Phase shift blank mask and photomask with absorbent CrSb film for EUV lithography

Abstract

A mask blank for EUV lithography is equipped with a reflective film formed on a substrate, a cap film formed on the reflective film, and an absorbing film formed on the cap film. The absorber film includes 30 at% to 60 at% of chromium (Cr), 40 at% to 70 at% of antimony (Sb), and 0 (at%) to 20 (at%) of nitrogen (N). Thinning of the absorber film thickness is possible, resulting in a reduction in the 3D effect and an improvement in dose to space (DtS) and normalized image logarithmic slope (NILS).

Description

Technical Field

[0001] The present invention relates to a blank mask and a photomask, and more particularly, to a binary type extreme ultraviolet (EUV) lithography blank mask equipped with an absorption film and a photomask manufactured using the blank mask. Background Art

[0002] A blank mask for EUV lithography is generally composed of two thin films on a substrate: a reflective film that reflects EUV light; and an absorbing film that absorbs EUV light. A photomask is produced by patterning the absorbing film of the blank mask. The absorbing film is patterned into a designed pattern, and therefore, EUV exposure light having a wavelength of 13.5 nm projected onto the photomask is reflected according to the pattern of the absorbing film, thereby exposing the wafer according to the pattern.

[0003] Commercially available blank masks for EUV generally use tantalum (Ta)-based materials for the absorber film. Tantalum (Ta)-based materials have the advantage of excellent cleaning and etching properties. However, the problem with tantalum (Ta)-based materials is that it is difficult to make the film thinner than 50nm to improve the 3D effect by reducing the thickness. In order to overcome this problem, materials with an extinction coefficient (k) higher than tantalum (Ta) may be considered. However, materials with a high extinction coefficient (k) have poor etching and cleaning properties and have not been commercialized to date. Summary of the invention

[0004] The present invention is designed to solve the aforementioned problems and an object of the present invention is to provide a method that allows manufacturing an absorbing film for binary type EUV blank masks having a high extinction coefficient (k), thereby enabling the production of absorbing films with a thickness of less than 50 nm, preferably less than 40 nm.

[0005] The invention provides a blank mask for extreme ultraviolet lithography, which comprises a substrate, a reflective film formed on the substrate, a cover film formed on the reflective film, and an absorption film formed on the cover film, wherein the absorption film comprises chromium (Cr) and antimony (Sb).

[0006] The absorption film may include chromium (Cr) 30 at % to 60 at %, antimony (Sb) 40 at % to 70 at %, and nitrogen (N) 0 (at %) to 20 (at %).

[0007] Preferably, the nitrogen (N) content in the absorber film is at least 1 at %.

[0008] The absorption film may further include one of oxygen (O) or carbon (C).

[0009] The absorption film may include oxygen (O) 0 at % to 10 at % and carbon (C) 0 at % to 10 at %.

[0010] The absorption film has an extinction coefficient (k) of 0.05 to 0.065 with respect to EUV exposure light having a wavelength of 13.5 nm.

[0011] The absorption film has a refractive index (n) of 0.930 to 0.945 with respect to EUV exposure light having a wavelength of 13.5 nm.

[0012] The absorption film has a thickness of 30 nm to 50 nm.

[0013] The absorption film has an absolute reflectivity of 3% or less with respect to EUV exposure light having a wavelength of 13.5 nm.

[0014] The blank mask of the present invention may further include a hard mask film formed on the absorption film, which is etched by a fluorine (F)-based gas.

[0015] The blank mask of the present invention may further include: an etching stopper film formed on the absorption film, which is etched by a fluorine (F)-based gas; and a hard mask film formed on the etching stopper film, which is etched by a chlorine (Cl)-based gas.

[0016] The etch stop film may be formed of a material including one or more of tantalum (Ta), silicon (Si), and platinum (Pt).

[0017] The etching stopper film has a thickness of 2 nm or less.

[0018] The hard mask film may be formed of a material including CrNb or CrSb.

[0019] According to another aspect of the present invention, a photomask for extreme ultraviolet lithography manufactured using a blank mask having a screen structure is provided.

[0020] According to the present invention, by using chromium (Cr) and antimony (Sb) as main materials of the absorption layer, it is possible to form an absorption layer having a high extinction coefficient (k).

[0021] Therefore, the absorption layer can be made thinner, thereby reducing the 3D effect and improving the dose to space (DtS) and normalized image log slope (NILS), thereby achieving excellent performance during wafer printing using a photomask. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 FIG. 4 is a diagram showing a binary extreme ultraviolet (EUV) lithography blank mask according to the present invention. DETAILED DESCRIPTION

[0023] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

[0024] Figure 1FIG. 4 is a diagram showing a binary extreme ultraviolet (EUV) lithography blank mask according to the present invention.

[0025] The binary EUV lithography blank mask according to the present invention includes a substrate 202, a reflective film 204 formed on the substrate 202, a cap film 205 formed on the reflective film 204, an absorption film 208 formed on the cap film 205, a hard mask film 209 formed on the absorption film 208, and a resist film 210 formed on the hard mask film 209. Optionally, an etching stop film may be further provided between the cap film 205 and the absorption film 208 or between the absorption film 208 and the hard mask film 209.

[0026] The substrate 202 is made of a low thermal expansion material (LTEM) substrate having a low thermal expansion coefficient suitable for a reflective blank mask using EUV exposure light.

[0027] The reflective film 204 has a function of reflecting EUV exposure light and has a multi-layer structure in which each layer has a different refractive index. Specifically, the reflective film 204 is formed by alternately stacking 40 to 60 layers of Mo material layers and Si material layers.

[0028] The cap film 205 prevents an oxide film from being formed on the reflective film 204 to maintain reflectivity of the reflective film 204 to EUV exposure light and prevents the reflective film 204 from being etched during patterning of the absorption film 208. The cap film 205 is formed of a material containing ruthenium (Ru) and has a thickness of 2 nm to 5 nm.

[0029] The absorption film 208 absorbs the exposure light to transfer the pattern onto the wafer using contrast, ie, the difference in reflectivity of the exposure light reflected by the reflection film 204 and the absorption film 208. In the present invention, the absorption film 208 is formed of a material containing chromium (Cr) and antimony (Sb).

[0030] For EUV exposure light having a wavelength of 13.5 nm, the extinction coefficient (k) of the absorption film 208 is between 0.050 and 0.065, preferably between 0.055 and 0.065. This allows the thickness of the absorption film 208 to be less than 50 nm, preferably less than 40 nm. The absorption film 208 has a refractive index (n) of 0.930 to 0.945 for EUV exposure light having a wavelength of 13.5 nm.

[0031] As a method of controlling the extinction coefficient (k) of the absorption film 208, the ratio of chromium (Cr) to antimony (Sb) may be adjusted. Preferably, the absorption film 208 has a composition of 30 at% to 60 at% of chromium (Cr), 40 at% to 70 at% of antimony (Sb), and 0 at% to 20 at% of nitrogen (N). If the content of chromium (Cr) is higher than 60 at%, the extinction coefficient (k) decreases, making it difficult to thin the absorption film 208, and if the content of chromium (Cr) is lower than 30 at%, it has a high extinction coefficient (k) but is easily affected by the solution used during cleaning.

[0032] In order to form the absorption film 208 having such a composition, the composition of the target in the sputtering process used to form the absorption film 208 can be controlled. Specifically, a co-sputtering method using targets of chromium (Cr), antimony (Sb), and CrSb can be applied. It is also possible to use a single target of a CrSb alloy, in which case the composition of the CrSb alloy target is Cr:Sb=30 to 40:70 to 60 (at%).

[0033] The extinction coefficient (k) of the absorption film 208 can be controlled by the content of nitrogen (N), oxygen (O) or carbon (C). Specifically, the extinction coefficient (k) decreases as the content of nitrogen (N) or oxygen (O) increases. Therefore, it is necessary to limit the content of nitrogen (N) and oxygen (O) in the absorption film 208, and specifically, the content of nitrogen (N) should be limited to 20at% or less to ensure a high extinction coefficient (k). However, since nitrogen (N) affects the line edge roughness after the patterning process, it is preferred to maintain a minimum content of nitrogen (N), for example, at least 1at%. The content of oxygen (O) is preferably 0at% to 10at%, and the content of carbon (C) is preferably 0at% to 10at%.

[0034] The absorption film 208 may be formed into a single layer structure, or may be formed into a multilayer structure having different composition ratios of constituent materials. The thickness of the absorption film 208 is 30 nm to 50 nm, preferably 35 nm to 45 nm. The absorption film 208 has an absolute reflectivity of 3% or less, preferably 2% or less, for EUV exposure light having a wavelength of 13.5 nm.

[0035] The absorption film 208 of the present invention is etched by a chlorine (Cl2)-based etching gas that does not contain oxygen (O2). Therefore, the cap film 205 under the absorption film 208 does not come into contact with oxygen (O2), thereby preventing damage to the cap film 205 even in the case of over-etching.

[0036] The hard mask film 209 is used as an etching mask during etching of the absorption film 208, and is formed of a material having an etching selectivity relative to the absorption film 208. The hard mask film 209 contains tantalum (Ta) and oxygen (O). When oxygen (O) is further contained, the hard mask film 209 containing tantalum (Ta) is etched by a fluorine (F)-based gas. The hard mask film 209 may also contain boron (B). The content of boron (B) in the hard mask film 209 is 20 at% or less, preferably 15 at% or less. The thickness of the hard mask film 209 is 5 nm or less, preferably 2 nm to 4 nm.

[0037] The resist film 210 is made of a chemically amplified resist (CAR) and has a thickness of 40 nm to 100 nm, preferably 40 nm to 80 nm.

[0038] In the structure described above, the hard mask film 209 is configured to be etched by a fluorine (F)-based gas in order to ensure the etching selectivity of the absorption film 208, thereby causing damage to the resist film 210 during the etching process. Generally speaking, the thickness damage of the resist film 210 during etching that occurs under a chlorine (Cl2)-based gas is smaller than that under a fluorine (F)-based gas. In addition, when a chlorine (Cl2)-based gas is used, a chlorine (Cl2)-based gas that does not contain oxygen (O2) will produce less thickness damage to the resist film 210. At the same time, the thickness of the resist film 210 directly affects the resolution of the photomask. When the resist film 210 is thick, the scattering of electrons during electron beam writing causes a critical dimension (CD) error. In addition, when a highly miniaturized pattern is formed, an aspect ratio problem of the resist film 210 may occur. In order to make the resist film 210 thinner, the hard mask film 209 may be formed of a material etched by a chlorine (Cl2)-based gas, such as a CrNb-based material or a CrSb-based material. However, in such a case, since both the absorption film 208 and the hard mask film 209 are etched by a chlorine (Cl2)-based gas, an etching stopper film etched by a fluorine (F)-based gas may be additionally formed between the absorption film 208 and the hard mask film 209.

[0039] The etching stopper film is formed of a material containing one or more of tantalum (Ta), silicon (Si), platinum (Pt), which is a material etched by a fluorine (F)-based gas. In addition, the etching stopper film further contains one or more of nitrogen (N), oxygen (O), and carbon (C). The thickness of the etching stopper film is 4 nm or less, preferably 2 nm or less. This thin thickness minimizes the problem of different profiles between the lower absorption film 208 and the etching stopper film during pattern formation. The etching stopper film has an etching selectivity of 5 or more relative to the absorption film 208 thereunder, and also has an etching selectivity of 5 or more relative to the hard mask film 208 thereover.

[0040] A process for manufacturing the blank mask of the present invention having the above configuration is as follows.

[0041] First, the reflective film 204 and the cap film 205 are formed on the substrate 204, and then the absorption film 208 is formed.

[0042] The absorption film 208 is formed on the cap film 205 by a sputtering method using a SbCrN material. The sputtering target composition used to form the absorption film 208 uses a ratio of Cr:Sb=40:60 (at%), argon (Ar) is injected at 30 sccm and nitrogen (N) is injected at 2 sccm, and a process power of 1.2 kW is applied. The absorption film 208 exhibits a refractive index (n) of 0.938 and an extinction coefficient (k) of 0.0602 for EUV exposure light having a wavelength of 13.5 nm, and the composition ratio of the absorption film 208 thin film analyzed by RBS shows a ratio of Cr:Sb=0.9:1.0.

[0043] Thereafter, a TaBO hard mask film 209 with a thickness of 4 nm is formed on the absorption film 208, and a resist film 210 is applied to complete the manufacture of a final blank mask.

[0044] In order to manufacture a blank mask according to another embodiment described above, an etching stopper film of a Ta-based material is formed on the absorption film 208, and then a CrNbN hard mask film 209 is formed. In this case, the etching stopper film is formed with a thin thickness of, for example, 2 nm. The etching stopper film may be formed of a material such as TaO, TaCO, TaON, TaCON, TaBO, TaBCO, TaBON, TaBCON, TaSbO, TaSbON, TaSbCO, TaSbCON, a Si-based or Pt-based material, and is etched by a fluorine (F)-based gas. Thereafter, the hard mask film 209 on the etching stopper film is formed with a thickness of 4 nm. Next, the hard mask film 209 is coated with a resist film 210 to complete the manufacture of the final blank mask.

[0045] A process of manufacturing a photomask using the blank mask having the above configuration is as follows.

[0046] First, a pattern of the resist film 210 is formed through an electron beam writing and developing process, and then the hard mask film 209 is etched using the resist film pattern as an etching mask. A fluorine (F)-based etching gas is used for etching the TaBO hard mask film 209.

[0047] After removing the resist film pattern, the absorption film 208 is etched using the pattern of the hard mask film 209 as an etching mask. For etching the absorption film 208, a chlorine (Cl 2 )-based gas excluding oxygen (O 2 ) is used.

[0048] In the present invention, the hard mask film 209 may not be removed, in which case the hard mask film 209 remains in the photomask to absorb the exposure light together with the absorption film 208. The hard mask film 209 may be removed by a separate etching process.

[0049] As in other embodiments described above, when an etching stopper film is provided, the hard mask film 209 is etched by a chlorine (Cl2)-based gas not containing oxygen (O2), and then the etching stopper film is etched by a fluorine (F)-based gas. The hard mask film 209 is etched and removed together in the etching process for patterning the absorption film 208. The etching stopper film may be removed after patterning the absorption film 208, or may be left without being removed to absorb exposure light together with the absorption film 208.

[0050] Although the details of the present invention have been described above with reference to the accompanying drawings through several embodiments of the present invention, the embodiments are only for illustrative and descriptive purposes and are not to be interpreted as limiting the scope of the present invention defined in the appended claims. It should be understood by those skilled in the art that various changes and other equivalent embodiments may be generated from these embodiments. Therefore, the scope of the present invention should be defined by the technical subject matter of the appended claims.

Claims

1. A blank mask for extreme ultraviolet lithography, comprising: Substrate, a reflective film formed on the substrate, a cover film formed on the reflective film, and The absorption film formed on the cap film includes chromium (Cr) and antimony (Sb).

2. The blank mask for extreme ultraviolet lithography according to claim 1, wherein the absorption film comprises chromium (Cr) 30 at % to 60 at %, antimony (Sb) 40 at % to 70 at %, and nitrogen (N) 0 (at %) to 20 (at %). 3 . The blank mask for extreme ultraviolet lithography according to claim 2 , wherein a nitrogen (N) content in the absorption film is at least 1 at %. 4 . The blank mask for EUV lithography according to claim 3 , wherein the absorption film further comprises one of oxygen (O) or carbon (C). 5 . The blank mask for EUV lithography according to claim 4 , wherein the absorption film comprises oxygen (O) 0 at % to 10 at % and carbon (C) 0 at % to 10 at %. 6 . The blank mask for EUV lithography according to claim 1 , wherein the absorption film has an extinction coefficient (k) of 0.05 to 0.065 with respect to EUV exposure light having a wavelength of 13.5 nm. 7 . The blank mask for EUV lithography according to claim 6 , wherein the absorption film has a refractive index (n) of 0.930 to 0.945 with respect to EUV exposure light having a wavelength of 13.5 nm. 8 . The blank mask for EUV lithography according to claim 7 , wherein the absorption film has a thickness of 30 nm to 50 nm. 9 . The blank mask for EUV lithography according to claim 8 , wherein the absorption film has an absolute reflectivity of 3% or less with respect to EUV exposure light having a wavelength of 13.5 nm.

10. The blank mask for EUV lithography according to any one of claims 1 to 9, further comprising a hard mask film formed on the absorption film, which is etched by a fluorine (F)-based gas.

11. The blank mask for extreme ultraviolet lithography according to any one of claims 1 to 9, further comprising: an etching stopper film formed on the absorption film, which is etched by a fluorine (F)-based gas, and The hard mask film formed on the etching stopper film is etched by a chlorine (Cl)-based gas. 12 . The blank mask for EUV lithography according to claim 11 , wherein the etch stop film is formed of a material including one or more of tantalum (Ta), silicon (Si), and platinum (Pt). 13 . The blank mask for EUV lithography according to claim 11 , wherein the etch stop film has a thickness of 2 nm or less. 14 . The blank mask for EUV lithography according to claim 12 , wherein the hard mask film is formed of a material including CrNb or CrSb.

15. A photomask for extreme ultraviolet lithography, which is manufactured using the blank mask according to claim 1.

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