Cleaning solution for removing metal resists, and cleaning method using the cleaning solution.

Abstract

A cleaning solution is used to clean metal inhibitors and contains a solvent and a strong acid that is liquid at 20°C. The pH value of the liquid obtained by diluting the cleaning solution with pure water by 10 times is measured to be below 2.5 using a pH meter.

Description

Cleaning solution for removing metal resists, and cleaning method using the cleaning solution. This invention relates to a cleaning solution for cleaning metal resists and a cleaning method using the cleaning solution. This patent application claims priority based on Japanese Patent Application No. 2021-202511, filed with the Japanese Patent Office on December 14, 2021, and incorporates the contents thereof. The fabrication of semiconductor circuits and devices has seen continuous miniaturization of the ultimate dimensions across generations. As these dimensions shrink, new materials and methods are sought to meet the requirements of processing increasingly fine structures and patterning. Pattern formation generally involves selectively exposing a thin layer of a radiation-sensitive material (resistor) to form a pattern that is transferred to subsequent layers or functional materials. A metal resist is proposed that simultaneously provides very high etching contrast and is suitable for providing good absorption for EUV (Extreme Ultraviolet) or EB (Electron Line) radiation (e.g., see Patent Document 1). When patterning with the aforementioned metal resist, the ligands coordinated with the metal peroxide in the metal resist decompose and undergo hydrolysis and condensation upon exposure, forming metal oxides, and the resist is insoluble in the developer. Next, by developing the resist, a pattern with high etch resistance can be formed. However, when patterning with metal resist, during the application of the metal resist to the substrate, metal peroxide molecular clusters may bond to the substrate surface, such as silicon wafers, resulting in residue. To remove such residue, it is proposed to use a cleaning solution containing an organic solvent and a carboxylic acid (for example, see Patent Document 2). [Prior Art Documents] [Patent Documents] [Patent Document 1] US Patent No. 9,176,377 [Patent Document 2] International Publication No. 2018 / 031896 [The problem that the invention aims to solve] The inventors have discovered through research that when using a cleaning solution containing organic solvents and solid acids such as oxalic acid and benzenesulfonic acid to clean a support containing a metal inhibitor, high metal removal performance can be achieved. However, during drying, the solid acid precipitates out, and organic matter remains on the treated surface, potentially contaminating the process equipment. Furthermore, the inventors have found that when liquid acids such as acetic acid are used instead of solid acids such as oxalic acid to suppress precipitation during drying, the metal removal performance is insufficient compared to using solid acids such as oxalic acid. This invention was made in view of the above circumstances. The objective is to provide a cleaning solution for cleaning metal inhibitors and a cleaning method using this solution, which improves metal removal performance and reduces organic matter residue. [Means for Solving the Problem] To address the aforementioned issues, the present invention employs the following configuration. The first aspect of the present invention is a cleaning solution, which is used to clean metal inhibitors and contains a solvent and a strong acid that is liquid at 20°C, wherein the pH value of the liquid obtained by diluting the aforementioned cleaning solution with pure water by 10 times is measured to be below 2.5 using a pH meter. A second aspect of the invention: a cleaning method comprising the step of cleaning an object with an adhering metal resist using a cleaning solution related to the first aspect described above. [Effects of the Invention] According to the present invention, a cleaning solution for cleaning metal inhibitors and a cleaning method using the cleaning solution can be provided, which improves metal removal and reduces organic residue. [Best Form of Invention] (Detergent) The first type of cleaning solution of this invention contains a solvent and a strong acid that is liquid at 20°C. This cleaning solution is used to clean metal resists. The cleaning solution of this embodiment, when diluted 10 times with pure water using a pH meter, has a pH value of 2.5 or lower, preferably 2.4 or lower, and even more preferably 2.3 or lower. If the pH value of the liquid obtained by diluting the cleaning solution 10 times with pure water is 2.5 or lower, the metal removal performance of the cleaning solution will be easily improved. The lower limit value is not particularly limited and can be negative. It is preferable to adjust it appropriately according to the process environment within the system using the cleaning solution of this embodiment, for example, to 0.1 or higher, preferably 1.0 or higher, and even more preferably 1.4 or higher. Furthermore, in this embodiment, the above pH values ​​are measured at room temperature. <Solvent> There are no particular limitations on the solvent, and examples include water and organic solvents. Examples of organic solvents include ethylene glycol ethers and esters such as propylene glycol methyl ether (PGME), propylene glycol methyl ethyl acetate (PGMEA), propylene glycol butyl ether (PGBE), and ethylene glycol methyl ether; alcohols such as ethanol, propanol, isopropanol, isobutanol, hexanol, ethylene glycol, and propylene glycol; cyclic esters such as γ-butyrolactone; esters such as n-butyl acetate and ethyl acetate; ketones such as 2-heptanone; liquid cyclic carbonates such as propylene carbonate and butyl carbonate; and cyclic cyclobutane such as cyclobutane. Among these, organic solvents without hydroxyl groups are preferred, ethylene glycol ethers and their esters or ketones are more preferred, propylene glycol methyl ethyl acetate (PGMEA) or 2-heptanone are more preferred, and propylene glycol methyl ethyl acetate (PGMEA) is particularly preferred. As a solvent, using an organic solvent without hydroxyl groups easily inhibits the esterification reaction of acids (strong acids) in the cleaning solution, thereby easily improving the long-term stability of the cleaning solution. If the cleaning solution of this embodiment includes water as a solvent, the water content relative to the total mass (100% by mass) of the cleaning solution is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. There is no particular limitation on the lower limit of the water content; for example, relative to the total mass (100% by mass) of the cleaning solution, it can be 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more. When the water content is within the above-mentioned preferred range, the metal removal performance of the cleaning solution will be easily improved. In this embodiment, a single solvent or a mixture of two or more solvents can be used. In the cleaning solution related to this embodiment, the solvent content relative to the total mass (100% by mass) of the cleaning solution is preferably 45-80% by mass, more preferably 50-75% by mass, even more preferably 55-70% by mass, and particularly preferably 58-65% by mass. When the solvent content is within the above-mentioned preferred range, the metal removal performance of the cleaning solution will be easily improved. <Strong Acids Liquid at 20°C> In this embodiment, the strong acid is only required to be liquid at 20°C, and there is no particular limitation. Preferably, the strong acid is one with a pKa of 2 or less. In this embodiment, the pKa value of the strong acid is calculated using the SPARC pKa calculation method. As a strong acid, it is preferably an organic acid selected from at least one of the group consisting of sulfuric acid (pKa: 0.81), phosphoric acid (pKa: 1.75), methanesulfonic acid (pKa: 0.42), phosphonic acid (pKa: 1.76), trifluoroacetic acid (pKa: 1.14), and trifluoromethanesulfonic acid (pKa: 0.98), and more preferably at least one of the group consisting of methanesulfonic acid, trifluoroacetic acid, phosphoric acid, and phosphonic acid. Among these, phosphoric acid is particularly preferred as a strong acid because semiconductor-grade materials are abundant, and compared to other acids, it has weaker odor and corrosiveness. In the cleaning solution of this embodiment, the content of strong acid relative to the total mass (100% by mass) of the cleaning solution is preferably 0.05 to 3% by mass, more preferably 0.07 to 2.75% by mass, even more preferably 0.08 to 2.5% by mass, and particularly preferably 0.09 to 2.1% by mass. When the content of strong acid is within the above-mentioned preferred range, the metal removal performance of the cleaning solution will be easily improved. <Other Components> Without impairing the effects of the present invention, in addition to the components described above, the cleaning solution of this type may also contain other components (hereinafter also referred to as "additives"). Examples of additives include organic acids other than the strong acids described above, inorganic fluorine acids, tetraalkylammonium compounds, surfactants, etc. Examples of organic acids include carboxylic acids such as acetic acid, formic acid, citric acid, oxalic acid, 2-nitrophenylacetic acid, 2-ethylhexanoic acid, and dodecanoic acid; glycolic acids such as ascorbic acid, tartaric acid, and glucuronic acid; sulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid; and phosphate esters such as bis(2-ethylhexyl)phosphoric acid, preferably organic acids that are liquid at room temperature such as acetic acid, formic acid, 2-ethylhexanoic acid, glucuronic acid, and bis(2-ethylhexyl)phosphoric acid. Examples of inorganic fluorine acids include hexafluorosilicic acid, hexafluorophosphate, and fluoroboric acid. Examples of tetraalkylammonium compounds include tetramethylammonium fluoride, tetrabutylammonium fluoride, and tetrabutylammonium fluorosilicate. Examples of surfactants include polyoxyalkylene alkylphenyl ether surfactants, polyoxyalkylene alkyl ether surfactants, block polymer surfactants composed of polyethylene oxide and polypropylene oxide, polyoxyalkylene distyrene phenyl ether surfactants, polyoxyalkylene tribenzylphenyl ether surfactants, and acetylene polyoxyalkylene surfactants. Acetic acid is preferred as an additive. Each additive may be used individually or in combination of two or more. If the cleaning solution of this embodiment contains additives, the content of the additives is preferably 1-60% by mass, more preferably 1-50% by mass, and even more preferably 1-45% by mass relative to the total mass (100% by mass) of the cleaning solution. If the cleaning solution of this embodiment contains acetic acid as an additive, the content of acetic acid relative to the total mass of the cleaning solution is preferably 30-45% by mass, more preferably 35-44% by mass, and even more preferably 37-43% by mass. When the content of acetic acid is within the above-mentioned preferred range, the metal removal performance of the cleaning solution will be easily improved. The cleaning solution of this embodiment can be a cleaning solution consisting only of a solvent, a strong acid, acetic acid, and unavoidable impurities (hereinafter also referred to as "cleaning solution A"). In cleaning solution A, the solvent content relative to the total mass (100% by mass) is preferably 45-80% by mass, more preferably 50-75% by mass, even more preferably 55-70% by mass, and particularly preferably 58-65% by mass. Furthermore, in cleaning solution A, the strong acid content relative to the total mass (100% by mass) is preferably 0.05-3% by mass, more preferably 0.07-2.75% by mass, even more preferably 0.08-2.5% by mass, and particularly preferably 0.09-2.1% by mass. Furthermore, in cleaning solution A, the acetic acid content relative to the total mass (100% by mass) is preferably 30-45% by mass, more preferably 35-44% by mass, and even more preferably 37-43% by mass. If the content of solvent, strong acid and acetic acid in cleaning solution A is within the above-mentioned preferred range, the metal removal performance of the cleaning solution will be easily improved. If the cleaning solution A contains water as a solvent, the water content relative to the total mass (100% by mass) of the cleaning solution A is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. There is no particular limitation on the lower limit of the water content; for example, relative to the total mass (100% by mass) of the cleaning solution A, it can be 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more. When the water content in the cleaning solution A is within the above-mentioned preferred range, the metal removal performance of the cleaning solution will be easily improved. The cleaning solution of this embodiment can be a cleaning solution consisting only of solvent, phosphoric acid, acetic acid, and unavoidable impurities (hereinafter also referred to as "cleaning solution B"). In cleaning solution B, the solvent content relative to the total mass (100% by mass) of cleaning solution B is preferably 45-80% by mass, more preferably 50-75% by mass, even more preferably 55-70% by mass, and particularly preferably 58-65% by mass. Furthermore, in cleaning solution B, the phosphoric acid content relative to the total mass (100% by mass) of cleaning solution B is preferably 0.05-3% by mass, more preferably 0.1-2.75% by mass, even more preferably 0.5-2.5% by mass, and particularly preferably 0.8-2.1% by mass. Furthermore, in cleaning solution B, the content of acetic acid relative to the total mass (100% by mass) of cleaning solution B is preferably 30-45% by mass, more preferably 35-44% by mass, even more preferably 37-43% by mass, and particularly preferably 37.5-40% by mass. When the contents of solvent, phosphoric acid, and acetic acid in cleaning solution B are within the aforementioned preferred ranges, the metal removal properties of the cleaning solution will be easily improved. The cleaning solution of this embodiment may include carboxylic acids such as acetic acid, formic acid, citric acid, oxalic acid, 2-nitrophenylacetic acid, 2-ethylhexanoic acid, and dodecanoic acid; glycolic acids such as ascorbic acid, tartaric acid, and glucuronic acid; sulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid; phosphate esters such as bis(2-ethylhexyl)phosphoric acid; organic acids such as hexafluorosilicic acid, hexafluorophosphate, and fluoroboric acid; tetraalkylammonium compounds such as tetramethylammonium fluoride, tetrabutylammonium fluoride, and tetrabutylammonium fluorosilate; or may not contain at least one surfactant selected from the group consisting of polyoxyalkylene alkylphenyl ether surfactants, polyoxyalkylene alkyl ether surfactants, block polymer surfactants composed of polyethylene oxide and polypropylene oxide, polyoxyalkylene distyrene phenyl ether surfactants, polyoxyalkylene tribenzylphenyl ether surfactants, and acetylene polyoxyalkylene surfactants. <Metal Resistant> The cleaning solution related to this embodiment is used to clean the metal resist. There are no particular limitations on the metal resist, and examples include at least one metal selected from the group consisting of Sn, Bi, Hf, Zr, In, Te, Sb, Ni, Co, Ti, W, Ta and Mo. The cleaning solution of this embodiment, as described above, contains a strong acid that is liquid at 20°C as its acid component. This enhances metal removal while suppressing precipitation during drying, thus reducing organic residue. In this embodiment, since the strong acid is liquid at room temperature, unlike solid acids such as oxalic acid and benzenesulfonic acid, it does not precipitate during drying. Furthermore, in this embodiment, the strong acid has a lower pKa than acetic acid, resulting in sufficient metal removal. Moreover, by including the strong acid in a solution diluted 10 times with pure water using a pH meter, the pH value of the resulting liquid is measured to be below 2.5, ensuring sufficient metal removal. Therefore, by using the cleaning solution of this embodiment, contamination of the process equipment can be prevented while achieving excellent metal removal performance. (Cleaning Method) The second aspect of the present invention is a cleaning method, which includes a step of cleaning an object with metal resist adhering to it using a cleaning liquid related to the first aspect described above (hereinafter sometimes simply referred to as the "cleaning step"). There is no particular limitation on the object to which the metal resist is applied; examples include a support with a metal resist and a process apparatus with a metal resist applied. Among these, a support with a metal resist is preferred as the object to which the metal resist is applied. There are no particular limitations on the support structure; any known type can be used, such as a substrate for electronic components or a substrate on which a specific wiring pattern is formed. More specifically, examples include metal substrates such as silicon wafers, copper, chromium, iron, and aluminum, or glass substrates. Regarding the metal inhibitor, it is the same as the metal inhibitor described in the cleaning solution related to the first state mentioned above. There are no particular limitations on the method of forming the metal resist. For example, the specifications in U.S. Patent No. 9,176,377B2, U.S. Patent Application Publication No. 2013 / 0224652, U.S. Patent No. 9,310,684, U.S. Patent Application Publication No. 2016 / 0116839, Jiang, Jing; Chakrabarty, Souvik; Yu, Mufei; et al., “Metal Oxide Nanoparticle Photoresists for EUV Patterning”, Journal of Photopolymer Science and Technology 27(5), 663-6662014, A Platinum-Fullerene Complex for Patterning Metal Containing Nanostructures, DXYang, A. Frommhold, DS He, ZYLi, RE Palmer, MA Lebedeva, TW Chamberlain, AN Khlobystov, APG Robinson, Proc SPIEA Advanced Lithography, Metal resists and patterning methods described in U.S. Patent Application Publication No. 2009 / 0155546 and U.S. Patent Application Publication No. 6,566,276, etc. Furthermore, as a method for forming metal inhibitors, a film-forming method for depositing a film containing metal oxides on a support by means of vapor phase growth, as described in Japanese Patent Application Publication Nos. 2015-201622 and Japanese Patent Application Publication Nos. 2020-84330, can be used. In this embodiment, the cleaning step is not particularly limited, and known cleaning methods in semiconductor manufacturing processes such as edge bead removal and back-side rinsing can be cited. In this embodiment, the cleaning step preferably includes applying the aforementioned cleaning solution related to the first embodiment along the periphery of the support to remove edge beads (hereinafter sometimes referred to as "edge rinsing") on the support containing the metal resist. The edge rinsing method is not particularly limited as long as it is a conventionally known process, such as the method described in International Publication No. 2018 / 031896. There is no particular limitation on the number of edge rinsing cycles; 1 to 20 cycles can be performed. Furthermore, two or more cleaning solutions can be used in edge rinsing. During edge rinsing, the drip volume of the cleaning solution is preferably 0.05 to 50 mL, more preferably 0.075 to 40 mL, and even more preferably 0.1 to 25 mL. In other embodiments, during edge rinsing, the flow rate of the cleaning solution is preferably 5 mL / min to 50 mL / min, and the spraying time is preferably 1 second to 5 minutes, and more preferably 5 seconds to 2 minutes. To evaluate the metal removal capability by edge flushing, residual metal on the support can be examined. Commercially available methods suitable for evaluating trace metals generally include inductively coupled plasma mass spectrometry (ICP-MS). To evaluate the support surface, vapor phase decomposition-inductively coupled plasma mass spectrometry (VPD-ICP-MS) can be used. This technique can be used to determine residual metal per unit area along the periphery of the wafer surface. In this embodiment, if the metal resist is a Sn-based resist, the amount of residual Sn is preferably 75 × 10⁻⁶. 10 atoms / cm 2 The following is also preferred: 70×10 10 atoms / cm 2 The following is preferred: 65×10 10 atoms / cm 2 The following is the optimal value: 60×10 10 atoms / cm 2 the following. According to the cleaning method described above for this embodiment, a cleaning solution containing a solvent and a strong acid that is liquid at 20°C is used to clean objects with adhering metal resists. This cleaning solution improves metal removal while inhibiting precipitation during drying, thus reducing organic residue and preventing contamination of the process equipment while providing excellent metal removal performance. [Example] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples. <Preparation of Cleaning Solution> (Examples 1-8, Comparative Examples 1-4) The components shown in Table 1 were mixed and the cleaning solutions of each example were prepared. In Table 1, each abbreviation symbol has the following meaning. Also, the values ​​represent the amount prepared (mass %). The pH of the cleaning solution in each example is the pH value of the liquid obtained by diluting each cleaning solution 10 times with pure water using a pH meter. PGMEA: Propylene glycol methyl ethyl acetate. <Evaluation of Sn Removal> 1.5 mL of organometallic tin oxide hydroxide resist (Inpria) was coated onto a Si wafer by spin coating at 2000 rpm for 60 seconds to form a Sn resist film. Next, 25 mL of the cleaning solution for each example was coated onto the Si wafer with the Sn resist film, and the wafer was spin-coated at 500 rpm for 25 seconds until dry. Then, 5 mL of a 7 / 3 mass mixture of propylene glycol methyl ether (PGME) and propylene glycol methyl ethyl acetate (PGMEA) was coated, and the wafer was spin-coated at 500 rpm for 60 seconds until dry, followed by a post-rinse. Finally, the residual Sn amount (×10⁻¹⁰) was measured using vapor phase decomposition-inductively coupled plasma mass spectrometry (VPD-ICP-MS) with ChemTrace (registered trademark). 10 atoms / cm 2 The residual Sn amount in the cleaning solution of Comparative Example 2 was used as the baseline value of 100, and the relative value was used as the assessment of the residual Sn amount. The results are shown in Table 2. <Evaluation of Residual Organic Matter> The presence of residual organic matter on the substrate is assessed by visually inspecting the surface of the cleaned substrate and by measuring the thickness of the metal resist layer on the cleaned substrate using a spectrophotometer. The results shown in Table 2 confirm that, compared to the cleaning solution of Comparative Example 2, the cleaning solutions of Examples 1-8 have lower residual Sn levels, thus demonstrating good metal removal performance. It is also confirmed that the cleaning solutions of Examples 1-8 have reduced residual organic matter levels. <Evaluation of Zr Removability> The zirconium hard mask precursor solution was prepared by adding 1.2 g of 80% 1-butanol solution of zirconium(IV) butoxide to a mixed solvent of 38 g ethanol and 0.8 g acetone. 1.5 mL of the above zirconium hard mask precursor solution was coated onto a Si wafer, and a Zr-containing film was formed by spin coating at 2000 rpm for 60 seconds. Next, 25 mL of the cleaning solution from each example was coated onto the Si wafer with the Zr-containing film, and the wafer was spin-coated at 500 rpm for 25 seconds until dry. Afterwards, 5 mL of a mixed solution of propylene glycol methyl ether (PGME) and propylene glycol methyl ethyl acetate (PGMEA) in a 7 / 3 mass ratio was coated, and the wafer was spin-coated at 500 rpm for 60 seconds until dry, followed by a post-rinse. Next, the residual Zr content (×10⁻⁶) was measured using vapor phase decomposition-inductively coupled plasma mass spectrometry (VPD-ICP-MS) via ChemTrace (registered trademark). 10 atoms / cm 2 The residual Zr content of the cleaning solution from Comparative Example 2 was used as the baseline value of 100, and the relative value was used as the assessment of the residual Zr content. The results are shown in Table 3. Table 3 The results shown in Table 3 confirm that the residual Zr content of the cleaning solution in Example 3 is lower than that in Comparative Example 2, thus demonstrating good metal removal performance. It is also confirmed that the residual organic matter content of the cleaning solution in Example 3 is reduced. The preferred embodiments of the present invention have been described above, but the invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications may be made to the structure without departing from the spirit of the invention. The invention is not limited by the foregoing description, but only by the scope of the claims outlined in the appendix.

Claims

1. A cleaning solution, used for cleaning metal inhibitors, and composed solely of propylene glycol methyl ethyl acetate (PGMEA), a strong acid that is liquid at 20°C, and water as an arbitrary component, wherein... The content of the strong acid, which is liquid at 20°C, is 0.05 to 3% by mass relative to the total mass of the cleaning solution. The content of the water is less than 30% by mass relative to the total mass of the cleaning solution. The pKa of the strong acid is less than 2. The pH value of the liquid obtained by diluting the cleaning solution with pure water 10 times is less than 2.5, as measured by a pH meter.

2. A cleaning solution, used for cleaning metal inhibitors, and comprising only propylene glycol methyl ethyl acetate (PGMEA), a strong acid that is liquid at 20°C, acetic acid, and water as an arbitrary component, wherein... The content of the strong acid, which is liquid at 20°C, is 0.05 to 3% by mass relative to the total mass of the cleaning solution. The content of the water is 0.5 to 20% by mass relative to the total mass of the cleaning solution. The pKa of the strong acid is less than 2. The pH value of the liquid obtained by diluting the cleaning solution with pure water 10 times is less than 2.5, as measured by a pH meter.

3. The cleaning solution as requested in item 2, wherein, The content of the aforementioned acetic acid is 30-45% by mass relative to the total mass of the cleaning solution.

4. The cleaning solution as requested in item 1, wherein, The aforementioned strong acid includes at least one selected from the group consisting of methanesulfonic acid, trifluoroacetic acid, phosphoric acid, and phosphonic acid.

5. The cleaning solution as requested in item 1, wherein, The aforementioned strong acid includes phosphoric acid.

6. A cleaning method comprising the step of using the cleaning solution of claim 1 to clean an object to which a metal resist is attached.

7. As in the cleaning method described in request item 6, wherein, The aforementioned object is a support structure equipped with a metallic resist.

8. As in the cleaning method described in request item 7, wherein, The cleaning solution described in claim 1 is applied along the periphery of the aforementioned support and the edge beads on the aforementioned support are removed.