Sapphire substrate with composite patterned microstructure and preparation method thereof

Abstract

The invention provides a sapphire substrate with a composite patterned microstructure and a preparation method of the sapphire substrate. An epitaxial layer structure comprises a sapphire substrate, a GaN patterned microstructure and a silicon oxide layer which are sequentially arranged from bottom to top; the GaN patterned microstructure is arranged on the surface of the sapphire substrate; and the silicon oxide layer is arranged on the surface of the GaN patterned microstructure. According to the invention, the lateral growth of the GaN epitaxial layer between the microstructures can be enhanced, the lateral growth advantage brought by the silicon oxide surface can be maintained, and the lateral expansion amount can be improved; and meanwhile, the problem that a pit is formed at the position due to the fact that the GaN microstructure absorbs ultraviolet light and is decomposed when the substrate is stripped by laser is avoided. The stripping efficiency and the device reliability are improved, the subsequent GaN layer epitaxial thickness is reduced, and the pit pinnacle stress influence is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor material processing, in particular to a sapphire substrate with a composite patterned microstructure and a preparation method thereof. Background Art

[0002] Sapphire (Al2O3) substrates are an important substrate material for GaN epitaxial growth due to their high-temperature stability, excellent optical transparency, and mature processing technology. However, the lattice mismatch between sapphire substrates and GaN has long made epitaxial growth of high-quality GaN challenging. In recent years, patterned sapphire substrates have gained widespread application in GaN epitaxy for LEDs. Patterned substrates can significantly improve epitaxy quality. Specifically, composite patterned microstructures combining vertically stacked sapphire and silicon oxide can inhibit GaN growth on the silicon oxide surface, enhance lateral growth of GaN epitaxy between microstructures, and thus improve GaN epitaxy quality. For devices requiring laser lift-off (LAS) on sapphire substrates, using conventional composite patterned microstructures combining vertically stacked sapphire and silicon oxide will cause the GaN grown in the grooved regions between the microstructures to absorb UV laser light and decompose. However, the microstructures themselves do not absorb UV laser light, causing the deeper GaN layers above the microstructures to decompose. This ultimately results in deep pits in the resulting device at the location of the microstructures, with high stress at the pit apex, which can put the device at risk of stress damage. Typically, a very thick GaN layer needs to be grown to ensure that the pits do not penetrate the epitaxial layer inside the device. However, this results in long MOCVD machine times and high manufacturing costs. Summary of the Invention

[0003] The present invention aims to provide a sapphire substrate with a composite patterned microstructure and its preparation method. This method involves forming GaN microstructures on a sapphire substrate and then coating the surface of the GaN microstructures with silicon oxide. This structure enhances the lateral growth of the GaN epitaxial layer between the microstructures, maintaining the lateral growth advantage provided by the silicon oxide surface. Furthermore, the GaN microstructures themselves absorb ultraviolet light and decompose during laser stripping of the substrate, improving stripping efficiency and device reliability. This reduces the thickness of the subsequent GaN epitaxial layer and mitigates the stress effects of pit tips.

[0004] To achieve the above object, the technical solution of the present invention is as follows: The present invention proposes a sapphire substrate with a composite patterned microstructure, wherein the epitaxial layer structure includes a sapphire substrate, a GaN patterned microstructure and a silicon oxide layer arranged in sequence from bottom to top; the GaN patterned microstructure is arranged on the surface of the sapphire substrate; and the silicon oxide layer is arranged on the surface of the GaN patterned microstructure.

[0005] Preferably, the sapphire substrate is a planar sapphire substrate.

[0006] Preferably, the upper surface of the planar sapphire substrate is covered with a plurality of GaN patterned microstructures in an array; the minimum spacing between the bottoms of two adjacent GaN patterned microstructures is 2 μm.

[0007] Preferably, the thickness of the silicon oxide layer is in the range of 200-500 nm.

[0008] Preferably, the GaN patterned microstructure is a conical structure.

[0009] Preferably, the silicon oxide layer only covers the sidewalls of the conical GaN patterned microstructure.

[0010] Preferably, the bottom diameter of the GaN patterned microstructure is 4-5 μm.

[0011] Preferably, the total height of the GaN patterned microstructure is 3-4 μm.

[0012] The present invention provides a method for preparing a sapphire substrate with a composite patterned microstructure, comprising the following steps: S1. Prepare sapphire substrate: Use a flat sapphire substrate; S2. Pre-treating the planar sapphire substrate to remove surface stains; S3, epitaxially growing a GaN layer on the upper surface of the pre-treated planar sapphire substrate using MOCVD technology, without doping; S4. Depositing a metal layer on the lower surface of the planar sapphire substrate and etching the metal layer to retain a metal layer area corresponding to the bottom surface shape of the GaN patterned microstructure, thereby forming an array of circular metal masks; S5. Spin-coating photoresist on the GaN layer on the upper surface of the planar sapphire substrate and irradiating ultraviolet light from the lower surface of the planar sapphire substrate for exposure. At this time, the photoresist in the corresponding areas of the circular metal mask arranged in an array is retained, forming an array of circular photoresists; S6. Etching is performed from the top surface of the planar sapphire using ICP dry etching. The GaN layer in the area not covered by the photoresist is preferentially etched away. As the etching proceeds, the circular photoresist is gradually removed from the edge to the inside, so that the GaN layer originally covered by the photoresist is etched away, forming a conical GaN patterned microstructure. S7, using tetramethylammonium hydroxide water bath to heat the sample to repair the surface damage of the GaN patterned microstructure introduced by dry etching; S8. Perform conventional inorganic and organic cleaning; S9, growing a silicon oxide layer on the upper surface of the planar sapphire substrate using a PECVD process; S10, spin-coating photoresist on the upper surface of the planar sapphire substrate, and irradiating ultraviolet light from the lower surface of the planar sapphire substrate for exposure. At this time, the photoresist in the area corresponding to the circular metal mask arranged in the array is retained, and the circular photoresist arranged in the array is formed again, exposing the area between the GaN patterned microstructures; S11, using hydrofluoric acid vapor wet etching to remove the silicon oxide layer in the area not covered by the photoresist, and then stripping the photoresist in the area; S12. Use wet etching to remove the circular metal masks arranged in an array on the lower surface of the planar sapphire substrate.

[0013] Preferably, the GaN layer growth method of S3 is replaced by: A GaN layer is epitaxially grown on the front side of a pre-treated planar sapphire substrate using HVPE technology and doped with silicon.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention realizes a sapphire substrate with a composite patterned microstructure, which can realize high-quality GaN device epitaxy. During laser stripping of the substrate, the GaN layer within the patterned microstructure absorbs ultraviolet light and decomposes. As a result, after the substrate is stripped, no obvious pits are formed in the composite patterned microstructure area, effectively solving the pit problem faced by traditional patterned microstructures. This is conducive to reducing the cost of device epitaxy and improving the reliability of devices after laser stripping.

[0015] (2) The present invention arranges circular metal masks in an array on the back of a planar sapphire substrate for photolithography of silicon oxide layers and GaN patterned microstructures, so that the two etchings can be strictly aligned, thereby avoiding alignment deviation caused by mask overlay. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural diagram of the present invention.

[0017] In the picture: 1-Sapphire substrate; 2-GaN patterned microstructure; 3-Silicon oxide layer. DETAILED DESCRIPTION

[0018] The following is combined with Figure 1 , the technical solution of the present invention is described in detail.

[0019] Example 1 The present invention provides a sapphire substrate with a composite patterned microstructure. The sapphire substrate with a composite patterned microstructure comprises, from bottom to top, a planar sapphire substrate 1, a GaN patterned microstructure 2, and a silicon oxide layer 3. The GaN patterned microstructure 2 is disposed on the surface of the sapphire substrate 1; the silicon oxide layer 3 is disposed on the surface of the GaN patterned microstructure 2.

[0020] A GaN patterned microstructure 2 is disposed on the top surface of a planar sapphire substrate 1. The GaN patterned microstructure 2 is conical in shape. Its base diameter is 4 microns and its total height is 3 microns. Several GaN patterned microstructures 2 are arranged in an array, covering the entire top surface of the planar sapphire substrate 1. The minimum spacing between the bases of two adjacent GaN patterned microstructures 2 is 2 microns.

[0021] The silicon oxide layer 3 has a thickness of 200 nm and only covers the sidewalls of the GaN patterned microstructures 2. The silicon oxide layer 3 does not exist in the region between two adjacent GaN patterned microstructures 2, and the upper surface of the planar sapphire substrate 1 is exposed in this region.

[0022] The present invention provides a method for preparing a sapphire substrate with a composite patterned microstructure, comprising the following steps: (1) Prepare sapphire substrate: Use a flat sapphire substrate; (2) Pretreatment of the planar sapphire substrate to remove surface stains; (3) epitaxially growing a GaN layer on the front surface of the pre-treated planar sapphire substrate using MOCVD technology, the growth temperature being 1100 degrees, and without doping; (4) A metal layer is deposited on the back of the planar sapphire substrate, and then the metal is etched. The area of ​​the metal layer that remains corresponds to the bottom shape of the GaN patterned microstructure, forming an array of circular metal masks. Photoresist is spin-coated on the GaN layer on the front of the planar sapphire substrate, and then ultraviolet light is irradiated from the back of the planar sapphire substrate for exposure. At this time, the photoresist in the area corresponding to the array of circular metal masks is retained, forming an array of circular photoresist. Then, ICP dry etching is used to etch from the front of the planar sapphire. The GaN layer in the area not covered by the photoresist is etched away first; as the etching proceeds, the circular photoresist is gradually removed from the edge to the inside, so that the GaN layer originally covered by the photoresist is etched to form a GaN patterned microstructure; (5) The sample was heated in a tetramethylammonium hydroxide water bath to repair the surface damage of the GaN patterned microstructure introduced by dry etching; (6) Perform routine inorganic and organic cleaning; (7) Growing a silicon oxide layer on the front side of a planar sapphire substrate using a PECVD process; (8) Spin-coat photoresist on the front of the planar sapphire substrate, and then expose it to ultraviolet light from the back of the planar sapphire substrate. At this time, the photoresist in the area corresponding to the arrayed circular metal mask is retained, and the arrayed circular photoresist is formed again, exposing the area between the GaN patterned microstructures. Use hydrofluoric acid vapor wet etching to remove the silicon oxide layer in the area not covered by the photoresist. Then peel off the regional photoresist.

[0023] (9) Wet etching removes the circular metal masks arranged in an array on the back side of the planar sapphire substrate.

[0024] Example 2 The GaN patterned microstructure 2 is a conical structure. Its base diameter is 5 microns and its total height is 4 microns. Several GaN patterned microstructures 2 are arranged in an array, covering the entire top surface of the planar sapphire substrate 1. The minimum spacing between the bases of two adjacent GaN patterned microstructures 2 is 2 microns.

[0025] The thickness of the silicon oxide layer 3 is 400 nm.

[0026] The rest is the same as that of the first embodiment.

[0027] Example 3 A GaN layer is epitaxially grown on the front side of a pre-treated planar sapphire substrate using HVPE technology and doped with silicon, with a total thickness of 4 microns.

[0028] The rest is the same as that of the first embodiment.

[0029] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions and effects do not exceed the scope of the technical solution of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A sapphire substrate with a composite patterned microstructure, characterized in that: The epitaxial layer structure comprises a sapphire substrate, a GaN patterned microstructure and a silicon oxide layer which are arranged in sequence from bottom to top; the GaN patterned microstructure is arranged on the surface of the sapphire substrate; and the silicon oxide layer is arranged on the surface of the GaN patterned microstructure.

2. The sapphire substrate with a composite patterned microstructure according to claim 1, characterized in that: The sapphire substrate is a planar sapphire substrate.

3. The sapphire substrate with a composite patterned microstructure according to claim 2, characterized in that: The upper surface of the planar sapphire substrate is covered with a plurality of GaN patterned microstructures in an array; the minimum spacing between the bottoms of two adjacent GaN patterned microstructures is 2 μm.

4. The sapphire substrate with a composite patterned microstructure according to claim 1, wherein: The thickness of the silicon oxide layer is in the range of 200-500 nm.

5. The sapphire substrate with a composite patterned microstructure according to claim 1, wherein: The GaN patterned microstructure is a conical structure.

6. The sapphire substrate with a composite patterned microstructure according to claim 5, characterized in that: The silicon oxide layer only covers the sidewalls of the conical GaN patterned microstructure.

7. The sapphire substrate with a composite patterned microstructure according to claim 5, characterized in that: The bottom diameter of the GaN patterned microstructure is 4-5 μm.

8. The sapphire substrate with a composite patterned microstructure according to claim 5, characterized in that: The total height of the GaN patterned microstructure is 3-4 μm.

9. The method for preparing a sapphire substrate with a composite patterned microstructure according to any one of claims 1 to 8, characterized in that: The steps include: S1. Prepare sapphire substrate: Use a flat sapphire substrate; S2. Pre-treating the planar sapphire substrate to remove surface stains; S3, epitaxially growing a GaN layer on the upper surface of the pre-treated planar sapphire substrate using MOCVD technology, without doping; S4. Depositing a metal layer on the lower surface of the planar sapphire substrate and etching the metal layer to retain a metal layer area corresponding to the bottom surface shape of the GaN patterned microstructure, thereby forming an array of circular metal masks; S5. Spin-coating photoresist on the GaN layer on the upper surface of the planar sapphire substrate and irradiating ultraviolet light from the lower surface of the planar sapphire substrate for exposure. At this time, the photoresist in the corresponding areas of the circular metal mask arranged in an array is retained, forming an array of circular photoresists; S6. Etching from the upper surface of the planar sapphire using ICP dry etching, with the GaN layer in the area not covered by the photoresist being etched away first; As etching progresses, the circular photoresist is gradually removed from the edge to the inside, so that the GaN layer originally covered by the photoresist is etched away, forming a conical GaN patterned microstructure; S7, using tetramethylammonium hydroxide water bath to heat the sample to repair the surface damage of the GaN patterned microstructure introduced by dry etching; S8. Perform conventional inorganic and organic cleaning; S9, growing a silicon oxide layer on the upper surface of the planar sapphire substrate using a PECVD process; S10, spin-coating photoresist on the upper surface of the planar sapphire substrate, and irradiating ultraviolet light from the lower surface of the planar sapphire substrate for exposure. At this time, the photoresist in the area corresponding to the circular metal mask arranged in the array is retained, and the circular photoresist arranged in the array is formed again, exposing the area between the GaN patterned microstructures; S11, using hydrofluoric acid vapor wet etching to remove the silicon oxide layer in the area not covered by the photoresist, and then stripping the photoresist in the area; S12. Use wet etching to remove the circular metal masks arranged in an array on the lower surface of the planar sapphire substrate.

10. The method for preparing a sapphire substrate with a composite patterned microstructure according to claim 9, wherein: The GaN layer growth method of S3 is replaced by: A GaN layer is epitaxially grown on the front side of a pre-treated planar sapphire substrate using HVPE technology and doped with silicon.

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