Ultra-low dielectric constant material based on multi-section layered combined wavelength coupling and preparation method thereof

Abstract

The application provides an ultra-low dielectric constant material based on multi-section layered combined wavelength coupling and a preparation method thereof, and at least comprises the following steps: S1, placing a substrate in a reaction chamber, performing segmented deposition of at least two deposition sections on the substrate to form a composite film; by adjusting the volume flow ratio of a pore former and a skeleton precursor in different deposition sections, the concentration of the pore former in the composite film is distributed in a gradient along the thickness direction of the composite film; S2, irradiating and curing the composite film by using at least two ultraviolet light sources with different wavelengths to obtain an ultra-low dielectric constant film. By adjusting the flow ratio of the pore former and the skeleton precursor in sections, a gradient distribution of the pore structure is formed in the thickness direction of the film, and the k value of the prepared ultra-low dielectric constant material is ensured to be not higher than 2.6; by using a combined wavelength light source, the removal of the pore former and the crosslinking of the skeleton are coordinated, so that the film can improve the Young's modulus while further reducing the dielectric constant.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, and in particular relates to an ultra-low dielectric constant material based on multi-segment layered wavelength coupling and its preparation method. Background Technology

[0002] As semiconductor logic processes have advanced to the 28nm node and below, interconnect capacitance-resistance (RC) delay has gradually replaced transistor switching delay, becoming a key bottleneck restricting chip performance improvement. To effectively reduce RC delay, the industry generally adopts a technical approach of introducing low-k or ultra-low-k materials in the back-end process (BEOL) of device technology to replace traditional silicon dioxide insulating materials.

[0003] Currently, plasma-enhanced chemical vapor deposition (PECVD) technology has been widely used in the preparation of ULK dielectric materials. Among them, the technical route of combining diethoxymethylsilane (m-DEMS) with α-terpinene (ATRP) and UV curing represents the cutting-edge process for the preparation of advanced ultra-low dielectric constant materials. This process adopts a classic "two-step" strategy for deposition and curing: first, m-DEMS is co-deposited as a matrix precursor and ATRP as a pore precursor using PECVD technology; then, UV photopyrolysis technology is used to treat the ATRP molecules, causing the organic phase (CH groups) of the ATRP molecules to pyrolyze and volatilize under UV light, forming a porous structure. At the same time, the silicon-oxygen framework (Si-O-Si network) is reconstructed to form a stable nanoporous structure, thereby realizing the preparation of ultra-low dielectric constant materials.

[0004] However, the preparation of ultra-low dielectric constant materials in the existing technology still has the following technical defects: 1) Single-wavelength UV curing cannot simultaneously meet the needs of pore-forming agent removal and framework crosslinking. Existing UV curing equipment mostly uses a single-wavelength UV light source. This single-wavelength UV light source can effectively initiate ATRP polymerization and control the formation of pore structures, but its role in breaking the silicon-oxygen bond (Si-O) to form active sites and lay the foundation for crosslinking is relatively limited, resulting in insufficient mechanical strength of the prepared material, which easily leads to interface failure and reliability risks. 2) Combined-wavelength curing has the problem of uneven penetration in thick film applications. Due to the significant differences in physical properties between the two different wavelengths of light in the combined wavelength, their penetration ability in the material is significantly different. When processing thicker films, the phenomenon of "excessive crosslinking on the surface and insufficient crosslinking at the bottom" is likely to occur. Excessive crosslinking on the surface will lead to an increase in the dielectric constant (k value) of the film, while insufficient crosslinking at the bottom will generate interface pores between the ULK material and the underlying nitrogen-doped silicon carbide (NDC) barrier layer, which also leads to reliability risks. 3) Homogeneous thin film structures make it difficult to balance the contradiction between low k-value and mechanical properties. Existing technologies usually form thin films with uniform porosity in the thickness direction. In order to obtain a lower k-value, the porosity must be increased, but this will lead to a sharp decrease in the mechanical strength of the film. Conversely, if the porosity is reduced in order to ensure mechanical strength, the k-value will increase. This homogeneous structure also has the problem of modulus abrupt change, which is prone to internal stress concentration, leading to film cracking. It is also difficult to simultaneously meet the dual requirements of bottom adhesion and surface etching resistance.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an ultra-low dielectric constant material based on multi-segment layered wavelength coupling and its preparation method, in order to solve the technical problem in the prior art that UV curing is difficult to achieve both efficient removal of ULK film pore-forming agent and sufficient cross-linking of the skeleton, resulting in the inability to ensure high mechanical strength and interface reliability while reducing dielectric constant.

[0007] To achieve the above and other related objectives, the present invention provides a method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling, the method comprising at least the following steps:

[0008] S1. A substrate is placed in a reaction chamber, and a reaction gas containing a framework precursor, a pore-forming agent, an oxidizing gas, and a carrier gas is introduced into the reaction chamber. Radio frequency power is applied to form plasma, and a composite film is formed by segmented deposition on the substrate. The segmented deposition includes at least two deposition sections. In different deposition sections, the volume flow rate ratio of the pore-forming agent to the framework precursor is adjusted so that the concentration of the pore-forming agent in the composite film is gradient-distributed along the thickness direction of the composite film.

[0009] S2. The composite film is irradiated and cured using at least two different wavelengths of ultraviolet light to obtain an ultra-low dielectric constant film.

[0010] Preferably, in step S1, a composite thin film is deposited on the substrate using a plasma-enhanced chemical vapor deposition process. The deposition process temperature is 200~350℃, the pressure in the reaction chamber is 2Torr~6Torr, and the radio frequency power is 600W~800W.

[0011] Preferably, the skeletal precursor comprises diethoxymethylsilane, and the pore-forming agent comprises α-terpinene.

[0012] Preferably, the oxidizing gas includes one or a combination of O2, N2O, and CO2.

[0013] Preferably, the carrier gas includes one or a combination of helium and argon.

[0014] Preferably, the segmented deposition includes 3 to 5 deposition segments, from the bottom deposition segment to the second-to-top deposition segment. In each deposition segment, the volumetric flow rate ratio of the pore-forming agent to the framework precursor increases in a gradient manner to form a gradient pore layer. In the top deposition segment, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1 to form a surface sealing layer.

[0015] Preferably, the segmented deposition includes three deposition sections: a first deposition section, a second deposition section, and a top deposition section. In the first deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1, used to form a bottom adhesion layer. In the second deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.8:1 to 1.5:1, used to form a main pore-forming layer. In the top deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1, used to form a surface sealing layer.

[0016] Preferably, the deposition time of the first deposition section is 5s to 10s.

[0017] Preferably, the deposition time of the second deposition section is 10s to 30s.

[0018] Preferably, the deposition time of the third deposition stage is 5s to 10s.

[0019] Preferably, in step S1, a stabilization treatment is required between two adjacent deposition sections, specifically including: stopping the introduction of the reaction gas, introducing an inert gas into the reaction chamber and applying a radio frequency power of 50W to 150W for 5s to 30s.

[0020] Preferably, the irradiation curing process in step S2 is carried out under a nitrogen or argon protective atmosphere, and the temperature during the irradiation curing process is 200℃~400℃, and the pressure in the reaction chamber is 2Torr~5Torr.

[0021] Preferably, in step S2, the composite film is irradiated and cured using a first ultraviolet light and a second ultraviolet light, wherein the wavelength range of the first ultraviolet light is 150nm~230nm and the wavelength range of the second ultraviolet light is 300nm~400nm.

[0022] Preferably, step S2 uses a time-division sequential irradiation mode to cure the composite film, specifically including: first curing with a first ultraviolet light for 1 min to 3 min, and then curing with a second ultraviolet light for 2 min to 5 min, wherein the irradiation intensity of the first ultraviolet light is 5 mW / cm² to 50 mW / cm², and the irradiation intensity of the second ultraviolet light is 20 mW / cm² to 100 mW / cm².

[0023] Preferably, step S2 uses a simultaneous irradiation mode to cure the composite film, specifically including: simultaneously irradiating and curing the composite film with a first ultraviolet light and a second ultraviolet light for 5 min to 10 min.

[0024] Preferably, in step S2, the composite film is subjected to irradiation curing using an alternating pulse irradiation mode, wherein the first ultraviolet light and the second ultraviolet light alternately and cyclically irradiate and cure the composite film.

[0025] Preferably, step S2 further includes a third ultraviolet light with a wavelength of 254 nm.

[0026] Preferably, after the irradiation curing treatment, step S2 further includes passivating the surface of the irradiated composite film with hydrogen-containing plasma. Specifically, the passivation treatment of the surface of the irradiated composite film with hydrogen-containing plasma involves introducing hydrogen-containing gas into the reaction chamber, applying 50W~150W of radio frequency power, and treating at 200~300℃ for 30s~120s to passivate the dangling bonds on the surface of the composite film.

[0027] The present invention also provides an ultra-low dielectric constant thin film, which is prepared by the above-described method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling. The ultra-low dielectric constant thin film includes at least a bottom adhesion layer, a main pore-forming layer and a surface sealing layer, and has a pore structure with a gradient distribution along the thickness direction. The porosity of the bottom adhesion layer is 5% to 15%, the porosity of the main pore-forming layer is 20% to 35%, and the porosity of the surface sealing layer is 5% to 15%.

[0028] Preferably, the dielectric constant of the ultra-low dielectric constant film is not higher than 2.6, the Young's modulus is 11 GPa to 14 GPa, and the hardness is 0.8 to 1.2 GPa.

[0029] As described above, the ultra-low dielectric constant material based on multi-segment layered wavelength coupling and its preparation method of the present invention have the following beneficial effects:

[0030] This invention achieves a gradient pore structure along the film thickness direction by segmentally controlling the flow ratio of the pore-forming agent to the framework precursor. This structure features a dense bottom layer, a highly porous middle layer, and a dense top layer. The low porosity of the bottom adhesion layer significantly enhances the interfacial adhesion between the film and the underlying substrate, effectively suppressing the risk of film peeling in subsequent processes. The high porosity of the middle main pore-forming layer maximizes the internal porosity, ensuring that the dielectric constant of the final ultra-low dielectric constant material does not exceed 2.6. The low porosity of the surface sealing layer forms a dense protective shell, significantly improving the film's oxidation resistance and wet etching resistance, preventing damage to the internal porous structure in subsequent processes. Furthermore, the use of a short wavelength... The combination of a primary ultraviolet light source and a secondary ultraviolet light source with a long wavelength achieves synergistic effects of pore-forming agent removal and full cross-linking of the framework. Short-wavelength high-energy photons efficiently decompose and remove the pore-forming agent to form nanopores, while long-wavelength low-energy photons enhance the cross-linking of the Si-O-Si framework, compensating for potential framework damage caused by short wavelengths. Furthermore, by using different wavelength irradiation sequences, the problem of "excessive cross-linking on the surface and insufficient cross-linking at the bottom" in thick film processing is solved, avoiding pore collapse caused by long-term processing. Compared to single-wavelength curing, the synergistic effect of this combination of wavelengths enables the film to improve Young's modulus while further reducing the dielectric constant, effectively resolving the technical contradiction between low k-value and high mechanical strength.

[0031] In this invention, the gradient pore structure creates a smooth transition of mechanical properties along the film thickness direction, avoiding stress concentration caused by abrupt changes in modulus in the homogeneous film layer, significantly reducing the cracking tendency of the film, and significantly increasing the critical cracking thickness, thereby greatly improving process tolerance, device yield, and reliability. The use of α-terpinene as a pore-forming agent, combined with the underlying densification structure, further strengthens the interfacial bonding between the ultra-low dielectric constant material and the underlying substrate. Furthermore, the segmented deposition process can be implemented on existing commercial PECVD equipment, requiring only program control of parameters such as gas flow rate and RF power in each deposition segment, without requiring hardware modifications, thus exhibiting good industrial applicability. UV curing with combined wavelengths can be achieved through a UV curing chamber equipped with multi-wavelength light sources, keeping energy consumption and process time within acceptable limits. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0033] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0034] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0035] This invention provides a method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling, the method comprising at least the following steps:

[0036] S1. A substrate is placed in a reaction chamber, and a reaction gas containing a framework precursor, a pore-forming agent, an oxidizing gas, and a carrier gas is introduced into the reaction chamber. Radio frequency power is applied to form plasma, and a composite film is formed by segmented deposition on the substrate. The segmented deposition includes at least two deposition sections. In different deposition sections, the volume flow rate ratio of the pore-forming agent to the framework precursor is adjusted so that the concentration of the pore-forming agent in the composite film is gradient-distributed along the thickness direction of the composite film.

[0037] S2. The composite film is irradiated with at least two different wavelengths of ultraviolet light to obtain an ultra-low dielectric constant film.

[0038] Specifically, this invention forms a composite film structure with a gradient distribution of pore-forming agent concentration along the thickness direction of the composite film through a segmented deposition process, and uses ultraviolet light of combined wavelengths for irradiation and curing treatment to achieve efficient removal of pore-forming agent and synergistic enhancement of skeleton crosslinking, ultimately obtaining a porous dielectric film with ultra-low dielectric constant (k value not greater than 2.6), high mechanical strength, excellent interfacial adhesion performance and good hydrophobicity.

[0039] As an example, in step S1, a composite thin film is deposited on the substrate using a plasma-enhanced chemical vapor deposition process. The deposition process temperature is 200~350℃, the pressure in the reaction chamber is 2Torr~6Torr, and the radio frequency power is 600W~800W.

[0040] Specifically, a parallel-plate or inductively coupled PECVD reactor suitable for plasma-enhanced chemical vapor deposition is used. The substrate to be deposited (such as a silicon wafer, a substrate with metal wiring, etc.) is placed on a support stage within the reaction chamber. After the reaction chamber is closed, the vacuum system is activated to evacuate the reaction chamber, bringing the background vacuum level to a predetermined value. In a preferred embodiment, the evacuation process lowers the reaction chamber pressure to below 0.02 Torr; in a more preferred embodiment, the background vacuum level is below 10 Torr. -6 During the vacuuming process, the stage can be heated simultaneously to ensure that the substrate temperature quickly reaches the preset temperature required for deposition after vacuuming is completed. Then, the substrate is heated to the preset temperature and kept stable. The substrate temperature is one of the key process parameters that affects the film deposition rate, film structure, and dielectric properties.

[0041] In a specific embodiment of the present invention, the deposition process temperature is equivalent to the substrate temperature, which is 200~350℃ (including any value within the range of 200℃, 220℃, 250℃, 280℃, 300℃, 320℃, 350℃, etc.). If the substrate temperature is too high, the pore-forming agent may decompose prematurely, affecting the uniformity of the pores. If the substrate temperature is too low, the reaction may be insufficient, resulting in insufficient film density. Preferably, the substrate temperature is 250℃~350℃.

[0042] In a specific embodiment of the present invention, the pressure in the reaction chamber may include any value within the range of 2 Torr, 3 Torr, 4 Torr, 5 Torr, 6 Torr, etc. The working pressure affects the mean free path and collision frequency of active species in the plasma, thereby affecting the deposition rate and microstructure of the film. The radio frequency power may include any value within the range of 600W, 650W, 700W, 750W, 800W, etc. The level of radio frequency power has a significant impact on plasma density, free radical yield and film deposition rate. If the radio frequency power is too high, it may cause the pore-forming agent to decompose prematurely, thereby reducing the porosity of the final film. If the radio frequency power is too low, the reaction will be insufficient, the deposition rate will be low and the degree of cross-linking of the skeleton will be insufficient.

[0043] As an example, the skeletal precursor includes diethoxymethylsilane, and the pore-forming agent includes α-terpinene.

[0044] Specifically, diethoxymethylsilane (m-DEOS, C5H) 14 Diethoxymethylsilane (O2Si) contains both ethoxy and methyl functional groups in its chemical structure. As a framework precursor, it exhibits excellent performance in the PECVD process. Its molecular structure provides the silicon, oxygen, and carbon elements required to form the carbon-doped silicon oxide framework. Its ethoxy group is easily broken under plasma irradiation to form a Si-O-Si network structure, while the methyl group (-CH3) remains in the framework as a hydrophobic group, giving the film good moisture resistance. The pore-forming agent is alpha-terpinene (ATRP), with the molecular formula C2. 10 H 16 α-Terpinene is a cyclic terpene organic compound with a carbon-carbon double bond structure. As a sacrificial pore-forming agent, α-terpinene can be stably embedded in the framework matrix during PECVD deposition and can be completely removed in subsequent post-processing through thermal decomposition or photodecomposition, forming nanoscale pores in situ. Compared with other pore-forming agents such as bicycloheptadecene (BCHD), using α-terpinene as a pore-forming agent can achieve higher mechanical strength and better interfacial adhesion properties.

[0045] As an example, oxidizing gases include one or a combination of O2, N2O, and CO2.

[0046] Preferably, O2 is used as the oxidizing gas to promote the formation of the Si-O-Si skeleton in diethoxymethylsilane.

[0047] As an example, the carrier gas includes one or a combination of helium and argon.

[0048] Preferably, helium is used as the carrier gas.

[0049] As an example, the segmented deposition includes 3 to 5 deposition segments, from the bottom deposition segment to the next top deposition segment. In each deposition segment, the volumetric flow rate ratio of the pore-forming agent to the framework precursor increases in a gradient manner to form a gradient pore layer. In the top deposition segment, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1 to form a surface sealing layer.

[0050] Specifically, segmented deposition proceeds from the bottom deposition segment (the lowest layer closest to the substrate) to the second-to-top deposition segment (the second-to-top layer). In each deposition segment, the flow ratio of pore-forming agent to framework precursor exhibits a gradient increase or stepwise change. This results in a gradient increase in the concentration of pore-forming agent in the composite film along the film thickness direction from the bottom layer to the top layer. After the pore-forming agent is removed in subsequent post-processing, the resulting pores are also a gradient porous structure with dense bottoms, loose tops, and varying middle sections. This creates a gradual transition layer of mechanical properties from the substrate surface to the top of the film within the composite film, effectively buffering internal stress, suppressing film cracking caused by modulus abrupt changes, improving the mechanical stability of the composite film, and significantly enhancing the interfacial adhesion between the ultra-low dielectric constant film and the underlying material, thus preventing delamination and peeling.

[0051] In order to form a surface sealing layer on top of the main ultra-low dielectric constant film with a gradient pore layer, the segmented deposition scheme of the present invention can also control the flow ratio of pore-forming agent to framework precursor to 0.1:1 to 0.5:1 (including any value in the range of 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, etc.) in the last deposition stage to deposit a dense surface sealing layer. This surface sealing layer can effectively block the penetration of chemical reagents and moisture in subsequent processes and protect the integrity of the internal porous structure.

[0052] In a specific embodiment of the present invention, the segmented deposition is preferably performed in 3 to 5 segments, forming 3 to 5 deposition segments. 3, 4, or 5 deposition segments can be formed. The process parameters for each deposition segment are independently controlled. In each deposition segment, a composite film is sequentially deposited on the substrate surface. This composite film is composed of a SiOC:H framework matrix formed from diethoxymethylsilane and a uniformly dispersed α-terpinene pore-forming agent phase. When 3 deposition segments are formed, the volumetric flow rate ratio of the pore-forming agent to the framework precursor in the first two deposition segments increases in a gradient manner, while in the last deposition segment, the flow rate ratio of the pore-forming agent to the framework precursor is controlled at 0.1:1 to 0.5:1. When four deposition sections are formed, the volumetric flow rate ratio of pore-forming agent to framework precursor in the first three deposition sections increases in a gradient manner, while the flow rate ratio of pore-forming agent to framework precursor in the last deposition section is controlled at 0.1:1 to 0.5:1. When five deposition sections are formed, the volumetric flow rate ratio of pore-forming agent to framework precursor in the first four deposition sections increases in a gradient manner (e.g., 0.2:1, 0.6:1, 1.0:1, 1.2:1), while the flow rate ratio of pore-forming agent to framework precursor in the last deposition section is controlled at 0.1:1 to 0.5:1. Thus, the concentration of pore-forming agent in the resulting composite film exhibits a "low-high-low" gradient distribution along the thickness direction.

[0053] As an example, the segmented deposition includes three deposition sections: a first deposition section, a second deposition section, and a top deposition section. In the first deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1, used to form a bottom adhesion layer. In the second deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.8:1 to 1.5:1, used to form a main pore-forming layer. In the top deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1, used to form a surface sealing layer.

[0054] Specifically, the thickness of the bottom adhesion layer formed in the first deposition stage is no greater than 100 nm, the thickness of the main pore-forming layer formed in the second deposition stage is no greater than 150 nm, and the thickness of the surface sealing layer formed in the third deposition stage is no greater than 100 nm.

[0055] As an example, the deposition time of the first deposition segment is 5s to 10s (e.g., 5s, 6s, 7s, 8s, 9s, 10s, etc.).

[0056] As an example, the deposition time of the second deposition stage is 10s to 30s (e.g., 10s, 15s, 20s, 25s, 30s, etc.).

[0057] As an example, the deposition time of the third deposition stage is 5s to 10s (e.g., 5s, 6s, 7s, 8s, 9s, 10s, etc.).

[0058] Specifically, all three deposition stages use diethoxymethylsilane (m-DEOS) as the framework precursor, α-terpinene (ATRP) as the pore-forming agent, oxygen (O2) as the oxidizing gas, and helium (He) as the carrier gas. The deposition conditions are RF power of 600W~800W, chamber pressure of 3Torr~5Torr, and substrate temperature of 250℃~350℃. In the first deposition stage, the flow ratio of α-terpinene to diethoxymethylsilane can be any value within the range of 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, etc. The pore-forming agent concentration in the first deposition stage is relatively low, forming a dense underlayer rich in Si-OC framework, exhibiting good interfacial adhesion properties and effectively buffering the stress between the subsequent porous layer and the underlying substrate. In the second deposition stage, the flow ratio of α-terpinene to diethoxymethylsilane can be... The pore-forming agent concentration in the second deposition stage is relatively high, forming the main porous layer of the composite film rich in α-terpinene pore-forming agent. After the pore-forming agent is removed in the subsequent post-processing, a high-porosity main dielectric layer will be formed, which is the core functional layer for achieving a low dielectric constant. In the third deposition stage, the flow ratio of α-terpinene to diethoxymethylsilane can be any value within the range of 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, etc. The pore-forming agent concentration is reduced again in the third deposition stage, forming a dense surface sealing layer, which can protect the porous structure in subsequent processes and provide a smooth interface for the deposition of the upper capping layer. Through the above three-stage deposition process, a composite film structure with a "low-high-low" gradient distribution of pore-forming agent concentration along the thickness direction is obtained.

[0059] In a specific embodiment of the present invention, during the segmented deposition process, a flow transition period is set between each deposition segment. That is, during the flow transition period, the flow ratio of α-terpinene to diethoxymethylsilane is continuously adjusted so that the pore-forming agent concentration in the composite film achieves a continuous gradient change, thereby avoiding interface defects caused by abrupt changes in the pore-forming agent concentration between each deposition segment.

[0060] As an example, in step S1, a stabilization process is required between two adjacent deposition sections, which specifically includes: stopping the flow of the reaction gas, introducing an inert gas into the reaction chamber and applying 50W to 150W of radio frequency power for 5s to 30s.

[0061] Specifically, the inert gas includes one or a mixture of helium or argon, the applied radio frequency can be any value in the range of 50W, 80W, 100W, 120W, 150W, etc., and the processing time can be any value in the range of 5s, 10s, 15s, 20s, 25s, 30s, etc.; after each deposition segment is completed, plasma stabilization treatment is performed to stabilize the deposition surface and prevent diffusion between deposition segments from causing ambiguity of the concentration gradient.

[0062] As an example, the irradiation curing process described in step S2 is carried out under a nitrogen or argon protective atmosphere, and the substrate temperature is 200°C to 400°C and the reaction chamber pressure is 2 Torr to 5 Torr during the irradiation curing process.

[0063] Specifically, after the segmented deposition in step S1 is completed, the RF power input is terminated and all gas supply is stopped. The pressure in the reaction chamber is maintained at 2 Torr~5 Torr (e.g., values ​​within the range of 2 Torr, 3 Torr, 4 Torr, 5 Torr, etc.), and the substrate temperature is maintained at 200~400℃ (e.g., values ​​within any range of 200, 250, 300, 350, 400, etc.). An inert atmosphere is introduced as a protective gas, and then the composite film is cured by ultraviolet irradiation with a combination of wavelengths.

[0064] As an example, in step S2, the composite film is irradiated with a first ultraviolet light and a second ultraviolet light, wherein the wavelength range of the first ultraviolet light is 150nm~230nm and the wavelength range of the second ultraviolet light is 300nm~400nm.

[0065] Specifically, the first ultraviolet light has high photon energy, which is sufficient to effectively break the C-C bonds and CH bonds in the α-terpinene porogen molecule, causing it to decompose into volatile small molecule products such as CO2 and H2O and diffuse out of the film, forming nanopores at the original positions occupied by the α-terpinene porogen. This wavelength has a highly efficient decomposition ability for the porogen, which is the key to achieving an ultra-low dielectric constant of the film. Preferably, the wavelength of the first ultraviolet light is 172 nm (high ultraviolet photon energy corresponds to about 7.2 eV). The second ultraviolet light has lower photon energy, which will not excessively damage the Si-O-Si framework structure of the film, but can excite the defect sites and dangling bonds in the diethoxymethylsilane framework, promote the recombination and cross-linking of the Si-O-Si network, thereby compensating for the framework damage that may be caused by short-wavelength curing. While removing the porogen, it maintains or even enhances the mechanical strength of the film. Preferably, the wavelength of the second ultraviolet light is 365 nm (high ultraviolet photon energy corresponds to about 3.4 eV).

[0066] In specific embodiments of the present invention, the irradiation curing method for irradiating and curing the composite film using at least two different wavelengths of ultraviolet light includes, but is not limited to, the following modes.

[0067] As an example, step S2 employs a time-division sequential irradiation mode to cure the composite film, specifically including: firstly, irradiating with a first ultraviolet light for 1 min to 3 min (including any value within the range of 1 min, 2 min, 3 min, etc.) to fully decompose the α-terpinene pore-forming agent; then irradiating with a second ultraviolet light for 2 min to 5 min (including any value within the range of 2 min, 3 min, 4 min, 5 min, etc.) to fully crosslink the framework. The irradiation intensity of the first ultraviolet light is 5 mW / cm² to 50 mW / cm² (including 5 mW / cm²). 2 10mW / cm 2 20mW / cm 2 30mW / cm 2 40mW / cm 2 50mW / cm 2 (Values ​​within any range), the intensity of the second ultraviolet light is 20 mW / cm². 2 ~100mW / cm 2 (including 20mW / cm², 40mW / cm², 50mW / cm², 60mW / cm², 80mW / cm²) 2 100mW / cm 2 (Values ​​within any range).

[0068] Preferably, the composite film is cured by time-division sequential irradiation: firstly, under a nitrogen atmosphere and a substrate temperature of 350°C, it is irradiated with 172nm first ultraviolet light (intensity 30mW / cm²) for 5 minutes to fully decompose and remove the α-terpinene pore-forming agent; then, it is irradiated with 365nm second ultraviolet light (intensity 50mW / cm²) for 15 minutes to strengthen the crosslinking network structure of the diethoxymethylsilane backbone. This combined curing scheme can achieve a pore-forming agent removal rate of over 98%, while the film shrinkage rate is controlled within 15%.

[0069] As an example, step S2 uses a simultaneous irradiation mode to cure the composite film, specifically including: simultaneously irradiating and curing the composite film with a first ultraviolet light and a second ultraviolet light for 5 min to 10 min.

[0070] Specifically, the first and second ultraviolet rays work synergistically in the film to simultaneously decompose the pore-forming agent and crosslink the framework; and simultaneously irradiate and cure for 5 min to 10 min (e.g., 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.).

[0071] As an example, in step S2, the composite film is irradiated and cured using an alternating pulse irradiation mode, wherein the first ultraviolet light and the second ultraviolet light alternately irradiate the composite film.

[0072] As an example, step S2 also includes a third ultraviolet light with a wavelength of 254 nm.

[0073] Specifically, a third type of ultraviolet light is introduced for irradiation and curing to supplement and adjust the degree of crosslinking of specific chemical bonds (such as Si-CH3) in the framework.

[0074] As an example, in step S2, after the irradiation treatment, the surface of the composite film after irradiation treatment is further treated with hydrogen-containing plasma. Specifically, the treatment of the surface of the composite film after irradiation treatment with hydrogen-containing plasma involves introducing hydrogen-containing gas into the reaction chamber, applying 50W~150W of radio frequency power, and treating it at 200~300℃ for 30s~120s to passivate the dangling bonds on the surface of the composite film.

[0075] Specifically, treating the surface of the composite thin film after irradiation with hydrogen-containing plasma can improve the hydrophobicity and surface uniformity of the final ultra-low dielectric constant material. In a preferred embodiment, hydrogen-containing gas is introduced, and the treatment is carried out at a radio frequency power of 50W~150W (e.g., 50W, 80W, 100W, 120W, 150W, etc.) and a temperature of 200~300℃ (e.g., 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, etc.) for 30s~120s (e.g., 30s, 50s, 80s, 100s, 120s, etc.). This treatment helps to passivate the dangling bonds on the thin film surface, reduce the water absorption tendency of the thin film, and improve its moisture resistance, thereby maintaining stable electrical properties in subsequent wet processes. The hydrogen-containing gas includes a mixture of hydrogen and argon.

[0076] The present invention also provides an ultra-low dielectric constant thin film, which is prepared by the above-described method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling. The ultra-low dielectric constant thin film includes at least a bottom adhesion layer, a main pore-forming layer and a surface sealing layer, and has a pore structure with a gradient distribution along the thickness direction. The porosity of the bottom adhesion layer is 5% to 15%, the porosity of the main pore-forming layer is 20% to 35%, and the porosity of the surface sealing layer is 5% to 15%.

[0077] Specifically, the ultra-low dielectric constant thin film prepared by the above preparation method has a nanoporous structure with a gradient distribution along the thickness direction. From the bottom adhesion layer, the main pore-forming layer to the surface sealing layer, the porosity of the bottom adhesion layer is 5%~15%, the porosity of the main pore-forming layer is 20%~35%, and the porosity of the surface sealing layer is 5%~15%. The porosity exhibits a "low-high-low" gradient distribution. The pore size is less than 2nm, preferably 0.9nm~1.2nm (e.g., 0.9nm~1.0nm, 0.9nm~1.1nm, 0.9~1.2nm, 1.0~1.2nm, etc.).

[0078] As an example, the dielectric constant of the ultra-low dielectric constant film is no higher than 2.6, the Young's modulus is 11 GPa to 14 GPa, and the hardness is 0.8 to 1.2 GPa.

[0079] Specifically, the final dielectric constant of the ultra-low dielectric constant film can be precisely controlled by adjusting the pore-forming agent / framework precursor flow ratio in each segment of the segmented deposition process and by using combined wavelength irradiation curing conditions. The dielectric constant is no higher than 2.6, preferably lower than 2.55; more preferably, the dielectric constant is 2.5. The film has a Young's modulus of 11~14 GPa and a hardness of 0.8~1.2 GPa. Furthermore, this ultra-low dielectric constant film not only exhibits good insulation but also withstands high voltage, with a leakage current density of 10 at a field strength of 1 MV / cm. -8 ~10 -9 A / cm 2 Within the order of magnitude range, the breakdown field strength is greater than 3MV / cm, which meets the reliability standards of semiconductor back-end processes.

[0080] To better understand the preparation method of ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling in this invention, the preparation method of ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling in this invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the invention in any way.

[0081] The equipment used in Examples 1-3 and Comparative Examples 1-2 below is a parallel plate PECVD reaction equipment; the substrates used are all 12-inch silicon wafers with a SiC barrier layer pre-deposited on the surface; diethoxymethylsilane (m-DEOS) is used as the backbone precursor and α-terpinene (ATRP) is used as the pore-forming agent; and plasma-enhanced chemical vapor deposition is used for deposition.

[0082] Example 1

[0083] This embodiment provides a method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling, which includes at least the following steps:

[0084] S1. Place the substrate on the support stage in the reaction chamber. After closing the reaction chamber, start the vacuum system to evacuate until the background pressure of the reaction chamber is below 10. -6 Torr heats the substrate to 300°C and maintains the temperature through a heating system embedded in the stage; a reaction gas containing diethoxymethylsilane (m-DEOS) vapor, α-terpinene (ATRP) vapor, oxygen (O2) and helium (He) carrier gas is introduced into the reaction chamber, and radio frequency power is applied to form plasma, and a composite film is formed by deposition in three deposition stages on the substrate;

[0085] First deposition stage: m-DEOS vapor flow rate is 300 sccm, ATRP vapor flow rate is 60 sccm (ATRP / m-DEOS flow rate ratio is 0.2:1), RF power is set to 790W, reaction chamber pressure is 3.5 Torr, substrate temperature is 300℃, and plasma-enhanced chemical vapor deposition is used to deposit a bottom adhesion layer with a thickness of 80nm on the substrate surface for 10s.

[0086] Second deposition stage: After the first deposition stage is completed, the reaction chamber conditions are maintained, the gas flow rate is adjusted, the m-DEOS vapor flow rate is 300 sccm, the ATRP vapor flow rate is increased (ATRP / m-DEOS flow rate ratio is 1.0:1), the RF power is set to 790W, the reaction chamber pressure is 3.5 Torr, the substrate temperature is 300℃, and plasma-enhanced chemical vapor deposition is used to deposit on the substrate surface for 25s to form a main porous layer rich in pore-forming agent with a thickness of 150nm;

[0087] Third deposition stage: After the second deposition stage is completed, the gas flow rate is adjusted, the ATRP / m-DEOS flow rate ratio is 0.2:1, the radio frequency power is set to 790W, the reaction chamber pressure is 3.5Torr, the substrate temperature is 300℃, and plasma-enhanced chemical vapor deposition is used to deposit a surface sealing layer with low pore-forming agent concentration and a thickness of 80nm on the substrate surface for 10s.

[0088] A composite film with a total thickness of 310 nm was obtained through deposition in three stages. The concentration of the pore-forming agent showed a gradient distribution of "low-high-low" along the thickness direction of the composite film.

[0089] S2. After deposition, turn off the RF power supply and stop the introduction of all gases. Maintain the pressure in the reaction chamber at 3 Torr, introduce nitrogen as a protective gas, and maintain the temperature at 350℃. Then, use a time-division sequential irradiation mode to cure the composite film.

[0090] The composite film was first irradiated with 172nm wavelength ultraviolet light at an intensity of 30mW / cm² for 2 min to allow the ATRP pore-forming agent to fully decompose and escape from the film.

[0091] Subsequently, the film was irradiated with a second ultraviolet light at a wavelength of 365nm, with an irradiation intensity of 50mW / cm² and an irradiation curing time of 5min, in order to strengthen the Si-O-Si crosslinking network of the diethoxymethylsilane skeleton and compensate for skeleton damage that may be caused by short-wavelength curing.

[0092] After irradiation curing, the temperature of the reaction chamber is lowered to room temperature to obtain a thin film with ultra-low dielectric constant.

[0093] The performance of the prepared ultra-low dielectric constant thin film was tested:

[0094] The dielectric constant k was determined to be 2.6–2.55 using the mercury probe method; the Young's modulus was determined to be 11–11.5 GPa using the nanoindentation method; the hardness was approximately 0.9–1.1 GPa; and the porosity was determined using the elliptic porosity determination method, with an overall porosity of approximately 20–28% and a pore size of approximately 0.9–1.1 nm.

[0095] Example 2

[0096] This embodiment provides a method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling. The difference between this method and that of Embodiment 1 is that:

[0097] In step S1, four sedimentary sections are used for deposition. Specific depositional parameters are shown in Table 1 below:

[0098] project Deposition time (s) ATRP / m-DEOS traffic ratio Radio frequency power (W) Stress (Torr) Temperature (°C) First sedimentary section 10 0.2:1 790 3.5 300 Second sedimentary section 20 0.5:1 790 3.5 300 Third sedimentary section 15 1.1:1 790 3.5 300 Fourth sedimentary section 10 0.3:1 790 3.5 300

[0099] In step S2, the composite film is irradiated and cured using a simultaneous irradiation mode. 172nm and 365nm ultraviolet light are turned on simultaneously with intensities of 25mW / cm² and 45mW / cm², respectively. The substrate temperature is 300℃ and the irradiation time is 7min. Other methods and steps are the same as in Example 1 and will not be repeated here.

[0100] Tests showed that the dielectric constant k of the ultra-low dielectric constant film prepared in this embodiment was 2.55~2.58, the Young's modulus was 12.5~12.8 GPa, the internal stress of the film was reduced by about 30~40% compared with the single-step deposition control sample in Comparative Example 1, the porosity in the thickness direction showed a smooth gradient change, and the interfacial adhesion performance was excellent.

[0101] Example 3

[0102] This embodiment provides a method for preparing an ultra-low dielectric constant thin film based on multi-segment layered wavelength coupling. The difference between this preparation method and that of Embodiment 2 is that: in step S2, the composite film is irradiated and cured using an alternating pulse irradiation mode. The composite film is irradiated and cured alternately with a first ultraviolet light of 172 nm (irradiation intensity of 30 mW / cm², irradiation for 30 s) and a second ultraviolet light of 365 nm (irradiation intensity of 50 mW / cm², irradiation for 90 s), for a total of 5 cycles, with a total effective irradiation time of about 10 min, and the substrate temperature is maintained at 350 °C. Other methods and steps are the same as in Embodiment 2 and will not be repeated here.

[0103] Tests showed that the dielectric constant k of the ultra-low dielectric constant film prepared in this embodiment was 2.52~2.48, the Young's modulus was 13~13.3 GPa, there were no obvious interface defects in the thickness direction of the film, and the mechanical properties were more smoothly distributed.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing a low dielectric constant material with single-segment single-wavelength coupling. The difference between this preparation method and Example 1 is that: in step S1, a single deposition segment is used for deposition, and the deposition conditions are: ATRP / m-DEOS flow ratio 0.6:1, RF power 790W, reaction chamber pressure 3.5 Torr, substrate temperature 300℃, and plasma-enhanced chemical vapor deposition is used to deposit on the substrate surface for 55s; in step S2, the composite film is irradiated and cured for 7min with a single wavelength of 365nm ultraviolet light, and the irradiation intensity is 35mW / cm²; other methods and steps are the same as in Example 1, and will not be repeated here.

[0106] Tests showed that the dielectric constant k of the low dielectric constant film prepared in this comparative example was 2.55~2.60, and the Young's modulus was only 9.0~9.5 GPa. The film had uniformly distributed pores in the thickness direction, but the interfacial adhesion strength was low.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing a multi-segment, layered, single-wavelength coupled low dielectric constant material. The difference between this preparation method and Example 1 is that in step S2, the composite film is irradiated and cured for 7 minutes with a single wavelength of 172nm ultraviolet light, and the irradiation intensity is 60mW / cm². Other methods and steps are the same as in Example 1 and will not be repeated here.

[0109] Tests showed that the ATRP pore-forming agent in the low dielectric constant film prepared in this comparative example was not completely removed (removal rate of about 70-80%), and the dielectric constant k value was 2.65-2.60. Residual organic impurities led to a higher dielectric constant, and the hydrophobicity and thermal stability of the film decreased.

[0110] The comparison results of Examples 1-3 and Comparative Examples 1-2 show that the gradient pore structure obtained by segmented deposition in the embodiments of the present invention, combined with the synergistic effect of efficient removal of pore-forming agent and full cross-linking of the skeleton achieved by UV curing with combined wavelengths, has achieved significant progress in terms of reducing dielectric constant, improving mechanical strength, enhancing interfacial adhesion and process stability.

[0111] In summary, this invention achieves a gradient pore structure along the film thickness direction by segmentally controlling the flow ratio of the pore-forming agent to the framework precursor. This structure features a dense bottom layer, a highly porous middle layer, and a dense top layer. The low porosity of the bottom adhesion layer significantly enhances the interfacial adhesion between the film and the underlying substrate, effectively suppressing the risk of film peeling in subsequent processes. The high porosity of the middle main pore-forming layer maximizes the internal porosity, ensuring that the dielectric constant of the final ultra-low dielectric material does not exceed 2.6. The low porosity of the surface sealing layer forms a dense protective shell, significantly improving the film's oxidation resistance and wet etching resistance, preventing damage to the internal porous structure in subsequent processes. Furthermore, the use of short wavelengths... The combination of a first ultraviolet light and a long-wavelength second ultraviolet light source achieves synergistic effects of pore-forming agent removal and full cross-linking of the framework. Short-wavelength high-energy photons efficiently decompose and remove the pore-forming agent to form nanopores, while long-wavelength low-energy photons enhance the cross-linking of the Si-O-Si framework and compensate for potential framework damage caused by short wavelengths. Furthermore, by using different wavelength irradiation sequences, the problem of "excessive cross-linking on the surface and insufficient cross-linking at the bottom" in thick film processing is solved, avoiding pore collapse caused by long-term processing. Compared with single-wavelength curing, the synergistic effect of this combination of wavelengths enables the film to improve Young's modulus while further reducing the dielectric constant, effectively resolving the technical contradiction between low k-value and high mechanical strength. In this invention, the gradient pore structure creates a smooth transition of mechanical properties along the film thickness direction, avoiding stress concentration caused by abrupt modulus changes in homogeneous films, significantly reducing the film's cracking tendency, and markedly increasing the critical cracking thickness, thereby greatly improving process tolerance, device yield, and reliability. The use of α-terpinene as a pore-forming agent, combined with the underlying densification structure, further strengthens the interfacial bonding between the ultra-low dielectric constant material and the underlying substrate. Furthermore, the segmented deposition process can be implemented on existing commercial PECVD equipment, requiring only programmatic control of parameters such as gas flow rate and RF power in each deposition segment, without requiring hardware modifications, thus exhibiting good industrial applicability. Combined wavelength ultraviolet curing can be achieved through a UV curing chamber equipped with multi-wavelength light sources, keeping energy consumption and process time within acceptable limits. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0112] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing ultra-low dielectric constant thin films based on multi-segment layered wavelength coupling, characterized in that: The preparation method includes at least the following steps: S1. A substrate is placed in a reaction chamber, and a reaction gas containing a framework precursor, a pore-forming agent, an oxidizing gas, and a carrier gas is introduced into the reaction chamber. Radio frequency power is applied to form plasma, and a composite film is formed by segmented deposition on the substrate. The segmented deposition includes at least two deposition sections. In different deposition sections, the volume flow rate ratio of the pore-forming agent to the framework precursor is adjusted so that the concentration of the pore-forming agent in the composite film is gradient-distributed along the thickness direction of the composite film. S2. The composite film is irradiated and cured using at least two different wavelengths of ultraviolet light to obtain an ultra-low dielectric constant film.

2. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: In step S1, a composite thin film is deposited on the substrate using plasma-enhanced chemical vapor deposition. The deposition temperature is 200~350℃, the pressure in the reaction chamber is 2Torr~6Torr, and the radio frequency power is 600W~800W. And / or, the skeleton precursor comprises diethoxymethylsilane, and the pore-forming agent comprises α-terpinene; And / or, oxidizing gases include one or a combination of O2, N2O, and CO2; And / or, the carrier gas includes one or a combination of helium and argon.

3. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: The segmented deposition includes 3 to 5 deposition segments, from the bottom deposition segment to the second-to-top deposition segment. In each deposition segment, the volumetric flow rate ratio of the pore-forming agent to the framework precursor increases in a gradient manner to form a gradient pore layer. In the top deposition segment, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1 to form a surface sealing layer.

4. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: The segmented deposition includes three deposition sections: a first deposition section, a second deposition section, and a top deposition section. In the first deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1, used to form a bottom adhesion layer. In the second deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.8:1 to 1.5:1, used to form a main pore-forming layer. In the top deposition section, the volumetric flow rate ratio of the pore-forming agent to the framework precursor is 0.1:1 to 0.5:1, used to form a surface sealing layer.

5. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 4, characterized in that: The deposition time of the first depositional section is 5s~10s; And / or, the deposition time of the second deposition section is 10s~30s; And / or, the deposition time of the third deposition section is 5s to 10s.

6. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: In step S1, a stabilization process is required between two adjacent deposition sections, specifically including: stopping the flow of the reaction gas, introducing an inert gas into the reaction chamber and applying a radio frequency power of 50W to 150W for 5s to 30s.

7. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: The irradiation curing process described in step S2 is carried out under a nitrogen or argon protective atmosphere, with a temperature of 200℃~400℃ and a reaction chamber pressure of 2Torr~5Torr.

8. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: In step S2, the composite film is irradiated and cured using a first ultraviolet light and a second ultraviolet light, wherein the wavelength range of the first ultraviolet light is 150nm~230nm and the wavelength range of the second ultraviolet light is 300nm~400nm.

9. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 8, characterized in that: Step S2 uses a time-division sequential irradiation mode to cure the composite film, specifically including: first curing with a first ultraviolet light for 1 min to 3 min, and then curing with a second ultraviolet light for 2 min to 5 min, wherein the irradiation intensity of the first ultraviolet light is 5 mW / cm² to 50 mW / cm², and the irradiation intensity of the second ultraviolet light is 20 mW / cm² to 100 mW / cm².

10. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 8, characterized in that: Step S2 involves simultaneously irradiating and curing the composite film using a simultaneous irradiation mode, specifically including simultaneously irradiating and curing the composite film with a first ultraviolet light and a second ultraviolet light for 5 to 10 minutes.

11. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 8, characterized in that: In step S2, the composite film is irradiated and cured using an alternating pulse irradiation mode, wherein the first ultraviolet light and the second ultraviolet light are alternately and cyclically irradiated and cured to form the composite film.

12. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 8, characterized in that: Step S2 also includes a third ultraviolet light with a wavelength of 254 nm.

13. The method for preparing ultra-low dielectric constant materials based on multi-segment layered wavelength coupling according to claim 1, characterized in that: Step S2, after the irradiation curing treatment, further includes passivating the surface of the irradiated composite film with hydrogen-containing plasma. Specifically, the passivation treatment of the surface of the irradiated composite film with hydrogen-containing plasma involves introducing hydrogen-containing gas into the reaction chamber, applying 50W~150W of radio frequency power, and treating at 200~300℃ for 30s~120s to passivate the dangling bonds on the surface of the composite film.

14. A thin film with ultra-low dielectric constant, characterized in that: The ultra-low dielectric constant thin film is prepared by the preparation method of the multi-segment layered wavelength coupling according to any one of claims 1 to 13. The ultra-low dielectric constant thin film includes at least a bottom adhesion layer, a main pore-forming layer and a surface sealing layer, and has a pore structure with a gradient distribution along the thickness direction. The porosity of the bottom adhesion layer is 5% to 15%, the porosity of the main pore-forming layer is 20% to 35%, and the porosity of the surface sealing layer is 5% to 15%.

15. The ultra-low dielectric constant thin film according to claim 14, characterized in that: The ultra-low dielectric constant film has a dielectric constant of no more than 2.6, a Young's modulus of 11 GPa to 14 GPa, and a hardness of 0.8 to 1.2 GPa.