Thin film structure for inhibiting warping in Micro-LED bonding process and preparation method thereof

Abstract

The invention 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 is characterized in that in the bonding process of a chip and a substrate, a target material thin film is deposited on the back surfaces of a sapphire substrate and a Si substrate; the thermal expansion coefficient of the target material film is between that of sapphire and that of Si. According to the method, warping caused by mismatching of thermal expansion coefficients of sapphire and Si in the flip-chip bonding process can be relieved.

Description

Technical Field

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

[0002] Display technology based on micro light-emitting diodes (Micro LEDs) has the advantages of high brightness, high resolution, wide color gamut and low power consumption. It is widely used in near-eye display, automotive lights, ultra-large display screens and other fields, and is considered to be a new generation of reality technology.

[0003] In the process of Micro-LED device integration, 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 with its unique advantages. Flip-chip bonding technology directly connects the LED chip to the driving substrate in a "flip-up" 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. Especially when it comes to the combination of sapphire substrate and Si substrate, the different thermal expansion coefficients of the two become the key factor restricting the bonding quality. A certain temperature and pressure need to be applied in flip-chip bonding. When the temperature is high, this difference in thermal expansion coefficient will cause extremely uneven stress distribution at the interface, which will cause the device to warp and deform. Warping not only affects the precise alignment between the chip and the substrate, but may also cause the failure of the electrical connection and even damage the Micro-LED structure, thereby significantly reducing the bonding yield and device reliability. Summary of the invention

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

[0005] To achieve the above object, the present invention provides the following solutions:

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

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

[0008] The present invention also provides a method for preparing a thin film structure for suppressing warping during a Micro-LED bonding process, comprising:

[0009] Step 101: placing the chip in a vacuum chamber of a PEALD device, introducing an Al source and a N source, and controlling the growth temperature in a range of 50° C. to 220° C.;

[0010] Step 102: Clean the Si substrate in HF to remove the SiO 2 layer, and then rinsed with deionized water and N 2 Blow dry;

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

[0012] Step 104: The cooled chip and substrate are cleaned with ethanol, blown dry, and then flip-chip bonded;

[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: Place the device after removing the sapphire substrate and the AlN film on the surface in a KOH solution and soak for 5 minutes to 60 minutes to remove the AlN film on the Si substrate.

[0015] Optionally, the Al source is trimethyl.

[0016] Optionally, the N source is plasma-enhanced N 2 / H 2 Mixed gas.

[0017] Optionally, the growth temperature in step 103 is within a range of 150°C to 200°C.

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

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

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

[0021] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0022] The present invention discloses a thin film structure for suppressing warping during Micro-LED bonding and a preparation method thereof, wherein the thin film structure comprises: during the bonding process of the chip and the substrate, a target material film is deposited on the back of a sapphire substrate and a Si substrate; the thermal expansion coefficient of the target material film is between sapphire and Si. The present invention alleviates the stress concentration and device warping problems caused by the mismatch of thermal expansion coefficients by introducing a buffer layer of the target thermal expansion coefficient, and improves the accuracy and yield of Micro-LED flip-chip bonding. It not only enhances the electrical connection stability of the device, but also optimizes the thermal management performance, laying a solid foundation for the high-performance integration and application of Micro-LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

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

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

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

[0027] Figure 4 Schematic diagram of the cross-sectional structure of the AlN film removed from the surface of the silicon substrate in this embodiment. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The object of the present invention is to provide a thin film structure for suppressing warping during Micro-LED bonding and a preparation method thereof, which can alleviate the warping caused by the mismatch of thermal expansion coefficients of sapphire and Si during flip-chip bonding.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

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

[0032] In this embodiment, due to the mismatch in thermal expansion coefficients between sapphire and Si, warping occurs during the heating and pressurizing bonding process, and the bonding yield decreases. Therefore, AlN is grown on the surfaces of sapphire and silicon respectively to form a sandwich structure with AlN on the top and bottom. This improves the warping phenomenon caused by the difference in thermal expansion coefficients and the changes in temperature and pressure during the bonding process, improves the bonding yield and luminescence level, and increases the reliability and life of the Micro-LED.

[0033] The corresponding preparation method is further proposed. The AlN film is grown on the back of the sapphire substrate of the Micro-LED chip using PEALD technology, and the AlN film is deposited on the back of the Si driving substrate. After the AlN is introduced, flip-chip bonding is performed, and a sandwich structure with AlN films on the top and bottom and the chip and substrate in the middle is formed. During the bonding process, the thermal expansion coefficient matching is optimized, the bonding stress and device warping are reduced, and the Micro-LED bonding yield and performance stability are improved. After the bonding process is completed, the Si substrate and sapphire substrate are peeled off and removed using lasers, chemical solutions, etc.

[0034] like Figure 1-Figure 4 As shown, the process specifically includes:

[0035] Step 101: Place the chip in the vacuum chamber of the PEALD equipment, introduce trimethylol as Al source, and plasma-generated N 2 / H 2 The mixed gas serves as a N source to control the growth temperature.

[0036] Step 102: Clean the Si substrate in HF to remove the SiO 2 layer, washed with deionized water and then with N 2 Blow dry.

[0037] Step 103: Place the cleaned substrate in the PEALD equipment, introduce trimethylol as Al source, and plasma N 2 / H 2 The mixed gas is used as the N source, and the growth temperature range is 150℃-200℃.

[0038] Step 104: After cooling, the chip and substrate are cleaned with ethanol, blown dry, and then flip-chip bonded. The bonding temperature is 150°C to 250°C, the bonding pressure is 1N to 30KN, and the bonding time is 10s to 60min. Figure 2 shown.

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

[0040] Step 106: Place the device after the sapphire substrate is removed in a KOH solution and soak for a certain period of time to remove the AlN film on the Si substrate.

[0041] Therefore, considering that the thermal expansion coefficient of AlN film is between that of sapphire and Si, and the growth process is simple and controllable, the preparation method proposed in this embodiment deposits a layer of AlN film on the back of the sapphire substrate of the LED chip and the back of the driving substrate respectively, and forms a structure in which the upper and lower sides of the device are AlN films, and the middle is the LED chip and the Si driving substrate, and utilizes the moderate thermal expansion coefficient and excellent mechanical properties of AlN to alleviate the warping caused by the mismatch of the thermal expansion coefficients of sapphire and Si during the flip-chip bonding process. The key points include the following steps:

[0042] (1) A layer of AlN is grown on the sapphire substrate of the Micro-LED chip and the back of the driver silicon substrate by plasma enhanced atomic layer deposition (PEALD);

[0043] (2) Bonding the LED chip with AlN thin film to the Si substrate through flip-chip bonding technology;

[0044] (3) Use laser stripping, chemical etching and other methods to remove the sapphire substrate and the AlN film on the surface;

[0045] (4) Use chemical etching or other methods to remove the AlN film on the surface of the silicon substrate.

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

[0047] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A thin film structure for suppressing warping during Micro-LED bonding, characterized in that: include: During the bonding process between the chip and the substrate, a thin film of the target material is deposited on the back of the sapphire substrate and the Si substrate; The thermal expansion coefficient of the target material film is between sapphire and Si.

2. The thin film structure for suppressing warping during Micro-LED bonding according to claim 1, characterized in that: The target material film is an AlN film.

3. A method for preparing a thin film structure for suppressing warping during Micro-LED bonding, characterized in that: include: Step 101: placing the chip in a vacuum chamber of a PEALD device, introducing an Al source and a N source, and controlling the growth temperature in a range of 50° C. to 220° C.; Step 102: The Si substrate is cleaned in HF to remove the SiO2 layer on the surface, and then washed with deionized water and dried with N2; Step 103: placing the cleaned substrate in a PEALD device, introducing an Al source and a N source, and setting a growth temperature range; Step 104: The cooled chip and substrate are cleaned with ethanol, blown dry, and then flip-chip bonded; Step 105: peeling off the sapphire substrate and the AlN film on the surface of the Micro-LED chip by laser or chemical solution; Step 106: Place the device after removing the sapphire substrate and the AlN film on the surface in a KOH solution and soak for 5 minutes to 60 minutes to remove the AlN film on the Si substrate.

4. The method for preparing a thin film structure for suppressing warping during Micro-LED bonding according to claim 3, characterized in that: The Al source is trimethyl.

5. The method for preparing a thin film structure for suppressing warping during Micro-LED bonding according to claim 3, characterized in that: The N source is a plasma-enhanced N2 / H2 mixed gas.

6. The method for preparing a thin film structure for suppressing warping during Micro-LED bonding according to claim 3, characterized in that: The growth temperature range in step 103 is 150° C.-200° C.

7. The method for preparing a thin film structure for suppressing warping during Micro-LED bonding according to claim 3, characterized in that: The bonding temperature of the flip-chip bonding in step 104 is 150° C. to 250° C.

8. The method for preparing a thin film structure for suppressing warping during Micro-LED bonding according to claim 3, characterized in that: The bonding pressure of the flip-chip bonding in step 104 is 1N to 30KN.

9. The method for preparing a thin film structure for suppressing warping during Micro-LED bonding according to claim 3, characterized in that: The bonding time of the flip-chip bonding in step 104 is 10 s to 60 min.

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