CN107622977B - Progressive laser stripping process for micron-sized sapphire substrate - Google Patents
Progressive laser stripping process for micron-sized sapphire substrate Download PDFInfo
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- CN107622977B CN107622977B CN201710776207.1A CN201710776207A CN107622977B CN 107622977 B CN107622977 B CN 107622977B CN 201710776207 A CN201710776207 A CN 201710776207A CN 107622977 B CN107622977 B CN 107622977B
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Abstract
The invention discloses a progressive laser peeling process for a micron-sized sapphire substrate, which comprises the following steps: 1) growing a required epitaxial layer on the surface of the sapphire substrate, and dividing a unit region of the epitaxial layer according to the requirement; 2) filling conductive insulating material between the cell regions as required: 3) bonding the epitaxial layer and the transfer substrate together; 4) and performing point-by-point scanning in an outside-in linear progressive scanning mode by using a single-beam or double-beam laser irradiation mode in a counterclockwise or clockwise direction to realize the separation of the sapphire substrate and the epitaxial layer and obtain a good stripping effect.
Description
Technical Field
The invention belongs to the field of high-precision laser processing, and particularly relates to a progressive laser stripping process for a micron-sized sapphire substrate.
Background
A visible Light and ultraviolet band Light Emitting Diode (LED) based on a III-N material system gradually realizes high-efficiency Light emission of infrared, red Light, green Light, blue Light and ultraviolet bands from the 60 th century, the semiconductor lighting technology is rapidly developed, the Light emitting efficiency of products is continuously improved, the traditional lighting mode is replaced to become a mainstream technology of the market, and the scale of the application market of the LED reaches hundreds of millions of yuan at the present stage, so that the III-N material has a very wide market development prospect.
The LED generally adopts a sapphire material as an epitaxial substrate, and an epitaxial structure layer is grown by utilizing a Metal Organic Chemical Vapor Deposition (MOCVD) technology, but the manufacturing and development of the high-power LED are seriously influenced due to the large lattice mismatch and thermal mismatch between the sapphire and a III-N material system and the poor heat-conducting property and electric conductivity of the material. The most common planar LED is formed by etching the P-GaN layer to the N-GaN layer using dry etching to expose the N-type contact region, and forming the N-type P-type electrode on the same side of the chip surface. The current flows through a luminous area of the LED along the horizontal direction, and because the transverse injection of electrons starts from one electrode to the other electrode, the current density distribution is uneven on the way, the current congestion effect is generated, meanwhile, the luminous is uneven, the heat distribution is uneven, the rapid aging and failure of the device are easily caused, and the size of a single LED chip and the luminous of the device are limited.
The technical bottleneck problem can be solved by adopting the vertical structure chip technology. The vertical structure chip puts two electrodes of LED in the both sides of LED film, and the electric current flows through the device along the vertical direction, promotes single-chip work current density by a wide margin, can prepare jumbo size list LED chip, thoroughly solves the insulating and not good problem of heat dissipation of sapphire simultaneously. The manufacture of the LED chip with the vertical structure mainly adopts a substrate transfer technology, firstly, channels among the chips are processed on an epitaxial layer, then the transfer substrate and the epitaxial wafer are bonded together by utilizing a wafer bonding technology, then, the epitaxial layer is irradiated by utilizing excimer laser from one side of sapphire, the sapphire substrate is removed by utilizing a laser stripping technology, and the epitaxial layer is transferred to other substrates with good electric conduction and heat conduction performances. At present, the most common laser stripping processing mode is to strip sapphire and an epitaxial layer in a reciprocating continuous progressive mode along the horizontal direction or the vertical direction, the method is simple in process and relatively low in requirements on equipment hardware and programming, but when laser irradiates an epitaxial layer interface, the epitaxial layer absorbs laser energy to decompose and generates large stress release and high-pressure nitrogen impact, and the reciprocating continuous progressive processing in the direction can seriously impact an un-stripped epitaxial function zone in the adjacent region, so that material damage is easily caused, the failure of a device or the leakage condition of the device is remarkably aggravated, and finally the process yield and the reliability of the device are greatly reduced.
Disclosure of Invention
The invention aims to provide a progressive micro-scale sapphire substrate laser stripping process, wherein a laser spot realizes the stripping of a sapphire substrate and an epitaxial layer according to an outside-in linear progressive point-by-point scanning mode, high-pressure nitrogen generated at the stripping moment can be more effectively released from the stripped periphery because the laser spot starts scanning from the periphery of a processed sample, so that the influence of the high-pressure nitrogen on adjacent devices at the laser stripping moment due to impact of the high-pressure nitrogen can be greatly reduced, the requirements on equipment movement and program execution complexity are greatly reduced in the linear spot moving mode compared with the circular or arc-shaped spiral outside-in progressive mode, meanwhile, the complete connection or spot overlapping of a stripping area can be more easily realized in a square or rectangular laser spot compared with a circular spot, and the stripping process period can be shortened by adopting a double-beam processing mode, by adopting the laser stripping process method, the stripping yield of the sapphire substrate can be effectively improved, and a better solution is provided for the large-scale production of the sapphire substrate.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme:
a progressive laser peeling process for a micron-sized sapphire substrate comprises the following steps:
1) the method comprises the steps of finishing growth of an epitaxial layer on a sapphire substrate, dividing unit regions of the epitaxial layer to form channels, preparing a hard or flexible conductive insulating layer in the channels among the unit regions of the epitaxial layer, and then preparing a first bonding layer on the surface of the epitaxial layer;
2) preparing a second adhesive layer on the whole transfer substrate;
3) adhering the first adhesive layer and the second adhesive layer together to join the transfer substrate and the epitaxial layer together;
4) selecting the shape of a light spot, laser energy and a laser beam, carrying out micron-scale movement by using the light spot or a carrier, and finally completely separating the sapphire substrate from the epitaxial layer by adopting linear inward progressive point-by-point scanning.
The further improvement of the invention is that in the step 4), the method also comprises a light spot overlapping irradiation stripping mode and a double-beam irradiation mode for carrying out laser stripping on the epitaxial layer.
The invention is further improved in that the area of the overlapping area of the laser spots is adjustable within the range of 10% -90%.
The further improvement of the invention is that in the step 4), the laser processing mode is to scan the light spots point by point in a micron-scale moving mode in a linear progressive mode from outside to inside.
The invention has the further improvement that the light spots adopt various light beam irradiation modes, the laser stripping of the sapphire substrate is realized by adopting a mode of whether the light spots are overlapped, and the laser stripping is realized by adopting a single light beam or double light beams in various light beam irradiation modes.
The invention is further improved in that the laser is a pulse or continuous laser light source, the light spot of the laser is square or rectangular, and the side length size of the laser is adjustable between tens of microns and thousands of microns.
The invention is further improved in that the scanning is performed in a straight line type progressive mode from outside to inside in a clockwise or anticlockwise direction and point by point from outside to inside according to the side length of the square or the rectangle.
The invention is further improved in that the micron-scale moving distance of the laser processing light spot is adjustable within the range of tens to thousands of microns.
A further improvement of the invention is that the movement in the micrometer range is effected by laser spot movement or carrier movement.
The invention has the following advantages:
compared with the existing horizontal or vertical reciprocating type sapphire substrate laser lift-off technology, the invention realizes the lift-off of the sapphire substrate by adopting a point-by-point scanning mode according to an outside-in linear type progressive mode and micron-scale movement. The method has the advantages that the process capability of the existing equipment is fully utilized, the modification and the complex moving programming of the machine hardware are reduced, the samples can be processed in batches, and the process complexity is reduced; meanwhile, a point-by-point scanning mode from outside to inside is adopted, the performance deterioration of devices possibly caused by two influences of high-pressure nitrogen impact and stress release at an interface at the moment of stripping is greatly reduced, the product and process yield is improved, the stripping process yield can be improved by more than 10% under the existing single-beam laser stripping process condition through process verification, and the method is suitable for large-scale batch production.
Drawings
FIG. 1 is a schematic view of a sapphire substrate and its epitaxial layer structure
FIG. 2 is a schematic view of a laser lift-off process according to example 1.
FIG. 3 is a schematic diagram of a laser lift-off process in accordance with example 2.
In the figure, 100-sapphire substrate, 101-epitaxial layer, 102-laser beam.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments.
Example 1:
the invention provides a progressive micro-scale sapphire substrate laser stripping process which specifically comprises the following steps:
(1) firstly, preparing a gallium nitride LED epitaxial layer 101 on a sapphire substrate 100 by using an epitaxial growth method, wherein the total thickness of the epitaxial layer 101 is controlled to be 5-10 microns; the device comprises a Buffer layer, an unintended doped layer U-GaN, heavily doped N-GaN, a multi-quantum well MQW, an electron blocking layer EBL and heavily doped P-GaN. The epitaxial growth method may be metal chemical vapor deposition, laser assisted molecular beam epitaxy, laser sputtering, or hydride vapor phase epitaxy. The deposited epitaxial film may be amorphous, polycrystalline, or single crystal structure, including but not limited to one of a mirror or micro/nano patterned sapphire substrate, preferably a mirror sapphire substrate; the epitaxial layer comprises one or more LED epitaxial structures formed in a reciprocating continuous progressive mode in the direction of a material system group of GaN/InGaN/AlGaN/AlInGaN and the like, and the preferred scheme is GaN/InGaN.
(2) Preparing a layer of metal indium on the surface of the epitaxial layer 101 through thermal evaporation, wherein the thickness of the metal indium is 1-tens of microns, heating the metal indium to be near the melting point, pressing a transfer substrate on the metal indium of the epitaxial layer 101, and cooling to bond the epitaxial layer 101 and the transfer substrate together.
(3) By using a single-beam excimer laser 102 with a wavelength of 248nm, a laser spot is square, the side length of the spot is 2mmX2mm, the moving distance is also 2mmX2mm from the outermost periphery of a wafer, and the peeling is progressively scanned point by point along a straight line from outside to inside in a clockwise direction (as shown in FIG. 2).
(4) And after the laser stripping procedure is finished, taking down the sapphire substrate which is completely stripped, cleaning the stripped gallium nitride interface by hydrochloric acid solution with the volume ratio of 1: 1, cleaning by deionized water, and blowing the stripped sample by nitrogen to finally obtain the completely stripped gallium nitride epitaxial layer.
Example 2:
the invention provides a progressive micro-scale sapphire substrate laser stripping process which specifically comprises the following steps:
(1) firstly, preparing an aluminum gallium nitride epitaxial layer 101 on a sapphire substrate 100 by using an epitaxial growth method, wherein the total thickness of the epitaxial layer 101 is controlled to be 5-10 microns; the Buffer layer structure comprises a Buffer layer, an AlN layer, a superlattice structure SL, heavily doped N-AlGaN, a multi-quantum well MQW, P-AlGaN and a heavily doped P-GaN contact layer. The epitaxial growth method may be metal chemical vapor deposition, laser assisted molecular beam epitaxy, laser sputtering, or hydride vapor phase epitaxy. The deposited epitaxial film may be of amorphous, polycrystalline, or single crystal structure, including but not limited to one of a mirror or micron/nanometer patterned sapphire substrate, preferably a micron-sized patterned sapphire substrate; the epitaxial layer comprises one or more LED epitaxial structures composed of GaN/AlN/AlGaN/AlInGaN and other material systems, and the preferred scheme is AlN/AlGaN.
(2) An adhesive layer is prepared on the epitaxial layer 101 by using electron beam and thermal evaporation process, and has a structure of Ni/Ag/Ti/Au/AuSn, and the total thickness of the adhesive layer is 0.9-10 microns (Ni thickness range)
The thickness range of Ag is 150-300nm, the thickness range of Ti is 100-500nm, the thickness range of Au is 200-5 um, and the thickness range of AuSn is 500-5 um); and preparing an adhesive layer on a transfer substrate by using an electron beam and thermal evaporation process, wherein the structure of the adhesive layer is Ti/Au/AuSn, the total thickness of the adhesive layer is 0.8-10 microns (the Ti thickness is in the range of 100-500nm, the Au thickness is in the range of 200-5 um, and the AuSn thickness is in the range of 500nm-5um), the adhesive layer material comprises one or more of metal materials such as indium, nickel, titanium, silver, aluminum, gold, platinum, gold tin and the like, the preferable scheme is a titanium, gold and gold tin composite layer, the transfer substrate comprises but not limited to Si, SiC, AlSi, Cu, CuMo and CuW, or a substrate with good mechanical property and the preferable scheme is CuW and Si, and the conductive and thermal conductive materials are subjected to heat setting.
(3) By using wafer bonding equipment, under the set bonding pressure, bonding temperature and process time, the epitaxial layer 101 and the two bonding layers on the transfer substrate are pressed together in a eutectic bonding mode, so that the gallium nitride epitaxial layer and the transfer substrate are connected together to form an integral material.
(4) And then, using a double-beam excimer laser 102 with the wavelength of 193nm, wherein the laser spot is square, the side length of the spot is 1mmX1mm, moving the wafer from the outermost periphery of the wafer according to an overlapped irradiation mode with the proportion of 50%, and gradually scanning and peeling point by point along a straight line from outside to inside in a clockwise direction (as shown in figure 3).
(5) And after the laser stripping procedure is completed, taking down the sapphire substrate which is completely stripped, cleaning the stripped aluminum gallium nitrogen interface by using acetic acid or oxalic acid solution, cleaning by using deionized water, and blowing the stripping sample by using nitrogen gas to finally obtain a completely stripped gallium nitride epitaxial layer.
The invention adopts the process optimization design idea, improves the original simpler reciprocating type laser stripping mode in the horizontal or vertical direction, reduces the influence on adjacent areas caused by high-pressure nitrogen impact or stress release at the stripping moment in the original laser stripping process, simultaneously simplifies the problems of high equipment requirement, higher program complexity and the like of other round or arc type stripping processes, and can improve the process and product yield. The method provides a new technical scheme for peeling the epitaxial layer and the sapphire substrate, and provides a technical approach with high process reliability for manufacturing III-N series vertical structure devices.
Claims (5)
1. A progressive laser peeling process for a micron-sized sapphire substrate is characterized by comprising the following steps:
1) the method comprises the steps of finishing growth of an epitaxial layer (101) on a sapphire substrate (100), dividing unit regions of the epitaxial layer (101) to form channels, preparing a hard or flexible insulating layer in the channels among the unit regions of the epitaxial layer, and then preparing a first bonding layer on the surface of the epitaxial layer (101);
2) preparing a second adhesive layer on the whole transfer substrate;
3) adhering the first adhesive layer and the second adhesive layer together to join the transfer substrate and the epitaxial layer together;
4) selecting light spot morphology, laser energy and laser beams, carrying out micron-scale movement by using light spots or carriers, scanning the laser (102) point by point in a linear inward progressive manner, scanning the light spots point by point in a micron-scale movement progressive manner in an outward-inward linear progressive manner, and finally completely separating the sapphire substrate (100) from the epitaxial layer (101);
the light spots adopt a plurality of light beam irradiation modes, the laser stripping of the sapphire substrate is realized by adopting an overlapping mode among the light spots, and the laser stripping is realized by adopting a single light beam or double light beams through the plurality of light beam irradiation modes; the laser is a pulse or continuous laser light source, the light spot of the laser is rectangular, and the side length size of the laser is adjustable between tens of microns and thousands of microns; and scanning in a straight line type progressive mode from outside to inside in a clockwise or anticlockwise direction from outside to inside point by point according to the side length of the rectangle.
2. The progressive laser lift-off process for the sapphire substrate as claimed in claim 1, wherein the step 4) further comprises a light spot overlapping irradiation lift-off mode and a double beam irradiation mode for laser lift-off of the epitaxial layer (101).
3. The progressive laser lift-off process for sapphire substrates of claim 2, wherein the area of the laser spot overlap region is adjustable between 10% and 90%.
4. The progressive micro-sapphire substrate laser lift-off process of claim 1, wherein the laser machining spot micro-scale movement distance is adjustable in a range of tens to thousands of micrometers.
5. The progressive micro-sapphire substrate laser lift-off process of claim 1, wherein micro-scale movement is achieved by laser spot movement or carrier movement.
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| CN109545931A (en) * | 2018-12-17 | 2019-03-29 | 佛山市国星半导体技术有限公司 | A kind of vertical structure LED wafer and stripping means |
| CN112750716B (en) * | 2019-10-29 | 2022-12-30 | 成都辰显光电有限公司 | Stripping device and stripping method for micro-element |
| CN113611779B (en) * | 2021-06-28 | 2023-09-08 | 厦门士兰明镓化合物半导体有限公司 | Deep ultraviolet LED chip with vertical structure, manufacturing method and epitaxial structure |
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| CN100463102C (en) * | 2004-11-23 | 2009-02-18 | 北京大学 | Large-area and low-power laser stripping method for GaN-base epitaxial layer |
| CN101555627B (en) * | 2009-04-30 | 2012-01-25 | 苏州纳晶光电有限公司 | Laser peeling method of gallium nitride-based epitaxial film |
| CN101879657B (en) * | 2009-05-08 | 2016-06-29 | 东莞市中镓半导体科技有限公司 | Solid laser lift equipment and stripping means |
| CN103943741A (en) * | 2013-01-17 | 2014-07-23 | 易美芯光（北京）科技有限公司 | Semiconductor light emitting device preparation method based on laser stripping |
| CN103839777A (en) * | 2014-03-11 | 2014-06-04 | 中国科学院半导体研究所 | Large area continuous lossless laser stripping method for gallium nitride film |
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