Blank masks and photomasks for extreme ultraviolet lithography equipped with hard mask films containing chromium and niobium.

Abstract

In the process of fabricating a photomask using an EUV blank mask equipped with an absorption film and a hard mask film, enabling the etching of the hard mask film using an oxygen-free etching gas makes it possible to thin the resist film and thereby achieve high resolution. [Solution] The blank mask for EUV lithography has a structure in which a reflective film, a capping film, an absorption film, and a hard mask film are sequentially stacked on a substrate. The hard mask film is formed from a material containing chromium (Cr), niobium (Nb), oxygen (O), and nitrogen (N), and a sufficient etching rate can be obtained even when using only chlorine-based etching gas that does not contain oxygen (O2). This prevents damage to the resist film caused by oxygen (O2), and since the capping film is not exposed to oxygen (O2) in the process of removing the hard mask film, damage to the capping film is prevented.

Description

Technical Field

[0001] The present invention relates to a blank mask and a photomask, and more particularly to a blank mask for extreme ultraviolet (EUV) lithography provided with a hard mask film and a photomask manufactured using the same.

Background Art

[0002] EUV lithography is a semiconductor device manufacturing technology that uses EUV exposure light with a wavelength of 13.5 nm. In EUV lithography, a reflective photomask is used in the wafer exposure process.

[0003] A blank mask for manufacturing an EUV photomask includes two thin films: a reflective film that reflects EUV light and an absorption film that absorbs EUV light on a substrate. The photomask is manufactured by patterning the absorption film of such a blank mask, and utilizes the principle of forming a pattern on a wafer using the difference in contrast between the reflectivity of the reflective film and the reflectivity of the absorption film.

[0004] FIG. 1 is a diagram showing the structure of a blank mask for extreme ultraviolet lithography. The blank mask for extreme ultraviolet lithography includes a substrate 102, a reflective film 104 formed on the substrate 102, a capping film 105 formed on the reflective film 104, an absorption film 106 formed on the capping film 105, a hard mask film 108 formed on the absorption film 106, and a resist film 110 formed on the hard mask film 108.

[0005] The reflective film 104 is generally formed as a multilayer structure in which layers of Mo material and Si material are alternately laminated 40 to 60 times. The capping film 105 is formed on top of the reflective film 104 and has the function of protecting the reflective film 104. The capping film 105 is generally formed from a material containing ruthenium (Ru) and has the function of protecting the reflective film 104 during etching for patterning of the absorption film 106. The absorption film 106 is generally formed from a material containing tantalum (Ta), and the hard mask film 108 is generally formed from a chromium compound, such as a material containing chromium (Cr) with nitrogen (N) and oxygen (O). The absorption film 106 can have a structure of two or more layers, in which case the uppermost layer of the absorption film 106 is composed of an inspection layer, and the layer below the inspection layer is composed of an absorption layer. The inspection layer is a layer used to inspect a fabricated blank mask using inspection light, and its sensitivity to the 193 nm wavelength of ArF inspection light is increased by being formed from a material containing oxygen (O) in tantalum (Ta).

[0006] To fabricate a photomask, a resist film 110 is exposed to light to form a predetermined pattern, which is then used to etch and pattern a hard mask film 108. The patterned hard mask film 108 is then used as an etching mask to pattern an absorption film 106.

[0007] In the etching process for patterning the chromium (Cr)-based hard mask film 108, a chlorine-based gas containing oxygen (O2) is used. This type of etching process causes greater damage to the resist film 110 compared to an etching process using a chlorine-based gas that does not contain oxygen (O2). Because of this, the thickness of the resist film 110 must be increased, which presents a problem in that it is difficult to thin the resist film 110 as needed to improve resolution.

[0008] Furthermore, in the patterning process of the absorption film 106 using the hard mask film 108, a fluorine (F)-based etching gas is used to etch the inspection layer, which is the uppermost layer of the absorption film 106, and a chlorine-based etching gas that does not contain oxygen (O2) is used to etch the absorption layer, which is the layer below the uppermost layer of the absorption film 106. When etching with a chlorine-based gas that does not contain oxygen (O2), the hard mask film 108 is not etched, so in order to remove the hard mask film 108, a removal step using a chlorine-based gas that contains oxygen (O2) must be added. In this case, there is a problem that the oxygen (O2) contained in the etching gas causes oxidation of the capping film 105, reducing its reflectivity. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention was devised to solve the above-mentioned problems, and the object of the present invention is to enable thinning of the resist film and thereby achieving high resolution by enabling etching of the hard mask film using an oxygen-free etching gas in the process of manufacturing a photomask using an EUV blank mask equipped with an absorption film and a hard mask film.

[0010] Another object of the present invention is to eliminate the need for an additional etching step to remove the hard mask film pattern by ensuring that the hard mask film pattern is removed during etching of the absorption film.

[0011] Another object of the present invention is to prevent damage to the capping film that occurs when using an etching gas containing oxygen (O2), thereby achieving high image contrast. [Means for solving the problem]

[0012] The blank mask for EUV lithography according to the present invention comprises a substrate; a reflective film formed on the substrate; a capping film formed on the reflective film; an absorption film formed on the capping film; and a layer formed on the absorption film containing chromium (Cr), niobium (Nb), oxygen (O), and nitrogen (N), with an XRR (X-ray reflectivity) measurement density of 5.0 to 6.5 g / cm³. 3 It is characterized by including a hard mask film;

[0013] The hard mask film is configured such that the FWHM (Full Width at Half Maximum) of the main peak located in the range of 2θ 40° or less, as measured by XRD (X-ray Diffraction), is 2.0 or greater.

[0014] The hard mask film contains Cr:Nb in an at% ratio of 3:7 to 7:3, preferably in an at% ratio of 4:6 to 6:4.

[0015] Preferably, the absorption film is configured such that at least its uppermost portion is etched by a fluorine-based etching gas.

[0016] Preferably, the absorption film includes an absorption layer disposed on the capping film and an inspection layer disposed on the absorption layer, wherein the inspection layer is etched with a fluorine-based gas and the absorption layer is etched with an oxygen (O2)-free chlorine-based gas.

[0017] Preferably, the inspection layer contains tantalum (Ta) and oxygen (O), and the absorption layer contains tantalum (Ta) but does not contain oxygen (O).

[0018] According to another aspect of the present invention, a photomask fabricated using a blank mask having the above-described configuration is provided. [Effects of the Invention]

[0019] According to the present invention, in the process of manufacturing a photomask using an EUV blank mask including an absorption film and a hard mask film, sufficient etching rate of the hard mask film can be obtained even by using only a chlorine-based etching gas that does not contain oxygen (O2).

[0020] Thereby, damage to the resist film caused by oxygen (O2) is prevented, so that the resist film can be thinned. For example, even if the resist film is configured to have a thickness of 40 nm or less, a sufficient thickness for etching the hard mask film can be ensured, thereby improving the pattern accuracy of the hard mask film, and as a result, improving the pattern accuracy of the absorption film can be achieved. In addition, since there is little damage to the resist film during etching of the hard mask film, it is possible to over-etch the hard mask film. Therefore, the effect of improving the pattern accuracy by over-etching can be obtained without making the resist film thicker than before.

[0021] Further, according to the present invention, since the capping film is not exposed to oxygen (O2) in the process of removing the hard mask film, a decrease in reflectivity due to damage to the capping film is prevented, thereby improving the image contrast.

Brief Description of the Drawings

[0022] [Figure 1] It is a diagram showing a thin film structure of a conventional blank mask for extreme ultraviolet lithography. [Figure 2] It is a diagram showing a thin film structure of an EUV blank mask according to the present invention.

Embodiments for Carrying Out the Invention

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

[0024] The blank mask of the present invention includes not only binary-type blank masks but also phase-shifting blank masks. In a binary-type blank mask, the absorption film has a function of absorbing EUV exposure light, and in a phase-shifting blank mask, the absorption film reverses the phase of the exposure light to generate destructive interference. In a phase-shifting blank mask, for the purpose of distinction from a binary-type blank mask, the absorption film is generally referred to as a "phase-shifting film". However, since the blank mask of the present invention includes both binary-type blank masks and phase-shifting blank masks, the "absorption film" in the present invention is used as a general term that collectively refers to the absorption film in a binary-type blank mask as well as the phase-shifting film in a phase-shifting blank mask. Furthermore, the blank mask of the present invention includes not only blank masks for 0.33 NA but also high-NA blank masks of 0.55 NA or more.

[0025] FIG. 2 is a diagram showing the thin film structure of a blank mask for extreme ultraviolet lithography according to the present invention. The blank mask for extreme ultraviolet lithography 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 absorption film 206 formed on the capping film 205, a hard mask film 208 formed on the absorption film 206, and a resist film 210 formed on the hard mask film 208. Further, the blank mask of the present invention can include additional thin films such as a conductive film (not shown) formed on the back surface of the substrate 202.

[0026] The substrate 202 has a low coefficient of thermal expansion within the range of 0 ± 1.0 × 10 -7 / °C in order to prevent pattern deformation and stress due to heat during exposure, so as to be suitable as a glass substrate for a reflective blank mask using EUV exposure light. Preferably, it is composed of an LTEM (Low Thermal Expansion Material) substrate having a low coefficient of thermal expansion within the range of 0 ± 0.3 × 10 -7 / °C. As the material of the substrate 202, SiO2-TiO2-based glass, multi-component glass ceramics, etc. can be used.

[0027] The reflective film 204 has the 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 stacking 40 to 60 alternating layers of Mo material and Si material. The reflective film 204 preferably has a reflectance of 60% or more, preferably 64% or more, for 13.5 nm EUV exposure light.

[0028] The capping film 205 prevents oxide film formation on the reflective film 204, maintaining the reflectivity of the reflective film 204 to EUV exposure light, and protects the reflective film 204 when patterning the absorption film 206. Generally, the capping film 205 is formed from a material containing ruthenium (Ru). The capping film 205 has a thickness of 2 to 5 nm.

[0029] The absorption film 206 is patterned during the process of fabricating the blank mask as a photomask, and the capping film 205 is exposed in the areas removed by the patterning. The absorption film 206 absorbs the exposure light, and as a result, the exposure light is divided into parts that are reflected by the reflective film 204 and parts that are absorbed by the absorption film 206, and these are then irradiated onto the wafer.

[0030] The absorption film 206 is formed of a substance that absorbs exposure light, and tantalum (Ta) is used as the basic material for such a substance. The absorption film 206 may contain additional metals along with Ta, such as molybdenum (Mo) or titanium (Ti). The absorption film 206 may further contain one or more of boron (B), oxygen (O), and nitrogen (N). Tantalum (Ta) is etchable by chlorine-based gases, and if oxygen (O) is also included in the tantalum (Ta), it is etchable by fluorine-based gases.

[0031] The absorption film 206 may have a single-layer structure. When the absorption film 206 has a single-layer structure, it is configured as a continuous film in which the uppermost layer is formed of a material etched by a fluorine-based etching gas.

[0032] The absorption film 206 may also have a structure of two or more layers. In the embodiment shown in Figure 2, the absorption film has a two-layer structure, specifically, the lower layer of the absorption film 206 is configured as the absorption layer 206a, and the upper layer is configured as the inspection layer 206b. The absorption layer 206a has the function of absorbing EUV exposure light, and the inspection layer 206b is used to inspect the fabricated blank mask using 193 nm ArF inspection light.

[0033] The inspection layer 206b is formed from a material containing oxygen (O) to reduce reflectivity with 193 nm inspection light. For example, the inspection layer 206b can be formed from TaO, TaBO, TaON, or TaBON. As mentioned above, when Ta contains oxygen (O), it is etched by a fluorine-based gas, so the inspection layer 206b is etched by a fluorine-based etching gas. As will be described later, the hard mask film 208 is etched by a chlorine-based gas, thereby giving the inspection layer 206b an etching selectivity ratio with respect to the hard mask film 208. The inspection layer 206b preferably has a minimum thickness for inspection function, for example, 2 to 5 nm.

[0034] The absorption layer 206a has the function of absorbing exposure light with a wavelength of 13.5 nm. Preferably, the absorption layer 206a contains tantalum (Ta) but does not contain oxygen (O) and is etchable with a chlorine-based gas. For example, the absorption layer 206a can be formed of TaB or TaBN. Since the absorption layer 206a is etched with a chlorine-based gas, it has an etching selectivity ratio with respect to the inspection layer 206b. As will be described later, the hard mask film 208 is also etched with a chlorine-based gas, so the hard mask film 208 is removed by etching during etching for patterning of the absorption layer 206a.

[0035] The hard mask film 208 functions as an etching mask for patterning the inspection layer 206b beneath it. For this purpose, the hard mask film 208 is composed of a material having an etching selectivity ratio with respect to the inspection layer 206b; specifically, the hard mask film 208 is composed of a material that is etched by a chlorine-based etching gas. Furthermore, to address the problems of the prior art, the hard mask film 208 must be composed of a material that is etched by a chlorine-based gas that does not contain oxygen (O2).

[0036] In this invention, a substance containing chromium (Cr), niobium (Nb), oxygen (O), and nitrogen (N) is presented as a substance that solves the above problems. The inventors of this invention have found that when chromium (Cr) is mixed with niobium (Nb), the hard mask film 208 can be etched with a chlorine-based gas that does not contain oxygen (O2).

[0037] Specifically, the hard mask film 208 is preferably configured to contain Cr:Nb in an at% ratio of 3:7 to 7:3, and more preferably in an at% ratio of Cr:Nb of 4:6 to 6:4. If the Nb content is lower than the above ratio, the etching rate with oxygen-free chlorine-based gas is relatively slow, making it difficult to thin the resist film 210. If the Nb content is higher than the above ratio, a problem arises in which resistance to cleaning solutions such as SPM decreases.

[0038] The hard mask film 208 preferably has an etching rate of 3.0 Å / sec or higher with a chlorine-based gas, and an etching selectivity ratio of 8:1 or higher with respect to the inspection layer 206b below it. Furthermore, the hard mask film 208 preferably has chemical stability such that the change in thickness after the cleaning process with respect to a cleaning solution such as SPM is 5 Å or less.

[0039] When one or more of nitrogen (N) and oxygen (O) are added to the hard mask film 208, the etching rate, etching selectivity ratio, and resistance to cleaning solutions can be adjusted by controlling the content. Experimental results showed that increasing the oxygen (O) content increased the etching rate against chlorine-based gases, but also increased the etching rate against fluorine-based gases, and above a certain content, the etching selectivity ratio actually decreased. Furthermore, it was confirmed that there is a direct proportional relationship between the nitrogen (N) content and the stability against cleaning solutions, but an inverse proportional relationship between the oxygen (O) content and the stability against cleaning solutions. Therefore, it is preferable that the oxygen (O) content be below a certain ratio.

[0040] The inventors of this invention conducted optimization experiments on the three properties mentioned above—etching rate, etching selectivity, and resistance to cleaning solutions—while varying the oxygen (O) and nitrogen (N) composition, ensuring that the Cr:Nb ratio was within the aforementioned range. As a result, they found that the XRR (X-ray reflectivity) measurement density of a CrNbON thin film with a certain composition ratio was 5.0 to 6.5 g / cm³. 3 We confirmed that the above three conditions are met when the material is within the specified range. Furthermore, XRD (X-ray Diffraction) measurements of the CrNbON thin film within the above density range showed that the FWHM (Full Width at Half Maximum) of the main peak located in the range of 2θ 40° or less was 2.0 or higher, confirming that this CrNbON thin film is in an amorphous state sufficient to secure an excellent profile.

[0041] In order for a CrNbON thin film to have the measured density within the range described above, the composition ratio of each element in the final formed thin film is adjusted by appropriately controlling the oxygen and nitrogen content during the sputtering process for thin film formation, while keeping the Cr:Nb content ratio within the range described above. At this time, the content of each element, Cr, Nb, O, and N, that yields the measured density within the range described above can be composed of various combinations of values.

[0042] The resist film 210 is composed of a chemically amplified resist (CAR). In this invention, the resist film 210 can have a thickness of 30 to 60 nm.

[0043] The process for manufacturing a photomask using the blank mask of the present invention having the above-described configuration is as follows.

[0044] First, a reflective film 204, a capping film 205, an absorption layer 206a, an inspection layer 206b, a hard mask film 208, and a resist film 210 are sequentially formed on the substrate 202. After exposing and patterning the resist film 210, the hard mask film 208 is patterned using the patterned resist film 210 as an etching mask. At this time, a chlorine-based gas that does not contain oxygen (O2), such as Cl2 and / or BCl3, is used for the etching process of the hard mask film 208.

[0045] After the patterning of the hard mask film 208 is complete, the resist film 210 is removed. The resist film 210 can also be removed by over-etching of the hard mask film 208 without a separate removal process. After the resist film 210 is removed, the inspection layer 206b is etched and patterned using the hard mask film 208 as an etching mask. A fluorine-based etching gas, such as SF6, is used for patterning the inspection layer 206b.

[0046] After the patterning of the inspection layer 206b is completed, the absorption layer 206a is patterned using the hard mask film 208 and the inspection layer 206b as etching masks. At this time, a chlorine-based gas that does not contain oxygen (O2), such as Cl2 and / or BCl3, is used for the etching process of the absorption layer 206a. While the absorption layer 206a is etched, the pattern of the hard mask film 208 is removed by the etching gas that etches the absorption layer 206a.

[0047] This process completes the manufacturing process of a photomask using the blank mask of the present invention.

[0048] According to the present invention, a sufficient etching rate for the hard mask film 208 can be obtained even when using only an oxygen-free (O2) chlorine-based etching gas in the process of manufacturing a photomask using an EUV blank mask equipped with an absorption film and a hard mask film. It has been confirmed that the etching rate is improved by approximately 1.2 to 2.0 times when etching the hard mask film 208 of the CrNbON material of the present invention with an oxygen-free (O2) chlorine-based gas compared to etching the hard mask film 108 of the CrCON material with an oxygen-free (O2) chlorine-based gas.

[0049] According to the present invention, damage to the resist film 210 caused by oxygen (O2) is prevented, making it possible to thin the resist film 210. In the conventional method, when etching a hard mask film 108 containing only Cr with an oxygen (O2)-containing chlorine gas, the thickness of the resist film 110 must be set to a sufficient thickness, for example, at least 80 nm or more, taking into account the damage to the resist film 110 caused by oxygen (O2). However, in the present invention, since an oxygen (O2)-free etching gas is used, damage to the resist film 210 is significantly reduced, and therefore, even if the thickness of the resist film 210 is set to 60 nm or less, sufficient thickness for etching the hard mask film 208 can be secured.

[0050] Furthermore, in conventional hard mask films 108, when attempting to improve pattern accuracy through over-etching, the resist film 110 must be formed with a thickness of, for example, about 100 nm to avoid damage to the resist film 110. However, in the present invention, the hard mask film 208 can be over-etched even when the resist film 210 is formed with a thickness of about 60 nm or even thinner, at 50 nm. Therefore, it is possible to improve pattern accuracy through over-etching while simultaneously thinning the resist film 210. Furthermore, according to the present invention, since the capping film 205 is not exposed to oxygen (O2) in the step of removing the hard mask film 208, a decrease in reflectivity due to damage to the capping film 205 is prevented.

[0051] Furthermore, according to the present invention, since the hard mask film 208 is removed during etching of the absorption layer 206a, there is an advantage that no additional steps are required to remove the hard mask film 208.

[0052] The present invention has been specifically described above using embodiments with reference to the drawings, but the embodiments are used solely for the purpose of illustrating and explaining the present invention and are not intended to limit the meaning or the scope of the present invention as defined in the claims. Therefore, a person with ordinary skill in the art of the present invention can make various modifications and equivalent other embodiments from the embodiments, and the scope of protection of the present invention should be determined by the technical matters in the claims.

Claims

1. substrate; A reflective film formed on the substrate; A capping film formed on the reflective film; An absorption film formed on the capping film; and, Formed on the aforementioned absorption film, containing chromium (Cr), niobium (Nb), oxygen (O), and nitrogen (N), with an XRR (X-ray reflectivity) measurement density of 5.0 to 6.5 g / cm³ ３ A hard mask film; A blank mask for extreme ultraviolet lithography characterized by containing [a specific component].

2. The hard mask film is characterized in that the FWHM (Full Width at Half Maximum) of the main peak located in the range of 2θ 40° or less, as measured by XRD (X-ray Diffraction), is 2.0 or greater, as described in claim 1, for use as a blank mask for extreme ultraviolet lithography.

3. The hard mask film is characterized by containing Cr:Nb in an at% ratio of 3:7 to 7:3, as described in claim 2, for use as a blank mask for extreme ultraviolet lithography.

4. The hard mask film is characterized by containing Cr:Nb in an at% ratio of 4:6 to 6:4, as described in claim 2, for use as a blank mask for extreme ultraviolet lithography.

5. The blank mask for extreme ultraviolet lithography according to any one of claims 1 to 4, characterized in that at least the uppermost part of the absorption film is etched with a fluorine-based etching gas.

6. The absorption film includes an absorption layer disposed on the capping film and an inspection layer disposed on the absorption layer. The inspection layer is etched with a fluorine-based gas, and the absorption layer is etched with oxygen (O ２ A blank mask for extreme ultraviolet lithography according to claim 5, characterized in that it is etched with a chlorine-free gas.

7. The inspection layer contains tantalum (Ta) and oxygen (O), The blank mask for extreme ultraviolet lithography according to claim 6, characterized in that the absorption layer contains tantalum (Ta) and does not contain oxygen (O).

8. A photomask fabricated using a blank mask for extreme ultraviolet lithography as described in any one of claims 1 to 4.

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