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: sequentially carrying out first-time polishing treatment and second-time polishing treatment on gallium nitride by using a first polishing solution, a first polishing pad, a second polishing solution and a second polishing pad to obtain polished gallium nitride. According to the method, the GaN surface is polished twice, the grinding material of the polishing solution and the type hardness trend of the polishing pad during the first polishing and the second polishing are limited, on the premise that the polishing rate is increased and the roughness of the GaN surface is reduced, the problem that micro cracks and internal cracks appear on the GaN surface after the GaN surface is treated through an existing polishing process is solved, and the quality of the GaN surface is improved. And the surface quality and the product percent of pass of GaN are greatly improved.

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] The research and application of gallium nitride (GaN) materials are currently at the forefront and hotspots of global semiconductor research. It is a new type of semiconductor material for developing microelectronic devices and optoelectronic devices. Together with semiconductor materials such as SiC and diamond, it is known as the third-generation semiconductor material after the first-generation Ge and Si semiconductor materials and the second-generation GaAs and InP compound semiconductor materials. It has properties such as a wide direct bandgap, strong atomic bonds, high thermal conductivity, good chemical stability, and strong anti-radiation ability, and has broad prospects in the applications of optoelectronics, high-temperature high-power devices, and high-frequency microwave devices.

[0003] High-performance GaN-based devices require GaN substrate materials with high surface quality. However, due to the high hardness and chemical inertness of GaN, the processing difficulty is very high. Due to the characteristics of high hardness, high brittleness, and good chemical stability of GaN, it is difficult to control the surface quality of GaN during chemical mechanical planarization (CMP). The existing methods for removing GaN mainly rely on mechanical friction, and the chemical reaction is insufficient, resulting in low removal efficiency and a very long polishing time. Therefore, it is of great significance to provide a method for polishing gallium nitride to solve the problems of slow polishing rate and poor surface quality after polishing in the existing gallium nitride polishing process, which leads to a low product qualification rate. 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] Performing a first polishing treatment and a second polishing treatment on gallium nitride in sequence with a first polishing liquid, a first polishing pad, a second polishing liquid, and a second polishing pad to obtain polished gallium nitride;

[0007] Wherein, the first polishing liquid is a polishing liquid with diamond as the abrasive;

[0008] The second polishing liquid is a polishing liquid with cerium dioxide as the abrasive;

[0009] The first polishing pad is a grid-type polishing pad, the second polishing pad is a spiral-type polishing pad, and the Shore hardness of the first polishing pad is 25 HD - 55 HD lower than that of the second polishing pad.

[0010] Currently, the polishing technology of GaN has problems of low material removal rate and poor surface quality after polishing. Among them, the low material removal rate is mainly because GaN has high hardness and strong chemical inertness. The inventors also tried to polish the GaN surface with ordinary abrasives, but the existing polishing fluids cannot effectively cut and wear the GaN surface, resulting in a low material removal rate per unit time. The main reasons for the poor surface quality after polishing include that the high hardness of GaN makes the abrasives in the polishing fluid prone to generate sub-micron cracks and internal cracks on the GaN surface during the polishing process, especially when the mechanical grinding effect is strong, thus reducing the product qualification rate.

[0011] Compared with the prior art, the present invention defines the first polishing conditions as a first polishing fluid with a specific abrasive and a first polishing pad of a specific type. Among them, the grid-type first polishing pad can evenly disperse the polishing fluid on the polishing pad, thereby improving the polishing efficiency of the GaN surface to a certain extent during the polishing process; by cooperating with the first polishing pad with lower hardness, it can also disperse the hardness of the diamond abrasive on the premise of reducing the surface roughness of GaN, and reduce the probability of micro-cracks and internal cracks in GaN, thereby improving the product qualification rate.

[0012] The present invention defines the second polishing conditions as a second polishing fluid with a specific abrasive and a second polishing pad of a specific type. The cerium dioxide abrasive is softer than the diamond abrasive. The inventors accidentally found during the experiment that appropriately increasing the Shore hardness of the second polishing pad can improve the polishing efficiency to a certain extent. At the same time, it can better repair the scratches caused by the first polishing fluid on the premise of reducing the surface roughness of GaN; in addition, the spiral-shaped second polishing pad is also beneficial to make the cerium dioxide abrasive contact the GaN surface more evenly. Further increasing the Shore hardness of the second polishing pad can reduce the problem of residual stress aggregation caused by the impact of the abrasive on the GaN surface or the deformation of the polishing pad during the polishing process, thereby significantly reducing the generation probability of internal cracks and surface micro-cracks.

[0013] The present invention performs two polishing treatments on the GaN surface and defines the abrasive of the polishing fluid and the type and hardness trend of the polishing pad during the first polishing and the second polishing. On the premise of improving the polishing rate and reducing the surface roughness of GaN, it also solves the problems of micro-cracks and internal cracks on the surface of GaN after being processed by the existing polishing process, and greatly improves the surface quality of GaN and the product qualification rate.

[0014] Preferably, the Shore hardness of the first polishing pad is 30HD - 40HD.

[0015] Preferably, the Shore hardness of the second polishing pad is 65HD - 80HD.

[0016] The present invention further defines the Shore hardness of the first polishing liquid and the second polishing liquid, which is beneficial to further improving the polishing rate, reducing the surface roughness of gallium nitride, and also improving the product qualification rate of polished gallium nitride.

[0017] Preferably, the particle size of the diamond is 2 μm to 3 μm.

[0018] The present invention further defines the particle size of the diamond, which enables the diamond to better cooperate with the grid-type first polishing pad. Thus, on the premise of improving the polishing rate and reducing the surface roughness, the surface quality of GaN can be further improved.

[0019] Preferably, the first polishing liquid is Lunars diamond polishing liquid.

[0020] Preferably, the first polishing pad is Xin Yunwei su800.

[0021] The preferred model of the first polishing pad is beneficial to further improving the polishing rate, reducing the surface roughness of GaN, and also improving the surface quality of GaN.

[0022] Preferably, the pressure of the first polishing treatment is 2 psi to 4 psi.

[0023] The preferred pressure is beneficial to further improving the polishing rate, reducing the surface roughness of GaN, and reducing the wear rate of the abrasive on the GaN surface.

[0024] Preferably, the flow rate of the first polishing liquid during the first polishing treatment is 150 mL / min to 200 mL / min.

[0025] Preferably, the rotation speed of the first polishing pad during the first polishing treatment is 108 rpm to 112 rpm.

[0026] Preferably, the acceleration of the first polishing pad during the first polishing treatment is 30 rpm to 50 rpm.

[0027] Preferably, the time of the first polishing treatment is 28 min to 32 min.

[0028] Preferably, the particle size of the cerium dioxide is 120 nm to 130 nm.

[0029] The present invention further defines the particle size of the cerium dioxide, which enables the cerium dioxide to better cooperate with the spiral-type polishing pad. Thus, on the premise of improving the polishing rate and reducing the surface roughness, the surface quality of GaN can be further improved.

[0030] Preferably, the second polishing liquid is Linghang cerium dioxide fine polishing liquid.

[0031] Preferably, the second polishing pad is Wanhua wh6000.

[0032] The model of the preferred second polishing pad is conducive to further improving the polishing rate, reducing the surface roughness of GaN, and also improving the surface quality of GaN.

[0033] Preferably, the pressure of the second polishing treatment is 7 psi to 10 psi.

[0034] The preferred pressure is conducive to further improving the polishing rate, reducing the surface roughness of GaN, and reducing the wear rate of the abrasive on the GaN surface.

[0035] Preferably, the flow rate of the second polishing liquid during the second polishing treatment is 150 mL / min to 200 mL / min.

[0036] Preferably, the rotation speed of the second polishing pad during the second polishing treatment is 108 rpm to 112 rpm.

[0037] Preferably, the acceleration of the second polishing pad during the second polishing treatment is 30 rpm to 50 rpm.

[0038] Preferably, the time of the second polishing treatment is 18 min to 22 min. Detailed implementation manners

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, 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.

[0040] Embodiment 1

[0041] This embodiment provides a method for polishing gallium nitride, including the following steps:

[0042] S1. Use Lunair diamond polishing liquid and Xin Yunwei su800 polishing pad to polish gallium nitride for 30 min to obtain first-treated gallium nitride; wherein, the pressure of the polishing treatment is 2 psi, the flow rate of Lunair diamond polishing liquid during the polishing treatment is 150 mL / min, the rotation speed of Xin Yunwei su800 polishing pad is 108 rpm, and the acceleration is 50 rpm;

[0043] S2. Use the leading cerium dioxide fine polishing liquid and the Wanhua wh6000 polishing pad to polish the first treated gallium nitride for 20 min to obtain polished gallium nitride. Among them, the pressure of the polishing treatment is 7 psi, the flow rate of the leading cerium dioxide fine polishing liquid during the polishing treatment is 150 mL / min, the rotation speed of the Wanhua wh6000 polishing pad is 112 rpm, and the acceleration is 30 rpm.

[0044] Example 2

[0045] This example provides a method for polishing gallium nitride, including the following steps:

[0046] S1. Use the Lunars diamond polishing liquid and the Xin Yunwei su800 polishing pad to polish gallium nitride for 32 min to obtain the first treated gallium nitride. Among them, the pressure of the polishing treatment is 4 psi, the flow rate of the Lunars diamond polishing liquid during the polishing treatment is 200 mL / min, the rotation speed of the Xin Yunwei su800 polishing pad is 112 rpm, and the acceleration is 30 rpm;

[0047] S2. Use the leading cerium dioxide fine polishing liquid and the Wanhua wh6000 polishing pad to polish the first treated gallium nitride for 22 min to obtain polished gallium nitride. Among them, the pressure of the polishing treatment is 10 psi, the flow rate of the leading cerium dioxide fine polishing liquid during the polishing treatment is 200 mL / min, the rotation speed of the Wanhua wh6000 polishing pad is 108 rpm, and the acceleration is 50 rpm.

[0048] Example 3

[0049] This example provides a method for polishing gallium nitride, including the following steps:

[0050] S1. Use the Lunars diamond polishing liquid and the Xin Yunwei su800 polishing pad to polish gallium nitride for 28 min to obtain the first treated gallium nitride. Among them, the pressure of the polishing treatment is 3 psi, the flow rate of the Lunars diamond polishing liquid during the polishing treatment is 180 mL / min, the rotation speed of the Xin Yunwei su800 polishing pad is 110 rpm, and the acceleration is 40 rpm;

[0051] S2. Use the leading cerium dioxide fine polishing liquid and the Wanhua wh6000 polishing pad to polish the first treated gallium nitride for 18 min to obtain polished gallium nitride. Among them, the pressure of the polishing treatment is 8 psi, the flow rate of the leading cerium dioxide fine polishing liquid during the polishing treatment is 180 mL / min, the rotation speed of the Wanhua wh6000 polishing pad is 110 rpm, and the acceleration is 40 rpm.

[0052] Comparative Example 1

[0053] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S1, the XinYunWei su800 polishing pad is replaced with the Wanhua wh6000 polishing pad;

[0054] Other components and operation steps are the same as those in Example 1.

[0055] Comparative Example 2

[0056] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S2, the Wanhua wh6000 polishing pad is replaced with the XinYunWei su800 polishing pad;

[0057] Other components and operation steps are the same as those in Example 1.

[0058] Comparative Example 3

[0059] This comparative example provides a method for polishing gallium nitride, including the following steps:

[0060] S1. Use Lunatron diamond polishing liquid and XinYunWei su800 polishing pad to polish gallium nitride for 50 minutes to obtain polished gallium nitride; wherein, the pressure of the polishing treatment is 2 psi, the flow rate of the Lunatron diamond polishing liquid during the polishing treatment is 150 mL / min, the rotation speed of the XinYunWei su800 polishing pad is 108 rpm, and the acceleration is 50 rpm.

[0061] Comparative Example 4

[0062] This comparative example provides a method for polishing gallium nitride, including the following steps:

[0063] S1. Use Navigator cerium dioxide fine polishing liquid and Wanhua wh6000 polishing pad to polish gallium nitride for 50 minutes to obtain polished gallium nitride; wherein, the pressure of the polishing treatment is 7 psi, the flow rate of the Navigator cerium dioxide fine polishing liquid during the polishing treatment is 150 mL / min, the rotation speed of the Wanhua wh6000 polishing pad is 112 rpm, and the acceleration is 30 rpm.

[0064] Comparative Example 5

[0065] This comparative example provides a method for polishing gallium nitride, which is different from Example 1 in that: in S1, the Lunatron diamond polishing liquid is replaced with AnChu ws606 sodium permanganate polishing liquid;

[0066] Other components and operation steps are the same as those in Example 1.

[0067] Polish the surface of the gallium nitride wafer by the polishing methods of Examples 1 to 3 and Comparative Examples 1 to 5. After polishing, detect the surface roughness of the gallium nitride wafer surface, and use a Park atomic force microscope to detect the surface roughness of the silicon wafer;

[0068] Polishing rate: The thickness of the wafer before polishing and the thickness of the wafer after polishing are measured by a metrology tool. The difference is the total removal amount corresponding to the polishing time. The total amount divided by the polishing time is the polishing rate;

[0069] The detection standard for the product qualification rate is as follows: 25 repetitions are set for each process. When the roughness is <0.5 nm and there are no surface cracks and internal cracks, it is a qualified product;

[0070] The specific detection results are shown in Table 1:

[0071] Table 1

[0072]

[0073] As can be seen from Table 1, compared with the gallium nitride polishing methods provided by Comparative Examples 1-6, the gallium nitride polishing method provided by the embodiment of the present invention not only has a high polishing rate within the same time, but also can greatly reduce the surface roughness of the gallium nitride wafer, and the product qualification rate can reach more than 95%. It solves the problem of microcracks and internal cracks on the surface of the gallium nitride wafer after the existing polishing process, and greatly improves the surface quality of GaN and the product qualification rate.

[0074] 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 in the protection scope of the present invention.

Claims

1. A method for gallium nitride polishing, characterized in that, It includes the following steps: Perform the first polishing treatment and the second polishing treatment on gallium nitride in sequence with a first polishing liquid, a first polishing pad, a second polishing liquid, and a second polishing pad to obtain polished gallium nitride; Among them, the first polishing liquid is a polishing liquid with diamond as the abrasive; The second polishing liquid is a polishing liquid with cerium dioxide as the abrasive; The first polishing pad is a grid-type polishing pad, the second polishing pad is a spiral-type polishing pad, and the Shore hardness of the first polishing pad is 25 HD to 55 HD lower than that of the second polishing pad.

2. The method for polishing gallium nitride according to claim 1, wherein The Shore hardness of the first polishing pad is 30 HD to 40 HD; and / or The Shore hardness of the second polishing pad is 65 HD to 80 HD.

3. The method for polishing gallium nitride according to claim 2, wherein The particle size of the diamond is 2 μm to 3 μm.

4. The method for polishing gallium nitride according to claim 1, characterized in that, The first polishing pad is Xin Yunwei su800.

5. The method for polishing gallium nitride according to claim 1, characterized in that, The pressure of the first polishing treatment is 2 psi to 4 psi.

6. The method for polishing gallium nitride according to claim 1, wherein The rotation speed of the first polishing pad during the first polishing treatment is 108 rpm to 112 rpm; and / or The acceleration of the first polishing pad during the first polishing treatment is 30 rpm to 50 rpm; and / or The time of the first polishing treatment is 28 min to 32 min.

7. The method for polishing gallium nitride according to claim 1, wherein, The particle size of the cerium dioxide is 120 nm to 130 nm.

8. The method for polishing gallium nitride according to claim 7, wherein The second polishing liquid is Linghang cerium dioxide fine polishing liquid.

9. The method for polishing gallium nitride according to claim 1, wherein The second polishing pad is Wanhua wh6000; and / or The pressure of the second polishing treatment is 7 psi to 10 psi.

10. The method for polishing gallium nitride according to claim 1, characterized in that, The rotation speed of the second polishing pad during the second polishing treatment is 108 rpm to 112 rpm; and / or The acceleration of the second polishing pad during the second polishing treatment is 30 rpm to 50 rpm; and / or The time of the second polishing treatment is 18 min to 22 min.

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