A method for lengthening an LED epitaxial wafer

Abstract

The present application relates to the technical field of LED epitaxial process, in particular to a lengthening method of LED epitaxial wafer. The lengthening method comprises the following steps: S1: placing the epitaxial wafer after growth interruption into a reaction cavity, heating the reaction cavity to 750-850 DEG C, while introducing 100-140 s of nitrogen and MO source; S2: setting the reaction time to 5-8 s, the pressure of the reaction cavity to 100-250 Toor, the temperature to 1050-1150 DEG C, the TMGa flux to 800-1000 sccm, and the SiH4 flux to 150-300 sccm; S3: setting the reaction time to 10-16 s, the pressure of the reaction cavity to 100-250 Toor, the temperature to 1050-1150 DEG C, and the TMGa flux to 800-1000 sccm; S4: repeating the steps S2 and S3 for 7-10 times to form an ultrathin n-type GaN layer; S5: growing a multi-quantum well layer and an epitaxial structure after the multi-quantum well layer. The lengthening method grows an ultrathin nGaN layer on the epitaxial layer where the down position is located to reestablish the n node basis, and grows the subsequent epitaxial layers on the basis to recover the performance of the epitaxial layer and improve the yield of the epitaxial wafer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LED epitaxial process, and particularly relates to a lengthening method of LED epitaxial wafer. BACKGROUND

[0002] At present, gallium nitride-based LED (light-emitting diode) is paid more and more attention and researched, and the epitaxial structure thereof is mainly composed of a substrate (sapphire substrate), a gallium nitride (GaN) or aluminum-doped gallium nitride (AlGaN) buffer layer, an undoped gallium nitride layer, an N-type doped layer, a stress release layer, an MQW (multi-quantum well) active region, a P-type AlGaN layer and a P-type layer. When current passes through, the electrons in the N-type region and the holes in the P-type region enter the MQW active region and recombine to emit visible light of a required waveband.

[0003] In the epitaxial production process of GaN-based LED, the MOCVD is shut down due to the fluctuation of power, gas and MO source flow, so that the growth process is suddenly interrupted, resulting in the scrap of the epitaxial wafer. The sudden situation causes the waste of cost. The Chinese patent with the publication number CN109390438A discloses a new epitaxial layer lengthening method. The MQW layer or the epitaxial wafer with growth interruption after the MQW layer is subjected to high-temperature treatment to occur a desorption effect, and the MQW layer and the epitaxial layer after the MQW layer are baked off. Then, the epitaxial wafer is subjected to high-temperature n-type GaN growth for 4-20 minutes. The epitaxial wafer is subjected to the normal condition of MQW growth until the epitaxial layer growth is completed. The lengthening method re-grows the MQW layer to keep the voltage, anti-static ability, service life and optical properties of the lengthened epitaxial wafer normal. However, the lengthening method is only suitable for the epitaxial wafer with growth interruption of the MQW layer or after the MQW layer, and is not suitable for the epitaxial wafer with growth interruption of the substrate to the MQW layer. SUMMARY

[0004] In order to overcome the defects of the prior art, the technical problem to be solved by the present application is to provide a lengthening method of LED epitaxial wafer, which is suitable for the epitaxial wafer with growth interruption of the substrate to the MQW layer.

[0005] In order to solve the above technical problem, the technical scheme adopted by the present application is as follows: a lengthening method of LED epitaxial wafer, comprising the following steps:

[0006] S1: placing the epitaxial wafer with growth interruption into a reaction cavity, heating the reaction cavity to 750-850℃, simultaneously introducing 100-140s of nitrogen and MO source;

[0007] S2: set the reaction time to 5-8s, the pressure of the reaction cavity to 100-250Toor, the temperature to 1050-1150℃, the TMGa (trimethylgallium) flux to 800-1000sccm, and the SiH4 flux to 150-300sccm;

[0008] S3: set the reaction time to 10-16s, the pressure of the reaction cavity to 100-250Toor, the temperature to 1050-1150℃, and the TMGa flux to 800-1000sccm;

[0009] S4: repeat the steps S2 and S3 for 7-10 times to form an ultrathin n-type GaN layer;

[0010] S5: grow a multi-quantum well layer and an epitaxial structure after the multi-quantum well layer.

[0011] The LED epitaxial wafer lengthening method has the advantages that for an epitaxial wafer that is suddenly interrupted during growth and has an interruption position between a bottom layer and a quantum well, an ultrathin nGaN layer is grown on the original structure to reestablish an n node basis, and subsequent epitaxial layers are grown on the basis of the ultrathin nGaN layer, so that the performance of the epitaxial wafer is restored, the epitaxial wafer that is interrupted is reused, and the scrap rate of an MOCVD production line is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 Fig. 1 shows Vf1 test results of epitaxial wafers after lengthening according to an embodiment and a comparative example;

[0013] Figure 2 Fig. 2 shows a Yield statistical diagram of epitaxial wafers after lengthening according to the embodiment and the comparative example. DETAILED DESCRIPTION

[0014] To make the technical content of the present application, the achieved purposes and effects clear, the following describes the present application in conjunction with the accompanying drawings.

[0015] The most critical idea of the present application is that an ultrathin nGaN layer is grown on an epitaxial layer where a machine is interrupted to reestablish an n node basis, and subsequent epitaxial layers are grown on the basis, so that the performance of the epitaxial layer is restored.

[0016] The LED epitaxial wafer lengthening method comprises the following steps:

[0017] S1: place the epitaxial wafer after interruption in a reaction cavity, heat the reaction cavity to 750-850℃, simultaneously introduce 100-140s of nitrogen, and introduce a MO source;

[0018] S2: set the reaction time to 5-8s, the pressure of the reaction cavity to 100-250Toor, the temperature to 1050-1150℃, the TMGa flux to 800-1000sccm, and the SiH4 flux to 150-300sccm;

[0019] S3: set the reaction time to 10-16s, the pressure of the reaction cavity to 100-250Toor, the temperature to 1050-1150℃, and the TMGa flux to 800-1000sccm;

[0020] S4: repeat the steps S2 and S3 for 7-10 times to form the ultra-thin n-type GaN layer;

[0021] S5: grow the multi-quantum well layer and the epitaxial structure after the multi-quantum well layer.

[0022] As can be known from the above description, the beneficial effects of the present application are that the present application develops a lengthening method for an LED epitaxial wafer, nitrogen is first introduced to purify the gas inside the reaction cavity, the MO source is pre-introduced in the pipeline to ensure the ammonia protective atmosphere in the cavity and make the MO source better connected; then the ultra-thin n-type GaN layer with a connecting effect is grown to lay a foundation for the growth of subsequent epitaxial layers, and then the normal multi-quantum well layer and the epitaxial structure after the multi-quantum well layer are grown. The lengthening method of the present application is simple to operate, the performance of the compensated epitaxial layer remains normal, the yield is more than 90%, and the scrap rate of the MOCVD production line is reduced.

[0023] The n-type GaN as an electron injection layer, the epitaxial wafer using the normal form n-type GaN for lengthening after shutdown is prone to voltage and ESD problems in subsequent chip processing, and too much or too little Si doping will cause abnormal electrical properties. In the present application, the n-type GaN layer containing SiH4 and the n-type GaN layer not containing SiH4 are alternately stacked, which can better control the Si doping content of the n-GaN layer.

[0024] The reaction time of S2 is relatively short, and if the reaction time increases, too much Si doping will be introduced into the n-type GaN, affecting the electrical property data. The reaction time of S3 is relatively long, and if the reaction time is shortened, the n-type GaN will grow too thin, thereby affecting the appearance of the output epitaxial wafer. When the temperature of S2 and S3 is too high, hexagonal protrusions appear, and when the temperature is low, pits appear; too high or too low SiH4 flux will affect the product voltage and yield.

[0025] Further, the epitaxial wafer is first taken out after the growth is interrupted, nitrogen is used for purging to confirm the interruption position, and then the epitaxial wafer is put into the reaction cavity.

[0026] As can be known from the above description, the purpose of this step is to blow off the dust generated by instantaneous shutdown, and the epitaxial wafer can be subjected to the next step only when the shutdown interruption position is between the N layer and the quantum well.

[0027] Further, the thickness of the ultra-thin n-type GaN layer is 190-210 nm.

[0028] As can be seen from the above description, the thickness is too thick to waste energy, and too thin to play the role of nGaN.

[0029] Further, the multi-quantum well layer is composed of 3-15 periods of InxGa1-xN (0 < x < 1) well layer and GaN barrier layer.

[0030] As can be seen from the above description, the InxGa1-xN (0 < x < 1) well layer and the GaN barrier layer exhibit the characteristics of absorbing sunlight with continuous energy levels, which makes them applicable in the field of photoelectric conversion.

[0031] Further, when growing the InxGa1-xN (0 < x < 1) well layer, the temperature of the reaction chamber is set to 770-830℃, and the pressure is set to 100-300 Torr.

[0032] Further, when growing the GaN barrier layer, the temperature of the reaction chamber is set to 870-930℃, and the pressure is set to 100-300 Torr.

[0033] As can be seen from the above description, the multi-quantum well structure can effectively confine electrons and holes therein, increase the superposition of electron and hole wave functions, and further increase the rate of electron and hole radiative recombination, thereby effectively improving the light-emitting efficiency.

[0034] Further, S5 specifically comprises: growing, on the ultra-thin n-type GaN layer, a multi-quantum well layer, a P-type Al y Ga 1-y N (0.1 < y < 0.5) electron blocking layer, a P-GaN layer, and a P-type contact layer in sequence.

[0035] Further, when growing the P-type Al y Ga 1-y N (0.1 < y < 0.5) electron blocking layer, the temperature of the reaction chamber is set to 850-1080℃, the pressure is set to 200-500 Torr, and the thickness is set to 40-90 nm.

[0036] As can be seen from the above description, the electron blocking layer can on the one hand block the diffusion of current downward to the P electrode, reduce the current density flowing to the active area under the P electrode metal, and thereby reduce the light loss caused by the light absorption and blocking of the P electrode metal; and on the other hand, guide the current to the area far away from the P electrode through the electron blocking layer, reduce the current crowding near the P electrode, and thereby improve the light output power.

[0037] Further, when growing the P-GaN layer, the temperature of the reaction chamber is set to 850-1080°C, the pressure is set to 100-300 Torr, and the thickness is set to 100-800 nm.

[0038] Further, after the growth of the P-type contact layer is completed, the temperature of the reaction chamber is reduced to 650-850°C, and annealing treatment is performed in a nitrogen atmosphere for 5-15 min, and the temperature is reduced to room temperature after the annealing.

[0039] As can be seen from the above description, a high P-type conductivity can be obtained after the annealing treatment.

[0040] Embodiment one of the present application is a lengthening method of an LED epitaxial wafer, comprising the following steps:

[0041] S1: after the growth is interrupted, the epitaxial wafer is first taken out, and then the epitaxial wafer is confirmed to be between the N layer and the quantum well at the interruption position after being purged with nitrogen.

[0042] S2: the epitaxial wafer after the growth is interrupted is placed into the reaction chamber, the temperature of the reaction chamber is continuously increased to 800°C, 120 s of nitrogen is introduced at the same time, and the MO source is introduced.

[0043] S3: the reaction time is set to 7 s, the pressure of the reaction chamber is set to 150 Torr, the temperature is set to 1100°C, the TMGa flux is set to 900 sccm, and the SiH4 flux is set to 200 sccm.

[0044] S4: the reaction time is set to 13 s, the pressure of the reaction chamber is set to 200 Torr, the temperature is set to 1100°C, and the TMGa flux is set to 900 sccm.

[0045] S5: the steps of S3 and S4 are repeated for 8 times to form a super-thin n-type GaN layer; the thickness of the super-thin n-type GaN layer is 200 nm.

[0046] S6: a multi-quantum well layer is grown on the super-thin n-type GaN layer, the multi-quantum well layer is composed of 10 periods of InxGa1-xN (0 < x < 1) well layers and GaN barrier layers; when the InxGa1-xN (0 < x < 1) well layer is grown, the temperature of the reaction chamber is set to 800°C, the pressure is set to 200 Torr, and the thickness is set to 4 nm; the growth temperature of the well layer is the same, and low-temperature growth is adopted; when the GaN barrier layer is grown, the temperature of the reaction chamber is set to 900°C, the pressure is set to 200 Torr, and the thickness is set to 13 nm.

[0047] S7: the temperature of the reaction chamber is set to 920°C, the pressure is set to 350 Torr, and a P-type Al y Ga 1-y N (0.1 < y < 0.5) electron blocking layer is grown on the multi-quantum well layer with a thickness of 60 nm.

[0048] S8: set the temperature of the reaction chamber to 920℃, the pressure to 200 Torr, and grow a P-GaN layer with a thickness of 500 nm on the P-type Al y Ga 1-y N(0.1<y<0.5) electron blocking layer.

[0049] S9: set the temperature of the reaction chamber to 900℃, the pressure to 200 Torr, and grow a P-type contact layer with a thickness of 200 nm on the P-GaN layer.

[0050] S10: after the growth of the P-type contact layer is completed, reduce the temperature of the reaction chamber to 700℃, and perform annealing treatment in a nitrogen atmosphere for 10 min; after annealing, reduce the temperature to room temperature, and obtain an elongated epitaxial wafer.

[0051] Embodiment two of the present application is a method for elongating an LED epitaxial wafer, comprising the following steps:

[0052] S1: after the growth is interrupted, first take out the epitaxial wafer, perform purging using nitrogen, and then confirm that the interrupted position is between the N layer and the quantum well.

[0053] S2: place the epitaxial wafer after the growth is interrupted into a reaction chamber, heat the reaction chamber to 750℃, simultaneously introduce 100 s of nitrogen, and introduce a MO source.

[0054] S3: set the reaction time to 5 s, the pressure of the reaction chamber to 250 Torr, the temperature to 1150℃, the TMGa flux to 800 sccm, and the SiH4 flux to 150 sccm.

[0055] S4: set the reaction time to 10 s, the pressure of the reaction chamber to 250 Torr, the temperature to 1150℃, and the TMGa flux to 800 sccm.

[0056] S5: repeat the steps of S3 and S4 for 7 times to form a super-thin n-type GaN layer; the thickness of the super-thin n-type GaN layer is 190 nm.

[0057] S6: grow a multi-quantum well layer on the super-thin n-type GaN layer; the multi-quantum well layer is composed of 3 periods of InxGa1-xN(0<x<1) well layers and GaN barrier layers; when growing the InxGa1-xN(0<x<1) well layer, set the temperature of the reaction chamber to 830℃, the pressure to 100 Torr, and the thickness to 4 nm; the growth temperature of the well layer is the same, and is low-temperature growth; when growing the GaN barrier layer, set the temperature of the reaction chamber to 930℃, the pressure to 100 Torr, and the thickness to 15 nm.

[0058] S7: set the temperature of the reaction chamber to 850℃, the pressure to 500 Torr, and grow a P-type Al y Ga1-y N(0.1<y<0.5) electron blocking layer.

[0059] S8: Set the temperature of the reaction chamber to 850℃, and the pressure to 300 Torr, and grow a P-GaN layer with a thickness of 100 nm on the N(0.1<y<0.5) electron blocking layer. y Ga 1-y N(0.1<y<0.5) electron blocking layer.

[0060] S9: Set the temperature of the reaction chamber to 850℃, and the pressure to 300 Torr, and grow a P-type contact layer with a thickness of 5 nm on the P-GaN layer.

[0061] S10: After the P-type contact layer is grown, reduce the temperature of the reaction chamber to 650℃, and perform annealing treatment in a nitrogen atmosphere for 15 min, and then reduce the temperature to room temperature after annealing, to obtain an extended epitaxial wafer.

[0062] Embodiment three of the present application is a lengthening method of an LED epitaxial wafer, comprising the following steps:

[0063] S1: After the growth is interrupted, first take out the epitaxial wafer, perform purging using nitrogen, and then confirm that the interrupted position is between the N layer and the quantum well.

[0064] S2: Put the epitaxial wafer after the growth is interrupted into the reaction chamber, heat the reaction chamber to 850℃, and simultaneously introduce 140 s of nitrogen and MO source.

[0065] S3: Set the reaction time to 8 s, the pressure of the reaction chamber to 100 Torr, the temperature to 1050℃, the TMGa flux to 1000 sccm, and the SiH4 flux to 300 sccm.

[0066] S4: Set the reaction time to 16 s, the pressure of the reaction chamber to 100 Torr, the temperature to 1050℃, and the TMGa flux to 1000 sccm.

[0067] S5: Repeat steps S3 and S4 for 10 times to form a super-thin n-type GaN layer; the thickness of the super-thin n-type GaN layer is 210 nm.

[0068] S6: Grow a multi-quantum well layer on the super-thin n-type GaN layer; the multi-quantum well layer is composed of 15 periods of InxGa1-xN(0<x<1) well layer and GaN barrier layer; when growing the InxGa1-xN(0<x<1) well layer, set the temperature of the reaction chamber to 770℃, the pressure to 300 Torr, and the thickness to 4 nm; the growth temperature of the well layer is the same, and is low-temperature growth; when growing the GaN barrier layer, set the temperature of the reaction chamber to 870℃, the pressure to 300 Torr, and the thickness to 9 nm.

[0069] S7: set the temperature of the reaction chamber to 1080℃, the pressure to 200 Torr, and grow a P-type Al y Ga 1-y N (0.1 < y < 0.5) electron blocking layer on the multi-quantum well layer.

[0070] S8: set the temperature of the reaction chamber to 1080℃, the pressure to 100 Torr, and grow a P-GaN layer with a thickness of 800 nm on the P-type Al y Ga 1-y N (0.1 < y < 0.5) electron blocking layer.

[0071] S9: set the temperature of the reaction chamber to 1050℃, the pressure to 100 Torr, and grow a P-type contact layer with a thickness of 300 nm on the P-GaN layer.

[0072] S10: after the P-type contact layer is grown, the temperature of the reaction chamber is reduced to 850℃, and annealing treatment is performed in a nitrogen atmosphere for 5 min; after annealing, the temperature is reduced to room temperature, and a lengthened epitaxial wafer is obtained.

[0073] The comparative example one of the present application is: the original lengthening method

[0074] The difference between the comparative example one and the example one is only that there is no S3-S5.

[0075] The lengthened epitaxial wafers in the example one and the comparative example one are sequentially subjected to epitaxial wafer cleaning -> MESA -> CBL -> ITO -> MET -> PV -> electrical alloying -> COW testing -> grinding and thinning -> cleaving -> sorting and full testing, and LED chips are prepared; the LED chips are made into 3*6 mil chip particles, 5 mA point testing is performed for sorting, Vf1 (forward voltage under a driving current of 0.1 uA) performance testing and yield statistics are performed, and the results are shown in Figure 1 and Figure 2 The yield cutoff standard is 2.5≤vf≤2.9.

[0076] It can be clearly seen from Figure 1 that the voltage of the epitaxial wafer lengthened by the method of the present application is significantly lower than that of the original lengthening method; and it can be known from Figure 2 that the yield of the epitaxial wafer using the method of the present application is in sharp contrast to that of the original lengthening method, and the yield of the present application reaches more than 90%.

[0077] In summary, the application provides a method for repairing an LED epitaxial wafer, wherein the dust generated by instantaneous downtime is first blown off, and the position of the epitaxial wafer downtime interruption is confirmed to be between the N layer and the quantum well; then nitrogen is introduced to purify the gas inside the reaction cavity, the MO source is pre-connected in the pipeline, the ammonia protective atmosphere in the cavity is ensured, and the MO source can be better connected; then a super-thin n-type GaN layer is grown to play a connecting role, and the subsequent epitaxial layer growth is based on it, and the normal multi-quantum well layer and the epitaxial structure after the multi-quantum well layer are grown. The repairing method of the application is simple in operation, the performance of the compensated epitaxial layer remains normal, the yield is more than 90%, and the scrap rate of the MOCVD production line is reduced.

[0078] The n-type GaN is used as an electron injection layer, and the epitaxial wafer repaired by using normal n-type GaN after downtime is prone to voltage and ESD problems in subsequent chip processing. Too much or too little Si doping will cause abnormal electrical properties. In the application, the n-type GaN layer containing SiH4 and the n-type GaN layer not containing SiH4 are alternately stacked, so that the Si doping content of the n-GaN layer can be better controlled.

[0079] The S2 reaction time is relatively short, and if the reaction time is increased, too much Si doping will be introduced into the n-type GaN, affecting the electrical property data. The S3 reaction time is relatively long, and if the reaction time is shortened, the n-type GaN will grow too thin, thereby affecting the appearance of the output epitaxial wafer. When the temperature of S2 and S3 is too high, hexagonal protrusions appear, and when the temperature is low, pits appear; too high or too low SiH4 flux will affect the product voltage and yield.

[0080] The above is only an embodiment of the application, and does not limit the patent scope of the application. Any equivalent transformation or direct or indirect application in related technical fields based on the content of the specification and drawings is also included in the patent protection scope of the application.

Claims

1. A method of lengthening an LED epitaxial wafer, characterized by, The method comprises the following steps: S1: placing the epitaxial wafer after growth interruption into a reaction cavity, heating the reaction cavity to 750-850℃, and introducing 100-140s of nitrogen and MO source; S2: setting the reaction time to 5-8s, the pressure of the reaction cavity to 100-250Torr, the temperature to 1050-1150℃, the TMGa flux to 800-1000sccm, and the SiH4 flux to 150-300sccm; S3: setting the reaction time to 10-16s, the pressure of the reaction cavity to 100-250Torr, and the temperature to 1050-1150℃, and the TMGa flux to 800-1000sccm; S4: repeating steps S2 and S3 for 7-10 times to form an ultrathin n-type GaN layer; S5: growing a multi-quantum well layer and an epitaxial structure after the multi-quantum well layer.

2. The method of claim 1, wherein the LED epitaxial wafer is a wafer having a plurality of LED chips formed therein. The epitaxial wafer is taken out after growth interruption, purged with nitrogen, and then placed into the reaction cavity.

3. The method of claim 1, wherein the LED epitaxial wafer is a wafer having a plurality of LED structures formed on a substrate, and the plurality of LED structures are formed in a matrix shape. The thickness of the ultrathin n-type GaN layer is 190-210nm.

4. The method of claim 1, wherein the LED epitaxial wafer is grown by metal organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE). The multi-quantum well layer is composed of 3-15 periods of InxGa1-xN (0 5. The method of claim 4, wherein the epitaxial wafer is a LED epitaxial wafer. When growing the InxGa1-xN (0 6. The method of claim 4, wherein the epitaxial wafer is a LED epitaxial wafer. When growing the GaN barrier layer, the temperature of the reaction cavity is set to 870-930℃, and the pressure is set to 100-300Torr.

7. The method of claim 1, wherein the LED epitaxial wafer is grown by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). The S5 is specifically: sequentially performing growth of a multi-quantum well layer, a P-type Al y Ga 1-y N(0.1 < y < 0.5) electron blocking layer, a P-GaN layer and a P-type contact layer on an ultra-thin n-type GaN layer.

8. The method of claim 7, wherein the plurality of LED epitaxial wafers are grown on a plurality of substrates, and the plurality of substrates are separated from the plurality of LED epitaxial wafers. Growth of the P-type Al y Ga 1-y N(0.1 < y < 0.5) electron blocking layer, the temperature of the reaction chamber is set to 850-1080 °C, the pressure is 200-500 Torr, and the thickness is 40-90 nm.

9. The method of claim 7, wherein the plurality of LED epitaxial wafers are grown on a plurality of substrates, and the plurality of substrates are separated from the plurality of LED epitaxial wafers. When growing the P-GaN layer, the temperature of the reaction cavity is set to 850-1080℃, the pressure is set to 100-300Torr, and the thickness is set to 100-800nm.

10. The method of claim 7, wherein the epitaxial wafer is a LED epitaxial wafer. After the growth of the P-type contact layer is completed, the temperature of the reaction cavity is reduced to 650-850℃, and annealing treatment is performed in a nitrogen atmosphere for 5-15min, and the temperature is reduced to room temperature after annealing.

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