KR20230171106A - Method for Patterning Quantum Dot Thin Film by Photolithography and Display Device Comprising the Quantum Dot Thin Film - Google Patents

Abstract

The present invention relates to a method of patterning a quantum dot thin film by photolithography and a display device including the patterned quantum dot thin film. Specifically, the method includes (a) forming a quantum dot layer on a substrate; (b) forming a metal oxide layer by depositing a metal oxide on the quantum dot layer by one or more atomic layer deposition methods; (c) applying a photoresist on the metal oxide layer, wherein the photoresist is a photoresist that does not contain a sulfonic acid group; and (d) exposing and developing the photoresist to form a quantum dot pattern. According to the method of the present invention, thin films of quantum dots, including In-based quantum dots, which are very vulnerable to chemical environments, can be patterned by conventional photolithography without problems such as quantum dot dissolution or loss of luminescence characteristics such as luminescence intensity or lifetime.

Description

Method for patterning a quantum dot thin film by photolithography and a display device including the quantum dot thin film {Method for Patterning Quantum Dot Thin Film by Photolithography and Display Device Comprising the Quantum Dot Thin Film}

The present invention relates to a method of patterning a quantum dot thin film by photolithography and a display device including the quantum dot thin film.

Photolithography, which uses photoresist, a polymer whose properties change depending on light, is generally used to implement microcircuits on a substrate. This is used as the most core process in today's semiconductor process, and as demand in the semiconductor field increases, the importance of photolithography technology development is also emerging.

Quantum dots (QDs) are being considered as next-generation self-luminous display materials due to their color purity, large-scale solution processability, and tunable electrical and optical properties. Despite recent advances in QD light-emitting diodes (QD-LEDs), including 20% external quantum efficiency and improved lifetime, multicolor pixel QD-LED devices still need development.

QDs are typically synthesized using wet chemistry in large-scale solution processes. Accordingly, when QDs are introduced into a multilayer thin film structure, the QD film may be damaged by the solvent. For example, when photoresist is coated on a QD film, the QD film is easily removed or the QD film and photoresist layer are mixed together. This is because QDs are easily dissolved or removed by the organic solvent used to dissolve the photoresist. This presents a serious issue in that QD films cannot be patterned using conventional photolithography.

Accordingly, alternative patterning methods such as inkjet and transfer printing have been used to form multicolor QD patterns. However, inkjet printing has a limited tact time and there is a problem of nozzle clogging in industrial applications. Additionally, transfer printing can form high-resolution patterns, but this process requires precise control of dynamic parameters such as pick-up and peel speeds, which limits process reproducibility. Therefore, there is a need to use conventional photolithography to pattern QD films.

The purpose of the present invention is to provide a method for patterning a quantum dot thin film by conventional photolithography without problems such as quantum dot dissolution or loss of luminescence characteristics such as luminescence intensity or lifetime.

Another object of the present invention is to provide a display device including a quantum dot thin film patterned by photolithography.

According to one aspect of the present invention, (a) forming a quantum dot layer on a substrate; (b) forming a metal oxide layer by depositing a metal oxide on the quantum dot layer by one or more atomic layer deposition methods; (c) applying a photoresist on the metal oxide layer, wherein the photoresist is a photoresist that does not contain a sulfonic acid group; and (d) exposing and developing the photoresist to form a quantum dot pattern. A method of patterning a quantum dot layer by photolithography is provided.

According to one embodiment, the quantum dot may include a Cd-based compound or an In-based compound.

According to one embodiment, the quantum dots are CdSe, CdS, CdTe, CdSeS, CdSeTe, CdSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, InN, InP, InAs , InSb, InNP, InNAs, InNSb, InPAs, InPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and InZnP.

According to one embodiment, the quantum dot may include at least one selected from the group consisting of InP, InNP, InPAs, InPSb, InAlNP, and InZnP.

According to one embodiment, the metal oxide layer may be a ZnO layer.

According to one embodiment, the photoresist includes an alkali-soluble resin and a photosensitizer, and the alkali-soluble resin and the photosensitizer do not include a sulfonic acid group.

According to one embodiment, the photoresist includes an alkali-soluble resin selected from cardo resin, acrylic resin, novolac resin, and polyimide resin, and the resin may not include a sulfonic acid group.

According to one embodiment, the alkali-soluble resin may include at least one acidic group selected from a carboxyl group and a phenolic hydroxyl group at the end of the main chain of the resin, or both, among the structural units of the resin.

According to one embodiment, the photoresist is benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin phenyl ether, benzyl dimethyl ketal, anthraquinone, naphthoquinone, 3 ,3-dimethyl-4-methoxybenzophenone, benzophenone, p,p'-bis(dimethylamino)benzophenone (p,p'-bis(diethylamino)benzophenone, p,p'-diethylamino Benzophenone, pivalone ethyl ether, 1,1-dichloroacetophenone, p-t-butyldichloroacetophenone, dimer of hexaaryl-imidazole, 2,2'-diethoxyacytophenone, 2,2'-diethoxy- 2-phenylacetophenone, 2,2'dichloro-4-phenoxyacetophenone, phenylglyoxylate, a-hydroxy-isobutylphenone, dibenzosphane, 1-(4-isopropylphenyl)-2-hyde It may contain at least one photosensitizer selected from the group consisting of oxy2-methyl-1-propanone, and 2-methyl-[4-(methylthio)petyl]-2-morpholino-1-propanone. there is.

According to one embodiment, the photoresist may be a negative photoresist.

According to another aspect of the present invention, a display device including a quantum dot layer patterned by the above-described method as a light-emitting layer is provided.

According to the present invention, thin films of quantum dots, including In-based quantum dots, which are known to be very vulnerable to chemical environments, can be patterned by conventional photolithography without problems such as quantum dot dissolution or loss of luminescence characteristics such as luminescence intensity or lifetime.

In Figure 1 (a) is a diagram schematically showing the process of patterning a quantum dot layer by photolithography according to an embodiment of the present invention; (b) is a diagram schematically showing the manufacturing process of a quantum dot light-emitting display according to an embodiment of the present invention.
In Figure 2 (a), the as-fabricated Cd-based QD film, after ALD ZnO deposition, and using a photoresist containing sulfonic acid groups (+ve PR) or a photoresist not containing sulfonic acid groups (-ve PR) PL spectrum after photolithography; (b) shows the as-fabricated InP-based QD film, after ALD ZnO deposition, and photolithography using a photoresist containing sulfonic acid groups (+ve PR) or a photoresist not containing sulfonic acid groups (-ve PR). This is the PL spectrum after; (c) shows the as-fabricated InP QD film, after ALD ZnO deposition, and exposed to ethyl acetate solvent and 1-Diazo-2-naphthol-4-sulfonic acid (DNS). This is the PL spectrum after
In Figure 3 (a) is the PL spectrum of the as-fabricated Cd-based QD film, after ALD ZnO deposition, after photoresist coating, after development, and after acetone immersion; (b) is the PL spectrum of the as-fabricated InP-based QD film, after ALD ZnO deposition, photoresist coating, development, and acetone soak; (c) is a green Cd-based QD film, after ALD ZnO deposition, and photolithography process using a photoresist containing sulfonic acid groups (+ve PR) or a photoresist not containing sulfonic acid groups (-ve PR, negative photoresist). is the PL life after; (d) PL lifetime after deposition of red InP-based QD film, ALD ZnO, and photolithography process using photoresist containing sulfonic acid groups (+ve PR) or photoresist not containing sulfonic acid groups (-ve PR); (e) is a PL spectrum obtained by experimenting with the InP-based QD film in the same manner as in (b) of FIG. 3, except that a positive photoresist was used as a photoresist that does not contain a sulfonic acid group.
Figure 4 is a fluorescence microscope image of the QD pattern. Specifically, these are images of (a) red, (b) green, and (c) blue Cd-based QD patterns after performing a photolithography process using a photoresist not containing a sulfonic acid group; Images of (d) red and (e) green InP-based QD patterns after performing a photolithographic process using a photoresist that does not contain sulfonic acid groups, and (f) an InP-based QD pattern obtained using a photolithography process. These are images of various shapes. All scale bars indicate 100 μm.
In Figure 5 (a) is a schematic diagram of the QD EL device used for pixel patterning; (b) is the predicted electronic band diagram of a QD EL device using green-emitting Cd-based QDs; (c) shows the current density and Brightness is expressed as a function of applied bias; (d) is a graph showing the current efficiency of the QD EL device as a function of current density.

Hereinafter, the present invention will be described in detail.

The terms used in this application are merely used to describe specific embodiments and are not intended to limit the invention. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the technical field to which the present invention pertains.

The features of various embodiments of the present invention can be partially or fully combined or combined with each other, and various technical interconnections and operations are possible, and each embodiment may be implemented independently of each other or may be implemented together in a related relationship. It may be possible.

Throughout the specification, when a part is said to “include”, “contain”, or “have” a certain component, this means that it may further include other components, unless specifically defined otherwise.

Terms such as first and second are used to distinguish one component from another component, and the components are not limited by the above-mentioned terms.

When a part of a layer, membrane, etc. is said to be “above/on” or “below/under” another part, it means that it is “directly above/on” or “immediately below/under” the other part, making it different from the other part. This includes not only cases where they are in contact with each other, but also cases where there are different parts in between. Conversely, when a part is said to be “right above/above” or “right below/below” another part, it means that there is no other part in between.

According to one aspect of the present invention, (a) forming a quantum dot layer on a substrate; (b) forming a metal oxide layer by depositing a metal oxide on the quantum dot layer by one or more atomic layer deposition methods; (c) applying a photoresist on the metal oxide layer, wherein the photoresist is a photoresist that does not contain a sulfonic acid group; and (d) exposing and developing the photoresist to form a quantum dot pattern. A method of patterning a quantum dot layer by photolithography is provided.

In step (a), the quantum dots are group II-VI compounds, group III-V compounds, group IV-VI compounds, group IV elements or compounds, group I-III-VI compounds, group II-III-VI compounds, I -It may include group II-IV-VI compounds or a combination thereof.

“Group II” herein may include Group IIA and Group IIB, and examples of Group II metals include, but are not limited to, Cd, Zn, Hg, and Mg. Additionally, “Group III” may include Group IIIA and Group IIIB, and examples of Group III metals include, but are not limited to, Al, In, Ga, and Tl. Additionally, “Group IV” may include Group IVA and Group IVB, and examples of Group IV metals may include, but are not limited to, Si, Ge, and Sn. Additionally, “Group I” may include Group IA and Group IB, and includes, but is not limited to, Li, Na, K, Rb, and Cs. Additionally, “Group V” includes Group VA and includes, but is not limited to, nitrogen, phosphorus, arsenic, antimony, and bismuth. Additionally, “Group VI” includes Group VIA and includes, but is not limited to, sulfur, selenium, and tellurium.

According to one embodiment, the quantum dot may include a Cd-based compound or an In-based compound, particularly an InP-based compound. For example, the quantum dots include CdSe, CdS, CdTe, CdSeS, CdSeTe, CdSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, InN, InP, InAs, InS b , InNP, InNAs, InNSb, InPAs, InPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and InZnP. Additionally, according to one embodiment, the quantum dots may include an InP-based compound. For example, the quantum dot may include at least one selected from the group consisting of InP, InNP, InPAs, InPSb, InAlNP, and InZnP.

The quantum dot may be surrounded by an organic ligand. The organic ligand helps the quantum dots to be well dispersed in the solvent, and commonly used organic ligands can be used. Specifically, 1-dodecanethiol, 3-mercaptopropionic acid, trioctylphosphine, trioctylphosphine oxide, oleic acid and oleic acid. Examples include primary amines such as oleylamine. The organic ligand may preferably be wet-coated on the shell surface of the quantum dot core that emits one color among red, green, and blue.

The quantum dots may have a particle size of about 1 nm or more and about 100 nm or less (e.g., particle diameter or, in the case of non-spherical particles, diameter calculated from the two-dimensional area of an electron microscope image of the particle). For example, the quantum dots may have a particle size of about 1 nm to about 50 nm. The wavelength of light that quantum dots emit varies depending on their size, and for use in display devices, quantum dots that preferably emit red (R), green (G), and blue (B) are required. The larger the quantum dot, the longer the wavelength of light it emits.

The quantum dots are commercially available or can be appropriately synthesized. The particle size of quantum dots can be controlled relatively freely during colloid synthesis, and the particle size can also be adjusted uniformly. When a quantum dot has a size of 10 nm or less, the quantum confinement effect, in which the band gap increases as the size decreases, may become more pronounced, and the energy density may increase accordingly. In colloidal synthesis, precursor materials are reacted in an organic solvent to grow crystal particles, and the organic solvent or a ligand compound can coordinate the surface of the quantum dots to control particle growth.

The quantum dots may be applied on a substrate by a solution process, for example, spin coating, to form a quantum dot layer.

The step (b) specifically includes first injecting a precursor for forming a metal oxide layer; adding an oxidizing agent; And it may include forming a metal oxide layer by oxidizing the precursor using atomic layer deposition.

The precursor is an oxide-based precursor and is not particularly limited as long as it can crosslink the surface of the quantum dot in the gas phase, but preferably one or more of diethylzinc (DEZ) and trimethylaluminum (TMA) can be used. there is. The oxidizing agent may be H ₂ O or O ₃ . The metal oxide layer may be a ZnO layer.

According to one embodiment, diethyl zinc (DEZ) is injected to cause a substitution reaction with the organic ligand of the quantum dot, then H ₂ O is added, and diethyl zinc can be oxidized to zinc oxide through atomic layer deposition. The oxidation process may be oxidized by an oxidizing agent contained in the atmosphere as the precursor is exposed to the atmosphere in a general atomic layer deposition process, but the precursor may also be oxidized by adding an additional oxidizing agent. As the resistance of the quantum dot thin film to organic solvents increases due to oxidation of the precursor, patterning can become more precise during the photolithography process, and as a result, high-resolution displays can be implemented.

The atomic layer deposition method may be performed one or more times, for example, 2 to 15 times.

Step (c) is a step of applying a photoresist on the metal oxide layer, and the photoresist is a photoresist that does not contain a sulfonic acid group. As shown in the following examples, when a photoresist containing a sulfonic acid group is used, the light emission of the quantum dots is lost. In particular, in the case of In-based quantum dots, which are sensitive to chemical environments, the light emission is lost by more than 70%. On the other hand, when a photoresist that does not contain a sulfonic acid group is used, the luminescence characteristics can be improved.

The photoresist may include an alkali-soluble resin. The alkali-soluble resin may be a resin that has an alkali-soluble group such as a hydroxyl group, a carboxyl group, or both, an acid value of 10 mgKOH/g or more, and a weight average molecular weight (Mw) of 500 to 150,000. According to one embodiment, the alkali-soluble resin may not contain a sulfonic acid group.

Resins included in the photoresist, especially alkali-soluble resins, include cardo resin, acrylic resin, novolak resin, polyimide resin, polyimide precursor, polybenzoxazole resin, polybenzoxazole precursor, and polyamide resin. , siloxane resin, etc., however, according to the present invention, the resin does not contain a sulfonic acid group. According to one embodiment, the photoresist may be a negative type, and a resin selected from cardo resin, acrylic resin, novolak resin, and polyimide resin may be preferable from the viewpoint of pattern processability and film reliability. According to another embodiment, the photoresist may be of a positive type, and from the viewpoint of pattern processability, a resin selected from polyimide resin, polyimide precursor, polybenzoxazole resin, polybenzoxazole precursor, and siloxane resin is preferred. can do. Here, the cardo resin is a cardo structure, that is, a resin having a skeletal structure in which two cyclic structures are bonded to quaternary carbon atoms constituting the cyclic structure, and a structure in which the main chain and the bulky side chain are connected by one element (cardo structure) ) and has a cyclic structure in a direction almost perpendicular to the main chain. According to one embodiment of the present invention, the photoresist may include a resin selected from cardo resin, acrylic resin, novolak resin, and polyimide resin, and the resin may not include a sulfonic acid group.

The resin contained in the photoresist, especially the alkali-soluble resin, preferably has an acidic group in the structural unit of the resin and/or at the terminal of its main chain in order to provide alkali solubility. Examples of acidic groups include carboxyl groups, phenolic hydroxyl groups, and sulfonic acid groups. However, since sulfonic acid groups are not used according to the present invention, it is preferable to use carboxyl groups and phenolic hydroxyl groups. According to one embodiment of the present invention, the resin may include at least one acidic group selected from a carboxyl group and a phenolic hydroxyl group at the main chain terminal of the resin, or both, among the structural units of the resin.

According to one embodiment of the present invention, the photoresist may be a negative photoresist. Negative photoresist has the characteristic of dissolving parts that do not receive light during exposure. According to one embodiment of the present invention, the photoresist may be a positive photoresist. Positive photoresist has the characteristic that the part exposed to light is dissolved during exposure, making it possible to implement QD patterns with higher resolution and multiple colors compared to negative photoresist. When the photoresist is removed by dissolving it with a developer after applying and exposing it, the quantum dot layer underneath the dissolved photoresist is also dissolved, thereby patterning the quantum dot layer.

The photoresist may contain a photosensitizer. The photosensitizer serves to solubilize or insolubilize the alkali-soluble resin in an alkaline developer. Accordingly, it is a key photosensitive component that allows the exposed and non-exposed areas of photoresist to be developed. According to one embodiment, the photosensitizer is a photosensitizer that does not contain a sulfonic acid group.

The photosensitizer is, for example, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin phenyl ether, benzyl dimethyl ketal, anthraquinone, naphthoquinone, 3,3-dimethyl. -4-methoxybenzophenone, benzophenone, p,p'-bis(dimethylamino)benzophenone (p,p'-bis(diethylamino))benzophenone, p,p'-diethylaminobenzophenone, Pivalone ethyl ether, 1,1-dichloroacetophenone, p-t-butyldichloroacetophenone, dimer of hexaaryl-imidazole, 2,2'-diethoxyacytophenone, 2,2'-diethoxy-2-phenyl Acetophenone, 2,2'-dichloro-4-phenoxyacetophenone, phenylglyoxylate, a-hydroxy-isobutylphenone, dibenzosphane, 1-(4-isopropylphenyl)-2-hydroxy- 2-methyl-1-propanone, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, diazonaphthoquinone, allyldiazonium salt, diallyliodonium salt, and It may be at least one selected from the group consisting of nitrobenzyl ester. Other examples of the photosensitizer include 2,3,4-trihydroxybenzophenone, 2,3,4,4'-tetrahydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,3,4,3 ',4',5'-hexahydroxybenzophenone, 4,4',1-(4-(1-(4-hydroxyphenyl)-1-methylethyl)phenyl)ethylidene)bisphenol, bisphenol-A , methyl gallate, propyl gallate, etc. may be further mentioned.

The photoresist may contain a solvent. The solvent may be any organic solvent known to be used in photoresist and is not particularly limited. For example, the solvent is N-methyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylacetamide, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether. , propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl lactate, ethyl lactate, methyl-1,2-butylene glycol acetate, 1,3-butylene glycol-3- Examples include monomethyl ether, methyl pyruvate, ethyl pyruvate, and methyl-3-methoxy propionate, and a mixed solvent of two or more of these solvents may be used.

Step (d) is a step of exposing and developing the photoresist to form a quantum dot pattern.

The exposure is performed by irradiating actinic radiation. Examples of the actinic rays include ultraviolet rays, visible rays, electron beams, and X-rays. According to one embodiment of the present invention, the exposure may be performed by irradiating ultraviolet rays, specifically i-rays (365 nm). In order to obtain a desired pattern, the exposure process is performed through a mask having the shape of the desired pattern.

The exposed film exposed by the above exposure is developed using an alkaline developer or the like. Examples of alkaline compounds used in alkaline developers include inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium silicate, sodium metasilicate, and aqueous ammonia; Primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-propylamine; Tertiary amines such as triethylamine and methyldiethylamine; Tetraalkylammonium hydroxides such as tetramethylammonium hydroxide (TMAH), quaternary ammonium salts such as choline; alcohol amines such as triethanolamine, diethanolamine, monoethanolamine, dimethylaminoethanol, and diethylaminoethanol; Rings such as pyrrole, piperidine, 1,8-diazabicyclo[5,4,0]-7-undecene, 1,5-diazabicyclo[4,3,0]-5-nonane, morpholine, etc. Organic alkalis such as amines are listed. The development can be performed, for example, by a dipping method, a spray method, a paddle method, etc.

According to the present invention, when the exposed or unexposed portion of the photoresist is dissolved due to the above phenomenon, the quantum dots under the dissolved photoresist are also dissolved.

Residual photoresist that has not been dissolved by development can be removed by, for example, immersion in acetone.

According to the present invention, the quantum dot layer patterned by the above-described method can be used as a light-emitting layer of a display device. Accordingly, according to another aspect of the present invention, a display device including a quantum dot layer patterned by photolithography as a light emitting layer as described above is provided.

Hereinafter, the present invention will be described in more detail with reference to examples to aid understanding of the present invention. However, the following examples are provided only to make the present invention easier to understand, and the content of the present invention is not limited by the following examples.

[Example 1] Patterning of quantum dot film

As shown in Figure 1 (a), the quantum dot film was patterned according to the following sequence.

The Si substrate was cleaned with isopropyl alcohol (IPA). The Si substrate was placed on a spin coater and fixed under vacuum, and dynamic spin coating of Cd-based quantum dot (QD) or InP-based QD was performed at 2000 rpm. The Si substrate was placed on a hot plate and heat treatment was performed at 140°C for 30 minutes. Place the heat-treated substrate in an ALD chamber at 130°C, pulse DEZ (diethyl zinc) for 0.1 seconds, purge with N2 gas for 15 seconds, pulse H2O reactant for 0.1 seconds, and purge for 50 seconds to perform ALD. ZnO was formed. The ALD process was performed for a total of 10 cycles. After ALD, the specimen was moved to the yellow room and diluted with propylene glycol monomethyl ether acetate (PGMEA) to make the PR thickness thinner. DNR L300 40 (Dongjin Semichem) (negative photoresist without sulfonic acid group) or AZ 12XT (Merck) ( Static coating (positive photoresist without sulfonic acid groups) was performed to obtain an appropriate thickness. After coating, the specimen was soft baked at 110°C for 3 minutes on a hot plate. To form a pattern, an exposure process of exposing UV corresponding to the i-line (365 nm) using a mask was performed for 100 seconds. After the exposure process was completed, post exposure bake was performed on a hot plate at 110°C for 3 minutes. To form a pattern, the photoresist was dissolved with a developer and distilled water, and at this time, the QDs under the photoresist that were washed by the developer were also dissolved. Finally, the QD pattern was completed by dipping in acetone to wash off the photoresist.

[Used QDs]: Red-emitting quantum dots - CdSe/CdS/CdZnS quantum dots, green-emitting quantum dots - CdZnSeS/ZnS quantum dots, InP/ZnSe/ZnS quantum dots, blue-emitting quantum dots - CdZnS/ZnS nanocrystals

[Experimental Example 1] Photoluminescence (PL) spectrum measurement

The photoluminescence (PL) spectra of the as-fabricated Cd-based QD film, after ALD ZnO deposition, and after photolithography using a photoresist containing a sulfonic acid group or a photoresist not containing a sulfonic acid group were measured, as shown in Figure 2. shown in

The PL intensity of Cd-based QDs slightly increased after depositing the ALD ZnO film due to the surface passivation of the QD film. However, after exposure to photoresist containing sulfonic acid groups (+ve PR), the PL intensity decreased by 33% for the green QD film and by 44% for the red QD film. However, when the QD film is patterned by photolithography (-ve PR) after coating with DNR-L300-40 (Dongjin Semichem) photoresist (negative photoresist), which does not contain a sulfonic acid group, the PL intensity changes between red emission and green emission Cd. It was almost stable for -series QD films. Surprisingly, the PL intensity of the Cd-based QD film was 3% (green) and 5% (red) higher after exposure to DNR-L300-40 photoresist.

InP-based QDs are known to be very vulnerable to chemical environments, and as shown in Figure 2 (b), significant PL reduction can occur even by the same photolithography process. The Pl intensity of the InP QDs decreased significantly (>70% reduction for both green and red InP QDs) after the patterning process using photoresist containing sulfonic acid groups (+ve PR). However, relatively high PL intensity was maintained when using DNR-L300-40 (Dongjin Semichem) photoresist (-ve PR, negative photoresist) that does not contain a sulfonic acid group. The insets in Figures 2 (a) and (b) show star-shaped test patterns obtained after using each photoresist, showing that the patterning process is feasible for both red-emitting and green-emitting QDs. It is believed that the reason why PL degradation is serious in InP QDs is because the sulfonic acid ester group present in the photoactive compound (PAC) is used in the photoresist.

In Figure 2 (c) shows the relative PL intensity of the QD film after exposing the photoresist to ethyl acetate solvent. Due to the solvent resistance of ZnO due to ALD, no significant PL reduction was observed even when exposed to solvent. However, when 1-diazo-2naphthyl-4-sulfonic acid (DNS) molecules were introduced into ethyl acetate solvent, a significant decrease in PL was observed. DNS has a similar chemical structure to the DNQ molecule used in PAC in photoresist. Since the solvent does not affect the QD film, it is reasonable to assume that the PL reduction occurred due to the deposition of DNS molecules on the top of the QD film. The inset in Figure 2(c) shows the structure of DNS and DNQ as PAC. Both chemicals have similar chemical reactivity, and DNQ, which has a chlorine group instead of the hydroxyl group of DNS, is expected to have similar functional groups. When a photoresist containing sulfonic acid groups is coated on top of the QD film, a significant positive PL reduction is observed even without any lithography steps such as UV exposure and development.

[Experimental Example 2] Measurement of PL intensity and PL lifespan at each lithography step

To determine the effect of each patterning step on the QD film, the PL intensity of each lithography step for Cd- and InP-based QD films was measured, and the results are shown in Figures 3 (a) and (b).

After coating with DNR-L300-40 (Dongjin Semichem) photoresist (-ve PR, negative photoresist), which does not contain a sulfonic acid group, the PL intensity was significantly reduced due to UV absorption by the photoresist itself. However, after removing the photoresist, the PL intensity recovered to its original value, indicating that the QD film was not damaged by contact with the photoresist.

The same experiment was performed on the InP-based red QD film, and the results are shown in Figure 3 (b). The PL intensity of the InP-based QD film increased significantly after 10 deposition cycles of ALD ZnO, probably due to surface passivation. The PL intensity decreased after photoresist coating due to UV absorption. However, after removing the photoresist using developer and acetone, the PL intensity was recovered. The band width of the peak did not show any significant difference. This indicates that photoresist coating, photoresist development, QD film etching, and photoresist stripping do not damage the QD film.

Meanwhile, for the InP-based red QD film, the PL spectrum was obtained in the same manner as in Figure 3 (b), except that AZ 12XT (+PR, positive resist) was used as a photoresist that does not contain a sulfonic acid group. and the results are shown in Figure 3(e). As shown in Figure 3 (b), the PL intensity decreased after photoresist coating due to UV absorption, but recovered after removal of the photoresist, and there was no significant difference in the peak band width.

To explain the luminescence behavior of the QD film and exclude geometrical effects on the PL measurement, the PL lifetime was measured, and the results are shown in Figures 3 (c) and (d).

The PL lifetime of the ALD ZnO-deposited Cd-based QD film (16.8 ns) was slightly longer than that of the as-fabricated QD film (16.1 ns), indicating a surface passivation effect. A significantly shorter PL lifetime (10.8 ns) was observed when the photolithography process was performed using a photoresist containing DNQ (containing sulfonic acid groups). However, when the photolithography process was performed using a photoresist without DNQ (-ve PR), the PL lifetime (15.3 ns) remained similar. A similar trend is observed for InP-based QD films, and the results are shown in Figure 3(d). When DNQ molecules were used in the photoresist (+ve PR), the PL lifetime of the InP series QD film was 19.7 ns, but after patterning using a photoresist without DNQ molecules (-ve PR), the PL life of the InP series QD film was 19.7 ns. The lifetime increased to 23.8 ns; This value is similar to the PL lifetime value (24.2 ns) of the as-fabricated InP-based QD film.

[Experimental Example 3] Observation of fluorescence microscope images of QD patterns

According to the example, after completing the photolithography process, high-resolution QD pixels were formed, and a fluorescence microscope image of the QD pattern is shown in FIG. 4.

As shown in Figure 4 (a), (b), and (c), the Cd-based QD film was successfully patterned into micrometer-sized primary (red, green, and blue) color pixels with a pixel density of 800 PPI. (The scale bar size in Figure 4 is 100 μm). Additionally, red and green InP-based QD film patterns were obtained with the same pixel density, as shown in Figures 4 (d) and (e). The red and green InP-based QD films showed strong fluorescence intensity after patterning. Additionally, various shape (tree and star) patterns and dot patterns were obtained by conventional photolithography processes.

[Example 2] Manufacturing of quantum dot LED

The glass substrate with the ITO pattern was cleaned with acetone, ethanol, and IPA (isopropyl alcohol). UV-ozone treatment was performed for 15 to 20 minutes. PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) poly-(styrenesulfonate)), a hole injection layer (HIL), was dropped on the substrate and spin-coated at 4000 rpm for 40 seconds. At this time, soft bake was performed at 120°C for 5 minutes, transferred to a glovebox in a nitrogen atmosphere, and hard bake was performed at 160°C for 10 minutes. During heat treatment, TFB (Poly[(9,9-dioctylfluorenyl-2,7-diyl)- -(4,40-(N-(4- -butylphenyl)-diphenylamin))) 5 mg and -TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) 1 mg was dissolved in 1 ml of m-xylene to prepare an HTL solution. The HTL solution was dropped on the heat-treated substrate, spin-coated at 3000 rpm for 30 seconds, and heat treated at 150°C for 30 minutes. Quantum dots (QD) were spin-coated on the heat-treated substrate for 30 seconds at 2000 rpm and heat-treated at 140°C for 30 minutes. The heat-treated substrate is taken out of the glovebox and placed in an ALD chamber at 130°C to proceed with ALD. DEZ was pulsed for 0.1 seconds and purged with N2 gas for 15 seconds. H2O was pulsed for 0.1 seconds and purged for 50 seconds to form a ZnO layer. ZnO formation by ALD proceeds for a total of 10 cycles. The specimen after ALD was subjected to a lithography process as in Example 1 described above. A resist containing a sulfonic acid group (AZ GXR 601) or a resist not containing a sulfonic acid group (DNR L300-40, or AZ 12XT) was used. The lithography-finished specimen was moved to a glovebox, and ZnO, an ETL (electron transport layer), was spin-coated at 2000 rpm for 30 seconds and heat treated at 110°C for 30 minutes. After the heat-treated specimen was taken out of the glovebox, Al was deposited using a thermal evaporator. After the deposited specimen was placed in a glovebox, an encapsulation process was performed using NoA (Norland Optical Adhesive) 8610B epoxy and coverslip.

[Experimental Example 4] EL device performance evaluation

A QD EL device was fabricated by patterning Cd-based QDs as a green light-emitting material, and a schematic diagram of the device is shown in Figure 5(a). Green Cd-based QDs were coated on the top of a typical HTL/HIL/ITO/substrate, ALD ZnO was deposited, and the QD film was patterned using photoresist+ that does not contain sulfonic acid groups. Figure 5(b) shows the electronic band diagram of the QD EL device shown in Figure 5(a). The device characteristics of the ALD ZnO deposited QD EL device and the QD EL device patterned using photoresist containing (AZ GXR-601) or not (DNR-L300-40) sulfonic acid groups are shown in Figure 5 (c). and (d).

ALD ZnO-deposited QD EL devices showed improved luminescence due to surface passivation of the QD film, while QD EL devices patterned using photoresist (+ve PR) containing sulfonic acid groups showed somewhat lower luminescence values. This is probably because the QD film was damaged during photoresist coating. This corresponds to the PL spectrum and PL lifetime results shown previously in Figures 2 and 3, respectively. However, when photoresist without sulfonic acid groups (no DNQ) (-ve PR) was used during QD patterning, luminescence was improved. Accordingly, the QD EL device patterned using a photoresist not containing a sulfonic acid group showed a peak current efficiency of 5.5 cd/A, which was 1.5 times higher than the peak current efficiency in the reference QD EL device.

Although the preferred embodiments of the present invention have been described in detail above, the above-described embodiments are presented as specific examples of the present invention, and the present invention is not limited thereto, and the scope of the present invention is defined by the claims described later. Various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in also fall within the scope of the present invention.

Claims (10)

(a) forming a quantum dot layer on a substrate;
(b) forming a metal oxide layer by depositing a metal oxide on the quantum dot layer by one or more atomic layer deposition methods;
(c) applying a photoresist on the metal oxide layer, wherein the photoresist does not contain a sulfonic acid group as a component; and
(d) exposing and developing the photoresist to form a quantum dot pattern,
Method for patterning a quantum dot layer by photolithography. According to paragraph 1,
A method wherein the quantum dots include a Cd-based compound or an In-based compound. According to paragraph 2,
The quantum dots are CdSe, CdS, CdTe, CdSeS, CdSeTe, CdSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, InN, InP, InAs, InSb, InNP , InNAs A method comprising at least one member selected from the group consisting of InNSb, InPAs, InPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and InZnP. According to paragraph 3,
The method wherein the quantum dots include at least one selected from the group consisting of InP, InNP, InPAs, InPSb, InAlNP, and InZnP. According to paragraph 1,
The method of claim 1, wherein the metal oxide layer is a ZnO layer. According to paragraph 1,
The method wherein the photoresist includes an alkali-soluble resin and a photosensitizer, and the alkali-soluble resin and the photosensitizer do not include a sulfonic acid group. According to paragraph 1,
The photoresist includes an alkali-soluble resin selected from cardo resin, acrylic resin, novolak resin, and polyimide resin, and the resin does not include a sulfonic acid group. In clause 7,
The method wherein the alkali-soluble resin contains at least one acidic group selected from a carboxyl group and a phenolic hydroxyl group at the main chain terminal of the resin, or both, among the structural units of the resin. According to paragraph 1,
The photoresist includes benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin phenyl ether, benzyl dimethyl ketal, anthraquinone, naphthoquinone, 3,3-dimethyl-4. -Methoxybenzophenone, benzophenone, p,p'-bis(dimethylamino)benzophenone (p,p'-bis(diethylamino))benzophenone, p,p'-diethylaminobenzophenone, pivalone Ethyl ether, 1,1-dichloroacetophenone, pt-butyldichloroacetophenone, dimer of hexaaryl-imidazole, 2,2'-diethoxyacytophenone, 2,2'-diethoxy-2-phenylacetophenone , 2,2'-dichloro-4-phenoxyacetophenone, phenylglyoxylate, a-hydroxy-isobutylphenone, dibenzosphane, 1-(4-isopropylphenyl)-2-hydroxy2-methyl -1-propanone, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, diazonaphthoquinone, allyldiazonium salt, diallyliodonium salt, and nitrobenzyl ester. A method comprising at least one photosensitizer selected from the group consisting of. A display device comprising a quantum dot layer patterned by the method according to any one of claims 1 to 9 as a light emitting layer.