Contact plugs and their formation methods, semiconductor device formation methods

Abstract

This invention provides a contact plug and its formation method, as well as a semiconductor device formation method. First, a first portion of the contact plug is formed. Then, a sacrificial layer is removed, causing the first portion of the contact plug to protrude from a first dielectric layer. A second portion of the contact plug is then formed within a third dielectric layer. The first and second portions of the contact plug are electrically connected to form the contact plug. An unexpected advantage of this invention is that, without adding a photomask, forming the first and second portions of the contact plug separately yields a contact plug with excellent structure and performance. Furthermore, by removing the sacrificial layer to cause the first portion of the contact plug to protrude from the first dielectric layer, and then forming a complete long contact plug from two short contact plug segments, the problem of poor contact hole filling ability caused by an excessively long contact plug is avoided, preventing voids and preventing open circuits between the contact plug and the upper metal layer.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit technology, and in particular to a contact plug and a method for forming the same, as well as a method for forming semiconductor devices. Background Technology

[0002] In advanced process development, when forming tungsten contact holes, because the tungsten contact holes penetrate three dielectric layers, the height of the contact plugs (tungsten plugs) used to connect the source and drain electrodes to the first metal layer (M1) becomes excessive, increasing the current flow path and resulting in excessively high resistance and capacitance values ​​in the contact plug section. Excessively long contact plugs can lead to poor hole-filling ability of the tungsten contact holes, the formation of tungsten seams and void defects, and can also cause contact open circuits between the contact plug and the first metal layer. Summary of the Invention

[0003] The purpose of this invention is to provide a contact plug and a method for forming the same, so as to solve at least one of the problems of excessively long contact plugs causing contact plug gaps, voids, and open circuits between the contact plug and the first metal layer.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for forming a contact plug, comprising:

[0005] A substrate is provided on which a MOS device and a first dielectric layer and a sacrificial layer are formed, respectively, on the MOS device;

[0006] The first portion of the contact hole is formed, which sequentially penetrates the sacrificial layer and the first dielectric layer and exposes the gate, source and drain of the MOS device;

[0007] A first portion of a contact plug is formed, wherein the first portion of the contact plug fills the first portion of the contact hole;

[0008] After the sacrificial layer is removed, a first portion of the contact plug protrudes from the first dielectric layer;

[0009] A second dielectric layer and a third dielectric layer are formed sequentially. The second dielectric layer covers the first dielectric layer and the first part of the contact plug. The second dielectric layer above the first part of the contact plug is higher than the second dielectric layer above the first dielectric layer. The third dielectric layer covers the second dielectric layer.

[0010] A chemical mechanical polishing process is performed to remove part of the third dielectric layer, and the second dielectric layer above the first portion of the contact plug is flush with the top surface of the third dielectric layer;

[0011] Remove the second dielectric layer above the first portion of the contact plug to form the second portion of the contact hole within the third dielectric layer;

[0012] A second part of a contact plug is formed, the second part of the contact plug being located within the second part of the contact hole, and the first part and the second part of the contact plug being electrically connected to form a contact plug.

[0013] Optionally, the step of forming the first portion of the contact plug includes:

[0014] A contact plug material layer is deposited, the contact plug material layer filling a first portion of the contact hole and extending onto the sacrificial layer;

[0015] A chemical mechanical polishing process is performed, and the polishing stops on the sacrificial layer. The contact plug material layer in the first part of the contact hole constitutes the first part of the contact plug.

[0016] Optionally, the first part and the second part of the contact plug are made of the same material.

[0017] Optionally, the step of forming the first portion of the contact hole includes:

[0018] An amorphous carbon layer, a silicon oxynitride layer, a bottom anti-reflective layer, and a photoresist layer are formed sequentially.

[0019] The photolithography and development processes are performed to form a patterned photoresist layer;

[0020] An etching process is performed, using the patterned photoresist layer as a mask, to etch the silicon oxynitride layer, the amorphous carbon layer, the sacrificial layer, and the first dielectric layer to form the first portion of the contact hole on the gate of the MOS device.

[0021] Optionally, a fill layer is formed between adjacent MOS devices, and the fill layer is further etched in the etching process to form the first portion of the contact hole on the source and drain of the MOS device.

[0022] Optionally, the third dielectric layer and the second dielectric layer are made of different materials, and the second dielectric layer and the first dielectric layer are made of different materials.

[0023] Optionally, the material of the first dielectric layer is silicon oxide, the material of the second dielectric layer is one of SiC, SiN, TiN, amorphous carbon, SiON, ELK or SiCN, and the material of the third dielectric layer is one of silicon oxide, SiC, SiN, TiN, amorphous carbon, SiON, ELK or SiCN.

[0024] Optionally, a dry etching process is used to remove the second dielectric layer on the first portion of the contact plug. In the dry etching process, the etching selectivity of the second dielectric layer and the third dielectric layer is different.

[0025] Based on the same inventive concept, the present invention also provides a contact plug, which is prepared by the contact plug forming method described in any of the above claims.

[0026] Based on the same inventive concept, the present invention also provides a method for forming a semiconductor device, including a method for forming a contact plug as described in any of the preceding claims.

[0027] In the contact plug formation method provided by the present invention, a first portion of a contact hole is first formed, which sequentially penetrates a sacrificial layer and a first dielectric layer to expose the gate, source, and drain of a MOS device; then, a first portion of a contact plug is formed, which fills the first portion of the contact hole; next, the sacrificial layer is removed, and the first portion of the contact plug protrudes from the first dielectric layer; then, a second dielectric layer and a third dielectric layer are sequentially formed, with the second dielectric layer covering the first dielectric layer and the first portion of the contact plug, the second dielectric layer above the first portion of the contact plug being higher than the second dielectric layer above the first dielectric layer, the third dielectric layer covering the second dielectric layer, and a chemical mechanical polishing process is performed to remove part of the third dielectric layer, so that the second dielectric layer above the first portion of the contact plug is flush with the top surface of the third dielectric layer; then, the second dielectric layer on the first portion of the contact plug is removed to form a second portion of the contact hole within the third dielectric layer; then, the second portion of the contact plug is formed, which is located within the second portion of the contact hole, and the first portion and the second portion of the contact plug are electrically connected to form the contact plug. An unexpected benefit of this invention is that, without adding a photomask, a contact plug with excellent structure and performance can be obtained by forming the first part and the second part of the contact plug separately. By removing the sacrificial layer to make the first part of the contact plug protrude from the first dielectric layer, and then forming a complete long contact plug by two short contact plug segments, the problem of poor contact hole filling ability caused by excessively long contact plugs can be avoided, defects such as voids can be prevented, and open circuit problems between the contact plug and the upper metal layer can be avoided. Attached Figure Description

[0028] Those skilled in the art will understand that the accompanying drawings are provided to better understand the invention and do not constitute any limitation on the scope of the invention.

[0029] Figure 1 This is a flowchart of the method for forming a contact plug according to an embodiment of the present invention.

[0030] Figure 2This is a schematic diagram of the semiconductor structure after the formation of the photoresist layer according to an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram of the semiconductor structure after the formation of a patterned photoresist layer according to an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of the semiconductor structure after the first part of the contact hole is formed, according to an embodiment of the present invention.

[0033] Figure 5 This is a schematic diagram of the semiconductor structure after the formation of the contact plug material layer according to an embodiment of the present invention.

[0034] Figure 6 This is a schematic diagram of the semiconductor structure after the first part of the contact plug is formed, according to an embodiment of the present invention.

[0035] Figure 7 This is a schematic diagram of the semiconductor structure after removing the sacrificial layer according to an embodiment of the present invention.

[0036] Figure 8 This is a schematic diagram of the semiconductor structure after the formation of the second dielectric layer and the third dielectric layer according to an embodiment of the present invention.

[0037] Figure 9 This is a schematic diagram of the semiconductor structure after removing part of the third dielectric layer according to an embodiment of the present invention.

[0038] Figure 10 This is a schematic diagram of the semiconductor structure after the second part of the contact hole is formed, according to an embodiment of the present invention.

[0039] Figure 11 This is a schematic diagram of the semiconductor structure after the second part of the contact plug is formed, according to an embodiment of the present invention.

[0040] In the attached figures: 10-substrate; 11-shallow trench isolation structure; 12-well region; 13-MOS device; 13a-gate; 13b-drain; 13c-source; 14-fill layer; 15-first dielectric layer; 16-sacrificial layer; 17-amorphous carbon layer; 18-silicon oxynitride layer; 19-bottom anti-reflective layer; 20-photoresist layer; 20a-patterned photoresist layer; 21-opening; 22-first portion of contact hole; 23-contact plug; 23a-contact plug material layer; 23b-first portion of contact plug; 23c-second portion of contact plug; 24-second dielectric layer; 25-third dielectric layer; 26-second portion of contact hole. Detailed Implementation

[0041] To make the objectives, advantages, and features of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to facilitate and clarify the explanation of the embodiments of this invention. Furthermore, the structures shown in the drawings are often part of the actual structures. In particular, different figures may emphasize different aspects and may sometimes use different scales.

[0042] As used in this invention, the singular forms “a,” “an,” and “the” include plural objects; the term “or” is generally used to mean “and / or”; the term “a number” is generally used to mean “at least one”; and the term “at least two” is generally used to mean “two or more”. Furthermore, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with “first,” “second,” or “third” may explicitly or implicitly include one or at least two of that feature. Additionally, as used in this invention, the placement of one element on another element generally only indicates a connection, coupling, cooperation, or transmission relationship between the two elements, which can be direct or indirect through an intermediate element. It should not be construed as indicating or implying a spatial positional relationship between the two elements, i.e., one element can be located arbitrarily inside, outside, above, below, or to one side of the other element, unless otherwise explicitly stated. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] Figure 1 This is a flowchart illustrating the method for forming a contact plug according to an embodiment of the present invention. Figure 1 As shown, this embodiment provides a method for forming a contact plug, including:

[0044] Step S10: Provide a substrate on which a MOS device and a first dielectric layer and a sacrificial layer are formed;

[0045] Step S20: Form a first portion of a contact hole, wherein the first portion of the contact hole sequentially penetrates the sacrificial layer and the first dielectric layer to expose the gate, source and drain of the MOS device;

[0046] Step S30: A first portion of a contact plug is formed, wherein the first portion of the contact plug fills the first portion of the contact hole;

[0047] Step S40: Remove the sacrificial layer, and the first portion of the contact plug protrudes from the first dielectric layer;

[0048] Step S50: A second dielectric layer and a third dielectric layer are formed sequentially. The second dielectric layer covers the first dielectric layer and the first part of the contact plug. The second dielectric layer above the first part of the contact plug is higher than the second dielectric layer above the first dielectric layer. The third dielectric layer covers the second dielectric layer.

[0049] Step S60: Perform a chemical mechanical polishing process to remove part of the third dielectric layer, and the second dielectric layer above the first portion of the contact plug is flush with the top surface of the third dielectric layer;

[0050] Step S70: Remove the second dielectric layer above the first portion of the contact plug to form the second portion of the contact hole within the third dielectric layer;

[0051] Step S80: A second part of the contact plug is formed. The second part of the contact plug is located inside the second part of the contact hole. The first part of the contact plug and the second part of the contact plug are electrically connected and constitute the contact plug.

[0052] To make the above-mentioned objects, features and beneficial effects of the present invention more apparent and understandable, the following description is provided in conjunction with the appendix to the specification. Figures 2 to 11 Specific embodiments of the present invention will be described in detail below.

[0053] like Figure 2As shown, a substrate 10 is provided, which serves as an operating platform for subsequent processes. The substrate 10 can be any substrate known to those skilled in the art for supporting semiconductor integrated circuit components, such as a bare die or a wafer processed by epitaxial growth. Specifically, the substrate can be, for example, a silicon-on-insulator (SOI) substrate, a bulk silicon substrate, a germanium substrate, a germanium-silicon substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate. In this embodiment, the substrate 10 is a silicon substrate. A shallow trench isolation structure 11 and a well region 12 are formed within the substrate 10. The shallow trench isolation structure 11 is used to isolate adjacent well regions 12. A MOS device 13 is formed on the substrate 10. The MOS device 13 can be a PMOS device or an NMOS device. The MOS device 13 includes a gate 13a, a drain 13b, and a source 13c. A filler layer 14 is formed between adjacent MOS devices 13. The top surface of the filler layer 14 is flush with the top surface of the MOS device 13. The filler layer 14 is made of, for example, silicon oxide and can be formed using a chemical vapor deposition process. A first dielectric layer 15 and a sacrificial layer 16 are also formed on the MOS device 13. The sacrificial layer 16 is made of a different material than the first dielectric layer 15. The first dielectric layer 15 is made of, for example, silicon oxide and can be formed using a chemical vapor deposition process. The sacrificial layer 16 is made of, for example, one of SiC, SiN, TiN, amorphous carbon, SiON, ELK, or SiCN. An amorphous carbon layer 17 (a-Carbon, AC), a silicon oxynitride layer 18 (SiON), a bottom anti-reflection layer 19 (BRAC), and a photoresist layer 20 are sequentially formed on the sacrificial layer 16. The silicon oxynitride layer 18 can serve as a bottom anti-reflection layer for photolithography, reducing the influence of standing wave effect, and can also serve as a hard mask layer, improving the selectivity of etching. The amorphous carbon layer 17 can be used as a hard mask layer in the etching process.

[0054] like Figure 3 As shown, a photolithography and development process is performed to form a patterned photoresist layer 20a. The patterned photoresist layer 20a has an opening 21, which corresponds to the gate, drain and source of the MOS device.

[0055] like Figure 4As shown, an etching process is performed, using the patterned photoresist layer 20a as a mask, to etch the silicon oxynitride layer 18, the amorphous carbon layer 17, the sacrificial layer 16, and the first dielectric layer 15 to form the first portion 22 of the contact hole on the gate 13a of the MOS device. The first portion 22 of the contact hole is an extension of the opening 21 within the sacrificial layer 16 and the first dielectric layer 15. The filling layer 14 is then etched to form the first portion 22 of the contact hole on the source 13c and drain 13b of the MOS device. After forming the first portion 22 of the contact hole, if the patterned photoresist layer 20a is not completely consumed, a photoresist removal process is required, typically using an ashing process or a stripping method to remove the remaining patterned photoresist layer 20a.

[0056] like Figure 5 As shown, a contact plug material layer 23a is deposited, which fills the first portion 22 of the contact hole and extends onto the sacrificial layer 16; the contact plug material layer 23a is, for example, tungsten. Before forming the contact plug material layer 23a, a tungsten barrier layer is first formed within the first portion 22 of the contact hole; the tungsten barrier layer is, for example, titanium (Ti) and titanium nitride (TiN). The tungsten barrier layer and the contact plug material layer 23a can be formed using a physical vapor deposition process.

[0057] like Figure 6 As shown, a chemical mechanical polishing process is performed, and the polishing stops on the sacrificial layer 16. The contact plug material layer in the first portion 22 of the contact hole constitutes the first portion 23b of the contact plug.

[0058] like Figure 7 As shown, after removing the sacrificial layer 16, the first portion 23b of the contact plug protrudes from the first dielectric layer 15. The sacrificial layer 16 can be removed using a dry etching process. Since the etching selectivity ratios of the sacrificial layer 16, the first dielectric layer 15, and the first portion 23b of the contact plug are different, only the sacrificial layer 16 can be removed.

[0059] like Figure 8As shown, a second dielectric layer 24 and a third dielectric layer 25 are formed sequentially. The second dielectric layer 24 covers the first dielectric layer 15 and the first portion 23b of the contact plug. The second dielectric layer 24 above the first portion 23b of the contact plug is higher than the second dielectric layer 24 above the first dielectric layer 15. The third dielectric layer 25 covers the second dielectric layer 24. Since the first portion 23b of the contact plug protrudes from the first dielectric layer 15 after the sacrificial layer 16 is removed, the second dielectric layer 24 on the first portion 23b of the contact plug is higher than the second dielectric layer 24 on the first dielectric layer 15 when the second dielectric layer 24 is formed. Then, when the third dielectric layer 25 is formed, it completely fills the groove between adjacent protruding second dielectric layers 24 and completely covers the second dielectric layer 24 on the first portion 23b of the contact plug. The third dielectric layer 25 and the second dielectric layer 24 are made of different materials. The material of the second dielectric layer 24 is, for example, one of SiC, SiN, TiN, amorphous carbon, SiON, ELK, or SiCN, and the material of the third dielectric layer 25 is, for example, one of silicon oxide, SiC, SiN, TiN, amorphous carbon, SiON, ELK, or SiCN. The second dielectric layer 24 and the third dielectric layer 25 can be formed using a chemical vapor deposition process.

[0060] like Figure 9 As shown, a chemical mechanical polishing process is performed to remove part of the third dielectric layer 25. The polishing stops on the second dielectric layer 24. The second dielectric layer 24 on the first portion 23b of the contact plug is located in the third dielectric layer 25 and is flush with the top surface of the third dielectric layer 25.

[0061] like Figure 10 As shown, the second dielectric layer 24 on the first portion 23b of the contact plug is removed to form the second portion 26 of the contact hole within the third dielectric layer 25. The second dielectric layer 24 on the first portion 23b of the contact plug can be removed using a dry etching process. Because the third dielectric layer 25 and the second dielectric layer 24 are made of different materials, the etching selectivity ratios for the third dielectric layer 25 and the second dielectric layer 24 are different in the dry etching process. Therefore, it is possible to remove only the second dielectric layer 24 on the first portion 23b of the contact plug.

[0062] like Figure 11As shown, a second portion 23c of the contact plug is formed, located within the second portion 26 of the contact hole. The first portion 23b and the second portion 23c of the contact plug constitute the contact plug 23. The steps for forming the second portion 23c of the contact plug are similar to those for forming the first portion 23b, including: depositing a contact plug material layer 23a, which fills the second portion 26 of the contact hole and extends onto the third dielectric layer 25; the contact plug material layer 23a is, for example, tungsten. Before forming the contact plug material layer 23a, a tungsten barrier layer is formed within the second portion 26 of the contact hole, such as titanium (Ti) and titanium nitride (TiN). The tungsten barrier layer and the contact plug material layer 23a can be formed using a physical vapor deposition process. A chemical mechanical polishing process is then performed, stopping the polishing on the third dielectric layer 25. The contact plug material layer within the second portion 26 of the contact hole constitutes the second portion 23c of the contact plug. This invention, without adding a photomask, forms the first and second parts of the contact plug through two metal deposition processes and a chemical mechanical polishing process, resulting in a contact plug with excellent structure and performance. Furthermore, a sacrificial layer defines the contact plug and non-contact plug regions. Then, a complete long contact hole is formed through two short contact hole processes; that is, a complete long contact plug is formed from two short contact plug segments. This avoids the problem of poor contact hole filling ability caused by excessively long contact plugs, as well as defects such as voids, and thus avoids open circuits between the contact plug and the upper metal layer.

[0063] like Figure 11As shown, this embodiment also provides a contact plug, fabricated using the contact plug formation method described in any of the above embodiments, comprising a substrate 10, wherein a shallow trench isolation structure 11 and a well region 12 are formed within the substrate 10, the shallow trench isolation structure 11 being used to isolate adjacent well regions 12. A MOS device 13 is formed on the substrate 10, the MOS device 13 being either a PMOS or an NMOS. The MOS device 13 includes a gate 13a, a drain 13b, and a source 13c. A filling layer 14 is formed between adjacent MOS devices 13, the top surface of the filling layer 14 being flush with the top surface of the MOS device 13. The MOS device 13 also has a first dielectric layer 15, a second dielectric layer 24, and a third dielectric layer 25, as well as a contact plug 23 on the gate 13a that penetrates the third dielectric layer 25, the second dielectric layer 24, and the first dielectric layer 15, and contact plugs 23 on the source 13c and the drain 13b that penetrate the third dielectric layer 25, the second dielectric layer 24, the first dielectric layer 15, and the fill layer 14. The contact plug 23 includes a first portion 23b and a second portion 23c. By forming a complete long contact plug 23 from two short first portions 23b and second portions 23c, the problem of poor filling ability of metal contact holes caused by excessively long contact plugs, as well as defects such as voids, can be prevented, thereby avoiding the problem of open circuits between the contact plug and the upper metal layer.

[0064] This invention also provides a method for forming a semiconductor device, which uses the contact plug forming method described above to form a plug.

[0065] In summary, in the contact plug formation method provided in this embodiment of the invention, the method involves first forming a first portion of a contact hole, which sequentially penetrates a sacrificial layer and a first dielectric layer to expose the gate, source, and drain of a MOS device; then forming a first portion of a contact plug, which fills the first portion of the contact hole; removing the sacrificial layer, which causes the first portion of the contact plug to protrude from the first dielectric layer; sequentially forming a second dielectric layer and a third dielectric layer, where the second dielectric layer covers the first dielectric layer and the first portion of the contact plug, the second dielectric layer above the first portion of the contact plug is higher than the second dielectric layer above the first dielectric layer, the third dielectric layer covers the second dielectric layer, and a chemical mechanical polishing process is performed to remove part of the third dielectric layer, making the second dielectric layer above the first portion of the contact plug flush with the top surface of the third dielectric layer; then removing the second dielectric layer on the first portion of the contact plug to form a second portion of the contact hole within the third dielectric layer; finally forming the second portion of the contact plug, which is located within the second portion of the contact hole, and the first portion and the second portion of the contact plug are electrically connected to form the contact plug. An unexpected benefit of this invention is that, without adding a photomask, a contact plug with excellent structure and performance can be obtained by forming the first and second parts of the contact plug through two metal deposition processes and chemical mechanical polishing. Furthermore, by defining the contact plug and non-contact plug regions with a sacrificial layer, and then forming a complete long contact plug from two short contact plug segments, the problem of poor contact hole filling ability caused by excessively long contact plugs, as well as defects such as voids, can be avoided, thus preventing open circuits between the contact plug and the upper metal layer.

[0066] Furthermore, it should be understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for forming a contact plug, characterized in that, include: A substrate is provided on which a MOS device and a first dielectric layer and a sacrificial layer are formed, respectively, on the MOS device; The first portion of the contact hole is formed, wherein the first portion of the contact hole sequentially penetrates the sacrificial layer and the first dielectric layer and exposes the gate, source and drain of the MOS device; A first portion of a contact plug is formed, wherein the first portion of the contact plug fills the first portion of the contact hole; After the sacrificial layer is removed, a first portion of the contact plug protrudes from the first dielectric layer; A second dielectric layer and a third dielectric layer are formed sequentially. The second dielectric layer covers the first dielectric layer and the first part of the contact plug. The second dielectric layer above the first part of the contact plug is higher than the second dielectric layer above the first dielectric layer. The third dielectric layer covers the second dielectric layer. A chemical mechanical polishing process is performed to remove part of the third dielectric layer, and the second dielectric layer above the first portion of the contact plug is flush with the top surface of the third dielectric layer; Remove the second dielectric layer above the first portion of the contact plug to form the second portion of the contact hole within the third dielectric layer; A second part of a contact plug is formed, the second part of the contact plug is located inside the second part of the contact hole, the first part of the contact plug and the second part of the contact plug are electrically connected and constitute a contact plug, the second part of the contact plug and the first part of the contact plug have the same width and the second part of the contact plug and the first part of the contact plug constitute a complete section of the contact plug.

2. The method for forming a contact plug according to claim 1, characterized in that, The steps of forming the first part of the contact plug include: A deposited contact plug material layer is formed, the contact plug material layer filling a first portion of the contact hole and extending onto the sacrificial layer; A chemical mechanical polishing process is performed, and the polishing stops on the sacrificial layer. The contact plug material layer in the first part of the contact hole constitutes the first part of the contact plug.

3. The method for forming a contact plug according to claim 1 or 2, characterized in that, The first part and the second part of the contact plug are made of the same material.

4. The method for forming a contact plug according to claim 1, characterized in that, The steps for forming the first portion of the contact hole include: An amorphous carbon layer, a silicon oxynitride layer, a bottom anti-reflective layer, and a photoresist layer are formed sequentially. The photolithography and development processes are performed to form a patterned photoresist layer; An etching process is performed, using the patterned photoresist layer as a mask, to etch the silicon oxynitride layer, the amorphous carbon layer, the sacrificial layer, and the first dielectric layer to form the first portion of the contact hole on the gate of the MOS device.

5. The method for forming a contact plug according to claim 4, characterized in that, A fill layer is formed between adjacent MOS devices, and the fill layer is further etched in the etching process to form the first portion of the contact hole on the source and drain of the MOS device.

6. The method for forming a contact plug according to claim 1, characterized in that, The third dielectric layer is made of a different material than the second dielectric layer, and the second dielectric layer is made of a different material than the first dielectric layer.

7. The method for forming a contact plug according to claim 6, characterized in that, The first dielectric layer is made of silicon oxide, the second dielectric layer is made of one of SiC, SiN, TiN, amorphous carbon, SiON, ELK, or SiCN, and the third dielectric layer is made of one of silicon oxide, SiC, SiN, TiN, amorphous carbon, SiON, ELK, or SiCN.

8. The method for forming a contact plug according to claim 6, characterized in that, The second dielectric layer on the first portion of the contact plug is removed using a dry etching process, wherein the etching selectivity ratios of the second dielectric layer and the third dielectric layer are different in the dry etching process.

9. A contact plug, characterized in that, It is prepared by the method for forming the contact plug as described in any one of claims 1 to 8.

10. A method for forming a semiconductor device, characterized in that, The method of forming the contact plug as described in any one of claims 1 to 8.

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