A processing method for roughening LED ITO film to increase light output efficiency

Abstract

This invention discloses a method for roughening ITO thin films in LEDs to increase light extraction efficiency, belonging to the field of semiconductor technology. This invention utilizes the "soft" window period of amorphous ITO. It precisely captures the "amorphous window period" after ITO film deposition and before heat treatment, when the film structure is loose, hardness is low, and chemical reactivity is high. Roughening treatment during this period is easier and more efficient, whether through chemical etching or physical processing, with extremely low risk of damage to the underlying epitaxial layer, thus synergistically optimizing performance. This invention offers good roughening effect and strong controllability: it employs a wet etching scheme, ensuring a uniform and controllable etching rate of amorphous ITO in a specific etching solution. By adjusting the concentration, temperature, and time of the etching solution, the surface roughness can be precisely controlled. Compared to etching crystalline ITO, amorphous etching more easily forms an ideal "matte" effect, is non-directional, has good uniformity, and improves light efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to a method for roughening LED ITO thin films to increase light extraction efficiency. Background Technology

[0002] Indium tin oxide (ITO) is widely used as the transparent conductive layer in LED chips due to its high light transmittance and excellent conductivity. However, because of the significant refractive index difference between ITO and air, light is prone to total internal reflection at the interface, resulting in a large amount of light being trapped inside the chip. Roughening the ITO surface is an effective way to disrupt the conditions for total internal reflection and improve light extraction efficiency.

[0003] Currently, the mainstream ITO roughening methods can be divided into two categories:

[0004] 1. In-situ roughening during deposition: By controlling deposition parameters (such as high deposition rate and high oxygen partial pressure), a rough surface is naturally formed on the thin film during growth. Although this method does not require post-processing, the rough morphology and the control of electrical properties are coupled and often difficult to balance. Furthermore, the films deposited at high deposition rates have poor density, which may affect the long-term reliability of the device.

[0005] 2. Roughening after deposition and annealing: This involves first depositing the ITO thin film and then annealing it at high temperature to allow for full crystallization. Roughening is then performed using methods such as dry etching, wet etching, or plasma bombardment. This method has the following inherent drawbacks:

[0006] a) Complex process and high cost: It requires additional etching equipment or complex wet etching process.

[0007] b) Limited roughening effect: Crystallized ITO films have a stable crystal structure. Roughening them is equivalent to "subtracting" from the dense material. The controllability of the rough morphology is poor, and surface defects are easily introduced during the processing.

[0008] Therefore, how to achieve effective and controllable roughening of the ITO surface without damaging the wafer or significantly increasing the complexity of the process remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] To address the aforementioned issues, this invention provides a method for roughening LED ITO thin films to increase light extraction efficiency. This method utilizes the characteristic that the ITO thin film is in an amorphous (or weakly crystalline) state after deposition and before heat treatment to roughen it. The ITO surface is etched using a certain concentration of NMP organic solvent, resulting in a relatively small change in surface roughness Ra and Rq, but a significant increase in Rz value, thereby increasing light extraction efficiency.

[0010] This invention is achieved through the following technical solution:

[0011] A method for roughening LED ITO thin films to increase light extraction efficiency includes the following steps:

[0012] Step 1, ITO thin film deposition: Prepare a sapphire substrate LED chip that has completed GaN-based epitaxial growth, and deposit an ITO thin film using an ion evaporation device at a temperature of 80℃~120℃.

[0013] Step 2: Wet etching roughening before heat treatment: Prepare a 3% NMP organic solvent etching solution, heat it to 85℃~95℃, immerse the chip with amorphous ITO deposited in the etching solution, and etch for 25-35 minutes. After removal, rinse with deionized water and dry with nitrogen. After etching, a uniform rough structure is formed on the ITO surface, and the roughness increases.

[0014] Step 3: High-temperature heat treatment annealing: The roughened chip is placed in a rapid annealing furnace and annealed at high temperature under a nitrogen atmosphere. The annealing temperature is 500℃~600℃, and the annealing time is 5~15 minutes. After annealing, the ITO film is fully crystallized, the light transmittance is increased to over 90%, and the rough surface morphology is maintained.

[0015] Step 4, Subsequent Processes: After annealing, the chip is removed and the subsequent normal processes such as electrode preparation, dicing, and testing are carried out.

[0016] Preferably, step one uses an ion evaporation device to deposit an ITO thin film at a temperature of 100°C, with a deposition rate of 4 Å / s and a thickness of 300 Å. The deposited ITO thin film is amorphous and has a smooth surface.

[0017] Preferably, in step one, the film roughness Ra is about 0.61 nm, Rq is about 0.802 nm, and Rz is about 15.6 nm.

[0018] Preferably, in step two, the film roughness Ra is 0.793 nm, Rq is 1.07 nm, and Rz is 29.9 nm.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. Core Innovation: Utilizing the "soft" window period of amorphous ITO. This invention precisely captures the "amorphous window period" after ITO film deposition and before heat treatment. At this time, the film structure is loose, the hardness is low, and the chemical activity is high. Roughening treatment is easier and more efficient, whether by chemical etching or physical processing, and the risk of damage to the underlying epitaxial layer is extremely low, thus synergistically optimizing performance.

[0021] 2. Excellent roughening effect and strong controllability: This invention adopts a wet etching scheme, in which the etching rate of amorphous ITO in a specific etching solution is uniform and controllable. By adjusting the concentration, temperature and time of the etching solution, the surface roughness can be precisely controlled. Compared with the etching of crystallized ITO, amorphous etching is more likely to form an ideal "matte" effect, which is non-directional, has good uniformity, and improves the light efficiency.

[0022] 3. Balancing Electrical and Optical Properties: This invention performs high-temperature annealing only after roughening is complete. The annealing process crystallizes ITO, restoring and improving its conductivity and light transmittance. On the other hand, the atomic migration during annealing helps repair surface micro-damage that may occur during roughening, ultimately obtaining an ITO film with both high light extraction efficiency and excellent electrical properties.

[0023] 4. Simplified process and reduced cost: When wet etching is used as a roughening method, this invention does not require expensive dry etching equipment. Only a simple wet etching process is needed to achieve excellent roughening effect, which greatly reduces equipment investment and process cost.

[0024] 5. Significant advantage of no damage: Since roughening occurs before heat treatment, it avoids the bombardment of crystallized ITO and the underlying epitaxial layer by high-energy plasma, fundamentally solving the problem of damage easily introduced by dry etching in existing technologies. Attached Figure Description

[0025] Figure 1 These are the AFM (2D) and AFM (3D) images of the thin film in step one of this invention;

[0026] Figure 2 The images show the AFM (2D) and AFM (3D) patterns of the thin film in step two of this invention.

[0027] Figure 3 This is a comparison chart of the light output power of the roughened LED chip and the unroughened chip according to the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings:

[0029] Example

[0030] A method for roughening LED ITO thin films to increase light extraction efficiency includes the following steps:

[0031] Step 1: ITO Thin Film Deposition: Prepare a sapphire substrate LED chip with completed GaN-based epitaxial growth. Using an ion evaporation apparatus, deposit an ITO thin film at 100°C with a deposition rate of 4 Å / s and a thickness of 300 Å. The deposited ITO film is amorphous with a smooth surface. Figure 1As shown, the film roughness Ra is approximately 0.61 nm, Rq is approximately 0.802 nm, and Rz is approximately 15.6 nm.

[0032] Step 2: Wet etching roughening before heat treatment: Prepare a 3% NMP organic solvent etching solution, heat it to 90℃, immerse the chip with deposited amorphous ITO in the etching solution, and etch for 30 minutes. After removal, rinse thoroughly with deionized water and dry with nitrogen. After etching, a uniform rough structure is formed on the ITO surface, and the roughness increases. Figure 2 As shown, the film roughness Ra is 0.793 nm, Rq is 1.07 nm, and Rz is 29.9 nm.

[0033] Step 3: High-temperature heat treatment annealing: The roughened chip is placed in a rapid annealing furnace and annealed at high temperature (550℃) for 10 minutes under a nitrogen atmosphere. After annealing, the ITO film is fully crystallized, the light transmittance increases to over 90%, and the rough surface morphology is maintained.

[0034] Step 4, Subsequent Processes: After annealing, the chip is removed and the subsequent normal processes such as electrode preparation, dicing, and testing are carried out.

[0035] like Figure 3 As shown, the LED chip processed in this embodiment has a light output power that is 0.78mW higher than that of the unprocessed chip under an injection current of 150mA.

[0036] The core process sequence of this invention is the technical route of "deposition → roughening → heat treatment", which is different from the traditional "deposition → heat treatment → roughening" route and the in-situ roughening route of "direct roughening during deposition".

[0037] Utilization of the amorphous window period: The key to the inventiveness of this invention lies in the roughening process of ITO thin films which are in an amorphous (or weakly crystalline) state after deposition and before heat treatment.

[0038] Wet etching roughening scheme: For amorphous ITO, a specific method for roughening is carried out using a specific etching solution (containing NMP organic solution) under specific process conditions (concentration, temperature, time).

[0039] The "roughening-crystallization" two-step method is a combination process of roughening first and then crystallizing. It is an optimized decoupling of optical performance (roughening) and electrical performance (crystallization), which can be controlled independently to achieve the technical effect of obtaining both.

[0040] Product structural features: The LED chip prepared by the method of the present invention has a unique microstructure feature of ITO film, namely a rough surface formed by amorphous etching and recrystallization. Its grain size, surface defect distribution, etc. are different from the rough surface formed by direct etching and crystallization of ITO, and can be distinguished by microscopic characterization.

[0041] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for roughening LED ITO thin films to increase light extraction efficiency, characterized in that: Includes the following steps: Step 1, ITO thin film deposition: Prepare a sapphire substrate LED chip that has completed GaN-based epitaxial growth, and deposit an ITO thin film using an ion evaporation device at a temperature of 80℃~120℃. Step 2: Wet etching roughening before heat treatment: Prepare a 3% NMP organic solvent etching solution, heat it to 85℃~95℃, immerse the chip with amorphous ITO deposited in the etching solution, and etch for 25-35 minutes. After removal, rinse with deionized water and dry with nitrogen. After etching, a uniform rough structure is formed on the ITO surface, and the roughness increases. Step 3: High-temperature heat treatment annealing: The roughened chip is placed in a rapid annealing furnace and annealed at high temperature under a nitrogen atmosphere. The annealing temperature is 500℃~600℃, and the annealing time is 5~15 minutes. After annealing, the ITO film is fully crystallized, the light transmittance is increased to over 90%, and the rough surface morphology is maintained. Step 4, Subsequent Processes: After annealing, the chip is removed and the subsequent normal processes such as electrode preparation, dicing, and testing are carried out.

2. The method for roughening LED ITO thin films to increase light extraction efficiency according to claim 1, characterized in that: Step one uses an ion evaporation device to deposit an ITO thin film at a temperature of 80℃~120℃, with a deposition rate of 4Å / s and a thickness of 300Å. The deposited ITO thin film is amorphous and has a smooth surface.

3. The method for roughening LED ITO thin films to increase light extraction efficiency according to claim 1, characterized in that: In step one, the film roughness Ra is approximately 0.61 nm, Rq is approximately 0.802 nm, and Rz is approximately 15.6 nm.

4. The method for roughening LED ITO thin films to increase light extraction efficiency according to claim 1, characterized in that: In step two, the film roughness Ra is 0.793 nm, Rq is 1.07 nm, and Rz is 29.9 nm.

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