A n-GaN surface roughening method for flip-chip wafer preparation and its application

Abstract

The present invention discloses an n-GaN surface roughening method for flip-chip wafer preparation and application, comprising: forming an AlGaN buffer layer, an undoped GaN layer, an N-type GaN layer, an MQW layer and a P-type GaN layer in sequence on a silicon substrate by epitaxial growth, together forming a silicon-based GaN wafer; combining the silicon-based GaN wafer with an LED wafer by metal bonding to form a flip-chip wafer; removing the silicon substrate of the flip-chip wafer to expose the AlGaN buffer layer, and partially etching the AlGaN buffer layer; depositing a first etching mask layer on the remaining AlGaN buffer layer, and etching to the undoped GaN layer; depositing a second etching mask layer on the undoped GaN layer, and etching to the N-type GaN layer to complete the n-GaN surface roughening; the roughening size of the present invention can be controlled at a nanometer level, effectively improving the light extraction efficiency of Micro-LED devices.

Description

Technical Field

[0001] The present invention relates to the field of micro-display technology, and in particular to an n-GaN surface roughening method for flip-chip wafer preparation and its application. Background Art

[0002] As the next generation display technology, Micro-LED technology has gradually attracted widespread attention due to its advantages such as high brightness, high contrast, fast response time and long life. However, Micro-LED still faces some technical challenges in practical applications, one of which is to improve the light extraction efficiency (LEE).

[0003] Micro-LED is made of GaN material. GaN has a high refractive index, which leads to a large refractive index difference at the interface with air, resulting in a strong total internal reflection effect, which limits the propagation of light from the inside of the chip to the outside, thereby reducing the light extraction efficiency. In order to overcome this problem, researchers have proposed a variety of surface treatment technologies, among which surface roughening technology has become an important solution due to its effectiveness and controllability.

[0004] Surface roughening technology aims to change the light propagation path, reduce total internal reflection, and improve light emission efficiency by introducing micro-nano-level rough structures on the LED surface. Currently, the common surface roughening method is to use KOH solution wet etching, which has problems such as uneven corrosion, poor process stability, and overly large roughening size. Summary of the invention

[0005] Technical purpose: In view of the shortcomings of the surface roughening in the prior art, the present invention discloses a method and application of n-GaN surface roughening for flip-chip wafer preparation. The method has stable process, the roughening size can be controlled at the nanometer level, and a uniform roughened interface can be obtained, which effectively improves the light extraction efficiency of Micro-LED devices.

[0006] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution:

[0007] A method for roughening an n-GaN surface for flip-chip wafer preparation, comprising:

[0008] An AlGaN buffer layer, an undoped GaN layer, an N-type GaN layer, a multiple quantum well (MQW) layer, and a P-type GaN layer are sequentially formed on a silicon substrate by epitaxial growth, together forming a silicon-based GaN wafer;

[0009] Combine the GaN-on-silicon wafer and LED wafer together through metal bonding to form a flip-chip wafer;

[0010] The silicon substrate of the flip-chip wafer is removed to expose the AlGaN buffer layer, and the AlGaN buffer layer is partially etched;

[0011] Depositing a first etching mask layer on the remaining AlGaN buffer layer, and etching to the undoped GaN layer;

[0012] A second etching mask layer is deposited on the undoped GaN layer, and the N-type GaN layer is etched to complete the roughening of the n-GaN surface.

[0013] The present invention also provides an application of the above-mentioned n-GaN surface roughening method for flip-chip wafer preparation in the field of Micro-LED devices.

[0014] Beneficial effects: The n-GaN surface roughening method and application for flip-chip wafer preparation provided by the present invention have the following beneficial effects:

[0015] The present invention adopts a multi-step mask etching process to form a first etching mask layer and a second etching mask layer respectively. Compared with the traditional wet etching method, it has higher process stability and precise size control ability. By adjusting the mask layer material and thickness, the size of the surface roughening can be precisely controlled to achieve optimization of optical performance; by performing nano-level surface roughening treatment on the n-GaN layer, the total internal reflection of light in the GaN material is effectively reduced, thereby greatly improving the light extraction efficiency.

[0016] The present invention simplifies the manufacturing process of Micro-LEDs by combining a flip-chip bonding process with a surface roughening technology, reduces the process steps, and improves the performance of the device. The silicon-based GaN wafer is selected and a flip-chip bonding process is adopted, which is easy to roughen and has a low processing cost, and can be applied to 4-inch to 12-inch wafer production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0018] Figure 1 It is a flow chart of the steps of the n-GaN surface roughening method of the present invention;

[0019] Figure 2 It is a structural schematic diagram of the n-GaN surface roughening method of the present invention;

[0020] Figure 3 This is an electron microscope image of the roughened surface in Example 1 of the present invention;

[0021] Figure 4 This is an electron microscope image of the roughened surface in Example 2 of the present invention.

[0022] In the figure: 1. Silicon substrate; 2. AlGaN buffer layer; 3. Undoped GaN layer; 4. N-type GaN layer; 5. MQW layer; 6. P-type GaN layer; 7. First bonding metal layer; 8. Second bonding metal layer; 9. LED wafer; 10. First etching mask layer; 11. Second etching mask layer. DETAILED DESCRIPTION

[0023] The present invention will be described more clearly and completely below by way of a preferred embodiment in conjunction with the accompanying drawings, but the present invention is not limited to the scope of the embodiment.

[0024] like Figure 1 and Figure 2 As shown, a method for roughening the surface of n-GaN applied to flip-chip wafer preparation comprises:

[0025] S101, forming an AlGaN buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, an MQW layer 5 and a P-type GaN layer 6 in sequence on a silicon substrate 1 by epitaxial growth, which together constitute a silicon-based GaN wafer, that is, Figure 2 In the part marked I, the specific steps are as follows: select an appropriate silicon wafer as a silicon substrate; first grow an AlGaN buffer layer 2 on the silicon substrate 1. Since there is a lattice mismatch and a difference in thermal expansion coefficient between silicon and GaN materials, the function of the AlGaN buffer layer 2 is to buffer this mismatch, thereby reducing lattice defects; in order to alleviate the lattice mismatch between AlGaN and N-type GaN and reduce the dislocation density, grow an undoped GaN layer 3 as a transition layer on the AlGaN buffer layer 2, and then grow an N-type GaN layer 4; on the N-type GaN layer 4, epitaxially grow a plurality of alternating AlGaN and GaN thin layers, which together constitute an MQW layer 5; and grow a P-type GaN layer 6 on the MQW layer 5.

[0026] S102, combining the silicon-based GaN wafer and the LED wafer 9 together through metal bonding to form a flip-chip wafer, that is, Figure 2 Part II in the figure includes the following steps:

[0027] Depositing a first bonding metal layer 7 on the P-type GaN layer 6;

[0028] Depositing a second bonding metal layer 8 on the LED wafer 9;

[0029] The first bonding metal layer 7 and the second bonding metal layer 8 are bonded together to form a flip-chip wafer.

[0030] S103, removing the silicon substrate 1 of the flip-chip wafer to expose the AlGaN buffer layer 2, and partially etching the AlGaN buffer layer 2, using a dry etching process or a wet etching process to remove the silicon substrate 1; using an inductively coupled plasma (ICP) etching process to partially etch the AlGaN buffer layer, retaining 50nm~100nm of the AlGaN buffer layer 2.

[0031] S104, depositing a first etching mask layer 10 on the remaining AlGaN buffer layer 2, and etching to the undoped GaN layer 3, the material of the first etching mask layer 10 is one or more of Ni, Al, Ti, ITO, Cr, Al2O3, and AlN, and the thickness ranges from 10nm to 800nm; using an ion beam (IBE) etching process to etch to the undoped GaN layer 3, over-etching 300nm to 800nm ​​of the undoped GaN layer 3.

[0032] S105, depositing a second etching mask layer 11 on the undoped GaN layer 3, etching to the N-type GaN layer 4 to complete the n-GaN surface roughening, the material of the second etching mask layer 11 is one or more of ZnO, AlN, ITO, Al2O3, SiN, SiO2, and the thickness ranges from 50nm to 2000nm; using an ICP etching process to etch to the N-type GaN layer, retaining 200nm to 1000nm of the N-type GaN layer.

[0033] The present invention also provides an application of the above-mentioned n-GaN surface roughening method for flip-chip wafer preparation in the field of Micro-LED devices, wherein the Micro-LED device comprises:

[0034] A silicon-based GaN wafer comprises a silicon substrate 1, an AlGaN buffer layer 2, an undoped GaN layer 3 and an N-type GaN layer 4 stacked in sequence, wherein the N-type GaN layer 4 is surface roughened by using the above-mentioned n-GaN surface roughening method for flip-chip wafer preparation;

[0035] The MQW layer 5 is located on the N-type GaN layer 4;

[0036] The P-type GaN layer 6 is located on the MQW layer 5 and is used to provide hole injection and cooperate with the N-type GaN layer 4 to form a PN junction;

[0037] A metal bonding layer, located on the P-type GaN layer, includes a first bonding metal layer 7 and a second bonding metal layer 8 stacked in sequence from bottom to top, wherein the first bonding metal layer 7 is deposited on the silicon-based GaN wafer, and the second bonding metal layer 8 is deposited on the LED wafer, and the two are used to combine the silicon-based GaN wafer with the LED wafer through a flip-chip wafer technology;

[0038] The LED wafer is located on the second bonding metal layer.

[0039] Example 1

[0040] In the n-GaN surface roughening method for flip-chip wafer preparation provided in this embodiment, the material of the second etching mask layer 11 is ITO, and the deposition thickness is 100 nm, which specifically includes the following steps:

[0041] An AlGaN buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, an MQW layer 5 and a P-type GaN layer 6 are sequentially formed on a silicon substrate 1 by epitaxial growth, together forming a silicon-based GaN wafer. Figure 2 The part marked I.

[0042] The GaN-on-silicon wafer and the LED wafer are combined together by metal bonding to form a flip-chip wafer. Figure 2 Part II in the figure includes the following steps:

[0043] Depositing a first bonding metal layer 7 on the P-type GaN layer 6;

[0044] Depositing a second bonding metal layer 8 on the LED wafer;

[0045] The first bonding metal layer 7 and the second bonding metal layer 8 are bonded together to form a flip-chip wafer.

[0046] The silicon substrate 1 of the flip-chip wafer is removed by a dry etching process or a wet etching process to expose the AlGaN buffer layer 2, and the AlGaN buffer layer 2 is partially etched by an ICP etching process to retain 50 nm of the AlGaN buffer layer 2.

[0047] 80 nm of Al2O3 is deposited on the remaining AlGaN buffer layer 2 as the first etching mask layer 10, and etching is performed to the undoped GaN layer 3, with an overetching depth of 300 nm.

[0048] 100 nm of ITO is deposited on the undoped GaN layer 3 as the second etching mask layer 11, and the N-type GaN layer 4 is etched to retain 500 nm of the N-type GaN layer 4 to complete the n-GaN surface roughening. Figure 3 As shown, D1 represents the roughened characteristic size of the N-type GaN layer after the n-GaN surface is roughened under a microscope in this embodiment, and the roughened size is controlled to be 200nm-500nm.

[0049] Example 2

[0050] In the n-GaN surface roughening method for flip-chip wafer preparation provided in this embodiment, the material of the second etching mask layer 11 is ITO, and the deposition thickness is 500nm, which specifically includes the following steps:

[0051] An AlGaN buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, an MQW layer 5 and a P-type GaN layer 6 are sequentially formed on a silicon substrate 1 by epitaxial growth, together forming a silicon-based GaN wafer. Figure 2 The part marked I.

[0052] The GaN-on-silicon wafer and the LED wafer are combined together by metal bonding to form a flip-chip wafer. Figure 2 Part II in the figure includes the following steps:

[0053] Depositing a first bonding metal layer 7 on the P-type GaN layer;

[0054] Depositing a second bonding metal layer 8 on the LED wafer;

[0055] The first bonding metal layer 7 and the second bonding metal layer 8 are bonded together to form a flip-chip wafer.

[0056] The silicon substrate 1 of the flip-chip wafer is removed by a dry etching process or a wet etching process to expose the AlGaN buffer layer 2, and the AlGaN buffer layer 2 is partially etched by an ICP etching process to retain 50 nm of the AlGaN buffer layer 2.

[0057] 80 nm of Al2O3 is deposited on the remaining AlGaN buffer layer 2 as the first etching mask layer 10, and etching is performed to the undoped GaN layer 3, with an overetching depth of 300 nm.

[0058] Deposit 500nm of ITO on the undoped GaN layer 3 as the second etching mask layer 11, etch to the N-type GaN layer 4, retain 500nm of the N-type GaN layer 4, and complete the n-GaN surface roughening, such as Figure 4 As shown, D1 and D2 represent the roughened characteristic sizes of the N-type GaN layer after the n-GaN surface roughening is performed in this embodiment under a microscope. At this time, the roughened size is controlled to be 1300nm~1800nm.

[0059] The present invention provides an n-GaN surface roughening method and application for flip-chip wafer preparation. Combining the characteristics of silicon-based GaN epitaxial structure and flip-chip bonding process, layered multi-step mask etching is adopted. First, the AlGaN buffer layer 2 is partially etched to obtain a rough surface. Then, a metal or metal oxide that is difficult to etch is selected as the first etching mask layer 10 and is etched to the undoped GaN layer 3 to complete the preliminary roughening. Then, an oxide or nitride that is difficult to etch is selected as the second etching mask layer 11 and is etched to the N-type GaN layer 4. Finally, a uniform and dense roughened surface is obtained, and the size can be controlled at the nanometer level, which effectively improves the light extraction efficiency of the Micro-LED device. Compared with the roughening method of the prior art, the layered multi-step mask etching will neither cause defects due to excessive roughening nor fail to achieve the effect of improving the light extraction efficiency due to insufficient roughening, and the roughening size is more controllable.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for roughening the surface of n-GaN used in flip-chip wafer preparation, characterized in that: include: An AlGaN buffer layer, an undoped GaN layer, an N-type GaN layer, an MQW layer and a P-type GaN layer are sequentially formed on a silicon substrate by epitaxial growth, together forming a silicon-based GaN wafer; Combine the GaN-on-silicon wafer and LED wafer together through metal bonding to form a flip-chip wafer; The silicon substrate of the flip-chip wafer is removed to expose the AlGaN buffer layer, and the AlGaN buffer layer is partially etched; Depositing a first etching mask layer on the remaining AlGaN buffer layer, and etching to the undoped GaN layer; Depositing a second etching mask layer on the undoped GaN layer, and etching to the N-type GaN layer to complete the n-GaN surface roughening; The material of the first etching mask layer is one or more of Ni, Al, Ti, ITO, Cr, Al2O3, and AlN, with a thickness range of 10nm~800nm; the material of the second etching mask layer is one or more of ZnO, AlN, ITO, Al2O3, SiN, and SiO2, with a thickness range of 50nm~2000nm.

2. The method for roughening the surface of n-GaN used in flip-chip wafer preparation according to claim 1, characterized in that: Combining GaN-on-silicon wafers with LED wafers through metal bonding to form a flip-chip wafer includes: Depositing a first bonding metal layer on the P-type GaN layer; depositing a second bonding metal layer on the LED wafer; The first bonding metal layer and the second bonding metal layer are bonded together to form a flip-chip wafer.

3. The method for roughening the surface of n-GaN used in flip-chip wafer preparation according to claim 1, characterized in that: The AlGaN buffer layer is partially etched using an ICP etching process, leaving 50nm~100nm of the AlGaN buffer layer.

4. The method for roughening the surface of n-GaN used in flip-chip wafer preparation according to claim 1, characterized in that: The IBE etching process is used to etch to the undoped GaN layer, and the undoped GaN layer of 300nm~800nm ​​is overetched.

5. The method for roughening the surface of n-GaN used in flip-chip wafer preparation according to claim 1, characterized in that: Use ICP etching to the N-type GaN layer, retaining 200~1000nm of the N-type GaN layer.

6. The method for roughening the surface of n-GaN used in flip-chip wafer preparation according to claim 1, characterized in that: The silicon substrate is removed using a dry etching process or a wet etching process.

7. An application of the n-GaN surface roughening method for flip-chip wafer preparation as described in any one of claims 1 to 6 in the field of Micro-LED devices.

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