JP2009116284A - Pellicle and method for manufacturing pellicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pellicle having a practical pellicle film for EUV, excellent in high transmissivity and chemical stability. <P>SOLUTION: The pellicle film 10 includes a silicon crystal film, the absorption coefficient of which is 0.005/nm or lower with respect to light having a wavelength of 13.5 nm, as a pellicle film 11. The silicon crystal film is an indirect transition type semiconductor film and therefore, the optical absorption coefficient thereof is relatively low. In particular, a single crystal silicon film has a lower absorption coefficient than an amorphous silicon film and a polysilicon film. Thus, it is easy to obtain desired transmissivity required of a pellicle film for EUV (Extreme Ultra Violet). Such a pellicle film as described above can be fabricated from an SOI (silicon-on-insulator) film obtained by thin-filming an SOI substrate (including a SOQ (silicon-on-quartz) substrate and an SOG (silicon-on-glass) substrate). When a pellicle film of a silicon crystal film is formed from the SOI substrate, formation of the pellicle film is completed under the temperatrue condition of around room temperature without addition of an excess stress during the formation of the pellicle film, and thereby, no distortion being induced in the film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pellicle for lithography, and more particularly to a pellicle suitable for lithography using extreme ultraviolet light (EUV: Extreme Ultra Violet) and a method for manufacturing the pellicle.

  As semiconductor devices are highly integrated, patterns formed by lithography have become finer, and devices having a pattern width of about 45 nm are now being put into practical use. Such a fine line pattern can be realized by lithography using a technique such as an ArF immersion method or a double exposure method, which is an improved technique of the conventional excimer exposure technique.

  However, in lithography based on such excimer exposure technology, it is difficult to cope with patterning that requires further miniaturization such as a pattern width of 32 nm or less, and extreme ultraviolet light (as a new exposure technology) Lithography using EUV (Extreme Ultra Violet) attracts attention.

  Development of new resists and pellicles as well as light sources is indispensable for the practical application of exposure technology using EUV light with a primary wavelength of 13.5 nm. While considerable progress has already been made, there are many unsolved technical issues that must be solved in order to realize a pellicle for EUV.

  The pellicle film provided on the EUV pellicle is required to have high transmittance and chemical stability with respect to EUV light as well as a dustproof function to prevent foreign matter from adhering to the photomask. The current situation is that there is no prospect of solving the problem of developing a material for a practical pellicle film having excellent stability.

  At present, no material is known that is transparent to light in the wavelength band having a main wavelength of 13.5 nm. However, since silicon has a relatively high transmittance for light in this wavelength band, it is used for EUV. Silicon has been attracting attention as a pellicle film material (for example, Shroff et al. “EUV pellicle Development for Mask Defect Control,” Emerging Lithographic Technologies X, Proc of SPIE Vol. 6151 615104-1 (2006): (non-patent Document 1), US Pat. No. 6,623,893 (patent document 1)).

  However, since silicon used as a pellicle film in Non-Patent Document 1 is a film deposited by a method such as sputtering, it is inevitably amorphous and has a high absorption coefficient in the EUV region, resulting in a high transmittance. Inevitably lower.

  The pellicle film disclosed in Patent Document 1 is also made of silicon, but it is assumed that this silicon film is deposited by a method such as CVD. In this case, the silicon film is amorphous. Or, since it becomes a polycrystalline film, the absorption coefficient in the EUV region must be increased.

In addition, as in the pellicle film disclosed in Patent Document 1 and Non-Patent Document 1, a strong stress is easily introduced into a silicon crystal formed by a sputtering method or a CVD method, and the optical film characteristics are caused by the stress. There is also a problem that it tends to deteriorate or become non-uniform.
U.S. Patent 6,623,893 Shroff et al. “EUV pellicle Development for Mask Defect Control,” Emerging Lithographic Technologies X, Proc of SPIE Vol.6151 615104-1 (2006). Edward D. Palik, ed., “Handbook of Optical Constants of Solids,” Academic Press, Orlando (1985). Edited by Koda Yamada "Cluster Ion Beam Fundamentals and Applications" Chapter 4 (Nikkan Kogyo)

  The present invention has been made in view of such problems, and an object of the present invention is to provide a pellicle having a practical EUV pellicle film excellent in high permeability and chemical stability. It is in.

  In order to solve such a problem, the pellicle of the present invention includes a silicon crystal film having a absorption coefficient of 0.005 / nm or less for light having a wavelength of 13.5 nm as a pellicle film.

  Preferably, the silicon crystal film is a single crystal silicon film, and the single crystal silicon film is obtained by thinning an SOI substrate. Note that the crystal plane orientation of the single crystal silicon film is preferably a (100) plane.

  The pellicle of the present invention may be provided with a protective film on at least one main surface of the silicon crystal film. In this case, the absorption coefficient of the protective film with respect to light having a wavelength of 13.5 nm is preferably 0.05 / nm or less.

The protective film is made of, for example, at least one material selected from the group consisting of SiC, SiO ₂ , Si ₃ N ₄ , SiON, Y ₂ O ₃ , YN, Mo, Ru, and Rh.

  A manufacturing method for realizing such a pellicle includes a step of providing a pellicle film holding portion on an SOI substrate having a silicon crystal film formed on one main surface, and removing a support substrate from the other main surface side of the SOI substrate. The silicon crystal film as a pellicle film, and the silicon crystal film has an absorption coefficient of 0.005 / nm or less for light having a wavelength of 13.5 nm.

  This manufacturing method may further include a step of forming a protective film on at least one surface of the silicon crystal film.

In this case, the protective film is formed by, for example, a film made of at least one material selected from the group consisting of SiC, SiO ₂ , Si ₃ N ₄ , SiON, Y ₂ O ₃ , YN, Mo, Ru, and Rh. It is performed by coating.

  As a method for coating the protective film, a gas cluster ion beam deposition method is preferable.

  In the present invention, a silicon crystal film having an absorption coefficient for light having a wavelength of 13.5 nm of 0.005 / nm or less is used as the pellicle film, so that it is practical and excellent in high permeability and chemical stability. A pellicle provided with a pellicle film for EUV can be provided.

  The structure of the pellicle of the present invention will be described below with reference to the drawings.

  1A and 1B are schematic cross-sectional views for explaining a structural example of a pellicle according to the present invention. This pellicle 10 has an absorption coefficient of 0.005 / nm or less for light having a wavelength of 13.5 nm. The pellicle film 11 is provided as a silicon crystal film, and the pellicle film 11 is bonded to the end surface of the pellicle frame 12.

  Since the silicon crystal film used as the pellicle film 11 is an indirect transition type semiconductor film, the light absorption coefficient is relatively low, and an amorphous silicon film or a polycrystalline silicon film can be used as long as it has the above absorption coefficient. Although it may be, it is preferably a single crystal silicon film. The reason is that an amorphous silicon film or a polycrystalline silicon film tends to have a high absorption coefficient for EUV light depending on its growth method and the like, and an extremely thin film for obtaining a desired transmittance as a pellicle film for EUV It is easy to occur.

  Amorphous silicon is widely used as a material for thin film solar cells because its absorption coefficient for visible light is about one digit larger than that of single crystal silicon, but the absorption coefficient for light in the EUV region is also low. Relatively high.

  FIG. 2 is an example in which absorption coefficients of single crystal silicon and amorphous silicon with respect to light having a wavelength near 13.5 nm are compared (Non-patent Document 2: Edward D. Palik, ed., “Handbook of Optical Constants of”. Solids, ”Academic Press, Orlando (1985)). Although it is expected that the optical properties of amorphous silicon may vary depending on the growth method, single crystal silicon has a lower absorption coefficient than amorphous silicon even in the EUV region as illustrated in this figure. Therefore, it is a preferable material for a pellicle film for EUV.

The reason why the absorption coefficient of the silicon crystal film as the pellicle film is limited is that the transmittance of EUV light is 50% or more even for a pellicle film having a thickness of about 150 nm. When the absorption coefficient of the pellicle film is α (nm ⁻¹ ) and the film thickness is x (nm), the intensity I of the light transmitted through the pellicle film is given by the following equation, where the intensity of the incident light is I ₀ .

  Therefore, the thickness x of the pellicle film necessary for setting the EUV light transmittance to 50% or more is approximately 0.693 / α, and if the absorption coefficient α is 0.005 / nm or less, the pellicle having a thickness of 140 nm is used. Even with a film, EUV transmittance of 50% can be secured.

  Such a pellicle film can be manufactured from an SOI film obtained by thinning an SOI substrate (“SOI substrate” is used as a term including an SOQ substrate and an SOG substrate in a broad sense) by a method described later, for example. In this case, if the crystal plane orientation of the single crystal silicon film is the (100) plane, there is an advantage that the workability is excellent.

In the pellicle 10 of the present invention, a protective film (13a, 13b) may be provided on at least one main surface of the silicon crystal film that is the pellicle film 11 to cover the silicon crystal surface (FIG. 1B). . Such a protective film plays a role of preventing the surface of the silicon crystal film from being oxidized by light from a high-power light source. For example, SiC, SiO ₂ , Si ₃ N ₄ , SiON, Y ₂ O ₃ And a ceramic film such as YN, a metal film such as Mo, Ru, and Rh, etc., and a film made of a material obtained by a combination thereof, or a film in a form in which a plurality of films are laminated It is also possible to do.

  There is no particular restriction on the method of forming the protective film, and film formation by a known CVD method, sputtering method, electron beam evaporation method, etc. is possible, but the theoretical density can be achieved by gas cluster ion beam (GCIB) evaporation method. Close dense high-density protective film can be formed, and high oxidation resistance can be expected even with a thin film (Non-Patent Document 3: Koda Yamada, “Cluster ion beam fundamentals and applications”, Chapter 4 Nikkan Kogyo). Therefore, the GCIB vapor deposition method is suitable as a method for forming a protective film that does not significantly reduce the transmittance as a pellicle.

  Since it is easy to form a protective film relatively thinly, its absorption coefficient does not have to be as low as that of a pellicle film, but the absorption coefficient for light having a wavelength of 13.5 nm is set to 0.05 / nm or less. It is preferable. When a protective film is provided, the thickness and the like of both are designed so that the transmittance of the EUV light transmitted through the protective film and the pellicle film is 50% or more.

  Silicon crystal can also be selected as the material of the pellicle frame 12. Silicon crystals (especially single crystals) have high purity and mechanical strength, and also have the advantage that dust generation when a pellicle frame is formed can be suppressed.

  In addition, when the permeable membrane (pellicle membrane and protective film) is soiled or cracked, it is necessary to replace the permeable membrane. For this reason, it is preferable that the permeable membrane can be easily attached and detached. Therefore, the adhesion between the pellicle frame and the pellicle film is not based on a fixing method using a general adhesive or solder, but a mechanical adhesive such as a removable adhesive, magnet, electrostatic chuck, or hook. It is preferable that the fixing method be used. Such a mechanical fixing member is preferably not easily deteriorated by irradiation with EUV light, or is preferably provided so as to be shielded from EUV light.

  The operation of attaching the pellicle to the photomask is usually performed under normal pressure, but EUV exposure is performed under vacuum. For this reason, it is desirable to provide a pressure adjustment mechanism in the pellicle frame. Such a pressure adjusting mechanism needs to have a structure that prevents foreign matters from entering when the gas flows in and out. Therefore, it is preferable to provide a filter capable of capturing even extremely fine foreign matter such as ULPA in the pressure adjusting mechanism. It is important that such a filter has an area such that the permeable membrane does not greatly expand or contract or break due to a non-uniform pressure difference.

  FIG. 3 is a diagram for explaining a process example of the pellicle manufacturing method of the present invention. A support substrate 1 of an SOI (Silicon On Insulator) substrate illustrated in FIG. 3A is a substrate having a surface on which an oxide film 1b is provided on a silicon substrate 1a, and an SOQ (Silicon On Quartz) substrate and an SOG (SOG) substrate. The support substrates 1 of the (Silicon On Glass) substrate are a quartz substrate and a glass substrate, respectively. A single crystal silicon crystal film 2 is provided on the main surface of the support substrate 1, and this silicon crystal film 2 becomes a pellicle film.

  The silicon substrate 1a serving as a support substrate for the SOI substrate is a commercially available single crystal silicon substrate grown by, for example, the CZ method (Czochralski method), and the surface of the single crystal silicon substrate 1a is subjected to thermal oxidation or the like. An oxide film 1b is previously formed to a thickness of about 100 nm by a method, and a single crystal silicon crystal film 2 as an SOI layer is formed thereon.

Each of the silicon crystal films 2 provided on these support substrates is a silicon single crystal (Nearly Perfect Crystal: NPC) thin film with few crystal defects such as COP, and the absorption coefficient of EUV light is approximately 0.0015 nm ^−1. The film has a thickness of about 70 nm.

  These SOI substrate, SOQ substrate, and SOG substrate are rectangular substrates having a short side of 122 mm and a long side of 149 mm, and a pellicle frame 12 made of silicon crystal is bonded to the silicon crystal film 2 on the surface side of the rectangular substrate ( FIG. 3 (B)). Then, polishing and etching are performed from the back side of the support substrate 1 (FIG. 3C) to obtain the silicon crystal film 2 held on the pellicle frame 12 (FIG. 3D). The pellicle frame 12 has a height of 7 mm and a thickness of 2 mm. A plurality of openings for mounting the ULPA filter are provided on the side surface, and a groove having a width of 1 mm and a depth of 2 mm is provided on the outermost periphery of the back surface. Is formed.

  In the case of an SOI substrate, first, the silicon substrate 1a as a supporting substrate is thinned to about 100 μm, and then the remaining silicon portion is etched away with a KOH etchant to expose the oxide film 1b, and then the oxide film 1b is formed with HF. To remove only the silicon crystal film 2.

In the case of the SOQ substrate and the SOG substrate, the supporting substrate 1 can be polished from the back surface to be thinned to about 100 μm, and then the remaining SiO ₂ portion can be removed by HF to make only the silicon crystal film 2.

  Finally, a ULPA filter is attached to the pellicle frame 12 that is integrated with the silicon crystal film 2, and a silicone adhesive for shielding exposure light is injected into the groove provided on the outermost periphery of the back surface of the pellicle frame 12. Thus, a pellicle 10 was obtained.

  When a silicon crystal pellicle film is formed using an SOI substrate, an SOQ substrate, or an SOG substrate as in the present invention, extreme stress is applied in the process of removing the support substrate to form a silicon crystal film alone. In addition, since the formation of the pellicle film is completed at a temperature of about room temperature, no distortion is introduced.

  A protective film as shown in FIG. 1 may be formed on the front and back surfaces of the silicon crystal film 11 supported by the pellicle frame 12 obtained as shown in FIG. Prior to the thinning, a protective film may be formed on the silicon crystal film 2 in advance.

  A silicon crystal film 11 supported on the pellicle frame 12 was obtained according to the process shown in FIG. Note that the thickness of the silicon crystal film 11 of this example is 20 nm. Then, an SiC thin film having a thickness of several nanometers was deposited on each of the front and back surfaces of the silicon crystal film 11 by gas cluster ion beam deposition to cover the silicon crystal film.

  Each of the pecrils obtained in Example 1 and Example 2 has an EUV light transmittance of 50% or more, and the throughput during EUV exposure is at a practical level, and a decrease in device yield due to foreign matter is completely observed. Not confirmed.

  According to the present invention, a pellicle provided with a practical EUV pellicle film excellent in high permeability and chemical stability is provided.

It is the cross-sectional schematic for demonstrating the structural example of the pellicle of this invention. This is an example in which absorption coefficients of single crystal silicon and amorphous silicon with respect to light having a wavelength near 13.5 nm are compared. It is a figure for demonstrating the process example of the pellicle manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Silicon crystal film 10 Pellicle 11 Pellicle film 12 Pellicle frame 13 Protective film

Claims (11)

A pellicle comprising a silicon crystal film having an absorption coefficient of 0.005 / nm or less for light having a wavelength of 13.5 nm as a pellicle film. The pellicle according to claim 1, wherein the silicon crystal film is a single crystal silicon film. The pellicle according to claim 2, wherein the single crystal silicon film is obtained by thinning an SOI substrate. The pellicle according to claim 2 or 3, wherein a crystal plane orientation of the single crystal silicon film is a (100) plane. The pellicle according to any one of claims 1 to 4, further comprising a protective film on at least one main surface of the silicon crystal film. 6. The pellicle according to claim 5, wherein the protective film has an absorption coefficient of 0.05 / nm or less for light having a wavelength of 13.5 nm. The protective _{layer, SiC, SiO 2, Si 3} N 4, SiON, Y 2 O 3, YN, Mo, Ru, and is made of at least one material of the group consisting of Rh claim 5 or 6 The pellicle according to 1. A step of providing a pellicle film holding portion on an SOI substrate having a silicon crystal film formed on one main surface; and a step of removing the support substrate from the other main surface side of the SOI substrate to make the silicon crystal film a pellicle film. And the silicon crystal film has an absorption coefficient for light having a wavelength of 13.5 nm of 0.005 / nm or less. The method for manufacturing a pellicle according to claim 8, further comprising a step of forming a protective film on at least one surface of the silicon crystal film. The protective film is formed by coating a film made of at least one material selected from the group consisting of SiC, SiO ₂ , Si ₃ N ₄ , SiON, Y ₂ O ₃ , YN, Mo, Ru, and Rh. The manufacturing method of the pellicle of Claim 9 performed. The method for producing a pellicle according to claim 10, wherein the coating method of the protective film is a gas cluster ion beam deposition method.

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