Rapid thermal annealing method for light-emitting diode product

Abstract

The invention relates to a rapid thermal annealing method for a light-emitting diode product, and aims to reduce internal stress generated in the manufacturing process, promote the repair of lattice defects and improve the voltage stability and brightness performance of the LED product by optimizing the gas introduction opportunity and a multi-stage cooling strategy in the annealing process. The method comprises the following steps: heating an LED sample to 500-1000 DEG C in a vacuum environment, keeping the temperature for a period of time, introducing process gas, and continuously introducing the process gas in the cooling process by adopting a multi-section cooling model to ensure the integrity of lattice recombination. By finely controlling the cooling rate and continuously supplying air, the stress can be effectively reduced, the crystal lattice size can be increased, the adhesive force between the ITO film and the bottom layer structure can be improved, and finally the electro-optical performance of the LED can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a rapid thermal annealing method for light emitting diode products. Background Art

[0002] Light-emitting diodes (LEDs) are widely used in various lighting and display fields, and the improvement of their performance mainly depends on the optimization of key materials in LED components. Indium tin oxide (ITO), as an important transparent conductive material, is widely used in LED products. In order to improve the conductivity and light transmittance of the ITO film, it is usually necessary to anneal it. Chinese patent CN106531615A provides a preparation method for improving the luminous efficiency of LED chips, in which an ITO transparent conductive layer is deposited by using reactive plasma deposition (RPD) technology under low-temperature peroxygen conditions, and the ohmic contact between the ITO film and the p-type GaN layer is improved by rapid thermal annealing (RTA) treatment. The annealing process is "heating to 525-575°C at a heating rate of 20-40°C / second, holding the temperature for 3-5 minutes, then cooling to 200-300°C through N2, and then cooling naturally in the air".

[0003] However, this traditional heating and cooling mode combined with gas has defects: in the case of lattice-mismatched film stacks, rapid cooling will interfere with the stress release of the entire structure, thereby affecting the adhesion of the film to the underlying layer. The stress generated by the film will affect its degree of adhesion to the underlying structure, thereby affecting the voltage performance of the product. In addition, during the cooling process, as long as the temperature is still above the crystallization temperature of the material, these thermal lattices still have the kinetic energy to reorganize and rearrange. Since the process gas is cut off at the end of the temperature holding, only nitrogen is introduced as a cooling method during this process, and it is impossible to capture the floating bonds and repair the defects remaining under the lattice displacement and reorganization caused during the slow cooling period, thereby affecting the photoelectric performance of the product.

[0004] In order to reduce stress in the manufacturing process, optimize the deficiencies in lattice defect repair, and further improve the electro-optical performance of LED products, it is necessary to optimize the cooling strategy and the timing of process gas introduction during annealing to reduce stress accumulation and improve the stability of the lattice structure. Summary of the invention

[0005] The purpose of the present invention is to provide an improved rapid thermal annealing method for light-emitting diode products, which effectively reduces the internal stress generated during the manufacturing process by optimizing the timing of process gas introduction and the cooling strategy, while promoting the repair of lattice defects, thereby improving the voltage stability and brightness performance of LED products.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A rapid thermal annealing method for a light emitting diode product comprises the following steps:

[0008] a. Heat the light-emitting diode product to a preset temperature range in a vacuum environment;

[0009] b. introducing the process gas after maintaining the temperature at the preset temperature for a period of time;

[0010] c. Cooling is performed through an n-stage cooling model, and the process gas is continuously introduced in at least a portion of the stage before the temperature is cooled to room temperature, wherein each cooling stage has a different cooling rate, and n is an integer greater than or equal to 2.

[0011] Preferably, the preset temperature range is 500-1000°C.

[0012] Preferably, step b continues at the preset temperature for 50-200 seconds.

[0013] Preferably, the process gas in step b includes but is not limited to oxygen, nitrogen or hydrogen. The following is a further comparative description of the process gas in the present invention:

[0014] a. Oxygen: This gas is more active than nitrogen and can combine with non-stable molecules to form oxides. It can effectively repair the oxygen-deficient bonding state of ITO during lattice rearrangement under high-temperature annealing, improve film value and light transmittance, and is the preferred process gas for the present invention.

[0015] b. Nitrogen: It is an inert gas with a low price. It is often used to break the air or cool down the vacuum machine. It does not react with molecules. The residual oxygen vacancies in the structure still exist. The light absorption caused by the defects and the quality problems caused by the difference in film value far outweigh the benefits brought by its contribution to the electrical properties of the carrier concentration in the film.

[0016] c. Hydrogen: For safety reasons, the use of hydrogen requires higher equipment safety protection measures, and the carrier gas must be mixed with nitrogen before introduction. Although it can provide H bonds to increase the ITO carrier concentration, it is more expensive.

[0017] Preferably, step c is performed after the gas supply is continuously supplied for 100-200 seconds in step b.

[0018] Preferably, the flow rate of the process gas in step b is not less than 1 sccm (standard cubic centimeter per minute).

[0019] Preferably, the process gas is continuously introduced during the entire cooling process in step c.

[0020] In step c, the n-stage cooling model is determined by the following method:

[0021] The cooling process is divided into several stages based on different process requirements;

[0022] Through the cooling curve formula: T n =T0*e [-αn*(tn-t0)] Find α n =-ln[(T n / T0) / t n ], the cooling rate of this stage is determined by the value of αn, where T0 is the starting temperature of each cooling process, T n The target temperature set for each cooling process, t n The cooling interval time set for the nth cooling process, α n is the cooling coefficient of the cooling process, T0, T n The unit is ℃, t n The unit is seconds.

[0023] The light-emitting diode product structure includes a substrate, a gallium nitride epitaxy, an insulating layer, an indium tin oxide layer and a metal layer, and can be applied to a structure of face-up, high voltage, flip-chip, vertical or any combination thereof, wherein the substrate can be silicon carbide, silicon, sapphire, etc., the gallium nitride epitaxy has a buffer layer and an undoped layer and PN polarity doped gallium nitride and a quantum well, the insulating layer can be silicon oxide, silicon nitride, aluminum oxide, etc., the metal can be a combination of chromium, aluminum, titanium, platinum, nickel, gold, and tin-gold, and the thickness of the indium tin oxide layer is 10nm to 300nm.

[0024] The molar ratio of indium to tin in the indium tin oxide layer is 90:10-97:3.

[0025] The rapid thermal annealing method of the present invention adopts a two-stage or multi-stage cooling model, and different cooling rates can be set for each cooling stage. This design allows the light-emitting diode product to be cooled more evenly and effectively during the rapid cooling process from high temperature to ensure the minimization of internal stress of the material and prevent structural damage. The method maintains the supply of process gas by extending the introduction time of the process gas throughout the cooling process, especially during the process of gradually cooling the material from a high temperature state to room temperature. This continuous gas supply helps to repair the defective states in the lattice displacement and recombination that may be caused by rapid cooling, thereby optimizing the crystal structure of the material and improving the electro-optical performance of the final product.

[0026] In addition, the multi-stage cooling strategy allows for fine control of the temperature drop rate, further reducing internal stress caused by temperature changes and optimizing product quality and performance.

[0027] Compared with the traditional annealing method, the improved method of the present invention brings obvious beneficial effects in the following aspects:

[0028] The reaction gas is relatively pure: unnecessary gas molecules in the atmosphere are extracted by vacuuming, and only gases effective for improving the performance of ITO (such as oxygen preferably used in the present invention) are introduced.

[0029] Stress reduction: By controlling the cooling rate through an n-stage cooling model, the internal stress accumulation caused by rapid cooling can be effectively reduced, and the mechanical strain and structural damage of the material can be avoided, especially in thicker ITO films.

[0030] Lattice optimization: Compared with the introduction of nitrogen, extending the supply time of oxygen during the cooling stage can better promote the optimization and reorganization of the lattice structure, reduce the number of grain boundaries, increase the unit cell size, and further improve the crystal quality of the film.

[0031] Improved product performance: By optimizing the annealing process, the voltage stability, conductivity and photoelectric conversion efficiency of LED components are improved, which ultimately improves the brightness and luminous efficacy of LED products and enhances the overall performance of the product.

[0032] Strong versatility: The present invention is applicable to a variety of light-emitting diode products, including face-mounted, high-voltage, flip-chip and vertical structure LED products. It is also compatible with different substrate materials (such as silicon carbide, silicon, sapphire, etc.), and can achieve significant performance improvements in LED products with different structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the two-stage cooling model of Example 1 of the present invention.

[0034] Figure 2 This is the n-stage cooling model of Example 2 of the present invention.

[0035] Figure 3 This is a comparative example of a traditional cooling model.

[0036] Figure 4 This is a SEM image of the lattice of the indium tin oxide layer after annealing in Example 2 of the present invention.

[0037] Figure 5 This is a SEM image of the lattice of the indium tin oxide layer after annealing in Comparative Example 2 of the present invention.

[0038] Figure 6 It is a box diagram of the grain size distribution of the ITO thin film samples of Examples 1 and 2 of the present invention and Comparative Examples 1 and 2.

[0039] Figure 7 These are the stress test results of the samples after annealing in Examples 1 and 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0040] Preferred embodiments of the present invention are given below in conjunction with the accompanying drawings to illustrate the technical solutions of the present invention in detail.

[0041] Example 1: A rapid thermal annealing system equipped with a dry mechanical pump is used, the maximum temperature of which can reach 1250°C, the heating rate is 10-30°C / second, and the temperature control capability is ±0.5°C. An LED sample consisting of a sapphire substrate, a gallium nitride epitaxial layer (including a buffer layer, an undoped layer, a PN polarity doped gallium nitride and a quantum well), a silicon oxide insulating layer, a 30nm thick indium tin oxide layer (the ratio of indium tin is 95:5), and a metal layer (a combination of aluminum and platinum) is processed. The sample is heated to 550°C at a rate of 10°C / second in the system and maintained at this temperature for 180 seconds, and then 5N pure oxygen is introduced and continuously supplied for 150 seconds before being cooled in two stages: first, the temperature is reduced to 450°C within 40 seconds and maintained at this temperature for 60 seconds, and then the temperature is reduced to room temperature, during which the gas is continuously supplied. The cooling model is as follows: Figure 1 shown.

[0042] Example 2: In the same rapid thermal annealing system as in Example 1, an LED sample consisting of a silicon substrate, a gallium nitride epitaxial layer (same as in Example 1), a silicon nitride insulating layer, a 90nm thick indium tin oxide layer (the ratio of indium to tin is 90:10), and a metal layer (a combination of chromium and nickel) was processed. The heating and oxygen introduction parameters of this sample were the same as in Example 1, but the following was used: Figure 2 As shown, it is a three-stage cooling model. The first stage cooling curve is the same as the first stage of Example 1, that is, t1 is 40 (seconds). Substituting it into the formula, the cooling coefficient value α1 is 0.0021. The second stage target temperature is set to 250°C. The second stage cooling time can be designed to be 121.5 seconds according to the formula, and finally it is reduced to room temperature. The third stage cooling time is designed to be 1096.4 seconds according to the formula. The specific calculation process is as follows:

[0043] (1) First calculate the cooling coefficient α1 of the first stage of cooling:

[0044] 450℃=550℃*e (-α1*40)

[0045] α1=0.0021

[0046] (2) Then bring the first stage cooling coefficient α1 into the second stage cooling model:

[0047] 250℃=450℃*e (-0.0021*t2)

[0048] t2=121.5(seconds)

[0049] (3) The final room temperature is set to 25°C. According to the formula, the cooling time t4 = 1096 seconds

[0050] 25℃=250℃*e (-0.0021*t3)

[0051] t3=1096.4(seconds)

[0052] Comparative Example 1: The same LED sample and annealing system as in Example 1 were used, except that oxygen was introduced only during the heating phase; the temperature was continuously lowered to room temperature in one step instead of using a two-stage cooling method. Figure 3 shown.

[0053] Comparative Example 2: The same LED sample and annealing system as in Example 2 were used, except that oxygen was introduced only during the heating phase; the temperature was continuously lowered to room temperature in one step instead of using n-stage cooling. Figure 3 shown.

[0054] Test results:

[0055] After annealing, the samples of the embodiment and the comparative example were photographed by SEM and the size of the ITO lattice on the surface was measured. The SEM images of the indium tin oxide layer lattice of the embodiment 2 and the comparative example 2 are as follows: Figure 4 and Figure 5 As shown. A total of 24 points are taken for each group of conditions. Figure 6 It can be seen that through n-stage cooling combined with continuous introduction of process oxygen, the lattice sizes of Examples 1 and 2 of the present invention are respectively larger than those of Comparative Examples 1 and 2, which directly proves that this method can effectively increase the unit cell size of the film and simultaneously reduce the number of grain boundaries.

[0056] The stress test was performed on the annealed samples of Examples 1 and 2 and Comparative Examples 1 and 2. Figure 7 As shown, the stress of Examples 1 and 2 of n-stage cooling is lower than that of Comparative Examples 1 and 2, and the effect of stress reduction weakens as the film thickness increases.

[0057] The annealed samples are made into final LED core particles according to the chip manufacturing process, and are tested and lit to collect relevant photoelectric data. The new design proposed by the present invention can reduce the voltage on the LED element by 0.005-0.01V and improve the overall brightness by within 0.5%.

Claims

1. A rapid thermal annealing method for light emitting diode products, characterized in that: The following steps are involved: a. Heat the light-emitting diode product to a preset temperature range in a vacuum environment; b. introducing the process gas after maintaining the temperature at the preset temperature for a period of time; c. Cooling is performed through an n-stage cooling model, and the process gas is continuously introduced in at least a portion of the stage before the temperature is cooled to room temperature, wherein each cooling stage has a different cooling rate, and n is an integer greater than or equal to 2.

2. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: The preset temperature range is 500-1000°C.

3. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: In step b, the temperature is maintained at the preset temperature for 50-200 seconds.

4. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: The process gas in step b includes but is not limited to oxygen, nitrogen or hydrogen.

5. The rapid thermal annealing method for light emitting diode products according to claim 4, characterized in that: In step b, the process gas is oxygen.

6. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: After the gas supply in step b continues for 100-200 seconds, proceed to step c.

7. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: In step b, the flow rate of the process gas is not less than 1 sccm.

8. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: In step c, process gas is continuously introduced during the entire cooling process.

9. The rapid thermal annealing method for light emitting diode products according to claim 1, characterized in that: The n-stage cooling model is determined by: The cooling process is divided into several stages based on different process requirements; The cooling curve formula is: T n =T0*e [-αn*(tn-t0)] Find α n =-ln[(T n / T0) / t n ], through α n The value of T0 determines the cooling rate of this stage, where T0 is the starting temperature of each cooling process, T n The target temperature set for each cooling process, t n The cooling interval time set for the nth cooling process, α n is the cooling coefficient of the cooling process.

10. The method according to any one of claims 1 to 9, wherein the light emitting diode product structure comprises a substrate, a gallium nitride epitaxial layer, an insulating layer, an indium tin oxide layer and a metal layer, characterized in that: The thickness of the indium tin oxide layer is 10 nm to 300 nm.

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