A rework method for a transparent conductive layer of a gallium arsenide-based LED die

Abstract

The application provides a rework method of a transparent conductive layer of a gallium arsenide-based LED die, comprising the following steps: (1) providing an LED die to be reworked; (2) protecting the metal electrode by using photoresist; (3) uniformly coating the gel etching solution on the surface of the TCL film layer and the protected metal electrode to form an etching gel film, and then performing constant temperature etching on the TCL film layer, and then cooling to room temperature and performing photoresist removal treatment; (4) protecting the metal electrode of the LED die treated in the step (3) by using photoresist, and then manufacturing the TCL film layer, removing the TCL film layer in the metal electrode area and performing photoresist removal treatment; and (5) performing high-temperature annealing on the LED die treated in the step (4), and the rework is completed. The rework method process is simple, the rework cycle of the LED die is shortened, the production cost is greatly reduced, the surface of the reworked die is clean, there is no side etching metal phenomenon, and the tested photoelectric parameters are normal.

Description

Technical Field

[0001] This invention relates to a method for reworking the transparent conductive layer of a gallium arsenide-based LED die, belonging to the field of semiconductor processing technology. Background Technology

[0002] LEDs (Light Emitting Diodes) are made of several thin layers of doped semiconductor material. One layer carries an excess of electrons, while another layer, lacking electrons, forms positively charged "holes." When current flows through them, electrons and holes combine and release energy, radiating light. LEDs are an energy-saving and environmentally friendly light source with advantages such as high luminous efficiency, long lifespan, high safety and reliability, and low power consumption. These advantages have led to their widespread application in the lighting industry.

[0003] LED chip structures generally consist of a substrate, an epitaxial layer, a transparent conductive layer (TCL), and a metal electrode layer, making the entire manufacturing process quite complex. When using gallium arsenide substrates to fabricate LED chip electrodes, the complexity of the entire process, the intricacy of the fabrication steps, and the uncontrollability of human operation inevitably lead to some defective wafers, such as abnormal wafer parameters, surface defects, and regional contamination. Abnormal wafer parameters are particularly common. To reduce manufacturing costs, these defective wafers are typically reworked by removing the surface electrodes and the TCL layer before remanufacturing. Currently, the front-end electrode fabrication generally includes the following processes: TCL fabrication - P-side metal electrode fabrication - thinning - N-side metal electrode fabrication - photoelectric parameter testing. Metal electrodes are typically fabricated using metals such as chromium, aluminum, titanium, beryllium, gold, platinum, silver, nickel, and germanium.

[0004] Currently, most abnormal parameters in wafers are caused by contact issues between the transparent conductive layer and the epitaxial layer during TCL manufacturing. The metal electrodes, being relatively stable, generally do not cause damage. The traditional rework process for wafers with abnormal TCL layers mainly includes the following steps: etching the TCL layer – etching the metal electrode – preparing the TCL layer – preparing the metal electrode. As can be seen, reworking any wafer involving the transparent conductive layer requires reworking both the TCL layer and the metal electrode. The metal electrode, in particular, consists of many layers, requiring layer-by-layer etching based on the metal's properties. Generally, aqua regia or strong acid solutions are used to remove all metal layers except for the chromium layer. Chromium requires separate cerium sulfate etching, making the process cumbersome, inefficient, and costly. Furthermore, the etching solutions currently used to remove the transparent conductive layer are strong acid or alkaline solutions, which corrode the metal electrode along with the transparent conductive layer. Therefore, if TCL can be reworked without damaging the metal electrodes, substrate, epitaxial layer, and other wafer structures, it will not only greatly reduce costs but also shorten rework time and improve overall manufacturing efficiency.

[0005] Chinese patent document CN104900490A (application number: 201510222207.8) discloses a method for recovering and reusing LED scrap wafer substrates. The method includes the following steps: Step (1) Cleaning the surface of the scrapped epitaxial wafer or wafer that was scrapped during the manufacturing process using a cleaning agent; Step (2) ICP etching the cleaned epitaxial wafer; Step (3) Cleaning the etched substrate wafer with a cleaning agent; Step (4) Spin-drying the cleaned substrate. This invention not only has a short process time, low cost, and high efficiency, but also solves the appearance abnormalities caused by "self-masking," effectively improving the regeneration effect. This method uses the ICP method to directly etch away the entire growth layer on the surface and then re-fabricate it. It does not fully utilize the part of the structure that was fabricated in the early stage, resulting in high cost.

[0006] Therefore, it is necessary to study a process method that can rework TCL without damaging other wafer structures such as metal electrodes and epitaxial layers. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for reworking the transparent conductive layer (TCL) of a gallium arsenide (GaAs)-based LED die. Compared to traditional methods that rework both the TCL layer and the metal electrodes, this invention's rework method can rework only the TCL layer without damaging the metal electrodes, epitaxial layer, or substrate.

[0008] Definitions:

[0009] LED: Light Emitting Diode;

[0010] TCL: Transparent Conductive Layer;

[0011] Room temperature: as is known in the field, refers to 25±2℃.

[0012] The technical solution of the present invention is as follows:

[0013] A method for reworking the transparent conductive layer of a gallium arsenide-based LED die includes the following steps:

[0014] (1) Provide an LED die with a TCL film layer defect to be reworked, wherein the structure of the LED die to be reworked includes, from bottom to top, a gallium arsenide substrate, an epitaxial layer, a TCL film layer, and a metal electrode;

[0015] (2) Use photoresist to protect the metal electrodes;

[0016] (3) Etching the TCL film: The colloidal etching solution is uniformly coated on the TCL film and the surface of the protected metal electrode to form an etching film. The TCL film is etched at a constant temperature, and then cooled to room temperature for adhesive removal.

[0017] (4) Use photoresist to protect the metal electrodes of the LED chip after step (3), then fabricate a TCL film, remove the TCL film in the metal electrode area and perform photoresist removal.

[0018] (5) The LED chip processed in step (4) is subjected to high-temperature annealing to complete the rework.

[0019] According to a preferred embodiment of the present invention, the epitaxial layer mentioned in step (1) is a film layer grown on a gallium arsenide substrate, and the structure from the substrate to the top is as follows: gallium arsenide substrate, N-type gallium arsenide ohmic contact layer, N-type gallium arsenide confinement layer, quantum well active layer, P-type confinement layer, P-type gallium arsenide ohmic contact layer, and P-type gallium phosphide window layer.

[0020] According to the present invention, the TCL film material in step (1) is a commonly used material in the art; preferably, the TCL film is a zinc oxide film or an ITO film.

[0021] According to a preferred embodiment of the present invention, in step (1), the metal electrode structure is a conventional electrode structure; the metal materials used in the metal electrode all have a purity of 5N or higher; preferably, the metal materials used in the metal electrode are one or a combination of two or more of Cr, Ti, Al, Au, Pt or Ni.

[0022] According to a preferred embodiment of the present invention, in step (2), when photoresist is used to protect the metal electrode, the thickness of the photoresist protective layer on the surface of the metal electrode is 0.5-1 μm; the surface of the metal electrode includes the upper surface and the side surface of the metal electrode.

[0023] According to the present invention, the photoresist mentioned in step (2) is a commonly used photoresist in the art; preferably, the photoresist is the KMP E3130B model photoresist from Beijing Kehua Microelectronics Materials Co., Ltd.

[0024] According to a preferred embodiment of the present invention, the colloidal etching solution in step (3) is a mixture of hydrochloric acid solution and photoresist, wherein the volume ratio of hydrochloric acid solution to photoresist in the mixture is 1:10-15; the mass fraction of the hydrochloric acid solution is 36-38%; and the photoresist is the same as that in step (2).

[0025] According to a preferred embodiment of the present invention, the colloidal etching solution described in step (3) is uniformly coated onto the TCL film layer and the surface of the protected metal electrode using a spin coater to form an etching film; the thickness of the etching film is 1-2 μm.

[0026] According to a preferred embodiment of the present invention, the temperature of the isothermal corrosion in step (3) is 50-70°C and the isothermal corrosion time is 10-15 min.

[0027] According to a preferred embodiment of the present invention, the adhesive removal process in step (3) is as follows: the LED chip is immersed in an organic solvent for 5-20 minutes, then rinsed with water and dried to complete the adhesive removal.

[0028] More preferably, the organic solvent is acetone, ethanol, benzene, toluene, methanol, or isopropanol; and the temperature of the organic solvent is 40-50°C.

[0029] According to a preferred embodiment of the present invention, the photoresist described in step (4) is the same as the photoresist described in step (2).

[0030] According to a preferred embodiment of the present invention, in step (4), when using photoresist to protect the metal electrode, the photoresist protective layer is only coated on the upper surface of the metal electrode, and the thickness of the photoresist protective layer on the upper surface of the metal electrode is 0.5-1 μm.

[0031] According to a preferred embodiment of the present invention, the material of the TCL film layer in step (4) is the same as that in step (1), and its preparation method is the prior art. Preferably, an electron beam evaporation stage is used for evaporation at room temperature.

[0032] According to a preferred embodiment of the present invention, in step (4), the TCL film layer in the electrode area is peeled off by peeling.

[0033] According to a preferred embodiment of the present invention, the method of degumming in step (4) is the same as that in step (3).

[0034] According to a preferred embodiment of the present invention, the annealing conditions in step (5) are: annealing in an oxygen atmosphere with an oxygen flow rate of 3 L / min; annealing temperature of 400 °C; and annealing time of 10 seconds.

[0035] The technical features and beneficial effects of this invention are as follows:

[0036] 1. The rework method of the present invention protects the metal electrode and slowly etches the TCL film layer using a specific colloidal etching solution, avoiding the drawbacks of directly using strong acid or strong alkaline solutions for etching. This allows the rate of side etching to be controlled, thus achieving the purpose of etching away the abnormal TCL film layer in the light-emitting area without damaging the metal electrode and the gallium phosphide window layer on the surface of the epitaxial layer.

[0037] 2. The preparation ratio of the colloidal etching solution in this invention is very important. If the hydrochloric acid content is too high, the etching rate will be too fast and cause lateral etching of the metal electrode. If the hydrochloric acid content is too low, the TCL film layer may not be completely etched, and the TCL film layer will have a residual bottom film, which will affect the current spread. In addition, if the ratio of hydrochloric acid to photoresist is unbalanced, the viscosity of the prepared solution will be unbalanced, and the film formation effect will not be achieved. The hydrochloric acid will evaporate after coating and will not play a etching role.

[0038] 3. The constant-temperature slow corrosion conditions in this invention are extremely important. Appropriate corrosion film thickness, corrosion temperature, and corrosion time can ideally control the extent of lateral corrosion. If the corrosion film thickness is too large, the corrosion temperature too high, or the corrosion time too long, lateral corrosion will occur on the metal electrode; conversely, if the corrosion film thickness is too small, the corrosion temperature too low, or the corrosion time too short, the TCL film will not be completely corroded, leaving a residual base film that affects current spread. Under the specific constant-temperature corrosion conditions of this invention, when the TCL film of the LED die is etched away, the lateral corrosion width will not exceed 0.5 μm, and a TCL film diameter not exceeding 0.5 μm will not affect the subsequent re-growth of the new film, resulting in good overall current spread.

[0039] 4. The wafers reworked using the method of this invention have clean surfaces, no side etching of metal, and all photoelectric parameters are normal, which can effectively avoid the problem of increased forward voltage after LED chip rework.

[0040] 5. The method of the present invention can be used for all LED chips with TCL and metal electrodes as the structure. Compared with the traditional method, the rework process of the present invention is simple, shortens the rework cycle of LED chips, and can greatly reduce production costs. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the cross-sectional structure of the LED chip to be reworked in step (1);

[0042] Figure 2 This is a schematic cross-sectional view of the LED chip structure after the metal electrode protection pattern is made in step (2);

[0043] Figure 3 This is a schematic cross-sectional view of the LED chip structure after the etched adhesive film has been coated in step (3);

[0044] Figure 4 This is a schematic diagram of the cross-sectional structure of the LED chip after the TCL film layer has been etched away in step (3);

[0045] Figure 5 This is a schematic cross-sectional view of the LED chip structure after the TCL film layer fabrication is completed in step (4);

[0046] 001 is the gallium arsenide substrate; 002 is the epitaxial layer; 003 is the TCL film layer; 004 is the metal electrode; 005 is the photoresist protective layer on the surface of the metal electrode; 006 is the etchant film. Detailed Implementation

[0047] The present invention will be further described below with reference to embodiments and accompanying drawings, but is not limited thereto.

[0048] Unless otherwise specified, the raw materials used in the following embodiments are all conventional raw materials that can be purchased commercially; and the methods used in the embodiments are all prior art unless otherwise specified.

[0049] The photoresist used in this embodiment is the KMP E3130B model photoresist from Beijing Kehua Microelectronics Materials Co., Ltd.

[0050] Example 1

[0051] A method for reworking the transparent conductive layer of a gallium arsenide-based LED die includes the following steps:

[0052] (1) Provide a TCL LED die with a defective film layer that needs to be reworked, the structure of the LED die to be reworked is as follows: Figure 1 As shown, from bottom to top, the components are: gallium arsenide substrate 001, epitaxial layer 002, TCL film layer 003, and metal electrode 004; the size of the LED die to be reworked is 5*8mil.

[0053] The epitaxial layer 002 is a film layer grown on the gallium arsenide substrate 001, and its structure from bottom to top is as follows: N-type gallium arsenide ohmic contact layer, N-type gallium arsenide confinement layer, quantum well active layer, P-type confinement layer, P-type gallium arsenide ohmic contact layer, and P-type gallium phosphide window layer.

[0054] The TCL film layer 003 is an ITO film layer;

[0055] The metal electrode 004 has a Cr / Au structure, wherein the thickness of the Cr layer is 1000 angstroms and the thickness of the Au layer is 29000 angstroms.

[0056] (2) Photoresist is used to protect the metal electrode 004, and the thickness of the photoresist protective layer 5 on the surface of the metal electrode is 0.8 μm; the surface of the metal electrode includes the upper surface and the side surface of the metal electrode, and its structural schematic diagram is shown below. Figure 2 As shown.

[0057] (3) Corrosion of TCL film:

[0058] A 37% hydrochloric acid solution and photoresist were mixed at a volume ratio of 1:12 to obtain a colloidal etching solution. Using a spin coater, the prepared colloidal etching solution was uniformly coated onto the TCL film layer of the LED chip treated in step (2) and the surface of the protected metal electrodes to form an etched film 6. The thickness of the etched film was 1.5 μm, and its structural schematic diagram is shown below. Figure 3 As shown in the diagram; then, the LED die with the etched adhesive film was placed in a 60℃ constant temperature chamber for 13 minutes for constant temperature etching, and then cooled to room temperature. Afterwards, the LED die with the TCL film removed was immersed in acetone at 50℃ for 15 minutes, then rinsed with water and dried to complete the adhesive removal process. A schematic diagram of the LED die after this step is shown in the diagram. Figure 4 As shown.

[0059] (4) Photoresist is coated on the upper surface of the metal electrode of the LED die after the treatment in step (3) to protect the metal electrode. The thickness of the photoresist protective layer is 0.8 μm. Then, TCL film 3 (material is ITO) is deposited at room temperature using an electron beam evaporation stage. The TCL film in the electrode area is peeled off by peeling. Then, the LED die with the peeled TCL film in the electrode area is immersed in acetone at 50℃ for 15 min, then rinsed with water and dried. The structural schematic diagram of the obtained LED die is shown below. Figure 5 As shown.

[0060] (5) Anneal the LED chip processed in step (4) in an oxygen atmosphere with an oxygen flow rate of 3L / min, an annealing temperature of 400℃, and an annealing time of 10 seconds. The rework is then complete.

[0061] After rework using the rework method described in this embodiment, the forward voltage VF1 of the obtained LED chip is 1.75V, while the forward voltage VF1 of the LED chip before rework is 2.90V.

[0062] According to the method of this embodiment, 200 TCL LED chips with abnormal film layers that need to be reworked were processed, the forward voltage VF1 of the reworked LED chips was tested, and its average value was calculated. The results are shown in Table 1.

[0063] Table 1. Average forward voltage VF1 of LED chips before and after rework

[0064] Test quantity / piece VF1 / v Before returning to work 200 2.93 After returning to work 200 1.78

[0065] As can be seen from the above, the photoelectric parameters of the wafers reworked by the method of the present invention are all normal. After rework, the forward voltage is reduced, which meets the requirements of the forward voltage parameters of LED chips (below 2.1V).

[0066] Example 2

[0067] A method for reworking the transparent conductive layer of a gallium arsenide-based LED die is described in Example 1, except that: in step (3), the thickness of the etched film is 1 μm, and the etching is carried out at a constant temperature of 70°C for 15 min.

[0068] After rework using the rework method described in this embodiment, the forward voltage VF1 of the obtained LED chip is 1.79V, while the forward voltage VF1 of the LED chip before rework is 2.94V.

[0069] Example 3

[0070] A method for reworking the transparent conductive layer of a gallium arsenide-based LED die is described in Example 1, except that: in step (3), the thickness of the etched film is 2 μm, and the etching is carried out at a constant temperature of 50°C for 10 min.

[0071] After rework using the rework method described in this embodiment, the forward voltage VF1 of the obtained LED chip is 1.77V, while the forward voltage VF1 of the LED chip before rework is 2.92V.

[0072] Comparative Example 1

[0073] A method for reworking the transparent conductive layer of a gallium arsenide-based LED die includes the following steps:

[0074] (1) Provide an LED die with a TCL film layer defect to be reworked, wherein the structure of the LED die to be reworked is the same as in Example 1;

[0075] (2) Remove TCL film: Immerse the LED chip in a 37% hydrochloric acid solution to remove the surface ITO film.

[0076] (3) Remove metal electrodes: Put the LED chip after step (2) into the gold etching solution to remove the gold layer, then put the chip into the chromium etching solution to remove the chromium metal, rinse it with water and dry it.

[0077] (4) The LED chip processed in step (3) is subjected to ITO film deposition, electrode mask pattern is made, metal electrode is deposited, and metal electrode pattern is obtained by peeling using a peeling method and then the adhesive is removed.

[0078] After rework using this comparative rework method, the forward voltage VF1 of the resulting LED chip is 1.85V, while the forward voltage VF1 of the LED chip before rework is 2.98V.

[0079] As can be seen from the comparison of Example 1 and Comparative Example 1, the rework method of the present invention is simple in process, does not require the removal of metal electrodes or the re-fabrication of metal electrodes, and significantly reduces the material and labor costs. According to calculations, the rework method of the present invention can save 70-90% of the rework costs.

Claims

1. A rework method of a transparent conductive layer of a gallium arsenide-based LED die, comprising the following steps: (1) providing an LED die to be reworked with an abnormal transparent conductive layer (TCL) film layer, the structure of the LED die to be reworked comprising, from bottom to top, a gallium arsenide substrate, an epitaxial layer, a TCL film layer, and a metal electrode; (2) protecting the metal electrode using photoresist; (3) etching the TCL film layer: uniformly applying a colloidal etching solution to the surface of the TCL film layer and the protected metal electrode to form an etching photoresist film, isothermally etching the TCL film layer, then cooling to room temperature, and performing a photoresist removal process; the colloidal etching solution is a mixture of hydrochloric acid solution and photoresist, the volume ratio of the hydrochloric acid solution to the photoresist in the mixture being 1:10-15, the mass fraction of the hydrochloric acid solution being 36-38%, the thickness of the etching photoresist film being 1-2 μm, and the isothermal etching temperature being 50-70°C, the isothermal etching time being 10-15 min; (4) protecting the metal electrode of the LED die after step (3) using photoresist, then fabricating a TCL film layer, removing the TCL film layer in the area of the metal electrode, and performing a photoresist removal process; (5) performing high-temperature annealing on the LED die after step (4) to complete the rework.

2. The method of claim 1, wherein the transparent conductive layer is a transparent conductive layer of a GaAs-based LED die. In step (2), when the metal electrode is protected using photoresist, the thickness of the photoresist protective layer on the surface of the metal electrode is 0.5-1 μm; the surface of the metal electrode includes the upper surface and the side surface of the metal electrode.

3. The method of claim 1, wherein the transparent conductive layer is a transparent conductive layer of a GaAs-based LED die. The photoresist in step (3) is the same as that in step (2).

4. The method of claim 1, wherein the transparent conductive layer is a transparent conductive layer of a GaAs-based LED die. In step (3), the colloidal etching solution is uniformly applied to the surface of the TCL film layer and the protected metal electrode by a spin coater to form an etching photoresist film.

5. The method of claim 1, wherein the transparent conductive layer is a transparent conductive layer of a GaAs-based LED die. In step (3), the photoresist removal process is performed by immersing the LED die in an organic solvent for 5-20 min, then rinsing with water, drying, and completing the photoresist removal; the organic solvent is acetone, ethanol, benzene, toluene, methanol, or isopropyl alcohol; the temperature of the organic solvent is 40-50°C.

6. The method of claim 1, wherein the transparent conductive layer is a transparent conductive layer of a GaAs-based LED die. In step (4), the photoresist is the same as that in step (2); when the metal electrode is protected using photoresist, the photoresist protective layer is only applied to the upper surface of the metal electrode, and the thickness of the photoresist protective layer on the upper surface of the metal electrode is 0.5-1 μm.

7. The method of claim 1, wherein the transparent conductive layer is a transparent conductive layer of a GaAs-based LED die. In step (4), the material of the TCL film layer is the same as that in step (1); the TCL film layer is deposited using an electron beam evaporation station at room temperature.

8. The method of claim 1, wherein the transparent conductive layer is a GaAs-based LED die. In step (4), the TCL film layer in the electrode area is peeled off by peeling; the photoresist removal process is the same as that in step (3).

9. The method of claim 1, wherein the transparent conductive layer is a GaAs-based LED die. In step (5), the annealing conditions are as follows: annealing in an oxygen atmosphere, oxygen flow rate being 3 L / min, annealing temperature being 400°C, and annealing time being 10 s.

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