Etching stop layer for reducing RC delay and preparation method thereof
By using a PECVD method to prepare multilayer nitrogen-doped carbon-based material layers, the dielectric constant of the SiCN etch stop layer was reduced, the RC delay problem was solved, and the adhesion and electrical properties of the dielectric layer were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-26
- Publication Date
- 2026-05-01
AI Technical Summary
The high dielectric constant of the existing SiCN etch stop layer leads to a serious RC delay problem, which is difficult to effectively reduce using existing technologies.
Multilayer nitrogen-doped carbon-based material layers were prepared using the PECVD method, including a first nitrogen-doped carbon-based material layer, a second nitrogen-doped carbon-based material layer, and a third nitrogen-doped carbon-based material layer. The carbon content was increased and the dielectric constant was reduced by introducing propylene gas. Identical first and third nitrogen-doped carbon-based material layers were set at the interface to maintain adhesion.
It effectively reduces the dielectric constant of the etch stop layer, reduces parasitic capacitance, lowers RC delay, improves the adhesion of the dielectric layer, and avoids current leakage and electromigration problems.
Smart Images
Figure CN121969034A_ABST
Abstract
Description
An etch stop layer for reducing RC delay and its preparation method Technical Field
[0001] This invention belongs to the field of semiconductor technology, specifically relating to an etch stop layer for reducing RC delay and its preparation method. Background Technology
[0002] In very large-scale integrated circuits (VLSI), copper has been widely used in back-end interconnects (BEOLs), and silicon carbonitride (SiCN) films have been used as etch stop layers and copper diffusion barrier layers for BEOLs. Plasma-enhanced chemical vapor deposition (PECVD) deposits SiCN barrier layers (k~5.3) to ensure Cu diffusion resistance. As device feature sizes continue to shrink, low-k porous materials with a dielectric constant of 2.5 (such as low-k SiOCH films) are used as intermetallic dielectric (IMD) layers. Although SiCN has a lower dielectric constant than silicon nitride (SIN) (k~7), its dielectric constant is still more than twice that of low-k SiOCH. SiCN, with a dielectric constant of k~5.3, serves as both a barrier layer and an interlayer dielectric. Together with low-k porous SiOCH films with a dielectric constant of 2.5, they form the IMD layer. The higher dielectric constant of SiCN compared to porous SiOCH is a major factor affecting the RC delay of BEOL devices. Therefore, developing etch stop layer materials with lower k is a direct way to reduce parasitic capacitance and RC delay. Summary of the Invention
[0003] In view of all or part of the deficiencies of the prior art described above, the object of the present invention is to provide an etch stop layer for reducing RC delay and a method for preparing the same, thereby reducing the dielectric constant k of the NDC barrier layer, such as the SiCN thin film, and thus reducing RC delay.
[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a method for preparing an etch stop layer to reduce RC delay, which employs plasma-enhanced chemical vapor deposition (PECVD) to perform the following deposition steps: Step S1, depositing a first nitrogen-doped carbon-based material layer on the surface of a dielectric layer, using a combination of tetramethylsilane and ammonia as the first reactant gas; Step S2, depositing a second nitrogen-doped carbon-based material layer on the surface of the first nitrogen-doped carbon-based material layer, using a combination of tetramethylsilane, ammonia, and propylene as the second reactant gas; Step S3, depositing a third nitrogen-doped carbon-based material layer on the surface of the second nitrogen-doped carbon-based material layer, using a combination of tetramethylsilane and ammonia as the third reactant gas.
[0005] Existing etch stop layers are typically monolayers of a first nitrogen-doped carbon-based material (NDC material, such as silicon carbonitride), with a dielectric constant of 5.3. This invention prepares a second nitrogen-doped carbon-based material layer. During the deposition of the second nitrogen-doped carbon-based material layer, propylene gas is added as a reactive gas. The carbon and hydrogen content of the second nitrogen-doped carbon-based material layer is higher than that of the first / third nitrogen-doped carbon-based material layers, but the nitrogen and silicon content is lower. The introduction of propylene gas makes the second nitrogen-doped carbon-based material layer a carbon-rich layer, thereby reducing the overall dielectric constant of the etch stop layer. Compared to ethylene, propylene also has carbon-carbon (CC) single bonds, which have lower polarizability, further reducing the overall dielectric constant of the etch stop layer, thus further reducing parasitic capacitance and RC delay. Compared to olefins with more than four carbon atoms, such as butene, propylene has a shorter carbon molecular chain, resulting in a film that maintains a high etch selectivity with low-k dielectric materials such as SiOCH low-k films.
[0006] Interfacial adhesion is considered to be related to chemical bonding configuration; that is, high bond energy is expected to contribute to high interfacial adhesion strength. For example, the bond energy of Si-O (452 kJ / mol) is higher than that of Si-C (347 kJ / mol). The more Si-C bonds formed at the interface, the lower the interfacial adhesion and the more prone it is to delamination. Interfacial delamination can adversely affect the performance of integrated circuits, and even lead to more serious current leakage and electromigration problems. Compared with directly using a carbon-rich second nitrogen-doped carbon-based material layer as an etch stop layer, the increased carbon content will affect the adhesion between the etch stop layer (overall NDC structure) and the dielectric layer (e.g., the interlayer dielectric layer of a metal interconnect structure). In this invention, a first nitrogen-doped carbon-based material layer and a third nitrogen-doped carbon-based material layer are also disposed on both sides of the second nitrogen-doped carbon-based material layer to maintain the adhesion between the overall NDC structure and the dielectric layer.
[0007] In some specific embodiments, the first nitrogen-doped carbon-based material layer is a first silicon carbonitride thin film, the second nitrogen-doped carbon-based material layer is a second silicon carbonitride thin film, and the third nitrogen-doped carbon-based material layer is a third silicon carbonitride thin film.
[0008] The first nitrogen-doped carbon-based material layer and the third nitrogen-doped carbon-based material layer are identical. That is, the first nitrogen-doped carbon-based material layer and the third nitrogen-doped carbon-based material layer have the same material composition and thickness.
[0009] In step S2, the flow rate ratio of the second reactant gas is controlled at tetramethylsilane:propylene:ammonia = 1:0.6:3, wherein the flow rate of tetramethylsilane is in the range of 1000-2000 sccm, the flow rate of propylene is in the range of 600-1200 sccm, and the flow rate of ammonia is in the range of 3000-6000 sccm.
[0010] In step S2, the deposition process conditions for the second nitrogen-doped carbon-based material layer are as follows: deposition temperature 300-400℃, deposition pressure 3-5 Torr, high-frequency radio frequency power 800-1200W, low-frequency radio frequency power 800-1100W; nitrogen is used as the carrier gas with a flow rate of 2000-4000 sccm.
[0011] In steps S1 and S3, the flow rate ratio of the first reactant gas and the third reactant gas is controlled at tetramethylsilane:ammonia = 0.3:1-0.6:1, the flow rate of tetramethylsilane is in the range of 1000-2000 sccm, and the flow rate of ammonia is in the range of 3000-6000 sccm.
[0012] In steps S1 and S3, the deposition process conditions for the first nitrogen-doped carbon-based material layer and the third nitrogen-doped carbon-based material layer are as follows: deposition temperature 300-400℃, deposition pressure 3-4 Torr, high-frequency radio frequency power 800-1200W, low-frequency radio frequency power 600-1200W; nitrogen is used as the carrier gas with a flow rate of 2000-4000 sccm.
[0013] In step S1, the dielectric layer is a first interlayer dielectric layer in the first metal interconnect structure, which is a porous carbon-doped silicon oxide layer. The first metal interconnect structure is a copper interconnect structure, and the process further includes: before depositing the first nitrogen-doped carbon-based material layer, using ammonia to perform plasma surface pretreatment on the copper interconnect structure to remove oxides from the copper surface. After step S3, the process further includes depositing a second interlayer dielectric layer on the surface of the third nitrogen-doped carbon-based material layer, which is a porous carbon-doped silicon oxide layer. The second interlayer dielectric layer can be further etched to obtain vias, and after filling with conductive material, a second metal interconnect structure is obtained. At this time, the etching stop layer is located between the first metal interconnect structure and the second metal interconnect structure, but it is not limited to this. The etching stop layer may also have only one side including the metal interconnect structure, while the other side may be the dielectric layer above the device.
[0014] The present invention also provides an etch stop layer for reducing RC delay, which is prepared by the above-described method for preparing an etch stop layer for reducing RC delay. The etch stop layer includes a composite barrier layer structure, which is composed of a first nitrogen-doped carbon-based material layer, a second nitrogen-doped carbon-based material layer and a third nitrogen-doped carbon-based material layer. The carbon content of the second nitrogen-doped carbon-based material layer is higher than that of the first nitrogen-doped carbon-based material layer and the third nitrogen-doped carbon-based material layer.
[0015] The thickness of the first and third nitrogen-doped carbon-based material layers is 30-60 angstroms. The thickness of the second nitrogen-doped carbon-based material layer is the target thickness minus the thicknesses of the first and third nitrogen-doped carbon-based material layers. The target thickness refers to the overall thickness of the final composite barrier layer structure, while the actual overall structure thickness can be adjusted as needed. Attached Figure Description
[0016] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0017] Figure 1 is a flowchart illustrating a method for preparing an etch stop layer to reduce RC delay provided by the present invention; Figure 2 is a schematic diagram of the overall structure after the etch stop layer in Embodiment 1 of the present invention is prepared; Figure 3 is an enlarged view of the etch stop layer in Figure 2.
[0018] Reference numerals: 1-Silicon dioxide layer; 2-Etch stop layer; 31-First metal interconnect structure; 32-Second metal interconnect structure; 311-First interlayer dielectric layer; 312-First copper interconnect; 321-Second interlayer dielectric layer; 322-Second copper interconnect; 211-First nitrogen-doped carbon-based material layer; 212-Second nitrogen-doped carbon-based material layer; 213-Third nitrogen-doped carbon-based material layer. Detailed Implementation
[0019] The technical solutions in specific embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0020] It should be noted that, in order to describe the technical solution more specifically, the steps described in the following embodiments do not strictly correspond one-to-one with the steps described in the invention content section.
[0021] Referring to Figure 2, in Example 1, an etch stop layer 2 is formed on a silicon dioxide layer 1, and a metal interconnect structure is formed on the etch stop layer 2. The etch stop layer 2 and the metal interconnect structure are formed alternately in sequence. This example only describes in detail the preparation method of one etch stop layer 2 (i.e., the preparation method of the etch stop layer 2 between two metal interconnect structures). The preparation methods of other etch stop layers 2 are similar and will not be described in detail here.
[0022] This embodiment provides a method for preparing an etch stop layer to reduce RC delay. Referring to Figures 1 to 3, the following deposition steps are performed using plasma-enhanced chemical vapor deposition (PECVD): Step S1: Provide a dielectric layer. In this embodiment, the dielectric layer is a first interlayer dielectric layer 311 in a first metal interconnect structure 31. A first copper interconnect 312 is formed in the first interlayer dielectric layer 311. The first interlayer dielectric layer 311 is a porous carbon-doped silicon oxide layer. In this embodiment, the first metal interconnect structure 31 is a copper interconnect structure. Ammonia is used to perform plasma surface pretreatment on the copper interconnect structure to remove oxides from the copper surface.
[0023] A first nitrogen-doped carbon-based material layer 211 is deposited on the surface of a copper interconnect structure. In this embodiment, the first nitrogen-doped carbon-based material layer 211 is a first silicon carbonitride thin film. The first reactant gas used is a combination of tetramethylsilane and ammonia, with the flow rate ratio of the first reactant gas controlled at tetramethylsilane:ammonia = 0.3:1-0.6:1. The flow rate of tetramethylsilane is in the range of 1000-2000 sccm, and the flow rate of ammonia is in the range of 3000-6000 sccm. The deposition process conditions are: deposition temperature 300-400℃, deposition pressure 3-4 Torr, high-frequency RF power 800-1200W, low-frequency RF power 600-1200W; nitrogen is used as the carrier gas with a flow rate of 2000-4000 sccm. The thickness of the first nitrogen-doped carbon-based material layer 211 is 30-60 angstroms.
[0024] Step S2: Deposit a second nitrogen-doped carbon-based material layer 212 on the surface of the first nitrogen-doped carbon-based material layer 211. In this embodiment, the second nitrogen-doped carbon-based material layer 212 is a second silicon carbonitride thin film. The second reaction gas used is a combination of tetramethylsilane, ammonia, and propylene. The flow rate ratio of the second reaction gas is controlled at tetramethylsilane:propylene:ammonia = 1:0.6:3. In other embodiments, the gas flow rate ratio can be adjusted according to the actual situation. The flow rate range of tetramethylsilane is 1000-2000 sccm, the flow rate range of propylene is 600-1200 sccm, and the flow rate range of ammonia is 3000-6000 sccm. The deposition process conditions are: deposition temperature 300-400℃, deposition pressure 3-5 Torr, high-frequency RF power 800-1200W, low-frequency RF power 800-1100W; nitrogen is used as the carrier gas, with a flow rate of 2000-4000 sccm. The thickness of the second nitrogen-doped carbon-based material layer 212 is the target thickness minus the thicknesses of the first nitrogen-doped carbon-based material layer 211 and the third nitrogen-doped carbon-based material layer 213, and is not specifically limited.
[0025] Step S3: Deposit a third nitrogen-doped carbon-based material layer 213 on the surface of the second nitrogen-doped carbon-based material layer 212. In this embodiment, the third nitrogen-doped carbon-based material layer 213 is a third silicon carbonitride thin film. The third reaction gas used is a combination of tetramethylsilane and ammonia. The flow rate ratio of the third reaction gas is controlled at tetramethylsilane:ammonia = 0.3:1-0.6:1, the flow rate of tetramethylsilane is 1000-2000 sccm, and the flow rate of ammonia is 3000-6000 sccm. The deposition process conditions are: deposition temperature 300-400℃, deposition pressure 3-4 Torr, high-frequency RF power 800-1200W, low-frequency RF power 600-1200W; nitrogen is used as the carrier gas, with a flow rate of 2000-4000 sccm. The thickness of the third nitrogen-doped carbon-based material layer 213 is 30-60 angstroms.
[0026] The preparation methods and thicknesses of the first nitrogen-doped carbon-based material layer 211 and the third nitrogen-doped carbon-based material layer 213 are the same.
[0027] A second interlayer dielectric layer 321 is deposited on the surface of the third nitrogen-doped carbon-based material layer 213. The second interlayer dielectric layer 321 is a porous carbon-doped silicon dioxide layer. The fabrication of the next metal interconnect structure continues. The second interlayer dielectric layer 321 can be further etched to form vias, which are then filled with conductive material to form a second copper interconnect 322, resulting in a second metal interconnect structure 32. At this point, the etch stop layer 2 is located between the first metal interconnect structure 31 and the second metal interconnect structure 32. In other embodiments, the etch stop layer 2 may only include a metal interconnect structure on one side, while the other side may be a dielectric layer above the device, such as the silicon dioxide layer 1; its specific location is not limited.
[0028] Example 2 provides an etch stop layer for reducing RC delay, which can be prepared by the method for preparing an etch stop layer for reducing RC delay provided in Example 1. It includes a composite barrier layer structure, which consists of a first nitrogen-doped carbon-based material layer 211, a second nitrogen-doped carbon-based material layer 212, and a third nitrogen-doped carbon-based material layer 213. The carbon content of the second nitrogen-doped carbon-based material layer 212 is higher than that of the first nitrogen-doped carbon-based material layer 211 and the third nitrogen-doped carbon-based material layer 213. The thickness of the first nitrogen-doped carbon-based material layer 211 and the third nitrogen-doped carbon-based material layer 213 is 30-60 angstroms, and the thickness of the second nitrogen-doped carbon-based material layer 212 is the target thickness minus the thickness of the first nitrogen-doped carbon-based material layer 211 and the third nitrogen-doped carbon-based material layer 213.
[0029] The average bond energy of a CC single bond is 83 kcal / mol (approximately 347 kJ / mol), the bond energy at which the first bond (π bond) of a C=C double bond breaks is approximately 265 kJ / mol, the average bond energy of a C=C double bond is 146 kcal / mol (approximately 614 kJ / mol), and the average bond energy of a CH bond is 99 kcal / mol (approximately 413 kJ / mol). The polarizability of a CC single bond is lower than that of a C=C double bond, and the average bond energy of a CC single bond is also lower than that of a C=C double bond. In Example 1, propylene (C3H6) gas was introduced during the deposition of the second silicon carbonitride (SiCN) thin film to increase its carbon content, thereby increasing the carbon content in the SiCN thin film to form carbon-rich SiCN. Introducing CC single bonds, which have lower polarizability, increases the content of CC single bonds with lower polarizability in the film compared to introducing ethylene gas, further reducing the overall dielectric constant k of the SiCN thin film, and thus further reducing the RC delay. To maintain the adhesion between the low-dielectric-constant SiCN layer and the porous SiOCH(BD2), a three-layer composite structure of NDC Ⅰ / NDC Ⅱ / NDC Ⅰ is adopted. For ease of distinction, the initial SiCN layer is designated as NDC Ⅰ (corresponding to the same first or third silicon carbonitride film), and the carbon-rich SiCN layer is designated as NDC Ⅱ (corresponding to the second silicon carbonitride film). NDC Ⅰ is used to maintain the adhesion between the overall NDC structure and the porous SiOCH(BD2), while NDC Ⅱ is used to reduce the dielectric constant of the overall NDC structure.
[0030] This invention employs PECVD technology, using tetramethylsilane and ammonia as gaseous precursors, to deposit a first SiCN layer with a dielectric constant of approximately 5.3. To further reduce the dielectric constant, a propylene gaseous precursor is introduced into the second SiCN layer as an additional carbon source, forming a second SiCN layer with a dielectric constant of approximately 3.6-3.7 (or lower). This results in an improvement of approximately 8-9% (or higher) in capacitance and RC ratio.
[0031] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.
Claims
1. A method for fabricating an etch stop layer to reduce RC delay, characterized in that, The following deposition steps are performed using plasma-enhanced chemical vapor deposition: Step S1, depositing a first nitrogen-doped carbon-based material layer (211) on the surface of the dielectric layer, using a combination of tetramethylsilane and ammonia as the first reaction gas; Step S2, depositing a second nitrogen-doped carbon-based material layer (212) on the surface of the first nitrogen-doped carbon-based material layer (211), using a combination of tetramethylsilane, ammonia, and propylene as the second reaction gas; Step S3, depositing a third nitrogen-doped carbon-based material layer (213) on the surface of the second nitrogen-doped carbon-based material layer (212), using a combination of tetramethylsilane and ammonia as the third reaction gas.
2. The method for preparing an etch stop layer to reduce RC delay according to claim 1, characterized in that, The first nitrogen-doped carbon-based material layer (211) is a first silicon carbonitride thin film, the second nitrogen-doped carbon-based material layer (212) is a second silicon carbonitride thin film, and the third nitrogen-doped carbon-based material layer (213) is a third silicon carbonitride thin film.
3. A method for preparing an etch stop layer to reduce RC delay according to claim 1 or 2, characterized in that, The first nitrogen-doped carbon-based material layer (211) and the third nitrogen-doped carbon-based material layer (213) are the same.
4. The method for preparing an etch stop layer to reduce RC delay according to claim 1, characterized in that, In step S2, the flow rate ratio of the second reactant gas is controlled at tetramethylsilane:propylene:ammonia = 1:0.6:3, wherein the flow rate of tetramethylsilane is in the range of 1000-2000 sccm, the flow rate of propylene is in the range of 600-1200 sccm, and the flow rate of ammonia is in the range of 3000-6000 sccm.
5. The method for preparing an etch stop layer to reduce RC delay according to claim 1, characterized in that, In step S2, the deposition process conditions for the second nitrogen-doped carbon-based material layer (212) are as follows: deposition temperature 300-400℃, deposition pressure 3-5 Torr, high frequency radio frequency power 800-1200W, low frequency radio frequency power 800-1100W; nitrogen is used as the carrier gas with a flow rate of 2000-4000 sccm.
6. The method for preparing an etch stop layer to reduce RC delay according to claim 1, characterized in that, In steps S1 and S3, the flow rate ratio of the first reactant gas and the third reactant gas is controlled at tetramethylsilane:ammonia = 0.3:1-0.6:1, the flow rate of tetramethylsilane is in the range of 1000-2000 sccm, and the flow rate of ammonia is in the range of 3000-6000 sccm.
7. The method for preparing an etch stop layer to reduce RC delay according to claim 1, characterized in that, In steps S1 and S3, the deposition process conditions for the first nitrogen-doped carbon-based material layer (211) and the third nitrogen-doped carbon-based material layer (213) are: deposition temperature 300-400℃, deposition pressure 3-4 Torr, high frequency radio frequency power 800-1200W, and low frequency radio frequency power 600-1200W. Nitrogen is used as the carrier gas at a flow rate of 2000-4000 sccm.
8. The method for preparing an etch stop layer to reduce RC delay according to claim 1, characterized in that, In step S1, the dielectric layer is the first interlayer dielectric layer (311) in the first metal interconnect structure (31), and the first interlayer dielectric layer (311) is a porous carbon-doped silicon oxide layer; The first metal interconnect structure (31) is a copper interconnect structure, and further includes: before depositing the first nitrogen-doped carbon-based material layer (211), using ammonia to perform plasma surface pretreatment on the copper interconnect structure to remove oxides on the copper surface; After step S3, a second interlayer dielectric layer (321) is deposited on the surface of the third nitrogen-doped carbon-based material layer (213), wherein the second interlayer dielectric layer (321) is a porous carbon-doped silicon oxide layer.
9. An etch stop layer for reducing RC delay, characterized in that, The method for preparing an etch stop layer to reduce RC delay according to any one of claims 1-8 includes a composite barrier layer structure, which is composed of a first nitrogen-doped carbon-based material layer (211), a second nitrogen-doped carbon-based material layer (212), and a third nitrogen-doped carbon-based material layer (213). The carbon content of the second nitrogen-doped carbon-based material layer (212) is higher than that of the first nitrogen-doped carbon-based material layer (211) and the third nitrogen-doped carbon-based material layer (213).
10. An etch stop layer for reducing RC delay according to claim 9, characterized in that, The thickness of the first nitrogen-doped carbon-based material layer (211) and the third nitrogen-doped carbon-based material layer (213) is 30-60 angstroms, and the thickness of the second nitrogen-doped carbon-based material layer (212) is the target thickness minus the thickness of the first nitrogen-doped carbon-based material layer (211) and the third nitrogen-doped carbon-based material layer (213).