BLANKMASK AND PHOTOMASK FOR EXTREME ULTRAVIOLET RAYS LITHOGRAPHY WITH ABSORBING FILM OF CrSb

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 type 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 EUV exposure light with a wavelength of 13.5 nm irradiated to the photomask is reflected according to the pattern of the absorbing film, exposing the wafer according to the pattern.

[0003] EUV blank masks currently being commercialized generally use tantalum (Ta)-based materials as the material for the absorbing film. Tantalum (Ta)-based materials have the advantage of excellent cleaning and etching properties. However, tantalum (Ta)-based materials have the problem that they are difficult to thin to less than 50 nm in thickness to improve the 3D effect. To remedy this, 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, which 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-mentioned object, the blank mask for extreme ultraviolet lithography according to the present invention is characterized in that it includes 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 % chromium (Cr), 40 to 70 at % antimony (Sb), and 0 to 20 at % nitrogen (N).

[0007] The nitrogen (N) content of the absorbing 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 film formed on the absorbing film and etched by a fluorine (F)-based gas, and a hard mask film formed on the etching stop film 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 including CrNb or CrSb.

[0019] According to another aspect of the present invention, there is provided a photomask for extreme ultraviolet lithography, which is manufactured using the blank mask having the above-mentioned configuration. Effect 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 the absorber film to be made thinner, 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 description of the drawings]

[0022] [Figure 1] FIG. 1 shows a binary type extreme ultraviolet lithography blank mask according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0024] FIG. 1 is a diagram showing a binary type extreme ultraviolet lithography blank mask 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 Low Thermal Expansion Material (LTEM) 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 multi-layer structure in which each layer has a different refractive index. Specifically, the reflective film 204 is formed by laminating 40 to 60 layers of Mo material and Si material layers alternately.

[0028] The capping film 205 serves to prevent the formation of an oxide film on the reflective film 204, thereby maintaining the reflectance of the reflective film 204 to EUV exposure light, and to prevent 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 made of a material containing chromium (Cr) and antimony (Sb).

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

[0031] The ratio of chromium (Cr) and antimony (Sb) can be adjusted as a method for controlling the extinction coefficient (k) of the absorbing film 208. Preferably, the absorbing film 208 has a composition of 30-60 at% chromium (Cr), 40-70 at% antimony (Sb), and 0-20 at% nitrogen (N). If the chromium (Cr) content is higher than 60 at%, the extinction coefficient (k) is low and it is not easy to make the absorbing film 208 thin, whereas if the chromium (Cr) content is lower than 30 at%, the absorbing film has a high extinction coefficient (k) but is vulnerable to solutions used during cleaning.

[0032] In order to form the absorbing film 208 having such a composition, it is possible to control the composition of the target in the sputtering process for forming the absorbing film 208. Specifically, a co-sputtering method can be applied using targets of chromium (Cr), antimony (Sb), and CrSb 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 using 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 needs to be limited, specifically, nitrogen (N) needs to be limited to 20 at% or less in order to ensure a high extinction coefficient (k). However, since nitrogen (N) affects line edge roughness after the patterning process, it is preferable to maintain the 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 in a single layer structure or a multi-layer structure with different composition ratios of the 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 absorbing film 208 of the present invention is etched by a chlorine (Cl2)-based etching gas that does not contain oxygen (O2). As a result, the capping film 205 under the absorbing film 208 is not in contact with oxygen (O2), and no damage is caused 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 absorbing film 208, and therefore the hard mask film 209 is formed of a material having an etching selectivity with respect to the absorbing 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 by 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). The resist film 210 has a thickness of 40 to 100 nm, and preferably 40 to 80 nm.

[0038] Meanwhile, in the above-mentioned structure, the hard mask film 209 is configured to be etched by a fluorine (F)-based gas in order to secure an etching selectivity to the absorbing film 208, so that the resist film 210 is damaged during the etching process. In general, the thickness damage of the resist film 210 during etching occurs less in a chlorine (Cl)-based gas than in a fluorine (F)-based gas. Also, even when a chlorine (Cl)-based gas is used, the thickness damage of the resist film 210 is less when a chlorine (Cl)-based gas that does not contain oxygen (O2) is used. Meanwhile, the thickness of the resist film 210 directly affects the resolution of the photomask. If the resist film 210 is thick, a CD (Critical Dimension) error is induced due to scattering of electrons during E-beam writing. Also, when a highly fine pattern is formed, an aspect ratio problem of the resist film 210 may occur. In order 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 absorbing 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 absorbing 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 a characteristic of being etched by fluorine-based (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. Such a thin thickness can minimize a problem that a profile between the lower absorbing film 208 and the etch stop layer may change during pattern formation. The etch stop layer has an etching selectivity of 5 or more with respect to the lower absorbing film 208, and also has an etching selectivity of 5 or more with respect to the upper hard mask film 208.

[0040] The process for producing the blank mask of the present invention having the above-mentioned 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 absorbing film 208 is formed on the capping film 205 by a sputtering method using a CrSbN material. The sputtering target composition for forming the absorbing film 208 was Cr:Sb=40:60 (at%), argon (Ar) 30sccm and nitrogen (N) 2sccm were injected, and the process power was 1.2kW. The absorbing film 208 exhibited a refractive index (n)=0.938 and an extinction coefficient (k)=0.0602 for EUV exposure light with a wavelength of 13.5nm, and the composition ratio of the absorbing film 208 was analyzed using RBS, and the ratio was Cr:Sb=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, in order to manufacture a blank mask according to the above-mentioned other embodiment, an etching stopper film made of a Ta-based material is formed on the absorbing film 208, and then a CrNbN hard mask film 209 is formed. At this time, the etching stopper film is formed to a thickness smaller than that of the hard mask film 209, for example, a thickness of 2 nm. The etching stopper film 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 by a fluorine (F)-based gas. Then, the hard mask film 209 on the etching stopper film is formed to a thickness of 4 nm. Then, a resist film 210 is coated on the hard mask film 209, completing the manufacture of the final blank mask.

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

[0046] First, a pattern of the resist film 210 is formed by an electron beam writing and developing 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 absorbing film 208 is etched using the pattern of the hard mask film 209 as an etching mask. For etching the absorbing film 208, a chlorine (Cl2)-based gas not containing oxygen (O2) 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 and functions to absorb the 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 (Cl2)-based gas not containing oxygen (O2), and then the etch stop layer is etched with a fluorine (F)-based gas. In an etching process for patterning the absorbing layer 208, the hard mask layer 209 is etched and removed. The etch stop layer may be removed after patterning the absorbing layer 208, or may remain without being removed and perform the function of absorbing exposure light together with the absorbing layer 208.

[0050] The present invention has been described in detail above by way of the embodiments with reference to the drawings, but the embodiments are merely used for the purpose of illustrating and explaining the present invention, and are not used for the purpose of limiting the meaning or the scope of the present invention described in the claims. Therefore, a person having ordinary skill in the art of the present invention can understand that various modifications and equivalent other embodiments are possible from the embodiments. Therefore, the true scope of protection of the present invention should be determined by the technical matters of the claims. [Explanation of symbols]

[0051] 202 Substrate 204 Reflective film 205 Capping Membrane 208 Absorbing 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); 1. A blank mask for extreme ultraviolet lithography comprising:

2. 2. The blank mask for extreme ultraviolet lithography according to claim 1, wherein the absorbing film contains 30 to 60 at % chromium (Cr), 40 to 70 at % antimony (Sb), and 0 to 20 at % nitrogen (N).

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

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

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

6. 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 having 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 refractive index (n) of 0.930 to 0.945 for EUV exposure light with a wavelength of 13.5 nm.

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

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

10. 10. 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.

11. an etching stopper film formed on the absorbing 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; 10. The blank mask for extreme ultraviolet lithography according to claim 1, further comprising:

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

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

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

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

Images