Corrosive liquid and coarsening method of nitrogen polar III-group nitride

Abstract

The invention discloses a nitrogen polar III-nitride corrosive liquid and a coarsening method, and the coarsening method comprises the following steps: providing a bonding wafer, removing a growth substrate of the bonding wafer, and exposing a III-nitride lamination layer of the bonding wafer; the exposed III-nitride laminated layer sequentially comprises an N-type layer, a light-emitting layer and a P-type layer from top to bottom; wherein the exposed surface of the N-type layer is a nitrogen polar surface; and placing the bonded wafer in a corrosive liquid for wet etching, wherein the wet etching enables coarsening particles to be formed on the surface of the N-type layer. According to the method, the ammonia water solution is adopted as the corrosive liquid, the proportion of the ammonia water to the water is adjusted, a dry etching process before coarsening does not need to be carried out, and the coarsening effects that coarsening particles of the nitrogen polar III-group nitride are evenly distributed and the particle size and the particle area are adjustable can be achieved through direct wet etching.

Description

Technical Field

[0001] This invention relates to the field of wet etching of semiconductor materials, and in particular to an etching solution and roughening method for nitrogen polar group III nitrides. Background Technology

[0002] Group III nitride semiconductor materials (including GaN, InN, and AlN) and their alloy systems (such as AlGaN, InGaN, and AlGaInN) have become core material systems for optoelectronic devices such as light-emitting diodes (LEDs), laser diodes, and solar cells due to their excellent optoelectronic properties, such as direct bandgap, high absorption coefficient, radiation resistance, and wide-spectrum tunable bandgap. However, the high refractive index of Group III nitride materials, such as GaN (approximately 2.5), results in a small critical angle for total internal reflection at the semiconductor / air interface (only about 24°), leading to low light extraction efficiency in traditional planar GaN-based LEDs.

[0003] Surface roughening technology is an effective means to improve light extraction efficiency. It can disrupt the total internal reflection conditions at the interface, allowing more light to escape from the chip. The current mainstream approach uses substrate transfer technology, which involves bonding the epitaxial layer to the substrate, removing the original growth substrate, exposing the n-type nitride on the nitrogen polar facet, and utilizing the high chemical reactivity of the nitrogen polar facet and the relatively thick material to roughen the surface. However, this approach still faces two major technical challenges in the roughening process.

[0004] 1. Complex process steps: For nitrogen polar group III nitride epitaxial layers containing AlN buffer layers, the traditional process requires first using dry etching to treat the surface of the AlN buffer layer, then using oxygen plasma to treat the surface after dry etching, and then using wet etching to roughen the surface. The multiple steps increase the complexity of the process.

[0005] 2. Difficulty in precisely controlling the roughening morphology: To avoid damaging the bonding surface, high-concentration inorganic strong bases (such as KOH solution) are often used as roughening solutions. However, such roughening solutions have excessively fast corrosion rates, which can easily lead to over-corrosion or non-uniform roughening. This is usually manifested as larger roughened particles and a lower proportion of unroughened or over-roughened particles, directly affecting the uniformity of light output from the device.

[0006] Taking Chinese invention patent CN111968907A as an example, it discloses a method for roughening nitrogen-polar group III nitrides. First, a nitrogen-polar AlN buffer layer is dry-etched. Then, oxygen plasma is used to treat the surface after dry etching. Finally, KOH solution is used to wet-roughen the group III nitride stack. However, this method requires dry etching, oxygen plasma treatment, and then wet etching, which has problems such as multiple operation steps, complex influencing factors, and poor controllability of the roughening effect. Its industrial practicality and ease of operation need improvement. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide an etching solution and roughening method for nitrogen polar group III nitrides. After removing the growth substrate of the bonded wafer, direct wet etching can form uniformly distributed roughened particles on the surface of nitrogen polar group III nitrides without the need for dry etching surface treatment. The operation is simple and has industrial applicability.

[0008] This invention provides a corrosion solution for nitrogen polar group III nitrides, comprising ammonia and water; the mass fraction of NH3 in the ammonia is 25% to 28%; and the volume ratio of ammonia to water is 1:2 to 1:8.

[0009] The etching solution for polar group III nitrides provided by this invention utilizes the coordination effect of NH3 by preparing an ammonia solution of appropriate concentration to reduce the reactivity at surface defects of group III nitrides, thereby weakening the influence of surface defects and allowing the etching reaction to proceed more uniformly across the surface, achieving uniform roughening. Therefore, this method eliminates the need for a pre-roughening dry etching process; direct wet etching can form uniformly distributed roughened particles on the surface of polar group III nitrides, making it simple to operate and industrially applicable.

[0010] The specific reaction mechanism is as follows: The corrosion of group III polar nitrogen nitrides in ammonia water is essentially a synergistic effect of alkaline hydrolysis and NH3 coordination dissolution. Ammonia water corrodes group III polar nitrogen nitrides through two pathways: ①OH - Attack: Ammonia water undergoes weak dissociation NH3⋅H2O⇌NH4 + +OH - OH - OH - It attacks Ga, Al, or In atoms on the surface of nitrogen-polar group III nitrides to form hydroxyl coordination compounds [Al(OH)4]. - [Ga(OH)4] - Or [In(OH)4] - ② NH3 coordination dissolution: The lone pair of electrons in the NH3 molecule reacts with Ga... 3+ Al 3+ or In 3+ The empty orbitals combine to form ammonia coordination compounds with higher solubility, which promotes the rapid dissolution of metal ions on the surface of group III nitrides. The coordination compounds detach from the surface, exposing new group III nitride atomic layers, which is conducive to the repeated corrosion cycle.

[0011] As an alternative to the corrosion solution of the present invention, the volume ratio of ammonia to water is 1:3 to 1:6.4.

[0012] As an optional embodiment of the corrosive liquid of the present invention, it also includes an inorganic strong alkali, wherein the mass fraction of the inorganic strong alkali is 0~2.0%.

[0013] As an alternative to the corrosion solution of this invention, the inorganic strong base is NaOH and / or KOH.

[0014] The present invention also provides a method for roughening nitrogen polar group III nitrides, using the above-mentioned etching solution, comprising the following steps: Step S1: Provide a bonding wafer, remove the growth substrate of the bonding wafer to expose the group III nitride stack of the bonding wafer; the exposed group III nitride stack includes an N-type layer, a light-emitting layer and a P-type layer from top to bottom; wherein the exposed surface of the N-type layer is the nitrogen polarity surface; Step S2: Place the bonding wafer in an etching solution for wet etching. Wet etching causes coarsening particles to form on the surface of the N-type layer.

[0015] The roughening method for nitrogen polar group III nitrides provided by this invention uses the etching solution provided by this invention. It eliminates the need for a dry etching process before roughening and can directly form uniformly distributed roughened particles on the surface of the N-type layer by wet etching. The method is simple to operate and has industrial applicability.

[0016] As an alternative to the roughening method of the present invention, the group III nitride stack is composed of Al x Ga y In (1-x-y) The material is composed of N, where 0≤x≤1 and 0≤y≤1; the N-type layer is N-type GaN.

[0017] As an optional embodiment of the roughening method of the present invention, in step S1, the N-type layer further includes a buffer layer, the exposed surface of the buffer layer is the nitrogen polar surface, and the nitrogen polar surface of the N-type layer faces upward; in step S2, wet etching removes the buffer layer and forms roughened particles on the surface of the N-type layer; the material of the buffer layer is AlN, GaN or AlGaN.

[0018] As an optional embodiment of the roughening method of the present invention, the temperature of wet corrosion in step S2 is 20℃~30℃; the time of wet corrosion is 30min~180min.

[0019] As an alternative to the roughening method of the present invention, the roughening particles are hexagonal pyramidal or pyramidal structures, and the roughening particles are uniformly distributed on the surface of the N-type layer.

[0020] As an optional embodiment of the coarsening method of the present invention, the size of the coarsened particles is greater than 500 nm and less than 2000 nm, and the area ratio of the coarsened particles on the N-type layer is greater than 70%.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, some of which will become clear as the description proceeds, and others will be learned by practicing the invention. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a group III nitride stack on a silicon substrate in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the bonding wafer structure in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the structure of a nitrogen polar group III nitride stack after wet etching in an embodiment of the present invention.

[0025] Figure 4 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 1.

[0026] Figure 5 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 2.

[0027] Figure 6 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 3.

[0028] Figure 7 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 4.

[0029] Figure 8 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 5.

[0030] Figure 9 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 6.

[0031] Figure 10 This is a microscopic image of the surface morphology after wet etching of nitrogen polar group III nitrides in Example 7.

[0032] Figure 11 The image shows the surface microstructure of the nitrogen polar group III nitride after wet etching, as shown in Comparative Example 1.

[0033] Figure 12 The image shows the surface microstructure of the nitrogen polar group III nitride after wet etching, as shown in Comparative Example 2.

[0034] Figure 13 The image shows the surface microstructure of the nitrogen polar group III nitride after wet etching, as shown in Comparative Example 3.

[0035] Figure 14The image shows the surface microstructure of the nitrogen polar group III nitride after wet etching, as shown in Comparative Example 4.

[0036] Figure 15 This is a schematic diagram illustrating the detection of particle contours using image processing software in an embodiment. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be noted that the accompanying drawings of the present invention use very simplified, non-precise proportions to facilitate and clearly illustrate the present invention.

[0038] In this application, "roughening" refers to the formation of coarse particles on the surface of nitrogen-polar Group III nitrides using wet etching, resulting in a rough surface with uniformly distributed unevenness. "Particle size" refers to the distance between two opposite flat edges in a top view of a hexagonal pyramid or pyramid. "Particle area ratio" refers to the ratio of the number of pixels in the particle area image to the total number of pixels in the image.

[0039] This application provides a corrosion solution for nitrogen polar group III nitrides, comprising ammonia and water; the mass fraction of NH3 in the ammonia is 25%–28%; the volume ratio of ammonia to water is 1:2 to 1:8. It should be noted that these values ​​include endpoint values, and exemplary examples include volume ratios of ammonia to water of 1:2, 1:2.5, 1:3, 1:4, 1:5, 1:6, and 1:8, but are not limited thereto.

[0040] In some embodiments, the volume ratio of ammonia to water is 1:3 to 1:6.4. It should be noted that the values ​​here include endpoint values.

[0041] In some embodiments, the corrosive solution further includes an inorganic strong base, the mass fraction of which is 0-2.0%. It should be noted that these values ​​include the right-hand side values, exemplarily representing 0.5%, 1%, 1.5%, and 2% mass fractions of the inorganic strong base, but not limited to these. Furthermore, according to the chemical equilibrium equation NH3 + H2O ⇌ NH3 ⋅ H2O ⇌ NH4... + +OH - It can be seen that adding an inorganic strong base to ammonia water will increase the concentration of OH- in the solution. - Increasing the concentration of NH3 in the corrosive solution leads to a shift in chemical equilibrium, which in turn increases the concentration of NH3 and promotes the formation of more soluble ammonia coordination compounds. While the addition of strong inorganic bases can accelerate the reaction rate, excessively high concentrations can result in over-corrosion or uneven corrosion. Therefore, controlling the mass fraction of the strong inorganic base within this range ensures both a faster reaction rate and uniform corrosion.

[0042] In some embodiments, the inorganic strong base is NaOH and / or KOH.

[0043] This application also provides a method for roughening nitrogen polar group III nitrides, using the above-mentioned etching solution, including the following steps: Step S1: Provide a bonding wafer 1000, remove the growth substrate 100 of the bonding wafer 1000, and expose the group III nitride stack 110 of the bonding wafer 1000; the exposed group III nitride stack 110 includes an N-type layer 102, a light-emitting layer 103 and a P-type layer 104 from top to bottom; wherein the exposed surface of the N-type layer 102 is the nitrogen polar surface; Step S2: Place the bonding wafer 1000 in an etching solution for wet etching. Wet etching causes coarsened particles 105 to form on the surface of the N-type layer 102.

[0044] In some embodiments, the group III nitride stack 110 is made of Al x Ga y In (1-x-y) The material is composed of N, where 0≤x≤1 and 0≤y≤1; the N-type layer 102 is N-type GaN.

[0045] In some embodiments, in step S1, the N-type layer 102 further includes a buffer layer 101, the exposed surface of the buffer layer 101 being the nitrogen polar surface, and the nitrogen polar surface of the N-type layer 102 facing upwards; in step S2, wet etching removes the buffer layer 101 and forms coarsened particles 105 on the surface of the N-type layer 102; the material of the buffer layer 101 is AlN, GaN, or AlGaN. It should be noted that retaining the buffer layer 101 and directly starting the etching from the nitrogen polar surface of the buffer layer 101 is beneficial for the control of wet etching and can achieve a more uniform coarsening effect on the surface of the N-type layer 102.

[0046] In some embodiments, the temperature of wet etching in step S2 is 20°C to 30°C; the time of wet etching is 30 min to 180 min. It should be noted that since ammonia is easily volatilized when heated, the etching temperature is controlled within this range, and temperature changes will affect the rate of wet etching. Furthermore, too short a wet etching time will lead to incomplete reaction, while too long a time will lead to over-etching. For the etching solution provided by this invention, controlling the etching time within this range enables a uniform roughening effect on the surface of the N-type layer 102.

[0047] In some embodiments, the coarsened particles 105 have a hexagonal pyramid or pyramidal structure and are uniformly distributed on the surface of the N-type layer 102. It should be noted that the more uniform the distribution of the coarsened particles 105, the more beneficial it is for light extraction.

[0048] In some embodiments, the size of the coarsened particles 105 is greater than 500 nm and less than 2000 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is greater than 70%. It should be noted that if the size of the coarsened particles 105 is too large or too small, it will not be conducive to light extraction. A significant improvement in light extraction efficiency can be achieved when the area ratio of the coarsened particles on the N-type layer is greater than 70%.

[0049] The following are some preferred embodiments and comparative examples of this application.

[0050] First, it should be noted that the ammonia solution used in all embodiments and comparative examples of this application is concentrated ammonia solution with an NH3 mass fraction of 25%–28%, and the nitrogen polarity group III nitrides being etched are also the same. The difference lies in the formulation of the etching solution used. The image processing method uses image processing software to detect particle contours (setting the binarization threshold to 190; contrast enhancement to 2; Gaussian blur kernel size to 9×9), such as... Figure 15 As shown. At the same time, the area ratio of coarsened particles 105 on the N-type layer 102 is calculated according to the formula: particle area ratio = number of pixels in the particle region image / total number of pixels in the image. Example 1

[0051] This embodiment provides a method for roughening nitrogen polar group III nitrides, including the following steps: Step S1: Provide a bonding wafer 1000, remove the growth substrate 100 of the bonding wafer 1000, and expose the group III nitride stack 110 of the bonding wafer 1000; the exposed group III nitride stack 110 includes an N-type layer 102, a light-emitting layer 103 and a P-type layer 104 from top to bottom; wherein the exposed surface of the N-type layer 102 is the nitrogen polar surface.

[0052] Specifically, a group III nitride stack 110 is grown on a growth substrate 100 using a metal-organic chemical vapor deposition method. The group III nitride stack 110, from bottom to top, includes a buffer layer 101, an N-type layer 102, a light-emitting layer 103, and a P-type layer 104, as shown below. Figure 1 As shown. The growth substrate 100 is a Si substrate; the buffer layer 101 is made of AlN and has a thickness of 300 nm; the N-type layer 102 is N-type GaN and has a thickness of 3000 nm; the light-emitting layer 103 is a GaN / InGaN multi-quantum-well active layer and has a thickness of 200 nm; and the P-type layer 104 is P-type GaN and has a thickness of 300 nm.

[0053] A high-reflectivity metal 200 and a bonding metal stack 201 are sequentially deposited on a P-type layer 104 using electron beam evaporation. The high-reflectivity metal 200 is made of Ni / Ag, and the bonding metal stack 201 is made of a combination of Cr, Pt, Ti, and Au. A bonding substrate 300, which is a Si substrate, is provided. A bonding metal stack 301 and a protective metal stack 302 are sequentially deposited on both sides of the bonding substrate 300 using electron beam evaporation. The bonding metal stack 301 on the front side of the bonding substrate 300 is made of a combination of Cr, Pt, Au, Cu, and In, and the protective metal stack 302 on the back side of the bonding substrate 300 is made of a combination of Cr, Pt, Au, and Cu. The group III nitride stack of the deposited metal stack is bonded to the front side of the bonding substrate 300 using wafer hot pressing bonding to obtain a bonding wafer 1000.

[0054] The growth substrate 100 is then removed using a wet etching method, exposing the nitrogen polar surface of the buffer layer 101, with the nitrogen polar surface of the N-type layer 102 facing upwards. Figure 2 As shown.

[0055] Step S2: Place the bonding wafer 1000 in a nitrogen-polar group III nitride etching solution for wet etching to remove the buffer layer 101 and form coarsened particles 105 on the surface of the N-type layer 102, such as... Figure 3 As shown, the surface microstructure of the N-type layer 102 after wet etching was characterized using scanning electron microscopy.

[0056] In this embodiment, the etching solution for the nitrogen-polar Group III nitrides is formulated as follows: the volume ratio of ammonia to water is approximately 1:2. The specific preparation process is as follows: 1200 mL of ammonia and 2400 mL of water are mixed evenly in a reaction vessel. The etching temperature is 30°C, and the roughening time is 180 min. The maximum particle size of the roughened particles 105 is 1030 nm, and the area ratio of the roughened particles 105 on the N-type layer 102 is 92.4%. Figure 4 As shown.

[0057] This embodiment achieves uniform roughening of the surface of the N-type layer 102, and the resulting roughened particles 105 have a large area ratio on the N-type layer 102, and the maximum particle size is moderate. Example 2

[0058] The main difference between this embodiment and Example 1 in the etching solution formulation is that the volume ratio of ammonia to water is 1:3. In this embodiment, the etching solution for nitrogen-polar Group III nitrides is prepared by mixing 1000 mL of ammonia and 3000 mL of water in a reaction vessel. The wet etching temperature is 30°C, and the wet etching time is 180 min. The maximum particle size of the coarsened particles 105 is 945 nm, and the area ratio of coarsened particles 105 on the N-type layer 102 is 89.3%. Figure 5 As shown.

[0059] This embodiment also achieves uniform roughening of the surface of the N-type layer 102. However, compared with Embodiment 1, this embodiment reduces the volume ratio of ammonia to water, that is, reduces the mass fraction of ammonia. As a result, the maximum particle size of the roughened particles 105 is reduced, and the area ratio of the roughened particles 105 on the N-type layer 102 is slightly reduced. Example 3

[0060] The etching solution formulation in this embodiment differs from Examples 1 and 2, with an ammonia-to-water volume ratio of 1:8. The specific preparation process is as follows: 400 mL of ammonia and 3200 mL of water are mixed evenly in a reaction vessel. The etching temperature is 30°C, and the roughening time is 180 min. The maximum particle size of the roughened particles 105 is 675 nm, and the area ratio of the roughened particles 105 on the N-type layer 102 is 76.4%. Figure 6 As shown.

[0061] Comparing Examples 1 and 2, it can be seen that further reducing the volume ratio of ammonia to water, i.e. further reducing the mass fraction of the ammonia solution, results in a continued decrease in the maximum particle size of the coarsened particles 105 and a continued decrease in the area ratio of the coarsened particles 105 on the N-type layer 102. Example 4

[0062] The etching solution formulation in this embodiment is basically the same as that in Example 2, with the main difference being the inclusion of 1.0% KOH by mass. The specific preparation process of the etching solution is as follows: 1000 mL of ammonia water, 3000 mL of water, and 40 g of KOH are stirred evenly in a reaction vessel until the solution becomes clear. The actual obtained KOH mass fraction is 1.0%, the wet etching temperature is 30℃, and the wet etching time is 60 min. The maximum particle size of the coarsened particles 105 is 1390 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is 75.5%. Figure 7 As shown.

[0063] Compared with Example 2, it can be seen that adding KOH to the corrosion solution can increase the corrosion rate and shorten the corrosion time required for uniform coarsening. However, the maximum particle size of the coarsened particles is increased, and the area ratio of the coarsened particles 105 on the N-type layer 102 is also reduced, but relatively uniform coarsening can still be achieved. Example 5

[0064] This embodiment is basically the same as Embodiment 4, with the main difference being that it contains 2.0% KOH by mass. The specific preparation process of the etching solution is as follows: 1000 mL of ammonia water, 3000 mL of water, and 80 g of KOH are stirred evenly in a reaction vessel until the solution is clear. The actual obtained KOH mass fraction is 2.0%, the wet etching temperature is 30℃, and the wet etching time is 60 min. The maximum particle size of the coarsened particles 105 is 1890 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is 73.7%. Figure 8 As shown.

[0065] Comparing Examples 2 and 4, it can be seen that increasing the concentration of KOH in the corrosion solution to 2% can further improve the corrosion rate, and the maximum particle size of the coarsened particles continues to increase, but the area ratio of the coarsened particles 105 on the N-type layer 102 continues to decrease. Example 6

[0066] The etching solution formulation in this embodiment is basically the same as that in Example 5, the main difference being that 2.0% KOH is replaced with 2.0% NaOH. The specific preparation process of the etching solution is as follows: 1000mL of ammonia water, 3000mL of water, and 80g of NaOH are stirred evenly in a reaction vessel until the solution is clear. The actual NaOH mass fraction obtained is 2.0%, the wet etching temperature is 30℃, and the wet etching time is 30min. The maximum particle size of the coarsened particles 105 is 1280nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is 90.2%. Figure 9 As shown.

[0067] Comparing Example 5, it can be seen that adding the same mass concentration of NaOH and KOH can achieve a uniform roughening effect. Example 7

[0068] The difference between the etching solution formulation in this embodiment and that in Example 4 is that the volume ratio of ammonia to water is 1:6.4. The specific preparation process of the etching solution is as follows: 500 mL of ammonia, 3200 mL of water, and 74 g of KOH are stirred evenly in a reaction vessel until the solution becomes clear. The actual mass fraction of KOH obtained is 1.0%, the wet etching temperature is 30℃, and the wet etching time is 60 min. The maximum particle size of the coarsened particles 105 is 965 nm, and the area ratio of coarsened particles 105 on the N-type layer 102 is 78.4%. Figure 10 As shown.

[0069] Compared with Example 4, it can be seen that when the mass fraction of KOH in the corrosive solution is the same, reducing the volume ratio of ammonia to water, i.e., reducing the mass fraction of ammonia, results in a decrease in the maximum particle size of the coarsened particles 105. However, the area ratio of the coarsened particles 105 on the N-type layer 102 is increased, and the surface of the N-type layer 102 achieves a more uniform coarsening effect.

[0070] The etching solutions used in Examples 1 to 7 can all achieve a uniform coarsening effect, with the maximum particle size of coarsened particles 105 ranging from 500 nm to 2000 nm and the area ratio of coarsened particles 105 on the N-type layer 102 being greater than 70%.

[0071] In summary, the etching solution provided by this invention exhibits excellent wet etching and surface roughening effects on nitrogen-polar Group III nitrides. The roughened particles form a uniform hexagonal pyramid or pyramidal structure, and the particle size and area are adjustable. The etching solution is simple to prepare, easy to use, and industrially applicable. Comparative Example 1

[0072] The main difference between the etching solution formulations of Comparative Example 1 and Example 1 is that the volume ratio of ammonia to water is less than 1:2. The etching solution was prepared by mixing 1200 mL of ammonia and 1800 mL of water in a reactor. The actual etching solution had a volume ratio of ammonia to water of 1:1.5, a wet etching temperature of 30°C, and a wet etching time of 180 min. The maximum particle size of the coarsened particles 105 was 320 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 was 85.1%. Figure 11 As shown.

[0073] As can be seen from Comparative Example 1, when the volume ratio of ammonia to water is less than 1:2, the concentration of ammonia is too high, and the maximum particle size of the coarsened particles 105 is less than 500 nm, which makes it impossible to achieve a uniform coarsening effect on the surface of the N-type layer 102. Comparative Example 2

[0074] The main difference between the etching solution formulations of Comparative Example 2 and Example 3 is that the volume ratio of ammonia to water is greater than 1:8. The etching solution was prepared by mixing 400 mL of ammonia and 3600 mL of water in a reactor. The actual etching solution had a volume ratio of ammonia to water of 1:9, a wet etching temperature of 30°C, and a wet etching time of 180 min. The maximum particle size of the coarsened particles 105 was 470 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 was 52.6%. Figure 12 As shown.

[0075] As can be seen from Comparative Example 3, when the volume ratio of ammonia to water is greater than 1:9, the concentration of ammonia is too low, the maximum particle size of the coarsened particles 105 is less than 500 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is less than 70%, making it impossible to achieve uniform coarsening on the surface of the N-type layer 102. Comparative Example 3

[0076] Comparative Example 1 is basically the same as Example 6, with the main difference being that it contains 4.0% KOH by mass. The specific preparation process of the etching solution is as follows: 1000 mL of ammonia water, 3000 mL of water, and 160 g of KOH are stirred evenly in a reaction vessel until the solution is clear. The actual obtained KOH mass fraction is 4.0%, the wet etching temperature is 30°C, and the wet etching time is 30 min. The maximum particle size of the coarsened particles 105 is 2330 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is 78.8%. Figure 13 As shown.

[0077] As can be seen from Comparative Example 6, when the concentration of the added inorganic strong alkali is too high, the maximum particle size of the coarsened particles 105 is greater than 2000 nm, and uniform coarsening cannot be achieved on the surface of the N-type layer 102. Comparative Example 4

[0078] Comparative Example 4 is a supplementary experiment demonstrating that the mass fraction of ammonia water is 0, where the mass fraction of KOH is 2.0%, and the remainder is water. The etching solution was prepared by mixing 4000 mL of water and 80 g of KOH in a reaction vessel until the solution became clear. The wet etching temperature was 30℃, and the wet etching time was 30 min. The maximum particle size of coarsened particles 105 was 2130 nm, and the area ratio of coarsened particles 105 on the N-type layer 102 was 66.0%. Figure 14 As shown.

[0079] Compared with Example 6, this comparative example uses a pure inorganic strong alkali solution as the etching liquid. The maximum particle size of the coarsened particles 105 is greater than 2000 nm, and the area ratio of the coarsened particles 105 on the N-type layer 102 is less than 70%, so uniform coarsening cannot be achieved on the surface of the N-type layer 102.

[0080] The embodiments described above are merely illustrative of the technical solutions of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solutions and inventive concepts of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A corrosive liquid for nitrogen polar group III nitrides, characterized in that: Includes ammonia and water; The mass fraction of NH3 in the ammonia water is 25%–28%. The volume ratio of ammonia to water is 1:2 to 1:

8.

2. The corrosive liquid according to claim 1, characterized in that: The volume ratio of ammonia to water is 1:3 to 1:6.

4.

3. The corrosive liquid according to claim 1, characterized in that: It also includes inorganic strong bases, wherein the mass fraction of the inorganic strong bases is 0~2.0%.

4. The corrosive liquid according to claim 3, characterized in that: The inorganic strong base is NaOH and / or KOH.

5. A method for roughening nitrogen polar group III nitrides, characterized in that, The method of using the corrosive liquid as described in any one of claims 1 to 4 includes the following steps: S1. Provide a bonding wafer, remove the growth substrate of the bonding wafer to expose the group III nitride stack of the bonding wafer; the exposed group III nitride stack includes an N-type layer, a light-emitting layer and a P-type layer from top to bottom; wherein the exposed surface of the N-type layer is the nitrogen polarity surface; S2. The bonding wafer is placed in the etching solution for wet etching, which causes coarsened particles to form on the surface of the N-type layer.

6. The coarsening method according to claim 5, characterized in that: The group III nitride stack is composed of Al x Ga y In (1-x-y) The material is composed of N, where 0≤x≤1 and 0≤y≤1; the N-type layer is N-type GaN.

7. The coarsening method according to claim 5, characterized in that: In step S1, the N-type layer further includes a buffer layer, the exposed surface of which is the nitrogen polar surface, and the nitrogen polar surface of the N-type layer faces upward; in step S2, wet etching removes the buffer layer and forms coarsened particles on the surface of the N-type layer; the material of the buffer layer is AlN, GaN, or AlGaN.

8. The coarsening method according to claim 5, characterized in that: In step S2, the temperature of wet etching is 20℃~30℃; the time of wet etching is 30min~180min.

9. The method for roughening nitrogen polar group III nitrides according to claim 5, characterized in that: The coarsened particles have a hexagonal pyramid or pyramidal structure and are uniformly distributed on the surface of the N-type layer.

10. The method for roughening nitrogen polar group III nitrides according to claim 5, characterized in that: The size of the coarsened particles is greater than 500 nm and less than 2000 nm, and the area of ​​the coarsened particles on the N-type layer is greater than 70%.

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