continuous shrinking of the critical dimension, a distance between interconnection lines in a semiconductor structure is getting closer, and parasitic capacitance is getting larger and larger. The parasitic capacitance can seriously affect the performance of the semiconductor structure, and especially reduce the operating speed and reliability of the semiconductor structure. 
     Therefore, how to reduce the parasitic capacitance in the semiconductor structure is currently an urgent technical problem to be solved. 
     SUMMARY 
     An embodiment of the present disclosure provides a manufacturing method of a semiconductor structure, including: providing a base with an electrical contact layer therein; forming an insulating layer on the base, the insulating layer having a through hole penetrating the insulating layer, and the through hole exposing a surface of the electrical contact layer; forming a sidewall layer on a sidewall of the through hole; forming a first isolation layer, the first isolation layer covering a surface of the sidewall layer and an exposed surface of the insulating layer; removing the sidewall layer to form a gap between the first isolation layer and the insulating layer; and forming a conducting layer filling the through hole, the conducting layer being electrically connected to the electrical contact layer. 
     An embodiment of the present disclosure further provides a semiconductor structure, including: a base with an electrical contact layer therein; an insulating layer located on the base, the insulating layer having a conducting layer therein, and the conducting layer being electrically connected to the electrical contact layer; and a first isolation layer located between the insulating layer and the conducting layer, the first isolation layer being also located on part of the sidewall of the insulating layer, a gap existing between the insulating layer and the first isolation layer, and the first isolation layer sealing the gap. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       One or more embodiments are exemplified by pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the accompanying drawings do not constitute a scale limitation. 
         FIG. 1  to  FIG. 11  are schematic structural diagrams corresponding to various steps of a manufacturing method of a semiconductor structure according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     It can be seen from the Background section that the parasitic capacitance in a semiconductor structure needs to be further reduced. A method for reducing the parasitic capacitance may include: forming a sacrificial layer between a conducting layer and an insulating layer which are adjacent, removing the sacrificial layer to form a gap, and sealing the gap. Since there is air in the gap and a dielectric constant of the air is low, the parasitic capacitance can be reduced. In a process step of sealing the gap, part of reaction gas can enter the gap and form a deposition layer at a bottom of the gap, thereby reducing the size of the gap. In addition, if improper sealing occurs, during subsequent deposition of a conducting material, the conducting material is likely to enter the gap, thereby causing electrical conduction between interconnection lines that should be isolated from each other. Therefore, the above method has a poor effect of reducing parasitic capacitance, and may also affect the yield of the semiconductor structure. 
     Embodiments of the present disclosure provide a manufacturing method of a semiconductor structure and a semiconductor structure. The manufacturing method of a semiconductor structure includes: providing a base with an electrical contact layer therein; forming an insulating layer on the base, the insulating layer having a through hole penetrating the insulating layer, and the through hole exposing a surface of the electrical contact layer; forming a sidewall layer on a sidewall of the through hole; forming a first isolation layer, the first isolation layer covering a surface of the sidewall layer and an exposed surface of the insulating layer; removing the sidewall layer to form a gap between the first isolation layer and the insulating layer; and forming a conducting layer filling the through hole, the conducting layer being electrically connected to the electrical contact layer. Since the first isolation layer covers the entire surface of the sidewall layer, the gap formed after the removal of the sidewall layer is completely surrounded by the first isolation layer and does not need to be sealed, thereby ensuring that the parasitic capacitance can be reduced to a great extent and improving the yield of the semiconductor structure. 
     In order to make the objectives, technical solutions, and advantages of the embodiments of the present disclosure more clear, various embodiments of the present disclosure will be detailed below in combination with the accompanying drawings. However, a person of ordinary skill in the art can understand that in each embodiment of the present disclosure, many technical details are provided for readers to better understand the present disclosure. However, even if these technical details are not provided and based on variations and modifications of the following embodiments, the technical solutions sought for protection in the present disclosure can also be implemented. 
       FIG. 1  to  FIG. 11  are schematic structural diagrams corresponding to various steps of a manufacturing method of a semiconductor structure according to a first embodiment of the present disclosure. A detailed description will be given below in conjunction with the drawings. 
     Referring to  FIG. 1 , a base  100  with an electrical contact layer  101  therein is provided. The base  100  may include structures such as wordlines, bitlines, sources, drains and the like. The base  100  may be made of silicon, sapphire, silicon carbide, gallium arsenide, aluminum nitride, zinc silicon oxide, or the like. 
     The electrical contact layer  101  is configured to achieve electrical connection between an internal structure of the base  100  and a conducting layer formed subsequently. In an example, the subsequently-formed conducting layer may be electrically connected to the bitlines in the base  100  through the electrical contact layer. In the present embodiment, the electrical contact layer  101  is made of copper. In other embodiments, the electrical contact layer  101  may also be made of a conducting material, such as polysilicon, tungsten, titanium, or the like. 
     In the present embodiment, the base  100  further has isolation structures  102  therein, and the isolation structure  102  is configured to isolate adjacent electrical contact layers  101 . In the present embodiment, the isolation structure  102  is made of silicon oxide. In other embodiments, the isolation structure  102  may also be made of an insulating material such as silicon carbide, silicon nitride, or the like. 
     Referring to  FIG. 1  to  FIG. 2 , an insulating layer  103  is formed on the base  100 . The insulating layer  103  has a through hole  110  penetrating the insulating layer  103 , and the through hole  110  exposes a surface of the electrical contact layer  101 . 
     The insulating layer  103  is configured to isolate the conducting layer formed in the through hole  110  subsequently. 
     The insulating layer  103  is located on the isolation structure  102 , and in a direction parallel to a surface of the base  100 , the isolation structure  102  is wider than the insulating layer  103  for the following reason: a gap, a first isolation layer and a second isolation layer will be formed subsequently on a sidewall of the insulating layer  103 , the isolation structure  102  is wider than the insulating layer  103 , and when a width difference meets a certain value range, the gap, the first isolation layer and the second isolation layer can directly face the isolation structure  102 , so that the entire surface of the electrical contact layer  101  is exposed to increase a contact area between the subsequently-formed conducting layer and the electrical contact layer  101 , thereby reducing contact resistance. 
     A width of the insulating layer  103  is greater than or equal to one-half of a width of the isolation structure  102  and less than or equal to the width of the isolation structure  102 . When the width of the insulating layer  103  is within the above range, the first and second isolation layers to be formed subsequently can be well supported and the stability of the semiconductor structure can be improved; and moreover enough space can also be reserved for the gap, the first isolation layer and the second isolation layer to be formed subsequently, so that the gap, the first isolation layer and the second isolation layer can be located on the isolation structure  102 , and the entire surface of the electrical contact layer  101  can be exposed to increase the contact area between the subsequently-formed conducting layer and the electrical contact layer  101 . 
     In the manufacturing method of a semiconductor structure according to the embodiment of the present disclosure, the first isolation layer covering the surface of the sidewall layer is formed, that is, also covers a top of the sidewall layer; after the sidewall layer is removed to form the gap, the first isolation layer completely seals the gap, and a step of sealing the gap is no longer required, thereby avoiding the formation of a deposition layer in the gap during the sealing process, or situations such as improper sealing, and then effectively reducing the parasitic capacitance of the semiconductor structure. 
     In the present embodiment, the insulating layer  103  and the isolation structure  102  are made of a same material, which can improve the tightness of adhesion between the insulating layer  103  and the isolation structure  102 , thereby improving the stability of the semiconductor structure. For example, the insulating layer  103  and the isolation structure  102  are both made of silicon dioxide. In other embodiments, the insulating layer  103  may also be made of a different material from the isolation layer; for example, the insulating layer  103  may be made of an insulating material such as silicon carbide, silicon nitride, or the like. 
     In the present embodiment, the process step for forming the insulating layer  103  and the through hole  110  is as follows. Referring to  FIG. 1 , an initial insulating layer  103   a  is formed on the base  100 , and a patterned photoresist layer  104  is formed on the initial insulating layer  103   a ; referring to  FIG. 2 , using the patterned photoresist layer  104  (see  FIG. 1 ) as a mask, the initial insulating layer  103   a  (see  FIG. 1 ) is etched to form the insulating layer  103 . 
     In the present embodiment, a chemical vapor deposition process is carried out to form the initial insulating layer  103   a . The chemical vapor deposition process has a high deposition rate and can shorten a process time. 
     In the present embodiment, a dry etching method is carried out to etch the initial insulating layer  103   a  until the electrical contact layer  101  is exposed, thus forming the insulating layer  103  and the through hole  110  exposing the electrical contact layer  101 . 
     Referring to  FIG. 3  to  FIG. 4 , a sidewall layer  105  is formed on the sidewall of the through hole  110 . 
     The sidewall layer  105  is configured to occupy a spatial position for the subsequent formation of the gap; that is, the position of the sidewall layer  105  is the position of the subsequently-formed gap. 
     The sidewall layer  105  should be made of a material which can be decomposed easily. In this way, during the subsequent removal of the sidewall layer  105  to form the gap, under the action of oxygen plasma, the sidewall layer  105  can be discharged as a gas after being decomposed. The sidewall layer  105  is made of amorphous carbon, hydrocarbon or a polymer, for example, C x H y . 
     In the present embodiment, in a direction perpendicular to the surface of the base  100 , a ratio of a height of the sidewall layer  105  to a height of the insulating layer  103  is greater than or equal to 0.3. That is, a top surface of the sidewall layer  105  may be flush with a top surface of the insulating layer  103  or may be lower than the top surface of the insulating layer  103 . 
     When the ratio of the height of the sidewall layer  105  to the height of the insulating layer  103  is greater than or equal to 0.3, the greater the height of the sidewall layer  105 , the greater the height of the gap to be formed subsequently, so that the parasitic capacitance can be reduced to a great extent. 
     Preferably, the top surface of the sidewall layer  105  is lower than the top surface of the insulating layer  103 , and the ratio of the height of the sidewall layer  105  to the height of the insulating layer  103  is less than or equal to 0.8. In this way, the subsequently-formed first isolation layer can be located on the sidewall of the insulating layer  103  exposed by the sidewall layer  105 ; that is, the subsequently-formed first isolation layer can be well supported by the sidewall of the insulating layer  103 , so that the first isolation layer is not likely to collapse and has a good stability. 
     The step of forming the sidewall layer  105  will be described in detail below. 
     Referring to  FIG. 3 , an initial sidewall layer  105   a  is formed on a surface of the insulating layer  103  and a bottom of the through hole  110 . In the present embodiment, an atomic layer deposition process is carried out to form the initial sidewall layer  105   a . The initial sidewall layer  105   a  formed by the atomic layer deposition process has a relatively even thickness. In other embodiments, a chemical vapor deposition process or a physical vapor deposition process may also be carried out to form the initial sidewall layer  105   a.    
     Referring to  FIG. 4 , the initial sidewall layer  105   a  located at the bottom of the through hole  110  and the top surface of the insulating layer  103  is removed (see  FIG. 3 ), and part of the initial sidewall layer  105   a  located on the sidewall of the through hole  110  is also removed; the remaining initial sidewall layer  105   a  serves as the sidewall layer  105   a.    
     That is, the top surface of the sidewall layer  105  is lower than the top surface of the insulating layer  103 , so that the first isolation layer formed subsequently also covers the sidewall of the insulating layer  103  exposed by the sidewall layer  105 . In this way, after the sidewall layer  105  is removed, since the first isolation layer is still supported by the sidewall of the insulating layer  103 , the first isolation layer has the good stability. 
     In other embodiments, the initial sidewall layer  105   a  located on the sidewall of the through hole  110  may not be removed; that is, the top surface of the formed sidewall layer  105  is flush with the top surface of the insulating layer  103 , and the first isolation layer formed subsequently can not cover the sidewall of the insulating layer  103 . 
     In the present embodiment, part of the initial insulating layer  105   a  is removed by dry etching (see  FIG. 3 ). 
     Referring to  FIG. 5 , a first isolation layer  106  is formed, and the first isolation layer  106  covers the surface of the sidewall layer  105  and an exposed surface of the insulating layer  103 . 
     Compared with the sidewall layer  105 , the first isolation layer  106  is required to be decomposed hardly. Therefore, the first isolation layer  106  is unlikely to be damaged during the subsequent removal of the sidewall layer  105  and thus achieves a better stability. 
     In addition, the first isolation layer  106  is relatively thin; for example, the thickness thereof may be less than 3 nm, so that an ion beam can more easily pass through the first isolation layer  106  and remove the sidewall layer  105 . 
     In addition, the first isolation layer  106  has holes, so that the ion beam can directly pass through the holes, and therefore the sidewall layer  105  can be removed more thoroughly. 
     In the present embodiment, the first isolation layer  106  is made of silicon dioxide. In other embodiments, the first isolation layer  106  may also be made of a silicon-oxyhydrocarbon. The silicon dioxide or silicon-oxyhydrocarbon is hardly decomposed under the action of oxygen plasma and has the good stability. 
     In the present embodiment, the first isolation layer  106  is formed by a low-temperature atomic layer deposition process. In this way, a thin first isolation layer  106  can be formed, so that the sidewall layer  105  completely covered by the first isolation layer  106  can be more easily removed later. A temperature range of the low-temperature atomic layer deposition process is in a low-temperature range of 50° C. to 135° C. Through the low-temperature atomic layer deposition process, the thickness of the first isolation layer  106  can be more accurately controlled to obtain a homogeneous thin first isolation layer  106 , and the first isolation layer  106  can have the characteristics of a flatter surface. 
     Referring to  FIG. 6 , the sidewall layer  105  is removed (see  FIG. 5 ) to form a gap  107  between the first isolation layer  106  and the insulating layer  103 . 
     A method for removing the sidewall layer  105  (see  FIG. 5 ) includes: providing a plasma source, causing an ion beam generated by the plasma source to react with the sidewall layer  105  after passing through the first isolation layer  106  and form reaction byproducts, and discharging at least part of the reaction byproducts through the first isolation layer  106 . Compared with a wet process, the above method has the advantages of fewer residues and higher cleanliness when used for removing the sidewall layer  105 . 
     In the present embodiment, oxygen is used as the plasma source, and the process steps for removing the sidewall layer  105  include: generating an ion beam based on the oxygen plasma source, and causing the ion beam to pass through the first isolation layer  106  through the holes in the first isolation layer  106  and react with the sidewall layer  105  (see  FIG. 5 ), so that the sidewall layer  105  is thermally decomposed to produce reaction byproducts such as carbon dioxide, carbon monoxide, water, methane and the like. Gases such as carbon dioxide, carbon monoxide, water and methane can pass through the holes in the first isolation layer  106  to be discharged. 
     A flow rate of oxygen is within a range of 100 sccm to 600 sccm. When the flow rate of oxygen is within the above range, oxygen can react sufficiently with the material of the sidewall layer  105 , so that the sidewall layer  105  can be more completely removed; and the first isolation layer  106  can be prevented from major damage, thus ensuring that the first isolation layer  106  has a high stability. 
     A radio frequency power is within a range of 500 W to 1000 W. When the radio frequency power is within the above range, the ion beam has sufficient energy to completely remove the sidewall layer  105 ; and major damage to the first isolation layer  106  can also be prevented, ensuring that the first isolation layer  106  has a high stability. 
     Referring to  FIG. 7 , a second isolation layer  108  is formed on the surface of the first isolation layer  106 . A density of the second isolation layer  108  is greater than that of the first isolation layer  106 . 
     It can be understood that, in order to make more ion beams pass through the first isolation layer  106 , so that the sidewall layer  105  is removed more completely, and the first isolation layer  106  has a lower density; after the removal of the sidewall layer  105 , formation of the denser second isolation layer  108  on the surface of the first isolation layer  106  can increase the density of the first isolation layer  106 , thereby improving the firmness and stability of the first isolation layer  106 . 
     The thickness of the second isolation layer  108  is greater than the thickness of the first isolation layer  106 , which can further improve the firmness of the first isolation layer  106 . Preferably, a ratio of the thickness of the second isolation layer  108  to the thickness of the first isolation layer  106  is within a range of 1.5:1 to 3:1. When the ratio of the thickness of the second isolation layer  108  to the thickness of the first isolation layer  106  is within the above range, the second isolation layer  108  can well reinforce the first isolation layer  106 . In addition, the second isolation layer  108  can occupy a reasonable area on the isolation structure  102 , so that the second isolation layer  108  can completely expose the surface of the electrical contact layer  101 , so as to increase the contact area between the electrical contact layer  101  and the subsequently-formed conducting layer. 
     In the present embodiment, the second isolation layer  108  and the first isolation layer  106  are made of a same material, which can ensure that the second isolation layer  108  and the first isolation layer  106  can be more closely attached, thereby further improving the reinforcement effect of the second isolation layer  108 . For example, the second isolation layer  108  and the first isolation layer  106  are both made of silicon dioxide. In other embodiments, the second isolation layer  108  may also be made of a different material from the first isolation layer  106 ; for example, the second isolation layer  108  may be made of silicon nitride. 
     The second isolation layer  108  is formed by an atomic layer deposition process or a chemical vapor deposition process with better step coverage. 
     Referring to  FIG. 8 , the first isolation layer  106  and the second isolation layer  108  located at the bottom of the through hole  110  and the top surface of the insulating layer  103  are removed. 
     In the present embodiment, a dry etching method is carried out to remove part of the first isolation layer  106  and part of the second isolation layer  108 . 
     After the removal of the part of the first isolation layer  106  and the part of the second isolation layer  108 , the remaining first isolation layer  106  and the remaining second isolation layer  108  expose the entire surface of the electrical contact layer  101 , thereby increasing the contact area between the subsequently-formed conducting layer and the electrical contact layer  101  and reducing the contact resistance. 
     In other embodiments, the remaining first isolation layer  106  and the remaining second isolation layer  108  may also expose only part of the surface of the electrical contact layer  101 . 
     Referring to  FIG. 9 , a barrier layer  109  covering the sidewall of the through hole  110  is deposited. 
     The barrier layer  109  is configured to block mutual diffusion between atoms in the subsequently-formed conducting layer and atoms in the second isolation layer  108 , and meanwhile can also increase the adhesion between the conducting layer and the second isolation layer  108 , thereby improving the stability and firmness of the subsequently-formed conducting layer. 
     In the present embodiment, the barrier layer  109  is also located at the bottom of the through hole  110 . The barrier layer  109  can also block the mutual diffusion between the atoms in the subsequently-formed conducting layer and atoms in the electrical contact layer  101 , and meanwhile can also increase the adhesion between the conducting layer and the electrical contact layer  101 . 
     The barrier layer  109  is made of tantalum, tantalum nitride, ruthenium, or rhenium. 
     In the present embodiment, the barrier layer  109  is formed by an atomic layer deposition process. 
     Referring to  FIG. 10 , a conducting layer  111  filling the through hole  110  (see  FIG. 9 ) is formed, and the conducting layer  111  is electrically connected to the electrical contact layer  101 . The conducting layer  111  is also higher than the top of the insulating layer  103 . 
     As an interconnection line in the semiconductor structure, the conducting layer  111  connects the structures in the base  100  together according to design requirements to achieve specific functions. 
     In the present embodiment, the conducting layer  111  is made of copper, gold, silver, titanium or tungsten. 
     In the present embodiment, the conducting layer  111  is formed by a chemical vapor deposition process. In other embodiments, a physical vapor deposition process may also be carried out to form the conducting layer  111 . 
     Referring to  FIG. 11 , planarization is performed to remove part of the conducting layer  111 , part of the insulating layer  103 , part of the first isolation layer  106  and part of the second isolation layer  108  which are higher than the gap  107 . 
     It should be noted that during the planarization, the process should be stopped at a position higher than the gap  107 , so as to ensure that the gap  107  is still in a sealed state. 
     In the present embodiment, the planarization is performed by chemical mechanical polishing. 
     In other embodiments, if the gap formed is located on the entire sidewall of the insulating layer  103 ; that is, in a direction perpendicular to the surface of the base  100 , the gap is as high as the insulating layer  103 ; then, during the planarization, in order to ensure the tightness of the gap, only the conducting layer  111  higher than the gap may be removed, while the insulating layer  103 , the first isolation layer  106 , the second isolation layer  108 , and the barrier layer  109  are retained. 
     In summary, in the present embodiment, the sidewall layer covered by the first isolation layer is removed by a plasma process, thereby forming a gap. A process step of sealing the gap is not required, so that the gap has a larger size and high stability, which can effectively reduce the parasitic capacitance of the semiconductor structure. 
     A second embodiment of the present disclosure provides a semiconductor structure.  FIG. 11  is a schematic diagram of the semiconductor structure according to the second embodiment of the present disclosure. Referring to  FIG. 11 , the semiconductor structure includes: a base  100  with an electrical contact layer  101  therein; an insulating layer  103  located on the base  100 , the insulating layer  103  having a conducting layer  111  therein, and the conducting layer  111  being electrically connected to the electrical contact layer  101 ; and a first isolation layer  106 , the first isolation layer being located between the insulating layer  103  and the conducting layer  111 , the first isolation layer  106  being also located on part of sidewalls of the insulating layer  103 , a gap  107  existing between the insulating layer  103  and the first isolation layer  106 , and the gap  107  being sealed by the first isolation layer  106 . 
     A detailed description will be given below in conjunction with the drawings. 
     Referring to  FIG. 11 , the base  100  may include structures such as wordlines, bitlines, sources, drains and the like. The base  100  may be made of silicon, sapphire, silicon carbide, gallium arsenide, aluminum nitride, zinc silicon oxide, or the like. 
     The electrical contact layer  101  is configured to achieve electrical connection between an internal structure of the base  100  and the conducting layer  111 . In an example, the conducting layer  111  may be electrically connected to the bitlines in the base  100  through the electrical contact layer  101 . In the present embodiment, the electrical contact layer  101  is made of copper. In other embodiments, the electrical contact layer  101  may also be made of a conducting material, such as polysilicon, tungsten, titanium, or the like. 
     The base  100  further has isolation structures  102  therein, and the isolation structure  102  is configured to isolate adjacent electrical contact layers  101 . In the present embodiment, the isolation structure  102  is made of silicon oxide. In other embodiments, the isolation structure  102  may also be made of an insulating material such as silicon carbide, silicon nitride, or the like. 
     The insulating layer  103  is configured to isolate adjacent conducting layers  111 . 
     The insulating layer  103  is located on the isolation structure  102 , and in a direction parallel to a surface of the base  100 , the isolation structure  102  is wider than the insulating layer  103  for the following reason: a gap, a first isolation layer and a second isolation layer will be formed subsequently on a sidewall of the insulating layer  103 , the isolation structure  102  is wider than the insulating layer  103 , and when a width difference meets a certain value range, the gap, the first isolation layer and the second isolation layer can directly face the isolation structure  102 , so that the entire surface of the electrical contact layer  101  is exposed to increase a contact area between the subsequently-formed conducting layer and the electrical contact layer  101 , thereby reducing contact resistance. 
     A width of the insulating layer  103  is greater than or equal to one-half of a width of the isolation structure  102  and less than or equal to the width of the isolation structure  102 . When the width of the insulating layer  103  is within the above range, the first isolation layer  106  and the second isolation layer  108  can be well supported and the stability of the semiconductor structure can be improved; and moreover enough space can also be reserved for the gap  107 , the first isolation layer  106  and the second isolation layer  108 , so that the gap  107 , the first isolation layer  106  and the second isolation layer  108  can be located on the isolation structure  102 , and the entire surface of the electrical contact layer  101  can be exposed to increase the contact area between the conducting layer  111  and the electrical contact layer  101 . 
     The insulating layer  103  is made of silicon dioxide, silicon nitride, or silicon carbide. 
     As an interconnection line in the semiconductor structure, the conducting layer  111  connects the structures in the base  100  together according to design requirements to achieve specific functions. 
     The conducting layer  111  is made of copper, gold, silver, titanium, or tin. 
     The first isolation layer  106  is configured to seal the gap  107 . Since the first isolation layer  106  is also located on the top of the gap  107 , the gap  107  does not need other isolation layers for sealing. 
     The first isolation layer  106  is also located on the isolation structure  102  and exposes the entire surface of the electrical contact layer  101  to increase the contact area between the electrical contact layer  101  and the conducting layer  111  and reduce the contact resistance. 
     The second isolation layer  108  covers the surface of the first isolation layer  106 , and a density of the second isolation layer  108  is greater than that of the first isolation layer  106 . 
     It can be understood that, during the formation of the gap  107 , in order to make more ion beams pass through the first isolation layer  106 , so that the first isolation layer  106  has a lower density; after the formation of the gap  107 , the denser second isolation layer  108  can increase the density of the first isolation layer  106 , thereby improving the firmness and stability of the first isolation layer  106 . 
     In a direction parallel to the surface of the base  100 , the thickness of the second isolation layer  108  is greater than the thickness of the first isolation layer  106 . In this way, the stability of the first isolation layer  106  can be improved, and problems such as collapse of the first isolation layer  106  can be avoided. Preferably, a ratio of the thickness of second isolation layer  108  to the thickness of the first isolation layer  106  is within a range of 1.5:1 to 3:1. When the ratio of the thickness of the second isolation layer  108  to the thickness of the first isolation layer  106  is within the above range, the second isolation layer  108  can well reinforce the first isolation layer  106 . In addition, the second isolation layer  108  can occupy a reasonable area on the isolation structure  102 , so that the second isolation layer  108  can completely expose the surface of the electrical contact layer  101 , so as to increase the contact area between the electrical contact layer  101  and the conducting layer  111 . 
     The first isolation layer  106  and the second isolation layer  108  are both located on the base  100  other than the electrical contact layer  101  and expose the entire surface of the electrical contact layer  101 . In this way, the contact area between the conducting layer  111  and the electrical contact layer  101  can be increased, thereby reducing the contact resistance and increasing the operating speed of the semiconductor structure. 
     In the present embodiment, the first isolation layer  106  is made of silicon dioxide. In other embodiments, the first isolation layer  106  may also be made of a silicon-oxyhydrocarbon. The silicon dioxide or silicon-oxyhydrocarbon is hardly decomposed under the action of oxygen plasma and has good stability. 
     In the present embodiment, the second isolation layer  108  and the first isolation layer  106  are made of a same material, which can ensure that the second isolation layer  108  and the first isolation layer  106  can be more closely attached, thereby further improving the reinforcement effect of the second isolation layer  108 . For example, the second isolation layer  108  and the first isolation layer  106  are both made of silicon dioxide. In other embodiments, the second isolation layer  108  may also be made of a different material from the first isolation layer  106 ; for example, the second isolation layer  108  may be made of silicon nitride. 
     In the present embodiment, a width of the gap  107  may be within a range of 1 nm to 5 nm. When the width of the gap  107  is within the above range, the parasitic capacitance can be effectively reduced, and the stability of the first isolation layer  106  and the second isolation layer  108  can be ensured. 
     In a direction perpendicular to the surface of the base  100 , a ratio of a height of the gap  107  to a height of the insulating layer  103  is greater than or equal to 0.3. The height of the gap  107  is within the above range; that is, the gap  107  occupies a large space and can reduce the parasitic capacitance to a great extent. 
     In one embodiment, in the direction perpendicular to the surface of the base  100 , the ratio of the height of the gap  107  to the height of the insulating layer  103  is greater than or equal to 0.9. That is, the contact area between the first isolation layer  106  and the insulating layer  103  is greater than or equal to 0.1 of a total area of the sidewall of the insulating layer  103 . If the contact area is within the above range, the first isolation layer  106  can be more closely attached to the sidewall of the insulating layer  103 , thereby ensuring that the first isolation layer  106  can completely seal the top of the gap  107 , so that the gap  107  has good airtightness and stability. In this way, the parasitic capacitance can be reduced effectively. 
     The semiconductor structure further includes a barrier layer  109  located between the first isolation layer  106  and the conducting layer  111 . In the present embodiment, the barrier layer  109  covers the surface of the second isolation layer  108 . The barrier layer  109  is configured to block mutual diffusion between atoms of the conducting layer  111  and atoms in the second isolation layer  108  and increase the adhesion between the barrier layer  109  and the second isolation layer  108 . 
     In the present embodiment, the barrier layer  109  also covers the surface of the electrical contact layer  101 . The barrier layer  109  is also configured to block the mutual diffusion between the atoms in the conducting layer  111  and atoms in the electrical contact layer  101  and increase the adhesion between the barrier layer  109  and the electrical contact layer  101 . 
     The barrier layer  109  is made of tantalum, tantalum nitride, ruthenium, or rhenium. 
     In summary, in the present embodiment, the first isolation layer  106  completely seals the gap  107 , so that the gap  107  has good airtightness and stability, which can effectively reduce the parasitic capacitance. 
     The ordinary skills in the art can understand that the implementations described above are particular embodiments for implementing the present disclosure. In practical uses, various changes in forms and details may be made to the implementations without departing from the spirit and scope of the present disclosure. Any person skilled in the art may make their own changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.