JP2010204424A - Blank for reflective photomask and reflective photomask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blank for a reflective photomask, which is clean against outgas components existing in a mask case made of resin and in clean room environment and can form minute patterns without contaminating inside an exposing device; and to provide the reflective photomask. <P>SOLUTION: The blank for a reflective photomask is clean to outgas components existing in a mask case made of resin and in clean room environment and can form minute patterns without contaminating inside an exposing device by including a protective film coated so that the outgas components may not adhere to the whole surface of the surroundings. The reflective photomask is also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reflective photomask blank and a reflective photomask.

  Lithography technology is used for nano-level microfabrication of circuit patterns such as LSI. In recent years, with higher integration, a technique for producing a finer pattern is required, and the wavelength of an exposure light source is being shortened. For example, the exposure light source has been shifted to a KrF excimer laser (wavelength 248 nm) and an ArF excimer laser (wavelength 193 nm). In addition, developments have been made in which soft X-rays having a shorter wavelength (wavelength: 13.5 nm) are used as an exposure light source.

  Lithography using soft X-rays as an exposure light source is called EUV (Extreme Ultra Violet) lithography. In EUV lithography, since the refractive index of a substance in the wavelength region of the exposure light source is slightly smaller than 1, a conventionally used refractive optical system cannot be used, and pattern transfer can be performed by using a reflective optical system. carry out. Further, since EUV light is absorbed by nitrogen and moisture, and a conventional transmission type photomask cannot be used, a reflection type photomask is used.

  A reflection type photomask uses a blank in which a multilayer reflection layer capable of reflecting EUV light is formed on a substrate having a low coefficient of thermal expansion, and an absorption layer is formed of a material having a high absorption rate for EUV light. Can be obtained by processing into a desired pattern. In many cases, a layer called a buffer layer or a capping layer is provided between the multilayer reflective layer and the absorbing layer in order to prevent a reduction in reflectance due to pattern defect correction or oxidation.

  As described above, EUV lithography has many parts that are remarkably different from the conventional lithography techniques, and immediate support for peripheral techniques is required.

  In an exposure apparatus for EUV lithography, since most substances absorb EUV light, the inside needs to be kept at a high vacuum. For this reason, even a very small amount of outgas components may cause carbon contamination, and is regarded as a problem for contamination of optical mirrors and the like. A high cleanliness is also required for the EUV photomask installed in the exposure apparatus.

  For example, Patent Document 1 proposes a reflective photomask in which only a pattern surface of a photomask is covered with a ruthenium film as a protective layer to prevent surface oxidation and carbon contamination due to EUV light irradiation. However, in actuality, the outgas component attached to the photomask not only during the exposure process but also before the installation in the exposure apparatus, for example, the outgas component generated from the resin mask case used for storing and transporting the photomask. It is also necessary to clean the outgas components present in the clean room atmosphere.

  In addition, the dimensional accuracy required for a photomask for EUV lithography is becoming stricter year by year. According to ITRS (The International Technology for Semiconductors: 2007), the CD mean to target is controlled at 3.6 nm in 2010. The situation has to be. For this reason, it is considered difficult to produce a photomask for EUV lithography by a method of forming a protective layer after forming a pattern portion as described in Patent Document 1, from the viewpoint of dimensional control.

JP 2003-318104 A

  The present invention relates to a blank for a reflective photomask and a reflective photomask capable of forming a fine pattern that is clean with respect to an outgas component present in a resin mask case or a clean room environment and does not contaminate the inside of the exposure apparatus. The purpose is to provide.

  The present invention according to claim 1 includes a substrate, a multilayer reflective film laminated on the substrate, a capping film laminated on the multilayer reflective film, and an absorption film laminated on the capping film. And a protective film coated on the entire periphery of the structure, the protective film comprising: (1) the EUV light reflectance (Rm) of the multilayer reflective film surface coated with a capping film, and a protective film; There is a film thickness of the protective film having an optical density (-log (Ra / Rm)) with a reflectance (Ra) on the formed absorption film exceeding 2.1, and (2) a capping film surface for the defect inspection wavelength light A blank for a reflective photomask, comprising a material having a film thickness of a protective film having a contrast ((Rm−Ra) / (Ra + Rm) × 100%) of 47% or more between the surface and the protective film surface It is.

  The present invention according to claim 2 is the reflective photomask blank according to claim 1, wherein the absorption film is a multilayer film composed of an upper absorption film and a lower absorption film. This is a photomask blank.

  A third aspect of the present invention is the reflective photomask blank according to the first or second aspect, wherein the multilayer reflective film is a multilayer reflective film in which molybdenum and silicon are laminated a plurality of times. The capping film is made of a material containing ruthenium, the absorption film is made of a material containing tantalum, the protective film contains ruthenium, and the thickness of the protective film is in the range of 1.5 nm to 2.5 nm. It is a blank for a reflective photomask characterized by being.

  The present invention described in claim 4 is a reflective photomask manufactured using the reflective photomask blank according to any one of claims 1 to 3.

  According to the present invention, since the entire surface of the structure is covered with the protective film, it is clean with respect to the outgas component present in the resin mask case and the clean room environment, and does not contaminate the inside of the exposure apparatus. A blank for a reflective photomask and a reflective photomask that can be patterned can be provided.

It is a schematic block diagram which shows the blank for reflective photomasks which concerns on embodiment of this invention. It is a graph which shows the comparison of the outgas component amount adhering to the outermost surface of the blank for reflective photomasks concerning embodiment of this invention, and the outermost surface of the conventional photomask blank. It is a graph which shows the relationship of the reflectance (Rm) of EUV light with respect to the film thickness of ruthenium at the time of forming a capping film on a multilayer reflective film. It is a graph which shows the relationship of the reflectance (Ra) of EUV light with respect to the film thickness of ruthenium at the time of forming a protective film on an upper layer absorption film. Ruthenium film with EUV light reflectivity (Rm) when ruthenium is formed as a capping film on the multilayer reflective film and reflectivity (Ra) when ruthenium is formed as a protective film on the upper absorption film It is a graph which shows the optical density with respect to thickness. The graph which calculated | required the reflectance (Ra) of the defect inspection wavelength light at the time of forming ruthenium as a protective film on an upper layer absorption film, and the contrast of a reflective part and an absorption part with respect to the film thickness of ruthenium as a protective film It is. It is a schematic block diagram which shows the reflection type photomask which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments, the same components are denoted by the same reference numerals, and redundant description among the embodiments is omitted.

  As shown in FIG. 1, a reflective photomask blank 10 according to an embodiment of the present invention is formed on a substrate 1, a multilayer reflective film 2 formed on the substrate 1, and a multilayer reflective film 2. A structure 7 having a capping film 3, a lower layer absorption film 4 formed on the capping film 3, and an upper layer absorption film 5 formed on the lower layer absorption film 4, and further, the entire periphery of the structure 7 is covered. And a protective film 6.

  The substrate 1 may be any material as long as the multilayer reflective film 2 can be uniformly formed on the substrate 1 with good adhesion and has a low coefficient of thermal expansion. Examples include low thermal expansion glass to which titanium is added, but the present invention is not limited thereto.

  The multilayer reflective film 2 is composed of molybdenum 2.8 nm and silicon 4.2 nm, and is laminated at 30 to 50 periods so as to have the maximum reflectance with respect to EUV light having a wavelength of 13 to 14 nm.

  The main role of the capping film 3 is to prevent a decrease in reflectance due to oxidation of the surface of the multilayer reflective film 2, and it becomes the outermost surface of the part that reflects EUV light when processed into the reflective photomask 20. Therefore, the capping film 3 needs to use a material that has a small extinction coefficient with respect to EUV light, has a large difference between the refractive index of the capping film 3 and the refractive index of vacuum, and is difficult to oxidize. In addition, it is required to have a property that the outgas component hardly adheres.

  Ruthenium can be selected as the material of the capping film 3 for the following reasons. Ruthenium is a material known as a measure for suppressing oxidation of optical mirrors (Proc. SPIE Vol. 5751, pp 118-125 (2005)). Furthermore, ruthenium was also confirmed to be a material to which outgas components are difficult to adhere by the following investigation. A sample with a ruthenium film and a sample with an upper absorption film 5 (in this case, a tantalum-based oxide film) are stored for 20 hours in an acrylic resin mask case that easily releases outgas components. TD-GC / MS "was used to investigate the amount of outgas components on the sample surface. From the results shown in FIG. 2, the ruthenium film had an outgas component amount of 1/10 or less than the tantalum oxide film.

  The film thickness of the capping film 3 needs to be designed so that the reflectance of EUV light does not decrease as much as possible. FIG. 3 shows a result obtained by calculating the reflectance (Rm) of EUV light with respect to the film thickness of ruthenium formed on the multilayer reflective film 2. From the result of FIG. 3, the film thickness of ruthenium as the capping film 3 is set to about 1 nm to 2.5 nm which hardly affects the reflectance of EUV light.

  The lower absorption film 4 absorbs EUV light irradiated when dry etching is performed to form a predetermined exposure transfer pattern, and is selected from heavy metals having high absorbability with respect to EUV light. As such a heavy metal, an alloy containing tantalum as a main component is preferably used. The film thickness of the lower absorption film 4 is determined by adjusting the entire film constituting the reflective photomask blank 10 in consideration of optical characteristics with respect to EUV light and DUV (Deep Ultra Violet) light used for defect inspection. 30 nm to 80 nm.

  A buffer layer made of a material resistant to the etching of the lower absorption film 4 and the upper absorption film 5 may be formed as an etching stopper between the capping film 3 and the lower absorption film 4.

  The upper absorption film 5 is a material that is antireflective with respect to DUV light used for defect inspection, and may be any material that can be processed by etching. Examples include materials containing tantalum as a main component and oxygen, but the present invention is not limited thereto. The film thickness of the upper absorption film 5 is determined by adjusting the entire film constituting the reflective photomask blank 10 in order to consider optical characteristics with respect to EUV light and DUV light used for defect inspection, but is about 10 nm to 30 nm. If it is.

The protective film 6 is formed so as to cover the entire surface around the structure 7. The protective film 6 is less likely to adhere outgas than the upper absorption film 5 and is made of a material that satisfies the following two conditions.
Condition 1: The optical density (= −log (Ra / Rm) between the EUV light reflectance (Rm) of the multilayer reflective film surface coated with the capping film and the reflectance (Ra) on the upper absorption film on which the protective film is formed. ) Must be greater than 2.1.
Condition 2: The contrast (= (Rm−Ra) / (Ra + Rm) × 100%) between the reflection part (capping film surface) and the absorption part (protective film surface) with respect to the defect inspection wavelength light (wavelength 257 nm) is 47% or more. There must be a protective film thickness.
Examples include ruthenium, chromium, platinum and the like.

  The case where ruthenium that can also be used as the material of the capping film 3 is used as the protective film 6 will be described in detail. The graph shown in FIG. 4 shows a multilayer reflection film 2 in which molybdenum and silicon are laminated in 40 cycles, a film thickness of 2.5 nm of a capping film 3 made of ruthenium, and a lower layer absorption made of an alloy mainly composed of tantalum. A ruthenium film as a protective film 6 covering the entire surface of the structure 7 having a film thickness 51.5 nm and a film thickness 15 nm of the upper absorption film 5 made of a material containing tantalum as a main component and containing oxygen. It is the result of calculating the EUV reflectance (Ra) with respect to thickness.

  The optical density (hereinafter referred to as “OD”) (= −log (Ra / Rm)) was calculated using Rm and Ra obtained in FIGS. 3 and 4 and shown in FIG. The required value (SEMI standard P38-1102) of the reflectance (Ra) on the upper absorption film for EUV light is 0.5% or less. The required value of EUV light reflectance (Rm) of the multilayer reflective film surface coated with the capping film (ITRS 2007: required value in 2010) is 66%. When calculated using these values, OD (= −log (Ra / Rm)) should be 2.1 or more.

  Next, the reflectance (Ra) of the defect inspection wavelength light when ruthenium as the protective film 6 is formed on the upper absorption film 5 in the light of wavelength 257 nm, which is a candidate for the defect inspection wavelength, the reflection portion 8 and the absorption portion The contrast with 9 (= (Rm−Ra) / (Ra + Rm) × 100%) was calculated with respect to the thickness of the protective film 6 of ruthenium and is shown in FIG. The required value (SEMI standard P38-1102) of the reflectance (Ra) on the upper absorption film with respect to the inspection wavelength (257 nm) is 20% or less. The required value (SEMI standard P38-1102) of reflectivity (Rm) for the inspection wavelength (257 nm) of the multilayer reflective film surface coated with the capping film is 55%. When calculated using these values, the contrast (= (Rm−Ra) / (Ra + Rm) × 100%) may be 47% or more.

  5 and 6, the protective film 6 using ruthenium satisfying the condition that the OD is 2.1 or more and the contrast is 47% or more may be about 1.5 nm to 2.5 nm. However, this numerical value is a multilayer reflective film 2 in which molybdenum and silicon are laminated in 40 cycles, a film thickness of 2.5 nm of a capping film 3 made of ruthenium, and a lower absorption film made of an alloy containing tantalum as a main component. 4 can be applied to the structure 7 having a film thickness 51.5 nm and a film thickness 15 nm of the upper absorption film 5 made of a material containing tantalum as a main component and containing oxygen.

  A structure 6 having a multilayer reflective film 2, a capping film 3, a lower layer absorption film 4, and an upper layer absorption film 5 formed on the substrate 1 constituting the reflective photomask blank 10, and a protective film 6 covering the whole, A sputtering method, a chemical vapor deposition method, a vacuum vapor deposition method, or the like can be used. Since the kinetic energy of the target atom is large, it is preferable to use a sputtering method that can form a strong and difficult-to-peel film.

  Next, a method for manufacturing the reflective photomask 20 of the present invention will be described.

  The reflective photomask 20 is produced by forming a desired pattern using the reflective photomask blank 10.

  First, a resist is applied to the pattern forming surface side of the reflective photomask blank 10, and a desired resist pattern is formed by performing drawing and developing processes using an electron beam drawing apparatus.

  Next, using the resist pattern as a mask, the protective film 6, the upper absorption film 5, and the lower absorption film 4 are processed by dry etching. Thereafter, a resist stripping process and a particle removing process are performed to complete a reflective photomask 20 as shown in FIG.

  An example of the reflective photomask blank 10 and the reflective photomask 20 of the present invention is shown below. However, the present invention is not limited to the examples.

<Example 1>
First, a 6-inch square low thermal expansion glass was prepared as a base substrate 1, and a multilayer reflective film 2 having a thickness of 280 nm was formed thereon by laminating molybdenum 2.8 nm and silicon 4.2 nm in 40 cycles. .

  Next, a capping film 3 made of ruthenium is formed with a film thickness of 2 nm on the multilayer reflective film 2, and then a lower layer absorption film 4 made of an alloy containing tantalum as a main component is formed with a film thickness of 51.5 nm. An upper absorption film 5 made of a material containing tantalum as a main component and containing oxygen was formed to a thickness of 15 nm, whereby a structure 7 was obtained. A sputtering method was used to form each film.

  Next, a protective film 6 made of ruthenium was formed to a thickness of 2.0 nm so as to cover the entire periphery of the structure 7, thereby obtaining a reflective photomask blank 10.

  Next, a resist was applied onto the reflective photomask blank 10 and a resist pattern was formed by electron beam drawing. Using the obtained resist pattern as a mask, dry etching of the protective film 6, the upper absorption film 5, and the lower absorption film 4 was performed using chlorine gas and fluorine gas.

  Next, a resist stripping process using an NMP-based solvent and sulfuric acid / hydrogen peroxide followed by a particle removal process using ammonia / hydrogen peroxide was performed to obtain a reflective photomask 20.

<Example 2>
A reflective photomask blank 10 was obtained without coating the protective film 6 on the entire surface of the structure 7. The method for forming the reflective photomask 20 is the same as in the first embodiment.

<Evaluation>
Example 1 and Example 2 were evaluated using “TD-GC / MS” for the amount of outgas component adhering to the surface after storing in an acrylic resin mask case for 20 hours.

  When the reflective photomask 20 obtained in Example 1 was evaluated, it was 2.4 ng / cm 2 in terms of hexadecane (C16).

  On the other hand, when the evaluation was performed using the reflective photomask 20 of Example 2, it was 30.2 ng / cm 2 in terms of hexadecane (C16).

  From the above, it has been confirmed that the reflective photomask 20 of the present invention has a protective film coated on the entire surrounding surface, so that the outgas component hardly adheres.

  The reflective photomask 20 of the present invention can have high cleanliness because the outgas component is less likely to adhere by covering the protective film 6 with ruthenium all around the structure 7. Therefore, a fine pattern required for the reflective photomask 20 for EUV lithography can be formed, which leads to an improvement in product yield.

  The present invention is expected to be used in a wide range of fields in which fine processing using extreme ultraviolet light in the soft X-ray region, that is, EUV (Extreme Ultra Violet) light is required. In particular, it is expected to be used as a reflective photomask blank and a reflective photomask used in the transfer of ultrafine circuit patterns required in the manufacturing process of semiconductor integrated circuits and the like.

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Multilayer reflective film 3 ... Capping film 4 ... Lower layer absorption film 5 ... Upper layer absorption film 6 ... Protective film 7 ... Structure 8 ... Reflection part 9 ... Absorption part 10 ... Reflective photomask blank 20 ... Reflective photomask

Claims (4)

A substrate,
A multilayer reflective film laminated on the substrate;
A capping film laminated on the multilayer reflective film;
A structure having an absorption film laminated on the capping film;
A protective film coated on the entire surrounding surface of the structure,
The protective film is
(1) The optical density (−log (Ra / Rm)) between the EUV light reflectance (Rm) of the multilayer reflective film surface coated with the capping film and the reflectance (Ra) on the absorption film on which the protective film is formed is There is a protective film thickness exceeding 2.1,
(2) It is made of a material having a film thickness of a protective film in which the contrast ((Rm−Ra) / (Ra + Rm) × 100%) between the capping film surface and the protective film surface with respect to the defect inspection wavelength light is 47% or more. A blank for a reflective photomask characterized by the above. The reflective photomask blank according to claim 1,
A reflective photomask blank, wherein the absorption film is a multilayer film comprising an upper absorption film and a lower absorption film. A blank for a reflective photomask according to claim 1 or 2,
The multilayer reflective film is a multilayer reflective film in which molybdenum and silicon are laminated several times.
The capping film is made of a material containing ruthenium,
The absorption film is made of a material containing tantalum,
The protective film contains ruthenium,
A reflective photomask blank, wherein the protective film has a thickness in a range of 1.5 nm to 2.5 nm.   A reflective photomask produced using the reflective photomask blank according to claim 1.

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