A kind of alkaline gallium nitride polishing liquid based on Fenton reaction and preparation method thereof

Abstract

The present invention belongs to the technical field of chemical mechanical polishing, and relates to an alkaline gallium nitride polishing liquid based on the Fenton reaction and a preparation method thereof. The alkaline gallium nitride polishing liquid provided by the present invention comprises hydrogen peroxide, silica abrasive, sodium bicarbonate, iron salt, dispersant, stabilizer, chelating agent and deionized water. The present invention can broaden the scope of application of the Fenton reaction to alkaline conditions by catalyzing hydrogen peroxide with an iron-based ion complex. The use of a stabilizer can promote the conversion of trivalent iron ions to ferrous ions, enhance the catalytic effect of ferrous ions, and extend the effective duration of the polishing liquid. The polishing liquid provided by the present invention is environmentally friendly, does not corrode processing equipment, has low cost, stable properties, is more convenient to operate without the need for additional auxiliary equipment, and can be stably stored for a long time.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical mechanical polishing and relates to an alkaline gallium nitride polishing liquid based on Fenton reaction and a preparation method thereof. Background Art

[0002] Gallium nitride (GaN) is a compound semiconductor material composed of nitrogen and gallium, and is a third-generation semiconductor material. Due to its wide bandgap characteristics, it is also known as a wide-bandgap semiconductor material. GaN materials possess a wide bandgap, high breakdown electric field, high thermal conductivity, high electron saturation velocity, and strong radiation resistance. Therefore, semiconductor devices made of GaN offer advantages over traditional silicon-based devices, such as high voltage and high temperature resistance, low power consumption, small size, and light weight. GaN is currently entering the large-scale application stage. In the power device field, GaN diodes, MOSFETs, and optoelectronic devices (LEDs) have begun commercial application, and it also has broad application potential in detection devices.

[0003] The precision of GaN substrate processing directly impacts device performance. Epitaxy and device applications place extremely stringent demands on GaN substrate surface quality. GaN's high hardness, brittleness, and chemical stability make traditional processing methods difficult to meet these requirements. Limited by processing technology, the efficiency of achieving high-quality GaN substrates is currently extremely low.

[0004] The processing of gallium nitride single crystals primarily involves slicing, grinding, and polishing, with polishing being the most critical step in determining surface quality. The polishing process for gallium nitride wafers can be divided into rough polishing and fine polishing. Rough polishing involves mechanical polishing, aiming to improve polishing efficiency. Key research directions in mechanical polishing of gallium nitride single crystal substrates focus on optimizing process parameters, improving wafer surface roughness, and increasing material removal rates. Chemical mechanical polishing (CMP) is the most widely used technique for fine polishing of gallium nitride. It achieves surface removal and planarization through the synergistic effects of chemical etching and mechanical abrasion. Its basic principle is that the gallium nitride wafer undergoes an oxidation reaction in the presence of a polishing solution, resulting in a soft layer that is relatively easy to remove under the mechanical action of abrasive particles. The Fenton reaction is a common chemical oxidation system. Its mechanism of action is that ferrous ions catalyze hydrogen peroxide to produce hydroxyl radicals, which oxidize the wafer, forming a soft layer that is easier to remove. However, the Fenton reaction suffers from several issues, including low oxidation efficiency, post-reaction deposition of ferric ions, and its limited operation in acidic environments. Numerous studies are currently exploring the application of the Fenton reaction in wafer processing, but it is less common in gallium nitride polishing. Currently, there are relatively few unassisted gallium nitride wafer polishing solutions. Chinese patent CN 112126357 B discloses a polishing solution that utilizes catalyst adsorption to assist in gallium nitride polishing, but this solution is only effective under acidic conditions. Chinese patent CN 117551393 A discloses a gallium nitride polishing solution for electrochemically assisted polishing, which is limited in application and requires external equipment. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides an alkaline gallium nitride polishing liquid based on the Fenton reaction and its preparation method. Iron ions are complexed by a complexing agent, which, with the aid of a stabilizer, allows the iron ions to circulate and catalyze hydrogen peroxide to continuously produce gallium oxynitride, forming a soft layer. This soft layer is then removed through the mechanical action of an abrasive.

[0006] A Fenton reaction-based alkaline gallium nitride polishing liquid comprises hydrogen peroxide, silica abrasive, sodium bicarbonate, iron salt, dispersant, stabilizer, complexing agent and deionized water. The weight percentages of the components are as follows: 5-30wt% hydrogen peroxide with a mass concentration of 30%, 0.01-15wt% silica abrasive, 0.01-1wt% sodium bicarbonate, 0.1-8wt% iron salt, 0.01-2wt% dispersant, 0.01-2wt% stabilizer, 0.1-8wt% complexing agent, and the balance is deionized water.

[0007] Preferably, the components of the polishing liquid are: 5-15wt% hydrogen peroxide with a mass concentration of 30%, 0.01-2wt% silica abrasive, 0.01-1 wt% sodium bicarbonate, 0.1-1 wt% iron salt, 0.05-1wt% dispersant, 0.5-1 wt% stabilizer, 0.1-2 wt% complexing agent, and the balance is deionized water.

[0008] Preferably, the dispersant is any one of surfactants such as cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, Tween, polyethylene glycol octylphenyl ether, etc.

[0009] Preferably, the stabilizer is any one of ether, hydroxylamine, zinc nitrate and zinc sulfate.

[0010] Preferably, the complexing agent is any one of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, and sodium pyrophosphate.

[0011] Preferably, the iron salt is ferrous sulfate.

[0012] The present invention also provides a method for preparing the polishing liquid, comprising the following steps: adding sodium bicarbonate to deionized water and stirring until completely dissolved; adding a complexing agent, an iron salt, a stabilizer, and a dispersant in sequence and stirring to dissolve; adding a silica abrasive and stirring and dispersing for 30-60 minutes; and finally adding hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid.

[0013] Beneficial effects of the present invention:

[0014] Compared with the prior art, the present invention is more convenient to operate without the need for additional auxiliary equipment. An iron-based ion complex is used to catalyze hydrogen peroxide. The applicable scope of the Fenton reaction is expanded to alkaline conditions. A stabilizer can promote the conversion of trivalent ferrous ions into ferrous ions, enhance the catalytic effect of ferrous ions, and extend the effective duration of the polishing liquid. The purpose is to improve the polishing efficiency and application range of the polishing liquid and obtain good polished surface quality of wafers. Furthermore, the polishing liquid does not corrode processing equipment, does not pollute the environment, is low in cost, and can be stably stored for a long time. Therefore, the polishing liquid is stable, efficient, simple to operate, and has a wide range of application environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an atomic force microscope (AFM) image of a gallium nitride substrate wafer after polishing with the polishing liquid of Example 1 of the present invention;

[0016] Figure 2 The graphs of the hydroxyl concentration changes over time for Example 1 and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] Example 1

[0019] A preparation method of alkaline gallium nitride polishing liquid based on Fenton reaction

[0020] Take 935g of deionized water, add 5g of sodium bicarbonate, and stir until completely dissolved; then add 5g of EDTA, 5g of ferrous sulfate, 10g of hydroxylamine, and 10g of hexadecyltrimethylammonium bromide, stir to dissolve, add 20g of silica abrasive Powder-A, stir and disperse for 30 minutes, and add 100g of hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid; the silica abrasive Powder-A has a diameter D = 30-60nm and a specific surface area of ​​21.95m 2 / g, and the surface roughness of the samples was observed using atomic force microscopy (AFM). Figure 1 shown.

[0021] Example 2

[0022] A preparation method of alkaline gallium nitride polishing liquid based on Fenton reaction

[0023] Take 935g of deionized water, add 5g of sodium bicarbonate, and stir until completely dissolved; then add 5g of diethylenetriamine pentaacetic acid, 5g of ferrous sulfate, 10g of ether, and 10g of sodium dodecylbenzene sulfonate, stir to dissolve, add 10g of silica abrasive Powder-A, stir and disperse for 35 minutes, and add 400g of hydrogen peroxide with a mass concentration of 30% to obtain the alkaline gallium nitride polishing liquid; the silica abrasive Powder-A has a diameter D = 30-60nm and a specific surface area of ​​21.95m 2 / g.

[0024] Example 3

[0025] A preparation method of alkaline gallium nitride polishing liquid based on Fenton reaction

[0026] Take 935g of deionized water, add 6g of sodium bicarbonate, and stir until completely dissolved; then add 15g of hydroxyethylethylenediaminetriacetic acid, 6g of ferrous sulfate, 10g of zinc nitrate, and 10g of hexadecyltrimethylammonium bromide, stir to dissolve, add 40g of silica abrasive Powder-B, stir and disperse for 40 minutes, and add 100g of hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid; the silica abrasive Powder-B has a diameter D = 90-100nm and a specific surface area of ​​18.32m 2 / g.

[0027] Example 4

[0028] A preparation method of alkaline gallium nitride polishing liquid based on Fenton reaction

[0029] Take 935g of deionized water, add 6g of sodium bicarbonate, and stir until completely dissolved; then add 10g of EDTA, 5g of ferrous sulfate, 10g of zinc sulfate, and 15g of sodium lauryl sulfate, stir to dissolve, add 40g of silica abrasive Powder-C, stir and disperse for 45 minutes, and add 200g of hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid; the silica abrasive Powder-C has a diameter D = 110-120nm and a specific surface area of ​​16.19m 2 / g.

[0030] Example 5

[0031] A preparation method of alkaline gallium nitride polishing liquid based on Fenton reaction

[0032] Take 935g of deionized water, add 5g of sodium bicarbonate, and stir until completely dissolved; then add 10g of hydroxyethylethylenediaminetriacetic acid, 10g of ferrous sulfate, 5g of ether, and 10g of polyethylene glycol octylphenyl ether, stir to dissolve, add 50g of silica abrasive Powder-B, stir and disperse for 50 minutes, and add 300g of hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid; the silica abrasive Powder-B has a diameter D = 90-100nm and a specific surface area of ​​18.32m 2 / g.

[0033] Example 6

[0034] A preparation method of alkaline gallium nitride polishing liquid based on Fenton reaction

[0035] Take 935g of deionized water, add 5g of sodium bicarbonate, and stir until completely dissolved; then add 5g of sodium pyrophosphate, 5g of ferrous sulfate, 10g of hydroxylamine, and 5g of Tween, stir to dissolve, add 100g of silica abrasive Powder-C, stir and disperse for 60 minutes, and add 400g of hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid; the silica abrasive Powder-C has a diameter D = 110-120nm and a specific surface area of ​​16.19m 2 / g.

[0036] Comparative Example 1

[0037] The remaining operating steps are the same as those in Example 1, except that the contents of the components in the polishing liquid are: 935g deionized water, 5g sodium bicarbonate, 5g ferrous sulfate and 100g hydrogen peroxide with a mass concentration of 30%, which are stirred evenly and the pH of the liquid is 9.8.

[0038] Comparative Example 2

[0039] The remaining operating steps are the same as those in Example 1, except that the contents of the components in the polishing liquid are: 935g deionized water, 5g sodium bicarbonate, 5g EDTA, 5g ferrous sulfate and 100g hydrogen peroxide with a mass concentration of 30%, which are stirred evenly and the pH of the liquid is 9.8.

[0040] Test Example 1

[0041] Polishing experiments were performed on the polishing solutions obtained in Examples 1-6 and Comparative Examples 1-2.

[0042] This polishing experiment uses a 2-inch GaN substrate and polishes the N side. The polishing parameters are set as follows: polishing pressure is 300g / cm 2 The polishing pad speed was 50 rpm, the polishing head speed was 40 rpm, the polishing liquid flow rate was 15 mL / min, and the polishing time was 60 min. After each polishing cycle, the polishing pad was replaced. The polished substrate was ultrasonically cleaned in the cleaning solution for 10 minutes and then dried with nitrogen. The results are shown in Table 1.

[0043] The polishing removal rate (MRR) is calculated as follows: MRR = Δm / ρS, where Δm is the difference in substrate wafer quality before and after polishing; ρ is the density of the substrate wafer; and S is the substrate area.

[0044] Surface defects were detected by visual inspection and defect surface detection light; surface roughness was detected using atomic force microscopy (AFM).

[0045] Table 1 Polishing test results of Examples 1-6 and Comparative Examples 1-2

[0046]

[0047] As can be seen from Table 1, Comparative Example 1 does not contain a complexing agent or stabilizer compared to Example 1. Ferrous ions cannot exist stably in an alkaline environment without a complexing agent. Consequently, ferric hydroxide precipitates form. This precipitate severely damages the wafer surface during polishing, resulting in poor processing quality.

[0048] As shown in Table 1, Comparative Example 2, compared to Example 1, does not contain a stabilizer. While it exhibits a moderate polishing effect, the absence of a stabilizer reduces the non-catalytic ferric iron back to catalytic ferrous iron. The oxidation effect weakens with increasing processing time. The excessive mechanical action of the abrasive results in poor processing quality.

[0049] Test Example 2

[0050] Equal amounts of the alkaline gallium nitride polishing solutions of Example 1 and Comparative Example 2 were taken to test the hydroxyl concentration.

[0051] Hydroxyl is the main free radical that plays an oxidizing role in the Fenton reaction. Testing its concentration can intuitively reflect the duration of the polishing liquid. The hydroxyl concentration test uses the common spectrophotometric method. The principle is that salicylic acid can capture hydroxyl radicals to generate 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid with characteristic absorption between the wavelength of 490-550nm. Fitting the characteristic peak can reflect the hydroxyl concentration. Take 3 ml of equal amounts of alkaline gallium nitride polishing liquid of Example 1 and Comparative Example 2 and put them into two quartz cuvettes respectively. Then add 2 ml of salicylic acid-ethanol indicator solution to start the reaction. Use a UV-visible scanning spectrophotometer for testing. Test the scanning curves of 15 minutes, 30 minutes, 45 minutes, and 60 minutes of reaction respectively. After the test, the characteristic absorption peak of 490-550nm of the obtained curve is fitted and integrated to obtain a line graph of the hydroxyl concentration change of Example 1 and Comparative Example 2, as shown in the figure. Figure 2 As shown in the figure, the hydroxyl concentration in Example 1 is significantly higher than that in Comparative Example 2 after 30 minutes. The only difference between the alkaline gallium nitride polishing solutions in Example 1 and Comparative Example 2 is the presence or absence of a stabilizer. This further demonstrates that the presence of a stabilizer can promote the conversion of ferric ions to ferrous ions, enhance the catalytic effect of ferrous ions, and extend the effective life of the polishing solution.

[0052] Based on Table 1 and the results of the examples, the present invention effectively overcomes various shortcomings in the prior art, and the alkaline gallium nitride polishing liquid based on the Fenton reaction has high industrial utilization value.

[0053] While the embodiments of the present invention have been described above through specific examples, those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different perspectives and applications without departing from the spirit of the present invention.

Claims

1. An alkaline gallium nitride polishing liquid based on the Fenton reaction, characterized in that: The alkaline gallium nitride polishing liquid includes hydrogen peroxide, silica abrasive, sodium bicarbonate, iron salt, dispersant, stabilizer, complexing agent and deionized water, wherein the weight percentage of each component is as follows: 5-30wt% hydrogen peroxide with a mass concentration of 30%, 0.01-15wt% silica abrasive, 0.01-1wt% sodium bicarbonate, 0.1-8wt% iron salt, 0.01-2wt% dispersant, 0.01-2wt% stabilizer, 0.1-8wt% complexing agent, and the balance is deionized water; the dispersant is any one of cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, Tween, and polyethylene glycol octylphenyl ether; the stabilizer is any one of ether, hydroxylamine, zinc nitrate, and zinc sulfate; the complexing agent is any one of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, and sodium pyrophosphate; and the iron salt is ferrous sulfate.

2. The alkaline gallium nitride polishing liquid according to claim 1, wherein The weight percentages of the components in the alkaline gallium nitride polishing liquid are as follows: 5-15wt% hydrogen peroxide with a mass concentration of 30%, 0.01-2wt% silica abrasive, 0.01-1 wt% sodium bicarbonate, 0.1-1 wt% iron salt, 0.05-1wt% dispersant, 0.5-1 wt% stabilizer, 0.1-2 wt% complexing agent, and the balance deionized water.

3. The method for preparing the alkaline gallium nitride polishing liquid according to claim 1 or 2, wherein: The polishing liquid is prepared by adding sodium bicarbonate to deionized water and stirring until completely dissolved; adding a complexing agent, an iron salt, a stabilizer, and a dispersant in sequence and stirring to dissolve; adding silica abrasive and stirring and dispersing for 30-60 minutes; and finally adding hydrogen peroxide with a mass concentration of 30% to obtain an alkaline gallium nitride polishing liquid.

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