CN102672355B - Scribing method of LED (light-emitting diode) substrate - Google Patents

Abstract

The invention provides a method for scribing an LED substrate, comprising: providing an LED substrate, the LED substrate comprising a substrate and an epitaxial layer on the substrate; Focusing into a linear spot, the linear spot is focused on the substrate surface in the LED substrate and its length is greater than or equal to the diameter of the LED substrate; using the linear spot to scan the substrate , so as to form a plurality of first grooves parallel to each other on the surface of the substrate; the substrate is scanned twice by using the linear spot to form a plurality of second grooves parallel to each other on the surface of the substrate. grooves, the second grooves are perpendicular to the extension direction of the first grooves. The invention can avoid thermal damage to the LED substrate during the scribing process, and is beneficial to improving the slicing efficiency.

Description

Scribing method of LED substrate

technical field

The invention relates to a scribing method for an LED substrate, in particular to a method for scribing an LED substrate by using a femtosecond laser.

Background technique

As we all know, the LED wafer is grown on the sapphire or silicon carbide substrate by vapor deposition method based on the light-emitting active layer of gallium nitride-based materials. At present, the size of the common LED wafer is 2 inches to 4 inches. The development of the LED industry, the reduction of LED prices and the improvement of luminous efficiency have driven the popularization of LED chips, which has also driven various technologies used in the LED field.

In the process of LED chip processing, the LED substrate must first be thinned. In order to separate each LED chip before packaging, it is also necessary to draw a groove on the back of the thinned LED substrate, so that the LED wafer can be easily processed. of the lobes. The commonly used scribing methods include the early diamond prop cutting to the currently popular ultraviolet nanosecond pulse laser scribing cutting. However, an important problem in laser scribing is that the excessively high laser energy at the focal point during the scribing process causes thermal damage, which leads to the diffusion of cracks near the scribing, or the reduction of luminous efficiency caused by thermal melting. Another problem of laser scribing is the scribing efficiency. From the early 3 pieces/hour to the current mainstream 10 pieces/hour, the speed of scribing efficiency has become the core competitive factor of laser scribing machines.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for scribing LED substrates, which can avoid thermal damage to the LED substrate during the slicing process and is beneficial to improve scribing efficiency.

In order to solve the above technical problems, the present invention provides a method for scribing LED substrates, including:

providing an LED substrate comprising a substrate and an epitaxial layer on the substrate;

Using a femtosecond laser system to focus femtosecond pulsed laser light into a linear spot, the linear spot is focused on the substrate surface in the LED substrate and its length is greater than or equal to the diameter of the LED substrate;

scanning the substrate by using the linear spot to form a plurality of first grooves parallel to each other on the surface of the substrate;

The substrate is scanned twice by using the linear spot to form a plurality of second grooves parallel to each other on the surface of the substrate, and the second grooves are perpendicular to the extending direction of the first grooves.

Optionally, the femtosecond laser system includes:

Femtosecond pulsed seed laser source;

The laser amplification and beam expansion device performs energy amplification, beam expansion and line focusing on the femtosecond pulse laser emitted by the femtosecond pulse seed laser source, and outputs the linear spot;

The carrying part is used for carrying the LED substrate, wherein the epitaxial layer faces the carrying part.

Optionally, the laser amplification and beam expansion device includes:

A laser amplifier, which amplifies the energy of the femtosecond pulsed laser;

A beam expander lens combination device, which expands the laser beam from the laser amplifier so that its size covers the LED substrate;

The cylindrical lens performs line focusing on the laser beam from the beam expander lens combination device, and outputs the linear light spot.

Optionally, the laser amplifier amplifies the femtosecond pulsed laser into a laser beam in the order of mJ~J.

Optionally, the laser amplification and beam expansion device also includes:

An optical gate, the laser beam output by the laser amplifier passes through the optical gate and then is transmitted to the beam expander lens combination device.

Optionally, the femtosecond laser system also includes:

a stepping motor, driving the carrying part to drive the LED substrate to move in a direction perpendicular to the linear light spot, the LED substrate is divided into multiple steps in the direction perpendicular to the linear light spot, the The stepping motor drives the LED substrate to move step by step so that the linear light spot scans the LED substrate step by step.

Optionally, the femtosecond laser system also includes:

A synchronous controller is used to synchronously control the stepping motor and the light gate, so that the number of laser pulses irradiated on the LED substrate after each step of the stepping motor is the same.

Optionally, the beam expander lens combination device includes a first circular convex lens and a second circular convex lens, and the laser beam from the laser amplifier sequentially passes through the first circular convex lens and the second circular convex lens before exiting , wherein the focal length of the first circular convex lens is smaller than the focal length of the second circular convex lens, and the distance between the first circular convex lens and the second circular convex lens is equal to the sum of their focal lengths.

Optionally, the femtosecond laser system also includes:

The adjusting mechanism is used to drive the cylindrical lens and each convex lens in the combination device of the beam expander to translate, and the direction of translation is along the propagating direction of the laser beam from the laser amplifier.

Optionally, the laser amplifier includes: a Glan prism, a Faraday isolator, a half-wave plate, a laser resonator, and a pump laser, wherein,

The femtosecond pulsed laser light emitted by the femtosecond pulsed seed laser source is reflected by the Glan prism and then sequentially passes through the Faraday isolator and the half-wave plate and enters one side of the laser resonator;

The pump laser emitted by the pump laser enters the other side of the laser resonator;

The energy-amplified laser beam emitted by the laser resonant cavity sequentially passes through the half-wave plate, the Faraday isolator and the Glan prism before exiting.

Optionally, the laser resonator includes: a first reflection mirror located on one side of the laser resonator, a concave mirror located on the other side of the laser resonator, a titanium sapphire crystal, a thin film polarizer, and a Pockels cell ,in,

The pump laser light emitted by the pump laser enters the titanium sapphire crystal through the concave mirror;

The femtosecond pulsed laser emitted by the half-wave plate is reflected by the thin film polarizer and then enters the first reflector through the Pockels cell, and the femtosecond pulsed laser reflected by the first reflector is transmitted through the Pockels cell. After passing through the Pockels cell and thin-film polarizer, it enters the titanium-sapphire crystal, and the light spots of the femtosecond pulsed laser and the pump laser overlap in the titanium-sapphire crystal.

Optionally, using the linear light spot to scan the substrate a second time includes: keeping the extension direction of the linear light spot unchanged, rotating the LED substrate by 90°, and then using the linear light spot The substrate is scanned a second time.

Optionally, a protective film is also provided between the carrying component and the epitaxial layer.

Optionally, the peak power of the linear light spot is 10 ¹² -10 ¹⁵ W.

Compared with the prior art, the present invention has the following advantages:

In the method for scribing an LED substrate according to the embodiment of the present invention, the femtosecond pulsed laser is focused into a linear light spot, and the linear light spot is focused on the substrate surface of the LED substrate. After the second scan, a first groove and a second groove perpendicular to each other are respectively formed on the surface of the substrate. Since the pulse time of the femtosecond laser is one millionth of the pulse time of the ordinary nanosecond laser, which is much shorter than the time for the heat generated by the laser to transfer to the lattice, it can completely eliminate the interaction between the laser and the LED substrate material. The resulting thermal damage has an impact on the LED substrate, and is conducive to improving production efficiency.

Description of drawings

Fig. 1 is the schematic flow chart of the scribing method of the LED substrate of the embodiment of the present invention;

Fig. 2 is the structural block diagram of the femtosecond laser system of the embodiment of the present invention;

Fig. 3 is a detailed structural diagram of the laser amplifier in Fig. 2;

4 is a cross-sectional view of an LED substrate placed on a carrier part in an embodiment of the present invention;

5 is a top view of the LED substrate after scribing in the embodiment of the present invention;

Fig. 6 is a cross-sectional view of an LED substrate after dicing in an embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Fig. 1 shows the flowchart of the scribing method of the LED substrate of the present embodiment, including:

Step S11, providing an LED substrate, the LED substrate comprising a substrate and an epitaxial layer on the substrate;

Step S12, using a femtosecond laser system to focus the femtosecond pulse laser into a linear spot, the linear spot is focused on the substrate surface in the LED substrate and its length is greater than or equal to the diameter of the LED substrate;

Step S13, scanning the substrate with the linear spot to form a plurality of first grooves parallel to each other on the surface of the substrate;

Step S14, using the linear spot to scan the substrate twice to form a plurality of second grooves parallel to each other on the surface of the substrate, the extension of the second grooves and the first grooves Direction is vertical.

Fig. 2 has shown the femtosecond laser system that the present embodiment adopts, comprises: femtosecond pulse seed laser source 12, laser amplification beam expander (comprising laser amplifier 20, shutter 21, beam expander lens combination device, cylindrical lens 11 ), the bearing part 8, and the synchronization controller 22.

Wherein, the femtosecond pulse seed laser source 12 is used to emit femtosecond pulse laser. As a non-limiting example, the femtosecond pulse seed laser source 12 in this embodiment can be realized by a mode-locked fiber femtosecond laser, and the specific parameters are as follows: the pulse width is between 20 ~ 150fs, the center wavelength is 800nm, and the repetition rate is 20~80MHz, the pulse energy is in the order of nJ~μJ, and the diameter of the circular spot emitted is 5mm~10mm.

The femtosecond pulse laser emitted by the femtosecond pulse seed laser source 12 passes through the laser amplifier 20, the shutter 21, the first convex lens 9, the second convex lens 10, and the cylindrical lens 11 in sequence, and then enters the LED substrate on the bearing part 8. In this embodiment, the LED substrate includes a stacked substrate 100 and an epitaxial layer 101, wherein the epitaxial layer 101 faces the carrying part 8, the substrate 100 faces the direction in which the femtosecond pulsed laser is incident, and there is a gap between the epitaxial layer 101 and the carrying part 8. A protective film 102 may be provided to prevent damage to the epitaxial layer 101 .

As shown in FIG. 2, in this embodiment, the plane where the surface of the LED substrate (more specifically, the surface on which the scribing operation will be performed on the substrate 100) is located is defined as the x-y plane, and the direction in which the femtosecond pulsed laser propagates is defined as the z direction. The z direction is perpendicular to the x-y plane.

The laser amplification and beam expansion device is used for energy amplification, beam expansion and line focusing of the femtosecond pulsed laser, and outputs a linear spot whose length is greater than or equal to the diameter of the LED substrate. In this embodiment, the laser amplification and beam expansion device includes: a laser amplifier 20, which amplifies the energy of the femtosecond pulse laser; a beam expansion lens combination device, which expands the laser beam from the laser amplifier so that its size can cover the entire LED Substrate; Cylindrical lens 11, which performs line focusing on the laser beam from the beam expander lens combination device, and outputs a linear spot. In addition, the laser amplification and beam expansion device also includes: an optical gate 21, the laser beam output by the laser amplifier 20 is transmitted to the beam expander lens combination device after passing through the optical gate, and the opening and closing of the optical gate 21 can control whether the laser beam exits.

Wherein, the beam expander lens combination device comprises a first circular convex lens 9 and a second circular convex lens 10, and the laser beam is emitted after passing through the first circular convex lens 9 and the second circular convex lens 10 in sequence, wherein the first circular convex lens The focal length 9 is smaller than the focal length of the second circular convex lens 10, and the distance between the first circular convex lens 9 and the second circular convex lens 10 is equal to the sum of their focal lengths. More specifically, the focal length of the second circular convex lens 10 is 5 to 10 times the focal length of the first circular convex lens 9, so that the light spot is enlarged from the original size of 5 mm to 10 mm to cover the entire LED substrate, for example, for a 2-inch LED For the substrate, the diameter of the expanded laser beam is 60 mm. For epitaxial wafers with a size of 4 inches or larger, more sets of circular convex lens combinations can be used to continuously expand the laser spot size. The femtosecond laser system of this embodiment also includes an adjustment mechanism (not shown in FIG. 1 ), which can adjust the positions of the first circular convex lens 9 and the second circular convex lens 10 along the optical axis, that is, can drive the first circular convex lens 9 and the second circular convex lens 10 translate along the direction of laser beam propagation.

The expanded laser beam passes through the cylindrical lens 11 to line-focus the laser beam and compress the spot in a single direction of x or y to form a linear spot. In addition, the adjustment structure in this embodiment can also translate the cylindrical lens 11, so as to adjust the focus position of the linear light spot to a predetermined area in the LED substrate, such as the surface or inside of the LED substrate. Due to the previous beam expansion, the length of the linear light spot emitted by the cylindrical lens 11 is equal to or greater than the diameter of the LED substrate.

In this embodiment, the carrying part 8 is driven by a stepping motor (not shown in FIG. 2 ), which can drive the LED substrate to move in a direction perpendicular to the linear light spot, for example, in the x direction or the y direction. For example, the LED substrate can be divided into multiple steps in a direction perpendicular to the linear light spot, and the stepping motor drives the LED substrate to move step by step, so that the linear light spot gradually scans the entire LED substrate.

The synchronous controller 22 can synchronously control the shutter 21 and the stepping motor, that is, control the stepping motor to drive the LED substrate to scan step by step, and control the exposure time of the shutter 21 corresponding to each scanning step. In this embodiment, the synchronous controller 22 sends a 100Hz~200Hz trigger pulse signal to the stepper motor and the shutter 21, and the exposure time of the shutter 21 and the time for the stepper motor to stay in each scanning step are set to 5ms~ 10ms, so that the number of laser pulses irradiated on the LED substrate in each scanning step is the same, which is 5-10, which is beneficial to ensure that the surface of the thinned LED substrate has good uniformity.

In addition, in this embodiment, the stepper motor controls the entire LED substrate to perform one-dimensional scanning in the direction perpendicular to the linear spot, and finally achieves the purpose of processing the entire LED substrate. This scanning method is different from the conventional repeated point Compared with array scanning, the processing time is greatly shortened and the production efficiency is improved.

The laser amplifier 20 can amplify the femtosecond pulsed laser into a laser beam in the order of mJ~J, and its specific structure can be any suitable amplifier structure known to those skilled in the art. Fig. 2 shows the concrete structure of the laser amplifier in the present embodiment, mainly comprises: Glan prism 35, Faraday isolator 34, half-wave plate 33, laser cavity, pumping laser 40, wherein, laser cavity comprises: Concave mirror 24 , titanium sapphire crystal 25 , thin film polarizer 29 , Speckel cell 30 , first reflector 31 .

The femtosecond pulsed laser light emitted by the femtosecond pulse seed laser source 12 is reflected by the mirror 36 to the Glan prism 35, and then passed through the Faraday isolator 34 and the half-wave plate 33 in sequence after being reflected by the Glan prism 35, and then passes through the reflector 32 Enter the laser resonant cavity after the reflection of and 28, in the laser resonant cavity, enter the Pockels cell 30 after the reflection of the film polarizer 29, after passing through the Pockels cell 30, it is reflected back to the Pockels by the first mirror 31 again The Pockels cell 30 passes through the Pockels cell 30 and then transmits to the reflector 27 through the film polarizer 29, and enters the titanium sapphire crystal 25 through the reflection of the reflector 27 and the reflector 26. On the other hand, the pumping laser light emitted by the pumping laser 40 passes through the convex lens 41, is reflected by the mirror 23 and enters the laser resonator cavity, and enters the titanium sapphire crystal 25 after passing through the concave mirror 24 in the laser resonator cavity. The light spots formed by the second pulse laser on the titanium sapphire crystal 25 overlap.

When the femtosecond pulse laser emitted by the femtosecond pulse seed laser source 12 passes through the laser amplifier, the energy of the pump laser 40 is continuously absorbed, so that the optical pulse energy of the femtosecond pulse laser reaches the mJ-J level from the nJ-uJ level, The repetition rate is 1kHz. The specific working process of the laser amplifier is as follows: firstly, the femtosecond pulse laser emitted by the femtosecond pulse seed laser source 12 is reflected by the plane mirror 36 and enters the laser amplifier. In the laser amplifier, the pumping laser 40 emits pumping laser light with a wavelength of 527nm, and the pumping laser enters the amplifying resonant cavity through the convex lens 41 and the reflecting mirror 23, and the two sides of the amplifying resonating cavity are concave mirror 24 and the first reflecting mirror respectively 31. The gain material in the cavity is titanium sapphire crystal 25. Firstly, the energy of the pump laser is concentrated on the titanium sapphire crystal 25, so that it achieves population inversion and forms a precondition for the femtosecond pulsed laser to be amplified. In addition, the femtosecond pulsed laser reflected by the reflector 36 is reflected by the Glan prism 35, passes through the Faraday isolator 34 and the half-wave plate 33, is reflected by the reflectors 32 and 28 and enters the laser resonant cavity, and the femtosecond pulsed laser is in the laser resonator The cavity continuously passes through the titanium sapphire crystal 25 in the particle number inversion state through oscillation, so that the pulse energy of the femtosecond pulse laser is continuously amplified. Moreover, a Pockels cell 30 and a thin-film polarizer 29 are installed in the laser resonator, so that the laser resonator is in a Q-switched operating state, so that the femtosecond pulsed laser is in the P polarization state when it oscillates in the laser resonator. When the voltage of Kerr cell 30 is high, the polarization state of the femtosecond pulsed laser is transformed into S polarization, thereby reflected by the film polarizer 29 to the outside of the laser resonator, and then reflected by the mirrors 28 and 32, making it pass through the half-wave plate 33 again And the Faraday isolator 34, adjusting the half-wave plate 33 to convert the output laser from S polarization to P polarization, and finally the Glan prism 35 transmits the laser beam with the output energy of mJ-J, and its repetition frequency is 1KHz. After the laser beam is linearly focused by the cylindrical lens 11, the peak power of the linear spot at the focal point is 10 ¹² -10 ¹⁵ W.

The femtosecond laser system provided in this embodiment vaporizes the wide-bandgap LED substrate material through a laser with extremely high instantaneous energy. Reaching an exponential increase, the material will produce a severe nonlinear effect at the linear spot, resulting in a multi-photon absorption process, that is to say, at the laser focus, the material substance can absorb multiple photon energies at the same time, so that for visible light Transparent wide-bandgap substances (such as sapphire) can absorb photon energy in the visible light band (such as femtosecond lasers are usually located in near-infrared light waves), so as to achieve the purpose of decomposing the substrate material. Such a process greatly eliminates the selectivity of materials to wavelength in laser processing, and greatly flexibly selects the area of laser processing materials. Moreover, during femtosecond laser processing of LED substrates, the absorption of laser pulse energy by the substrate material is completed within femtoseconds, which is much shorter than the time for the heat generated by the laser to transfer to the crystal lattice (usually picoseconds order of magnitude), thus eliminating the thermal effect caused by the interaction between the laser and the material, thereby completely eliminating the influence of thermal damage on the epitaxial layer, and the topography quality of the laser processed area is also improved.

Fig. 4 is a cross-sectional view of the LED substrate placed on the carrier part 8, Fig. 5 is a top view of the LED substrate after slicing, and Fig. 6 is a cross-sectional view of the LED substrate after slicing, the following is combined with Fig. 2 and 4 to 6 describe the scribing method of the LED substrate in this embodiment in detail.

First, an LED substrate is provided, and the LED substrate includes a substrate 100 and an epitaxial layer 101 on the substrate 100 .

Then place the LED substrate on the carrying part 8 , the epitaxial layer 101 in the LED substrate faces the carrying part 8 , and the substrate 100 faces the laser incident direction. In this embodiment, a protective film 102 is also provided between the carrying component 8 and the epitaxial layer 101 . For example, the epitaxial layer 101 can be pasted on the protective film 102 and then placed on the carrier part 8 .

Next, focus the linear light spot output by the laser amplifier and beam expander on the surface of the substrate 100 . Specifically, on the optical path along the laser beam propagation, the positions of the first circular convex lens 9 and the second circular convex lens 10 are adjusted so that the laser beam emitted by the second circular convex lens is collimated, and the original spot size The expansion from the original diameter of 5 mm to 10 mm can cover the entire substrate 100 . Of course, in other specific embodiments, if the size of the light spot is still smaller than the size of the LED substrate after being combined by a group of circular convex lenses, a group of Or a combination of multiple groups of circular convex lenses to continuously expand the spot size until it can cover the entire LED substrate, and at the same time adjust the horizontal position of each circular convex lens to ensure that the laser beam passing through the last circular lens is collimated. The expanded and collimated laser beam emitted from the second circular convex lens 10 passes through the cylindrical lens 11 for line focusing. By adjusting the position of the cylindrical lens 11 along the optical path, the focal point is on the surface of the substrate 100, and the focused linear The length of the light spot is greater than or equal to the diameter of the LED substrate.

Afterwards, the carrying member 8 is driven to gradually move and scan in a direction perpendicular to the linear spot, and a plurality of first grooves parallel to each other are formed on the surface of the substrate 100 . Specifically, the synchronous controller 22 can be programmed to synchronously control the stepping motor and the shutter 21, that is, the exposure time of the shutter 21 and the time that the stepping motor stays in each scanning step are set as preset time , for example 5ms~10ms. Set the scanning mode of the stepping motor, and control the scanning direction of the bearing part 8 along the direction perpendicular to the linear spot, that is, along the x direction (if the linear spot is along the y direction) or the y direction (if the linear spot is along the y direction) ) to scan once.

Rotate the whole LED substrate afterwards, for example after rotating 90°, make the extension direction of the first groove perpendicular to the extension direction of the linear light spot, and drive the bearing part 8 to perform secondary scanning along the direction perpendicular to the linear light spot, A plurality of second grooves are formed on the surface of 100, and the extension direction of the second grooves is perpendicular to the first grooves, forming a network structure as shown in FIG. 5 . The compensation for the above two scans can be set according to the size of chips of different sizes, forming the first and second grooves intersecting in a network, which is convenient for the subsequent chip separation process.

In the prior art, the pulse time of traditional nanosecond lasers used for processing LED substrates is fixed at the nanosecond ( ^10-6 s) level, and the output pulse energy is at the mJ-J level, even if the laser focused through the lens way, the peak power at the focal point is only on the order of megawatts (10 ⁶ W), and it is difficult to reach the threshold of the nonlinear effect of sapphire materials. Sapphire materials cannot absorb laser energy efficiently, so it is difficult to effectively vaporize sapphire materials to achieve processing purpose of the substrate. On the other hand, even if the groove is formed on the substrate by continuously increasing the pulse output energy of the laser to meet the laser energy threshold required for the vaporization of the sapphire material, the first disadvantage is that the excessive laser pulse output energy interacts with the material. When it acts, it will produce strong stress diffusion, which will seriously affect the epitaxial layer. In addition, due to the long pulse time of nanosecond lasers, the process of processing materials is accompanied by thermal damage. Excessive laser pulse output energy will make this thermal damage more serious and destroy the epitaxial layer of the entire LED substrate.

However, in this embodiment, the energy of the laser ^beam output by the laser amplifier 20 is also on the order of mJ~J, which avoids the negative impact of excessive output energy of the laser pulse. On the order of ¹⁵ W, such a peak power can easily reach the energy threshold of sapphire material and achieve the purpose of processing sapphire substrate. At the same time, since the pulse time of the femtosecond laser is much shorter than that of the nanosecond laser, it means that the time for the interaction between the laser and the material is much shorter than the time for the heat generated by the interaction between the laser and the material to be transferred to the material lattice, so in In the process of processing the sapphire substrate, the influence of thermal damage on the epitaxial layer can be eliminated.

It should be noted that before scribing the substrate 100, the substrate 100 can also be thinned and planarized, and the thinning process can also be completed by using the femtosecond laser system shown in FIG. The linear light spot is focused inside the substrate 100 and then scanned in a direction perpendicular to the linear light spot.

In addition, the substrate material in the LED substrate in this embodiment is sapphire, but in other specific embodiments, it can also be silicon carbide, aluminum oxide, gallium nitride, zinc oxide, etc.

Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection should be based on the scope defined by the claims of the present invention.

Claims (11)

1. A method for scribing LED substrates, characterized in that, comprising: providing an LED substrate comprising a substrate and an epitaxial layer on the substrate; Using a femtosecond laser system to focus femtosecond pulsed laser light into a linear spot, the linear spot is focused on the substrate surface in the LED substrate and its length is greater than or equal to the diameter of the LED substrate; The substrate is scanned by using the linear light spot to form a plurality of first grooves parallel to each other on the surface of the substrate, and the scanning is that the LED substrate is in a direction perpendicular to the linear light spot. One-dimensional scanning on scanning the substrate twice by using the linear spot to form a plurality of second grooves parallel to each other on the surface of the substrate, the second grooves being perpendicular to the extending direction of the first grooves, The second scan is a one-dimensional scan of the LED substrate in a direction perpendicular to the linear spot; Wherein, the femtosecond laser system includes: Femtosecond pulsed seed laser source; The laser amplification and beam expansion device performs energy amplification, beam expansion and line focusing on the femtosecond pulse laser emitted by the femtosecond pulse seed laser source, and outputs the linear spot; a carrying part for carrying the LED substrate, wherein the epitaxial layer faces the carrying part; The laser amplification and beam expansion device includes: A laser amplifier, which amplifies the energy of the femtosecond pulsed laser, and the laser amplifier amplifies the femtosecond pulsed laser into a laser beam on the order of mJ to J; A beam expander lens combination device, which expands the laser beam from the laser amplifier so that its size covers the LED substrate; The cylindrical lens performs line focusing on the laser beam from the beam expander lens combination device, and outputs the linear light spot. 2. The scribing method of the LED substrate according to claim 1, wherein the laser beam amplification device further comprises: An optical gate, the laser beam output by the laser amplifier passes through the optical gate and then is transmitted to the beam expander lens combination device. 3. The scribing method of LED substrate according to claim 2, is characterized in that, described femtosecond laser system also comprises: a stepping motor, driving the carrying part to drive the LED substrate to move in a direction perpendicular to the linear light spot, the LED substrate is divided into multiple steps in the direction perpendicular to the linear light spot, the The stepping motor drives the LED substrate to move step by step so that the linear light spot scans the LED substrate step by step. 4. The dicing method of the LED substrate according to claim 3, wherein the femtosecond laser system further comprises: A synchronous controller is used to synchronously control the stepping motor and the light gate, so that the number of laser pulses irradiated on the LED substrate after each step of the stepping motor is the same. 5. The method for scribing LED substrates according to claim 1, wherein the beam expander lens combination device comprises a first circular convex lens and a second circular convex lens, and the laser beams from the laser amplifier are sequentially After passing through the first circular convex lens and the second circular convex lens, the focal length of the first circular convex lens is smaller than the focal length of the second circular convex lens, and the distance between the first circular convex lens and the second circular convex lens is The distance between them is equal to the sum of their focal lengths. 6. The dicing method of the LED substrate according to claim 5, wherein the femtosecond laser system further comprises: The adjusting mechanism is used to drive the cylindrical lens and each convex lens in the combination device of the beam expander lens to translate, and the direction of translation is along the propagating direction of the laser beam from the laser amplifier. 7. The scribing method of the LED substrate according to claim 1, wherein the laser amplifier comprises: a Glan prism, a Faraday isolator, a half-wave plate, a laser resonator, and a pump laser, wherein, The femtosecond pulsed laser light emitted by the femtosecond pulsed seed laser source is reflected by the Glan prism and then sequentially passes through the Faraday isolator and the half-wave plate and enters one side of the laser resonator; The pump laser emitted by the pump laser enters the other side of the laser resonator; The energy-amplified laser beam emitted by the laser resonant cavity sequentially passes through the half-wave plate, the Faraday isolator and the Glan prism before exiting. 8. The method for scribing LED substrates according to claim 7, wherein the laser resonant cavity comprises: a first mirror located on one side of the laser resonant cavity, and a first reflector located on the other side of the laser resonant cavity side concave mirror, titanium sapphire crystal, thin film polarizer, Pockels cell, among them, The pump laser light emitted by the pump laser enters the titanium sapphire crystal through the concave mirror; The femtosecond pulsed laser emitted by the half-wave plate is reflected by the film polarizer and then enters the first reflector through the Pockels cell, and the femtosecond pulsed laser reflected by the first reflector is transmitted through the first reflector. After passing through the Pockels cell and thin-film polarizer, it enters the titanium-sapphire crystal, and the light spots of the femtosecond pulsed laser and the pump laser overlap in the titanium-sapphire crystal. 9. The method for scribing LED substrates according to claim 1, wherein the second scan of the substrate using the linear light spot comprises: keeping the extending direction of the linear light spot unchanged, The LED substrate is rotated by 90°, and then the substrate is scanned twice with the linear light spot. 10 . The method for dicing LED substrates according to claim 1 , wherein a protective film is also provided between the carrying member and the epitaxial layer. 11 . 11. The method for scribing LED substrates according to any one of claims 1 to 10, wherein the peak power of the linear light spot is 10 ¹² -10 ¹⁵ W.