TWI861714B - Laser lift off method and laser lift off device - Google Patents

Abstract

A laser lift off method is adapted to separate an epitaxial layer of a wafer from a substrate of the wafer. The laser lift off method includes following steps. A central area and at least one annular area are defined on the wafer, wherein the at least one annular area surrounds the central area. A plurality of first processing tracks is planned in the at least one annular area, and a plurality of second processing tracks is planned in the central area, wherein the first processing tracks are extended along a radial direction of the wafer or are inclined to the radial direction of the wafer. The at least one annular area is processed by a laser beam along the first processing tracks, the central area is processed by the laser beam along the second processing tracks. A laser lift off device is also provided.

Description

Laser stripping method and laser stripping equipment

The present invention relates to a laser processing method and equipment, in particular to a laser stripping method and laser stripping equipment.

Micro LED Display is a display that uses micro LED as a light source. Micro LED is a light-emitting diode (LED) that is thinned, miniaturized, and arrayed, and the size of the LED is reduced to the micron level. The manufacturing process of the micro LED display includes forming an epitaxial layer including multiple micro dices on a wafer substrate, and then performing mass transfer to transfer the micro dices to a driving substrate.

Before mass transfer, a laser stripping step is performed to separate the epitaxial layer from the wafer substrate. How to control the laser for processing is an important key to the laser stripping step.

The present invention provides a laser peeling method suitable for separating the epitaxial layer from the substrate, which can avoid the problems caused by stress concentration during the laser processing.

The present invention also provides a laser stripping device using the method, which is suitable for separating the epitaxial layer from the substrate and can avoid problems caused by stress concentration caused by laser processing during the laser processing.

To achieve the above advantages, an embodiment of the present invention provides a laser stripping method suitable for separating the epitaxial layer of a wafer from a substrate. The laser stripping method includes: dividing the wafer into a central area and at least one annular area, and the at least one annular area surrounds the central area; planning a plurality of first processing tracks in the at least one annular area, and planning a plurality of second processing tracks in the central area, wherein the plurality of first processing tracks extend along the radial direction of the wafer or extend inclined to the radial direction of the wafer; processing the at least one annular area with a laser beam along the plurality of first processing tracks, and then processing the central area with a laser beam along the plurality of second processing tracks. There are multiple annular regions, which are arranged in sequence from the outside to the inside. The step of processing at least one annular region along multiple first processing tracks with a laser beam includes processing the multiple annular regions in sequence from the outside to the inside. The multiple first processing tracks of some of the multiple annular regions extend along the radial direction of the wafer, and the multiple first processing tracks of another part of the multiple annular regions extend obliquely to the radial direction of the wafer.

In one embodiment of the present invention, a plurality of first processing tracks of a plurality of annular regions adjacent to the outer side extend along the radial direction of the wafer.

In one embodiment of the present invention, the aforementioned plurality of second processing tracks include a plurality of straight tracks parallel to each other or a plurality of annular tracks arranged in sequence from the outside to the inside.

In one embodiment of the present invention, when processing at least one annular area mentioned above, a scanning galvanometer module is used to enable the laser beam to move along the first axis and the second axis on the wafer, and the wafer is driven to move by a two-dimensional moving platform.

In one embodiment of the present invention, when processing the above-mentioned central area, the laser beam can move along the first axis and the second axis on the wafer through the scanning galvanometer module, while the two-dimensional moving platform carrying the wafer remains stationary.

In one embodiment of the present invention, when processing at least one annular area and the central area mentioned above, a laser beam is triggered by a fixed-distance pulse.

In one embodiment of the present invention, the laser beam is a flat-top beam.

An embodiment of the present invention provides a laser stripping device, which is suitable for separating an epitaxial layer of a wafer from a substrate, and the laser stripping device includes a control module and a laser light source. The control module is suitable for dividing a wafer into a central area and at least one annular area, the at least one annular area surrounds the central area, and is suitable for planning a plurality of first processing tracks in the at least one annular area, and planning a plurality of second processing tracks in the central area, wherein the plurality of first processing tracks extend along the radial direction of the wafer or extend obliquely to the radial direction of the wafer. The laser light source is electrically connected to the control module, and the control module is suitable for driving the laser light source to provide a laser beam along a plurality of first processing tracks to process at least one annular area, and then driving the laser light source to provide a laser beam along a plurality of second processing tracks to process the central area.

In one embodiment of the present invention, the laser stripping device further includes a scanning galvanometer module electrically connected to a control module, wherein the control module is suitable for controlling the scanning galvanometer module so that the laser beam can move along the first axis and the second axis on the wafer; and a two-dimensional moving platform electrically connected to the control module and suitable for carrying the wafer, wherein the control module is suitable for controlling the movement of the two-dimensional moving platform.

In one embodiment of the present invention, the above-mentioned laser stripping device further includes an optical diffraction element, which is arranged on the transmission path of the laser beam to convert the laser beam into a flat-top beam.

As described above, the laser stripping method of the present invention divides the wafer into a central area and at least one annular area, and during processing, the laser beam is first processed along the annular area located at the periphery, and then the central area located at the center is processed. Therefore, the stress generated during laser processing can be released to avoid stress concentration in a local area of the substrate. In addition, when processing the annular area, by allowing the processing path planned on the annular area to extend along the radial direction of the wafer or to extend obliquely to the radial direction of the wafer, the area of overlap of the laser beam spot on the wafer during processing can be reduced so as to perform processing uniformly, which helps to separate the epitaxial layer from the substrate.

In order to make the above and other purposes, features and advantages of the present invention more clearly understood, the following is a detailed description of the embodiments with the help of the attached drawings.

10: Wafer

10a: Epitaxial layer

10b: Substrate

20: Laser stripping equipment

21: Control module

22: Laser light source

23: Scanning galvanometer module

23a: First scanning galvanometer

23b: Second scanning galvanometer

23c: Projection lens

24: Two-dimensional mobile platform

25: Optical diffraction element

26: Mobile photomask

26a: Translucent pattern

27: Light guiding element

X: First axis

Y: Second axis

S1: Central area

S2, S2a, S2b, S2c, S2d: annular area

T1, T1a, T1b, T1c, T1d, T1e, T1f, T1g, T1h: First processing track

T2a, T2b: Second processing track

T3: The third processing track

T4: Straight track

T5: Arc track

T6: Straight track

L: Laser beam

D1: First direction

D2: Second direction

D3: First direction

D4: Second direction

W1: radial direction

W2: Circumferential direction

R: Radius

S110: Step

S120: Step

S130: Step

FIG1 is a flow chart of a laser stripping method according to an embodiment of the present invention; FIG2A and FIG2B are block diagrams and structure diagrams of a laser stripping device according to an embodiment of the present invention; FIG3A and FIG3B are schematic diagrams of wafers in different embodiments of the present invention; FIG4 is an overall schematic diagram of the trajectory of the laser beam processing trajectory in the embodiment of FIG1; FIG5 is a schematic diagram of the processing of a fixed-distance trigger pulse laser; FIG6A to FIG6D are schematic diagrams of the trajectory of the laser beam processing trajectory in the embodiment of FIG1; FIG7 is a schematic diagram of the trajectory of the laser beam processing trajectory in another embodiment of the present invention.

In the following article, the terms used in the description of the embodiments of the present invention, such as "upper", "lower", etc., indicating the orientation or position relationship, are described according to the orientation or position relationship shown in the drawings used. The above terms are only for the convenience of describing the present invention and are not intended to limit the present invention, that is, they do not indicate or imply that the components mentioned must have a specific orientation or be constructed in a specific orientation. In addition, the terms "first", "second", etc. mentioned in this specification or the scope of the patent application are only used to name the element or distinguish different embodiments or scopes, and are not used to limit the upper or lower limit of the number of elements.

FIG1 is a flow chart of a laser stripping method according to an embodiment of the present invention. FIG2A is a block diagram of a laser stripping device according to an embodiment of the present invention. FIG2B is a structural diagram of the laser stripping device in the embodiment of FIG2A. FIG3A and FIG3B are schematic diagrams of wafer stripping in different embodiments of the present invention, and FIG4 is an overall schematic diagram of the trajectory of the laser beam processing trajectory in the embodiment of FIG1.

Referring to FIGS. 1 to 4 , the laser stripping method of this embodiment is suitable for separating the epitaxial layer 10a of the wafer 10 from the substrate 10b. The laser stripping method includes the following steps. Step S110: dividing the wafer 10 into a central region S1 and at least one annular region S2, wherein the annular region S2 surrounds the central region S1. Step S120: planning a plurality of first processing tracks T1 in the at least one annular region S2, and planning a plurality of second processing tracks T2a in the central region S1, wherein the plurality of first processing tracks T1 extend along the radial direction W1 of the wafer 10 or extend obliquely to the radial direction W1 of the wafer 10. Step S130: Use the laser beam L to process at least one annular area S2 along the first processing trajectory T1, and then use the laser beam L to process the central area S1 along the second processing trajectory T2a.

As shown in FIG. 3A , in one embodiment, the wafer 10 processed by the laser stripping method includes, for example, an epitaxial layer 10a and a substrate 10b, wherein the epitaxial layer 10a covers the entire surface of one side of the substrate 10b, and a buffer layer 10c is provided at the junction of the epitaxial layer 10a and the substrate 10b. When the laser beam L irradiates the wafer 10 along the first processing track T1 or the second processing track T2a (not shown), the irradiation area of the laser beam L can, for example, irradiate a portion of the buffer layer 10c, so that the buffer layer 10c reacts, thereby enabling the epitaxial layer 10a to be separated from the substrate 10b. (In order to conveniently indicate the irradiation position of the laser beam L, the laser beam L irradiated along the first processing track T1 or the second processing track T2a at different times is drawn in the same figure in FIG3A)

As shown in FIG. 3B , in other embodiments, the epitaxial layer 10a on the wafer 10 is processed to be divided into a plurality of grains D spaced apart from each other, and an adhesive 11 may be provided between the grains D and the grains D. The adhesive 11 may be, for example, a colloid or anisotropic conductive film (ACF), etc. The adhesive 11 may also be contained between the substrate 10b and the plurality of grains D (not shown), but not limited thereto. Each grain D may be, for example, a micrograin, and its length, width, and thickness may be, for example, less than 100 μm, and may even be less than 50 μm, for example, less than 10 μm, but not limited thereto. The grain D may also be a grain of a larger size, for example, with a length, width, and thickness of approximately 100 to 1000 μm. In addition, the above-mentioned micrograins may be micro-light-emitting diodes (Micro LEDs), but the present invention is not limited thereto. When the laser beam L irradiates the wafer 10 along the first processing track T1 or the second processing track T2a (not shown), the irradiation area of the laser beam L may include, for example, the crystal grain D and the adhesive 11, or only a portion of the adhesive 11, so that the element formed by the crystal grain D and the adhesive 11 is separated from the substrate 10b together. (In order to conveniently indicate the irradiation position of the laser beam L, the laser beam L irradiated along the first processing track T1 or the second processing track T2a at different time points is drawn in the same figure in FIG. 3B)

The equipment for implementing the above-mentioned laser stripping method is shown in FIG. 2A and FIG. 2B. In this embodiment, the laser stripping device 20 for implementing the above-mentioned laser stripping method includes a control module 21 and a laser light source 22. The control module 21 is suitable for dividing the wafer 10 into a central area S1 and an annular area S2. The annular area S2 surrounds the central area S1 and is suitable for planning a plurality of first processing tracks T1 in the annular area S2, and planning a plurality of second processing tracks T2a in the central area S1, wherein the first processing track T1 extends along the radial direction W1 of the wafer 10 or extends obliquely to the radial direction W1 of the wafer 10.

The laser light source 22 is electrically connected to the control module 21. The control module 21 is adapted to drive the laser light source 22 to provide a laser beam along the first processing trajectory T1 to process the annular area S2, and then drive the laser light source 22 to provide a laser beam along the second processing trajectory T2a to process the central area S1. In this embodiment, the laser beam L processed along the first processing trajectory T1 and the second processing trajectory T2a is, for example, a flat-top beam. Specifically, the laser beam emitted by the laser light source 22 is, for example, a Gaussian beam. The laser stripping device 20 of this embodiment further includes an optical diffraction element 25, which is disposed on the transmission path of the laser beam to convert the laser beam (Gaussian beam) into the above-mentioned flat-top beam, but the present invention does not limit the energy distribution form of the laser beam L.

As shown in FIG. 2A and FIG. 2B , in the present embodiment, the laser stripping device 20 further includes, for example, a scanning galvanometer module 23 and a two-dimensional moving platform 24. The scanning galvanometer module 23 is electrically connected to the control module 21, and the control module 21 is suitable for controlling the scanning galvanometer module 23 so that the laser beam L can move on the wafer 10, for example, along the first axis X and the second axis Y. The angle θ between the first axis X and the second axis Y is, for example, 90 degrees, but the present invention is not limited thereto. In addition, the laser stripping device 20 may further include other elements disposed between the scanning galvanometer module 23 and the laser light source 22, such as a movable light mask 26 and a light guiding element 27. The movable light mask 26 has a plurality of light-transmitting patterns 26a of different shapes. The control module 21 is, for example, electrically connected to the movable mask 26 to control the movement of the movable mask 26 so that the laser beam passes through one of the appropriate light-transmitting patterns 26a, thereby changing the spot shape of the laser beam when irradiating the wafer 10. In addition, the light guiding element 27 is used to guide the laser beam L to the scanning galvanometer module 23. In this embodiment, the light guiding element 27 includes, for example, two reflective elements, but the present invention does not limit the type and number of the light guiding element 27.

In this embodiment, the scanning galvanometer module 23 includes, for example, a first scanning galvanometer 23a, a second scanning galvanometer 23b, and a projection lens 23c. The first scanning galvanometer 23a is controlled by the control module 21 to swing, and is suitable for reflecting the laser beam generated by the laser light source 22 within a preset angle range, and making the laser beam L suitable for moving, for example, along the direction of the first axis X when irradiating the wafer 10. The second scanning galvanometer 23b is controlled by the control module 21 to swing, and is suitable for reflecting the laser beam L from the first scanning galvanometer 23a within a preset angle range, and making the laser beam L move, for example, along the direction of the second axis Y when finally irradiating the wafer 10. The projection lens 23c is located between the second scanning galvanometer 23b and the two-dimensional moving platform 24, and is used to project the laser beam L onto the two-dimensional moving platform 24.

The two-dimensional moving platform 24 is electrically connected to the control module 21. The two-dimensional moving platform 24 is suitable for carrying the wafer 10 and is controlled by the control module 21 to drive the wafer 10 to move in the first direction D1 parallel to the first axis X and the second direction D2 parallel to the second axis Y during processing. Thus, during processing, the control module 21 controls the scanning galvanometer module 23 and the two-dimensional moving platform 24 to operate simultaneously. The four-axis simultaneous driving method of the two moving axes of the scanning galvanometer module 23 and the two-dimensional moving platform 24 can accelerate the processing speed and reduce the time required for processing.

The two-dimensional moving platform 24 of this embodiment refers to a platform that can move in at least two dimensions during processing, rather than a platform that is limited to moving in only two dimensions. In other words, the two-dimensional moving platform 24 of this embodiment can also be a platform that can drive the wafer 10 to move in three dimensions or even rotate along an axis. In addition, the relationship between the extension direction of the first direction D1 and the extension direction of the first axis X, and the extension direction of the second direction D2 and the extension direction of the second axis Y do not necessarily have to be parallel to each other.

Please refer to FIG. 4 . In the present embodiment, the control module 21 plans four annular regions S2 on the wafer 10, which are respectively annular regions S2a, annular regions S2b, annular regions S2c and annular regions S2d in descending order of radius. The shape of the first processing track T1a on the outermost annular region S2a is, for example, extending along the radial direction of the wafer 10, while the shapes of the first processing tracks T1b, T1c and T1d on the other three annular regions S2b, S2c and S2d are, for example, all extending along the radial direction inclined to the wafer 10. In this embodiment, the slopes of the first processing trajectory T1b, the first processing trajectory T1c and the first processing trajectory T1d inclined relative to the radial direction W1 are different, for example, but not limited to this. The second processing trajectory T2a located in the central area S1 is, for example, a plurality of parallel straight line trajectories, but not limited to this.

In this embodiment, when processing the annular area S2, the control module 21, for example, first calculates the relative motion coordinates, controls the two-dimensional moving platform 24 to drive the wafer 10 to move, and simultaneously controls the scanning galvanometer module 23 to change the direction of the laser beam L, and moves the laser beam L along the first processing track T1 through the four-axis synchronization. Afterwards, when processing to the central area S1, the control module 21, for example, controls the two-dimensional moving platform not to move, and only controls the laser beam L to move along the second processing track T2a by controlling the scanning galvanometer module 23, but is not limited thereto.

FIG5 is a schematic diagram of processing by a fixed-distance triggered pulse laser. In this embodiment, the control module 21, for example, has a position synchronized output (Position Synchronized Output/PSO) function and, for example, adopts a fixed-distance pulse triggering method to drive the laser beam L for processing. For such advantages, please refer to FIG5. In FIG5, the processing trajectory of the laser beam L, for example, is sequentially along the straight track T4, the arc track T5 and finally returns to the straight track T6. The moving distance per unit time of the laser beam L on the straight track T4 and the straight track T6 will be different from the moving distance per unit time of the laser beam L on the arc track T5. Since this embodiment uses a fixed-distance pulse trigger to drive the laser beam L for processing, rather than a timed pulse trigger to drive the laser beam L for processing, the fixed-distance pulse trigger method can reduce the spot overlap area of the laser beam L on the arc track T5 compared to the timed pulse trigger method.

FIG. 6A to FIG. 6D are schematic diagrams of the processing trajectory of the laser beam L in the embodiment of FIG. 1. Referring to FIG. 6A to FIG. 6D, during processing, the laser beam L, for example, first processes along the first processing trajectory T1a on the outermost annular area S2a, and then processes the inner annular areas S2b, S2c and S2d in sequence after the processing is completed, and the center area S1 is processed only after all the annular areas S2a, S2b, S2c and S2d are processed. Through the above-mentioned processing method of processing from the outer area to the inner area of the wafer 10 (not shown), the stress generated on the wafer 10 during laser processing can be effectively released.

In this embodiment, the processing trajectory of the laser beam L includes, in addition to the first processing trajectory T1 along the radial direction W1 of the wafer 10 or a straight trajectory inclined to the radial direction W1 of the wafer 10, a plurality of third processing trajectories T3 extending along the circumferential direction W2 of the wafer 10. As can be seen from Figures 6A to 6C, during processing, the laser beam L can be processed alternately along the first processing trajectory T1 and the third processing trajectory T3, but it is not limited to this method.

FIG7 is a schematic diagram of the trajectory of the laser beam L processing trajectory in another embodiment of the present invention. As shown in FIG6, in this embodiment, the first processing trajectories T1e, T1f, T1g and T1h located on the four annular areas S2a, S2b, S2c and S2d are, for example, straight line trajectories distributed along the radial direction W1 of the wafer 10. And the processing trajectory of the laser beam L on the annular area S2 does not include the third processing trajectory T3 moving along the circumferential direction W2. In this embodiment, the second processing trajectory T2b located in the central area S1 is an annular trajectory, which can be, for example, a plurality of concentric circles with a common center point.

As described above, the laser stripping method of the present invention can release the stress generated during laser processing and avoid stress concentration in a local area of the substrate by dividing the wafer into a central area and at least one annular area, and allowing the laser beam to process along the annular area located at the periphery first, and then processing the central area located at the center. In addition, when processing the annular area, by allowing the processing path planned on the annular area to extend along the radial direction of the wafer or extend inclined to the radial direction of the wafer, the area of overlap of the laser beam spot on the wafer during processing can be reduced so as to perform processing uniformly, which helps to separate the epitaxial layer from the substrate.

Although the present invention has been disclosed as above by the embodiments, it is not intended to limit the present invention. Those with common knowledge in the technical field to which the present invention belongs may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of the patent application attached hereto.

S1: Central area S2, S2a, S2b, S2c, S2d: Annular area T1, T1a, T1b, T1c, T1d: First processing track T2a: Second processing track T3: Third processing track W1: Radial direction W2: Circumferential direction

Claims (10)

A laser stripping method is suitable for separating an epitaxial layer of a wafer from a substrate. The laser stripping method comprises: dividing a central area and at least one annular area on the wafer, wherein the at least one annular area surrounds the central area; planning a plurality of first processing tracks in the at least one annular area, and planning a plurality of second processing tracks in the central area, wherein the first processing tracks extend along the radial direction of the wafer or extend obliquely to the radial direction of the wafer; processing the at least one annular area with a laser beam along the first processing tracks, and then The laser beam processes the central area along the second processing trajectories; wherein the number of the at least one annular area is multiple, and the annular areas are arranged in sequence from an outer side to an inner side, and the step of processing the at least one annular area along the first processing trajectories with the laser beam includes processing the annular areas in sequence from the outer side to the inner side; the first processing trajectories of some of the annular areas extend along the radial direction of the wafer, and the first processing trajectories of the other part of the annular areas extend obliquely to the radial direction of the wafer. The laser stripping method as described in claim 1, wherein the first processing tracks of the annular regions adjacent to the outer side extend along the radial direction of the wafer. The laser stripping method as described in claim 1, wherein the second processing tracks include multiple straight tracks parallel to each other or multiple annular tracks arranged in sequence from the outside to the inside. The laser stripping method as described in claim 1, wherein when processing the at least one annular region, a scanning galvanometer module is used to enable the laser beam to move along a first axis and a second axis on the wafer, and a two-dimensional moving platform is used to drive the wafer to move. The laser stripping method as described in claim 1, wherein when processing the central area, a scanning galvanometer module is used to enable the laser beam to move along a first axis and a second axis on the wafer, while a two-dimensional moving platform carrying the wafer remains stationary. As described in claim 1, in the laser stripping method, when processing the at least one annular area and the central area, the laser beam is triggered by a fixed-distance pulse. The laser stripping method as described in claim 1, wherein the laser beam is a flat-top beam. A laser stripping device is suitable for separating an epitaxial layer of a wafer from a substrate, and the laser stripping device includes: a control module, suitable for dividing a central area and at least one annular area on the wafer, the at least one annular area surrounds the central area, and suitable for planning a plurality of first processing tracks in the at least one annular area, and planning a plurality of second processing tracks in the central area, wherein the first processing tracks extend along the radial direction of the wafer or extend obliquely to the radial direction of the wafer; and a laser light source, electrically connected to the control module, the control module is suitable for driving the laser light source to provide a laser beam The at least one annular region is processed along the first processing trajectories, and then the laser light source is driven to provide the laser beam to process the central region along the second processing trajectories; wherein the at least one annular region is multiple in number, the annular regions are arranged in sequence from an outer side to an inner side, and the laser beam processes the annular regions in sequence from the outer side to the inner side along the first processing trajectories; the first processing trajectories of some of the annular regions extend along the radial direction of the wafer, and the first processing trajectories of the other part of the annular regions extend obliquely to the radial direction of the wafer. The laser stripping device as described in claim 8 further includes: a scanning galvanometer module electrically connected to the control module, wherein the control module is suitable for controlling the scanning galvanometer module so that the laser beam can move along a first axis and a second axis on the wafer; and a two-dimensional moving platform electrically connected to the control module and suitable for carrying the wafer, wherein the control module is suitable for controlling the movement of the two-dimensional moving platform. The laser stripping device as described in claim 8 further includes an optical diffraction element disposed on the transmission path of the laser beam to convert the laser beam into a flat-top beam.

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