A PI-assisted Micro-LED mass transfer method

Abstract

The invention discloses a PI-assisted Micro-LED mass transfer method, comprising the following steps: preparing a Micro-LED chip on a substrate; setting a bonding layer and a UV debonding layer on the surface of a first substrate; temporarily bonding the first substrate to the n-type electrode and the p-type electrode of the Micro-LED chip; peeling the Micro-LED chip onto the UV debonding layer; forming a PI cured film on the surface of the Micro-LED chip; setting a PI semi-cured film on the surface of a second substrate, bonding the PI cured film to the semi-cured film, separating the UV debonding layer from the Micro-LED chip, and transferring the Micro-LED chip to the second substrate; transferring the Micro-LED chip to a circuit board; and removing the PI cured film and the PI semi-cured film. The present invention can meet the needs of large-scale, high-yield, low-cost and high-speed transfer of mass transfer, and is compatible with chip transfers of various sizes.

Description

Technical Field

[0001] The present invention relates to a semiconductor manufacturing method, and specifically to a PI-assisted Micro-LED mass transfer method. Background Art

[0002] Micro-LED display technology is the most promising next-generation new display technology. Compared with traditional LCD and OLED displays, Micro-LED has unique advantages such as higher brightness, lower power consumption, higher resolution, faster response speed, and longer life. In addition to its great application potential in traditional displays such as mobile phones, TVs, and computers, it has absolute advantages in new display applications such as virtual reality (VR) and augmented reality (AR). However, the price of Micro-LED display products has remained high, which has severely restricted its commercial development. The difficulty in reducing the cost of Micro-LED display technology is mainly due to its relatively complex processing technology, and mass transfer technology is one of the biggest challenges facing Micro-LED display in reducing costs.

[0003] The current mainstream Micro-LED mass transfer technologies mainly include PDMS stamps, fluid self-assembly, electromagnetic transfer, laser-assisted mass transfer, etc. Among them, the PDMS stamp transfer speed yield is limited and expensive, fluid self-assembly is difficult to achieve small-size chip transfer, electromagnetic transfer requires special design of the Micro-LED chip structure, and laser-assisted mass transfer has a low yield. The Chinese patent with publication number CN115083990A discloses a Micro-LED mass transfer method, but it has the following disadvantages: 1. It requires precise control of the viscosity of the thermal release tape, and the transfer yield is low; 2. Transfer probes need to be set up separately for chips of different sizes, which is costly and not universal; 3. The thermal release tape faces the problem of viscosity recovery under long-term high temperature at excessively high temperatures, which greatly affects the transfer yield. Therefore, it puts forward high requirements on the bonding temperature and bonding time, and it is difficult to balance the temperature and time of heating and bonding of the thermal release tape. In general, these existing technologies are difficult to meet the needs of mass transfer for large-scale, high-yield, low-cost and high-speed transfer. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a PI-assisted Micro-LED mass transfer method.

[0005] Technical solution: The PI-assisted Micro-LED mass transfer method described in the present invention includes the following steps:

[0006] Step 1: preparing a Micro-LED chip on a substrate, and disposing an n-type electrode and a p-type electrode on the same side surface of the Micro-LED chip;

[0007] Step 2: Arrange a bonding layer and a UV debonding layer on the surface of the first substrate;

[0008] Step 3, temporarily bonding the first substrate to the n-type electrode and the p-type electrode of the Micro-LED chip through a UV debonding layer;

[0009] Step 4: Peel the Micro-LED chip onto the UV debonding layer and separate it from the substrate;

[0010] Step 5, spin-coating the PI solution on the surface of the Micro-LED chip away from the UV debonding layer, heating and curing, and forming a PI cured film;

[0011] Step 6: arranging a PI semi-cured film on the surface of the second substrate, bonding the PI cured film to the PI semi-cured film, separating the UV debonding layer with reduced viscosity after UV irradiation from the Micro-LED chip, and transferring the Micro-LED chip connected with the PI cured film to the second substrate based on the PI semi-cured film;

[0012] Step 7: The PI cured film and the PI semi-cured film on the second substrate are selectively removed by etching, and bonding metal is evaporated at the electrode position of the circuit board, so that the Micro-LED chip on the second substrate is selectively transferred to the circuit board, and the bonding metal is heated and bonded with the n-type electrode and the p-type electrode;

[0013] Step 8: Remove the PI cured film and PI semi-cured film of the Micro-LED chip.

[0014] Furthermore, in step 1, the Micro-LED chip is one or more of a blue light GaN epitaxial layer, a green light GaN epitaxial layer, and a red light GaN epitaxial layer, with a thickness of 3 to 8 μm. The substrate is any one of sapphire, silicon, silicon carbide, and quartz.

[0015] Preferably, the quantum well In composition of the blue light GaN epitaxial layer is 0.15-0.25, the quantum well In composition of the green light GaN epitaxial layer is 0.25-0.3, and the quantum well In composition of the red light GaN epitaxial layer is 0.3-0.7.

[0016] Furthermore, in step 2, the viscosity of the UV debonding layer is 2000-30000 mN / mm, and the viscosity decreases by more than 90% after UV irradiation. The first substrate is a transparent substrate, any one of sapphire, quartz, glass, PET, and PC.

[0017] Furthermore, in step 4, the stripping is performed by laser stripping using a 248 nm KrF excimer laser.

[0018] Furthermore, in step five, the temperature of heating and curing is 80~150℃, the time is 3~10min, and the thickness of the PI curing film is 0.5~5 μm. Before the Micro-LED peeled off from the first substrate is transferred to the second substrate, a layer of PI curing film is spin-coated on the back of the Micro-LED to connect each discrete Micro-LED chip. When the size of the Micro-LED is miniaturized to below 50μm, the transfer yield of the Micro-LED chip will be greatly reduced due to the reduction of the bonding area, which puts higher requirements on the viscosity of the adhesive part on the second substrate. The use of PI curing film can significantly reduce the viscosity requirements of the adhesive part on the second substrate.

[0019] Furthermore, in step six, the thickness of the PI semi-cured film is 0.5~5 μm. If the thickness of the PI semi-cured film is less than 0.5 μm, the semi-cured film will not be sticky enough, which will increase the difficulty of transferring the Micro-LED chip to the second substrate; if the thickness of the PI semi-cured film is greater than 5 μm, it will increase the difficulty of removal. The effect of adding the PI semi-cured film is that the viscosity of the PI disappears after curing, and it has viscosity in the semi-cured state, which can realize the transfer of the Micro-LED with the PI cured film to the semi-cured film.

[0020] Furthermore, in step seven, etching is performed by RIE or ICP etching in an O2 atmosphere, and the bonding metal is an alloy formed by one or more of In, Sn, and Au, which is a low melting point bonding metal.

[0021] Furthermore, the preparation method also includes step eight, repeating steps one to seven, replacing the Micro-LED chips with Micro-LED chips of different colors, and finally obtaining Micro-LED chips of different colors periodically arranged on the surface of the circuit board.

[0022] Furthermore, the Micro-LED chip is replaced with a three-color stacked Micro-LED chip.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0024] 1. It can meet the needs of large-scale, high-yield, low-cost and high-speed transfer of mass transfer, significantly improve the transfer yield of Micro-LED in each transfer step, low cost and compatible with the transfer of Micro-LED chips of various sizes;

[0025] 2. Inserting the PI curing layer can achieve the transfer of Micro-LED chips of different sizes from the first substrate to the second substrate, greatly improving the transfer yield and reducing the viscosity requirements of the adhesive part on the second substrate;

[0026] 3. Using PI semi-cured film as the bonding part of the second substrate can not only meet the viscosity requirements for transferring the Micro-LED chip to the second substrate, but also improve the yield of transferring the Micro-LED chip on the second substrate to the circuit board by taking advantage of its easy separation from the second substrate after heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the structure of the product obtained in step 1 of Example 1 of the present invention;

[0028] Figure 2 is a schematic diagram of the structure of the product obtained in step 3 of Example 1 of the present invention;

[0029] Figure 3 is a schematic diagram of the structure of the product obtained in step 5 of Example 1 of the present invention;

[0030] Figure 4 is a schematic diagram of the structure of the product obtained in step 6 of Example 1 of the present invention;

[0031] Figure 5 is a schematic diagram of the structure of the product obtained in step 7 of Example 1 of the present invention;

[0032] Figure 6 is a schematic diagram of the structure of the product obtained in step eight of Example 1 of the present invention;

[0033] Figure 7 is a schematic structural diagram of Embodiment 1 of the present invention;

[0034] Figure 8 is a schematic diagram of the structure of the product obtained in step 6 of Example 2 of the present invention;

[0035] Fig. 9 It is a structural diagram of embodiment 2 of the present invention. DETAILED DESCRIPTION

[0036] Example 1

[0037] A PI-assisted Micro-LED mass transfer method comprises the following steps:

[0038] Step 1, such as Figure 1As shown, a double-polished patterned sapphire substrate 1 is provided, and the thickness of the substrate 1 is 750 μm. A GaN epitaxial layer with a thickness of 4 to 8 μm is grown on the substrate 1, and a blue LED epitaxial wafer, i.e., a blue light Micro-LED chip 2, is formed by controlling the quantum well growth conditions, and the chip size is below 100 μm, and the preferred chip size is 1 μm to 50 μm. By controlling the quantum well growth conditions, blue, green, and red LED epitaxial wafers can be formed respectively, wherein the quantum well In component of the blue light LED epitaxial wafer is 0.15 to 0.25, the quantum well In component of the green light epitaxial wafer is 0.25 to 0.3, and the quantum well In component of the red light is 0.3 to 0.7. The electrical injection electrodes of the Micro-LED chip 2 are an n-type electrode 3 and a p-type electrode 4, which are arranged on the same surface of the Micro-LED chip 2.

[0039] Step 2, provide a first substrate 7, and set a bonding film on one side of the first substrate 7, the bonding film is a double-sided tape, including a bonding layer 6 bonded to the first substrate 7 and a UV dissolving layer 5 corresponding to the bonding layer 6. The UV dissolving layer 5 has a medium viscosity of 2000~30000 mN / mm, and the viscosity drops significantly to 90% of the initial viscosity after UV irradiation. The bonding layer 6 is a high-viscosity tape with a viscosity of 10000~40000 mN / mm. The first substrate 7 is a transparent substrate sapphire, which can also be replaced by any one of quartz, glass, PET, and PC.

[0040] Step 3: temporarily bond the first substrate 7 to the Micro-LED chip 2 on the substrate 1 through the UV debonding layer 5, and the UV debonding layer 5 is bonded to the electrode surface of the Micro-LED chip 2, such as Figure 2 shown.

[0041] Step 4: Separate the Micro-LED chip 2 from the substrate 1 by laser stripping using a 248 nm KrF excimer laser, and strip the Micro-LED chip 2 to the UV debonding layer 5 of the first substrate 7. The Micro-LED chip 2 is completely attached to the UV debonding layer 5 on the first substrate 7.

[0042] Step 5: The back side of the Micro-LED chip 2 is placed upward, and the PI solution is evenly spin-coated onto the back side of the Micro-LED chip 2 on the first substrate 7 by a coating system, and heated and cured at 80-150° C. for 3-10 minutes to form a PI cured film 8 with a thickness of 0.5-5 μm on the back side of the Micro-LED chip 2 for connecting the separated Micro-LED chips 2. Figure 3 shown.

[0043] Step six, provide a second substrate 10, and set a PI semi-cured film 9 on one side of the second substrate 10, that is, spin-coat a mixed solution of the PI solution and the solution with elastic dynamic release properties onto the second substrate 10, and bake at 60°C~100°C for 0.1~5min to form a sticky film. The thickness of the PI semi-cured film 9 is about 0.5~5 μm. Bond the Micro-LED chip 2 connected to the first substrate 7 through the PI cured film 8 to the second substrate 10 based on the PI semi-cured film 9, separate the UV debonding layer 5 and the first substrate 7 whose viscosity is weakened after UV irradiation, and transfer the Micro-LED chip 2 connected to the PI cured film 8 to the second substrate 10 based on the PI semi-cured film 9, so as to realize the positive placement of the chip on the second substrate 10, as shown in FIG. Figure 4 shown.

[0044] Step 7: RIE or ICP etching technology in an O2 atmosphere is used to remove the PI cured film 8 and PI semi-cured film 9 between the Micro-LED chips 2 on the second substrate 10. The Micro-LED chip 2 is independently placed on the second substrate 10, which is conducive to the selective transfer to the circuit board 12 in the next step. The Micro-LED chip 2 is combined with the second substrate 10 through the PI semi-cured film 9. Figure 5 shown.

[0045] Step eight, evaporate a low-melting-point bonding metal 11 at the electrode position of the circuit board 12. The low-melting-point bonding metal 11 is In, and can also be replaced by an alloy formed by one or more of In, Sn, and Au. The blue light Micro-LED chip 2 on the second substrate 10 is selectively transferred to the corresponding position of the circuit board 12. When the pulsed laser irradiates the PI semi-cured film 9 through the second substrate 10, high-pressure gas is instantly generated, and the Micro-LED chip 2 is separated from the second substrate 10 by the expansion and pushing action of the bubbles, thereby realizing the transfer to the circuit board 12. The position of the pulsed laser is controlled by the pulsed laser dynamic release technology to accurately release the Micro-LED chip 2 to the corresponding position of the circuit board 12. The Micro-LED chip 2 is heated and bonded to the circuit board 12 through the bonding metal 11, such as Figure 6 shown.

[0046] Step nine, using RIE or ICP etching technology in an O2 atmosphere to remove the PI cured film 8 and the PI semi-cured film 9 on the back of the Micro-LED chip 2, and completing the mass transfer of the blue light Micro-LED chip 2 on the circuit board 12.

[0047] Step 10, repeating steps 1 to 9 twice, replacing the blue light Micro-LED chip 2 with a green light Micro-LED chip 2 for the first time, and replacing the blue light Micro-LED chip 2 with a red light Micro-LED chip 2 for the second time, and obtaining the blue, green and red light periodically arranged Micro-LED chips 2 on the circuit board 12. By setting different positions of the n-type electrode 3 and the p-type electrode 4, different emission wavelengths can be obtained, such as Figure 7 shown.

[0048] Example 2

[0049] like Figure 8~Figure 9 , a PI-assisted Micro-LED mass transfer method, comprising the following steps:

[0050] Step 1: Provide a double-polished patterned sapphire substrate 1 with a thickness of 750 μm. Grow a three-color stacked Micro-LED chip 13 on the substrate 1. The size of the three-color stacked Micro-LED chip 13 is less than 100 μm, and the preferred size is 1 μm to 50 μm. The electrical injection electrodes of the three-color stacked Micro-LED chip 13 are an n-type electrode 3 and a p-type electrode 4, which are arranged on the same surface.

[0051] Step 2, provide a first substrate 7, and set a bonding film on one side of the first substrate 7, the bonding film is a double-sided tape, including a bonding layer 6 bonded to the first substrate 7 and a UV dissolving layer 5 corresponding to the bonding layer 6. The UV dissolving layer 5 has medium viscosity, and the viscosity is significantly reduced to 90% of the initial viscosity after UV light. The bonding layer 6 is a high-viscosity tape, and the first substrate 7 is a transparent substrate sapphire, which can also be replaced by any one of quartz, glass, PET, and PC.

[0052] Step three, temporarily bonding the first substrate 7 to the three-color stacked Micro-LED chip 13 on the substrate 1 through the UV debonding layer 5 , and the UV debonding layer 5 is bonded to the electrode surface of the three-color stacked Micro-LED chip 13 .

[0053] Step four, the substrate 1 of the three-color stacked Micro-LED chip 13 is separated by laser stripping using a 248 nm KrF excimer laser, and the three-color stacked Micro-LED chip 13 is stripped to the UV debonding layer 5 of the first substrate 7, and all the three-color stacked Micro-LED chips 13 are attached to the UV debonding layer 5 on the first substrate 7.

[0054] Step five: The three-color stacked Micro-LED chip 13 is placed with its back side facing upwards, and the PI solution is evenly spin-coated onto the back side of the three-color stacked Micro-LED chip 13 on the first substrate 7 through a coating system, and then heated and cured at 80-150°C for 3-10 minutes to form a PI cured film 8 with a thickness of 0.5-5 μm on the back side of the three-color stacked Micro-LED chip 13, which is used to connect the separated three-color stacked Micro-LED chips 13.

[0055] Step 6: Provide a second substrate 10, and set a PI semi-cured film 9 on one side of the second substrate 10, that is, spin-coat a mixed solution of the PI solution and the solution with elastic dynamic release properties onto the second substrate 10, and bake at 60°C~100°C for 0.1~5min to form a sticky film. The thickness of the PI semi-cured film 9 is about 0.5~5 μm. Bond the three-color stacked Micro-LED chip 13 connected to the first substrate 7 through the PI cured film 8 to the second substrate 10 based on the PI semi-cured film 9, separate the UV debonding layer 5 and the first substrate 7 whose viscosity is weakened after UV irradiation, and transfer the Micro-LED chip connected to the PI cured film 8 to the second substrate 10 based on the PI semi-cured film 9, so as to realize the positive placement of the chip on the second substrate 10.

[0056] Step seven, use RIE or ICP etching technology under O2 atmosphere to remove the PI cured film 8 and PI semi-cured film 9 in the gap between the three-color stacked Micro-LED chips 13 on the second substrate 10. The three-color stacked Micro-LED chips 13 are placed independently on the second substrate 10, which is conducive to the selective transfer to the circuit board 12 in the next step. The three-color stacked Micro-LED chips 13 are combined with the second substrate 10 through the PI semi-cured film 9.

[0057] Step eight, evaporate low melting point bonding metal 11 at the electrode position of circuit board 12, low melting point bonding metal 11 is In. Selectively transfer the blue light three-color stacked Micro-LED chip 13 on the second substrate 10 to the corresponding position of the circuit board 12. When the pulse laser irradiates the PI semi-cured film 9 through the second substrate 10, high pressure gas is instantly generated, and the three-color stacked Micro-LED chip 13 is separated from the second substrate 10 by bubble expansion and pushing action, and the transfer to the circuit board 12 is realized. The position of the pulsed laser is controlled by the pulsed laser dynamic release technology to accurately release the three-color stacked Micro-LED chip 13 to the corresponding position of the circuit board 12.

Claims

1. A PI-assisted Micro-LED mass transfer method, characterized in that: The following steps are involved: Step 1: preparing a Micro-LED chip (2) on a substrate (1), wherein an n-type electrode (3) and a p-type electrode (4) are arranged on the same side surface of the Micro-LED chip (2); Step 2: providing a bonding layer (6) and a UV debonding layer (5) on the surface of the first substrate (7); Step three, temporarily bonding the first substrate (7) to the n-type electrode (3) and the p-type electrode (4) of the Micro-LED chip (2) via a UV debonding layer (5); Step 4: peeling the Micro-LED chip (2) onto the UV debonding layer (5) and separating it from the substrate (1); Step 5, spin-coating the PI solution on the surface of the Micro-LED chip (2) away from the UV debonding layer (5), and heating and curing to form a PI cured film (8); Step 6: arranging a PI semi-cured film (9) on the surface of the second substrate (10), bonding the PI cured film (8) to the PI semi-cured film (9), separating the UV debonding layer (5) whose viscosity is weakened after UV irradiation from the Micro-LED chip (2), and transferring the Micro-LED chip (2) connected to the PI cured film (8) to the second substrate (10) based on the PI semi-cured film (9); Step seven, selectively removing the PI cured film (8) and the PI semi-cured film (9) on the second substrate (10) by etching, evaporating a bonding metal (11) at the electrode position of the circuit board (12), so that the Micro-LED chip (2) on the second substrate (10) is selectively transferred to the circuit board (12), and the bonding metal (11) is heated and bonded to the n-type electrode (3) and the p-type electrode (4); Step eight, removing the PI cured film (8) and the PI semi-cured film (9) on the Micro-LED chip (2).

2. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: In the step 1, the Micro-LED chip (2) is one or more of a blue light GaN epitaxial layer, a green light GaN epitaxial layer, and a red light GaN epitaxial layer, and has a thickness of 3 to 8 μm.

3. The PI-assisted Micro-LED mass transfer method according to claim 2, characterized in that: The quantum well In composition of the blue light GaN epitaxial layer is 0.15-0.25, the quantum well In composition of the green light GaN epitaxial layer is 0.25-0.3, and the quantum well In composition of the red light GaN epitaxial layer is 0.3-0.

7.

4. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: In the step 2, the viscosity of the UV debonding layer (5) is 2000-30000 mN / mm, and the viscosity decreases by more than 90% after UV irradiation.

5. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: In the step 4, the peeling is performed by laser peeling using a 248 nm KrF excimer laser.

6. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: In the step 5, the temperature of heating and curing is 80-150° C., the time is 3-10 min, and the thickness of the PI cured film (8) is 0.5-5 μm.

7. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: In step six, the thickness of the PI semi-cured film (9) is 0.5-5 μm.

8. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: In the step seven, the etching is performed by RIE or ICP etching in an O2 atmosphere, and the bonding metal (11) is an alloy formed by one or more of In, Sn, and Au.

9. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: The method further comprises step eight, repeating steps one to seven, replacing the Micro-LED chips (2) with Micro-LED chips (2) of different colors, and finally obtaining Micro-LED chips (2) of different colors periodically arranged on the surface of the circuit board (12).

10. The PI-assisted Micro-LED mass transfer method according to claim 1, characterized in that: The Micro-LED chip (2) is replaced by a three-color stacked Micro-LED chip (13).

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