An AlGaN-based ultraviolet light-emitting diode device LED and a preparation method thereof

Abstract

The application discloses an AlGaN-based ultraviolet light-emitting diode (LED) device and a preparation method thereof. The method provided by the application comprises the following steps: realizing full-structure epitaxial growth of the ultraviolet LED with a smooth surface and no cracks by crack presetting and filling and other epitaxial processes on a GaN / sapphire template; and then removing the sapphire substrate by using a laser stripping method, and combining with an ultraviolet LED preparation process to obtain a thin film flip-chip ultraviolet LED chip. The method provided by the application not only improves the problem of low light extraction efficiency of the ultraviolet LED device, but also eliminates the dependence of the ultraviolet LED device on the AlN template, reduces the production cost, has important significance for performance improvement and industrial application of the AlGaN-based ultraviolet LED device, and is suitable for vigorous promotion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of group III nitride semiconductor preparation, and particularly relates to a thin film flip-chip AlGaN-based ultraviolet light-emitting diode structure epitaxy and device preparation. BACKGROUND

[0002] In recent years, AlGaN-based solid-state ultraviolet light sources are widely used in the fields of ultraviolet curing, biomedical treatment, sterilization and disinfection, etc., and are considered as one of the most potential and valuable directions in the field of group III nitride semiconductors. Compared with gaseous light sources such as mercury lamps, the AlGaN-based solid-state ultraviolet light sources have the advantages of environmental protection, small size, low energy consumption and long service life, and are an ideal choice to replace traditional ultraviolet light sources. However, so far, it is still a great challenge to realize high-performance AlGaN-based ultraviolet light sources such as ultraviolet light-emitting diodes (LEDs), mainly in the form of low electrical-to-optical conversion efficiency (WPE).

[0003] The main factor restricting the electrical-to-optical conversion efficiency of the ultraviolet LED is the low light extraction efficiency (LEE), mainly in the form that in the flip-chip chip retaining the AlN / sapphire, due to the difference in refractive index between AlN, sapphire and air, the escape cone of the outgoing light at the sapphire / air interface is limited within a range of 26°, resulting in that the light extraction efficiency of the device is only about 5%. Although the full reflection at the sapphire substrate / air interface can be effectively eliminated by improving the packaging technology and designing the sapphire back light structure, the problem of light full reflection still exists at the internal AlN / sapphire interface, which seriously restricts the further improvement of the light extraction efficiency.

[0004] At present, the thin film flip-chip (TFFC) chip prepared by peeling off the substrate is an effective means to completely solve the above-mentioned problem of full reflection, and has important significance for improving the light extraction efficiency and the electrical-to-optical conversion efficiency of the ultraviolet LED. One of the fastest and most effective methods to realize the substrate peeling off is the laser lift-off (LLO) technology, which has shown great commercial value and application prospect in InGaN blue light LEDs and micro-LEDs.

[0005] However, in the AlGaN-based ultraviolet LED, the laser lift-off method has not been widely used to remove the substrate, on the one hand, because the short-wavelength and high-power laser meeting the AlN absorption is relatively expensive, and on the other hand, more importantly, the high-hardness Al metal deposited by the decomposition of AlN during the laser lift-off process will cause the breakage of the epitaxial wafer, affecting the device preparation. How to remove the sapphire substrate by the laser lift-off method on the basis of ensuring the integrity of the epitaxial wafer and improving the light extraction efficiency of the device is a key problem for the large-scale promotion and application of the AlGaN-based ultraviolet LED. SUMMARY

[0006] The application aims to provide a thin film flip-chip AlGaN-based ultraviolet light emitting diode device LED and a preparation method thereof.

[0007] To achieve the above-mentioned purpose, the application provides the following technical scheme.

[0008] In a first aspect, the application provides a preparation method of a thin film flip-chip AlGaN-based ultraviolet light emitting diode device LED, comprising the following steps.

[0009] S1, epitaxially growing a GaN template on a sapphire substrate to obtain a GaN template layer;

[0010] S2, epitaxially growing a preset crack layer on the GaN template layer;

[0011] S3, epitaxially growing an AlGaN crack filling layer on the preset crack layer;

[0012] S4, epitaxially growing an ultraviolet LED structure on the AlGaN crack filling layer, the ultraviolet LED structure comprising an n-AlGaN layer, an active region multi-quantum well layer, a p-AlGaN electron blocking layer, a p-AlGaN layer and a p-GaN layer;

[0013] S5, preparing an n-type electrode on the n-AlGaN layer and a p-type electrode on the p-GaN layer; depositing an isolation layer between the n-type electrode and the p-type electrode; leading out a metal layer on the n-type electrode and bonding the metal layer with a substrate;

[0014] S6, peeling off the sapphire substrate;

[0015] S7, removing the GaN template layer and roughening a surface of the preset crack layer;

[0016] S8, etching the preset crack layer, the AlGaN crack filling layer and the ultraviolet LED structure, leading out the n-type electrode and the p-type electrode, dicing, packaging and completing the preparation of the thin film flip-chip ultraviolet LED.

[0017] In step S1, the thickness of the GaN template layer is 1-10 μm, preferably 3-6 μm.

[0018] The surface of the GaN template layer is crack-free and has an atomically flat surface topography.

[0019] The GaN template layer is obtained by epitaxial growth through a MOCVD method, and in actual implementation, the process parameter conditions can be adjusted according to actual requirements, such as a growth temperature of 1040 ℃, a growth pressure of 300 mbar, and a growth rate of 2 μm / h.

[0020] In step S2, the material of the preset crack layer is AlN or AlGaN; in the preset crack layer, the mole fraction of Al component is 30%-100%, preferably 60%-90%, such as 80%. By controlling the mole fraction of Al component in the preset crack layer, the preset crack layer has no absorption to active region light emission.

[0021] The thickness of the preset crack layer is 10-300 nm, preferably 30-150 nm, such as 90 nm.

[0022] The preset crack layer is obtained by epitaxial growth through a MOCVD method. In actual implementation, the process parameter conditions can be adjusted according to actual requirements, such as a growth temperature of 1100 ℃ and a growth pressure of 100 mbar.

[0023] In step S3, in the AlGaN crack filling layer, the mole fraction of Al component is 30%-90%, preferably 50%-80%, such as 65%. By controlling the mole fraction of Al component in the AlGaN crack filling layer, the AlGaN crack filling layer has no absorption to active region light emission.

[0024] The thickness of the AlGaN crack filling layer is 100-2000 nm, preferably 300-1000 nm, such as 600 nm.

[0025] The AlGaN crack filling layer surface has no crack and has an atomic-level flat step morphology.

[0026] The AlGaN crack filling layer is obtained by epitaxial growth through a MOCVD method. In actual implementation, the process parameter conditions can be adjusted according to actual requirements, such as a growth temperature of 1100 ℃ and a growth pressure of 100 mbar.

[0027] In steps S4 and S5, each film layer can be prepared by using a conventional process in the field of ultraviolet light emitting diode devices, and the process parameter conditions can be adjusted according to actual requirements.

[0028] In step S4, the mole fraction of Al component in the n-AlGaN layer is 20-100%, preferably 50-60%; the thickness of the n-AlGaN layer is 0.5-1.5 μm, preferably 1 μm.

[0029] The active region multi-quantum well layer is a plurality of periods of AlGaN / AlGaN multi-quantum well structure, and the light-emitting wavelength is 210-350 nm, preferably 220-310 nm.

[0030] In the p-AlGaN electron blocking layer, the mole fraction of Al component is 20-100%, for example, 60-70%.

[0031] In the p-AlGaN layer, the mole fraction of Al component is 20-100%, for example, 50-60%.

[0032] The thickness of the p-GaN layer is 1-200 nm, for example, 10-20 nm.

[0033] In step S5, the n-type electrode and the p-type electrode are prepared by photolithography and ICP etching technology.

[0034] Taking the n-type electrode of Ti / Al / Ni / Au as an example, the preparation conditions are as follows: annealing at 800-900 °C for 30-40 s in N2 atmosphere, preferably at 850 °C for 35 s. The thicknesses of the Ti / Al / Ni / Au are 30 nm, 180 nm, 50 nm and 100 nm, respectively.

[0035] Taking the p-type electrode of Ni / Au as an example, the preparation conditions are as follows: annealing at 500-600 °C for 250-350 s in O2 atmosphere, preferably at 550 °C for 300 s; the thicknesses of the Ni / Au are 10 nm and 50 nm, respectively.

[0036] The thickness of the isolation layer is 700-900 nm, for example, 800 nm.

[0037] In step S6, the separation of the sapphire substrate is achieved by a laser with a wavelength equal to or shorter than 364 nm, for example, a 355 nm Nd:YAG laser (triple frequency).

[0038] In step S7, the GaN template layer is removed by ICP etching. In actual implementation, the process parameter conditions can be adjusted according to actual needs, for example, etching in a Cl2 / Ar / BCl3 atmosphere for 30 min.

[0039] The surface of the pre-crack layer is roughened by wet etching. In actual implementation, the process parameter conditions can be adjusted according to actual needs, for example, etching with KOH solution for 30 s.

[0040] In step S8, the etching is achieved by photolithography and ICP technology. In actual implementation, the process parameter conditions can be adjusted according to actual needs.

[0041] In a second aspect, the present invention provides a thin film flip-chip AlGaN-based ultraviolet light emitting diode device obtained by the preparation method.

[0042] According to an embodiment of the present invention, the thin film flip-chip AlGaN-based ultraviolet light-emitting diode device comprises the following components: a bonding substrate, a metal layer, an isolation layer, an n-type electrode, a p-type electrode, a p-electrode interface, and an ultraviolet LED structure;

[0043] The ultraviolet LED structure consists of the following components: a pre-set crack layer, an AlGaN crack-filling layer, an n-AlGaN layer, an active region multi-quantum well layer, a p-AlGaN electron blocking layer, a p-AlGaN layer, and a p-GaN layer.

[0044] The design principles of the present invention are as follows:

[0045] The present invention overcomes the limitations of the existing technology and innovatively proposes epitaxial growth of a GaN template on a sapphire substrate, which facilitates the peeling of the sapphire substrate by a laser peeling method. On the basis of the GaN template, a pre-crack layer and an AlGaN crack-filling layer are further epitaxially grown to fully release the tensile stress caused by the lattice mismatch between the upper AlGaN layer and the GaN template, thereby obtaining a high-quality, surface-crack-free ultraviolet LED epitaxial structure. The sapphire substrate is then completely peeled off by laser peeling, and the GaN template layer is removed. Finally, in conjunction with the LED device preparation process, the preparation of a thin-film flip-chip AlGaN-based ultraviolet light-emitting diode device (LED) is realized.

[0046] The beneficial effects achieved by the present invention are as follows:

[0047] This invention addresses the problem of surface cracks in epitaxial wafers caused by a large lattice mismatch (tensile stress) between the GaN template and the UV LED structure, and provides a crack control method. This method achieves wafer-scale, high-yield, crack-free laser lift-off of sapphire substrates, solving the problem of total light reflection at the wafer's internal interface and effectively improving the device's light extraction efficiency. This enables the large-scale production of high-yield, high-efficiency, thin-film flip-chip AlGaN-based UV LEDs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the process for preparing thin-film flip-chip AlGaN-based ultraviolet LED devices.

[0049] Figure 2 This is a schematic diagram of the overall structure obtained in steps S1-S4 of the method for preparing a thin-film flip-chip AlGaN-based ultraviolet LED device provided in Example 1.

[0050] Figure 3Schematic diagram of steps S6-S7 in the preparation method of the thin film flip-chip AlGaN-based ultraviolet LED device provided in Example 1; wherein (a) represents step S6, (b) represents removal of the GaN template layer in step S7, and (c) represents surface roughening of the preset crack layer in step S7.

[0051] Wherein: 1 is a sapphire substrate, 2 is a GaN template layer, 3 is a preset crack layer, 4 is an AlGaN crack filling layer, 5 is an n-AlGaN layer, 6 is an active region multi-quantum well layer, 7 is a p-AlGaN electron blocking layer, 8 is a p-AlGaN layer, 9 is a p-GaN layer, 10 is an n-type electrode, 11 is a p-type electrode, 12 is an isolation layer, 13 is a metal layer, 14 is a bonding substrate, and 15 is a p-electrode interface.

[0052] Figure 4 Comparison results of light output power of the thin film flip-chip AlGaN-based ultraviolet LED chip provided in Example 1 and the comparative example. DETAILED DESCRIPTION

[0053] The application will be further described in conjunction with specific embodiments, but the application is not limited to the following embodiments.

[0054] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0055] The reagents, biological materials, instruments, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0056] Example 1, preparation of a thin film flip-chip AlGaN-based ultraviolet LED with a wavelength of 280 nm

[0057] As shown in Figure 1 , the operation steps of the epitaxy and preparation method of the thin film flip-chip AlGaN-based ultraviolet LED with a light-emitting wavelength of 280 nm are as follows:

[0058] S1: A 5 μm thick GaN template layer 2 was epitaxially grown on a sapphire substrate 1 by the MOCVD method; the growth conditions were: growth temperature 1040°C, growth pressure 300 mbar, and growth rate 2 μm / h;

[0059] S2: A 90 nm thick Al 0.8 Ga 0.2 N was epitaxially grown on the GaN template layer 2 by the MOCVD method as a preset crack layer 3; the growth conditions were: growth temperature 1100°C, growth pressure 100 mbar;

[0060] S3: A 600 nm thick Al 0.65 Ga 0.35N layer, as AlGaN crack filling layer 4; growth conditions: growth temperature 1100℃, growth pressure 100mbar;

[0061] S4: epitaxially growing UV LED structure on AlGaN crack filling layer 4 by MOCVD method, as shown in the structure includes: 1μm thick n-Al Figure 2 0.55 Ga 0.45 N layer 5, 5 cycles of Al 0.37 Ga 0.63 N(2nm) / Al 0.5 Ga 0.5 N(10nm) multiple quantum well layer 6, 10nm thick p-Al 0.65 Ga 0.35 N electron blocking layer 7, 50nm thick p-Al 0.55 Ga 0.45 N layer 8, 10nm thick p-GaN layer 9; UV LED active region light wavelength 280nm;

[0062] S5: depositing Ti / Al / Ni / Au electrode on the surface of n-AlGaN layer 5 by photolithography and ICP etching technology, and forming n-type electrode 10 by rapid annealing at 850℃ in N2 atmosphere for 35s; depositing Ni / Au electrode on the surface of p-GaN layer 9, and forming p-type electrode 11 by rapid annealing at 550℃ in O2 atmosphere for 300s; depositing SiO2 isolation layer 12 between n-type electrode and p-type electrode;

[0063] By photolithography and ICP etching technology, depositing 2μm thick Au metal layer 13 to lead out n-type electrode 10, and at the same time as the bonding metal layer; by bonding technology, bonding wafer with bonding substrate 14 high n-doped Si piece together;

[0064] The thickness of Ti / Al / Ni / Au electrode is respectively: 30nm, 180nm, 50nm, 100nm; its preparation process conditions are: temperature is 850℃, time is 35s;

[0065] The thickness of Ni / Au electrode is respectively: 10nm, 50nm; its preparation process conditions are: temperature is 550℃ in O2 atmosphere, time is 300s.

[0066] The thickness of isolation layer is: 800nm;

[0067] S6: using 355nm Nd:YAG laser (three times frequency) to strip sapphire substrate 1, as shown in (a) of Figure 3

[0068] ​​S7: removing the residual GaN template layer 2 on the film by ICP etching to expose the surface of the pre-crack layer 3, as shown in Figure 3 (b); and then roughening the surface of the pre-crack layer 3 by wet etching, as shown in Figure 3 (c);

[0069] The parameter conditions for removing the GaN template layer are as follows: ICP etching is used, and etching is performed in a Cl2 / Ar / BCl3 atmosphere for 30 min, and the specific conditions can be adjusted according to actual conditions;

[0070] The parameter conditions for roughening the pre-crack layer are as follows: KOH solution etching is used, and etching is performed for 30 s, and the specific conditions can be adjusted according to actual conditions;

[0071] S8: etching from the surface of the pre-crack layer 3 downward by photolithography and ICP etching technology to expose and lead out the p-type electrode 11 metal as a p-electrode interface 15; and then breaking and packaging to obtain a film flip-chip AlGaN-based ultraviolet LED chip;

[0072] The parameter conditions for etching are as follows: ICP etching is used in a Cl2 / Ar / BCl3 atmosphere until the material is completely etched clean, and the specific conditions can be adjusted according to actual conditions.

[0073] Comparative Example 1: Flip-chip AlGaN-based ultraviolet LED epitaxy and preparation with a wavelength of 280 nm

[0074] S1: growing a 2-μm-thick AlN template on a sapphire substrate by a MOCVD method;

[0075] S2: epitaxially growing an ultraviolet LED structure on the AlN / sapphire template, including a 1-μm-thick n-type Al 0.55 Ga 0.45 N layer, 5 periods of Al 0.37 Ga 0.63 N (2 nm) / Al 0.5 Ga 0.5 N (10 nm) multiple quantum well structure, a 10-nm-thick p-Al 0.65 Ga 0.35 N electron blocking layer, a 50-nm-thick p-Al 0.55 Ga 0.45 N layer, and a 10-nm-thick p-GaN layer; the ultraviolet LED active region has a light-emitting wavelength of 280 nm;

[0076] S3: Ti / Al / Ni / Au electrodes are deposited on the surface of the n-AlGaN layer through photolithography and ICP etching technology, and then rapidly annealed in an N2 atmosphere at 850°C for 35 seconds to form an ohmic contact. Ni / Au electrodes are deposited on the surface of the p-GaN layer, and then rapidly annealed in an O2 atmosphere at 550°C for 300 seconds to form an ohmic contact. A SiO2 layer is then deposited to isolate the n- and p-electrodes. 2μm thick Au metal is deposited through photolithography and ICP etching technology to lead out the n-type and p-type electrodes.

[0077] S4: Splitting and packaging to obtain flip-chip AlGaN-based ultraviolet LED chips.

[0078] Effect verification

[0079] The thin film flip-chip AlGaN-based UV LED structure described in Example 1 and the flip-chip UV LED structure described in Comparative Example 1 were tested and compared. The results are as follows: Figure 4 As shown:

[0080] At an operating current of 100 mA, the light output power of the thin film flip-chip AlGaN-based ultraviolet LED described in Example 1 reaches 31.8 mW, which is much greater than the flip-chip ultraviolet LED described in Comparative Example 1 (17.2 mW).

[0081] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED, comprising the following steps: S1, epitaxially growing a GaN template on a sapphire substrate to obtain a GaN template layer; S2, epitaxially growing a pre-crack layer on the GaN template layer; wherein, The material of the pre-crack layer is AlN or AlGaN; the molar fraction of the Al component in the pre-crack layer is 30%-100%; the thickness of the pre-crack layer is 10-300 nm; S3, epitaxially growing an AlGaN crack-filling layer on the pre-crack layer; S4, epitaxially growing a UV LED structure on the AlGaN crack-filling layer, comprising an n-AlGaN layer, an active region multi-quantum well layer, a p-AlGaN electron blocking layer, a p-AlGaN layer, and a p-GaN layer; S5. Forming an n-type electrode on the n-AlGaN layer and a p-type electrode on the p-GaN layer by photolithography and ICP etching techniques; depositing an isolation layer between the n-type electrode and the p-type electrode; leading a metal layer on the n-type electrode, and bonding the metal layer to a substrate; S6, peeling off the sapphire substrate; S7, removing the GaN template layer and roughening the surface of the pre-crack layer; S8, etching the pre-crack layer, the AlGaN crack-filling layer and the ultraviolet LED structure, and leading out the p-type electrode, cracks, and packaging to complete the preparation of the thin film flip-chip ultraviolet LED.

2. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1, characterized in that: In step S1, the surface of the GaN template layer is free of cracks and has an atomically smooth surface morphology; The thickness of the GaN template layer is 1-10 μm.

3. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S1, the GaN template layer is obtained by epitaxial growth through the MOCVD method.

4. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S2, the pre-crack layer is obtained by epitaxial growth using a MOCVD method.

5. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S3, the molar fraction of the Al component in the AlGaN crack-filling layer is 30%-90%; The thickness of the AlGaN crack-filling layer is 100-2000 nm; The AlGaN crack-filling layer has no cracks on its surface and has an atomic-level flat step morphology.

6. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S3, the AlGaN crack-filling layer is obtained by epitaxial growth using a MOCVD method.

7. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S6, the stripping of the sapphire substrate is achieved by using a laser with a wavelength equal to or shorter than 364 nm.

8. The method for preparing a thin film flip-chip AlGaN-based ultraviolet light-emitting diode device LED according to claim 1 or 2, characterized in that: In step S7, the GaN template layer is removed by ICP etching; The surface of the pre-crack layer is roughened by wet etching.

9. A thin film flip-chip AlGaN-based ultraviolet light emitting diode device LED obtained by the preparation method according to any one of claims 1 to 8.

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