Method for manufacturing and cleaning LED mounting substrate

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 manufacturing method of an LED mounting board, 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 produce a 4-inch display substrate using LEDs called micro LEDs that are 100 μm square or less, millions of micro LEDs are required. Micro LEDs, which are tiny devices measuring several tens of μm, 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 off the micro LED chip from the sapphire substrate. The LLO process is a process in which, for example, an excimer laser is irradiated onto the GaN layer of the LED chip, and the GaN layer is decomposed into gaseous N2 and metallic Ga, thereby peeling off the LED chip from the sapphire substrate. This results in a receptor substrate with a large number of optical devices arranged on its surface.

[0005] Such a method is not limited to optical devices, but can also be applied to the manufacture of a receptor substrate having a plurality of transfer objects, such as fine semiconductor devices, arranged on its surface.

[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] JP 2020-4478 A Summary of the Invention [Problem to be solved by the invention]

[0008] During the LLO process, opaque metal Ga precipitates on the surface of the peeled micro LED chip. When the precipitated metal Ga 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 examining various possibilities for the cause of this connection failure, the inventors noticed that the shape of the bump before connection had changed from the original. They then discovered that the change was caused by the bump being dissolved or denatured by the acidic cleaning solution in the cleaning process.

[0009] Here, when the LED chip was LLO'd from the sapphire substrate to the receptor substrate, the surface with the bumps was attached to the receptor substrate and seemed 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 other steps, and the cleaning solution penetrated through the gap and dissolved and degraded the bumps.

[0010] As shown in Fig. 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 present inventors first considered protecting the bumps from the cleaning solution by deeply embedding the bumps in the adhesive layer of the receptor substrate. However, it was found that this method, although it could protect the bumps from the cleaning solution, made it difficult to peel the adhesive layer from the bumps in the subsequent process.

[0011] Here, being close to gallium in the periodic table means being close to the position of gallium in the 4th period and the 13th group 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 metallic Ga from components such as LED chips that have metallic Ga and metals other than metallic Ga on their surfaces without affecting the metals other than metallic Ga.

[0013] The present invention has been made to solve the above problems, and has an object to provide a manufacturing method for an LED mounted substrate capable of manufacturing an LED mounted substrate by selectively removing metal Ga (hereinafter sometimes simply referred to as "Ga" or "gallium") adhering to an LED chip 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, 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 having 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 such a manufacturing method for 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 producing 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 mass% or more and a saturated concentration or less, and the alkaline cleaning solution may have a temperature of 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 surface of the LED chip that is to be bonded to the receptor substrate may have bumps.

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

[0022] In this case, the bump may be formed of lead-free solder and may 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.

[0023] The method for manufacturing an LED mounting substrate of the present invention is particularly effective when used with 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 board.

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

[0027] Such a cleaning solution makes it possible to selectively remove unnecessary gallium without dissolving or modifying metals such as bumps of 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 such a cleaning method for cleaning an LED chip, unnecessary gallium can be selectively removed without dissolving or modifying metals such as bumps of the LED chip.

[0032] At this time, 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 with 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, during the cleaning, the gallium and the metal other than gallium can be brought into contact with the alkaline cleaning solution.

[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 part may be substrate-shaped and fixed to another substrate during the cleaning, the gallium may be present on the side of the part opposite to the other substrate, and the metal other than the gallium may be present on the side of the part facing the other substrate.

[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. The metal other than gallium may include at least one metal selected from the group consisting of copper, silver, indium, and tin. 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. Effect of the Invention

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

[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 on the LED chip.

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

[0045] In addition, according to the cleaning method for selectively removing gallium of the present invention, it is possible to selectively remove unnecessary gallium from a part 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 bumps 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 and gallium removed and gallium can be selectively removed, the metals other than the bumps and gallium may be dissolved to a practical extent. [Brief description of the drawings]

[0047] [Figure 1] 4 is a diagram illustrating an example of a cleaning process according to the present invention. [Diagram 2] The conditions and evaluation results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown below. [Diagram 3] The evaluation results of Example 4 are shown. [Figure 4] 4 shows the evaluation results of Comparative Example 3. [Diagram 5] FIG. 1 is a diagram (periodic table) for explaining examples of metal elements that are targets / not targets 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 PREFERRED EMBODIMENTS

[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 manufacturing method for an LED mounting substrate capable of manufacturing an LED mounting substrate by selectively removing metallic Ga adhering to an LED chip 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, 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 having gallium and metals other than gallium on its surface without dissolving or modifying metals other than gallium.

[0050] As a result of extensive investigations into the above-mentioned problems, the inventors have discovered that a method for manufacturing an LED mounted substrate, which includes a step of cleaning an LED chip transferred from a sapphire substrate to a receptor substrate by laser lift-off, with an alkaline cleaning solution, can selectively remove unnecessary gallium without dissolving or denaturing metals such as bumps of the LED chip, thereby producing a high-quality LED mounted substrate and reducing connection defects of the LED chip, thereby completing the present invention.

[0051] The inventors have also discovered that an alkaline cleaning solution for cleaning an LED chip provided on a sapphire substrate after it is transferred 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 have 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 have completed the present invention.

[0053] The present inventors have also discovered 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 with an alkaline cleaning solution, which makes it possible to selectively remove unnecessary gallium in a simple manner without dissolving or denaturing the metal other than gallium, and thus completed the present invention.

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

[0055] As described above, the present inventors have conducted intensive research to solve the above problems, and have 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 by the simple method of using an alkaline aqueous solution as a cleaning solution in this way can lead to simplification of the production process and improvement of the yield, and is a very big step toward reducing the price of micro LED displays, which are said to cost several tens of millions of yen per unit. The present invention will be described in more detail below.

[0056] [Cleaning solution] The cleaning solution according to the present invention is an alkaline cleaning solution for cleaning an LED chip provided on a sapphire substrate after it is transferred to a receptor substrate by laser lift-off. The cleaning solution according to the present invention can selectively remove unnecessary gallium without dissolving or modifying metals such as bumps of 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 preferable. It can selectively remove Ga stably and reliably without dissolving or denaturing metals such as bumps of 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 hydrogen carbonate, and potassium acetate. Such an aqueous solution is relatively easy to obtain and handle, and is low in cost.

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

[0060] [Manufacturing method for LED mounting board] The manufacturing method of the LED mounting substrate according to the present invention includes a step of cleaning the LED chip 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) can be applied. These methods will be described briefly below with reference to Figs. 6 and 7.

[0061] In Gap-LLO, first, as shown in Fig. 6(a), a sapphire substrate 1 having an LED chip 5 or the like as an object to be transferred and a receptor substrate 2 such as 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 chip 5 and the adhesive layer 3, i.e., a gap is provided. In this state, a laser 20 is irradiated from a laser oscillator 110 to the interface 11 between the sapphire substrate 1 and the multiple LED chips 5 through the surface of the sapphire substrate 1 opposite to the LED chips 5. The laser 20 is generally irradiated to the entire surface of the interface 11 between the sapphire substrate 1 and each LED chip 5 in sequence.

[0062] For example, in the case of a sapphire substrate 1 provided with a plurality of LED chips 5 including a gallium nitride semiconductor layer such as a GaN layer at the interface 11, the GaN layer is decomposed (ablation) by irradiation with the laser 20. When the bonding strength (adhesive strength, joining strength, etc.) between the LED chips 5 and the sapphire substrate 1 is weakened by ablation, the LED chips 5 are peeled off from the sapphire substrate 1. In addition, gas (e.g., nitrogen gas) is generated by the decomposition of the GaN layer. The pressure of this gas gives the peeled LED chips 5 a propulsive force toward the receptor substrate 2, and they move through the space between the sapphire substrate 1 and the receptor substrate 2, and 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 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 opposed to 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 20, the sapphire substrate 1 is removed as shown in Fig. 7(b), completing the transfer of the LED chip 5 from the sapphire substrate 1 to the receptor substrate 2.

[0064] In such an LLO process, decomposition of gallium nitride semiconductor layers such as the GaN layer leaves metallic Ga remaining on components such as the LED chip 5. In order to remove this metallic Ga, in the present invention, the LED chip 5 is cleaned using an alkaline cleaning solution. This makes it possible to selectively remove unnecessary gallium without dissolving or denaturing metals such as bumps on the LED chip, thereby reducing connection failures in the LED chip.

[0065] As the alkaline cleaning liquid used here, the above-mentioned alkaline cleaning liquid can be used.

[0066] The alkali concentration of the alkaline cleaning solution is preferably 0.5% by mass or more and saturation concentration or less. 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. If the temperature is too high, the gallium removal effect will not change, so it may be 80°C or less. Furthermore, the time for cleaning 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. If the cleaning time is too long, the gallium removal effect will not change, so it may be 1 hour or less. Furthermore, by appropriately combining the above-mentioned alkali concentration, the temperature of the alkaline cleaning solution, and the 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 to the receptor substrate. The LED chip also has bumps on the side that is bonded to the receptor substrate. The gallium on the surface opposite to the receptor substrate can be easily removed by cleaning with an alkaline cleaning solution.

[0068] In the manufacturing method of the LED mounting board according to the present invention, the bumps are preferably formed of lead-free solder, and more preferably have at least one selected from SnAgCu (SAC) alloy, SnZnBi alloy, SnCu alloy, SnAgInBi alloy, SnZnAl alloy, 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 cleaning is performed with an alkaline cleaning solution.

[0069] FIG. 1 shows an example of a process for cleaning an LED chip with an alkaline cleaning solution. As shown in FIG. 1, in the process for cleaning an LED chip with an alkaline cleaning solution in the manufacturing method of an LED mounting board 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 makes it possible to selectively remove 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 container filled with an alkaline cleaning solution 6, and then cleaning is performed with pure water or the like an appropriate number of times, and then drying (air drying) can be performed.

[0070] [How to clean LED chips] The present invention also provides a cleaning method for cleaning the LED chip separated from the sapphire substrate by the above-mentioned laser lift-off, using an alkaline cleaning solution. Such a cleaning method can easily and selectively remove only gallium by cleaning without dissolving or denaturing metals other than gallium, thereby reducing connection failures of the LED chip. In addition, in such a cleaning method according to the present invention, it is preferable that the LED chip is transferred onto a receptor substrate. A specific example of the cleaning method for the LED chip 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 the LED chip separated from the sapphire substrate by the laser lift-off as described above with an alkaline cleaning solution, only gallium can be selectively removed without dissolving or modifying metals other than gallium. As a result of further research, it has been found that, not only from LED chips, but also when selectively removing gallium from parts having gallium and metals other than gallium on the surface, the parts can be selectively removed without dissolving or modifying metals other than gallium by a very simple method of cleaning the parts with an alkaline cleaning solution.

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

[0073] In addition, it is preferable that the part to be cleaned is in the form of a substrate and is fixed to another substrate during cleaning, that the gallium is present on the side of the part opposite to the other substrate, 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 or modification 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 a state of oxide or nitride. These states may also be mixed. The ratio of gallium 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] 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 that are 1 cm long, 1 cm wide, and 1 mm thick, and measure their masses W0. If there is a natural oxide film or the like on the surface of the substrate, remove it in advance. (C) Divide the alkaline solution into two containers, each containing 500 milliliters, and immerse the gallium substrate and the substrate of a metal other than gallium in the alkaline solution adjusted to the expected cleaning conditions, for example, 25°C, for three minutes in each container. The positions of the substrates in each container during immersion are adjusted so that they do not differ significantly between the two substrates and thus do not affect the amount of dissolution. If the substrates are completely dissolved, the thickness of the substrates prepared in (B) above is increased. (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 substrates are dissolved only in the thickness direction. (G) The selectivity ratio is calculated from the obtained dissolution rate value according to the following formula. Selectivity ratio = dissolution rate of gallium (μm / min) / dissolution rate of other metals (μm / min)

[0078] When 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, the selectivity may be less than 1.

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

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

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

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

[0083] Example 1 Cleaning was performed using an alkaline cleaning solution, a 5% by mass aqueous solution of KOH (potassium hydroxide). The receptor substrate with the LED chip transferred thereon was immersed in the cleaning solution for 3 minutes at a cleaning temperature of 25°C (room temperature). As in 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 an alkaline cleaning solution, a 2.34 mass % aqueous solution of TMAH (tetramethylammonium hydroxide), was used as the cleaning solution.

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

[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 metal Ga adhering to the LED chip was removed regardless of the type of cleaning solution. Meanwhile, neither the In bumps nor the SAC bumps were dissolved by cleaning. It was found that only the metal Ga can be selectively dissolved and removed by cleaning with an alkaline cleaning solution. Meanwhile, 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 The SAC bumps were immersed in the same alkaline cleaning solution (5 mass% KOH (potassium hydroxide) aqueous solution) as in Example 1, and then coated with an IPA solution of abietic acid, which is a component of flux, and dried at 40°C. After that, the bumps were heated to 250°C on a hot plate. FIG. 3 shows the evaluation results using an optical microscope. As shown in FIG. 3, the color of the bumps changed after heating at 250°C, and it can be seen that the SAC bumps were dissolved. Flux is used for the purpose of improving the melting and wettability of solder by reducing the oxide film on the bump surface and ensuring electrical connection. Therefore, the fact that the SAC bumps were melted by the treatment in Example 4 means that the cleaning treatment in Example 4 did not cause any denaturation of the SAC bumps. The composition of the SAC bumps used was Sn=96.5 mass%, Ag=3.0 mass%, and Cu=0.5 mass%.

[0090] Comparative Example 3 The SAC bumps were immersed in the same acid cleaning solution (12.3 mass% HCl aqueous solution (hydrochloric acid)) as in Comparative Example 1, and then coated with an IPA solution of abietic acid, which is a component of the flux, and dried at 40°C. After that, they were heated to 250°C on a hot plate. FIG. 4 shows the evaluation results using an optical microscope. As shown in FIG. 4, the color of the bumps did not change before and after heating at 250°C, and it can be seen that the SAC bumps did not dissolve. This is thought to be because the alloy composition of Sn / Ag / Cu changed due to cleaning with the acid cleaning solution, and the melting point increased, and it is thought that the bumps were modified from the state they are normally used in. In other words, it was found that although the SAC bumps themselves do not dissolve due to the acid cleaning solution, the composition and the like are modified, and the electrical characteristics of the LED chips change. This suggests the occurrence of connection failure.

[0091] As described above, according to the examples of the present invention, it is possible to remove only gallium 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, comprising a step of cleaning an LED chip transferred from a sapphire substrate to 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 a surface opposite to the receptor substrate, and the gallium is removed by the cleaning step. [3]: The method for manufacturing an LED mounting substrate according to [1] or [2] above, wherein the alkaline concentration of the alkaline cleaning solution is 0.5 mass % or more and a saturation concentration or less. [4]: The method for manufacturing an LED-mounted substrate according to [1], [2] or [3] above, 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 mounting substrate according to [1], [2], [3] or [4] above, wherein the time for cleaning with the alkaline cleaning solution is from 10 seconds to 1 hour. [6]: A method for manufacturing an LED mounting substrate according to [1], [2], [3], [4] or [5] above, having a bump on the surface of the LED chip that is to be 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 bump has 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 immersed together with the receptor substrate in the alkaline cleaning solution to clean it.

[10] : A cleaning solution used to clean an LED chip mounted on a sapphire substrate after it is transferred to a receptor substrate by laser lift-off. The cleaning solution is alkaline.

[11] : The cleaning solution according to

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

[12] : The cleaning solution according to

[10] or

[11] above, which 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 method comprising cleaning the component with 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] above, 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, and the metal other than the gallium is present on the other substrate side of the component.

[18] : The cleaning method according to

[15] ,

[16] or

[17] above, wherein the metal other than gallium has 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] above, 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 is copper, silver or tin.

[0093] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A method for manufacturing an LED mounting substrate, comprising the 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 a decomposition residue of a gallium nitride semiconductor produced by the laser lift-off on a surface opposite to the receptor substrate, The LED chip has a bump formed of lead-free solder on a surface of the LED chip that is to be bonded to the receptor substrate, a gap is provided 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 based semiconductor is GaN.

3. A method for manufacturing an LED mounting substrate, comprising the 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 a bump on a surface thereof that is to be bonded to the receptor substrate; the bump has 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 provided 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 metallic 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 have 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. The method for manufacturing an LED mounting substrate according to any one of claims 1 to 3, wherein the alkaline cleaning solution has a pH of 9.5 to 14.

0.

10. The method for manufacturing an LED mounting substrate according to any one of claims 1 to 3, 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 hydrogen carbonate, and potassium acetate.

11. The method for manufacturing an LED mounted substrate according to any one of claims 1 to 3, further comprising providing an adhesive layer on a surface of the receptor substrate on which 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 a surface thereof.

13. A cleaning method for cleaning an LED chip separated from a sapphire substrate by laser lift-off, comprising the steps of: the separated LED chip has, on its surface, a decomposition residue of the gallium nitride semiconductor produced by the laser lift-off and a bump formed of lead-free solder; A cleaning method in which the decomposition residue and the bumps are brought into contact with an alkaline cleaning solution to remove the decomposition residue.

14. 14. The cleaning method according to claim 13, wherein the LED chip is transferred onto a receptor substrate.

15. 1. A cleaning method for selectively removing gallium from a component having gallium and bumps on a surface thereof, comprising the steps of: the bump has 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 cleaning method in which the component is cleaned by bringing an alkaline cleaning solution into contact with the gallium and the bumps, thereby selectively removing the gallium.

16. 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, 16. The cleaning method according to claim 15, wherein the bumps are present on the component on a side of the other substrate.

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