CN113690171A - Mass transfer method of Micro-LED chips - Google Patents
Mass transfer method of Micro-LED chips Download PDFInfo
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- CN113690171A CN113690171A CN202111051684.4A CN202111051684A CN113690171A CN 113690171 A CN113690171 A CN 113690171A CN 202111051684 A CN202111051684 A CN 202111051684A CN 113690171 A CN113690171 A CN 113690171A
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- 239000000758 substrate Substances 0.000 claims abstract description 99
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- 235000013870 dimethyl polysiloxane Nutrition 0.000 claims abstract 26
- CXQXSVUQTKDNFP-UHFFFAOYSA-N octamethyltrisiloxane Chemical compound C[Si](C)(C)O[Si](C)(C)O[Si](C)(C)C CXQXSVUQTKDNFP-UHFFFAOYSA-N 0.000 claims abstract 26
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 24
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
- H01L21/6838—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping with gripping and holding devices using a vacuum; Bernoulli devices
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
- H01L21/6835—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using temporarily an auxiliary support
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/15—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components with at least one potential-jump barrier or surface barrier specially adapted for light emission
- H01L27/153—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components with at least one potential-jump barrier or surface barrier specially adapted for light emission in a repetitive configuration, e.g. LED bars
- H01L27/156—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components with at least one potential-jump barrier or surface barrier specially adapted for light emission in a repetitive configuration, e.g. LED bars two-dimensional arrays
Abstract
The embodiment of the invention discloses a massive transfer method of Micro-LED chips, which comprises the following steps: providing a sapphire substrate, and forming an LED chip array on the sapphire substrate; adhering a blue film on the first surface of the LED chip array and removing the sapphire substrate; stretching the blue film to enable the chip spacing in the LED chip array to reach a preset distance; adsorbing a second surface of the LED chip array by the super-resolution PDMS stamp and removing the blue film, wherein the area of the super-resolution PDMS stamp adsorbing the LED chip array comprises a hole array consisting of a plurality of holes, the size of each hole is smaller than the size of the chip of the LED chip array, and the density of the holes of the hole array is greater than the density of the chip of the LED chip array; and moving the super-resolution PDMS stamp to the driving substrate, and then stripping the super-resolution PDMS stamp so as to transfer the LED chip array to the driving substrate. According to the embodiment of the invention, the seal does not need to be aligned when adsorbing the LED chip, so that the operation is simplified, the transfer speed is increased, and the transfer efficiency and accuracy are further improved.
Description
Technical Field
The embodiment of the invention relates to the technical field of semiconductors, in particular to a massive transfer method of Micro-LED chips.
Background
Micro Light-Emitting diodes (Micro-LEDs) are a new generation of Display technology, and compared with OLED (Organic Light Emitting Diode) technology, Micro-LEDs have higher brightness, better Light Emitting efficiency, and lower power consumption, so that the market prospect is promising.
In the manufacturing process of the Micro-LED display device, a large number of Micro-LED chips need to be transferred from an original substrate to a driving circuit substrate to be arranged in an array, which is called as mass transfer of the Micro-LED chips. The stamp transfer technology is one of the chip bulk transfer technologies, as shown in fig. 1, a stamp 1 is provided with a plurality of protrusions 2 for adsorbing a chip 3, when transferring, the protrusions 2 are aligned with the chip 3, then the chip 3 is adsorbed by the protrusions 2, the stamp 1 is moved to the position above a driving substrate 4, the chip 3 is aligned with the driving substrate 4, and finally the stamp 1 is peeled off to transfer the chip 3 to the driving substrate 4. The Micro-LED chip size is very small (typically tens of microns) and slight deviations in alignment can have an effect on the final device formation. The existing high-precision alignment equipment is usually used in a wafer factory, and can achieve nanometer precision, but the cost can be said to be day price. The Micro-LED bulk transfer technology processing method is generally a packaging factory, and high-price high-precision alignment equipment is not used in a condition, so that the flip precision in the current bulk transfer is difficult to reach several micrometers. Meanwhile, the stamp is usually peeled off by heating or pressurizing, and the stamp protrusion expands outward by heating and pressurizing, which may cause deviation between the aligned chip and the driving substrate, thereby affecting the performance of the device.
Disclosure of Invention
In view of this, the embodiment of the present invention provides a massive transfer method for Micro-LED chips, so as to reduce alignment difficulty and transfer difficulty of the Micro-LED chips and improve transfer accuracy.
The embodiment of the invention provides a massive transfer method of Micro-LED chips, which comprises the following steps:
providing a sapphire substrate, and forming an LED chip array on the sapphire substrate;
adhering a blue film on the first surface of the LED chip array and removing the sapphire substrate;
stretching the blue film to enable the chip spacing in the LED chip array to reach a preset distance;
adsorbing a second surface of the LED chip array through a super-resolution PDMS stamp and removing the blue film, wherein the area, adsorbing the LED chip array, of the super-resolution PDMS stamp comprises a hole array consisting of a plurality of holes, the size of each hole is smaller than that of the chip of the LED chip array, and the hole density of the hole array is larger than that of the chip of the LED chip array;
and removing the super-resolution PDMS stamp from the driving substrate to transfer the LED chip array to the driving substrate.
Further, before adhering a blue film to the first surface of the LED chip array and removing the sapphire substrate, the method further includes:
and forming a protective layer completely covering the LED chip array on the first surface of the LED chip array.
Further, the adhering the blue film on the first surface of the LED chip array and removing the sapphire substrate includes:
and adhering a blue film on the protective layer and removing the sapphire substrate by a laser lift-off technology.
Further, before the super-resolution PDMS stamp adsorbs the second surface of the LED chip array and the blue film is removed, the method further includes:
providing a silicon substrate, and forming a plurality of column structures on the silicon substrate, wherein the size of the column structures is equal to or smaller than that of the holes;
gluing the silicon substrate in a glass ware, and injecting PDMS mixed liquid into the glass ware;
the glassware is heated and baked, so that the PDMS mixed liquid is solidified to form a super-resolution PDMS stamp;
and stripping the silicon substrate to obtain the super-resolution PDMS stamp.
Further, before the glass vessel is filled with the PDMS mixed liquid, the method further includes:
and carrying out hydrophobic treatment on the surface of the silicon substrate.
Further, before the step of baking the PDMS mixture, the method further includes:
and placing the glassware in a vacuum box to remove bubbles from the PDMS mixed solution.
Further, the PDMS mixed liquid is a mixed liquid of a curing agent and a PDMS solution, and the mixing ratio of the curing agent to the PDMS solution is 0.1-0.2.
Further, the adsorbing the second surface of the LED chip array and removing the blue film by the super-resolution PDMS stamp includes:
and adsorbing the second surface of the LED chip array through the super-resolution PDMS stamp, and removing the blue film and the protective layer.
Further, the step of peeling off the super-resolution PDMS stamp after moving the super-resolution PDMS stamp to the driving substrate to transfer the LED chip array to the driving substrate includes:
adsorbing one surface, which is not adsorbed by the LED chip array, of the super-resolution PDMS stamp by a transfer head, moving the super-resolution PDMS stamp to the position above a driving substrate, and aligning the LED chip array with the driving substrate;
and irradiating the super-resolution PDMS stamp by laser to peel off the LED chip array from the super-resolution PDMS stamp and transfer the LED chip array to the driving substrate.
Further, the hole density of the hole array is 5 times of the chip density of the LED chip array.
The huge transfer method of the Micro-LED chip provided by the embodiment of the invention realizes huge transfer of the LED chip array by using the super-resolution PDMS stamp, and alignment is not needed when the stamp adsorbs the LED chip, so that the operation is simplified, the transfer speed is accelerated, and the transfer efficiency and the accuracy are further improved. Meanwhile, the super-resolution PDMS stamp can be suitable for mass transfer of various LED chip arrays, and the applicability of the super-resolution PDMS stamp is improved.
Drawings
FIG. 1 is a schematic diagram of a prior art stamp transfer technique for Micro-LED chips;
FIG. 2 is a schematic flow chart illustrating a mass transfer method for Micro-LED chips according to an embodiment of the present invention;
FIG. 3 is a schematic flow chart illustrating a mass transfer method for Micro-LED chips according to a second embodiment of the present invention;
fig. 4 is a schematic structural diagram of a super-resolution PDMS stamp according to an embodiment of the present invention;
fig. 5A is a schematic diagram of an LED chip array according to a second embodiment of the present invention;
FIG. 5B is a schematic diagram illustrating the formation of a passivation layer in bulk transfer of a Micro-LED chip according to a second embodiment of the present invention;
FIG. 5C is a schematic view of an adhesion blue film in bulk transfer of Micro-LED chips according to a second embodiment of the present invention;
FIG. 5D is a schematic diagram illustrating stretching of a blue film in bulk transfer of a Micro-LED chip according to a second embodiment of the present invention;
fig. 5E is a schematic diagram of adsorbing a super-resolution PDMS stamp in the macro transfer of the Micro-LED chip according to the second embodiment of the present invention;
FIG. 5F is a schematic diagram illustrating the removal of the blue film and the passivation layer during mass transfer of the Micro-LED chip according to the second embodiment of the present invention;
fig. 5G is a schematic diagram illustrating the transfer of the LED chip array to the driving substrate according to the second embodiment of the invention;
fig. 6A is a schematic diagram of a silicon substrate for forming a super resolution PDMS stamp according to a second embodiment of the present invention;
fig. 6B is a schematic view of injecting a PDMS mixture in a super-resolution PDMS stamp forming process according to the second embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Before discussing exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although a flowchart may describe the steps as a sequential process, many of the steps can be performed in parallel, concurrently or simultaneously. In addition, the order of the steps may be rearranged. A process may be terminated when its operations are completed, but may have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc.
Furthermore, the terms "first," "second," and the like may be used herein to describe various orientations, actions, steps, elements, or the like, but the orientations, actions, steps, or elements are not limited by these terms. These terms are only used to distinguish one direction, action, step or element from another direction, action, step or element. The terms "first", "second", etc. are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "plurality", "batch" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
Example one
Fig. 2 is a schematic flow chart of a mass transfer method for Micro-LED chips according to an embodiment of the present invention, and for convenience of description, the Micro-LED chips are hereinafter referred to as LED chips. As shown in fig. 2, a mass transfer method for Micro-LED chips according to an embodiment of the present invention includes:
s110, providing a sapphire substrate, and forming an LED chip array on the sapphire substrate.
Specifically, a GaN epitaxial layer is grown on a sapphire substrate to form an LED chip epitaxial structure, and then the epitaxial structure is etched to form a plurality of independent LED chips. Generally, these multiple independent LED chips are arranged in an array, and thus are called as an LED chip array.
And S120, adhering a blue film on the first surface of the LED chip array and removing the sapphire substrate.
Specifically, the first surface of the LED chip array is the opposite surface away from the sapphire substrate, i.e., the surface of the LED chip not in contact with the sapphire substrate. The LED chips are adhered to the blue film, and then the sapphire substrate is peeled off, so that the LED chip array is completely separated from the sapphire substrate to become an independent individual.
S130, stretching the blue film to enable the chip spacing in the LED chip array to reach a preset distance.
Specifically, the chip pitch refers to a distance between every two LED chips in the LED chip array. When the LED chip array is transferred to the driving substrate, the driving substrate is provided with corresponding chip bearing positions, and the preset distance is a distance matched with the distance between the chip bearing positions on the driving substrate. And stretching the blue film to enable the distance between the chips to reach a preset distance, so that the LED chips can be accurately combined with the chip bearing positions of the driving substrate.
S140, adsorbing the second surface of the LED chip array through the super-resolution PDMS stamp and removing the blue film, wherein the area, where the super-resolution PDMS stamp adsorbs the LED chip array, comprises a hole array consisting of a plurality of holes, the size of each hole is smaller than the chip size of the LED chip array, and the hole density of the hole array is larger than the chip density of the LED chip array.
Specifically, the second surface of the LED chip array is a surface away from the blue film, that is, a surface exposed after the LED chip array and the sapphire substrate are peeled off. The LED chip array is adsorbed by a super-resolution PDMS (Polydimethylsiloxane) seal, and then the blue film is removed, so that only the LED chip array is adsorbed on the super-resolution PDMS seal.
Referring to fig. 4, the surface of the super-resolution PDMS stamp 500 is a grid-like structure, which is equivalent to etching a plurality of holes 510 on a layer of PDMS film, and the plurality of holes 510 actually form a hole array. The depth of the hole 510 is smaller than the thickness of the PDMS film, i.e., smaller than the height of the super-resolution PDMS stamp 500. The shape of the hole 510 can be selected from circular, square, rectangular, hexagonal, etc. as desired. The size of the hole 510 is smaller than that of the LED chip 200, so that the LED chip 200 is prevented from falling into the hole 510 of the super-resolution PDMS stamp 500 when the LED chip array is attached.
Further, in order to prevent the LED chips 200 from turning over when partially covered on the holes 510, the density of the holes is greater than that of the chips in the LED chip array, i.e. the holes 51 are more densely arranged than the LED chips 200. Preferably, the hole density of the hole array is 5 times the chip density of the LED chip array. Therefore, a certain contact area between the LED chip 200 and the surface of the super-resolution PDMS stamp 500 can be ensured, and the adsorption force of the super-resolution PDMS stamp 500 can be ensured. In addition, when the LED chip 200 completely covers 1 or more than 1 hole 510, the covered holes 510 will form a closed space, and during the adsorption, the air in the covered holes 510 is discharged due to the longitudinal pressure (gravity of the LED chip 200, the pressing force of the transfer tool, etc.), so that the closed space formed by the covered holes 510 generates a negative pressure, thereby further increasing the adsorption force of the super-resolution PDMS stamp 500 on the LED chip 200.
In this embodiment, the surface of the super-resolution PDMS stamp is in a grid structure, and any place on the surface can adsorb the LED chip, so that the super-resolution PDMS stamp does not need to be aligned to each LED chip when adsorbing the LED chip array, and the super-resolution PDMS stamp is directly attached to the LED chip array, thereby achieving more convenient and faster operation.
S150, moving the super-resolution PDMS stamp to a driving substrate, and then stripping the super-resolution PDMS stamp to transfer the LED chip array to the driving substrate.
Specifically, the super-resolution PDMS stamp is adsorbed or grabbed on the surface, not in contact with the LED chip array, of the super-resolution PDMS stamp through a transfer tool, the super-resolution PDMS stamp is moved to the position above the driving substrate, the LED chip in the LED chip array is aligned with the chip bearing position in the driving substrate, and then the super-resolution PDMS stamp is peeled off from the LED chip array, so that the LED chip array is combined with the driving substrate.
According to the huge transfer method of the Micro-LED chip provided by the embodiment of the invention, the huge transfer of the LED chip array is realized by using the super-resolution PDMS stamp, and the alignment is not needed when the stamp adsorbs the LED chip, so that the operation is simplified, the transfer speed is accelerated, and the transfer efficiency and the accuracy are further improved. Meanwhile, the super-resolution PDMS stamp can be suitable for mass transfer of various LED chip arrays, and the applicability of the super-resolution PDMS stamp is improved.
Example two
Fig. 3 is a schematic flow chart of a mass transfer method for Micro-LED chips according to a second embodiment of the present invention, which is a further refinement of the second embodiment. As shown in fig. 3, a mass transfer method for Micro-LED chips according to a second embodiment of the present invention includes:
s201, providing a sapphire substrate, and forming an LED chip array on the sapphire substrate.
Specifically, a GaN epitaxial layer is grown on a sapphire substrate 100 to form an LED chip epitaxial structure, and then the epitaxial structure is etched to form a plurality of individual LED chips 200, as shown in fig. 5A. Generally, these multiple independent LED chips 200 are arranged in an array, and are referred to as an LED chip array 200 (it is understood that the LED chips and the LED chip array are substantially the same, and for convenience of description, reference numeral 200 is used for both).
S202, forming a protection layer which completely covers the LED chip array on the first surface of the LED chip array.
Specifically, in order to avoid damage to the LED chip during the subsequent substrate peeling, photoresist spin coating is performed on the surface of the LED chip array 200 to form the protection layer 300, so that the LED chip array 200 is completely covered by the protection layer 300, as shown in fig. 5B.
S203, adhering a blue film on the protective layer and removing the sapphire substrate by a laser lift-off technology.
Specifically, as shown in fig. 5C, a blue film 400 having an adhesive is attached to the protective layer 300, and the blue film 400 temporarily supports the LED chip array 200. The sapphire substrate 100 is then separated from the LED chip array 200 by a laser lift-off technique to remove the sapphire substrate 100.
S204, stretching the blue film to enable the chip spacing in the LED chip array to reach a preset distance.
Specifically, the chip pitch refers to a distance between every two LED chips in the LED chip array. When the LED chip array is transferred to the driving substrate, the driving substrate is provided with corresponding chip bearing positions, and the preset distance is a distance matched with the distance between the chip bearing positions on the driving substrate. As shown in fig. 5D, the blue film 400 is stretched to make the chip pitch reach a predetermined distance, so that the LED chip 200 can be accurately combined with the chip carrying position of the driving substrate.
S205, providing a silicon substrate, and forming a plurality of column structures on the silicon substrate, wherein the size of the column structures is equal to or smaller than that of the holes. In this embodiment, the size of the pillar-shaped structure of the silicon substrate is equal to or slightly smaller than the size of the hole of the stamp. Because the difference of the thermal expansion coefficients is hundreds of times, the silicon is 2.5 ppm/DEG C, and the stamp material PDMS is 340 ppm/DEG C. The PDMS needs to be in an oven above 60 ℃ during curing, so that the holes are enlarged due to more shrinkage than the Si structure after cooling to room temperature, and the size of the columnar structure is equal to or slightly smaller than that of the holes of the stamp.
Specifically, as shown in fig. 6A, after performing steps of hydrophobization, spin-coating a photoresist, uv exposure, reverse baking, flood exposure, development, hardening, etching, removing a photoresist, cleaning, and the like on a silicon substrate 60, a plurality of pillar structures 61 are formed, and the pillar structures 61 form a pillar array. The size of the pillar structure 61 is the size of the hole 510 of the super-resolution PDMS stamp 500. Specifically, the specific parameters performed in one embodiment to achieve the machining accuracy of 1um are as follows:
1. hydrophobization treatment: HMDS 4000r 40s spin coating; baking at 100 deg.C for 1 min.
2. Spin coating of photoresist: AZ 52144000 r 40s spin coating; baking at 100 deg.C for 1 min.
3. Ultraviolet exposure: low vacuum 23.5mW/cm 24.3s.
4. And (3) reverse baking: baking at 120 deg.C for 40 s.
5. Flood exposure: 23.5mW/cm 240 s.
6. And (3) developing: RZX-303870 s.
7. Hardening the film: baking at 120 deg.C for 2 min.
Wherein, step 4 reversal drying and step 5 flood exposure are optional, and depending on the mask plate light and shade design, parameters are influenced by instruments, reagents, temperature and humidity, and certain errors and effect differences exist.
S206, gluing the silicon substrate in a glass ware, and injecting PDMS mixed liquid into the glass ware.
Specifically, as shown in fig. 6B, the silicon substrate 60 is glued in the glass vessel 70 using a double-sided tape or the like, the surface of the silicon substrate 60 is hydrophobized, and then the PDMS mixed liquid 80 is poured into the glass vessel 70. The PDMS mixed liquid 80 is a mixed liquid of a curing agent and a PDMS solution, the mixing ratio of the curing agent to the PDMS solution is 0.1-0.2, and the adsorption strength of the finally formed super-resolution PDMS stamp on the LED chip can be adjusted according to different mixing ratios. After the PDMS mixed liquid 80 is injected into the glassware 70, the glassware can be placed in a vacuum box to remove bubbles from the PDMS mixed liquid, so as to avoid bubble holes in the subsequently formed super-resolution PDMS stamp. Bubbles in PDMS occurred because stirring was performed using a rotor or a glass rod, and a large amount of air was mixed due to the high viscosity of the solution. The vacuum method removes bubbles and places the glass ware injected with PDMS in a vacuum box, and the bubbles in the liquid can float out due to the negative pressure of the environment. In an alternative embodiment, the glass vessel filled with PDMS may be placed in a centrifugal stirrer by centrifugation, and the stirring and defoaming are combined into one.
In an alternative embodiment, heat resistant tape may be used to seal the silicon wafer edge and attached to the glass. After several times of PDMS stamping, damaged PDMS remains on the surface of the silicon wafer. The tape-fixing method can remove the silicon wafer for cleaning, while the double-sided tape method is not.
In other alternative embodiments, in addition to glassware, plastic ware may be used, and the use of plastic for surface hydrophobization may avoid damage to the PDMS stamp during subsequent demolding.
S207, baking the glassware to solidify the PDMS mixed liquid to form a super-resolution PDMS stamp.
And S208, stripping the silicon substrate to obtain the super-resolution PDMS stamp.
Specifically, the glass vessel 70 containing the PDMS mixed solution is placed in an oven, and is subjected to heat drying at a temperature of about 60 ℃ for about 3 hours, so that the PDMS mixed solution 80 is cured, and the super-resolution PDMS stamp is formed. Finally, the cured object is taken out of the glass vessel 70, and the silicon substrate 60 is peeled off, so as to obtain the super resolution PDMS stamp 500, as shown in fig. 4. Before the super-resolution PDMS stamp 500 is used to transfer a large amount of LED chips, the super-resolution PDMS stamp 500 may be trimmed as needed.
S209, adsorbing the second surface of the LED chip array through the super-resolution PDMS stamp, and removing the blue film and the protective layer. The area, adsorbing the LED chip array, of the super-resolution PDMS stamp comprises a hole array consisting of a plurality of holes, the size of each hole is smaller than that of the LED chip array, and the hole density of the hole array is larger than that of the LED chip array.
Specifically, as shown in fig. 5E and 5F. Firstly, the exposed surface of the super-resolution PDMS stamp 500, from which the sapphire substrate 100 is peeled off from the LED chip array 200, is adsorbed, and then the blue film 400 and the protective layer 300 are removed, so that only the LED chip array 200 is adsorbed on the super-resolution PDMS stamp 500.
Further, referring to fig. 3, the super-resolution PDMS stamp 500 includes a plurality of holes 510, and the plurality of holes 510 actually constitute a hole array. The depth of the hole 510 is less than the height of the super-resolution PDMS stamp 500. The shape of the hole 510 can be selected from circular, square, rectangular, hexagonal, etc. as desired. The size of the hole 510 is smaller than that of the LED chip 200, so that the LED chip 200 is prevented from falling into the hole 510 of the super-resolution PDMS stamp 500 when the LED chip array is attached. The hole density of the hole array is larger than the chip density of the LED chip array, i.e. the holes 51 are arranged more densely than the LED chips 200.
S210, adsorbing one surface, which is not adsorbed by the LED chip array, of the super-resolution PDMS stamp through a transfer head, moving the super-resolution PDMS stamp to the position above a driving substrate, and aligning the LED chip array with the driving substrate.
S211, irradiating the super-resolution PDMS stamp through laser, and enabling the LED chip array to be stripped from the super-resolution PDMS stamp and transferred to the driving substrate.
Specifically, as shown in fig. 5G, the super-resolution PDMS stamp 500 is moved to above the driving substrate 600 by adsorbing or grabbing the surface of the super-resolution PDMS stamp 500 not in contact with the LED chip array 200 by a transfer tool, and the LED chips in the LED chip array 200 are aligned with the chip carrying positions (not shown in the figure) in the driving substrate 600. Then, the super-resolution PDMS stamp 500 is irradiated by laser, so that the super-resolution PDMS stamp 500 is separated from the LED chip array 200, and the LED chip array 200 falls into the driving substrate 600, thereby realizing mass transfer.
When the super-resolution PDMS stamp 500 is irradiated with laser to be peeled off, the laser is simultaneously irradiated on the LED chip 200, the super-resolution PDMS stamp 500 and the LED chip array 200 are simultaneously thermally expanded, and due to the difference between the thermal expansion coefficients of the PDMS material and the LED chip 200, the super-resolution PDMS stamp 500 and the LED chip array 200 are separated to release Micro-LEDs in a specific area, and then the driving substrate is heated to realize flip chip bonding. In an alternative embodiment, if large area transfer is desired, laser irradiation is not required: and pressing the contact driving substrate and the Micro-LED formed on the PDMS after alignment, heating by a hot plate, completing the inverted welding, and then peeling off the PDMS integrally.
When thermal expansion occurs in the super-resolution PDMS stamp 500, thermal expansion stress is generated. For the conventional PDMS stamp transfer technique, as shown in fig. 1, the protrusion 2 on the stamp 1 expands due to the thermal expansion stress, so that the position of the chip 3 adsorbed by the protrusion is slightly shifted (for example, slightly shifted to the left), and the chip 3 and the driving substrate 4 are aligned before the stamp 1 is peeled off by the laser, so that the chip 3 and the driving substrate 4 are shifted after the stamp 1 is peeled off, and the bonding accuracy between the chip 3 and the driving substrate 4, that is, the transfer accuracy is affected. In the embodiment of the invention, the contact surface of the super-resolution PDMS stamp 500 and the LED chip is in a grid structure, and when the super-resolution PDMS stamp 500 thermally expands, the thermal expansion stress is released into the holes through the holes 510, so that the possibility of the position deviation of the LED chip 200 adsorbed by the super-resolution PDMS stamp 500 is reduced, and the transfer accuracy of the LED chip is improved.
Optionally, when the super-resolution PDMS stamp 500 is controlled to be peeled off from the LED chip array 200, a method of directly bending the edge of the super-resolution PDMS stamp 500 may also be used. Because the contact surface of the super-resolution PDMS stamp 500 and the LED chip array 200 is in a grid-like structure, and the distance between grids is relatively short, the super-resolution PDMS stamp 500 can be peeled off by bending from the edge of the whole super-resolution PDMS stamp 500 (which is equivalent to that a layer of film with a grid-like structure is adhered on the surface of the LED chip array 200 and is peeled off from the edge of the film, air enters between the surface of the LED chip array 200 and the film to promote the separation of the film and the surface of the LED chip array 200), and the method of peeling off by adopting the shearing force, the compressive stress, the thermal expansion and the like of an independent columnar structure (such as the protrusion 2 shown in fig. 1) is not needed.
According to the huge transfer method of the Micro-LED chip provided by the embodiment of the invention, the huge transfer of the LED chip array is realized by using the super-resolution PDMS stamp, and the alignment is not needed when the stamp adsorbs the LED chip, so that the operation is simplified, the transfer speed is accelerated, and the transfer efficiency and the accuracy are further improved. Meanwhile, the super-resolution PDMS stamp can be suitable for mass transfer of various LED chip arrays, and the applicability of the super-resolution PDMS stamp is improved. Furthermore, the holes of the super-resolution PDMS stamp can release thermal expansion stress inwards when being stripped, so that the position of the LED chip is ensured not to move, and the transfer precision of the LED chip is further improved.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A mass transfer method of Micro-LED chips is characterized by comprising the following steps:
providing a sapphire substrate, and forming an LED chip array on the sapphire substrate;
adhering a blue film on the first surface of the LED chip array and removing the sapphire substrate;
stretching the blue film to enable the chip spacing in the LED chip array to reach a preset distance;
adsorbing a second surface of the LED chip array through a super-resolution PDMS stamp and removing the blue film, wherein the area, adsorbing the LED chip array, of the super-resolution PDMS stamp comprises a hole array consisting of a plurality of holes, the size of each hole is smaller than that of the chip of the LED chip array, and the hole density of the hole array is larger than that of the chip of the LED chip array;
and removing the super-resolution PDMS stamp from the driving substrate to transfer the LED chip array to the driving substrate.
2. The method of claim 1, wherein before adhering the blue film to the first surface of the array of LED chips and removing the sapphire substrate, further comprising:
and forming a protective layer completely covering the LED chip array on the first surface of the LED chip array.
3. The method of claim 2, wherein the adhering a blue film to the first surface of the array of LED chips and removing the sapphire substrate comprises:
and adhering a blue film on the protective layer and removing the sapphire substrate by a laser lift-off technology.
4. The method of claim 1, wherein before the adsorbing the second surface of the LED chip array by the super-resolution PDMS stamp and 2 removing the blue film, further comprising:
providing a silicon substrate, and forming a plurality of column structures on the silicon substrate, wherein the size of the column structures is equal to or smaller than that of the holes;
gluing the silicon substrate in a glass ware, and injecting PDMS mixed liquid into the glass ware;
the glassware is heated and baked, so that the PDMS mixed liquid is solidified to form a super-resolution PDMS stamp;
and stripping the silicon substrate to obtain the super-resolution PDMS stamp.
5. The method of claim 4, wherein prior to injecting the PDMS mixture into the glass vessel, further comprising:
and carrying out hydrophobic treatment on the surface of the silicon substrate.
6. The method of claim 4, wherein before the step of baking the PDMS mixture, the method further comprises:
and placing the glassware in a vacuum box to remove bubbles from the PDMS mixed solution.
7. The method according to claim 4, wherein the PDMS mixture is a mixture of a curing agent and a PDMS solution, and the mixing ratio of the curing agent to the PDMS solution is between 0.1 and 0.2.
8. The method of claim 3, wherein the adsorbing the second surface of the LED chip array and removing the blue film by the super-resolution PDMS stamp comprises:
and adsorbing the second surface of the LED chip array through the super-resolution PDMS stamp, and removing the blue film and the protective layer.
9. The method of claim 1, wherein the moving the super-resolution PDMS stamp to a driving substrate and then peeling off the super-resolution PDMS stamp to transfer the LED chip array to the driving substrate comprises:
adsorbing one surface, which is not adsorbed by the LED chip array, of the super-resolution PDMS stamp by a transfer head, moving the super-resolution PDMS stamp to the position above a driving substrate, and aligning the LED chip array with the driving substrate;
and irradiating the super-resolution PDMS stamp by laser to peel off the LED chip array from the super-resolution PDMS stamp and transfer the LED chip array to the driving substrate.
10. The method of any one of claims 1-9, wherein the hole density of the array of holes is 5 times the chip density of the array of LED chips.
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