Addition process of extreme ultraviolet photomask protective film carbon nanotubes

Abstract

The invention relates to an extreme ultraviolet (EUV) photomask protective film carbon nanotube adding process, which comprises the following steps of: providing a substrate, and carrying an EUV photomask protective film on the substrate; the method comprises the following steps: pre-treating a carbon nano-tube so as to enable the carbon nano-tube to be electrified; carrying out segregation treatment on the charged carbon nanotubes so as to screen out carbon nanotubes with compliant electric quantity and / or carbon nanotubes with non-compliant electric quantity; carrying out direct current acceleration on the carbon nano-tubes with the electric quantity compliance so as to enable the carbon nano-tubes to be attached to the substrate, and forming a preliminary film layer; and adjusting the film quality of the initial film layer to form a final film layer. The invention provides an integration process, solves the core problem of uneven dispersion of the existing process, innovatively introduces a corona electrification and segregation process in the field of semiconductors according to the requirements of the photomask protective film, and brings a brand new performance optimization path or function implementation mode for the photomask protective film.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for extreme ultraviolet (EUV) photomask protective films, and specifically to a process for adding carbon nanotubes to EUV photomask protective films. Background Technology

[0002] Extreme ultraviolet (EUV) lithography, a core supporting technology in advanced semiconductor manufacturing, enables continuous miniaturization of chip feature sizes thanks to its shorter exposure wavelength, making it crucial for driving the development of 5nm and below process technologies. The EUV photomask protector (EUV Pellicle), a core component of the EUV lithography system, plays a vital role in protecting the photomask from particle contamination and lithographic defects, while simultaneously meeting stringent requirements such as high transmittance, low absorption loss, excellent mechanical stability, and anti-static interference. Carbon nanotubes (CNTs), with their ultra-high mechanical strength, excellent conductivity, and extremely low EUV light absorption coefficient, have become an ideal functional material for optimizing the performance of EUV photomask protectors. By adding CNTs to the protective film substrate, the tensile strength of the film can be significantly improved, static dissipation ability can be enhanced, and particle contamination caused by electrostatic adsorption can be avoided, without affecting the transmission efficiency of EUV light. Therefore, the quality of the CNT addition process directly determines the overall performance of the EUV photomask protector.

[0003] Currently, the mainstream carbon nanotube addition processes in the industry mainly include three types: liquid phase filtration, vapor phase deposition, and composite structure methods (such as BN-CNT composite process). However, all of the above processes have insurmountable technical defects in practical applications and cannot meet the high precision and high stability requirements of EUV lithography for protective films: 1) Liquid phase filtration: This process disperses carbon nanotubes in a liquid medium and then filters them through a filter membrane to achieve the adhesion of carbon nanotubes to the substrate surface. The core problem is that a high-temperature drying process is required after filtration to remove the liquid medium, and the uneven moisture content of the film layer during the drying process... Uniform evaporation leads to an imbalance in the stress distribution within the film, ultimately causing instability in the tensile properties of the protective film and severely affecting the positioning accuracy during photolithography. Simultaneously, during the transfer of the dried carbon nanotube film from the filter membrane to the EUV photomask protective film substrate, defects such as scratches and particulate contamination are easily introduced, resulting in a significant reduction in product yield. Furthermore, carbon nanotubes in the liquid phase system are prone to secondary agglomeration, making uniform dispersion difficult and further affecting the consistency of film performance. 2) Vapor deposition: This process decomposes the carbon source gas at high temperatures (typically above 600℃), causing carbon atoms to deposit on the substrate surface. The deposition of carbon nanotube films is a complex process. The process temperature is far higher than the heat resistance limit of the EUV photomask protective film substrate (mostly polymer or ultrathin metal film). High temperatures can cause thermal deformation of the substrate, and the difference in thermal expansion coefficients between the carbon nanotube film and the substrate generates significant thermal stress, easily leading to cracking and peeling of the film. Furthermore, vapor deposition requires extremely high uniformity of the temperature and gas flow fields in the reaction chamber, resulting in high equipment manufacturing and maintenance costs. Moreover, achieving uniform deposition of carbon nanotube films on large-area substrates (such as 300mm photomasks) is difficult, with film thickness deviations typically exceeding [a certain threshold]. 10%, which cannot meet the requirements of high-precision photolithography; 3) Composite structure method (such as BN-CNT): This process coats the surface of carbon nanotubes with a layer of insulating material such as boron nitride (BN) to balance the conductivity and insulation requirements of the film. However, this process is complicated and requires multiple steps such as carbon nanotube preparation, surface modification, and coating deposition, resulting in low production efficiency. Moreover, during the coating process, the boron nitride layer is prone to problems such as pinholes, local uncoated areas, or uneven coating thickness, which leads to a decrease in the anti-fouling ability and mechanical stability of the film, and cannot effectively give full play to the synergistic performance advantages of carbon nanotubes and coating materials. Summary of the Invention

[0004] This invention provides a process for adding carbon nanotubes to an extreme ultraviolet photomask protective film, which solves the problems of uniformity and integrity of coating and inability to adjust thickness in the current carbon nanotube addition process, while achieving energy saving and high-efficiency production.

[0005] This invention provides a process for adding carbon nanotubes to an extreme ultraviolet (EUV) photomask protective film, comprising the following steps: A substrate is provided on which an extreme ultraviolet (EUV) photomask protective film is carried; The carbon nanotubes are pretreated to make them chargeable; The charged carbon nanotubes were subjected to a separation process to screen out carbon nanotubes with compliant charge and / or non-compliant charge. The charged carbon nanotubes are subjected to DC acceleration to allow them to adhere to the substrate and form a preliminary film layer; and The initial membrane layer is adjusted to form the final membrane layer.

[0006] Furthermore, the substrate includes either a polymer substrate or a metal substrate.

[0007] Furthermore, the preprocessing includes: The carbon nanotubes were dried to control the ambient humidity at a low level (relative humidity of 20-40%); and The dried carbon nanotubes are electrostatically charged by corona electrodes to achieve electrostatic dispersion and prevent agglomeration.

[0008] Furthermore, in the drying process, the drying temperature is 65~135℃, the drying time is 200~300 min, and the relative humidity is 29%.

[0009] Furthermore, corona charging of the dried carbon nanotubes using a corona electrode includes: A voltage is applied to the corona electrode to generate a corona discharge, thereby creating an electric field; and Carbon nanotubes collide with charged ions in the electric field, eventually acquiring the same negative charge. Using the repulsive force between the charges, the carbon nanotube aggregates are broken up, forming monodisperse or small aggregated particles.

[0010] Furthermore, the spacing between the corona electrodes is 365~415mm, and the voltage is 10kV~100kV. By adjusting the spacing of the corona electrodes and the applied voltage, the electric field strength is controlled to ensure uniform charge density of the carbon nanotubes, thereby avoiding failure of subsequent separation and screening processes due to uneven charge distribution.

[0011] Furthermore, the separation treatment of charged carbon nanotubes includes: Charged carbon nanotubes are injected perpendicularly into a uniform magnetic field at a fixed velocity (10⁵~10⁶ m / s) and undergo circular motion; and Based on the different mass-to-charge ratios of charged carbon nanotubes, the nanotubes are deflected with different deflection radii, allowing the charged nanotubes to undergo DC acceleration. The principle of the separation process is as follows: charged carbon nanotubes are injected perpendicularly into a uniform magnetic field at a fixed velocity, and are subjected to a Lorentz force that is always perpendicular to the velocity direction, thus causing them to undergo uniform circular motion. According to the Lorentz force deflection formula R=(M×v) / (q×B), the deflection radius R of the target charged particle is ensured to be exactly equal to the distance from the slit to the center of the magnet, where M is the average mass of the carbon nanotube, v is the velocity of the carbon nanotube, q is the charge, and B is the magnetic field strength; M / q (mass-to-charge ratio) becomes the only factor determining the deflection radius, therefore, ions with different M / q ratios will be deflected with different radii.

[0012] Furthermore, the magnetic field strength B is set according to R=(M×v) / (q×B) to allow the charged carbon nanotubes to pass through.

[0013] Furthermore, the compliant carbon nanotubes are carbon nanotubes with a charge specification > 1116 mAh / g, and the non-compliant carbon nanotubes are carbon nanotubes with a charge specification < 1116 mAh / g.

[0014] Furthermore, the DC acceleration of the charged carbon nanotubes includes: The substrate is fixed on a movable carrier platform; After separation, the carbon nanotubes enter the acceleration zone (located between the separation treatment zone and the substrate), and a reverse voltage (500~800V) is applied to accelerate the charged carbon nanotubes, causing them to adhere to the substrate surface and form a preliminary film layer. Monitoring the electrostatic potential on the substrate surface is used to confirm the adhesion status of the carbon nanotubes; and The magnitude of the reverse voltage is adjusted according to the adhesion state to ensure uniform adhesion of carbon nanotubes.

[0015] Furthermore, the reverse voltage is 500~800V.

[0016] Furthermore, the thickness of the preliminary film layer is 5~25nm.

[0017] Furthermore, an array of electrostatic sensors is used to monitor the electrostatic potential on the substrate surface, with the array of electrostatic sensors uniformly distributed above the substrate. For example, if the array of electrostatic sensors detects that the electrostatic potential in a certain area is lower than a preset value (e.g., -50V, corresponding to excessive thickness), the inverting voltage of the carrier stage in that area is immediately reduced (e.g., from 80V to 60V) to weaken the attractive force and reduce the adhesion of carbon nanotubes; if the electrostatic potential is higher than the preset value (e.g., -30V, corresponding to excessive thickness), the inverting voltage is increased (e.g., from 80V to 100V) to ensure that the overall substrate adhesion thickness deviation is ≤5%.

[0018] Furthermore, the process of adjusting the membrane quality of the preliminary membrane layer includes: The movable carrier plate is heated, and a secondary voltage in the same direction as the voltage is applied to the preliminary film layer to supplement the charge density of the preliminary film layer, so that the repulsive force between particles is more uniform, local agglomeration is avoided, and the film layer density is improved.

[0019] Furthermore, during the heating process, the heating temperature is 50~200℃ (the heating temperature is adjusted according to the substrate material); the secondary voltage is 50~200V; the high temperature promotes the diffusion and bonding of carbon nanotubes with the substrate surface, enhances the adhesion of the film layer, and the stress control of the film layer can be increased as needed, which is controlled by the voltage magnitude.

[0020] Furthermore, the process of adjusting the membrane quality of the preliminary membrane layer also includes: Adjusting the acceleration distance from the acceleration zone to the substrate; and Adjust the moving speed of the movable carrier platform.

[0021] Furthermore, the acceleration distance is 300~400mm; the moving speed is 0.5~5 mm / min. The moving speed of the movable carrier stage is related to the acceleration distance: a longer acceleration distance results in a slower moving speed, ensuring that each point on the substrate has sufficient time to receive particles.

[0022] Furthermore, the process of adjusting the membrane quality of the preliminary membrane layer also includes: Adjusting the incident three-dimensional angle of carbon nanotubes (the incident three-dimensional angle is the angle between the incident surface of the carbon nanotube and the substrate plane). Adjust the reaction chamber pressure of the movable carrier stage, and set the reaction chamber pressure to 500~760 torr.

[0023] Furthermore, the incident three-dimensional angle is 15 to -15 degrees.

[0024] Furthermore, the preprocessing also includes: The substrate is subjected to plasma cleaning to remove oil and / or impurities, thereby enhancing the adhesion of carbon nanotubes.

[0025] The present invention has at least the following beneficial effects: 1) The present invention provides an integrated and consolidated process. Through precise screening of electrostatic dispersion and segregation treatment in the pretreatment, the dispersion efficiency of carbon nanotubes is >95%, the content of agglomerates is <10%, and the particle size distribution is controlled within the ideal range of 10~500nm, solving the core problem of uneven dispersion in existing processes; 2) The present invention does not require high-temperature processing, avoiding film cracking and peeling caused by thermal stress, and the film tension is uniform; the real-time thickness control of DC acceleration process and the multi-parameter coordination of film quality adjustment process ensure that the film thickness deviation is ≤3%, and the tensile strength of the photomask protective film is increased by ≥20%, meeting the stringent requirements of EUV lithography; 3) The present invention innovatively introduces the corona charging and segregation process from the semiconductor field to meet the needs of photomask protective films, bringing a brand-new performance optimization path or functional realization method to photomask protective films. Detailed Implementation

[0026] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0027] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0028] It should also be noted that, in the embodiments of the present invention, only a portion of the parts or components may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, the required parts or components can be added as needed for specific scenarios.

[0029] It should also be noted that within the scope of this invention, the terms "same", "equal", and "equal to" do not mean that the two values ​​are absolutely equal, but allow for a certain reasonable error. In other words, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0030] Furthermore, the embodiments of the present invention describe the process steps in a specific order. However, this is only for the convenience of distinguishing each step, and is not a limitation on the order of each step. In different embodiments of the present invention, the order of each step can be adjusted according to the process.

[0031] The following embodiment provides a process for adding carbon nanotubes to an extreme ultraviolet (EUV) photomask protective film, including the following steps: Provide a substrate on which an extreme ultraviolet (EUV) photomask protective film is carried, the substrate including either a polymer substrate or a metal substrate; Pre-treating carbon nanotubes to make them charged; The charged carbon nanotubes were subjected to a separation process to screen out carbon nanotubes with compliant charge and / or non-compliant charge (carbon nanotubes with compliant charge are those with a charge specification > 1116 mAh / g, and carbon nanotubes with non-compliant charge are those with a charge specification < 1116 mAh / g). DC acceleration was applied to carbon nanotubes with compliant charge to allow them to adhere to a substrate and form a preliminary film; and The initial membrane layer is adjusted to form the final membrane layer.

[0032] Preprocessing includes: Plasma cleaning is performed on the substrate to remove oil and / or impurities, thereby enhancing the adhesion of carbon nanotubes. Carbon nanotubes were dried to maintain a low relative humidity (20-40%). The drying temperature was 65-135℃, and the drying time was 200-300 min. The dried carbon nanotubes are electrostatically dispersed by corona-electrode electrodes to prevent agglomeration. A voltage is applied to the corona electrodes to generate a corona discharge, creating an electric field. The carbon nanotubes collide with charged ions in this field, eventually acquiring the same negative charge. The repulsive force between these charges breaks up the agglomerates, forming monodisperse or small clusters. The spacing between the corona electrodes is 365–415 mm, and the voltage is 10–100 kV. By adjusting the electrode spacing and the applied voltage, the electric field strength is controlled to ensure uniform charge density of the carbon nanotubes, preventing uneven charging from causing subsequent separation and screening failures. The separation process for charged carbon nanotubes includes: Charged carbon nanotubes are injected perpendicularly into a uniform magnetic field at a fixed velocity (10⁵~10⁶ m / s) and undergo circular motion; and Based on the different mass-to-charge ratios of charged carbon nanotubes, the nanotubes are deflected with different deflection radii, allowing those with compliant charge to undergo DC acceleration. The principle of the separation process is as follows: Charged carbon nanotubes are injected perpendicularly into a uniform magnetic field at a fixed velocity, experiencing a Lorentz force always perpendicular to the velocity direction, thus undergoing uniform circular motion. According to the Lorentz force deflection formula R=(M×v) / (q×B), the deflection radius R of the target charged particles is ensured to be exactly equal to the distance from the slit to the center of the magnet, where M is the average mass of the carbon nanotube, v is the velocity of the carbon nanotube, q is the charge, and B is the magnetic field strength. M / q (mass-to-charge ratio) becomes the sole factor determining the deflection radius; therefore, ions with different M / q ratios will be deflected with different radii. The magnetic field strength B is set according to R=(M×v) / (q×B) to allow the compliant charged carbon nanotubes to pass through.

[0033] DC acceleration of compliant carbon nanotubes includes: Fix the substrate onto the movable carrier plate stage; After separation, the carbon nanotubes enter the acceleration zone (located between the separation treatment zone and the substrate). A reverse voltage is applied to accelerate the carbon nanotubes with compliant charge, causing them to adhere to the substrate surface and form a preliminary film. An array of electrostatic sensors was used to monitor the electrostatic potential on the substrate surface to confirm the adhesion status of carbon nanotubes; and Adjust the magnitude of the reverse voltage according to the adhesion state to ensure uniform adhesion of carbon nanotubes.

[0034] Preliminary membrane quality conditioning includes: The movable carrier stage is heated, and a secondary voltage in the same direction as the initial voltage is applied to the preliminary film layer to supplement the charge density of the preliminary film layer, making the repulsive force between particles more uniform, avoiding local agglomeration, and improving the film layer density. During heating, the heating temperature is 50~200℃ (the heating temperature is adjusted according to the substrate material); the secondary voltage is 50~200V; the high temperature promotes the diffusion and bonding of carbon nanotubes to the substrate surface, enhancing the film layer adhesion.

[0035] Preliminary membrane quality conditioning also includes: Adjust the acceleration distance from the acceleration zone to the substrate; and Adjust the moving speed of the movable carrier stage. The acceleration distance is 300~400mm; the moving speed is 0.5~5 mm / min. The moving speed of the movable carrier stage is related to the acceleration distance: the longer the acceleration distance, the slower the moving speed, ensuring that each point on the substrate has enough time to receive particles.

[0036] Preliminary membrane quality conditioning also includes: Adjusting the incident three-dimensional angle of the carbon nanotubes (the incident three-dimensional angle is the angle between the incident surface of the carbon nanotube and the substrate plane), the incident three-dimensional angle is 15 to -15 degrees; and Adjust the reaction chamber pressure of the movable carrier stage, setting the reaction chamber pressure to 500~760 torr.

[0037] The results of this embodiment are as follows: Carbon nanotube dispersion efficiency: highest efficiency >95%; Carbon nanotube aggregate content: <10% for the separation process; Carbon nanotube particle size distribution: 10~500nm ideal range; Electrical conductivity: ≥10 S / m; Mechanical properties: The tensile strength of the photomask protective film is increased by ≥20%.

[0038] While some embodiments of the present invention have been described in this application, those skilled in the art will understand that these embodiments are merely illustrative. Numerous variations, alternatives, and improvements will arise in those skilled in the art under the teachings of this invention without departing from its scope. The appended claims are intended to define the scope of the invention and thereby cover methods and structures within the scope of the claims themselves and their equivalents.

Claims

1. A process for adding carbon nanotubes to an extreme ultraviolet (EUV) photomask protective film, characterized in that, Includes the following steps: A substrate is provided on which an extreme ultraviolet (EUV) photomask protective film is carried; The carbon nanotubes are pretreated to make them chargeable; The charged carbon nanotubes were subjected to a separation process to screen out carbon nanotubes with compliant charge and / or non-compliant charge. The charged carbon nanotubes are subjected to DC acceleration to allow them to adhere to the substrate and form a preliminary film layer. as well as The initial membrane layer is adjusted to form the final membrane layer.

2. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 1, characterized in that, The preprocessing includes: Drying process for carbon nanotubes; and The dried carbon nanotubes are corona-charged using a corona electrode to achieve electrostatic dispersion of the carbon nanotubes.

3. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 2, characterized in that, Corona charging of dried carbon nanotubes using a corona electrode includes: A voltage is applied to the corona electrode to generate a corona discharge, thereby creating an electric field; and Carbon nanotubes collide with charged ions in the electric field and eventually acquire the same negative charge.

4. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 2, characterized in that, The aforementioned separation treatment of charged carbon nanotubes includes: Charged carbon nanotubes are injected perpendicularly into a uniform magnetic field at a fixed velocity and move in a circular motion; and Depending on the different mass-to-charge ratios of the charged carbon nanotube particles, the carbon nanotubes deflect with different deflection radii, enabling the charged carbon nanotubes to undergo DC acceleration.

5. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 2, characterized in that, The compliant carbon nanotubes are those with a charge specification > 1116 mAh / g, and the non-compliant carbon nanotubes are those with a charge specification < 1116 mAh / g.

6. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 2, characterized in that, The DC acceleration of the charged carbon nanotubes includes: The substrate is fixed on a movable carrier platform; After separation, the carbon nanotubes enter the acceleration zone and a reverse voltage opposite to the voltage is applied to accelerate the charged carbon nanotubes, causing them to adhere to the substrate surface and form a preliminary film layer. Monitoring the electrostatic potential on the substrate surface is used to confirm the adhesion status of the carbon nanotubes; and The magnitude of the reverse voltage is adjusted according to the adhesion state to ensure uniform adhesion of carbon nanotubes.

7. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 6, characterized in that, The aforementioned process for adjusting the membrane quality of the preliminary membrane layer includes: The movable carrier stage is heated, and a secondary voltage in the same direction as the voltage is applied to the preliminary film layer.

8. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 6, characterized in that, The process of adjusting the membrane quality of the preliminary membrane layer further includes: Adjusting the acceleration distance from the acceleration zone to the substrate; and Adjust the moving speed of the movable carrier platform.

9. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 6, characterized in that, The process of adjusting the membrane quality of the preliminary membrane layer further includes: Adjusting the incident three-dimensional angle of carbon nanotubes; and Adjust the reaction chamber pressure of the movable carrier stage.

10. The process for adding carbon nanotubes to the extreme ultraviolet photomask protective film according to claim 1, characterized in that, The preprocessing also includes: The substrate is subjected to plasma cleaning to remove oil and / or impurities.