Pellicle for protecting EUV photomask using reinforeced pad

Abstract

The present invention relates to a pellicle for protecting an EUV photomask equipped with a reinforcing pad, and more specifically, to a pellicle for protecting an EUV photomask equipped with a reinforcing pad that can prevent damage to the membrane that occurs when cleaning a pellicle after etching is completed by forming a reinforcing pad on the edge of a silicon-based membrane. The present invention provides a pellicle for protecting an EUV photomask equipped with a reinforcing pad, characterized by comprising: a pellicle frame formed of a silicon substrate; a silicon-based membrane formed on the upper surface of the pellicle frame; and a reinforcing pad formed on the front edge of the silicon-based membrane.

Description

Technology Field

[0001] The present invention relates to a pellicle for protecting an EUV photomask equipped with a reinforcing pad, and more specifically, to a pellicle for protecting an EUV photomask equipped with a reinforcing pad that can prevent damage to the membrane that occurs when the pellicle is cleaned after etching is completed by forming a reinforcing pad on the edge of a silicon-based membrane. Background Technology

[0002] With the recent advancement of nanotechnology, there has been a gradual increase in the development of pellicle technology that protects the photomask of a lithographic apparatus used to form nano-scale circuit patterns on a wafer, thereby enabling the production of high-yield semiconductor chips. A fine circuit pattern is formed on the photomask, and the circuit pattern of the photomask is formed on a silicon wafer through the lithographic apparatus. However, if fine dust adheres to the photomask due to atmospheric contamination, the shape of the fine dust is also formed on the silicon wafer, leading to product defects.

[0003] In particular, extra ultraviolet (EUV) lithography equipment is equipment that forms a fine circuit pattern of several nanometers on a photomask and forms a circuit pattern on a silicon substrate by irradiating extreme ultraviolet light. By performing the lithography process with a light source having an extreme ultraviolet wavelength, it is possible to produce semiconductor circuit patterns more finely, reduce the number of process steps to increase productivity, and secure high-performance chips.

[0004] Accordingly, along with the development of extreme ultraviolet lithography equipment, competition to develop pellicles that protect photomasks and shield silicon substrates from atmospheric contamination to reduce defects is also intensifying.

[0005] A pellicle is a structure made of a thin film placed over a photomask. It protects the photomask by preventing foreign substances from adhering to it, and also prevents deformation of the circuit pattern caused by the projection of foreign substance images onto the silicon substrate by defocusing the images of the foreign substances. Conventional projection-type optical exposure equipment uses fixed pellicles that are replaced at appropriate times, thereby allowing the process to proceed efficiently by reducing costs associated with mask cleaning or replacement.

[0006] However, in the case of EUV lithography equipment, the short wavelength of extreme ultraviolet light causes most of the light to be absorbed by conventional organic material pellicles, leading to various problems with the application of existing pellicles.

[0007] Accordingly, certain prerequisites are required for pellicles used in EUV lithography equipment. The requirements for EUV pellicles include 1) high transmittance of over 90%, 2) mechanical stability, and 3) minimization of thermal deformation. Accordingly, EUV pellicles require a transmittance of over 90% and mechanical stability at a thickness of 60 nm or less. Polysilicon, CNT, graphene, and silicon carbide (SiC) are emerging as materials that satisfy these conditions, and the number of patent applications related to related technologies is also increasing. Prior art literature

[0008] Published Patent Application No. 10-2022-0056609 (Published May 6, 2022) Published Patent Application No. 10-2022-0017137 (Published February 11, 2022) Published Patent Application No. 10-2021-0022001 (Published March 2, 2021) Published Patent Application No. 10-2022-0139656 (Published October 17, 2022) The problem to be solved

[0009] To solve the above-mentioned problems, the present invention aims to provide a pellicle for protecting an EUV photomask equipped with a reinforcing pad that can prevent damage caused by the surface tension of water that may occur during cleaning of the silicon frame by forming a reinforcing pad on a silicon-based membrane to form a frame by partially removing the silicon deposited on the silicon-based membrane through etching. means of solving the problem

[0010] To achieve the above objective, the present invention provides a pellicle for protecting an EUV photomask equipped with a reinforcing pad, characterized by comprising: a pellicle frame formed of a silicon substrate; a silicon-based membrane formed on the upper surface of the pellicle frame; and a reinforcing pad formed on the front edge of the silicon-based membrane.

[0011] In the present invention, the pellicle frame is characterized by the fact that the silicon-based membrane is deposited on the front surface of a silicon substrate, and the back surface of the silicon substrate on which the silicon-based membrane is deposited is removed by etching to form a frame.

[0012] In the present invention, the silicon-based membrane is characterized by being composed of any one of polysilicon, silicon oxide, silicon nitride, silicon carbide, or silicon tetrachloride.

[0013] In the present invention, the reinforcing pad is characterized by having one of silicon, a silicon-based membrane, or a metal deposited and formed on the edge of the silicon-based membrane.

[0014] In the present invention, the reinforcing pad is characterized by being formed by spraying and drying a carbon nanotube solution or a graphene solution on the edge of a silicon-based membrane.

[0015] In the present invention, the reinforcing pad is characterized by being formed by distributing metal powder or nanowires on the edge of a silicon-based membrane and melting the distributed metal powder or nanowires.

[0016] In the present invention, the silicon-based membrane is characterized by having a capping layer further deposited and formed on the front surface.

[0017] In the present invention, the capping layer is characterized by being composed of any one of nano-graphite, carbon nanosheet, carbon nanotube, and B4C (boron carbide). Effects of the invention

[0018] The present invention has the advantage of achieving cost reduction and process simplification when manufacturing a pellicle because a silicon-based membrane is directly deposited on a pellicle frame and a reinforcing pad is formed on the silicon-based membrane deposited on the pellicle frame.

[0019] In addition, the present invention has the advantage of minimizing damage to the silicone membrane caused by surface tension from the washing water when washing the silicone membrane equipped with a reinforcing pad.

[0020] In addition, since the present invention directly attaches a silicone-based membrane equipped with a reinforcing pad to the frame by deposition, there is no need to adhere the membrane to the pellicle frame, which has the advantage of preventing damage to the membrane and ensuring good workability. Brief explanation of the drawing

[0021] FIG. 1 is a side view of a pellicle for protecting an EUV photomask equipped with a reinforcing pad according to the present invention. FIG. 2 is a flowchart of a method for manufacturing a pellicle for protecting an EUV photomask equipped with a reinforcing pad according to the present invention. FIG. 3 is an example of a flowchart illustrating a silicon membrane capping layer deposition step further included according to the present invention. FIG. 4 is an example of a flowchart illustrating the placement of a shadow mask in the reinforcing pad forming step according to the present invention. FIG. 5 is a structural diagram illustrating, step-by-step, a method for manufacturing a pellicle for protecting an EUV photomask equipped with a reinforcing pad according to the present invention. FIG. 6 is a structural diagram illustrating the further deposition of a capping layer on a silicon-based membrane according to the present invention. FIG. 7 is a structural diagram illustrating that a reinforcing pad is formed by placing a shadow mask in the reinforcing pad forming step according to the present invention. FIG. 8 is a cross-sectional view illustrating the relationship between a reinforcing pad, a pellicle frame, and a silicone-based membrane in a pellicle completed according to the method for manufacturing a pellicle according to the present invention. FIG. 9 is a cross-sectional view illustrating the surface tension of water acting on the membrane when the pellicle is lifted after washing in the method for manufacturing a pellicle according to the present invention. Specific details for implementing the invention

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, this description is intended to be detailed enough for a person skilled in the art to easily practice the invention, and does not imply that the technical scope and concept of the present invention are limited thereby.

[0023] FIG. 1 is a drawing showing the configuration of an EUV photomask protective pellicle (1) equipped with a reinforcing pad according to the present invention. As shown in the drawing, the EUV photomask protective pellicle (1) equipped with a reinforcing pad comprises a pellicle frame (20') formed from a silicon substrate, a silicon-based membrane (10) deposited on the upper surface of the pellicle frame (20'), and a reinforcing pad (30) formed on the front edge of the silicon-based membrane (10). Below, we will examine the configuration and manufacturing methods of the EUV photomask protective pellicle (1) equipped with a reinforcing pad.

[0024] First, a pellicle frame (20') is formed by depositing a silicon-based membrane (10) on the front surface of a silicon substrate (20) and removing the back surface of the silicon substrate (20) on which the silicon-based membrane (10) is deposited by etching. The silicon-based membrane (10) deposited on the silicon substrate (20) may be made of polysilicon, silicon oxide, silicon nitride, silicon carbide, or silicon tetrachloride.

[0025] Next, the reinforcing pad (30) can be formed by depositing any one of silicon, a silicon-based membrane, or a metal on the front surface of the silicon-based membrane (10). Additionally, the reinforcing pad (30') can be formed by spraying and drying a carbon nanotube solution or a graphene solution on the edge of the silicon-based membrane. Additionally, the reinforcing pad (30') can be formed by distributing metal powder or nanowires on the edge of the silicon-based membrane and melting the distributed metal powder or nanowires.

[0026] Next, a capping layer (11) may be further deposited and formed on the front surface of the silicon-based membrane (10) as shown in FIG. 5. The capping layer (11) is composed of any one of nano-graphite, carbon nanosheet, carbon nanotube, and B4C (boron carbide).

[0027] A manufacturing method is shown in FIG. 2. The manufacturing method of FIG. 2 is a method for manufacturing an EUV photomask protective pellicle equipped with a reinforcing pad according to the present invention. As shown in the drawing, the method for manufacturing an EUV photomask protective pellicle equipped with a reinforcing pad comprises: (a) a step of depositing a silicon-based membrane of a certain thickness on the front surface of a silicon substrate of a certain size (S1); (b) a step of forming a reinforcing pad on the front edge of the silicon-based membrane (S2); (c) a step of etching masking the edge of the back surface of the silicon substrate so that the edge of the back surface of the silicon substrate is not etched (S3); (d) a step of manufacturing a pellicle composed of a pellicle frame and a silicon-based membrane by removing the etched masked back surface of the silicon substrate by etching (S4); and (e) a step of completing the manufacturing of the pellicle by washing the pellicle and removing the remaining etching solution (S5). Each step will be explained in detail below.

[0028] First, a step (S1) of depositing a silicon-based membrane of a certain thickness on the front surface of a silicon substrate of a certain size is performed. A silicon substrate of a size corresponding to an EUV photomask is prepared. A silicon-based membrane (10) of a certain thickness is deposited on the prepared silicon substrate (20). The deposition of the silicon-based membrane can be formed by a vacuum deposition method, a chemical vapor deposition method, or a sputtering method. In FIGS. 6(a) and FIGS. 7(a), a silicon substrate (20) on which a silicon-based membrane (10) is formed is illustrated. Here, the silicon-based membrane may be made of any one of polysilicon, silicon oxide, silicon nitride, silicon carbide, or silicon tetrachloride. Additionally, the flowchart of FIG. 3 and the structural diagram of FIG. 5 illustrate that a capping layer (11) is further deposited and formed on the front surface of a silicon-based membrane (10). First, a silicon-based membrane (10) is deposited on a silicon substrate (20) (S11'), and a capping layer (11) is further deposited and formed on the front surface of the silicon-based membrane (10) (S12'). The capping layer (11) may be made of any one of nano-graphite, carbon nanosheet, carbon nanotube, and boron carbide (B4C).

[0029] Next, the step (S2) of forming a reinforcing pad on the front edge of the silicone-based membrane is performed. Various embodiments of the method of forming the reinforcing pad (30) on the front edge of the silicone-based membrane (10) are presented depending on whether a shadow mask (40) is installed.

[0030] As illustrated in FIG. 6, the method for forming a reinforcing pad of the first embodiment comprises: (b-1) a step (S21) of spaced-apart a shadow mask (40) of a certain size on the front side of a silicon-based membrane (10) so as to form a reinforcing pad of a certain width on the edge of the silicon-based membrane (10); and (b-2) a step (S22) of depositing and forming a reinforcing pad on the edge of the silicon-based membrane (10) where the shadow mask (40) is spaced-apart. First, the step (S21) is to spaced-apart a shadow mask (40) of a certain size on the front side of the silicon-based membrane (10) so as to form a reinforcing pad of a certain width on the edge of the silicon-based membrane (10). The shadow mask (40) is positioned at a certain distance from the front side of the silicon-based membrane (10) to prevent deposition on the inner side excluding the edges in order to form a reinforcing pad. The shadow mask (40) is positioned on the front side of the silicon-based membrane (10), and the reinforcing pad is deposited using a deposition equipment (100) while the shadow mask (40) is positioned (S22). The deposition method for the reinforcing pad (30) can be vacuum deposition (Evaporation), chemical vapor deposition (CVD), or sputtering. As a vacuum deposition method, resistance thermal evaporation and electron beam evaporation can be used. Additionally, the reinforcing pad can be deposited on the edges excluding the shadow mask (40) using the chemical vapor deposition (CVD) method. In addition, a vacuum deposition method using sputtering can be used. Sputtering is a method of forming a film on a substrate by accelerating a gas such as ionized argon into a plasma at a relatively low vacuum level and causing it to collide with a target and ejecting atoms, and a reinforcing pad (30) can be formed on the edge of a silicon-based membrane (10) through the same process.Deposited materials that form the reinforcing pad include silicon, graphene, metal, etc.

[0031] A method for forming a reinforcing pad of the second embodiment having the same form as FIG. 6 comprises: (b-1) a step (S21') of placing a shadow mask (40) at a certain distance from the front surface of a silicon-based membrane (10) to form a reinforcing pad (30) on the edge of a silicon-based membrane (10); and (b-2) a step (S22') of forming a reinforcing pad (30') by spraying a carbon nanotube solution or a graphene solution onto the edge of a silicon-based membrane (10) using a spraying device (100) while the shadow mask (40) is placed at a certain distance. First, the step (S21') is to place a shadow mask (40) of a certain size at a certain distance from the front surface of the silicon-based membrane (10) so that a reinforcing pad of a certain width can be formed on the edge of the silicon-based membrane (10). Next, a reinforcing pad is formed on the edge of a silicon-based membrane (10) that is spaced apart from a shadow mask (40). The method of forming the reinforcing pad involves spraying a carbon nanotube solution or a graphene solution to form a reinforcing pad on the edge portion excluding the shadow mask (40). When the carbon nanotube or graphene solution is sprayed, heat is applied to dry the edge portion to form the reinforcing pad. A carbon nanotube solution can be prepared by dispersing carbon nanotube powder in an acidic solution, and a graphene solution (graphene oxide) can be prepared by oxidizing graphene by introducing graphene powder into an acidic solution.

[0032] As illustrated in FIG. 7, the method for forming a reinforcing pad of the third embodiment comprises: (b-1) a step of supplying a certain amount of coating material along the edge of a silicone-based membrane (S21"); (b-2) a step of spreading the coating material to a certain width along the edge of the silicone-based membrane (S22"); and (b-3) a step of applying heat to the coating material spread to a certain width to melt it and form a reinforcing film (S23"). First, a certain amount of coating material is supplied along the edge of the silicone-based membrane (10) (S21"). A certain amount of coating material is supplied by a dispenser. Next, a coating material is spread to a certain width on the edge of the silicon-based membrane (10) using a spreading device (S22). Once the coating material is spread to a certain width, the coating material is melted using a melting device (100) to form a reinforcing pad (30) (S23). The coating material may be a metal powder that is not removed by the silicon etching solution. The metal powder consists of nano-sized powder, and can be melted by applying light or a laser to the metal powder.

[0033] As illustrated in FIG. 7, the method of obtaining a reinforcing pad (30) by melting is the same. However, the method of forming the reinforcing pad of the fourth embodiment consists of (b-1) a step of arranging nanowires along the edge of a silicon-based membrane (S21"') and (b-2) a step of forming a reinforcing pad by melting the nanowires arranged at a certain width along the edge of the silicon-based membrane (S22"'). First, to form a reinforcing pad of a certain width along the edge of the silicon-based membrane (10), nanowires are arranged at a certain width along the edge (S21"'). The nanowires can be made of metal or non-metal. Representative examples include metal nanowires such as gold nanowires, silver nanowires, and copper nanowires, and non-metal nanowires such as silicon nanowires and oxide nanowires. Next, the nanowires spread out to a certain width are melted by a melting device (100) to form a reinforcing pad (30) (S22).

[0034] FIGS. 6(c) and FIGS. 7(b) illustrate a cross-sectional view in which the reinforcing pads (30, 30', 30") are formed on the edge of a silicon-based membrane (10) deposited on a silicon substrate (20) after the formation of the reinforcing pads (30, 30', 30") is completed.

[0035] Next, a step (S3) of etching masking is performed on the back edge of the silicon substrate so that the back edge of the silicon substrate is not etched. Once the reinforcing pads (30, 30', 30") are formed, the silicon substrate (20) must be removed by etching so that extreme ultraviolet rays can pass through the membrane. To this end, a step of etching masking is performed so that the edge of the silicon substrate (20) is not removed by etching. Etching masking (50) is a step of forming a certain pattern on the edge using a photomask and ensuring that a part of the edge is not etched.

[0036] Next, step (S4) is performed to manufacture a pellicle (1) composed of a pellicle frame (20') and a silicon-based membrane (10) by removing the back side of the etched-masked silicon substrate (20) by etching. As shown in FIGS. 6(e) and FIGS. 7(d), a pellicle (1) composed of a pellicle frame (20') and a silicon-based membrane (10) is manufactured by removing the etched-masked edge portion from the back side of the silicon substrate by etching. The silicon substrate (20) is mostly removed by etching except for the edge portion, and accordingly, only the silicon-based membrane (10) remains, allowing it to function as a pellicle (1).

[0037] Next, the manufacturing of the pellicle is completed by washing the pellicle and removing the remaining etching solution (S5). Since the silicon substrate (20) is etched with the etching solution, the etching solution may remain on the pellicle frame (20') and the silicon-based membrane (10). Therefore, the step of washing the pellicle (1) is performed to remove the etching solution. The washing of the pellicle (1) can be performed by vertically inserting it into a water tank and lifting it back up. As shown in FIG. 8, during the washing step of the pellicle (1), the silicon substrate is removed except for the edges, and the silicon-based membrane (10) is attached to the pellicle frame (20'). FIG. 8 is a diagram showing the relationship between the reinforcing pad (30, 30', 30") and the inner end of the pellicle frame (20') after the silicon substrate (20) is removed by etching. FIG. 9 is a diagram showing that water droplets (61) in the water tank (60) act as surface tension on the silicon-based membrane (30, 30', 30"). As shown in the drawings, the reinforcing pad (30, 30', 30") is formed by encroaching upon the inner end (21') of the pellicle frame. The reason for this is that during the cleaning step, the surface tension of the water droplets remaining on the inner end (21') side pulls on the nano-sized membrane, causing damage such as breakage, so the reinforcing pad (30, 30', 30") is formed to pass past the inner end (21'). The inclined surface (22') of the pellicle frame (20') is formed by etching with an etching solution, and the etching is generally performed to the extent that it is close to a vertical line, so that the surface area of ​​the inclined surface is widened and a sufficiently large number of water droplets (61) can remain on the inclined surface. The surface tension (f) of the water droplets (61), which are considerably large particles s) can exert a large force on a silicon-based membrane (10) having a thickness in the nano range. Accordingly, the reinforcing pad (30, 30', 30") has the effect of protecting the silicon-based membrane (10) and reducing the defect rate. Also, as shown in FIG. 6, 'L' is a perforated part that acts as a window through which extreme ultraviolet rays passing through the photomask in the EUV equipment pass, 'ℓ1' is the width of the pellicle frame (20'), and 'ℓ2' represents the total length of the reinforcing pad (30, 30', 30"), and 'ℓ' indicates the difference between the width of the reinforcing pad (30, 30', 30") and the width of the pellicle frame. Therefore, 'ℓ' has a range of 0 ≤ 'ℓ', and the maximum size can be determined by the 'L' value related to the size of the photomask.

[0038] As described above, the EUV photomask protective pellicle (1) equipped with a reinforcing pad according to the present invention has the advantage of preventing damage to the vulnerable part because, when the reinforced silicon-based membrane (10) is attached to the pellicle frame (20'), the strength of the silicon-based membrane attached to the inner end of the pellicle frame, which is the vulnerable part, can be reinforced. Accordingly, it has the advantage of minimizing the defect rate during the production of the pellicle. In addition, the silicon-based membrane (20) manufactured by the above method has a thickness of 5 nm to 100 nm and can have an extreme ultraviolet transmittance of 90 to 96% with a wavelength of 13.5 nm.

[0039] Although the embodiments described above are exemplary, it is obvious to those skilled in the art that the present invention may be embodied in various other forms without departing from the spirit and scope thereof. Accordingly, the embodiments described above should be regarded as exemplary rather than restrictive, and all embodiments within the scope of the appended claims and their equivalents shall be deemed to be included within the scope of the present invention. Explanation of the symbols

[0040] 1 : Pellicle 10, 10' : Silicon-based membrane 20: Silicon substrate 20' : Pellicle frame 21' : Inner end of pellicle frame 22' : Inclined surface 30, 30', 30" : Reinforcement pad 40 : Shadow Mask 50 : Etching masking 60 : Aquarium 61 : Water droplet 100 : Equipment (deposition, spraying, melting)

Claims

Claim 1 A pellicle for protecting an EUV photomask equipped with a reinforcing pad, comprising: a pellicle frame formed from a silicon substrate; a silicon-based membrane deposited on the upper surface of the pellicle frame; and a reinforcing pad formed on the front edge of the silicon-based membrane, which encroaches upon the inner end of the silicon-based membrane to withstand the surface tension of water during washing after etching of the silicon substrate; wherein the pellicle frame is characterized in that the silicon-based membrane is deposited on the front surface of the silicon substrate, and the back surface of the silicon substrate on which the silicon-based membrane is deposited is removed by etching to form the frame. Claim 2 delete Claim 3 A pellicle for protecting an EUV photomask equipped with a reinforcing pad, wherein, in claim 1, the silicon-based membrane is composed of any one of polysilicon, silicon oxide, silicon nitride, silicon carbide, or silicon tetrachloride. Claim 4 A pellicle for protecting an EUV photomask equipped with a reinforcing pad according to claim 1, wherein the reinforcing pad is one of silicon, a silicon-based membrane, or a metal deposited and formed on the edge of the silicon-based membrane. Claim 5 A pellicle for protecting an EUV photomask according to claim 1, wherein the reinforcing pad is formed by carbon nanotubes or graphene formed by spraying and drying a carbon nanotube solution or a graphene solution on the edge of the silicon-based membrane. Claim 6 A pellicle for protecting an EUV photomask according to claim 1, wherein the reinforcing pad is characterized by being composed of molten metal powder or nanowires at the edge of the silicon-based membrane. Claim 7 A pellicle for protecting an EUV photomask equipped with a reinforcing pad, wherein, in claim 1, the silicon-based membrane further has a capping layer formed by depositing on its front surface, the capping layer being composed of any one of nano-graphite, carbon nanosheet, carbon nanotube, and B4C (boron carbide).

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