Method for Coating CNT strand in Membrane employed in Spectral Purity Filter or Pellicle used in Exposure Device

Abstract

A method for coating CNT strands on a membrane for SPF or pellicle used in an exposure apparatus is disclosed. A membrane formed from CNT strands is placed in a chamber, and the interior of the chamber is configured into a silane-based and / or CH-based precursor gas environment. Under the configured environment, the process temperature inside the chamber is maintained at 700 to 1000°C for 0.2 to 1.5 hours to form a coating layer of a carbon-based material on the surface of the CNT strands. A coating layer of a carbon-based material having a thin thickness of less than 1 nm is formed on the CNT strands constituting the membrane. This coating layer prevents damage to the membrane caused by reaction with hydrogen radicals, and furthermore, because the thickness of the coating layer is extremely thin, a decrease in the transmittance of the membrane does not occur.

Description

Technology Field

[0001] The present invention relates to a membrane provided in a Spectral Purity Filter (SPF) or a Pellicle, and more specifically, to a method for coating CNT strands of a membrane made of Carbon Nanotubes (CNT) provided in an SPF or a Pellicle used in an exposure apparatus. Background Technology

[0003] In the EUV (Extreme Ultra-Violet) lithography process, an EUV light source with a wavelength of 13.5 nm is used. However, the EUV light source emits exposure light that includes various wavelengths in addition to the 13.5 nm wavelength. Since wavelengths other than the EUV wavelength reduce the precision of the EUV lithography process, they must be suppressed as much as possible. However, there are technical limitations to manufacturing a light source that generates only wavelengths within a specific range. Therefore, a method of filtering the exposure light using a Spectral Purity Filter (SPF) that allows only the wavelengths corresponding to EUV to pass through among the wavelengths of light emitted from the EUV light source is used.

[0004] Figure 1 illustrates the state in which an SPF is installed and used within an exposure apparatus. The exposure apparatus is equipped with a light source that generates EUV exposure light and an in-band filter that primarily filters the exposure light from the light source. An SPF (Spectral Purufy Filter) is installed at the end of the in-band filter. Exposure light generated from the EUV light source is incident on the SPF, and this exposure light contains light of various wavelengths along with the EUV wavelength. The SPF is capable of allowing light of a wavelength of 13.5 nm, which corresponds to the EUV exposure light, to pass through while blocking light of other wavelengths; in particular, blocking wavelengths of 190–400 nm, which are highly sensitive to PR (Photoresist) during the photolithography process, is a very important factor in the function of the SPF. The exposure light that passes through the SPF is patterned by passing through a photomask and then irradiated onto a wafer.

[0005] Meanwhile, in the EUV lithography process, a method is used to attach a pellicle (not shown in FIG. 1) to the top of the photomask arranged as shown in FIG. 1 to prevent impurities from adhering to the surface of the photomask. As circuit line widths become finer, the size of impurities that can affect pattern damage also decreases, making the role of the pellicle for photomask protection increasingly important. (For reference, in FIG. 1, for the convenience of illustration, it is depicted as if the EUV exposure light passes through the photomask and is irradiated onto the wafer; however, in reality, a reflective photomask rather than a transmissive photomask is used in the EUV lithography process, so the EUV exposure light is reflected from the photomask before being irradiated onto the wafer.)

[0006] SPF and pellicles basically have the same structure. Hereinafter, the term 'membrane structure' is used as a comprehensive term that includes SPF and pellicles.

[0007] FIG. 2 is a drawing illustrating the basic structure of a membrane structure (100) used as SPF or pellicle.

[0008] The membrane structure (100) is composed of a membrane (20) and a support member (10). The membrane (20) functions to transmit extreme ultraviolet exposure light of a wavelength of 13.5 nm. The support member (10) functions to support the membrane (20). Generally, the support member (10) is formed by etching the substrate after the membrane (20) is formed on a transparent substrate, and thereby the membrane structure (100) is manufactured.

[0009] Under this basic structure, when the membrane structure (100) is used as an SPF, the membrane structure (100) is mounted on the end of the in-band filter as shown in FIG. 1, and when the membrane structure (100) is used as a pellicle, the membrane structure (100) is mounted on the upper part of the photomask of FIG. 1. Since the characteristics required for the membrane (20) differ somewhat depending on whether the membrane structure (100) is used as an SPF or a pellicle, the membrane (20) is manufactured to have physical, material, and structural characteristics that meet these requirements.

[0010] The membrane (20) must have high transmittance for EUV wavelength exposure light, and must have the characteristic of radiating heat generated by the transmission of EUV exposure light during the exposure process, and must also have mechanical strength that is not easily broken as it is composed of a very thin film. In order to meet these various requirements, various studies have been conducted on the material constituting the membrane (20), and recently, CNT (Carbon Nanotube) is being studied as a promising material. Since CNT has high thermal resistance and mechanical strength, it provides the advantage of being able to secure high transmittance by fabricating it into a very thin film.

[0011] FIG. 3 is a schematic diagram illustrating the structure of a membrane formed from CNTs, illustrating an example in which the membrane is composed solely of CNTs. Individual CNT strands (22) within the membrane (20) are arranged to extend approximately horizontally, forming threads of appropriate length, and are arranged in a form in which multiple CNT strands (22) are intertwined. The overall shape of the membrane (20) is formed by this arrangement of CNT strands (22). Individual CNT strands (22) have a thickness of approximately 0.4 to 3 nm in the case of single-walled CNTs, and a thickness of approximately 2 to 100 nm in the case of multi-walled CNTs.

[0012] The interior of the exposure device in which SPF or pellicle is used is configured as an environment where a large amount of hydrogen radicals exist. These hydrogen radicals react with the membrane (20), and this can cause damage to the membrane (20). CNT materials are known to be particularly vulnerable to reactions with hydrogen radicals. Since damage to the membrane (20) causes problems such as reduced transmittance and breakage, the membrane (20) must be able to suppress reactivity with hydrogen radicals as much as possible. Various methods can be considered for this purpose, and in the present invention, a method of coating CNT strands (22) is considered as one of the methods.

[0013] FIG. 4 is an enlarged view of the CNT strands within the membrane of FIG. 3, showing the coated state of the CNT strands. As shown in FIG. 4, individual CNT strands (22) are coated to form a coating layer (25) on their surface, thereby preventing hydrogen radicals from coming into direct contact with the CNT strands (22). This can improve the durability of the membrane (20).

[0014] Physical vapor deposition (PVD) and chemical vapor deposition (CVD) can be considered as methods for coating CNT strands (22). However, a problem has arisen where coating by PVD is performed only on the CNT strands (22) near the surface in the thickness direction of the membrane (20), and not in the inner region in the thickness direction of the membrane (20). Consequently, the problem of still being vulnerable to hydrogen radicals penetrating into the inner part of the membrane (20) cannot be solved. Coating by CVD has the advantage of being able to be performed even in the inner region in the thickness direction of the membrane (20). However, a problem has arisen where the thickness (t2) of the coating layer (25) resulting from the coating is excessively thick and cannot be controlled to a thin thickness. Specifically, in the case of the coating layer (25) formed by CVD, the thickness (t2) is at least 1 nm or more, which causes a decrease in overall transmittance. In addition, although the deposition efficiency is superior compared to PVD, there are limitations in coating individual CNT strands (22) even in the case of deposition by CVD. The problem to be solved

[0016] The present invention was devised to solve the above-mentioned problems, and the objective of the present invention is to provide a method of protecting a membrane from damage caused by reaction with hydrogen radicals by coating the CNT strands of a membrane formed of CNTs, while ensuring that the coating layer is composed of an extremely thin thickness so that a decrease in transmittance does not occur. means of solving the problem

[0018] To achieve the above objective, the present invention provides a method for coating CNT strands on a membrane for SPF or pellicle used in an exposure apparatus, comprising: a) receiving the membrane formed of CNT strands in a chamber; b) creating a silane-based and / or CH-based precursor gas environment inside the chamber; and c) maintaining the process temperature inside the chamber at 700 to 1000°C for 0.2 to 1.5 hours under the environment created by step b) to form a coating layer of a carbon-based material on the surface of the CNT strands.

[0019] In step b) above, the precursor gas is supplied at a rate of 50 to 100 cc / min to maintain the environment.

[0020] The thickness of the coating layer is preferably 0.2 to 2 nm, and more preferably 0.7 to 1.2 nm.

[0021] Before step b) above, an additional pretreatment step may be performed to remove organic matter and impurities from the surface of the membrane.

[0022] The above pretreatment step includes maintaining a process temperature of 700 to 1000°C in an Ar or N2 gas atmosphere for a predetermined period of time. Effects of the invention

[0024] According to the present invention, a coating layer of a carbon-based material having a thin thickness of less than 1 nm is formed on a CNT strand constituting a membrane. This coating layer prevents damage to the membrane caused by reaction with hydrogen radicals, and also, since the thickness of the coating layer is extremely thin, a decrease in the permeability of the membrane does not occur. Brief explanation of the drawing

[0026] FIG. 1 is a drawing illustrating the state in which a membrane structure is mounted and used within an exposure device. Figure 2 is a drawing illustrating the structure of a general membrane structure. FIG. 3 is a schematic diagram illustrating the structure of a membrane formed from CNTs. FIG. 4 is an enlarged view of the CNT strands within the membrane of FIG. 3. Specific details for implementing the invention

[0027] In the following description of the present invention, the general configurations of the SPF (Spectral Purify Filter) and Pellicle described with reference to FIGS. 1 to 4 are omitted from redundant description and are adopted as configurations of the present invention. Below, the method of forming the coating layer (25) of FIG. 4, which is a characteristic configuration of the present invention, is described in detail.

[0028] The present invention provides a method for coating CNT strands on a membrane for SPF and pellicle used in an exposure apparatus.

[0029] A membrane (25) formed from CNT strands (22) is accommodated in a chamber. At this time, the membrane (25) may be formed independently by a separate process, or it may be formed independently and then attached to a support member (10) by transfer to form a membrane structure (100) as shown in FIG. 2.

[0030] Prior to the process for forming the coating layer (25), a pretreatment process is first performed to remove organic matter and impurities from the surface of the membrane (20). The pretreatment process is performed by creating an Ar or N2 gas atmosphere inside the chamber and maintaining a process temperature of 700 to 1000°C for a predetermined time. Here, the predetermined time is set, for example, to 5 ± 2 minutes and can be appropriately adjusted to a range that can achieve the purpose of the pretreatment process.

[0031] After the pretreatment process is completed, the interior of the chamber is configured with a silane-based and / or CH-based precursor gas environment. SiH4 can be used as the silane-based gas, and CH4 can be used as the CH-based gas.

[0032] Under the precursor gas environment thus formed, the process temperature inside the chamber is maintained at a predetermined temperature for a predetermined time. As a result, the surface of the CNT strand (22) reacts with the pretreatment gas, and a coating layer (25) of a carbon-based material is formed by surface treatment. Here, the carbon-based material refers to, for example, SiC or a carbon compound. During the execution of this process, the precursor gas is supplied at a rate of 50 to 100 cc / min to maintain the aforementioned precursor gas environment.

[0033] The coating layer (25) formed by such a process has a thickness (t2) of 0.2 to 2 nm. Preferably, the coating layer (25) is formed such that its thickness (t2) is 0.7 to 1.2 nm. To achieve this, the process temperature and process time must be appropriately set.

[0034] The process temperature is set from the perspective of appropriately controlling the reaction energy for forming a coating layer (25) on the CNT strand (22). If the reaction energy is too low, the reaction does not occur, and the coating layer (25) is not formed properly. If the reaction energy is too high, decomposition of the CNT strand (22) may occur, and the thickness of the coating layer (25) may increase. In addition, the precursor gas may become a plasma state, and in this case, the plasma itself becomes a factor causing damage to the CNT strand (22). Considering this, the process temperature is preferably set to 700 to 1000°C, and more preferably to 800 ± 50°C. At this process temperature, a coating layer (25) is formed in which carbon (C) fills partial defects in the CNT strand (22). That is, the CNT strand (22) has a hexagonal carbon bonding structure but is inherently defective, and active reactions with hydrogen radicals occur in these defective parts. In the present invention, under this process temperature, a coating layer (25) is formed that fills the defective parts of the CNT strand (22) through a surface treatment reaction of carbon of the precursor gas on the CNT strand (22). In addition, under this process temperature, it is possible to form a coating layer (25) with a thickness (t2) of less than 0.5 nm by adjusting the process time.

[0035] Preferably, the process time is set to 0.2 to 1.5 hours, and more preferably to 1.0 ± 0.2 hours. Outside this time range, the coating layer (25) is formed incompletely or with an excessively thick thickness.

[0036] Although the present invention has been specifically described through its structure with reference to the drawings, this is for the purpose of illustrative explanation and description of the invention and is not intended to limit the meaning or scope of the invention. Therefore, those skilled in the art will understand that various modifications and equivalent alternative structures are possible, and the true scope of protection of the invention should be determined by the technical details of the patent claims. Explanation of the symbols

[0038] 10 : Support 20 : Membrane 22: CNT strand 25: Coating layer 100 : Membrane structure

Claims

Claim 1 A method for coating CNT strands on a membrane for SPF or pellicle used in an exposure apparatus, comprising: a) a step of receiving the membrane formed of CNT strands in a chamber; b) a step of creating a silane-based and CH-based precursor gas environment inside the chamber, wherein the precursor gas is supplied at a rate of 50 to 100 cc / min and the precursor gas environment is maintained; and c) a step of forming a SiC coating layer with a thickness of 0.2 to 2 nm on the surface of the CNT strands by maintaining the process temperature inside the chamber at 800 ± 50℃ for 0.2 to 1.5 hours under the environment created by step b). Claim 2 delete Claim 3 delete Claim 4 A method according to claim 1, characterized in that the thickness of the coating layer is 0.7 to 1.2 nm. Claim 5 A method according to claim 1 or 4, further comprising a pretreatment step for removing organic matter and impurities from the surface of the membrane prior to step b). Claim 6 A method according to claim 5, wherein the pretreatment step comprises maintaining a process temperature of 700 to 1000°C in an Ar or N2 gas atmosphere for a predetermined period of time.

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