Solvent mixture

Abstract

The present disclosure provides a solvent mixture comprising an ionic liquid of Formula I: wherein each of R1, R2, R3, and R4is independently selected from the group consisting of hydrogen, -CH2-OH, and C1-C4 alkyl groups; and a glycol ether solvent of Formula II: wherein R5is selected from the group consisting of hydrogen and C1-C4 alkyl; R6is selected from the group consisting of -CH2- or -CH2-CH2-; R7is selected from the group consisting of hydrogen and C1-C2 alkyl; and n is an integer from 1 to 4.

Description

Technical Field

[0001] This disclosure relates generally to solvents, and more specifically to solvent mixtures for use as a substitute for N-methyl-2-pyrrolidone in electronic applications. Background Technology

[0002] N-Methyl-2-pyrrolidone (NMP) is one of the most widely used organic compounds due to its ideal combination of properties, including good solubility, low cost, and low viscosity. In the electronics industry, it is used as a solvent in a variety of applications, such as in stripping formulations for removing cured photoresists used in high-resolution patterns. It is also used in methods for the synthesis of photosensitive polyimide (PSPI), where it serves as a solvent to dissolve the monomers of PSPI to facilitate its polymerization.

[0003] However, in recent decades, NMP has received a declining reputation due to concerns about human health. For example, NMP is classified as "H360" under the Globally Harmonized Classification and Labelling System (GHS), meaning it "may impair fertility or the health of an unborn child." Consequently, some regulations restrict the use and / or amount of NMP in the aforementioned formulations. Therefore, there is a need in the art to find an alternative solvent that can maintain the performance of NMP while providing better environmental health and safety properties. Summary of the Invention

[0004] This disclosure provides a solvent, and more specifically, a solvent mixture for use as a substitute for N-methyl-2-pyrrolidone (NMP) in electronic applications. For decades, the search for alternatives to NMP has been a focus due to its potential health concerns. Several NMP alternatives have been developed, but their performance and cost have not yet been satisfactory for the electronics industry. Developing alternative solvents for NMP suitable for electronic applications has been a challenge due to the stringent requirements for balancing solvent toxicity and solubility. However, the solvent mixture disclosed herein addresses these shortcomings discussed herein and above.

[0005] For the purposes of this disclosure, the solvent mixtures of this disclosure comprise ionic liquids of formula I:

[0006] Each of R1, R2, R3, and R4 is independently selected from hydrogen, -CH2-OH, and C1-C4 alkyl groups; and the glycol ether solvent of formula II:

[0007] Wherein R5 is selected from the group consisting of hydrogen and C1-C4 alkyl groups; R6 is selected from the group consisting of -CH2- or -CH2-CH2-; R7 is selected from the group consisting of hydrogen and C1-C2 alkyl groups; and n is an integer from 1 to 4. For this disclosure, the ionic liquid of formula I is formed in a one-step acid-base neutralization reaction between an organic acid and an organic base. For this disclosure, the organic acid is selected from the group consisting of glycolic acid, lactic acid, acetic acid, formic acid, citric acid, tartaric acid, malic acid, oxalic acid, benzoic acid, salicylic acid, propionic acid, and combinations thereof; and the organic base is selected from the group consisting of monoethanolamine (MEA), monoisopropanolamine (MIPA), N-methylethanolamine (NMEA), triethylamine (TEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and combinations thereof. For this disclosure, for the one-step acid-base neutralization reaction, the molar ratio of the organic acid and organic base used to form the ionic liquid of formula I is from 1:1 to 1:4.

[0008] For the purposes of this disclosure, the glycol ether solvent of Formula II includes two or more glycol ether solvents of Formula II. In one embodiment, for the first glycol ether solvent of the two or more glycol ether solvents of Formula II, R6 is -CH2- and R7 is hydrogen, and for the second glycol ether solvent of the two or more glycol ether solvents of Formula II, R6 is -CH2- and R7 is C1 alkyl.

[0009] For the purposes of this disclosure, the ionic liquid of Formula I and the glycol ether solvent of Formula II have a mass ratio of 1:1 to 1:4. For the purposes of this disclosure, when n in Formula II is equal to 4, the mass ratio of the ionic liquid of Formula I to the glycol ether of Formula II is 1:1. For the purposes of this disclosure, when n in Formula II is 1 to 3, the mass ratio of the ionic liquid to the glycol ether solvent is 2:3 to 1:4.

[0010] For the purposes of this disclosure, when n is 2 for the glycol ether solvent of Formula II and the ionic liquid of Formula I is formed from glycolic acid and MIPA in a 2:3 molar ratio, the mass ratio of the ionic liquid to the glycol ether solvent in the solvent mixture is 1:4. For the purposes of this disclosure, the solvent mixture is free of heteroatoms, wherein the definition of heteroatoms includes halogen atoms. In other words, the solvent mixture contains no halogen atoms, and only carbon, hydrogen, oxygen, and nitrogen are present in the solvent mixture.

[0011] This disclosure also includes a method comprising: providing a surface having a photoresist layer; and peeling at least a portion of the photoresist layer from the surface using a solvent mixture of the present disclosure. For the purposes of this disclosure, the photoresist layer is selected from a layer formed of a photosensitive polyimide layer, a phenolic resin layer, an acrylic layer, or a combination thereof. This disclosure also includes another method: providing a solvent mixture of the present disclosure; and dissolving monomers used to form the photoresist layer using the solvent mixture. For the purposes of this disclosure, the monomers used to form the photoresist layer are selected from monomers used to form a photosensitive polyimide layer. Attached Figure Description

[0012] Figure 1 Demonstration of qualified and unqualified photoresist stripping performance according to this disclosure is provided.

[0013] Figure 2 A diagram of the PSPI monomer dissolution evaluation performed according to this disclosure is provided, and evaluation results of negligible, partial dissolution, and dissolution are presented. Detailed Implementation

[0014] This disclosure provides a solvent, and more specifically, a solvent mixture for replacing N-methyl-2-pyrrolidone (NMP) in electronic applications, such as electronic processing, particularly photoresist stripping, including photosensitive polyimide synthesis (PSPI) and its stripping. For decades, the search for alternatives to NMP has been a focus due to its potential health concerns. Several NMP alternatives have been developed, but their performance and cost have not been satisfactory for the electronics industry. Developing alternative solvents for NMP suitable for electronic applications has been a challenge due to the stringent requirements of balancing solvent toxicity and solubility. However, the solvent mixture of this disclosure addresses these shortcomings discussed herein and above.

[0015] For the purposes of this disclosure, the solvent mixtures of this disclosure comprise ionic liquids of formula I:

[0016] Each of R1, R2, R3, and R4 is independently selected from hydrogen, -CH2-OH, and C1-C4 alkyl groups; and the glycol ether solvent of formula II:

[0017] Wherein R5 is selected from the group consisting of hydrogen and C1-C4 alkyl groups; R6 is selected from the group consisting of -CH2- or -CH2-CH2-; R7 is selected from the group consisting of hydrogen and C1-C2 alkyl groups; and n is an integer from 1 to 4. For the purposes of this disclosure, in specific embodiments of the ionic liquid of formula I, R1 is selected from hydrogen and C1 alkyl groups; R2 is hydrogen, and R3 is selected from hydrogen and C1 alkyl groups. For example, for the ionic liquid of formula I, R1, R2, and R3 are hydrogen. Alternatively, for the ionic liquid of formula I, R1 and R2 are hydrogen, and R3 is a C1 alkyl group. In another embodiment, for the ionic liquid of formula I, R1 is a C1 alkyl group, and R2 and R3 are hydrogen. Similarly, for the purposes of this disclosure, specific embodiments of R4 in the ionic liquid of formula I may be C1 alkyl groups or hydrogen. Other structures of the ionic liquid of formula I are possible as provided herein. For the purposes of this disclosure, specific examples of glycol ether solvents of formula II may include those wherein R5 is a C2 alkyl group, R6 is -CH2-, R7 is hydrogen, and n is 2. In another example, R5 is a C3 alkyl group, R6 is -CH2-, R7 is a C1 alkyl group, and n is 1. In yet another example, R5 is a C4 alkyl group, R6 is -CH2-, R7 is a C1 alkyl group, and n is 1. Other structures of glycol ether solvents of formula II are possible as provided herein.

[0018] For the purposes of this disclosure, the ionic liquid of Formula I is formed in a one-step acid-base neutralization reaction between an organic acid and an organic base. For the purposes of this disclosure, the organic acid is selected from the group consisting of glycolic acid, lactic acid, acetic acid, formic acid, citric acid, tartaric acid, malic acid, oxalic acid, benzoic acid, salicylic acid, propionic acid, and combinations thereof. Preferably, the organic acid is selected from the group consisting of glycolic acid, lactic acid, and combinations thereof. For the purposes of this disclosure, the organic base is selected from the group consisting of monoethanolamine (MEA), monoisopropanolamine (MIPA), N-methylethanolamine (NMEA), triethylamine (TEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and combinations thereof. Preferably, the organic base is selected from the group consisting of MEA, NMEA, MIPA, and combinations thereof. For the purposes of this disclosure, preferred combinations of organic acid and organic base include, but are not limited to, lactic acid and NMEA; lactic acid and MIPA; lactic acid and MEA; glycolic acid and NMEA; and glycolic acid and MIPA.

[0019] The ionic liquid of this disclosure is prepared by mixing an organic acid and an organic base in a designed molar ratio. For example, the organic base can be slowly poured into the organic acid and mixed at room temperature (23°C), wherein the temperature of the resulting mixture can be controlled due to the exothermic nature of the acid-base neutralization reaction, as is known in the art. For this disclosure, for a one-step acid-base neutralization reaction, the molar ratio of the organic acid and organic base used to form the ionic liquid of formula I can be from 1:1 to 1:4 (organic acid:organic base). Preferably, for a one-step acid-base neutralization reaction, the molar ratio of the organic acid and organic base used to form the ionic liquid of formula I can be from 1:1 to 1:2 (organic acid:organic base). Particularly preferred molar ratios include 1:1, 1:1.5, and 1:2 (organic acid:organic base).

[0020] For the purposes of this disclosure, the glycol ether solvent of Formula II may be selected from the group consisting of: diethylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol mono-n-butyl ether, and combinations thereof. Other glycol ether solvents of Formula II are also possible. Commercially available examples of glycol ether solvents of Formula II include, but are not limited to, diethylene glycol monoethyl ether (DOW) and DOWANOL (trade name DOWANOL). ™ (DOW) sells diethylene glycol monoethyl ethers, such as propylene glycol n-propyl ether and propylene glycol n-butyl ether.

[0021] For the purposes of this disclosure, the glycol ether solvent of Formula II may optionally include two or more glycol ether solvents of Formula II. For example, in one embodiment, for the first glycol ether solvent of two or more glycol ether solvents of Formula II, R6 is -CH2- and R7 is hydrogen, and for the second glycol ether solvent of two or more glycol ether solvents of Formula II, R6 is -CH2- and R7 is C1 alkyl. Other combinations of two or more glycol ether solvents of Formula II are possible.

[0022] For the purposes of this disclosure, the solvent mixture can be formed by mixing an ionic liquid of Formula I as provided herein with a glycol ether solvent of Formula II as provided herein. As provided herein, the mixing can be carried out at room temperature, wherein the resulting solvent mixture can be allowed to stand at room temperature to allow any bubbles formed to dissipate until it is used. For embodiments of the solvent mixture, the ionic liquid of Formula I and the glycol ether solvent of Formula II can have a mass ratio of 1:1 to 1:4. For the purposes of this disclosure, this mass ratio of the ionic liquid of Formula I to the glycol ether solvent of Formula II for the solvent mixture can preferably depend on the values ​​of the variables in the ionic liquid of Formula I and the glycol ether solvent of Formula II. For example, when n in Formula II is equal to 4, the mass ratio of the ionic liquid of Formula I to the glycol ether of Formula II is 1:1. In another embodiment, when n in Formula II is 1 to 3, the mass ratio of the ionic liquid to the glycol ether solvent is 2:3 to 1:4. In one or even more specific embodiments, when n of the glycol ether solvent of Formula II is 2, and the ionic liquid of Formula I is formed from glycolic acid and MIPA in a 2:3 molar ratio, the mass ratio of the ionic liquid to the glycol ether solvent in the solvent mixture is 1:4.

[0023] For the purposes of this disclosure, the solvent mixture is free of heteroatoms. As used herein, a heteroatom is defined as any atom that is not carbon, hydrogen, oxygen, or nitrogen, and may include sulfur, phosphorus, lithium, magnesium, and halogen atoms such as fluorine, chlorine, bromine, and iodine. In other words, the solvent mixture is free of halogen atoms, and only carbon, hydrogen, oxygen, and nitrogen are present in the solvent mixture.

[0024] For the purposes of this disclosure, the solvent mixtures may optionally comprise one or more of the following: polyglycols, ethylene glycol ethers, and / or propylene glycol ethers. Examples of suitable polyglycols include, but are not limited to, triethylene glycol and tetraethylene glycol. Examples of suitable ethylene glycol ethers include, but are not limited to, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol phenyl ether, ethoxytriethylene glycol, and methoxytriethylene glycol. Examples of suitable ethylene glycol ethers include, but are not limited to, propylene glycol n-propyl ether, propylene glycol n-butyl ether, propylene glycol phenyl ether, dipropylene glycol n-propyl ether, and dipropylene glycol n-butyl ether.

[0025] This disclosure also includes a method comprising: providing a surface having a photoresist layer, and stripping at least a portion of the photoresist layer from the surface using a solvent mixture of the present disclosure. For the purposes of this disclosure, the photoresist layer is selected from a layer formed of a photosensitive polyimide layer, a phenolic resin layer, an acrylic layer, or a combination thereof. For the purposes of this disclosure, the photoresist-containing surface as provided herein may be contacted with the solvent mixture for a period of time, ranging from 30 seconds to 30 minutes; 30 seconds to 2 minutes; or 2 minutes to 30 minutes. The photoresist-containing surface may be contacted with the solvent mixture at temperatures ranging from 20°C to 70°C; 20°C to 50°C; or 20°C to 35°C. Substrates cleaned according to this method are also possible, with surfaces being wafer-type semiconductor substrates, as known in the art.

[0026] This disclosure may also include the use of solvent mixtures of this disclosure to remove unwanted materials from a surface. Undesirable materials can be any material that interferes with the final function of the surface. When the surface comprises a semiconductor substrate (e.g., a wafer), unwanted materials may include, for example, resist residues or metal ions. In addition to being used to remove photoresist layers, the solvent mixtures of this disclosure can also be used in etching, ashing, and / or wet chemical applications to remove photoresist and / or etching residues. Furthermore, the solvent mixtures of this disclosure can be used in applications such as coating, electroplating, imaging, surface treatment, processing, cleaning, and sterilization. While the solvent mixtures of this disclosure are readily applicable to the semiconductor industry, their use is not limited to any particular industry but can be applied to a variety of technical fields requiring the removal of contaminants at an extremely fine scale (e.g., near the molecular level). The methods of this disclosure may also include cleaning organic and inorganic compounds from semiconductor substrates, including post-etching and post-ashing residues.

[0027] This disclosure also includes another method: providing the solvent mixture of this disclosure; and dissolving the monomers used to form the photoresist layer with the solvent mixture. For the purposes of this disclosure, the monomers used to form the photoresist layer are selected from monomers known in the art for forming photosensitive polyimide layers. Other monomers are also possible, including monomers for forming phenolic resin layers or acrylic layers. For example, the solvent mixture claimed herein exhibits good performance in dissolving monomers used for the synthesis of photosensitive polyimide (PSPI). Therefore, the solvent mixture of this disclosure can be used for the synthesis of PSPI and the removal of PSPI in photolithography processes.

[0028] Some embodiments of this disclosure will now be described in detail in the following examples.

[0029] Example

[0030] In the embodiments, various terms and names for materials are used, including, for example, the following:

[0031] Material

[0032] The materials used in the embodiments and / or comparative examples include the following.

[0033] Table 1

[0034] Product Formula

[0035] Comparative Example 1 (CE1) is NMP, CE2 is diethylene glycol monoethyl ether, and CE3 is propylene glycol n-propyl ether. Other CEs and Examples (IEs) provided herein are mixtures of ionic liquids and glycol ether solvents as provided in Tables 2A to 2D. Ionic liquids are prepared by mixing different organic acids with different amines provided in Tables 2A to 2D.

[0036] Table 2A - Formulations of Comparative Examples (CE) and Examples of the Invention (IE)

[0037] Table 2B - Formulations for CE and IE

[0038] Table 2C - Formulations for CE and IE

[0039] Table 2D - Formulations for CE and IE

[0040] Preparation of ionic liquids

[0041] Ionic liquids were prepared by mixing organic acids and organic bases in the designed molar ratios provided in Tables 2A to 2D. Specifically, amines were slowly poured into organic acids at room temperature (23°C) with constant stirring. During this process, the temperature of the system increased due to the exothermic nature of acid-base neutralization. The ionic liquids were then cooled to room temperature for further experiments.

[0042] Preparation of solvent mixtures

[0043] The designed amount of glycol ether solvent was added to the ionic liquid, and a solvent mixture was prepared by mixing. After preparation, the solvent mixture was allowed to stand at room temperature until the bubbles disappeared.

[0044] Evaluation of photoresist peeling performance

[0045] 3 mL of SFP-1400 photoresist solution was dropped onto the surface of a glass substrate (100 mm × 100 mm × 1 mm). The glass substrate was spin-coated with the photoresist solution at 500 rpm for 10 seconds (SSUS MicroTech LabSpin 6 / 8, with a SUSS MicroTec HP8 used for pre-backing). The spin speed was then increased to 1000 rpm and held for 30 seconds to obtain a 1 μm thick photoresist film. The photoresist film was heated at 130 °C (Thermo SCIENTIFIC Heratherm OMH100) for 10 minutes under a dry nitrogen (N2) atmosphere to completely evaporate the solvent and cure the photoresist film. Then, approximately 100 μL of each prepared solvent was dropped onto the photoresist film at room temperature. The glass substrate was gently shaken during testing, and the time for complete removal of the photoresist was recorded. For the purposes of this disclosure, the stripping time 40s is considered acceptable.

[0046] PSPI monomer solubility evaluation

[0047] PSPI monomers consist of dianhydrides and diamines. Their structures are shown below:

[0048] To evaluate the solubility of the two monomers, 2,500 g of solvent was dispensed into a glass vial. Then, 0.125 g of the dianhydride monomer and 0.125 g of the diamine monomer were added to the solvent mixture and shaken to disperse evenly. The entire system was then placed in a 65°C oven for 2 hours (h), after which any residue was observed. Based on performance, results were categorized into three levels: negligible (Neg.), partially dissolved (PD), and dissolved (Dis.). Only results showing "dissolved" were acceptable.

[0049] Evaluation criteria

[0050] Figure 1 The peeling performance of qualified and unqualified photoresist was demonstrated. Regarding the evaluation of PSPI monomer dissolution... Figure 2 Results for negligible, partial, and complete dissolution were presented. Of these states, only "complete dissolution" was considered acceptable. For the evaluation of photoresist stripping performance, a result within 40 seconds was achieved. Figure 1 The state shown above is acceptable. If the state is displayed after 40 seconds... Figure 1 If it is located on the lower side, then it should be considered unqualified.

[0051] Photoresist peeling performance

[0052] Table 3A - Photoresist stripping performance for each embodiment

[0053] Table 3B - Photoresist stripping performance for each embodiment

[0054] Table 3C - Photoresist stripping performance for each embodiment

[0055] Table 3C (continued). Photoresist stripping performance for each embodiment.

[0056] PSPI monomer solubility

[0057] Table 4. PSPI monomer solubility performance for each embodiment

[0058] Table 4 (continued). PSPI monomer solubility performance for each example

[0059] Table 4 (continued). PSPI monomer solubility performance for each example

[0060] Data Analysis

[0061] Evaluation criteria

[0062] In this disclosure, the developed solvent mixture is applied in the field of electronic processing. More specifically, the solvent mixture is used for photoresist stripping and the synthesis or stripping of photosensitive polyimides. Therefore, performance evaluation should be applicable to both applications.

[0063] While not wishing to be bound by theory, it is believed that (1) the use of ionic liquids as defined herein to increase the polarity of the glycol ether solvents provided herein, and (2) the generally high viscosity of ionic liquids, allows the viscosity of the solvent mixture to be adjusted to an acceptable level to achieve good performance when the glycol ether solvents provided herein are mixed with the ionic liquids. The viscosity of each embodiment is summarized in Table 5 below:

[0064] Table 5A Viscosity of CE

[0065] Table 5B Viscosities of CE and IE

[0066] Table 5C IE

[0067] Viscosity measurement of solvent mixtures

[0068] Viscosity measurements were performed at room temperature (22°C) on the Hamilton Microlab Star (manufactured by Hamilton Robotics, inc., Reno, NV). This is a high-throughput liquid processor with eight independent channels that uses air displacement for aspiration and dispensing of liquids and uses differential pressure sensors to continuously monitor the pressure within the pipette tips. Specifically, 1.00 g of each solvent mixture was transferred to glass vials and placed in 96-well plates. The samples were then sent to the Hamilton Microlab Star for testing. Results were read on the screen after 20 minutes of testing.

[0069] For photoresist stripping applications, the results are shown in Table 3. It can be seen that the stripping performance gradually improves with increasing solvent mass ratio. When the mass ratio of ionic liquid to glycol ether solvent reaches 1:4, the performance is comparable to NMP. Furthermore, diethylene glycol monoethyl ether exhibits the best performance compared to other glycol ether solvents. This result is believed to be mainly attributable to two reasons. First, when complexed with a glycol ether solvent, the ionic liquid is diluted, and the viscosity decreases (Table 5). Therefore, increasing the amount of glycol ether solvent gradually reduces the viscosity of the system and improves the stripping performance. Second, the polarity of the photoresist applied in this disclosure is close to that of diethylene glycol monoethyl ether. However, complexation with the ionic liquid increases the polarity of the system. According to the principle of "like dissolves like," the smaller the mass ratio of the ionic liquid, the better the stripping performance should be.

[0070] Table 4 presents the results regarding the solubility of PSPI monomers. The addition of ionic liquids significantly improves solubility compared to pure glycol ether solvents. Furthermore, ionic liquids composed of lactic acid and amines exhibit better performance than glycolic acid. The preferred amine selection is NMEA > MIPA > MEA. For solvent selection, optimal performance is achieved when using diethylene glycol monoethyl ether and tetraethylene glycol. Ethylene glycol-based solvents offer better overall performance than propylene glycol-based solvents.

[0071] As previously stated, the solvent mixture should exhibit good photoresist stripping and PSPI monomer dissolution properties. Therefore, some good results in Tables 3 and 4 are classified as "Comparative Examples." Only samples demonstrating good performance in both applications can be classified as "Examples of the Invention."

Claims

1. A solvent mixture, said solvent mixture comprising: Ionic liquids of formula I: Each of R1, R2, R3, and R4 is independently selected from hydrogen, -CH2-OH, and C1-C4 alkyl groups; and Diol ether solvent of formula II: R5 is selected from the group consisting of hydrogen and C1-C4 alkyl groups; R6 is selected from the group consisting of -CH2- or -CH2-CH2-; R7 is selected from the group consisting of hydrogen and C1-C2 alkyl groups; and n is an integer from 1 to 4.

2. The solvent mixture according to claim 1, wherein the ionic liquid of formula I is formed in a one-step acid-base neutralization reaction between an organic acid and an organic base.

3. The solvent mixture according to claim 2, wherein the organic acid is selected from the group consisting of glycolic acid, lactic acid, acetic acid, formic acid, citric acid, tartaric acid, malic acid, oxalic acid, benzoic acid, salicylic acid, propionic acid, and combinations thereof; and The organic base is selected from the group consisting of monoethanolamine (MEA), monoisopropanolamine (MIPA), N-methylethanolamine (NMEA), triethylamine (TEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and combinations thereof.

4. The solvent mixture according to any one of claims 2 to 3, wherein for the one-step acid-base neutralization reaction, the molar ratio of the organic acid to the organic base is 1:1 to 1:

4.

5. The solvent mixture according to any one of claims 1 to 4, wherein the glycol ether solvent comprises two or more glycol ether solvents of formula II.

6. The solvent mixture according to claim 5, wherein for the first glycol ether solvent of two or more glycol ether solvents of formula II, R6 is -CH2- and R7 is hydrogen, and for the second glycol ether solvent of two or more glycol ether solvents of formula II, R6 is -CH2- and R7 is C1 alkyl.

7. The solvent mixture according to any one of claims 1 to 6, wherein the ionic liquid and the glycol ether solvent in the solvent mixture have a mass ratio of 1:1 to 1:

4.

8. The solvent mixture according to any one of claims 1 to 7, wherein when n in formula II is equal to 4, the mass ratio of the ionic liquid to the glycol ether solvent is 1:

1.

9. The solvent mixture according to any one of claims 1 to 7, wherein when n in formula II is 1 to 3, the mass ratio of the ionic liquid to the glycol ether solvent is 2:3 to 1:

4.

10. The solvent mixture according to any one of claims 1 to 7, wherein n is 2 for formula II, and the ionic liquid is formed from glycolic acid and MIPA in a 2:3 molar ratio, wherein the mass ratio of the ionic liquid to the glycol ether solvent in the solvent mixture is 1:

4.

11. The solvent mixture according to any one of claims 1 to 10, wherein the solvent mixture is free of heteroatoms.

12. A method, the method comprising: Provides a surface with a photoresist layer; as well as At least a portion of the photoresist layer is stripped from the surface using a solvent mixture according to any one of claims 1 to 11.

13. The method of claim 12, wherein the photoresist layer is selected from a layer formed of a photosensitive polyimide layer, a phenolic resin layer, an acrylic layer, or a combination thereof.

14. A method comprising: Provide a solvent mixture according to any one of claims 1 to 11; as well as The monomers used to form the photoresist layer are dissolved in the solvent mixture.

15. The method of claim 14, wherein the monomer used to form the photoresist layer is selected from monomers used to form the photosensitive polyimide layer.

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