Gallium nitride polishing method

Abstract

The invention relates to the technical field of polishing, and particularly discloses a gallium nitride polishing method. The gallium nitride polishing method provided by the invention comprises the following steps: S1, carrying out polishing treatment on gallium nitride by using a first polishing solution and a first polishing pad to obtain first treated gallium nitride; s2, carrying out polishing treatment on the first treated gallium nitride by using a second polishing solution and a second polishing pad to obtain second treated gallium nitride; and S3, carrying out polishing treatment on the second treated gallium nitride by using a third polishing solution and a third polishing pad to obtain the polished gallium nitride. According to the method, rough polishing, medium polishing and fine polishing are sequentially conducted on gallium nitride through the three times of polishing treatment processes, the polishing rate during gallium nitride polishing is greatly increased, the roughness of the surface of the gallium nitride wafer is reduced, and the prepared gallium nitride wafer meets the extremely high requirement of high-end device manufacturing for the quality of the surface of gallium nitride.

Description

Technical Field

[0001] The present invention relates to the technical field of polishing, and specifically discloses a method for polishing gallium nitride. Background Art

[0002] As an important semiconductor material, GaN is widely used in the fields of optoelectronic devices, power electronic devices, etc. In the complex process flow of semiconductor integrated circuit manufacturing, GaN materials need to be integrated synergistically with other substrate materials such as silicon and silicon carbide, or different functional layer materials. Chemical mechanical polishing technology can be well compatible with existing semiconductor manufacturing processes, such as lithography, etching, thin film deposition and other steps, ensuring the coherence and stability of the entire process flow and reducing the difficulty of process integration. Due to the high hardness and brittleness of GaN, it is difficult to obtain a flat surface with high precision and low roughness on its surface by conventional mechanical processing methods, and defects such as cracks and scratches are likely to occur. Therefore, it is necessary to rely on chemical mechanical polishing, a process that combines chemical corrosion and mechanical grinding, to achieve high-quality surface treatment. Moreover, GaN has good chemical stability and is not prone to violent reactions with common chemical reagents such as acids and alkalis at room temperature. Relying solely on chemical corrosion is difficult to accurately control the material removal amount. Chemical mechanical polishing that combines mechanical grinding can use mechanical force to assist chemical reagents to break the stable structure between surface atoms, accelerate the removal process, and achieve planarization.

[0003] Existing GaN removal methods mainly rely on mechanical friction, resulting in insufficient chemical reactions, low removal efficiency, and long polishing time. Moreover, traditional silica sol polishing liquids are difficult to fully contact the GaN surface, making the oxidation reaction unable to proceed sufficiently, thereby affecting its removal rate. At the same time, due to its high hardness and high brittleness characteristics, during the CMP process, it is easy to cause damage on the surface and subsurface, such as cracks and scratches. It is difficult to obtain a nanoscale ultra-smooth gallium nitride surface. In addition, the material removal rate of GaN is low, the polishing time is long, a large amount of polishing liquid needs to be consumed, increasing production costs. GaN has a large hardness and will also wear the polishing pad, polishing head, etc. during the polishing process, requiring frequent replacement, increasing equipment maintenance costs. Therefore, aiming at the problems of low polishing rate, poor surface quality, and high processing costs in GaN polishing, its polishing process is improved. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for polishing gallium nitride.

[0005] The present invention provides a method for polishing gallium nitride, comprising the following steps:

[0006] S1. Polishing gallium nitride with a first polishing liquid and a first polishing pad to obtain first-treated gallium nitride;

[0007] S2. Use a second polishing liquid and a second polishing pad to polish the first processed gallium nitride to obtain second processed gallium nitride;

[0008] S3. Use a third polishing liquid and a third polishing pad to polish the second processed gallium nitride to obtain polished gallium nitride;

[0009] Among them, the first polishing liquid is a polishing liquid with diamond as the abrasive;

[0010] The second polishing liquid is a polishing liquid with alumina as the abrasive;

[0011] The third polishing liquid is a polishing liquid with silica as the abrasive;

[0012] The Shore hardness of the first polishing pad is 65HD - 75HD;

[0013] The Shore hardness of the second polishing pad is 55HD - 60HD;

[0014] The Shore hardness of the third polishing pad is 30HD - 40HD.

[0015] Since the gallium nitride material is very hard, it is difficult to reduce the surface roughness of the gallium nitride wafer while achieving a high removal rate. The inventor has proved through experiments that when only using a polishing liquid with diamond as the abrasive to perform chemical mechanical planarization on the gallium nitride wafer, although a large amount of gallium nitride can be removed in a short time to improve the removal rate of gallium nitride, the surface of the gallium nitride wafer is severely scratched; if only using a polishing liquid with alumina as the abrasive or a polishing liquid with silica as the abrasive to polish the gallium nitride wafer, its removal efficiency is very low. If a large amount of removal is desired, it takes several hours or even more than ten hours, thus increasing the equipment cost, consumable cost, and labor cost. Therefore, it is of great significance to provide a gallium nitride polishing method to improve the removal rate of gallium nitride and reduce the surface roughness of gallium nitride.

[0016] The inventor has also experimented during the research process with using a polishing liquid with diamond as the abrasive, a polishing liquid with alumina as the abrasive, and a polishing liquid with silica as the abrasive mixed as a mixed polishing liquid to polish gallium nitride, but the final roughness of the gallium nitride wafer obtained is still very poor, and the polishing removal rate of gallium nitride has not been significantly improved. The inventor accidentally discovered through a large number of experiments that when the above three polishing liquids are used separately to polish gallium nitride and polished in a certain order and with a polishing pad with an appropriate Shore hardness, the surface roughness of the gallium nitride wafer is greatly reduced, and the polishing rate during the polishing of gallium nitride is also increased.

[0017] In S1, when selecting a polishing liquid with diamond as the abrasive and using a first polishing pad with a Shore hardness of 65HD to 75HD to polish gallium nitride, a large amount of gallium nitride on the wafer surface can be removed during the first polishing, thus shortening the time of the entire polishing process. In addition, the protruding parts on the gallium nitride surface can be preferentially ground, initially improving the surface flatness, reducing the height difference of large unevenness, and providing a relatively flat basis for the more refined surface treatment in the second polishing process.

[0018] Furthermore, the present invention selects a polishing liquid with alumina as the abrasive and uses a second polishing pad with a Shore hardness of 55HD to 60HD to polish the first-treated gallium nitride. The second polishing can further perform more refined grinding on the gallium nitride surface, further improving the surface flatness. By the second polishing process, the workload and time of the third polishing process can be reduced, and the efficiency and quality of the polishing process can be improved.

[0019] In S3, when selecting a polishing liquid with silica as the abrasive and using a third polishing pad with a Shore hardness of 30HD to 40HD to polish gallium nitride, micro-defects and extremely fine scratches remaining after the second polishing can be accurately removed without introducing new damages and defects, making the gallium nitride surface reach an atomic-level or near-atomic-level smoothness.

[0020] By defining the abrasive of the polishing liquid and the Shore hardness of the polishing pad used during the three polishing processes, the above three polishing processes are used to perform rough polishing, medium polishing, and fine polishing on gallium nitride in sequence, greatly improving the polishing rate during gallium nitride polishing, reducing the surface roughness of the gallium nitride wafer, and making the prepared gallium nitride wafer meet the extremely high requirements for the surface quality of gallium nitride in high-end device manufacturing.

[0021] Preferably, in S1, the mass percentage content of diamond in the first polishing liquid is 1% to 5%.

[0022] By defining the usage amount of diamond in the first polishing liquid, the surface flatness of gallium nitride can be quickly improved, and then the removal rate of gallium nitride during polishing can be increased.

[0023] Further preferably, the particle size of the diamond is 1μm to 3μm.

[0024] Further preferably, in S1, the first polishing liquid further includes a first oxidant, a lubricant, a first stabilizer, a first pH regulator, and water.

[0025] Further preferably, in S1, the first polishing liquid comprises the following components in mass percentages: 2% - 10% diamond, 1% - 5% first oxidant, 1% - 5% lubricant, 1% - 5% first stabilizer, 1% - 3% first pH regulator, and the balance is water.

[0026] Further preferably, the first oxidant is hydrogen peroxide.

[0027] Further preferably, the lubricant is glycerol.

[0028] Further preferably, the first stabilizer is sodium silicate.

[0029] Further preferably, the first pH regulator is potassium hydroxide.

[0030] Preferably, in S1, the first polishing pad is a polyamide polishing pad.

[0031] Through the reasonable cooperation between the preferably first polishing pad and the first polishing liquid, while improving the surface removal efficiency of gallium nitride during polishing, the surface roughness of gallium nitride is also reduced.

[0032] Preferably, in S1, the polishing pressure for the polishing treatment is 7 psi - 12 psi.

[0033] Preferably, in S1, the polishing time for the polishing treatment is 20 min - 40 min.

[0034] By limiting the polishing pressure and time of the first polishing treatment in S1, the present invention can maximize the flatness of gallium nitride by the first polishing liquid and will not overly scratch or damage gallium nitride.

[0035] Preferably, in S1, the flow rate of the first polishing liquid during the polishing treatment is 100 mL / min - 200 mL / min.

[0036] As a preferred embodiment, in S1, during the polishing treatment, the first polishing pad needs to be trimmed while polishing.

[0037] Preferably, in S2, the mass percentage content of alumina in the second polishing liquid is 10% - 20%.

[0038] By limiting the content of alumina in the second polishing liquid, the present invention is beneficial to further improve the flatness during the second polishing and minimize the work and time of the third polishing to the greatest extent.

[0039] Further preferably, the particle size of the alumina is 0.5 μm - 2 μm.

[0040] Further preferably, in S2, the second polishing liquid further comprises a first surfactant, a second oxidant, a second stabilizer, a second pH regulator and water.

[0041] Further preferably, in S2, the second polishing liquid comprises the following components in mass percentages: 10% - 20% of alumina, 5% - 10% of the first surfactant, 10% - 15% of the second oxidant, 1% - 3% of the second stabilizer, 3% - 5% of the second pH regulator, and the balance being water.

[0042] Further preferably, the first surfactant is sodium dodecyl sulfate.

[0043] Further preferably, the second oxidant is hydrogen peroxide.

[0044] Further preferably, the second stabilizer is disodium 4,5 - dihydroxy - 1,3 - benzenedisulfonate.

[0045] Further preferably, the second pH regulator is nitric acid.

[0046] Preferably, in S2, the second polishing pad is a polyurethane polishing pad.

[0047] The preferred second polishing pad can be reasonably combined with the second polishing liquid to improve the removal efficiency of gallium nitride and reduce the surface roughness of the gallium nitride wafer.

[0048] Preferably, in S2, the polishing pressure for the polishing treatment is 5 psi - 10 psi.

[0049] Preferably, in S2, the polishing time for the polishing treatment is 20 min - 40 min.

[0050] By limiting the polishing pressure and polishing time of the second polishing treatment in S2, the present invention can greatly improve the efficiency and quality of the entire polishing process.

[0051] Preferably, in S2, the flow rate of the second polishing liquid during the polishing treatment is 100 mL / min - 200 mL / min.

[0052] Preferably, in S3, the mass percentage content of silica in the third polishing liquid is 15% - 25%.

[0053] Further preferably, the particle size of the silica is 100 nm - 150 nm.

[0054] Further preferably, in S3, the third polishing liquid further comprises a second surfactant, a third oxidant, a third pH regulator and water.

[0055] Further preferably, in S3, the third polishing liquid comprises the following components in mass percentages: 15% - 25% of silicon dioxide, 5% - 10% of a second surfactant, 10% - 20% of a third oxidant, 3% - 5% of a third pH regulator, and the balance is water.

[0056] Further preferably, the second surfactant is fatty alcohol polyoxyethylene ether.

[0057] Further preferably, the third oxidant is hydrogen peroxide.

[0058] Further preferably, the third pH regulator is nitric acid.

[0059] Preferably, in S3, the third polishing pad is a polyurethane polishing pad.

[0060] Preferably, in S3, the polishing pressure for the polishing treatment is 5 psi - 10 psi.

[0061] Preferably, in S3, the polishing time for the polishing treatment is 20 min - 40 min.

[0062] The present invention further defines the pressure and time of the third polishing treatment in S3, which is beneficial to further improving the surface removal rate of gallium nitride and the surface roughness of gallium nitride.

[0063] Preferably, in S3, the flow rate of the third polishing liquid during the polishing treatment is 100 mL / min - 200 mL / min.

[0064] As a preferred embodiment, in S2 and S3, after the polishing treatment is completed, only the second polishing pad and the third polishing pad need to be trimmed. Specific Embodiments

[0065] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0066] Embodiment 1

[0067] This embodiment provides a method for polishing gallium nitride, comprising the following steps:

[0068] S1. Use a first polishing liquid and a polyamide polishing pad with a Shore hardness of 65 HD to polish gallium nitride. The flow rate of the first polishing liquid is 100 mL / min, the polishing pressure is 7 psi, and the polishing time is 20 min. During the polishing process, the first polishing pad needs to be trimmed while polishing to obtain first-treated gallium nitride. Among them, the first polishing liquid includes the following components by mass percentage: 5% diamond with a particle size of 1 μm, 1% hydrogen peroxide, 5% glycerol, 1% sodium silicate, 3% potassium hydroxide, and the balance is water;

[0069] S2. Use a second polishing liquid and a polyurethane polishing pad with a Shore hardness of 55 HD to polish the first-treated gallium nitride. The flow rate of the second polishing liquid is 100 mL / min, the polishing pressure is 5 psi, and the polishing time is 20 min to obtain second-treated gallium nitride. The second polishing liquid includes the following components by mass percentage: 10% alumina with a particle size of 0.5 μm, 10% sodium dodecyl sulfate, 10% hydrogen peroxide, 3% disodium 4,5-dihydroxy-1,3-benzenedisulfonate, 3% nitric acid, and the balance is water;

[0070] S3. Use a third polishing liquid and a polishing pad with a Shore hardness of 30 HD to polish the second-treated gallium nitride. The flow rate of the third polishing liquid is 100 mL / min, the polishing pressure is 10 psi, and the polishing time is 20 min to obtain polished gallium nitride. The third polishing liquid includes the following components by mass percentage: 25% silica with a particle size of 100 nm, 5% fatty alcohol polyoxyethylene ether, 20% hydrogen peroxide, 3% nitric acid, and the balance is water.

[0071] Example 2

[0072] This example provides a method for polishing gallium nitride, including the following steps:

[0073] S1. Use a first polishing liquid and a polyamide polishing pad with a Shore hardness of 75 HD to polish gallium nitride. The flow rate of the first polishing liquid is 200 mL / min, the polishing pressure is 12 psi, and the polishing time is 40 min. During the polishing process, the first polishing pad needs to be trimmed while polishing to obtain first-treated gallium nitride. Among them, the first polishing liquid includes the following components by mass percentage: 1% diamond with a particle size of 3 μm, 5% hydrogen peroxide, 1% glycerol, 5% sodium silicate, 1% potassium hydroxide, and the balance is water;

[0074] S2. Use a second polishing liquid and a polyurethane polishing pad with a Shore hardness of 60 HD to polish the first treated gallium nitride. The flow rate of the second polishing liquid is 200 mL / min, the polishing pressure is 10 psi, and the polishing time is 40 min to obtain the second treated gallium nitride. The second polishing liquid comprises the following components in mass percentages: 20% of alumina with a particle size of 2 μm, 5% of sodium dodecyl sulfate, 15% of hydrogen peroxide, 1% of disodium 4,5-dihydroxy-1,3-benzenedisulfonate, 5% of nitric acid, and the balance is water;

[0075] S3. Use a third polishing liquid and a polishing pad with a Shore hardness of 40 HD to polish the second treated gallium nitride. The flow rate of the third polishing liquid is 200 mL / min, the polishing pressure is 5 psi, and the polishing time is 40 min to obtain the polished gallium nitride. The third polishing liquid comprises the following components in mass percentages: 15% of silica with a particle size of 150 nm, 10% of fatty alcohol polyoxyethylene ether, 10% of hydrogen peroxide, 5% of nitric acid, and the balance is water.

[0076] Example 3

[0077] This example provides a method for polishing gallium nitride, which comprises the following steps:

[0078] S1. Use a first polishing liquid and a polyamide polishing pad with a Shore hardness of 70 HD to polish gallium nitride. The flow rate of the first polishing liquid is 150 mL / min, the polishing pressure is 10 psi, and the polishing time is 30 min. During the polishing process, the first polishing pad needs to be trimmed while polishing to obtain the first treated gallium nitride. Among them, the first polishing liquid comprises the following components in mass percentages: 2% of diamond with a particle size of 2 μm, 3% of hydrogen peroxide, 4% of glycerol, 3% of sodium silicate, 2% of potassium hydroxide, and the balance is water;

[0079] S2. Use a second polishing liquid and a polyurethane polishing pad with a Shore hardness of 58 HD to polish the first treated gallium nitride. The flow rate of the second polishing liquid is 150 mL / min, the polishing pressure is 6 psi, and the polishing time is 30 min to obtain the second treated gallium nitride. The second polishing liquid comprises the following components in mass percentages: 15% of alumina with a particle size of 1 μm, 8% of sodium dodecyl sulfate, 12% of hydrogen peroxide, 2% of disodium 4,5-dihydroxy-1,3-benzenedisulfonate, 4% of nitric acid, and the balance is water;

[0080] S3. Polish the second treated gallium nitride using a third polishing liquid and a polishing pad with a Shore hardness of 35 HD. The flow rate of the third polishing liquid is 150 mL / min, the polishing pressure is 8 psi, and the polishing time is 30 min to obtain polished gallium nitride. The third polishing liquid comprises the following components in mass percentage: 20% of silicon dioxide with a particle size of 120 nm, 7% of fatty alcohol polyoxyethylene ether, 14% of hydrogen peroxide, 4% of nitric acid, and the balance is water.

[0081] Comparative Example 1

[0082] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S1, the Shore hardness of the polishing pad is 90 HD;

[0083] Other components and operation steps are the same as those in Example 1.

[0084] Comparative Example 2

[0085] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S2, the Shore hardness of the polishing pad is 45 HD;

[0086] Other components and operation steps are the same as those in Example 1.

[0087] Comparative Example 3

[0088] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S3, the Shore hardness of the polishing pad is 20 HD;

[0089] Other components and operation steps are the same as those in Example 1.

[0090] Comparative Example 4

[0091] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: S1 is omitted, specifically as follows:

[0092] S2. Polish the first treated gallium nitride using a second polishing liquid and a polyurethane polishing pad with a Shore hardness of 55 HD. The flow rate of the second polishing liquid is 200 mL / min, the polishing pressure is 5 psi, and the polishing time is 40 min to obtain the second treated gallium nitride. The second polishing liquid comprises the following components in mass percentage: 10% of alumina with a particle size of 0.5 μm, 10% of sodium dodecyl sulfate, 10% of hydrogen peroxide, 3% of disodium 4,5-dihydroxy-1,3-benzenedisulfonate, 3% of nitric acid, and the balance is water;

[0093] S3. Polish the second treated gallium nitride using a third polishing liquid and a polishing pad with a Shore hardness of 30 HD. The flow rate of the third polishing liquid is 100 mL / min, the polishing pressure is 10 psi, and the polishing time is 20 min to obtain polished gallium nitride. The third polishing liquid comprises the following components in mass percentage: 25% of silica with a particle size of 100 nm, 5% of fatty alcohol polyoxyethylene ether, 20% of hydrogen peroxide, 3% of nitric acid, and the balance is water;

[0094] Other components, operation steps are the same as those in Example 1.

[0095] Comparative Example 5

[0096] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S2, alumina is replaced with an equal amount of diamond;

[0097] Other components, operation steps are the same as those in Example 1.

[0098] Polish the surface of the gallium nitride wafer by the polishing methods of Examples 1 - 3 and Comparative Examples 1 - 5. After polishing, detect the surface roughness of the gallium nitride wafer, and use a Park atomic force microscope to detect the surface roughness of the silicon wafer;

[0099] Polishing rate: Measure the thickness of the wafer before polishing and the thickness of the wafer after polishing by a metrology tool, and the difference is the total removal amount corresponding to the polishing time. The total amount divided by the polishing time is the polishing rate; The specific detection results are shown in Table 1:

[0100] Table 1

[0101]

[0102] As can be seen from Table 1 of the present invention, when polishing gallium nitride by the polishing method provided by the present invention, the gallium nitride is rough polished, medium polished and fine polished successively through three polishing processes, which greatly improves the polishing rate during the polishing of gallium nitride and reduces the surface roughness of the gallium nitride wafer, making the prepared gallium nitride wafer meet the extremely high requirements for the surface quality of gallium nitride in high - end device manufacturing. From the comparative examples of the present invention, it can be seen that whether changing the hardness of the polishing pad, changing the abrasive in the polishing liquid during polishing in any step, or changing the polishing steps, the surface roughness of the finally obtained gallium nitride will increase, greatly reducing the polishing quality.

[0103] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for polishing gallium nitride, characterized in that: The steps include: S1, polishing gallium nitride using a first polishing liquid and a first polishing pad to obtain a first treated gallium nitride; S2, polishing the first treated gallium nitride using a second polishing liquid and a second polishing pad to obtain a second treated gallium nitride; S3, polishing the second-treated gallium nitride using a third polishing liquid and a third polishing pad to obtain polished gallium nitride; Wherein, the first polishing liquid is a polishing liquid using diamond as an abrasive; The second polishing liquid is a polishing liquid using aluminum oxide as an abrasive; The third polishing liquid is a polishing liquid using silicon dioxide as an abrasive; The Shore hardness of the first polishing pad is 65HD to 75HD; The Shore hardness of the second polishing pad is 55HD to 60HD; The third polishing pad has a Shore hardness of 30HD to 40HD.

2. The gallium nitride polishing method according to claim 1, characterized in that: In S1, the mass percentage of diamond in the first polishing liquid is 1% to 5%.

3. The gallium nitride polishing method according to claim 1 or 2, characterized in that: The diamond particle size is 1 μm to 3 μm.

4. The gallium nitride polishing method according to claim 1, characterized in that: In S1, the polishing pressure of the polishing process is 7psi to 12psi; and / or In S1, the polishing treatment time is 20 minutes to 40 minutes.

5. The gallium nitride polishing method according to claim 1, characterized in that: In S2, the mass percentage of aluminum oxide in the second polishing liquid is 10% to 20%.

6. The gallium nitride polishing method according to claim 1 or 5, characterized in that: The particle size of the aluminum oxide is 0.5 μm to 2 μm.

7. The gallium nitride polishing method according to claim 1, characterized in that: In S2, the polishing pressure of the polishing process is 5psi to 10psi; and / or In S2, the polishing treatment time is 20 minutes to 40 minutes.

8. The gallium nitride polishing method according to claim 1, characterized in that: In S3, the mass percentage of silicon dioxide in the third polishing liquid is 15% to 25%.

9. The gallium nitride polishing method according to claim 1 or 8, characterized in that: The particle size of the silicon dioxide is 100nm to 150nm.

10. The gallium nitride polishing method according to claim 1, characterized in that: In S3, the polishing pressure of the polishing process is 5psi to 10psi; and / or In S3, the polishing treatment time is 20 minutes to 40 minutes.

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