Grinding and polishing solution for gallium nitride wafer

Abstract

The invention provides a grinding and polishing solution for a gallium nitride wafer. The polishing solution comprises the following components in percentage by mass: 15-25% of a polishing abrasive; 3-5% of a permanganate oxidant; 5-8% of a pH regulator; 0.1-1% of a carboxylic acid complexing agent; 0.05-5% of a sulfonic acid complexing agent; 0.01%-0.5% of an amino polyacid complexing agent; 0.01-0.5% of a dispersant, and deionized water. The grinding and polishing solution provided by the invention can improve the material removal rate when the gallium nitride wafer is subjected to chemical mechanical polishing, the material removal rate is improved to 350 nm / h, a high-quality gallium nitride surface with low surface roughness and no defect is obtained, and the surface roughness Ra of the gallium nitride wafer is less than or equal to 0.15 nm.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor epitaxial processing technology, and in particular relates to a grinding and polishing slurry for gallium nitride wafers. Background Technology

[0002] Gallium nitride (GaN) wafers are obtained by heteroepitaxial growth on sapphire substrates using MOCVD and HVPE techniques, followed by sapphire substrate removal. To obtain the finished GaN wafer, the Ga face, N face, and sides of the GaN single crystal need to be ground. Chemical mechanical polishing (CMP) is a crucial step in gallium nitride (GaN) wafer processing. Its roles in GaN wafer fabrication include: effectively removing surface scratches and unevenness left over from previous processes (rough / fine polishing) through the synergistic effect of chemical etching and mechanical polishing, achieving an atomically smooth surface to meet the stringent substrate flatness requirements of device fabrication; mechanical polishing introduces subsurface damage (such as dislocations and microcracks) to the GaN wafer surface, while the chemical etching in CMP selectively dissolves this damaged layer, reducing defect density and improving crystal quality; precise control of material removal (typically <1 μm / min) ensures uniform wafer thickness (TTV < 1 μm), which is essential for applications requiring thinning processes, such as power devices; and the polishing slurry can regulate the chemical state of the GaN surface, forming an easily removable soft oxide layer (such as Ga2O3) while avoiding metal contamination. The polishing slurry is a chemical... The components of polishing slurry, a key material in the mechanical grinding process, directly affect the removal rate during polishing and the surface roughness after polishing. It is also an important part of cost control in enterprise production. Summary of the Invention

[0003] In view of the above-mentioned background technology requirements, the purpose of this invention is to provide a grinding and polishing method for gallium nitride single crystal substrates, which improves the efficiency and quality of the grinding and polishing process and reduces production costs.

[0004] To achieve the above and other related objectives, the present invention provides a polishing slurry for gallium nitride wafers. The polishing slurry comprises, by mass percentage: 15-25% polishing abrasive; 3-5% permanganate oxidant; 5-8% pH adjuster; 0.1-1% carboxylic acid complexing agent; 0.05-5% sulfonic acid complexing agent; 0.01-0.5% amino polyacid complexing agent; 0.01-0.5% dispersant; and deionized water.

[0005] Preferably, the polishing abrasive comprises nanoscale silicon oxide, which includes silicon oxide with a first particle size and silicon oxide with a second particle size, wherein the particle size of the first particle size silicon oxide is 15~30nm and the particle size of the second particle size silicon oxide is 70~80nm.

[0006] Preferably, the first-size silicon dioxide accounts for 40-50% of the polishing abrasive, and the second-size silicon dioxide accounts for 50-60% of the polishing abrasive.

[0007] Preferably, the permanganate oxidant is one or more of potassium permanganate, sodium permanganate, or ammonium permanganate.

[0008] Preferably, the pH adjuster is phosphoric acid or nitric acid.

[0009] Preferably, the pH adjuster adjusts the pH value of the polishing liquid to 2-3.

[0010] Preferably, the carboxylic acid complexing agent is one or more of citric acid, oxalic acid, and tartaric acid.

[0011] Preferably, the sulfonic acid complexing agent is one or more of p-toluenesulfonic acid, benzenesulfonic acid, and 4-methyl-1,3-benzenedisulfonic acid.

[0012] Preferably, the amino polyacid complexing agent is one or both of ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid.

[0013] Preferably, the dispersant is one or more of sodium polyacrylate, ammonium polyacrylate, or polyethylene glycol.

[0014] As described above, the polishing slurry for gallium nitride wafers provided by this invention can improve the material removal rate during chemical mechanical polishing of gallium nitride wafers, increasing the material removal rate to 350 nm / h, and obtaining a high-quality gallium nitride surface with low surface roughness and no defects. The surface roughness Ra of the gallium nitride wafer is less than or equal to 0.15 nm. Detailed Implementation

[0015] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0016] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components.

[0017] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0018] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0019] This patent provides a polishing slurry for gallium nitride wafers. The polishing slurry comprises, by mass percentage: 15-25% polishing abrasive; 3-5% permanganate oxidant; 5-8% pH adjuster; 0.1-1% carboxylic acid complexing agent; 0.05-5% sulfonic acid complexing agent; 0.01-0.5% amino polyacid complexing agent; 0.01-0.5% dispersant; and deionized water.

[0020] Specific descriptions of the components in the polishing slurry: Nanoscale silicon dioxide is selected as the polishing abrasive in the polishing slurry, with a particle size between 15 and 80 nm. The nanoscale silicon dioxide in the polishing abrasive includes two particle sizes: a first-size silicon dioxide and a second-size silicon dioxide. The first-size silicon dioxide has a smaller particle size than the second-size silicon dioxide. Its main function is to perform fine polishing on the surface of gallium nitride single crystals; the first-size silicon dioxide has a particle size of 15-30 nm. The second-size silicon dioxide's main function is to improve the efficiency of mechanical removal; its particle size is 70-80 nm. The mixing ratio of the first-size silicon dioxide to the second-size silicon dioxide is controlled at 1:1 to 1.5, which can be understood as the first-size silicon dioxide accounting for 40-50% of the polishing abrasive, and the second-size silicon dioxide accounting for 50-60%.

[0021] Permanganate oxides, as the main strong oxidizing agent in polishing slurries, react with gallium nitride (GaN) material surfaces by releasing active oxygen molecules and manganese oxides, forming a low-bonding Ga2O3 oxide film. This significantly reduces the surface hardness of GaN materials, facilitating subsequent mechanical grinding removal. The redox product MnO2 of permanganate oxides works synergistically with sulfonic acid complexing agents to dissolve metal ions, preventing residual particles from causing scratches. The permanganate oxidizing agent can be one or more of potassium permanganate, sodium permanganate, or ammonium permanganate.

[0022] The polishing slurry uses a pH adjuster to maintain a pH value between 2 and 3, thus creating a suitable environment for high oxidation activity. Phosphoric acid or nitric acid are typically chosen as the pH adjuster.

[0023] Carboxylic acid complexing agents possess multiple functions, including complexation, corrosion inhibition, and pH adjustment. They form stable, water-soluble complexes with metal ions (Ga³⁺) through the lone pair of electrons in the carboxyl group, preventing metal residue during polishing. Simultaneously, they inhibit excessive corrosion of GaN. Furthermore, they suppress the precipitation of byproducts. During permanganate oxide polishing, the redox product MnO₂ easily deposits on the polishing pad; using carboxylic acid complexing agents converts this into a soluble manganese complex, extending the polishing pad's lifespan and reducing the defect rate. One or more of citric acid, oxalic acid, and tartaric acid can be selected as the carboxylic acid complexing agent.

[0024] The sulfonic acid groups in sulfonic acid complexing agents form soluble complexes with Ga³⁺, accelerating the dissolution of the oxide layer. Under acidic conditions (pH 1.5–4), sulfonic acid complexing agents stabilize the complexed metal ions, inhibiting the precipitation of transition metal ions such as Ga³⁺ and Mn²⁺ in the polishing solution. Sulfonic acid complexing agents can be one or more of p-toluenesulfonic acid, benzenesulfonic acid, and 4-methyl-1,3-benzenedisulfonic acid.

[0025] Aminopolyacid complexing agents bind to metal ions through multidentate coordination, regulating the kinetic balance of chemical reactions and improving surface quality. Their hexadecimal coordination structure chelates Ga³⁺, achieving atomic-level surface finishing. Through highly selective chelation, these complexing agents achieve a precise balance between chemical etching and mechanical removal in gallium nitride polishing. The aminopolyacid complexing agents are selected from one or both of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DITA).

[0026] The main function of dispersants is to improve the uniformity of abrasive dispersion, maintain uniform suspension of abrasive particles, prevent agglomeration, and thus reduce surface scratches. Dispersants can be one or more of sodium polyacrylate, ammonium polyacrylate, or polyethylene glycol. Sodium polyacrylate and ammonium polyacrylate form a protective layer on the abrasive particle surface through polymer chain adsorption, preventing agglomeration through steric hindrance. Polyethylene glycol forms a steric hindrance layer on the abrasive particle surface through hydrophobic groups, while its hydrophilic groups bind with water molecules to enhance dispersibility. Specific Implementation Example 1 A polishing slurry for gallium nitride wafers, comprising the following components by mass percentage: The abrasive consists of 10% silica polishing abrasive with a particle size of 15-30 nm, 15% silica polishing abrasive with a particle size of 70-80 nm, 3.5% potassium permanganate, 8% phosphoric acid, 0.5% citric acid, 0.1% p-toluenesulfonic acid, 0.01% ethylenediaminetetraacetic acid, 0.05% ammonium polyacrylate, and deionized water. Specific Implementation Example 2 A polishing slurry for gallium nitride wafers, comprising the following components by mass percentage: The composition includes 12% silica polishing abrasive with a particle size of 15-30 nm, 12% silica polishing abrasive with a particle size of 70-80 nm, 3.5% sodium permanganate, 5% nitric acid, 0.5% oxalic acid, 0.1% p-toluenesulfonic acid, 0.01% ethylenediaminetetraacetic acid, 0.05% sodium polyacrylate, and deionized water. Specific Implementation Example 3 A polishing slurry for gallium nitride wafers, comprising the following components by mass percentage: The abrasive consists of 10% silica polishing abrasive with a particle size of 15-30 nm, 15% silica polishing abrasive with a particle size of 70-80 nm, 3.5% potassium permanganate, 8% phosphoric acid, 0.5% citric acid, 0.1% benzenesulfonic acid, 0.01% ethylenediaminetetraacetic acid, 0.1% polyethylene glycol, and deionized water.

[0030] The polishing slurries provided in the three embodiments above can increase the material removal rate (MRR) to 350 nm / h during chemical mechanical polishing (CMP) of gallium nitride wafers (which have undergone Ga and N-side polishing), and the surface roughness Ra of the gallium nitride wafers is less than or equal to 0.15 nm. Therefore, the present invention effectively overcomes the shortcomings of the prior art and has high industrial application value.

[0031] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A grinding and polishing slurry for gallium nitride wafers, characterized in that: The polishing slurry comprises the following components by mass percentage: Polishing abrasive 15~25%; 3-5% permanganate oxidant; pH adjuster 5-8%; Carboxylic acid complexing agents 0.1-1%; Sulfonic acid complexing agents 0.05~5%; Aminopolyacid complexing agents: 0.01~0.5%; Dispersant 0.01-0.5% And deionized water.

2. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The polishing abrasive includes nanoscale silicon oxide, which includes silicon oxide with a first particle size and silicon oxide with a second particle size. The first particle size silicon oxide has a particle size of 15~30nm, and the second particle size silicon oxide has a particle size of 70~80nm.

3. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The first-size silica accounts for 40-50% of the polishing abrasive, and the second-size silica accounts for 50-60% of the polishing abrasive.

4. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The permanganate oxidant is one or more of potassium permanganate, sodium permanganate, or ammonium permanganate.

5. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The pH adjuster is phosphoric acid or nitric acid.

6. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The pH adjuster adjusts the pH value of the polishing liquid to 2-3.

7. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The carboxylic acid complexing agent is one or more of citric acid, oxalic acid, and tartaric acid.

8. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The sulfonic acid complexing agent is one or more of p-toluenesulfonic acid, benzenesulfonic acid, and 4-methyl-1,3-benzenedisulfonic acid.

9. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The amino polyacid complexing agent is one or both of ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid.

10. The polishing slurry for gallium nitride wafers as described in claim 1, characterized in that, The dispersant is one or more of sodium polyacrylate, ammonium polyacrylate, or polyethylene glycol.