Method for preparing mixed photoresist and metal electrode

Abstract

The application provides a preparation method of a mixed photoresist and a metal electrode, and relates to the technical field of light emission. The raw material of the mixed photoresist comprises a negative photoresist and a light-absorbing photoresist, and the volume ratio of the two is (2.5-3.5):1. The preparation method of the metal electrode comprises the following steps: using the negative photoresist to perform first coating on a surface with a set structure, so as to obtain a first photoresist layer; continuing to use the mixed photoresist to perform second coating, so as to obtain a second photoresist layer; exposing the double-layer photoresist layer, so as to obtain a double-layer photoresist layer with a set pattern; arranging a metal layer on the second photoresist layer with the set pattern; and stripping the double-layer photoresist layer under the metal layer, so as to obtain the metal electrode.

Description

Technical Field

[0001] This application relates to the field of light-emitting technology, and in particular to a method for preparing a hybrid photoresist and metal electrode. Background Technology

[0002] Micro LED display technology refers to a display technology that uses self-emissive, micrometer-sized LEDs as light-emitting pixel units, assembling them onto a driving panel to form a high-density LED array. Due to its characteristics such as high brightness, high luminous efficiency, high contrast, fast response, long lifespan, wide color gamut, self-emission, and seamless splicing, its performance far surpasses existing LCD and OLED display devices, and it is considered the next-generation display technology after LCD and OLED.

[0003] Micro LEDs are self-emissive, requiring no backlight. Compared to OLEDs, they are easier to color-tune and offer higher resolution (1500ppi), faster response times (ns-level), longer lifespan, and higher brightness. However, in current technologies, the electrode size precision of high-resolution micro LEDs is not high. Summary of the Invention

[0004] The purpose of this application is to provide a method for fabricating a hybrid photoresist and a metal electrode. By providing a hybrid photoresist that can reduce light intensity and using it on the surface of a negative photoresist layer in a lift-off process, the photolithographic exposure dose when light reaches the negative photoresist layer is reduced, thereby reducing the exposure intensity received by the negative photoresist, improving the photolithographic accuracy of the negative photoresist layer, and thus improving the dimensional accuracy of the metal electrode.

[0005] To achieve the above objectives, the technical solution of this application is as follows:

[0006] In a first aspect, this application provides a hybrid photoresist, the raw materials of which include negative photoresist and matte photoresist, wherein the volume ratio of the negative photoresist to the matte photoresist in the hybrid photoresist is (2.5-3.5):1.

[0007] Preferably, the matte photoresist includes black photoresist.

[0008] Secondly, this application provides a method for preparing a metal electrode, the method comprising:

[0009] A first photoresist layer is obtained by applying a negative photoresist to the surface of the defined structure.

[0010] A second photoresist layer is obtained by applying a hybrid photoresist to the surface of the first photoresist layer; the hybrid photoresist includes the hybrid photoresist described in the first aspect.

[0011] The first photoresist layer and the second photoresist layer are exposed to obtain the first photoresist layer and the second photoresist layer with a set pattern respectively.

[0012] A metal layer is disposed on a second photoresist layer having the defined pattern;

[0013] The first photoresist layer and the second photoresist layer under the metal layer are peeled off to obtain a metal film layer, which is a metal electrode.

[0014] Preferably, the exposure dose is 80 mJ / cm². 2 -100mJ / cm 2 .

[0015] Preferably, the first thickness of the sum of the first photoresist layer and the second photoresist layer is 1.5-2 times the second thickness of the metal film layer.

[0016] Preferably, after the first coating, the process further includes: pre-baking the negative photoresist;

[0017] After the second coating is performed, the process further includes pre-baking the mixed photoresist.

[0018] Preferably, the method further includes at least one of the following conditions:

[0019] a. The first coating and the second coating each independently comprise preparations using a spin coating process;

[0020] b. The spin coating process includes: first performing a first low-speed spin coating, then performing a high-speed spin coating, and then performing a second low-speed spin coating;

[0021] c. The spin coating speed for the first low-speed spin coating and the second low-speed spin coating is 300rpm-500rpm, and the spin coating time is 5s-10s;

[0022] d. The high-speed spin coating has a spin speed of 1500rpm-2500rpm and a spin coating time of 50s-70s;

[0023] e. After the first coating is performed, the method further includes: pre-baking the negative photoresist at 100℃-120℃ for 2min-4min;

[0024] f. After the second coating is performed, the process further includes: pre-baking the mixed photoresist at 100℃-120℃ for 3-5 minutes;

[0025] g. The thickness of the first photoresist layer is 6μm-8μm, the thickness of the second photoresist layer is 1μm-2μm, and the total thickness of the photoresist layer after the first photoresist layer and the second photoresist layer are stacked is 3μm-4μm;

[0026] h. After exposure, the process further includes: baking at 100℃-120℃ for 5min-10min, then developing in a developer solution, and finally post-baking at 100℃-120℃ for 3min-5min.

[0027] Thirdly, this application also provides a method for fabricating a micro LED chip, comprising: providing a micro LED epitaxial wafer and etching a surface structure on the micro LED epitaxial wafer;

[0028] A metal electrode is prepared on the surface of the mesa structure using the metal electrode preparation method described in the second aspect;

[0029] A passivation layer is prepared on the surface of the metal electrode, and the passivation layer is etched to obtain an electrode contact hole.

[0030] Preferably, at least one of the following conditions is also met:

[0031] g. The micro-LED epitaxial wafer comprises, from bottom to top, a substrate, a buffer layer, a third semiconductor layer, a first semiconductor layer, a multi-quantum-well structure, and a second semiconductor layer;

[0032] h. The etching includes: removing a portion of the second semiconductor layer and the multiple quantum well structure on the microLED epitaxial wafer using inductively coupled plasma etching to expose the first semiconductor layer;

[0033] i. The method for preparing the passivation layer includes plasma-enhanced chemical vapor deposition;

[0034] j. The etching includes processes performed using dry etching and / or wet etching.

[0035] Fourthly, this application provides a micro LED chip, which is fabricated using the micro LED chip fabrication method described in the third aspect.

[0036] Fifthly, this application also provides a micro light-emitting device, including the micro LED chip described in the fourth aspect.

[0037] The beneficial effects of this application are:

[0038] The hybrid photoresist provided in this application has negative photoresist properties because both the negative photoresist and the matte photoresist in its raw materials have negative photoresist properties that cross-link and harden after exposure. At the same time, the matte photoresist itself has a very strong light-shielding effect. By mixing it with the negative photoresist, the entire hybrid photoresist can also have a certain effect of reducing light intensity.

[0039] The metal electrode fabrication method provided in this application uses the aforementioned mixed photoresist and applies it to the surface of the resist layer formed by the negative photoresist in the lift-off process. This reduces the photolithographic exposure when light reaches the negative photoresist, significantly lowering the exposure intensity received by the negative photoresist and thus improving the photolithographic precision of the negative photoresist. With the same lithography machine, this improves processing accuracy and the dimensional accuracy of the metal electrode after resist removal, thereby enhancing the photoelectric performance of the micro-LED chip containing the metal electrode. Furthermore, it improves the versatility of the lithography machine, allowing lithography machines with higher exposure limits to be applied to more semiconductor product processing scenarios, such as for fabricating products with high-precision metal electrodes.

[0040] In the method for fabricating micro LED chips provided in this application, by using the above-mentioned method for fabricating metal electrodes, small-sized, high-precision metal electrodes can be fabricated, thereby achieving the fabrication requirements of high-resolution, high-pixel-density micro LED chips. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0042] Figure 1 This is a flowchart of the fabrication process for metal electrodes;

[0043] Figure 2 This is a schematic diagram of the initial structure of a micro LED epitaxial wafer;

[0044] Figure 3 A schematic diagram of the mesa structure after etching a micro-LED epitaxial wafer;

[0045] Figure 4 A schematic diagram of the structure after metal electrodes are installed on the platform structure;

[0046] Figure 5 A schematic diagram of a structure with a passivation layer on the surface of a metal electrode;

[0047] Figure 6 A schematic diagram of the structure after etching the passivation layer;

[0048] Figure 7 The photolithography image after exposure and development of the double-layer photoresist of Example 1;

[0049] Figure 8 The microscopic pattern after vapor deposition stripping in Example 1;

[0050] Figure 9 The image is a microscopic photolithography pattern of the negative photoresist layer in Comparative Example 1 after exposure and development.

[0051] Figure 10 The image shows the microscopic pattern after the negative photoresist layer of Comparative Example 1 has been vapor-deposited and stripped. Detailed Implementation

[0052] As used in this article:

[0053] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0054] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0055] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0056] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0057] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiplier). It is important to understand that, unlike the number of parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0058] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0059] The inventors of this application discovered, in fabricating high-resolution, high-pixel-density micro-light-emitting devices, that it is necessary to fabricate thick, small-sized metal electrodes on a bonding metal layer, specifically metal electrodes with a thickness of 1-2 μm and a diameter of 1-2 μm. This requires the use of a high-precision, thick, and easily peelable negative photoresist fabricated using a lift-off process. When peeling off the negative photoresist, it is necessary for the photoresist to achieve both the required thickness after exposure and high-precision curing dimensions under these conditions, ensuring that the metal electrodes left on the substrate after photoresist peeling accurately reflect the desired electrode pattern. While high-viscosity negative photoresist can meet the high-thickness requirement, it cannot form a high-precision pattern that meets the metal electrode dimensions after exposure using a photolithography machine. This prevents the subsequently fabricated metal electrodes from reaching the predetermined size, thus affecting the performance of the micro-light-emitting device.

[0060] In actual operation, the inventors of this application found that after coating with negative photoresist, performing photolithography with a conventional photolithography machine, and developing with a developer, some photoresist will remain in areas that were not directly exposed to light radiation. As a result, after removing the photoresist in the lift-off process, the pattern of the remaining metal layer will deviate from the expected pattern. Especially for small-sized metal electrodes with a diameter of only 1-2 μm, if too much photoresist remains on the metal layer pattern, it will inevitably lead to a large deviation between the final metal electrode size and the expected size.

[0061] Further research revealed that the reason why negative photoresist leaves some photoresist residue in areas not exposed to light after photolithography is due to overexposure. Reducing the exposure level of the photolithography machine can significantly reduce photoresist residue. However, for ordinary photolithography machines, even when adjusted to the equipment's minimum exposure level (80 mJ / m²), the residue remains significantly reduced. 2Even with these methods, photoresist will still remain, and the pattern of the metal electrode layer will still not meet the design requirements unless a lithography machine with a lower exposure is used, which would mean investing in higher production costs.

[0062] To address this, this application proposes using a special photoresist to reduce the light sensitivity of negative photoresist. When this special photoresist is applied to the surface of the negative photoresist, it blocks and absorbs some of the light, reducing the light intensity that ultimately reaches the underlying negative photoresist layer. This allows the negative photoresist layer to harden under normal exposure doses, thus ensuring the dimensions of the metal layer fabricated by the lift-off process without exposure to light.

[0063] Firstly, the special photoresist proposed in this application is a hybrid photoresist, the raw materials of which include negative photoresist and matte photoresist. The volume ratio of the negative photoresist and the matte photoresist in the hybrid photoresist is (2.5-3.5):1, for example, it can be 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1 or any value between (2.5-3.5):1.

[0064] In a preferred embodiment, the matte photoresist comprises black photoresist.

[0065] It should be noted that both negative photoresist and black photoresist can be any type of colloid available on the market.

[0066] The preparation method of the above-mentioned mixed photoresist specifically includes: mixing the two photoresists according to the formula ratio, and then using a vacuum degassing machine to perform vacuum degassing treatment to ensure that there are no air bubbles in the mixed photoresist.

[0067] Secondly, this application provides a method for preparing a metal electrode, such as... Figure 1 As shown, it includes:

[0068] S1. Apply a negative photoresist to the surface of the defined structure to obtain a first photoresist layer;

[0069] S2. A second coating is performed on the surface of the first photoresist layer using a mixed photoresist to obtain a second photoresist layer; the mixed photoresist includes the mixed photoresist described in the first aspect.

[0070] S3. Expose the first photoresist layer and the second photoresist layer to obtain the first photoresist layer and the second photoresist layer with a set pattern.

[0071] S4. A metal layer is disposed on the second photoresist layer having the set pattern;

[0072] S5. The first photoresist layer and the second photoresist layer under the metal layer are peeled off to obtain a metal film layer as a metal electrode.

[0073] It should be noted that the structure mentioned in S1 mainly refers to the substrate structure on which metal electrodes need to be fabricated. For micro-light-emitting devices, this substrate actually refers to a micro-LED epitaxial wafer with a mesa structure. By fabricating metal electrodes on the micro-LED epitaxial wafer, a micro-LED chip can be fabricated, and thus a micro-light-emitting device can be obtained.

[0074] In a preferred embodiment, the exposure dose required during exposure in S3 is 80 mJ / cm². 2 -100mJ / cm 2 The exposure dose is mainly the preferred exposure amount required for the mixed photoresist at the volume ratio of (2.5-3.5):1. If the exposure dose is increased, it can be adjusted by increasing the proportion of matte photoresist in the mixed photoresist. Conversely, if the exposure dose is decreased, the proportion of matte photoresist in the mixed photoresist is reduced.

[0075] In a preferred embodiment, the first thickness of the sum of the first photoresist layer and the second photoresist layer is 1.5 to 2 times the second thickness of the metal film layer, for example, it can be 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times or 2 times.

[0076] It is understandable that when using the lift-off process to prepare metal films, if the thickness of the photoresist layer to be peeled off is close to the thickness of the metal film, it is easy for the metal film layer that needs to be peeled off to be located on the surface of the photoresist layer to stick together with the metal film layer that does not need to be peeled off, which will result in a lower precision of the metal film layer after peeling off.

[0077] In a preferred embodiment, after the first coating in S1, the process further includes pre-baking the first photoresist layer made of negative photoresist. More preferably, the pre-baking is performed at 100°C-120°C for 2-4 minutes, and more preferably, it is performed on a hot plate at 110°C for 2 minutes.

[0078] In a preferred embodiment, after the second coating in S2, the process further includes pre-baking the second photoresist layer made of the mixed photoresist. More preferably, the pre-baking is performed at 100°C-120°C for 3-5 minutes, and more preferably, it is performed on a hot plate at 110°C for 3 minutes.

[0079] It should be noted that the pre-baking process mainly removes most of the solvent inside the photoresist by baking, so that the photoresist layer can be initially cured.

[0080] In a preferred embodiment, the first coating in S1 and the second coating in S2 are respectively prepared using a spin coating process.

[0081] More preferably, when spin-coating with negative photoresist, a first low-speed spin-coating can be performed first, followed by a high-speed spin-coating, and then a second low-speed spin-coating. Similarly, when spin-coating with mixed photoresist on the surface of the first photoresist layer, a first low-speed spin-coating can be performed first, followed by a high-speed spin-coating, and then a second low-speed spin-coating.

[0082] More preferably, the spin-coating speeds of the first and second low-speed spin coatings are 300 rpm to 500 rpm, for example, 300 rpm, 400 rpm, 500 rpm, or any value between 300 rpm and 500 rpm, and the low-speed spin-coating time is 5 s to 10 s, for example, 5 s, 6 s, 7 s, 8 s, 9 s, 10 s, or any value between 5 s and 10 s. The spin-coating speeds and times of the first and second low-speed spin coatings can be the same or different. More preferably, the parameters for both the first and second low-speed spin coatings are that they are maintained at 500 rpm for 5 s.

[0083] It should be noted that the first low-speed spin coating is performed mainly to cover the photoresist to the surface of the entire substrate structure, which is actually to cover the entire surface of the micro LED epitaxial wafer with mesa structure.

[0084] More preferably, the spin coating speed of the high-speed spin coating is 1500rpm-2500rpm, for example, it can be 1500rpm, 1800rpm, 1900rpm, 2000rpm, 2200rpm, 2500rpm, or any value between 1500rpm and 2500rpm, and the spin coating time is 50s-70s, for example, it can be 50s, 55s, 60s, 65s, 70s, or any value between 50s and 70s. More preferably, the parameter for high-speed spin coating is to maintain 2000rpm for 60s.

[0085] In a preferred embodiment, the thickness of the first photoresist layer obtained in S1 is 6μm-8μm, and the thickness of the second photoresist layer obtained in S2 is 1μm-2μm. Because the two photoresists will dissolve each other during spin coating, the total thickness of the photoresist layer after the first and second photoresist layers are stacked is 3μm-4μm.

[0086] In a preferred embodiment, after exposure, step S3 further includes: baking at 100°C-120°C for 5-10 minutes, followed by development in a developing solution, and then post-baking at 100°C-120°C for 3-5 minutes. More preferably, after baking on a hot plate at 110°C for 10 minutes, the sample is immersed in a developing solution for 2 minutes, and then post-baked on a hot plate at 110°C for 3 minutes.

[0087] Understandably, the 5-10 minute baking time is primarily to ensure the cross-linking reaction in the exposed photoresist is fully completed, especially in the underlying first photoresist layer. The subsequent post-baking process is to further remove the solvent from the photoresist layer. The choice of developer depends mainly on the type of photoresist itself.

[0088] Furthermore, after development in the developer solution, the developed sample undergoes microscopic examination to ensure that the pattern is clean and free of large areas of photoresist residue. Following post-baking, dry plasma stripping is performed, for example, by placing the sample in an Asher or Descum stripping system to ensure no photoresist residue remains within the pattern.

[0089] It should be noted that before setting the metal layer in S4, the total thickness of the first and second photoresist layers needs to be tested using a profilometer. Only when the total thickness is confirmed to be 1.5-2 times the planned metal coating thickness can the metal coating process be carried out. For example, an electron beam evaporation coating process can be used.

[0090] In a preferred embodiment, the stripping process in S5 specifically includes: immersing the sample with the metal layer in a photoresist remover or acetone, then using ultrasonic treatment to completely remove the first and second photoresist layers. At this time, the metal layer on the surface of the second photoresist layer is also removed. After that, the sample is taken out, cleaned and dried with deionized water, and then examined under a microscope.

[0091] Thirdly, this application also provides a method for fabricating a micro LED chip, comprising:

[0092] (1) Provide a micro LED epitaxial wafer, and etch a surface structure on the micro LED epitaxial wafer;

[0093] (2) A metal electrode is prepared on the surface of the platform structure using the metal electrode preparation method described in the second aspect above;

[0094] (3) A passivation layer is prepared on the surface of the metal electrode, and the passivation layer is etched to obtain an electrode contact hole.

[0095] In a preferred embodiment, the micro-LED epitaxial wafer 100 comprises, from bottom to top, a substrate 110, a buffer layer 120, a third semiconductor layer 130, a first semiconductor layer 140, a multiple quantum well structure 150, and a second semiconductor layer 160, as follows: Figure 2 As shown. The epitaxial wafer can be pre-prepared or deposited layer by layer on the substrate. It should be understood that the embodiment listed is only an exemplary micro-LED epitaxial wafer structure, and the epitaxial wafer may also include other layers or other structures, which are not specifically limited herein.

[0096] The mesa structure 200 obtained by etching on the micro-LED epitaxial wafer, such as Figure 3 As shown. The mesa structure 200 includes multiple protrusions 210, which can be used to form an array, thereby forming a chip array.

[0097] In a preferred embodiment, the etching includes: removing a portion of the second semiconductor layer and the multiple quantum well structure on the microLED epitaxial wafer using inductively coupled plasma etching to expose the first semiconductor layer.

[0098] Specifically, photoresist is spin-coated onto the surface of the micro-LED epitaxial wafer, and a surface pattern is photolithographically etched. Then, inductively coupled plasma etching (ICP) is used, employing a mixed gas of Cl2 and Ar, to etch from the second semiconductor layer 160 until the first semiconductor layer 140 is exposed. Finally, the photoresist is removed to form... Figure 3 The mesa structure 200 is shown. Then, a metal electrode 170 is prepared on the surface of the mesa structure 200 using the metal electrode preparation method described in the second aspect above, as shown. Figure 4 As shown.

[0099] In a preferred embodiment, such as Figure 5 As shown, the method for preparing the passivation layer 180 on the surface of the metal electrode 170 includes plasma-enhanced chemical vapor deposition. The passivation layer 180 can be made of materials such as silicon dioxide, silicon nitride, or aluminum oxide.

[0100] In a preferred embodiment, etching the passivation layer 180 specifically includes using dry etching and / or wet etching processes. If the process requirements are not high, dry etching or wet etching alone can be used to obtain the electrode contact hole 190. If the process requirements are high, dry etching is used first, followed by wet etching, to finally etch the electrode contact hole 190. Figure 6 As shown.

[0101] Fourthly, this application also provides a micro LED chip, which is fabricated using the micro LED chip fabrication method described in the third aspect above.

[0102] Fifthly, this application provides a micro light-emitting device, including the micro LED chip described in the fourth aspect above.

[0103] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate this application and should not be regarded as limiting the scope of this application.

[0104] Example 1

[0105] This embodiment provides a hybrid photoresist, the preparation method of which includes:

[0106] Negative photoresist and black photoresist were mixed in a volume ratio of 3:1, and then placed in a vacuum degassing machine for vacuum degassing to obtain mixed photoresist.

[0107] This embodiment provides a metal electrode, the preparation method of which may include:

[0108] (1) Spin-coating a negative photoresist onto a 4-inch wafer sample to obtain a negative photoresist layer. The spin-coating parameters can be 500rpm / 5s-2000rpm / 60s-500rpm / 5s. Then, pre-baking is performed on a hot plate at 110℃ for 2 minutes to remove most of the solvent inside the first photoresist layer and allow it to be initially cured.

[0109] (2) Spin-coating the mixed photoresist provided in this embodiment on the first photoresist layer in step (1) to obtain a mixed photoresist layer. The spin-coating parameters can be 500rpm / 5s-2000rpm / 60s-500rpm / 5s. Then, pre-baking is performed on a hot plate at 110℃ for 3 minutes to remove most of the solvent in the second photoresist layer and allow it to be initially cured.

[0110] (3) Place the sample obtained in step (2) into a photolithography machine for exposure, with an exposure dose of 80 mJ / cm². 2 After exposure, the sample is placed on a hot plate at 110°C for 10 minutes to allow the cross-linking reaction in the double-layer photoresist to proceed fully. Then, the sample is placed in the developer for about 2 minutes.

[0111] (4) After development, perform microscopic examination to ensure that the pattern is clean and free of large pieces of photoresist residue; then place the sample on a hot plate at 110°C for 3 minutes and bake to further remove the solvent in the photoresist.

[0112] (5) An Asher apparatus can be used to perform oxygen plasma dry stripping on the sample. The sample is placed in the apparatus to ensure that there is no photoresist residue inside the pattern. During implementation, the processing conditions can be 100w for 5 minutes.

[0113] (6) Use a profilometer to measure the thickness of the double-layer photoresist layer on the sample surface in step (5). After confirming that the thickness is between 1.5 and 2 times the planned thickness of the metal coating, the sample is then vapor-deposited to obtain the metal layer.

[0114] (7) Immerse the coated sample in the resist stripping solution in step (6), then use ultrasound to remove the double-layer photoresist layer outside the pattern and the metal on its surface. Finally, rinse with deionized water and examine the pattern under a microscope.

[0115] Example 2

[0116] This embodiment provides a hybrid photoresist, the preparation method of which includes:

[0117] Negative photoresist and black photoresist were mixed in a volume ratio of 2.5:1, and then placed in a vacuum degassing machine for vacuum degassing to obtain mixed photoresist.

[0118] This embodiment provides a metal electrode, which is prepared using the same method as in Embodiment 1, except that: the hybrid photoresist used in step (2) is the one described in this embodiment; and the exposure dose in step (3) is 90 mJ / cm. 2 .

[0119] Comparative Example 1

[0120] This comparative example provides a metal electrode, which is prepared in the same way as in Example 1, except that step (2) is omitted. After obtaining the negative photoresist layer in step (1), the sample of the single-layer negative photoresist layer is placed in a photolithography machine for exposure, development and other processes.

[0121] Comparative Example 2

[0122] This comparative example provides a hybrid photoresist, the same as in Example 1.

[0123] This comparative example provides a metal electrode, which is prepared in the same way as in Example 1, except that step (1) can be omitted. Instead, the mixed photoresist is directly spin-coated onto the surface of a 4-inch wafer sample to obtain a single layer of mixed photoresist. Then, the sample with the single layer of mixed photoresist is placed in a photolithography machine for exposure, development and other processes.

[0124] After examining the metal electrodes prepared in Example 1 and Comparative Example 1 under a microscope, the results are as follows: Figures 7-10 As shown.

[0125] Figure 7 This is a photolithography microscopy image of the double-layer photoresist (negative photoresist layer + mixed photoresist layer) in Example 1 after exposure and development. The striped patterns are the striped holes left after photolithography development. There are ten stripes in total, with widths from largest to smallest as follows: 5μm, 4μm, 3μm, 2μm, 1μm, 1μm, 0.8μm, 0.8μm, 0.5μm, and 0.5μm. Figure 8 This is a microscopic image after step (7) of Example 1. Figure 9 The image shown is a photolithography microscopy image of the single-layer negative photoresist layer of Comparative Example 1 after exposure and development. The photolithography plate and photolithography conditions used are exactly the same as those in Example 1. Figure 10 This is a microscopic image of the single-layer negative photoresist layer in Comparative Example 1 after it has been peeled off.

[0126] Will Figure 7 and Figure 9 By comparison, it can be found that the pattern size obtained after photolithography in Example 1 is larger than that in Comparative Example 1. In particular, the pattern width at the longest strip in the middle of the two images is clearly visible. Figure 7 Width ratio at the longest bar Figure 9 It is larger; and Figure 7 The pattern boundary in the middle is compared to Figure 9 The pattern boundaries are also clearer. This indicates that the technical solution of this application used in Embodiment 1 reduces the exposure intensity of the negative photoresist and reduces the residual photoresist area in the unexposed region.

[0127] Will Figure 8 and Figure 10 By comparison, it is obvious that Figure 10 The metal layer obtained after evaporation and stripping has a relatively high rate of detachment. Figure 8 The situation is even more serious, especially the strip metal with a width of less than 1μm, which all fell off. This indicates that under the same exposure conditions, Example 1 can effectively reduce the exposure intensity of the negative photoresist, ensuring the size of the evaporated metal and the metal obtained after stripping. It also proves that the negative photoresist will cause residual photoresist at the bottom of the metal pattern due to excessive exposure dose, which will make the metal obtained after evaporation and stripping easy to fall off.

[0128] In Comparative Example 2, because the negative photoresist and the black photoresist require different solvents, the mixed photoresist formed after their mixing will undergo mutual solubility after suspension coating, resulting in a thinner overall photoresist layer. Consequently, a thicker metal layer cannot be obtained. Therefore, the metal layer thickness after metal deposition and stripping in Comparative Example 2 does not meet the requirements.

[0129] Comparing the pattern size and pattern boundaries of the metal electrodes prepared in the above embodiments and comparative examples, it is evident that by covering the surface of the negative photoresist layer with mixed photoresist, the photolithographic exposure amount reaching the negative photoresist is significantly reduced, thus lowering the exposure intensity received by the negative photoresist and improving the photolithographic precision of the negative photoresist. Under the same photolithography machine, this improves processing accuracy and the dimensional accuracy of the metal electrodes after resist stripping, thereby enhancing the photoelectric performance of the micro-LED chip containing the metal electrodes. Furthermore, it improves the versatility of the photolithography machine, allowing this type of low-performance photolithography machine with a high exposure limit to be applied to more semiconductor product processing scenarios, such as for fabricating products with high-precision metal electrodes. In addition, the metal electrodes in the embodiments of this application can also be fabricated on the mesa structure of the micro-LED epitaxial wafer. By using the micro-LED chip fabrication method provided above, a micro-LED chip can be prepared. Because the metal electrodes on this micro-LED chip are small and highly precise, the area utilization rate of the epitaxial wafer is greatly increased, which helps to fabricate high-PPI, high-resolution display arrays.

[0130] This application also provides a micro-light-emitting device, which includes the aforementioned micro-LED chip. This micro-light-emitting device can be applied to electronic devices to realize extended reality (XR) technologies such as augmented reality (AR), virtual reality (VR), and mixed reality (MR). For example, the micro-light-emitting device can be a projection part of an electronic device, such as a projector or head-up display (HUD); or it can be a display part of an electronic device, such as a smartphone, smartwatch, laptop, tablet, dashcam, navigator, head-mounted device, or any device with a display screen; or it can be an illumination part of an electronic device, such as a vehicle or streetlight, or any device with an illumination component.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0132] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a metal electrode, characterized in that, The method includes: A first photoresist layer is obtained by applying a negative photoresist to the surface of the defined structure. A second photoresist layer is obtained by applying a mixed photoresist to the surface of the first photoresist layer. The first photoresist layer and the second photoresist layer are exposed to obtain the first photoresist layer and the second photoresist layer with a set pattern. A metal layer is disposed on a second photoresist layer having the defined pattern; The first and second photoresist layers under the metal layer are peeled off to obtain a metal film layer, which is a metal electrode. The raw materials of the hybrid photoresist include negative photoresist and matte photoresist, and the volume ratio of the negative photoresist to the matte photoresist in the hybrid photoresist is (2.5-3.5):1; The matte photoresist includes black photoresist.

2. The preparation method according to claim 1, characterized in that, The exposure dose is 80 mJ / cm. 2 -100mJ / cm 2 .

3. The preparation method according to claim 1 or 2, characterized in that, The first thickness of the first photoresist layer and the second photoresist layer stacked together is 1.5-2 times the second thickness of the metal film layer.

4. The preparation method according to claim 1, characterized in that, After the first coating is applied, the process further includes: pre-baking the negative photoresist. After the second coating is performed, the process further includes pre-baking the mixed photoresist.

5. The preparation method according to claim 1, characterized in that, The method includes at least one of the following conditions: a. The first coating and the second coating each independently comprise preparations using a spin coating process; b. The spin coating process includes: first performing a first low-speed spin coating, then performing a high-speed spin coating, and then performing a second low-speed spin coating; c. The spin coating speed for the first low-speed spin coating and the second low-speed spin coating is 300rpm-500rpm, and the spin coating time is 5s-10s; d. The high-speed spin coating has a spin speed of 1500rpm-2500rpm and a spin coating time of 50s-70s; e. After the first coating is performed, the method further includes: pre-baking the negative photoresist at 100℃-120℃ for 2min-4min; f. After the second coating is performed, the method further includes: pre-baking the mixed photoresist at 100℃-120℃ for 3min-5min; g. The thickness of the first photoresist layer is 6μm-8μm, the thickness of the second photoresist layer is 1μm-2μm, and the total thickness of the photoresist layer after the first photoresist layer and the second photoresist layer are stacked is 3μm-4μm; h. After exposure, the process further includes: baking at 100℃-120℃ for 5min-10min, then immersing in a developer for development, and finally baking at 100℃-120℃ for 3min-5min after removal.

6. A method for fabricating a micro LED chip, characterized in that, include: A micro LED epitaxial wafer is provided, and a surface structure is etched on the micro LED epitaxial wafer; A metal electrode is prepared on the surface of the platform structure using the metal electrode preparation method according to any one of claims 1-5; A passivation layer is prepared on the surface of the metal electrode, and the passivation layer is etched to obtain an electrode contact hole.

7. The method for fabricating a micro LED chip as described in claim 6, characterized in that, It also meets at least one of the following conditions: g. The micro-LED epitaxial wafer comprises, from bottom to top, a substrate, a buffer layer, a third semiconductor layer, a first semiconductor layer, a multi-quantum-well structure, and a second semiconductor layer; h. The etching includes: removing a portion of the second semiconductor layer and the multiple quantum well structure on the microLED epitaxial wafer using inductively coupled plasma etching to expose the first semiconductor layer; i. The method for preparing the passivation layer includes plasma-enhanced chemical vapor deposition; j. The etching includes processes performed using dry etching and / or wet etching.

8. A micro LED chip, characterized in that, It is prepared using the method for preparing the micro LED chip according to claim 6 or 7.

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