Pellicle, exposure plate with pellicle, exposure method, and semiconductor manufacturing method

Abstract

To provide pellicle frames and pellicles characterized by sufficient ventilation ability, efficient processability of the pellicle frames, and superior adhesion to masks.SOLUTION: The present invention provides a pellicle frame in a frame shape, with an upper end face for placing a pellicle film and a lower end face opposite a photomask. A notch is provided from an outer side to an inner side of the upper end face. The present invention also provides a pellicle including the pellicle frame as a component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pellicle frame and a pellicle that are attached as dust removal devices to a photomask for lithography.

Background Art

[0002] In recent years, the design rules of LSIs have been miniaturized to sub-quarter microns, and accordingly, the short wavelength of the exposure light source has been progressing. That is, the exposure light source has shifted from g-line (436 nm) and i-line (365 nm) using a mercury lamp to KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc., and further, EUV (Extreme Ultra Violet) light with a main wavelength of 13.5 nm is being studied for EUV exposure.

[0003] In the manufacture of semiconductors such as LSIs and super LSIs or the manufacture of liquid crystal display panels, light is irradiated onto a semiconductor wafer or a raw plate for liquid crystal to form a pattern. In this case, if dust adheres to the photomask for lithography and the reticle (hereinafter collectively referred to as the "exposure original plate") used, since this dust absorbs light or bends light, the transferred pattern is deformed, the edge becomes rough, and there is a problem that the base is blackened and contaminated, and dimensions, quality, appearance, etc. are impaired.

[0004] These operations are usually performed in a clean room, but it is still difficult to always keep the exposure original plate clean. Therefore, a method of performing exposure after attaching a pellicle as dust protection on the surface of the exposure original plate is generally adopted. In this case, foreign matter does not directly adhere to the surface of the exposure original plate but adheres to the pellicle. Therefore, if the focus is set on the pattern of the exposure original plate during lithography, the foreign matter on the pellicle becomes irrelevant to the transfer.

[0005] The basic structure of this pellicle consists of a pellicle film with high transmittance to the light used for exposure stretched across the upper end surface of the pellicle frame, and an airtight gasket formed on the lower end surface. The airtight gasket is generally made of an adhesive layer. The pellicle film is made of nitrocellulose, cellulose acetate, fluorine-based polymers, etc., which transmit light used for exposure well (g-line (436 nm), i-line (365 nm) from a mercury lamp, KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc.), but for EUV exposure, ultrathin silicon films and carbon films are being considered as pellicle films.

[0006] Due to the limitations of the exposure equipment, there are several restrictions on pellicle frames used for EUV exposure. Because the space for pellicle placement within the EUV exposure equipment is small, the height of the pellicle must be 2.5 mm or less.

[0007] Furthermore, since EUV exposure is performed under high vacuum, the EUV pellicle needs to withstand the pressure change from atmospheric pressure to vacuum, and the ventilation area of ​​the EUV pellicle is required to be large. Therefore, Patent Documents 2 and 3 propose a pellicle frame with a filter that provides a large ventilation area. Because the pellicle height is low, it is preferable to install the filter parallel to the film when attaching it. However, when the filter is installed on the upper or lower end of the pellicle frame, a curve occurs in the ventilation path. The presence of a curve in the ventilation path can cause significant resistance, especially when returning pressure from high vacuum to atmospheric pressure, leading to a pressure difference between the inside and outside of the pellicle and raising concerns about damage to the pellicle film. While this is not a problem when returning pressure gradually, it has become clear that there are cases where it is necessary to return from high vacuum to atmospheric pressure more quickly from a workability standpoint. Additionally, when cleaning the pellicle frame, it is difficult to thoroughly clean the ventilation path with curves, raising concerns about the remaining foreign matter.

[0008] Patent Document 4 proposes a pellicle in which the mask and pellicle are mechanically fixed via a retaining spring provided on the pellicle and fasteners called studs on the mask. In this pellicle, a gap of 200-300 μm is created between the mask and the pellicle to allow for ventilation, so the ventilation capacity is sufficient. However, when the pellicle is mechanically fixed, metal-to-metal contact inevitably occurs at the connection point. When metal-to-metal contact occurs, there is a concern that it may lead to dust generation.

[0009] The specification of Japanese Patent Application No. 2017-197004, previously filed by the present applicant, proposes a pellicle frame with numerous through-holes on its sides. However, creating a large-area ventilation area using only through-holes requires drilling a very large number of holes, which is difficult and costly, especially when manufacturing the pellicle frame from easily damaged materials. Furthermore, it has been found that if cleaning is insufficient and foreign matter remains in the through-holes, it is difficult to detect the foreign matter because visual inspection cannot be performed inside the through-holes.

[0010] Furthermore, the specification of Japanese Patent Application No. 2017-196982, filed earlier by the present applicant, proposes a pellicle frame with a notch on its lower end surface that serves as both a gripping portion for a peeling jig and a ventilation portion. While this offers sufficient ventilation and workability, it has the drawback of reducing the contact area between the pellicle frame and the mask. Due to the reduced contact area, there is a concern that the pellicle may fall off if used for extended periods. While using a strong adhesive could be considered to prevent the pellicle from falling off, the pellicle needs to be removed from the mask after use or if a problem occurs with the pellicle. If the adhesive is too strong, strong force will be applied to the pellicle when it is peeled off, making it highly likely that the pellicle film will be damaged. Since damage to the pellicle film would contaminate the mask, it is difficult to use a strong adhesive. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2016-200616 [Patent Document 2] Japanese Patent Publication No. 2017-83791 [Patent Document 3] Japanese Patent Publication No. 2016-191902 [Patent Document 4] International Publication No. 2016 / 124536 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention has been made in view of the above circumstances, and aims to provide a pellicle frame and a pellicle using the pellicle frame that can withstand pressure changes from atmospheric pressure to vacuum when EUV exposure is performed under high vacuum, without causing damage to the pellicle film, without the need to install numerous through holes, without making it difficult to detect foreign matter, without damaging the pellicle film even when using a strong adhesive or adhesive, and with a very low possibility of peeling even after long-term use. [Means for solving the problem]

[0013] The inventors have discovered that by providing a frame-shaped pellicle frame having an upper end surface for which a pellicle film is attached and a lower end surface facing a photomask, and by providing a notch from the outer surface to the inner surface of the upper end surface of the pellicle frame, the adhesive area between the pellicle frame and the pellicle film is reduced. However, since it is not necessary to peel the pellicle film from the pellicle frame, a strong adhesive or adhesive can be used. Furthermore, since the load on the adhesive area is only on the pellicle film, the possibility of peeling off even after long-term use is very low, leading to the present invention.

[0014] Accordingly, the present invention provides the following pellicle frame and pellicle. 1. A frame-shaped pellicle frame having an upper end surface on which a pellicle film is provided and a lower end surface facing a photomask, characterized in that at least one notch is provided extending from the outer surface to the inner surface of the upper end surface. 2. The notch portion is formed from the outer surface to the inner surface, and the above-described pellicle frame according to claim 1. 3. The pellicle frame according to claim 1 or 2, having a thickness of less than 2.5 mm and made of titanium. 4. The pellicle frame according to claim 1 or 2, having a thickness of less than 2.5 mm and made of silicon crystal. 5. A pellicle comprising the pellicle frame according to any one of claims 1 to 4 as a component. 6. The pellicle according to claim 5, wherein an adhesive is provided on the upper end surface of the pellicle frame except for the notch portion.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a pellicle frame and a pellicle having sufficient ventilation ability, good pellicle frame processability, and good adhesion to a mask.

Brief Description of the Drawings

[0016] [Figure 1] It is a perspective view showing an example of the pellicle frame of the present invention. [Figure 2] It shows another example of the pellicle frame of the present invention, (A) is a plan view from the upper end surface side, and (B) is a front view seen from the short side outer surface side. [Figure 3] It is a schematic view showing a state where the pellicle of the present invention is attached to a photomask.

Modes for Carrying Out the Invention

[0017] The pellicle frame of the present invention is a frame-shaped pellicle frame having an upper end surface on which a pellicle film is provided and a lower end surface facing a photomask.

[0018] If the pellicle frame is frame-shaped, its shape corresponds to the shape of the photomask to which the pellicle is attached. Generally, it is a rectangular (rectangular or square) frame shape.

[0019] Furthermore, the pellicle frame has a surface for attaching the pellicle film (referred to here as the upper surface) and a surface that faces the photomask when the photomask is attached (referred to here as the lower surface).

[0020] Typically, a pellicle film is attached to the upper end surface of the pellicle frame via an adhesive, and an adhesive for attaching the pellicle to the photomask is attached to the lower end surface; however, this is not always the case.

[0021] There are no restrictions on the material of the pellicle frame, and known materials can be used. For EUV pellicle frames, materials with a low coefficient of thermal expansion are preferred because they may be exposed to high temperatures. Examples include Si, SiO2, SiN, quartz, Invar, titanium, and titanium alloys. Among these, titanium and titanium alloys are preferred due to their ease of processing and light weight.

[0022] While there are no particular limitations on the dimensions of the pellicle frame, the height of the EUV pellicle is limited to 2.5 mm or less, so the thickness of the EUV pellicle frame is smaller than that, less than 2.5 mm.

[0023] Furthermore, the thickness of the pellicle frame for EUV is preferably 1.5 mm or less, taking into account the thickness of the pellicle film, mask adhesive, etc.

[0024] The pellicle frame of the present invention has notches provided on the upper end surface of the pellicle frame, extending from the outer surface to the inner surface. There are no restrictions on the location or number of notches, but the total area of ​​the openings should be 20 mm². 2 It is preferable to have a minimum of 30 mm 2 It is preferable to keep it as above.

[0025] In addition, the sides of the pellicle frame are usually provided with jig holes used for handling and peeling the pellicle from the photomask. The size of the jig holes is 0.5 to 1.0 mm in length in the thickness direction of the pellicle frame (diameter in the case of a circular frame). There are no restrictions on the shape of the holes; they can be circular or rectangular. Also, while jig holes are usually holes that do not penetrate from the outer surface to the inner surface, ventilation holes that penetrate from the outer surface to the inner surface may be provided separately from the jig holes. In the case of ventilation holes, there are no restrictions on their placement or number.

[0026] Furthermore, a filter may be provided in the notch formed from the outer surface to the inner surface of the pellicle frame. In this case, the filter may be provided so as to cover either the inner or outer surface of the pellicle frame.

[0027] In the present invention, a pellicle film is provided on the upper end surface of the pellicle frame as described above, via an adhesive or bonding agent. There are no restrictions on the material of the adhesive or bonding agent; known materials can be used. The adhesive or bonding agent is provided on the upper end surface of the pellicle frame, excluding the notched portion. To strongly hold the pellicle film, an adhesive or bonding agent with strong adhesive strength is preferred.

[0028] There are no particular restrictions on the material of the pellicle film mentioned above, but it is preferable to use a material with high transmittance at the wavelength of the exposure light source and high light resistance. For example, for EUV exposure, an ultrathin silicon film or carbon film is used.

[0029] Furthermore, a mask adhesive is formed on the lower end surface of the pellicle frame for attachment to a photomask. Generally, it is preferable that the mask adhesive be provided around the entire circumference of the pellicle frame.

[0030] As the mask adhesive mentioned above, any known adhesive can be used, and acrylic adhesives or silicone adhesives are preferably used. The adhesive may be processed into any shape as needed.

[0031] A release layer (separator) may be attached to the lower end surface of the mask adhesive to protect the adhesive. The material of the release layer is not particularly limited, but for example, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polypropylene (PP), etc. may be used. In addition, if necessary, a release agent such as a silicone-based release agent or a fluorine-based release agent may be applied to the surface of the release layer.

[0032] Here, Figure 1 shows an example of the pellicle frame 1 of the present invention, where, in each drawing, reference numeral 11 denotes the inner surface of the pellicle frame, reference numeral 12 denotes the outer surface of the pellicle frame, reference numeral 13 denotes the upper end surface of the pellicle frame, and reference numeral 14 denotes the lower end surface of the pellicle frame. In the upper end surface of the pellicle frame 1 in Figure 1, one notch 10, 10 is provided on the upper end surface on the short side, but not on the long side. Normally, a jig hole used to peel the pellicle from the photomask is provided on the long side of the pellicle frame, but this is not specifically shown in Figure 1.

[0033] Figure 2 shows an example in which the upper end surface of the pellicle frame 1 has one notch 10, 10 on each of the short-side upper end surfaces, and one notch 10, 10 on each of the long-side upper end surfaces, for a total of four notches. In Figure 2, the notches are formed to connect from the outer surface to the inner surface. In Figure 2, the symbol W indicates the width of the notch, the symbol D indicates the depth of the notch, and the symbol T indicates the height of the notch.

[0034] Figure 3 shows the pellicle 20, in which the pellicle film 2 is bonded and stretched to the upper end surface of the pellicle frame 1 with adhesive 4. Furthermore, the pellicle 2 is peelably bonded to the photomask 3 with adhesive 5, protecting the patterned surface on the photomask 3. [Examples]

[0035] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0036] [Example 1] Titanium (coefficient of linear expansion: 8.4 × 10⁻⁶) -6 (1 / K), density: 4.5g / cm 3 A pellicle frame (external dimensions 150mm x 118mm x 1.5mm, frame width 4.0mm) was manufactured using [material name].

[0037] Two jig holes, 1 mm in diameter and 1.2 mm deep, were provided on the outer surface of the long side of the pellicle frame, 52 mm away from the center of the side towards the corner. A notch measuring 90 mm wide, 0.1 mm high, and 4 mm deep was provided on the upper end surface of the center of each side of the pellicle frame. This notch extends from the outer surface to the inner surface.

[0038] The pellicle frame was cleaned, and a mixture of 100 parts by mass of silicone adhesive (X-40-3264, manufactured by Shin-Etsu Chemical Co., Ltd.) and 1 part by mass of hardener (PT-56, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and mixed. This mixture was applied to the upper end surface of the pellicle frame to a width of 1 mm and a thickness of 0.1 mm, except for the notched areas. Additionally, a mixture of 100 parts by mass of acrylic adhesive (SK-Dyne 1495, manufactured by Soken Chemical Co., Ltd.) and 0.1 part by mass of hardener (L-45, manufactured by Soken Chemical Co., Ltd.) was added and mixed. This mixture was applied to the entire circumference of the lower end surface of the pellicle frame to a width of 1 mm and a thickness of 0.1 mm.

[0039] Subsequently, the pellicle frame was heated at 90°C for 12 hours to cure the adhesive on the upper and lower ends of the pellicle frame. Next, an ultra-thin silicone film was used as the pellicle film, and this ultra-thin silicone film was pressed onto the adhesive formed on the upper end of the pellicle frame to complete the pellicle.

[0040] This pellicle was attached to a 150mm x 150mm quartz mask to be used as a substitute for a photomask.

[0041] [Example 2] A titanium pellicle frame was manufactured (external dimensions 150mm x 118mm x 1.5mm, frame width 4mm).

[0042] Two jig holes, 1 mm in diameter and 1.2 mm deep, were provided on the outer surface of the long side of the pellicle frame, 52 mm away from the center of the side towards the corner. Two notches, 50 mm wide, 0.1 mm high, and 4 mm deep, were provided on the upper end surface of the long side of the pellicle frame, spaced 15 mm apart. Two notches, 40 mm wide, 0.1 mm high, and 4 mm deep, were provided on the upper end surface of the short side of the pellicle frame, spaced 15 mm apart. These notches extend from the outer surface to the inner surface.

[0043] The pellicle frame was cleaned, and a mixture of 100 parts by mass of silicone adhesive (X-40-3264, manufactured by Shin-Etsu Chemical Co., Ltd.) and 1 part by mass of hardener (PT-56, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and mixed. This mixture was then applied to the upper end surface of the pellicle frame to a width of 1 mm and a thickness of 1 mm, except for the notched areas. The same silicone adhesive was also applied to the lower end surface of the pellicle frame to a width of 1 mm and a thickness of 1 mm around its entire circumference.

[0044] Subsequently, the pellicle frame was heated at 90°C for 12 hours to cure the adhesive on the upper and lower ends of the pellicle frame. Next, an ultra-thin silicone film was used as the pellicle film, and this ultra-thin silicone film was pressed onto the adhesive formed on the upper end of the pellicle frame to complete the pellicle.

[0045] This pellicle was attached to a 150mm x 150mm quartz mask to be used as a substitute for a photomask.

[0046] [Comparative Example 1] A titanium pellicle frame (external dimensions 150mm x 118mm x 1.5mm, frame width 4mm) was fabricated. No notches were provided on each side of the pellicle frame; instead, 20 through-holes with a diameter of 0.8mm were provided on each side to serve as ventilation. Otherwise, the configuration is the same as in Example 1.

[0047] [Comparative Example 2] A titanium pellicle frame (external dimensions 150mm x 118mm x 1.5mm, frame width 4mm) was fabricated. The configuration is the same as in Example 1, except that a notch was provided on the lower end surface in the center of each side of the pellicle frame.

[0048] The pellicles of Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to the following adhesion stability tests, breathability tests, and post-cleaning foreign matter inspections. The evaluation results are shown in Table 1.

[0049] [Patch Stability Test] A pellicle attached to a quartz substrate was placed with the pellicle facing downwards, heated in an oven to 80°C, and left for one week to check for any pellicle fallout. As a result, only in Comparative Example 2 did the pellicle fall out.

[0050] [Air permeability test] The pellicle attached to the quartz substrate is placed in a vacuum chamber, and 1E-4 (1.0 × 10⁻¹⁰) is removed in 1 minute. -4 The pressure was reduced to ) Pa. Then, it was returned to atmospheric pressure over 2 minutes, and the condition of the pellicle membrane was checked. No abnormalities were found in the pellicle membrane in either Example 1, 2 or Comparative Example 1, 2.

[0051] [Foreign object inspection after cleaning] After cleaning the pellicle frame, the surface of the pellicle frame was inspected for foreign matter under fluorescent light and in a dark room using concentrated light. No foreign matter was found in either Example 1, 2 or Comparative Example 1, 2. In Comparative Example 1, since the presence or absence of foreign matter inside the through-holes could not be confirmed by visual inspection, the pellicle frame was cleaned, and then a microscope was used to check for the presence or absence of foreign matter inside the through-holes. Of the 80 through-holes, foreign matter of approximately 100 μm was confirmed in 2 locations. Furthermore, because visual observation was performed using a microscope, a large amount of foreign matter adhered to the surface of the pellicle frame as a result of using the microscope.

[0052] [Table 1]

[0053] From Table 1 above, it can be seen that the pellicles of Examples 1 and 2, by using a pellicle frame with a notch at the upper end, allow for easier foreign object inspection, have better adhesion stability, and have sufficient breathability compared to the pellicles of Comparative Examples 1 and 2. [Explanation of symbols]

[0054] 1 Pellicle Frame 11. Inner side of the pellicle frame 12. Outer surface of the pellicle frame 13. Upper end surface of the pellicle frame 14. Lower end surface of the pellicle frame 10 Notches W: Width of the notch D Depth of the notch Height of the T-shaped notch 20 Pellicles 2. Pellicle membrane 3 Photomasks 4. Pellicle film adhesive 5. Photomask adhesive

Claims

1. Pellicle membrane and A pellicle comprising a rectangular frame-shaped pellicle frame having an upper end surface on the side on which the pellicle membrane is provided and a lower end surface which is the end surface opposite to the upper end surface, Ventilation portions having recesses extending from the outer surface toward the inner surface on the upper end surface are formed on all four sides of the pellicle frame, and recesses are not formed at each corner of the pellicle frame or in its vicinity. The aforementioned ventilation section serves as a ventilation passage that allows air to circulate between the inside and outside of the pellicle. However, the pellicle is characterized in that a filter having substantially the same shape as the recess is placed inside the recess, and the portion of the recess on the upper end surface is flattened.

2. The pellicle according to claim 1, wherein a filter is provided on the inner or outer surface of the pellicle frame so as to cover the recess.

3. The pellicle according to claim 1 or 2, wherein a mask adhesive is formed on the lower end surface.

4. An exposure master plate with a pellicle, characterized by having the pellicle described in any one of claims 1 to 3 attached to the exposure master plate.

5. An exposure method characterized by using an exposure master plate with a pellicle as described in claim 4.

6. A method for manufacturing a semiconductor, characterized by exposure using an exposure master plate with a pellicle as described in claim 4.

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