CN112786753A - LED chip and manufacturing method - Google Patents
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
- H01L33/22—Roughened surfaces, e.g. at the interface between epitaxial layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0095—Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination
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Abstract
The invention relates to an LED chip and a manufacturing method thereof, and discloses an LED chip which comprises a transparent substrate, wherein the substrate is provided with a front surface and a back surface which are opposite, an LED unit is arranged on the front surface of the substrate, a coarsened layer arranged in parallel with the front surface is arranged on the substrate, and the coarsened layer is a deteriorated layer formed by laser burning. The invention also discloses a method for coarsening the light-emitting surface of the LED chip, wherein the laser burning is used for forming the deteriorated layer in the substrate, and the laser burning trace on the deteriorated layer is used as a coarsening structure of the coarsened layer, so that the problem of low efficiency of the conventional method for coarsening the light-emitting surface by wet etching or dry etching is solved.
Description
Technical Field
The invention relates to the technical field of semiconductor solid illumination, in particular to an LED chip and a manufacturing method thereof.
Background
Light Emitting Diodes (LEDs) emit Light by energy released by recombination of electrons and holes, have high efficiency of electro-optic conversion, and are widely used in the fields of illumination, display, and the like.
In the LED chip structure, the luminous efficiency of the chip can be effectively improved by forming a pattern structure (such as a photonic crystal structure or a rough surface). The pattern structure is obtained by treating the surface of the material layer mainly by wet etching or dry etching. The wet roughening is generally performed in a high-temperature etching solution, and the non-roughened structure is required to be protected in order to avoid damaging the structure. Dry roughening is typically etching by plasma bombardment of the surface, which also needs to be performed under a mask. Thus resulting in a less efficient way of achieving a patterned structure with existing wet or dry etches.
Disclosure of Invention
The present invention is directed to an LED chip having a roughened layer formed by laser firing on or in a substrate surface thereof.
The specific scheme is as follows:
an LED chip comprises a transparent substrate, the substrate is provided with a front surface and a back surface which are opposite, the front surface of the substrate is provided with an LED unit, the substrate is provided with a coarsening layer which is arranged in parallel with the front surface, and the coarsening layer is an altered layer formed by laser burning.
In some embodiments, the roughened layer is located within or on the back side of the substrate.
In some embodiments, the roughened layer has roughened structures with a longitudinal depth recessed into the substrate.
In some embodiments, the longitudinal depth of the roughened structure is non-uniformly disposed.
In some embodiments, the sidewalls of the substrate have a roughness structure fired by a laser.
In some embodiments, the LED unit comprises a semiconductor epitaxial layer, the distance from the roughened layer to the epitaxial layer being 20 μm or more.
The invention also provides a manufacturing method of the LED chip, which comprises the following steps:
providing a transparent substrate, wherein the substrate is provided with a front surface and a back surface which are opposite, and an LED unit is formed on the front surface of the substrate;
a roughened layer parallel to the front surface is formed on the substrate, and the roughened layer is formed by laser firing to form an altered layer.
In some embodiments, the method comprises the steps of:
s00, providing an LED wafer, wherein the LED wafer comprises a substrate and a plurality of LED units located on the substrate, and the LED units are in a flip structure;
s10, carrying out surface invisible cutting on the substrate, and burning in the substrate to form a metamorphic layer parallel to the back surface of the substrate;
and S20, thinning the back surface of the substrate on the side away from the epitaxial structure, after the back surface is thinned to the target thickness, splitting the substrate to form a plurality of LED chips, wherein each LED chip has an altered layer in the substrate, and the altered layer is a coarsened layer of the LED chip.
In some embodiments, in the step S10, the altered layer is formed by laser ablation with the same depth of focus.
In some embodiments, in step S10, the altered layer is formed by laser ablation with different focal depths.
In some embodiments, in step S20, when the substrate is thinned to the target thickness, the substrate is subjected to the stress of the altered layer and is separated along the generating surface of the altered layer to expose the altered layer.
In some embodiments, there is also a step S01 between step S00 and step S10,
and S01, thinning the back of the substrate on the side away from the epitaxial structure for the first time to reduce the thickness of the substrate to the first thickness, wherein the thinned thickness is smaller than the depth of the surface type invisible cutting in the substrate.
In some embodiments, there is also a step S02 between step S01 and step S10,
and S02, performing linear invisible cutting on the substrate, wherein laser is focused to a first depth in the substrate during the linear invisible cutting so as to form a plurality of linear laser scratches in the substrate, the position of each laser scratch is located between two adjacent LED units so as to define the size of each LED chip, and the first depth is greater than the depth of the planar invisible cutting in the substrate.
In some embodiments, in step S20, when the thickness of the substrate is reduced to the target thickness, the substrate is subjected to the stress of the laser scratch to crack the LED wafer along the laser scratch, so as to form a plurality of LED chips.
In some embodiments, before performing step S20, a step of attaching a film is further included, where the step of attaching a film is to attach an adhesive film covering all the epitaxial cells on the surface of the epitaxial cells.
In some embodiments, in the step S20, the LED wafer maintains its integrity while the substrate is thinned to the target thickness.
In some embodiments, step S3 is further included: and splitting the substrate by utilizing a plurality of laser scratches formed by linear invisible cutting on the substrate to form a plurality of LED chips.
Compared with the prior art, the LED chip and the manufacturing method thereof provided by the invention have the following advantages:
1. the coarsening structure of the LED chip provided by the invention is formed by laser burning, and compared with the coarsening structure formed by the existing wet etching or dry etching, the coarsening structure does not need to be carried out under a mask, so that the processes of forming the mask before etching and removing the mask after etching are omitted, and the coarsening efficiency can be greatly increased. And the formed coarsening structure can have deeper longitudinal coarsening depth, and the deeper longitudinal coarsening depth can increase the light extraction rate of the LED chip.
2. The LED manufacturing method provided by the invention utilizes laser invisible cutting to form the coarsening structure of the light-emitting surface, the coarsening structure is not limited on the surface of the substrate, has a certain laser burning depth and better light extraction rate, and the coarsening step is combined with the splitting and grinding processes, so that the complicated photoetching and ICP (inductively coupled plasma) processes in the previous process are not needed, the process is simple, the efficiency is high, and the damage to the chip structure is small.
Drawings
Fig. 1 shows a schematic cross-sectional structure of an LED chip in embodiment 1.
Fig. 2 is a schematic cross-sectional view of another LED chip in embodiment 1.
Fig. 3 shows a schematic flow chart of a method for roughening a light emitting surface of an LED chip in embodiment 2.
Fig. 4 shows a schematic cross-sectional structure of an LED wafer in embodiment 2.
Fig. 5 is a schematic cross-sectional view of an LED wafer in example 2 after a substrate is thinned once.
Fig. 6 is a schematic cross-sectional view illustrating a substrate of an LED wafer after line-type recessive cutting in embodiment 2.
Fig. 7 is a schematic cross-sectional view of an LED wafer in example 2 after surface-type undercutting of a substrate.
Fig. 8 is a schematic cross-sectional view of an LED wafer in example 2 after the substrate is thinned twice.
Fig. 9 is a schematic cross-sectional view of an LED wafer in example 2 after the substrate is thinned twice.
Fig. 10 is a schematic cross-sectional view illustrating a cross-sectional structure of an LED wafer in example 2 after an adhesive film is attached to an epitaxial layer.
Detailed Description
To further illustrate the various embodiments, the invention provides the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the embodiments. Those skilled in the art will appreciate still other possible embodiments and advantages of the present invention with reference to these figures. Elements in the figures are not drawn to scale and like reference numerals are generally used to indicate like elements.
The invention will now be further described with reference to the accompanying drawings and detailed description.
Example 1
Referring to fig. 1 and 2, the LED chip is a flip chip, and includes a transparent substrate 10, where the substrate 10 has a front surface and a back surface opposite to the front surface, the front surface of the substrate has an LED unit 20, and the back surface of the substrate 10 is a light emitting surface.
The substrate 10 in this embodiment may be a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, or the like, and in this embodiment, the substrate is a sapphire substrate, the epitaxial structure is formed on a c-plane of the sapphire substrate, and the c-plane of the sapphire substrate is defined as a front surface, and the opposite other surface is a back surface. The substrate may be planar (i.e., the front surface of the substrate is a flat surface) or the front surface may have a patterned structure.
The LED unit 20 includes an epitaxial structure formed by an epitaxial process and an electrode structure formed by a chip process.
Specifically, the epitaxial structure includes at least a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer, which are sequentially stacked on the front surface of the substrate. For example, the first conductive type semiconductor layer in this embodiment is an N-type nitride layer 201, the active layer is a mqw layer 202, and the second conductive type semiconductor layer is a P-type nitride layer 203. The N-type nitride layer, the multi-quantum well layer and the P-type nitride layer are basic constituent units of an epitaxial structure of the LED chip, and on the basis, the epitaxial structure can further comprise other functional structure layers with an optimization effect on the performance of the LED chip. The epitaxial structure may be formed on the substrate by Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), epitaxial Growth (epitaxial Growth Technology), Atomic beam Deposition (ALD), and the like.
The chip process forms the current spreading layer 204, the DBR layer 205, the P electrode 206 and the N electrode 207 on the epitaxial structure.
In this embodiment, the substrate 10 has a rough layer 100 disposed parallel to the front surface, and the rough layer 100 is formed by laser ablation to form a modified layer.
Specifically, as shown in fig. 1, the roughened layer 100 may be located on a light-emitting surface, that is, the roughened layer 100 acts on the light-emitting surface of the LED chip.
The roughening layer 100 may also be located inside the substrate, as shown in fig. 2.
The laser ablation here refers to that a laser emitter is controlled to emit laser pulses with certain power, wavelength and focal length into a substrate according to a specific frequency so as to form an altered layer structure at a preset position in the substrate, the altered layer structure is generally a cavity or cavity with a loose material structure, when the laser pulses bombard the substrate in a dense arrangement of surface lasers or line lasers, a rough surface can be formed in the substrate or on the surface of the substrate, and the rough surface can be used as a coarsened structure. Compared with the coarsening structure formed by the existing wet etching or dry etching, the coarsening structure does not need to be carried out under a mask, so that the processes of forming the mask before etching and removing the mask after etching are omitted, and the coarsening efficiency can be greatly increased.
In some embodiments, the rough layer 100 may be obtained by laser firing with the same focal depth, or by laser firing with different focal depths, and the roughened structures on the rough layer obtained by laser firing with different depths form structures with different shapes, and the roughened structures make the roughening effect more remarkable. Compared with the coarsening structure which is realized by the anisotropy of the substrate material through the existing wet etching or dry etching, the coarsening structure formed through multiple times of laser burning can have deeper longitudinal coarsening depth, and the deeper longitudinal coarsening depth can increase the light extraction rate of the LED chip.
Example 2
The embodiment provides a method for roughening a light emitting surface of an LED chip, referring to fig. 3, which includes the following steps:
step S00: an LED wafer (wafer) is provided, the LED wafer comprising a substrate and a plurality of LED units on the substrate, each LED unit comprising an epitaxial structure formed on the substrate by an epitaxial process and an electrode formed on the epitaxial structure by a chip process.
The substrate may be a sapphire substrate, a silicon carbide substrate, a nitride substrate, or the like. In this embodiment, the substrate is a sapphire substrate, the epitaxial structure is formed on a c-plane of the sapphire substrate, and the c-plane of the sapphire substrate is defined as a front surface and the opposite other surface is defined as a back surface.
Referring to fig. 4, fig. 4 is a schematic cross-sectional structure diagram of an LED wafer in this embodiment. The epitaxial structure includes at least a first conductive type semiconductor layer, an active layer, and a second conductive type semiconductor layer sequentially stacked on a front surface of a substrate. For example, the first conductive type semiconductor layer in this embodiment is an N-type nitride layer, the active layer is a nitride-based quantum well layer, and the second conductive type semiconductor layer is a P-type nitride layer. The N-type nitride layer, the multi-quantum well layer and the P-type nitride layer are basic constituent units of an epitaxial structure of the LED chip, and on the basis, the epitaxial structure can further comprise other functional structure layers with an optimization effect on the performance of the LED chip. The epitaxial structure may be formed on the substrate by Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), epitaxial Growth (epitaxial Growth Technology), Atomic beam Deposition (ALD), and the like.
The chip manufacturing process in this embodiment may include the following steps:
(1) the size of the chip is defined by an ICP (inductively coupled plasma etching) dry etching method, and the mesa is etched to expose the N-type nitride layer.
(2) And evaporating a transparent current expansion layer on the P-type nitride layer, wherein the material of the current expansion layer can be ITO, GTO, GZO, ZnO or the combination of several materials.
(3) The first metal electrode is manufactured through photoetching and evaporation process, and the electrode material is a combination of metals such as Cr, Pt, Au, Ti, Ni, Al and the like. Wherein the first metal electrode is in contact with the current spreading layer and the N-type nitride layer, respectively.
(4) Depositing DBR layer (Bragg reflection layer) on the structure, wherein the DBR layer is SiO2、TiO2And an insulating layer of an alternating structure covering the entire chip area.
(5) Exposing the transparent current expansion layer and part of the N-type nitride layer corresponding to the first metal electrode by dry etching;
(6) and manufacturing a second metal electrode by photoetching and evaporation processes, combining the second metal electrode and the first metal to form an P, N electrode, wherein the surface layer of the P, N electrode can be made of Au material, so that a plurality of LED units with flip-chip structures are manufactured.
The chip manufacturing process is only one method provided in the present embodiment, and is not limited thereto, and other methods for implementing the LED unit with the flip-chip structure are also applicable thereto.
Step S01: and thinning the back surface of the side of the substrate, which faces away from the epitaxial structure, for the first time to reduce the thickness of the substrate to the first thickness L1.
Referring to fig. 5, fig. 5 is a schematic cross-sectional structure diagram of the substrate and the surface structure thereof after step S01.
The first thinning in this embodiment is achieved by grinding and polishing, which not only thins the thickness of the substrate, but also reduces the stress of the substrate and the epitaxial structure. In addition, the grinding and polishing can also ensure that the surface of the substrate is flattened to be transparent and bright, so as to be beneficial to the laser stealth cutting process in the next step. The first thickness L1 is greater than the target thickness, for example, a conventional sapphire substrate with a thickness of 600-750 μm is taken as an example, and the substrate is thinned to 400-500 μm after one polishing, but the invention is not limited thereto, and the invention can be determined according to the actual situation.
Step S02: and carrying out linear invisible cutting on the substrate, focusing laser at a first depth in the substrate to form a plurality of laser scratches in the substrate, wherein the position of each laser scratch is positioned between two adjacent LED units to define the size of each LED chip.
The stealth cutting is to control a laser emitter to emit laser pulses with certain power, wavelength and focal length into a substrate according to a specific frequency so as to form an altered layer structure at a preset position in the substrate, wherein the altered layer structure is generally a cavity or cavity with a loose material structure (i.e. a laser scratch), and the laser scratch can be a continuous straight line or can be formed by laser holes arranged at intervals in sequence. During invisible cutting, laser enters the substrate and forms laser scratches in the substrate, and the laser scratches form a network structure formed by the longitudinal linear channels and the transverse linear channels, so that the size of each LED chip is defined. In this embodiment, the frequency and power of the laser are not limited in the stealth dicing process, and are determined according to actual conditions.
Referring to fig. 6, fig. 6 is a schematic cross-sectional structure diagram of the substrate and its surface structure after step S02. In fig. 6, reference numeral 101 denotes a laser scratch formed by linear stealth dicing.
Step S10: and carrying out surface type invisible cutting on the substrate, focusing laser on a second depth smaller than the first depth in the substrate, and forming a burning surface parallel to the back surface of the substrate in the substrate.
It should be understood that the depth referred to in the present embodiment is based on the back surface of the substrate as a reference, and the deeper the depth, the closer the depth to the epitaxial structure.
For example, assuming that the final thickness of the chip is 100 μm, the laser focusing depth in the linear stealth cutting is 330 to 360 μm (based on the thickness after one grinding is 400 μm), and the chip is still a complete wafer after the linear laser stealth cutting without cracking due to the thicker substrate. After the linear recessing, a surface recessing is performed, and the depth of the surface recessing is set to the thickness required by the final chip, for example, in the above step, the depth of the secondary laser focus is set to 300 μm, so that the chip with the final thickness of 100 μm can be obtained. The secondary stealth laser can be surface laser or dense arrangement of line laser, the laser burns the surface in the substrate, dense metamorphic layer structures (namely forming explosion traces) are formed in the sapphire after the laser burns, and the metamorphic layer structures are uneven planes formed in the sapphire.
Referring to fig. 7, fig. 7 is a schematic cross-sectional structure diagram of the substrate and the surface structure thereof after step S10. In fig. 7, reference numeral 102 denotes an explosion trace formed by the face-type stealth dicing.
Step S20: and thinning the back surface of the side of the substrate, which faces away from the epitaxial structure, for the second time so as to thin the thickness of the substrate to the target thickness L2.
Referring to fig. 8 and 9, fig. 8 and 9 are schematic cross-sectional structural views of the substrate and the surface structure thereof after step S20. The second thinning in this embodiment is achieved by grinding and polishing.
Referring to fig. 8, when the substrate is ground to a target thickness L2, the substrate of the altered layer on the side away from the epitaxial structure is separated by the action of the internal stress on the secondary laser action surface, and the laser-burned altered layer is exposed, even if the roughened structure layer of the substrate is used as a light-emitting surface due to the secondary laser burning.
Or referring to fig. 9, when the substrate is ground to the target thickness L2, the substrate on the side away from the epitaxial structure is not ground to the altered layer, and the altered layer is still located inside the substrate, i.e. the coarsening structure layer formed by the secondary laser burning is located inside the substrate. The method for roughening the light-emitting surface of the LED chip provided by the embodiment utilizes laser invisible cutting to form the roughened structure of the light-emitting surface, the roughened structure is not limited on the surface of a substrate, a certain laser burning depth is achieved, the light extraction rate is better, the roughening step is combined with a splitting and grinding process, the previous complicated photoetching and ICP (inductively coupled plasma) process is not needed, the process is simple, and the damage to the chip structure is small.
In some embodiments, the coarsening structure can be obtained by one-time laser burning, or can be obtained by multiple laser burning with different depths, and the coarsening structures with different depths are realized together.
The primary laser ablation here means that the depth of focus of the laser beam is the same when performing the surface stealth dicing, and for example, the laser ablation is performed by densely arranging surface laser beams or line laser beams while maintaining the depth of focus of the laser beam at 300 μm. The multiple laser cauterization with different depths refers to multiple surface cauterization, the depth of each surface cauterization is different, for example, 3 surface cauterizations are included, the laser focusing depth is 300 μm during the first surface cauterization, 302 μm during the second surface cauterization, and 305 μm during the third surface cauterization, thus a coarsening structure with the longitudinal depth of about 5 μm can be formed.
In some embodiments, step S30 is further included: and splitting, namely splitting the substrate by utilizing a plurality of laser scratches formed by linear invisible cutting on the substrate to form a plurality of LED chips. The splinter process can be realized by adopting a normal cracking or dorsal cracking mode in the prior art, the specific process of normal cracking or dorsal cracking is well known to those skilled in the art, and details are not described herein.
However, this step S30 is not necessary, and the method in this embodiment may further control the depth of the plurality of laser scratches formed by the linear stealth dicing, so that when the second thinning is performed on the side of the substrate away from the epitaxial structure in step S20, after the substrate is ground and polished to the target thickness, the substrate is subjected to the stress in the laser scratches, the LED wafer is cracked along the laser scratches, and the LED wafer is directly split to form a plurality of LED chips (die). Compared with the step S30, the method combines the process flows of the secondary thinning and the splitting into one step, that is, when the secondary thinning is performed, after the substrate is ground and polished to the target thickness, the substrate is subjected to the internal stress of the laser scribing crack to generate the crack to realize the splitting, so that the splitting process in the step S3 is not needed. Because the process of splitting by using a cleaver is not needed, the difficulty of splitting the small-size chip is reduced, and the method is particularly suitable for manufacturing the small-size chip.
In order to prevent the LED wafer from splitting during the secondary thinning to form a plurality of LED chips from scattering, a film pasting step can be added before the secondary thinning.
Referring to fig. 10, fig. 10 is a schematic cross-sectional structure diagram of the substrate and its surface structure after the film attaching step. The sticking film is a sticky film which is stuck on the surface of the epitaxial unit, the sticky film has certain stickiness and can be stuck on the epitaxial unit and cover all the epitaxial units on the substrate, the sticky film has a certain protection effect by covering the epitaxial surface of the LED wafer, and a formed single LED chip can be stuck on the sticky film after the LED wafer is subjected to the splitting process. The adhesive film may be a UV film, a blue film, or the like. Reference numeral 30 in fig. 10 denotes an adhesive film.
While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (17)
1. An LED chip comprising a transparent substrate having opposing front and back surfaces, the front surface of the substrate having LED units thereon, characterized in that: the substrate has a roughened layer parallel to the front surface, and the roughened layer is an altered layer formed by laser firing.
2. The LED chip of claim 1, wherein: the roughened layer is located inside or on the back surface of the substrate.
3. The LED chip of claim 1, wherein: the roughened layer has a roughened structure having a longitudinal depth recessed into the substrate.
4. The LED chip of claim 3, wherein: the longitudinal depth of the coarsening structure is non-uniformly arranged.
5. The LED chip of claim 1, wherein: the substrate has a sidewall connecting the front and back surfaces, the sidewall having a roughness burned by a laser, the roughness being spaced from the front surface of the substrate by a distance greater than zero.
6. The LED chip of claim 1, wherein: the LED unit comprises a semiconductor epitaxial layer, and the distance from the coarsened layer to the epitaxial layer is more than 20 mu m.
7. A manufacturing method of an LED chip is characterized by comprising the following steps:
providing a transparent substrate, wherein the substrate is provided with a front surface and a back surface which are opposite, and the front surface of the substrate is provided with an LED unit;
a roughened layer parallel to the front surface is formed on the substrate, and the roughened layer is formed by laser firing to form an altered layer.
8. The method of manufacturing of claim 7, comprising the steps of:
s00, providing an LED wafer, wherein the LED wafer comprises a substrate and a plurality of LED units positioned on the substrate;
s10, carrying out surface invisible cutting on the substrate, and burning in the substrate to form a metamorphic layer parallel to the back surface of the substrate;
and S20, thinning the back surface of the substrate on the side away from the epitaxial structure, after the back surface is thinned to the target thickness, splitting the substrate to form a plurality of LED chips, wherein each LED chip has an altered layer in the substrate, and the altered layer is a coarsened layer of the LED chip.
9. The method of claim 8, wherein: in step S10, the altered layer is formed by laser ablation with the same depth of focus.
10. The method of claim 8, wherein: in step S10, the altered layer is formed by laser firing with different focal depths.
11. The method of claim 8, wherein: in step S20, when the thickness of the substrate is reduced to the target thickness, the substrate is subjected to the stress of the altered layer and is separated along the altered layer generating surface to expose the altered layer.
12. The method of claim 8, wherein: there is also step S01 between step S00 and step S10,
and S01, thinning the back of the substrate on the side away from the epitaxial structure for the first time to reduce the thickness of the substrate to the first thickness, wherein the thinned thickness is smaller than the depth of the surface type invisible cutting in the substrate.
13. The method of claim 12, wherein: there is also step S02 between step S01 and step S10,
and S02, performing linear invisible cutting on the substrate, wherein laser is focused to a first depth in the substrate during the linear invisible cutting so as to form a plurality of linear laser scratches in the substrate, the position of each laser scratch is located between two adjacent LED units so as to define the size of each LED chip, and the first depth is greater than the depth of the planar invisible cutting in the substrate.
14. The method of claim 13, wherein: in step S20, when the thickness of the substrate is reduced to the target thickness, the substrate is subjected to the stress of the laser scratch to crack the LED wafer along the laser scratch, so as to form a plurality of LED chips.
15. The method of claim 14, wherein: before the step S20, a step of attaching a film is further included, in which an adhesive film covering all the epitaxial cells is attached to the surface of the epitaxial cells.
16. The method of claim 13, wherein: in step S20, when the thickness of the substrate is reduced to the target thickness, the LED wafer maintains its integrity.
17. The method of claim 16, wherein: further comprising step S3: and splitting the substrate by utilizing a plurality of laser scratches formed by linear invisible cutting on the substrate to form a plurality of LED chips.
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