Blank masks and photomasks for extreme ultraviolet lithography with CrSb absorbing films

Abstract

To provide a method that allows the fabrication of an absorption film for a binary-type EUV blankmask with a high extinction coefficient (k), enabling the production of an absorption film with a thickness of 50 nm or less, preferably 40 nm or less.SOLUTION: Blankmasks for EUV lithography are equipped with a reflective film formed on the substrate, a capping film formed on the reflective film, and an absorption film formed on the capping film. The absorption film includes chromium (Cr) 30 to 60 at%, antimony (Sb) 40 to 70 at%, and nitrogen (N) 0 to 20 (at%). Thinning of the absorption film thickness is possible, resulting in a reduction of the 3D effect, and improvements in Dose to Space (DtS) and Normalized Image Log Slope (NILS).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a blank mask and a photomask, and more particularly to a blank mask for binary extreme ultraviolet lithography having an absorbing film and a photomask manufactured using the same. [Background technology]

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

[0003] Currently commercialized EUV blank masks generally use tantalum (Ta)-based materials as the absorber material. Tantalum (Ta)-based materials have the advantage of excellent cleaning and etching properties. However, when it comes to thinning tantalum (Ta)-based materials, there is a problem in that it is difficult to thin them down to 50 nm or less to improve the 3D effect. To solve this problem, materials with a higher extinction coefficient (k) than tantalum (Ta) can be considered. However, materials with a high extinction coefficient (High k) have poor etching and cleaning properties and have not been commercialized to date. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to provide a method for fabricating an absorbing film of a binary-type EUV blank mask that can ensure a high extinction coefficient (k) and has a thickness of 50 nm or less, preferably 40 nm or less. [Means for solving the problem]

[0005] In order to achieve the above object, the blank mask for extreme ultraviolet lithography according to the present invention is characterized by comprising a substrate, a reflective film formed on the substrate, a capping film formed on the reflective film, and an absorbing film formed on the capping film and containing chromium (Cr) and antimony (Sb).

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

[0007] The nitrogen (N) content of the absorption film is preferably 1 at % or more.

[0008] The absorbing film may further contain either oxygen (O) or carbon (O).

[0009] The absorbing film may contain 0 to 10 at % of oxygen (O) and 0 to 10 at % of carbon (C).

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

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

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

[0013] The absorbing film has an absolute reflectance of 3% or less for 13.5 nm EUV exposure light.

[0014] The blank mask for extreme ultraviolet lithography of the present invention may further include a hard mask film formed on the absorbing film and etched by a fluorine (F)-based gas.

[0015] The blank mask for extreme ultraviolet lithography of the present invention may further include an etching stop layer formed on the absorbing layer and etched by a fluorine (F)-based gas, and a hard mask layer formed on the etching stop layer and etched by a chlorine (Cl)-based gas.

[0016] The etch stop layer may contain one or more of tantalum (Ta), silicon (Si), and platinum (Pt).

[0017] The etch stop layer has a thickness of 2 nm or less.

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

[0019] According to another aspect of the present invention, there is provided a photomask for extreme ultraviolet lithography, which is fabricated using the blank mask having the above-described configuration. [Effects of the Invention]

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

[0021] This allows for a thinner absorber film, reducing the 3D effect and improving DtS (Dose to Space) and NILS (Normalized Image Log Slope), achieving excellent performance during wafer printing using a photomask. [Brief explanation of the drawings]

[0022] [Figure 1] 1 shows a binary extreme ultraviolet lithography blank mask according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will now be described in more detail with reference to the drawings.

[0024] FIG. 1 is a diagram showing a blank mask for binary extreme ultraviolet lithography according to the present invention.

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

[0026] The substrate 202 is made of a LTEM (Low Thermal Expansion Material) substrate having a low thermal expansion coefficient so as to be suitable as a glass substrate for a reflective blank mask that utilizes EUV exposure light.

[0027] The reflective film 204 has a function of reflecting EUV exposure light and has a multilayer 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 and Si material.

[0028] The capping film 205 prevents the formation of an oxide film on the reflective film 204, thereby maintaining the reflectivity of the reflective film 204 to EUV exposure light, and prevents the reflective film 204 from being etched when patterning the absorbing film 208. The capping film 205 is made of a material containing ruthenium (Ru) and has a thickness of 2 to 5 nm.

[0029] The absorbing film 208 absorbs the exposure light and transfers a pattern onto a wafer using the difference in reflectance between the exposure light reflected by the reflective film 204 and the exposure light reflected by the absorbing film, i.e., contrast. In the present invention, the absorbing film 208 is formed of a material containing chromium (Cr) and antimony (Sb).

[0030] The extinction coefficient (k) of the absorbing film 208 for EUV exposure light with a wavelength of 13.53 nm is 0.050 to 0.065, and preferably 0.055 to 0.065. This allows the thickness of the absorbing film 208 to be reduced to 50 nm or less, and preferably 40 nm or less. The absorbing film 208 has a refractive index (n) of 0.930 to 0.945 for EUV exposure light with a wavelength of 13.5 nm.

[0031] The extinction coefficient (k) of the absorbing film 208 can be controlled by adjusting the ratio of chromium (Cr) to antimony (Sb). Preferably, the absorbing film 208 has a composition of 30 to 60 at% chromium (Cr), 40 to 70 at% antimony (Sb), and 0 to 20 at% nitrogen (N). If the chromium (Cr) content is higher than 60 at%, the extinction coefficient (k) is low, making it difficult to thin the absorbing film 208. If the chromium (Cr) content is lower than 30 at%, the absorbing film 208 has a high extinction coefficient (k), but is vulnerable to solutions used during cleaning.

[0032] In order to form the absorber film 208 having such a composition, it is possible to control the composition of the target in the sputtering process for forming the absorber film 208. Specifically, a co-sputtering method can be applied using chromium (Cr), antimony (Sb), and CrSb targets as sputtering targets. Meanwhile, it is also possible to use a single target of CrSb alloy, and in this case, the composition of the CrSb alloy target is configured as Cr:Sb=30-40:70:60 (at%).

[0033] Meanwhile, the extinction coefficient (k) of the absorbing film 208 can be controlled by adjusting the content of any one of nitrogen (N), oxygen (O), and carbon (O). Specifically, the extinction coefficient (k) decreases as the content of nitrogen (N) and oxygen (O) increases. Therefore, the content of nitrogen (N) and oxygen (O) in the absorbing film 208 must be limited. Specifically, nitrogen (N) must be limited to 20 at% or less to ensure a high extinction coefficient (k). However, because nitrogen (N) affects line edge roughness after the patterning process, it is preferable to maintain a minimum nitrogen (N) content, for example, 1 at% or more. The oxygen (O) content is preferably 0 to 10 at% and the carbon (C) content is preferably 0 to 10 at%.

[0034] The absorbing film 208 may be formed as a single layer structure or a multilayer structure with different composition ratios of components. The absorbing film 208 has a thickness of 30 to 50 nm, preferably 35 to 45 nm. The absorbing film 208 has an absolute reflectance of 3% or less, preferably 2% or less, for EUV exposure light with a wavelength of 13.5 nm.

[0035] The absorber film 208 of the present invention is etched by a chlorine (Cl2)-based etching gas that does not contain oxygen (O2). This prevents the capping film 205 below the absorber film 208 from coming into contact with oxygen (O2), and therefore, no damage occurs to the capping film 205 even if overetching is performed.

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

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

[0038] Meanwhile, in the above-described structure, the hard mask film 209 is configured to be etched with a fluorine (F)-based gas to ensure etching selectivity relative to the absorbing film 208, which causes damage to the resist film 210 during the etching process. Generally, thickness damage to the resist film 210 during etching occurs less with a chlorine (Cl)-based gas than with a fluorine (F)-based gas. Even when a chlorine (Cl)-based gas is used, damage to the thickness of the resist film 210 is less when a chlorine (Cl)-based gas without oxygen (O) is used. Meanwhile, the thickness of the resist film 210 directly affects the resolution of the photomask. A thick resist film 210 can cause CD (critical dimension) errors due to electron scattering during E-beam writing. Furthermore, when forming highly fine patterns, the aspect ratio of the resist film 210 can be affected. To facilitate thinning of the resist film 210, the hard mask film 209 may be formed of a material that is etched by a chlorine (Cl)-based gas, for example, a CrNb-based material or a CrSb-based material. However, in this case, since both the absorber film 208 and the hard mask film 209 are etched by a chlorine (Cl)-based gas, an etch stop film that is etched by a fluorine (F)-based gas may be further formed between the absorber film 208 and the hard mask film 209.

[0039] The etch stop layer is formed of a material containing one or more of tantalum (Ta), silicon (Si), and platinum (Pt), and these materials have the property of being etched by fluorine (F) gas. The etch stop layer may further contain one or more of nitrogen (N), oxygen (O), and carbon (C). The etch stop layer has a thickness of 4 nm or less, preferably 2 nm or less. This thin thickness minimizes the problem of profile variations between the underlying absorber layer 208 and the etch stop layer during pattern formation. The etch stop layer has an etch selectivity of 5 or more relative to the underlying absorber layer 208 and also to the overlying hard mask layer 208.

[0040] The process for producing the blank mask of the present invention having the above-described structure is as follows.

[0041] First, a reflective film 204 and a capping film 205 are formed on a substrate 202, and then an absorbing film 208 is formed.

[0042] The absorber layer 208 is formed on the capping layer 205 by sputtering a CrSbN material. The sputtering target composition for forming the absorber layer 208 was Cr:Sb=40:60 (at%), argon (Ar) 30 sccm and nitrogen (N) 2 sccm were injected, and the process power was 1.2 kW. The absorber layer 208 exhibited a refractive index (n) of 0.938 and an extinction coefficient (k) of 0.0602 for EUV exposure light with a wavelength of 13.5 nm. Analysis of the composition ratio of the absorber layer 208 using RBS revealed a Cr:Sb ratio of 0.9:1.0.

[0043] Thereafter, a TaBO hard mask film 209 was formed to a thickness of 4 nm on the absorbing film 208, and a resist film 210 was coated thereon to complete the fabrication of the final blank mask.

[0044] Meanwhile, to fabricate the blank mask according to the other embodiment described above, an etch stop layer made of a Ta-based material is formed on the absorption layer 208, and then a CrNbN hard mask layer 209 is formed. The etch stop layer is formed to a thickness thinner than the hard mask layer 209, for example, 2 nm. The etch stop layer may be formed of TaO, TaCO, TaON, TaCON, TaBO, TaBCO, TaBON, TaBCON, TaSbO, TaSbON, TaSbCO, TaSbCON, Si-based, or Pt-based material, and is etched using a fluorine (F)-based gas. Then, a hard mask layer 209 is formed on the etch stop layer to a thickness of 4 nm. A resist layer 210 is then coated on the hard mask layer 209, completing the fabrication of the final blank mask.

[0045] The process for producing a photomask using the blank mask having the above-described structure is as follows.

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

[0047] The resist film pattern is removed, and the absorber film 208 is etched using the pattern of the hard mask film 209 as an etching mask. For etching the absorber film 208, a chlorine (Cl2)-based gas that does not contain oxygen (O2) is used.

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

[0049] When an etch stop layer is provided as in the other embodiments described above, the hard mask layer 209 is etched with a chlorine (Cl)-based gas that does not contain oxygen (O), and then the etch stop layer is etched with a fluorine (F)-based gas. During the etching process for patterning the absorbing layer 208, the hard mask layer 209 is etched and removed together. The etch stop layer may be removed after patterning the absorbing layer 208, or may remain and function as an absorber of exposure light together with the absorbing layer 208.

[0050] Although the present invention has been specifically described above by way of examples with reference to the drawings, the examples are merely used for the purpose of illustrating and explaining the present invention, and are not intended to be limiting in meaning or to limit the scope of the present invention as described in the claims. Therefore, a person skilled in the art of the present invention will understand that various modifications and equivalent embodiments are possible from the examples. Therefore, the true scope of protection of the present invention should be determined by the technical details of the claims. [Explanation of symbols]

[0051] 202 Substrate 204 Reflective film 205 Capping Film 208 Absorbent membrane 209 Hard mask film 210 Resist film

Claims

1. A substrate; a reflective film formed on the substrate; a capping film formed on the reflective film; an absorbing film formed on the capping film and containing chromium (Cr) and antimony (Sb); Including, The absorbing film contains 30 to 60 at % of chromium (Cr), 40 to 70 at % of antimony (Sb), and 0 to 20 at % of nitrogen (N).

2. 2. The blank mask for extreme ultraviolet lithography according to claim 1, wherein the nitrogen (N) content of said absorbing film is 1 at % or more.

3. 3. The blank mask for extreme ultraviolet lithography according to claim 2, wherein the absorbing film further contains either oxygen (O) or carbon (O).

4. 4. The blank mask for extreme ultraviolet lithography according to claim 3, wherein the absorbing film contains 0 to 10 at % of oxygen (O) and 0 to 10 at % of carbon (C).

5. 2. The blank mask for extreme ultraviolet lithography according to claim 1, wherein the absorbing film has an extinction coefficient (k) of 0.05 to 0.065 for EUV exposure light with a wavelength of 13.5 nm.

6. 6. The blank mask for extreme ultraviolet lithography according to claim 5, wherein the absorbing film has a refractive index (n) of 0.930 to 0.945 for EUV exposure light with a wavelength of 13.5 nm.

7. 7. The blank mask for extreme ultraviolet lithography according to claim 6, wherein the absorbing film has a thickness of 30 to 50 nm.

8. 8. The blank mask for extreme ultraviolet lithography according to claim 7, wherein the absorbing film has an absolute reflectance of 3% or less for 13.5 nm EUV exposure light.

9. 9. The blank mask for extreme ultraviolet lithography according to claim 1, further comprising a hard mask film formed on the absorbing film and etched by a fluorine (F)-based gas.

10. an etching stopper film formed on the absorption film and etched by a fluorine (F)-based gas; a hard mask layer formed on the etching stop layer and etched by a chlorine (Cl)-based gas; 9. The blank mask for extreme ultraviolet lithography according to claim 1, further comprising:

11. 11. The blank mask for extreme ultraviolet lithography according to claim 10, wherein the etching stop layer is formed of a material containing at least one of tantalum (Ta), silicon (Si), and platinum (Pt).

12. 11. The blank mask for extreme ultraviolet lithography according to claim 10, wherein the etching stop film has a thickness of 2 nm or less.

13. 12. The blank mask for extreme ultraviolet lithography according to claim 11, wherein the hard mask film is formed of a material containing CrNb or CrSb.

14. A photomask for extreme ultraviolet lithography, produced using the blank mask according to claim 1.

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