KR20230094636A - Micro LED display manufacturing method - Google Patents

Abstract

The present invention relates to a method for manufacturing a micro LED display and, more specifically, to a method for manufacturing a micro LED display, which can prevent wiring from being disconnected at the interface between micro LED chips and a passivation layer, thereby reducing the defect rate and increasing the yield. The method can form a first passivation layer to have a height lower than or equal to that of the top surface or the positive and negative electrodes of the micro LED chips (formed to have reduced step difference as much as possible), and can form a first wiring layer to have a thickness greater than the gap between the first passivation layer and the top surface of the micro LED chips to prevent the first wiring layer connected to the micro LED chips from being disconnected near the interface between the micro LED chips and the first passivation layer during curing of the first passivation layer, thereby reducing the defect rate of the micro LED display and increasing the yield. Furthermore, the method can form the electrodes to be relatively great by rearranging the electrodes, not to require high alignment accuracy when the micro LED display is mounted on a final target substrate, thereby being very simple and easy compared to conventional methods requiring high alignment accuracy, when flip chips with very small electrodes are mounted on a final substrate.

Description

Micro LED display manufacturing method {Micro LED display manufacturing method}

The present invention relates to a method for manufacturing a micro LED display, and more particularly, to a method for manufacturing a micro LED display capable of reducing the occurrence rate of defects and increasing the yield by preventing disconnection of wires at the interface between a micro LED chip and passivation.

In general, a micro light emitting device is an LED having a horizontal and vertical length of 100 μm or less. Recently, a TV using such a fine-sized micro light emitting device as a light source has been introduced and attracts attention. It is known that using a micro light emitting device as a light source for a display has the advantage of having fewer parts than LCD and longer lifespan than OLED, as well as fast light efficiency and response speed.

However, since the micro light emitting device is small in size, there are some difficulties in applying it as a display light source.

In the conventional micro LED display manufacturing process, the micro LED chip manufactured on the wafer is directly transferred to the back plane through a transfer device.

Therefore, if a defective chip is generated through inspection after transferring the micro LED chip to the rear substrate, the defective chip must be removed from the rear substrate and repaired, causing damage to the rear substrate. In addition, when it is impossible to repair the defective chip, the entire rear substrate has to be discarded, resulting in a decrease in the yield of the display module, which leads to an increase in price.

Republic of Korea Patent Publication 10-2020-0004688 Republic of Korea Patent Publication 10-2020-0026777 Korean Registered Patent No. 10-2225498

The present invention is to solve the above conventional problems, and to manufacture a micro LED display that can easily replace defective chips and shorten the manufacturing process by replacing defective chips by transferring them to an intermediate substrate before transferring them to a rear substrate. Its purpose is to provide a method.

In addition, an object of the present invention is to provide a method for manufacturing a micro LED display capable of preventing a phenomenon in which a wiring layer is disconnected near an interface between a micro LED chip and a passivation layer during a curing process of the passivation layer.

A method for manufacturing a micro LED display according to the present invention for achieving the above object includes a first transfer step of transferring a micro LED chip formed on a growth substrate to be disposed on a first surface of an intermediate substrate; an inspection step of inspecting the micro LED chip transferred to the intermediate substrate; a replacement step of removing the defective micro LED chips selected in the inspection step from the intermediate substrate and replacing them with good micro LED chips; a fixing step of fixing the micro LED chip on the intermediate substrate to the intermediate substrate; a wiring step of forming a wiring part on the micro LED chip fixed to the intermediate substrate; and a second transfer step of transferring only the micro LED chips from the intermediate substrate onto a rear substrate serving as a backplane.

The wiring step of the micro LED display manufacturing method according to the present invention includes the first passivation layer forming step of forming a first passivation layer to surround the first surface of the intermediate substrate and the micro LED chip together, and the upper side of the micro LED chip. A photoresist layer forming step of forming a photoresist layer on the first passivation layer to have a larger area than the micro LED chip; a first etching step of etching and removing a portion of the first passivation layer; A photoresist layer removal step of removing the photoresist layer on the first passivation layer; a second etching step of etching and removing a portion of the first passivation layer so that the electrodes and upper surface of the micro LED chip are all exposed to the outside; A first wiring layer forming step of forming a first wiring layer to be electrically connected to an electrode of a micro LED chip, and a second passivation layer forming step of forming a second passivation layer on the first passivation layer and the first wiring layer; A third etching step of etching and removing a portion of the second passivation layer to expose a portion of the upper surface of the first wiring layer of the micro LED chip; and a second passivation layer electrically connected to the first wiring layer. It is characterized in that it includes a second wiring layer forming step of forming a wiring layer.

In the second etching step of the micro LED display manufacturing method according to the present invention, the first passivation layer is deformed during curing after the first wiring layer forming step, and the first passivation layer and the micro LED chip are deformed in the vicinity of the interface. In order to prevent the first wiring layer from being disconnected, the first passivation layer is removed so that the distance between the top surface of the micro LED chip and the top surface of the first passivation layer is smaller than the thickness of the first wiring layer. .

The second wiring layer formed in the second wiring layer forming step of the micro LED display manufacturing method according to the present invention is formed to be exposed on the second passivation layer and a second anode connected to the first connection electrode of the rear substrate. It is characterized in that it includes a wiring layer and a second cathode wiring layer formed to be exposed on the second passivation layer and connected to the second connection electrode of the rear substrate.

The first passivation layer formed in the example of the second passivation layer forming step of the micro LED display manufacturing method according to the present invention is characterized in that it includes a black matrix.

The second transfer step is a connection step of electrically connecting a rear substrate functioning as a backplane on the second wiring layer, and a bonding force between the micro LED chip and the intermediate substrate can be weakened or released from the intermediate substrate side. A separation step of separating the micro LED chip and the first passivation layer from the intermediate substrate after irradiating the laser toward the interface between the intermediate substrate and the micro LED chip and the interface between the intermediate substrate and the first passivation layer for a predetermined time. .

In the micro LED display manufacturing method according to the present invention, the height of the first passivation layer is formed to be lower or equal to the height of the upper surface of the micro LED chip or the positive and negative electrodes (formed to minimize the step difference), and the thickness of the first wiring layer A phenomenon in which the first wiring layer connected to the micro LED chip is disconnected near the interface between the micro LED chip and the first passivation layer during curing of the first passivation layer by forming the first passivation layer thicker than the gap between the top surface of the micro LED chip. can be prevented, and through this, the defect occurrence rate of the micro LED display can be reduced and the yield can be increased.

In addition, in the method of manufacturing a micro LED display according to the present invention, electrodes can be formed to be relatively large through rearrangement of electrodes, so that high alignment accuracy is not required when mounted on a final target substrate. When mounting on a board, it has the advantage of being very simple and easy compared to the conventional method that requires high alignment accuracy.

1 to 13 are views showing a micro LED display manufacturing method according to the present invention.
14 is a view for comparing the structure of a micro LED chip package manufactured by the method for manufacturing a micro LED display according to the present invention and the structure of a conventional micro LED chip.

Hereinafter, a micro LED display manufacturing method according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 to 13 show a micro LED display manufacturing method according to the present invention. 1 to 13, a method of manufacturing a micro LED display according to the present invention includes a first transfer step of transferring a micro LED chip 20 formed on a growth substrate to be disposed on a first surface of an intermediate substrate 10; an inspection step of inspecting the micro LED chip 20 transferred to the intermediate substrate 10; a replacement step of removing the defective micro LED chips 20 selected in the inspection step from the intermediate substrate 10 and replacing them with good micro LED chips 20; a fixing step of fixing the micro LED chip 20 on the intermediate substrate 10 to the intermediate substrate 10; a wiring step of forming a wiring part on the micro LED chip 20 fixed to the intermediate substrate 10; A second transfer step of transferring only the micro LED chips 20 from the intermediate substrate 10 onto the rear substrate 80 serving as a backplane;

1 shows a structure in which a micro LED chip 20 is transferred onto an intermediate substrate 10 . Referring to FIG. 1 , in the first transfer step, the micro LED chip 20 is transferred to the intermediate substrate 10 .

The micro LED chip 20 may be disposed on the first surface 11 in the upper direction of the intermediate substrate 10 . Here, the intermediate substrate 10 may be formed of a transparent substrate so that light output from the micro LED chip 20 is transmitted. For example, it may be a substrate made of any one of glass, sapphire, PET, or PI. As the intermediate substrate 10, various substrates such as a rigid substrate or a flexible substrate may be used.

In addition, the micro LED chip 20 is used to reproduce colors such as R, G, and B (RED, Green, Blue), and may be manufactured on a growth substrate. In addition, a positive electrode 201 and a negative electrode 22 are provided on the upper surface of the micro LED chip 20, respectively, and the micro LED chip 20 is connected to each other to form one pixel P composed of R, G, and B. Arranged adjacently at set intervals, the three micro LED chips 20 are composed of R, G, and B, respectively.

Meanwhile, the micro LED chip 20 may be adhered and fixed to the intermediate substrate 10 by a transparent adhesive layer. That is, before the first transfer step of transferring the micro LED chip 20 to the intermediate substrate 10, a step of forming a transparent adhesive layer on the intermediate substrate 10 may be further included.

The transparent adhesive layer may be patterned on the intermediate substrate 10 through a photolithography process. For example, a transparent adhesive layer may be deposited on the first surface 11 of the intermediate substrate 10, and portions where the micro LED chip 20 is not disposed may be removed through a plasma etching process.

The transparent adhesive layer may be formed of any one of PSA, silicon-based, acrylic-based, and epoxy materials, and any material capable of adhering the micro LED chip 20 to the intermediate substrate 10 while curing in response to heat and UV light. Any material can be used. The micro LED chip 20 is adhered to the intermediate substrate 10 by a transparent adhesive layer, and has a predetermined adhesive strength to relatively easily separate the defective micro LED chips 20 selected from the intermediate substrate 10 in the inspection step described later. can be bonded to. Here, the adhesive force of the transparent adhesive layer can be adjusted by adjusting the temperature or UV light.

In the inspection step, the micro LED chip 20 transferred to the intermediate substrate 10 is measured using a micro PL or EL method, and whether or not the micro LED chip 20 is defective is determined according to the measurement result.

In the replacement step, the defective micro LED chip 20 selected in the inspection step is removed from the intermediate substrate 10 and replaced with a good micro LED chip 20 . The sorted defective micro LED chips 20 may be individually or simultaneously removed after location determination.

As a method of removing the defective micro LED chip 20, it may be removed by using laser ablation, an electrostatic chuck, or a magnetic chuck.

In the fixing step, the micro LED chip 20 on the intermediate substrate 10 is fixed to the intermediate substrate 10 by permanently curing the transparent adhesive layer through a heat or UV curing method.

In the wiring step, after going through the fixing step, wiring parts are formed on all the micro LED chips 20 fixed on the intermediate substrate 10 .

The wiring step includes a first passivation layer 30 forming step, a photoresist layer 40 forming step, a first etching step, a photoresist layer 40 removing step, a second etching step, and a first etching step. It may include a wiring layer forming step, a second passivation layer 60 forming step, a tertiary etching step, and a second wiring layer forming step.

2 shows a step of forming the first passivation layer 30 .

Referring to FIG. 2 , in the step of forming the first passivation layer 30 , the first passivation layer 30 is formed to surround the first surface of the intermediate substrate 10 and the micro LED chip 20 together. At this time, the first passivation layer 30 is preferably formed to cover all of the micro LED chips 20 disposed on the intermediate substrate 10 . In addition, the first passivation layer 30 may be formed over the entire intermediate substrate 10 or may be formed independently for each pixel P area composed of three micro LED chips 20 .

The first passivation layer 30 may be formed of an insulating material, for example, acrylic, poly(methyl methacrylate) (PMMA), benzocyclobutene (BCB), polyimide, acrylate, epoxy and polyester, etc. can be formed as Preferably, the first passivation layer 30 may include a material capable of absorbing light, for example, a black matrix, and when the black matrix is applied, light is emitted through the intermediate substrate 10. Mixing of colors can be prevented.

3 shows a photoresist layer 40 forming step.

Referring to FIG. 3 , in the step of forming the photoresist layer 40, the photoresist layer 40 is formed on the first passivation layer 30 above the micro LED chip 20 to have a larger area than the micro LED chip 20. form At this time, the photoresist layer 40 may be formed in an area corresponding to the first passivation layer 30, or independently only in a portion corresponding to the pixel P area composed of three micro LED chips 20. can also be formed. Preferably, in the first etching step and the second etching step to be described later, all of the first passivation layer 30 around the pixel P region is removed so that each pixel P region can be distinguished. It is formed independently only in the part corresponding to the area.

4 shows the first etching step.

Referring to FIG. 4 , in the first etching step, a portion of the first passivation layer 30 is etched and removed. More specifically, in the first etching step, the first passivation layer 30 corresponding to the periphery of the pixel (P) area, which is the edge area of the first passivation layer 30, is removed by a predetermined thickness to remove the first passivation layer 30 corresponding to the pixel (P) area. A step is created between the first passivation layer 30 and the first passivation layer 30 around the pixel (P) region. In the first etching step, a reactive ion etching (RIE) method may be applied.

The photoresist layer 40 removing step removes the photoresist layer 40 on the first passivation layer 30 so that the first passivation layer 30 is exposed as shown in FIG. 5 after the first etching step. .

6 shows a second etching step.

Referring to FIG. 6 , in the second etching step, the first passivation layer 30 remaining after the first etching step is etched to a predetermined thickness so that the electrode and upper surface of the micro LED chip 20 are all exposed to the outside. . In the second etching step, a reactive ion etching (RIE) method may be applied as applied in the first etching step.

In the second etching step, the first passivation layer 30 is removed so that the distance between the electrode or the upper surface of the micro LED chip 20 and the upper surface of the first passivation layer 30 is smaller than the thickness of the first wiring layer described later. It is desirable to do This is because the first passivation layer 30 is deformed while curing the first passivation layer 30 on the intermediate substrate 10 after the first wiring layer forming step described later, and the first passivation layer 30 and the micro LED chip 20 This is to prevent the first wiring layer from being disconnected in the vicinity of the interface.

7 shows a step of forming the first wiring layer.

Referring to FIG. 7 , in the first wiring layer forming step, after the second etching step is completed, the first wiring layer is formed to be connected to and connected to the positive electrode 201 and the negative electrode 22 provided on the upper surface of the micro LED chip 20, respectively. form

In the first wiring layer forming step, the first wiring layer formed is connected to the first anode wiring layer 51 connected to and connected to the positive electrode 201 of the micro LED chip 20 and the negative electrode 22 of the micro LED chip 20. and a first cathode wiring layer 52 connected thereto.

In the step of forming the second passivation layer 60, as shown in FIG. 8, the second passivation layer 60 is formed to a certain thickness so as to surround the first passivation layer 30 and the first wiring layer together. Here, the second passivation layer 60 may be formed to cover the entire first wiring layer. The material of the second passivation layer 60 may be formed of, for example, acrylic, poly(methyl methacrylate) (PMMA), benzocyclobutene (BCB), polyimide, acrylate, epoxy, and polyester. .

9 shows a third etching step.

Referring to FIG. 9 , in the third etching step, a portion of the second passivation layer 60 is etched and removed so that a portion of the upper surface of the first wiring layer connected to the positive and negative electrodes of the micro LED chip 20 is exposed. In the third etching step, holes penetrating vertically are formed in the region of the second passivation layer 60 corresponding to the upper portion of the first wiring layer.

10 shows a step of forming a second wiring layer.

Referring to FIG. 10 , in the step of forming the second wiring layer, a second wiring layer is formed on the second passivation layer 60 to be electrically connected to the first wiring layer. The second wiring layer formed in the second wiring layer forming step includes a conductive material and extends through the second passivation layer 60 to be exposed on the surface of the second passivation layer 60 .

Also, the second wiring layer may include a second anode wiring layer 71 and a second cathode wiring layer 72 . The second anode wiring layer 71 is formed such that one side is connected to and connected to the first anode wiring layer 51 and penetrates the second passivation layer 60 to expose the other side to the surface of the second passivation layer 60. do. The second cathode wiring layer 72 is formed such that one side is connected to and connected to the first cathode wiring layer 52 and penetrates the second passivation layer 60 to expose the other side to the surface of the second passivation layer 60. do.

11 shows a second transfer step.

Referring to FIG. 11, the second transfer step is a step of transferring only the micro LED chips 20 packaged from the intermediate substrate 10 onto the back substrate functioning as a backplane, and may include a connection step and a separation step. there is.

The connecting step electrically connects the rear substrate 80 functioning as a backplane on the second wiring layer including the second anode wiring layer 71 and the second cathode wiring layer 72 .

The rear substrate 80 may include a thin film transistor (TFT) or PCB as a backplane. Here, the thin film transistor may include a gate electrode, an active layer electrically insulated from the gate electrode by a gate insulating layer, and a circuit unit having a source electrode and a drain electrode electrically connected to the active layer. In addition, first connection electrodes 81 and second connection electrodes 82 connected to the thin film transistor (TFT) are formed on the lower surface of the rear substrate 80 to be exposed.

The rear substrate 80 is attached so that the first connection electrodes 81 and the second connection electrodes 82 are in contact with the second anode wiring layers 71 and the second cathode wiring layers 72 of the second wiring layer, respectively. The first connection electrodes 81 and the second connection electrodes 82 may be attached to the second anode wiring layers 71 and the second cathode wiring layers 72 through bonding to contact each other.

For example, the second anode wiring layer 71 connected to the positive electrode 21 of the micro LED chip 20 may be connected to the first connection electrodes 81 of the rear substrate 80, and the micro LED chip 20 The second cathode wiring layer 72 connected to the negative electrode 22 of may be connected to the second connection electrodes 82 of the back substrate 80 . In addition, as a method of attaching the rear substrate 80 and the wiring part, it can be attached using a metal solder bump, a stud bump, a vertical conductive film, or a bonding material such as ACF, ACA, or SAP. .

After attaching and connecting the rear substrate 80 on the second wiring layer, as shown in FIG. 12, the second passivation layer 60 and an underfill for filling a resin between the second wiring layer and the rear substrate 80 ) process can be performed.

After the underfill process is completed, a separation step is performed as shown in FIG. 13 . The separation step is a step of separating the intermediate substrate 10 and the micro LED chip 20, and the intermediate substrate 10 side is capable of weakening or releasing the bonding force or adhesive force between the micro LED chip 20 and the intermediate substrate 10. After irradiating a laser toward the interface between the intermediate substrate 10 and the micro LED chip 20 and the interface between the intermediate substrate 10 and the first passivation layer 30 for a certain period of time, the micro LED chip 20 and the first passivation Layer 30 is separated from intermediate substrate 10 . The micro LED display module separated from the intermediate substrate 10 may be mounted pixel by pixel on the final target substrate.

As described above, in the manufacturing method of the micro LED display according to the present invention, the height of the first passivation layer 30 is formed to be lower than or equal to the upper surface of the micro LED chip 20 or the heights of the positive electrode 201 and the negative electrode 22 And, by forming the thickness of the first wiring layer thicker than the distance between the first passivation layer 30 and the upper surface of the micro LED chip 20, the micro LED chip 20 and the micro LED chip 20 are removed during curing of the first passivation layer 30. It is possible to prevent a phenomenon in which the wiring layer is disconnected near the interface of the first passivation layer 30, and through this, there is an advantage in that the rate of occurrence of defects in the micro LED display can be reduced and the yield can be increased.

Meanwhile, FIG. 14 shows a micro LED chip package manufactured by the micro LED display manufacturing method according to the present invention and a micro LED chip having a conventional flip chip structure.

Referring to FIG. 14A, the micro LED chip package P manufactured by the micro LED display manufacturing method according to the present invention includes second wiring layers 71 and 72 connected to the connection electrodes of the rear substrate through the rearrangement structure of the wiring layers. It is formed to have a relatively larger area than the positive electrode 21 and the negative electrode 22 of the micro LED chip 20. On the other hand, in the micro LED chip 20A of the conventional flip chip structure shown in FIG. 14B, the size of the electrodes 21A and 22A is very small, and the size of the connection electrodes on the rear substrate or the final substrate is also very small, and the size of each other is very small. Since they are spaced apart at a narrow interval, high alignment accuracy is required to align the electrodes 21A and 22A of the micro LED chip 20A to the connecting electrodes of the rear substrate or the final substrate when mounted on the rear substrate or final substrate.

In the micro LED chip package P manufactured according to the micro LED display manufacturing method according to the present invention, the second wiring layers 71 and 72 are relatively wider than the positive electrodes 21 and negative electrodes 22 of the micro LED chip 20. Since it is formed to have a large area, it does not require high align accuracy as in the prior art to connect to the connection electrode of the rear substrate or the final target substrate, so it has the advantage of being very simple and easy to manufacture compared to the prior art.

The micro LED display manufacturing method according to the present invention described above has been described with reference to the accompanying drawings, but this is only exemplary, and various modifications and other equivalent embodiments can be made by those skilled in the art. will understand that

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

10: intermediate board
20: micro LED chip
21: positive electrode
22: negative electrode
30: first passivation layer
40: photoresist layer
51: first anode wiring layer
52: first cathode wiring layer
60: second passivation layer
71: second anode wiring layer
72: second cathode wiring layer
80: rear board
81: first connection electrode
82: second connection electrode

Claims (5)

a first transfer step of transferring the micro LED chip formed on the growth substrate to be disposed on the first surface of the intermediate substrate; an inspection step of inspecting the micro LED chip transferred to the intermediate substrate; a replacement step of removing the defective micro LED chips selected in the inspection step from the intermediate substrate and replacing them with good micro LED chips; a fixing step of fixing the micro LED chip on the intermediate substrate to the intermediate substrate; a wiring step of forming a wiring part on the micro LED chip fixed to the intermediate substrate; In the micro LED display manufacturing method comprising a; second transfer step of transferring only the micro LED chips from the intermediate substrate onto a rear substrate functioning as a backplane,
The wiring step is
A first passivation layer forming step of forming a first passivation layer to surround the first surface of the intermediate substrate and the micro LED chip;
A photoresist layer forming step of forming a photoresist layer on the first passivation layer above the micro LED chip to have a larger area than the micro LED chip;
A first etching step of etching and removing a portion of the first passivation layer;
A photoresist layer removal step of removing the photoresist layer;
A second etching step of etching and removing a portion of the first passivation layer so that the electrode and upper surface of the micro LED chip are all exposed to the outside;
A first wiring layer forming step of forming a first wiring layer to be electrically connected to the electrode of the micro LED chip;
a second passivation layer forming step of forming a second passivation layer on the first passivation layer and the first wiring layer;
a third etching step of etching and removing a portion of the second passivation layer so that a portion of the upper surface of the first wiring layer of the micro LED chip is exposed;
and a second wiring layer forming step of forming a second wiring layer on the second passivation layer to be electrically connected to the first wiring layer. According to claim 1,
The second etching step is
The top surface of the micro LED chip and the top surface of the first passivation layer may be prevented from being disconnected near the interface between the first passivation layer and the micro LED chip while the first passivation layer is deformed during curing. The method of manufacturing a micro LED display, characterized in that by removing the first passivation layer so that the distance between them is smaller than the thickness of the first wiring layer. According to claim 1,
The second wiring layer is
a second anode wiring layer formed to be exposed on the second passivation layer and connected to the first connection electrode of the rear substrate;
A micro LED display manufacturing method comprising a second cathode wiring layer formed to be exposed on the second passivation layer and connected to the second connection electrode of the rear substrate. According to claim 1,
The first passivation layer is a micro LED display manufacturing method, characterized in that it comprises a black matrix (black matrix). According to claim 1,
The second transfer step is
A connection step of electrically connecting a rear substrate functioning as a backplane on the second wiring layer;
After irradiating a laser toward the interface between the intermediate substrate and the micro LED chip and the interface between the intermediate substrate and the first passivation layer from the side of the intermediate substrate for a predetermined time to weaken or release the bonding force between the micro LED chip and the intermediate substrate, A micro LED display manufacturing method comprising a separation step of separating the micro LED chip and the first passivation layer from the intermediate substrate.

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