KR102732599B1 - Method for selectively transferring micro LEDs - Google Patents

Abstract

The method for selectively transferring micro LED chips of the present invention comprises: a process of attaching a polydimethylsiloxane (PDMS) sheet onto a first substrate; a process of aligning a wafer on which micro LED chips are arranged on the PDMS sheet so that the micro LED chips face the PDMS sheet, and then pressing the wafer and the first substrate; a process of transferring the micro LED chips onto the first substrate through a laser lift-off process; a process of attaching an environmentally variable adhesive sheet, the adhesive strength of which is generated, extinguished, or weakened depending on at least one environmental condition of temperature, pressure, gas atmosphere, and light wavelength, onto a second substrate; a process of aligning the first substrate on which the micro LED chips are arranged so that the micro LED chips face the environmentally variable adhesive sheet, and then transferring the micro LED chips of the first substrate onto the second substrate through a high-temperature and pressurization transfer process; a process of aligning the second substrate to a panel on which bonding pads are formed at at least one selective location, and bonding the second substrate to the panel; a process of irradiating a laser at the selective location; and a process of separating the second substrate from the panel;

Description

{Method for selectively transferring micro LEDs}

The present invention relates to a micro LED selective transfer method.

The development of high-definition displays using LED chips is actively underway. LED chips are mounted directly on the unit pixel electrode lines of a backplane substrate equipped with a driving circuit.

Recently, as the unit pixel size for high-resolution displays decreases, very small micro LED chips of 100 ㎛ or less in size are being used. Therefore, if a process of directly mounting micro LED chips on a backplane substrate using a general pick and place machine is selected, the process time may significantly increase and the mounting error rate may increase.

To solve these problems, various mass transfer technologies for micro LED chips are being developed to simultaneously mount a large number of micro LED chips on a backplane substrate.

These mass transfer techniques include methods that utilize electrostatic force, methods that utilize magnetic force, and methods that utilize adhesive force.

A mass transfer technology for mounting a large number of micro LED chips on a substrate at once is being developed, but a technology for transferring only some of the large number of micro LED chips mounted on a carrier substrate to the substrate is required.

That is, a technology for transferring only a portion of micro LEDs with an ultra-small pixel size of 10 micrometers or less to a desired substrate is required in the art.

The purpose of the present invention is to provide a micro LED selective transfer method capable of transferring some of a plurality of micro LEDs onto a substrate.

In order to achieve the above object, the present invention provides a method for selectively transferring micro LED chips, comprising: a first process of attaching a polydimethylsiloxane (PDMS) sheet onto a first substrate; a second process of aligning a wafer on which micro LED chips are arranged on the PDMS sheet so that the micro LED chips face the PDMS sheet, and then pressing the wafer and the first substrate; a third process of transferring the micro LED chips onto the first substrate through a laser lift-off process; a fourth process of attaching an environmentally variable adhesive sheet onto a second substrate; a fifth process of aligning the first substrate on which the micro LED chips are arranged on the second substrate so that the micro LED chips face the environmentally variable adhesive sheet, and then transferring the micro LED chips of the first substrate onto the second substrate through a high-temperature and pressurization transfer process; a sixth process of aligning the second substrate to a panel on which bonding pads are formed at at least one selective location, and bonding the second substrate to the panel; a seventh process of irradiating a laser at the selective location; and an eighth process of separating the second substrate from the panel.

The above environmentally variable adhesive sheet can have adhesive strength generated, extinguished, or weakened depending on at least one environmental condition of temperature, pressure, gas atmosphere, and light wavelength.

The above environmentally variable adhesive sheet may include a heat-change sheet or heat-change tape in which adhesive strength is generated within a specific temperature range and the adhesive strength disappears or weakens to 0.1 N or less when the specific temperature range is exceeded.

The above environmentally variable adhesive sheet has adhesive strength that occurs within a specific wavelength range of light, and the adhesive strength may disappear or weaken when the wavelength range is exceeded.

Some of the above bonding pads may function as reference marks that serve as reference points when aligning the second substrate and the panel.

The first substrate and the second substrate may be glass substrates.

The above seventh process can utilize the LIFT (Laser-Induced-Forward-Transfer) method.

The above first process and the above second process can be performed in a room temperature environment.

According to the micro LED selective transfer method according to the present invention, selected micro LED chips among a plurality of LED chips formed on a wafer can be easily transferred to a desired substrate.

FIG. 1 is a drawing for explaining a first process of a micro LED selective transfer method according to an embodiment of the present invention.
FIG. 2 is a drawing for explaining a second process of a micro LED selective transfer method according to an embodiment of the present invention.
FIG. 3 is a drawing for explaining a third process of a micro LED selective transfer method according to an embodiment of the present invention.
FIG. 4 is a drawing for explaining a fourth process of a micro LED selective transfer method according to an embodiment of the present invention.
FIG. 5 is a drawing for explaining a fifth process of a micro LED selective transfer method according to an embodiment of the present invention.
FIG. 6 is a drawing for explaining a sixth process of a micro LED selective transfer method according to an embodiment of the present invention.
FIG. 7 is a drawing for explaining the seventh process and the eighth process of the micro LED selective transfer method according to an embodiment of the present invention.

The following merely illustrates the principles of the present invention. Therefore, those skilled in the art will be able to invent various devices that implement the principles of the present invention and are included within the concept and scope of the present invention, even though they are not explicitly described or illustrated in the specification.

Furthermore, it should be understood that all conditional terms and embodiments listed in this specification are, in principle, expressly intended only for the purpose of making the concept of the present invention understood, and are not limited to the embodiments and conditions specifically listed as such.

In describing the present invention, terms such as first, second, etc. may be used to describe various components, but the components may not be limited by the terms.

For example, without departing from the scope of the present invention, the first component could be named the second component, and similarly, the second component could also be named the first component.

When it is said that a component is connected or coupled to another component, it can be understood that it may be directly connected or coupled to that other component, but there may also be other components in between.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention, and the singular expression may include the plural expression unless the context clearly indicates otherwise.

In this specification, terms such as “include” or “have” are intended to specify the presence of a feature, number, process, operation, component, part or combination thereof described in the specification, and can be understood as not excluding in advance the possibility of the presence or addition of one or more other features, numbers, processes, operations, components, parts or combinations thereof.

According to one embodiment of the present invention, a micro LED selective transfer method includes a first process of attaching a polydimethylsiloxane (PDMS) sheet onto a first substrate, a second process of aligning a wafer having micro LED chips arranged thereon on the PDMS sheet so that the micro LED chips face the PDMS sheet, and then pressing the wafer and the first substrate, a third process of transferring the micro LED chips onto the first substrate through a laser lift-off process, a fourth process of attaching an environmentally variable adhesive sheet onto a second substrate, a fifth process of aligning the first substrate having the micro LED chips arranged thereon on the second substrate so that the micro LED chips face the environmentally variable adhesive sheet, and then transferring the micro LED chips of the first substrate onto the second substrate through a high-temperature and pressurization transfer process, a sixth process of aligning the second substrate to a panel having bonding pads formed at at least one selective location and bonding the second substrate to the panel, a seventh process of irradiating a laser at the selective location, and an eighth process of separating the second substrate from the panel.

Hereinafter, a micro LED chip separation and transfer method according to a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.

A micro LED selective transfer method according to an embodiment of the present invention includes a process (first process) of attaching a polydimethylsiloxane (PDMS) sheet (120) onto a first substrate (110a). The first process can be performed in a room temperature environment. The room temperature range refers to a range of 15 degrees Celsius to 25 degrees Celsius.

The first substrate (110a) may be a glass substrate.

A polydimethylsiloxane (PDMS) sheet is a synthetic rubber material that can stably adhere to a relatively wide area of a first substrate (110a), and has the advantage of being able to stably adhere to an uneven surface. Referring to Fig. 1, a PDMS sheet (120) having a carrier film (20) attached to one surface is laminated onto a first substrate (110a), and then the carrier film (20) is removed.

Specifically, a PDMS sheet (120) having a carrier film (20) attached to one surface thereof is positioned so that the other surface of the PDMS sheet (120) faces the first substrate (110a), and then positioned between a pair of roll laminators (10a, 10b). Then, the PDMS sheet (120) and the first substrate (110a) are pressed by the pair of roll laminators (10a, 10b) to attach the PDMS sheet (120) to the first substrate (110a). Thereafter, the carrier film (20) attached to one surface of the PDMS sheet (120) is removed.

Next, the micro LED selective transfer method according to an embodiment of the present invention includes a process (second process) of aligning a wafer (30) having micro LED chips (200) arranged thereon on a PDMS sheet (120) so that the micro LED chips (200) face the PDMS sheet (120), and then pressing the wafer (30) and the first substrate (110a). The second process can be performed in a room temperature environment.

Specifically, referring to FIG. 2, a plurality of micro LED chips (Light emitting element chips) are formed on a wafer (30). The wafer (30) is preferably a sapphire wafer. Next, a bonding layer (210) is formed on the plurality of micro LED chips (200) formed on the wafer (30). The bonding layer (210) may include a tin (Sn) bonding material or an indium (In) bonding material. The bonding layer may be formed on a micro LED bonding pad or a TFT panel bonding pad through a plating process.

After aligning the wafer (30) on which the micro LED chips (200) are arranged on the PDMS sheet (120) so that the micro LED chips (200) face the PDMS sheet (120), the wafer (30) and the first substrate (110a) are pressed. In this case, the lower stage (40) may be positioned below the first substrate (110a) to support the first substrate (110a).

Next, the micro LED selective transfer method according to an embodiment of the present invention includes a process (third process) of transferring the micro LED chips onto the first substrate through a laser lift-off process.

Referring to FIG. 3, after the second process, the micro LED chips (200) on the wafer (30) come into contact with the PDMS sheet (120) on the first substrate (110a).

Specifically, a plurality of micro LED chips (200) formed on a wafer (30) are separated from the wafer (30) through a laser lift off process and attached to a PDMS sheet (120) of a first substrate (110a). The laser lift off (LLO) process is a process of removing the bonding force between the plurality of micro LED chips (200) and the wafer (30) by exposing the wafer (30) on which the plurality of micro LED chips (200) are formed to a laser.

Through this laser lift-off process, the micro LED chips (200) can be transferred onto the first substrate (110a). When the micro LED chips (200) are separated from the wafer (30), the micro LED chips (200) can be easily adhered to the PDMS sheet (120) due to the bonding layer (210) formed on the micro LED chips (200).

Next, the micro LED selective transfer method according to the embodiment of the present invention includes a process (fourth process) of attaching an environmentally variable adhesive sheet (130) on a second substrate (110b).

The second substrate (110b) may be a glass substrate.

The environmentally variable adhesive sheet (130) can have adhesive strength generated, extinguished, or weakened depending on at least one environmental condition of temperature, pressure, gas atmosphere, and light wavelength. That is, the material of the environmentally variable adhesive sheet can react to at least one of temperature, pressure, gas atmosphere, and light wavelength.

For example, as an environmentally variable adhesive sheet (130) that can be applied in the fourth process, a heat-change sheet or heat-change tape coated with an adhesive that generates adhesive force within a specific temperature range and disappears or weakens when the temperature range is exceeded may be applied, or, differently, a material that has a characteristic of generating adhesive force when exposed to light of a specific wavelength condition and disappearing or weakening the adhesive force when the specific wavelength condition is exceeded may be applied, or a material that has a characteristic of generating adhesive force in a specific gas atmosphere and disappearing or weakening the adhesive force when the specific gas atmosphere is released may be applied.

The above-mentioned environment variable adhesive sheet (130) can be formed in a sheet shape using a polymer, and the polymer sheet can be formed on a jig formed including PET (Polyethylene terephthalate), PEN (Polyethylene naphthalate), PA (Polyamide), PI (Polyimide), PC (polycarbonate), PVC (Polyvinyl Chloride), Quartz, Glass, Metal, Plastic, or a support formed of an elastic material.

Meanwhile, the environment variable adhesive sheet (130) may also apply a structure in which adhesive force is generated, extinguished, or weakened by a temperature difference. In this case, the environment variable adhesive sheet (130) may be made of a transfer material that has high adhesive force at a temperature of 80 degrees (℃) but low adhesive force at a temperature of 3 degrees or lower.

Referring to Fig. 4, an environmentally variable adhesive sheet (130) having a carrier film (22) attached to one side thereof is laminated onto a second substrate (110b), and then the carrier film (22) is removed.

Specifically, an environmentally variable adhesive sheet (130) having a carrier film (22) attached to one surface thereof is positioned so that the other surface of the environmentally variable adhesive sheet (130) faces the second substrate (110b), and then positioned between a pair of roll laminators (10a, 10b). Then, the environmentally variable adhesive sheet (130) and the second substrate (110b) are pressed by the pair of roll laminators (10a, 10b) to attach the environmentally variable adhesive sheet (130) to the second substrate (110b). Thereafter, the carrier film (22) attached to one surface of the environmentally variable adhesive sheet (130) is removed.

Then, the micro LED selective transfer method according to an embodiment of the present invention includes a process (fifth process) of aligning the first substrate (110a) on which the micro LED chips are arranged on the second substrate (110b) so that the micro LED chips (200) face the environment-variable adhesive sheet (130), and then transferring the micro LED chips (200) of the first substrate (110a) onto the second substrate (110b) through a high-temperature and pressure transfer process.

In the fifth process, the second substrate (110b) is positioned on the hot plate (40). The hot plate (40) can have a temperature of 80 degrees. As the second substrate (110b) is positioned on the hot plate (40), the adhesive force of the environment-variable adhesive sheet (130) positioned on the second substrate (110b) is generated. That is, the adhesive force of the environment-variable adhesive sheet (130) is generated within a predetermined temperature range, and the adhesive force disappears or weakens when the predetermined temperature range is exceeded.

In this embodiment, the environmentally variable adhesive sheet (130) is described as being made of a temperature-responsive material as an example, but it is obvious to those skilled in the art that the present invention is not limited thereto. For example, the environmentally variable adhesive sheet (130) may be made of a material that generates adhesive force in response to, for example, pressure, gas atmosphere, or wavelength of light.

In this way, in the fifth process, the adhesive force of the environment variable adhesive sheet (130) is generated by positioning the second substrate (110b) on the hot plate (40). At this time, the first substrate (110a) on which the micro LED chips are arranged is positioned so that the micro LED chips (200) face the environment variable adhesive sheet (130). Thereafter, when the first substrate (110a) is pressed against the second substrate (110b), the micro LED chips (200) of the first substrate (110a) can be transferred onto the second substrate (110b).

In this way, all of the micro LED chips of the first substrate (110b) can be transferred to the second substrate (110b) through high-temperature pressurization treatment.

Then, the micro LED selective transfer method according to the embodiment of the present invention includes a process (sixth process) of aligning the second substrate to a panel having bonding pads formed at at least one selective location and bonding the second substrate to the panel.

Specifically, referring to FIG. 6, a plurality of micro LED chips (200) are positioned on an environmentally variable adhesive sheet (130) of a second substrate (110b). Bonding pads (300) are formed at at least one selective position on the panel (140). The at least one selected position may be a position on the panel (140) where the micro LED chip (200) is to be placed, i.e., a chip attachment position.

The panel (140) may be a TFT panel. The bonding pad (300) is, for example, an element used to bond a micro LED chip (200) to the panel (140). In addition, bonding pads (300a, 300b) that may be fiducial marks are formed at an edge or a predetermined position of the panel (140). The bonding pads (300a and 300b) that function as fiducial marks enable accurate alignment when aligning the panel (140) and the second substrate (110b).

That is, in the sixth process, the second substrate (110b) and the panel (140) are aligned at an accurate position based on the reference mark so that the micro LED chips (200) of the second substrate (110b) and the bonding pads (300) of the panel (140) face each other. Then, the panel (140) and the second substrate (110b) are bonded. Accordingly, as illustrated in (b) of FIG. 6, the micro LED chips (200) can be bonded to the bonding pads (300) formed at the selected positions of the panel (140) and the second substrate (110b).

Finally, the micro LED selective transfer method according to an embodiment of the present invention includes a seventh process of irradiating a laser to the selective location, and an eighth process of separating the second substrate from the panel.

Specifically, referring to Fig. 7(a), a laser is irradiated to a bonding pad (300) formed at a selective location of the panel (140) while the panel (140) and the second substrate (110b) are bonded. Specifically, a laser having a wavelength of 940 nm can be selectively irradiated to a chip attachment location according to the resolution of the TFT panel (140) through a LIFT (Laser-Induced-Forward-Transfer) method.

Accordingly, the bonding layer (210) of the micro LED chip (200) is melted so that the micro LED chip (200) can be bonded to the bonding pad (300). Accordingly, the micro LED chip (200) can be mounted on the TFT panel (140). Thereafter, an environment in which the adhesive strength of the environment-variable adhesive sheet (130) is weakened or removed is provided so that the environment-variable adhesive sheet (130) is removed. For example, the display panel can be manufactured by removing the environment-variable adhesive sheet (130) at a temperature of 3°C.

Although the micro LED chip selective transfer method according to the present invention described above has been described with reference to the attached drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom.

Therefore, the true scope of technical protection of the present invention should be determined solely by the technical idea of the appended claims.

30: Wafer 110a: First substrate
110b: Second substrate 120: PDMS sheet
130: Environmental variable adhesive sheet 300: Bonding pad
200: Micro LED chip 400: TFT panel

Claims (8)

A first process of attaching a polydimethylsiloxane (PDMS) sheet onto a first substrate;
A second process of aligning a wafer having micro LED chips arranged on the PDMS sheet so that the micro LED chips face the PDMS sheet and then bonding the wafer and the first substrate;
A third process of transferring the micro LED chips onto the first substrate through a laser lift-off process;
A fourth process of attaching an environmentally variable adhesive sheet on a second substrate;
A fifth process of aligning the first substrate on which the micro LED chips are arranged on the second substrate so that the micro LED chips face the environmentally variable adhesive sheet, and then transferring the micro LED chips of the first substrate onto the second substrate through a transfer process;
A sixth process of aligning the second substrate to a panel having bonding pads formed at at least one selective location and bonding the second substrate to the panel;
A seventh process of irradiating a laser to the above-mentioned selective location; and
An eighth process for separating the second substrate from the panel;
The above environmentally variable adhesive sheet has adhesive strength in a specific wavelength range of light, and the adhesive strength disappears or weakens when the wavelength range is exceeded.
The above environmentally variable adhesive sheet is composed of a polymer sheet formed using a polymer, and the polymer sheet is formed on a jig formed including PET (Polyethylene terephthalate), PEN (Polyethylene naphthalate), PA (Polyamide), PI (Polyimide), PC (polycarbonate), PVC (Polyvinyl Chloride), Quartz, Glass, Metal, Plastic materials or a support formed of an elastic material. A method for selectively transferring a micro LED chip.
delete delete delete A method for selectively transferring a micro LED chip in accordance with claim 1, wherein some of the bonding pads function as reference marks that serve as reference points when aligning the second substrate and the panel.
A method for selectively transferring a micro LED chip in claim 1, wherein the first substrate and the second substrate are glass substrates.
In the first paragraph, the seventh process is a micro LED chip selective transfer method using a LIFT (Laser-Induced-Forward-Transfer) method.
A method for selectively transferring a micro LED chip in claim 1, wherein the first process and the second process are performed in a room temperature environment.

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