A method for exfoliating a GaN epitaxial layer from a growth substrate

Abstract

The application discloses a method for peeling off a GaN epitaxial layer from a growth substrate, which comprises the following steps: providing a GaN epitaxial wafer comprising a growth substrate, a GaN etching layer and a GaN epitaxial layer; preparing a flat edge electrode arranged on the GaN etching layer; providing a stabilized direct current power supply, and connecting a positive electrode with the flat edge electrode; forming a flexible substrate on the upper surface of the GaN epitaxial layer; preparing liquid plastic, and applying the liquid plastic on the upper surface of the flexible substrate, the exposed peripheral side of the flexible substrate and the peripheral side of the GaN epitaxial layer to form a protective layer; irradiating the liquid plastic with an ultraviolet lamp; preparing an electrolyte, and etching the GaN etching layer in the electrolyte; and removing the liquid plastic. By applying the liquid plastic on the flexible substrate and the GaN epitaxial layer, the formed protective layer can protect the flexible substrate from being eroded by the electrolyte and provide stress support for the flexible substrate, the GaN epitaxial layer can be quickly and large-area peeled off, and the peeling-off process is not prone to polluting the electrolyte and interrupting the etching.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method for peeling GaN epitaxial layers from a growth substrate. Background Technology

[0002] GaN, a typical representative of third-generation wide-bandgap semiconductor materials, boasts a bandgap of 3.4 eV. Its high chemical stability, strong radiation resistance, and excellent thermal conductivity make it a preferred material for manufacturing blue LEDs. GaN-based LEDs, due to their energy-saving, environmentally friendly, high-quality display, long lifespan, and wide range of applications, are also known as fourth-generation lighting sources and are attracting increasing attention. In the lighting industry, they are gradually replacing traditional incandescent and fluorescent light sources, becoming the mainstream light source.

[0003] Currently, GaN-based LED devices typically grow GaN semiconductor layers using methods such as metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Sapphire (Al₂O₃) is commonly used as the growth substrate. However, sapphire is a hard, electrically insulating material with very poor thermal conductivity (only 45 W / m). This limits its use as a light-emitting diode, requiring it to be fixed to sapphire, making it difficult to fabricate flexible devices, and resulting in extremely poor thermal conductivity. Therefore, if the epitaxial GaN layer could be peeled off, the feasibility of subsequent device design would be greatly improved.

[0004] Currently, laser lift-off (LLO), stress lift-off (SLO), or chemical lift-off (CLO) methods are commonly used to separate epitaxial layers from the growth substrate. Among these, laser lift-off (LLO) is susceptible to problems because the heat generated by the laser beam during lift-off can affect the properties of the epitaxial layer itself. Stress lift-off (SLO) is difficult to control and time-consuming due to the quality and thickness of the epitaxial layer, and it can even be difficult to lift thicker epitaxial layers.

[0005] Chemical lift-off (CLO) – an electrochemical etching method – is used to separate the epitaxial GaN layer from the sapphire growth substrate. During the lift-off process, the corrosion of the highly doped gallium nitride by the electrolyte may damage the original structure, causing the reaction to terminate prematurely and making it difficult to lift off over a large area. Furthermore, the stress distribution and adhesion of the sticky lift-off substrate are also affected by the electrolyte etching, thus affecting the final lift-off effect. Summary of the Invention

[0006] In view of the above problems, the present invention overcomes at least one of them by proposing a method for peeling off a GaN epitaxial layer from a growth substrate.

[0007] The technical solution adopted in this invention is as follows:

[0008] This application provides a method for peeling off a GaN epitaxial layer from a growth substrate, comprising the following steps:

[0009] A GaN epitaxial substrate is provided, the GaN epitaxial substrate comprising a growth substrate, a GaN etching layer and a GaN epitaxial layer;

[0010] A flat-edge electrode is fabricated on the GaN etched layer;

[0011] A regulated DC power supply is provided, and the positive terminal of the regulated DC power supply is connected to the flat-edge electrode to form an anode for electrochemical etching. The negative terminal of the regulated DC power supply is also connected to form a cathode for electrochemical etching.

[0012] An adhesive polymer film is provided, and the surface of the adhesive polymer film is adhered to the upper surface of the GaN epitaxial layer to form a flexible substrate;

[0013] A liquid plastic is prepared and applied to the upper surface of the flexible substrate, the exposed peripheral side of the flexible substrate, and the peripheral side of the GaN epitaxial layer to form a protective layer. The protective layer on the flexible substrate is used to provide stress support for the flexible substrate and protect the flexible substrate from the corrosion of the electrolyte. The protective layer on the peripheral side of the GaN epitaxial layer is used to reinforce the protective layer on the flexible substrate and protect the GaN epitaxial layer from the corrosion of the electrolyte.

[0014] The liquid plastic is irradiated with an ultraviolet lamp to solidify it.

[0015] Prepare an electrolyte solution, place the electrochemically etched cathode and the GaN etched layer into the electrolyte solution to form a closed circuit, turn on the regulated DC power supply, and cause the GaN etched layer to undergo electrochemical corrosion in the electrolyte solution to achieve the peeling of the GaN epitaxial layer from the substrate.

[0016] Remove the liquid plastic from the flexible substrate.

[0017] On the one hand, liquid plastics have excellent adhesion, electrical insulation, heat resistance and chemical stability. On the other hand, liquid plastics have low shrinkage and water absorption rates and good mechanical strength, which allows the formed protective layer to protect the flexible substrate from the corrosion of the electrolyte and provide stress support to the flexible substrate.

[0018] This invention involves coating a flexible substrate and a GaN epitaxial layer with liquid plastic, then etching the GaN etching layer, and finally peeling off the GaN epitaxial layer. This method can quickly and extensively peel off the GaN epitaxial layer, and the peeling process is less likely to contaminate the electrolyte and interrupt the etching process. The peeled GaN film has a low surface roughness and is relatively intact, making it well-suited for subsequent device fabrication.

[0019] Furthermore, the specific steps for fabricating the flat-edge electrode include:

[0020] First, the GaN epitaxial layer is photolithographically processed to fabricate the mounting surface of the flat-edge electrode, which is disposed on the GaN etched layer.

[0021] Metal is plated on the mounting surface of the flat-edge electrode to form a flat-edge electrode.

[0022] The flat-edge electrode is placed on the GaN etching layer so that the GaN etching layer also becomes the anode of electrochemical etching to achieve the etching purpose.

[0023] Furthermore, the process includes applying a ring of liquid plastic to the GaN etched layer and closely adhering to the outer periphery of the protective layer, and then irradiating the applied liquid plastic with an ultraviolet lamp to solidify the liquid plastic, thereby further reinforcing the protective layer.

[0024] Applying another layer of liquid plastic and connecting it to the flexible substrate and the protective layer outside the GaN epitaxial layer can further fix the protective layer on the GaN epitaxial substrate.

[0025] Furthermore, during the electrochemical corrosion of the GaN etched layer, the entire GaN etched layer is immersed in the electrolyte, and the flat-edge electrode is located 1–6 cm above the liquid surface.

[0026] Furthermore, the GaN epitaxial substrate is prepared by metal-organic chemical vapor deposition, specifically including: first forming a doped GaN etching layer on the growth substrate, and then forming an undoped GaN epitaxial layer on the GaN etching layer.

[0027] In practical applications, GaN epitaxial substrates prepared by metal-organic chemical vapor deposition also include a GaN buffer layer, which is disposed between the substrate and the GaN etched layer, and the thickness of the GaN buffer layer is 200-400 nm.

[0028] Furthermore, the growth substrate is a sapphire growth substrate, and the doping concentration of the GaN etched layer is 4 × 10⁻⁶. 18 ~5×10 19 cm -3The thickness is 1 to 2 micrometers, and the thickness of the GaN epitaxial layer is 200 to 400 nm.

[0029] In practical applications, the thickness of the GaN etched layer is 200–400 nm. The selected GaN etched layer has a high doping concentration, which helps to save materials and reduce costs.

[0030] Furthermore, the flexible substrate is a blue film or a UV film, and the flexible substrate is used to provide stress support for the stripped GaN epitaxial layer.

[0031] Furthermore, polystyrene or polycarbonate plastic is dissolved in chloroform to form the liquid plastic.

[0032] Furthermore, the electrolyte is an oxalic acid solution with a concentration of 0.3–0.4 mol / L.

[0033] Furthermore, the liquid plastic can be removed by acid or alkali corrosion or by mechanical cutting.

[0034] The beneficial effects of this invention are:

[0035] (1) On the one hand, liquid plastics have excellent adhesion, electrical insulation, heat resistance and chemical stability. On the other hand, liquid plastics have low shrinkage and water absorption and good mechanical strength, which makes the formed protective layer able to protect the flexible substrate from the corrosion of the electrolyte and provide stress support to the flexible substrate.

[0036] (2) The present invention coats liquid plastic on the flexible substrate and GaN epitaxial layer, then etches the GaN etching layer, and then peels off the GaN epitaxial layer on top. This method can quickly and extensively peel off the GaN epitaxial layer, and the peeling process is not easy to contaminate the electrolyte and interrupt the etching. The peeled GaN film has a low surface roughness and is relatively intact, which can be well used for subsequent device construction.

[0037] (3) The selected GaN etching layer has a high doping concentration, which helps to save materials and costs.

[0038] In this invention, a highly doped gallium nitride sacrificial layer is etched to remove the epitaxial gallium nitride layer on top. This method can quickly and over a large area remove the GaN epitaxial layer, and the removed GaN film has a low surface roughness and is relatively intact, making it well-suited for subsequent device fabrication. Attached Figure Description

[0039] Figure 1 This is a cross-sectional schematic diagram of the GaN epitaxial structure in the main view direction according to an embodiment of the present invention;

[0040] Figure 2This is a top-view cross-sectional schematic diagram of the epitaxial structure of GaN according to an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram showing the positional relationship between the flat-edge electrode and the electrolyte surface in an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the cathode, anode, and GaN etched layer being placed in the electrolyte during electrochemical etching, according to an embodiment of the present invention.

[0043] Figure 5 This is a schematic diagram of an optical microscope image of the GaN epitaxial layer after stripping in Embodiment 1 of the present invention;

[0044] Figure 6 This is a Raman spectroscopy image of the GaN epitaxial layer after peeling in Embodiment 1 of the present invention;

[0045] Figure 7 This is a SEM image of the GaN epitaxial layer after stripping in Embodiment 1 of the present invention.

[0046] The labels for the attached figures are as follows:

[0047] 1. Growth substrate; 2. GaN etched layer; 3. GaN epitaxial layer; 4. Flat-edge electrode; 5. Flexible substrate; 6. Protective layer; 7. GaN buffer layer; 8. Electrolyte surface. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings.

[0049] Example 1

[0050] This application provides a method for peeling off a GaN epitaxial layer from a growth substrate, comprising the following steps:

[0051] like Figure 1 and Figure 2 As shown, a GaN epitaxial substrate is provided, which includes a growth substrate 1, a GaN etching layer 2, and a GaN epitaxial layer 3;

[0052] A flat-edge electrode 4 is fabricated and disposed on the GaN etched layer 2;

[0053] A regulated DC power supply is provided, and the positive terminal of the regulated DC power supply is connected to the flat-edge electrode 4 to form the anode of electrochemical etching. The negative terminal of the regulated DC power supply is also connected to form the cathode of electrochemical etching.

[0054] A viscous polymer film is provided, and the surface of the viscous polymer film is adhered to the upper surface of the GaN epitaxial layer 3 to form a flexible substrate 5;

[0055] Liquid plastic is prepared and applied to the upper surface of flexible substrate 5, the exposed periphery of flexible substrate 5, and the periphery of GaN epitaxial layer 3 to form a protective layer 6. The protective layer 6 on flexible substrate 5 is used to provide stress support for flexible substrate 5 and protect flexible substrate 5 from the corrosion of electrolyte. The protective layer 6 on the periphery of GaN epitaxial layer 3 is used to reinforce the protective layer 6 on flexible substrate 5 and protect GaN epitaxial layer 3 from the corrosion of electrolyte.

[0056] The liquid plastic is irradiated with an ultraviolet lamp to solidify it.

[0057] like Figure 4 As shown (DC power supply is not shown in the figure), prepare the electrolyte, put the electrochemically etched cathode and GaN etched layer 2 into the electrolyte to form a closed circuit, turn on the regulated DC power supply, so that the GaN etched layer 2 undergoes electrochemical corrosion in the electrolyte to achieve the separation of GaN epitaxial layer 3 from the substrate.

[0058] Remove the liquid plastic from the flexible substrate 5.

[0059] On the one hand, liquid plastics have excellent adhesion, electrical insulation, heat resistance and chemical stability. On the other hand, liquid plastics have low shrinkage and water absorption and good mechanical strength, which makes the formed protective layer 6 able to protect the flexible substrate 5 from the corrosion of the electrolyte and provide stress support for the flexible substrate 5.

[0060] like Figure 5 As shown, the present invention involves coating a liquid plastic over a flexible substrate and a GaN epitaxial layer 3, then etching a GaN etching layer 2, and finally peeling off the GaN epitaxial layer 3. This method can quickly and extensively peel off the GaN epitaxial layer 3, and the peeling process is less likely to contaminate the electrolyte and interrupt the etching process. The peeled GaN film has a low surface roughness and is relatively intact, making it well-suited for subsequent device fabrication.

[0061] In this embodiment, the concentration of the liquid plastic is 0.5 mol / L.

[0062] In this embodiment, the planar dimensions of the flexible substrate 5 are 5cm × 5cm.

[0063] In this embodiment, the protective layer 6 coated on the flexible substrate 5 has a planar dimension of 5.5cm × 5.5cm.

[0064] In this embodiment, the specific steps for preparing the flat-edge electrode 4 include:

[0065] First, the GaN epitaxial layer 3 is photolithographically processed to fabricate the mounting surface of the flat-edge electrode 4, which is then placed on the GaN etched layer 2.

[0066] Metal is plated on the mounting surface of the flat-edge electrode 4 to form the flat-edge electrode 4.

[0067] The flat-edge electrode 4 is placed on the GaN etching layer 2 so that the GaN etching layer 2 also becomes the anode of electrochemical etching to achieve the purpose of etching.

[0068] In this embodiment, the cathode for electrochemical etching is a Pt electrode, and the flat-edge electrode 4 is made of gold.

[0069] In this embodiment, a ring of liquid plastic is applied to the GaN etched layer 2 and closely adhering to the outer periphery of the protective layer 6, and then the applied liquid plastic is irradiated with an ultraviolet lamp to solidify the liquid plastic, thereby further reinforcing the protective layer 6.

[0070] In this embodiment, the liquid plastic near the flat electrode 4 solidifies to form a coating 8 mm wide, which can also prevent liquid splashing from corroding the flat electrode 4.

[0071] In this embodiment, the coated liquid plastic is irradiated with a 365nm ultraviolet lamp for 10 minutes to cure it.

[0072] Apply another layer of liquid plastic and connect it to the flexible substrate 5 and the protective layer 6 outside the GaN epitaxial layer 3 to further fix the protective layer 6 onto the GaN epitaxial substrate.

[0073] In this embodiment, a GaN epitaxial substrate is prepared by metal-organic chemical vapor deposition. The specific steps include: first forming a doped GaN etching layer 2 on the growth substrate 1, and then forming an undoped GaN epitaxial layer 3 on the GaN etching layer 2.

[0074] In this embodiment, the GaN epitaxial substrate prepared by metal-organic chemical vapor deposition further includes a GaN buffer layer 7, which is disposed between the substrate and the GaN etched layer 2, and the thickness of the GaN buffer layer 7 is 200-400 nm.

[0075] In this embodiment, the growth substrate 1 is a sapphire growth substrate 1, and the doping concentration of the GaN etched layer 2 is 4×10⁻⁶. 18 ~5×10 19 cm -3 The thickness is 1-2 micrometers, and the thickness of GaN epitaxial layer 3 is 200-400 nm.

[0076] In practical applications, the thickness of GaN etched layer 2 is 200–400 nm. The selected GaN etched layer 2 has a high doping concentration, which helps to save materials and reduce costs.

[0077] In this embodiment, the flexible substrate 5 is a blue film or a UV film, and the flexible substrate 5 is used to provide stress support for the stripped GaN epitaxial layer 3.

[0078] In this embodiment, polystyrene plastic or polycarbonate plastic is dissolved in chloroform to form liquid plastic.

[0079] In this embodiment, the electrolyte is an oxalic acid solution with a concentration of 0.3–0.4 mol / L.

[0080] In this embodiment, the liquid plastic is removed by acid-base corrosion or by mechanical cutting.

[0081] like Figure 3 As shown, in this embodiment, when the GaN etched layer 2 undergoes electrochemical corrosion, the entire GaN etched layer 2 is immersed in the electrolyte, and the flat-edge electrode 4 is located 1 cm above the electrolyte surface 8.

[0082] In this embodiment, the DC power supply voltage is set to 35V, and the time for the GaN epitaxial layer 3 to be peeled off from the growth substrate 1 by etching the GaN etching layer 2 is 12 hours.

[0083] The protective layer 6 formed by the liquid plastic effectively provides stress support, protects the electrolyte from contamination, and allows the reaction to proceed smoothly without interruption.

[0084] like Figure 6 As shown, according to Raman analysis, the Raman peak positions of the peeled film match the characteristic peak positions of GaN, such as... Figure 7 As shown in the SEM results, this method is effective in removing the GaN epitaxial layer 3.

[0085] Example 2

[0086] The difference between this embodiment and embodiment 1 is that, in this embodiment, when the GaN etched layer 2 undergoes electrochemical corrosion, the GaN etched layer 2 is completely immersed in the electrolyte, and the flat-edge electrode 4 is located 5 cm above the electrolyte surface 8.

[0087] In this embodiment, the DC power supply voltage is set to 35V, and the GaN epitaxial layer 3 is peeled off from the growth substrate 1 by etching the GaN etching layer 2 in 24 hours.

[0088] The above description is merely a preferred embodiment of the present invention and does not limit the scope of patent protection of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, whether directly or indirectly applied to other related technical fields, are similarly included within the scope of protection of the present invention.

Claims

1. A method of exfoliating a GaN epitaxial layer from a growth substrate, the method comprising: The method comprises the following steps: providing a GaN epitaxial wafer, which comprises a growth substrate, a GaN etching layer and a GaN epitaxial layer; preparing a flat edge electrode, which is arranged on the GaN etching layer; providing a stabilized direct current power supply, and connecting the positive pole of the stabilized direct current power supply with the flat edge electrode to form an anode of electrochemical etching, and connecting the negative pole of the stabilized direct current power supply to form a cathode of electrochemical etching; providing a viscous polymer film, and sticking the surface of the viscous polymer film to the upper surface of the GaN epitaxial layer to form a flexible substrate; preparing a liquid plastic, and applying the liquid plastic to the upper surface of the flexible substrate, the exposed peripheral side of the flexible substrate and the peripheral side of the GaN epitaxial layer to form a protective layer, which is used to provide stress support for the flexible substrate and protect the flexible substrate from electrolyte corrosion, and the protective layer on the peripheral side of the GaN epitaxial layer is used to reinforce the protective layer on the flexible substrate and protect the GaN epitaxial layer from electrolyte corrosion; irradiating the applied liquid plastic with an ultraviolet lamp to solidify the liquid plastic; preparing an electrolyte, and putting the cathode of electrochemical etching and the GaN etching layer into the electrolyte to form a closed loop, and then turning on the stabilized direct current power supply to cause electrochemical corrosion of the GaN etching layer in the electrolyte to achieve separation of the GaN epitaxial layer from the substrate; removing the liquid plastic on the flexible substrate.

2. A method of exfoliating a GaN epitaxial layer from a growth substrate as claimed in claim 1, wherein, The specific steps for preparing the flat edge electrode comprise: firstly performing photolithography on the GaN epitaxial layer to process a mounting surface of the flat edge electrode, which is arranged on the GaN etching layer; plating metal on the mounting surface of the flat edge electrode to form the flat edge electrode.

3. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by applying a laser beam to the growth substrate. The method further comprises applying a ring of liquid plastic to the peripheral side of the GaN etching layer and closely to the peripheral side of the protective layer, and then irradiating the applied liquid plastic with an ultraviolet lamp to solidify the liquid plastic, so as to further reinforce the protective layer.

4. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by applying a laser beam to the growth substrate. When the GaN etching layer is electrochemically corroded, the GaN etching layer is totally immersed in the electrolyte, and the flat edge electrode is located 1-6 cm above the liquid surface.

5. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by a method comprising: The GaN epitaxial wafer is prepared by metal organic chemical vapor deposition, and the specific steps comprise: firstly forming a doped GaN etching layer on the growth substrate, and then forming an undoped GaN epitaxial layer on the GaN etching layer.

6. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by a method comprising: The growth substrate is a sapphire growth substrate, the doping concentration of the GaN etching layer is 4×10 18 ~5×10 19 cm -3 -2 microns, and the thickness of the GaN epitaxial layer is 200-400 nm.

7. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by a method comprising: The flexible substrate is a blue film or a UV film, which is used to provide stress support for the GaN epitaxial layer after separation.

8. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by, Polystyrene plastic or polycarbonate plastic is dissolved in chloroform to form the liquid plastic.

9. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by, The electrolyte is an oxalic acid solution, and the concentration of the oxalic acid solution is 0.3-0.4 mol / L.

10. The method of claim 1, wherein the GaN epitaxial layer is separated from the growth substrate by, The liquid plastic is removed by acid-base etching or by mechanical cutting.

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