Anti-reflection coating for photoresist and preparation method of anti-reflection coating

Abstract

The invention belongs to the technical field of anti-reflection coatings, and particularly relates to an anti-reflection coating for photoresist and a preparation method of the anti-reflection coating. The coating comprises perfluoropolyether-polyhedral oligomeric silsesquioxane, the structural formula of the coating is # imgabs0 #, R is CH2CH (CH3) 2, and n is equal to (3-6). The preparation method of the coating comprises the following steps: dissolving perfluoropolyether-polyhedral oligomeric silsesquioxane in a solvent to prepare a solution, stirring at room temperature for 24 hours, filtering, coating, removing the solvent, crosslinking and curing to form the coating. By introducing an inorganic-organic hybrid skeleton and a rigid cage structure in a POSS structure and a fluorocarbon chain of perfluoropolyether, the thermal stability, hydrophobicity and etching resistance of the coating are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coating preparation, and particularly relates to an anti-reflective coating for photoresist and a preparation method thereof. Background Art

[0002] During the photolithography process, when light passes through the photoresist and strikes the substrate, some of the light is reflected back into the photoresist, creating a standing wave effect and reflection interference. This standing wave effect can cause uneven light intensity distribution in the exposed area of ​​the photoresist, leading to blurred and distorted pattern edges. Reflection interference can also cause overexposure or abnormal exposure of the photoresist.

[0003] As integrated circuits continue to increase in density and linewidths shrink, the demand for photolithographic precision is becoming increasingly stringent, and the use of anti-reflective coatings (ARCs) is becoming increasingly widespread and critical. In advanced logic chip manufacturing (such as 7nm and 5nm processes) and memory chip manufacturing (such as NAND and DRAM), AR coatings are crucial materials for ensuring lithographic pattern accuracy, improving device performance and yield. They are also used in lithographic processes in the manufacturing of microelectromechanical systems (MEMS) and optoelectronic devices.

[0004] However, at present, most of them are made of organic polymers, and the chemical bond energy in the molecular chain is relatively low. For example, common nitrogen-containing heterocyclic polymers, phenolic resin polymers, etc., their molecular chains are subjected to high temperatures (baking, post-exposure baking and other steps in the photolithography process, the temperature can reach 100-200 ° C), the chain segment movement is intensified, and the chemical bonds are prone to breakage or rearrangement, resulting in thermal decomposition, carbonization or structural deformation of the coating, which reduces the anti-reflective performance and impairs the accuracy of the photolithography pattern. In addition, organic polymers are highly soluble in certain chemical solvents (developers, etchants, etc. in the photolithography process). Some organic anti-reflective coatings based on acrylates will undergo a hydrolysis reaction of the ester group in an alkaline developer, causing the coating to gradually dissolve, resulting in a reduction in the thickness of the anti-reflective coating, damage to the structure, and an inability to effectively suppress light reflection, thereby reducing the accuracy of the photolithography pattern transfer.

[0005] In view of the above-mentioned deficiencies, the present invention improves the two major pain points of the existing anti-reflective coating for photoresist, namely insufficient thermal stability and poor resistance to chemical solvents. Summary of the Invention

[0006] The present invention provides an anti-reflective coating for photoresist and a preparation method thereof. The coating contains perfluoropolyether-cage silsesquioxane (structural formula shown in formula I), wherein R=CH2CH(CH3)2 and n=(3-6).

[0007]

[0008] Furthermore, the method for preparing the coating comprises the following steps:

[0009] Perfluoropolyether-cage silsesquioxane was dissolved in a mixed solvent of propylene glycol methyl ether acetate and cyclohexanone to prepare a solution, which was stirred at room temperature for 24 hours and then filtered twice with a 0.2 μm filter element; a spin coating process was used to remove the solvent, and the solution was cross-linked and cured to form a coating.

[0010] Furthermore, the mass ratio of propylene glycol methyl ether acetate and cyclohexanone is (7:3)-(8:2).

[0011] Furthermore, the spin coating process has a first stage rotation speed of 500-600 rpm and a time of 10-15 seconds, and a second stage rotation speed of 2500-3000 rpm and a time of 30-40 seconds, for example, initially 500 rpm / 5 seconds, accelerating to 3000 rpm / 30 seconds.

[0012] Furthermore, the solvent can be removed by heating, such as soft baking at 110-120° C. for 50-60 seconds.

[0013] Furthermore, the cross-linking curing temperature is 170-180° C., and the time is 90-100 seconds.

[0014] Preferably, the optimal solid content of the perfluoropolyether-cage silsesquioxane in the solution is 10-15 wt %.

[0015] Furthermore, the preparation method of the perfluoropolyether-cage silsesquioxane comprises the following steps:

[0016] (1) Preparation of hexafluoropropylene oxide: Solvent A and initiator were added to a reactor in proportion, stirred evenly, and hexafluoropropylene gas was introduced. After reacting for 1 hour, hexafluoropropylene oxide was separated by vacuum distillation and condensed in a cold trap to obtain a transparent liquid.

[0017] (2) Preparation of hexafluoropropylene oxide oligomers: Solvent B and catalyst were added to a dry reactor under nitrogen protection. After stirring, the temperature was lowered to -10°C, and hexafluoropropylene oxide gas was introduced. The reaction was stirred at 0.3 MPa for 4 hours. After the reaction was completed, the catalyst was removed by filtration, and the reaction was carried out under reduced pressure distillation. The fraction at 70-90°C was collected to obtain hexafluoropropylene oxide oligomers.

[0018] (3) Preparation of mercaptan-terminated hexafluoropropylene oxide oligomer: under nitrogen protection, hexafluoropropylene oxide oligomer and potassium thioacetate were added to dimethyl sulfoxide solvent in proportion, placed in a reactor, stirred evenly, and subjected to nucleophilic substitution reaction at 20-50°C for 6-7 hours. After the reaction, the generated potassium fluoride was removed by filtration, and the filtrate was distilled under reduced pressure to remove the solvent; the obtained product was then dissolved in methanol, sodium borohydride was added, and a reduction reaction was carried out at 0-30°C for 4 hours. After the reaction was completed, dilute hydrochloric acid was added for neutralization, and the product was extracted with an organic solvent. The product was separated and purified by distillation and column chromatography to obtain mercaptan-terminated hexafluoropropylene oxide oligomer.

[0019] (4) Preparation of monovinyl heptaisobutyl POSS: triethylamine and isobutyltrichlorosilane were added to a toluene solvent in proportion, stirred evenly, and then a mixed solution of vinyltrichlorosilane and water was slowly added dropwise to form a reaction system. The reaction was continued at 25°C-30°C with continuous stirring for 24 hours. After the reaction was completed, the generated ammonium chloride was filtered out, and the filtrate was distilled under reduced pressure to remove toluene. The residue was recrystallized with n-hexane, filtered, and dried to obtain monovinyl heptaisobutyl POSS.

[0020] (5) Preparation of perfluoropolyether-cage silsesquioxane: Thiol-terminated hexafluoropropylene oxide copolymer and monovinyl heptaisobutyl POSS were added to tetrahydrofuran solvent in a certain proportion and stirred evenly. Then, chloroplatinic acid-tetrahydrofuran solution was added as a catalyst to form a reaction system. The reaction was continued with stirring at 60-80°C for 8-12 hours. After the reaction was completed, the solvent tetrahydrofuran was removed by distillation under reduced pressure to obtain perfluoropolyether-cage silsesquioxane.

[0021] The preparation chemical reaction equation of the perfluoropolyether-cage silsesquioxane is as follows:

[0022]

[0023] Wherein, R=CH2CH(CH3)2, n=(3-6).

[0024] Preferably, the solvent A in step (1) is one of perfluoromethylcyclohexane and perfluorohexane, and the amount used is 3-4 times the mass of hexafluoropropylene.

[0025] Preferably, the initiator in step (1) is one of benzoyl peroxide, di-tert-butyl peroxide or azobisisobutyronitrile, and the amount of the initiator is 0.5%-1% of the mass of hexafluoropropylene.

[0026] Preferably, the solvent B in step (2) is one of diethylene glycol dimethyl ether and cyclopentane sulfone, and the amount of the solvent used is 3-5 times the mass of hexafluoropropylene oxide.

[0027] Preferably, the catalyst in step (2) is one of cesium fluoride (CsF) and tetrabutylammonium fluoride (TBAF), and the amount of the catalyst is 3%-5% by mass of fluoropropylene oxide.

[0028] Preferably, in step (3), the molar ratio of the hexafluoropropylene oxide oligomer to potassium thioacetate is 1:(1-1.5), the amount of DMSO used is 2-3 times the mass of the hexafluoropropylene oxide oligomer, the amount of sodium borohydride used is 1.5-2 times the mass of the product, and the amount of methanol used is 8-10 times the mass of the product.

[0029] Preferably, the molar ratio of isobutyltrichlorosilane to vinyltrichlorosilane in step (4) is (7-8):1; the amount of triethylamine used is 0.5-0.6 times the sum of the masses of isobutyltrichlorosilane and vinyltrichlorosilane; the amount of toluene used is (4-6) times the total mass of the chlorosilanes; and the amount of n-hexane used is (6-8) times the mass of the residual substance.

[0030] Preferably, the molar ratio of the mercaptan-terminated oligomer to the monovinyl heptaisobutyl POSS described in step (5) is (1.3-1.5): 1, the amount of tetrahydrofuran is 5-6 times the total mass of the reactants (the sum of the mass of the mercaptan-terminated oligomer and the monovinyl heptaisobutyl POSS), and the amount of chloroplatinic acid is 30-50ppm of the total mass of the reactants (the sum of the mass of the mercaptan-terminated oligomer and the monovinyl heptaisobutyl POSS).

[0031] The beneficial effects of the present invention are as follows: the present invention solves the problems of insufficient thermal stability and poor chemical solvent resistance of anti-reflective coatings for photoresists, by introducing an inorganic-organic hybrid skeleton and a rigid cage structure in a POSS structure to limit the thermal motion of molecular chain segments, reducing chain relaxation and slip at high temperatures, thereby significantly improving thermal stability; by introducing perfluoropolyether segments, the shielding effect of fluorine atoms is utilized to provide strong hydrophobicity and low surface energy, thereby improving the hydrolysis resistance to developer and the etching resistance in subsequent processes.

[0032] In addition, the fluorocarbon chain segments of perfluoropolyether give the coating extremely low surface energy to form a "fluorine repellent layer", which effectively resists the adsorption of photoresist residues, metal ions and organic matter (such as hydrocarbon volatiles), reducing the difficulty of the post-development cleaning step. The fluorine element also reduces the refractive index of the coating, which can accurately match the optical interface between the photoresist and the substrate, suppressing the reflectivity to <0.5%, significantly reducing the standing wave effect and graphic distortion caused by scattered light, and improving the lithography resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] like Figure 1 The infrared spectrum of the perfluoropolyether-cage silsesquioxane of Example 1 is shown in the range of 800-850 cm -Region 1 corresponds to the symmetrical stretching vibration absorption peak of the Si-O-Si bond, which is between 1000-1100 cm -1 The strong absorption peak in the region corresponds to the antisymmetric stretching vibration absorption peak of the Si-O-Si bond, which is at 1200-1300 cm -1 The absorption peak of the carbon-fluorine (CF) bond in the polyether segment appears at 1000-1100 cm - The peak in the 1 region corresponds to the absorption peak of carbon-oxygen (CO) bond, while the peak in the 600-700 cm -1 The peak appearing in the region corresponds to the absorption peak of the sulfur-carbon (SC) bond. The above results successfully illustrate the successful synthesis of the product. DETAILED DESCRIPTION

[0034] The technical solutions of the present invention are further explained below in conjunction with embodiments, and the technical solutions in the embodiments of the present invention are clearly and completely described.

[0035] Example 1

[0036] Preparation of thiol-terminated perfluoropolyether:

[0037] 53g of perfluoromethylcyclohexane was added to the reactor as a solvent, followed by the addition of 0.225g of benzoyl peroxide as an initiator. After stirring and dispersing evenly, 15g of hexafluoropropylene gas was introduced at 25°C and normal pressure, stirring was maintained and the reaction was carried out for 1 hour. After the reaction was completed, vacuum distillation was carried out at 10Kpa, and the gaseous product was introduced into a cold trap at -78°C. After condensation, a transparent hexafluoropropylene oxide liquid was obtained. Under nitrogen protection, 68g of diethylene glycol dimethyl ether was added to a dry 250mL reactor as a solvent, and 0.7g of cesium fluoride was added as a catalyst. After stirring was turned on to evenly disperse the catalyst, 17g of hexafluoropropylene oxide gas was introduced, the pressure in the reactor was controlled to be maintained at 0.3MPa, and the reaction was stirred for 4 hours. After the reaction, vacuum distillation was performed at 20 kPa, and the fraction at 70-90°C was collected to obtain hexafluoropropylene oxide oligomers. In a nitrogen-protected reactor, 50 g of hexafluoropropylene oxide oligomers with a molecular weight of 600, 14 g of potassium thioacetate, and 120 g of dimethyl sulfoxide (DMSO) were added and stirred at 40°C for 6 hours. After the reaction, the mixture was cooled to room temperature, the solids formed were filtered out, and the filtrate was vacuum distilled to remove DMSO at 60°C and 1 kPa. 10 g of the product was dissolved in 90 g of methanol, 18 g of sodium borohydride was added, and the temperature was controlled at 20°C for 4 hours. After the reaction was completed, 1 mol / L dilute hydrochloric acid was slowly added dropwise to pH 6. The mixture was extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and filtered. The dichloromethane was first evaporated from the filtrate under normal pressure, and low-boiling substances were then removed by vacuum distillation. Finally, silica gel column chromatography was performed to obtain the target product, thiol-terminated hexafluoropropylene oxide oligomers.

[0038] Preparation of monovinyl heptaisobutyl POSS:

[0039] In a four-necked flask protected by nitrogen, 250g of dry toluene was added as a solvent, followed by the addition of 38g of triethylamine and 60g of isobutyltrichlorosilane, and the mixture was stirred and mixed evenly. 8g of vinyltrichlorosilane and 3g of deionized water were prepared into a mixed solution, which was slowly added dropwise to the reaction system through a constant pressure dropping funnel within 1 hour. After the addition was complete, the reaction was stirred continuously at 25°C for 24 hours. After the reaction was completed, the solid was filtered and the filtrate was distilled under reduced pressure at 60°C and 1kPa to remove the toluene solvent. The residue was recrystallized with n-hexane, and the crystalline product was filtered and placed in a vacuum drying oven and dried at 50°C for 12 hours to obtain monovinyl heptaisobutyl POSS.

[0040] Preparation of perfluoropolyether-cage silsesquioxane:

[0041] In a 250mL three-necked flask protected by nitrogen, 100g of anhydrous tetrahydrofuran was added as a solvent. 11.8g of mercaptan-terminated hexafluoropropylene oxide oligomer (molecular weight 600) and 8.4g of monovinyl heptaisobutyl POSS were added to the flask and stirred for 30 minutes to dissolve it completely. Subsequently, 0.3ml of 0.005mol / L chloroplatinic acid-tetrahydrofuran solution was added as a catalyst, the reaction system was warmed to 70°C, and the stirring reaction was continued for 10 hours. After the reaction was completed, the tetrahydrofuran solvent was removed by distillation under reduced pressure. Perfluoropolyether-cage silsesquioxane was obtained.

[0042] Example 2

[0043] Preparation of thiol-terminated perfluoropolyether:

[0044] 45g of perfluorohexane as a solvent was added to a reactor, followed by 0.15g of benzoyl peroxide as an initiator. After stirring and dispersing evenly, 15g of hexafluoropropylene gas was introduced at 25°C and atmospheric pressure. Stirring was maintained and the reaction was allowed to proceed for 1 hour. After the reaction was completed, vacuum distillation was performed at 10kPa. The gaseous product was introduced into a cold trap at -78°C and condensed to obtain a transparent hexafluoropropylene oxide liquid. Under nitrogen protection, 51g of sulfolane as a solvent was added to a dry 250mL reactor, followed by 0.5g of tetrabutylammonium fluoride as a catalyst. After stirring to ensure uniform dispersion of the catalyst, 17g of hexafluoropropylene oxide gas was introduced. The pressure in the reactor was maintained at 0.3MPa, and the reaction was continued with stirring for 4 hours. After the reaction, vacuum distillation was performed at 20 kPa, and the fraction at 70-90°C was collected to obtain hexafluoropropylene oxide oligomers. In a nitrogen-protected reactor, 50 g of hexafluoropropylene oxide oligomers with a molecular weight of 600, 11 g of potassium thioacetate, and 100 g of dimethyl sulfoxide (DMSO) were added and stirred at 40°C for 6 hours. After the reaction, the mixture was cooled to room temperature, the solids formed were removed by filtration, and the filtrate was vacuum distilled at 60°C and 1 kPa to remove DMSO. 10 g of the product was dissolved in 80 g of methanol, 15 g of sodium borohydride was added, and the temperature was controlled at 20°C for 4 hours. After the reaction was completed, 1 mol / L dilute hydrochloric acid was slowly added dropwise to pH 6, and the mixture was extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and filtered. The dichloromethane was first evaporated from the filtrate under normal pressure, and low-boiling materials were removed by vacuum distillation. Finally, silica gel column chromatography was performed to obtain the target product, thiol-terminated hexafluoropropylene oxide oligomers.

[0045] Preparation of monovinyl heptaisobutyl POSS:

[0046] In a four-necked flask protected by nitrogen, 230g of dry toluene was added as a solvent, followed by the addition of 33g of triethylamine and 66g of isobutyltrichlorosilane, and the mixture was stirred and mixed evenly. 8g of vinyltrichlorosilane and 3g of deionized water were prepared into a mixed solution, which was slowly added dropwise to the reaction system through a constant pressure dropping funnel within 1 hour. After the addition was completed, the reaction was stirred continuously at 25°C for 24 hours. After the reaction was completed, the solid was filtered and the filtrate was distilled under reduced pressure at 60°C and 1kPa to remove the toluene solvent. The residue was recrystallized with n-hexane, and the crystalline product was filtered and placed in a vacuum drying oven and dried at 50°C for 12 hours to obtain monovinyl heptaisobutyl POSS.

[0047] Preparation of perfluoropolyether-cage silsesquioxane:

[0048] In a 250mL three-necked flask protected by nitrogen, 100g of anhydrous tetrahydrofuran was added as a solvent. 11.5g of thiol-terminated hexafluoropropylene oxide oligomer (molecular weight 600) and 8.4g of monovinyl heptaisobutyl POSS were added to the flask and stirred for 30 minutes to completely dissolve them. Subsequently, 0.3ml of 0.005mol / L chloroplatinic acid-tetrahydrofuran solution was added as a catalyst, the reaction system was heated to 70°C, and the reaction was stirred for 10 hours. After the reaction was completed, the tetrahydrofuran solvent was removed by distillation under reduced pressure. Perfluoropolyether-cage silsesquioxane was obtained.

[0049] Example 3

[0050] Preparation of thiol-terminated perfluoropolyether:

[0051] 60g of perfluoromethylcyclohexane was added to a reactor as a solvent, followed by 0.3g of azobisisobutyronitrile as an initiator. After stirring and dispersing evenly, 15g of hexafluoropropylene gas was introduced at 25°C and normal pressure. Stirring was maintained and the reaction was allowed to proceed for 1 hour. After the reaction was completed, vacuum distillation was performed at 10KPa, and the gaseous product was introduced into a cold trap at -78°C. After condensation, a transparent hexafluoropropylene oxide liquid was obtained. Under nitrogen protection, 80g of cyclopentane was added as a solvent to a dry 250mL reactor, and 0.8g of tetrabutylammonium fluoride was added as a catalyst. After stirring to uniformly disperse the catalyst, 17g of hexafluoropropylene oxide gas was introduced, and the pressure in the reactor was controlled to maintain at 0.3MPa. The reaction was continued with stirring for 4 hours. After the reaction is completed, vacuum distillation is performed under a pressure of 20KPa, and the fraction at 70-90°C is collected to obtain hexafluoropropylene oxide polymer; in a nitrogen-protected reactor, 50g of hexafluoropropylene oxide polymer with a molecular weight of 600, 15g of potassium thioacetate and 150g of dimethyl sulfoxide (DMSO) are added and stirred at 40°C for 6 hours. After the reaction is completed, it is cooled to room temperature, the solid generated is filtered out, and the filtrate is vacuum distilled to remove DMSO under the conditions of 60°C and 1kPa. 10g of the product is dissolved in 100g of methanol, 20g of sodium borohydride is added, and the temperature is controlled at 20°C for 4 hours. After the reaction is completed, 1mol / L dilute hydrochloric acid is slowly added dropwise to pH 6, extracted three times with dichloromethane, the organic phases are combined, dried over anhydrous sodium sulfate and filtered. The filtrate is firstly distilled off dichloromethane under normal pressure, and then low-boiling substances are removed by reduced pressure distillation, and finally the target product, thiol-terminated hexafluoropropylene oxide oligomer, is obtained by silica gel column chromatography.

[0052] Preparation of monovinyl heptaisobutyl POSS:

[0053] In a nitrogen-protected four-necked flask, 270 g of dry toluene was added as a solvent, followed by the addition of 42 g of triethylamine and 70 g of isobutyltrichlorosilane, and the mixture was stirred and mixed evenly. 8 g of vinyltrichlorosilane and 3 g of deionized water were prepared into a mixed solution, which was slowly added dropwise to the reaction system through a constant pressure dropping funnel over 1 hour. After the addition was complete, the reaction was stirred continuously at 25 ° C for 24 hours. After the reaction was completed, the solid was filtered to remove the solid, and the filtrate was distilled under reduced pressure at 60 ° C and 1 kPa to remove the toluene solvent. The residue was recrystallized with n-hexane, and the crystalline product was filtered and placed in a vacuum drying oven and dried at 50 ° C for 12 hours to obtain monovinyl heptaisobutyl POSS.

[0054] Preparation of perfluoropolyether-cage silsesquioxane:

[0055] In a 250mL three-necked flask protected by nitrogen, 100g of anhydrous tetrahydrofuran was added as a solvent. 12.1g of thiol-terminated hexafluoropropylene oxide oligomer (molecular weight of about 600) and 8.4g of monovinyl heptaisobutyl POSS were added to the flask and stirred for 30 minutes to completely dissolve them. Subsequently, 0.3ml of 0.005mol / L chloroplatinic acid-tetrahydrofuran solution was added as a catalyst, the reaction system was heated to 70°C, and the reaction was stirred for 10 hours. After the reaction was completed, the tetrahydrofuran solvent was removed by distillation under reduced pressure. Perfluoropolyether-cage silsesquioxane was obtained.

[0056] test

[0057] The perfluoropolyether-cage silsesquioxane (10 g) of Examples 1-3 was dissolved in a mixed solvent of propylene glycol methyl ether acetate (63 g) and cyclohexanone (27 g). The mixture was stirred at room temperature for 24 hours and then filtered twice through a 0.2 μm filter cartridge. The mixture was spin-coated on a 4-inch wafer produced by Novel Crystal Technology, Japan, using a coating amount of 1 ml and a coating thickness of 100 nm. The mixture was soft-baked at 120° C. for 60 seconds to remove the solvent and cross-linked and cured at 180° C. for 90 seconds to form a final coating. The following tests were performed, and the test results are shown in Table 1.

[0058] (1) Thermal stability test: Thermogravimetric analysis was performed using a 209F3 thermogravimetric analyzer from NETZSCH, Germany. The thermal decomposition initial temperature was defined as the weight loss of 5%.

[0059] (2) Solvent resistance test: The prepared examples were placed in AZ400K series developer produced by Merck, Germany for 24 hours, and the mass loss was observed.

[0060] (3) Anti-reflection test: The coating's ability to suppress interfacial reflection is evaluated by measuring the intensity of reflected light at a specific wavelength. A UV-visible-near-infrared spectrophotometer is used to emit 193nm wavelength light suitable for ArF lithography, and the instrument automatically calculates the reflectivity.

[0061] Table 1

[0062] Thermal decomposition initial temperature Mass loss rate Light reflectivity Example 1 312℃ 0.05％ 0.347％ Example 2 305℃ 0.09％ 0.410％ Example 3 310℃ 0.07％ 0.385％

[0063] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. An antireflective coating for photoresist, characterized in that The coating comprises perfluoropolyether-cage silsesquioxane, the structural formula of which is: Wherein, R=CH2CH(CH3)2, n=(3-6).

2. A method for preparing a reflective coating for photoresist according to claim 1, characterized in that: The method comprises the following steps: dissolving perfluoropolyether-cage silsesquioxane in a solvent to prepare a solution, stirring at room temperature for 24 hours, filtering, coating, removing the solvent, cross-linking and curing to form a coating.

3. The method for preparing a reflective coating for photoresist according to claim 2, wherein: The solvent is a mixed solvent consisting of propylene glycol methyl ether acetate and cyclohexanone, and the mixing ratio is (7:3)-(8:2).

4. The method for preparing a reflective coating for photoresist according to claim 2, wherein: The spin coating process has a first-stage rotation speed of 500-600 rpm and a duration of 10-15 seconds, and a second-stage rotation speed of 2500-3000 rpm and a duration of 30-40 seconds; the cross-linking curing temperature is 170-180° C. and the duration is 90-100 seconds.

5. The method for preparing a reflective coating for photoresist according to claim 2, wherein: The solid content of the perfluoropolyether-cage silsesquioxane in the solution is 10-15 wt %.

6. The method for preparing a reflective coating for photoresist according to claim 2, wherein: The preparation method of the perfluoropolyether-cage silsesquioxane comprises the following steps: (1) Preparation of hexafluoropropylene oxide oligomers: Solvent B and a catalyst were added to a dry reactor under nitrogen protection, stirred evenly, cooled to -10°C, and hexafluoropropylene oxide gas was introduced. The mixture was stirred and reacted at 0.3 MPa for 4 hours. After the reaction was completed, the catalyst was removed by filtration, and the mixture was distilled under reduced pressure. The fraction at 70-90°C was collected to obtain hexafluoropropylene oxide oligomers. (2) Preparation of mercaptan-terminated hexafluoropropylene oxide oligomer: adding hexafluoropropylene oxide oligomer and potassium thioacetate to dimethyl sulfoxide, placing in a reactor, stirring evenly, and conducting a nucleophilic substitution reaction at 20-50°C for 6-7 hours. After the reaction is completed, filtering is performed, and the filtrate is distilled under reduced pressure to remove the solvent; the obtained product is then dissolved in methanol, sodium borohydride is added, and a reduction reaction is carried out. After the reaction is completed, dilute hydrochloric acid is added for neutralization, and the product is extracted with an organic solvent. The product is separated and purified by distillation and column chromatography to obtain a mercaptan-terminated hexafluoropropylene oxide oligomer; (3) Preparation of monovinyl heptaisobutyl POSS: triethylamine and isobutyltrichlorosilane were added to toluene in proportion, stirred evenly, and then a mixed solution of vinyltrichlorosilane and water was slowly added dropwise to form a reaction system. The mixture was stirred and reacted at 25-30°C for 24 hours. After the reaction was completed, the generated ammonium chloride was filtered out, and the filtrate was distilled under reduced pressure, recrystallized, filtered, and dried to obtain monovinyl heptaisobutyl POSS. (4) Preparation of perfluoropolyether-cage silsesquioxane: Thiol-terminated hexafluoropropylene oxide oligomer and monovinyl heptaisobutyl POSS were added to tetrahydrofuran solvent and stirred evenly. Chloroplatinic acid-tetrahydrofuran solution was added as a catalyst to form a reaction system. The reaction was continued by stirring at 60-80°C for 8-12 hours. After the reaction was completed, tetrahydrofuran was removed by vacuum distillation to obtain perfluoropolyether-cage silsesquioxane.

7. The method for preparing a reflective coating for photoresist according to claim 6, wherein: The solvent B in step (1) is one of diethylene glycol dimethyl ether, cyclopentane or perfluoropolyether, and the amount of the solvent is 3-5 times the mass of hexafluoropropylene oxide; The catalyst in step (1) is one of cesium fluoride and tetrabutylammonium fluoride, and the amount of the catalyst is 3%-5% by mass of hexafluoropropylene oxide.

8. The method for preparing a reflective coating for photoresist according to claim 6, wherein: The molar ratio of the hexafluoropropylene oxide oligomer to potassium thioacetate in step (2) is 1: (1-1.5), the amount of DMSO used can be 2-3 times the mass of the hexafluoropropylene oxide oligomer; the amount of sodium borohydride used is 1.5-2 times the mass of the product, and the amount of methanol used is 8-10 times the mass of the product.

9. The method for preparing a reflective coating for photoresist according to claim 6, wherein: The molar ratio of isobutyltrichlorosilane to vinyltrichlorosilane in step (3) is (7-8):1; the amount of triethylamine used is 0.5-0.6 times the total mass of chlorosilane.

10. The method for preparing a reflective coating for photoresist according to claim 6, wherein: The mass ratio of mercaptan-terminated oligomer and POSS described in step (4) is (1.3-1.5): 1, and the consumption of tetrahydrofuran (THF) is 5-6 times of the sum of the mass of mercaptan-terminated oligomer and monovinyl seven isobutyl POSS, and the consumption of chloroplatinic acid is 30-50ppm of the sum of the mass of mercaptan-terminated oligomer and monovinyl seven isobutyl POSS.

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