阅读说明：本技术 半导体结构及其形成方法 (Semiconductor structure and forming method thereof ) 是由 于海龙 荆学珍 于 2020-05-29 设计创作，主要内容包括：一种半导体结构及其形成方法,形成方法包括：提供基底,基底包括衬底、位于衬底上的栅极结构以及位于栅极结构两侧的源漏掺杂层,基底上形成有覆盖栅极结构和源漏掺杂层的第一介电材料层；刻蚀第一介电材料层,形成露出源漏掺杂层或者栅极结构的开口,剩余的第一介电材料层作为第一介电层；在开口中形成接触插塞；刻蚀部分厚度的第一介电层,在接触插塞的顶部之间形成凹槽；在凹槽中形成第二介电层,第二介电层的介电常数低于第一介电层的介电常数。本发明实施例中,所述第二介电层的绝缘性优于所述第一介电层的绝缘性,因此所述第二介电层使得相邻所述接触插塞的顶部不易发生桥接,有利于优化半导体结构的电学性能。(A semiconductor structure and a forming method thereof are provided, wherein the forming method comprises the following steps: providing a substrate, wherein the substrate comprises a substrate, a gate structure positioned on the substrate and source and drain doping layers positioned on two sides of the gate structure, and a first dielectric material layer covering the gate structure and the source and drain doping layers is formed on the substrate; etching the first dielectric material layer to form an opening exposing the source-drain doping layer or the grid structure, wherein the rest first dielectric material layer is used as a first dielectric layer; forming a contact plug in the opening; etching part of the first dielectric layer to form a groove between the tops of the contact plugs; and forming a second dielectric layer in the groove, wherein the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer. In the embodiment of the invention, the insulating property of the second dielectric layer is superior to that of the first dielectric layer, so that the top of the adjacent contact plug is not easy to bridge by the second dielectric layer, and the electrical property of the semiconductor structure is favorably optimized.)

1. A method of forming a semiconductor structure, comprising:

providing a substrate, wherein the substrate comprises a substrate, a gate structure positioned on the substrate and source-drain doping layers positioned on two sides of the gate structure, and a first dielectric material layer covering the gate structure and the source-drain doping layers is formed on the substrate;

etching the first dielectric material layer to form an opening exposing the source-drain doping layer or the grid structure, wherein the rest first dielectric material layer is used as a first dielectric layer;

forming a contact plug in the opening;

etching part of the thickness of the first dielectric layer to form a groove between the tops of the contact plugs;

and forming a second dielectric layer in the groove, wherein the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer.

2. The method of forming a semiconductor structure of claim 1, wherein a material of the second dielectric layer comprises SiN.

3. The method of forming a semiconductor structure of claim 1, wherein forming a second dielectric layer in the recess comprises: forming a second dielectric material layer conformally covering the groove and the contact plug;

and removing the second dielectric material layer higher than the contact plug, and using the remaining second dielectric material layer positioned in the groove as a second dielectric layer.

4. The method of claim 3, wherein the second dielectric material layer is formed using an atomic layer deposition process, a physical vapor deposition process, or a chemical vapor deposition process.

5. The method of claim 1, wherein the opening is formed with a top lateral dimension greater than a bottom lateral dimension of the opening in a lateral direction perpendicular to an extension direction of the gate structure.

6. The method of forming a semiconductor structure of claim 5, wherein the step of forming the opening comprises: forming a shielding layer on the first dielectric material layer;

etching the first dielectric material layer by using the shielding layer as a mask and adopting an anisotropic dry etching process to form an initial opening in the first dielectric material layer;

and etching the top of the initial opening by adopting an isotropic dry etching process to form an opening, wherein the rest first dielectric material layer is used as a first dielectric layer.

7. The method for forming a semiconductor structure according to claim 1 or 5, wherein the depth of the groove is 2 nm to 5 nm in the process of etching a part of the thickness of the first dielectric layer to form the groove.

8. The method as claimed in claim 1 or 5, wherein a lateral dimension of a top of the recess is 10 nm to 16 nm in forming the recess with a lateral direction perpendicular to an extending direction of the gate structure.

9. The method for forming a semiconductor structure according to claim 1 or 5, wherein a recess is formed between tops of the contact plugs by etching a part of the thickness of the first dielectric layer using an isotropic dry etching process.

10. The method of forming a semiconductor structure of claim 9, wherein the isotropic dry etch process comprises a SiCoNi etch process or a Certas etch process.

11. The method of forming a semiconductor structure according to claim 1 or 5, wherein in the opening, the step of forming a contact plug comprises: forming a contact plug material layer on the opening and the first dielectric layer; and removing the contact plug material layer higher than the first dielectric layer, wherein the rest contact plug material layer positioned in the opening is used as a contact plug.

12. The method of claim 11, wherein a chemical mechanical planarization process is used to remove the contact plug material layer above the first dielectric layer.

13. The method of forming a semiconductor structure of claim 1 or 5, further comprising: after the opening is formed and before the contact plug is formed, conformally covering an anti-diffusion layer on the side wall and the bottom surface of the opening;

in the process of forming the contact plug, the contact plug is formed on the diffusion preventing layer;

in the process of forming the groove, the groove is surrounded by the first dielectric layer and the diffusion preventing layer.

14. The method for forming a semiconductor structure according to claim 13, wherein a material of the diffusion prevention layer comprises TaN or TiN.

15. A semiconductor structure, comprising:

a substrate;

the grid structure is positioned on the substrate;

the source-drain doping layer is positioned on the substrate at two sides of the grid structure;

the first dielectric layer is positioned on the grid structure, the source-drain doping layer and the substrate;

the contact plug is positioned in the first dielectric layer and is in contact with the gate structure or the source-drain doping layer, and the top of the contact plug protrudes out of the surface of the first dielectric layer;

and the second dielectric layer is positioned on the first dielectric layer between the tops of the contact plugs, and the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer.

16. The semiconductor structure of claim 15, wherein a material of the second dielectric layer comprises SiN.

17. The semiconductor structure of claim 15, wherein the second dielectric layer has a thickness of 2 nm to 5 nm.

18. The semiconductor structure of claim 15, wherein a lateral dimension of a top portion of the second dielectric layer is 10 nm to 16 nm, taken transverse to an extension direction of the gate structure.

19. The semiconductor structure of claim 15, wherein a top lateral dimension of the contact plug is greater than a bottom lateral dimension of the contact plug, taken transverse to an extension direction of the gate structure.

20. The semiconductor structure of claim 15, wherein the semiconductor structure further comprises: and the anti-diffusion layer is positioned between the first dielectric layer and the contact plug, between the contact plug and the grid structure, between the contact plug and the source-drain doping layer and between the contact plug and the second dielectric layer.

Technical Field

Embodiments of the present invention relate to the field of semiconductor manufacturing, and in particular, to a semiconductor structure and a method for forming the same.

Background

As semiconductor manufacturing technology becomes more sophisticated, integrated circuits have also undergone significant changes, and the number of components integrated on the same chip has increased from the first tens, hundreds to the present millions. In order to meet the circuit density requirements, the fabrication process of semiconductor integrated circuit chips utilizes batch processing techniques to form various types of complex devices on a substrate and interconnect them for complete electronic functionality, mostly using ultra-low k interlevel dielectric layers between conductive lines as the dielectric material for isolating the metal interconnects, and interconnect structures for providing wiring between the devices on the IC chip and the entire package. In this technique, devices such as Field Effect Transistors (FETs) are first formed on the surface of a semiconductor substrate, and then interconnect structures are formed in Back End of Line (BEOL) fabrication processes for integrated circuits.

As moore's law predicts, the shrinking dimensions of semiconductor substrates and the formation of more transistors on semiconductor substrates to improve device performance, the use of interconnect structures to connect the transistors is a necessary option. However, compared with the miniaturization and the increase of the integration of components, the number of conductor connecting lines in the circuit is continuously increased, the forming quality of the interconnection structure has great influence on the reliability of circuit connection, and the normal operation of the semiconductor device can be seriously influenced.

Disclosure of Invention

Embodiments of the present invention provide a semiconductor structure and a method for forming the same, which improve electrical properties of the semiconductor structure.

To solve the above problems, an embodiment of the present invention provides a method for forming a semiconductor structure, including: providing a substrate, wherein the substrate comprises a substrate, a gate structure positioned on the substrate and source-drain doping layers positioned on two sides of the gate structure, and a first dielectric material layer covering the gate structure and the source-drain doping layers is formed on the substrate; etching the first dielectric material layer to form an opening exposing the source-drain doping layer or the grid structure, wherein the rest first dielectric material layer is used as a first dielectric layer; forming a contact plug in the opening; etching part of the thickness of the first dielectric layer to form a groove between the tops of the contact plugs; and forming a second dielectric layer in the groove, wherein the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer.

Optionally, the material of the second dielectric layer includes SiN.

Optionally, the step of forming a second dielectric layer in the groove includes: forming a second dielectric material layer conformally covering the groove and the contact plug; and removing the second dielectric material layer higher than the contact plug, and using the remaining second dielectric material layer positioned in the groove as a second dielectric layer.

Optionally, the second dielectric material layer is formed by an atomic layer deposition process, a physical vapor deposition process, or a chemical vapor deposition process.

Optionally, in the step of forming the opening with a direction perpendicular to the extending direction of the gate structure as a lateral direction, a top lateral dimension of the opening is larger than a bottom lateral dimension of the opening.

Optionally, the step of forming the opening includes: forming a shielding layer on the first dielectric material layer; etching the first dielectric material layer by using the shielding layer as a mask and adopting an anisotropic dry etching process to form an initial opening in the first dielectric material layer; and etching the top of the initial opening by adopting an isotropic dry etching process to form an opening, wherein the rest first dielectric material layer is used as a first dielectric layer.

Optionally, during the process of etching a part of the thickness of the first dielectric layer to form a groove, the depth of the groove is 2 nm to 5 nm.

Optionally, the extending direction perpendicular to the gate structure is taken as a lateral direction, and during the process of forming the groove, a lateral dimension of a top of the groove is 10 nm to 16 nm.

Optionally, an isotropic dry etching process is used to etch a part of the thickness of the first dielectric layer, and a groove is formed between tops of the contact plugs.

Optionally, the isotropic dry etching process includes a SiCoNi etching process or a Certas etching process.

Optionally, in the opening, the step of forming a contact plug includes: forming a contact plug material layer on the opening and the first dielectric layer; and removing the contact plug material layer higher than the first dielectric layer, wherein the rest contact plug material layer positioned in the opening is used as a contact plug.

Optionally, a chemical mechanical planarization process is used to remove the contact plug material layer above the first dielectric layer.

Optionally, the method for forming the semiconductor structure further includes: after the opening is formed and before the contact plug is formed, conformally covering an anti-diffusion layer on the side wall and the bottom surface of the opening; in the process of forming the contact plug, the contact plug is formed on the diffusion preventing layer; in the process of forming the groove, the groove is surrounded by the first dielectric layer and the diffusion preventing layer.

Optionally, the material of the diffusion barrier layer includes TaN or TiN.

Correspondingly, the embodiment of the invention also provides a semiconductor structure, which comprises a substrate; the grid structure is positioned on the substrate; the source-drain doping layer is positioned on the substrate at two sides of the grid structure; the first dielectric layer is positioned on the grid structure, the source-drain doping layer and the substrate; the contact plug is positioned in the first dielectric layer and is in contact with the gate structure or the source-drain doping layer, and the top of the contact plug protrudes out of the surface of the first dielectric layer; and the second dielectric layer is positioned on the first dielectric layer between the tops of the contact plugs, and the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer.

Optionally, the material of the second dielectric layer includes SiN.

Optionally, the thickness of the second dielectric layer is 2 nm to 5 nm.

Optionally, the lateral dimension of the top of the second dielectric layer is 10 nm to 16 nm, taking the extension direction perpendicular to the gate structure as the lateral direction.

Optionally, the lateral direction is perpendicular to the extending direction of the gate structure, and the top lateral dimension of the contact plug is larger than the bottom lateral dimension of the contact plug.

Optionally, the semiconductor structure further includes: and the anti-diffusion layer is positioned between the first dielectric layer and the contact plug, between the contact plug and the grid structure, between the contact plug and the source-drain doping layer and between the contact plug and the second dielectric layer.

Compared with the prior art, the technical scheme of the embodiment of the invention has the following advantages:

in the method for forming the semiconductor structure provided by the embodiment of the invention, the first dielectric material layer is etched to form an opening exposing the source-drain doping layer or the gate structure; forming a contact plug in the opening; and etching the first dielectric layer with partial thickness, forming a groove between the tops of the contact plugs, and forming a second dielectric layer in the groove, wherein the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer, and the insulativity of the second dielectric layer is superior to that of the first dielectric layer, so that the second dielectric layer enables the tops of the adjacent contact plugs not to be easily bridged, and the electrical property of the semiconductor structure is favorably optimized.

Drawings

Fig. 1 to 3 are schematic structural diagrams corresponding to respective steps in a method for forming a semiconductor structure;

FIGS. 4 to 11 are schematic structural diagrams corresponding to steps of a method for forming a semiconductor structure according to an embodiment of the present invention;

fig. 12 is a schematic structural diagram of a semiconductor structure of the present invention.

Detailed Description

The semiconductor structure formed at present still has a problem of poor performance. The reason for the poor performance of the semiconductor structure is analyzed in combination with a method for forming the semiconductor structure.

Fig. 1 to 3 are schematic structural diagrams corresponding to respective steps in a method for forming a semiconductor structure.

As shown in fig. 1, providing a base 1, where the base 1 includes a substrate, a gate structure (not shown) on the substrate, and source-drain doping layers (not shown) on two sides of the gate structure; forming a first dielectric material layer 2 covering the gate structure and the source-drain doping layer on the substrate 1; and etching the first dielectric material layer 2 to form an initial opening 3 exposing the source-drain doping layer or the grid structure.

As shown in fig. 2, an isotropic dry etching process is used to etch the top of the initial opening 3 to form an opening 5, and the remaining first dielectric material layer 2 serves as a first dielectric layer 4.

In the opening 5, as shown in fig. 3, a contact plug 6 is formed.

In order to reduce the contact resistance between the contact plug 6 and the next-stage interconnect structure, after the initial opening 3 is formed, an isotropic dry etching process is generally used to etch the top of the initial opening 3, so that the top of the initial opening 3 is enlarged to form an opening 5, which is transverse to the extending direction of the gate structure, accordingly, the top transverse dimension of the contact plug 6 formed in the opening 5 is larger than the bottom transverse dimension of the contact plug 6, accordingly, the space between the first dielectric layers 4 between the tops of the contact plugs 6 is reduced, and the top of the contact plug 6 is prone to have a leakage current, resulting in poor electrical performance of the semiconductor structure.

In order to solve the technical problem, an embodiment of the present invention provides a method for forming a semiconductor structure, including: providing a substrate, wherein the substrate comprises a substrate, a gate structure positioned on the substrate and source-drain doping layers positioned on two sides of the gate structure, and a first dielectric material layer covering the gate structure and the source-drain doping layers is formed on the substrate; etching the first dielectric material layer to form an opening exposing the source-drain doping layer or the grid structure, wherein the rest first dielectric material layer is used as a first dielectric layer; forming a contact plug in the opening; etching part of the thickness of the first dielectric layer to form a groove between the tops of the contact plugs; and forming a second dielectric layer in the groove, wherein the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer.

In the method for forming the semiconductor structure provided by the embodiment of the invention, the first dielectric material layer is etched to form an opening exposing the source-drain doping layer or the gate structure; forming a contact plug in the opening; and etching the first dielectric layer with partial thickness, forming a groove between the tops of the contact plugs, and forming a second dielectric layer in the groove, wherein the dielectric constant of the second dielectric layer is lower than that of the first dielectric layer, and the insulativity of the second dielectric layer is superior to that of the first dielectric layer, so that the second dielectric layer enables the tops of the adjacent contact plugs not to be easily bridged, and the electrical property of the semiconductor structure is favorably optimized.

In order to make the aforementioned objects, features and advantages of the embodiments of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below.

Fig. 4 to fig. 11 are schematic structural diagrams corresponding to steps in an embodiment of a method for forming a semiconductor structure according to the present invention.

Referring to fig. 4, a substrate 100 is provided, where the substrate 100 includes a substrate (not shown in the figure), a gate structure (not shown in the figure) on the substrate, and source-drain doping layers (not shown in the figure) on two sides of the gate structure, and a first dielectric material layer 101 covering the gate structure and the source-drain doping layers is formed on the substrate 100.

The substrate is used for providing a process platform for the subsequent formation of a semiconductor structure.

In this embodiment, the substrate is a silicon substrate. In other embodiments, the material of the substrate may also be other materials such as germanium, silicon carbide, gallium arsenide, or indium gallium arsenide, and the substrate may also be other types of substrates such as a silicon-on-insulator substrate or a germanium-on-insulator substrate.

In embodiments of the present invention, which take the form of a fin field effect transistor (FinFET), the substrate typically further includes a fin (not shown) on the substrate. In other embodiments, taking a gate all around transistor (GAA) as an example, the substrate further includes one or more channel layers suspended at intervals in a normal direction of the substrate surface, and a gate structure all around the channel layer.

The fin is used to provide a channel of a fin field effect transistor.

In this embodiment, the fin portion and the substrate are obtained by etching the same semiconductor layer. In other embodiments, the fin may also be a semiconductor layer epitaxially grown on the substrate, so as to achieve the purpose of precisely controlling the height of the fin.

Therefore, in this embodiment, the fin portion and the substrate are made of the same material, and the fin portion is made of silicon. In other embodiments, the material of the fin may also be germanium, silicon carbide, gallium arsenide, or indium gallium arsenide.

The gate structure is used to control the opening and closing of the channel in the fin during operation of the semiconductor structure.

In this embodiment, the gate structure includes a gate dielectric layer (not shown) and a gate layer (not shown) on the gate dielectric layer.

The gate dielectric layer is used for realizing electric isolation between the gate electrode layer and the fin portion. It should be noted that, in this embodiment, the gate structure is a metal gate structure, and the gate dielectric layer is made of a high-k dielectric material. Wherein, the high-k dielectric material is a dielectric material with a relative dielectric constant larger than that of silicon oxide.

In this embodiment, the gate dielectric layer is made of HfO₂. In other embodiments, the material of the gate dielectric layer may also be selected from ZrO₂HfSiO, HfSiON, HfTaO, HfTiO, HfZrO or Al₂O₃One or more of them.

The gate layer serves as an electrode for electrically connecting to an external circuit, and in this embodiment, the gate layer is made of magnesium-tungsten alloy. In other embodiments, the material of the metal gate structure may also be W, Al, Cu, Ag, Au, Pt, Ni, Ti, or the like.

When the semiconductor structure works, the source-drain doped layer provides stress for a channel, and the migration rate of carriers is improved.

In this embodiment, the semiconductor structure is used to form an NMOS (negative channel Metal Oxide semiconductor), and the source-drain doped layer is used as a source and a drain of the NMOS. When the semiconductor structure works, the source-drain doped layer applies tensile stress (tensile stress) to a channel below the gate structure, and the tensile stress can improve the migration rate of electrons.

In other embodiments, the semiconductor structure is used to form a PMOS (positive Channel metal oxide semiconductor), and the source and drain doped layers are used as a source and a drain of the PMOS. When the semiconductor structure works, the source-drain doped layers apply compressive stress (compressive stress) to a channel below the gate structure, and the compressive stress can improve the mobility of holes.

The first layer of dielectric material 101 serves to electrically isolate adjacent devices.

In this embodiment, the material of the first dielectric material layer 101 is an insulating material. Specifically, the material of the first dielectric material layer 101 includes silicon oxide. The silicon oxide is a dielectric material with a common process and low cost, has high process compatibility, and is beneficial to reducing the process difficulty and the process cost for forming the first dielectric material layer 101.

Specifically, the first dielectric material layer 101 includes an interlayer dielectric layer (not shown) and a back-end dielectric layer (not shown) on the interlayer dielectric layer.

The interlayer dielectric layer covers the substrate, the fin portion and the source-drain doping layer, and also covers the side wall of the grid structure to expose the top surface of the grid structure.

The back-end dielectric layer is used for electrically isolating adjacent devices of adjacent back-ends. The back section dielectric layer is positioned on the interlayer dielectric layer and the grid structure.

Referring to fig. 5 and 6, the first dielectric material layer 101 is etched to form an opening 102 (as shown in fig. 6) exposing the source-drain doping layer or the gate structure, and the remaining first dielectric material layer 101 serves as a first dielectric layer 103.

The openings 102 provide a process space for the subsequent formation of contact plugs, and the first dielectric layer 103 between the openings 102 is used for electrically isolating the subsequently formed contact plugs.

In the step of forming the opening 102, a lateral direction perpendicular to the extending direction of the gate structure is taken as a lateral direction, and a top lateral dimension of the opening 102 is larger than a bottom lateral dimension of the opening 102. And forming a contact plug in the opening 102, wherein correspondingly, the size of the top of the contact plug is larger than that of the bottom of the contact plug, and the top of the contact plug is connected with a subsequent interconnection structure, so that the contact resistance of the contact plug and the interconnection structure is favorably reduced, and the electrical performance of the semiconductor structure is favorably optimized.

Specifically, the step of forming the opening 102 includes:

as shown in fig. 5, a shielding layer (not shown) is formed on the first dielectric material layer 101; and etching the first dielectric material layer 101 by using the shielding layer as a mask and adopting an anisotropic dry etching process to form an initial opening 104 in the first dielectric material layer.

The initial opening 104 provides for the subsequent formation of an opening.

In this embodiment, the anisotropic dry etching process has a better etching profile controllability, which is beneficial to enabling the morphology of the initial opening 104 to meet the process requirements, and is also beneficial to improving the removal efficiency of the first dielectric material layer 101. In the process of the anisotropic dry etching process, the top of the source-drain doped layer or the interlayer dielectric layer can be used as an etching stop position, so that the damage to other film layer structures is reduced.

As shown in fig. 6, an isotropic dry etching process is used to etch the top of the initial opening 104 to form an opening 102, and the remaining first dielectric material layer 101 serves as a first dielectric layer 103.

The opening 102 provides a process space for the subsequent formation of a contact plug.

In this embodiment, the isotropic etching process can etch the first dielectric material layer 101 along a direction perpendicular to the sidewall of the initial opening 104, and the dry etching process has a good etching precision, which is beneficial to accurately controlling the etching amount of the first dielectric material layer 101, so that the top transverse dimension of the formed opening 102 meets the process requirements.

Specifically, the dry etching process using isotropy includes a SiCoNi etching process or a Certas etching process.

Referring to fig. 7 to 9, in the opening 102, a contact plug 105 (shown in fig. 9) is formed.

The contact plug 105 is used for connecting the gate structure or the source-drain doping layer with the interconnection structure of the back section.

The material of the contact plug 105 includes: w, Al, Cu, Ag, Au, Pt, Ni or Ti.

In the opening 102, the step of forming a contact plug 105 includes: forming a contact plug material layer 106 on the opening 102 and the first dielectric layer 103 (as shown in fig. 8); the contact plug material layer 106 above the first dielectric layer 103 is removed, and the contact plug material layer 106 remaining in the opening 102 serves as a contact plug 105.

In this embodiment, an electrochemical plating process is used to fill the contact plug material layer 106 in the opening 102. The electrochemical plating process has the advantages of simple operation, high deposition speed, low cost and the like.

In this embodiment, the contact plug material layer 106 above the first dielectric layer 103 is removed by a chemical mechanical planarization process. Chemical Mechanical Planarization (CMP) is a global surface planarization technique that precisely and uniformly polishes a film layer on a wafer to a desired thickness and flatness.

The method for forming the semiconductor structure further comprises the following steps: after the opening 102 is formed and before the contact plug 105 is formed, a metal silicide layer 107 is formed on the top of the source-drain doped layer or the gate structure.

The metal silicide layer 107 is used to reduce the contact resistance between the contact plug 105 and the gate structure or the source-drain doping layer, thereby improving the electrical performance of the device.

In this embodiment, the metal silicide layer 107 is formed by a metal silicide process.

In this embodiment, the material of the metal silicide layer 107 is nickel silicide. In other embodiments, the material of the metal silicide layer may also be a cobalt silicide or a titanium silicide.

The method for forming the semiconductor structure further comprises the following steps: after the metal silicide layer 107 is formed, before the contact plug 105 is formed, an anti-diffusion layer 108 is conformally covered on the side wall and the bottom surface of the opening 102.

The diffusion preventing layer 108 is used to block ions in the contact plugs 105 from diffusing into the first dielectric layer 103, which is beneficial to enable the first dielectric layer 103 to better electrically isolate adjacent contact plugs 105.

In this embodiment, the material of the diffusion barrier layer 108 includes TaN or TiN.

Note that, in the process of forming the contact plug 105, the contact plug 105 is formed on the diffusion preventing layer 108.

Referring to fig. 10, a portion of the thickness of the first dielectric layer 103 is etched to form a recess 109 between the tops of the contact plugs 105.

The recess 109 provides space for the subsequent formation of a second dielectric layer having a dielectric constant less than that of the first dielectric layer.

In this embodiment, a recess 109 is formed between the tops of the contact plugs 105 by etching a part of the first dielectric layer 103 with an isotropic dry etching process.

The isotropic etching process has isotropic etching characteristics.

Taking the extending direction perpendicular to the gate structure as a transverse direction, because the top transverse dimension of the contact plugs 105 is larger than the bottom transverse dimension of the contact plugs 105, and correspondingly, the top transverse dimension of the first dielectric layer 103 between the contact plugs 105 is smaller than the bottom transverse dimension of the first dielectric layer 103 between the contact plugs 105, by etching the top of the first dielectric layer 103 by using an isotropic etching process, the top transverse dimension of the groove 109 is correspondingly smaller than the bottom transverse dimension of the groove 109.

Specifically, the isotropic dry etching process includes a SiCoNi etching process or a Certas etching process.

In this embodiment, the material of the first dielectric layer 103 includes silicon oxide, and correspondingly, the etching gas used in the isotropic dry etching process includes HF.

It should be noted that, in the process of etching a part of the thickness of the first dielectric layer 103 to form the groove 109, the groove 109 should not be too deep nor too shallow. If the recess 109 is too deep, an excessive process time is required to form the recess 109, which results in a poor formation efficiency of the semiconductor structure, and if the recess 109 is too deep, during a subsequent process of forming a second dielectric layer in the recess 109, a hole is likely to exist in the second dielectric layer, which tends to reduce an electrical isolation effect of the second dielectric layer on the top of the contact plug 105. If the recess 109 is too shallow, the second dielectric layer subsequently formed in the recess 109 is correspondingly thinner, and the second dielectric layer may not function well to electrically isolate the top of the contact plug 105, resulting in an insignificant improvement of the electrical performance of the semiconductor structure. In this embodiment, the depth of the groove 109 is 2 nm to 5 nm.

In the process of forming the groove 109, the lateral dimension of the top of the groove 109 is not too large or too small, taking the extending direction perpendicular to the gate structure as the lateral direction. If the lateral dimension of the top of the recess 109 is too large, the recess 109 is located between the tops of the contact plugs 105, and the lateral dimension of the top of the corresponding contact plug 105 is small, so that the contact resistance between the contact plug 105 and a subsequently formed interconnection structure is large, which results in a small operating current of the semiconductor structure, and is not favorable for improving the electrical performance of the semiconductor structure. If the lateral dimension of the top of the recess 109 is too small, the second dielectric layer subsequently formed in the recess 109 may not significantly improve the electrical isolation between the tops of adjacent contact plugs 105. In this embodiment, the top of the groove 109 has a lateral dimension of 10 nm to 16 nm.

Note that, in the process of forming the groove 109, the groove 109 is surrounded by the first dielectric layer 103 and the diffusion preventing layer 108.

Referring to fig. 11, a second dielectric layer 110 is formed in the recess 109, and the dielectric constant of the second dielectric layer 110 is lower than that of the first dielectric layer 103.

Forming a second dielectric layer 110 in the recess 109, wherein the dielectric constant of the second dielectric layer 110 is lower than the dielectric constant of the first dielectric layer 103, and the insulation of the second dielectric layer 110 is superior to the insulation of the first dielectric layer 103, so that the second dielectric layer 110 makes the top of the adjacent contact plug 105 not easily bridged, which is beneficial to optimizing the electrical performance of the semiconductor structure.

In this embodiment, the material of the second dielectric layer 110 includes SiN.

The step of forming the second dielectric layer 110 in the recess 109 comprises: forming a second dielectric material layer (not shown) conformally covering the recess 109 and the contact plug 105; the second dielectric material layer higher than the contact plug 105 is removed, and the remaining second dielectric material layer in the groove 109 serves as a second dielectric layer 110.

In this embodiment, the second dielectric material layer is formed by an Atomic Layer Deposition (ALD) process. The atomic layer deposition process comprises multiple atomic layer deposition cycles, the gap filling performance and the step coverage performance of the atomic layer deposition process are good, the conformal coverage capability of the second dielectric material layer is correspondingly improved, and holes are not prone to exist in the second dielectric material layer correspondingly. In other embodiments, the second dielectric material layer may also be formed by a Chemical Vapor Deposition (CVD) process or a Physical Vapor Deposition (PVD) process.

In this embodiment, a Chemical Mechanical Polishing (CMP) process is used to remove the second dielectric material layer higher than the contact plug 105. The chemical mechanical polishing process is a global surface planarization technique. In other embodiments, a dry etching process may be used to remove the second dielectric material layer higher than the contact plug 105.

In other embodiments, after the second dielectric material layer is formed, the second dielectric material layer in the groove is used as the second dielectric layer, and the second dielectric material layer higher than the contact plug is remained as the etch stop layer in the back-end process.

Correspondingly, the embodiment of the invention also provides a semiconductor structure. Referring to fig. 12, a schematic structural diagram of an embodiment of a semiconductor structure of the present invention is shown.

The semiconductor structure includes: a substrate (not shown in the figures); a gate structure (not shown) on the substrate; source and drain doping layers (not shown in the figure) positioned on the substrate at two sides of the gate structure; the first dielectric layer 203 is positioned on the gate structure, the source-drain doping layer and the substrate; a contact plug 205 located in the first dielectric layer 203 and contacting with the gate structure or the source-drain doping layer, wherein the top of the contact plug 205 protrudes out of the surface of the first dielectric layer 203; a second dielectric layer 210 on the first dielectric layer 203 between the tops of the contact plugs 205, the second dielectric layer 210 having a dielectric constant lower than that of the first dielectric layer 203.

In the semiconductor structure, the top of the contact plug 205 protrudes from the surface of the first dielectric layer 203; a second dielectric layer 210 on the first dielectric layer 203 between the tops of the contact plugs 205, the second dielectric layer 210 having a dielectric constant lower than that of the first dielectric layer 203. The dielectric constant of the second dielectric layer 210 is lower than that of the first dielectric layer 203, and the insulating property of the second dielectric layer 210 is better than that of the first dielectric layer 203, so that the top of the adjacent contact plug 205 is not easily bridged by the second dielectric layer 210, which is beneficial to optimizing the electrical performance of the semiconductor structure.

In this embodiment, the substrate is a silicon substrate. In other embodiments, the material of the substrate may also be other materials such as germanium, silicon carbide, gallium arsenide, or indium gallium arsenide, and the substrate may also be other types of substrates such as a silicon-on-insulator substrate or a germanium-on-insulator substrate.

In embodiments of the present invention, which take the form of a fin field effect transistor (FinFET), the substrate typically further includes a fin (not shown) on the substrate. In other embodiments, taking a gate all around transistor (GAA) as an example, the substrate further includes one or more channel layers suspended at intervals in a normal direction of the substrate surface, and a gate structure all around the channel layer.

The fin is used to subsequently provide a channel for a fin field effect transistor during operation of the semiconductor structure.

In this embodiment, the fin portion and the substrate are obtained by etching the same semiconductor layer. In other embodiments, the fin may also be a semiconductor layer epitaxially grown on the substrate, so as to achieve the purpose of precisely controlling the height of the fin.

Therefore, in this embodiment, the fin portion and the substrate are made of the same material, and the fin portion is made of silicon. In other embodiments, the material of the fin may also be germanium, silicon carbide, gallium arsenide, or indium gallium arsenide.

The gate structure is used to control the opening and closing of the channel in the fin during operation of the semiconductor structure.

In this embodiment, the gate structure includes a gate dielectric layer (not shown) and a gate layer (not shown) on the gate dielectric layer.

The gate dielectric layer is used for realizing electric isolation between the gate electrode layer and the fin portion. The gate dielectric layer is made of a high-k dielectric material. Wherein, the high-k dielectric material is a dielectric material with a relative dielectric constant larger than that of silicon oxide.

In this embodiment, the gate dielectric layer is made of HfO₂. In other embodiments, the material of the gate dielectric layer may also be selected from ZrO₂HfSiO, HfSiON, HfTaO, HfTiO, HfZrO or Al₂O₃One or more of them.

The gate layer serves as an electrode for electrically connecting to an external circuit, and in this embodiment, the gate layer is made of magnesium-tungsten alloy. In other embodiments, the material of the metal gate structure may also be W, Al, Cu, Ag, Au, Pt, Ni, Ti, or the like.

When the semiconductor structure works, the source-drain doped layer provides stress for a channel, and the migration rate of carriers is improved.

In this embodiment, the semiconductor structure is an NMOS, and the source-drain doped layer is used as a source and a drain of the NMOS. When the semiconductor structure works, the source-drain doped layer applies tensile stress to a channel below the gate structure, and the channel is stretched to improve the migration rate of electrons.

In other embodiments, the semiconductor structure is a PMOS, and the source-drain doped layers are used as a source and a drain of the PMOS. When the semiconductor structure works, the source-drain doped layers apply compressive stress to the channel below the gate structure, and the compressed channel can improve the mobility of holes.

The first dielectric layer 203 serves to electrically isolate adjacent devices.

In this embodiment, the material of the first dielectric layer 203 is an insulating material. Specifically, the material of the first dielectric layer 203 includes silicon oxide. The silicon oxide is a dielectric material with a common process and low cost, has high process compatibility, and is beneficial to reducing the process difficulty and the process cost for forming the first dielectric layer 203.

Specifically, the first dielectric layer 203 includes an interlayer dielectric layer (not shown) and a back-end dielectric layer (not shown) on the interlayer dielectric layer.

In this embodiment, the interlayer dielectric layer covers the substrate, the fin portion and the source-drain doping layer, and also covers the side wall of the gate structure to expose the top surface of the gate structure.

The back-end dielectric layer is used for electrically isolating the interconnection structures of the adjacent back-ends. The back section dielectric layer is positioned on the interlayer dielectric layer and the grid structure.

The contact plug 205 is used to connect the gate structure or the source-drain doped layer with the interconnect structure of the back end.

The material of the contact plug 205 includes: w, Al, Cu, Ag, Au, Pt, Ni or Ti.

Taking the extending direction perpendicular to the gate structure as a transverse direction, the transverse dimension of the top of the contact plug 205 is larger than the transverse dimension of the bottom of the contact plug 205, and accordingly, the top of the contact plug 205 is connected with a subsequent interconnection structure, which is beneficial to reducing the contact resistance of the contact plug 205 and the interconnection structure and optimizing the electrical performance of the semiconductor structure.

The dielectric constant of the second dielectric layer 210 is lower than that of the first dielectric layer 203, and the insulating property of the second dielectric layer 210 is better than that of the first dielectric layer 203, so that the top of the adjacent contact plug 205 is not easily bridged by the second dielectric layer 210, which is beneficial to optimizing the electrical performance of the semiconductor structure.

In this embodiment, the material of the second dielectric layer 210 includes SiN.

It should be noted that the second dielectric layer 210 should not be too thick, nor too thin. If the second dielectric layer 210 is too thick, an excessive process time is required to form the second dielectric layer 210, resulting in a poor formation efficiency of a semiconductor structure, and if the second dielectric layer 210 is too deep, a hole is easily formed in the second dielectric layer 210 during the formation of the second dielectric layer 210, resulting in a poor electrical isolation effect of the second dielectric layer 210 from the top of the contact plug 205. If the second dielectric layer 210 is thin, the second dielectric layer 210 may not function well to electrically isolate the top of the contact plug 205, resulting in an insignificant improvement in the electrical performance of the semiconductor structure. In this embodiment, the thickness of the second dielectric layer 210 is 2 nm to 5 nm.

It should be noted that the lateral dimension of the top of the second dielectric layer 210 is neither too large nor too small, taking the extension direction perpendicular to the gate structure as the lateral direction. If the lateral dimension of the top of the second dielectric layer 210 is too large, the second dielectric layer 210 is located between the tops of the contact plugs 205, and the lateral dimension of the top of the corresponding contact plug 205 is small, so that the contact resistance between the contact plug 10 and a subsequently formed interconnection structure is large, which results in a small operating current of the semiconductor structure and is not favorable for improving the electrical performance of the semiconductor structure. If the lateral dimension of the top of the second dielectric layer 210 is too small, the second dielectric layer 210 has an insignificant effect of improving the electrical isolation between the tops of the adjacent contact plugs 205, and the top of the contact plug 105 is prone to have a leakage current, resulting in poor electrical performance of the semiconductor structure. In this embodiment, the lateral dimension of the top of the second dielectric layer 210 is 10 nm to 16 nm.

The semiconductor structure further includes: and the metal silicide layer 207 is positioned between the source-drain doped layer and the contact plug 205, or positioned between the gate structure and the contact plug 205.

The metal silicide layer 207 is used to reduce the contact resistance between the contact plug 205 and the gate structure or the source-drain doping layer, thereby improving the electrical performance of the device.

In this embodiment, the material of the metal silicide layer 207 is nickel-silicon compound. In other embodiments, the material of the metal silicide layer may also be a cobalt silicide or a titanium silicide.

The semiconductor structure further includes: and the anti-diffusion layer 208 is located between the contact plug 205 and the first dielectric layer 203, between the contact plug 205 and the gate structure, between the contact plug 205 and the source-drain doping layer, and between the contact plug 205 and the second dielectric layer 210.

The diffusion preventing layer 208 is used to block ions in the contact plugs 205 from diffusing into the first dielectric layer 203, which is beneficial to enable the first dielectric layer 203 to better electrically isolate adjacent contact plugs 205.

In this embodiment, the material of the diffusion barrier layer 208 includes TaN or TiN.

The semiconductor structure of this embodiment may be formed by the formation method described in the foregoing embodiment, or may be formed by other formation methods. For a detailed description of the semiconductor structure in this embodiment, reference may be made to the corresponding description in the foregoing embodiments, and details of this embodiment are not repeated herein.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.