Wafer-level high-precision and low-crosstalk LED microarray fabrication method

Abstract

The present invention relates to a wafer-level method for fabricating a high-precision, low-crosstalk LED microarray. The method sequentially prepares a buffer layer, an optically sensitive sacrificial interlayer, and a flip-chip LED semiconductor material wafer layer on a substrate. The wafer layer, along with the N-type and P-type electrodes, is then segmented and excess portions removed to produce an array of flip-chip LED chips. The two electrodes of each flip-chip LED chip correspond to a pair of bonding posts on the substrate. The height of the bonding posts on the die-bonding pads is adjusted based on the height compensation of the two electrodes of each flip-chip LED chip, ensuring that the sum of the heights of the electrodes and corresponding bonding posts of all flip-chip LED chips is consistent. Laser beams are then irradiated onto the substrate to cause each flip-chip LED chip to fall off onto the substrate. Finally, the electrodes of each flip-chip LED chip are bonded and fixed to the corresponding bonding posts, completing the fabrication of a monochromatic LED microarray. The method achieves high production precision and high flatness in the light emission direction of the entire array.

Description

Technical field:

[0001] The present invention belongs to the technical field of active light-emitting display, and relates to a method for preparing a high-precision, low-crosstalk, ultra-high-density LED microarray based on wafer level. Background technology:

[0002] LED display [including Micro-LED (Mini-LED) display] is a new type of flat panel display technology that has attracted much attention in recent years. It has the advantages of wide color gamut, high luminous efficiency, fast response speed, and wide operating temperature range. It is widely used in high-end display, flat panel display backlight and lighting fields, and has important application prospects.

[0003] The core component of LED display is an LED panel formed by a number of LED chips neatly arranged on a substrate. The manufacturing process of this component mainly includes the preparation of the LED chip layer, the preparation of the substrate, and the precise bonding of the LED chip and the substrate. The existing method of making the LED chip layer includes: forming a buffer layer, an N-type semiconductor layer, a light-emitting layer, and a P-type semiconductor layer on the substrate in sequence; opening a groove extending to the N-type semiconductor layer on the P-type semiconductor layer, and forming an isolation groove extending to the substrate on the N-type semiconductor layer in the groove; forming an N-type electrode on the N-type semiconductor layer in the groove, and forming a P-type electrode on the P-type semiconductor layer; such as Figure 1 As shown, A1 is the substrate and buffer layer, CL is the undivided flip-chip LED semiconductor material wafer layer, and JL is the N-type electrode and P-type electrode formed on the flip-chip LED semiconductor material wafer layer.

[0004] Currently, the LED chip array bonding method is as follows: (1) First, the LED chip layer is pasted on the blue film with the substrate facing up and the electrodes facing down. Then, the substrate and buffer layer are removed by grinding or laser peeling. Then, the flip-chip LED semiconductor material wafer layer and the N-type electrode and P-type electrode are divided by mechanical or laser methods to form a number of independent flip-chip LED chips. (2) The independent flip-chip LED chips are separated and pasted on the expanded blue film. (3) The N-type electrode and P-type electrode of each flip-chip LED chip are bonded to the metal solder of the corresponding bonding pad on the substrate through a fully automatic bonding machine to form an LED panel.

[0005] At present, the size of LED display screens is gradually decreasing, and the arrangement density of LED chips is gradually increasing. Therefore, the size of LED chips used in display screens is correspondingly reduced, so that micro light-emitting diode (Micro LED) chips with a size of micron level are widely used in display screens. According to the above process, the flip-chip LED chip array is fixed. The accuracy difference of the die-bonding machine causes deviations in the arrangement of LED chips on the formed LED substrate. Since each chip is independent of each other, during the process of multiple chip transfers and die-bonding, it is inevitable that there will be a certain deviation between the actual position of some chips fixed on the control circuit and the pre-designed position. At this time, the size of the chip is only at the micron level, so a small deviation will cause the pixels of the display panel to fail, and it is difficult to correct, resulting in a high defect rate of the display panel and increased production costs.

[0006] Thanks to advances in materials and laser technology, the industry has introduced a new approach to address the challenge of die-bonding alignment deviation, addressing the density challenges of LED chips. Lasers directly release the underlying intermediate material, causing it to decompose under the laser's action until the chip is released, thus achieving transfer. Thermal decomposition can occur indirectly through the heat generated by the laser and the device, as seen in the work of Karlitskaya et al. Thermal decomposition can also occur directly between the laser and the intermediate material. Karlitskaya et al. have successfully applied this mechanism to mass transfer technology. The beam-addressed release (BAR) technology developed by QMAT utilizes a thermal release mechanism. Laser light is directed through a transparent substrate onto a laser release layer, transferring the chip from the source substrate to the target substrate through photothermal action. This method can achieve a transfer rate of 1 billion chips per hour at pulse rates of 100 kHz to 1 MHz. The principle of laser ablation release involves irradiating a sacrificial layer with laser light. The laser beam ablates the material in a controlled manner, and the resulting gaseous products impact the chip above it, achieving release and transfer. This method draws on research into the mechanisms of laser ablation of polymers. In 2002, laser induction front transfer (LIFT) technology was introduced. Llberto Piqué et al., Karlitskaya et al., Marinov V et al. developed the LEAP process based on LIFT technology, using transfer and assembly as devices. They used laser technology to complete chip peeling, transfer, and assembly, and successfully used it for non-linear RFID chip transfer.

[0007] In the LIFT process, an excimer laser (193nm) is used to act on the metal / polymer layer to achieve thermal release; in the LDW process, an excimer laser (248nm) is used to irradiate the "double-stick" tape (Microposit) to ablate the sacrificial polymer; in the tmSLADT process, UV laser pulses are used to ablate the polyesterimide sacrificial layer to achieve dynamic release; in the SLLO process, a diode-pumped solid-state laser is used to irradiate GaN to decompose it into Ga and N2.

[0008] The glass wafer using the above method is mainly to first prepare an optically sensitive sacrificial interlayer on the substrate and buffer layer, and then generate a flip-chip LED semiconductor material wafer layer on the optically sensitive sacrificial interlayer; finally, a mechanical or laser method is used to separate the flip-chip LED semiconductor material wafer layer and the N-type electrode and P-type electrode to form a number of independent flip-chip LED chips. Because the flip-chip LED chips are arranged relatively closely at this time (belonging to the non-customized array (conventional)), the flip-chip LED chips are aligned one by one with the corresponding die bonding pads on the substrate during the die bonding process, and a laser beam of a specific wavelength is used to irradiate the substrate and the optically sensitive sacrificial interlayer, so that the adhesion of the optically sensitive sacrificial interlayer is reduced, and the flip-chip LED chip is detached and accurately landed on the substrate, and the two electrodes are bonded to the corresponding metal solder. After the die bonding of one flip-chip LED chip is completed, the substrate, optically sensitive sacrificial interlayer and flip-chip chip array are translated as a whole to bond the next flip-chip LED chip. Although this method reduces the deviation in the arrangement of LED chips, when releasing the chips, slight deviations in the chip electrode height and the stacking of the pad solder will affect the light consistency of the flip-chip LED chip array. In addition, the side light emission of the LED chip array after the die is fixed aggravates the optical interference between pixels, which is not conducive to high-definition display quality and effects. Another hidden danger of this translation release process is that once the cumulative error of the translation process reaches a certain limit, the consistency of the array will deteriorate. In addition, the efficiency of this method is relatively low, which is not conducive to the industrialization of high-density flip-chip LED module products. Summary of the invention:

[0009] The technical problem to be solved by the present invention is to provide a method for preparing a high-precision and low-crosstalk LED microarray based on wafer level, which can improve the efficiency of die bonding and has high die bonding accuracy.

[0010] In order to solve the above technical problems, the wafer-level high-precision and low-crosstalk LED microarray preparation method of the present invention includes the following two technical solutions.

[0011] Technical solution 1:

[0012] The LED microarray is a single-color LED microarray, and its preparation method is as follows:

[0013] A buffer layer, an optically sensitive sacrificial interlayer, and a monochrome flip-chip LED semiconductor material wafer layer are sequentially prepared on a substrate. Finally, the monochrome flip-chip LED semiconductor material wafer layer, the N-type electrode, and the P-type electrode are segmented and excess monochrome flip-chip LED semiconductor wafer layer is removed to obtain a monochrome flip-chip LED chip array, wherein the two electrodes of each monochrome flip-chip LED chip correspond to the positions of a pair of bonding pillars P2 on the substrate.

[0014] Detect the height of the two electrodes of each single-color flip-chip LED chip, and adjust the height of the bonding pillars on the die-bonding pad based on the detection results to make the sum of the heights of the electrodes and corresponding bonding pillars of all single-color flip-chip LED chips consistent;

[0015] The monochrome flip-chip LED chip array is placed downward and the two electrodes of each monochrome flip-chip LED chip are aligned with the corresponding bonding columns; the substrate is irradiated with a laser beam to cause each monochrome flip-chip LED chip to fall off, and finally, the electrodes of each monochrome flip-chip LED chip are bonded and fixed to the corresponding bonding columns to complete the preparation of the monochrome LED microarray.

[0016] Technical solution 2:

[0017] The LED microarray is a full-color LED microarray, and its preparation method is as follows:

[0018] A buffer layer, an optically sensitive sacrificial interlayer, and a red flip-chip LED semiconductor material wafer layer are sequentially prepared on the substrate. Finally, the red flip-chip LED semiconductor material wafer layer, the N-type electrode, and the P-type electrode are segmented and the excess red flip-chip LED semiconductor wafer layer is removed to obtain a red flip-chip LED chip array, wherein the two electrodes of each red flip-chip LED chip correspond to the positions of a pair of bonding pillars P2 on the substrate.

[0019] Detect the height of the two electrodes of each red flip-chip LED chip, and adjust the height of the bonding pillars on the die-bonding pad based on the detection results to make the sum of the heights of the electrodes and corresponding bonding pillars of all red flip-chip LED chips consistent;

[0020] The red flip-chip LED chip array is placed downward, and the two electrodes of each red flip-chip LED chip are aligned with the corresponding bonding pillars. The substrate is irradiated with a laser beam to cause each red flip-chip LED chip to fall off. Finally, the electrodes of each red flip-chip LED chip are bonded and fixed to the corresponding bonding pillars to complete the preparation of the red LED microarray.

[0021] The green LED microarray and the blue LED microarray are prepared on the substrate using the same method as that for preparing the red LED microarray, thereby completing the preparation of the full-color LED microarray.

[0022] A flip-chip LED semiconductor material wafer layer having the same shape and size as the substrate is prepared on the optically sensitive sacrificial interlayer.

[0023] A plurality of long strip-shaped flip-chip LED semiconductor material wafer layers are prepared on the optically sensitive sacrificial interlayer.

[0024] The flip-chip LED semiconductor material wafer layer is removed from the redundant flip-chip LED semiconductor wafer layer by using a mask etching method.

[0025] An inward-reflective coating is prepared on both sides of each flip-chip LED chip.

[0026] The height of the bonding pillars on the die attach pad is compensated and adjusted using an evaporation method.

[0027] Furthermore, a laser beam is used to sequentially irradiate different positions of the substrate, causing each flip-chip LED chip to fall off in sequence.

[0028] Furthermore, the substrate can be divided into multiple areas, and multiple laser beams can be used to irradiate a certain area of the substrate at the same time, so that all flip-chip LED chips in the area fall off at the same time; multiple laser beams can be used to irradiate each area in turn until the flip-chip LED chips in all areas fall off.

[0029] Furthermore, the substrate can be irradiated with a laser array at the same time to cause all flip-chip LED chips to fall off at the same time.

[0030] Beneficial effects:

[0031] 1) The present invention uses a wafer-based process for producing Micro-LED (Mini-LED) microarrays, achieving high production accuracy and laying the foundation for high-precision die bonding for panels.

[0032] 2) Since the Micro-LED (Mini-LED) microarray process is completed on the wafer, not only can the arrangement and position of each chip be set according to the substrate, but the electrodes can also be accurately produced as required;

[0033] 3) Since the arrangement spacing of each chip is determined by the die bonding position of the microarray panel, there is enough space between the chips to complete the coating of the internal reflection material, which can reduce the optical cross-interference between the chips and improve the display clarity and contrast;

[0034] 4) The height difference between the metal solder of the panel die bonding pad and the semiconductor chip electrode is matched to ensure the flatness of the light output direction of the entire array;

[0035] 5) The entire wafer is uniformly coated with a photosensitive sacrificial interlayer with a laser of a specific wavelength, which facilitates the overall precise placement of the Micro-LED (Mini-LED) microarray from the wafer to the corresponding pads of the die-bonding panel under the action of the laser beam array, completing the preparation of high-precision and low-crosstalk Micro-LED (Mini-LED) microarrays;

[0036] The present invention is applicable to the preparation of Micro-LED and Mini-LED microarrays. Description of the drawings:

[0037] Figure 1 Schematic diagram of the LED chip layer prepared using existing technology.

[0038] Figure 2 This is a top view of the LED chip layer prepared by the present invention.

[0039] Figure 3 This is a side view of the LED chip layer prepared by the present invention.

[0040] Figure 4 This is the main view of the substrate.

[0041] Figure 5 A side view of the substrate.

[0042] Figure 6 Schematic diagram of each flip-chip LED chip after being bonded and fixed to the bonding column.

[0043] Figure 7 Schematic diagram of generating multiple long strips of red-based flip-chip LED semiconductor material wafer layers on an optically sensitive sacrificial interlayer.

[0044] Figure 8 Schematic diagram of the prepared red-based flip-chip LED chip array. Specific implementation method:

[0045] Example 1: Method for preparing a monochromatic wafer-level high-precision low-crosstalk LED microarray

[0046] Step 1: First, a buffer layer is prepared on the substrate, an optically sensitive sacrificial interlayer is prepared on the buffer layer, and then a flip-chip LED semiconductor material wafer layer is generated on the optically sensitive sacrificial interlayer. Finally, the flip-chip LED semiconductor material wafer layer and the N-type electrode and the P-type electrode are divided and the redundant flip-chip LED semiconductor wafer layer is removed to obtain a monochrome flip-chip LED chip array; Figure 2 、 3 As shown, A is the substrate and buffer layer, S is the optically sensitive sacrificial interlayer, C is the flip-chip LED chip, and C11 and C12 are the two electrodes of the flip-chip LED chip; Figure 4 、 5 As shown, the substrate B has a die-bonding pad array, and a bonding column P2 is fixed on each die-bonding pad P1; every two bonding columns P2 form a pair; the two electrodes of each flip-chip LED chip in the flip-chip LED chip array correspond to the positions of a pair of bonding columns P2.

[0047] The flip-chip LED semiconductor material wafer layer can be etched with a mask to remove excess parts, leaving each flip-chip LED chip.

[0048] Step 2: Prepare an inward-reflective coating on both sides C21 and C22 of each flip-chip LED chip. The coating material can be silver or other metal reflective layer. Since silver is conductive, it is necessary to grind off the coating near the electrodes and the electrode parts after the reflective layer is prepared to prevent leakage. This can reduce optical cross-interference between the flip-chip LED chips and improve display clarity and contrast.

[0049] Step 3: Detect the height of the two electrodes of each flip-chip LED chip, and adjust the height of the bonding pillars on the die-bonding pad by evaporation based on the detection results, so that the sum of the heights of the electrodes and corresponding bonding pillars of all flip-chip LED chips is consistent;

[0050] Step 4: Place the prepared flip-chip LED chip array downward and the substrate upward, and align the two electrodes of each flip-chip LED chip with the corresponding bonding posts. The substrate and the base plate can be of the same shape and size. After the four edges are aligned, the electrodes of each flip-chip LED chip are aligned with the corresponding bonding posts. Alternatively, the position parameters of the substrate and the flip-chip LED chip array can be stored in a control system, and a servo control method can be used for position alignment.

[0051] Step 5: Use a laser beam of a specific wavelength to irradiate the substrate from above to reduce the adhesion of the optically sensitive sacrificial interlayer S. Each flip-chip LED chip is separated from the optically sensitive sacrificial interlayer S and falls onto the substrate B. At this time, the two electrodes of each flip-chip LED chip are precisely aligned with the corresponding bonding pillars, as shown in FIG. Figure 5 As shown, finally, the electrodes of each flip-chip LED chip are bonded and fixed to the corresponding bonding pillars by a hot pressing method; the preparation of the monochrome LED microarray is completed; the flip-chip LED chips of the prepared monochrome LED microarray are highly consistent, neatly arranged, and have good consistency.

[0052] A laser array can be used to simultaneously irradiate the substrate, causing all flip-chip LED chips to fall off at the same time; or one or several laser beams can be used to simultaneously irradiate the substrate, causing one or some flip-chip LED chips to fall off at the same time; and then another part of the substrate can be irradiated to cause another part of the flip-chip LED chips to fall off at the same time, until all the flip-chip LED chips fall off the substrate.

[0053] Example 2: Method for preparing a full-color (non-powder-coated) wafer-level monochromatic wafer-level high-precision low-crosstalk LED microarray

[0054] In this embodiment, a red-primary color flip-chip LED chip array is first prepared according to the same method as the embodiment, and the electrodes of each red-primary color flip-chip LED chip R are bonded and fixed to the corresponding bonding columns on the substrate; a green-primary color flip-chip LED chip array is prepared according to the same method, and the electrodes of each green-primary color flip-chip LED chip are bonded and fixed to the corresponding bonding columns on the substrate; finally, a blue-primary color flip-chip LED chip array is prepared according to the same method, and the electrodes of each blue-primary color flip-chip LED chip are bonded and fixed to the corresponding bonding columns on the substrate; thus, the preparation of the full-color LED microarray is completed.

[0055] When preparing a red-based flip-chip array, multiple long strips of red-based flip-chip LED semiconductor material wafer layers E can also be generated on the optically sensitive sacrificial interlayer, such as Figure 7 、 8 As shown, the redundant parts are removed in the same manner as in the first embodiment, and red primary color flip chips B are fabricated in the remaining parts; green and blue primary color flip chip arrays can also be fabricated using this method.

[0056] The present invention is not limited to the above-described embodiments. In Embodiment 1, multiple elongated monochromatic flip-chip LED semiconductor material wafer layers can also be formed on an optically sensitive sacrificial interlayer. Similarly, in Embodiment 2, a grid-like monochromatic flip-chip LED semiconductor material wafer layer can also be formed on an optically sensitive sacrificial interlayer. It is reasonably foreseeable that those skilled in the art will be able to devise numerous simple variations based on the above technical solutions. Therefore, any simple variations based on the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a high-precision, low-crosstalk LED microarray based on wafer level, characterized in that The LED microarray is a single-color LED microarray, and its preparation method is as follows: A buffer layer, an optically sensitive sacrificial interlayer, and a monochrome flip-chip LED semiconductor material wafer layer are sequentially prepared on a substrate. Finally, the monochrome flip-chip LED semiconductor material wafer layer, the N-type electrode, and the P-type electrode are segmented and excess monochrome flip-chip LED semiconductor wafer layer is removed to obtain a monochrome flip-chip LED chip array, wherein the two electrodes of each monochrome flip-chip LED chip correspond to the positions of a pair of bonding posts on the substrate. Detect the height of the two electrodes of each single-color flip-chip LED chip, and adjust the height of the bonding pillars on the die-bonding pad based on the detection results to make the sum of the heights of the electrodes and corresponding bonding pillars of all single-color flip-chip LED chips consistent; The monochrome flip-chip LED chip array is placed downward and the two electrodes of each monochrome flip-chip LED chip are aligned with the corresponding bonding columns; the substrate is irradiated with a laser beam to cause each monochrome flip-chip LED chip to fall off, and finally, the electrodes of each monochrome flip-chip LED chip are bonded and fixed to the corresponding bonding columns to complete the preparation of the monochrome LED microarray.

2. A method for preparing a high-precision, low-crosstalk LED microarray based on wafer level, characterized in that The LED microarray is a full-color LED microarray, and its preparation method is as follows: A buffer layer, an optically sensitive sacrificial interlayer, and a red flip-chip LED semiconductor material wafer layer are sequentially prepared on the substrate. Finally, the red flip-chip LED semiconductor material wafer layer, the N-type electrode, and the P-type electrode are segmented and the excess red flip-chip LED semiconductor wafer layer is removed to obtain a red flip-chip LED chip array, wherein the two electrodes of each red flip-chip LED chip correspond to the positions of a pair of bonding pillars P2 on the substrate. Detect the height of the two electrodes of each red flip-chip LED chip, and adjust the height of the bonding pillars on the die-bonding pad based on the detection results to make the sum of the heights of the electrodes and corresponding bonding pillars of all red flip-chip LED chips consistent; The red flip-chip LED chip array is placed downward, and the two electrodes of each red flip-chip LED chip are aligned with the corresponding bonding pillars. The substrate is irradiated with a laser beam to cause each red flip-chip LED chip to fall off. Finally, the electrodes of each red flip-chip LED chip are bonded and fixed to the corresponding bonding pillars to complete the preparation of the red LED microarray. The green LED microarray and the blue LED microarray are prepared on the substrate using the same method as that for preparing the red LED microarray, thereby completing the preparation of the full-color LED microarray.

3. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that A flip-chip LED semiconductor material wafer layer having the same shape and size as the substrate is prepared on the optically sensitive sacrificial interlayer.

4. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that A plurality of long strip-shaped flip-chip LED semiconductor material wafer layers are prepared on the optically sensitive sacrificial interlayer.

5. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that The flip-chip LED semiconductor material wafer layer is removed from the redundant flip-chip LED semiconductor wafer layer by using a mask etching method.

6. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that An inward-reflective coating is prepared on both sides of each flip-chip LED chip.

7. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that The height of the bonding pillars on the die attach pad is compensated and adjusted using an evaporation method.

8. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that A laser beam is used to sequentially irradiate different positions of the substrate, causing each flip-chip LED chip to fall off in sequence.

9. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that The substrate is divided into multiple areas, and multiple laser beams are used to irradiate a certain area of the substrate at the same time, so that all flip-chip LED chips in the area fall off at the same time; multiple laser beams are used to irradiate each area in turn until the flip-chip LED chips in all areas fall off.

10. The method for preparing a high-precision, low-crosstalk LED microarray based on wafer level according to claim 1 or 2, characterized in that The substrate is irradiated with a laser array at the same time, causing all flip-chip LED chips to fall off at the same time.

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