LED mounting substrate manufacturing method and cleaning method

Abstract

To provide a method for manufacturing an LED mounting substrate by selectively removing metal Ga adhered to LED chips transferred from a sapphire substrate to a receptor substrate by laser lift-off without dissolving or denaturing other metals.SOLUTION: In the process for cleaning LED chips with alkaline cleaning solution in a method for manufacturing an LED mounting substrate, it is preferable to clean LED chips 5 transferred on a receptor substrate 2 by immersing the entire receptor substrate 2 in the alkaline cleaning solution 6. A gallium 4 can be selectively removed more easily, reliably, and stably. More specifically, the receptor substrate 2 on which LED chips 5 are transferred is immersed in a cleaning container filled with the alkaline cleaning solution 6, followed by appropriate number of washes with pure water, etc., and then dried.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an LED-mounted substrate, a cleaning solution, and a cleaning method. [Background technology]

[0002] In recent years, nitride semiconductor optical devices have come to be used as backlights for liquid crystal displays and signage displays.

[0003] Optical devices are mass-produced on sapphire substrates, for example, using semiconductor processes. To create a 4-inch display substrate using LEDs called micro-LEDs, which are 100 μm square or less, several million micro-LEDs are required. Micro-LEDs are tiny devices measuring several tens of μm in size, and are used after being separated from the sapphire substrate used for epitaxial growth.

[0004] In the manufacturing process of micro LED displays, laser lift-off (LLO) is performed to peel the micro LED chip from the sapphire substrate. The LLO process involves irradiating the GaN layer of the LED chip with an excimer laser, decomposing the GaN layer into gaseous N2 and metallic Ga, thereby peeling the LED chip from the sapphire substrate. This results in a receptor substrate with numerous optical devices arranged on its surface.

[0005] This method is not limited to optical devices, but can also be applied to the manufacture of receptor substrates on which a plurality of transfer objects, such as minute semiconductor devices, are arranged.

[0006] For example, Patent Document 1 proposes a method for transferring an object to be transferred from a donor substrate to a receptor substrate with high precision using laser irradiation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2020-4478 Summary of the Invention [Problem to be solved by the invention]

[0008] During the LLO process, opaque metallic Ga precipitates on the surface of the peeled micro LED chip. When the metallic Ga precipitated on the LED chip was removed with an acidic cleaning solution and the cleaned LED chip was mounted on a substrate, a connection failure occurred. After investigating various possibilities for the cause of this connection failure, the inventors noticed that the shape of the bumps before connection had changed from their original state. They then determined that this change was caused by the bumps being dissolved or denatured by the acidic cleaning solution used in the cleaning process.

[0009] Here, when the LED chip was transferred from the sapphire substrate to the receptor substrate, the bumped surface was attached to the receptor substrate and was supposed to be protected from the cleaning solution, but it was dissolved and degraded during the cleaning process. In other words, it was thought that there was a gap between the LED chip and the receptor substrate due to the bumps, and the cleaning solution penetrated through this gap, dissolving and degrading the bumps.

[0010] As shown in Figure 5, metals used in bumps (such as In and SnAgCu alloys (SAC)) and Ga (gallium) are often close to each other in the periodic table, and it was thought that it would be difficult to selectively remove gallium when the bumps and gallium are in contact with the cleaning solution. Therefore, the inventors first considered protecting the bumps from the cleaning solution by deeply embedding the bumps in the adhesive layer of the receptor substrate. However, while this method could protect the bumps from the cleaning solution, it was found that it made it difficult to peel the adhesive layer from the bumps in subsequent processes.

[0011] Here, being close to gallium in the periodic table means being close to the 4th period, 13th group, which is the position of gallium on the periodic table. For example, it may be a position in the range of the 3rd period to the 6th period and the 11th group to the 15th group, or a position in the range of the 3rd period to the 5th period and the 11th group to the 14th group.

[0012] Thus, it was found that there is a need for a cleaning method and a cleaning solution that can selectively remove metal Ga from components such as LED chips that have metal Ga and metals other than metal Ga on their surfaces without affecting the metals other than metal Ga.

[0013] The present invention has been made to solve the above problems, and aims to provide a method for manufacturing an LED-mounted substrate that can selectively remove metal Ga (hereinafter, sometimes simply referred to as "Ga" or "gallium") adhering to an LED chip that has been transferred from a sapphire substrate to a receptor substrate by laser lift-off, without dissolving or modifying other metals, to manufacture an LED-mounted substrate; a cleaning solution that can be used for this method; a cleaning method that selectively removes gallium adhering to an LED chip without dissolving or modifying other metals; and a cleaning method that selectively removes gallium from a component that has gallium and metals other than gallium on its surface, without dissolving or modifying metals other than gallium. [Means for solving the problem]

[0014] The present invention has been made to achieve the above-mentioned object, and provides a method for manufacturing an LED mounting substrate, which includes a step of cleaning, with an alkaline cleaning solution, an LED chip transferred from a sapphire substrate to a receptor substrate by laser lift-off.

[0015] According to this method for manufacturing an LED mounting substrate, unnecessary gallium can be removed without dissolving or modifying metals such as bumps of the LED chip, thereby making it possible to manufacture a high-quality LED mounting substrate.

[0016] At this time, the LED chip transferred onto the receptor substrate has gallium on the surface opposite to the receptor substrate, and the gallium can be removed by the cleaning step.

[0017] The cleaning step in the method for manufacturing an LED mounting substrate of the present invention is particularly effective in removing gallium from such LED chips.

[0018] In this case, the alkaline cleaning solution may have an alkali concentration of 0.5% by mass or more and a saturated concentration or less, and the temperature of the alkaline cleaning solution may be 5° C. or more and 80° C. or less, and the cleaning time with the alkaline cleaning solution may be 10 seconds or more and 1 hour or less.

[0019] Under these conditions, gallium can be selectively removed more stably and reliably.

[0020] In this case, the LED chip may have bumps on the surface that is to be bonded to the receptor substrate.

[0021] The method for manufacturing an LED mounting substrate of the present invention is particularly effective when manufacturing an LED mounting substrate having bumps from such LED chips.

[0022] In this case, the bumps may be formed of lead-free solder and may contain at least one selected from a SnAgCu-based alloy, a SnZnBi-based alloy, a SnCu-based alloy, a SnAgInBi-based alloy, a SnZnAl-based alloy, and indium as a main component.

[0023] The method for manufacturing an LED mounting substrate of the present invention is particularly effective when targeting LED chips having such bumps.

[0024] At this time, the LED chip transferred onto the receptor substrate can be cleaned by immersing the receptor substrate together with the LED chip in the alkaline cleaning solution.

[0025] This makes it easier to manufacture the LED mounting substrate.

[0026] The present invention also provides an alkaline cleaning solution for cleaning an LED chip provided on a sapphire substrate after transferring the LED chip to a receptor substrate by laser lift-off.

[0027] Such a cleaning solution can selectively remove unnecessary gallium without dissolving or modifying metals such as bumps on the LED chip.

[0028] In this case, the cleaning liquid may have a pH of 9.5 to 14.0. The cleaning liquid may be an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium hydrogen carbonate, and potassium acetate.

[0029] This allows for easier and more stable cleaning.

[0030] The present invention also provides a cleaning method for cleaning an LED chip separated from a sapphire substrate by laser lift-off, the cleaning method using an alkaline cleaning solution.

[0031] According to this cleaning method for cleaning an LED chip, unnecessary gallium can be selectively removed without dissolving or modifying metals such as bumps on the LED chip.

[0032] In this case, the LED chip can be transferred onto a receptor substrate.

[0033] The cleaning method of the present invention is particularly effective when cleaning such LED chips.

[0034] The present invention also provides a cleaning method for selectively removing gallium from a component having gallium and a metal other than gallium on its surface, the cleaning method comprising cleaning the component using an alkaline cleaning solution.

[0035] According to such a cleaning method for selectively removing gallium, gallium can be selectively removed in a simple manner without dissolving or modifying metals other than gallium.

[0036] In this case, the alkaline cleaning solution can be brought into contact with the gallium and the metals other than gallium during the cleaning.

[0037] This makes it possible to selectively remove gallium in a simpler manner without dissolving or modifying metals other than gallium.

[0038] In this case, the component may be substrate-shaped and fixed to another substrate during the cleaning, the gallium may be present on the surface of the component opposite to the other substrate side, and the metal other than the gallium may be present on the other substrate side of the component.

[0039] The cleaning method of the present invention is particularly effective when cleaning such parts.

[0040] In this case, the metal other than gallium may include at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin, and bismuth. Also, the metal other than gallium may include at least one metal selected from the group consisting of copper, silver, indium, and tin. Also, the metal other than gallium may include copper, silver, and tin.

[0041] Such metals other than gallium are more stable and do not dissolve or denature. [Effects of the Invention]

[0042] As described above, according to the method for manufacturing an LED mounting substrate of the present invention, it is possible to selectively remove unnecessary gallium without dissolving or modifying metals such as bumps on the LED chip, thereby manufacturing a high-quality LED mounting substrate and reducing connection defects of the LED chips.

[0043] Furthermore, the cleaning solution of the present invention can selectively remove unnecessary gallium without dissolving or modifying metals such as bumps on the LED chip, thereby reducing connection failures in the LED chip.

[0044] Furthermore, according to the cleaning method for cleaning LED chips separated from sapphire substrates by laser lift-off of the present invention, it is possible to selectively remove unnecessary gallium without dissolving or modifying metals such as bumps on the LED chip, thereby reducing connection failures of the LED chips.

[0045] Furthermore, according to the cleaning method for selectively removing gallium of the present invention, it is possible to selectively remove unnecessary gallium from a component having gallium and a metal other than gallium on the surface in a simple manner without dissolving or modifying the metal other than gallium.

[0046] In the present invention, it is preferable that metals other than the metals of the bumps etc. and gallium are not dissolved at all, however, if the amount of gallium removed is greater than the amount of metals other than the bumps etc. and gallium removed and gallium can be selectively removed, the metals other than the bumps etc. and gallium may be dissolved to a practical extent. [Brief explanation of the drawings]

[0047] [Figure 1] 1 is a diagram illustrating an example of a cleaning step according to the present invention. [Figure 2] The conditions and evaluation results for Examples 1 to 3 and Comparative Examples 1 and 2 are shown below. [Figure 3] The evaluation results of Example 4 are shown below. [Figure 4] 4 shows the evaluation results of Comparative Example 3. [Figure 5] FIG. 1 is a diagram (periodic table) for explaining examples of metal elements that are / are not targeted for removal by cleaning. [Figure 6] FIG. 1 is a schematic diagram illustrating Gap-Laser Lift-Off (Gap-LLO). [Figure 7] FIG. 1 is a schematic diagram illustrating contact-laser lift-off (Contact-LLO). DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention will be described in detail below, but the present invention is not limited thereto.

[0049] As described above, there has been a demand for a method for manufacturing an LED mounting substrate that can selectively remove metallic Ga adhering to an LED chip that has been transferred from a sapphire substrate to a receptor substrate by laser lift-off without dissolving or modifying other metals, a cleaning solution that can be used for this method, a cleaning method that selectively removes gallium adhering to an LED chip without dissolving or modifying other metals, and a cleaning method that selectively removes gallium from components that have gallium and metals other than gallium on their surfaces without dissolving or modifying metals other than gallium.

[0050] As a result of extensive research into the above-mentioned problems, the inventors have discovered that a method for manufacturing an LED mounting substrate, which includes a step of cleaning an LED chip transferred from a sapphire substrate onto a receptor substrate by laser lift-off, with an alkaline cleaning solution, can selectively remove unnecessary gallium without dissolving or modifying metals such as bumps on the LED chip, thereby making it possible to manufacture a high-quality LED mounting substrate and reduce connection defects in the LED chips, thereby completing the present invention.

[0051] The inventors have also discovered that an alkaline cleaning solution for cleaning an LED chip mounted on a sapphire substrate after transferring it to a receptor substrate by laser lift-off can selectively remove unnecessary gallium without dissolving or denaturing metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip, and have completed the present invention.

[0052] The inventors also discovered that a cleaning method for cleaning an LED chip separated from a sapphire substrate by laser lift-off, which uses an alkaline cleaning solution, makes it possible to selectively remove unnecessary gallium without dissolving or denaturing metals such as bumps on the LED chip, and thus completed the present invention.

[0053] The present inventors have also discovered that a cleaning method for selectively removing gallium from a component having gallium and a metal other than gallium on its surface, in which the component is cleaned using an alkaline cleaning solution, makes it possible to selectively remove unnecessary gallium in a simple manner without dissolving or denaturing the metal other than gallium, and have completed the present invention.

[0054] The following description will be made with reference to the drawings.

[0055] As described above, the inventors of the present invention conducted extensive research to solve the above-mentioned problems and surprisingly found that by using an alkaline aqueous solution as a cleaning solution, gallium can be selectively removed without affecting metals other than gallium, even if the bumps are not physically protected. The fact that gallium can be selectively removed using the simple method of using an alkaline aqueous solution as a cleaning solution can simplify the production process and improve yields, and is a major step toward reducing the cost of micro LED displays, which are said to cost tens of millions of yen per unit. The present invention is described in more detail below.

[0056] [Cleaning solution] The cleaning solution of the present invention is an alkaline cleaning solution for cleaning an LED chip mounted on a sapphire substrate after it has been transferred to a receptor substrate by laser lift-off. The cleaning solution of the present invention can selectively remove unnecessary gallium without dissolving or denaturing metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip.

[0057] Such a cleaning solution is not particularly limited as long as it is alkaline, but a solution with a pH of 9.5 to 14.0 is preferred. It can selectively remove Ga stably and reliably without dissolving or denaturing metals such as bumps on the LED chip.

[0058] The cleaning solution according to the present invention may be an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium hydrogencarbonate, and potassium acetate. Such aqueous solutions are relatively easy to obtain and handle, and are low in cost.

[0059] The preferred conditions for cleaning using the cleaning solution according to the present invention will be described later.

[0060] [LED mounting board manufacturing method] The method for manufacturing an LED mounting substrate according to the present invention includes a step of cleaning the LED chips transferred from the sapphire substrate to the receptor substrate by laser lift-off with an alkaline cleaning solution. The laser lift-off method is not particularly limited, but gap-laser lift-off (Gap-LLO) and contact-laser lift-off (Contact-LLO) are applicable. These methods are outlined below with reference to FIGS. 6 and 7.

[0061] In Gap-LLO, first, as shown in Fig. 6(a), a sapphire substrate 1 having, for example, LED chips 5 as transfer objects and a receptor substrate 2, for example, a quartz substrate, having an adhesive layer 3 such as silicone on its surface, are placed opposite each other with a space between the LED chips 5 and the adhesive layer 3, i.e., a gap being provided. In this state, a laser 20 is emitted from a laser oscillator 110 through the surface of the sapphire substrate 1 opposite the LED chips 5, onto the interfaces 11 between the sapphire substrate 1 and the multiple LED chips 5. The laser 20 is generally irradiated onto the entire surface of the interface 11 between the sapphire substrate 1 and each LED chip 5 one by one in sequence.

[0062] For example, in the case of a sapphire substrate 1 provided with multiple LED chips 5, each of which includes a gallium nitride semiconductor layer such as a GaN layer at its interface 11, irradiation with a laser 20 decomposes the GaN layer (ablation). Ablation weakens the bonding strength (adhesion, joining, etc.) between the LED chips 5 and the sapphire substrate 1, causing the LED chips 5 to peel off from the sapphire substrate 1. Furthermore, decomposition of the GaN layer generates gas (e.g., nitrogen gas). The pressure of this gas propels the peeled LED chips 5 toward the receptor substrate 2, moving them through the space between the sapphire substrate 1 and the receptor substrate 2 until they reach the adhesive layer 3 on the receptor substrate 2. In this way, the LED chips 5 are transferred onto the receptor substrate 2. Next, as shown in FIG. 6(b), the sapphire substrate 1 is removed. This completes the transfer of the LED chips 5 from the sapphire substrate 1 to the receptor substrate 2.

[0063] Contact-LLO is similar to Gap-LLO except that, during irradiation with a laser beam 20, a sapphire substrate 1 having an LED chip 5 as a transfer target and a receptor substrate 2 having an adhesive layer 3 on its surface are placed opposite each other with the LED chip 5 and the adhesive layer 3 in contact with each other, as shown in Fig. 7(a). After irradiation with the laser beam 20, the sapphire substrate 1 is removed as shown in Fig. 7(b), thereby completing the transfer of the LED chip 5 from the sapphire substrate 1 to the receptor substrate 2.

[0064] During the LLO process, decomposition of gallium nitride semiconductor layers such as GaN layers leaves metallic Ga remaining on components such as the LED chip 5. To remove this metallic Ga, the LED chip 5 is cleaned using an alkaline cleaning solution in the present invention. This allows for selective removal of unnecessary gallium without dissolving or denaturing metals such as bumps on the LED chip, thereby reducing connection failures in the LED chip.

[0065] The alkaline cleaning solution used here can be the alkaline cleaning solution described above.

[0066] The alkaline concentration of the alkaline cleaning solution is preferably 0.5% by mass or more and less than the saturation concentration. The temperature of the alkaline cleaning solution is preferably 5°C or more and 80°C or less. The temperature of the cleaning solution is preferably 5°C or more, so that it does not freeze. Even if the temperature is too high, the gallium removal effect will not change, so it can be 80°C or less. Furthermore, the cleaning time with the alkaline cleaning solution is preferably 10 seconds or more and 1 hour or less. By setting the cleaning time to 10 seconds or more, Ga can be selectively removed more stably and reliably. Even if the cleaning time is too long, the gallium removal effect will not change, so it can be 1 hour or less. By appropriately combining the above-mentioned alkaline concentration, temperature of the alkaline cleaning solution, and cleaning time, gallium can be selectively removed more stably and reliably.

[0067] The LED chip transferred onto the receptor substrate as described above has gallium on the surface opposite the receptor substrate. The LED chip also has bumps on the side that will be attached to the receptor substrate. The gallium on the surface opposite the receptor substrate can be easily removed by cleaning with an alkaline cleaning solution.

[0068] In the LED mounting substrate manufacturing method according to the present invention, the bumps are preferably formed of lead-free solder, and more preferably have at least one selected from the group consisting of SnAgCu (SAC) alloys, SnZnBi alloys, SnCu alloys, SnAgInBi alloys, SnZnAl alloys, and indium as a main component. In particular, when such bumps are used, dissolution and modification (damage) of the bumps can be stably and reliably prevented even when the bumps are cleaned with an alkaline cleaning solution.

[0069] FIG. 1 shows an example of a process for cleaning LED chips with an alkaline cleaning solution. As shown in FIG. 1, in the process for cleaning LED chips with an alkaline cleaning solution in the manufacturing method for an LED-mounted substrate according to the present invention, it is preferable to clean the LED chip 5 transferred onto the receptor substrate 2 by immersing the receptor substrate 2 together with the receptor substrate 2 in an alkaline cleaning solution 6. This method allows for selective removal of gallium 4 more simply, reliably, and stably. More specifically, as shown in FIG. 1, the receptor substrate 2 on which the LED chip 5 has been transferred is immersed in a cleaning vessel filled with alkaline cleaning solution 6, and then washed with pure water or the like an appropriate number of times, followed by drying (air drying).

[0070] [How to clean LED chips] The present invention also provides a cleaning method for cleaning LED chips separated from sapphire substrates by the laser lift-off method described above using an alkaline cleaning solution. This cleaning method easily and selectively removes only gallium without dissolving or denaturing metals other than gallium, thereby reducing connection failures of the LED chips. In addition, in this cleaning method according to the present invention, it is preferable that the LED chips are transferred onto a receptor substrate. A specific example of the LED chip cleaning method is the same as that described above with reference to FIG. 1.

[0071] [Cleaning method for selectively removing gallium from components] The present inventors have found that by cleaning an LED chip separated from a sapphire substrate by laser lift-off as described above with an alkaline cleaning solution, it is possible to selectively remove only gallium without dissolving or denaturing metals other than gallium. As a result of further research, they have found that, not only from LED chips, but also when selectively removing gallium from components having gallium and metals other than gallium on their surfaces, the extremely simple method of cleaning the component with an alkaline cleaning solution can selectively remove gallium without dissolving or denaturing metals other than gallium.

[0072] In such a cleaning method, it is particularly preferable to carry out cleaning by bringing gallium and metals other than gallium into contact with an alkaline cleaning solution, which allows selective removal of gallium in a simpler manner without dissolving or denaturing metals other than gallium.

[0073] Furthermore, it is preferable that the part to be cleaned is in the form of a substrate and is fixed to another substrate during cleaning, and that the gallium is present on the surface of the part opposite to the other substrate side, and that the metal other than gallium is present on the other substrate side of the part.

[0074] The metal other than gallium is preferably one having at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin and bismuth, more preferably one having at least one metal selected from the group consisting of copper, silver, indium and tin, and even more preferably one having copper, silver and tin. If the metal other than gallium is such a metal, dissolution and denaturation during cleaning can be more stably suppressed.

[0075] In the present invention, the gallium to be removed may be present in a state of 100% purity, or in the form of an oxide or nitride. These states may also be present in a mixture. The gallium content of the target to be removed is effective when it is 50% by volume or more, preferably 70% by volume or more, and more preferably 90% by volume or more.

[0076] Furthermore, in the present invention, it is more effective to have a larger selectivity, which is the ratio of the dissolution rate of gallium to the dissolution rate of other metals. This selectivity may be 1 or more, 5 or more, or 10 or more. From the viewpoint of the working environment and workability, the upper limit of this selectivity may be about 100, about 50, or about 20.

[0077] Here, the dissolution rate (μm / min) can be measured, for example, by the following methods (A) to (G). (A) Prepare an alkaline cleaning solution to be used for cleaning, for example, 1 liter of a 5 mass % KOH (potassium hydroxide) aqueous solution. (B) Prepare a gallium substrate and a metal substrate other than gallium, each 1 cm long, 1 cm wide, and 1 mm thick, and measure their masses W0. If there is a natural oxide film on the surface of the substrate, remove it beforehand. (C) Divide the alkaline aqueous solution into two containers, each containing 500 ml, and immerse the gallium substrate and the metal substrate other than gallium in the alkaline aqueous solution adjusted to the intended cleaning conditions, for example, 25°C, for three minutes. The positions of the substrates in each container during immersion are adjusted so that the positions are not too different between the two substrates and do not affect the amount of dissolution. If the substrates are to be completely dissolved, increase the thickness of the substrates prepared in (B) above. (D) Each substrate is removed from the alkaline aqueous solution and washed at room temperature. (E) The mass W1 of each substrate after cleaning is measured. (F) Calculate the dissolution rate (μm / min) from the difference between the mass W0 and the mass W1 and the specific gravity of each substrate, assuming that the substrate dissolves only in the thickness direction. (G) The selectivity ratio is calculated from the obtained dissolution rate value according to the following formula. Selectivity ratio = Gallium dissolution rate (μm / min) / Other metal dissolution rate (μm / min)

[0078] It should be noted that the selectivity may be less than 1 if the contact area between the metal other than gallium and the cleaning solution is sufficiently smaller than the contact area between gallium and the cleaning solution.

[0079] While the above has described a method for cleaning an object containing gallium and a metal other than gallium, the technical concept of the present invention can also be applied to a method for cleaning an object containing a combination of other metals, such as a method for cleaning an object containing a combination of a specific metal and a metal that is close to that metal in the periodic table (for example, a metal within ±2 of the period or ±2 of the specific metal). [Example]

[0080] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0081] An LED chip with bumps on one side was transferred to a receptor substrate by laser lift-off, and then cleaned. LED chips were prepared using both In (indium) bumps and SAC bumps.

[0082] (Evaluation before cleaning) First, when the LED chip was observed under an optical microscope before cleaning, it was confirmed that gallium had adhered to the surface of the LED chip opposite to the surface on which the bumps were formed. The presence or absence of gallium adhesion after cleaning and the occurrence of dissolution of the bumps due to cleaning can be distinguished by differences in color. The observation results are shown in the "Before Cleaning Photograph" in Figure 2.

[0083] Example 1 Cleaning was performed using an alkaline cleaning solution, a 5% by mass aqueous solution of potassium hydroxide (KOH). The receptor substrate with the LED chip transferred was immersed in the cleaning solution for 3 minutes at a cleaning temperature of 25°C (room temperature). As with the evaluation before cleaning, the LED chip was observed using an optical microscope to evaluate whether or not gallium had adhered and whether or not the bumps had dissolved.

[0084] Example 2 Cleaning and evaluation were carried out in the same manner as in Example 1, except that a 2.34 mass % aqueous solution of TMAH (tetramethylammonium hydroxide), which is an alkaline cleaning liquid, was used as the cleaning liquid.

[0085] Example 3 Cleaning and evaluation were carried out in the same manner as in Example 1, except that a 10 mass % aqueous solution of Na2CO3 (sodium carbonate), which is an alkaline cleaning solution, was used as the cleaning solution.

[0086] (Comparative Example 1) Cleaning and evaluation were carried out in the same manner as in Example 1, except that a 12.3 mass % HCl aqueous solution (hydrochloric acid), which is an acidic cleaning solution, was used as the cleaning solution.

[0087] (Comparative Example 2) Cleaning and evaluation were carried out in the same manner as in Example 1, except that a 6 mass % H2SO4 aqueous solution (sulfuric acid), which is an acidic cleaning solution, was used as the cleaning solution.

[0088] The evaluation results are shown in Figure 2. In Examples 1-3, it was confirmed that the metallic Ga adhering to the LED chip was removed regardless of the type of cleaning solution. On the other hand, neither the In bumps nor the SAC bumps were dissolved by cleaning. It was found that cleaning with an alkaline cleaning solution can selectively dissolve and remove only the metallic Ga. On the other hand, in Comparative Examples 1 and 2, where cleaning was performed with an acidic cleaning solution, it was confirmed that the In bumps were dissolved. However, dissolution of the SAC bumps was not confirmed.

[0089] Example 4 After immersion in the same alkaline cleaning solution (5% by mass potassium hydroxide (KOH) aqueous solution) as in Example 1, the SAC bumps were coated with an IPA solution of abietic acid, a component of flux, and dried at 40°C. The bumps were then heated to 250°C on a hot plate. Figure 3 shows the results of evaluation using an optical microscope. As shown in Figure 3, the color of the bumps changed after heating at 250°C, indicating that the SAC bumps had dissolved. Flux is used to reduce the oxide film on the bump surface, thereby improving the melting and wettability of solder and ensuring electrical connection. Therefore, the melting of the SAC bumps after treatment as in Example 4 means that the cleaning treatment in Example 4 did not cause any degradation of the SAC bumps. The composition of the SAC bumps used was Sn = 96.5% by mass, Ag = 3.0% by mass, and Cu = 0.5% by mass.

[0090] (Comparative Example 3) After immersion in the same acidic cleaning solution (12.3% by mass HCl aqueous solution (hydrochloric acid)) as in Comparative Example 1, the SAC bumps were coated with an IPA solution of abietic acid, a component of the flux, and dried at 40°C. They were then heated to 250°C on a hot plate. Figure 4 shows the results of evaluation using an optical microscope. As shown in Figure 4, the color of the bumps did not change before and after heating at 250°C, indicating that the SAC bumps did not dissolve. This is thought to be because cleaning with the acidic cleaning solution changed the Sn / Ag / Cu alloy composition, raising the melting point and causing a change from the state of the bumps normally used. In other words, although the SAC bumps themselves did not dissolve when exposed to the acidic cleaning solution, their composition and other factors were changed, resulting in changes in the electrical properties of the LED chip. This suggests the occurrence of connection defects.

[0091] As described above, it was found that according to the examples of the present invention, only gallium can be removed by cleaning without dissolving or modifying metals other than gallium.

[0092] The present specification includes the following aspects. [1]: A method for manufacturing an LED mounting substrate, which includes a step of cleaning an LED chip transferred from a sapphire substrate onto a receptor substrate by laser lift-off, with an alkaline cleaning solution. [2]: The method for manufacturing an LED mounting substrate according to [1] above, wherein the LED chip transferred onto the receptor substrate has gallium on the surface opposite to the receptor substrate, and the gallium is removed by the cleaning step. [3]: The method for manufacturing an LED-mounted substrate according to [1] or [2], wherein the alkaline concentration of the alkaline cleaning solution is 0.5 mass % or more and a saturated concentration or less. [4]: The method for manufacturing an LED-mounted substrate according to [1], [2], or [3], wherein the temperature of the alkaline cleaning solution is 5°C or higher and 80°C or lower. [5]: The method for manufacturing an LED-mounted substrate according to [1], [2], [3] or [4], wherein the time for cleaning with the alkaline cleaning solution is 10 seconds or more and 1 hour or less. [6]: A method for manufacturing an LED mounting substrate according to [1], [2], [3], [4] or [5], having bumps on the surface of the LED chip that is bonded to the receptor substrate. [7]: The method for manufacturing an LED mounting substrate according to [6] above, wherein the bumps are formed using lead-free solder. [8]: The method for manufacturing an LED mounting substrate according to [6] or [7] above, wherein the bumps have at least one selected from a SnAgCu-based alloy, a SnZnBi-based alloy, a SnCu-based alloy, a SnAgInBi-based alloy, a SnZnAl-based alloy, and indium as a main component. [9]: The method for manufacturing an LED mounting substrate according to [1], [2], [3], [4], [5], [6], [7] or [8], wherein the LED chip transferred onto the receptor substrate is cleaned by immersing the receptor substrate together with the LED chip in the alkaline cleaning solution.

[10] : An alkaline cleaning solution for cleaning an LED chip mounted on a sapphire substrate after transferring it to a receptor substrate by laser lift-off.

[11] : The cleaning solution according to

[10] , wherein the cleaning solution has a pH of 9.5 to 14.0.

[12] : The cleaning solution according to

[10] or

[11] , wherein the cleaning solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium hydrogen carbonate, and potassium acetate.

[13] : A cleaning method for cleaning LED chips separated from a sapphire substrate by laser lift-off, the cleaning method using an alkaline cleaning solution.

[14] : The cleaning method according to

[13] above, wherein the LED chip is transferred onto a receptor substrate.

[15] : A cleaning method for selectively removing gallium from a component having gallium and a metal other than gallium on its surface, the cleaning method comprising cleaning the component using an alkaline cleaning solution.

[16] : The cleaning method according to

[15] , wherein the alkaline cleaning solution is brought into contact with the gallium and the metal other than gallium during the cleaning.

[17] : The cleaning method according to

[15] or

[16] , wherein the component is substrate-shaped and is fixed to another substrate during the cleaning, the gallium is present on the surface of the component opposite to the other substrate side, and the metal other than gallium is present on the other substrate side of the component.

[18] : The cleaning method according to

[15] ,

[16] or

[17] , wherein the metal other than gallium contains at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin and bismuth.

[19] : The cleaning method according to

[15] ,

[16] ,

[17] or

[18] , wherein the metal other than gallium has at least one metal selected from the group consisting of copper, silver, indium and tin.

[20] : The cleaning method according to

[15] ,

[16] ,

[17] ,

[18] or

[19] , wherein the metal other than gallium includes copper, silver and tin.

[0093] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention.

Claims

1. A method for manufacturing an LED mounting substrate, comprising a step of cleaning an LED chip transferred from a sapphire substrate onto a receptor substrate by laser lift-off with an alkaline cleaning solution, the LED chip transferred onto the receptor substrate has, on a surface opposite to the receptor substrate, decomposition residues of the gallium nitride semiconductor produced by the laser lift-off; The LED chip has bumps formed of lead-free solder on the surface thereof that is bonded to the receptor substrate, a gap is formed between the LED chip and the receptor substrate, through which the alkaline cleaning liquid can penetrate; The method for manufacturing an LED mounting substrate, wherein the decomposition residue is removed by the cleaning step.

2. 2. The method for manufacturing an LED mounting substrate according to claim 1, wherein the gallium nitride semiconductor is GaN.

3. A method for manufacturing an LED mounting substrate, comprising a step of cleaning an LED chip transferred from a sapphire substrate onto a receptor substrate by laser lift-off with an alkaline cleaning solution, The LED chip transferred onto the receptor substrate has metallic gallium on a surface opposite to the receptor substrate, The LED chip has bumps on the surface that is bonded to the receptor substrate, the bumps contain at least one selected from a SnAgCu-based alloy, a SnZnBi-based alloy, a SnCu-based alloy, a SnAgInBi-based alloy, a SnZnAl-based alloy, and indium as a main component; a gap is formed between the LED chip and the receptor substrate, through which the alkaline cleaning liquid can penetrate; The method for manufacturing an LED mounting substrate, wherein the metal gallium is removed by the cleaning step.

4. The method for manufacturing an LED mounting substrate according to any one of claims 1 to 3, wherein the alkaline cleaning solution has an alkali concentration of 0.5 mass% or more and a saturated concentration or less.

5. The method for manufacturing an LED mounting substrate according to any one of claims 1 to 3, wherein the temperature of the alkaline cleaning solution is 5°C or higher and 80°C or lower.

6. The method for manufacturing an LED mounting substrate according to any one of claims 1 to 3, wherein the time for cleaning with the alkaline cleaning solution is 10 seconds or more and 1 hour or less.

7. 3. The method for manufacturing an LED mounting substrate according to claim 1, wherein the bumps contain at least one selected from the group consisting of a SnAgCu-based alloy, a SnZnBi-based alloy, a SnCu-based alloy, a SnAgInBi-based alloy, a SnZnAl-based alloy, and indium as a main component.

8. 4. The method for manufacturing an LED mounting substrate according to claim 1, wherein the LED chip transferred onto the receptor substrate is cleaned by immersing the receptor substrate together with the LED chip in the alkaline cleaning solution.

9. 4. The method for manufacturing an LED mounting substrate according to claim 1, wherein the alkaline cleaning solution has a pH of 9.5 to 14.

0.

10. 4. The method for manufacturing an LED mounting substrate according to claim 1, wherein the alkaline cleaning solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium bicarbonate, and potassium acetate.

11. 4. The method for manufacturing an LED mounted substrate according to claim 1, wherein an adhesive layer is provided on the surface of the receptor substrate on the side where the LED chip is to be transferred.

12. The method for manufacturing an LED mounting substrate according to claim 11, wherein the receptor substrate is a quartz substrate having an adhesive layer on its surface.

13. A cleaning method for cleaning an LED chip separated from a sapphire substrate by laser lift-off, comprising: the separated LED chip has, on its surface, decomposition residue of the gallium nitride semiconductor produced by the laser lift-off and bumps formed of lead-free solder; The LED chip is transferred onto a receptor substrate; A cleaning method in which the decomposition residue and the bumps are cleaned by bringing an alkaline cleaning solution into contact with the decomposition residue and the bumps, thereby removing the decomposition residue.

14. 1. A cleaning method for selectively removing gallium from a component having gallium and bumps on its surface, comprising: the bumps contain at least one selected from a SnAgCu-based alloy, a SnZnBi-based alloy, a SnCu-based alloy, a SnAgInBi-based alloy, a SnZnAl-based alloy, and indium as a main component; the component is in the form of a substrate, and the cleaning is performed in a state where the component is fixed to another substrate; the gallium is present on a surface of the component opposite to the other substrate side, the bump is present on the other substrate side of the component, A cleaning method in which the component is cleaned so that an alkaline cleaning solution contacts the gallium and the bumps, thereby selectively removing the gallium.

Images