A thin film structure for inhibiting warping in a micro-led bonding process and a preparation method thereof

Abstract

The application discloses a thin film structure for inhibiting warping in a Micro-LED bonding process and a preparation method thereof, and relates to the technical field of display packaging. The thin film structure comprises the following steps: in the bonding process of a chip and a substrate, a target material thin film is deposited on the back surface of a sapphire substrate and a Si substrate; and the thermal expansion coefficient of the target material thin film is between that of the sapphire and the Si. The application can relieve warping caused by the mismatching of the thermal expansion coefficients of the sapphire and the Si in the flip-chip bonding process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of display packaging, in particular to a thin film structure for suppressing warping in the bonding process of Micro-LED and a preparation method thereof. BACKGROUND

[0002] Micro LED-based display technology has the advantages of high luminous brightness, high resolution, wide color gamut and low power consumption, and is widely used in near-eye display, automotive headlights, ultra-large display screen and other fields, and is considered to be a new generation of reality technology.

[0003] In the integration process of Micro-LED devices, the selection and implementation of bonding technology is one of the key links that affect the final performance of the device. At present, flip-chip bonding technology has become the mainstream choice in the industry due to its unique advantages. Flip-chip bonding technology connects LED chips to the driving substrate in a "flip-chip" manner, which not only shortens the current path and improves the electrical performance, but also promotes the effective dissipation of heat, which is beneficial to improving the overall efficiency and stability of the device. However, despite the many advantages of flip-chip bonding technology, it still faces many challenges in actual operation. In particular, when it comes to the combination of sapphire substrates and Si substrates, the different thermal expansion coefficients of the two become a key factor that restricts the bonding quality. In flip-chip bonding, a certain temperature and pressure need to be applied. When the temperature is high, the difference in thermal expansion coefficient will cause the stress distribution at the interface to be extremely uneven, which will in turn cause the warping deformation of the device. Warping not only affects the precise alignment between the chip and the substrate, but also can cause the failure of electrical connection, and even damage the Micro-LED structure, thereby significantly reducing the yield of bonding and the reliability of the device. SUMMARY

[0004] The purpose of the present application is to provide a thin film structure for suppressing warping in the bonding process of Micro-LED and a preparation method thereof, which can alleviate the warping caused by the mismatch of the thermal expansion coefficients of sapphire and Si in the flip-chip bonding process.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] A thin film structure for suppressing warping in the bonding process of Micro-LED, comprising: depositing a target material thin film on the back surface of a sapphire substrate and a Si substrate during the bonding process of a chip and a substrate; the thermal expansion coefficient of the target material thin film is between sapphire and Si.

[0007] Optionally, the target material thin film is an AlN thin film.

[0008] The present application also provides a preparation method of a thin film structure for suppressing warping in the bonding process of Micro-LED, comprising:

[0009] Step 101: placing the chip in the vacuum chamber of the PEALD device, inputting the Al source and the N source, and controlling the growth temperature in the range of 50-220℃;

[0010] Step 102: cleaning the Si substrate in HF to remove the SiO2 layer on the surface, and then cleaning in deionized water and drying with N2;

[0011] Step 103: placing the cleaned substrate in the PEALD device, inputting the Al source and the N source, and setting the growth temperature range;

[0012] Step 104: cleaning the cooled chip and substrate with ethanol, drying, and then performing flip-chip bonding;

[0013] Step 105: peeling off the sapphire substrate and the AlN film on the surface of the Micro-LED chip by laser or chemical solution;

[0014] Step 106: placing the device after removing the sapphire substrate and the AlN film on the surface in KOH solution, soaking for 5-60min, and removing the AlN film on the Si substrate.

[0015] Optionally, the Al source is trimethyl.

[0016] Optionally, the N source is plasmaized N2 / H2 mixed gas.

[0017] Optionally, the growth temperature range in step 103 is 150-200℃.

[0018] Optionally, the bonding temperature of flip-chip bonding in step 104 is 150-250℃.

[0019] Optionally, the bonding pressure of flip-chip bonding in step 104 is 1-30KN.

[0020] Optionally, the bonding time of flip-chip bonding in step 104 is 10s-60min.

[0021] According to the embodiments of the present application, the following technical effects are provided:

[0022] This invention discloses a thin film structure and its fabrication method for suppressing warpage during Micro-LED bonding. The thin film structure includes: depositing a target material thin film on the back side of a sapphire substrate and a Si substrate during the chip-substrate bonding process; the thermal expansion coefficient of the target material thin film is between that of sapphire and Si. This invention alleviates stress concentration and device warpage caused by thermal expansion coefficient mismatch by introducing a buffer layer with the target thermal expansion coefficient, and improves the accuracy and yield of Micro-LED flip bonding. It not only enhances the electrical connection stability of the device but also optimizes thermal management performance, laying a solid foundation for the high-performance integration and application of Micro-LEDs. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the cross-sectional structure of the chip and substrate after AlN growth and deposition in this embodiment;

[0025] Figure 2 This is a schematic diagram of the cross-sectional structure of the chip and substrate after bonding in this embodiment;

[0026] Figure 3 This is a schematic diagram of the cross-sectional structure of the AlN thin film after removing the sapphire substrate and surface in this embodiment;

[0027] Figure 4 This is a schematic diagram of the cross-sectional structure of the AlN thin film removed from the surface of the silicon substrate in this embodiment. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The purpose of this invention is to provide a thin film structure and its preparation method that suppress warping during Micro-LED bonding, which can alleviate warping caused by the mismatch of thermal expansion coefficients of sapphire and Si during flip bonding.

[0030] In order to make the above objectives, characteristics and advantages of the present application more apparent, further detailed description will be given below in combination with the drawings and specific embodiments.

[0031] The present application provides a thin film structure for inhibiting warping in the bonding process of Micro-LED, comprising: in the bonding process of the chip and the substrate, depositing a target material thin film on the back of the sapphire substrate and the Si substrate; the thermal expansion coefficient of the target material thin film is between sapphire and Si. Wherein, the target material thin film adopts AlN thin film.

[0032] In this embodiment, since the thermal expansion coefficients of sapphire and Si do not match, warping is formed in the bonding process of heating and pressing, and the bonding yield is reduced, therefore AlN is grown on the surfaces of sapphire and silicon respectively, forming a sandwich structure with AlN on the upper and lower surfaces, improving the warping phenomenon caused by the difference in thermal expansion coefficient and the change process of temperature and pressure in the bonding process, improving the bonding yield and light emitting level, and improving the reliability and life of Micro-LED.

[0033] And further proposed is a corresponding preparation method, using PEALD technology to grow AlN thin film on the back of the sapphire substrate of the Micro-LED chip, and depositing AlN thin film on the back of the Si driving substrate, after introducing AlN, then performing flip-chip bonding, at this time forming a sandwich structure with AlN thin film on the upper and lower surfaces, and the chip and the substrate in the middle. In the bonding process, the thermal expansion coefficient matching is optimized, the bonding stress and device warping are reduced, and the bonding yield and performance stability of Micro-LED are improved. After the bonding process is completed, the Si substrate and the sapphire substrate are removed by peeling off using laser, chemical solution and the like.

[0034] As shown in Figures 1-4 , the process specifically includes:

[0035] Step 101: Place the chip in the vacuum chamber of the PEALD device, introduce trimethyl as the Al source, and ionized N2 / H2 mixed gas as the N source, and control the growth temperature.

[0036] Step 102: Clean the Si substrate in HF to remove the surface SiO2 layer, and then clean with deionized water and dry with N2.

[0037] Step 103: Place the cleaned substrate in the PEALD device, introduce trimethyl as the Al source, and ionized N2 / H2 mixed gas as the N source, and the growth temperature interval is 150-200℃.

[0038] Step 104: After cooling, the chip and the substrate are cleaned with ethanol, and then flip chip bonding is performed after being dried. The bonding temperature is 150-250°C, the bonding pressure is 1-30KN, and the time is 10-60min, as shown in Figure 2

[0039] Step 105: The Micro-LED chip substrate and the surface AlN film are peeled off by laser, chemical solution, etc.

[0040] Step 106: The device after removing the sapphire substrate is placed in KOH solution for a certain time to remove the AlN film on the Si substrate.

[0041] Therefore, since the thermal expansion coefficient of the AlN film is between that of sapphire and Si, and the growth process is simple and controllable, the preparation method proposed in the embodiment forms a structure in which the upper and lower surfaces of the device are both AlN films, and the LED chip and the Si driving substrate are in the middle, by depositing an AlN film on the back surface of the sapphire substrate of the LED chip and the back surface of the driving substrate, respectively, in the flip chip bonding process, and the warping caused by the mismatch of the thermal expansion coefficients of sapphire and Si in the flip chip bonding process is relieved by using the moderate thermal expansion coefficient and excellent mechanical properties of AlN. The key steps include the following steps:

[0042] (1) An AlN film is grown on the back surface of the sapphire substrate of the Micro-LED chip and the driving Si substrate by plasma enhanced atomic layer deposition (PEALD), respectively;

[0043] (2) The LED chip with the grown AlN film and the Si substrate are bonded by flip chip bonding technology;

[0044] (3) The sapphire substrate and the surface AlN film are removed by laser peeling, chemical etching, etc.

[0045] (4) The AlN film on the surface of the Si substrate is removed by chemical etching, etc.

[0046] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0047] The principles and implementation manners of the present application are described by using specific examples in this paper. The above description of the embodiments is only used to help understand the core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range will be changed. In conclusion, the content of the specification should not be understood as a limitation of the present application.​

Claims

1. A thin film structure for suppressing warpage in a Micro-LED bonding process, characterized in that, The application relates to a method for preparing a micro-LED chip. In the bonding process of a chip and a substrate, a target material thin film is deposited on the back surface of a sapphire substrate and a Si substrate; The back surface is the other surface opposite to the bonding surface; the thermal expansion coefficient of the target material thin film is between that of sapphire and Si.

2. The thin film structure for suppressing warpage in a Micro-LED bonding process according to claim 1, wherein The target material thin film is an AlN thin film. 3.A method for preparing a thin film structure for suppressing warpage in a Micro-LED bonding process, characterized in that, The application relates to a method for preparing a micro-LED chip. Step 101: placing a chip in a vacuum chamber of a PEALD device, inputting an Al source and an N source, and controlling the growth temperature, wherein the temperature range is 50 DEG C-220 DEG C; Step 102: placing a Si substrate in HF for cleaning, removing the SiO2 layer on the surface, and then blowing dry with N2 after cleaning with deionized water; Step 103: placing the cleaned substrate in the PEALD device, inputting the Al source and the N source, and setting the growth temperature range; Step 104: cleaning the cooled chip and substrate with ethanol, blowing dry, and then carrying out flip-chip bonding; Step 105: stripping the sapphire substrate and the AlN thin film on the surface of the micro-LED chip by means of laser or chemical solution; Step 106: placing the device after removing the sapphire substrate and the AlN thin film on the surface in KOH solution, soaking for 5 min-60 min, and removing the AlN thin film on the Si substrate.

4. The method of claim 3, wherein the method further comprises: The Al source is trimethyl.

5. The method of claim 3, wherein the method further comprises: The N source is plasmaized N2 / H2 mixed gas.

6. The method of claim 3, wherein the method further comprises: The growth temperature range in the step 103 is 150 DEG C-200 DEG C.

7. The method of claim 3, wherein the method further comprises: The bonding temperature of the flip-chip bonding in the step 104 is 150 DEG C-250 DEG C.

8. The method of claim 3, wherein the method further comprises: The bonding pressure of the flip-chip bonding in the step 104 is 1N-30KN.

9. The method of claim 3, wherein the method further comprises: The bonding time of the flip-chip bonding in the step 104 is 10s-60min.

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